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1

Sub-femto-Tesla Scalar Atomic Magnetometer with Spin-squeezing  

NASA Astrophysics Data System (ADS)

Atomic shot noise sets the fundamental limit on precision of atomic frequency measurements. Spin-squeezing techniques can reduce long-term atomic shot noise for systems with non-linear spin-relaxation processes [1]. Magnetometers using dense hot alkali-metal vapors are naturally limited by such non-linear relaxation due to spin-exchange collisions. We have developed a scalar atomic magnetometer utilizing a multi-pass atomic cell [2] to interact with 10^13 atoms with an optical density of 5000. By operating the magnetometer in a pulsed mode with high initial spin polarization and two probe measurement pulses, we have realized magnetic field sensitivity of 0.5 fT/?Hz, already more than an order of magnitude better than previous state-of-the-art for scalar atomic magnetometers. We are continuing to refine this system to realize an improvement in the long-term sensitivity from spin-squeezing measurements beyond the present magnetic field sensitivity records.[4pt] [1] G. Vasilakis, V. Shah, M. V. Romalis, Phys. Rev. Lett. 106, 143601 (2011). [2] S. Li, P. Vachaspati, D. Sheng, N. Dural, M. V. Romalis, Phys. Rev. A 84, 061403R (2011).

Sheng, Dong; Li, Shuguang; Dural, Nezih; Romalis, Michael

2012-06-01

2

Magnetic Fields  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

3

Magnetic Fields  

NSDL National Science Digital Library

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

Stern, David

2005-01-04

4

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

5

Exploring Magnetic Field Lines  

NSDL National Science Digital Library

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

Nasa

2012-06-26

6

Earth's Inconstant Magnetic Field  

NSDL National Science Digital Library

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

2007-04-27

7

Exploring Magnetic Fields  

NSDL National Science Digital Library

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

8

Exploring Magnetic Fields  

NSDL National Science Digital Library

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

9

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,

10

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

11

Mapping Magnetic Fields  

NSDL National Science Digital Library

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

12

Magnetic field mapper  

NASA Technical Reports Server (NTRS)

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

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

1969-01-01

13

The Declining Magnetic Field  

NSDL National Science Digital Library

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

14

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

15

Drawing Magnetic Fields  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

16

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

17

Circuits and Magnetic Fields  

NSDL National Science Digital Library

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

Vu Bioengineering Ret Program

18

Photospheric magnetic fields  

NASA Technical Reports Server (NTRS)

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

Howard, R.

1972-01-01

19

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

20

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

21

Magnetic Field Viewing Cards  

NASA Astrophysics Data System (ADS)

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

Kanim, Stephen; Thompson, John R.

2005-09-01

22

The galactic magnetic field  

Microsoft Academic Search

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

T A Spoelstra; T. A. T

1977-01-01

23

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

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

Stern, David

2005-04-27

24

Magnetic fields at Neptune  

SciTech Connect

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

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

1989-12-15

25

Sonoluminescence in High Magnetic Fields  

Microsoft Academic Search

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

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

1996-01-01

26

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic Bar Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticBarField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

27

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

28

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

29

Solar Magnetic Fields.  

National Technical Information Service (NTIS)

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

M. Cimino

1966-01-01

30

Coronal magnetic fields  

Microsoft Academic Search

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

R. Pallavicini

1986-01-01

31

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

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

Smith, E. J.

1995-01-01

32

The nonequilibrium of magnetic fields  

Microsoft Academic Search

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

E. N. Parker

1981-01-01

33

Microinhomogeneities in Magnetic Fields  

Microsoft Academic Search

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

H. H. Brown Jr.; F. Bitter

1956-01-01

34

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

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

Ilin, Andrew V.

2006-01-01

35

Magnetic ionization fronts. I. Parallel magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

1998-03-01

36

Eruptive solar magnetic fields  

NASA Technical Reports Server (NTRS)

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

Low, B. C.

1981-01-01

37

The Sun and Magnetic Fields  

NSDL National Science Digital Library

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

38

HMI Magnetic Field Products  

NASA Astrophysics Data System (ADS)

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

Hoeksema, Jon T.; HMI Magnetic Field Team

2013-07-01

39

Magnetic Field and Life  

NSDL National Science Digital Library

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

40

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

41

The interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

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

Davis, L., Jr.

1972-01-01

42

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

Johnson, Roberta

2000-07-01

43

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

44

Magnetic Field of the Earth  

NSDL National Science Digital Library

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

Merritt, Mrs.

2005-10-18

45

THE GALACTIC MAGNETIC FIELD  

SciTech Connect

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

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

2012-12-10

46

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

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

Gardiner, T. A.; Frank, A.

2000-01-01

47

The WIND magnetic field investigation  

Microsoft Academic Search

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

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

1995-01-01

48

Low field magnetic resonance imaging  

DOEpatents

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

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

2010-07-13

49

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

50

Fast superconducting magnetic field switch  

SciTech Connect

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

Goren, Y.; Mahale, N.K.

1995-12-31

51

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

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

Wyntjes, Geert

2002-02-01

52

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

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

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

53

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

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

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

54

Fast superconducting magnetic field switch  

DOEpatents

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

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

1996-01-01

55

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

56

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

57

Reconnection of Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Birn, J.; Priest, E. R.

2007-01-01

58

Matter in strong magnetic fields  

Microsoft Academic Search

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

Dong Lai

2001-01-01

59

Magnetic fields around evolved stars  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

60

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

61

Magnetic response to applied electrostatic field in external magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

62

The Extended Coronal Magnetic Field.  

National Technical Information Service (NTIS)

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

J. M. Wilcox

1970-01-01

63

Flares and Changing Magnetic Fields.  

National Technical Information Service (NTIS)

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

D. M. Rust

1972-01-01

64

Dresden pulsed magnetic field facility  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

65

Origin of cosmic magnetic fields.  

PubMed

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

Campanelli, Leonardo

2013-08-01

66

Magnetic field sensor by orthoferrites  

Microsoft Academic Search

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

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

1997-01-01

67

THE CLUSTER MAGNETIC FIELD INVESTIGATION  

Microsoft Academic Search

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

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

1997-01-01

68

Dresden pulsed magnetic field facility  

Microsoft Academic Search

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

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

2007-01-01

69

Superconductivity at High Magnetic Fields  

Microsoft Academic Search

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

T. G. Berlincourt; R. R. Hake

1963-01-01

70

High latitude solar magnetic fields  

NASA Technical Reports Server (NTRS)

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

Murray, Norman

1992-01-01

71

PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS  

SciTech Connect

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

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

2012-06-20

72

Magnetic field structure evolution in rotating magnetic field plasmas  

SciTech Connect

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

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

2008-07-15

73

Spinning magnetic fields  

Microsoft Academic Search

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

Jovan Djuric

1975-01-01

74

Magnetic fields in galaxy clusters  

NASA Astrophysics Data System (ADS)

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

Brüggen, M.

2013-06-01

75

Preflare magnetic and velocity fields  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

76

Magnetic Field Effect Transistors.  

National Technical Information Service (NTIS)

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

J. T. Spencer P. A. Dowben

1990-01-01

77

Magnetic Fields in the Sun.  

National Technical Information Service (NTIS)

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

D. J. Mullan

1974-01-01

78

The polar heliospheric magnetic field  

NASA Technical Reports Server (NTRS)

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

Jokipii, J. R.; Kota, J.

1989-01-01

79

Theorem on magnet fringe field.  

National Technical Information Service (NTIS)

Transverse particle motion in particle accelerators is governed almost totally by non-solenoidal magnets for which the body magnetic field can be expressed as a series expansion of the normal (b(sub n)) and skew (a(sub n)) multipoles, B(sub y) + iB(sub x)...

J. Wei R. Talman

1995-01-01

80

Majorana Neutrinos and Magnetic Fields.  

National Technical Information Service (NTIS)

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

J. Schechter J. W. F. Valle

1981-01-01

81

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

82

Neutron in Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

83

Solar magnetic fields and convection  

Microsoft Academic Search

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

J. H. Piddington

1976-01-01

84

Solar magnetic fields: an introduction  

Microsoft Academic Search

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

S. K. Solanki

85

Spontaneous thermal magnetic field fluctuation  

SciTech Connect

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

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

2007-06-15

86

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

87

Optical sensor of magnetic fields  

DOEpatents

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

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

1986-03-25

88

Chiral transition with magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

89

Magnetic field analysis and optimal design of magnetic bearing  

Microsoft Academic Search

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

Han Wu; Chunguang Xu; Dingguo Xiao; Juan Hao

2009-01-01

90

Magnetic fields in quiescent prominences  

SciTech Connect

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

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

1990-09-01

91

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

92

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

93

Alternating magnetic field assisted magnetization reversal in ferromagnetic antidot  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

94

High-field magnets and high-field superconductors  

Microsoft Academic Search

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

Simon Foner; Francis Bitter

1995-01-01

95

Magnetic Fields in Irregular Galaxies: NGC 4214  

Microsoft Academic Search

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

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

2006-01-01

96

Solar magnetic fields - The Italian contribution  

Microsoft Academic Search

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

D. Fabbri; G. Godoli; F. Mazzucconi

1982-01-01

97

Progress in Solar Magnetic Field Extrapolation  

Microsoft Academic Search

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

Juan Hao; Mei Zhang

2007-01-01

98

Satellite to study earth's magnetic field  

NASA Technical Reports Server (NTRS)

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

1979-01-01

99

Observations of Mercury's magnetic field  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

100

Deflections in magnet fringe fields.  

PubMed

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

Papaphilippou, Y; Wei, J; Talman, R

2003-04-01

101

Magnetic field tomography, helical magnetic fields and Faraday depolarization  

NASA Astrophysics Data System (ADS)

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

Horellou, C.; Fletcher, A.

2014-07-01

102

Formation of Magnetic Particle Chains in Ultra High Magnetic Field  

Microsoft Academic Search

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

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

2007-01-01

103

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

104

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

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

105

Magnetic Fields of the Earth and Sun  

NSDL National Science Digital Library

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

106

BEC manipulation with fictitious magnetic fields  

Microsoft Academic Search

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

Jeffrey Heward; Mark Edwards; Charles W. Clark

2010-01-01

107

Flares and changing magnetic fields  

Microsoft Academic Search

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

David M. Rust

1972-01-01

108

Ohm's Law for Mean Magnetic Fields.  

National Technical Information Service (NTIS)

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

A. H. Boozer

1986-01-01

109

Crystal field and magnetic properties  

NASA Technical Reports Server (NTRS)

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

Flood, D. J.

1977-01-01

110

Swarm: ESA's Magnetic Field Mission  

Microsoft Academic Search

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

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

2010-01-01

111

Transverse Magnetic Field Propellant Isolator  

NASA Technical Reports Server (NTRS)

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

Foster, John E.

2000-01-01

112

Large-scale solar magnetic fields  

Microsoft Academic Search

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

R. Howard

1977-01-01

113

Magnetic fields in the sun  

NASA Technical Reports Server (NTRS)

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

Mullan, D. J.

1974-01-01

114

Magnetic field of the Earth  

NASA Astrophysics Data System (ADS)

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

Popov, Aleksey

2013-04-01

115

Electron dynamics in inhomogeneous magnetic fields.  

PubMed

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

Nogaret, Alain

2010-06-30

116

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

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

Kitazawa, K.

1990-01-01

117

Oxide superconductors under magnetic field  

NASA Technical Reports Server (NTRS)

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

Kitazawa, K.

1991-01-01

118

Dynamics of Magnetic Bubbles in Acoustic and Magnetic Fields  

Microsoft Academic Search

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

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

2009-01-01

119

Diagnostics of vector magnetic fields  

NASA Technical Reports Server (NTRS)

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

Stenflo, J. O.

1985-01-01

120

Explaining Mercury's peculiar magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

121

Magnetic domain structure in thin film under alternate magnetic field  

Microsoft Academic Search

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

M. Mino; H. Yamazaki

2004-01-01

122

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

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

Mino, M.; Yamazaki, H.

123

Magnetic domain structure in thin film under alternate magnetic field  

NASA Astrophysics Data System (ADS)

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

Mino, M.; Yamazaki, H.

2004-05-01

124

Comparing Magnetic Fields on Earth and Mars  

NASA Video Gallery

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

125

Measurements of Solar Vector Magnetic Fields  

NASA Technical Reports Server (NTRS)

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

Hagyard, M. J. (editor)

1985-01-01

126

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

127

Magnetic order of UPt3 in high magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

1998-08-01

128

Crustal Magnetic Fields of Terrestrial Planets  

Microsoft Academic Search

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

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

2010-01-01

129

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

130

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA’s Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth’s interior and near-Earth electro-magnetic environment. After release from a single launcher, a side-by-side flying slowly decaying lower pair of satellites will be released at an initial altitude of about 490 km together with a third satellite that will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations that are required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission aims to provide a unique view into Earth core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the development phase, will be addressed. The mission is scheduled for launch in 2012.

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

2010-12-01

131

Magnetic field sensors using GMR multilayer  

Microsoft Academic Search

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

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

1994-01-01

132

The measurement of solar magnetic fields  

Microsoft Academic Search

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

J. O. Stenflo

1978-01-01

133

MR imaging at high magnetic fields  

Microsoft Academic Search

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

Masaya Takahashi; Hidemasa Uematsu; Hiroto Hatabu

2003-01-01

134

Magnetic field navigation in an indoor environment  

Microsoft Academic Search

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

William Storms; Jeremiah Shockley; John Raquet

2010-01-01

135

PLASMA CONFINEMENT USING ROTATING MAGNETIC FIELDS  

Microsoft Academic Search

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

H. Blevin; P. C. Thonemann

1961-01-01

136

Magnetic field quality analysis using ANSYS.  

National Technical Information Service (NTIS)

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

D. Dell'Orco Y. Chen

1991-01-01

137

Magnetic field effect for cellulose nanofiber alignment  

Microsoft Academic Search

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

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

2008-01-01

138

An ancient lunar magnetic dipole field  

Microsoft Academic Search

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

S. K. Runcorn

1975-01-01

139

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

140

Magnetic field gradient measurement on magnetic cards using magnetic force microscopy  

Microsoft Academic Search

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

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

2002-01-01

141

Magnetic Fields in Molecular Clouds  

NASA Astrophysics Data System (ADS)

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

Hildebrand, R. H.

2009-12-01

142

Interplanetary magnetic field data book  

NASA Technical Reports Server (NTRS)

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

King, J. H.

1975-01-01

143

The Giotto magnetic field investigation  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

144

Graphene in high magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

145

Suppression of magnetic relaxation by a transverse alternating magnetic field  

SciTech Connect

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

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

2007-07-15

146

Magnetic field sources and their threat to magnetic media  

NASA Technical Reports Server (NTRS)

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

Jewell, Steve

1993-01-01

147

Magnetic nanostructures as amplifiers of transverse fields in magnetic resonance.  

PubMed

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

Barbic, Mladen; Scherer, Axel

2005-09-01

148

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

Microsoft Academic Search

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

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

2011-01-01

149

Magnetic field in a turbulent galactic disk  

Microsoft Academic Search

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

Katarzyna Otmianowska-Mazur; Marek Urbanik; Artur Terech

1992-01-01

150

Quantitative model of the magnetospheric magnetic field  

Microsoft Academic Search

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

W. P. Olson; K. A. Pfitzer

1974-01-01

151

Spin dephasing in a magnetic dipole field.  

PubMed

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

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

2012-05-01

152

Magnetic field effects on microwave absorbing materials  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

153

The Wind Magnetic Field Investigation  

NASA Astrophysics Data System (ADS)

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

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

1995-02-01

154

Topological Description of Coronal Magnetic Fields.  

National Technical Information Service (NTIS)

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

M. A. Berger

1986-01-01

155

Structured electrodeposition in magnetic gradient fields  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

156

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

157

Anhysteretic Remanent Magnetization in Small Steady Fields  

Microsoft Academic Search

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

Bob J. Patton; John L. Fitch

1962-01-01

158

On Magnetic Field Generation Mechanisms in Astrophysics  

Microsoft Academic Search

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

O. G. Cherny

2011-01-01

159

Orienting Paramecium with intense static magnetic fields  

Microsoft Academic Search

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

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

2004-01-01

160

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

161

The structure of helical interplanetary magnetic fields  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

162

Analysis of magnetic field levels at KSC  

NASA Technical Reports Server (NTRS)

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

Christodoulou, Christos G.

1994-01-01

163

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

164

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

NASA Astrophysics Data System (ADS)

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

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

165

Effects of magnetic fields on mosquitoes.  

PubMed

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

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

2000-06-01

166

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

167

Magnetic fields in the early Universe  

NASA Astrophysics Data System (ADS)

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

Subramanian, K.

