Fast backprojection-based reconstruction of spectral-spatial EPR images from projections with the constant sweep of a magnetic field.

Science.gov (United States)

Komarov, Denis A; Hirata, Hiroshi

2017-08-01

In this paper, we introduce a procedure for the reconstruction of spectral-spatial EPR images using projections acquired with the constant sweep of a magnetic field. The application of a constant field-sweep and a predetermined data sampling rate simplifies the requirements for EPR imaging instrumentation and facilitates the backprojection-based reconstruction of spectral-spatial images. The proposed approach was applied to the reconstruction of a four-dimensional numerical phantom and to actual spectral-spatial EPR measurements. Image reconstruction using projections with a constant field-sweep was three times faster than the conventional approach with the application of a pseudo-angle and a scan range that depends on the applied field gradient. Spectral-spatial EPR imaging with a constant field-sweep for data acquisition only slightly reduces the signal-to-noise ratio or functional resolution of the resultant images and can be applied together with any common backprojection-based reconstruction algorithm. Copyright © 2017 Elsevier Inc. All rights reserved.

Effects of the pulse-driven magnetic field detuning on the calibration of coil constants while using noble gases

Directory of Open Access Journals (Sweden)

Jing Wang

2018-04-01

Full Text Available In the calibration of coil constants using the Free Induction Decay (FID signal of noble gases, we analyse the effects of the pulse-driven magnetic field detuning on the calibration results. This method is based on the inverse relation between the π/2 pulse duration and its amplitude. We confirmed that obtaining a precise frequency is a prerequisite for ensuring the accuracy of research using the initial amplitude of the FID signal. In this paper, the spin dynamics of noble gases and its time-domain solution under the driving pulse have been discussed with regard to different detuning ranges. Experimental results are in good agreement with our theoretical predictions, which indicate the correctness of our theoretical deduction. Therefore, the frequency of the pulse-driven magnetic field is an important factor to the calibration of coil constants, it should be determined with a high degree of accuracy.

Magnetic properties of HoVOΛ4 in high magnetic fields

International Nuclear Information System (INIS)

Andronenko, S.I.; Bazhan, A.N.; Ioffe, V.A.; Udalov, Yu.P.

1985-01-01

Values magnetization and susceptibility of HoVO 4 , Van Vleck paramagnetic are specified in the 4.2-40 K temperature range and magnetic fields up to 50 kOe. Magnetic properties of HoVO 4 are analyzed using a theoretical model in which the interaction of rare earth ions with the crystal- and magnetic fields is considered. A possibility of rare earth ion interaction with the Bsub(1g), Bsub(2g), Asub(1g) symmetry deformations is also considered. It is stated that magnetic properties of HoVO 4 are completely explained within the frames of the crystal field model; the rare earth ion interactions with deformations are insignificant. Anisotropy of magnetization in the (001) plane is determined by the crystal field B 4 4 , B 6 4 constants; the constants being shown to be positive

Exact Green's function method of solar force-free magnetic-field computations with constant alpha. I - Theory and basic test cases

Science.gov (United States)

Chiu, Y. T.; Hilton, H. H.

1977-01-01

Exact closed-form solutions to the solar force-free magnetic-field boundary-value problem are obtained for constant alpha in Cartesian geometry by a Green's function approach. The uniqueness of the physical problem is discussed. Application of the exact results to practical solar magnetic-field calculations is free of series truncation errors and is at least as economical as the approximate methods currently in use. Results of some test cases are presented.

Spin echoes of nuclear magnetization diffusing in a constant magnetic field gradient and in a restricted geometry

International Nuclear Information System (INIS)

Sen, P.N.; Andre, A.; Axelrod, S.

1999-01-01

We study the influence of restriction on Carr - Purcell - Meiboom - Gill spin echoes response of magnetization of spins diffusing in a bounded region in the presence of a constant magnetic field gradient. Depending on three main length scales: L S pore size, L G dephasing length and L D diffusion length during half-echo time, three main regimes of decay have been identified: free, localization and motionally averaging regime. In localization regime, the decay exponent depends on a fractional power (2/3) of the gradient, denoting a strong breakdown of the second cumulant or the Gaussian phase approximation (GPA). In the other two regimes, the exponent depends on the gradient squared, and the GPA holds. We find that the transition from the localization to the motionally averaging regime happens when the magnetic field gradients approach special values, corresponding to branch points of the eigenvalues. Transition from one regime to another as a function of echo number for a certain range of parameters is discussed. In this transition region, the signal shows large oscillations with echo number. For large n, asymptotic behavior sets in as a function of n for the decay exponent per echo. This is true for all values of the parameters L S , L G , and L D . copyright 1999 American Institute of Physics

Magnetic field measurements of JT-60SA CS model coil

Energy Technology Data Exchange (ETDEWEB)

Obana, Tetsuhiro, E-mail: obana.tetsuhiro@LHD.nifs.ac.jp [National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292 (Japan); Takahata, Kazuya; Hamaguchi, Shinji; Chikaraishi, Hirotaka; Mito, Toshiyuki; Imagawa, Shinsaku [National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292 (Japan); Kizu, Kaname; Murakami, Haruyuki; Natsume, Kyohei; Yoshida, Kiyoshi [Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki 311-0193 (Japan)

2015-01-15

Highlights: • Magnetic fields of the JT-60SA CS model coil were measured. • While the coil current was held constant at 20 kA, magnetic fields varied slightly with several different long time constants. • We investigated coils consisting of CIC conductors and having long time constants. - Abstract: In a cold test of the JT-60SA CS model coil, which has a quad-pancake configuration consisting of a Nb{sub 3}Sn cable-in-conduit (CIC) conductor, magnetic fields were measured using Hall sensors. For a holding coil current of 20 kA, measured magnetic fields varied slightly with long time constants in the range 17–571 s, which was much longer than the time constant derived from a measurement using a short straight sample. To validate the measurements, the magnetic fields of the model coil were calculated using a computational model representing the positions of Nb{sub 3}Sn strands inside the CIC conductor. The calculated results were in good agreement with the measurements. Consequently, the validity of the magnetic field measurements was confirmed. Next, we investigated other coils consisting of CIC conductors and having long time constants. The only commonality among the coils was the use of CIC conductors. At present, there is no obvious way to prevent generation of such magnetic-field variations with long time constants.

Constant Electric and Magnetic Fields Effect on the Structuring and Thermomechanical and Thermophysical Properties of Nanocomposites Formed from Pectin-Cu(2+)-Polyethyleneimine Interpolyelectrolyte-Metal Complexes.

Science.gov (United States)

Demchenko, V; Shtompel', V; Riabov, S; Lysenkov, E

2015-12-01

Applying wide-angle X-ray scattering method, thermomechanical analysis, and differential scanning calorimetry, the structural organization and properties of nanocomposites formed by chemical reduction of Сu(2+) cations in the interpolyelectrolyte-metal complex (pectin-Cu(2+)-polyethyleneimine) under the influence of a constant magnetic and electric fields have been studied. It has been found that the chemical reduction of Cu(2+) cations in the interpolyelectrolyte-metal complex bulk under constant electric and magnetic fields leads to formation of nanocomposite consisting of interpolyelectrolyte complex, including pectin-polyethyleneimine and nanoparticles of the metal Cu phase, whereas nanocomposite with Cu/Cu2O nanoparticles is formed in original state (without any field). It was observed that, under constant field, nanocomposites obtained have higher structural glass-transition temperatures and thermal stability.

Magnetic field decay in model SSC dipoles

International Nuclear Information System (INIS)

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

1988-08-01

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

The quantum oscillator on complex projective space (Lobachewski space) in a constant magnetic field and the issue of generic boundary conditions

International Nuclear Information System (INIS)

Giri, Pulak Ranjan

2007-01-01

We perform a one-parameter family of self-adjoint extensions characterized by the parameter ω 0 . This allows us to get generic boundary conditions for the quantum oscillator on N-dimensional complex projective space (CP N ) and on its non-compact version, i.e., Lobachewski space (L N ) in the presence of a constant magnetic field. As a result, we get a family of energy spectra for the oscillator. In our formulation the already known result of this oscillator also belongs to the family. We have also obtained an energy spectrum which preserves all the symmetries (full-hidden symmetry and rotational symmetry) of the oscillator. The method of self-adjoint extensions has also been discussed for a conic oscillator in the presence of the constant magnetic field

Calculation of the structural properties of a strange quark star in the presence of a strong magnetic field using a density dependent bag constant

Institute of Scientific and Technical Information of China (English)

Gholam Hossein Bordbar; Hajar Bahri; Fatemeh Kayanikhoo

2012-01-01

We have calculated the structural properties of a strange quark star with a static model in the presence of a strong magnetic field.To this end,we use the MITbag model with a density dependent bag constant.To parameterize the density dependence of the bag constant,we have used our results for the lowest order constrained variational calculation of the asymmetric nuclear matter.By calculating the equation of state of strange quark matter,we have shown that the pressure of this system increases by increasing both density and magnetic field.Finally,we have investigated the effect of density dependence of the bag constant on the structural properties of a strange quark star.

Relativistic stars with purely toroidal magnetic fields

International Nuclear Information System (INIS)

Kiuchi, Kenta; Yoshida, Shijun

2008-01-01

We investigate the effects of the purely toroidal magnetic field on the equilibrium structures of the relativistic stars. The basic equations for obtaining equilibrium solutions of relativistic rotating stars containing purely toroidal magnetic fields are derived for the first time. To solve these basic equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for calculating relativistic rotating stars containing no magnetic field to incorporate the effects of the purely toroidal magnetic fields. By using the numerical scheme, we then calculate a large number of the equilibrium configurations for a particular distribution of the magnetic field in order to explore the equilibrium properties. We also construct the equilibrium sequences of the constant baryon mass and/or the constant magnetic flux, which model the evolution of an isolated neutron star as it loses angular momentum via the gravitational waves. Important properties of the equilibrium configurations of the magnetized stars obtained in this study are summarized as follows: (1) For the nonrotating stars, the matter distribution of the stars is prolately distorted due to the toroidal magnetic fields. (2) For the rapidly rotating stars, the shape of the stellar surface becomes oblate because of the centrifugal force. But, the matter distribution deep inside the star is sufficiently prolate for the mean matter distribution of the star to be prolate. (3) The stronger toroidal magnetic fields lead to the mass shedding of the stars at the lower angular velocity. (4) For some equilibrium sequences of the constant baryon mass and magnetic flux, the stars can spin up as they lose angular momentum.

Spectra of magnetic chain graphs: coupling constant perturbations

Czech Academy of Sciences Publication Activity Database

Exner, Pavel; Manko, S. S.

2015-01-01

Roč. 48, č. 12 (2015), s. 125302 ISSN 1751-8113 R&D Projects: GA ČR(CZ) GA14-06818S Institutional support: RVO:61389005 Keywords : quantum graph * magnetic field * coupling constant perturbation * eigenvalues in gaps * weak coupling Subject RIV: BE - Theoretical Physics Impact factor: 1.933, year: 2015

Fast superconducting magnetic field switch

Science.gov (United States)

Goren, Yehuda; Mahale, Narayan K.

1996-01-01

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.

Fast superconducting magnetic field switch

International Nuclear Information System (INIS)

Goren, Y.; Mahale, N.K.

1996-01-01

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

Corrections for a constant radial magnetic field in the muon g - 2 and electric-dipole-moment experiments in storage rings

Energy Technology Data Exchange (ETDEWEB)

Silenko, Alexander J. [Belarusian State University, Research Institute for Nuclear Problems, Minsk (Belarus); Joint Institute for Nuclear Research, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation)

2017-10-15

We calculate the corrections for constant radial magnetic field in muon g - 2 and electric-dipole-moment experiments in storage rings. While the correction is negligible for the current generation of g - 2 experiments, it affects the upcoming muon electric-dipole-moment experiment at Fermilab. (orig.)

Magnetization reversal mechanisms under oblique magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Ntallis, N.; Efthimiadis, K.G., E-mail: kge@auth.gr

2017-03-01

In this work finite element micromagnetic simulations were performed in order to study the reversal mechanisms of spherical ferromagnetic particles with uniaxial magnetocrystalline anisotropy, when they are magnetized along an oblique direction with respect to the anisotropy axis. Magnetization loops are taken in different directions of external magnetic field, at different anisotropy constants and particle sizes. In the simulation results, the three reversal mechanisms (coherent, curling and domains) are observed and new phenomena arise due to the action of oblique magnetic fields. Moreover, the dependence of the critical fields with respect to the angle of the external field is presented. - Highlights: • Finite element micromagnetic simulation of the three different reversal mechanisms. • For the curling mechanism, the new phenomenon is the rotation of the vortex. • In the domain reversal mechanism, the formed domain wall is smaller than 180°. • In soft ferromagnetic particles a rearrangement of the magnetic domains is observed.

Superconductor shields test chamber from ambient magnetic fields

Science.gov (United States)

Hildebrandt, A. F.

1965-01-01

Shielding a test chamber for magnetic components enables it to maintain a constant, low magnetic field. The chamber is shielded from ambient magnetic fields by a lead foil cylinder maintained in a superconducting state by liquid helium.

Electron drag by solitons in superlattices in an external magnetic field

International Nuclear Information System (INIS)

Vyazovskii, M.V.; Syrodoev, G.A.

1996-01-01

The soliton-electric effect accompanying the propagation of an electromagnetic soliton along an axis of a superlattice in an external magnetic field directed along the magnetic field of the soliton is studied. It is assumed that the duration γ-1 of the soliton pulse is much shorter than the free flight time of an electron. It is shown that in the absence of a constant magnetic field the drag current varies as sin(αsech2γt) (α is a constant determined by the parameters of the superlattice). In the presence of a constant magnetic field of intensity H0>>Hs, where Hs is the amplitude of the soliton field, the drag current oscillates

Corrections for a constant radial magnetic field in the muon \\varvec{g}-2 and electric-dipole-moment experiments in storage rings

Science.gov (United States)

Silenko, Alexander J.

2017-10-01

We calculate the corrections for constant radial magnetic field in muon {g}-2 and electric-dipole-moment experiments in storage rings. While the correction is negligible for the current generation of {g}-2 experiments, it affects the upcoming muon electric-dipole-moment experiment at Fermilab.

Pulsed Magnetic Field Improves the Transport of Iron Oxide Nanoparticles through Cell Barriers

Science.gov (United States)

Min, Kyoung Ah; Shin, Meong Cheol; Yu, Faquan; Yang, Meizhu; David, Allan E.; Yang, Victor C.; Rosania, Gus R.

2013-01-01

Understanding how a magnetic field affects the interaction of magnetic nanoparticles (MNPs) with cells is fundamental to any potential downstream applications of MNPs as gene and drug delivery vehicles. Here, we present a quantitative analysis of how a pulsed magnetic field influences the manner in which MNPs interact with, and penetrate across a cell monolayer. Relative to a constant magnetic field, the rate of MNP uptake and transport across cell monolayers was enhanced by a pulsed magnetic field. MNP transport across cells was significantly inhibited at low temperature under both constant and pulsed magnetic field conditions, consistent with an active mechanism (i.e. endocytosis) mediating MNP transport. Microscopic observations and biochemical analysis indicated that, in a constant magnetic field, transport of MNPs across the cells was inhibited due to the formation of large (>2 μm) magnetically-induced MNP aggregates, which exceeded the size of endocytic vesicles. Thus, a pulsed magnetic field enhances the cellular uptake and transport of MNPs across cell barriers relative to a constant magnetic field by promoting accumulation while minimizing magnetically-induced MNP aggregates at the cell surface. PMID:23373613

Quantum kinematic theory of a point charge in a constant magnetic field

International Nuclear Information System (INIS)

Krause, J.

1996-01-01

A group-theoretic quantization method is applied to the open-quote open-quote complete symmetry group close-quote close-quote describing the motion of a point charge in a constant magnetic field. Within the regular ray representation, the Schroedinger operator is obtained as the Casimir operator of the extended Lie algebra. Configuration ray representations of the complete group cast the Schroedinger operator into the familiar space-time differential operator. Next, open-quote open-quote group quantization close-quote close-quote yields the superselection rules, which produce irreducible configuration ray representations. In this way, the Schroedinger operator becomes diagonalized, together with the angular momentum. Finally, the evaluation of an invariant integral, over the group manifold, gives rise to the Feynman propagation kernel left-angle t',x'|t,x right-angle of the system. Everything stems from the assumed symmetry group. Neither canonical quantization nor the path-integral method is used in the present analysis. copyright 1996 The American Physical Society

Master formulas for the dressed scalar propagator in a constant field

Energy Technology Data Exchange (ETDEWEB)

Ahmad, Aftab [Department of Physics, Gomal University, 29220 D.I. Khan, K.P.K (Pakistan); Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Ciudad Universitaria, Morelia 58040, Michoacán (Mexico); Ahmadiniaz, Naser, E-mail: Ahmadiniaz@ibs.re.kr [Center for Relativistic Laser Science, Institute for Basic Science, Gwangju 61005 (Korea, Republic of); Department of Physics, Kunsan National University, Kunsan 54150 (Korea, Republic of); Corradini, Olindo [Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, Via Campi 213/A, I-41125 Modena (Italy); INFN, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna (Italy); Kim, Sang Pyo [Center for Relativistic Laser Science, Institute for Basic Science, Gwangju 61005 (Korea, Republic of); Department of Physics, Kunsan National University, Kunsan 54150 (Korea, Republic of); Schubert, Christian [Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Ciudad Universitaria, Morelia 58040, Michoacán (Mexico)

2017-06-15

The worldline formalism has previously been used for deriving compact master formulas for the one-loop N-photon amplitudes in both scalar and spinor QED, and in the vacuum as well as in a constant external field. For scalar QED, there is also an analogous master formula for the propagator dressed with N photons in the vacuum. Here, we extend this master formula to include a constant field. The two-photon case is worked out explicitly, yielding an integral representation for the Compton scattering cross section in the field suitable for numerical integration in the full range of electric and magnetic field strengths.

