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1

Printed magnetic field probe with enhanced performances  

Microsoft Academic Search

A novel circular magnetic field probe is proposed, and measured results are presented. The proposed probe is easily fabricated by printing technology. A set of quasi-periodic notches was embedded into the connecting portion and acted as a microstrip filter. The experimental results indicate that the proposed probe effectively suppresses the inherent resonances of the circular loop, and the usable frequency

Shun-Yun Lin; Shang-Kuei Yen; Wen-Shyang Chen; Pao-Hsia Cheng

2009-01-01

2

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

3

Probing Magnetic Fields with GALFACTS  

NASA Astrophysics Data System (ADS)

GALFACTS is a large-area spectro-polarimetric survey on the Arecibo Radio telescope. It uses the seven-beam focal plane feed array receiver system (ALFA) to carry out an imaging survey project of the 12,700 square degrees of sky visible from Arecibo at 1.4 GHz with 8192 spectral channels over a bandwidth of 300 MHz sampled at 1 millisecond. The aggregate data rate is 875 MB/s. GALFACTS observations will create full-Stokes image cubes at an angular resolution of 3.5' with a band-averaged sensitivity of 90 ?Jy, allowing sensitive imaging of polarized radiation and Faraday Rotation Measure from both diffuse emission and extragalactic sources. GALFACTS is a scientific pathfinder to the SKA in the area of cosmic magnetism. Key to magnetism science with the SKA is the technique of RM synthesis. The technique of RM synthesis is introduced and we discuss practical aspects of RM synthesis including efficient computational techniques and detection thresholds in the resulting Faraday spectrum. We illustrate the use of the technique by presenting the current development of the RM synthesis pipeline for GALFACTS and present early results.

George, S. J.; Stil, J. M.; Andrecut, M.; Taylor, A. R.

2012-09-01

4

Behavior of a Single Langmuir Probe in a Magnetic Field.  

ERIC Educational Resources Information Center

Describes an experiment to demonstrate the influence of a magnetic field on the behavior of a single Langmuir probe. The experiment introduces the student to magnetically supported plasma and particle behavior in a magnetic field. (GA)

Pytlinski, J. T.; And Others

1978-01-01

5

Magnetic and Electric Field Probes for Transient Measurements.  

National Technical Information Service (NTIS)

The effectiveness of recently developed magnetic and electric field probes is evaluated. Three probes were evaluated: a high-frequency, wide-band variable mu magnetometer, with a small sensor head for measuring inside enclosures, covering a 10-Hz to 10-MH...

K. W. Tomlinson

1969-01-01

6

Field measuring probe for SSC (Superconducting Super Collider) magnets  

SciTech Connect

The field probe developed for measuring the field in SSC dipole magnets is an adaptation of the rotating tangential coil system in use at Brookhaven for several years. Also known as the MOLE, it is a self-contained room-temperature mechanism that is pulled through the aperture of the magnet with regular stops to measure the local field. Several minutes are required to measure the field at each point. The probe measures the multipole components of the field as well as the field angle relative to gravity. The sensitivity of the coil and electronics is such that the field up to the full 6.6 T excitation of the magnet as well as the field when warm with only 0.01 T excitation can be measured. Tethers are attached to both ends of the probe to carry electrical connections and to supply dry nitrogen to the air motors that rotate the tangential windings as well as the gravity sensor. A small computer is attached to the probe for control and for data collection, analysis and storage. Digital voltmeters are used to digitize the voltages from the rotating coil and several custom circuits control motor speeds in the probe. The overall diameter of the probe is approximately 2 cm and its length is 2.4 m; the field sensitive windings are 0.6 m in length.

Ganetis, G.; Herrera, J.; Hogue, R.; Skaritka, J.; Wanderer, P.; Willen, E.

1987-03-01

7

Performance of field measuring probes for SSC magnets  

SciTech Connect

Several years of experience have been acquired on the operation of probes (``moles``) constructed for the measurement of the multipole components of the magnetic fields of SSC magnets. The field is measured by rotating coils contained in a 2.4-m long tube that is pulled through the aperture of the magnet by an external device-the transporter. In addition to the measuring coils, the tube contains motors for rotating the coil and a system for sensing local vertical using gravity sensors to provide an absolute reference for the field measurements. We describe the steps that must be taken in order to ensure accurate, repeatable measurements; the design changes that have been motivated by difficulties encountered (noise, vibration, variations in temperature); and other performance issues. The mechanical interface between the probe and the hewn tube of the magnet is also described.

Thomas, R.; Ganetis, G.; Herrera, J.; Hogue, R.; Jain, A.; Louie, W.; Marone, A.; Wanderer, P.

1993-12-31

8

Magnetic field effect on cylindrical impedance probe diagnostics  

NASA Astrophysics Data System (ADS)

To test geometry independence predicted theoretically in earlier work with spherical impedance probes,ootnotetextD.N. Walker, R.F. Fernsler, D.D. Blackwell, W.E. Amatucci, Phys. Plasmas 17, 113503 (2010) we used a 100-1 (length -- radius) aspect ratio cylindrical probe. In the impedance measurements, a network analyzer supplies a millivolt driving rf signal and plasma diagnostics are based on the real and imaginary parts of the complex plasma impedance returned by the analyzer for a given probe bias. The theoretical basis of the work indicates that in the thin sheath limit the results should be independent of probe geometry. With probe alignment along a small magnetic field ˜ 2 gauss, we compared the cylinder's impedance-based plasma measurements to those for which we swept the same cylinder as a Langmuir probe.ootnotetextNRL Memorandum Report 6750-11-9331 (2011) In both cases the impedance probe format showed a higher density, the same plasma potential, and a comparable electron temperature to the Langmuir sweep. We will present recent data showing the effect of varying the orientation and magnitude of the applied field.

Walker, David; Fernsler, Richard; Blackwell, David; Amatucci, William

2011-11-01

9

Probing magnetic fields in volume with multifrequency polarized synchrotron emission  

NASA Astrophysics Data System (ADS)

We investigate the problem of probing the local spatial structure of the magnetic field of the interstellar medium using multifrequency polarized maps of the synchrotron emission at radio wavelengths. We focus in this paper on the three-dimensional (3D) reconstruction of the largest scales of the magnetic field, relying on the internal depolarization (due to differential Faraday rotation) of the emitting medium as a function of electromagnetic frequency. We argue that multiband spectroscopy in the radio wavelengths, developed in the context of high-redshift extragalactic HI lines, can be a very useful probe of the 3D magnetic field structure of our Galaxy when combined with a maximum a posteriori reconstruction technique. When starting from a fair approximation of the magnetic field, we are able to recover the true one by using a linearized version of the corresponding inverse problem. The spectral analysis of this problem allows us to specify the best sampling strategy in electromagnetic frequency and predicts a spatially anisotropic distribution of posterior errors. The reconstruction method is illustrated for reference fields extracted from realistic magnetohydrodynamical simulations.

Thiébaut, J.; Prunet, S.; Pichon, C.; Thiébaut, E.

2010-03-01

10

Detection of High-Frequency Magnetic Fields by a GMI Probe  

Microsoft Academic Search

A giant magnetoimpedance (GMI) probe was fabricated in order to detect high-frequency magnetic fields. Magnetic near field measurements were carried out using the probe. A microstrip line driven by a current whose frequency was changed from 500 Hz to 1 GHz was used as a signal source in the measurements. The probe could clearly detect the characteristics of the field

Kenji Tan; Takashi Komakine; Kiyoshi Yamakawa; Yoshiki Kayano; Hiroshi Inoue; Masahiro Yamaguchi

2006-01-01

11

Magnetic field probes for use in radio frequency plasma  

SciTech Connect

An impedance analyzer has been used in the characterization of a magnetic induction probe (B-dot probe) for use in plasma. The role of the impedance analyzer was to determine the frequency response of a B-dot probe up to 100 MHz. The probe was specifically designed to take measurements in rf plasma driven at 13.56 MHz. Probe sensitivity and calibration are considered based on the impedance values obtained when a B-dot probe is swept over a wide frequency range. Effects such as unbalanced loads based on transmission line inductances and termination impedance are shown to be limiting factors on the probes useful frequency range. The use of an impedance analyzer allows these effects to readily be characterized.

Reilly, Michael P.; Miley, George H. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 S. Wright Street, 216 Talbot Laboratory, MC-234 Urbana, Illinois 61801 (United States); Lewis, William [ERC Inc. Knight High School, 37423 70th Street East, Palmdale, California 93552 (United States)

2009-05-15

12

Optical magnetic field probe working up to 15 GHz using CdTe electrooptic Crystals  

Microsoft Academic Search

This paper presents a new type of optical magnetic field probe designed to detect magnetic near-fields with high accuracy up to 15 GHz. The probe head consists of a loop antenna element and CdTe electrooptic crystals. The probe using CdTe has a resonant frequency higher than that of a previous probe using LiNbO3 because CdTe has a dielectric constant lower

Eiji Suzuki; Satoru Arakawa; Hiroyasu Ota; Ken Ichi Arai; Risaburo Sato

2005-01-01

13

An Alternating Current Probe for Measurement of Magnetic Fields  

Microsoft Academic Search

A method of measuring magnetic field strengths is described which utilizes the incremental permeability of a small Permalloy core. Alternating-current excitation is used which in turn permits amplification and hence a relatively high sensitivity and accuracy.

E. C. Gregg

1947-01-01

14

Optimal design of eddy current testing probe using fluxset magnetic field sensors  

Microsoft Academic Search

A numerical method is presented for the calculation of the signal picked up by eddy current testing (ECT) probes made of an exciting coil and fluxset type magnetic field sensors. The magnetic field generated by the interaction of the exciting coil and the non-ferromagnetic metal plate specimen is calculated by the solution of a boundary integral equation with singular kernel.

J. Pavo; K. Miya

1996-01-01

15

THE MAGNETIC FIELD IN TAURUS PROBED BY INFRARED POLARIZATION  

SciTech Connect

We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A{sub V} {approx} 9 mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82 {mu}G and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales ({approx}2 pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.

Chapman, Nicholas L.; Goldsmith, Paul F.; Pineda, Jorge L.; Li Di [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 301-429, Pasadena, CA 91109 (United States); Clemens, D. P. [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Krco, Marko, E-mail: nchapman@u.northwestern.edu [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States)

2011-11-01

16

Probing magnetic order in CuFeO2 through nuclear forward scattering in high magnetic fields  

NASA Astrophysics Data System (ADS)

Determining the magnetic order of solids in high magnetic fields is technologically challenging. Here we probe the cascade of magnetic phase transitions in frustrated multiferroic CuFeO2 using nuclear forward scattering (NFS) in pulsed magnetic fields up to 30 T. Our results are in excellent agreement with detailed neutron diffraction experiments, currently limited to 15 T, while providing experimental confirmation of the proposed higher field phases for both H?c and H?c. We thus establish NFS as a valuable tool for spin structure studies in very high fields, both complementing and expanding on the applicability of existing techniques.

Strohm, C.; Lummen, T. T. A.; Handayani, I. P.; Roth, T.; Detlefs, C.; van der Linden, P. J. E. M.; van Loosdrecht, P. H. M.

2013-08-01

17

2H transmit-receive NMR probes for magnetic field monitoring in MRI.  

PubMed

Measuring image encoding fields in real time and applying the information in postprocessing offer improved image quality for MRI, particularly for applications that are intrinsically sensitive to gradient imperfections. For this task, a stand-alone magnetometer system based on multiple (2)H transmit-receive NMR probes has been developed. The conceptual advantages of changing to (2)H NMR probes for (1)H magnetic field monitoring are elucidated here, and the practical design of the probes is described. In comparison to previous (1)H NMR probe-based designs, (2)H probes are perfectly decoupled from standard (1)H imaging. Utilization of RF shielding or other nonoptimal decoupling schemes is therefore not needed. Probes based on (2)H nuclei are also more easily miniaturized for high-resolution imaging. This is particularly important for diffusion tensor and phase-contrast imaging, which rely on strong motion-sensitizing gradients. The presented (2)H NMR probes have been shown to fulfill the requirements for accurate (1)H imaging down to image resolutions of 0.2 mm. Using susceptibility matching techniques, the probe's B(0) inhomogeneity-induced signal dephasing is reduced and monitoring periods beyond 200 msec are achieved. The benefit of real time magnetic field monitoring is highlighted for phase-contrast and non-Cartesian multishot imaging. PMID:21254204

Sipilä, Pekka; Greding, Sebastian; Wachutka, Gerhard; Wiesinger, Florian

2011-01-19

18

A rotating coil probe for the magnetic field measurement on a long pulsed tokamak  

NASA Astrophysics Data System (ADS)

In order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as the International Thermonuclear Experimental Reactor (ITER), it is urged to establish a reliable method which is free from the zero-level drift of the integrator as well as the radiation damage for the steady-state magnetic field measurement. For this purpose, we have developed a hybrid system, a combination of a conventional magnetic probe for the measurement of fast varying magnetic field and a rotating coil magnetic probe for that of slowly varying field. The rotating coil is energized by an air turbine to avoid electromagnetic interference and the induce signal with a constant rotation frequency is picked up through a transformer to eliminate mechanical contacts. An automatic gain control circuit is also designed for the compensation of rotation speed fluctuation. The system is proved to achieve a flat frequency response with a proper choice of cross over frequency for high- and low-frequency systems. The rotating coil probe is tested for over 170 h without any trouble. The probe was applied to the poloidal magnetic field measurement on the TRIAM-1M long pulsed tokamak, and proved to work satisfactorily.

Fujita, J.; Matsuura, K.; Kawahata, K.; Fujiwaka, S.; Itoh, S.; Sato, K. N.; Nakamura, K.; Zushi, H.; Sakamoto, M.; Hanada, K.; Jotaki, E.; Makino, K.

1999-01-01

19

High frequency probes of superconductivity and magnetism in anisotropic materials in very high magnetic field  

NASA Astrophysics Data System (ADS)

In this dissertation, I present a study of a wide range of organic and inorganic materials using radio frequency (rf) measurement methods. The organic samples under study were lambda-(BETS)2 GaCl4 and lambda-(BETS)2 FeCl4. In the lambda-(BETS)2 GaCl4, the H-T superconductivity phase diagram was studied using the tunnel diode oscillator (TDO) method and compared with simultaneous four terminals resistivity measurements. These simultaneous measurements show signs of para-conductivity in this material. The same method was used to study the lambda-(BETS)2 FeCl4 sample which is a field induced superconductor (FISC). The inorganic materials that I have studied include Ba 0.55K0.45Fe2 As2 and USb2. In Ba0.55K0.45Fe 2As2 (which belongs to the recently discovered Pnictide superconductors family), I have studied the H-T phase diagram for magnetic fields applied parallel and perpendicular to the crystallographic c-axis up to 65 tesla and in temperature as low as 4 K. Ba0.55K0.45 Fe2As2 was studied by a new rf technique that I have developed recently (PDO?Proximity Detector Oscillator). The rf measurements of Ba0.55 K0.45Fe2 As2 from my work support the prediction of an unconventional multigap superconductivity in this material. In the USb 2 sample, a Fermi surfaces measurement was performed by the TDO rf probe and by a torque magnetometer for comparison purposes in high magnetic fields up to 65 tesla and in temperatures above 0.5 K. I found that both the rf and the torque measurements reveal a cylindrical Fermi surface with approximately the same effective mass. However, the rf and the torque measurements reveal some differences in the frequencies obtained from the FFT obtained for each method. In this dissertation, most of the measurements were performed using rf probes like the TDO or the PDO. The PDO method has successfully replaced the TDO method to perform rf measurements in all different kinds of magnets (dc and pulsed).

Altarawneh, Moaz

20

Primary processing of magnetic field data aboard a space probe  

Microsoft Academic Search

The real-time processing of magnetometric data on a space probe is examined. The design and components of the three-component vector magnetometer used in this study are discussed. The on-board computer used to digitize the three signal components consists of: a processor; memory; and input, control, calibration, time, output, and interrupt ports. The functions of these components and the tasks of

D. Lenners; H. J. Linthe

1987-01-01

21

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer  

Microsoft Academic Search

The Electron Reflectometer (ER) on board Mars Global Surveyor measures the energy and angular distributions of solar wind electrons and ionospheric photoelectrons. These data can be used in conjunction with magnetometer data to probe Mars' crustal magnetic field and to study Mars' ionosphere and solar wind interaction. During aerobraking, ionospheric measurements were obtained in the northern hemisphere at high solar

R. P. Lin; C. Mazelle; H. Rème; P. A. Cloutier; J. E. P. Connerney; M. H. Acuña; N. F. Ness

2001-01-01

22

PROBING THE LARGE-SCALE TOPOLOGY OF THE HELIOSPHERIC MAGNETIC FIELD USING JOVIAN ELECTRONS  

SciTech Connect

Jupiter's magnetosphere acts as a point source of near-relativistic electrons within the heliosphere. In this study, three solar cycles of Jovian electron data in near-Earth space are examined. Jovian electron intensity is found to peak for an ideal Parker spiral connection, but with considerable spread about this point. Assuming the peak in Jovian electron counts indicates the best magnetic connection to Jupiter, we find a clear trend for fast and slow solar wind to be over- and under-wound with respect to the ideal Parker spiral, respectively. This is shown to be well explained in terms of solar wind stream interactions. Thus, modulation of Jovian electrons by corotating interaction regions (CIRs) may primarily be the result of changing magnetic connection, rather than CIRs acting as barriers to cross-field diffusion. By using Jovian electrons to remote sensing magnetic connectivity with Jupiter's magnetosphere, we suggest that they provide a means to validate solar wind models between 1 and 5 AU, even when suitable in situ solar wind observations are not available. Furthermore, using Jovian electron observations as probes of heliospheric magnetic topology could provide insight into heliospheric magnetic field braiding and turbulence, as well as any systematic under-winding of the heliospheric magnetic field relative to the Parker spiral from footpoint motion of the magnetic field.

Owens, M. J.; Horbury, T. S. [Space and Atmospheric Physics, Imperial College, London SW7 2AZ (United Kingdom); Arge, C. N. [Air Force Research Laboratory/Space Vehicles Directorate, Kirtland Air Force Base, NM 87117 (United States)

2010-05-10

23

Sun-Earth Magnetic connection probed with radio bursts and magnetic field extrapolation  

Microsoft Academic Search

Energetic particles accelerated in the solar corona can be detected by spacecraft in interplanetary space provided there is either (i) a direct magnetic connection between the spacecraft and the acceleration region, or (ii) transport of particles across magnetic field lines in the corona or interplanetary space. We use type III radio bursts associated with locally produced Langmuir waves observed by

G. Lointier; K.-L. Klein; S. Hoang

2004-01-01

24

Electric field coupling suppression using via fences for magnetic near-field shielded-loop coil probes in low temperature co-fired ceramics  

Microsoft Academic Search

Two types of low-cost and robust magnetic near-field probes manufactured in low temperature co-fired ceramics (LTCC) are presented in this paper. The shielded-loop coil and via fences are used in the probes to provide better electric field coupling suppression. Type I probe is designed to receive horizontal magnetic field, via fences are inserted in the loop aperture and along sides

Yien-Tien Chou; Hsin-Chia Lu

2011-01-01

25

Probing the Solar Magnetic Field with a Sun-Grazing Comet  

NASA Astrophysics Data System (ADS)

On 15 and 16 December 2011, Sun-grazing comet C/2011 W3 (Lovejoy) passed deep within the solar corona, effectively probing a region that has never been visited by spacecraft. Imaged from multiple perspectives, extreme ultraviolet observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combined a state-of-the-art magnetohydrodynamic model of the solar corona and a model for the motion of emitting cometary tail ions in an embedded plasma. The observed tail motions reveal the inhomogeneous magnetic field of the solar corona. We show how these motions constrain field and plasma properties along the trajectory, and how they can be used to meaningfully distinguish between two classes of magnetic field models.

Downs, Cooper; Linker, Jon A.; Miki?, Zoran; Riley, Pete; Schrijver, Carolus J.; Saint-Hilaire, Pascal

2013-06-01

26

Magnetic near field probe based on the high-frequency carrier type thin-film magnetic field sensor  

Microsoft Academic Search

Summary form only given. Rapid growth of information technology (IT) markets has raised a need of magnetic near field measurements on densely packaged PCBs and LSIs for the detection of the source current of electromagnetic emission and the evaluation of electronic signal integrity. This paper proposes a new application of the high frequency carrier type magnetic field sensor (or so-called

M. Yamaguchi; H. Kikuchi; S. Sugimoto; K.-I. Arai; M. Iwanami; A. Nakamura; S. Hoshino

2002-01-01

27

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer  

NASA Astrophysics Data System (ADS)

The Electron Reflectometer (ER) on board Mars Global Surveyor measures the energy and angular distributions of solar wind electrons and ionospheric photoelectrons. These data can be used in conjunction with magnetometer data to probe Mars' crustal magnetic field and to study Mars' ionosphere and solar wind interaction. During aerobraking, ionospheric measurements were obtained in the northern hemisphere at high solar zenith angles (SZAs, typically ~78°). The ionopause was crossed at altitudes ranging from 180 km to over 800 km, with a median of 380 km. The 400-km-altitude polar mapping orbit allows observations at SZAs from 25° to 155° in both the northern and southern hemispheres. The near-planet ionosphere and magnetotail structure of the night hemisphere is dominated by the presence of intense crustal magnetic fields, which can exceed 200 nT at the spacecraft altitude. Closed field lines anchored to highly elongated crustal sources form ``magnetic cylinders,'' which exclude solar wind plasma traveling up the magnetotail. When the spacecraft passes through one of these structures, the ER count rate falls to the instrumental background, representing an electron flux drop of at least two orders of magnitude. A map of these flux dropouts in longitude and latitude closely resembles a map of the crustal magnetic sources. When the crustal magnetic cylinders rotate into sunlight, they fill with ionospheric plasma. Since many of these crustal fields are locally strong enough to stand off the solar wind to altitudes well above 400 km, the ionosphere can extend much higher than would otherwise be possible in the absence of crustal fields. Even weak crustal fields may locally bias the median ionopause altitude, which provides an indirect method of detecting crustal fields using ER observations.

Mitchell, D. L.; Lin, R. P.; Mazelle, C.; Rème, H.; Cloutier, P. A.; Connerney, J. E. P.; Acuña, M. H.; Ness, N. F.

2001-10-01

28

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

SciTech Connect

A modified {dot {ital B}} circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo {ital et} {ital al}., Plasma Sources Sci. Technol. {bold 4}, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular emphasis on the importance of the Hall effect [D. C. Black {ital et} {ital al}., Phys. Plasma {bold 1}, 3115 (1994)] and plasma microinstabilities [R. M. Mayo {ital et} {ital al}., Phys. Plasma {bold 2}, 337 (1995)] to plasma transport in coaxial plasma sources. The miniature magnetic probe array consists of ten spatially separated coils wound on an Acetal form of dimensions 2.38 cm by 0.32 cm by 0.32 cm. At five positions, with roughly 0.32 cm separation, two mutually perpendicular coils are wound to measure the magnetic field in the {cflx {theta}} and {cflx {ital z}} directions. The modification to the signal processing circuitry consists of the use of a step-up transformer to boost the probe signal prior to filtering and acquiring the signal at the data acquisition system. This additional means of amplifying the signal allows for reduction in the size of the probe, and thus helps minimize the perturbing effect of the magnetic probe on the plasma. An additional advantage of using a signal transformer is that it provides electrical isolation between the experiment and the data acquisition system. {copyright} {ital 1996 American Institute of Physics.}

Black, D.C.; Mayo, R.M. [Department of Nuclear Engineering, North Carolina State University, Raleigh, North Carolina 27695-7909 (United States)

1996-04-01

29

A study on magnetic near-field measurements above a patch antenna using an optical waveguide probe with a loop element  

Microsoft Academic Search

We developed a magnetic field probe consisting of a LiNbO3 optical waveguide modulator and a loop antenna element for accurate magnetic near-field measurements in the gigahertz range. We confirmed the probe invasiveness by measuring magnetic field distributions above a patch antenna operating at 2.49 GHz using the probe. Then we compared those measured results with those for shielded loop probes.

Masanon Takahashi; Huoyasu Ota; Ken Ichi Arai; R. Sato

2004-01-01

30

Magnetic field and quadruple Langmuir probe measurements in the plume of the plasmoid thruster experiment  

NASA Astrophysics Data System (ADS)

The development of high specific impulse rocket engines is essential for fast and efficient space travel. The plasmoid thruster, a novel propulsion concept with the potential for producing a high specific impulse, was investigated in light of this need. This pulsed inductive rocket utilizes the Lorentz force to accelerate plasmoids and produce thrust. The Plasmoid Thruster Experiment (PTX) was designed to experimentally evaluate the thruster concept. PTX operates by producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. Measurements of the plasmoid magnetic fields, electron temperature (Te), electron number density (n e) and Mach number (M) were taken in the PTX plume with a B? probe array and a quadruple Langmuir probe. The measurements were used for calculating exit velocity and Isp. High-speed photographs were also obtained for capturing images of the plasmoids and estimating their velocity. The magnetic field data showed behavior characteristic of plasmoids, such as the occurrence of the maximum axial magnetic field on axis and magnetic field reversal. The quadruple Langmuir probe data revealed several factors that influence thruster operation, including propellant choice, supply pressure and propellant injection timing (tpuff). For Ar propellant at supply pressures of 14--34 psig and tpuff = 2200 mus, Te ranged from 2--7 eV, ne ranged from 1.5 x 1020 m-3 to 3.5 x 1020 m-3, and M ranged from 3.3--3.8 in PTX. For H2 propellant, T e ranged from 15--27 eV, ne ranged from 0.8 x 1020 m-3 to 1.5 x 1020 m-3, and M ranged from 1.4--2.6, for supply pressures of 9--38 psig and tpuff = 1200--2400 mus. Analysis of the plume measurements yielded high thruster exit velocities, indicating that the plasmoid thruster can produce a high Isp. Velocities of 24 km/s, 35 km/s and 46 km/s were calculated for supply pressures of 38 psig, 24 psig and 9 psig of H2 propellant, respectively. These exit velocities deliver Isp values of 2,400 s, 3,500 s and 4,600 s respectively for the unoptimized plasmoid thruster.

Koelfgen, Syri Jo

31

Probing the Nature of the Weakest Intergalactic Magnetic Fields with the High-Energy Emission of Gamma-Ray Bursts  

Microsoft Academic Search

We investigate the delayed, secondary GeV-TeV emission of gamma-ray bursts and its potential to probe the nature of intergalactic magnetic fields. Geometrical effects are properly taken into account for the time delay between primary high-energy photons and secondary inverse Compton photons from electron-positron pairs, which are produced in gamma-gamma interactions with background radiation fields and deflected by intervening magnetic fields.

Kiyotomo Ichiki; Susumu Inoue; Keitaro Takahashi

2008-01-01

32

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe  

NASA Astrophysics Data System (ADS)

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ˜3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.

Grabovski, E. V.; Mitrofanov, K. N.; Koshelev, A. Yu.; Samokhin, A. A.; Aleksandrov, V. V.; Gritsuk, A. N.; Laukhin, Ya. N.; Oleinik, G. M.; Frolov, I. N.

2011-07-01

33

Versatile 4 K nuclear magnetic resonance probe and cryogenic system for small-bore high-field Bitter magnets  

Microsoft Academic Search

A complete design for a versatile nuclear magnetic resonance cryostat\\/probe system specifically adapted for small 32 mm bore bitter magnets is described. The probe solves two main problems associated with constrained environments (1) high voltage arcing across cold tuned circuits in helium atmosphere and (2) loss of temperature control due to helium bubbles in a long Dewar tail at high

A. P. Reyes; H. N. Bachman; W. P. Halperin

1997-01-01

34

A magnetometer probe to measure magnetic fields from 10-2 to less than 10-8 T  

Microsoft Academic Search

By use of an air bearing a spinning-plate magnetometer has been made in which the rotor can run virtually indefinitely without wear and at very constant speed. The voltage output of the probe is proportional to magnetic field strength over six orders of magnitude and can measure steady or slowly varying fields from about 10-2 T down to less than

A. C. Rose-Innes

1977-01-01

35

Phase-controlled pulse propagation in media with cross coupling of electric and magnetic probe field component  

SciTech Connect

Light propagation is discussed in media with a cross coupling of the electric and magnetic component of an applied probe field. We derive the wave equations for a probe pulse propagating through such a medium and solve them analytically in Fourier space using the slowly varying envelope approximation. Our analysis reveals the influence of the different medium response coefficients on the propagation dynamics. We apply these results to a specific example system in which cross couplings are induced in an atomic medium by additional control fields. We show that the cross couplings render the propagation dynamics sensitive to the relative phase of the additional fields, and this phase dependence enables one to control the pulse during its propagation through the medium. Our results demonstrate that the magnetic field component of a probe beam can crucially influence the system dynamics already at experimentally accessible parameter ranges in dilute vapors.