2010-01-01

168

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

169

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

170

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS  

SciTech Connect

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

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

2009-05-10

171

Exploring Magnetic Fields in Your Environment  

NSDL National Science Digital Library

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

172

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

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

V. A. Sheminova

2009-01-01

173

Horizontal magnetic fields in the solar photosphere  

Microsoft Academic Search

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

V. A. Sheminova

2009-01-01

174

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

175

The National High Magnetic Field Laboratory  

Microsoft Academic Search

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

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

2001-01-01

176

Representation of magnetic fields in space  

NASA Technical Reports Server (NTRS)

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

Stern, D. P.

1975-01-01

177

Primordial magnetic fields from superconducting cosmic strings  

Microsoft Academic Search

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

Konstantinos Dimopoulos

1998-01-01

178

DC-based magnetic field controller  

DOEpatents

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

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

1994-01-01

179

Manipulating Cells with Static Magnetic Fields  

Microsoft Academic Search

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

J. M. Valles; K. Guevorkian

2005-01-01

180

Possible Generation of Self-Magnetic Fields  

SciTech Connect

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

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

2001-09-15

181

Static uniform magnetic fields and amoebae  

SciTech Connect

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

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

1997-03-01

182

Probing interstellar magnetic fields with Supernova remnants  

NASA Astrophysics Data System (ADS)

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

Kothes, Roland; Brown, Jo-Anne

2009-04-01

183

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

185

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2012. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently approaching the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products to the Swarm user community. The setup of Swarm ground segment and the contents of the data products will be addressed. More information on the Swarm mission can be found at the mission web site (see URL below).

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

2011-12-01

186

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

187

Swarm: ESA's Magnetic Field Mission  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

188

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

189

Plasma behaviour in a rotating magnetic field  

Microsoft Academic Search

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

M. R. Shubaly

1974-01-01

190

Magnet calculations at the Grenoble High Magnetic Field Laboratory  

Microsoft Academic Search

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

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

2002-01-01

191

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

Microsoft Academic Search

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

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

2004-01-01

192

Flow Transitions in a Rotating Magnetic Field  

NASA Technical Reports Server (NTRS)

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

Volz, M. P.; Mazuruk, K.

1996-01-01

193

Horizontal magnetic fields in the solar photosphere  

NASA Astrophysics Data System (ADS)

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

Sheminova, V. A.

2009-05-01

194

Ferroelectric Cathodes in Transverse Magnetic Fields  

SciTech Connect

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

Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

2002-07-29

195

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

196

Magnetic monopole field exposed by electrons  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

197

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

198

Concentrator of magnetic field of light  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

199

Ohm's Law for Mean Magnetic Fields.  

National Technical Information Service (NTIS)

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

A. H. Boozer

1984-01-01

200

Magnetic field evolution in interacting galaxies  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

201

Magnetic field properties of SSC model dipole magnets  

SciTech Connect

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

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

1992-09-01

202

Enhancement of thermal conductivity of magnetic nanofluids in magnetic field  

Microsoft Academic Search

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

Innocent Nkurikiyimfura; Yanmin Wangl; Zhidong Panl; Dawei Hul

2011-01-01

203

The AGN origin of cluster magnetic fields  

NASA Astrophysics Data System (ADS)

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

Xu, Hao

204

Atoms in Crossed Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Korevaar, Eric John

1987-09-01

205

Magnetism and local molecular field.  

PubMed

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

Néel, L

1971-12-01

206

Photospheric magnetic field rotation: Rigid and differential  

Microsoft Academic Search

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

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

1970-01-01

207

Photospheric Magnetic Field Rotation: Rigid And Differential.  

National Technical Information Service (NTIS)

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

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

1970-01-01

208

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

209

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

210

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

211

Thinned fiber Bragg grating magnetic field sensor with magnetic fluid  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

212

Protecting SQUID metamaterials against stray magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

213

Coronal magnetic fields and the solar wind  

NASA Technical Reports Server (NTRS)

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

Newkirk, G., Jr.

1972-01-01

214

Capillary hydrodynamic effects in high magnetic fields  

Microsoft Academic Search

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

B. M. Berkovskii; N. N. Smirnov

1988-01-01

215

Magnetic Dipole Fields in Unsaturated Cubic Crystals  

Microsoft Academic Search

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

L. W. McKeehan

1933-01-01

216

Coronal magnetic fields produced by photospheric shear  

SciTech Connect

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

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

1987-10-01

217

Coronal magnetic fields produced by photospheric shear  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

218

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

219

Disruption of coronal magnetic field arcades  

NASA Technical Reports Server (NTRS)

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

Mikic, Zoran; Linker, Jon A.

1994-01-01

220

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

Microsoft Academic Search

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

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

1970-01-01

221

Diffusion of magnetic field via turbulent reconnection  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

222

Bipolar Flow in a Special Magnetic Field.  

National Technical Information Service (NTIS)

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

V. N. Danilov

1964-01-01

223

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

224

Does the solar magnetic field increase?  

Microsoft Academic Search

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

V. A. Kotov; I. V. Kotova

2001-01-01

225

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

226

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

227

High magnetic field facility at Osaka University  

Microsoft Academic Search

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

A. Yamagishi; M. Date

1989-01-01

228

Lightning Magnetic Field Measurements around Langmuir Laboratory  

Microsoft Academic Search

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

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

2010-01-01

229

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

230

Heliospheric Magnetic Field Structure At Solar Maximum  

Microsoft Academic Search

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

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

2002-01-01

231

Plasma in a Rotating Magnetic Field  

Microsoft Academic Search

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

Mauro Bologna; Bernardo Tellini; Filippo Giraldi

2008-01-01

232

Manipulation of molecular structures with magnetic fields  

Microsoft Academic Search

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

Marius Iosif Boamfa

2003-01-01

233

Coulomb crystals in the magnetic field.  

PubMed

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

Baiko, D A

2009-10-01

234

Sns ring dipole magnetic field quality.  

National Technical Information Service (NTIS)

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

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

2002-01-01

235

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

236

Solar Magnetic Field: Zeeman and Hanle Effects  

NASA Astrophysics Data System (ADS)

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

Stenflo, J.; Murdin, P.

2001-10-01

237

First VIKING results: magnetic field measurements  

Microsoft Academic Search

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

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

1988-01-01

238

Two-axis magnetic field sensor  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

239

The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Nakotte, Heinz

2001-11-01

240

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

241

Photospheric sources of magnetic field aligned currents  

NASA Astrophysics Data System (ADS)

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

Nordlund, A.

242

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

243

Permanent magnet edge-field quadrupole  

DOEpatents

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

244

Magnetic resonance imaging: effects of magnetic field strength  

SciTech Connect

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

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

1984-04-01

245

Organic Superconductors at Extremely High Magnetic Fields  

ScienceCinema

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

246

Processing of polymers in high magnetic fields  

SciTech Connect

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

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

1996-05-01

247

Levitation of a magnet by an alternating magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

248

Magnetic Helicity and Large Scale Magnetic Fields: A Primer  

NASA Astrophysics Data System (ADS)

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

Blackman, Eric G.

2014-04-01

249

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

250

Dynamic Magnetic Field Applications for Materials Processing  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

251

Interstellar Magnetic Field Surrounding the Heliopause  

NASA Astrophysics Data System (ADS)

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

Whang, Y. C.

2010-02-01

252

INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE  

SciTech Connect

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

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

2010-02-20

253

Magnetic-field-controlled reconfigurable semiconductor logic.  

PubMed

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

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

2013-02-01

254

Bending of magnetic filaments under a magnetic field  

NASA Astrophysics Data System (ADS)

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

Shcherbakov, Valera P.; Winklhofer, Michael

2004-12-01

255

Polarized radiation diagnostics of stellar magnetic fields  

NASA Astrophysics Data System (ADS)

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

Mathys, Gautier

256

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

Microsoft Academic Search

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

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

2008-01-01

257

Dirac equation in magnetic-solenoid field  

Microsoft Academic Search

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

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

2004-01-01

258

Write field asymmetry in perpendicular magnetic recording  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

259

Aligning Paramecium caudatum with Static Magnetic Fields  

Microsoft Academic Search

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

Karine Guevorkian; James M. Valles

2006-01-01

260

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

261

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

262

Faraday's Magnetic Field Induction Experiment  

NSDL National Science Digital Library

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

Davidson, Michael

2010-12-29

263

The Measurement of Magnetic Fields  

ERIC Educational Resources Information Center

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

Berridge, H. J. J.

1973-01-01

264

Biological effects of high DC magnetic fields  

SciTech Connect

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

Tenforde, T.S.

1981-06-01

265

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

266

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.

267

Magnetic cosserat continuum theory to simulate behavior of magnetic powder during compaction in applied magnetic field  

Microsoft Academic Search

Numerical method based on the Cosserat continuum theory is proposed for simulating behavior of a magnetic powder in an applied\\u000a magnetic field. The Maxwell stress is induced in the magnetic powder. During powder forming process in the magnetic field,\\u000a the magnetic particles are thus rotated and transferred by both mechanical and magnetic interaction. To simulate such powder\\u000a behavior, we formulate

Hidetoshi Kotera; Muneo Sawada; Susumu Shima

1998-01-01

268

3D analysis of applied field effect on trapped magnetic field during pulsed field magnetization of bulk superconductor  

NASA Astrophysics Data System (ADS)

External applied field effect in magnetization process by pulsed field (PFM) method of rectangular bulk superconductor is analysed by solving the A-V magnetic equation coupled to the thermal one in order to show the influence of the amplitude of the external field on the trapped magnetic field of bulk superconductor. A numerical model based on the control volume method (CVM) has been developed, which uses a power-law model with temperature dependency and magnetic field dependence on critical current density. For low cooling temperature Tco = 20 K, a good distribution of the trapped magnetic field of the bulk superconductor is obtained when we applied high external field.

Lotfi Khene, Mohamed; Alloui, Lotfi; Mimoune, Souri Mohamed; Bouillault, Frédéric; Feliachi, Mouloud

2014-04-01

269

Atoms in crossed electric and magnetic fields  

SciTech Connect

Extensive experimental and theoretical work pertaining to three interesting aspects of the interaction of atoms with crossed electric and magnetic fields is presented. The first experiment discussed deals with the effects of weak crossed fields on sodium atoms. A fluorescence spectrum of laser-excited sodium n = 11 states in an electric field of 2560 V/cm perpendicular to a magnetic field of 4.4 kG is presented, along with a comparison to theory. The data show the important effects of m-mixing and residual degeneracies that remain in the crossed fields. The next topic presented is the theoretical prediction of novel resonances, termed quasi-Penning resonances, corresponding to electron states localized away from the nucleus at the Stark saddlepoint in strong crossed electric and magnetic fields. The stability and possibility for observation of these resonances is explored. Finally, extensive experimental maps of data are presented that compare laser-induced ionization spectra of sodium atoms in crossed electric and magnetic fields to spectra in an electric field atone. The experiment explores the energy region of the electric-field saddlepoint, where quasi-Penning resonances are predicted to occur. The magnetic field is too weak for the observation of these resonances, but the experiment provides important groundwork for the understanding of future experiments in strong crossed fields.

Korevaar, E.J.

1987-01-01

270

Evolution of the interplanetary magnetic field  

SciTech Connect

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

McComas, D.J.

1993-05-01

271

Evolution of the interplanetary magnetic field  

SciTech Connect

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

McComas, D.J.

1993-01-01

272

Magnetic field generation at high magnetic Reynolds number  

NASA Technical Reports Server (NTRS)

The lowest-order contribution of finite electrical resistivity to the process of magnetic-field regeneration at high magnetic Reynolds number is calculated. It is found that finite resistivity changes the calculated regeneration rate by less than a factor of 2.

Levy, E. H.

1978-01-01

273

Magnetic field induced transition in vanadium spinels.  

PubMed

We study vanadium spinels AV2O4 (A = Cd,Mg) in pulsed magnetic fields up to 65 T. A jump in magnetization at ?0H?40??T is observed in the single-crystal MgV2O4, indicating a field induced quantum phase transition between two distinct magnetic orders. In the multiferroic CdV2O4, the field induced transition is accompanied by a suppression of the electric polarization. By modeling the magnetic properties in the presence of strong spin-orbit coupling characteristic of vanadium spinels, we show that both features of the field induced transition can be successfully explained by including the effects of the local trigonal crystal field. PMID:24483929

Mun, E D; Chern, Gia-Wei; Pardo, V; Rivadulla, F; Sinclair, R; Zhou, H D; Zapf, V S; Batista, C D

2014-01-10

274

[Working in the magnetic field of ultrahigh field MRI].  

PubMed

Development of magnetic resonance imaging (MRI) device technology continues to increase the static magnetic flux densities applied and consequently leads to considerably increased occupational exposure. This has already made it necessary to review limits of occupational exposure and to postpone European legal regulations for occupational exposure to electromagnetic fields. This raises the question whether and if so which adverse health effects and health risks might be associated with occupational exposure to MRI ultra-high static magnetic fields. Based on a survey on interaction mechanisms recommendations and safety rules are presented to help minimize adverse health effects of emerging ultra-high field MRI. PMID:23680824

Leitgeb, N; Gombotz, H

2013-05-01

275

The field of a screened magnetic dipole  

NASA Technical Reports Server (NTRS)

The purpose of this note is to quantitatively study the asymptotic behavior of the dipole magnetic field in the tail region of a paraboloidal or cylindrical model of the magnetosphere, assuming the complete screening of the internal field by magnetopause currents. This screening assumption is equivalent to imposing the boundary condition that the normal component of the magnetic field is zero at the magnetopause. With this boundary condition, the screened dipole field falls off exponentially with distance down the tail, in sharp constrast to the bare dipole field. Analytic expressions for a cylindrical and paraboloidal magnetopause are given.

Greene, J. M.; Miller, R. L.

1994-01-01

276

XUV harmonic enhancement by magnetic fields  

SciTech Connect

We examine three ways to enhance harmonic output of an XUV planar free-electron laser (FEL) operating in the Compton regime. The first method is to increase the rms static magnetic field, making it as large as possible. The second is by adding effective magnetic fields at the harmonics, thereby increasing the coupling to the harmonics. The third is by phase programming; i.e. programming the magnetic field to introduce jumps in the phase of the electrons as they move through phase space.

Elliott, C.J.; Schmitt, M.J.

1986-09-01

277

Magnetic field quality analysis using ANSYS  

SciTech Connect

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results show that the ANSYS solution converges toward the analytical solution and that the error on the multipole coefficients depends linearly on the square of the mesh size. This shows the good accuracy of ANSYS in computing the multipole coefficients. 2 refs., 16 figs., 4 tabs.

Dell'Orco, D.; Chen, Y.

1991-03-01

278

Chern band insulators in a magnetic field.  

PubMed

The effect of a magnetic field on a two-dimensional Chern band insulator is discussed. It is shown that, unlike the trivial insulator, an anomalous Hall insulator with Chern number C becomes a metal when a magnetic field is applied at constant particle density, for any C > 0. For a time-reversal invariant topological insulator with a spin Chern resolved number, C? = ?C? = C, the magnetic field induces a spin polarized spin Hall insulator. We consider also the effect of a superlattice potential and extend previous results for the quantization of the Hall conductance of filled Hofstadter bands to this problem. PMID:24627894

Araújo, Miguel A N; Castro, Eduardo V

2014-02-19

279

Coronal magnetic fields and energetic particles  

NASA Technical Reports Server (NTRS)

An examination was made of magnetic field effects in coronal and interplanetary space on propagation and storage of energetic particles from the flare site to 1 AU. Attempts were made to determine how several characteristics of solar energetic particle emissions are influenced by detailed configuration of the corona magnetic fields below 2.5 solar radii. Solar energetic particles are followed in the ambient magnetic field from injection above a flare until they either: (1) impact on the photosphere, (2) escape into interplanetary space, or (3) mirrow at some distant location in the corona.

Newkirk, G., Jr.

1973-01-01

280

Aligning Paramecium caudatum with static magnetic fields.  

PubMed

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5 x 10(-5) Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields >3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or antiparallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, nonphysiological response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, Deltachi(p), of a whole Paramecium: Deltachi(p) = (6.7+/- 0.7) x 10(-23) m(3). We show how the measured Deltachi(p) compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, noninvasive, quantitative means to manipulate swimming populations of unicellular organisms. PMID:16461406

Guevorkian, Karine; Valles, James M

2006-04-15

281

The theory of the Galactic magnetic field  

NASA Technical Reports Server (NTRS)

The paper discusses the role of the magnetic field in determining the large scale structure and dynamics of the interstellar medium. It then discusses the origin and maintenance of the Galactic field. The two major competing theories are that the field is primordial and connected to an intergalactic field or that the field is removed from and regenerated within the Galaxy. Finally, cosmic ray acceleration and confinement in the interstellar medium are discussed.

Zweibel, Ellen G.