Large Quantum Probability Backflow and the Azimuthal Angle-Angular Momentum Uncertainty Relation for an Electron in a Constant Magnetic Field

Science.gov (United States)

Strange, P.

2012-01-01

In this paper we demonstrate a surprising aspect of quantum mechanics that is accessible to an undergraduate student. We discuss probability backflow for an electron in a constant magnetic field. It is shown that even for a wavepacket composed entirely of states with negative angular momentum the effective angular momentum can take on positive…

Levitation of a magnet by an alternating magnetic field

International Nuclear Information System (INIS)

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

2013-01-01

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. (paper)

The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid

International Nuclear Information System (INIS)

Parekh, Kinnari; Upadhyay, R.V.

2017-01-01

Ultrasonic wave propagation in the aqueous magnetic fluid is investigated for different particle concentrations. The sound velocity decreases while acoustic impedance increases with increasing concentrations. The velocity anisotropy is observed upon application of magnetic field. The velocity anisotropy fits with Tarapov’s theory suggests the presence of aggregates in the system. We report that these aggregates are thermodynamically unstable and the length of aggregate changes continuously with increasing concentration and, or magnetic field and resulted in a decrease in effective magnetic moment. The Taketomi's theory fits well with the experimental data suggesting that the particle clusters are aligned in the direction of the magnetic field. The radius of cluster found to increase with increasing concentration, and then decreases whereas the elastic force constant increases and then becomes constant. The increase in cluster radius indicates elongation of aggregate length due to tip-to-tip interaction of aggregates whereas for higher concentration, the lateral alignment is more favorable than tip-to-tip alignment of aggregates which reduces the cluster radius making elastic force constant to raise. Optical images show that the chains are fluctuating and confirming the lateral alignment of chains at higher fields. - Highlights: • Magnetic field induced aggregates investigated using ultrasonic wave in aqueous magnetic fluid. • Velocity anisotropy induces upon applications of magnetic field. • Tarapov’s theory fit shows reduction in effective magnetic moment as concentration increases. • Taketomi's theory shows alignment of clusters in field direction. • Cluster radius increases and then decreases with increasing volume fractions. • Optical images show that fluctuating chains and lateral alignment of chains at higher fields.

The effect of magnetic field induced aggregates on ultrasound propagation in aqueous magnetic fluid

Energy Technology Data Exchange (ETDEWEB)

Parekh, Kinnari, E-mail: kinnariparekh.rnd@charusat.ac.in [Dr. KC Patel R& D Center, Charotar University of Science & Technology, Changa, 388421 Dist. Anand, Gujarat (India); Upadhyay, R.V. [PD Patel Institute of Applied Sciences, Charotar University of Science & Technology, Changa, 388421 Dist. Anand, Gujarat (India)

2017-06-01

Ultrasonic wave propagation in the aqueous magnetic fluid is investigated for different particle concentrations. The sound velocity decreases while acoustic impedance increases with increasing concentrations. The velocity anisotropy is observed upon application of magnetic field. The velocity anisotropy fits with Tarapov’s theory suggests the presence of aggregates in the system. We report that these aggregates are thermodynamically unstable and the length of aggregate changes continuously with increasing concentration and, or magnetic field and resulted in a decrease in effective magnetic moment. The Taketomi's theory fits well with the experimental data suggesting that the particle clusters are aligned in the direction of the magnetic field. The radius of cluster found to increase with increasing concentration, and then decreases whereas the elastic force constant increases and then becomes constant. The increase in cluster radius indicates elongation of aggregate length due to tip-to-tip interaction of aggregates whereas for higher concentration, the lateral alignment is more favorable than tip-to-tip alignment of aggregates which reduces the cluster radius making elastic force constant to raise. Optical images show that the chains are fluctuating and confirming the lateral alignment of chains at higher fields. - Highlights: • Magnetic field induced aggregates investigated using ultrasonic wave in aqueous magnetic fluid. • Velocity anisotropy induces upon applications of magnetic field. • Tarapov’s theory fit shows reduction in effective magnetic moment as concentration increases. • Taketomi's theory shows alignment of clusters in field direction. • Cluster radius increases and then decreases with increasing volume fractions. • Optical images show that fluctuating chains and lateral alignment of chains at higher fields.

Construction of Solar-Wind-Like Magnetic Fields

Science.gov (United States)

Roberts, Dana Aaron

2012-01-01

Fluctuations in the solar wind fields tend to not only have velocities and magnetic fields correlated in the sense consistent with Alfven waves traveling from the Sun, but they also have the magnitude of the magnetic field remarkably constant despite their being broadband. This paper provides, for the first time, a method for constructing fields with nearly constant magnetic field, zero divergence, and with any specified power spectrum for the fluctuations of the components of the field. Every wave vector, k, is associated with two polarizations the relative phases of these can be chosen to minimize the variance of the field magnitude while retaining the\\random character of the fields. The method is applied to a case with one spatial coordinate that demonstrates good agreement with observed time series and power spectra of the magnetic field in the solar wind, as well as with the distribution of the angles of rapid changes (discontinuities), thus showing a deep connection between two seemingly unrelated issues. It is suggested that using this construction will lead to more realistic simulations of solar wind turbulence and of the propagation of energetic particles.

Waves on the surface of a magnetic fluid layer in a traveling magnetic field

International Nuclear Information System (INIS)

Zimmermann, K.; Zeidis, I.; Naletova, V.A.; Turkov, V.A.

2004-01-01

The plane flow of a layer of incompressible viscous magnetic fluid with constant magnetic permeability under the action of a traveling magnetic field is analyzed. The strength of the magnetic field producing a sinusoidal traveling small-amplitude wave on the surface of a magnetic fluid is found. This flow can be used in designing mobile robots

Computing magnetic anisotropy constants of single molecule magnets

Indian Academy of Sciences (India)

We present here a theoretical approach to compute the molecular magnetic anisotropy parameters, and for single molecule magnets in any given spin eigenstate of exchange spin Hamiltonian. We first describe a hybrid constant -valence bond (VB) technique of solving spin Hamiltonians employing full spatial ...

Master formulas for the dressed scalar propagator in a constant field

Directory of Open Access Journals (Sweden)

Aftab Ahmad

2017-06-01

Full Text Available The worldline formalism has previously been used for deriving compact master formulas for the one-loop N-photon amplitudes in both scalar and spinor QED, and in the vacuum as well as in a constant external field. For scalar QED, there is also an analogous master formula for the propagator dressed with N photons in the vacuum. Here, we extend this master formula to include a constant field. The two-photon case is worked out explicitly, yielding an integral representation for the Compton scattering cross section in the field suitable for numerical integration in the full range of electric and magnetic field strengths.

Magnetic field induced dynamical chaos.

Science.gov (United States)

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

2013-12-01

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

Magnetic anisotropy study of UGe2in a static high magnetic field

International Nuclear Information System (INIS)

Sakon, T; Saito, S; Koyama, K; Awaji, S; Sato, I; Nojima, T; Watanabe, K; Motokawa, M; Sato, N K

2006-01-01

UGe 2 has orthorhombic C mmm crystalline symmetry and shows ferromagnetic Heavy-Fermion (HF) Superconductor, which provides superconductivity under pressure in the range from 1.0 GPa to 1.5 GPa. Magnetic field dependence of magnetization shows strong magnetic anisotropy. When a magnetic field is applied parallel to easy axis (a-axis), magnetization presents ferromagnetic behavior. At 4.2 K, which is much lower than the Curie temperature T c = 54 K. Spontaneous magnetization is 1.4 μ B /U, and the magnetization gradually increase with increasing field. On the contrary, when a field is applied parallel to hard axis (b-axis or c-axis), magnetization increases linearly with increasing magnetic field. As for H//b-axis, magnetization is 0.23 μ B /U even at 27 T. Magnetocrystalline anisotropy constant is obtained as 230 [T μ B ] 3.4[kJ/kg] at 4.2 K. This value is comparable with rare-earth magnet Nd 2 Fe 17 , which is typical strongly correlated ferromagnet

Nucleation of bulk superconductivity close to critical magnetic fields

DEFF Research Database (Denmark)

Fournais, Søren; Kachmar, Ayman

2011-01-01

We consider the two-dimensional Ginzburg–Landau functional with constant applied magnetic field. For applied magnetic fields close to the second critical field HC2 and large Ginzburg–Landau parameter, we provide leading order estimates on the energy of minimizing configurations. We obtain a fine ...

Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

Energy Technology Data Exchange (ETDEWEB)

Ismael, Muneer A. [Mechanical Engineering Department, Engineering College, University of Basrah, Basrah (Iraq); Mansour, M.A. [Department of Mathematics, Assuit University, Faculty of Science, Assuit (Egypt); Chamkha, Ali J. [Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Rashad, A.M., E-mail: am_rashad@yahoo.com [Department of Mathematics, Aswan University, Faculty of Science, Aswan 81528 (Egypt)

2016-10-15

Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

International Nuclear Information System (INIS)

Ismael, Muneer A.; Mansour, M.A.; Chamkha, Ali J.; Rashad, A.M.

2016-01-01

Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

Modelling of a plasma column sustained by a travelling circularly polarized electromagnetic wave (m=1 mode) in the presence of a constant axial magnetic field

International Nuclear Information System (INIS)

Benova, E.; Staikov, P.; Zhelyazkov, I.

1992-01-01

A set of equations modelling a low-pressure plasma column sustained by a travelling electromagnetic wave in the dipolar mode in the presence of a constant external magnetic field is presented. It is shown that, from a practical point of view, only the m = 1 mode (the right-hand-polarized wave) can sustain plasma columns in a wide region of gas-discharge conditions: plasma radius R, wave frequency ω, magnetic field B 0 and low pressures, irrespective of the nature of the gas. The main result of this study is that the magnetic field makes it possible to sustain a plasma column for values of σ smaller than σ cr = 0.3726, below which, in the absence of a magnetic field, the dipolar wave cannot produce a plasma. Moreover, at a fixed wave power, the magnetic field - in contrast with the case of plasma columns sustained by azimuthally symmetric waves - increases the plasma density and its axial gradient. The limit of an infinite external magnetic field (Ω → ∞) is also considered. A three-dimensional wave structure is obtained, and it indicates that the wave can be a generalized surface mode, a pure surface or a pseudosurface one. (author)

Features of the magnetic field of a rectangular combined function bending magnet

International Nuclear Information System (INIS)

Hwang, C.S.; National Chiao Tung Univ., Hsinchu; Chang, C.H.; Hwang, G.J.; Uen, T.M.; Tseng, P.K.; National Taiwan Univ., Taipei

1996-01-01

Magnetic field features of the combined function bending magnet with dipole and quadrupole field components are essential for the successful operation of the electron beam trajectory. These fields also dominate the photon beam quality. The vertical magnetic field B y (x,y) calculation is performed by a computer code MAGNET at the magnet center (s = 0). Those results are compared with the 2-D field measurement by the Hall probe mapping system. Also detailed survey has been made of the harmonic field strength and the main features of the fundamental integrated strength, effective length, magnetic symmetry, tilt of the pole face, offset of the field center and the fringe field. The end shims that compensate for the strong end negative sextupole field to increase the good field region for the entire integrated strength are discussed. An important physical feature of this combined function bending magnet is the constant ratio of dipole and quadrupole strength ∫Bds/∫Gds which is expressed as a function of excitation current in the energy range 0.6 to 1.5 GeV

Coupling between eddy current and deflection in cantilevered beams in magnetic fields

International Nuclear Information System (INIS)

Hua, T.Q.

1986-01-01

Experiments were performed to investigate the coupling between eddy currents and deflection in cantilevered beams in longitudinal and transverse magnetic fields. This coupling effect reduces the current, deflection, and material stress to levels far less severe than would be predicted if coupling is disregarded. The experiments were conducted using the FELIX (Fusion ELectromagnetic Induction experiment) facility at the Argonne National Laboratory. The beams, which provide a simple model for the limiter blades in a tokamak fusion reactor, are subjected to crossed time-varying and constant magnetic fields. The time-varying field simulates the decaying field during a plasma disruption and the constant field models the toroidal field. Several test pieces are employed to allow variations in thicknesses and mechanical and electrical properties. Various magnetic field levels and decay time constants of time-varying are used to study the extent of the coupling from weak to strong coupling. The ratios of constant field to time-varying field are kept in the range from 10:1 to 20:1 as would be appropriate to tokamak limiters. Major parameters measured as functions of time are beam deflection, measured with an electro-optical device; total circulating current, measured with a Rogowski coil; strain recorded by strain gauges; and magnetic fields measured with Hall probes

Influence of magnetic fields on structural martensitic transitions

Energy Technology Data Exchange (ETDEWEB)

Lashley, J C [Los Alamos National Laboratory; Cooley, J C [Los Alamos National Laboratory; Smith, J L [Los Alamos National Laboratory; Fisher, R A [NON LANL; Modic, K A [Los Alamos National Laboratory; Yang, X- D [TEMPLE UNIV; Riseborough, P S [TEMPLE UNIV.; Opeil, C P [BOSTON COLLEGE; Finlayson, T R [UNIV OF MELBOURNE; Goddard, P A [UNIV OF OXFORD; Silhanek, A V [INPAC

2009-01-01

We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high-magnetic fields. The magnetic field dependence is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework which can be used to describe the effect of magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant.

Microscopic observation of magnetic bacteria in the magnetic field of a rotating permanent magnet.

Science.gov (United States)

Smid, Pieter; Shcherbakov, Valeriy; Petersen, Nikolai

2015-09-01

Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.

Determination of the saturation magnetization, anisotropy field, mean field interaction, and switching field distribution for nanocrystalline hard magnets

International Nuclear Information System (INIS)

McCallum, R. William

2005-01-01

For a uniaxial nanocrystalline magnetic material, the determination of the saturation magnetization, M s , requires measurements of the magnetization at fields which exceed the anisotropy field. For a typical RE-Tm compound, where RE=rare earth and Tm=transition metal, this may require fields above 7 T if the approach to saturation law is used. However for an isotropic material composed of a random distribution of non-interacting uniaxial grains, both M s and the anisotropy filed, H a , may be determined by fitting the Stoner-Wohlfarth (SW) model (Philos. Trans. Roy. Soc. 240 (1948) 599) to the reversible part of the demagnetization curve in the first quadrant. Furthermore, using the mean field interaction model of Callen, Liu and Cullen [2], a quantitative measure of the interaction strength for interacting particles may be determined. In conjunction with an analytical fit to the first quadrant demagnetization curve of the SW model, this allows M s , H a and the mean field interaction constant of a nanocrystalline magnet to be determined from measurements below 5 T. Furthermore, comparison of the model solution for the reversible magnetization with experimental data in the 2nd and 3rd quadrants allows the accurate determination of the switching field distribution. In many cases the hysteresis loop may be accurately described by a normal distribution of switching fields

Eigenfunction method and mass operator in the quantum electrodynamics of a constant field

International Nuclear Information System (INIS)

Ritus, V.I.

1978-01-01

A method is presented for the calculation of radiative effects in the quantum electrodynamics of an intense constant field. It is based on the application of the mass operator eigenfunctions and on diagonalization of the operator. A compact expression for the proper value of the electron mass operator in an arbitrary constant field and the corresponding elastic scattering amplitude are found. The imaginary part of the amplitude determines the decay rate of various states of the electron in the field; the real part contains the mass shift and the anomalous magnetic and electric moments as functions of the field and electron momentum. THe anomalous electric moment which arises in a field with a pseudoscalar EH not equal to 0 and the anomalous magnetic moment in an electric field which tends to the double Schwinger value with increase of the field strength are found and investigated in detail as are the mass shift and decay rate of the ground state of an electron in an electric field. In a weak field the mass shift contains the linear with respect to the field modulus classical term which characterizes the effect of acceleration on the structure of electron

Magnetic fields in an expanding universe

International Nuclear Information System (INIS)

Kastor, David; Traschen, Jennie

2014-01-01

We find a solution to 4D Einstein–Maxwell theory coupled to a massless dilaton field, for all values of the dilaton coupling, describing a Melvin magnetic field in an expanding universe with ‘stiff matter’ equation of state parameter w = +1. As the universe expands, magnetic flux becomes more concentrated around the symmetry axis for dilaton coupling a<1/√3 and more dispersed for a>1/√3. An electric field circulates around the symmetry axis in the direction determined by Lenz's law. For a = 0 the magnetic flux through a disc of fixed comoving radius is proportional to the proper area of the disc. This result disagrees with the usual expectation based on a test magnetic field that this flux should be constant, and we show why this difference arises. We also find a Melvin solution in an accelerating universe with w = −7/9 for a dilaton field with a certain exponential potential. (paper)

Exact numerical solutions of the Schrödinger equation for a two-dimensional exciton in a constant magnetic field of arbitrary strength

Energy Technology Data Exchange (ETDEWEB)

Hoang-Do, Ngoc-Tram [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam); Pham, Dang-Lan [Institute for Computational Science and Technology, Quang Trung Software Town, District 12, Ho Chi Minh City (Viet Nam); Le, Van-Hoang, E-mail: hoanglv@hcmup.edu.vn [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam)

2013-08-15

Exact numerical solutions of the Schrödinger equation for a two-dimensional exciton in a constant magnetic field of arbitrary strength are obtained for not only the ground state but also high excited states. Toward this goal, the operator method is developed by combining with the Levi-Civita transformation which transforms the problem under investigation into that of a two-dimensional anharmonic oscillator. This development of the non-perturbation method is significant because it can be applied to other problems of two-dimensional atomic systems. The obtained energies and wave functions set a new record for their precision of up to 20 decimal places. Analyzing the obtained data we also find an interesting result that exact analytical solutions exist at some values of magnetic field intensity.