Fleischhaker, Robert; Evers, Joerg [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)

2009-12-15

36

Magnetic field effects on hydrogen abstraction of thiobenzophenone as a probe of microviscosity.  

PubMed

Hydrogen abstraction reactions of thiobenzophenone with thiophenol in solutions of varying viscosities (?=0.29-42.0 cP) were studied by a nanosecond laser flash photolysis under magnetic fields of 0-15.5 T. In alcoholic solutions, the escaped radical yield (Y) of thiobenzophenone ketyl radical showed appreciable magnetic field effects (MFEs). The observed MFEs can be interpreted with the ?g mechanism through the triplet radical pair. The relative escaped radical yield (R(1.7T)=Y(1.7T)/Y(0T)) decreased with increasing ? at 0probe reaction, microviscosities of sodium dodecyl sulfate (SDS) and Brij35 micellar solutions were estimated. PMID:21322618

Tanaka, Miyuki; Yago, Tomoaki; Sakaguchi, Yoshio; Takamasu, Tadashi; Wakasa, Masanobu

2011-02-15

37

Probing of field-induced structures and tunable rheological properties of surfactant capped magnetically polarizable nanofluids.  

PubMed

Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths. PMID:23210900

Felicia, Leona J; Philip, John

2012-12-18

38

Internal magnetic probe data from ZT-40  

SciTech Connect

Measurements of magnetic field distribution as a function of time and radius were made in ZT-40 with its ceramic vacuum vessel. Data were obtained with a 10-station, 20-coil magnetic probe, measuring the B/sub p/ and B/sub epsilon/ orthogonal field components in deuterium plasma discharges. Sheath formation and diffusion, magnetic axis location and motion, the effect of the probe on the plasma, and the consistency of flux measurements with external probes are examined.

Burkhardt, L.C.; Phillips, J.A.

1981-05-01

39

Magnetic-field-assisted rapid ultrasensitive immunoassays using Fe3O4/ZnO/Au nanorices as Raman probes.  

PubMed

Rapid and ultrasensitive immunoassays were developed by using biofunctional Fe3O4/ZnO/Au nanorices as Raman probes. Taking advantage of the superparamagnetic property of the nanorices, the labeled proteins can rapidly be separated and purified with a commercial permanent magnet. The unsusceptible multiphonon resonant Raman scattering of the nanorices provided a characteristic spectroscopic fingerprint function, which allowed an accurate detection of the analyte. High specificity and selectivity of the assay were demonstrated. It was found that the diffusion barriers and the boundary layer effects had a great influence on the detection limit. Manipulation of the nanorice probes using an external magnetic field can enhance the assay sensitivity by several orders of magnitude, and reduce the detection time from 1 h to 3 min. This magnetic-field-assisted rapid and ultrasensitive immunoassay based on the resonant Raman scatting of semiconductor shows significant value for potential applications in biomedicine, food safety, and environmental defence. PMID:20667438

Hong, Xia; Chu, Xueying; Zou, Peng; Liu, Yichun; Yang, Guoliang

2010-07-25

40

Solar Magnetic Field  

NASA Astrophysics Data System (ADS)

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

Schüssler, M.; Murdin, P.

2000-11-01

41

Wave Science with the Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields of waves which mediate these processes. A large range of field regimes are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field interactions, NASA has selected the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Radiation Belt Storm Probes (RBSP). EMFISIS is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer and measures AC electric and magnetic fields from 10 Hz to 400 kHz. The broad frequency range of the Waves instrument enables the identification of resonances and cutoffs from Waves to achieve high cadence, accurate plasma density measurements that are essential to RBSP theory and modeling efforts. In combination with the selected double probe electric field and particle investigations on RBSP, EMFISIS will provide the essential measurements necessary to open the frontier of predictive capability for the Earth's highly variable radiation belts. We discuss of the key scientific goals of the EMFISIS investigation with particular attention to the wave physics of the radiation belts.

Bounds, S. R.; Kletzing, C. A.; Kurth, W. S.; Acuna, M. H.; Torbert, R. B.; Thorne, R.; Jordanova, V.; Smith, C.; Santolik, O.; Pfaff, R.; Rpwlamd, D.; Hospodarsky, G.; Baumjohann, W.; Nakamura, R.; Puhl-Quinn, P.

2008-12-01

42

Photonic electromagnetic field probes  

Microsoft Academic Search

Summary form only given. Optically sensed probes designed to accurately measure electromagnetic fields are described. The probes use passive electrooptic modulators of Pockels cell or integrated optics designs to transfer the electromagnetic signal to an optical carrier propagating in a fibre-optic link. This approach eliminates the need for active components or power sources in the probe head. It minimizes the

M. Kanda; K. D. Masterson; D. R. Novotny

1992-01-01

43

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified {dot {ital B}} circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo {ital et} {ital al}., Plasma Sources Sci. Technol. {bold 4}, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow

D. C. Black; R. M. Mayo

1996-01-01

44

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified B˙ circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo etal., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular

D. C. Black; R. M. Mayo

1996-01-01

45

Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-Ray Background.  

National Technical Information Service (NTIS)

The intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the extragalactic gamma-ray background, through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragal...

T. M. Venters V. Pavlidou

2012-01-01

46

Probing the Role of Magnetic Fields in Star Formation with BLAST-Pol  

NASA Astrophysics Data System (ADS)

Polarimetry is a powerful tool for studying the importance of magnetic fields in the star formation process. However, at present there are very few submm/mm polarimetry observations of large scale fields within molecular clouds. BLAST-Pol, the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry, maps linearly polarized dust emission at 250, 350 and 500 microns; it has the unique combination of sensitivity to large scale magnetic fields, and arcminute resolution necessary to trace fields into prestellar cores and dense filaments. In this presentation I will give a brief overview of the instrument, its performance during the first BLAST-Pol science flight completed in January 2011, and plans for future flights. I will also show preliminary maps from the first science flight and explain how these maps will be used to study the relationship between large and small scale magnetic fields in molecular clouds, the degree of order in the field, and the relationship between the magnetic field structure and the morphology of filaments and cores within the clouds. The BLAST-Pol collaboration gratefully acknowledges the support of NASA, NSF Office of Polar Programs, the CSA (Canada), the STFC (UK), NSERC (Canada), and the Leverhulme Trust (UK).

Fissel, Laura M.; BLAST-Pol Collaboration

2012-01-01

47

Synchronized time- and high-field-resolved all-optical pump-probe magneto-optical setup based on a strong alternating magnetic field and its application in magnetization dynamics of high coercivity magnetic medium  

NASA Astrophysics Data System (ADS)

An alternating magnetic field (AMF) apparatus is developed and composed of an electromagnet and driving power supply. The structure of the electromagnet and configuration of the driving supply are described in detail. The apparatus can produce a peak magnetic field up to 9000 Oe and above under a small driving power at its resonance frequency of 1.14 kHz. Based on synchronization between the AMF and the femtosecond laser pulse train, a photomagnetic synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup is developed. This setup has the ability to reinitialize any magnetic states between two successive laser pulses so that irreversible magnetization reversal dynamics can be studied. Dynamic Kerr hysteresis loops and magnetization reversal dynamics of high coercivity ferromagnetic TbFeCo and FePt films are demonstrated using this setup, showing importance of this synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup in the research of ultrafast magnetization dynamics.

Wang, Zi-Xin; Li, Jia-Ming; Deng, Jun-Qi; Chen, Zhi-Feng; Lai, Tian-Shu

2011-03-01

48

New Probes of Intergalactic Magnetic Fields by Radiometry and Faraday Rotation  

Microsoft Academic Search

The energy injection of galactic black holes (BH) into the intergalactic medium via extragalactic radio source jets and lobes is sufficient to magnetize the IGM in the filaments and walls of Large Scale Structure at ˜ 0.1muG or more. It appears that this process of galaxy-IGM feedback is the primary source of IGM cosmic rays(CR) and magnetic field energy. Large

Philipp P. Kronberg

2004-01-01

49

Magnetic field enhanced nano-tip fabrication for four-probe STM studies  

NASA Astrophysics Data System (ADS)

We present an improved method for fabricating tungsten STM tips for measuring nanoscale objects using a multiprobe STM. The tips were prepared by a 'drop-off' technique combined with a magnetic field. For magnetic field strengths above 150 Oe the electrolyte was seen to rotate about the tungsten anode. This rotation reduced the adhesion of bubbles and led to a reduction in the cone angle of the tips produced. This property is advantageous for multiprobe measurements as it allows one to bring multiple tips into close proximity.

McKendry, J. E.; Allen, C. S.; Critchley, K.; Górzny, M. ?.; Walton, A. S.; Evans, S. D.

2008-02-01

50

The Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field regimes are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field interactions, NASA has selected the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Radiation Belt Storm Probes (RBSP). EMFISIS is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer and measures AC electric and magnetic fields from 10 Hz to 400 kHz. The broad frequency range of the Waves instrument enables the identification of resonances and cutoffs from Waves to achieve high cadence, accurate plasma density measurements that are essential to RBSP theory and modeling efforts. The instruments are integrated through a Central Data Processor Unit (CDPU) which provides for flexible instrument operations in both burst and survey telemetry modes that can be optimized to address the specific physics of the many radiation belt processes. The EMFISIS multi-institution team comprises a group of knowledgeable space physics investigators, both experimental and theoretical with the requisite capability, desire, and experience to accomplish the goals of the RBSP mission to further space weather capability. In combination with the selected double probe electric field and particle investigations on RBSP, EMFISIS will provide the essential measurements necessary to open the frontier of predictive capability for the Earth's highly variable radiation belts.

Kletzing, Craig

51

Initial Results From The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on the Van Allen Probes  

NASA Astrophysics Data System (ADS)

The physics of the creation, loss, and transport of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field and particle interactions are involved in this physics from large-scale ring current ion and magnetic field dynamics to microscopic kinetic interactions of whistler-mode chorus waves with energetic electrons. To measure these kinds of radiation belt interactions, NASA implemented the two-satellite Van Allen Probes mission. As part of the mission, the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation is an integrated set of instruments consisting of a tri-axial fluxgate magnetometer (MAG) and a Waves instrument which includes a tri-axial search coil magnetometer (MSC). These wave measurements include AC electric and magnetic fields from 10Hz to 400 kHz. We show examples of plasmapause identification and variation determined by the upper hybrid resonance, low frequency ULF pulsations, and whistler mode waves including upper and lower band chorus. These data are compared with particle measuements to show relationships between wave activity and particle energization.

Kletzing, Craig

2013-04-01

52

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

53

A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field  

NASA Astrophysics Data System (ADS)

Orbital limited motion theory has been applied to two biased probes in a low beta Polywell. The cases studied include electron injection, magnetic field scaling, Polywell bias scaling, and radial position profiles. Langmuir's original orbital limited motion results for a monoenergetic electron beam are shown to be in excellent agreement for electron injection into the Polywell. A distribution function is proposed for the electron plasma characteristics in the centre of the magnetic null and confirmed with experimental results. A translational stage was used to measure the radial plasma potential profile. In other experiments, two probes were used to simultaneously measure the profiles in both the null and a position halfway along a corner cusp. The results confirm a radial potential well created by electron trapping in the device. In addition, we present preliminary results of the potential well scaling with the magnetic field, Polywell bias voltage, and the injected beam current. The electron population was found to maintain non-equilibrium in all cases studied.

Carr, Matthew; Khachan, Joe

2013-05-01

54

ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD  

SciTech Connect

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Xue, Liang, E-mail: zhangyi@mail.ihep.ac.cn [School of Physics, Shandong University, Ji'nan 250100 (China)

2012-05-01

55

Magnetic-field probing of an SU(4) Kondo resonance in a single-atom transistor.  

PubMed

Semiconductor devices have been scaled to the point that transport can be dominated by only a single dopant atom. As a result, in a Si fin-type field effect transistor Kondo physics can govern transport when one electron is bound to the single dopant. Orbital (valley) degrees of freedom, apart from the standard spin, strongly modify the Kondo effect in such systems. Owing to the small size and the s-like orbital symmetry of the ground state of the dopant, these orbital degrees of freedom do not couple to external magnetic fields which allows us to tune the symmetry of the Kondo effect. Here we study this tunable Kondo effect and demonstrate experimentally a symmetry crossover from an SU(4) ground state to a pure orbital SU(2) ground state as a function of magnetic field. Our claim is supported by theoretical calculations that unambiguously show that the SU(2) symmetric case corresponds to a pure valley Kondo effect of fully polarized electrons. PMID:22400874

Tettamanzi, G C; Verduijn, J; Lansbergen, G P; Blaauboer, M; Calderón, M J; Aguado, R; Rogge, S

2012-01-25

56

Microprobe for Measuring Magnetic Fields  

Microsoft Academic Search

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

D. D. Roshon Jr.

1962-01-01

57

Probing many-electron QED effects in the presence of magnetic fields  

NASA Astrophysics Data System (ADS)

Current progress in ab initio QED calculations of the hyperfine structure and the g-factor of highly charged Li-like ions is presented. Special attention is paid to the recent evaluation of the two-photon exchange corrections in the presence of a magnetic field. The most accurate theoretical values for the specific difference between the hyperfine splittings of H- and Li-like bismuth ions as well as for the g-factor of the Li-like silicon ion are presented.

Volotka, Andrey V.; Glazov, Dmitry A.; Andreev, Oleg V.; Shabaev, Vladimir M.; Tupitsyn, Ilya I.; Plunien, Günter

2013-09-01

58

Magnetic field and magnetic isotope effects in organic photochemical reactions. A novel probe of reaction mechanisms and a method for enrichment of magnetic isotopes  

Microsoft Academic Search

A brief qualitative description of the theory of intersystem crossing (ISC) in radical pairs is presented. It provides a simple unified theoretical basis for understanding chemically induced nuclear polarization (CIDNP), the magnetic spin isotope effect, and magnetic field effects on chemical reactions. Examples are given in which the magnetic spin isotope effect is employed to separate ¹³C (a magnetic isotope)

Nicholas J. Turro; Bernhard Kraeutler

1980-01-01

59

A probe for the measurement of the transport critical current density of superconductors in high magnetic fields and at temperatures between 2 and 150 K  

Microsoft Academic Search

A new probe has been designed for the measurement of the critical current density (Jc(B,T)) of both high- and low-temperature superconductors as a function of field and temperature. With this probe, voltage-current characteristics can be measured in small bore high-field magnets in the temperature range from 2-150 K with noise levels of typically 350 nV RMS. Excellent temperature accuracy and

C. M. Friend; D. P. Hampshire

1995-01-01

60

Magnetic Field Measurement System  

SciTech Connect

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

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

2007-01-19

61

The Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

Microsoft Academic Search

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field dynamics and time scales are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field

C. A. Kletzing; W. Kurth; M. Acuna; R. Torbert; R. Thorne; V. Jordanova; S. Bounds; C. Smith; O. Santolik; R. Pfaff; D. Rowland; G. Hospodarsky; W. Baumjohann; R. Nakamura; P. Puhl-Quinn

2006-01-01

62

Wave Science with the Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

Microsoft Academic Search

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields of waves which mediate these processes. A large range of field regimes are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field interactions,

S. R. Bounds; C. A. Kletzing; W. S. Kurth; M. H. Acuna; R. B. Torbert; R. Thorne; V. Jordanova; C. Smith; O. Santolik; R. Pfaff; D. Rpwlamd; G. Hospodarsky; W. Baumjohann; R. Nakamura; P. Puhl-Quinn

2008-01-01

63

The Electric and Magnetic Field Instrument Suite with Integrated Science (EMFISIS) on the Radiation Belt Storm Probes  

Microsoft Academic Search

The physics of the creation and loss of radiation belt particles is intimately connected to the electric and magnetic fields which mediate these processes. A large range of field regimes are involved in this physics from ring current magnetic fields to microscopic kinetic interactions such as whistler-mode chorus waves with energetic electrons. To measure these key field interactions, NASA has

Craig Kletzing

2008-01-01

64

Magnetic hyperfine fields at 119Sn probe nuclei on the R sites of the cubic rare-earth Laves-phase compounds RFe2 and RCo2  

Microsoft Academic Search

The magnetic hyperfine interaction of the 119Sn probe nucleus on the R site of the ferro- and ferrimagnetic RFe2 (R = Sm-Tm, Lu, Zr, Hf and U) and RCo2 (R = Gd-Er) compounds has been investigated by Mössbauer spectroscopy technique. It was found that the magnetic hyperfine fields (Bhf) exhibit quite different behaviours in the two series of the compounds.

N. N. Delyagin; V. I. Krylov

2007-01-01

65

Force-Detected Nuclear Magnetic Resonance Probe  

NASA Astrophysics Data System (ADS)

Magnetic resonance force microscopy (MRFM) entails measuring the force on spins in a sample by a nearby magnetic grain as they are cyclically flipped by RF radiation in the presence of a background magnetic field. The sample is glued to a cantilever, which acts as the force detector. We have constructed a compact, LHe-cooled MRFM probe which fits in a 1'' tube, minimizing thermal drift, and allowing testing in storage dewars. The RF field is generated by a 700 ?m diameter coil in a tuned and matched tank circuit. Joule and RF heating control sample temperature. The sample is mounted on a silicon-nitride cantilever, and its magnetization is modulated at the cantilever resonance frequency by interrupted adiabatic rapid passage. Probe performance is demonstrated by measuring a 10 fN magnetic resonance signal from a sample of Nd doped Ca^19F_2.

Harrell, Lee E.; Thurber, Kent; Fainchtein, Raul; Marohn, John A.; Smith, Doran D.

2000-03-01

66

Nanometer Scale Distance Measurements for Biological Systems using Gd^3+-based Spin Probes at High Magnetic Fields  

NASA Astrophysics Data System (ADS)

Determination of nanometer-scale distances is critical for understanding structure and dynamics of proteins. Electron Paramagnetic Resonance (EPR), primarily below 1 T, is used to complement other structural techniques by quantifying sparse distances up to 8 nm in biomolecules labeled with nitroxide-based radicals. EPR becomes more powerful with increasing magnetic fields and frequencies. At 95 GHz (3.5 T), Gd^3+ ions have shown clear advantages over nitroxide probes (Potapov, JACS 2010). We show that these advantages are even more dramatic at 240 GHz (8.5 T). The width of Gd^3+'s central EPR transition narrows with increasing average distance between Gd^3+ ions out to distances as long as 5 nm. This doubles the distances accessible with nitroxides in continuous wave measurements, which can be carried out above the 200K protein-glass transition and with broad distance distributions. Temperature-dependent measurements of the phase memory times at 8.5 T and low temperatures show distance dependence out to 10 nm. Measurements of Gd^3+ labeled Proteorhodopsin confirm that phase memory times remain long enough to observe distance dependence in a spin-labeled protein. This work is supported by the National Science Foundation and the Binational Science Foundation.

Edwards, Devin; Goldfarb, Daniella; Han, Songi; Sherwin, Mark

2012-02-01

67

Integrated Magnetic Loop Probe in GaAs Technology for Active Near-Field Sensor  

Microsoft Academic Search

This paper reports on design, simulation and measurement of miniature rectangular loops in OMMIC ED02AH GaAs technology. The loops are intended for integration on chip with other active circuitry for near-field scanning of printed circuit boards (PCB) as well as large scale integrated (LSI) circuits. Our target frequency range is from 1 MHz to 3 GHz and is planned to

Nasir Uddin; Matthias Spang; Andreas Thiede

2008-01-01

68

Magnetic Measurements at 'GANIL' M-HALL Probe Utilization.  

National Technical Information Service (NTIS)

This work was intended for developing a magnetic field measuring bench, and for investigating the various methods of magnetic measurements capable to answer the requirements from GANIL users: NMR, magnetoresistance, Hall probes, rotating coils. Two method...

H. Znaidi

1978-01-01

69

Broadband calibration of radio-frequency magnetic induction probes  

Microsoft Academic Search

We describe broadband calibration of a magnetic induction probe using a network analyzer. Our procedure uses a small driver coil and the scattering matrix associated with the coil-probe pair. This allows rapid, high-resolution measurements of the amplitude and phase of the probe’s response to oscillating magnetic fields. Our setup gives high accuracy between 100 kHz and 100 MHz and less

S. Messer; D. D. Blackwell; W. E. Amatucci; D. N. Walker

2006-01-01

70

Negative Differential Velocity in Artificial Crystals Probed by High Magnetic Fields  

NASA Astrophysics Data System (ADS)

Progress in the synthesis and engineering of semiconductor materials has led to improved device performances and functionalities. In particular, in the last decade, there has been considerable interest in the physics and applications of highly-mismatched alloys in which small and highly-electronegative isovalent N-atoms are incorporated onto the anion sublattice of a III-V compound semiconductor.1 The most studied material is the GaAs1-xNx alloy. Our magnetotunnelling studies have shown that a small percentage of N (x < 1%) perturbs dramatically the electronic properties of the host GaAs crystal leading to a large increase of the electron effective mass and an unusual response of the energy-wavevector dispersions to hydrostatic pressure.2-6 These effects differ from the smoother variation of the energy band gap and electron effective mass with alloy composition observed in other semiconductor compounds, such as InyGa1-yAs. The incorporation of N in GaAs gives rise to a qualitatively different type of alloy phenomenon: N-impurities and N-clusters tend to localize the extended Bloch states of GaAs at resonant energies in the conduction band (CB), thus fragmenting the energy-wavevector dispersion relations. The possibility of tailoring the electronic properties of III-V compounds by N-incorporation has stimulated proposals for innovative devices in optoelectronics and high frequency (terahertz, THz) electronics.7 However, to date, the implementation of dilute nitrides in these technologies presents several challenges, including a degradation of the electron mobility. Also, despite a rapidly expanding body of work on the electronic properties of GaAs1-xNx, the range of N-concentrations over which this alloy behaves as a good conductor is not yet well established. Our magnetotransport experiments have revealed how the incorporation of N in GaAs affects the electrical conductivity. Our studies in n-type GaAs1-xNx epilayers revealed a large increase of the resistivity, ?, for x > 0.2%, which we have attributed to the emergence of defect states with deep (~ 0.3 eV) energy levels. Electron trapping onto these states was not observed at low x (x = 0.2%). In this ultra-dilute alloy regime and at low electric fields (F < 1 kV/cm) the electrical conductivity retains the characteristic features of transport through extended states, albeit with relatively low mobility (µ ~ 0.1 m2/Vs at RT) due to scattering of electrons by N-atoms. We have focused our research on this ultra-dilute regime and exploited the admixing of the localized single N-impurity level with the extended conduction band states of GaAs to realize an unusual type of negative differential velocity (NDV) effect: at large F (> 1 kV/cm), electrons gain sufficient energy to approach the energy of the resonant N-level, where they become spatially localized.7-10 This Resonant Electron Localization in Electric Field, to which we give the acronym RELIEF, leads to NDV and strongly non-linear current-voltage characteristics. We envisage that the RELIEF-effect could be observed in other III-N-V alloys, such as InP1-xNx and InAs1-xNx. In these compounds the nature of the resonant interaction between the N-level and the conduction band states of the host-crystal is still relatively unexplored. However, it is clear that the different energy positions of the N-level relative to the conduction band minimum of different materials could offer new degrees of freedom in the design of the electronic band structure and electron dynamics. The RELIEF-effect may open up prospects for future applications in fast electronics. We have shown that the maximum response frequency, fmax, of a RELIEF-diode can be tuned by the applied electric field in the THz frequency range.7 This is of potential technological significance for the development of detectors/sources in the 0.6-1 THz region, which is not currently attainable using conventional Transferred Electron Devices and Quantum Cascade Lasers. Our recent studies of GaAs1-xNx have also shown a fast response of the current in the sub-T

Patanè, A.

71

The use of magnetic field effects on photosensitizer luminescence as a novel probe for optical monitoring of oxygen in photodynamic therapy  

NASA Astrophysics Data System (ADS)

The effect of a magnetic field on the steady-state and time-resolved optical emission of a custom fullerene-linked photosensitizer (PS) in liposome cell phantoms was studied at various oxygen concentrations (0.19-190 µM). Zeeman splitting of the triplet state and hyperfine coupling, which control intersystem crossing between singlet and triplet states, are altered in the presence of low magnetic fields (B < 320 mT), perturbing the luminescence intensity and lifetime as compared to the triplet state at B = 0. Measurements of the luminescence intensity and lifetime were performed using a time-domain apparatus integrated with a magnet. We propose that by probing magnet-affected optical emissions, one can monitor the state of oxygenation throughout the course of photodynamic therapy. Since the magnetic field effect (MFE) operates primarily by affecting the radical ion pairs related to type I photodynamic action, the enhancement or suppression of the MFE can be used as a measure of the dynamic equilibrium between the type I and II photodynamic pathways. The unique photo-initiated charge-transfer properties of the PS used in this study allow it to serve as both cytotoxic agent and oxygen probe that can provide in situ dosimetric information at close to real time.

Mermut, O.; Diamond, K. R.; Cormier, J.-F.; Gallant, P.; Hô, N.; Leclair, S.; Marois, J.-S.; Noiseux, I.; Morin, J.-F.; Patterson, M. S.; Vernon, M. L.

2009-01-01

72

Standard probes for electromagnetic field measurements  

Microsoft Academic Search

Discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The standard probes described are an electrically short dipole, a resistively-loaded dipole, a half-wave dipole, an electrically small loop, and a resistively-loaded loop. A single-turn loop designed for simultaneous measurement of the electric and magnetic components of

Motohisa Kanda

1993-01-01

73

Development of a high sensitivity, inductively coupled, miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified B˙ circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular emphasis on the importance of the Hall effect to plasma transport

D. C. Black; R. M. Mayo

1995-01-01

74

Surface and Interface Magnetism Using Radioactive Probes  

NASA Astrophysics Data System (ADS)

Magnetic properties of impurities at ferromagnetic surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the ultra-high vacuum chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. We present the measurements of magnetic hyperfine fields ( B hf) at 111Cd probe atoms (i) in Pd covered by Ni, (ii) on Pd-decorated Ni surfaces, (iii) and on pure Ni surfaces at a variety of local structures like terraces, steps, kinks. The results yield a deep insight into the interplay of structural surface roughness and magnetic roughness on the atomic scale. Correlating the experimental B hf values with the number of their nearest Ni and Pd neighbours, the coordination number, nonlinear dependences were found. These findings are compared with recent theoretical studies which were prompted by the experiments.

Manzhur, Y.; Prandolini, M. J.; Potzger, K.; Weber, A.; Zeitz, W.-D.; Bertschat, H. H.; Dietrich, M.

2005-01-01

75

Study of interaction of proflavin with triethylamine in homogeneous and micellar media: Photoinduced electron transfer probed by magnetic field effect  

NASA Astrophysics Data System (ADS)

Interaction of triethylamine (TEA) with cationic proflavin (PF +) in homogeneous and micellar media is studied using absorption spectroscopy, steady-state as well as time-resolved fluorescence spectroscopy and laser flash photolysis in conjunction with an external magnetic field. The two prime phenomena that have been highlighted in this study are photoinduced electron transfer (PET) and ground-state complex formation. This study shows that it is the medium which determines the reaction pathways to be followed. Magnetic field effect (MFE) helps to elucidate the reaction mechanism involved and this work also highlights the distance dependence factor associated with MFE.