1987-01-01

282

Magnetic resonance imaging: effects of magnetic field strength  

Microsoft Academic Search

Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. For any one spin echo sequence, gray\\/white matter contrast decreases and muscle\\/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then

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

1984-01-01

283

Structure of the magnetic field and plasma motions in the elements ofthe solar magnetic field  

Microsoft Academic Search

The structure of the solar magnetic field elements has been investigated on the basis of the observational data obtained for several regions of the quiet photosphere. Simultaneous measurements of the longitudinal magnetic field and radial velocity were carried out in the Fe I lambda5250.2 Å line in 1975. On the basis of the observations all the components of the magnetic

S. I. Gopasyuk; L. B. Demkina

1985-01-01

284

Magnetic fields of the terrestrial planets  

NASA Technical Reports Server (NTRS)

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

Russell, C. T.

1993-01-01

285

Some Structural Properties of Solar Magnetic Fields  

NASA Astrophysics Data System (ADS)

We discuss some results of the study of spatial characteristics of solar magnetic fields. The analysis is based on the magnetic field data obtained with a new spectromagnetograph installed on the IZMIRAN Tower Telescope (Fe I 6302.5 Å) (Kozhevatov et al., 2002), the data of the MSFC solar vector magnetograph (Fe I 5250.2 Å) and the data of longitudinal magnetic 96 m daily maps of SOHO/MDI magnetograph (Ni I 6768 Å) downloaded through Internet. Our study was directed in some different ways: the fractal properties of sunspots; fractal properties of space distribution of the magnetic fields along great distances comparable with the size of active regions or active complexes; fractal properties of active and quiet regions as global entities. To do it we used some different methods, particularly, the well known method using the relation between the area and the perimeter of magnetic field lines (see (Feder, 1988; Meunier, 1999; Nesme-Ribes at al., 1996; Balke et al., 1993)) and technique developed by Higuchi (1988), who applied it to the investigation of long time series. Note also that magnetic structure in terms of the fractal models was developed earlier in (Zelenyi & Milovanov, 1991; Milovanov & Zelenyi, 1993; Mogilevskii, 1994; Mogilevskii, 2001; Abramenko et al., 2002; Abramenko, 2005; Salakhudinova & Golovko, 2005). The main results are: 1. Fractal analysis of sunspot magnetic field indicated the existence of three families of self-similar contour lines roughly belonging to the umbra, penumbra and the ambient photosphere correspondingly. The greatest fractal dimension corresponds to the regions of weakest fields (ambient photosphere), the least one corresponds to the intermediate region (penumbra). 2. More detailed analysis shows that the fractal coefficient has a maximum (about 1.50) near the umbra--penumbra interface. 3. The global fractal numbers of space distribution of magnetic field on solar surface is closely connected with the mean absolute values of the longitudinal magnetic field for this surface. The fractal numbers diminish with the rising of mean magnetic field (from values about 2.0 for the relatively quiet region to 1- 1.2 for very active regions). 4. The dependences of fractal numbers of the space distribution of longitudinal and transversal fields versus mean longitudinal field are similar by their character but the fractal values for transversal field are higher than the corresponding factor values for longitudinal field by factor about 1.5. This means that the distribution of transversal field along the space is more chaotic than the distribution of longitudinal field.

Ioshpa, B.; Mogilevskii, E.; Obridko, V.

2007-05-01

286

Coronal Magnetic Fields Produced by Photospheric Shear,  

National Technical Information Service (NTIS)

The magneto-frictional method for computing force-free fields examines the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. The energy of the sheared field can be arbitrarily large compar...

J. A. Klimchuk P. A. Sturrock W. H. Yang

1988-01-01

287

Coronal Magnetic Fields Produced by Photospheric Shear.  

National Technical Information Service (NTIS)

The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be ...

P. A. Sturrock W. Yang

1987-01-01

288

Compact Electric- And Magnetic-Field Sensor  

NASA Technical Reports Server (NTRS)

Compact sensor measures both electric and magnetic fields. Includes both short electric-field dipole and search-coil magnetometer. Three mounted orthogonally providing triaxial measurements of electromagnetic field at frequencies ranging from near 0 to about 10 kHz.

Winterhalter, Daniel; Smith, Edward

1994-01-01

289

Measurement of the magnetic field of the CDF magnet  

SciTech Connect

The magnetic field of the CDF (Collider Detector at Fermilab) superconducting solenoid has been measured using a newly designed field mapping device. NMR probes and a system of three orthogonal search coils were used as sensing elements. The central uniform region inside the solenoid coil and the fringing field in the conical end plugs were measured. The detailed field distribution and its characteristics are described.

Yamada, R.; Newman-Holmes, C.; Schmidt, E.E.

1985-11-01

290

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

291

Magnetic field gradient effects on Rayleigh-Taylor instability with continuous magnetic field and density profiles  

SciTech Connect

In this paper, the effects of magnetic field gradient (i.e., the magnetic field transition layer effects) on the Rayleigh-Taylor instability (RTI) with continuous magnetic field and density profiles are investigated analytically. The transition layers of magnetic field and density with two different typical profiles are studied and the analytic expressions of the linear growth rate of the RTI are obtained. It is found that the magnetic field effects strongly reduce the linear growth rate of the RTI, especially when the perturbation wavelength is short. The linear growth rate of the RTI increases with the thickness of the magnetic field transition layer, especially for the case of small thickness of the magnetic field transition layer. When the magnetic field transition layer width is long enough, the linear growth rate of the RTI can be saturated. Thus when one increases the width of the magnetic field transition layer, the linear growth rate of the RTI increases only in a certain range, which depends on the magnetic field strength. The numerical results are compared with the analytic linear growth rates and they agree well with each other.

Yang, B. L. [Graduate School, China Academy of Engineering Physics, Beijing 100088 (China); Wang, L. F.; Ye, W. H. [HEDPS and CAPT, Peking University, Beijing 100871 (China); LCP, Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China); Xue, C. [LCP, Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)

2011-07-15

292

On the Helicity of Open Magnetic Fields  

NASA Astrophysics Data System (ADS)

We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically open. It is demonstrated that, while the magnetic helicity is gauge-dependent, its value in any gauge may be physically interpreted as the average winding number among all pairs of field lines with respect to some orthonormal frame field. In fact, the choice of gauge is equivalent to the choice of reference field in the relative helicity, meaning that the magnetic helicity is no less physically meaningful. We prove that a particular gauge always measures the winding with respect to a fixed frame, and propose that this is normally the best choice. For periodic fields, this choice is equivalent to measuring relative helicity with respect to a potential reference field. However, for aperiodic fields, we show that the potential field can be twisted. We prove by construction that there always exists a possible untwisted reference field.

Prior, C.; Yeates, A. R.

2014-06-01

293

Vector magnetic field camera for permanent magnets inspection  

NASA Astrophysics Data System (ADS)

Permanent magnets are widely used in many applications. A fast and reliable system for online evaluation of permanent magnets is required for their quality assurance. Therefore, a new measurement system has been developed to measure the spatial distribution of the vector magnetic field. The system consists of a complex Hall transducer, an analog multiplexer, a mechanical XYZ scanner and a control computer. The matrix of Hall sensors is designed in this way that all 3 components can be measured at once in multiple points. Such kind of transducer enables to reduce the time needed for inspection. The similar matrix transducer was also utilized to evaluate state of magnetized ferromagnetic materials.

Chady, T.; Psuj, G.; Todaka, T.; Enokizono, M.

2013-01-01

294

Magnetic monopoles in field theory and cosmology.  

PubMed

The existence of magnetic monopoles is predicted by many theories of particle physics beyond the standard model. However, in spite of extensive searches, there is no experimental or observational sign of them. I review the role of magnetic monopoles in quantum field theory and discuss their implications for particle physics and cosmology. I also highlight their differences and similarities with monopoles found in frustrated magnetic systems. PMID:23166376

Rajantie, Arttu

2012-12-28

295

Juno and Jupiter's Magnetic Field (Invited)  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

296

Megagauss Magnetic Fields in Semiconductor Physics  

NASA Astrophysics Data System (ADS)

A review of megagauss experiments using different kinds of field generator up to 1,000 T is given. The effiency of the single-turn coil, the electromagnetic and the explosive flux-compression, and finally the nearly steady-state long-pulse generators are presented. The basic feature of magnetic fields in semiconductor physics is related to the quantity of the magnetic length ? = (?/eB)1/2 where ? and e are natural constants with the usual meaning and B is the magnetic flux density. For B = 100 T we obtain ? = 2.56 nm. The parameter ? is a measure for the extension of the corresponding wavefunction of the charged particle and completely independent of the cyclotron mass. It should be noted that megagauss magnetic fields and nano structures have thus a natural correspondence: the magnetic length ? serves as a length measure in space in the nm-regime to be tuned by the external magnetic field. A second feature of megagauss fields is the generally extremely short pulse of field realization accompanied by a very high dB/dt. In this way the fields are "transient" and can be used to study the dynamics of the charge-carrier system. Also "eddy current"-effects can modify the system and manifest in new physical phenomena. Setup, performance and data analysis are demonstrated in different examples.

von Ortenberg, Michael

297

High-field superconducting nested coil magnet  

NASA Technical Reports Server (NTRS)

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

Laverick, C.; Lobell, G. M.

1970-01-01

298

Large Scale Solar Magnetic Fields: Temporal Variations  

Microsoft Academic Search

The temporal evolution of the solar magnetic field during solar cycles 20 21 and 22 has been investigated by means of spherical harmonic decomposition and subsequent time series analysis. A 33 yr and a 25 yr time series of daily magnetic maps of the solar photosphere recorded at the Mount Wilson and NSO\\/Kitt Peak observatories respectively were used to calculate

R. Knaack; J. O. Stenflo

2004-01-01

299

Toroidal Plasma Containment with Rotating Magnetic Field.  

National Technical Information Service (NTIS)

Experimental investigations were conducted on a toroidal plasma with alternating pinch- and theta-pinch magnetic fields as well as with a theta-pinch and with a screw pinch. For the alternating pinch, the resultant magnetic vector is rotating, so that the...

D. E. Brown H. G. Loos

1966-01-01

300

Global Solar Magnetic Field Maps using ADAPT  

Microsoft Academic Search

Estimates of the global solar photospheric magnetic field distribution are critical for space weather forecasting. These global magnetic charts are the essential data input for accurate modeling of the corona and solar wind, which is vital for gaining the basic understanding necessary to improve forecasting models needed for Air Force operations. In this poster, we describe our efforts and progress

Carl John Henney; C. N. Arge; J. Koller; W. A. Toussaint; S. Young; D. MacKenzie; J. W. Harvey

2010-01-01

301

The Creation of Cosmic Magnetic Fields  

Microsoft Academic Search

In 1983, on the basis of Scriptures implying the original created material of the earth was water, I proposed that God created the water with the spins of its hydrogen nuclei initially aligned in one direction (Humphreys, 1983). That would produce a strong magnetic field. After 6,000 years of decay, including energy losses from magnetic reversals during the Genesis Flood,

D. Russell Humphreys

2008-01-01

302

Neutrino flavor conversion in random magnetic fields  

Microsoft Academic Search

If massive neutrinos possess magnetic moments, a magnetic field can cause a spin flip. In the case of Dirac neutrinos the spin flip converts an active neutrino into a sterile one and vice versa. By constrast, if neutrinos are Majorana particles, a spin flip converts them to a neutrino of a different flavor. We examine the behavior of neutrinos in

G. Domokos; S. Kovesi-Domokos

1997-01-01

303

Magnetic Fields in the Solar Convection Zone  

Microsoft Academic Search

Recent studies of the dynamic evolution of magnetic flux tubes in the solar convection zone are reviewed with focus on emerging flux tubes responsible for the formation of solar active regions. The current prevailing picture is that active regions on the solar surface originate from strong toroidal magnetic fields generated by the solar dynamo mechanism at the thin tachocline layer

Yuhong Fan

2004-01-01

304

Magnetic field decay in isolated neutron stars  

Microsoft Academic Search

Three mechanisms that promote the loss of magnetic flux from an isolated neutron star - Ohmic decay, ambipolar diffusion, and Hall drift - are investigated. Equations of motions are solved for charged particles in the presence of a magnetic field and a fixed background of neutrons, while allowing for the creation and destruction of particles by weak interactions. Although these

Peter Goldreich; Andreas Reisenegger

1992-01-01

305

Electrically driven vortices in multipolar magnetic fields  

NASA Astrophysics Data System (ADS)

The flow generated in a thin layer of an electrically conducting fluid by the interaction of a steady, uniform electric current with a superposition of dipolar permanent magnets, is studied experimentally and theoretically. The experiment is carried out in a rectangular plexiglass cell with a shallow layer of an electrolytic solution. Small permanent magnets are placed externally in the central part of the cell bottom in an array that may include one, two or four dipole magnets. The direct electric current which is injected thorugh two opposite walls (copper electrodes) interacts with the magnetic field distribution generating a Lorentz force that drives different vortex patterns depending on the number of dipoles, their location and the orientation of their magnetic dipole moment. The theoretical two-dimensional model that describes the flow produced by a single dipole magnet, providing non-linear convective effects are neglected, is extended to consider the influence of additional magnets.

Cuevas, Sergio

2002-11-01

306

The Magnetic Field of Helmholtz Coils  

ERIC Educational Resources Information Center

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

Berridge, H. J. J.

1975-01-01

307

Earth's Magnetic Field in the past.  

National Technical Information Service (NTIS)

Variations of the Earth's magnetic field in the past are known because they were recorded in various ferrimagnetic minerals such as titanomagnetite and maghemite. This article describes the principal techniques and sample materials (volcanic lava, sedimen...

D. J. R. Nordemann

1982-01-01

308

Turbulent Diffusion in a Magnetic Field.  

National Technical Information Service (NTIS)

The turbulent diffusion in a magnetic field is studied. The special case where the turbulence is caused by non collisionnal drif instabilities is considered in some detail. (Atomindex citation 11:495636)

P. Rolland

1978-01-01

309

Airborne Electroprospecting with Rotating Magnetic Fields.  

National Technical Information Service (NTIS)

The document contains reports on airborne electroprospecting methods, theory of the rotating magnetic field method, a quantitative comparison of the amount of data obtainable from different methods, interpretation of anomaly curves distorted by the inerti...

Y. B. Shaub

1970-01-01

310

Digital Computer Solution of Magnetic Field Problems.  

National Technical Information Service (NTIS)

A computer program for the analysis of magnetic field problems involving ferromagnetic materials is described. A discussion of the equations describing such problems, the boundary conditions employed, and the method of modeling on a digital computer is pr...

C. M. DeSantis

1970-01-01

311

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

Magnetic field response sensors designed as passive inductor-capacitor circuits produce magnetic field responses whose harmonic frequencies correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induction. A radio frequency antenna produces the time varying magnetic field used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for discerning changes in sensor s response kequency, resistance and amplitude is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminating the need to have a data acquisition channel dedicated to each sensor. The method does not require the sensors to be in proximity to any form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor); Shams, Qamar A. (Inventor); Fox, Robert L. (Inventor); Fox, Christopher L. (Inventor); Fox, Melanie L. (Inventor); Bryant, Robert G. (Inventor)

2006-01-01

312

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

A measurement acquisition method that alleviates many shortcomings of traditional measurement systems is presented in this paper. The shortcomings are a finite number of measurement channels, weight penalty associated with measurements, electrical arcing, wire degradations due to wear or chemical decay and the logistics needed to add new sensors. The key to this method is the use of sensors designed as passive inductor-capacitor circuits that produce magnetic field responses. The response attributes correspond to states of physical properties for which the sensors measure. A radio frequency antenna produces a time-varying magnetic field used to power the sensor and receive the magnetic field response of the sensor. An interrogation system for discerning changes in the sensor response is presented herein. Multiple sensors can be interrogated using this method. The method eliminates the need for a data acquisition channel dedicated to each sensor. Methods of developing magnetic field response sensors and the influence of key parameters on measurement acquisition are discussed.

Woodard, Stanley E.; Taylor, Bryant D.; Shams, Qamar A.; Fox, Robert L.

2005-01-01

313

Fractal structure of the interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

Under some conditions, time series of the interplanetary magnetic field strength and components have the properties of fractal curves. Magnetic field measurements made near 8.5 AU by Voyager 2 from June 5 to August 24, 1981 were self-similar over time scales from approximately 20 sec to approximately 3 x 100,000 sec, and the fractal dimension of the time series of the strength and components of the magnetic field was D = 5/3, corresponding to a power spectrum P(f) approximately f sup -5/3. Since the Kolmogorov spectrum for homogeneous, isotropic, stationary turbulence is also f sup -5/3, the Voyager 2 measurements are consistent with the observation of an inertial range of turbulence extending over approximately four decades in frequency. Interaction regions probably contributed most of the power in this interval. As an example, one interaction region is discussed in which the magnetic field had a fractal dimension D = 5/3.

Burlaga, L. F.; Klein, L. W.

1986-01-01

314

Magnetic field calculation on CDF detector (I)  

SciTech Connect

Magnetic field and flux distribution for the CDF detector is calculated using a TRIM program. The flux distribution in the system is calculated at several different excitation levels with an expected B-H curve.

Yamada, R.