Exact numerical solutions of the Schrödinger equation for a two-dimensional exciton in a constant magnetic field of arbitrary strength

International Nuclear Information System (INIS)

Hoang-Do, Ngoc-Tram; Pham, Dang-Lan; Le, Van-Hoang

2013-01-01

Exact numerical solutions of the Schrödinger equation for a two-dimensional exciton in a constant magnetic field of arbitrary strength are obtained for not only the ground state but also high excited states. Toward this goal, the operator method is developed by combining with the Levi-Civita transformation which transforms the problem under investigation into that of a two-dimensional anharmonic oscillator. This development of the non-perturbation method is significant because it can be applied to other problems of two-dimensional atomic systems. The obtained energies and wave functions set a new record for their precision of up to 20 decimal places. Analyzing the obtained data we also find an interesting result that exact analytical solutions exist at some values of magnetic field intensity

Monolayer phosphorene under time-dependent magnetic field

Science.gov (United States)

Nascimento, J. P. G.; Aguiar, V.; Guedes, I.

2018-02-01

We obtain the exact wave function of a monolayer phosphorene under a low-intensity time-dependent magnetic field using the dynamical invariant method. We calculate the quantum-mechanical energy expectation value and the transition probability for a constant and an oscillatory magnetic field. For the former we observe that the Landau level energy varies linearly with the quantum numbers n and m and the magnetic field intensity B0. No transition takes place. For the latter, we observe that the energy oscillates in time, increasing linearly with the Landau level n and m and nonlinearly with the magnetic field. The (k , l) →(n , m) transitions take place only for l = m. We investigate the (0,0) →(n , 0) and (1 , l) and (2 , l) probability transitions.

Influence of the Gilbert damping constant on the flux rise time of write head fields

International Nuclear Information System (INIS)

Ertl, Othmar; Schrefl, Thomas; Suess, Dieter; Schabes, Manfred E.

2005-01-01

Magnetic recording at fast data rates requires write heads with rapid rise times of the magnetic flux during the write process. We present three-dimensional (3D) micromagnetic finite element calculations of an entire ring head including 3D coil geometry during the writing of magnetic bits in granular media. The simulations demonstrate how input current profiles translate into magnetization processes in the head and which in turn generate the write head field. The flux rise time significantly depends on the Gilbert damping constant of the head material. Low damping causes incoherent magnetization processes, leading to long rise times and low head fields. High damping leads to coherent reversal of the magnetization in the head. As a consequence, the gap region can be quickly saturated which causes high head fields with short rise times

Particle-in-cell simulations of collisionless magnetic reconnection with a non-uniform guide field

International Nuclear Information System (INIS)

Wilson, F.; Neukirch, T.; Harrison, M. G.; Hesse, M.; Stark, C. R.

2016-01-01

Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov–Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium.

Modeling of Local Magnetic Field Enhancements within Solar Flux Ropes

OpenAIRE

Romashets, E; Vandas, M; Poedts, Stefaan

2010-01-01

To model and study local magnetic-field enhancements in a solar flux rope we consider the magnetic field in its interior as a superposition of two linear (constant alpha) force-free magnetic-field distributions, viz. a global one, which is locally similar to a part of the cylinder, and a local torus-shaped magnetic distribution. The newly derived solution for a toroid with an aspect ratio close to unity is applied. The symmetry axis of the toroid and that of the cylinder may or may not coinci...

On the eigenvalues of S.Π for arbitrary spin in a constant magnetic field

International Nuclear Information System (INIS)

Jayaraman, J.; Oliveira, M.A.B. de.

1985-01-01

Utilizing the intimate connection of a charged particle in a nomogeneous magnetic field to that of a harmonic oscillator, it was established in a recent communication that the eigenvalue spectrum of the matrix operator S.Π for spin 1 is purely real for any intensity of the external magnetic field thereby removing a false impression to the contrary in the recent literature. Here these results are extended to arbitrary spin the reality of the eigenvalue spectrum. The case of spin 3/2 is discussed in some details and it is demonstrated that the complex eigenvalues implied the spectrum by a recent analysis of Weaver, for sufficiently intense magnetic field, when the particle number n assumes values 0 and 1 do not in fact appear at all. (Author) [pt

Magnetic field mediated conductance oscillation in graphene p–n junctions

Science.gov (United States)

Cheng, Shu-Guang

2018-04-01

The electronic transport of graphene p–n junctions under perpendicular magnetic field is investigated in theory. Under low magnetic field, the transport is determined by the resonant tunneling of Landau levels and conductance versus magnetic field shows a Shubnikov–de Haas oscillation. At higher magnetic field, the p–n junction subjected to the quasi-classical regime and the formation of snake states results in periodical backscattering and transmission as magnetic field varies. The conductance oscillation pattern is mediated both by magnetic field and the carrier concentration on bipolar regions. For medium magnetic field between above two regimes, the combined contributions of resonant tunneling, snake states oscillation and Aharanov–Bohm interference induce irregular oscillation of conductance. At very high magnetic field, the system is subjected to quantum Hall regime. Under disorder, the quantum tunneling at low magnetic field is slightly affected and the oscillation of snake states at higher magnetic field is suppressed. In the quantum Hall regime, the conductance is a constant as predicted by the mixture rule.

Background Independent Open String Field Theory and Constant B-Field

OpenAIRE

Nemeschansky, D.; Yasnov, V.

2000-01-01

We calculate the background independent action for bosonic and supersymmetric open string field theory in a constant B-field. We also determine the tachyon effective action in the presence of constant B-field.

Fringe Field Effects on Bending Magnets, Derived for TRANSPORT/TURTLE

Energy Technology Data Exchange (ETDEWEB)

Molloy, Riley [Arizona State Univ., Tempe, AZ (United States); Blitz, Sam [Arizona State Univ., Tempe, AZ (United States)

2013-08-05

A realistic magnetic dipole has complex effects on a charged particle near the entrance and exit of the magnet, even with a constant and uniform magnetic field deep within the interior of the magnet. To satisfy Maxwell's equations, the field lines near either end of a realistic magnet are significantly more complicated, yielding non-trivial forces. The effects of this fringe field are calculated to first order, applying both the paraxial and thin lens approximations. We find that, in addition to zeroth order effects, the position of a particle directly impacts the forces in the horizontal and vertical directions.

Low pressure arc discharge lamp apparatus with magnetic field generating means

Science.gov (United States)

Grossman, Mark W.; George, William A.; Maya, Jakob

1987-01-01

A low-pressure arc discharge apparatus having a magnetic field generating means for increasing the output of a discharge lamp is disclosed. The magnetic field generating means, which in one embodiment includes a plurality of permanent magnets, is disposed along the lamp for applying a constant transverse magnetic field over at least a portion of the positive discharge column produced in the arc discharge lamp operating at an ambient temperature greater than about 25.degree. C.

Low pressure arc discharge lamp apparatus with magnetic field generating means

Science.gov (United States)

Grossman, M.W.; George, W.A.; Maya, J.

1987-10-06

A low-pressure arc discharge apparatus having a magnetic field generating means for increasing the output of a discharge lamp is disclosed. The magnetic field generating means, which in one embodiment includes a plurality of permanent magnets, is disposed along the lamp for applying a constant transverse magnetic field over at least a portion of the positive discharge column produced in the arc discharge lamp operating at an ambient temperature greater than about 25 C. 3 figs.

Low energy constituent quark and pion effective couplings in a weak external magnetic field

Science.gov (United States)

Braghin, Fábio L.

2018-03-01

An effective model with pions and constituent quarks in the presence of a weak external background electromagnetic field is derived by starting from a dressed one gluon exchange quark-quark interaction. By applying the auxiliary field and background field methods, the structureless pion limit is considered to extract effective pion and constituent quark couplings in the presence of a weak magnetic field. The leading terms of a large quark and gluon masses expansion are obtained by resolving effective coupling constants which turn out to depend on a weak magnetic field. Two pion field definitions are considered for that. Several relations between the effective coupling constants and parameters can be derived exactly or in the limit of very large quark mass at zero and weak constant magnetic field. Among these ratios, the Gell-Mann-Oakes-Renner and the quark level Goldberger-Treiman relations are obtained. In addition to that, in the pion sector, the leading terms of Chiral Perturbation Theory coupled to the electromagnetic field are recovered. Some numerical estimates are provided for the effective coupling constants and parameters.

Pair production by a constant external field in noncommutative QED

International Nuclear Information System (INIS)

Chair, N.; Sheikh-Jabbari, M.M.

2000-09-01

In this paper we study QED on the noncommutative space in the constant electro-magnetic field background. Using the explicit solutions of the noncommutative version of Dirac equation in such background, we show that there are well-defined in and out-going asymptotic states and also there is a causal Green's function. We calculate the pair production rate in this case. We show that at tree level noncommutativity will not change the pair production and the threshold electric field. We also calculate the pair production rate considering the first loop corrections. In this case we show that the threshold electric field is decreased by the noncommutativity effects. (author)

Determination of Coronal Magnetic Fields from Vector Magnetograms

Science.gov (United States)

Mikic, Zoran

1997-01-01

During the course of the present contract we developed an 'evolutionary technique' for the determination of force-free coronal magnetic fields from vector magnetograph observations. The method can successfully generate nonlinear force- free fields (with non-constant-a) that match vector magnetograms. We demonstrated that it is possible to determine coronal magnetic fields from photospheric measurements, and we applied it to vector magnetograms of active regions. We have also studied theoretical models of coronal fields that lead to disruptions. Specifically, we have demonstrated that the determination of force-free fields from exact boundary data is a well-posed mathematical problem, by verifying that the computed coronal field agrees with an analytic force-free field when boundary data for the analytic field are used; demonstrated that it is possible to determine active-region coronal magnetic fields from photospheric measurements, by computing the coronal field above active region 5747 on 20 October 1989, AR6919 on 15 November 1991, and AR7260 on 18 August 1992, from data taken with the Stokes Polarimeter at Mees Solar Observatory, University of Hawaii; started to analyze active region 7201 on 19 June 1992 using measurements made with the Advanced Stokes Polarimeter at NSO/Sac Peak; investigated the effects of imperfections in the photospheric data on the computed coronal magnetic field; documented the coronal field structure of AR5747 and compared it to the morphology of footpoint emission in a flare, showing that the 'high- pressure' H-alpha footpoints are connected by coronal field lines; shown that the variation of magnetic field strength along current-carrying field lines is significantly different from the variation in a potential field, and that the resulting near-constant area of elementary flux tubes is consistent with observations; begun to develop realistic models of coronal fields which can be used to study flare trigger mechanisms; demonstrated that

Ionization waves caused by the effects of a magnetic field

International Nuclear Information System (INIS)

Miura, Kosuke; Imazu, Shingo

1980-01-01

The self-excited ionization waves was observed in the Ne positive column. The experiments were made for Ne gas from 0.07 to 1.0 Torr, with the magnetic field from 0 to 3.33 kG. The discharge current were 10 to 300 mA. The longitudinal magnetic field was made by an air-core solenoid coil. The axial electric field was measured by two wall probes. The frequency, wave length and amplitude of waves were measured with a photo multiplier. It was found that the longitudinal magnetic field caused new self-excited ionization waves. The frequency of these waves decreased monotonously with increasing field. The behaviors of the wave length and amplitude were complicate, and the cause of these phenomena is related to the ionization waves due to the spatial resonance of electron gas, namely s-waves, p-waves and fluid γ-waves. The threshold of the magnetic field to cause the ionization waves increased with increasing gas pressure, and with decreasing discharge current in the range 0.07 to 0.44 Torr. The frequency of the self-excited ionization waves occurred at zero field was almost constant in the field-frequency relation. A simple dispersion equation was derived, and the Novak constant can be introduced. (J.P.N.)

Behavior of small ferromagnetic particles in traveling magnetic field

Science.gov (United States)

Deych, V. G.; Terekhov, V. P.

1985-03-01

Forces and moments acting on a magnetizable body in a traveling magnetic field are calculated for a body with dimensions much smaller than the wavelength of the magnetic field. It is assumed that a particle of given linear dimension does not have a constant magnetic moment. The material of a particle is characterized by its magnetic permeability and electrical conductivity. The hypothesis that rotation plays a major role in the behavior of small particles is confirmed and the fact that a small particle rolls on a plane, without sliding, when the surface is perfectly rough, in the opposite direction from which the magnetic field travels is explained. Calculations are based on the magnetohydrodynamic equations for a quasi steady magnetic field, and the induced Foucault eddy currents are considered. The results are applicable to transport of ferrofluids and to such metallurgical devices as separators.

Magnetic field exposure stiffens regenerating plant protoplast cell walls.

Science.gov (United States)

Haneda, Toshihiko; Fujimura, Yuu; Iino, Masaaki

2006-02-01

Single suspension-cultured plant cells (Catharanthus roseus) and their protoplasts were anchored to a glass plate and exposed to a magnetic field of 302 +/- 8 mT for several hours. Compression forces required to produce constant cell deformation were measured parallel to the magnetic field by means of a cantilever-type force sensor. Exposure of intact cells to the magnetic field did not result in any changes within experimental error, while exposure of regenerating protoplasts significantly increased the measured forces and stiffened regenerating protoplasts. The diameters of intact cells or regenerating protoplasts were not changed after exposure to the magnetic field. Measured forces for regenerating protoplasts with and without exposure to the magnetic field increased linearly with incubation time, with these forces being divided into components based on the elasticity of synthesized cell walls and cytoplasm. Cell wall synthesis was also measured using a cell wall-specific fluorescent dye, and no changes were noted after exposure to the magnetic field. Analysis suggested that exposure to the magnetic field roughly tripled the Young's modulus of the newly synthesized cell wall without any lag.

Diffusion affected magnetic field effect in exciplex fluorescence

International Nuclear Information System (INIS)

Burshtein, Anatoly I.; Ivanov, Anatoly I.

2014-01-01

The fluorescence of the exciplex, 1 [D +δ A −δ ], formed at contact of photoexcited acceptor 1 A * with an electron donor 1 D, is known to be very sensitive to an external magnetic field, reducing the spin conversion efficiency in the resulting geminate radical ion pair, 1,3 [D + …A − ]. The relative increase of the exciplex fluorescence in the highest magnetic field compared to the lowest one, known as the magnetic field effect, crucially depends on the viscosity of the solvent. This phenomenon first studied experimentally is at first reproduced here theoretically. The magnetic field effect is shown to vanish in both limits of high and low solvent diffusivity reaching a maximum in between. It is also very sensitive to the solvent dielectric constant and to the exciplex and radical-ion pair conversion rates

Diffusion affected magnetic field effect in exciplex fluorescence

Science.gov (United States)

Burshtein, Anatoly I.; Ivanov, Anatoly I.

2014-07-01

The fluorescence of the exciplex, 1[D+δA-δ], formed at contact of photoexcited acceptor 1A* with an electron donor 1D, is known to be very sensitive to an external magnetic field, reducing the spin conversion efficiency in the resulting geminate radical ion pair, 1, 3[D+…A-]. The relative increase of the exciplex fluorescence in the highest magnetic field compared to the lowest one, known as the magnetic field effect, crucially depends on the viscosity of the solvent. This phenomenon first studied experimentally is at first reproduced here theoretically. The magnetic field effect is shown to vanish in both limits of high and low solvent diffusivity reaching a maximum in between. It is also very sensitive to the solvent dielectric constant and to the exciplex and radical-ion pair conversion rates.

Magnetic field effects on brain monoamine oxidase activity

Energy Technology Data Exchange (ETDEWEB)

Borets, V.M.; Ostrovskiy, V.Yu.; Bankovskiy, A.A.; Dudinskaya, T.F.

1985-03-01

In view of the increasing use of magnetotherapy, studies were conducted on the effects of 35 mTesla magnetic fields on monoamine oxidase activity in the rat brain. Under in vitro conditions a constant magnetic field in the continuous mode was most effective in inhibiting deamination of dopamine following 1 min exposure, while in vivo studies with 8 min or 10 day exposures showed that inhibition was obtained only with a variable field in the continuous mode. However, inhibition of dopamine deamination was only evident within the first 24 h after exposure was terminated. In addition, in none of the cases was norepinephrine deamination inhibited. The effects of the magnetic fields were, therefore, transient and selective with the CNS as the target system. 9 references.

Constant force linear permanent magnet actuators

NARCIS (Netherlands)

Paulides, J.J.H.; Encica, L.; Meessen, K.J.; Lomonova, E.A.

2009-01-01

In applications, such as vibration isolation, gravity compensation, pick-and-place machines, etc., there is a need for (long-stroke) passive constant force actuators combined with tubular permanent magnet actuators to minimize the power consumption, hence, passively counteract the gravitational

Hearing the zero locus of a magnetic field

International Nuclear Information System (INIS)

Montgomery, R.

1995-01-01

We investigate the ground state of a two-dimensional quantum particle in a magnetic field where the field vanishes nondegenerately along a closed curve. We show that the ground state concentrates on this curve as e/h tends to infinity, where e is the charge, and that the ground state energy grows like (e/h) 2/3 . These statements are true for any energy level, the level being fixed as the charge tends to infinity. If the magnitude of the gradient of the magnetic field is a constant b 0 along its zero locus, then we get the precise asymptotics (e/h) 2/3 (b 0 ) 2/3 E * + O(1) for every energy level. The constant E * ≅ .5698 is the infimum of the ground state energies E(β) of the anharmonic oscillator family -d 2 /dy 2 + (1/2 y 2 - β) 2 . (orig.)