Chakraborty, Brotati; Basu, Samita

2009-08-01

76

Magnetic fields in astrophysics  

Microsoft Academic Search

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

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

1983-01-01

77

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

78

The induced magnetic field.  

PubMed

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

Islas, Rafael; Heine, Thomas; Merino, Gabriel

2011-08-17

79

Atom Probe Field Ion Microscopy  

Microsoft Academic Search

This book is one of the series of `Monographs on the physics and chemistry of materials', published by the Clarendon Press. Its title is perhaps unduly restrictive inasmuch as the identification of single atoms in the field ion microscope (Atom probe FIM) is merely the end stage in a long chain of computer-assisted operations plus the equally important task of

T Mulvey

1997-01-01

80

Energetic charged particles as probes of the geometry and topology of the interplanetary magnetic field: The detection of coronal mass ejections  

SciTech Connect

The large-scale structure of the interplanetary magnetic field has been inferred almost exclusively from single point measurements obtained by spacecraft. It has recently been appreciated that energetic charged particles can yield new information about the interplanetary fields since they originate at the sun and are constrained to follow the field lines out to the points of observation. The author reviews the results of particle probes, particularly bidirectional flows (BDFs), to detect coronal mass ejections (CMEs). While a good association, possibly one-to-one, has been assumed between BDFs and CMEs, there is now evidence to suggest that some CMEs do not produce BDFs and that many BDFs are not due to CMEs.

Kahler, S.W.

1994-09-01

81

Infrared lines as probes of solar magnetic features. XIII. The relative flux in weak and strong quiet-sun magnetic fields  

NASA Astrophysics Data System (ADS)

An estimate of the fraction of magnetic flux in intrinsically weak-field form, i.e. fields with less than 1 kG intrinsic strength, in the quiet Sun is presented. We find that on average approximately 2/3 of the flux is in weak-field form, although our data allow a range of values between 25%\\ and 85%. These estimates have been derived with the help of radiative transfer model calculations from low-noise scans through the quiet Sun at fixed wavelengths within a Zeeman sensitive spectral line at 1.56 mu m. They represent the first rapidly modulated polarimetric observations of solar 1.56 mu m radiation. These scans show that the polarimetric signature near the core of the line exhibits a very different spatial structure than in the outer line wings. Since the outer part of the line profile is only sensitive to intrinsically strong magnetic fields, while the central part reacts also to intrinsically weak fields, this implies that intrinsically weak fields are distributed differently on the surface than strong fields are (weak-field features lie closer together). The spatial distribution suggests that the strong fields we are observing are network elements, whereas the weak fields are intranetwork features. Further results, such as the average distance between weak and strong field features, flux distribution, spatial power spectra and the Stokes asymmetry of intrinsically weak fields are also presented. In particular, we find that the flux per magnetic feature is distributed lognormally, in agreement with a similar finding for sunspot umbral areas by Bogdan et al. (1988).

Meunier, N.; Solanki, S. K.; Livingston, W. C.

1998-03-01

82

Magnetic Fields Matter  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

83

Near Field Spectroscopy of Quantum Dots Under Magnetic Field  

Microsoft Academic Search

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

Anna Zora; Constantinos Simserides; Georgios Triberis

2005-01-01

84

Near Field Spectroscopy of Quantum Dots Under Magnetic Field  

Microsoft Academic Search

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

Anna Zora; Constantinos Simserides; Georgios Triberis

2004-01-01

85

Electric field probes for cellular phone dosimetry  

Microsoft Academic Search

Miniature implantable electric field probes (E-field Probes) enable the measurements of microwave electric fields induced in biological subjects by relatively low level exposures. Using these instruments, the rate of energy deposition (Specific Absorption Rate or SAR) can be determined throughout models or actual bodies of laboratory animals and humans exposed to emissions from cellular phones and other radiators. E-field probes

Howard I. Bassen

1997-01-01

86

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

87

Contributions of the electronic spin and orbital current to the CoCl4(2-) magnetic field probed in polarised neutron diffraction experiments.  

PubMed

Polarised neutron diffraction experiments conducted at 4.2 K on Cs(3)CoCl(5) crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl(4)(2-) molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, ?(2), less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed. PMID:22897255

Cassam-Chenaï, Patrick; Jayatilaka, Dylan

2012-08-14

88

Contributions of the electronic spin and orbital current to the CoCl42- magnetic field probed in polarised neutron diffraction experiments  

NASA Astrophysics Data System (ADS)

Polarised neutron diffraction experiments conducted at 4.2 K on Cs3CoCl5 crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl42- molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, ?2, less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed.

Cassam-Chenaï, Patrick; Jayatilaka, Dylan

2012-08-01

89

Contributions of the electronic spin and orbital current to the CoCl{sub 4}{sup 2-} magnetic field probed in polarised neutron diffraction experiments  

SciTech Connect

Polarised neutron diffraction experiments conducted at 4.2 K on Cs{sub 3}CoCl{sub 5} crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl{sub 4}{sup 2-} molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, {chi}{sup 2}, less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed.

Cassam-Chenaie, Patrick [Laboratoire J. A. Dieudonne, UMR 6621 du CNRS, Faculte des Sciences, Parc Valrose, 06108 Nice cedex 2 (France); Jayatilaka, Dylan [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)

2012-08-14

90

Using variable-frequency asymmetries to probe the magnetic field dependence of radial transport in a Malmberg-Penning trap  

NASA Astrophysics Data System (ADS)

A new experimental technique is used to study the dependence of asymmetry-induced radial particle flux ? on axial magnetic field B in a modified Malmberg-Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity vr = E?/B and in the zeroth order azimuthal drift velocity v? = Er/B. To separate these, we employ the hypothesis that the latter always enters the physics in the combination ?-l?R, where ?R = v?/r is the column rotation frequency and ? and l are the asymmetry frequency and azimuthal mode number, respectively. Points where ?-l?R = 0 are then selected from a ? vs r vs ? data set, thus insuring that any function of this combination is constant. When the selected flux ?sel is plotted versus the density gradient, a roughly linear dependence is observed, showing that this selected flux is diffusive. This linear dependence is roughly independent of the bias of the center wire in our trap ?cw. Since in our experiment ?R is proportional to ?cw, this latter point shows that our technique has successfully removed any dependence on ?R and its derivatives, thus confirming our hypothesis. The slope of a least-squares fitted line through the ?sel vs density gradient data then gives the diffusion coefficient D0 under the condition ?-l?R = 0. Varying the magnetic field, we find D0 is proportional to B-1.33+/-0.05, a scaling that does not match any theory we know. These findings are then used to constrain the form of the empirical flux equation. It may be possible to extend this technique to give the functional dependence of the flux on ?-l?R.

Eggleston, D. L.

2009-03-01

91

Thermalization in external magnetic field  

NASA Astrophysics Data System (ADS)

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

Ali-Akbari, Mohammad; Ebrahim, Hajar

2013-03-01

92

Electron motion in fast magnetically insulated ion probes  

Microsoft Academic Search

Simulations have been performed to determine the time-dependent response of an intense ion beam incident on a transverse magnetic field. The geometry is appropriate for the simulation of a magnetically insulated ion probe. For a case with parameters such that the beam electrons should be stripped from the ions, the electrons nevertheless drift with the beam at a reduced velocity.

T. R. Lockner; J. W. Poukey

1983-01-01

93

Using variable-frequency asymmetries to probe the magnetic field dependence of radial transport in a Malmberg-Penning trap  

SciTech Connect

A new experimental technique is used to study the dependence of asymmetry-induced radial particle flux {gamma} on axial magnetic field B in a modified Malmberg-Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity v{sub r} = E{sub {theta}}/B and in the zeroth order azimuthal drift velocity v{sub {theta}} = E{sub r}/B. To separate these, we employ the hypothesis that the latter always enters the physics in the combination {omega}-l{omega}{sub R}, where {omega}{sub R} = v{sub {theta}}/r is the column rotation frequency and {omega} and l are the asymmetry frequency and azimuthal mode number, respectively. Points where {omega}-l{omega}{sub R} = 0 are then selected from a {gamma} vs r vs {omega} data set, thus insuring that any function of this combination is constant. When the selected flux {gamma}{sub sel} is plotted versus the density gradient, a roughly linear dependence is observed, showing that this selected flux is diffusive. This linear dependence is roughly independent of the bias of the center wire in our trap {phi}{sub cw}. Since in our experiment {omega}{sub R} is proportional to {phi}{sub cw}, this latter point shows that our technique has successfully removed any dependence on {omega}{sub R} and its derivatives, thus confirming our hypothesis. The slope of a least-squares fitted line through the {gamma}{sub sel} vs density gradient data then gives the diffusion coefficient D{sub 0} under the condition {omega}-l{omega}{sub R} = 0. Varying the magnetic field, we find D{sub 0} is proportional to B{sup -1.33{+-}}{sup 0.05}, a scaling that does not match any theory we know. These findings are then used to constrain the form of the empirical flux equation. It may be possible to extend this technique to give the functional dependence of the flux on {omega}-l{omega}{sub R}.

Eggleston, D. L. [Occidental College, Los Angeles, California (United States)

2009-03-30

94

Microwave resonances of a hairpin probe in a magnetized plasma  

SciTech Connect

The effect due to the electron cyclotron frequency on the microwave resonances of a hairpin probe is investigated in a moderate to strongly magnetized plasma. The magnetic field is independently varied over a wide range from 0.01-0.13 T while maintaining the local plasma density constant. At strong magnetic fields the resonance frequency is found to be lower than that measured in vacuum implying that the relative plasma dielectric permittivity, epsilon{sub p}>1. It is proposed that the experiments reported here are consistent with a permittivity model that includes magnetic field.

Gogna, G. S.; Karkari, S. K. [National Centre for Plasma Science and Technology, School of Physics, Dublin City University, Dublin 9 (Ireland)

2010-04-12

95

The magnetic-distortion probe: Velocimetry in conducting fluids  

NASA Astrophysics Data System (ADS)

A new type of velocimeter, capable of local velocity measurements in conducting fluids, is introduced. The principle of the ``magnetic-distortion probe'' is based on the measurement of the induced magnetic field by the flow of a conducting fluid in the vicinity of a localized magnetic field. The new velocimeter has no moving parts, and can be enclosed in a sealed cap, easing the implementation in harsh environments, such as liquid metals. The proposed method allows one to probe both the continuous part and fluctuations of the velocity, the temporal and spatial resolution being linked to the actual geometric configuration of the probe. A prototype probe has been tested in a gallinstan pipe flow and in a fully turbulent flow of liquid gallium generated by the counter rotation of two coaxial impellers in a cylinder. The signals have been compared to a reference potential probe and show very good agreement both for time-averaged velocities and turbulent fluctuations. The prototype is shown to detect motion from a few cm s-1 to a few m s-1. Moreover, the use of the magnetic-distortion probe with large-scale applied magnetic field is discussed.

Miralles, Sophie; Verhille, Gautier; Plihon, Nicolas; Pinton, Jean-François

2011-09-01

96

Induced Magnetic Anisotropy of Ferrofluid Frozen in Magnetic Fields  

Microsoft Academic Search

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

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

1989-01-01

97

The Magnetic Field  

NSDL National Science Digital Library

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

Barker, Jeffrey

98

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles  

Microsoft Academic Search

Solar energetic particles (SEPs) have been used as probes of magnetic cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not

S. W. Kahler; D. V. Reames

1991-01-01

99

Photospheric Magnetic Field: Quiet Sun  

NASA Astrophysics Data System (ADS)

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

Solanki, S. K.

2009-06-01

100

Broadband calibration of radio-frequency magnetic induction probes  

SciTech Connect

We describe broadband calibration of a magnetic induction probe using a network analyzer. Our procedure uses a small driver coil and the scattering matrix associated with the coil-probe pair. This allows rapid, high-resolution measurements of the amplitude and phase of the probe's response to oscillating magnetic fields. Our setup gives high accuracy between 100 kHz and 100 MHz and less accuracy outside this range. We present over 1800 sensitivity measurements between 30 kHz and 1 GHz. The ideal probe response is compared to calibrations done with two different driver coils. We discuss several hurdles in probe design and calibration, as well as several high-frequency effects.

Messer, S.; Blackwell, D. D.; Amatucci, W. E.; Walker, D. N. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States)

2006-11-15

101

Magnetic Field Problem  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

102

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

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

Beck, Rainer; Wielebinski, Richard

103

Intergalactic magnetic fields  

Microsoft Academic Search

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

A. A. Ruzmajkin

1991-01-01

104

Magnetic Field Example 1  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2008-02-19

105

The Magnetic Field  

NSDL National Science Digital Library

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

Universe, Windows T.

1997-12-03

106

Melatonin and magnetic fields.  

PubMed

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

Karasek, Michal; Lerchl, Alexander

2002-04-01

107

Nuclear magnetic resonance apparatus for pulsed high magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

108

Pulsars as excellent probes for the magnetic structure in our Milky Way  

NASA Astrophysics Data System (ADS)

In this invited talk, I first discuss the advantages and disadvantages of many probes for the magnetic fields of the Milky Way. I conclude that pulsars are the best probes for the magnetic structure in our Galaxy, because magnetic field strength and directions can be derived from their dispersion measures (DMs) and rotation measures (RMs). Using the pulsars as probes, magnetic field structures in the Galactic disk, especially the field reversals between the arms and interarm regions, can be well revealed from the distribution of RM data. The field strengths on large scales and small scales can be derived from RM and DM data. RMs of extragalactic radio sources can be used as the indication of magnetic field directions in the spiral tangential regions, and can be used as probes for the magnetic fields in the regions farther away than pulsars when their median RMs are compared with pulsar RMs.

Han, JinLin

2013-03-01

109

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

110

Probing Gravitational Sensitivity in Biological Systems Using Magnetic Body Forces  

NASA Astrophysics Data System (ADS)

We have commissioned a superconducting solenoid based apparatus designed to exert strong magnetic body forces on biological specimens and other organic materials in ambient environmental conditions for extended periods. In its room temperature bore, it can produce a maximum magnetic field-field gradient product of 16 T^2-cm-1 which is sufficient to levitate frog embryos Xenopus Laevis[1]. We will discuss how we are applying these magnetic body forces to probe the known influences of gravitational forces on frog embryos and the swimming behavior of Paramecium Caudatum. In the process, we will describe a novel method for measuring the diamagnetic susceptibilities of specimens such as paramecia.

Valles, James; Guevorkian, Karine; Wurzel, Samuel; Mihalusova, Mariana

2003-03-01

111

On Cosmic Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Florido, E.; Battaner, E.

2010-12-01

112

Magnetic fields at Uranus  

Microsoft Academic Search

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

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

1986-01-01

113

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

114

Movable magnetic probe system in the T-10 tokamak.  

PubMed

New magnetic probe system is installed on the T-10 tokamak to investigate fast-scale magnetic perturbations (f up to 2 MHz). The system is based on vertical and horizontal magnetic probes made by nickel wire in glass enamel isolation (effective area 20-250 cm(2)) separated from the support structures by ceramic spacers (5-10 mm). The probe system is mounted on the top of movable rode allowing positioning along vertical axis close to the plasma boundary at the low field side of the torus. Additional positioning system allows rotation of the probes around the vertical axis on pulse-to-pulse basis. The probes are directly connected to the analog-to-digital converter (ADC) module (acquisition rate 60 MHz) through short (~4 m) coaxial cables. The system allowed identification of the fast-scale magnetic oscillations (0.2-0.5 MHz) during energy quench phase of the disruption instability in plasma with high density. Amplitude of the fast-scale magnetic oscillations decays with distance from the plasma boundary 2-10 times faster than one of the standard magnetohydrodynamic modes. PMID:22299949

Savrukhin, P V; Shestakov, E A

2012-01-01

115

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

116

Manipulating Cells with Static Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Valles, J. M.; Guevorkian, K.

2005-07-01

117

The advantages of the magnetic structure in ferromagnetic-film-coated carbon nanotube probes  

NASA Astrophysics Data System (ADS)

The magnetic structures of ferromagnetic-film-coated carbon nanotube (CNT) probes and conventional pyramidal probes for a magnetic force microscope (MFM) were simulated using three-dimensional micromagnetic simulation. The CNT-MFM probes with a total probe diameter less than 60 nm are almost uniformly magnetized along the longitudinal direction of the CNT, which is the ideal magnetic structure for MFM observations. On the other hand, the pyramidal probes had a vortex structure around the point tip, which suggests that they require a greater thickness of the ferromagnetic film because only part of the magnetic moment participates in the detection of the z-component of the stray field from samples. The advantages of the CNT-MFM probe are uniform magnetization along the longitudinal direction and magnetic imaging ability using a smaller coating thickness.

Manago, T.; Asada, H.; Uzumaki, T.; Takano, F.; Akinaga, H.; Kuramochi, H.

2012-01-01

118

The FIELDS experiment for Solar Probe Plus  

NASA Astrophysics Data System (ADS)

Many of our basic ideas on the plasma physics of acceleration, energy flow, and dissipation, and structure of the solar wind have never been rigorously confronted by direct experimental measurements in the region where these processes are actually occurring. Although Alfven waves, shocks, and magnetic reconnection are often invoked as heating mechanisms, there have never been any direct measurements of Alfvenic waves nor the associated Poynting flux nor any measurements of ion or electron kinetic energy flux in the region from 10 R_s to 30 R_s where the final stages of wind acceleration are believed to occur. The radial profiles of both slow and fast solar wind acceleration are based on remote-sensing measurements and have been obtained for only a few selected events. Thus, the spatial radial and perpendicular scales of the acceleration process have been averaged by line-of-sight effects and the possibility of intense localized acceleration cannot be ruled out. The Solar Probe Plus (SPP) mission calls for the high quality fields and particles measurements required to solve the coronal heating and wind acceleration problem. The SPP 'FIELDS' experiment measures the electric and magnetic fields fundamental to the plasma physics of the structured and turbulent solar wind, flux ropes, collisionless shocks, and magnetic reconnection. FIELDS will make the first-ever measurements of the DC/Low-Frequency electric field inside of 1 AU allowing for in situ, high cadence measurements of the Poynting vector, the Elsasser variables, and E/B diagnostics of the wave spectrum to fce in the solar wind. SPP/FIELDS measures the radio wave (type III and II) signatures of microflares, energized electrons, and CME propagation. SPP/ FIELDS measures the plasma electron density to ~2% accuracy and the core electron temperature to ~5-10% accuracy more than 90% of the time at perihelion. FIELDS will also measure the in situ density fluctuation spectrum and structures at a very high cadence (? 10 kHz) and provide definitive signatures of the turbulent nature and heating of the solar wind plasma. Furthermore, SPP/FIELDS measures the impact rate and sig- natures of dust from micron- to nano-scales, by measuring the voltage signature of dust impacts on the spacecraft. FIELDS will also measure the floating potential of the SPP spacecraft, which is essential for correcting in situ electron data. The SPP/FIELDS experiment combines four (4) deployable electric antennas, fluxgate and search coil magnetometers and the associated signal processing electronics into a scientifically and technically integrated package. SPP/FIELDS makes very high cadence measurements of fields and density and employs an internal burst memory for intelligent data selection. FIELDS is required to measure very large plasma potentials and electric fields (~10V) and uses floating ground (+/- 100V) power preamplifiers. The SPP/FIELDS team has performed 3D plasma simulations of the SPP spacecraft plasma environ- ment, which reveal enormous voltage fluctuation levels in the plasma wake behind the spacecraft. This voltage noise dominates the true signal by orders of magnitude in the critical DC/LF frequency range. Therefore, we are proposing a design which places the four (4) electric antennas in front of the spacecraft ahead of the heat shield.

Bale, S.; Spp/Fields Team

2010-12-01

119

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

120

Magnetic Field Lines  

NSDL National Science Digital Library

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

Horton, Michael

2009-05-30

121

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

122

Characteristics of magnetic force microscopy magnetics on high moment perpendicular magnetic recording writers with high coercivity probes  

NASA Astrophysics Data System (ADS)

High resolution magnetic force microscopy (MFM) imaging with high coercivity probes on perpendicular magnetic recording (PMR) writers directly characterizes magnetic field contour for the writer main pole as well as its shields' magnetic state. Evolution of write bubble and return field was analyzed by MFM imaging in dynamic phase detection scheme. Different write field components and their out of plane second order derivatives were calculated via finite element modeling. The MFM imaged write field distribution correlates well with the PMR writer out of plane write field component. Magnetic responses of the PMR writer main pole, trailing and side shields are quantified. The trailing and side shields exhibit complicated magnetic saturation behaviors comparing with the PMR writer pole. The side shield's magnetic response is dependent upon its initial equilibrium state.

Liu, Feng; Li, Shaoping; Bai, Daniel; Wang, James; Li, Zhanjie; Han, Dehua; Pan, Tao; Mao, Sining

2012-04-01

123

Magnetic field confinement for magnetically levitated vehicles  

SciTech Connect

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

Proise, M.

1993-05-25

124

Magnetic Probe Construction using Thick-film Technology  

SciTech Connect

Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultra-high vacuum and high-temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 degrees C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low-frequency coils have a measured coupling area of 296-323 cm squared and a frequency response of about 300 kHz. High-frequency coils have a design coupling area of 12-15 cm squared.

Takahashi, H.; Sakakibara, S.; Kubota, Y.; and Yamada, H.

2001-02-02

125

Determination of interfacial dielectric constant of AOT-based reverse micelle by probing magnetic field effect on pyrene?DMA exciplex luminescence  

NASA Astrophysics Data System (ADS)

The effect of magnetic field on the luminescence of pyrene-DMA exciplex confined within the reverse micellar (RM) environment of various cavity sizes is reported. The field-modulated change in luminescence ? ?/ ?) at various w values is strikingly similar to the ? ?/ ? vs dielectric constant ( ?) variation of solvent mixtures which suggests that ? of the RM interface is primarily responsible for the variation of magnetic field effect (MFE). The interfacial dielectric constant at different w values may be evaluated on the basis of the above similarity.

Pratim Parui, Partha; Narayan Nath, Deb; Chowdhury, Mihir

2004-10-01

126

High magnetic field generation for laser-plasma experiments  

Microsoft Academic Search

An electromagnetic solenoid was developed to study the effect of magnetic fields on electron thermal transport in laser plasmas. The solenoid, which is driven by a pulsed power system supplying 30 kJ, achieves magnetic fields of 13 T. The field strength was measured on the solenoid axis with a magnetic probe and optical Zeeman splitting. The measurements agree well with

B. B. Pollock; D. H. Froula; P. F. Davis; J. S. Ross; S. Fulkerson; J. Bower; J. Satariano; D. Price; K. Krushelnick; S. H. Glenzer

2006-01-01

127

Planetary magnetic fields  

Microsoft Academic Search

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

David J. Stevenson

2003-01-01

128

Magnetic Multipole Field Model  

NSDL National Science Digital Library

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

Christian, Wolfgang; Cox, Anne; Franciscouembre

2010-02-14

129

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

130

Crustal magnetic field of Mars  

Microsoft Academic Search

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

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

2004-01-01

131

Electron effective mass and Si-donor binding energy in GaAs1-xNx probed by a high magnetic field  

NASA Astrophysics Data System (ADS)

We study the magnetoresistance of the dilute nitride alloy GaAs1-xNx in magnetic fields up to 47T . We observe a strong magnetophonon resonance effect and a large transverse magnetoresistance, which provide the means of measuring the N-induced enhancement of the electron effective mass and of investigating the magnetic freeze-out of conduction electrons on Si donors in GaAs1-xNx .

Allison, G.; Spasov, S.; Patanè, A.; Eaves, L.; Kozlova, N. V.; Freudenberger, J.; Hopkinson, M.; Hill, G.

2008-03-01

132

Probing Magnetic Nanostructures on the Atomic Scale  

NASA Astrophysics Data System (ADS)

Magnetic nanostructures are increasing data storage capacities and are promising candidates for implementations of novel spin-based computation techniques. The relative simplicity and reduced dimensionality of nanoscale magnetic structures also make them attractive model systems for studying fundamental interactions between quantum spins. We used a scanning tunneling microscope to build individual magnetic nanostructures one atom at a time. By measuring their spin-excitation spectra with inelastic electron tunneling spectroscopy, we determined the orientation and strength of the anisotropies of individual Fe and Mn atoms on copper nitride. First-principles calculations indicate that the magnetic atoms become incorporated into a polar covalent surface molecular network, making them similar to the building blocks of molecular magnets. In linear chains of up to 10 Mn atoms, we observed excitations of the coupled atomic spins that can change both the total spin and its orientation. The large magnetic anisotropy and strong spin-coupling manifested in these structures, which provide atom-by-atom accessibility via local probes, have the potential to produce atomic-scale magnetic structures that have a stable magnetization at low temperatures. * This work was done in collaboration with C.-Y. Lin, A.F. Otte, M. Ternes, C.P. Lutz, B.A. Jones, and A.J. Heinrich at the IBM Almaden Research Center, San Jose, CA 95120 USA.

Hirjibehedin, Cyrus F.

2008-03-01

133

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

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

Beck, Rainer

2012-05-01

134

Orienting Paramecium with intense static magnetic fields  

NASA Astrophysics Data System (ADS)

Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic fields, 2.5 T < B < 8 T were applied to immobilized (non-swimming) Paramecium Caudatum that were suspended in a density matched medium. The organisms align with their long axis parallel to the applied magnetic field. Their intrinsic diamagnetic anisotropy is 3x10-11 in cgs units. We will discuss the implications of these results for employing magnetic fields to probe the behavior of swimming Paramecium. [1] J. M. Valles, Jr. et al., Expt. Cell Res.274, 112-118 (2002).

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

2004-03-01

135

Magnetic Probe to Study Plasma Jets for Magneto-Inertial Fusion  

SciTech Connect

A probe has been constructed to measure the magnetic field of a plasma jet generated by a pulsed plasma rail-gun. The probe consists of two sets of three orthogonally-oriented commercial chip inductors to measure the three-dimensional magnetic field vector at two separate positions in order to give information about the magnetic field evolution within the jet. The strength and evolution of the magnetic field is one of many factors important in evaluating the use of supersonic plasma jets for forming imploding spherical plasma liners as a standoff driver for magneto-inertial fusion.

Martens, Daniel [Los Alamos National Laboratory; Hsu, Scott C. [Los Alamos National Laboratory

2012-08-16

136

Probes for High Field Solid-state NMR of Lossy Biological Samples  

PubMed Central

In solid-state NMR exphydrated samples biopolymers are susceptible to radio-frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed.

Grant, Christopher V.; Wu, Chin H.; Opella, Stanley J.

2010-01-01

137

Magnetic field annihilators: invisible magnetization at the magnetic equator  

Microsoft Academic Search

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

S. Maus; V. Haak

2003-01-01

138

High magnetic field generation for laser-plasma experiments  

SciTech Connect

An electromagnetic solenoid was developed to study the effect of magnetic fields on electron thermal transport in laser plasmas. The solenoid, which is driven by a pulsed power system supplying 30 kJ, achieves magnetic fields of 13 T. The field strength was measured on the solenoid axis with a magnetic probe and optical Zeeman splitting. The measurements agree well with analytical estimates. A method for optimizing the solenoid design to achieve magnetic fields exceeding 20 T is presented.

Pollock, B. B.; Froula, D. H.; Davis, P. F.; Ross, J. S.; Fulkerson, S.; Bower, J.; Satariano, J.; Price, D.; Krushelnick, K.; Glenzer, S. H. [Lawrence Livermore National Laboratory, University of California, P.O. Box 808, Livermore, California 94551 (United States)

2006-11-15

139

High Magnetic field generation for laser-plasma experiments  

SciTech Connect

An electromagnetic solenoid was developed to study the effect of magnetic fields on electron thermal transport in laser plasmas. The solenoid, which is driven by a pulsed power system suppling 30 kJ, achieves magnetic fields of 13 T. The field strength was measured on the solenoid axis with a magnetic probe and optical Zeeman splitting. The measurements agree well with analytical estimates. A method for optimizing the solenoid design to achieve magnetic fields exceeding 20 T is presented.