1983-01-20

315

The Polar BEAR magnetic field experiment  

NASA Astrophysics Data System (ADS)

The objectives and the instrumentation of the Polar BEAR magnetic field experiment are described along with the preliminary results from simultaneous measurements of Birkeland currents and UV auroral emissions. The experiment consists of an integrated sensor head, analog electronics, and digital electronics. The sensor head is a single unit containing sensor windings for each of the three orthogonal axes, oriented parrallel to the spacecraft coordinates; to minimize interference from spacecraft-generated magnetic fields, the sensor unit is located at the end of the +y solar panel. The digital electronics package is essentially identical to that flown on HILAT. A signal processor digitizes the analog outputs of the three orthogonal axes of the flux-gate magnetometer to a 13-bit resolution, yielding a magnetic field range of + or - 63,000 nT and a resolution of 15.2 nT. The full-resolution magnetic field values are recovered by data processing techniques on the ground.

Bythrow, Peter F.; Potemra, Thomas A.; Zanetti, Lawrence J.; Mobley, Frederick F.; Scheer, Leonard

1987-09-01

316

Discontinuities in the magnetic field near Enceladus  

NASA Astrophysics Data System (ADS)

The plasma interaction of Saturn's icy moon Enceladus generates a hemisphere coupling current system that directly connects the giant planet's northern and southern polar magnetosphere. Based on Cassini magnetometer observations from all 20 targeted Enceladus flybys between 2004 and 2014, we study the magnetic field discontinuities associated with these hemisphere coupling currents. We identify a total number of 11 events during which the magnetic field was discontinuous at the surface of the Enceladus flux tube (defined by the bundle of magnetic field lines tangential to the solid body of the moon). A minimum variance analysis is applied to calculate the surface normals of these discontinuities. In agreement with theoretical expectations, the normals are found to be perpendicular to the surface of the Enceladus flux tube. The variation of the hemisphere coupling currents with Enceladean longitude leaves a clear imprint in the strengths of the observed magnetic field jumps as well.

Simon, Sven; Saur, Joachim; Treeck, Shari C.; Kriegel, Hendrik; Dougherty, Michele K.

2014-05-01

317

Improved Spindle Cusp Magnetic Field for ECRIS  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

318

Magnetic field anisotropy based MR tractography  

NASA Astrophysics Data System (ADS)

Non-invasive measurements of structural orientation provide unique information regarding the connectivity and functionality of fiber materials. In the present study, we use a capillary model to demonstrate that the direction of fiber structure can be obtained from susceptibility-induced magnetic field anisotropy. The interference pattern between internal and external magnetic field gradients carries the signature of the underlying anisotropic structure and can be measured by MRI-based water diffusion measurements. Through both numerical simulation and experiments, we found that this technique can determine the capillary orientation within 3°. Therefore, susceptibility-induced magnetic field anisotropy may be useful for an alternative tractography method when diffusion anisotropy is small at higher magnetic field strength without the need to rotate the subject inside the scanner.

Han, S. H.; Song, Y. K.; Cho, F. H.; Ryu, S.; Cho, G.; Song, Y.-Q.; Cho, H.

2011-10-01

319

Magnetic tunnel junctions for low magnetic field sensing  

NASA Astrophysics Data System (ADS)

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

Liu, Xiaoyong

320

The magnetic field investigation on Cluster  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

321

Strain Sensors for High Field Pulse Magnets  

Microsoft Academic Search

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

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

2009-01-01

322

A novel CMOS magnetic field sensor array  

Microsoft Academic Search

A CMOS magnetic field sensor array that can be implemented along with analog and digital signal processing circuitry in the form of a single integrated circuit for instrumentation or measurement is discussed. The design realizes a single sensor device through interconnection of a few n-channel magnetic-field-sensitive MOSFETs (MAGFETs) in one circuit. The experimental measurements suggest that the interconnection, which forms

Durgamadhab Misra

1990-01-01

323

Growing Magnetic Fields in Central Compact Objects  

NASA Astrophysics Data System (ADS)

We study the effects of growth models of magnetic fields in Central Compact Objects (CCOs). Such a field evolution is not a new idea (Blandford, Applegate, & Hernquist 1983) but the evolutionary implications not have been followed up completely (Michel 1994). We discussed the new class of neutron stars which belong to five main types that have mainly been recognized in the last ten years. The possibility that a rapid weakly magnetized pulsar might have formed in SN1987A is commented.

Bernal, C. G.; Page, D.

2011-10-01

324

The AMPTE CCE Magnetic Field Experiment  

Microsoft Academic Search

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

T. A. Potemra; L. J. Zanetti; M. H. Acuna

1985-01-01

325

Laminated magnet field coil sheath  

DOEpatents

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

Skaritka, J.R.

1987-05-15

326

Laminated magnet field coil sheath  

DOEpatents

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

Skaritka, John R. (Coram, NY)

1987-12-01

327

Magnetic field enhanced cake filtration of superparamagnetic PVAc-particles  

Microsoft Academic Search

The combination of two classical separation methods, cake filtration and magnetic field driven separation, for superparamagnetic nanocomposites results in positive synergetic effects and in extension of the field of application of the cake filtration process. In inhomogeneous magnetic fields magnetic particles experience a magnetic force. Experimental results show that two different effects of the magnetic field influence the cake building

C. Eichholz; M. Stolarski; V. Goertz; H. Nirschl

2008-01-01

328

Comparison of the Mean Photospheric Magnetic Field and the Interplanetary Magnetic Field.  

National Technical Information Service (NTIS)

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

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

1970-01-01

329

Dynamics of nonadiabatic charged particles in the magnetic dipole field with imposed homogeneous magnetic field  

Microsoft Academic Search

The model of charged particles motion in the summary dipole and external uniform, parallel to dipole, field is considered. External field associates with the effect of magnetic perturbation. Such problem appears, for example, for protons in geomagnetic field during the magnetic storm. In contrast to traditional model, not the line of force, but the so-called Central Trajectory (CT-trajectory which passes

I. V. Amirkhanov; E. P. Zhidkov; Yu. G. Dzyuba; A. N. Ilina; V. D. Ilin

1994-01-01

330

Untwisting magnetic fields in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is the tenuous atmosphere of the Sun characterized by a temperature of the order of million degrees Kelvin, an ambient magnetic field of 10 to 15 Gauss and a very high magnetic Reynolds number because of which it qualifies as a near-ideal magnetofluid system. It is well known that for such a system, the magnetic flux across every fluid surface remains effectively constant to a good approximation. Under this so called ``frozen-in'' condition then, it is possible to partition this magnetofluid into contiguous magnetic subvolumes each entrapping its own subsystem of magnetic flux. Thin magnetic flux tubes are an elementary example of such magnetic subvolumes evolving in time with no exchange of fluid among them. The internal twists and interweaving of these flux tubes, collectively referred as the magnetic topology, remains conserved under the frozen-in condition. Because of the dynamical evolution of the magnetofluid, two such subvolumes can come into direct contact with each other by expelling a third interstitial subvolume. In this process, the magnetic field may become discontinuous across the surface of contact by forming a current sheet there. Because of the small spatial scales generated by steepening of magnetic field gradient, the otherwise negligible resistivity becomes dominant and allows for reconnection of field lines which converts magnetic energy into heat. This phenomenon of spontaneous current sheet formation and its subsequent resistive decay is believed to be a possible mechanism for heating the solar corona to its million degree Kelvin temperature. In this work the dynamics of spontaneous current sheet formation is explored through numerical simulations and the results are presented.

Bhattacharyya, Ramit; Smolarkiewicz, Piotr; Chye Low, Boon

2012-07-01

331

Magnetic field transfer device and method  

DOEpatents

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

Wipf, Stefan L. (Hamburg, DE)

1990-01-01

332

Magnetic field transfer device and method  

DOEpatents

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

Wipf, S.L.

1990-02-13

333

Interstellar magnetic fields: An observational perspective  

SciTech Connect

The plausibility of magnetic molecular clouds is established. It is shown that the empirically known relations between spectral line width, density, and cloud size can be derived from a virial equilibrium model where gravity is balanced by the sum of magnetic and pressure support. It is shown that substitution of measured density, cloud size, and line width measurements into the model can predict observed field strength to within a factor of two. The Zeeman effect is discussed and new measurements are presented for magnetic field strength based on OH and HI Zeeman observations at the Arecibo and Green Bank telescopes. The Barnard 1 (B1) region, in the Perseus Molecular Cloud Complex, is discussed in detail. OH spectral line intensity maps are presented for the regions where the OH Zeeman effect was observed, which allow, for the first time, comparison of observed field strength values with predicted field strength values, using emission from a single molecular species. Spatial structure of magnetic fields in molecular clouds are investigated. New optical polarization maps are presented for the dark clouds in Perseus, Taurus, and Ophiuchus. The polarization observed is attributed to preferential extinction of background starlight by magnetically aligned dust grains in the clouds, and we analyze the polarization maps as maps of the projection of the magnetic field onto the plane of the sky.

Goodman, A.A.

1989-01-01

334

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping  

NASA Astrophysics Data System (ADS)

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

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

2002-08-01

335

Differential rotation of the photospheric magnetic field  

Microsoft Academic Search

The differential rotation of the large-scale photospheric magnetic field has been investigated with an autocorrelation technique using synoptic charts of the photospheric field during the interval 1959–66. Near the equator the rotation period of the field is nearly the same as the rotation rate of long-lived sunspots studied by Newton and Nunn. Away from the equatorial zone the field has

John M. Wilcox; Robert Howard

1970-01-01

336

Electric/Magnetic Field Sensor.  

National Technical Information Service (NTIS)

A UNLV novel electric/magnetic dot sensor comprises: a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conduct...

M. Popek R. A. Schill

2005-01-01

337

Strong Magnetic Fields in Lattice QCD  

NASA Astrophysics Data System (ADS)

Hadronic matter in very strong (hadron-scale) magnetic fields acquires many new interesting properties. Some of these properties can be studied with the help of lattice simulations in quenched lattice gauge theory. One of the interesting effects is the chiral magnetic effect, that is, the enhancement of the fluctuations of currents and charge densities by the magnetic field. By virtue of the Green-Kubo dispersion relations, this enhancement of fluctuations corresponds to the enhancement of the electric conductivity of hadronic matter. We review here the results of our recent studies of this phenomenon.

Buividovich, P. V.; Luschevskaya, E. V.; Polikarpov, M. I.; Chernodub, M. N.

2011-10-01

338

Asymptotic freedom in strong magnetic fields.  

PubMed

Perturbative gluon exchange interaction between quark and antiquark, or in a 3q system, is enhanced in a magnetic field and may cause vanishing of the total qq[over ¯] or 3q mass, and even unlimited decrease of it-recently called the magnetic collapse of QCD. The analysis of the one-loop correction below shows a considerable softening of this phenomenon due to qq[over ¯] loop contribution, similar to the Coulomb case of QED, leading to approximately logarithmic damping of gluon exchange interaction (?O(1/ln|eB|)) at large magnetic field. PMID:23679595

Andreichikov, M A; Orlovsky, V D; Simonov, Yu A

2013-04-19

339

Bootstrapping the Coronal Magnetic Field with STEREO  

NASA Astrophysics Data System (ADS)

The 3D coronal magnetic field obtained from stereoscopically triangulated loops has been compared with standard photospheric magnetogram extrapolations. We found a large misalignment of 20-40 deg, depending on the complexity of an AR (Sandman et al. 2009; DeRosa et al. 2009). These studies prove that the magnetic field in the photosphere is not force-free and fundamentally cannot reproduce the coronal magnetic field. Bootstrapping with coronal loop 3D geometries are required to improve modeling of the coronal field. Such coronal field bootstrapping methods are currently developed using stereoscopically triangulated loops from STEREO/EUVI and preliminary results show already a significantly reduced misalignment of 10-20 deg.

Aschwanden, Markus J.

2010-05-01

340

Suppressing drift chamber diffusion without magnetic field  

NASA Astrophysics Data System (ADS)

The spatial resolution in drift chamber detectors for ionizing radiation is limited by diffusion of the primary electrons. A strong magnetic field along the drift direction is often applied (Fancher et al., Nucl. Instr. and Meth. A 161 (1979) 383) because it suppresses the transverse diffusion, improving the resolution but at considerable increase in cost and complexity. Here we show that transverse track diffusion can be strongly suppressed without any magnetic field. This is achieved by using a gas additive which reversibly captures primary ionization electrons, forming negative ions. The ions drift with thermal energies even at very high drift fields and low pressures ( E/P=28.5 V/ cm torr), and the diffusion decreases with increasing drift field. Upon arrival at the avalanche region of the chamber the negative ions are efficiently stripped and ordinary avalanche gain is obtained. Using this technique, r.m.s. transverse diffusion less than 200 ?m has been achieved over a 15 cm drift path at 40 torr with zero magnetic field. The method can provide high spatial resolution in detectors with long drift distances and zero magnetic field. Negative ion drift chambers would be particularly useful at low pressures and in situations such as space-based or underground experiments where detector size scaleability is important and cost, space, or power constraints preclude the use of a magnetic field.

Martoff, C. J.; Snowden-Ifft, D. P.; Ohnuki, T.; Spooner, N.; Lehner, M.

2000-02-01

341

Near equipment magnetic field verification and scaling  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

342

Magnetic Field Generation by Relativistic Shear Flows  

NASA Astrophysics Data System (ADS)

We report PIC simulation results of magnetic field generation by relativistic shear flows. We find that the shear flow boundary layer in initially non-magnetic shear flows is unstable to the growth of oblique 2-stream and Weibel instabilities near the boundary layer. Such instabilities generate current sheets and loops which eventually form nonlinear ordered structures resembling magnetic flux tubes with alternating polarity, orthogonal to the shear flow direction. Peak magnetic fields can reach almost equipartition values. The size and amplitude of such magnetic structures reach a steady state when the free energy input of the shear flow is balanced by turbulence dissipation. Nonthermal particles are efficiently accelerated, likely by the drift-kink instability, into a power-law energy distribution. These results have important implications for many astrophysical settings, including multi-component blazar jets and gamma-ray bursts. This work was supported by NSF AST0909167 and NASA Fermi grants.

Liang, Edison; Boettcher, Markus; Smith, Ian

2011-11-01

343

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

Magnetic field response sensors designed as passive inductor- capacit or circuits produce magnetic field responses whose harmonic frequenci es correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induc tion. A radio frequency antenna produces the time varying magnetic fi eld used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for disce rning changes in sensor's response frequency, resistance and amplitud e is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminat ing the need to have a data acquisition channel dedicated to each se nsor. The method does not require the sensors to be in proximity to a ny form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

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

2007-01-01

344

Magnetic fields in the solar photosphere.  

PubMed

Recent high-resolution observations of the surface of the Sun have revealed the fine structure of a vast array of complex photospheric magnetic features. Observations of these magnetic field structures have already greatly enhanced our theoretical understanding of the interactions between magnetic fields and turbulent convection, and future photospheric observations will inevitably present new theoretical challenges. In this review, I discuss recent progress that has been made in the modelling of photospheric magnetic fields. In particular, I focus upon the complex field structures that are observed within the umbrae and the penumbrae of sunspots. On a much smaller scale, I also discuss models of the highly localized magnetic field structures that are observed in less magnetically active regions of the photosphere. As the spatial resolution of telescopes has improved over the last few years, it has now become possible to observe these features in detail, and theoretical models can now describe much of this behaviour. In the last section of this review, I discuss some of the remaining unanswered questions. PMID:18812304

Bushby, Paul J

2008-12-13

345

Magnetic fields of Jupiter and Saturn  

SciTech Connect

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

Ness, N.F.

1981-01-01

346

Magnetic marker based homogeneous bioassays utilizing rotating magnetic fields  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles (MNPs) as markers in bioassays utilizing rotating instead of alternating magnetic fields predict an improved sensitivity regarding quantitative protein detection. This finding is based on numerical solutions of the Fokker-Planck equation and pronounced for increasing field amplitudes. In order to verify this prediction, the phase lag change of MNPs in rotating magnetic fields up to 5 mT is measured. The magnetic markers are functionalized single core iron oxide nanoparticles with different sizes. Antibodies which specifically bind to the MNPs cause the phase lag change. The increase of the phase lag change strongly depends on the particle parameters. MNPs with a core diameter of 30 nm show for 5 mT, a significant difference between the two field types. This difference is less pronounced for the 25 nm MNPs due to the increasing influence of Néel relaxation processes and for the 40 nm particles, due to the reduced saturation magnetization. A further improvement for the 30 nm MNPs with field amplitudes over 5 mT is simulated based on the determined particle parameters.

Dieckhoff, Jan; Schilling, Meinhard; Ludwig, Frank

2014-05-01

347

Magnetic resonance imaging: effects of magnetic field strength.  