Effect of Weak Magnetic Field on Bacterial Growth

Science.gov (United States)

Masood, Samina

Effects of weak magnetic fields are observed on the growth of various bacterial strains. Different sources of a constant magnetic field are used to demonstrate that ion transport in the nutrient broth and bacterial cellular dynamics is perturbed in the presence of weak magnetic field which affects the mobility and absorption of nutrients in cells and hence their doubling rate. The change is obvious after a few hours of exposure and keeps on increasing with time for all the observed species. The growth rate depends on the field strength and the nature of the magnetic field. The field effect varies with the shape and the structure of the bacterial cell wall as well as the concentration of nutrient broth. We closely study the growth of three species Escherichia coli, Pseudomonas aeruginosa and Staphylococcus epidermidis with the same initial concentrations at the same temperature in the same laboratory environment. Our results indicate that the weak static field of a few gauss after a few hours gives a measurable change in the growth rates of all bacterial species. This shows that the same magnetic field has different effects on different species in the same environment.

Delayed demagnetization jumps in (NdDy)(FeCo)B magnets in a steady-state magnetic field

Science.gov (United States)

L'vova, G. L.; Kirman, M. V.; Koplak, O. V.; Kucheryaev, V. V.; Valeev, R. A.; Piskorskii, V. P.; Morgunov, R. B.

2017-11-01

Spontaneous demagnetization jumps are observed in sintered magnets (Nd0.6Dy0.4)16(Fe0.77Co0.23)78B6 in a constant magnetic field after a sharp decrease in an external magnetic field from the value corresponding to the saturation to a value close to the coercive force. It is shown that the number of the magnetization jumps is proportional to their amplitudes. A low value of the autocorrelation coefficient between the jump amplitude and the time of its appearance ( R white magnetic noise is observed. The distribution of the magnetic field gradient has been obtained near the sample surface that makes it possible to distinguish domains and the grain magnetization in the dependence on the direction of the texturing of the sintered magnet.

Indoor localization using magnetic fields

Science.gov (United States)

Pathapati Subbu, Kalyan Sasidhar

Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing

Measurement and reconstruction of the BEBC magnetic field map

CERN Document Server

Häbel, E; Wittgenstein, F

1973-01-01

The superconducting magnet of the Big European Bubble Chamber (BEBC) has been excited with currents up to 5035 A corresponding to a magnetic induction of 3.1 Tesla at the center of the chamber. Since one expected that during the charging of the magnet coils long time constant eddy currents would be induced by the varying radial field components, a system of 181 Hall-probes was installed on the boundary of the chamber body allowing to survey the magnetic field map. This Hall-probe system together with an NMR-probe (nuclear magnetic resonance) enabled us to measure and reconstruct to an accuracy of better than 0.1% the field map of BEBC, which in itself is uniform to within 3% inside the visible fiducial volume of the Chamber. Direct evidence was also given for field map distortions due to the eddy current field which amounted to about 0.7% of the maximum recorded field values at the chamber center. (7 refs).

Measurement and reconstruction of the BEBC magnetic field map

CERN Document Server

Häbel, E; Wittgenstein, F

1973-01-01

The superconducting magnet of the Big European Bubble Chamber (BEBC) has been excited with currents up to 5035 A corresponding to a magnetic induction of 3.1 Tesla at the center of the chamber. Since one expected that during the charging of the magnet coils long time constant eddy currents would be induced by the varying radial field components, a system of 181 Hall-probes was installed on the boundary of the chamber body allowing to survey the magnetic field map. This Hall-probe system together with an NMR-probe (nuclear magnetic resonance) enabled us to measure and reconstruct to an accuracy of better than 0.1the field map of BEBC, which in itself is uniform to within 3 191332nside the visible fiducial volume of the Chamber. Direct evidence was also given for field map distortions due to the eddy current field which amounted to about 0.723420f the maximum recorded field values at the chamber center. (7 refs).

Destabilizing effect of time-dependent oblique magnetic field on magnetic fluids streaming in porous media.

Science.gov (United States)

El-Dib, Yusry O; Ghaly, Ahmed Y

2004-01-01

The present work studies Kelvin-Helmholtz waves propagating between two magnetic fluids. The system is composed of two semi-infinite magnetic fluids streaming throughout porous media. The system is influenced by an oblique magnetic field. The solution of the linearized equations of motion under the boundary conditions leads to deriving the Mathieu equation governing the interfacial displacement and having complex coefficients. The stability criteria are discussed theoretically and numerically, from which stability diagrams are obtained. Regions of stability and instability are identified for the magnetic fields versus the wavenumber. It is found that the increase of the fluid density ratio, the fluid velocity ratio, the upper viscosity, and the lower porous permeability play a stabilizing role in the stability behavior in the presence of an oscillating vertical magnetic field or in the presence of an oscillating tangential magnetic field. The increase of the fluid viscosity plays a stabilizing role and can be used to retard the destabilizing influence for the vertical magnetic field. Dual roles are observed for the fluid velocity in the stability criteria. It is found that the field frequency plays against the constant part for the magnetic field.

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

Science.gov (United States)

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

2009-07-01

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 these assumptions, we study the dependence of Hanle effect on the magnetic field correlation length, its angular, and strength distributions. Methods: We introduce a fairly general random magnetic field model characterized by a correlation length and a magnetic field vector distribution. Micro-turbulence is recovered when the correlation length goes to zero and macro-turbulence when it goes to infinity. Radiative transfer equations are established for the calculation of the mean Stokes parameters and they are solved numerically by a polarized approximate lambda iteration method. Results: We show that optically thin spectral lines and optically very thick ones are insensitive to the correlation length of the magnetic field, while spectral lines with intermediate optical depths (around 10-100) show some sensitivity to this parameter. The result is interpreted in terms of the mean number of scattering events needed to create the surface polarization. It is shown that the single-scattering approximation holds good for thin and thick lines but may fail for lines with intermediate thickness. The dependence of the polarization on the magnetic field vector probability density function (PDF) is examined in the micro-turbulent limit. A few PDFs with different angular and strength distributions, but equal mean value of the magnetic field, are considered. It is found that the polarization is in general quite sensitive to the shape of the magnetic field strength PDF and somewhat to the angular distribution. Conclusions: The mean field derived from Hanle effect analysis of

Diffusion affected magnetic field effect in exciplex fluorescence

Energy Technology Data Exchange (ETDEWEB)

Burshtein, Anatoly I. [Weizmann Institute of Science, Rehovot 76100 (Israel); Ivanov, Anatoly I., E-mail: Anatoly.Ivanov@volsu.ru [Volgograd State University, University Avenue, 100, Volgograd 400062 (Russian Federation)

2014-07-14

The fluorescence of the exciplex, {sup 1}[D{sup +δ}A{sup −δ}], formed at contact of photoexcited acceptor {sup 1}A{sup *} with an electron donor {sup 1}D, is known to be very sensitive to an external magnetic field, reducing the spin conversion efficiency in the resulting geminate radical ion pair, {sup 1,3}[D{sup +}…A{sup −}]. The relative increase of the exciplex fluorescence in the highest magnetic field compared to the lowest one, known as the magnetic field effect, crucially depends on the viscosity of the solvent. This phenomenon first studied experimentally is at first reproduced here theoretically. The magnetic field effect is shown to vanish in both limits of high and low solvent diffusivity reaching a maximum in between. It is also very sensitive to the solvent dielectric constant and to the exciplex and radical-ion pair conversion rates.

Large-scale vortices in compressible turbulent medium with the magnetic field

Science.gov (United States)

Gvaramadze, V. V.; Dimitrov, B. G.

1990-08-01

An averaged equation which describes the large scale vortices and Alfven waves generation in a compressible helical turbulent medium with a constant magnetic field is presented. The presence of the magnetic field leads to anisotropization of the vortex generation. Possible applications of the anisotropic vortex dynamo effect are accretion disks of compact objects.

Neutron scattering study of magnetic and crystalline electirc field interactions in RCrO3

International Nuclear Information System (INIS)

Shamir, N.

1978-05-01

Magnetic and crystalline electric field interactions in the compounds RCrO 3 (R-rare earth) , were studied by neutron scattering. Elastic neutron scattering was utilized in the study of the temperature dependence of the Cr 3+ and Ho 3+ magnetic reflections in Lu CrO 3 and HoCrO 3 , respectively. Analysis of this temperature dependence yielde constant canting angles for the Cr 3+ and Ho 3+ magnetic moments. Molecular magnetic field constants and crystalline electric field splitting were also calculated from the temperature dependence of the Ho 3+ magnetic reflection. These parameters were obtained directly by inelastic neutron scattering measurement. Inelastic neutron scattering measurements of crystlline electric field transitions of R 3+ (R=Pr, Nd, Tb, Ho, Er, Tm, Yb) in RCrO 3 , formed the basis for the calculation of the common crystalline electirc field parameters of the heavy R 3+ ions. (author)

Effect of sample shape on nonlinear magnetization dynamics under an external magnetic field

International Nuclear Information System (INIS)

Vagin, Dmitry V.; Polyakov, Oleg P.

2008-01-01

Effect of sample shape on the nonlinear collective dynamics of magnetic moments in the presence of oscillating and constant external magnetic fields is studied using the Landau-Lifshitz-Gilbert (LLG) approach. The uniformly magnetized sample is considered to be an ellipsoidal axially symmetric particle described by demagnetization factors and uniaxial crystallographic anisotropy formed some angle with an applied field direction. It is investigated as to how the change in particle shape affects its nonlinear magnetization dynamics. To produce a regular study, all results are presented in the form of bifurcation diagrams for all sufficient dynamics regimes of the considered system. In this paper, we show that the sample's (particle's) shape and its orientation with respect to the external field (system configuration) determine the character of magnetization dynamics: deterministic behavior and appearance of chaotic states. A simple change in the system's configuration or in the shapes of its parts can transfer it from chaotic to periodic or even static regime and back. Moreover, the effect of magnetization precession stall and magnetic moments alignment parallel or antiparallel to the external oscillating field is revealed and the way of control of such 'polarized' states is found. Our results suggest that varying the particle's shape and fields' geometry may provide a useful way of magnetization dynamics control in complex magnetic systems

Magnetic properties of the Ce2Fe17-x Mn x helical magnets up to high magnetic fields

International Nuclear Information System (INIS)

Kuchin, A.G.; Mushnikov, N.V.; Bartashevich, M.I.; Prokhnenko, O.; Khrabrov, V.I.; Lapina, T.P.

2007-01-01

Magnetic properties of the Ce 2 Fe 17- x Mn x , x=0-2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5-1 are helical antiferromagnets and those with 1 B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce 2 Fe 17- x Mn x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce 2 Fe 17- x Mn x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce 2 Fe 17- x Mn x , x=0.5-2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated

Magnetization Switching of a Co /Pt Multilayered Perpendicular Nanomagnet Assisted by a Microwave Field with Time-Varying Frequency

Science.gov (United States)

Suto, Hirofumi; Kanao, Taro; Nagasawa, Tazumi; Mizushima, Koichi; Sato, Rie

2018-05-01

Microwave-assisted magnetization switching (MAS) is attracting attention as a method for reversing nanomagnets with a high magnetic anisotropy by using a small-amplitude magnetic field. We experimentally study MAS of a perpendicularly magnetized nanomagnet by applying a microwave magnetic field with a time-varying frequency. Because the microwave field frequency can follow the nonlinear decrease of the resonance frequency, larger magnetization excitation than that in a constant-frequency microwave field is induced, which enhances the MAS effect. The switching field decreases almost linearly as the start value of the time-varying microwave field frequency increases, and it becomes smaller than the minimum switching field in a constant-frequency microwave field. To obtain this enhancement of the MAS effect, the end value of the time-varying microwave field frequency needs to be almost the same as or lower than the critical frequency for MAS in a constant-frequency microwave field. In addition, the frequency change typically needs to take 1 ns or longer to make the rate of change slow enough for the magnetization to follow the frequency change. This switching behavior is qualitatively explained by the theory based on the macrospin model.

Statistical mechanics of a plasma in a very strong magnetic field

International Nuclear Information System (INIS)

Psimopoulos, M.

1980-03-01

Using the guiding centre model the behaviour of a plasma in the presence of a very strong constant magnetic field has been studied. The validity of the model is discussed and the conditions concerning the strength of the magnetic field are derived. Both the equilibrium and the non-equilibrium aspects of the problem are considered. (U.K.)

Highly accurate analytical energy of a two-dimensional exciton in a constant magnetic field

International Nuclear Information System (INIS)

Hoang, Ngoc-Tram D.; Nguyen, Duy-Anh P.; Hoang, Van-Hung; Le, Van-Hoang

2016-01-01

Explicit expressions are given for analytically describing the dependence of the energy of a two-dimensional exciton on magnetic field intensity. These expressions are highly accurate with the precision of up to three decimal places for the whole range of the magnetic field intensity. The results are shown for the ground state and some excited states; moreover, we have all formulae to obtain similar expressions of any excited state. Analysis of numerical results shows that the precision of three decimal places is maintained for the excited states with the principal quantum number of up to n=100.

Highly accurate analytical energy of a two-dimensional exciton in a constant magnetic field

Energy Technology Data Exchange (ETDEWEB)

Hoang, Ngoc-Tram D. [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam); Nguyen, Duy-Anh P. [Department of Natural Science, Thu Dau Mot University, 6, Tran Van On Street, Thu Dau Mot City, Binh Duong Province (Viet Nam); Hoang, Van-Hung [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam); Le, Van-Hoang, E-mail: levanhoang@tdt.edu.vn [Atomic Molecular and Optical Physics Research Group, Ton Duc Thang University, 19 Nguyen Huu Tho Street, Tan Phong Ward, District 7, Ho Chi Minh City (Viet Nam); Faculty of Applied Sciences, Ton Duc Thang University, 19 Nguyen Huu Tho Street, Tan Phong Ward, District 7, Ho Chi Minh City (Viet Nam)

2016-08-15

Explicit expressions are given for analytically describing the dependence of the energy of a two-dimensional exciton on magnetic field intensity. These expressions are highly accurate with the precision of up to three decimal places for the whole range of the magnetic field intensity. The results are shown for the ground state and some excited states; moreover, we have all formulae to obtain similar expressions of any excited state. Analysis of numerical results shows that the precision of three decimal places is maintained for the excited states with the principal quantum number of up to n=100.

Magnetic monopole and vector field of the spin 0

International Nuclear Information System (INIS)

Pantyushin, A.A.

2001-01-01

The motion of electrically charged particles in uniform magnetic field by time is considered. It is found out that additional force acting on eclectically charged particle from the spin 0 vector field side is proportional to the magnetic field. Proportion coefficient is equal to eg/4π (g - unknown parameter, determining of the rate and character of source non-preservation) - the analogue of constant thin structure α=e 2 /4π. Obtained results give evidence to suppose that for explanation of indicated experiments the monopole introduction is not essential

Incompressible Steady Flow with Tensor Conductivity Leaving a Transverse Magnetic Field

International Nuclear Information System (INIS)

Witalis, E.A.

1965-12-01

The straight channel flow of an inviscid, incompressible fluid with tensor conductivity is considered when the flow leaves a region of constant transverse magnetic field. The channel walls are taken to be insulating, and an eddy current system arises. This is investigated by the method of magnetic field analysis as given by Witalis. The spatial distribution of magnetic field and ohmic power loss, both parallel and transverse to the flow, are given as functions of the Hall parameter with consideration also to the magnetic Reynolds number of the fluid. MHD power generator aspects of this problem and the results are discussed

Incompressible Steady Flow with Tensor Conductivity Leaving a Transverse Magnetic Field

Energy Technology Data Exchange (ETDEWEB)

Witalis, E A

1965-12-15

The straight channel flow of an inviscid, incompressible fluid with tensor conductivity is considered when the flow leaves a region of constant transverse magnetic field. The channel walls are taken to be insulating, and an eddy current system arises. This is investigated by the method of magnetic field analysis as given by Witalis. The spatial distribution of magnetic field and ohmic power loss, both parallel and transverse to the flow, are given as functions of the Hall parameter with consideration also to the magnetic Reynolds number of the fluid. MHD power generator aspects of this problem and the results are discussed.

FOREWORD: Focus on Materials Analysis and Processing in Magnetic Fields Focus on Materials Analysis and Processing in Magnetic Fields

Science.gov (United States)

Sakka, Yoshio; Hirota, Noriyuki; Horii, Shigeru; Ando, Tsutomu

2009-03-01

papers of the proceedings are published in Journal of Physics: Conference Series. Tournier and Beaugnon review experimental texturing in metallic melts by cooling in magnetic fields, which is modeled in detail in a study by Tournier. Wang et al provide further experimental results on the solidification of Mn-90.4 wt % Sb alloy in magnetic fields. The orientations of grains and particles induced by magnetic fields is reported by Horii et al (rare-earth-doped cuprates), Tanaka et al (barium-bismuth titanate ceramics), Liu and Schwartz (Bi2Sr2CaCu2Ox/AgMg wires) and Tsuda and Sakka (carbon nanotubes). Gielen et al present a model of how to quantify a molecular alignment using magnetic birefringence, and Ando et al simulate the movement of feeble particles in magnetic fields. Hirota et al report the experimental control of the lattice constant in a triangular lattice of feeble magnetic particles. The size separation of diamagnetic particles by magnetic fields is experimentally studied by Tarn et al and theoretically studied by Fukui et al. A setup measuring x-ray diffraction patterns in magnetic fields up to 5 T and temperatures above 200 oC has been developed by Mitsui et al. We hope that this focus issue will help readers to understand several aspects of materials analysis and processing in magnetic fields at the frontier of the science.

Calculation of magnetic hyperfine constants

International Nuclear Information System (INIS)

Bufaical, R.F.; Maffeo, B.; Brandi, H.S.