Pollock, B B; Froula, D H; Davis, P F; Ross, J S; Fulkerson, S; Bower, J; Satariano, J; Price, D; Glenzer, S H

2006-05-01

140

Electrostatic probe disruption of drift waves in magnetized microdischarges  

SciTech Connect

Ultrahigh speed images of ExB discharges are collected during electrostatic probing of magnetized microdischarges. Two azimuthally separated floating micro-Langmuir probes inserted into an axisymmetric microscale magnetically confined plasma are used to characterize azimuthal drift waves. The images reveal features associated with probe intrusion, showing how the electrostatic probes may disrupt the otherwise coherent azimuthal waves. The resulting wave dispersion calculated from the probe signals is consistent with the disruptions seen in the images. These images demonstrate how probe measurements of fluctuations and turbulence, even when probe dimensions are much smaller than characteristic discharge scales, must be interpreted with caution.

Ito, T. [Frontier Research Base for Global Young Researchers, Frontier Research Center, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Cappelli, M. A. [Department of Mechanical Engineering, High Temperature Gasdynamics Laboratory, Stanford University, Stanford, California 94305-3032 (United States)

2009-05-25

141

The NBS-LANL RTM end-magnet field mapper  

Microsoft Academic Search

A computer-controlled magnetic field mapper is under construction at the National Bureau of Standards to map the end magnets of the NBS-LANL racetrack microtron (RTM). The mapper consists of a large, two-dimensional translation stage which simultaneously positions a nuclear magnetic resonance (NMR) magnetometer probe in the 55 cm x 135 cm uniform field region and a temperature-compensated Hall effect probe

E. R. Lindstrom; P. H. Debenham; D. L. Mohr; N. R. Yoder

1983-01-01

142

Liquid crystal fiber optic electric field probe  

NASA Astrophysics Data System (ADS)

Polymer dispersed liquid crystal inserted between two multimode optical fiber end faces forms the basis of an electric field probe. This probe has an active volume of about 0.001 mm3 and approximates a point measurement. The linear relation between detector output and electric field in the 600-800 V/cm range is adequate for most electric power distribution systems. As the contrast ratio of this transducer is large, it can be used as an on-off detector for high voltage equipment.

Lacquet, Beatrys M.; Swart, Pieter L.; Spammer, Stephanus J.

1995-09-01

143

Probing the Role of Magnetic-Field Variations in NOAA AR 8038 in Producing a Solar Flare and CME on 12 May 1997  

NASA Astrophysics Data System (ADS)

We carried out a multi-wavelength study of a Coronal Mass Ejection (CME) and an associated flare, occurring on 12 May 1997. We present a detailed investigation of magnetic-field variations in NOAA Active Region 8038 which was observed on the Sun during 7 - 16 May 1997. This region was quiet and decaying and produced only a very small flare activity during its disk passage. However, on 12 May 1997 it produced a CME and associated medium-size 1B/C1.3 flare. Detailed analyses of H? filtergrams and SOHO/MDI magnetograms revealed continual but discrete surge activity, and emergence and cancellation of flux in this active region. The movie of these magnetograms revealed the two important results that the major opposite polarities of pre-existing region as well as in the emerging-flux region were approaching towards each other and moving magnetic features (MMF) were ejected from the major north polarity at a quasi-periodicity of about ten hours during 10 - 13 May 1997. These activities were probably caused by magnetic reconnection in the lower atmosphere driven by photospheric convergence motions, which were evident in magnetograms. The quantitative measurements of magnetic-field variations such as magnetic flux, gradient, and sunspot rotation revealed that in this active region, free energy was slowly being stored in the corona. Slow low-layer magnetic reconnection may be responsible for the storage of magnetic free energy in the corona and the formation of a sigmoidal core field or a flux rope leading to the eventual eruption. The occurrence of EUV brightenings in the sigmoidal core field prior to the rise of a flux rope suggests that the eruption was triggered by the inner tether-cutting reconnection, but not the external breakout reconnection. An impulsive acceleration, revealed from fast separation of the H ? ribbons of the first 150 seconds, suggests that the CME accelerated in the inner corona, which is also consistent with the temporal profile of the reconnection electric field. Based on observations and analysis we propose a qualitative model, and we conclude that the mass ejections, filament eruption, CME, and subsequent flare were connected with one another and should be regarded within the framework of a solar eruption.

Jain, Rajmal; Awasthi, Arun K.; Chandel, Babita; Bharti, Lokesh; Hanaoka, Y.; Kiplinger, A. L.

2011-07-01

144

Magnetic Field Measurements in Beam Guiding Magnets  

Microsoft Academic Search

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

K. N. Henrichsen

1998-01-01

145

Energetic Electron Probes of Magnetic Cloud Topology  

NASA Astrophysics Data System (ADS)

Magnetic clouds (MCs) are large interplanetary coronal mass ejections (ICMEs) of enhanced fields with rotations indicative of magnetic flux ropes originally connected to the Sun. The MC models require field lines with larger pitch angles and longer lengths with increasing distance from the MC axis. While the models can provide good fits to the observations, the global magnetic field geometry has not been tested, particularly for the field-line lengths. Impulsive solar energetic (E > 30 keV) electron events occurring within MCs can be used to infer the propagation distance and magnetic field-line length from the Sun at the point in the MC where the electron onset occurs. We surveyed the 18 MCs listed on the Wind/MFI MC list in or near which solar electron events were observed by the SSL/Berkeley 3DP instrument on the Wind spacecraft. By plotting the electron onset times as functions of their speeds for each event and taking their solar injections to coincide with observed type III radio bursts in the Wind/WAVES detector, the travel distances of the electrons along the field lines of the MCs were computed. Those electron travel distances were compared with the field-line lengths computed from two different MC model fits to test the models.

Kahler, S. W.; Krucker, S.; Szabo, A.

2009-12-01

146

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

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

Balogh, André; Erdõs, Géza

2013-06-01

147

Associated electron and proton transfer between Acridine and Triethylamine in AOT reverse micelles probed by laser flash photolysis with magnetic field  

NASA Astrophysics Data System (ADS)

Laser flash photolysis with magnetic field (MF ˜0.08 T) has been used to study interaction between Acridine (Acr) and Triethylamine (TEA) in reverse micelles with w0 = 2.5-40. Dynamic protonation equilibrium exists between 3Acr and 3AcrH +. The intermediates indicate excited-state proton transfer (PT) between 3AcrH + and TEA. However, application of MF highlights the formation of geminate radical ion pairs (RIPs) with triplet spin-correlation, a signature of latent photoinduced electron transfer between 3AcrH + and TEA co-exists with PT. Magnetic field effect (MFE) is prominent for smaller w0 showing importance of optimum separation between RIP to maximize MFE, whereas PT remains unaltered.

Sarangi, Manas Kumar; Basu, Samita

2011-04-01

148

Ion Beam Probing of Electrostatic Fields.  

National Technical Information Service (NTIS)

The determination of a cylindrically symmetric, time-independent electrostatic potential V in a magnetic field B with the same symmetry by measurements of the deflection of a primary beam of ions is analyzed and substantiated by examples. Special attentio...

H. Persson

1979-01-01

149

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

150

Probing the magnetic states in a ferromagnet using a superconductor  

NASA Astrophysics Data System (ADS)

In a superconductor (S)/ferromagnet (F) bilayer, the superconducting properties of the S layer are sensitive to the domain pattern in the adjacent F layer.[1-2] We exploit this effect to investigate Ni films, which instead of retaining in-plane anisotropy as usual, unexpectedly acquire perpendicular anisotropy when the thickness is above a critical value. Using Ni/Nb bilayers, the perpendicular magnetization component can be sensitively probed by the measurements of the superconducting transition of Nb in a magnetic field, which alters the domain pattern in Ni. Above the critical Ni thickness, an in-plane magnetic field can manipulate the stripe domains in Ni between parallel stripes and random labyrinth states resulting in as much as 90 mK in the transition temperature of the Nb layer. This clearly demonstrates that superconductor is a sensitive probe of the magnetic domain state of a ferromagnet. In turn, the results also show that along the parallel stripe domains, superconductivity is less detrimental. [1]. A. Yu. Rusanov, M. Hesselberth, J. Aarts, and A. I. Buzdin, Phys. Rev. Lett. 93, 057002 (2004). [2]. L. Y. Zhu, T. Y. Chen, and C. L. Chien, Phys. Rev. Lett. 101, 017004 (2008).

Zhu, Leyi; Chen, Tingyong; Chien, Chia-Ling

2009-03-01

151

Heavy fermions in high magnetic fields  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The National High Magnetic Field Laboratory (NHMFL) has established major new facilities at LANL. This project sought to explore some exciting new problems in condensed matter physics that could be studied using these facilities. We studied the behavior of heavy-fermion compounds in high-magnetic fields. The unusual properties of these materials are governed by small energy scales arising from strong many-body correlations, demonstrating that the fields that can be achieved in the NHMFL can be used to probe these correlations.

Trugman, S.; Bedell, K.; Bonca, J.; Gulacsi, M. [Los Alamos National Lab., NM (United States); Yu, C. [California Univ., Irvine, CA (United States)

1996-05-01

152

Magnetic fields and cancer  

SciTech Connect

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

Jones, T.L.

1993-10-01

153

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

154

Magnetic field effects on the near field spectra of quantum dots  

Microsoft Academic Search

We theoretically investigate the linear near field absorption spectra of semiconductor quantum dots under magnetic field of variable orientation. We examine if the application of the magnetic field alone is sufficient to cause - increasing the spot illuminated by the near field probe - unexpected features to the absorption spectra.

Anna Zora; Constantinos Simserides; Georgios Triberis

2005-01-01

155

Magnetization reversal in ultrashort magnetic field pulses  

NASA Astrophysics Data System (ADS)

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

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

2000-08-01

156

Magnetic Field Problem: Current and Magnets  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

157

Magnetic Field Issues in Magnetic Resonance Imaging  

Microsoft Academic Search

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

Labros Spiridon Petropoulos

1993-01-01

158

Active probes for creating H-field probes for flat frequency response  

Microsoft Academic Search

This paper presents an approach to obtain a flat frequency response from the first order derivative behavior of an electrically small loop and electrically short electric field probe by using them in combination with active oscilloscope probes. An H-field probe made in flex circuit technology was designed to operate up to about 5 GHz. These probes have loop dimensions as

Surbhi Mittal; Ji Zhang; David Pommerenke; James L. Drewniak; Kuifeng Hu; Xiaopeng Dong

2009-01-01

159

Probing the mid-infrared spectrum of YBa2Cu3O6.0 with high magnetic fields and Zink doping  

NASA Astrophysics Data System (ADS)

The mid-infrared phonon and spin-wave spectrum of antiferromagnetic YBa2Cu3O6.0 was investigated by infrared transmission measurements ( k ??c-axis) at T=4K. Peaks at 178 meV, 346 meV and 470 meV were previously interpreted as excitations of single magnons of the optical branch and of bimagnons, respectively. Infrared measurements in high magnetic fields up to 16.5 Tesla and on samples doped with 5% of Zink have been performed to query this interpretation.

Grüninger, M.; van der Marel, D.; van Bentum, P. J. M.; Erb, A.; Wolf, Th.; Kopp, T.

1996-02-01

160

Integrated semiconductor magnetic field sensors  

Microsoft Academic Search

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

H. P. Baltes; R. S. Popovic

1986-01-01

161

Structural optimization of 2-D array probe for alternating current field measurement  

Microsoft Academic Search

A double U-shaped orthogonal inducer for the alternating current field measurement (ACFM) is presented, which could extend the limitation of the direction of tested cracks and decrease the loss of magnetic flux compared to the single rectangular inducer. The structure of the testing probe was optimized to meet the expectations of the pointwise magnetic field measurement and to decrease every

Chen Guo-ming; Li Wei; Wang Ze-xin

2007-01-01

162

Planetary magnetic fields  

NASA Astrophysics Data System (ADS)

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

Stevenson, David J.

2003-03-01

163

High sensitivity piezomagnetic force microscopy for quantitative probing of magnetic materials at the nanoscale.  

PubMed

Accurate scanning probing of magnetic materials at the nanoscale is essential for developing and characterizing magnetic nanostructures, yet quantitative analysis is difficult using the state of the art magnetic force microscopy, and has limited spatial resolution and sensitivity. In this communication, we develop a novel piezomagnetic force microscopy (PmFM) technique, with the imaging principle based on the detection of magnetostrictive response excited by an external magnetic field. In combination with the dual AC resonance tracking (DART) technique, the contact stiffness and energy dissipation of the samples can be simultaneously mapped along with the PmFM phase and amplitude, enabling quantitative probing of magnetic materials and structures at the nanoscale with high sensitivity and spatial resolution. PmFM has been applied to probe magnetic soft discs and cobalt ferrite thin films, demonstrating it as a powerful tool for a wide range of magnetic materials. PMID:23720016

Chen, Qian Nataly; Ma, Feiyue; Xie, Shuhong; Liu, Yuanming; Proksch, Roger; Li, Jiangyu

2013-05-29

164

Spin Polarized Electron Probes and Magnetic Nanostructures  

SciTech Connect

OAK B188 This report summarizes progress to date in our theoretical research program, for the period from July 1, 2002 to November 1, 2003. In addition, our research priorities for the coming year are set forth. The reporting period has been a most exciting and significant one. For the past several years, one of our principal thrust areas has been development of the theory of spin dynamics in magnetic nanostructures with emphasis on the use of spin polarized electrons as probes of short wavelength spin dynamics in such entities. Our program stimulated the first experiment which detected large wave vector spin waves in ultrathin films in 1999 through spin polarized electron loss spectroscopy (SPEELS); the publication which announced this discovery was a joint publication between a group in Halle (Germany) with our theory effort. The continued collaboration has led to the design and implementation of the new SPEELS spectrometer and we now have in hand the first detailed measurements of spin wave dispersion in an ultrathin film. A second such spectrometer is now operational in the laboratory of Prof. H. Hopster, at UC Irvine. We are thus entering a most exciting new era in the spectroscopy of spin excitations in magnetic nanostructures. During the reporting period, we have completed very important new analyses which predict key aspects of the spectra which will be uncovered by these new instruments, and the calculations continue to be developed and to expand our understanding. In addition, we have initiated a new series of theoretical studies directed toward spin dynamics of single magnetic adatoms on metal surfaces, with STM based studies of this area n mind. In the near future, these studies will continue, and we will expand our effort into new areas of spin dynamics in magnetic nanostructures.

D.L. Mills

2003-10-15

165

Magnetic nanoparticles: Internal probes and heaters within living cells  

Microsoft Academic Search

Tagging living cells with magnetic nanoparticles raised increasing interest in the fields of magnetic resonance imaging, magnetic hyperthermia, cell sorting or tissue engineering. Here, we demonstrate that the confinement of magnetic nanoparticles at the intracellular level, inside endosomes vesicles, allows developing original magnetic manipulations in response to different magnetic field solicitations. These manipulations are used to deform cellular internal membrane,

Claire Wilhelm; Florence Gazeau

2009-01-01

166

Intergalactic magnetic fields, and some connections with cosmic rays  

Microsoft Academic Search

An overview is presented of the methods of probing for the geometry, and strength of intergalactic magnetic fields. Recent results are briefly surveyed for galaxy halos, galaxy clusters, and the intergalactic medium on various scales, and some rele vant physical processes and radiation processes are mentioned, as well as the “coupling” between intergalactic magnetic fields and cosmic rays.

Philipp P. Kronberg

1996-01-01

167

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles  

SciTech Connect

Magnetic clouds are large (<0.25 AU) interplanetary regions with topologies consistent with those of magnetic loops. They are of interest because they may be an interplanetary signature of coronal mass ejections. Clouds have been identified in solar wind data by their magnetic properties and by the presence of bidirectional particle fluxes. Two possible closed magnetic topologies have been considered for clouds: (1) an elongated bottle with field lines rooted at both ends in the Sun and (2) a detached magnetic bubble or plasmoid consisting of closed field lines. The inferred topologies are also consistent with open field lines that converge beyond 1 AU. The authors have used solar energetic particles (SEPs) as probes of the cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the Sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

Kahler, S.W. (Boston Coll., Newton, MA (USA)); Reames, D.V. (NASA Goddard Space Flight Center, Greenbelt, MD (USA))

1991-06-01

168

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

169

Using Coordinated Observations in Polarized White Light and Faraday Rotation to Probe the Spatial Position and Magnetic Field of an Interplanetary Sheath  

NASA Astrophysics Data System (ADS)

Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons and therefore depend on both viewing geometry and electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component B ? and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modeling of an Earth-directed shock and synthesize the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depends on scattering angle, WL radiance I decreases with heliocentric distance r roughly according to the expression Ivpropr –3. The sheath region downstream of the Earth-directed shock is well viewed from the L4 and L5 Lagrangian points, demonstrating the benefits of these points in terms of space weather forecasting. The spatial position of the main scattering site r sheath and the mass of plasma at that position M sheath can be inferred from the polarization of the shock-associated enhancement in WL radiance. From the FR measurements, the local B ?sheath at r sheath can then be estimated. Simultaneous observations in polarized WL and FR can not only be used to detect CMEs, but also to diagnose their plasma and magnetic field properties.

Xiong, Ming; Davies, Jackie A.; Feng, Xueshang; Owens, Mathew J.; Harrison, Richard A.; Davis, Chris J.; Liu, Ying D.

2013-11-01

170

Evolution of twisted magnetic fields  

SciTech Connect

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

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

1985-02-01

171

Design and implementation of a dc-based magnetic field controller.  

National Technical Information Service (NTIS)

This invention is comprised of a magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, ...

D. K. Kotter R. A. Rankin J. P. Morgan

1990-01-01

172

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

173

Stellar atmospheres with magnetic field  

Microsoft Academic Search

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

K. Stepien

1980-01-01

174

Magnetic fields in galactic jets  

Microsoft Academic Search

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

A. Ferrari

1982-01-01

175

Protogalactic evolution and magnetic fields  

Microsoft Academic Search

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

Harald Lesch; Masashi Chiba

1994-01-01

176

Protogalactic evolution and magnetic fields  

Microsoft Academic Search

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

H. Lesch; M. Chiba

1995-01-01

177

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

178

Using Monoenergetic Proton Radiography to Probe Magnetic Reconnection of Laser-Generated Plasma Bubbles  

NASA Astrophysics Data System (ADS)

The magnetic topology changes due to reconnection of laser-generated magnetic fields, which can affect energy transport inside hohlraums and around inertial confinement fusion (ICF) capsule implosions. To probe and better understand this effect, a series of experiments were conducted in which the interaction of azimuthal magnetic fields surrounding laser-produced plasma bubbles was imaged using face-on monoenergetic proton radiography. The timing of the interaction beams with respect to each other and to the backlighter was varied to provide snapshots of the reconnection both during and after the laser-foil interaction. Images and quantitative field-mapping demonstrate a change in magnetic topology during the bubble interaction. Future work will entail side-on radiography of interacting plasma bubbles to probe for Hall fields associated with fast magnetic reconnection. This work was performed at the LLE NLUF, and was supported in part by the US DOE, LLNL, and LLE.

Rosenberg, M.; Li, C.; Seguin, F. H.; Frenje, J.; Manuel, M.; Petrasso, R.; Stoeckl, C.; Glebov, V.; Kilkenny, J.; Nikroo, A.

2011-11-01

179

Magnetic resonance imaging of time-varying magnetic fields from therapeutic devices.  

PubMed

While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields such as those generated by transcranial magnetic stimulators and radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this study. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by a figure-eight coil inside simple phantoms over a range of frequencies and intensities using a 7T small animal MRI scanner. The method was able to reconstruct the three-dimensional components of the oscillating magnetic field vector. PMID:23355446

Hernandez-Garcia, Luis; Bhatia, Vivek; Prem-Kumar, Krishan; Ulfarsson, Magnus

2013-01-28

180

Consistency relation for cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

If cosmic magnetic fields are indeed produced during inflation, they are likely to be correlated with the scalar metric perturbations that are responsible for the cosmic microwave background anisotropies and large scale structure. Within an archetypical model of inflationary magnetogenesis, we show that there exists a new simple consistency relation for the non-Gaussian cross correlation function of the scalar metric perturbation with two powers of the magnetic field in the squeezed limit where the momentum of the metric perturbation vanishes. We emphasize that such a consistency relation turns out to be extremely useful to test some recent calculations in the literature. Apart from primordial non-Gaussianity induced by the curvature perturbations, such a cross correlation might provide a new observational probe of inflation and can in principle reveal the primordial nature of cosmic magnetic fields.

Jain, Rajeev Kumar; Sloth, Martin S.

2012-12-01

181

The Sun's global magnetic field.  

PubMed

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

Mackay, Duncan H

2012-07-13

182

Microwave Measurements of Coronal Magnetic Field  

Microsoft Academic Search

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

K. Shibasaki

2006-01-01

183

Magnetic Field of Mars  

NASA Astrophysics Data System (ADS)

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

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

2000-07-01

184

The NBS-LANL RTM end-magnet field mapper  

SciTech Connect

A computer-controlled magnetic field mapper is under construction at the National Bureau of Standards to map the end magnets of the NBS-LANL racetrack microtron (RTM). The mapper consists of a large, two-dimensional translation stage which simultaneously positions a nuclear magnetic resonance (NMR) magnetometer probe in the 55 cm x 135 cm uniform field region and a temperature-compensated Hall effect probe in the fringe field region. A computer-based control system automatically positions the probes at points on a selected grid and records the measured field values and positions in computer memory. In this paper the authors describe the field mapping requirements, the mapper, its operation, and the field measurements and analysis that are to be performed.

Lindstrom, E.R.; Debenham, P.H.; Mohr, D.L.; Yoder, N.R.

1983-08-01

185

Evolution of primordial magnetic fields  

NASA Astrophysics Data System (ADS)

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

Banerjee, R.

2013-06-01

186

Prospects for neutron probed magnetic resonance imaging  

SciTech Connect

The information gained from magnetic resonance imaging has provided useful insight into many insulators. Extending this technique to conductors requires an alternative means of spin manipulation besides electromagnetic radiation. A method to use neutron measurement of the Zeeman splitting to measure the relaxation time is described. The Zeeman splitting is observed by a neutron spectrometer as an incoherent signal with an energy transfer equal to the Zeeman energy. This energy scale is so small that fields in excess of 15 T are required to sufficiently separate this line from other incoherent processes. Once the Zeeman splitting is observed, a perturbation of the system is required to enable measurement of the nuclear spin relaxation time; the physical quantity measured in a Nuclear Magnetic Resonance experiment. The proposed perturbation is a pulsed field of 10 T. The relaxation of the Zeeman splitting back to the 15 T condition is then recorded as a function of time. The resultant data is the aforementioned measure of the relaxation time. With the ability to measure the relaxation times the image map can be created by rastering the sample with respect to the beam.

Granroth, Garrett E [ORNL

2009-01-01

187

Magnetic Classification of Meteorites and Asteroid Probing  

NASA Astrophysics Data System (ADS)

Magnetic susceptibility (X) provides a versatile rapid and non destructive way to quan- tify the amount of magnetic minerals (FeNi metal, magnetic oxides and sulfides) on large volume of material. As petrological studies of meteorites suggest that this param- eter should be quite discriminant, we assembled a database of measurements on about 1000 stony meteorites from various European collections: Helsinki, Madrid, Paris, Prague, Roma, Siena, Vatican, and other smaller collections. From 1 to >20 pieces and 1 to >100 cc per meteorite allow to define a representative mean value, using a large coil (8 cm) Kappabridge. For ordinary chondrites, it appears that weathering is responsible for a systematic bias toward low logc for Antarctic (Frontier Mountain) and non Antarctic (mainly from Sahara) finds. Once only falls are considered a quite narrow range of logc is observed for a given class, with no effect of petrological grade except for LL. High grade LLs (heated above 400C) develop the weakly magnetic antitaenite-tetrataenite phases [3] during slow cooling, explaining the difference with low grade taenite-bearing LLs. Outliers from H and L classes are grade 6 material (showing metal segregation) or intermediate types: H/L and L/LL. Once these out- liers are excluded, well defined means for H and L are observed with no overlap at 2 s.d.; this agrees with the lack of overlap on metal amount. The standard deviation for all falls of a given class is only slightly higher than the averaged standard deviation for multiple pieces of the same fall. This supports the hypothesis that all falls from a given ordinary chondrite class (H or L) may come from the same homogeneous par- ent body. For non ordinary chondrites and achondrites, weakly magnetic classes are HED, Aubrites and SNC (below LL), strongly ones are E (above H) and Ureilites (in the L-H range), while C chondrites are spread in the whole range, again with each class showing restricted variation. On objects without intrinsic magnetic field the only way to measure X is to use a lander able to apply a small coil on the surface to mea- sure. Existing pocket susceptometer with a 25 mm radius loop and penetration depth of 30 mm are easily adaptable to such a purpose with a payload of less than 50 g (not counting the mobile arm). Such a petrophysical tool would have the advantage of its penetration depth with respect to all other chemical and mineralogical analysers that obtain essentially surface information prone to bias by space weathering. It should allow to attribute the asteroid to a meteorite class.

Rochette, P.; Sagnotti, L.; Chevrier, V.; Consolmagno, G.; Denise, M.; Folco, L.; Osete, M.; Pesonen, L.

188

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

189

ANOMALOUS COSMIC RAYS AS PROBES OF MAGNETIC CLOUDS  

SciTech Connect

We report, for the first time, the observation near the Earth of anomalous cosmic ray (ACR) particles throughout the interiors of interplanetary magnetic clouds (MCs) at the same intensity as outside the MCs. ACRs, accelerated in the outer heliosphere, have unique elemental abundances making their identity unambiguous as they probe these clouds from the outside. Thus, MCs, carried out from the Sun by coronal mass ejections (CMEs), are seen to contain no structures that are magnetically closed to the penetration of ions with energies above a few MeV amu{sup -1}. As the MCs expand outward, they must fill their increasing volume with ACRs dynamically, to the same degree as neighboring 'open' field lines. These observations cast doubt on conventional ideas about the closed field topologies of MCs and the cross-field transport of energetic particles. The ACR observations conflict with some reports of significant exclusion from MCs of solar energetic particles (SEPs) of comparable energy and rigidity. A process that allows cross-field transport of ACRs may also allow similar transport of SEPs late in events, causing the large spatial extent and uniformity of SEPs in 'invariant spectral regions' extending far behind CME-driven shock waves.

Reames, D. V. [Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Kahler, S. W. [Air Force Research Laboratory, RVBXS, 29 Randolph Rd., Hanscom AFB, MA 01731 (United States); Tylka, A. J. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)], E-mail: dvreames@umd.edu

2009-08-01

190

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

191

Origin of cosmic magnetic fields.  

PubMed

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

Campanelli, Leonardo

2013-08-06

192

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

193

Structural anisotropy and internal magnetic fields in trabecular bone: Coupling solution and solid dipolar interactions  

Microsoft Academic Search

We investigate the use of intermolecular multiple-quantum coherence to probe structural anisotropy in trabecular bone. Despite the low volume fraction of bone, the bone–water interface produces internal magnetic field gradients which modulate the dipolar field, depending on sample orientation, choice of dipolar correlation length, correlation gradient direction, and evolution time. For this system, the probing of internal magnetic field gradients

Louis-S. Bouchard; Felix W. Wehrli; Chih-Liang Chin; Warren S. Warren

2005-01-01

194

Estimation of fluctuating magnetic fields by an atomic magnetometer  

SciTech Connect

We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

Petersen, Vivi; Moelmer, Klaus [QUANTOP--Danish National Research Foundation Center for Quantum Optics, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2006-10-15

195

Estimation of fluctuating magnetic fields by an atomic magnetometer  

NASA Astrophysics Data System (ADS)

We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

Petersen, Vivi; Mølmer, Klaus

2006-10-01

196

Laboratory Measurements of Astrophysical Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

197

Materials Processing in Magnetic Fields  

NASA Astrophysics Data System (ADS)

The latest in lattice QCD -- Quark-gluon plasma physics -- String theory and exact results in quantum field theory -- The status of local supersymmetry.Supersymmetry in nuclei -- Inflation, dark matter, dark energy -- How many dimensions are really compactified? -- Horizons -- Neutrino oscillations physics -- Fundamental constants and their possible time dependence.Highlights from BNL. new phenomena at RHIC -- Highlights from BABAR -- Diffraction studied with a hard scale at HERA -- The large hadron collider: a status report -- Status of non-LHC experiments at CERN -- Highlights from Gran Sass.Fast automatic systems for nuclear emulsion scanning: technique and experiments -- Probing the QGP with charm at ALICE-LHC -- magnetic screening length in hot QCD -- Non-supersymmetric deformation of the Klebanov-Strassler model and the related plane wave theory -- Holographic renormalization made simple: an example -- The kamLAND impact on neutrino oscillations -- Particle identification with the ALIC TOF detector at very high multiplicity -- Superpotentials of N = 1 SUSY gauge theories -- Measurement of the proton structure function F2 in QED compton scattering at HERA -- Yang-Mills effective action at high temperature -- The time of flight (TOF) system of the ALICE experiment -- Almost product manifolds as the low energy geometry of Dirichlet Brane.