PubMed

Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. The T1 relaxation of gray matter, white matter, and muscle increases and T2 decreases with field strength, while T1 of fat remains relatively constant and T2 increases. As a consequence, for any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields. PMID:6701302

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

1984-04-01

348

Poloidal magnetic fields in superconducting neutron stars  

NASA Astrophysics Data System (ADS)

We develop the formalism for computing the magnetic field within an axisymmetric neutron star with a strong type II superconductor core surrounded by a normal conductor. The formalism takes full account of the constraints imposed by hydrostatic equilibrium with a barotropic equation of state. A characteristic of this problem is that the currents and fields need to be determined simultaneously and self-consistently. Within the core, the strong type II limit B ? H allows us to compute the shapes of individual field lines. We specialize to purely poloidal magnetic fields that are perpendicular to the equator, and develop the `most dipolar case' in which field lines are vertical at the outer radius of the core, which leads to a magnetic field at the stellar surface that is as close to a dipole as possible. We demonstrate that although field lines from the core may only penetrate a short distance into the normal shell, boundary conditions at the inner radius of the normal shell control the field strength on the surface. Remarkably, we find that for a Newtonian N = 1 polytrope, the surface dipole field strength is Bsurf ? Hb?b/3, where Hb is the magnetic field strength at the outer boundary of the type II core and ?bR is the thickness of the normal shell. For reasonable models, Hb ? 1014 G and ?b ? 0.1 so the surface field strength is Bsurf ? 3 × 1012 G, comparable to the field strengths of many radio pulsars. In general, Hb and ?b are both determined by the equation of state of nuclear matter and by the mass of the neutron star, but Bsurf ˜ 1012 G is probably a robust result for the `most dipolar' case. We speculate on how the wide range of neutron star surface fields might arise in situations with less restrictions on the internal field configuration. We show that quadrupolar distortions are ˜-10-9(Hb/1014 G)2 and arise primarily in the normal shell for B ? Hb.

Henriksson, K. T.; Wasserman, I.

2013-06-01

349

Magnetic Fields in the Early Universe  

ScienceCinema

Magnetic fields are present everywhere: Earth, other planets, stars, galaxies, galaxy clusters and probably all over the Universe. They extend over kiloparsecs and more, with constant amplitude and direction, and they have tangled components as well. When and how were they created, can we understand the mechanisms, do they influence particle physics, how stable are these fields?

350

A communication system using magnetic fields  

Microsoft Academic Search

A new wireless communication system using a low frequency signal transmitted by current loop antennas is proposed. The communication range is relatively small (about several meters) so that the range is included in near field of a carrier signal. The use of magnetic fields makes it possible to provide high quality communication in an unfavorable environment where metal or fluids

Yun-Jae Won; Shin-Jae Kang; Sun-Hee Kim; David Choi; Seung-Ok Lim

2009-01-01

351

High Field Solenoid Magnets for Muon Cooling  

Microsoft Academic Search

Magnets made with high-temperature superconducting (HTS) coils operating at low temperatures have the potential to produce extremely high fields for use in accelerators and beam lines. The specific application of interest that we are proposing is to use a very high field (of the order of 50 Tesla) solenoid to provide a very small beta region for the final stages

S. A. Kahn; M. Alsharo; P. Hanlet; R. P. Johnson; M. Kuchnir; D. Newsham; R. C. Gupta; R. B. Palmer; E. Willen

352

Particle Acceleration in Stressed Coronal Magnetic Fields  

Microsoft Academic Search

This Letter presents an analysis of particle acceleration in a model of the complex magnetic field environment in the flaring solar corona. A slender flux tube, initially in hydrodynamic equilibrium, is stressed by random photospheric motions. A three-dimensional MHD code is used to follow the stochastic development of transient current sheets. These processes generate a highly fragmented electric field, through

R. Turkmani; L. Vlahos; K. Galsgaard; P. J. Cargill; H. Isliker

2005-01-01

353

Plasma Acceleration by Using Rotating Magnetic Field  

Microsoft Academic Search

Novel plasma acceleration method using transverse rotating magnetic field (RMF) was proposed and investigated using small pre-experimental setup. Interaction between the steady azimuthal current driven by the RMF and the radial bias field will generate axial electromagnetic force, which is expected to provide effective plasma acceletation. Plasma with density of ne > 3 × 1018[m-3] generated by the RMF was

Michiaki Inomoto

2008-01-01

354

The remanent magnetic field of the moon  

Microsoft Academic Search

Measurements of the moon's remanent magnetic field near the Apollo landing sites and from lunar orbit with the Apollo subsatellites are reviewed. Contour maps are presented for the intensity of the radial, eastward, and northward components of the remanent field as measured with Apollo subsatellite magnetometers at altitudes of 10 to 170 km. Attempts to fit the subsatellite measurements to

P. J. Coleman Jr.; C. T. Russell

1977-01-01

355

Passive magnetic shielding in static gradient fields  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

356

DC-magnetic field vector measurement  

NASA Technical Reports Server (NTRS)

A magnetometer experiment was designed to determine the local magnetic field by measuring the total of the Earth's magnetic field and that of an unknown spacecraft. The measured field vector components are available to all onboard experiments via the Spacelab command and data management system. The experiment consists of two parts, an electronic box and the magnetic field sensor. The sensor includes three independent measuring flux-gate magnetometers, each measuring one component. The physical background is the nonlinearity of the B-H curve of a ferrite material. Two coils wound around a ferrite rod are necessary. One of them, a tank coil, pumps the ferrite rod at approximately 20 kilohertz. As a consequence of the nonlinearity, many harmonics can be produced. The second coil (i.e., the detection coil) resonates to the first harmonic. If an unknown dc or low-frequency magnetic field exists, the amplitude of the first harmonic is a measure for the unknown magnetic field. The voltages detected by the sensors are to be digitized and transferred to the command and data management system.

Schmidt, R.

1981-01-01

357

DC-magnetic field vector measurement  

NASA Astrophysics Data System (ADS)

A magnetometer experiment was designed to determine the local magnetic field by measuring the total of the Earth's magnetic field and that of an unknown spacecraft. The measured field vector components are available to all onboard experiments via the Spacelab command and data management system. The experiment consists of two parts, an electronic box and the magnetic field sensor. The sensor includes three independent measuring flux-gate magnetometers, each measuring one component. The physical background is the nonlinearity of the B-H curve of a ferrite material. Two coils wound around a ferrite rod are necessary. One of them, a tank coil, pumps the ferrite rod at approximately 20 kilohertz. As a consequence of the nonlinearity, many harmonics can be produced. The second coil (i.e., the detection coil) resonates to the first harmonic. If an unknown dc or low-frequency magnetic field exists, the amplitude of the first harmonic is a measure for the unknown magnetic field. The voltages detected by the sensors are to be digitized and transferred to the command and data management system.

Schmidt, R.

1981-11-01

358

Evaluating Mean Magnetic Field in Flare Loops  

NASA Astrophysics Data System (ADS)

We apply a new method to measure the mean magnetic field in flare loops by analyzing multiple-wavelength observations of a two-ribbon flare. The flare exhibits apparent expansion motion of the ribbons in the lower-atmosphere and rising motion of the top of newly formed flare loops observed in X-rays. These apparent motion patterns are signatures of progressive magnetic reconnection proceeding in a macroscopically organized manner, which may be approximated by a 2D model. Therefore, the reconnection rate is expressed in terms of the reconnection electric field E. As the reconnection flux along the newly formed flare loop is conserved, the relation holds that, when averaged over time, E = VrBr = VtBt, where Vr and Br refer to the ribbon expansion speed and magnetic field swept by the ribbons, and Vt and Bt denote the apparent rising speed of the X-ray source and mean magnetic field at the loop top. By directly measuring Vr, Br, and Vt, we find Bt to be 120 and 60 G, respectively, during two emission peaks 5 min apart in the impulsive phase. An estimate of magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding B = 250, 120 G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately weighted value of magnetic field from the loop top to the loop leg. Therefore, the two methods to evaluate magnetic field in flaring loops produce fully consistent results, which provides evidence that parameters of reconnection rate derived from ribbon motions are quantitatively valid. This work is supported by NSF grant and by NSF grant ATM-0748428 and NASA grant NNX08AE44G to Montana State University and NSF grants AST-0607544 and ATM-0707319 and NASA grant NNG06GJ40G to New Jersey Institute of Technology.

Qiu, Jiong; Gary, D. E.; Fleishman, G. D.

2009-05-01

359

Magnetic edge states in graphene in nonuniform magnetic fields  

Microsoft Academic Search

We theoretically study the electronic properties of a graphene sheet on the xy plane in a spatially nonuniform magnetic field, B=B0z in one domain and B=B1z in the other domain, in the quantum Hall regime, and in the low-energy limit. We find that the magnetic edge states of the Dirac fermions, formed along the boundary between the two domains, have

H.-S. Sim

2008-01-01

360

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

Microsoft Academic Search

Spin ice in a magnetic field in the [111] direction displays two\\u000amagnetization plateaux, one at saturation and an intermediate one with finite\\u000aentropy. We study the crossovers between the different regimes from a point of\\u000aview of (entropically) interacting defects. We develop an analytical theory for\\u000athe nearest-neighbor spin ice model, which covers most of the magnetization\\u000acurve. We

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

2004-01-01

361

Hyperon bulk viscosity in strong magnetic fields  

SciTech Connect

We study the bulk viscosity of neutron star matter including {lambda} hyperons in the presence of quantizing magnetic fields. Relaxation time and bulk viscosity due to both the nonleptonic weak process involving {lambda} hyperons and direct Urca processes are calculated here. In the presence of a strong magnetic field of 10{sup 17} G, the hyperon bulk viscosity coefficient is reduced, whereas bulk viscosity coefficients due to direct Urca processes are enhanced compared with their field free cases when many Landau levels are populated by protons, electrons, and muons.

Sinha, Monika; Bandyopadhyay, Debades [Theory Division and Centre for Astroparticle Physics, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India)

2009-06-15

362

Opening the cusp. [using magnetic field topology  

NASA Technical Reports Server (NTRS)

This paper discusses the magnetic field topology (determined by the superposition of dipole, image, and uniform fields) for mapping the cusp to the ionosphere. The model results are compared to both new and published observations and are then used to map the footprint of a flux transfer event caused by a time variation in the merging rate. It is shown that the cusp geometry distorts the field lines mapped from the magnetopause to yield footprints with dawn and dusk protrusions into the region of closed magnetic flux.

Crooker, N. U.; Toffoletto, F. R.; Gussenhoven, M. S.

1991-01-01

363

Estimate of the primordial magnetic field helicity.  

PubMed

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

Vachaspati, T

2001-12-17

364

Plasma heating in a variable magnetic field  

SciTech Connect

The problem of particle acceleration in a periodically variable magnetic field that either takes a zero value or passes through zero is considered. It is shown that, each time the field [0]passes through zero, the particle energy increases abruptly. This process can be regarded as heating in the course of which plasma particles acquire significant energy within one field period. This mechanism of plasma heating takes place in the absence of collisions between plasma particles and is analogous to the mechanism of magnetic pumping in collisional plasma considered by Alfven.

Kichigin, G. N., E-mail: king@iszf.irk.ru [Russian Academy of Sciences, Institute of Solar-Terrestrial Physics (Russian Federation)

2013-05-15

365

Compute Values of Earth's Magnetic Field  

NSDL National Science Digital Library

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

366

Trajectories in Electric and Magnetic Fields Model  

NSDL National Science Digital Library

The Trajectories in Electric and Magnetic Fields model computes a family of trajectories of charges emitted from a point source isotropically and with the same energy. These trajectories create focal points and caustic surfaces meeting the symmetry line in conical cusps. The simulation enables users to study these trajectories in both crossed and parallel magnetic fields. The user can vary the initial particle velocity and the field strengths. The Trajectories in Electric and Magnetic Fields model was developed using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. 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.

Christian, Wolfgang

2012-10-25

367

Measuring vector magnetic fields in solar prominences  

NASA Astrophysics Data System (ADS)

We present spectropolarimetric observations in the He I 1083.0 nm multiplet of a quiescent, hedgerow solar prominence. The data were taken with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife; Canary Islands; Spain). The observed He I circular and linear polarization signals are dominated by the Zeeman effect and by atomic level polarization and the Hanle effect, respectively. These observables are sensitive to the strength and orientation of the magnetic field vector at each spatial point of the field of view. We determine the magnetic field vector of the prominence by applying the HAZEL inversion code to the observed Stokes profiles. We briefly discuss the retrieved magnetic field vector configuration.

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

2013-05-01

368

Intermittent character of interplanetary magnetic field fluctuations  

SciTech Connect

Interplanetary magnetic field magnitude fluctuations are notoriously more intermittent than velocity fluctuations in both fast and slow wind. This behavior has been interpreted in terms of the anomalous scaling observed in passive scalars in fully developed hydrodynamic turbulence. In this paper, the strong intermittent nature of the interplanetary magnetic field is briefly discussed comparing results performed during different phases of the solar cycle. The scaling properties of the interplanetary magnetic field magnitude show solar cycle variation that can be distinguished in the scaling exponents revealed by structure functions. The scaling exponents observed around the solar maximum coincide, within the errors, to those measured for passive scalars in hydrodynamic turbulence. However, it is also found that the values are not universal in the sense that the solar cycle variation may be reflected in dependence on the structure of the velocity field.

Bruno, Roberto; Carbone, Vincenzo; Chapman, Sandra; Hnat, Bogdan; Noullez, Alain; Sorriso-Valvo, Luca [IFSI/INAF, via Fosso del Cavaliere, I-00133 Rome (Italy); Dipartimento di Fisica, Universita della Calabria, and CNISM, Unita di Cosenza, Arcavacata di Rende I-87036 (Italy); Centre for Fusion, Space and Astrophysics, University of Warwick, Warwick CV4 7AL (United Kingdom); Observatoire de la Cote d'Azur, Boulevard de l'Observatoire, F-06304 Nice (France); LICRYL, INFM/CNR, I-87036 Arcavacata di Rende (Italy)

2007-03-15

369

Venus Deep Nightside Magnetic Fields Revisited  

NASA Astrophysics Data System (ADS)

We reexamined the near-Venus deep nightside magnetic fields observed by the Pioneer Venus Orbiter(PVO) over two decades ago. This analysis was in part inspired by recent discussions of the possibilities of identifying a weak planetary dynamo or remanent magnetic field, and in part by the availability of numerical simulations of weak field plasma interactions using the BATS-R-US MHD code. The data were first scrutinized for statistically significant regions of radial field in the near-midnight low altitude wake from the prime mission periapsis of ~150km up to about 450 km. Radial field 'maps' were constructed for a range of altitudes in both solar wind interaction and planetary geographical coordinate systems. The results suggested the presence of weak radial fields above ~250km that show a persistent North-South sign bias. This behavior is not seen at the lowest altitudes probed, and is present regardless of the interplanetary magnetic field sector. The MHD simulations provided basic pictures of what might be expected for a hypothetical planet with a weak but still detectable dipole field that is comparable to the solar wind interaction-related draped interplanetary field. These show similar tendencies, illustrating that models are essential to the interpretation of potential weak intrinsic field signatures at planets such as Venus. Further modeling specific to Venus is needed to make further progress.

Villarreal, M. N.; Luhmann, J. G.; Ma, Y.; Russell, C. T.; Wei, H.; Zhang, T.

2011-12-01

370

Magnetic nanoparticles for applications in oscillating magnetic field  

SciTech Connect

Enzymatic and thermochemical catalysis are both important industrial processes. However, the thermal requirements for each process often render them mutually exclusive: thermochemical catalysis requires high temperature that denatures enzymes. One of the long-term goals of this project is to design a thermocatalytic system that could be used with enzymatic systems in situ to catalyze reaction sequences in one pot; this system would be useful for numerous applications e.g. conversion of biomass to biofuel and other commodity products. The desired thermocatalytic system would need to supply enough thermal energy to catalyze thermochemical reactions, while keeping the enzymes from high temperature denaturation. Magnetic nanoparticles are known to generate heat in an oscillating magnetic field through mechanisms including hysteresis and relaxational losses. We envisioned using these magnetic nanoparticles as the local heat source embedded in sub-micron size mesoporous support to spatially separate the particles from the enzymes. In this study, we set out to find the magnetic materials and instrumental conditions that are sufficient for this purpose. Magnetite was chosen as the first model magnetic material in this study because of its high magnetization values, synthetic control over particle size, shape, functionalization and proven biocompatibility. Our experimental designs were guided by a series of theoretical calculations, which provided clues to the effects of particle size, size distribution, magnetic field, frequency and reaction medium. Materials of theoretically optimal size were synthesized, functionalized, and their effects in the oscillating magnetic field were subsequently investigated. Under our conditions, the materials that clustered e.g. silica-coated and PNIPAM-coated iron oxides exhibited the highest heat generation, while iron oxides embedded in MSNs and mesoporous iron oxides exhibited the least bulk heating. It is worth noting that the specific loss power of PNIPAM-coated Fe{sub 3}O{sub 4} was peculiarly high, and the heat loss mechanism of this material remains to be elucidated. Since thermocatalysis is a long-term goal of this project, we also investigated the effects of the oscillating magnetic field system for the synthesis of 7-hydroxycoumarin-3-carboxylic acid. Application of an oscillating magnetic field in the presence of magnetic particles with high thermal response was found to effectively increase the reaction rate of the uncatalyzed synthesis of the coumarin derivative compared to the room temperature control.