1975-01-01

The magnetic hyperfine constants of the V sub(K) center in CaF 2 , SrF 2 and BaF 2 have been calculated assuming a phenomenological model, based on the F 2 - 'central molucule', to describe the wavefunction of the defect. Calculations have shown that introduction of a small degree of covalence, between this central molecule and neighboring ions, is necessary to improve the electronic structure description of the defect. It was also shown that the results for the hyperfine constants are strongly dependent on the relaxations of the ions neighboring the central molecule; these relaxations have been determined by fitting the experimental data. The present results are compared with other previous calculations where similar and different theoretical methods have been used

ION KINETIC ENERGY CONSERVATION AND MAGNETIC FIELD STRENGTH CONSTANCY IN MULTI-FLUID SOLAR WIND ALFVÉNIC TURBULENCE

Energy Technology Data Exchange (ETDEWEB)

Matteini, L.; Horbury, T. S.; Schwartz, S. J. [The Blackett Laboratory, Imperial College London, SW7 2AZ (United Kingdom); Pantellini, F. [LESIA, Observatoire de Paris, CNRS, UPMC, Universit Paris-Diderot, 5 Place Jules Janssen, F-92195 Meudon (France); Velli, M. [Department of Earth, Planetary, and Space Sciences, UCLA, California (United States)

2015-03-20

We investigate the properties of plasma fluid motion in the large-amplitude, low-frequency fluctuations of highly Alfvénic fast solar wind. We show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles which, due to their drift with respect to protons at about the Alfvén speed along the magnetic field, do not partake in the fluid low-frequency fluctuations. Using their velocity to transform the proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is the origin of the observed constancy of the magnetic field; while the constant velocity corresponding to constant energy can only be observed in the frame of the fluctuations, the corresponding constant total magnetic field, invariant for Galilean transformations, remains the observational signature in the spacecraft frame of the constant total energy in the Alfvén turbulence frame.

Three-dimensional computation of magnetic fields and Lorentz forces of an LHC dipole magnet

International Nuclear Information System (INIS)

Daum, C.; Avest, D. ter

1989-07-01

Magnetic fields and Lorentz forces of an LHC dipole magnet are calculated using the method of image currents to represent the effect of the iron shield. The calculation is performed for coils of finite length using a parametrization for coil heads of constant perimeter. A comparison with calculations based on POISSON and TOSCA is made. (author). 5 refs.; 31 figs.; 6 tabs

Magnetic field modification of ultracold molecule-molecule collisions

International Nuclear Information System (INIS)

Tscherbul, T V; Suleimanov, Yu V; Aquilanti, V; Krems, R V

2009-01-01

We present an accurate quantum mechanical study of molecule-molecule collisions in the presence of a magnetic field. The work focuses on the analysis of elastic scattering and spin relaxation in collisions of O 2 ( 3 Σ g - ) molecules at cold (∼0.1 K) and ultracold (∼10 -6 K) temperatures. Our calculations show that magnetic spin relaxation in molecule-molecule collisions is extremely efficient except at magnetic fields below 1 mT. The rate constant for spin relaxation at T=0.1 K and a magnetic field of 0.1 T is found to be as large as 6.1x10 -11 cm -3 s -1 . The magnetic field dependence of elastic and inelastic scattering cross sections at ultracold temperatures is dominated by a manifold of Feshbach resonances with the density of ∼100 resonances per Tesla for collisions of molecules in the absolute ground state. This suggests that the scattering length of ultracold molecules in the absolute ground state can be effectively tuned in a very wide range of magnetic fields. Our calculations demonstrate that the number and properties of the magnetic Feshbach resonances are dramatically different for molecules in the absolute ground and excited spin states. The density of Feshbach resonances for molecule-molecule scattering in the low-field-seeking Zeeman state is reduced by a factor of 10.

Magnetic field strength dependence of the magnetostriction of rare-earth iron garnets

International Nuclear Information System (INIS)

Zvezdin, A.K.; Levitin, R.Z.; Popov, A.I.; Silant'ev, V.I.

1981-01-01

The magnetostriction of holmium-yttrium iron garnets Hosub(x)Ysub(3-x)Fesub(5)Osub(12) (x=3 or 1.05) is measured in pulsed magnetic fields up to 200 kOe at 78 K. It is shown that the magnetostriction constants lambda 111 and lambda 100 of these ferrimagnets depends on the magnetic field strength. The magnetostriction constant of the iron garnet Ho 3 Fe 5 O 12 increases and of the iron garnet Hosub(1.05)Ysub(1.95)Fesub(5)Osub(12) decreases with increase of the field strength. The field dependences of the anisotropic magnetostriction constants lambda 111 and lambda 100 for Hosub(1.05)Ysub(1.95)Fesub(5)Osub(12) are fundamentally different. Thus lambda 111 depends quadratically on the total effective field Hsub(eff) whereas lambda 100 depends almost linearly on Hsub(eff). A theoretical analysis of the magneto-elastic interaction in rare-earth iron garnets is carried out [ru

Anchoring Polar Magnetic Field in a Stationary Thick Accretion Disk

Energy Technology Data Exchange (ETDEWEB)

Samadi, Maryam; Abbassi, Shahram, E-mail: samadimojarad@um.ac.ir [Department of Physics, School of Sciences, Ferdowsi University of Mashhad, Mashhad, 91775-1436 (Iran, Islamic Republic of)

2017-08-20

We investigate the properties of a hot accretion flow bathed in a poloidal magnetic field. We consider an axisymmetric viscous-resistive flow in the steady-state configuration. We assume that the dominant mechanism of energy dissipation is due to turbulence viscosity and magnetic diffusivity. A certain fraction of that energy can be advected toward the central compact object. We employ the self-similar method in the radial direction to find a system of ODEs with just one varible, θ in the spherical coordinates. For the existence and maintenance of a purely poloidal magnetic field in a rotating thick disk, we find that the necessary condition is a constant value of angular velocity along a magnetic field line. We obtain an analytical solution for the poloidal magnetic flux. We explore possible changes in the vertical structure of the disk under the influences of symmetric and asymmetric magnetic fields. Our results reveal that a polar magnetic field with even symmetry about the equatorial plane makes the disk vertically thin. Moreover, the accretion rate decreases when we consider a strong magnetic field. Finally, we notice that hot magnetized accretion flows can be fully advected even in a slim shape.

Magnetic flux density distribution in superconducting cylinders of arbitrary cross section subjected to an axial magnetic field

Science.gov (United States)

Fournet, G.

1982-07-01

We show here how the application of the critical state model allows one to determine the magnetic flux density B⃗ in each point of a superconducting cylinder with an arbitrary cross section subjected to axial magnetic fields Hz; the B = 0 boundaries of the regions occupied by the vortices are so defined. We successively consider the cases where the critical current density Jc is either isotropic (constant or an arbitrary function of B) or tensorial, which means, for our problem, the use of two components Jcx and Jcy (either constant or depending on B but Jcx/Jcy remaining constant).

Quantum revivals in the motion of electron in magnetic field

International Nuclear Information System (INIS)

Filipowicz, P.; Mostowski, J.

1981-01-01

We show that the motion of a relativistic electron in constant homogeneous magnetic field exhibits quasiperiodic behaviour (quantum revivals) and discuss the possibility of their observation. (author)

Touchless attitude correction for satellite with constant magnetic moment

Science.gov (United States)

Ao, Hou-jun; Yang, Le-ping; Zhu, Yan-wei; Zhang, Yuan-wen; Huang, Huan

2017-09-01

Rescue of satellite with attitude fault is of great value. Satellite with improper injection attitude may lose contact with ground as the antenna points to the wrong direction, or encounter energy problems as solar arrays are not facing the sun. Improper uploaded command may set the attitude out of control, exemplified by Japanese Hitomi spacecraft. In engineering practice, traditional physical contact approaches have been applied, yet with a potential risk of collision and a lack of versatility since the mechanical systems are mission-specific. This paper puts forward a touchless attitude correction approach, in which three satellites are considered, one having constant dipole and two having magnetic coils to control attitude of the first. Particular correction configurations are designed and analyzed to maintain the target's orbit during the attitude correction process. A reference coordinate system is introduced to simplify the control process and avoid the singular value problem of Euler angles. Based on the spherical triangle basic relations, the accurate varying geomagnetic field is considered in the attitude dynamic mode. Sliding mode control method is utilized to design the correction law. Finally, numerical simulation is conducted to verify the theoretical derivation. It can be safely concluded that the no-contact attitude correction approach for the satellite with uniaxial constant magnetic moment is feasible and potentially applicable to on-orbit operations.

Effects of electric and magnetic fields on the electronic properties of zigzag carbon and boron nitride nanotubes

Science.gov (United States)

Chegel, Raad; Behzad, Somayeh; Ahmadi, Eghbal

2012-04-01

We have investigated the electronic properties of zigzag CNTs and BNNTs under the external transverse electric field and axial magnetic field, using tight binding approximation. It was found that after switching on the electric and magnetic fields, the band modification such as distortion of the degeneracy, change in energy dispersion, subband spacing and band gap size reduction occurs. The band gap of zigzag BNNTs decreases linearly with increasing the electric field strength but the band gap variation for CNTs increases first and later decreases (Metallic) or first hold constant and then decreases (semiconductor). For type (II) CNTs, at a weak magnetic field, by increasing the electric field strength, the band gap remains constant first and then decreases and in a stronger magnetic field the band gap reduction becomes parabolic. For type (III) CNTs, in any magnetic field, the band gap increases slowly until reaches a maximum value and then decreases linearly. Unlike to CNTs, the magnetic field has less effects on the BNNTs band gap variation.

Generation of uniform magnetic field using a spheroidal helical coil structure

International Nuclear Information System (INIS)

Öztürk, Yavuz; Aktaş, Bekir

2016-01-01

Uniformity of magnetic fields are of great importance especially in magnetic resonance studies, namely in magnetic resonance spectroscopy applications (NMR, FMR, ESR, EPR etc.) and magnetic resonance imaging applications (MRI, FMRI). Field uniformity is also required in some other applications such as eddy current probes, magnetometers, magnetic traps, particle counters etc. Here we proposed a coil winding regime, which follows the surface of a spheroid (an ellipsoid of rotation); in light of previous theoretical studies suggesting perfect uniformity for a constant ampere per turn in the axial direction thereof. We demonstrated our theoretical results from finite element calculations suggesting 0.15% of field uniformity for the proposed structure, which we called a Spheroidal Helical Coil. (paper)

Fractional dynamics of charged particles in magnetic fields

Science.gov (United States)

Coronel-Escamilla, A.; Gómez-Aguilar, J. F.; Alvarado-Méndez, E.; Guerrero-Ramírez, G. V.; Escobar-Jiménez, R. F.

2016-02-01

In many physical applications the electrons play a relevant role. For example, when a beam of electrons accelerated to relativistic velocities is used as an active medium to generate Free Electron Lasers (FEL), the electrons are bound to atoms, but move freely in a magnetic field. The relaxation time, longitudinal effects and transverse variations of the optical field are parameters that play an important role in the efficiency of this laser. The electron dynamics in a magnetic field is a means of radiation source for coupling to the electric field. The transverse motion of the electrons leads to either gain or loss energy from or to the field, depending on the position of the particle regarding the phase of the external radiation field. Due to the importance to know with great certainty the displacement of charged particles in a magnetic field, in this work we study the fractional dynamics of charged particles in magnetic fields. Newton’s second law is considered and the order of the fractional differential equation is (0;1]. Based on the Grünwald-Letnikov (GL) definition, the discretization of fractional differential equations is reported to get numerical simulations. Comparison between the numerical solutions obtained on Euler’s numerical method for the classical case and the GL definition in the fractional approach proves the good performance of the numerical scheme applied. Three application examples are shown: constant magnetic field, ramp magnetic field and harmonic magnetic field. In the first example the results obtained show bistability. Dissipative effects are observed in the system and the standard dynamic is recovered when the order of the fractional derivative is 1.

Diffusion of cosmic rays at EeV energies in inhomogeneous extragalactic magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Batista, Rafael Alves; Sigl, Günter, E-mail: rafael.alves.batista@desy.de, E-mail: guenter.sigl@desy.de [II. Institut für Theoretische Physik, Universität Hamburg Luruper Chaussee 149, 22761, Hamburg (Germany)

2014-11-01

Ultra-high energy cosmic rays can propagate diffusively in cosmic magnetic fields. When their propagation time is comparable to the age of the universe, a suppression in the flux relative to the case in the absence of magnetic fields will occur. In this work we find an approximate parametrization for this suppression for energies below ∼ Z EeV using several magnetic field distributions obtained from cosmological simulations of the magnetized cosmic web. We assume that the magnetic fields have a Kolmogorov power spectrum with the field strengths distributed according to these simulations. We show that, if magnetic fields are coupled to the matter distribution, low field strengths will fill most of the volume, making the suppression milder compared to the case of a constant magnetic field with strength equal to the mean value of this distribution. We also derive upper limits for this suppression to occur for some models of extragalactic magnetic fields, as a function of the coherence length of these fields.

Cosmic Magnetic Fields

Science.gov (United States)

Sánchez Almeida, J.; Martínez González, M. J.

2018-05-01

Magnetic fields play an important role in many astrophysical processes. They are difficult to detect and characterize since often their properties have to be inferred through interpreting the polarization of the light. Magnetic fields are also challenging to model and understand. Magnetized plasmas behave following highly non-linear differential equations having no general solution, so that every astrophysical problem represents a special case to be studied independently. Hence, magnetic fields are often an inconvenient subject which is overlooked or simply neglected (the elephant in the room, as they are dubbed in poster of the school). Such difficulty burdens the research on magnetic fields, which has evolved to become a very technical subject, with many small disconnected communities studying specific aspects and details. The school tried to amend the situation by providing a unifying view of the subject. The students had a chance to understand the behavior of magnetic fields in all astrophysical contexts, from cosmology to the Sun, and from starbursts to AGNs. The school was planed to present a balanced yet complete review of our knowledge, with excursions into the unknown to point out present and future lines of research. The subject of Cosmic Magnetic Fields was split into seven different topics: cosmic magnetic field essentials, solar magnetic fields, stellar magnetic fields, the role of magnetic fields on AGN feedback, magnetic fields in galaxies, magnetic fields in galaxy clusters and at larger scales, and primordial magnetic fields and magnetic fields in the early Universe. The corresponding lectures were delivered by seven well known and experienced scientists that have played key roles in the major advances of the field during the last years: F. Cattaneo, P. Judge, O. Kochukhov, R. Keppens, R. Beck, K. Dolag, and F. Finelli. Their lectures were recorded and are freely available at the IAC website: http://iactalks.iac.es/talks/serie/19.

Wigner functions for fermions in strong magnetic fields

Science.gov (United States)

Sheng, Xin-li; Rischke, Dirk H.; Vasak, David; Wang, Qun

2018-02-01

We compute the covariant Wigner function for spin-(1/2) fermions in an arbitrarily strong magnetic field by exactly solving the Dirac equation at non-zero fermion-number and chiral-charge densities. The Landau energy levels as well as a set of orthonormal eigenfunctions are found as solutions of the Dirac equation. With these orthonormal eigenfunctions we construct the fermion field operators and the corresponding Wigner-function operator. The Wigner function is obtained by taking the ensemble average of the Wigner-function operator in global thermodynamical equilibrium, i.e., at constant temperature T and non-zero fermion-number and chiral-charge chemical potentials μ and μ_5, respectively. Extracting the vector and axial-vector components of the Wigner function, we reproduce the currents of the chiral magnetic and separation effect in an arbitrarily strong magnetic field.

Measurement and modeling of magnetic hysteresis under field and stress application in iron–gallium alloys

International Nuclear Information System (INIS)

Evans, Phillip G.; Dapino, Marcelo J.

2013-01-01

Measurements are performed to characterize the hysteresis in magnetomechanical coupling of iron–gallium (Galfenol) alloys. Magnetization and strain of production and research grade Galfenol are measured under applied stress at constant field, applied field at constant stress, and alternately applied field and stress. A high degree of reversibility in the magnetomechanical coupling is demonstrated by comparing a series of applied field at constant stress measurements with a single applied stress at constant field measurement. Accommodation is not evident and magnetic hysteresis for applied field and stress is shown to be coupled. A thermodynamic model is formulated for 3-D magnetization and strain. It employs a stress, field, and direction dependent hysteron that has an instantaneous loss mechanism, similar to Coulomb-friction or Preisach-type models. Stochastic homogenization is utilized to account for the smoothing effect that material inhomogeneities have on bulk processes. - Highlights: ► We conduct coupled experiments and develop nonlinear thermodynamic models for magnetostrictive iron–gallium (Galfenol) alloys. ► The measurements show unexpected kinematic reversibility in the magnetomechanical coupling. ► This is in contrast with the magnetomechanical coupling in steel which is both thermodynamically and kinematically irreversible. ► The model accurately describes the measurements and provides a framework for understanding hysteresis in ferromagnetic materials which exhibit kinematically reversible magnetomechanical coupling.

Investigation of magnetic fluids exhibiting field-induced increasing loss peaks

International Nuclear Information System (INIS)

Fannin, P.C.; Marin, C.N.; Couper, C.

2010-01-01

A theoretical analysis to explain an increase of the Brownian loss peak with increasing polarizing field, H, in a magnetic fluid, is presented. The model is based on the competition between the Brownian and Neel relaxation processes. It is demonstrated that in magnetic fluids with particles having small anisotropy constant, small average magnetic diameter and narrow particle size distribution an increase of the Brownian loss peak with the polarizing field can be observed. The theoretical results are compared with the experimental results of an Isopar M-based magnetic fluid with magnetite particles stabilized with oleic acid and the model explains qualitatively the main characteristics of the experimental results.