Schneider-Muntau, Hans J.; Wada, Hitoshi

198

A magnetically levitated, automated, contact analytical probe tool  

Microsoft Academic Search

With the challenge of the shrinking dimensions in the fabrication process, demands are growing for higher precision and more powerful analytical probing stations to be used for characterization and failure analysis of integrated circuits. A magnetic levitation-based approach to analytical probing stations is proposed and investigated in this paper. This approach permits the process to be automated while maintaining better

Shiaw-Jong Steve Chen; Ilene J. Busch-Vishniac

1995-01-01

199

Magnetic field in a finite toroidal domain  

SciTech Connect

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

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

2010-05-15

200

Magnetic Compton scattering: A reliable probe to investigate magnetic properties  

NASA Astrophysics Data System (ADS)

Magnetic Compton scattering (MCS) is an ideal technique for the study of magnetic properties of ferro/ferrimagnetic materials because this method reveals the spin-polarized electron momentum density and yields the absolute and site dependent spin moments. The quantity measured in the MCS, so called magnetic Compton profile, is defined as the difference in the one-dimensional projection of the spin-polarized electron momentum density for majority and minority spin bands. In MCS, the Doppler broadening of the scattered radiation provides information on the correlation between the spin moment and the spin-polarized electron states of the valence electrons. It can also distinguish the spin polarization of itinerant electrons, because their momentum is narrow around the center of the profile. In this paper, temperature and field dependent spin momentum densities in Zn doped Ni ferrite namely, Ni1-xZnxFe2O4(x = 0.0,0.1,0.2), hole doped manganites like La0.7Ca0.3Mn1-xAlxO3(x = 0,0.02and0.06) and half Heusler alloys Cu1-xNixMnSb(x = 0.17,0.22) are reviewed. The decomposition of profiles in terms of site specific magnetic moments and their role in the formation of total spin moment is also discussed.

Ahuja, B. L.

2013-02-01

201

Induced Magnetic Fields in Solar System Bodies  

NASA Astrophysics Data System (ADS)

Electromagnetic induction is a powerful technique to study the electrical conductivity of the interior of the Earth and other solar system bodies. Information about the electrical conductivity structure can provide strong constraints on the associated internal composition of planetary bodies. Here we give a review of the basic principles of the electromagnetic induction technique and discuss its application to various bodies of our solar system. We also show that the plasma environment, in which the bodies are embedded, generates in addition to the induced magnetic fields competing plasma magnetic fields. These fields need to be treated appropriately to reliably interpret magnetic field measurements in the vicinity of solar system bodies. Induction measurements are particularly important in the search for liquid water outside of Earth. Magnetic field measurements by the Galileo spacecraft provide strong evidence for a subsurface ocean on Europa and Callisto. The induction technique will provide additional important constraints on the possible subsurface water, when used on future Europa and Ganymede orbiters. It can also be applied to probe Enceladus and Titan with Cassini and future spacecraft.

Saur, Joachim; Neubauer, Fritz M.; Glassmeier, Karl-Heinz

2010-05-01

202

Effect of Ge substitution for Si on the magnetic hyperfine field in LaMn2Si2 compound measured by perturbed angular correlation spectroscopy with 140Ce as probe nuclei  

NASA Astrophysics Data System (ADS)

The effect of substitution of Ge for Si in LaMn2Si2 compound on the magnetic hyperfine field (Bhf) has been investigated by perturbed ?-? angular correlation (PAC) spectroscopy using 140La(140Ce) as probe nuclei. This compound exhibits antiferromagnetism followed by a ferromagnetic ordering when temperature decreases. The behavior of the ferromagnetic transition when Ge gradually replaces Si, with concentrations of 20%, 40%, 80%, and 100% is discussed. PAC measurements were carried out in the temperature range from 15 K to 325 K. Results for LaMn2Si2 compound showed that the dependence of Bhf with temperature follows the expected behavior for the host magnetization and could be fitted by a Brillouin function for JMn = 5/2. However, the temperature dependence of Bhf for compounds when Si is gradually replaced by Ge showed a deviation from such a behavior, which gradually increases up to a strong deviation observed for LaMn2Ge2. This striking behavior was ascribed to the hybridization of d band of the host and f band of the Ce impurities, which is stronger when the unit cell volume increase as Si ions are substituted by Ge atoms.

Bosch-Santos, B.; Carbonari, A. W.; Cabrera-Pasca, G. A.; Costa, M. S.; Saxena, R. N.

2013-05-01

203

Magnetic fields and scintillator performance  

SciTech Connect

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

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

1995-06-01

204

Hand-Held Schlieren Photography with Light Field Probes  

Microsoft Academic Search

We introduce a new approach to capturing refraction in transparent media, which we call Light Field Back- ground Oriented Schlieren Photography (LFBOS). By op- tically coding the locations and directions of light rays emerging from a light field probe, we can capture changes of the refractive index field between the probe and a camera or an observer. Rather than using

Gordon Wetzstein; Ramesh Raskar; Wolfgang Heidrich

2011-01-01

205

Lorentz Mapping of Magnetic Fields in Hot Dense Plasmas  

SciTech Connect

Unique detection of electromagnetic fields and identification of field type and strength as a function of position were used to determine the nature of self-generated fields in a novel experiment with laser-generated plasma bubbles on two sides of a plastic foil. Field-induced deflections of monoenergetic 15-MeV probe protons passing through the two bubbles, measured quantitatively with proton radiography, were combined with Lorentz mapping to provide separate measurements of magnetic and electric fields. The result was absolute identification and measurement of a toroidal magnetic field around each bubble and determination that any electric field component parallel to the foil was below measurement uncertainties.

Petrasso, R. D.; Li, C. K.; Seguin, F. H.; Rygg, J. R.; Frenje, J. A.; Betti, R.; Knauer, J. P.; Meyerhofer, D. D.; Amendt, P. A.; Froula, D. H.; Landen, O. L.; Patel, P. K.; Ross, J. S.; Town, R. P. J. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2009-08-21

206

Pattern formation in a complex plasma in high magnetic fields.  

PubMed

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments. PMID:21699308

Schwabe, M; Konopka, U; Bandyopadhyay, P; Morfill, G E

2011-05-27

207

Pattern Formation in a Complex Plasma in High Magnetic Fields  

SciTech Connect

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments.

Schwabe, M.; Konopka, U.; Bandyopadhyay, P.; Morfill, G. E. [Max-Planck-Institut fuer extraterrestrische Physik, D-85748 Garching (Germany)

2011-05-27

208

MANUFACTURING OF MAGNETIC PROBE COILS FOR DIII-D  

SciTech Connect

OAK-B135 The magnetic diagnostics program at DIII-D adds to its in-vessel installations of induction-type loops and coils almost every year. The current design of toroidal and poloidal magnetic field coils (45-50 kHz, N {center_dot} A = 0.06 m{sup 2}) has been in existence since 1987. Many coils were installed in DIII-D during that year and are still operating and reliable today. The high reliability of the coils is owing to the use of a continuous length of mineral-insulated cable, eliminating any electrical connections inside the vacuum vessel. The geometry of the probes was designed to achieve a bandwidth of 50 kHz, despite the conducting shell formed by the stainless steel sheath of the mineral-insulated cable. The bandwidth is sensitive to the details of the cable dimensions and winding technique, and care must be taken in the fabrication in order to maintain this specification. With possible future magnetic diagnostics installations IN ITER and other long-pulse machines requiring large numbers of coils and/or multiple layers per coil, the manufacturing scale-up, quality control, and the development of layered coils should all be investigated in addition to the obvious issues such as irradiation effects.

BOZEK,A.S; STRAIT,E.J

2003-10-01

209

Magnetic field structure of Mercury  

NASA Astrophysics Data System (ADS)

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

Hiremath, K. M.

2012-04-01

210

A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments  

NASA Astrophysics Data System (ADS)

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 ?m diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

Smith, Doran D.; Alexson, Dimitri A.; Garbini, Joseph L.

2013-09-01

211

Cosmic Magnetic Fields – An Overview  

Microsoft Academic Search

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

Richard Wielebinski; Rainer Beck

2010-01-01

212

Magnetic Pumping in Spatially Inhomogeneous Magnetic Fields.  

National Technical Information Service (NTIS)

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

H. P. Furth R. A. Ellis

1972-01-01

213

Simulations of Photospheric Magnetic Fields  

Microsoft Academic Search

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

A. A. Smith; H. B. Snodgrass

1999-01-01

214

Measuring Earth's Magnetic Field Simply.  

ERIC Educational Resources Information Center

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

Stewart, Gay B.

2000-01-01

215

Magnetic Field Waves at Uranus.  

National Technical Information Service (NTIS)

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

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

1991-01-01

216

Thermometers in Low Magnetic Fields  

Microsoft Academic Search

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

G. Gersak; S. Begus

2010-01-01

217

Lanthanides as NMR probes of fast molecular dynamics at high magnetic fields and temperature sensors: conformational interconversion of erbium ethylenediaminetetraacetate complexes.  

PubMed

(1)H NMR measurements are reported for D2O solutions of paramagnetic complex [Er(H2O)(EDTA(4-))](-) (I) for temperature interval 273-319 K. Diamagnetic complex [Lu(H2O)(EDTA(4-))](-) (II) was used as an NMR reference compound. The spectra obtained have been analyzed using a band-shape analysis technique in the framework of dynamic NMR (DNMR) taking into account the temperature dependence of lanthanide-induced shifts. Intramolecular dynamics in I was assigned to the interconversion of ?-?E-???? and ?-?E-???? conformers with estimated activation free energy ?G(‡)(298 K) = 50 ± 4 kJ/mol. The methodology of paramagnetic 4f-element probe applications on the example of Er(3+) for the study of free-energy changes in chemical exchange processes, as well as the advantages of this method in comparison with DNMR studies of diamagnetic substances, is discussed. In accordance with the literature reviewed, the fulfilled experimental study is the first example of intramolecular dynamics determination for erbium complexes. An additional advantage of the investigation is in the approach proposed which extends the range of measurement of the NMR rate constants for paramagnetic 4f-element complexes compared to diamagnetic ones. Coordination compounds investigated represent a new type of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solutions. PMID:23587055

Babailov, Sergey P; Stabnikov, Pavel A; Zapolotsky, Eugeny N; Kokovkin, Vasily V

2013-04-15

218

Theorem on magnet fringe field  

SciTech Connect

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

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

1995-12-31

219

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

PubMed

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

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

2012-10-01

220

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

221

Complications in the measurement of the magnetic field penetration depth in YBa sub 2 Cu sub 3 O sub x and Bi sub 2 Sr sub 2 CaCu sub 2 O sub x superconductors by electron spin resonance line broadening of surface paramagnetic probes  

SciTech Connect

The electron spin resonance line broadening of a paramagnetic probe on an oxide superconductor below the superconducting critical transition temperature is shown to depend on the parallel or perpendicular orientation of the probe to the applied magnetic field. This effect must be considered when using the line broadening associated with the magnetic flux lattice to measure the magnetic field penetration depth. The appropriate values at 0 K of the magnetic field penetration depth in YBa{sub 2}Cu{sub 3}O{sub x} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} sintered superconductors are 1,400 and 2,850 {angstrom}, respectively. A strong effect of silver doping in YBaCuO superconductors on the magnetic field penetration depth is also shown. It is shown that the temperature below the superconducting critical transition temperature at which significant liner broadening from the flux lattice occurs is better identified as the magnetic flux lattice melting temperature. This is particularly clear in the BiSrCaCuO superconductor in which the flux lattice melting temperature lies significantly below the superconducting critical transition temperature. This also supports that line broadening associated with the magnetic flux lattice can be isolated from other sources of broadening.

Masiakowski, J.T.; Puri, M.; Kevan, L. (Univ. of Houston, TX (United States))

1991-10-31

222

Holographic non-Fermi liquid in a background magnetic field  

SciTech Connect

We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS{sup 4} black hole background. Introducing a similar fermionic probe in a dyonic AdS{sup 4} black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion's charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.

Basu, Pallab; He Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1 (Canada)

2010-08-15

223

Dynamic nuclear polarization at high magnetic fields  

PubMed Central

Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (?w) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (?e/?l), being ?660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (?5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms—the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in ?w and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments.

Maly, Thorsten; Debelouchina, Galia T.; Bajaj, Vikram S.; Hu, Kan-Nian; Joo, Chan-Gyu; Mak-Jurkauskas, Melody L.; Sirigiri, Jagadishwar R.; van der Wel, Patrick C. A.; Herzfeld, Judith; Temkin, Richard J.; Griffin, Robert G.

2009-01-01

224

High field magnetic resonance  

US Patent & Trademark Office Database

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

2010-09-21

225

A versatile variable field module for Asylum Cypher scanning probe system  

NASA Astrophysics Data System (ADS)

Atomic force microscopy (AFM) has become one of the most widely used techniques for measuring and manipulating various characteristics of materials at the nanoscale. However, there are very limited option for the characterization of field dependence properties. In this work, we demonstrate a versatile variable field module (VFM) with magnetic field up to 1800 Oe for the Asylum Research Cypher system. The magnetic field is changed by adjusting the distance between a rare earth magnet and the AFM probe. A built-in Hall sensor makes it possible to perform in-situ measurements of the field. Rotating the magnet makes it possible to do angular field dependent measurements. The capability of the VFM system is demonstrated by degaussing a floppy disk media with increasing magnetic field. The written bits are erased at about 800 Oe. Angular dependence measurements clearly show the evolution of magnetic domain structures. A completely reversible magnetic force microscopy (MFM) phase contrast is observed when the magnetic field is rotated by 180^o. Further demonstration of successful magnetic switching of CoFe2O4 pillars in CoFe2O4-BiFeO3 nanocomposites will be presented and field dependent MFM and piezoresponse force microscopy (PFM) will be discussed.

Liu, Hongxue; Comes, Ryan; Lu, Jiwei; Wolf, Stuart; Hodgson, Jim; Rutgers, Maarten

2013-03-01

226

Magnetization measurement of YBa2Cu3Oy in high magnetic fields up to 30 T  

NASA Astrophysics Data System (ADS)

Magnetization measurements on high-quality untwinned YBa2Cu3Oy single crystals are performed in magnetic fields up to 30 T using a Hall probe magnetometry. We find an anomalous second peak in the magnetization hysteresis curve, which is different from the previously reported ``fish tail''. This behavior is interpreted in terms of the field-driven transition from the vortex lattice or the Bragg glass to the disordered vortex glass phases with increasing magnetic field. We discuss, furthermore, the influence of disorder of the system on the transition.

Kobayashi, N.; Nishizaki, T.; Naito, T.; Awaji, S.; Watanabe, K.

1998-05-01

227

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.  

SciTech Connect

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

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

2004-10-03

228

Magnetic fields in neutron stars  

NASA Astrophysics Data System (ADS)

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

Viganò, Daniele

2013-09-01

229

An analysis and optimization of elliptical RF probes used in magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

In magnetic resonance imaging of the entire body, it is often desirable to use an elliptical RF probe, rather than a circular one. As an ellipse more closely conforms to the anatomical cross section of the human thorax and head, better filling factors and therefore improved signal-to-noise ratios may be achieved by the use of elliptical RF coils. The probe is usually of bird-cage type, but the rungs are of finite width due to the high-frequency signals involved. This paper presents a method for computing the magnetic fields produced inside elliptical probes, and the current distributions on the rungs. A slotted shield is assumed to surround the probe, and its influence on field homogeneity is studied. In particular, the currents in a 16-runged unshielded elliptical coil of practical interest were determined optimally in one case, using simulated annealing to optimize the homogeneity of the magnetic field within the probe. The effects of a segmented shield of both elliptical and circular cross section on this coil are discussed, and the results are confirmed by experiment.

Forbes, Lawrence K.; Crozier, Stuart; Doddrell, David M.

1996-09-01

230

Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities  

SciTech Connect

By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time.

Demidov, V. I.; Koepke, M. E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Raitses, Y. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2010-10-15

231

Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities.  

PubMed

By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time. PMID:21033993

Demidov, V I; Koepke, M E; Raitses, Y

2010-10-01

232

Black holes and magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

233

Helical Magnetic Fields from Sphaleron Decay and Baryogenesis  

SciTech Connect

Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

Copi, Craig J. [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Ferrer, Francesc [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Department of Physics, Washington University, St. Louis, Missouri 63130 (United States); Vachaspati, Tanmay [CERCA, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7079 (United States); Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Achucarro, Ana [Instituut-Lorentz for Theoretical Physics, Leiden (Netherlands); Department of Theoretical Physics, The University of the Basque Country UPV-EHU, 48940 Bilbao (Spain)

2008-10-24

234

Magnetic-field-enhanced carbon solution in proeutectoid ferrite  

NASA Astrophysics Data System (ADS)

Modification of phase solubility of Fe–C system by magnetic field has been recognized by thermodynamic calculations and indirectly by microstructural examinations. However, there has been no direct experimental verification and the underlying physical mechanism is not fully uncovered. In this work, the enhanced carbon content in proeutectoid ferrite under a 12 T magnetic field is evidenced through wavelength-dispersive spectroscopy using a Shimadzu 1610 electron probe microanalyser measurements. The magnetic-field-enhanced carbon solution reduces the demagnetization energy of the system and makes it energetically more stable.

Zhang, X. X.; Xu, N.; Wang, S. J.; Zhang, Y. D.; Raulot, J.-M.; Esling, C.; Zhao, X.; Zuo, L.

2013-09-01

235

Beyond Solar-B: MTRAP, the Magnetic TRAnsition Region Probe  

Microsoft Academic Search

The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of

J. M. Davis; R. L. Moore; D. H. Hathaway

2003-01-01

236

Simulations of magnetic fields in the cosmos  

Microsoft Academic Search

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

M. Brüggen; M. Hoeft

2006-01-01

237

Indoor localization using magnetic fields  

NASA Astrophysics Data System (ADS)

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

Pathapati Subbu, Kalyan Sasidhar

238

HMI Magnetic Field Data Products  

NASA Astrophysics Data System (ADS)

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

Hoeksema, J.; Hmi, M. T.

2008-05-01

239

Tunneling in a magnetic field  

SciTech Connect

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

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

2006-05-15

240

Detecting Solar Axions Using Earth's Magnetic Field  

NASA Astrophysics Data System (ADS)

We show that solar axion conversion to photons in the Earth’s magnetosphere can produce an x-ray flux, with average energy ????4keV, which is measurable on the dark side of the Earth. The smallness of the Earth’s magnetic field is compensated by a large magnetized volume. For axion masses ma?10-4eV, a low-Earth-orbit x-ray detector with an effective area of 104cm2, pointed at the solar core, can probe the photon-axion coupling down to 10-11GeV-1, in 1 yr. Thus, the sensitivity of this new approach will be an order of magnitude beyond current laboratory limits.

Davoudiasl, Hooman; Huber, Patrick

2006-10-01

241

Oblique ion collection in the drift approximation: How magnetized Mach probes really work  

NASA Astrophysics Data System (ADS)

The anisotropic fluid equations governing a frictionless obliquely flowing plasma around an essentially arbitrarily shaped three-dimensional ion-absorbing object in a strong magnetic field are solved analytically in the quasineutral drift approximation, neglecting parallel temperature gradients. The effects of transverse displacements traversing the magnetic presheath are also quantified. It is shown that the parallel collection flux density dependence upon the external Mach number is n?cs exp[-1-(M??-M? cot ?)], where ? is the angle (in the plane of field and drift velocity) of the object-surface to the magnetic-field and M?? is the external parallel flow. The perpendicular drift, M?, appearing here consists of the external E?B drift plus a weighted sum of the ion and electron diamagnetic drifts that depends upon the total angle of the surface to the magnetic field. It is that somewhat counterintuitive combination that an oblique (transverse) Mach probe experiment measures.

Hutchinson, I. H.

2008-12-01

242

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

243

Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales  

NASA Astrophysics Data System (ADS)

Many synchrotron radiation techniques have been developed in the last 15 years for studying the magnetic properties of thin-film materials. The most attractive properties of synchrotron radiation are its energy tunability and its time structure. The first property allows measurements in resonant conditions at an absorption edge of each of the magnetic elements constituting the probed sample, and the latter allows time-resolved measurements on subnanosecond timescales. In this review, we introduce some of the synchrotron-based techniques used for magnetic investigations. We then describe in detail X-ray magnetic circular dichroism (XMCD) and how time-resolved XMCD studies can be carried out in the pump-probe mode. Finally, we illustrate some applications to magnetization reversal dynamics in spin valves and tunnel junctions, using fast magnetic field pulses applied along the easy magnetization axis of the samples. Thanks to the element-selectivity of X-ray absorption spectroscopy, the magnetization dynamics of the soft (Permalloy) and the hard (cobalt) layers can be studied independently. In the case of spin valves, this allowed us to show that two magnetic layers that are strongly coupled in a static regime can become uncoupled on nanosecond timescales.Present address: Universidade Federal do Paraná, Centro Politécnico CP 19011, Curitiba - PR CEP 81531-990, Brazil

Pizzini, Stefania; Vogel, Jan; Bonfim, Marlio; Fontaine, Alain

244

Analytical Methods for Characterizing Magnetic Resonance Probes  

PubMed Central

SUMMARY The efficiency of Gd(III) contrast agents in magnetic resonance image enhancement is governed by a set of tunable structural parameters. Understanding and measuring these parameters requires specific analytical techniques. This Feature describes strategies to optimize each of the critical Gd(III) relaxation parameters for molecular imaging applications and the methods employed for their evaluation.

Manus, Lisa M.; Strauch, Renee C.; Hung, Andy H.; Eckermann, Amanda L.; Meade, Thomas J.

2012-01-01

245

Wall scanning probe for high-field side plasma measurements on Alcator C-Mod  

SciTech Connect

A new, high-field side scanning probe has been added to Alcator C-Mod's complement of edge diagnostics. The wall scanning probe is designed to provide all the benefits of a linear plunge, multielectrode scanning probe while working from the confined space of the inner tokamak wall. The drive mechanism is an embedded coil which produces a torque with the ambient toroidal magnetic field when energized, thus allowing the probe to plunge to different preprogramed depths at different times during a plasma discharge. The probe tip is designed for easy replacement and is presently configured to operate as a modified, high heat-flux ''Gundestrup-type'' probe with four tungsten electrodes. The probe has demonstrated the ability to obtain cross-field profiles for electron temperature, density, floating potential, and plasma flow information (parallel and perpendicular to B) up to a depth of a few millimiters inside the last-closed flux surface in standard C-Mod discharges. The tungsten-tipped probe has proved very robust and shows little or no damage though it routinely handles surface heat fluxes on the order of 100 MW/m{sup 2} at peak insertion.

Smick, Noah; LaBombard, Brian [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2009-02-15

246

Magnetic Field from Loops Model  

NSDL National Science Digital Library

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

Christian, Wolfgang; Hwang, Fu-Kwun

2008-11-17

247

A magnetically driven oscillating probe microscope for operation in liquids  

Microsoft Academic Search

Oscillating probe atomic force microscopy in fluids is simplified when an oscillating force is applied directly to a magnetized cantilever using a solenoid. The response of the detector is simpler than that obtained with acoustic excitation. Reliable operation over a broad frequency range is achieved with excitation amplitudes of a few nm. This lower amplitude appears to facilitate imaging by

Wenhai Han; S. M. Lindsay; Tianwei Jing

1996-01-01

248

Magnetic field generation in Galactic molecular clouds  

NASA Astrophysics Data System (ADS)

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

Istomin, Ya. N.; Kiselev, A.

2013-10-01

249

FIELD CHARACTERIZATION OF XFEL QUADRUPOLE MAGNETS  

Microsoft Academic Search

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

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

250

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

251

Magnetic fields in extragalactic jets  

Microsoft Academic Search

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

William K. Rose

1987-01-01

252

Magnetic fields in extragalactic jets  

Microsoft Academic Search

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

William K. Rose

1987-01-01

253

The somatosensory evoked magnetic fields  

Microsoft Academic Search

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

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

2000-01-01

254

Electromagnetic field focusing (EFF) probe—a new neurosurgical tool  

Microsoft Academic Search

Summary The electromagnetic field focusing (EFF) probe is capable of producing well circumscribed, intense heat at the point of contact with the tissue. Experimental studies were carried out to assess this probe as a neurosurgical tool using 38 rats and 4 mice with mammary carcinoma. The study on the rats included study of the cutting, coagulating and vaporizing effect on

A. A. Patil; W. S. Yamanashi; J. L. Valentine; D. Hill; O. F. Filip

1987-01-01

255

Magnetic Field Issues in Magnetic Resonance Imaging.  

NASA Astrophysics Data System (ADS)

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

Petropoulos, Labros Spiridon

256

Experimental and Numerical Study of Sensitivity Improvement in Near-Field Probes Using Single-Negative Media  

Microsoft Academic Search

In this paper, we present experimental verification of the sensitivity improvement of evanescent-field probes using single-negative (SNG) metamaterials. Artificial magnetic materials are designed and fabricated to realize a ??-negative SNG material. The response of an electrically small probe to an electrically small target is investigated numerically and experimentally. The deviation in the phase of reflection coefficient due to the target

Muhammed Said Boybay; Omar M. Ramahi

2009-01-01

257

Magnetic Nanosensors for Probing Molecular Interactions  

Microsoft Academic Search

Magnetic nanosensors exhibiting high specificity and biocompatibility have been synthesized for the in vitro and in vivo detection\\u000a of molecular interactions. Upon target-induced nanoassembly formation, a sensitive and dosedependent decrease in the spin-spin\\u000a relaxation time (T2) of adjacent water molecules was observed. Various molecular targets ranging from DNAoligonucleotides, proteins, small molecules,\\u000a and even whole viruses have been detected using this

J. Manuel Perez; Charalambos Kaittanis

258

Advances in Magnetic Field Sensors  

Microsoft Academic Search

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

Pavel Ripka; Michal Janosek

2010-01-01

259

Random Field Effect in Magnets.  

National Technical Information Service (NTIS)

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

R. J. Birgeneau

1982-01-01

260

Magnetic Field Waves at Uranus.  

National Technical Information Service (NTIS)

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

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

1994-01-01

261

NMR detection and one-dimensional imaging using the inhomogeneous magnetic field of a portable single-sided magnet.  

PubMed

A portable, nuclear magnetic resonance (NMR) probe is described which utilises the intrinsic inhomogeneity of the field produced by a single-sided magnet to provide spatial encoding of the NMR signal. The probe uses a longitudinally magnetized hollow cylinder, and a figure-8 radiofrequency (RF) surface coil. The system has been used to measure NMR relaxation times and one-dimensional NMR profiles of rubber phantoms. PMID:15705508

Rahmatallah, S; Li, Y; Seton, H C; Mackenzie, I S; Gregory, J S; Aspden, R M

2005-03-01

262

NMR imaging in the earth's magnetic field.  