Peeraphatdit, Chorthip

2010-12-15

371

Whistler modes with wave magnetic fields exceeding the ambient field.  

PubMed

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background. PMID:16606272

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

2006-03-10

372

Whistler Modes with Wave Magnetic Fields Exceeding the Ambient Field  

SciTech Connect

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background.

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

2006-03-10

373

Atlas of Photospheric Magnetic Field Observations and Computed Coronal Magnetic Fields. 1976-1985.  

National Technical Information Service (NTIS)

Daily magnetogram observations of the large scale photospheric magnetic field have been made. These measurements provide a homogeneous record of the changing solar field through most of Solar Cycle 21. Using the photospheric data, the configuration of the...

J. T. Hoeksema P. H. Scherrer

1986-01-01

374

Electric/magnetic field sensor  

DOEpatents

A UNLV novel electric/magnetic dot sensor includes a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conductor seamlessly secured to a second conductor within a second sheath; and the first sheath and the second sheath positioned adjacent each other. The UNLV novel sensor can be made by removing outer layers in a segment of coaxial cable, leaving a continuous link of essentially uncovered conductor between two coaxial cable legs.

Schill, Jr., Robert A. (Henderson, NV); Popek, Marc [Las Vegas, NV

2009-01-27

375

Coronal magnetic fields produced by photospheric shear  

SciTech Connect

The magneto-frictional method for computing force-free fields examines the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. The energy of the sheared field can be arbitrarily large compared with the potential field. It is possible to fit the magnetic energy, as a function of shear amplitude, by a simple functional form. The fit parameters depend only on the distribution of normal field in the photosphere and the form of the shearing displacement. The energy is relatively more enhanced if the shear occurs: (1) where the normal field is strongest; (2) in the inner region of the dipole, near the axis; or (3) over a large fraction of the dipole area.

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

1988-04-01

376

Coronal magnetic fields produced by photospheric shear  

SciTech Connect

The magnetofrictional method for computing force-free fields is used to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It is found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear amplitude, by a simple functional form. The fit parameters depend only on the distribution of normal field in the photosphere and the form of the shearing displacement. They show that the energy is relatively more enhanced if the shear occurs: (1) where the normal field is strongest; and/or (2) in the inner region of the dipole, near the axis; and/or (3) over a large fraction of the dipole area. 22 references.

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

1988-12-01

377

Coronal magnetic fields produced by photospheric shear  

NASA Technical Reports Server (NTRS)

The magnetofrictional method for computing force-free fields is used to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It is found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear amplitude, by a simple functional form. The fit parameters depend only on the distribution of normal field in the photosphere and the form of the shearing displacement. They show that the energy is relatively more enhanced if the shear occurs: (1) where the normal field is strongest; and/or (2) in the inner region of the dipole, near the axis; and/or (3) over a large fraction of the dipole area.

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

1988-01-01

378

Recent Insights into Saturn's Intrinsic Magnetic Field  

NASA Astrophysics Data System (ADS)

The arrival of the Cassini spacecraft in mid-2004 initiated a new era of exploration of Saturn's magnetic field. Based on the Cassini magnetometer measurements, several distinct features of the intrinsic magnetic field of Saturn have been discovered recently. 1) The field is extremely axisymmetry: no unambiguous non-axisymmetric magnetic moment can be detected with an upper limit on the dipole tilt of 0.06 degrees; 2) no secular variation is detected when compared to the field measured by Pioneer-Voyager 30 years ago; 3) degree 4 and 5 axisymmetric moments are identified for the first time; 4) the power spectrum of the magnetic field has a zig-zag shape up to degree 5 with pronounced odd degree moments whose powers become comparable when downward continued to 0.4 Saturn radii; 5) the magnetic field inside Saturn is strongly concentrated near the spin-poles, in contrast to the well-defined polar field minina observed at the surface of the Earth's core and in geodynamo models. What structure and dynamics inside this planet produce these observed features? The observed extreme axisymmetry is widely regarded as resulting from the skin effect of an overlying thin stably-stratified conducting layer. However, extreme axisymmetric field can also directly be reproduced by the interior dynamo process. Furthermore, state-of-the-art calculations of the equation of the state (EOS) of hydrogen-helium mixtures predict helium immiscibility throughout a significant proportion of Saturn, which contradicts the thin stable layer picture. We will discuss three different possible dynamos which could reproduce the magnetic field observations. To distinguish which model is operating require deeper understanding of the properties of the interior of Saturn. Based on a series of numerical dynamo simulations, we suggest that a rocky core smaller than previous estimates inside this planet combined with modestly higher heat flow at high latitude on the dynamo outer boundary can reproduce the observed poleward concentration of the magnetic field. Another possibility is that the Saturnian dynamo is a thin shell dynamo with stably stratified conducting interior. The thin shell dynamo region is the helium rain forming layer, while the stably stratified interior is the helium evaporating layer. This interior structure is consistent with the most recent hydrogen-helium EOS calculations. A mechanically driven spherical Couette dynamo could be another alternative which shows intriguingly similar magnetic field properties to those observed at Saturn.

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

2012-12-01

379

BEC manipulation with fictitious magnetic fields  

NASA Astrophysics Data System (ADS)

The interaction of Bose-Einstein condensate (BEC) atoms with counterpropagating laser beams can often be represented by fictitious magnetic fields [1]. These fictitious fields can be combined with ordinary magnetic fields to produce total fields whose amplitudes vary in space on the scale of the laser wavelength. When the strengths of such magnetic fields are positioned in the neighborhood of a Feshbach resonance, it can produce a spatial variation of the binary scattering length of the condensate atoms. We have studied how these fields can be used to engineer the shape and behavior of BEC's for typical experimental arrangements. We present results for ^87Rb condensate shapes for BEC that can be formed when condensates are formed in the presence of spatially varying scattering lengths as well as the effects of turning on and off the fictitious magnetic fields in the presence of expanding condensates. All of the behaviors presented represent solutions of the time--independent and time--dependent Gross--Pitaevskii (GP) equation. Finally we comment briefly on cases where the GP equation breaks down.[4pt] [1] I. Deutsch and P. Jessen, 57, 1972 (1998).

Heward, Jeffrey; Edwards, Mark; Clark, Charles W.

2010-03-01

380

Three-dimensional magnetic-field sensors  

Microsoft Academic Search

Devices sensitive to all three components of a magnetic-field vector are presented. The sensitivity to two field components in the plane of the chip is achieved by merging two one-dimensional vertical magnetotransistors positioned at a 90-deg angle to each other. An additional surface-collector pair makes this device also sensitive to the last field component, which is perpendicular to the plane

Srdjan Kordic; Peter J. A. Munter

1988-01-01

381

The Magnetic Field Inside the Sun  

NASA Astrophysics Data System (ADS)

Duvall, Harvey and Pomerantz (1986) reported the existence of a "structural asymmetry" inside the Sun. The authors show here that this asymmetry is not a consequence of the Sun's rotation. They attribute the asymmetry, rather, to a toroidal magnetic field inside the Sun. Consistency requires a field of about one megagauss located in the lower part of the convection zone. Accounting for such a field would wreak havoc on our understanding of the solar dynamo and convection.

Dziembowski, W.; Goode, P. R.

382

Magnetic Field Response Measurement Acquisition System  

NASA Technical Reports Server (NTRS)

This paper presents a measurement acquisition method that alleviates many shortcomings of traditional measurement systems. The shortcomings are a finite number of measurement channels, weight penalty associated with measurements, electrical arcing, wire degradations due to wear or chemical decay and the logistics needed to add new sensors. Wire degradation has resulted in aircraft fatalities and critical space launches being delayed. The key to this method is the use of sensors designed as passive inductor-capacitor circuits that produce magnetic field responses. The response attributes correspond to states of physical properties for which the sensors measure. Power is wirelessly provided to the sensing element by using Faraday induction. A radio frequency antenna produces a time-varying magnetic field used to power the sensor and receive the magnetic field response of the sensor. An interrogation system for discerning changes in the sensor response frequency, resistance and amplitude has been developed and is presented herein. Multiple sensors can be interrogated using this method. The method eliminates the need for a data acquisition channel dedicated to each sensor. The method does not require the sensors to be near the acquisition hardware. Methods of developing magnetic field response sensors and the influence of key parameters on measurement acquisition are discussed. Examples of magnetic field response sensors and the respective measurement characterizations are presented. Implementation of this method on an aerospace system is discussed.

Woodard, Stanley E.; Taylor,Bryant D.; Shams, Qamar A.; Fox, Robert L.

2007-01-01

383

Magnetic fields of the outer planets  

NASA Technical Reports Server (NTRS)

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

Connerney, J. E. P.

1993-01-01

384

Holographic ? mesons in an external magnetic field  

NASA Astrophysics Data System (ADS)

We study the ? meson in a uniform magnetic field eB using a holographic QCD-model, more specifically a D4/D8/overline{D8} brane setup in the confinement phase at zero temperature with two quenched flavours. The parameters of the model are fixed by matching to corresponding dual field theory parameters at zero magnetic field. We show that the up- and down-flavour branes respond differently to the presence of the magnetic field in the dual QCD-like theory, as expected because of the different electromagnetic charge carried by up- and down-quark. We discuss how to recover the Landau levels, indicating an instability of the QCD vacuum at eB=m_{?}^2 towards a phase where charged ? mesons are condensed, as predicted by Chernodub using effective QCD-models. We improve on these existing effective QCD-model analyses by also taking into account the chiral magnetic catalysis effect, which tells us that the constituent quark masses rise with eB. This turns out to increase the value of the critical magnetic field for the onset of ? meson condensation to eB? 1.1m_{?}^2? 0.67Ge{{V}^2} . We briefly discuss the influence of pions, which turn out to be irrelevant for the condensation in the approximation made.

Callebaut, N.; Dudal, D.; Verschelde, H.

2013-03-01

385

[Static magnetic fields and its biomedical effects].  

PubMed

Nowadays, health care products based on static magnetic fields (SMF) and merchandise of magnetic therapy are popular around the world. But the biomedical effects of SMF to animals or human beings remain a widely concerned controversy. In this paper, the recent researches in China and abroad about the biomedical effects of SMF were reviewed in three levels: the cellular, animal and human levels. Nevertheless, these data were not consistent with each other and even some contradicts others' researches. So, it is necessary to do more and further studies on SMF dosing regiman, sham control magnetic device and blinding procedures to obtain the optimal magnetic intensity, the desired therapeutic effects in practical cases and prepare for applying the SMF in biomedical fields more effectively in the future. PMID:23488161

Wu, Jiang; Hu, Lijiang; Fang, Zhicai; Chen, Huaiqing

2013-02-01

386

ESA's Magnetic Field Mission Swarm  

Microsoft Academic Search

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

R. Haagmans; Y. Menard; M. Kern; M. Drinkwater

2007-01-01

387

ESA's Magnetic Field Mission Swarm  

Microsoft Academic Search

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

R. Haagmans; M. Kern; G. Plank; Y. Menard

2008-01-01

388

The Cassini Magnetic Field Investigation  

Microsoft Academic Search

The dual technique magnetometer system onboard the Cassini orbiter is described. This instrument consists of vector helium and fluxgate magnetometers with the capability to operate the helium device in a scalar mode. This special mode is used near the planet in order to determine with very high accuracy the interior field of the planet. The orbital mission will lead to

M. K. Dougherty; S. Kellock; D. J. Southwood; A. Balogh; E. J. Smith; B. T. Tsurutani; B. Gerlach; K.-H. Glassmeier; F. Gleim; C. T. Russell; G. Erdos; F. M. Neubauer; S. W. H. Cowley

2004-01-01

389

Magnetic-field measurements using an integrated resonant magnetic-field sensor  

Microsoft Academic Search

The present paper introduces a magnetic-field sensor based on a resonating single-crystal silicon structure. The excitation of the resonator is achieved by the Lorentz force generated by a sinusoidal current flowing through a rectangular coil deposited on the surface of the structure. The amplitude of the vibration, which is proportional to the magnetic field, is detected by sensing capacitors. Because

Zs. Kádár; A. Bossche; P. M. Sarro; J. R. Mollinger

1998-01-01

390

Production of repeating pulsed high magnetic field  

Microsoft Academic Search

Pulsed high magnetic fields up to 20T with a duration of 1 ms are repeated 20 000 times with a duty cycle of 0.5 Hz. The magnet is a water cooled Bitter type composed of copper and FRP disks stacked in turn. This will be useful to increase the S\\/N ratio of physical experiments, expecially when used with other equipment

M. Motokawa; H. Nojiri; J. Ishihara; K. Ohnishi

1989-01-01

391

Low-magnetic field control of electromagnon  

Microsoft Academic Search

Since the 1960s, there has been intense debate concerning the presence of the spin excitation driven by the electric field of light E^phi in ferroelectric magnets. This is recently revived by the observation of the absorption peak structure around 3 meV in a ferroelectric magnet TbMnO3 [1]. As an origin of this excitation, the hybridized spin excitation with electric polarization

N. Kida; S. Ishiwata; Y. Taguchi; R. Shimano; T. Arima; Y. Tokura

2009-01-01

392

Magnetic-field enhancement in gold nanosandwiches  

Microsoft Academic Search

Using dispersive finite-difference time-domain (D-FDTD) simulations, we show that a pair of gold nanodisks stacked in a 'sandwich'-like (end-fire) configuration produces a large enhancement of the magnetic field when irradiated with a plane optical wave, if the distance between the nanodisks is optically small. The effect, which can be rationalized in terms of a magnetic dipole resonance, is due the

T. Pakizeh; M. S. Abrishamian; N. Granpayeh; A. Dmitriev; M. Käll

2006-01-01

393

Dynamo Activity In Imposed DC Magnetic Fields  

Microsoft Academic Search

A widely accepted mechanism for the spontaneous appearance of large-scale magnetic fields in magnetofluids is the turbulent inverse cascade of magnetic helicity. The evidence for the effect is largely computational, and has been acquired by using spectral-method codes and imposing three-dimensional (3D) rectangular periodic boundary conditions. We report here similar investigations of the phenomenon that result when a uniform external

D. C. Montgomery; W. H. Matthaeus; L. J. Milano; P. Dmitruk

2003-01-01

394

Magnetic Field Effects on Plasma Plumes  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

395

Magnetic Fields from QCD Phase Transitions  

NASA Astrophysics Data System (ADS)

We study the evolution of QCD phase transition-generated magnetic fields (MFs) in freely decaying MHD turbulence of the expanding universe. We consider an MF generation model that starts from basic non-perturbative QCD theory and predicts stochastic MFs with an amplitude of the order of 0.02 ?G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: a "weakly helical" turbulence regime, when magnetic helicity increases during decay, and "fully helical" turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective MF being 0.007 nG. We demonstrate that the considered model of magnetogenesis can provide the seed MF for galaxies and clusters.

Tevzadze, Alexander G.; Kisslinger, Leonard; Brandenburg, Axel; Kahniashvili, Tina

2012-11-01

396

SSC collider dipole magnets field angle data  

SciTech Connect

In the fabrication of both 40 and 50 mm collider dipole superconducting magnets, surveys of the direction of the magnetic field along their length have been taken. This data besides being used for certifying compliance with the specifications for the finished magnet, yields interesting information on the straightness and rigidity of the coil placement between some stages in their manufacture and testing. A discussion on the measuring equipment and procedures is given. All of the 40 mm magnets that were built or cryostat at Fermilab have at least one of these surveys, and a summary of the data on them is presented. Most of the 50 mm magnets built and cold tested at Fermilab have been surveyed before and after insertion in the cryostat and before and after being cold tested. A summary of this data is also presented.

Kuchnir, M.; Bleadon, M.; Schmidt, E.; Bossert, R.; Carson, J.; Delchamps, S.W.; Gourlay, S.; Hanft, R.; Koska, W.; Lamm, M.J.; Mazur, P.O.; Orris, D.; Ozelis, J.; Strait, J.; Wake, M. (Fermi National Accelerator Lab., Batavia, IL (United States)); DiMarco, J.; Devred, A.; Kuzminski, J.; Yu, Y.; Zheng, H. (Superconducting Super Collider Lab., Dallas, TX (United States)); Ogitsu, T. (Superconducting Super Collider

1992-09-01

397

A model of the magnetosheath magnetic field during magnetic clouds  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

398

Polymerization of biological molecules under high magnetic fields  

Microsoft Academic Search

The polymerization process of fibrin, one of the diamagnetic molecules in blood plasma, is carried out in a static high magnetic field up to 8 T. SEM images of the polymerized samples show a clear magnetic field effect, i.e. alignment of fibers along the field. Magnetic birefringence using pulsed high magnetic fields is also investigated.