Confining gauge theories and holographic entanglement entropy with a magnetic field

Energy Technology Data Exchange (ETDEWEB)

Dudal, David [KU Leuven Campus Kortrijk - KULAK, Department of Physics,Etienne Sabbelaan 51 bus 7800, Kortrijk, 8500 (Belgium); Ghent University, Department of Physics and Astronomy,Krijgslaan 281-S9, Gent, 9000 (Belgium); Mahapatra, Subhash [KU Leuven Campus Kortrijk - KULAK, Department of Physics,Etienne Sabbelaan 51 bus 7800, Kortrijk, 8500 (Belgium)

2017-04-06

We consider the soft wall model for a heuristic holographical modelling of a confining gauge theory and discuss how the introduction of a (constant) magnetic field influences the (de)confinement phase structure. We use the entanglement entropy as a diagnostic tool in terms of the length of an entangling strip geometry. Due to the anisotropy introduced by the magnetic field, we find that the results depend on the orientation of the strip relative to the field. This allows to identify a richer, anisotropic, interplay between confinement and a magnetic field than possibly can be extracted from a more standard order parameter as, for example, the Polyakov loop expectation value.

Time-dependent behavior of magnetic fields confined by conducting walls

International Nuclear Information System (INIS)

Kidder, R.E.; Cecil, A.B.

1983-01-01

An equation is derived which describes the total current flowing in a moving conducting surface surrounding a magnetic field, where diffusion of the field into the conductor is taken into account. Analytic and numerical solutions of the current equation are obtained for the cases of exponential and linear compression of the magnetic field with time, respectively. It is assumed that the electrical conductivity is constant, that the conducting surfaces are axially symmetric, and that the thickness and radius of curvature of the conducting walls is large compared with the effective depth of penetration of the field

Ballooning modes on open magnetic field lines

International Nuclear Information System (INIS)

Hameiri, E.

1999-01-01

The ballooning instability on open magnetic field lines is given a thorough mathematical analysis. It is shown that resistive bounding ends (endplates) induce the same stability properties as insulating ends. When unstable, the maximal growth rate increases monotonically with boundary resistivity. An interchange instability may be present, and one necessary condition for its stability is that ∫dl/B be constant on pressure surfaces. (This is an equilibrium existence condition for systems with closed magnetic field lines.) Another necessary condition for interchange stability has the same form as in the closed line case. Precise necessary and sufficient stability criteria are given for various types of bounding ends, including insulating, resistive, and perfectly conducting. copyright 1999 American Institute of Physics

Is X-ray emissivity constant on magnetic flux surfaces?

International Nuclear Information System (INIS)

Granetz, R.S.; Borras, M.C.

1997-01-01

Knowledge of the elongations and shifts of internal magnetic flux surfaces can be used to determine the q profile in elongated tokamak plasmas. X-ray tomography is thought to be a reasonable technique for independently measuring internal flux surface shapes, because it is widely believed that X-ray emissivity should be constant on a magnetic flux surface. In the Alcator C-Mod tokamak, the X-ray tomography diagnostic system consists of four arrays of 38 chords each. A comparison of reconstructed X-ray contours with magnetic flux surfaces shows a small but consistent discrepancy in the radial profile of elongation. Numerous computational tests have been performed to verify these findings, including tests of the sensitivity to calibration and viewing geometry errors, the accuracy of the tomography reconstruction algorithms, and other subtler effects. We conclude that the discrepancy between the X-ray contours and the magnetic flux surfaces is real, leading to the conclusion that X-ray emissivity is not exactly constant on a flux surface. (orig.)

Mitigating reentry radio blackout by using a traveling magnetic field

Directory of Open Access Journals (Sweden)

Hui Zhou

2017-10-01

Full Text Available A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positioning System (GPS and the typical telemetry system are also discussed. Compared with the constant magnetic-window method, the TMF method needs lower magnetic field strength and is easier to realize in the engineering field.

Mitigating reentry radio blackout by using a traveling magnetic field

Science.gov (United States)

Zhou, Hui; Li, Xiaoping; Xie, Kai; Liu, Yanming; Yu, Yuanyuan

2017-10-01

A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF) is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positioning System (GPS) and the typical telemetry system are also discussed. Compared with the constant magnetic-window method, the TMF method needs lower magnetic field strength and is easier to realize in the engineering field.

Magnetic Field

DEFF Research Database (Denmark)

Olsen, Nils

2015-01-01

he Earth has a large and complicated magnetic field, the major part of which is produced by a self-sustaining dynamo operating in the fluid outer core. Magnetic field observations provide one of the few tools for remote sensing the Earth’s deep interior, especially regarding the dynamics...... of the fluid flow at the top of the core. However, what is measured at or near the surface of the Earth is the superposition of the core field and fields caused by magnetized rocks in the Earth’s crust, by electric currents flowing in the ionosphere, magnetosphere, and oceans, and by currents induced...... in the Earth by time-varying external fields. These sources have their specific characteristics in terms of spatial and temporal variations, and their proper separation, based on magnetic measurements, is a major challenge. Such a separation is a prerequisite for remote sensing by means of magnetic field...

A general nonlinear magnetomechanical model for ferromagnetic materials under a constant weak magnetic field

Energy Technology Data Exchange (ETDEWEB)

Shi, Pengpeng; Zheng, Xiaojing, E-mail: xjzheng@xidian.edu.cn [School of Mechano-Electronic Engineering, Xidian University, Xi' an 710071, Shaanxi (China); Jin, Ke [School of Aerospace Science and Technology, Xidian University, Xi' an 710071, Shaanxi (China)

2016-04-14

Weak magnetic nondestructive testing (e.g., metal magnetic memory method) concerns the magnetization variation of ferromagnetic materials due to its applied load and a weak magnetic surrounding them. One key issue on these nondestructive technologies is the magnetomechanical effect for quantitative evaluation of magnetization state from stress–strain condition. A representative phenomenological model has been proposed to explain the magnetomechanical effect by Jiles in 1995. However, the Jiles' model has some deficiencies in quantification, for instance, there is a visible difference between theoretical prediction and experimental measurements on stress–magnetization curve, especially in the compression case. Based on the thermodynamic relations and the approach law of irreversible magnetization, a nonlinear coupled model is proposed to improve the quantitative evaluation of the magnetomechanical effect. Excellent agreement has been achieved between the predictions from the present model and previous experimental results. In comparison with Jiles' model, the prediction accuracy is improved greatly by the present model, particularly for the compression case. A detailed study has also been performed to reveal the effects of initial magnetization status, cyclic loading, and demagnetization factor on the magnetomechanical effect. Our theoretical model reveals that the stable weak magnetic signals of nondestructive testing after multiple cyclic loads are attributed to the first few cycles eliminating most of the irreversible magnetization. Remarkably, the existence of demagnetization field can weaken magnetomechanical effect, therefore, significantly reduces the testing capability. This theoretical model can be adopted to quantitatively analyze magnetic memory signals, and then can be applied in weak magnetic nondestructive testing.

Neutral beam injection and plasma convection in a magnetic field

International Nuclear Information System (INIS)

Okuda, H.; Hiroe, S.

1988-06-01

Injection of a neutral beam into a plasma in a magnetic field has been studied by means of numerical plasma simulations. It is found that, in the absence of a rotational transform, the convection electric field arising from the polarization charges at the edges of the beam is dissipated by turbulent plasma convection, leading to anomalous plasma diffusion across the magnetic field. The convection electric field increases with the beam density and beam energy. In the presence of a rotational transform, polarization charges can be neutralized by the electron motion along the magnetic field. Even in the presence of a rotational transform, a steady-state convection electric field and, hence, anomalous plasma diffusion can develop when a neutral beam is constantly injected into a plasma. Theoretical investigations on the convection electric field are described for a plasma in the presence of rotational transform. 11 refs., 19 figs

Analytic computation of the quantum levels of a two-dimensional hydrogenic donor in the presence of a constant magnetic field of arbitrary strength

Energy Technology Data Exchange (ETDEWEB)

Villalba, Victor M.; Pino, Ramiro [Instituto Venezolano de Investigaciones Cientificas, Caracas (Venezuela)

2001-03-01

In this article we review different techniques for computing the energy spectrum of 2 D hydrogenic donors and two-electron quantum dots in the presence of a constant, magnetic field perpendicular to the plane of the electron. We compute the 1S, 2P- and 3D- energy levels via a scaled variational mixed-bases method. We compare our results with those obtained with the shifted 1/N method. [Spanish] En el presente articulo se exhiben distintos metodos para calcular el espectro de energia de donores hidrogenicos y puntos cuanticos con dos electrones en presencia de un campo magnetico constante perpendicular al plano del electron. Se calculan los niveles de energia 1S, 2P- y 3D- con ayuda del metodo variacional de bases mixtas con escalamiento. Comparamos nuestro resultados con los obtenidos con ayuda del metodo 1/N con corrimiento.

Magnetic field effects on electrical parameters of rf excited CO{sub 2} lasers

Energy Technology Data Exchange (ETDEWEB)

Tavassoli, S.H. [Laser Research Institute and Physics Department of Shahid Beheshti University, Evin, Tehran (Iran, Islamic Republic of)]. E-mail: h-tavassoli@cc.sbu.ac.ir; Latifi, H. [Laser Research Institute and Physics Department of Shahid Beheshti University, Evin, Tehran (Iran, Islamic Republic of)

2005-02-14

In the present Letter a rf excited CO{sub 2} laser embedded in an external, constant, and homogeneous magnetic field is considered. The magnetic field effects on some discharge parameters such as V-I characteristics, impedance of sheaths and positive column of plasma, intensity of visible emission from plasma and thickness of positive column are investigated. There is an increase in thickness of positive column and output power in presence of magnetic field. Magnetic field leads to an increase in the discharge voltage and impedance for lower current densities and a decrease for higher ones. There is a current density in which the magnetic field has no effects on discharge voltage and impedance. There are two peaks on intensity of visible emission from the discharge which at higher magnetic field are pushed out toward the electrodes.

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS

International Nuclear Information System (INIS)

2004-01-01

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

Buoyant convection during Czochralski silicon growth with a strong, non-uniform, axisymmetric magnetic field

Science.gov (United States)

Khine, Y. Y.; Walker, J. S.

1995-02-01

This paper treats the buoyant convection during the Czochralski growth of silicon crystals with a steady, strong, non-uniform, axisymmetric magnetic field. We consider a family of magnetic fields which includes a uniform axial magnetic field and a "cusp" field which is produced by identical solenoids placed symmetrically above and below the plane of the crystal-melt interface and free surface. We investigate the evolution of the buoyant convection as the magnetic field is changed continuously from a uniform axial field to a cusp field, with a constant value of the root-mean-squared magnetic flux density in the melt. We also investigate changes as the magnetic flux density is increased. While the cusp field appears very promising, perfect alignment between the local magnetic field vector and the crystal-melt interface or free surface is not possible, so the effects of a slight misalignment are also investigated.

Damping Dependence of Reversal Magnetic Field on Co-based Nano-Ferromagnetic with Thermal Activation

Directory of Open Access Journals (Sweden)

Nadia Ananda Herianto

2015-02-01

Full Text Available Currently, hard disk development has used HAMR technology that applies heat to perpendicular media until near Curie temperature, then cools it down to room temperature. The use of HAMR technology is significantly influence by Gilbert damping constants. Damping affects the magnetization reversal and coercivity field. Simulation is used to evaluate magnetization reversal by completing Landau-Lifshitz-Gilbert explicit equation. A strong ferromagnetic cobalt based material with size 50×50×20 nm3 is used which parameters are anisotropy materials 3.51×106 erg/cm3, magnetic saturation 5697.5 G, exchange constant 1×10-7 erg/cm, and various Gilbert damping from 0.09 to 0.5. To observe the thermal effect, two schemes are used which are Reduced Barrier Writing and Curie Point Writing. As a result, materials with high damping is able to reverse the magnetizations faster and reduce the energy barrier. Moreover, it can lower the minimum field to start the magnetizations reversal, threshold field, and probability rate. The heating near Curie temperature has succeeded in reducing the reversal field to 1/10 compared to writing process in absence of thermal field.

Fragmentation of a Filamentary Cloud Permeated by a Perpendicular Magnetic Field

Energy Technology Data Exchange (ETDEWEB)

Hanawa, Tomoyuki [Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, Chiba 263-8522 (Japan); Kudoh, Takahiro [Faculty of Education, Nagasaki University, 1-14 Bonkyo-machi, Nagasaki, Nagasaki 852-8521 (Japan); Tomisaka, Kohji [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)

2017-10-10

We examine the linear stability of an isothermal filamentary cloud permeated by a perpendicular magnetic field. Our model cloud is assumed to be supported by gas pressure against self-gravity in the unperturbed state. For simplicity, the density distribution is assumed to be symmetric around the axis. Also for simplicity, the initial magnetic field is assumed to be uniform, and turbulence is not taken into account. The perturbation equation is formulated to be an eigenvalue problem. The growth rate is obtained as a function of the wavenumber for fragmentation along the axis and the magnetic field strength. The growth rate depends critically on the outer boundary. If the displacement vanishes in regions very far from the cloud axis (fixed boundary), cloud fragmentation is suppressed by a moderate magnetic field, which means the plasma beta is below 1.67 on the cloud axis. If the displacement is constant along the magnetic field in regions very far from the cloud, the cloud is unstable even when the magnetic field is infinitely strong. The cloud is deformed by circulation in the plane perpendicular to the magnetic field. The unstable mode is not likely to induce dynamical collapse, since it is excited even when the whole cloud is magnetically subcritical. For both boundary conditions, the magnetic field increases the wavelength of the most unstable mode. We find that the magnetic force suppresses compression perpendicular to the magnetic field especially in regions of low density.

Exact Foldy-Wouthuysen transformation for gravitational waves and magnetic field background

International Nuclear Information System (INIS)

Goncalves, Bruno; Obukhov, Yuri N.; Shapiro, Ilya L.

2007-01-01

We consider an exact Foldy-Wouthuysen transformation for the Dirac spinor field on the combined background of a gravitational wave and constant uniform magnetic field. By taking the classical limit of the spinor field Hamiltonian, we arrive at the equations of motion for the nonrelativistic spinning particle. Two different kinds of gravitational fields are considered and in both cases the effect of the gravitational wave on the spinor field and on the corresponding spinning particle may be enforced by a sufficiently strong magnetic field. This result can be relevant for astrophysical applications and, in principle, useful for creating the gravitational wave detectors based on atomic physics and precise interferometry

Movement of liquid metal in welding bath during welding in longitudinal magnetic field

International Nuclear Information System (INIS)

Kovalev, I.M.; Rybakov, A.S.

1977-01-01

The specific features are considered of liquid metal flow in a bath during welding of steel 12Kh18N10T plates with a non-consumable electrode in argon under interaction of the arc and bath with a longitudinal constant magnetic field. In controlling the velocity field of metal flow, the longitudinal magnetic field permits to form a seam at automatic welding of horizontal joints on a vertical plane

Heat kernel expansion for fermionic billiards in an external magnetic field

International Nuclear Information System (INIS)

Antoine, M.; Comtet, A.; Knecht, M.

1989-05-01

Using Seeley's heat kernel expansion, we compute the asymptotic density of states of the Dirac operator coupled to a magnetic field on a two dimensional manifold with boundary (fermionic billiard). Local boundary conditions compatible with vector current conservation depend on a free parameter α. It is shown that the perimeter correction identically vanishes for α = 0. In that case, the next order constant term is found to be proportional to the Euler characteristic of the manifold. These results are independent of the external magnetic field and of the shape of the billiard, provided the boundary is sufficiently smooth. For the flat circular billiard, the constant term is found to be - 1/12, in agreement with a numerical result by M.V. BERRY and R.J. MONDRAGON (1987)

Magnetic and magnetoelastic anomalies of an Er.sub.2./sub.Co.sub.17./sub. single crystal in high magnetic fields

Czech Academy of Sciences Publication Activity Database

Andreev, Alexander V.; Skourski, Y.; Kuz'min, M.D.; Yasin, S.; Zherlitsyn, S.; Daou, R.; Wosnitza, J.; Iwasa, A.; Kondo, A.; Matsuo, A.; Kindo, K.

2011-01-01

Roč. 83, č. 18 (2011), "184422-1"-"184422-9" ISSN 1098-0121 R&D Projects: GA ČR GA202/09/0339 Institutional research plan: CEZ:AV0Z10100520 Keywords : magnetic and magnetoelastic anomalies * high magnetic fields * anisotropy constants Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011

Trapped field recovery of bulk superconductor magnets by static field magnetization

Energy Technology Data Exchange (ETDEWEB)

Deng, Z., E-mail: zigang@kaiyodai.ac.jp [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

2011-11-15

A series of initial trapped fields after ZFC or FC magnetization are used to simulate the attenuated trapped field. It is possible and easy to recover the lost trapped field and regain the best trapped field performance as before. In the re-magnetization process, the initial magnetic flux inside the bulk magnets will help to recover the trapped field. The optimum recovery field is recommended to be 2.5 times the saturation field of the bulk at LN2 temperature. Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa{sub 2}Cu{sub 3}O{sub y} (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

Modelling the Earth's Main Magnetic Field by the spinning Astrid-2 satellite

DEFF Research Database (Denmark)

Merayo, Jose Maria Garcia; Jørgensen, Peter Siegbjørn; Risbo, T.

1999-01-01

and therefore the mapping of the Earth's magnetic field may be possible. The spinning of the spacecraft about a certain axis makes the stabilisation in space possible. This fact and the well distributed data over the globe makes the magnetic data well suited for the estimation of the magnetic field model......The Swedish micro-satellite Astrid-2 was successfully launched into a near polar orbit last December 98. Despite the fact that its primary mission was the research of Auroral phenomena, the magnetic instrumentation has been designed to accomplish high resolution vector field magnetic measurements...... at the spacecraft altitude (circa 1000km). Several methods for field modelling are presented in this paper with the assumption that the direction of the spin axis is nearly constant. In any case the orientation of the magnetometer is to bedetermined simultaneously with the instrument calibration and main field...