PubMed

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

Stepisnik, J; Erzen, V; Kos, M

1990-09-01

263

Separation of magnetic field lines  

SciTech Connect

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

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

2012-11-15

264

Active Region Magnetic Fields. I. Plage Fields  

NASA Astrophysics Data System (ADS)

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

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

1997-01-01

265

Electron dynamics in inhomogeneous magnetic fields.  

PubMed

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

Nogaret, Alain

2010-06-04

266

Magnetic fields in the cosmos  

SciTech Connect

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

Parker, E.N.

1983-08-01

267

Behavior of magnetic liquids in an inhomogeneous magnetic field  

SciTech Connect

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

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

1986-01-01

268

Novel rotating field probe for inspection of tubes  

SciTech Connect

Inspection of steam generator tubes in nuclear power plants is extremely critical for safe operation of the power plant. In the nuclear industry, steam generator tube inspection using eddy current techniques has evolved over the years from a single bobbin coil, to rotating probe coil (RPC) and array probe, in an attempt to improve the speed and reliability of inspection. The RPC probe offers the accurate spatial resolution but involves complex mechanical rotation. This paper presents a novel design of eddy current probes based on rotating fields produced by three identical coils excited by a balanced three-phase supply. The sensor thereby achieves rotating probe functionality by electronic means and eliminates the need for mechanical rotation. The field generated by the probe is largely radial that result in induced currents that flow circularly around the radial axis and rotating around the tube at a synchronous speed effectively producing induced eddy currents that are multidirectional. The probe will consequently be sensitive to cracks of all orientations in the tube wall. The finite element model (FEM) results of the rotating fields and induced currents are presented. A prototype probe is being built to validate simulation results.

Xin, J.; Tarkleson, E.; Lei, N.; Udpa, L.; Udpa, S. S. [Nondestructive Evaluation Laboratory, Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI, 48824 (United States)

2012-05-17

269

Laser Trapping of a Metallic Probe for Near Field Microscopy  

Microsoft Academic Search

A metallic particle is an ideal scattering probe in near-field microscopy. The Laser trapping technique, which enables us\\u000a to capture a microscopic object using radiation pressure force, has been applied to trap a nanometer-sized metallic particle\\u000a and to scan the particle over a sample surface as a near-field probe. In this section the mechanism and experimental verification\\u000a of three-dimensional laser

Tadao Sugiura

2001-01-01

270

Probing the energy barriers and magnetization reversal processes of nanoperforated membrane based percolated media  

NASA Astrophysics Data System (ADS)

Magnetization reversal processes in Co/Pt multilayers prepared on nanoperforated templates are probed by magnetization relaxation measurements. The signature of pinning controlled domain wall movement as expected for percolated media is identified. This contrasts with the nucleation-type reversal mechanism of a Co/Pt reference film prepared on a smooth substrate. A zero field energy barrier of 93kBT is determined by fluctuation field measurements and is elucidated by micromagnetic calculations using the nudged elastic band method. This value is sufficiently large to qualify the material as a promising percolated medium.

Neu, V.; Schulze, C.; Faustini, M.; Lee, J.; Makarov, D.; Suess, D.; Kim, S.-K.; Grosso, D.; Schultz, L.; Albrecht, M.

2013-04-01

271

SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields  

Microsoft Academic Search

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

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

2004-01-01

272

Two dimensional frustrated magnets in high magnetic field  

Microsoft Academic Search

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

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

2009-01-01

273

Near-field Optical Measurement using Nano-Prism Probes  

NASA Astrophysics Data System (ADS)

Recently, a nano-prism (NP) structure has drawn attention as an optical nano-antenna due to its exotic optical properties, while it has been extremely difficult to prepare a probe terminated with a NP for near-field optical measurement. Herein, we report a method to mass-produce pristine NP-probes. Our fabrication process allowed us to prepare NPs with sharp edge at the end of the probes, which significantly enhanced the electric fields around the probes and made the NP-probes ideal for nano-optical applications. We performed the apertureless near-field scanning optical microscopy on gold nanoparticles using a NP-probe, revealing the field localization at the vertices of the NP. We also achieved high resolution topographic imaging on carbon nanotubes and successfully performed the tip-enhanced Raman spectroscopy (TERS) experiment on brilliant cresyl blue (BCB) molecules, revealing a significant field localization at the sharp edge of the NP. This method could be a major breakthrough and provide tremendous flexibility for near-field optical applications.

Kim, Taekyeong; Lee, Byung Yang; Heo, Kwang; Hong, Seunghun; Jeon, Ki Seok; Kim, Hyung Min; Suh, Yung Doug; Kim, Deok Soo; Kim, Zee Hwan

2010-03-01

274

Calibration methods of a 2 GHz evanescent microwave magnetic probe for noncontact and nondestructive metal characterization for corrosion, defects, conductivity, and thickness nonuniformities  

Microsoft Academic Search

A near-field magnetic-dipole probe suitable for noncontact and nondestructive imaging of metals is described and the effects of resonator coupling strength, operation frequency, and the probe wire tip geometry on the conductivity resolution of the probe are experimentally determined. Using a simplified circuit model of the resonator, we were able to interpret the system's output and predict the magnitude of

Run Wang; Frank Li; Massood Tabib-Azar

2005-01-01

275

A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy  

NASA Astrophysics Data System (ADS)

We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm2Co17 permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 ?m, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement.

Yamaguchi, Akinobu; Saito, Hiromasa; Shimizu, Masayoshi; Miyajima, Hideki; Matsumoto, Satoru; Nakamura, Yoshiharu; Hirohata, Atsufumi

2008-08-01

276

The HMI Magnetic Field Pipeline  

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

277

Magnetic Resonance Imaging System Based on Earth's Magnetic Field  

Microsoft Academic Search

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

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

2004-01-01

278

Magnetic Relaxation with Oscillating Field Current Drive on MST  

NASA Astrophysics Data System (ADS)

In oscillating field current drive (OFCD), poloidal and toroidal ac magnetic fields with the same frequency but different phases are inductively applied to the plasma to drive dc plasma current through magnetic relaxation. Measurements of the dynamo mechanisms associated with magnetic relaxation are conducted during OFCD for a variety of phases both to better understand the phase-dependent relaxation dynamics and to aid in optimizing OFCD performance. The fluctuation-induced dynamo || and its constituent Hall dynamo ||ne are measured in the edge using insertable probes. The fluctuation-induced magnetic helicity flux is also measured. All three are enhanced during OFCD by a factor of two relative to standard RFP operation and, as expected, the induced transport of helicity is in the inward radial direction. Probes used include a secondary-emission capacitive probe that was developed to measure electric fields and tested by comparison to Langmuir probe measurements. Measurement of the Hall ne dynamo in the core using far-infrared interferometry-polarimetry is in progress as well. This work is supported by the US DOE.

Stone, D. R.; Almagri, A. F.; Fiksel, G.; McCollam, K. J.; Sarff, J. S.; Brower, D. L.; Ding, W. X.; Lin, L.

2011-11-01

279

Probing the magnetic topologies of magnetic clouds by means of solar energetic particles. (Reannouncement with new availability information)  

SciTech Connect

Magnetic clouds are large (<0.25 AU) interplanetary regions with topologies consistent with those of magnetic loops. They are of interest because they may be an interplanetary signature of coronal mass ejections. Clouds have been identified in solar wind data by their magnetic properties and by the presence of bidirectional particle fluxes. Two possible closed magnetic topologies have been considered for clouds: (1) an elongated bottle with field lines rooted at both ends in the Sun and (2) a detached magnetic bubble or plasmoid consisting of closed field lines. The inferred topologies are also consistent with open field lines that converge beyond 1 AU. We have used solar energetic particles (SEPs) as probes of the cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the Sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

Kahler, S.W.; Reames, D.V.

1991-06-01

280

Magnetic field dependence of the correlation gap in SmB{sub 6}  

SciTech Connect

We have used magnetoresistance measurements to probe the effect of large magnetic fields on the stability of the electronic gap {delta} in SmB{sub 6}. Although the Zeeman splitting in a 18 Telsa field is comparable to the ambient pressure {delta}, and even exceeds {delta} at 56 kbar, {delta} is in both cases almost completely unaffected by the magnetic field.

Cooley, J.C.; Aronson, M.C. [Univ. of Michigan, Ann Arbor, MI (United States); Lacerda, A. [National High Magnetic Field Laboratory, Los Alamos, NM (United States); Canfield, P.C. [Iowa State Univ. of Science and Technology, Ames, IA (United States); Fisk, Z. [Los Alamos National Laboratory, Los Alamos, NM (United States)

1994-06-11

281

Magnetic field of atrial depolarization.  

PubMed

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

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

282

Compressing magnetic fields with high-energy lasers  

NASA Astrophysics Data System (ADS)

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+3He fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC [J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4 [S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)].

Knauer, J. P.; Gotchev, O. V.; Chang, P. Y.; Meyerhofer, D. D.; Polomarov, O.; Betti, R.; Frenje, J. A.; Li, C. K.; Manuel, M. J.-E.; Petrasso, R. D.; Rygg, J. R.; Séguin, F. H.

2010-05-01

283

Compressing magnetic fields with high-energy lasers  

SciTech Connect

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+{sup 3}He fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC[J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4[S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)].

Knauer, J. P. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Gotchev, O. V. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Chang, P. Y. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Physics and Astronomy, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Meyerhofer, D. D.; Betti, R. [Lab. for Laser Energetics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Physics and Astronomy, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Polomarov, O. [Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Dept. of Mechanical Engineering, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Frenje, J. A.; Li, C. K.; Manuel, M. J.-E.; Petrasso, R. D. [Fusion Science Center for Extreme States of Matter and Fast Ignition Physics, Univ. of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139 (United States)

2010-05-15

284

Bending of magnetic filaments under a magnetic field  

Microsoft Academic Search

Magnetic beads and superparamagnetic (SP) colloid particles have successfully been employed for micromechanical manipulation of soft material, in situ probing of elastic properties, and design of smart materials (ferrogels). Here we derive analytical expressions for the equilibrium shape of magnetic fibers, considering two end-member cases, (a) SP or single-domain particles concentrated at the free end of cantilevered rods or tubes,

Valera P. Shcherbakov; Michael Winklhofer

2004-01-01

285

Anisotropic Magnetism in Field-Structured Composites  

SciTech Connect

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

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

1999-06-24

286

Studies on Somatosensory Evoked Magnetic Fields.  

National Technical Information Service (NTIS)

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

J. Huttunen

1987-01-01

287

Luminescence in applied magnetic fields  

NASA Astrophysics Data System (ADS)

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

Crosby, G. A.

1989-08-01

288

Simulations of Photospheric Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

1999-05-01

289

Field Concentrator Based Resonant Magnetic Sensor  

Microsoft Academic Search

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

S. Brugger; P. Simon; O. Paul

2006-01-01

290

Color Superconducting Matter in a Magnetic Field  

SciTech Connect

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

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

2008-01-25

291

Atomic Resolution Magnetic Resonance Diffraction using Magnetic Probes  

NASA Astrophysics Data System (ADS)

We will present our recent proposal [1] for the observation of sharp spectral peaks in the magnetic resonance signal for the case of a crystal in close proximity of a ferromagnetic nanosphere. The appearance of the peaks is a direct signature of the discrete atomic sites in the crystal lattice, and the positions of the spectral peaks are sensitive to the crystal unit cell size thereby providing a magnetic resonance diffraction method for determination of the basic parameters of the crystal at the atomic scale. The technique relaxes the challenging requirements for single spin detection instrument proposals by allowing many spins to coherently contribute to the magnetic resonance signal while still revealing atomic resolution information. Therefore, the technique provides a magnetic resonance alternative to the other three well-known atomic resolution crystallography techniques of x-ray, electron, and neutron diffraction. Applications to the studies of crystals, thin films, and crystallites will be discussed, and potential measurement methods for the confirmation of the diffraction theory will be proposed [2]. The analysis suggests that the long desired goal of detecting atomic resolution magnetic resonance diffraction [3] is well within reach of current experimental techniques such as Magnetic Resonance Force Microscopy (MRFM) [4]. [1] M. Barbic J. Appl. Phys. vol. 91, p. 9987 (2002). [2] M. Barbic and A. Scherer J. Appl. Phys. vol. 92, p. 7345 (2002). [3] P. Mansfield and P. K. Grannell J. Phys. C: Solid State Phys. vol. 6, p. L422 (1973). [4] Sidles J. A. et al. Rev. Mod. Phys. vol. 67, p. 249 (1995).

Barbic, Mladen

2003-03-01

292

Studies of surface magnetism using electron and ion beam probes  

NASA Astrophysics Data System (ADS)

Spin polarization analysis of electrons from ferromagnets has proven to be a valuable tool for the study of near-surface magnetism. High-resolution imaging of domains and domain walls in the scanning electron microscope is demonstrated. Analysis of the temperature dependence of Stoner excitations in Ni may be carried out in a 'complete' inelastic electron scattering experiment with a polarized electron source. Examples for probing the electronic structure of epitaxially grown thin films of Co on Cu(100) by spin-polarized photoemission are given. Two recent applications of ion beam probes are discussed: (1) the analysis of ion-excited spin-polarized secondary electrons and its use for 'magnetic sputter depth profiling', and (2) the capture of polarized electrons in ion-surface scattering resulting in the emission of circularly polarized light.

Kirschner, J.

1988-11-01

293

Developments of scanning probe microscopy with stress/strain fields  

NASA Astrophysics Data System (ADS)

An innovative stress/strain fields scanning probe microscopy in ultra high vacuum (UHV) environments is developed for the first time. This system includes scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). Two piezo-resistive AFM cantilever probes and STM probes used in this system can move freely in XYZ directions. The nonoptical frequency shift detection of the AFM probe makes the system compact enough to be set in the UHV chambers. The samples can be bent by an anvil driven by a step motor to induce stress and strain on their surface. With a direct current (dc) power source, the sample can be observed at room and high temperatures. A long focus microscope and a monitor are used to observe the samples and the operation of STM and AFM. Silicon(111) surface in room temperature and silicon(001) surface in high temperature with stress were investigated to check the performance of the scanning probe microscope.

Guo, H. X.; Fujita, D.

2011-12-01

294

Phosphate vibrations probe local electric fields and hydration in biomolecules  

PubMed Central

The role of electric fields in important biological processes like binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and quantify that sensitivity, allowing local electric field measurements to be made in phosphate-containing biological systems without chemical modification.

Levinson, Nicholas M.; Bolte, Erin E.; Miller, Carrie S.

2011-01-01

295

Numerical Simulation In Magnetic Drug Targeting. Magnetic Field Source Optimization  

Microsoft Academic Search

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

A. Dobre; A. M. Morega

296

Magnetic fields in the early Universe  

Microsoft Academic Search

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

Dario Grasso; Hector R. Rubinstein

2001-01-01

297

Primordial magnetic field limits from cosmological data  

SciTech Connect

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

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

2010-10-15

298

Penetration of plasma across a magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2009-08-01

299

Magnetic field reversals in the Milky Way  

Microsoft Academic Search

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

J. P. Vallee

1996-01-01

300

Transmission line magnetic fields; Measurements and calculations  

Microsoft Academic Search

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

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

1992-01-01

301

Primordial magnetic field limits from cosmological data  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

302

Extragalactic background light and extragalactic magnetic fields  

NASA Astrophysics Data System (ADS)

VHE ?-rays from distant blazars several hundred Mpc away are attenuated through pair production interactions on extragalactic background light (EBL). Subsequent to their generation, electron/positron pairs proceed to produce ?-rays through IC interactions leading to the development of an electromagnetic (EM) cascade. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving ?-ray emission is dependent on the strength of the EGMF. The GeV-TeV spectral shape of blazars has, thus, the potential to probe the EGMF strength along the line of sight to the object. Focusing on the specific example cases of the blazar 1ES 0229+200 and PKS 2155-304, bounds on the EGMF are obtained using both the spectral and angular observational information from the these two blazars.

Taylor, Andrew M.

2012-12-01

303

DC Electric Field Measurement by the Double Probe System Aboard Geotail and its Simulation  

NASA Astrophysics Data System (ADS)

We summarize the characteristics of the DC electric field measurement by the double probe system, PANT and EFD-P, aboard Geotail. The accuracy and correction factors for the gain (effective length) and off-set, which depends on ambient plasma conditions, are provided. Accurate measurements of electric fields are essential for space plasma studies, for example, plasma convection, wave-particle interactions, violation of MHD approximation, etc. One typical measurement techniques is the 'Double Probe method', identical to that of a voltmeter: the potential difference between two top-hat probes [cf. Pedersen et al., 1984]. This method can measure electric fields passively and continuously in all plasma conditions. However, the accuracy of the measured electric field values is limited. The probe measurement is also subjected to the variable gain (effective length) of the probe antenna and the artificial offset of the measured values. Those depend on a) the disturbance from ambient plasma and b) the disturbance from the spacecraft and the probe itself. In this paper, we show the results of the characteristics of DC electric field measurement by the PANT probe and the EFD-P (Electric Field Detector - Probe technique) receiver aboard Geotail [Tsuruda et al., 1994], in order to evaluate the accuracy, gain, and offset controlled by ambient plasmas. We conclude that the Geotail electric field measurement by the double probe system has the accuracy 0.4 mV/m for Ex and 0.3 mV/m for Ey, after the correction of the gain and offset. In better conditions, accuracy of Ey is 0.2 mV/m. The potential accuracy would be better because those values are limited by the accuracy of the particle measurement especially in low density conditions. In practical use, the corrections by long-term variation and spacecraft potential are effective to refine the electric field data. The characteristics of long-term variation and the dependences on ambient plasma are not fully understood well, yet. Further works will be needed based on the calibrated LEP data after 1998. It will also cover the conditions rejected in this paper, i.e., low density regions, potential controlled period, electric field quasi-parallel to magnetic field, etc. The comparison with EFD-B (EFD - Beam technique) data will also be included in order to reject the ambiguity in particle observations. In addition, we are trying to establish the numerical model of the double probe system for the full-quantitative understanding of the effect of potential structure and photoelectron distributions. Those will be the basis for planned experiments, BepiColombo to Mercury, ERG to the inner magnetosphere, and the multi-spacecraft magnetospheric mission SCOPE.

Kasaba, Y.; Hayakawa, H.; Ishisaka, K.; Okada, T.; Matsuoka, A.; Mukai, T.; Okada, M.

2005-12-01

304

Electromagnetic field focusing (EFF) probe in aneurysm thrombosis  

Microsoft Academic Search

Summary Due to its capability of producing a well localized intense heat field of predictable dimensions, the electromagnetic field focusing probe was evaluated experimentally as a surgical tool in aneurysm thrombosis. Aneurysm models were created by anastomosing a segment of vein to the abdominal aorta. Seventy-five such aneurysms were created in seventy-five animals. The aneurysms were then placed under the

A.-A. Patil; W. Yamanashi; J. Valentine; D. Hill; R. E. Woosley; O. F. Filip

1986-01-01

305

Evolution of normal pulsar magnetic fields  

NASA Astrophysics Data System (ADS)

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

Sun, Xiaohui; Han, Jinlin

2002-06-01

306

Magnetic field induced lattice ground states from holography  

NASA Astrophysics Data System (ADS)

We study the holographic field theory dual of a probe SU(2) Yang-Mills field in a background (4 + 1)-dimensional asymptotically Anti-de Sitter space. We find a new ground state when a magnetic component of the gauge field is larger than a critical value. The ground state forms a triangular Abrikosov lattice in the spatial directions perpendicular to the magnetic field. The lattice is composed of superconducting vortices induced by the condensation of a charged vector operator. We perform this calculation both at finite temperature and at zero temperature with a hard wall cutoff dual to a confining gauge theory. The study of this state may be of relevance to both holographic condensed matter models as well as to heavy ion physics. The results shown here provide support for the proposal that such a ground state may be found in the QCD vacuum when a large magnetic field is present.

Bu, Yan-Yan; Erdmenger, Johanna; Shock, Jonathan P.; Strydom, Migael

2013-03-01

307

Initial Results of the SSPX Transient Internal Probe System for Measuring Toroidal Field Profiles  

NASA Astrophysics Data System (ADS)

Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. The Sustained Spheromak Physics Experiment (SSPX) is using a field profile diagnostic called the Transient Internal Probe (TIP). TIP consists of a verdet-glass bullet that is used to measure the magnetic field by Faraday rotation. This probe is shot through the spheromak by a light gas gun at speeds near 2 km/s. An argon laser is aligned along the path of the probe. The light passes through the probe and is retro-reflected to an ellipsometer that measures the change in polarization angle. The measurement is spatially resolved down to the probes’ 1 cm length to within 15 Gauss. Initial testing results are given. This and future data will be used to determine the field profile for equilibrium reconstruction. TIP can also be used in conjunction with wall probes to map out toroidal mode amplitudes and phases internally. This work was performed under the auspices of US DOE by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Holcomb, C. T.; Jarboe, T. R.; Mattick, A. T.; Hill, D. N.; McLean, H. S.; Wood, R. D.; Cellamare, V.

2000-10-01

308

Crustal Magnetic Fields of Terrestrial Planets  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

309

Holographic Description of Strongly Correlated Electrons in External Magnetic Fields  

NASA Astrophysics Data System (ADS)

We study the Fermi level structure of 2+1-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordström black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. We compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. As expected, the Hall conductivity is quantized according to integer Quantum Hall Effect (QHE) at weak magnetic fields. At strong magnetic fields, new plateaus typical for the fractional QHE appear. Our pattern closely resembles the experimental results on graphite which are described using the fractional filling factor proposed by Halperin.

Gubankova, E.; Brill, J.; ?ubrovi?, M.; Schalm, K.; Schijven, P.; Zaanen, J.

310

Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations  

NASA Astrophysics Data System (ADS)

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (?peprobe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

Heinrich, Jonathon R.; Cooke, David L.

2013-09-01

311

NMR detection and one-dimensional imaging using the inhomogeneous magnetic field of a portable single-sided magnet  

Microsoft Academic Search

A portable, nuclear magnetic resonance (NMR) probe is described which utilises the intrinsic inhomogeneity of the field produced by a single-sided magnet to provide spatial encoding of the NMR signal. The probe uses a longitudinally magnetised hollow cylinder, and a figure-8 radiofrequency (RF) surface coil. The system has been used to measure NMR relaxation times and one-dimensional NMR profiles of

S. Rahmatallah; Y. Li; H. C. Seton; I. S. Mackenzie; J. S. Gregory; R. M. Aspden

2005-01-01

312

NMR detection and one-dimensional imaging using the inhomogeneous magnetic field of a portable single-sided magnet  

NASA Astrophysics Data System (ADS)

A portable, nuclear magnetic resonance (NMR) probe is described which utilises the intrinsic inhomogeneity of the field produced by a single-sided magnet to provide spatial encoding of the NMR signal. The probe uses a longitudinally magnetised hollow cylinder, and a figure-8 radiofrequency (RF) surface coil. The system has been used to measure NMR relaxation times and one-dimensional NMR profiles of rubber phantoms.

Rahmatallah, S.; Li, Y.; Seton, H. C.; MacKenzie, I. S.; Gregory, J. S.; Aspden, R. M.

2005-03-01

313

The origins of lunar crustal magnetic fields  

NASA Astrophysics Data System (ADS)

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

Halekas, Jasper S.

314

Magnetic field observations in Comet Halley's coma  

NASA Astrophysics Data System (ADS)

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

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

1986-05-01

315

Detecting the orientation of magnetic fields in galaxy clusters  

NASA Astrophysics Data System (ADS)

Clusters of galaxies, filled with hot magnetized plasma, are the largest bound objects in existence and an important touchstone in understanding the formation of structures in our Universe. In such clusters, thermal conduction follows field lines, so magnetic fields strongly shape the cluster's thermal history; that some have not since cooled and collapsed is a mystery. In a seemingly unrelated puzzle, recent observations of Virgo cluster spiral galaxies imply ridges of strong, coherent magnetic fields offset from their centre. Here we demonstrate, using three-dimensional magnetohydrodynamical simulations, that such ridges are easily explained by galaxies sweeping up field lines as they orbit inside the cluster. This magnetic drape is then lit up with cosmic rays from the galaxies' stars, generating coherent polarized emission at the galaxies' leading edges. This immediately presents a technique for probing local orientations and characteristic length scales of cluster magnetic fields. The first application of this technique, mapping the field of the Virgo cluster, gives a startling result: outside a central region, the magnetic field is preferentially oriented radially as predicted by the magnetothermal instability. Our results strongly suggest a mechanism for maintaining some clusters in a `non-cooling-core' state.

Pfrommer, Christoph; Jonathan Dursi, L.

2010-07-01

316

The resonant radio-frequency magnetic probe tuned by coaxial cable.  

PubMed

In this paper, the resonant rf magnetic probe is upgraded by replacing the rotary capacitor in the old version with the series-connected coaxial cable. The numerical calculation and the measurement with the prototype probe show that the rf magnetic probe can achieve resonance at a middle length of the series-connected coaxial cable. The good electrical symmetry of the new rf magnetic probe is ensured by both the identity of series-connected coaxial cables and the new structure of the primary winding. Practical measurements conduced on an rf inductively coupled plasma source demonstrate that performances of the new rf magnetic probe are good. PMID:22938337

Sun, B; Huo, W G; Ding, Z F

2012-08-01

317

Design and calibration of electric field probes in the range 10-120 MHz.  

PubMed

In view of potential thermal hazards, there is a need to determine the specific absorption rate (SAR) distributions associated with radiofrequency coils used in magnetic resonance imaging (MRI) (typically 10-120 MHz). Electric field (E-field) distributions in tissue-equivalent phantoms may be determined using a probe comprising a dipole antenna and a detector. The geometry of the dipole dictates the sensitivity of the device, thus two designs are discussed in this paper. Both probes are compact, have a spatial resolution of 2.5 cm3, operate at MR frequencies and have a response independent of the dielectric characteristics of the phantom material. Calibration of these probes requires a system capable of producing a known E-field both in air and in a tissue-like medium at frequencies between 10 and 120 MHz. Transverse electromagnetic wave (TEM) cells answering these specifications are described and the calibration procedure outlined. Accurately calibrated E-field probes can make field measurements in phantoms which can be used to verify predictions from numerical models. These numerical techniques may then be used to predict E-fields, and hence SAR, in patients. PMID:9253046

Taylor, H C; Burl, M; Hand, J W

1997-07-01

318

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas.  

PubMed

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jime?nez-Go?mez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfve?n eigenmodes, which could be a serious issue for future fusion reactors. PMID:24089823

Haskey, S R; Blackwell, B D; Seiwald, B; Hole, M J; Pretty, D G; Howard, J; Wach, J

2013-09-01

319

A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas  

NASA Astrophysics Data System (ADS)

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

Haskey, S. R.; Blackwell, B. D.; Seiwald, B.; Hole, M. J.; Pretty, D. G.; Howard, J.; Wach, J.

2013-09-01

320

Development of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors  

NASA Astrophysics Data System (ADS)

Eddy Current Technique is a powerful method of inspection of metal parts. When size of flaws decreases, inspection areas become hardly accessible or material is magnetic, traditional winding coil probes are less efficient. Thanks to new CIVA simulation tools, we have designed and optimized advanced EC probes: flexible EC probe based on micro-coil arrays and EC probe with magnetic sensors, including specific electronics.

Marchand, B.; Decitre, J.-M.; Sergeeva-Chollet, N.; Skarlatos, A.