A. Yamagishi; T. Takeuchi; M. Date; T. Higashi

1989-01-01

399

High magnetic field ohmically decoupled non-contact technology  

Microsoft Academic Search

Methods and apparatus are described for high magnetic field ohmically decoupled non-contact treatment of conductive materials in a high magnetic field. A method includes applying a high magnetic field to at least a portion of a conductive material; and applying an inductive magnetic field to at least a fraction of the conductive material to induce a surface current within the

John Wilgen; Roger Kisner; Gerard Ludtka; Gail Ludtka; Roger Jaramillo

2009-01-01

400

High magnetic field ohmically decoupled non-contact technology  

DOEpatents

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

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

2009-05-19

401

The symmetry properties of planetary magnetic fields  

NASA Technical Reports Server (NTRS)

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

Raedler, Karl-Heinz; Ness, Norman F.

1990-01-01

402

Observation of Magnetic Fields Generated by Tsunamis  

NASA Astrophysics Data System (ADS)

Tsunamis produce perturbations in the Earth's magnetic field by electromagnetic induction. Recent deployments of highly accurate magnetometers and the exceptionally deep solar minimum provided ideal conditions to observe these small signals from the tsunami resulting from the strong Chilean earthquake on 27 February 2010. Magnetic observatory measurements on Easter Island, 3500 kilometers west of the epicenter, show a periodic signal of 1 nanotesla, coincident in time with recordings from the local tide gauge. The detection of these magnetic signals represents a milestone in understanding tsunami-induced electromagnetic effects.

Manoj, Chandrasekharan; Maus, Stefan; Chulliat, Arnaud

2011-01-01

403

High-field superconducting accelerator magnets  

SciTech Connect

The next generation of accelerators for high-energy physics will require high-field, small-bore dipole magnets: in the region of 10 T and 40-mm diam. For such magnets, there is a great incentive to attain high overall current density through increasing the current density within the superconductor and minimizing the copper stabilizer. Both Nb-Ti operating at 1.8 K and Nb/sub 3/sn at 4.2 are candidate superconductors. Two programs in the US and one in Japan are directed toward the development of such magnets. The program at LBL is described below.

Taylor, C.; Meuser, R.; Caspi, S.; Gilbert, W.; Hassenzahl, W.; Peters, C.; Wolgast, R.

1982-05-01

404

Magnetic field draping about coronal mass ejecta  

SciTech Connect

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

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

1987-01-01

405

INTRINSIC BISPECTRA OF COSMIC MAGNETIC FIELDS  

SciTech Connect

Forthcoming data sets from the Planck experiment and others are in a position to probe the cosmic microwave background (CMB) non-Gaussianity with higher accuracy than has yet been possible, and potentially open a new window into the physics of the very early universe. However, a signal need not necessarily be inflationary in origin, and possible contaminants should be examined in detail. One such is provided by early universe magnetic fields, which can be produced by a variety of models including during an inflationary phase, at phase transitions, or seeded by cosmic defects. Should such fields have been extant in the early universe, they would provide a natural source of CMB non-Gaussianity. Knowledge of the CMB angular bispectrum requires the complete Fourier-space (or 'intrinsic') bispectrum. In this paper, I consider in detail the intrinsic bispectra of an early-universe magnetic field for a range of power-law magnetic spectra.

Brown, Iain A., E-mail: i.a.brown@astro.uio.no [Institute of Theoretical Astrophysics, University of Oslo, 0315 Oslo (Norway)

2011-06-01

406

Enhanced Cloud Disruption by Magnetic Field Interaction  

NASA Astrophysics Data System (ADS)

We present results from the first three-dimensional numerical simulations of moderately supersonic cloud motion through a tenuous, magnetized medium. We show that the interaction of the cloud with a magnetic field perpendicular to its motion has a great dynamical impact on the development of instabilities at the cloud surface. Even for initially spherical clouds, magnetic field lines become trapped in surface deformations and undergo stretching. The consequent field amplification that occurs there and, in particular, its variation across the cloud face then dramatically enhance the growth rate of Rayleigh-Taylor unstable modes, hastening the cloud disruption. Animations and color images from this work have been posted at http://www.msi.umn.edu/Projects/twj/mhd3d/.

Gregori, G.; Miniati, Francesco; Ryu, Dongsu; Jones, T. W.

1999-12-01

407

Bound states in a strong magnetic field  

SciTech Connect

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

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

2013-03-25

408

Validation of SWMF magnetic field and plasma  

NASA Astrophysics Data System (ADS)

The Space Weather Modeling Framework (SWMF), using the coupled BATSRUS model, the Rice Convection Model, and an ionosphere electrodynamics solver, is used to simulate 10 space weather events. The simulations are completed in near real time using a limited amount of computational resources. Satellite-specific magnetic field, plasma energy-density spectra, and integrated particle density and temperature are compared against in situ measurements to validate the coupled system. Results are examined both qualitatively and quantitatively to assess model performance. The results show that the system is adept at reproducing large-scale magnetic field variations and predicts plasma temperature and density at values near to the measured mean. Smaller-scale features, such as dipolarizations of the magnetic field at geosynchronous locations, are not reproduced well. Lack of cold particle sources in the inner magnetosphere causes the particle results to suffer. This work is part of a larger effort to thoroughly validate the SWMF.

Welling, D. T.; Ridley, A. J.

2010-03-01

409

Field Line Resonances of Hydromagnetic Alfven Waves in Dipole Magnetic Field.  

National Technical Information Service (NTIS)

Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic fi...

L. Chen S. C. Cowley

1989-01-01

410

A magnetically field-controllable phononic crystal  

NASA Astrophysics Data System (ADS)

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

Bayat, Alireza; Gordaninejad, Faramarz

2014-04-01

411

Equivalent source mapping of lunar magnetic field  

NASA Astrophysics Data System (ADS)

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

Toyoshima, M.; Shibuya, H.

2007-12-01

412

Holographic fermions 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 gague/gravity duality 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 nonmagnetic 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. Next, we compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. For dual fermions with a large charge, many different Fermi surfaces contribute and the Hall conductivity is quantized as expected for integer quantum Hall effect (QHE). At strong magnetic fields, as additional Fermi surfaces open up, new plateaus typical for the fractional QHE appear. The somewhat irregular pattern in the length of fractional QHE plateaus resembles the outcomes of experiments on thin graphite in a strong magnetic field. Finally, motivated by the absence of the sign problem in holography, we suggest a lattice approach to the AdS calculations of finite density systems.

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

2011-11-01

413

Magnetic translation algebra with or without magnetic field  

NASA Astrophysics Data System (ADS)

The magnetic translation algebra plays an important role in the quantum Hall effect. Murthy and Shankar have shown how to realize this algebra using fermionic bilinears defined on a two-dimensional square lattice. We show that, in any dimension d, it is always possible to close the magnetic translation algebra using fermionic bilinears, be it in the continuum or on the lattice. We also show that these generators are complete in even, but not odd, dimensions, in the sense that any fermionic Hamiltonian in even dimensions that conserves particle number can be represented in terms of the generators of this algebra, whether or not time-reversal symmetry is broken. As an example, we reproduce the f-sum rule of interacting electrons at vanishing magnetic field using this representation. We also show that interactions can significantly change the bare band width of lattice Hamiltonians when represented in terms of the generators of the magnetic translation algebra.

Mudry, Christopher; Chamon, Claudio

2013-03-01

414

Lunar magnetic permeability, magnetic fields, and electrical conductivity temperature  

NASA Technical Reports Server (NTRS)

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

Parkin, C. W.

1978-01-01

415

Broadband antenna systems for lightning magnetic fields  

NASA Technical Reports Server (NTRS)

Broadband magnetic antenna systems suitable for recording submicrosecond field changes are described, and typical data from distant lightning are presented. Two types of systems are described, one with a high-impedance antenna loop connected to the integrator by a twisted pair of coaxial cables and another with the antenna loop and twisted signal loops formed from a single piece of coaxial cable. Data for correlated magnetic and electric field waveforms from lightning at a distance of 50 to 100 km are presented and are shown to be almost identical.

Krider, E. P.; Noggle, R. C.

1975-01-01

416

Ultracold plasma dynamics in a magnetic field  

NASA Astrophysics Data System (ADS)

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

Zhang, Xianli

417

High-field magnetization of metallic glasses  

SciTech Connect

Magnetization measurements in fields to 20 T (16 MA/m) have been made at room temperature on as-cast samples of several compositions of metallic glasses, to see whether or not the results are consistent with neutron diffraction and Moessbauer measurements that show moment canting, or incomplete ferromagnetic alignment of moments, in these materials. The results can be interpreted with the ferromagnetic with wandering axis (FWA)'' model of Chudnofsky, but the data fit equally well to the spin-wave model used by Pauthenet to fit high-field magnetization data on crystalline ferromagnets.

Graham, C.D. Jr.; Gibbs, M.R.J. (Univ. of Bath (United Kingdom). School of Physics)

1993-11-01

418

Possible production mechanisms of lunar magnetic fields.  

NASA Technical Reports Server (NTRS)

Demonstration of the impossibility of the production of local surface magnetic fields on the moon by conduction currents in the lunar soil and in local lunar atmospheres by volcanic eruption. However, it is suggested that convection currents produced by the ionization (by radiation and/or by triboelectric effects) of volcanic-ash-particle flows may produce the local magnetic fields of about 1000 gamma that are believed to have existed on the moon about 3.5 x 10 to the 9th years ago. A simple electrogasdynamic model for such flows and experiments for further investigation of this hypothesis are discussed.

Cap, F. F.

1972-01-01

419

Oxford pulsed magnetic field facility  

NASA Astrophysics Data System (ADS)

We give here a description of the newly commissioned 60 tesla or more pulsed field facility constructed over the last three years. It comprises a 800 kJ 32 mF capacitor bank, a high current switch using either an ignitron or thyristor stack, and a crowbar circuit. The system is designed to be flexible enough to cope with a wide variety of coils allowing pulse lengths of up to 100 ms to be produced. The design philosophy, control, monitoring, data collection, and safety will be discussed.

Siertsema, W. John; Jones, Harry

1994-07-01

420

The Cassini Magnetic Field Investigation  

NASA Astrophysics Data System (ADS)

The dual technique magnetometer system onboard the Cassini orbiter is described. This instrument consists of vector helium and fluxgate magnetometers with the capability to operate the helium device in a scalar mode. This special mode is used near the planet in order to determine with very high accuracy the interior field of the planet. The orbital mission will lead to a detailed understanding of the Saturn/Titan system including measurements of the planetary magnetosphere, and the interactions of Saturn with the solar wind, of Titan with its environments, and of the icy satellites within the magnetosphere.

Dougherty, M. K.; Kellock, S.; Southwood, D. J.; Balogh, A.; Smith, E. J.; Tsurutani, B. T.; Gerlach, B.; Glassmeier, K.-H.; Gleim, F.; Russell, C. T.; Erdos, G.; Neubauer, F. M.; Cowley, S. W. H.

2004-09-01

421

Permanent Magnet Spiral Motor for Magnetic Gradient Energy Utilization: Axial Magnetic Field  

NASA Astrophysics Data System (ADS)

The Spiral Magnetic Motor, which can accelerate a magnetized rotor through 90% of its cycle with only permanent magnets, was an energy milestone for the 20th century patents by Kure Tekkosho in the 1970's. However, the Japanese company used old ferrite magnets which are relatively weak and an electrically-powered coil to jump start every cycle, which defeated the primary benefit of the permanent magnet motor design. The principle of applying an inhomogeneous, anisotropic magnetic field gradient force Fz = ? cos J dB/dz, with permanent magnets is well-known in physics, e.g., Stern-Gerlach experiment, which exploits the interaction of a magnetic moment with the aligned electron spins of magnetic domains. In this case, it is applied to dB/d? in polar coordinates, where the force F? depends equally on the magnetic moment, the cosine of the angle between the magnetic moment and the field gradient. The radial magnetic field increases in strength (in the attractive mode) or decreases in strength (in the repulsive mode) as the rotor turns through one complete cycle. An electromagnetic pulsed switching has been historically used to help the rotor traverse the gap (detent) between the end of the magnetic stator arc and the beginning (Kure Tekko, 1980). However, alternative magnetic pulse and switching designs have been developed, as well as strategic eddy current creation. This work focuses on the switching mechanism, novel magnetic pulse methods and advantageous angular momentum improvements. For example, a collaborative effort has begun with Toshiyuki Ueno (University of Tokyo) who has invented an extremely low power, combination magnetostrictive-piezoelectric (MS-PZT) device for generating low frequency magnetic fields and consumes ``zero power'' for static magnetic field production (Ueno, 2004 and 2007a). Utilizing a pickup coil such as an ultra-miniature millihenry inductor with a piezoelectric actuator or simply Wiegand wire geometry, it is shown that the necessary power for magnetic field switching device can be achieved in order to deflect the rotor magnet in transit. The Wiegand effect itself (bistable FeCoV wire called ``Vicalloy'') invented by John Wiegand (Switchable Magnetic Device, US Patent No.4,247,601), utilizing Barkhausen jumps of magnetic domains, is also applied for a similar achievement (Dilatush, 1977). Conventional approaches for spiral magnetic gradient force production have not been adequate for magnetostatic motors to perform useful work. It is proposed that integrating a magnetic force control device with a spiral stator inhomogeneous axial magnetic field motor is a viable approach to add a sufficient nonlinear boundary shift to apply the angular momentum and potential energy gained in 315 degrees of the motor cycle.

Valone, Thomas F.

2010-01-01

422

Magnetic fields of HgMn stars?  

NASA Astrophysics Data System (ADS)

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15 G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims: We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system AR Aur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. Methods: We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. Results: Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars as well as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars. Based on observations obtained at the European Southern Observatory (ESO programmes 076.D-0169(A), 076.D-0172(A), 084.D-0338(A), 085.D-0296(A), 085.D-0296(B), 087.D-0049(A), 088.D-0284(A)), SOFIN observations at the 2.56 m Nordic Optical Telescope on La Palma, and observations obtained with the CORALIE Echelle Spectrograph on the 1.2 m Euler Swiss telescope on La Silla, Chile.Tables 2-7, 9, 10 are only available in electronic form at http://www.aanda.org

Hubrig, S.; González, J. F.; Ilyin, I.; Korhonen, H.; Schöller, M.; Savanov, I.; Arlt, R.; Castelli, F.; Lo Curto, G.; Briquet, M.; Dall, T. H.

2012-11-01

423

Coronal and interplanetary magnetic field models  

NASA Astrophysics Data System (ADS)

We provide an historical perspective of coronal and interplanetary field models. The structure of the interplanetary medium is controlled by the coronal magnetic field from which the solar wind emanates. This field has been described with ``Source Surface'' (SS) and ``Heliospheric Current Sheet'' (HCS) models. The ``Source Surface'' model was the first to open the solar field into interplanetary space using volumetric coronal currents, which were a ``source'' for the IMF. The Heliospheric Current Sheet (HCS) model provided a more physically realistic solution. The field structure was primarily a dipole, however, without regard to sign, the shape appeared to be a monopole pattern (uniform field stress). Ulysses has observed this behavior. Recently, Sheeley and Wang have utilized the HCS field model to calculate solar wind structures fairly accurately. Fisk, Schwadron, and Zurbuchen have investigated small differences from the SS model. These differences allow field line motions reminiscent of a ``timeline'' or moving ``streakline'' in a flow field, similar to the smoke pattern generated by a skywriting plane. Differences exist in the magnetic field geometry, from the Parker ``garden hose'' model affecting both the ``winding angle'' as well as the amount of latitudinal ``wandering.''

Schatten, Kenneth H.

1999-06-01

424

Proton Deflectometry of Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

Highly penetrating proton beams, generated by irradiating a thin foil target with picosecond laser pulses at intensities up to 10^20 Wcm-2 have been used to detect electric and magnetic fields in laser-produced plasmas [1]. More recently experiments to characterize the transient electric and magnetic fields using mono-energetic protons from imploding D^3He-filled capsules have been performed [2]. In the deflectometry technique a beam of protons is passed through a mesh to generate a grid of proton beamlets. This proton beam is passed through the laser-generated plasma and the grid deflection can be measured. We report on LASNEX calculations of such laser-produced plasmas, which predict electric fields of the order of 10^9V/m and 1MG magnetic fields. We will show Lsp calculations of proton transport through such electric and magnetic fields and compare them to the experimental data. [1] A. J. Mackinnon, et al., Rev. Sci. Instrum. 75, 3531 (2004). [2] C. K. Li, et al., Bull. Am. Phys. Soc 50, 266 (2005). This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. The experimental work was performed at the LLE National User's Facility under grant number DE-SC52-04NA25436.

Town, R. P. J.; Edwards, M. J.; Landen, O. L.; MacKinnon, A. J.; Patel, P. K.; Tabak, M.; Li, C. K.; Petrasso, R. D.; Seguin, F. H.