Focus on Materials Analysis and Processing in Magnetic Fields

Directory of Open Access Journals (Sweden)

Yoshio Sakka, Noriyuki Hirota, Shigeru Horii and Tsutomu Ando

2009-01-01

of MAP3. Other papers of the proceedings are published in Journal of Physics: Conference Series. Tournier and Beaugnon review experimental texturing in metallic melts by cooling in magnetic fields, which is modeled in detail in a study by Tournier. Wang et al provide further experimental results on the solidification of Mn-90.4 wt % Sb alloy in magnetic fields. The orientations of grains and particles induced by magnetic fields is reported by Horii et al (rare-earth-doped cuprates, Tanaka et al (barium-bismuth titanate ceramics, Liu and Schwartz (Bi2Sr2CaCu2Ox/AgMg wires and Tsuda and Sakka (carbon nanotubes. Gielen et al present a model of how to quantify a molecular alignment using magnetic birefringence, and Ando et al simulate the movement of feeble particles in magnetic fields. Hirota et al report the experimental control of the lattice constant in a triangular lattice of feeble magnetic particles. The size separation of diamagnetic particles by magnetic fields is experimentally studied by Tarn et al and theoretically studied by Fukui et al. A setup measuring x-ray diffraction patterns in magnetic fields up to 5 T and temperatures above 200 oC has been developed by Mitsui et al.We hope that this focus issue will help readers to understand several aspects of materials analysis and processing in magnetic fields at the frontier of the science.

Magnetization measurement of single La0.67Ca0.33MnO3 nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator

International Nuclear Information System (INIS)

Antonio, D.; Dolz, M.I.; Pastoriza, H.

2010-01-01

Using a silicon micromechanical resonator as a sensitive magnetometer, the authors have studied both experimentally and theoretically the magnetic behavior of two isolated ferromagnetic nanotubes of perovskite La 0.67 Ca 0.33 MnO 3 . The article investigates the specific configuration where a magnetic field H is applied perpendicular to the magnetic easy axis of an isolated nanotube characterized by an uniaxial anisotropy constant K. In this situation, the magnetization M reduces the effective elastic constant k M of the resonator. This softening of the mechanical system is opposed to the hardening effect of M observed in a previous work, where H was applied parallel to the easy axis. Moreover, in this magnetic field configuration two distinct magnetization regimes are manifested, depending on the magnitude of H. For H>>2K/M the magnetization is almost parallel to the applied magnetic field and for H<<2K/M it is almost parallel to the easy axis of the nanotube. At a certain value of H there is a sharp transition from one regime to the other, accompanied by a peak in the energy dissipation.

Investigation of polycrystalline Nd2Fe14B texturing by solidification in a magnetic field

International Nuclear Information System (INIS)

Paduani, C.; Ducruet, C.; Rivoirard, S.; Rango, P. de; Tournier, R.

2001-01-01

A polycrystalline sample of Nd 2 Fe 14 B was prepared by induction melting and solidification in an intense applied magnetic field, to study the alignment due to residual magnetocrystalline anisotropy of this compound near the melting point. A well-defined direction of the thermal gradient perpendicular to the magnetic field was achieved by means of an appropriate experimental set-up. The results of measurements indicate that the sample is substantially textured, but not in parallel to the elaboration field. A numerical method is utilized for the determination of anisotropy parameters in Nd 2 Fe 14 B compound, involving the analysis of measured magnetization curves. The minimization of the free-energy density, expanded in terms of these constants, is performed to determine the sub-lattice terms which are necessary to calculate the polarization curves. A fitting of the measured magnetization curves obtained at room temperature is realized to obtain the anisotropy constants, texture parameters and saturation magnetization

Skyrmion robustness in noncentrosymmetric magnets with axial symmetry: The role of anisotropy and tilted magnetic fields

Science.gov (United States)

Leonov, A. O.; Kézsmárki, I.

2017-12-01

We investigate the stability of Néel skyrmions against tilted magnetic fields in polar magnets with uniaxial anisotropy ranging from easy-plane to easy-axis type. We construct the corresponding phase diagrams and investigate the internal structure of skewed skyrmions with displaced cores. We find that moderate easy-plane anisotropy increases the stability range of Néel skyrmions for fields along the symmetry axis, while moderate easy-axis anisotropy enhances their robustness against tilted magnetic fields. We stress that the direction along which the skyrmion cores are shifted depends on the symmetry of the underlying crystal lattice. The cores of Néel skyrmions, realized in polar magnets with Cn v symmetry, are displaced either along or opposite to the off-axis (in-plane) component of the magnetic field depending on the rotation sense of the magnetization, dictated by the sign of the Dzyaloshinskii constant. The core shift of antiskyrmions, present in noncentrosymmetric magnets with D2 d symmetry, depends on the in-plane orientation of the magnetic field and can be parallel, antiparallel, or perpendicular to it. We argue that the role of anisotropy in magnets with axially symmetric crystal structure is different from that in cubic helimagnets. Our results can be applied to address recent experiments on polar magnets with C3 v symmetry, GaV4S8 and GaV4Se8 , and Mn1.4Pt0.9Pd0.1Sn with D2 d symmetry.

Omnigenous magnetic fields

International Nuclear Information System (INIS)

Stupakov, G.V.

1982-01-01

In omnigenous magnetic fields particles' drift surfaces coincide with plasma magnetic surfaces. In this paper we formulate equations of omnigenous magnetic fields in natural curvilinear coordinates. An analysis of fields which are omnigenous only in the paraxial approximation is presented. (author)

Does Magnetic Field Affect Malaria Parasite Replication in Human Red Blood Cells?

Science.gov (United States)

Chanturiya, Alexandr N.; Glushakova, Svetlana; Yin, Dan; Zimmerberg, Joshua

2004-01-01

Digestion of red blood cell (RBC) hemoglobin by the malaria parasite results in the formation of paramagnetic hemazoin crystals inside the parasite body. A number of reports suggest that magnetic field interaction with hamazoin crystals significantly reduces the number of infected cells in culture, and thus magnetic field can be used to combat malaria. We studies the effects of magnetic filed on the Plasmodium falciparum asexual life cycle inside RBCs under various experimental conditions. No effect was found during prolonged exposure of infected RBCs to constant magnetic fields up to 6000 Gauss. Infected RBCs were also exposed, under temperature-controlled conditions, to oscillating magnetic fields with frequencies in the range of 500-20000 kHz, and field strength 30-600 Gauss. This exposure often changed the proportion of different parasite stages in treated culture compared to controls. However, no significant effect on parasitemia was observed in treated cultures. This result indicates that the magnetic field effect on Plasmodium falciparum is negligible, or that hypothetical negative and positive effects on different stages within one 48-hour compensate each other.

Nuclear magnetic resonance and earth magnetic field

International Nuclear Information System (INIS)

Anon.

1998-01-01

Nuclear magnetic resonance concerns nuclei whose spin is different from 0. These nuclei exposed to a magnetic field is comparable to a peg top spinning around its axis while being moved by a precession movement called Larmor precession. This article presents an experiment whose aim is to reveal nuclear magnetism of nuclei by observing Larmor precession phenomena due to the earth magnetic field. The earth magnetic field being too weak, it is necessary to increase the magnetization of the sample during a polarization phase. First the sample is submitted to a magnetic field B perpendicular to the earth magnetic field B 0 , then B is cut off and the nuclei move back to their equilibrium position by executing a precession movement due to B 0 field. (A.C.)

Influence of external magnetic field, finite-size effects and chemical potential on the phase transition of a complex scalar field

Energy Technology Data Exchange (ETDEWEB)

Cavalcanti, E.; Castro, E.; Malbouisson, A.P.C. [Centro Brasileiro de Pesquisas Fisicas/MCTI, Rio de Janeiro, RJ (Brazil); Linhares, C.A. [Universidade do Estado do Rio de Janeiro, Instituto de Fisica, Rio de Janeiro, RJ (Brazil)

2017-10-15

A scalar model is built, as a quantum field theory defined on a toroidal topology, to describe a phase transition in films subjected to periodic boundary conditions and influenced by an external and constant magnetic field. Criticality is studied and the relations between the critical temperature, the film thickness, the magnetic field strength and the chemical potential are investigated. Since the model describes a second-order phase transition a comparison with the Ginzburg-Landau theory is made. (orig.)

Linear Optical Response of Silicon Nanotubes Under Axial Magnetic Field

Science.gov (United States)

Chegel, Raad; Behzad, Somayeh

2013-01-01

We investigated the optical properties of silicon nanotubes (SiNTs) in the low energy region, E < 0.5 eV, and middle energy region, 1.8 eV < E < 2 eV. The dependence of optical matrix elements and linear susceptibility on radius and magnetic field, in terms of one-dimensional (1-d) wavevector and subband index, is calculated using the tight-binding approximation. It is found that, on increasing the nanotube diameter, the low-energy peaks show red-shift and their intensities are decreased. Also, we found that in the middle energy region all tubes have two distinct peaks, where the energy position of the second peak is approximately constant and independent of the nanotube diameter. Comparing the band structure of these tubes in different magnetic fields, several differences are clearly seen, such as splitting of degenerate bands, creation of additional band-edge states, and bandgap modification. It is found that applying the magnetic field leads to a phase transition in zigzag silicon hexagonal nanotubes (Si h-NTs), unlike in zigzag silicon gear-like nanotubes (Si g-NTs), which remain semiconducting in any magnetic field. We found that the axial magnetic field has two effects on the linear susceptibility spectrum, namely broadening and splitting. The axial magnetic field leads to the creation of a peak with energy less than 0.2 eV in metallic Si h-NTs, whereas in the absence of a magnetic field such a transition is not allowed.

Air core notch-coil magnet with variable geometry for fast-field-cycling NMR.

Science.gov (United States)

Kruber, S; Farrher, G D; Anoardo, E

2015-10-01

In this manuscript we present details on the optimization, construction and performance of a wide-bore (71 mm) α-helical-cut notch-coil magnet with variable geometry for fast-field-cycling NMR. In addition to the usual requirements for this kind of magnets (high field-to-power ratio, good magnetic field homogeneity, low inductance and resistance values) a tunable homogeneity and a more uniform heat dissipation along the magnet body are considered. The presented magnet consists of only one machined metallic cylinder combined with two external movable pieces. The optimal configuration is calculated through an evaluation of the magnetic flux density within the entire volume of interest. The magnet has a field-to-current constant of 0.728 mT/A, allowing to switch from zero to 0.125 T in less than 3 ms without energy storage assistance. For a cylindrical sample volume of 35 cm(3) the effective magnet homogeneity is lower than 130 ppm. Copyright © 2015 Elsevier Inc. All rights reserved.

Probe branes thermalization in external electric and magnetic fields

International Nuclear Information System (INIS)

Ali-Akbari, M.; Ebrahim, H.; Rezaei, Z.

2014-01-01

We study thermalization on rotating probe branes in AdS 5 ×S 5 background in the presence of constant external electric and magnetic fields. In the AdS/CFT framework this corresponds to thermalization in the flavour sector in field theory. The horizon appears on the worldvolume of the probe brane due to its rotation in one of the sphere directions. For both electric and magnetic fields the behaviour of the temperature is independent of the probe brane dimension. We also study the open string metric and the fluctuations of the probe brane in such a set-up. We show that the temperatures obtained from open string metric and observed by the fluctuations are larger than the one calculated from the induced metric

The changes of macroscopic features and microscopic structures of water under influence of magnetic field

International Nuclear Information System (INIS)

Pang Xiaofeng; Deng Bo

2008-01-01

Influences of magnetic field on microscopic structures and macroscopic properties of water are studied by the spectrum techniques of infrared, Raman, visible, ultraviolet lights and X-ray. From these investigations, we know that the magnetic fields change the distribution of molecules and electrons, cause displacements and polarization of molecules and atoms, result in changes of dipole-moment transition and vibrational states of molecules and variation of transition probability of electrons, but does not alter the constitution of molecules and atoms. These are helpful in seeking the mechanism of magnetization of water. Meanwhile, we also measure the changed rules of the surface tension force, soaking effect or angle of contact, viscosity, rheology features, refraction index, dielectric constant and electric conductivity of magnetized water relative to that of pure water. The results show that the magnetic fields increase the soaking degree and hydrophobicity of water to materials, depress its surface-tension force, diminish the viscosity of war, enhance the feature of plastic flowing of water, and increase the refraction index, dielectric constant and electric conductivity of water after magnetization. These changes are caused by the above changes of microscopic structures under the action of magnetic field. Therefore, our studies are significant in science and has practical value of applications

Force-free magnetic fields - The magneto-frictional method

Science.gov (United States)

Yang, W. H.; Sturrock, P. A.; Antiochos, S. K.

1986-01-01

The problem under discussion is that of calculating magnetic field configurations in which the Lorentz force j x B is everywhere zero, subject to specified boundary conditions. We choose to represent the magnetic field in terms of Clebsch variables in the form B = grad alpha x grad beta. These variables are constant on any field line so that each field line is labeled by the corresponding values of alpha and beta. When the field is described in this way, the most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. We show that such field configurations may be calculated by a magneto-frictional method. We imagine that the field lines move through a stationary medium, and that each element of magnetic field is subject to a frictional force parallel to and opposing the velocity of the field line. This concept leads to an iteration procedure for modifying the variables alpha and beta, that tends asymptotically towards the force-free state. We apply the method first to a simple problem in two rectangular dimensions, and then to a problem of cylindrical symmetry that was previously discussed by Barnes and Sturrock (1972). In one important respect, our new results differ from the earlier results of Barnes and Sturrock, and we conclude that the earlier article was in error.

Rectification of harmonically oscillating magnetic fields in quarter circular Josephson junctions

International Nuclear Information System (INIS)

Shaju, P.D.; Kuriakose, V.C.

2003-01-01

A novel method for rectifying harmonically varying magnetic fields is demonstrated using fluxons in quarter circular Josephson junctions (JJs). A JJ with a quarter circular geometry terminated with a load resistor at one end is found to be capable of rectifying alternating fields when biased with a constant dc current. An external magnetic field applied parallel to the dielectric barrier of the junction interacts with the edges of the junction and make asymmetric boundary conditions. These asymmetric boundary conditions facilitate fluxon penetration under a dc bias from one end of the junction in alternate half cycles of the applied field. Thus effective rectification of the field can be achieved using quarter circular JJs. This unique phenomenon is specific to this geometry and can be exploited for making superconducting magnetic field rectifiers. This proposed device is expected to have important applications in millimeter and sub-millimeter radio wave astronomy

Novel Electrochemical Phenomena in Magnetic Fields(Research in High Magnetic Fields)

OpenAIRE

Mogi, Iwao; Kamiko, Masao

1996-01-01

Recent two topics are given of electrochemical studies in steady magnetic fields at the High Field Laboratory of Tohoku University. One is the magnetic-field-induced diffusion-limited-aggregation in the pattern formation of silver electrodeposits . The other is the magnetic field effect on the learning effect in a dopant-exchange process of an organic conducting polymer polypyrrole.

Oxygen consumption and mortality rate of mice after X radiation under the influence of magnetic fields

International Nuclear Information System (INIS)

Rekbi, M.

1984-01-01

In this work it was studied whether an influence on the oxygen use was to be expected as a result of a magnetic pulsating field. This could not be determined. An increased effect of the magnetic field with respect to the reduction of the mortality rate was, however, to be observed. Thereby the influence of similar constant and pulsating fields was discussed from various perspectives. The question of the biological effect mechanism of the magnetic field (main issue of the influence of the magnetic field during or after the irradiation) can only be answered by further comprehensive investigations. (orig./MG) [de

Field-induced non-collinear magnetic structures in amorphous Co80-xDy xB20 alloys

International Nuclear Information System (INIS)

Annouar, F.; Roky, K.; Lassri, H.; Elmoussaoui, A.; Driouch, L.; Ayadi, M.; Omri, M.; Krishnan, R.

2005-01-01

Amorphous Co 80-x Dy x B 20 alloys have been prepared by melt spinning technique and their magnetic properties have been studied. The mean field theory has been used to explain the temperature dependence of the magnetization. High-field magnetization studies performed at 4.2 K in magnetic fields up to 38 T have revealed, for samples with stoichiometry close to that of a compensated ferrimagnet, a magnetic behavior that is characteristic of a non-collinear magnetic structure of the Dy and Co sublattices. From the non-collinear regime the exchange interactions between the Co and Dy magnetic sublattices and the magnetic anisotropy constants have been evaluated

Pulsed magnetic field generation suited for low-field unilateral nuclear magnetic resonance systems

Science.gov (United States)

Gaunkar, Neelam Prabhu; Selvaraj, Jayaprakash; Theh, Wei-Shen; Weber, Robert; Mina, Mani

2018-05-01

Pulsed magnetic fields can be used to provide instantaneous localized magnetic field variations. In presence of static fields, pulsed field variations are often used to apply torques and in-effect to measure behavior of magnetic moments in different states. In this work, the design and experimental performance of a pulsed magnetic field generator suited for low static field nuclear magnetic resonance (NMR) applications is presented. One of the challenges of low bias field NMR measurements is low signal to noise ratio due to the comparable nature of the bias field and the pulsed field. Therefore, a circuit is designed to apply pulsed currents through an inductive load, leading to generation of pulsed magnetic fields which can temporarily overpower the effect of the bias field on magnetic moments. The designed circuit will be tuned to operate at the precession frequency of 1H (protons) placed in a bias field produced by permanent magnets. The designed circuit parameters may be tuned to operate under different bias conditions. Therefore, low field NMR measurements can be performed for different bias fields. Circuit simulations were used to determine design parameters, corresponding experimental measurements will be presented in this work.