2013-01-01

321

Magnetic field seeding by galactic winds  

Microsoft Academic Search

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

Serena Bertone; Corina Vogt; Torsten Enßlin

2006-01-01

322

Invited Safety of Strong, Static Magnetic Fields  

Microsoft Academic Search

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

John F. Schenck

2000-01-01

323

Intergalactic Magnetic Fields from Quasar Outflows  

Microsoft Academic Search

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

Steven R. Furlanetto; Abraham Loeb

2001-01-01

324

Magnetic fields in Local Group dwarf irregulars  

Microsoft Academic Search

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

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

2011-01-01

325

Deformation of Water by a Magnetic Field  

ERIC Educational Resources Information Center

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

Chen, Zijun; Dahlberg, E. Dan

2011-01-01

326

Baking a magnetic-field display  

NASA Astrophysics Data System (ADS)

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

Cavanaugh, Terence; Cavanaugh, Catherine

1998-02-01

327

Exploring Magnetic Fields with a Compass  

ERIC Educational Resources Information Center

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

Lunk, Brandon; Beichner, Robert

2011-01-01

328

Cluster magnetic fields from galactic outflows  

Microsoft Academic Search

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

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

2009-01-01

329

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

330

An Extraordinary Magnetic Field Map of Mars  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

331

Langmuir probe measurements in the intense RF field of a helicon discharge  

NASA Astrophysics Data System (ADS)

Helicon discharges have extensively been studied for over 25 years both because of their intriguing physics and because of their utility in producing high plasma densities for industrial applications. Almost all measurements so far have been made away from the antenna region in the plasma ejected into a chamber where there may be a strong magnetic field (B-field) but where the radiofrequency (RF) field is much weaker than under the antenna. Inside the source region, the RF field distorts the current-voltage (I-V) characteristic of the probe unless it is specially designed with strong RF compensation. For this purpose, a thin probe was designed and used to show the effect of inadequate compensation on electron temperature (Te) measurements. The subtraction of ion current from the I-V curve is essential; and, surprisingly, Langmuir's orbital motion limited theory for ion current can be used well beyond its intended regime.

Chen, Francis F.

2012-10-01

332

A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments.  

PubMed

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 ?m diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner. PMID:24089869

Smith, Doran D; Alexson, Dimitri A; Garbini, Joseph L

2013-09-01

333

Rotating magnetic beacons magnetic field strength size in SAGD  

Microsoft Academic Search

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

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

2010-01-01

334

Branched nanotubes, nanowires and nanofibers for magnetic scanned probe sensing  

NASA Astrophysics Data System (ADS)

We have prepared branched nanotubes, nanowires and nanofibers made from carbon, zinc oxide and polymer, respectively, to be used as probe tips in nanoscale scanned probe sensing. Some of these devices are in "divining rod" geometry and, with a magnetic nanoparticle fixed to the tip, can be employed as high resolution MFM and MRFM sensors. The electrical, including piezoelerical, transport properties of isolated Y-shaped multiwalled carbon nanotubes, and of tri- and tetrapod ZnO2 nanowires, each having diameters between 20 and 100 nm, are being investigated toward this end. The polymer devices are fabricated via a multiphoton polymerization technique that affords complete 3D microstructure capability with sub-200 nm resolution.

Oh, J. I.; Sun, Y.; Banerjee, D.; Ren, Z. F.; Lafratta, C. N.; Praino, J.; Baldacchini, T.; Fourkas, J. T.; Naughton, M. J.; Li, W. Z.

2004-03-01

335

Unique topological characterization of braided magnetic fields  

NASA Astrophysics Data System (ADS)

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

Yeates, A. R.; Hornig, G.

2013-01-01

336

Atom probe field ion microscopy of high resistivity materials  

SciTech Connect

Over the last 30 years the atom probe has proved to be a powerful tool for studying nanometer-sized compositional fluctuations in a wide range of metallic alloys but has had only limited applications to semiconductors and ceramics. One of the primary reasons for this difference is the higher resistivity of semiconducting and ceramic specimens. Because of this high resistivity, the high voltage field evaporation pulse is attenuated before it reaches the apex of the specimen thereby making the pulse ineffective for field evaporation. Experiments have demonstrated that both variants of the voltage-pulsed atom probe (i.e., those instruments in which the field evaporation pulse is applied directly to the specimen and those in which the negative pulse is applied to a counter electrode in front of the specimen) are equally affected. In this overview, the limits of applicability of the voltage-pulsed atom probe to high resistivity materials are examined. In this study, a wide range of materials have been examined to determine whether field ion microscopy and voltage-pulsed field evaporation can be achieved and the results are summarized in the report. Field ion microscopy including dc field evaporation was possible for all materials except bulk ceramic insulators and glasses. Field ion microscopy requires some conductivity both to achieve a high electric field at the apex of the specimen, and also to support the field ion current. In contrast, voltage-pulsed field evaporation requires transmission of the pulse to the apex of the specimen. All metallic alloys including high resistance alloys and metallic glasses were successfully field evaporated with a voltage pulse. Specimens that were produced from bulk material of several conducting ceramics including MoSi, TiB and TiC were also successfully field evaporated with a voltage pulse.

Sibrandij, S.J.; Larson, D.J.; Miller, M.K.

1998-02-01

337

Boston University Physics Applets: Magnetic Field Demonstration  

NSDL National Science Digital Library

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

Duffy, Andrew

2008-08-23

338

Pulsed beams as field probes for precision measurement  

SciTech Connect

We describe a technique for mapping the spatial variation of static electric, static magnetic, and rf magnetic fields using a pulsed atomic or molecular beam. The method is demonstrated using a beam designed to measure the electric dipole moment of the electron. We present maps of the interaction region, showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with 25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm resolution. This diagnostic technique is very powerful in the context of high-precision atomic and molecular physics experiments, where pulsed beams have not hitherto found widespread application.

Hudson, J. J.; Ashworth, H. T.; Kara, D. M.; Tarbutt, M. R.; Sauer, B. E.; Hinds, E. A. [Centre for Cold Matter, Blackett Laboratory, Imperial College London, London SW7 2AZ (United Kingdom)

2007-09-15

339

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

340

Bipolar pulse field for magnetic refrigeration  

DOEpatents

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

Lubell, M.S.

1994-10-25

341

Near-Field Magnetic Dipole Moment Analysis.  

National Technical Information Service (NTIS)

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

P. K. Harris

2003-01-01

342

Constant Current Source for Stable Magnetic Fields.  

National Technical Information Service (NTIS)

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

K. Weyand

1976-01-01

343

THE EARTH'S YOUNG MAGNETIC FIELD  

Microsoft Academic Search

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

Trevor Major

344

Atom probe field ion microscopy of titanium aluminides  

SciTech Connect

Titanium aluminides have a number of potential high temperature applications due to their good elevated-temperature mechanical properties, low density, and good creep and oxidation resistance. However, fabrication of commercial components of these materials has been impeded by their poor mechanical properties at ambient temperatures. Significant efforts with various degrees of success have been made to improve the mechanical properties of these TiAl alloys by doping them with a variety of different elements including B, C, Cr, Er, Fe, Mn, Mo, Ni, Nb, P, Si, Ta, V and W. One of the optimum analytical tools for investigating the effects of these additions on the microstructure is the atom probe field ion micro scope. However, relatively few studies of titanium aluminides, compared to some other intermetallic compounds, have performed by atom probe field ion microscopy. This lack of attention can be attributed to the brittle nature of the material, in-situ transformations that occur during the field ion microscopy and preferential evaporation problems that were encountered in some of the early studies. The atom probe field ion microscope used for the current experiments has a low base pressure ({approximately} 2 {times} 10{sup 9} Pa) and careful attention was paid to optimizing the experimental parameters. All the examples shown were obtained from specimens prepared by standard electropolishing techniques. To demonstrate the suitability of the technique to these materials, several different titanium aluminides have been characterized in the atom probe.

Larson, D.J.; Miller, M.K.

1998-01-01

345

Kelvin probe force microscopy using near-field optical tips  

Microsoft Academic Search

We report on the use of near-field optical force sensors for Kelvin probe force microscopy (KPFM) and surface potential measurements. It is shown that a very good potential sensitivity of less than 5 mV can be obtained using such tips. In addition, it is found that the contact potential difference measured using these tips is independent of the scanning height,

R. Shikler; Y Rosenwaks

2000-01-01

346

MEMS Electric-Field Probes for Laboratory Plasmas  

Microsoft Academic Search

This paper presents microfabricated sensors for directly measuring fine-scale plasma parameters in typical laboratory plasmas. Microfabricated probes have the potential to significantly advance basic plasma physics by enabling the measurement of fundamental processes under controlled conditions. Historically, the spatial scales of the finest electromagnetic-field fluctuations in laboratory plasmas have been too small for conventionally fabricated tools to sense. The new

Janet A. Stillman; Franklin C. Chiang; Patrick Pribyl; W. Gekelman; M. Nakamoto; Jack W. Judy

2009-01-01

347

Ion collection by probing objects in flowing magnetized plasmas  

Microsoft Academic Search

A new 1-D collisionless kinetic model is developed for the flow of ions to probing structures in drifting plasmas. The cross field flow into the presheath is modelled by accounting consistently for particle exchange between the collection flux tube and the outer plasma. Numerical solutions of the self-consistent plasma\\/sheath equations are obtained with arbitrary external ion temperature and parallel plasma

Kyu-Sun Chung; Chung

1989-01-01

348

Probing the electromagnetic field distribution within a metallic nanodisk.  

PubMed

A Co nanolayer is used as a local probe to evaluate the vertical inhomogeneous distribution of the electromagnetic (EM) field within a resonant metallic nanodisk. Taking advantage of the direct relation between the magneto-optical activity and the electromagnetic field intensity in the Co layer, it is shown that the nonuniform EM distribution within the nanodisk under plasmon resonant conditions has maximum values close to the upper and lower flat faces, and a minimum value in the middle. PMID:21972067

Meneses-Rodríguez, David; Ferreiro-Vila, Elías; Prieto, Patricia; Anguita, José; González, María U; García-Martín, José M; Cebollada, Alfonso; García-Martín, Antonio; Armelles, Gaspar

2011-10-04

349

Arc Discharges in a Curved Magnetic Field.  

National Technical Information Service (NTIS)

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

F. C. Schueller

1974-01-01

350

Is the intergalactic magnetic field primordial?  

Microsoft Academic Search

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

Martin Beech

1985-01-01

351

Intergalactic magnetic field and galactic WARPS  

Microsoft Academic Search

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

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

1990-01-01

352

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

353

Is the intergalactic magnetic field primordial?  

NASA Astrophysics Data System (ADS)

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

Beech, M.

1985-11-01

354

Static uniform magnetic fields and amoebae  

SciTech Connect

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

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

1997-03-01

355

Probing the quality of Ni filled nanoporous alumina templates by magnetic techniques.  

PubMed

Pulsed electrodeposition prepared porous alumina templates with Ni nanowires pore filling ranged from 1 to 100%, depending on the alumina barrier-layer thickness, were probed by continuous wave ferromagnetic resonance at room temperature. For completely filled samples, a single resonance peak was observed in the whole range of angles between the applied magnetic field and normal to the sample plane. Its position was described by Kittel formula that takes into account shape anisotropy of individual Ni wires and dipolar interactions between them. For the samples with lower pore filling the effective anisotropy field decreased and the resonance linewidth in the perpendicular configuration increased. Also a quite intense second peak was observed at lower fields for these samples. These changes are associated with reduction of pore filling percentage that can lead to decrease of dipolar interactions between nanowires and to appearance of magnetic inhomogeneities inside wires. PMID:23035501

Sousa, C T; Leitão, D C; Proença, M P; Apolinário, A; Azevedo, A M; Sobolev, N A; Bunyaev, S A; Pogorelov, Yu G; Ventura, J; Araújo, J P; Kakazei, G N

2012-09-01

356

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

357

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

358

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

SciTech Connect

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V. (Materials Science Division); (Univ. of Porto); (National Academy of Sciences Ukraine); (Univ. of Alabama); (Ohio State Univ.); (Oakland Univ.)

2008-06-01

359

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

PubMed

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions. PMID:18681017

Kakazei, G N; Mewes, T; Wigen, P E; Hammel, P C; Slavin, A N; Pogorelov, Yu G; Costa, M D; Golub, V O; Guslienko, K Yu; Novosad, V

2008-06-01

360

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

361

Site and probe dependence of hyperfine magnetic field in L2 1 Heusler alloys X 2 MnZ (X=Ni, Cu, Rh, Pd and Z=Ga, Ge, In, Sn, Pb)  

Microsoft Academic Search

Results of TDPAC and Mössbauer measurements of hyperfine magnetic fields in L21 Heusler alloys X2MnZ are given. TDPAC utilized Cd-111 from In-111 at the Z site and Ag-111 at the X site, and Ru-99 from Rh-99 at the X site. Mössbauer studies utilized Sn-119 at the Z site or at the Mn site. A compilation of hmf values is presented,

S. Jha; H. M. Seyoum; M. Demarco; G. M. Julian; D. A. Stubbs; J. W. Blue; M. T. X. Silva; A. Vasquez

1983-01-01

362

A scanning Hall probe microscope for high resolution magnetic imaging down to 300 mK  

SciTech Connect

We present the design, construction, and performance of a low-temperature scanning Hall probe microscope with submicron lateral resolution and a large scanning range. The detachable microscope head is mounted on the cold flange of a commercial {sup 3}He-refrigerator (Oxford Instruments, Heliox VT-50) and operates between room temperature and 300 mK. It is fitted with a three-axis slip-stick nanopositioner that enables precise in situ adjustment of the probe location within a 6x6x7 mm{sup 3} space. The local magnetic induction at the sample surface is mapped with an easily changeable microfabricated Hall probe [typically GsAs/AlGaAs or AlGaAs/InGaAs/GaAs Hall sensors with integrated scanning tunnel microscopy (STM) tunneling tips] and can achieve minimum detectable fields {>=}10 mG/Hz{sup 1/2}. The Hall probe is brought into very close proximity to the sample surface by sensing and controlling tunnel currents at the integrated STM tip. The instrument is capable of simultaneous tunneling and Hall signal acquisition in surface-tracking mode. We illustrate the potential of the system with images of superconducting vortices at the surface of a Nb thin film down to 372 mK, and also of labyrinth magnetic-domain patterns of an yttrium iron garnet film captured at room temperature.

Khotkevych, V. V.; Bending, S. J. [Department of Physics, University of Bath, Claverton Down, BA2 7AY Bath (United Kingdom); Milosevic, M. V. [Department of Physics, University of Bath, Claverton Down, BA2 7AY Bath (United Kingdom); Department Fysica, Universiteit Antwerpen, Groenenborgelaan 171, 2020 Antwerpen (Belgium)

2008-12-15

363

A scanning Hall probe microscope for high resolution magnetic imaging down to 300 mK.  

PubMed

We present the design, construction, and performance of a low-temperature scanning Hall probe microscope with submicron lateral resolution and a large scanning range. The detachable microscope head is mounted on the cold flange of a commercial (3)He-refrigerator (Oxford Instruments, Heliox VT-50) and operates between room temperature and 300 mK. It is fitted with a three-axis slip-stick nanopositioner that enables precise in situ adjustment of the probe location within a 6x6x7 mm(3) space. The local magnetic induction at the sample surface is mapped with an easily changeable microfabricated Hall probe [typically GsAs/AlGaAs or AlGaAs/InGaAs/GaAs Hall sensors with integrated scanning tunnel microscopy (STM) tunneling tips] and can achieve minimum detectable fields >or=10 mG/Hz(1/2). The Hall probe is brought into very close proximity to the sample surface by sensing and controlling tunnel currents at the integrated STM tip. The instrument is capable of simultaneous tunneling and Hall signal acquisition in surface-tracking mode. We illustrate the potential of the system with images of superconducting vortices at the surface of a Nb thin film down to 372 mK, and also of labyrinth magnetic-domain patterns of an yttrium iron garnet film captured at room temperature. PMID:19123570

Khotkevych, V V; Milosevi?, M V; Bending, S J

2008-12-01

364

Five years of magnetic field management  

SciTech Connect

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

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

1995-01-01

365

Quark matter in a strong magnetic field  

SciTech Connect

The effect of a strong magnetic field on the stability and gross properties of bulk as well as quasibulk quark matter is investigated using the conventional MIT bag model. Both the Landau diamagnetism and the paramagnetism of quark matter are studied. How the quark hadron phase transition is affected by the presence of a strong magnetic field is also investigated. The equation of state of strange quark matter changes significantly in a strong magnetic field. It is also shown that the thermal nucleation of quark bubbles in a compact metastable state of neutron matter is completely forbidden in the presence of a strong magnetic field. {copyright} {ital 1996 The American Physical Society.}

Chakrabarty, S. [Department of Physics, University of Kalyani, District: Nadia, West Bengal 741 235 (India)]|[Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007 (India)

1996-07-01

366

Coherent-population-trapping transients induced by a modulated transverse magnetic field  

NASA Astrophysics Data System (ADS)

We present theoretical results of coherent-population-trapping transients induced by a modulated transverse magnetic field (TMF). The application of a transverse magnetic field causes the appearance of new ? subsystems, creation of new dark states, and rearrangement of the population among the Zeeman sublevels. We show that transients appear as the system is switched between steady-state situations, and we identify the various level system components of the total probe absorption. We discuss the time-dependent evolution of the probe absorption caused by the modulated TMF in the presence and absence of a constant longitudinal magnetic field (LMF). The differences between TMF modulation and LMF modulation are discussed.

Margalit, L.; Rosenbluh, M.; Wilson-Gordon, A. D.

2013-08-01

367

Two dimensional frustrated magnets in high magnetic field  

NASA Astrophysics Data System (ADS)

Frustrated magnets in high magnetic field have a long history of offering beautiful surprises to the patient investigator. Here we present the results of extensive classical Monte Carlo simulations of a variety of models of two dimensional magnets in magnetic field, together with complementary spin wave analysis. Striking results include (i) a massively enhanced magnetocaloric effect in antiferromagnets bordering on ferromagnetic order, (ii) a route to an m = 1/3 magnetization plateau on a square lattice, and (iii) a cascade of phase transitions in a simple model of AgNiO2.

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

2009-01-01

368

The Magnetic Fields of the Quiet Sun  

NASA Astrophysics Data System (ADS)

This work reviews our understanding of the magnetic fields observed in the quiet Sun. The subject has undergone a major change during the last decade (quiet revolution), and it will remain changing since the techniques of diagnostic employed so far are known to be severely biased. Keeping these caveats in mind, our work covers the main observational properties of the quiet Sun magnetic fields: magnetic field strengths, unsigned magnetic flux densities, magnetic field inclinations, as well as the temporal evolution on short time-scales (loop emergence), and long time-scales (solar cycle). We also summarize the main theoretical ideas put forward to explain the origin of the quiet Sun magnetism. A final prospective section points out various areas of solar physics where the quiet Sun magnetism may have an important physical role to play (chromospheric and coronal structure, solar wind acceleration, and solar elemental abundances).

Sánchez Almeida, J.; Martínez González, M.

2011-04-01

369

Development of ultra-low magnetic field sensors with magnetic tunneling junctions  

NASA Astrophysics Data System (ADS)

The discovery of tunneling magnetoresistance (TMR) has enhanced the magnetoresistance (MR) ratio from the giant magnetoresistance (GMR) regime of around 10% to over 400% at room temperature. A combination of magnetic tunnel junctions with high magnetoresistance ratio and soft magnetic layers enables the development of ultra-low magnetic field sensor with sensitivity down to the scale of picoTesla. A magnetic field sensor with such high sensitivity would have important applications in biomedicine, information storage, and remote sensing such as higher resolution images for cardiograph and magnetic resonance imaging and thus earlier detection of abnormal health condition; higher hard-disk density; and remote sensing of metallic objects. We have constructed an automated four-probe electrical measurement system for measuring TMR of magnetic tunnel junctions with high throughput, enabling us to optimize the properties of the devices. Magnetron sputtering is used to deposit thin films with thickness ranged from angstroms to nanometers. Photolithography and ion plasma etching are applied to pattern the devices. The devices have a range of size from 10 ?m x 10 ?m to 80 ?m x 80 ?m. The device is composed of the bottom electrode, free soft magnetic layer, insulating oxide layer, pinned layer, pinning layer, and top electrode. The magnetization of the free layer can be rotated by the external magnetic field which in turn changes the resistance of the device and provide the sensing capability. The system structure, design consideration, fabrication process, and preliminary experimental results are discussed and presented in this paper.

Pong, Philip W. T.; Bonevich, John E.; Egelhoff, William F., Jr.

2007-09-01

370

Magnetohydrodynamic mode identification from magnetic probe signals via a matched filter method  

NASA Astrophysics Data System (ADS)

A matched filter analysis has been developed to identify the amplitude and phase of magnetohydrodynamic modes in DIII-D tokamak plasmas using magnetic probe signals (?Bp). As opposed to conventional Fourier spatial analysis of toroidally spaced probes, this analysis includes data from both toroidally and poloidally spaced magnetic probe arrays. Using additional probes both improves the statistics of the analysis and more importantly incorporates poloidal information into the mode analysis. The matched filter is a numeric filter that matches signals from the magnetic probes with numerically predicted signals for the mode. The numerical predictions are developed using EFIT equilibrium reconstruction data as input to the stability code GATO and the vacuum field code VACUUM. Changes is the plasma equilibrium that occur on the same time scale as the mode are taken into account by modeling simple matched filter vectors corresponding to changes in total plasma current, plus vertical and horizontal plasma shifts. The matched filter method works well when there is good understanding of a mode and good modeling of its structure. Matched filter analysis results for a fast growing ideal kink mode, where equilibrium change effects are minimal, show the effectiveness of this method. A slow growing resistive-wall mode (RWM) is also analyzed using the matched filter method. The method gives good results for identifying the amplitude and phase of the RWM but the simple equilibrium vectors are insufficient for complete elimination of equilibrium changes on this time scale. An analysis of the computational requirements of the scheme indicates that real-time application of the matched filter for RWM identification will be possible.

Edgell, Dana H.; Kim, Jin-Soo; Bogatu, Ioan N.; Humphreys, David A.; Turnbull, Alan D.

2002-04-01

371

PRINCIPLE OF CORRECTION OF ASYMMETRIC MAGNETIC FIELDS IN BENDING MAGNETS  

Microsoft Academic Search

The generation of a high quality electron beam by a race- track microtron (RTM) requires highly precise magnetic fields in the two reversing magnets. At the RTM cascade MAMI (Mainz Microtron), a precision of 10 ?4 for the ver- tical field component By was achieved by symmetrical sur- face coils placed at the upper and lower pole surface in each

F. Hagenbuck; P. Jennewein; K.-H. Kaiser; H.-J. Kreidel; U. Ludwig-Mertin; M. Seidl

2002-01-01

372

Pressure dependence of magnetic states in Laves Phase RCo2 (R = Dy, Ho, and Er) compounds probed by XMCD  

NASA Astrophysics Data System (ADS)

In order to probe pressure-induced modification in Co magnetic state in Laves phase RCo2 (R = Dy, Ho, and Er) compounds, we have measured X-ray magnetic circular dichroism (XMCD) under high pressure. The R L2-edge XMCD indicates that Co magnetic moment MCo gradually decreases as the pressure increases. The Co K-edge XMCD shows that the effect of R molecular field is significantly suppressed under high pressure. As a result, it is revealed that the pressure variation of MCo is closely associated with R-Co interaction. The Co magnetic state is separately discussed from that of R partner.

Watanabe, S.; Ishimatsu, N.; Maruyama, H.; Chaboy, J.; Laguna-Marco, M. A.; Boada, R.; Kawamura, N.

2009-11-01

373

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

374

Magnetohydrodynamics of the Earth'S Magnetic Field.  

National Technical Information Service (NTIS)

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

G. Venezian

1967-01-01

375

Cosmic Rays in the Earth'S Magnetic Field.  

National Technical Information Service (NTIS)

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

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

1973-01-01

376

The Evolution of the Earth's Magnetic Field.  

ERIC Educational Resources Information Center

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

Bloxham, Jeremy; Gubbins, David

1989-01-01

377

Tracing magnetic fields with ground state alignment  

NASA Astrophysics Data System (ADS)

Observational studies of magnetic fields are vital as magnetic fields play a crucial role in various astrophysical processes, including star formation, accretion of matter, transport processes (e.g. transport of heat), and cosmic rays. The existing ways of magnetic field studies have their limitations. Therefore, it is important to explore new effects that can bring information about magnetic field. We identified a process “ground state alignment” as a new way to determine the magnetic field direction in diffuse medium. 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 alignment is due to anisotropic radiation impinging on the atom/ion, while 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 (1G?B?10-15G). Compared to the upper level Hanle effect, atomic realignment is most suitable for the studies of magnetic field in the diffuse medium, where magnetic field is relatively weak. The corresponding physics of alignment is based on solid foundations of quantum electrodynamics and in a different physical regime the alignment has become a part of solar spectroscopy. In fact, the effects of atomic/ionic alignment, including the realignment in magnetic field, 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. It is very encouraging that a variety of atoms with fine or hyperfine splitting of the ground or metastable states exhibit the alignment and the resulting polarization degree in some cases exceeds 20%. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this paper, 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, including those in the early universe.

Yan, Huirong; Lazarian, A.

2012-08-01

378

Attenuation of surface-enhanced Raman scattering of magnetic-plasmonic FePt@Ag core-shell nanoparticles due to an external magnetic field  

NASA Astrophysics Data System (ADS)

The surface-enhanced Raman scattering (SERS) activities of Ag and FePt@Ag nanoparticle probes were examined using thiophenol as a Raman reporter molecule in the absence and presence of a magnetic field. Under external magnetic fields of different field strength, the SERS activities of both types of nanoparticles (NPs) were weakened as a function of magnetic field strength. The attenuation degree of SERS activity by the magnetic field in the case of FePt@Ag NPs is found to be two times higher than for Ag NPs, because the superparamagnetic FePt cores enhance the local magnetic field at the area of the Ag shells.

Trang, Nguyen T. T.; Thuy, Trinh T.; Mott, Derrick M.; Koyano, Mikio; Maenosono, Shinya

2013-06-01

379

Unsteady wandering magnetic field lines, turbulence and laboratory flux ropes  

NASA Astrophysics Data System (ADS)

We describe earth bound laboratory experiment investigations of patchy, unsteady, bursty, patchy magnetic field structures that are unifying features of magnetic reconnection and turbulence in helio, space and astro physics. Macroscopic field lines occupy cross sectional areas, fill up three dimensional (3D) volumes as flux tubes. They contain mass with Newtonian dynamics that follow magneto-hydro-dynamic (MHD) equations of motion. Flux rope geometry can be ubiquitous in laminar reconnection sheet geometries that are themselves unstable to formation of secondary "islands" that in 3D are really flux ropes. Flux ropes are ubiquitous structures on the sun and the rest of the heliosphere. Understanding the dynamics of flux ropes and their mutual interactions offers the key to many important astrophysical phenomena, including magnetic reconnection and turbulence. We describe laboratory investigations on RSX, where 3D interaction of flux ropes can be studied in great detail. We use experimental probes inside the the flux ropes to measure the magnetic and electric fields, current density, density, temperatures, pressure, and electrostatic and vector plasma potentials. Macroscopic magnetic field lines, unsteady wandering characteristics, and dynamic objects with structure down to the dissipation scale length can be traced from data sets in a 3D volume. Computational approaches are finally able to tackle simple 3D systems and we sketch some intriguing simulation results that are consistent with 3D extensions of typical 2D cartoons for magnetic reconnection and turbulence.

Intrator, T.; Sears, J.; Weber, T.; Liu, D.; Pulliam, D.; Lazarian, A.

2011-12-01

380

Plasma Flow Measurement using Mach Probe and Laser-Induced Fluorescence in Weakly Magnetized Plasmas  

NASA Astrophysics Data System (ADS)

A Mach probe (MP) is generally used for the measurement of plasma flow velocity in the edge of magnetic fusion devices, space propulsion systems, processing plasmas, sheath and pre- sheath regions. Although several un-magnetized MP theories are available, their validity has not been fully confirmed, and should be checked by comparative (or simultaneous) measurement with another diagnostic tool such as laser-induced fluorescence (LIF). The plasma flow velocity was measured via an MP and LIF method in Ar plasma generated by LaB6 cathode of Diversified Plasma Simulator - Modification (DiPS-M). The MP and LIF measurements are performed in the ranges of magnetic field intensities, 100 < B < 1000 (Gauss) and the various neutral pressures, 1

Woo, Hyun-Jong; Chung, Kyu-Sun; Park, Eun-Kyung; Lee, Myoung-Jae

2010-11-01

381

Magnetic Field Investigations During ROSETTA's Steins Flyby  

NASA Astrophysics Data System (ADS)

During the recent Steins flyby of the ROSETTA spacecraft magnetic field measurements have been made with both, the RPC orbiter magnetometer and the ROMAP lander magnetometer. These combined magnetic field measurements allow a detailed examination of any magnetic signatures caused either directly by the asteroid or indirectly by Steins different modes of interaction with the solar wind. Comparing our measurements with simulation results show that Steins does not possess a significant remanent magnetization. The magnetization is estimated at less than 1 mAm2/kg. This is significantly different from results at Braille and Gaspra.