2006-10-01

425

The National High Magnetic Field Laboratory  

NASA Astrophysics Data System (ADS)

The National High Magnetic Field Laboratory (NHMFL) is a collaboration between Florida State University, the University of Florida, and the Los Alamos National Laboratory. The DC Field Facilities are located at the main campus for the NHMFL in Tallahassee, Florida and are described in this paper. The DC Field Facility has a variety of resistive and superconducting magnets. The DC Field Facility infrastructure, the most powerful in the world, is able to provide 57 MW of continuous low noise DC power. Constant magnetic fields of up to 45 tesla in a 32 mm bore and 20 tesla in 195 mm bore are available at no charge to the user community. The users of the facility are selected by a peer reviewed process. Roughly 400 research groups visit the lab to conduct experiments each year. Experimental capabilities provided by the NHMFL are magneto-optics, millimeter wave spectroscopy, magnetization, dilatometry, specific heat, electrical transport, ultrasound, low to medium resolution NMR, EMR, and materials processing. Measurements of properties can be made on samples at temperatures from 20 mK to 1000 K, pressures from ambient to 10 GPa, orientation and currents from 1 pA to 10 kA.

Hannahs, S. T.; Palm, E. C.

2010-04-01

426

Tracing the Magnetic Field in Orion A  

NASA Technical Reports Server (NTRS)

We use extensive 350 micron polarimetry and continuum maps obtained with Hertz and SHARC II along with HCN and HCO(sup +) spectroscopic data to trace the orientation of the magnetic field in the Orion A star-forming region. Using the polarimetry data, we find that the direction of the projection of the magnetic field in the plane of the sky relative to the orientation of the integral-shaped filament varies considerably as one moves from north to south. While in IRAS 05327-0457 and OMC-3 MMS 1-6 the projection of the field is primarily perpendicular to the filament it becomes better aligned with it at OMC-3 MMS 8-9 and well aligned with it at OMC-2 FIR 6. The OMC-2 FIR 4 cloud, located between the last two, is a peculiar object where we find almost no polarization. There is a relatively sharp boundary within its core where two adjacent regions exhibiting differing polarization angles merge. The projected angle of the field is more complicated in OMC-1 where it exhibits smooth variations in its orientation across the face of this massive complex. We also note that while the relative orientation of the projected angle of the magnetic field to the filament varies significantly in the OMC-3 and OMC-2 regions, its orientation relative to a fixed position on the sky shows much more stability. This suggests that, perhaps, the orientation of the field is relatively unaffected by the mass condensations present in these parts of the molecular cloud. By combining the polarimetry and spectroscopic data we were able to measure a set of average d u e s for the inclination angle of the magnetic field relative to the line of sight. We find that the field is oriented quite close to the plane of the sky in most places. More precisely, the inclination of the magnetic field is approx. = 73 deg around OMC-3 MMS 6, approx. = 74 deg at OMC-3 MMS 8-9, approx. = 80 deg at OMC-2 FIR 4, approx. = 65 deg in the northeastern part of OMC-1, and approx. = 49 deg in the Bas. The small difference in the inclination of the field between OMC-3 and OMC-2 seems to strengthen the idea that the orientation of the magnetic field is relatively unaffected by the agglomeration of matter located in these regions. We also present polarimetry data for the OMC-4 region located some 13 min. south of OMC-1.

Dowell, C. Darren; Hildebrand, Roger H.; Dotson, Jessie L.; Vaillancourt, John E.; Phillips, Thomas G.; Peng, Rui-Sheng; Bastien, Pierre

2003-01-01

427

Multi-coil magnetic field modeling.  

PubMed

The performance of multi-coil (MC) magnetic field modeling is compared to dedicated wire patterns for the generation of spherical harmonic (SH) shapes as these are the workhorse for spatial encoding and magnetic field homogenization in MR imaging and spectroscopy. To this end, an example 48 channel MC setup is analyzed and shown to be capable of generating all first through fourth order SH shapes over small and large regions-of-interest relevant for MR investigations. The MC efficiency for the generation of linear gradient fields shares the same order of magnitude with classic and state-of-the-art SH gradient coils. MC field modeling becomes progressively more efficient with the synthesis of more complex field shapes that require the combination of multiple SH terms. The possibility of a region-specific optimization of both magnetic field shapes and generation performance with the MC approach are discussed with emphasis on the possible trade-off between the field accuracy and generation efficiency. MC shimming has been shown previously to outperform current SH shimming. Along with the efficiency gains of MC shimming shown here, the MC concept has the potential to (1) replace conventional shim systems that are based on sets of dedicated SH coils and (2) allow optimal object-specific shim solutions similar to object-specific RF coils. PMID:24095841

Juchem, Christoph; Green, Dan; de Graaf, Robin A

2013-11-01

428

Magnetic field strength of active region filaments  

NASA Astrophysics Data System (ADS)

Aims: We study the vector magnetic field of a filament observed over a compact active region neutral line. Methods: Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 Å spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and PCA-based atomic polarization inversions. Results: The inferred magnetic field strengths in the filament are around 600-700 G by all these three methods. Longitudinal fields are found in the range of 100-200 G whereas the transverse components become dominant, with fields as high as 500-600 G. We find strong transverse fields near the neutral line also at photospheric levels. Conclusions: Our analysis indicates that strong (higher than 500 G, but below kG) transverse magnetic fields are present in active region filaments. This corresponds to the highest field strengths reliably measured in these structures. The profiles of the helium 10 830 Å lines observed in this active region filament are dominated by the Zeeman effect.

Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.; Manso Sainz, R.; Shimizu, T.

2009-07-01

429

Pulsar studies and magnetic fields in galaxies  

NASA Astrophysics Data System (ADS)

In recent years, I have mainly worked on the two research areas: pulsar polarization and magnetic fields in galaxies. Together with my cooperators, we have observed about 150 pulsars in total and will do another 100 in near future. We did systematical studies on circular polarization of pulsars and obtained several intriguing results. Using pulsars as probes, we detected the magnetic field reversals from spiral arm to arm in our Galaxy. We found that the B-field has a bi-symmetric structure in the disk. We also obtained the unique measurements of the vertical component of the B-field in the solar vicinity. From the anti-symmetric distribution of Galactic rotation measure sky, we identified the B-field structure produced by A0 dynamo in the Galactic halo or thick disk. The magnetic fields in the disk of our Galaxy and M31 were found to be very extended. The spiral B-field we detected from NGC 2997 suggests that there may be two kinds of dynamos operating in one galaxy.

Han, Jinlin

2001-06-01

430

Biomaterials and Magnetic fields for Cancer Therapy  

NASA Technical Reports Server (NTRS)

The field of biomaterials has emerged as an important topic in the purview of NASA s new vision of research activities in the Microgravity Research Division. Although this area has an extensive track record in the medical field as borne out by the routine use of polymeric sutures, implant devices, and prosthetics, novel applications such as tissue engineering, artificial heart valves and controlled drug delivery are beginning to be developed. Besides the medical field, biomaterials and bio-inspired technologies are finding use in a host of emerging interdisciplinary fields such as self-healing and self-assembling structures, biosensors, fuel systems etc. The field of magnetic fluid technology has several potential applications in medicine. One of the emerging fields is the area of controlled drug delivery, which has seen its evolution from the basic oral delivery system to pulmonary to transdermal to direct inoculations. In cancer treatment by chemotherapy for example, targeted and controlled drug delivery has received vast scrutiny and substantial research and development effort, due to the high potency of the drugs involved and the resulting requirement to keep the exposure of the drugs to surrounding healthy tissue to a minimum. The use of magnetic particles in conjunction with a static magnetic field allows smart targeting and retention of the particles at a desired site within the body with the material transport provided by blood perfusion. Once so located, the therapeutical aspect (radiation, chemotherapy, hyperthermia, etc.) of the treatment, now highly localized, can be implemented.

Ramachandran, Narayanan; Mazuruk, Konstanty

2003-01-01

431

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

Microsoft Academic Search

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

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

2009-01-01

432

Sensor for detecting changes in magnetic fields  

DOEpatents

A sensor is described for detecting changes in the magnetic field of the equilibrium-field coil of a Tokamak plasma device that comprises a pair of bifilar wires disposed circumferentially, one inside and one outside the equilibrium-field coil. Each is shorted at one end. The difference between the voltages detected at the other ends of the bifilar wires provides a measure of changing flux in the equilibrium-field coil. This difference can be used to detect faults in the coil in time to take action to protect the coil.

Praeg, W.F.

1980-02-26

433

Dispersion of Magnetic Fields in Molecular Clouds  

NASA Astrophysics Data System (ADS)

Chandrasekhar & Fermi (1953) used the dispersion of starlight polarization vectors about contours of Galactic latitude to determine the strength of the magnetic field in the arms of the Galaxy. The same technique, the Chandrasekhar Fermi (CF) method, has been applied to estimates of field strengths in the relatively dense medium of molecular clouds. The basis for deriving field strengths from dispersion measurements is the same for observations of Galactic arms or molecular clouds: in either case dispersion decreases as the field strengthens. But in the case of the Galactic arms, the dispersion is due to magnetohydrodynamic (MHD) waves; the displacements are perpendicular to the direction of propagation. In the case of turbulent dispersion in molecular clouds, there is no preferred direction. The turbulent component can be in any orientation and may have structure due to effects such as differential rotation, gravitational collapse, or expanding H II regions. Consequently, dispersion measured about mean fields, assumed straight, may be much larger than should be attributed to MHD waves or turbulence. Dispersion measured about model large-scale fields that give approximate fits to a polarization map will result in better estimates but still give inaccurate values of the turbulent component. Here we describe a method for determining magnetic field dispersion about local structured fields, without assuming any model for the large-scale field. To do this, we use the second-order structure function of the measured polarization vectors to separate the turbulent component of the dispersion from the large-scale field. Our study incorporates the effect on the measured dispersion of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam. Our method provides accurate, independent estimates of the turbulent to mean magnetic field strength ratio. We discuss applications to the molecular clouds Orion, M17, and DR21.

Vaillancourt, John E.; Hildebrand, R. H.; Houde, M.

2009-05-01

434

Dispersion of Magnetic Fields in Molecular Clouds  

NASA Astrophysics Data System (ADS)

Chandrasekhar & Fermi (1953) used the dispersion of starlight polarization vectors about contours of Galactic latitude to determine the strength of the magnetic field in the arms of the Galaxy. The same technique, the Chandrasekhar-Fermi (CF) method, has been applied to estimates of field strengths in the relatively dense medium of molecular clouds. The basis for deriving field strengths from dispersion measurements is the same for observations of Galactic arms or molecular clouds: in either case dispersion decreases as the field strengthens. But in the case of the Galactic arms, the dispersion is due to magnetohydrodynamic (MHD) waves; the displacements are perpendicular to the direction of propagation. In the case of turbulent dispersion in molecular clouds, there is no preferred direction. The turbulent component can be in any orientation and may have structure due to effects such as differential rotation, gravitational collapse, or expanding H II regions. Consequently, dispersion measured about mean fields, assumed straight, may be much larger than should be attributed to MHD waves or turbulence. Dispersion measured about model large-scale fields that give approximate fits to a polarization map will result in better estimates but still give inaccurate values of the turbulent component. Here we describe a method for determining magnetic field dispersion about local structured fields, without assuming any model for the large-scale field. To do this, we use the second-order structure function of the measured polarization vectors to separate the turbulent component of the dispersion from the large-scale field. Our study incorporates the effect on the measured dispersion of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam. Our method provides accurate, independent estimates of the turbulent to mean magnetic field strength ratio. We discuss applications to the molecular clouds Orion, M17, and DR21.

Vaillancourt, John E.; Houde, M.; Hildebrand, R. H.

2010-01-01

435

ANCHORING MAGNETIC FIELD IN TURBULENT MOLECULAR CLOUDS  

SciTech Connect

One of the key problems in star formation research is to determine the role of magnetic fields. Starting from the atomic intercloud medium which has density n {sub H} approx 1 cm{sup -3}, gas must accumulate from a volume several hundred pc across in order to form a typical molecular cloud. Star formation usually occurs in cloud cores, which have linear sizes below 1 pc and densities n {sub H2} > 10{sup 5} cm{sup -3}. With current technologies, it is hard to probe magnetic fields at scales lying between the accumulation length and the size of cloud cores, a range corresponds to many levels of turbulent eddy cascade, and many orders of magnitude of density amplification. For field directions detected from the two extremes, however, we show here that a significant correlation is found. Comparing this result with molecular cloud simulations, only the sub-Alfvenic cases result in field orientations consistent with our observations.

Li Huabai; Goodman, Alyssa [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Darren Dowell, C. [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, MS 320-47, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Hildebrand, Roger [Enrico Fermi Institute and Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Novak, Giles, E-mail: hli@cfa.harvard.ed [Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

2009-10-20

436

Low-magnetic field control of electromagnon  

NASA Astrophysics Data System (ADS)

Since the 1960s, there has been intense debate concerning the presence of the spin excitation driven by the electric field of light E^? in ferroelectric magnets. This is recently revived by the observation of the absorption peak structure around 3 meV in a ferroelectric magnet TbMnO3 [1]. As an origin of this excitation, the hybridized spin excitation with electric polarization (now called electromagnon) was considered [2]. However, this issue remains controversial by our THz spectroscopic studies on a family of RMnO3 [3] (R = Tb, Dy, and Gd0.7Tb0.3) in a variety of spin phases tuned by temperature and magnetic field. Here we report an optical investigation of the low-energy (2-10 meV) spin dynamics for other ferroelectric magnets, hexaferrite, by using THz time-domain spectroscopy. We find the signature of the genuine electromagnon at THz frequencies. As a manifestation of the strong magnetoelectric coupling inherent to the electromagnon, we demonstrate the low-magnetic field (˜ 100 Oe) control of the optical constants at THz frequencies. [1] A. Pimenov et al., Nat. Phys. 2, 97 (2006). [2] D. Senff et al., PRL 98, 137206 (2007). [3] N. Kida et al., PRB 78, 104414 (2008); Y. Takahashi et al., PRL 101, 187201 (2008); N. Kida et al., J. Phys. Soc. Jpn. Dec. issue (2008).

Kida, N.; Ishiwata, S.; Taguchi, Y.; Shimano, R.; Arima, T.; Tokura, Y.

2009-03-01

437

BEC manipulation with fictitious magnetic fields and Feshbach resonances  

Microsoft Academic Search

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

Jeffrey Heward; Mark Edwards; Charles W. Clark

2010-01-01

438

Studies of solar magnetic fields during the solar maximum year  

NASA Technical Reports Server (NTRS)

Observations and studies of solar magnetic fields that were carried out during the period of the solar maximum year (SMY) January 1980 to June 1981, are reviewed with the goal of providing a summary of what was learned about solar magnetic fields during the SMY. Such subjects as the relationship between solar magnetic fields and flares, the role of magnetic fields in the sunspot phenomenon, the magnetic-canopy structure overlying the supergranular network as well as the turbulent magnetic fields within the network, the fields within the polar crown prominences, and the solar magnetic cycle are addressed.

Hagyard, M. J.

1984-01-01

439

The ULF Magnetic Fields Generated by Thunderstorms  

NASA Astrophysics Data System (ADS)

It has long been known that thunderstorms produce strong electric field fluctuations in their immediate vicinity but it has been little recognized that these storms are also a source of strong ULF magnetic field fluctuations (ULF; frequencies less than 5 Hz). Some characteristics of the magnetic field fluctuations were documented for a thunderstorm occurring in 1990 [Fraser-Smith, Geophys. Res. Letts., 20, 467-470, 1993]. We now describe further measurements of these magnetic field changes for an additional intense thunderstorm that passed over the San Francisco Bay area on 8-9 September 1999. The thunderstorm is further characterized by measurements of its associated lightning by the National Lightning Detection Network (NLDN). As compared with the results reported for the 1990 thunderstorm, the new measurements were made by two separate and independently-operated measurement systems. In addition, they have greater time resolution and more components of the magnetic field changes are measured. These thunderstorm-related ULF magnetic field changes must extend up through the electromagnetic-phenomena-rich space between the thunderstorms and the ionosphere and they have the potential to generate both ULF electric currents and ULF hydromagnetic waves in the lower ionosphere. This latter possibility suggests, once again, that thunderstorms may be an important and little studied source of ULF energy in the magnetosphere. In this context, it is important to note that although thunderstorms tend to occur predominantly in the equatorial regions, there can be substantial activity at middle latitudes and even, on occasion, at higher latitudes. As a result, the thunderstorm-related ULF hydromagnetic waves can be injected into the magnetosphere over a broad range of geomagnetic latitudes and not just confined to low latitudes.

Fraser-Smith, A. C.; Kjono, S. N.

2013-12-01

440

Dynamic evolution of coronal magnetic fields  

NASA Technical Reports Server (NTRS)

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

Steinolfson, Richard S.

1986-01-01