Glassmeier, K.; Auster, H.; Richter, I.; Motschmann, U.; RPC/ROMAP Teams

2009-05-01

382

Seeing the corona with the solar probe plus mission: the wide-field imager for solar probe+ (WISPR)  

NASA Astrophysics Data System (ADS)

The Solar Probe Plus (SPP) mission scheduled for launch in 2018, will orbit between the Sun and Venus with diminishing perihelia reaching as close as 7 million km (9.86 solar radii) from Sun center. In addition to a suite of in-situ probes for the magnetic field, plasma, and energetic particles, SPP will be equipped with an imager. The Wide-field Imager for the Solar PRobe+ (WISPR), with a 95° radial by 58° transverse field of view, will image the fine-scale coronal structure of the corona, derive the 3D structure of the large-scale corona, and determine whether a dust-free zone exists near the Sun. Given the tight mass constrains of the mission, WISPR incorporates an efficient design of two widefield telescopes and their associated focal plane arrays based on novel large-format (2kx2k) APS CMOS detectors into the smallest heliospheric imaging package to date. The flexible control electronics allow WISPR to collect individual images at cadences up to 1 second at perihelion or sum several of them to increase the signal-to-noise during the outbound part of the orbit. The use of two telescopes minimizes the risk of dust damage which may be considerable close to the Sun. The dependency of the Thomson scattering emission of the corona on the imaging geometry dictates that WISPR will be very sensitive to the emission from plasma close to the spacecraft in contrast to the situation for imaging from Earth orbit. WISPR will be the first `local' imager providing a crucial link between the large scale corona and the in-situ measurements.

Vourlidas, Angelos; Howard, Russell A.; Plunkett, Simon P.; Korendyke, Clarence M.; Carter, Michael T.; Thernisien, Arnaud F. R.; Chua, Damien H.; Van Duyne, Peter; Socker, Dennis G.; Linton, Mark G.; Liewer, Paulett C.; Hall, Jeffrey R.; Morrill, Jeff S.; DeJong, Eric M.; Mikic, Zoran; Rochus, Pierre L. P. M.; Bothmer, Volker; Rodman, Jens; Lamy, Philippe

2013-09-01

383

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

NASA Astrophysics Data System (ADS)

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

Cohen, I.; Bagenal, F.

2008-12-01

384

Measuring exposed magnetic fields of welders in working time.  

PubMed

The assessment of the occupational electromagnetic field exposure of welders is of great importance, especially in shielded-arc welding, which uses relatively high electric currents of up to several hundred amperes. In the present study, we measured the magnetic field exposure level of welders in the course of working. A 3-axis Hall magnetometer was attached to a subject's wrist in order to place the sensor probe at the closest position to the magnetic source (a cable from the current source). Data was acquired every 5 s from the beginning of the work time. The maximum exposed field was 0.35-3.35 mT (Mean ± SD: 1.55 ± 0.93 mT, N=17) and the average value per day was 0.04-0.12 mT (Mean ± SD: 0.07 ± 0.02 mT, N=17). We also conducted a finite element method-based analysis of human hand tissue for the electromagnetic field dosimetry. In addition, the magnetic field associated with grinders, an air hammer, and a drill using electromagnetic anchorage were measured; however, the magnetic fields were much lower than those generated in the welding process. These results agreed well with the results of the electromagnetic field dosimetry (1.49 mT at the wrist position), and the calculated eddy current (4.28 mA/m(2)) was much lower than the well-known guideline thresholds for electrical nerve or muscular stimulation. PMID:21670555

Yamaguchi-Sekino, Sachiko; Ojima, Jun; Sekino, Masaki; Hojo, Minoru; Saito, Hiroyuki; Okuno, Tsutomu

2011-01-01

385

Magnetic fields around BOK globules: CCD polarimetry of CB 4  

NASA Astrophysics Data System (ADS)

The small Bok globule CB 4 was probed using a CCD imaging polarimeter in order to create a detailed map of the magnetic field associated with this cloud. Stars as faint as 17th mag at V band were measured polarimetrically with uncertainties less than 1%. Sky transmission variations were minimized via a system of synchronous polaroid rotation and bidirectional charge shifting. In all, 80 stars behind the periphery of the globule were accurately analyzed polarimetrically. The large-scale (1-2 pc) magnetic field direction around CB 4 was found to be very uniform (P.A. = 63.3 deg +/- 1.1 deg). Double-Gaussian fitting of the polarization position angle histogram gave a dispersion of 10 deg about the primary field direction. Possible field-line compression was found inward of approximately 0.2 pc from the cloud center. No appreciable twisting of field lines was found. By plotting stellar separations against differences of polarization angles, CB 4 was found to have a magnetic field decorrelation length of approximately 0.1 pc, similar to the size of the visually opaque cire, but much smaller than the size of the bright optical rim or CO half-power contour of approximately 0.5 pc. The magnetic field decorrelation length may be related to a characteristic transient clumping size, or perhaps even to clumps of a more permanent nature.

Kane, Brian D.; Clemens, Dan P.; Leach, Robert W.; Barvainis, Richard

1995-05-01

386

Constrained superfields and supersymmetric magnetic field systems  

SciTech Connect

After Lancaster the authors examine chiral constraints in N = 2 superspace formulation for supersymmetric magnetic field systems. Such odd constraints are connected with the so-called spin-orbit coupling procedure of supersymmetrization. They propose new even constraints for magnetic supersymmetric systems and relate them to the standard procedure enhanced by Witten. These models describing spin-one half particles moving in a plane with a transverse magnetic field are compared and discussed. The cases of a constant magnetic field and of the harmonic oscillator are connected through different correspondences.

Dehin, D.; Hussin, V. (Universite de Liege, Physique Theorique et Mathematique, Institut de Physique au Sart Tilman, Batiment B.5, B-4000 Liege (BE))

1988-01-01

387

Ionospheric electric fields, currents, and resulting magnetic fields variations  

NASA Astrophysics Data System (ADS)

This thesis uses an equivalent circuit model to calculate ionospheric electric fields, current densities and introduced magnetic fields variations on the ground. The role of the field aligned current is examined. Using different wind models, we studied the electric field variations with altitude, season and solar activity. The ionospheric eastward electric field changes very little within the whole ionosphere. The southward (equatorward) electric field is large and changes quickly with height in the E region although it is nearly constant in the F region. The prereversal enhancement of the eastward electric field is produced by the F region dynamo. We conclude that the Forbes and Gillette tidal wind can reproduce most features of the Jicamarca experiment and the AE-E and DE-2 satellite observations of the electric fields. The HWM90 empirical wind model failed to produce the observed electric field and it seems the semidiurnal wind in HWM90 is too strong. The field aligned current is located mainly in the E and low F region. The non-coincidence of the geomagnetic and geographic equators has a strong effect on the field aligned current in the equatorial zone. The field aligned currents driven by Forbes' winds for March equinox and December solstice flow mainly from the southern to northern hemisphere in the morning and vice versa in the afternoon at F region heights. The observed magnetic field variations on the ground are well reproduced in our simulations. The field aligned current is the main contributor to the eastward magnetic field component in the equatorial zone. The longitudinal inequality of the northward magnetic field is introduced mainly by the variations of the local magnetic field intensity. The electric field variations have only a minor effect. The northward magnetic field variations with the solar activity are introduced by changes of the E region equatorward electric field and the Hall conductivity.

Du, Junhu

388

Magnetic field associated with active electrochemical corrosion  

Microsoft Academic Search

The purpose of this work is to provide a better understanding of the underlying sources of the magnetic field associated with ongoing electrochemical corrosion, to investigate the spatio-temporal information content of the corrosion magnetic field, and to evaluate its potential utility in non-invasive quantification of hidden corrosion. The importance of this work lies in the fact that conventional electrochemical instruments

Afshin Abedi

2000-01-01

389

Coronal Heating and the Photospheric Magnetic Field  

Microsoft Academic Search

Since magnetic field typically plays a role (either active or passive) in coronal heating theories, it may be possible to evaluate these theories by investigating the relationship between the coronal energy budget (the total power requirement of the corona) and measurable properties of the photospheric magnetic field. The X-ray flux is a useful proxy for the total power required to

C. E. Parnell; P. A. Sturrock

1997-01-01

390

Variability and topology of solar magnetic field  

Microsoft Academic Search

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

E. A. Gavryuseva

2006-01-01

391

Astrophysical magnetic fields and nonlinear dynamo theory  

Microsoft Academic Search

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

Axel Brandenburg; Kandaswamy Subramanian

2005-01-01

392

Coulomb crystals in the magnetic field  

NASA Astrophysics Data System (ADS)

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?1014G ). 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.

Baiko, D. A.

2009-10-01

393

Magnetic field decay in model SSC dipoles  

Microsoft Academic Search

The authors 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

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

1989-01-01

394

Biological effects of high DC magnetic fields  

Microsoft Academic Search

The principal focus of the program is the analysis of magnetic field effects on physiological functions in experimental animals and selected organ and tissue systems. A major research effort has involved the use of electrical recording techniques to detect functional alterations in the cardiovascular, neural, and visual systems during the application of DC magnetic fields. These systems involve ionic conduction

Tenforde

1981-01-01

395

Magnetic fields and the solar corona  

Microsoft Academic Search

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

Gordon Newkirk; Martin D. Altschuler

1970-01-01

396

Pure phase encode magnetic field gradient monitor  

Microsoft Academic Search

Numerous methods have been developed to measure MRI gradient waveforms and k-space trajectories. The most promising new strategy appears to be magnetic field monitoring with RF microprobes. Multiple RF microprobes may record the magnetic field evolution associated with a wide variety of imaging pulse sequences. The method involves exciting one or more test samples and measuring the time evolution of

Hui Han; Rodney P. MacGregor; Bruce J. Balcom

2009-01-01

397

Efficient Characterization of Magnetic Field Sources  

Microsoft Academic Search

A technique for the estimation of the magnetic field intensity emitted by industrial installations is presented. The method is best-suited for investigation of environmental magnetic field for health purposes. Simulation and measurement case-studies supporting the provided theoretical results are discussed

M. Bertocco; F. Dughiero; C. Greggio; E. Sieni; A. Sona

2006-01-01

398

Magnetic fields, branes, and noncommutative geometry  

Microsoft Academic Search

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

Daniela Bigatti; Leonard Susskind

2000-01-01

399

Directional discontinuities in the interplanetary magnetic field  

Microsoft Academic Search

It is shown that the interplanetary magnetic field has different characteristics on different scales, and it is noted that a given physical theory may not be applicable or relevant on all scales. Four scales are defined in terms of time intervals on which the data may be viewed. Many discontinuities in the magnetic-field direction are seen on the mesoscale (˜

Leonard F. Burlaga

1969-01-01

400

Magnetic Fields, Ball Lightning and Campanology  

Microsoft Academic Search

WOODING suggests1 that ball lightning is a plasma vortex ring structure produced by a process similar to the ablation of a solid surface by a high power laser pulse. A plasma vortex ring structure requires a magnetic field; here I present two pieces of evidence to show that a magnetic field is associated with ball lightning, and which may help

A. J. F. Blair

1973-01-01

401

Magnetic field propagation in a stellar dynamo  

Microsoft Academic Search

Numerical simulations of stellar dynamos are reviewed. Dynamic dynamo models solve the nonlinear, three-dimensional, time-dependent, magnetohydrodynamic equations for the convective velocity, the thermodynamic variables, and the generated magnetic field in a rotating, spherical shell of ionized gas. When the dynamo operates in the convection zone, the simulated magnetic fields propagate away from the equator in the opposite direction inferred from

Gary A. Glatzmaier

1985-01-01

402

Ground Vehicle Navigation Using Magnetic Field Variation  

NASA Astrophysics Data System (ADS)

The Earth's magnetic field has been the bedrock of navigation for centuries. The latest research highlights the uniqueness of magnetic field measurements based on position due to large scale variations as well as localized perturbations. These observable changes in the Earth's magnetic field as a function of position provide distinct information which can be used for navigation. This dissertation describes ground vehicle navigation exploiting variation in Earth's magnetic field using a self-contained navigation system consisting of only a magnetometer and magnetic field maps. In order to achieve navigation, effective calibration enables repeatable magnetic field measurements from different vehicles and facilitates mapping of the observable magnetic field as a function of position. A new modified ellipsoid calibration technique for strapdown magnetometers in large vehicles is described, as well as analysis of position measurement generation comparing a multitude of measurement compositions using existing and newly developed likelihood techniques. Finally, navigation solutions are presented using both a position measurement and direct incorporation of the magnetometer measurements via a particle filter to demonstrate road navigation in three different environments. Emphatically, the results affirm that navigation using magnetic field variation in ground vehicles is viable and achieves adequate performance for road level navigation.

Shockley, Jeremiah A.

403

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

404

Hydrogen atom moving across a magnetic field  

SciTech Connect

A hydrogen atom moving across a magnetic field is considered in a wide region of magnitudes of magnetic field and atom momentum. We solve the Schroedinger equation of the system numerically using an imaginary time method and find wave functions of the lowest states of atom. We calculate the energy and the mean electron-nucleus separation as a function of atom momentum and magnetic field. All the results obtained could be summarized as a phase diagram on the 'atom-momentum - magnetic-field' plane. There are transformations of wave-function structure at critical values of atom momentum and magnetic field that result in a specific behavior of dependencies of energy and mean interparticle separation on the atom momentum P. We discuss a transition from the Zeeman regime to the high magnetic field regime. A qualitative analysis of the complicated behavior of wave functions vs P based on the effective potential examination is given. We analyze a sharp transition at the critical momentum from a Coulomb-type state polarized due to atom motion to a strongly decentered (Landau-type) state at low magnetic fields. A crossover occurring at intermediate magnetic fields is also studied.

Lozovik, Yu.E.; Volkov, S.Yu. [Institute of Spectroscopy, Troitsk, Moscow region, 142190 (Russian Federation)

2004-08-01

405

Magnetic isotope and magnetic field effects on the DNA synthesis.  

PubMed

Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases ? with isotopic ions (24)Mg(2+), (25)Mg(2+) and (26)Mg(2+) in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases ? carrying (24)Mg(2+) and (26)Mg(2+) ions with spinless, non-magnetic nuclei (24)Mg and (26)Mg. However, (25)Mg(2+) ions with magnetic nucleus (25)Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases ? with (24)Mg(2+) and (26)Mg(2+) 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 Zn(2+) ions carrying magnetic (67)Zn and non-magnetic (64)Zn 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

2013-07-13

406

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).

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

2013-01-01

407

Toxoplasma gondii DNA detection with a magnetic molecular beacon probe  

NASA Astrophysics Data System (ADS)

Toxoplasma Gondii infection is widespread in humans worldwide and reported infection rates range from 3%-70%, depending on the populations or geographic areas, and it has been recognized as a potential food safety hazard in our daily life. A magnetic molecular beacon probe (mMBP), based on theory of fluorescence resonance energy transfer (FRET), was currently reported to detect Toxoplasma Gondii DNA. Nano-sized Fe3O4 were primarily prepared by coprecipitation method in aqueous phase with NaOH as precipitator, and was used as magnetic core. The qualified coreshell magnetic quantum dots (mQDs), i.e. CdTe(symbol)Fe3O4, were then achieved by layer-by-layer method when mol ratio of Fe3O4/CdTe is 1/3, pH at 6.0, 30 °C, and reactant solution was refluxed for 30 min, the size of mQDs were determined to be 12-15 nm via transmission electron microscopy (TEM). Over 70% overlap between emission spectrum of mQDs and absorbance spectrum of BHQ-2 was observed, this result suggests the synthesized mQDs and BHQ-2 can be utilized as energy donor and energy acceptor, respectively. The sensing probe was fabricated and a stem-loop Toxoplasma Gondii DNA oligonucleotide was labeled with mQDs at the 5' end and BHQ-2 at 3' end, respectively. Target Toxoplasma gondii DNA was detected under conditions of 37 °C, hybridization for 2h, at pH8.0 in Tris-HCl buffer. About 30% recovery of fluorescence intensity was observed via fluorescence spectrum (FS) after the Toxoplasma gondii DNA was added, which suggested that the Toxoplasma Gondii DNA was successfully detected. Specificity investigation of the mMBP indicated that relative low recovery of fluorescence intensity was obtained when the target DNA with one-base pair mismatch was added, this result indicated the high specificity of the sensing probe. Our research simultaneously indicated that mMBP can be conveniently separated from the unhybridized stem-loop DNA and target DNA, which will be meaningful in DNA sensing and purification process.

Xu, Shichao; Yao, Cuicui; Wei, Shuoming; Zhang, Jimei; Dai, Zhao; Zheng, Guo; Sun, Bo; Han, Qing; Hu, Fei; Zhou, Hongming

2008-12-01

408

Vehicle detection using a magnetic field sensor  

Microsoft Academic Search

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

S. V. Marshall

1978-01-01

409

Intergalactic Magnetic Fields from Quasar Outflows  

Microsoft Academic Search

Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of\\u000a a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and\\u000a calculate their distribution as a function magnetic field strength at different redshifts. We find that by a redshift \\u000a z ~ <\\/font\\u000a>3z \\\\sim

Steven Furlanetto; Abraham Loeb

2002-01-01

410

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

411

High Field Magnets With HTS Conductors  

Microsoft Academic Search

Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires is being pursued. Two specific projects are underway. The first is a user magnet with a 17 T YBCO coil set which, inside an LTS outsert, will generate a combined field of

H. W. Weijers; U. P. Trociewitz; W. D. Markiewicz; J. Jiang; D. Myers; E. E. Hellstrom; A. Xu; J. Jaroszynski; P. Noyes; Y. Viouchkov; D. C. Larbalestier

2010-01-01

412

Magnetic Instabilities in High Field Superconductors  

Microsoft Academic Search

In the process of magnetizing cylindrical specimens of a typical high field superconductor Nb-50 at.%Ti, flux jumps were induced by magnetic disturbances. The stability limit field Hfj increased steadily with increasing temperature, and no magnetic instability occurred for temperatures in excess of about 6.5 K. The calculation of Hfj was performed taking into account the cylindrical sample geometry and the

Tatsuo Akachi; Takeshi Ogasawara; Ko Yasukochi

1981-01-01

413

Site and probe dependence of hyperfine magnetic field in L21 Heusler alloys X2MnZ (X=Ni, Cu, Rh, Pd and Z=Ga, Ge, In, Sn, Pb)  

NASA Astrophysics Data System (ADS)

Results of TDPAC and Mössbauer measurements of hyperfine magnetic fields in L21 Heusler alloys X2MnZ are given. TDPAC utilized Cd-111 from In-111 at the Z site and Ag-111 at the X site, and Ru-99 from Rh-99 at the X site. Mössbauer studies utilized Sn-119 at the Z site or at the Mn site. A compilation of hmf values is presented, and estimates of the polarized electron density are given for 1 nn, 2 nn, and 3 nn of the Mn ions in these alloys.

Jha, S.; Seyoum, H. M.; Demarco, M.; Julian, G. M.; Stubbs, D. A.; Blue, J. W.; Silva, M. T. X.; Vasquez, A.

1983-12-01

414

Swinging reciprocating Mach probes for the high field side scrape-off layer in DIII-D  

NASA Astrophysics Data System (ADS)

A new pair of in situ reciprocating Mach probes termed swing probes has been deployed on the DIII-D centerpost for the 2012 experimental campaign. When not deployed, the entire assembly is housed in a <5 cm space underneath the centerpost tiles. This design is unique in that the probe swings vertically through the edge plasma, taking measurements along a 180° arc with a 20 cm radius. The motion is powered by actuator coils that interact with the tokamak's magnetic field. Two electrodes maintain a Mach-pair orientation throughout the swing and provide measurements of saturation current, electron temperature, and parallel flow speeds up to the separatrix.

Tsui, C. K.; Taussig, D. A.; Watkins, M. G.; Boivin, R. L.; Stangeby, P. C.

2012-10-01

415

Swinging reciprocating Mach probes for the high field side scrape-off layer in DIII-D.  

PubMed

A new pair of in situ reciprocating Mach probes termed swing probes has been deployed on the DIII-D centerpost for the 2012 experimental campaign. When not deployed, the entire assembly is housed in a <5 cm space underneath the centerpost tiles. This design is unique in that the probe swings vertically through the edge plasma, taking measurements along a 180° arc with a 20 cm radius. The motion is powered by actuator coils that interact with the tokamak's magnetic field. Two electrodes maintain a Mach-pair orientation throughout the swing and provide measurements of saturation current, electron temperature, and parallel flow speeds up to the separatrix. PMID:23126897

Tsui, C K; Taussig, D A; Watkins, M G; Boivin, R L; Stangeby, P C

2012-10-01

416

Swinging reciprocating Mach probes for the high field side scrape-off layer in DIII-D  

SciTech Connect

A new pair of in situ reciprocating Mach probes termed swing probes has been deployed on the DIII-D centerpost for the 2012 experimental campaign. When not deployed, the entire assembly is housed in a <5 cm space underneath the centerpost tiles. This design is unique in that the probe swings vertically through the edge plasma, taking measurements along a 180 Degree-Sign arc with a 20 cm radius. The motion is powered by actuator coils that interact with the tokamak's magnetic field. Two electrodes maintain a Mach-pair orientation throughout the swing and provide measurements of saturation current, electron temperature, and parallel flow speeds up to the separatrix.

Tsui, C. K.; Stangeby, P. C. [University of Toronto Institute for Aerospace Studies, Toronto M3H 5T6 (Canada); Taussig, D. A.; Watkins, M. G.; Boivin, R. L. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

2012-10-15

417

Warm inflation in presence of magnetic fields  

NASA Astrophysics Data System (ADS)

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; Sánchez, Ángel; Ayala, Alejandro; Mizher, Ana Julia

2013-07-01

418

Ohm's law for mean magnetic fields  

SciTech Connect

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

Boozer, A.H.

1984-11-01

419

Near-field scanning optical microscopy with an active probe  

NASA Astrophysics Data System (ADS)

A near-field scanning optical microscopy (NSOM) system employing a very-small-aperture laser (VSAL) as an active probe is reported in this Letter. The VSAL in our experiment has an aperture size of 300 nm×300 nm and a near-field spot size of about 600 nm. The resolution of the NSOM system with the VSAL can reach about 600 nm, and even 400 nm. Considering the high output power of the VSAL, such a NSOM system is a potentially useful tool for nanodetection, data storage, nanolithography, and nanobiology.

Gan, Qiaoqiang; Song, Guofeng; Yang, Guohua; Xu, Yun; Gao, Jianxia; Li, Yuzhang; Cao, Qing; Chen, Lianghui; Lu, Haiwei; Chen, Zhonghao; Zeng, Wei; Yan, Rongjin

2006-03-01

420

Near field optical probe for critical dimension measurements  

DOEpatents

A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations.

Stallard, Brian R. (Albuquerque, NM); Kaushik, Sumanth (Cambridge, MA)

1999-01-01

421

Near field optical probe for critical dimension measurements  

DOEpatents

A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below is disclosed. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations. 8 figs.

Stallard, B.R.; Kaushik, S.

1999-05-18

422

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

NASA Astrophysics Data System (ADS)

Observations of Mercury's internal magnetic field during MESSENGER's first flyby (M1) and the first and third flybys of Mariner 10 (M10-I, M10-III) suggest that small-scale crustal magnetic fields, if they exist, are at the limit of resolution. Small-scale crustal fields are most easily identified near closest approach (CA) as features with wavelengths comparable to, or larger than, the spacecraft altitude. One small feature (< 4 nT in magnitude) encountered near CA during MESSENGER's first flyby may be either a crustal magnetic field or a plasma pressure effect. By means of Parker's constrained optimization approach, with no assumptions on the direction of magnetization, we can place constraints on the product of magnetization and magnetized layer thickness from such observations. The second flyby (M2) will allow additional constraints to be placed on the presence of small-scale fields, and correlations will be possible among topographic profiles measured by the Mercury Laser Altimeter (MLA), features seen on MESSENGER and Mariner 10 images, and any variations in the internal field. This flyby will acquire the first images of the CA region of M10-III, which has been pivotal in establishing the dipolar character of Mercury's magnetic field. Our ability to isolate small-scale crustal magnetic fields has been hindered by the limited coverage to date, as well as the difficulty in isolating the internal field. Across the terrestrial planets and the Moon, minimum magnetization contrast and iron abundance in the crust show a positive correlation. This correlation suggests that crustal iron content plays a determining role in the strength of crustal magnetization.

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

2008-12-01

423

3D Localization of a Thin Steel Rod Using Magnetic Field Sensors: Feasibility and Preliminary Results  

Microsoft Academic Search

We present the design, setup and preliminary results for a navigation system based on magnetic field sensors. Our system localizes the tip of a magnetized steel rod with diameter 0.5 mm in a cubic workspace with 30 mm edge length. We plan to localize electrodes and probes during surgeries, e.g. for small animal research like neurosurgery in rats. Only the

Maximilian Heinig; Ralf Bruder; Alexander Schlaefer; Achim Schweikard

2010-01-01

424

The Protogalactic Origin for Cosmic Magnetic Fields  

Microsoft Academic Search

It is demonstrated that strong magnetic fields are produced from a zero\\u000ainitial magnetic field during the pregalactic era, when galaxies are first\\u000aforming. Their development proceeds in three phases. In the first phase, weak\\u000amagnetic fields are created by the Biermann battery mechanism, acting in\\u000ashocked parts of the intergalactic medium where caustics form and intersect. In\\u000athe second

Russell M. Kulsrud; Renyue Cen; Jeremiah P. Ostriker; Dongsu Ryu

1996-01-01

425

Turbulence and Magnetic Fields in Astrophysical Plasmas  

Microsoft Academic Search

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

Alexander A. Schekochihin; Steven C Cowley

2007-01-01

426

Ohm's law for mean magnetic fields  

SciTech Connect

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

Boozer, A.H.

1986-05-01

427

Emittance measurement in a magnetic field  

SciTech Connect

Emittance can be measured by intercepting an electron beam on a range thick plate and then observing the expansion of beamlets transmitted through small holes. The hole size is selected to minimize space charge effects. In the presence of a magnetic field the beamlets have a spiral trajectory and the usual field free formulation must be modified. To interpret emittance in the presence of a magnetic field an envelope equation is derived in the appropriate rotating frame. 1 ref.

Boyd, J.K.

1991-04-15

428

The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission  

NASA Astrophysics Data System (ADS)

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ˜15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the "highest quality" events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

Wygant, J. R.; Bonnell, J. W.; Goetz, K.; Ergun, R. E.; Mozer, F. S.; Bale, S. D.; Ludlam, M.; Turin, P.; Harvey, P. R.; Hochmann, R.; Harps, K.; Dalton, G.; McCauley, J.; Rachelson, W.; Gordon, D.; Donakowski, B.; Shultz, C.; Smith, C.; Diaz-Aguado, M.; Fischer, J.; Heavner, S.; Berg, P.; Malsapina, D. M.; Bolton, M. K.; Hudson, M.; Strangeway, R. J.; Baker, D. N.; Li, X.; Albert, J.; Foster, J. C.; Chaston, C. C.; Mann, I.; Donovan, E.; Cully, C. M.; Cattell, C. A.; Krasnoselskikh, V.; Kersten, K.; Brenneman, A.; Tao, J. B.

2013-10-01

429

Magnetic field effects on dielectrophoresis in manganites  

NASA Astrophysics Data System (ADS)

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

Grant, Daniel; Dragiev, Galin; Biswas, Amlan

2013-03-01

430

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.