Induced magnetic-field effects in inductively coupled plasmas

International Nuclear Information System (INIS)

Cohen, R.H.; Rognlien, T.D.

1995-01-01

In inductive plasma sources, the rapid spatial decay of the electric field arising from the skin effect produces a large radio frequency (RF) magnetic field via Faraday's law. We previously determined that this magnetic field leads to a reduction of the electron density in the skin region, as well as a reduction in the collisionless heating rate. The electron deficit leads to the formation of an electrostatic potential which pulls electrons in to restore quasineutrality. Here we calculate the electron density including both the induced and electrostatic fields. If the wave frequency is not too low, the ions respond only to the averaged fields, and hence the electrostatic field is oscillatory, predominantly at the second harmonic of the applied field. We calculate the potential required to establish a constant electron density, and compare with numerical orbit-code calculations. For times short compared to ion transit times, the quasineutral density is just the initial ion density. For timescales long enough that the ions can relax, the density profile can be found from the solution of fluid equations with an effective (ponderomotive-like) potential added. Although the time-varying electrostatic potential is an extra source of heating, the net effect of the induced magnetic and electrostatic fields through trapping, early turning, and direct heating is a significant reduction in collisionless heating for parameters of interest

Extinction of photoemission of Mn-Doped ZnS nanofluid in weak magnetic field

Science.gov (United States)

Vu, Anh-Tuan; Bui, Hong-Van; Pham, Van-Ben; Le, Van-Hong; Hoang, Nam-Nhat

2016-08-01

The observation of extinction of photoluminescence of Mn-doped ZnS nanofluid under applying of weak magnetic field is reported. At a constant field of 270 Gauss and above, the exponential decays of photoluminescent intensity was observed in disregard of field direction. About 50% extinction was achieved after 30 minute magnetization and a total extinction after 1 hour. The memory effect preserved for more than 2 hours at room temperature. This extinction was observed in a system with no clear ferromagnetic behavior.

Influence of an ac magnetic field and induced magnetic anisotropy on the surface magnetoimpedance tensor in an amorphous wire

International Nuclear Information System (INIS)

Chen, A P; Zhukova, V; Zhukov, A; Dominguez, L; Chizhik, A; Blanco, J M; Gonzalez, J

2004-01-01

The influence of an ac magnetic field and the induced magnetic anisotropy (by field annealing and torsion annealing) on the magnetoimpedance (MI) tensor in an amorphous wire has been analysed. The experimental measurements were carried out in an amorphous wire of composition (Co 0.94 Fe 0.06 ) 72.5 Si 12.5 B 15 , with a negative, nearly zero magnetostriction constant, excited either by an ac circular, h φ , or an axial, h z , magnetic field created by an ac electric current passing along the wire or through an exciting coil mounted on the wire, respectively. The ac current amplitude was changed from 7.5 to 40 mA and the current frequency f was varied from 1.5 to 20 MHz. The induced magnetic anisotropies modify the MI response drastically. The field annealed sample shows a unique peak of the MI effect, while the torsion annealed sample presents an asymmetric giant magnetoimpedance ratio associated with the induced magnetic anisotropy which provokes such thermal treatments

Magnetic field of the Earth

Science.gov (United States)

Popov, Aleksey

2013-04-01

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

A dynamic model of the eye nystagmus response to high magnetic fields.

Science.gov (United States)

Glover, Paul M; Li, Yan; Antunes, Andre; Mian, Omar S; Day, Brian L

2014-02-07

It was recently shown that high magnetic fields evoke nystagmus in human subjects with functioning vestibular systems. The proposed mechanism involves interaction between ionic currents in the endolymph of the vestibular labyrinth and the static magnetic field. This results in a Lorentz force that causes endolymph flow to deflect the cupulae of the semi-circular canals to evoke a vestibular-ocular reflex (VOR). This should be analogous to stimulation by angular acceleration or caloric irrigation. We made measurements of nystagmus slow-phase velocities in healthy adults experiencing variable magnetic field profiles of up to 7 T while supine on a bed that could be moved smoothly into the bore of an MRI machine. The horizontal slow-phase velocity data were reliably modelled by a linear transfer function incorporating a low-pass term and a high-pass adaptation term. The adaptation time constant was estimated at 39.3 s from long exposure trials. When constrained to this value, the low-pass time constant was estimated at 13.6 ± 3.6 s (to 95% confidence) from both short and long exposure trials. This confidence interval overlaps with values obtained previously using angular acceleration and caloric stimulation. Hence it is compatible with endolymph flow causing a cupular deflection and therefore supports the hypothesis that the Lorentz force is a likely transduction mechanism of the magnetic field-evoked VOR.

A dynamic model of the eye nystagmus response to high magnetic fields

International Nuclear Information System (INIS)

Glover, Paul M; Li, Yan; Antunes, Andre; Mian, Omar S; Day, Brian L

2014-01-01

It was recently shown that high magnetic fields evoke nystagmus in human subjects with functioning vestibular systems. The proposed mechanism involves interaction between ionic currents in the endolymph of the vestibular labyrinth and the static magnetic field. This results in a Lorentz force that causes endolymph flow to deflect the cupulae of the semi-circular canals to evoke a vestibular–ocular reflex (VOR). This should be analogous to stimulation by angular acceleration or caloric irrigation. We made measurements of nystagmus slow-phase velocities in healthy adults experiencing variable magnetic field profiles of up to 7 T while supine on a bed that could be moved smoothly into the bore of an MRI machine. The horizontal slow-phase velocity data were reliably modelled by a linear transfer function incorporating a low-pass term and a high-pass adaptation term. The adaptation time constant was estimated at 39.3 s from long exposure trials. When constrained to this value, the low-pass time constant was estimated at 13.6 ± 3.6 s (to 95% confidence) from both short and long exposure trials. This confidence interval overlaps with values obtained previously using angular acceleration and caloric stimulation. Hence it is compatible with endolymph flow causing a cupular deflection and therefore supports the hypothesis that the Lorentz force is a likely transduction mechanism of the magnetic field-evoked VOR. (paper)

Open-Access, Low-Magnetic-Field MRI System for Lung Research

Science.gov (United States)

Mair, Ross W.; Rosen, Matthew S.; Tsai, Leo L.; Walsworth, Ronald L.; Hrovat, Mirko I.; Patz, Samuel; Ruset, Iullian C.; Hersman, F. William

2009-01-01

An open-access magnetic resonance imaging (MRI) system is being developed for use in research on orientational/gravitational effects on lung physiology and function. The open-access geometry enables study of human subjects in diverse orientations. This system operates at a magnetic flux density, considerably smaller than the flux densities of typical other MRI systems, that can be generated by resistive electromagnet coils (instead of the more-expensive superconducting coils of the other systems). The human subject inhales air containing He-3 or Xe-129 atoms, the nuclear spins of which have been polarized by use of a laser beam to obtain a magnetic resonance that enables high-resolution gas space imaging at the low applied magnetic field. The system includes a bi-planar, constant-current, four-coil electromagnet assembly and associated electronic circuitry to apply a static magnetic field of 6.5 mT throughout the lung volume; planar coils and associated circuitry to apply a pulsed magnetic-field-gradient for each spatial dimension; a single, detachable radio-frequency coil and associated circuitry for inducing and detecting MRI signals; a table for supporting a horizontal subject; and electromagnetic shielding surrounding the electromagnet coils.

Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

Science.gov (United States)

Woolley, Robert D.

1998-01-01

A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.

Total Magnetic Field Signatures over Submarine HVDC Power Cables

Science.gov (United States)

Johnson, R. M.; Tchernychev, M.; Johnston, J. M.; Tryggestad, J.

2013-12-01

Mikhail Tchernychev, Geometrics, Inc. Ross Johnson, Geometrics, Inc. Jeff Johnston, Geometrics, Inc. High Voltage Direct Current (HVDC) technology is widely used to transmit electrical power over considerable distances using submarine cables. The most commonly known examples are the HVDC cable between Italy and Greece (160 km), Victoria-Tasmania (300 km), New Jersey - Long Island (82 km) and the Transbay cable (Pittsburg, California - San-Francisco). These cables are inspected periodically and their location and burial depth verified. This inspection applies to live and idle cables; in particular a survey company could be required to locate pieces of a dead cable for subsequent removal from the sea floor. Most HVDC cables produce a constant magnetic field; therefore one of the possible survey tools would be Marine Total Field Magnetometer. We present mathematical expressions of the expected magnetic fields and compare them with fields observed during actual surveys. We also compare these anomalies fields with magnetic fields produced by other long objects, such as submarine pipelines The data processing techniques are discussed. There include the use of Analytic Signal and direct modeling of Total Magnetic Field. The Analytic Signal analysis can be adapted using ground truth where available, but the total field allows better discrimination of the cable parameters, in particular to distinguish between live and idle cable. Use of a Transverse Gradiometer (TVG) allows for easy discrimination between cable and pipe line objects. Considerable magnetic gradient is present in the case of a pipeline whereas there is less gradient for the DC power cable. Thus the TVG is used to validate assumptions made during the data interpretation process. Data obtained during the TVG surveys suggest that the magnetic field of a live HVDC cable is described by an expression for two infinite long wires carrying current in opposite directions.

Dipole-magnet field models based on a conformal map

Directory of Open Access Journals (Sweden)

P. L. Walstrom

2012-10-01

Full Text Available In general, generation of charged-particle transfer maps for conventional iron-pole-piece dipole magnets to third and higher order requires a model for the midplane field profile and its transverse derivatives (soft-edge model to high order and numerical integration of map coefficients. An exact treatment of the problem for a particular magnet requires use of measured magnetic data. However, in initial design of beam transport systems, users of charged-particle optics codes generally rely on magnet models built into the codes. Indeed, if maps to third order are adequate for the problem, an approximate analytic field model together with numerical map coefficient integration can capture the important features of the transfer map. The model described in this paper is based on the fact that, except at very large distances from the magnet, the magnetic field for parallel pole-face magnets with constant pole gap height and wide pole faces is basically two dimensional (2D. The field for all space outside of the pole pieces is given by a single (complex analytic expression and includes a parameter that controls the rate of falloff of the fringe field. Since the field function is analytic in the complex plane outside of the pole pieces, it satisfies two basic requirements of a field model for higher-order map codes: it is infinitely differentiable at the midplane and also a solution of the Laplace equation. It is apparently the only simple model available that combines an exponential approach to the central field with an inverse cubic falloff of field at large distances from the magnet in a single expression. The model is not intended for detailed fitting of magnetic field data, but for use in numerical map-generating codes for studying the effect of extended fringe fields on higher-order transfer maps. It is based on conformally mapping the area between the pole pieces to the upper half plane, and placing current filaments on the pole faces. An

Magnetic Fields Versus Gravity

Science.gov (United States)

Hensley, Kerry

2018-04-01

Deep within giant molecular clouds, hidden by dense gas and dust, stars form. Unprecedented data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the intricate magnetic structureswoven throughout one of the most massive star-forming regions in the Milky Way.How Stars Are BornThe Horsehead Nebulasdense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [NASA/ESA/Hubble Heritage Team]Simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. In reality, however, star formation is more complicated than a simple give and take between gravity and pressure. Thedusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.How can we learn about the magnetic fields of distant objects? One way is by measuring dust polarization. An elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. This systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains emission perpendicular to the local magnetic field. This allows us to infer the direction of the magnetic field from the direction of polarization.Magnetic field orientations for protostars e2 and e8 derived from Submillimeter Array observations (panels a through c) and ALMA observations (panels d and e). Click to enlarge. [Adapted from Koch et al. 2018]Tracing Magnetic FieldsPatrick Koch (Academia Sinica, Taiwan) and collaborators used high-sensitivity ALMA observations of dust polarization to learn more about the magnetic field morphology of Milky Way star-forming region W51. W51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and North.The ALMA observations reveal

Behavior of moving plasma in solenoidal magnetic field in a laser ion source

International Nuclear Information System (INIS)

Ikeda, S.; Takahashi, K.; Okamura, M.; Horioka, K.

2016-01-01

In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons

Behavior of moving plasma in solenoidal magnetic field in a laser ion source

Energy Technology Data Exchange (ETDEWEB)

Ikeda, S., E-mail: ikeda.s.ae@m.titech.ac.jp [Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8502 (Japan); Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0108 (Japan); Takahashi, K. [Department of Electrical Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2137 (Japan); Okamura, M. [Collider-Accelerator Department, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Horioka, K. [Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8502 (Japan)

2016-02-15

In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons.

Behavior of moving plasma in solenoidal magnetic field in a laser ion source

Science.gov (United States)

Ikeda, S.; Takahashi, K.; Okamura, M.; Horioka, K.

2016-02-01

In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons.

One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

Science.gov (United States)

Rath, Shubhalaxmi; Patra, Binoy Krishna

2017-12-01

We have studied how the equation of state of thermal QCD with two light flavors is modified in a strong magnetic field. We calculate the thermodynamic observables of hot QCD matter up to one-loop, where the magnetic field affects mainly the quark contribution and the gluon part is largely unaffected except for the softening of the screening mass. We have first calculated the pressure of a thermal QCD medium in a strong magnetic field, where the pressure at fixed temperature increases with the magnetic field faster than the increase with the temperature at constant magnetic field. This can be understood from the dominant scale of thermal medium in the strong magnetic field, being the magnetic field, in the same way that the temperature dominates in a thermal medium in the absence of magnetic field. Thus although the presence of a strong magnetic field makes the pressure of hot QCD medium larger, the dependence of pressure on the temperature becomes less steep. Consistent with the above observations, the entropy density is found to decrease with the temperature in the presence of a strong magnetic field which is again consistent with the fact that the strong magnetic field restricts the dynamics of quarks to two dimensions, hence the phase space becomes squeezed resulting in the reduction of number of microstates. Moreover the energy density is seen to decrease and the speed of sound of thermal QCD medium increases in the presence of a strong magnetic field. These findings could have phenomenological implications in heavy ion collisions because the expansion dynamics of the medium produced in non-central ultra-relativistic heavy ion collisions is effectively controlled by both the energy density and the speed of sound.

Magnetic fields produced by rotating symmetrical bodies with homogeneous surface charge density

International Nuclear Information System (INIS)

Espejel-Morales, R; Murguía-Romero, G; Calles, A; Cabrera-Bravo, E; Morán-López, J L

2016-01-01

We present a numerical calculation for the stationary magnetic field produced by different rotating bodies with homogeneous and constant surface charge density. The calculation is done by superposing the magnetic field produced by a set of loops of current which mimic the magnetic field produced by belts of current defined by slices of fixed width. We consider the cases of a sphere, ellipsoids, open and closed cylinders and a combination of these in a dumbbell -like shell. We also plot their magnetic field lines using a technique that make use of the Runge–Kutta fourth-order method. Up to our knowledge, the case of closed cylinders was not calculated before. In contrast to previous results, we find that the magnetic field inside finite hollow bodies is homogeneous only in the case of a sphere. This is consequence of the fact that, for the sphere, the surface of any slice taken perpendicularly to the rotation axis, depends only on its thickness, like in the case of an infinite cylinder. (paper)

Numerical investigation of a plasma beam entering transverse magnetic fields

International Nuclear Information System (INIS)

Koga, J.; Geary, J.L.; Tajima, T.; Rostoker, N.

1988-11-01

We study plasma beam injection into transverse magnetic fields using both electrostatic and electromagnetic particle-in-cell (PIC) codes. In the case of small beam momentum or energy (low drift kinetic /beta/) we study both large and small ion gyroradius beams. Large ion gyroradius beams with a large dielectric constant /epsilon/ /muchreverse arrowgt/ (M/m)/sup /1/2// are found to propagate across the magnetic field via E /times/ B drifts at nearly the initial injection velocity, where /epsilon/ = 1 + (/omega//sup pi//sup 2/)/(/Omega//sub i//sup 2/) and (M/m) is the ion to electron mass ratio. Beam degradation and undulations are observed in agreement with previous experimental and analytical results. When /epsilon/ is on the order of (M/m)/sup /1/2//, the plasma beam propagates across field lines at only half its initial velocity and loses its coherent structure. When /epsilon/ is much less than (M/m)/sup /1/2//, the beam particles decouple at the magnetic field boundary, scattering the electrons and slightly deflecting the ions. For small ion gyroradius beam injection a flute type instability is observed at the beam magnetic fields interface. In the case of large beam momentum or energy (high drift kinetic /beta/) we observe good penetration of a plasma beam which shields the magnetic field from the interior of the beam (diagmagnetism). 25 refs., 13 figs., 1 tab

Preliminary Planck constant measurements via UME oscillating magnet Kibble balance

Science.gov (United States)

Ahmedov, H.; Babayiğit Aşkın, N.; Korutlu, B.; Orhan, R.

2018-06-01

The UME Kibble balance project was initiated in the second half of 2014. During this period we have studied the theoretical aspects of Kibble balances, in which an oscillating magnet generates AC Faraday’s voltage in a stationary coil, and constructed a trial version to implement this idea. The remarkable feature of this approach is that it can establish the link between the Planck constant and a macroscopic mass by one single experiment in the most natural way. Weak dependences on variations of environmental and experimental conditions, small size, and other useful features offered by this novel approach reduce the complexity of the experimental set-up. This paper describes the principles of the oscillating magnet Kibble balance and gives details of the preliminary Planck constant measurements. The value of the Planck constant determined with our apparatus is \\boldsymbol{h}/{{\\boldsymbol{h}}\\boldsymbol 90}={1}{.000} {004}~ , with a relative standard uncertainty of 6 ppm.

Optimisation of applied field pulses for microwave assisted magnetic recording

Directory of Open Access Journals (Sweden)

Simon John Greaves

2017-05-01

Full Text Available Grains in a recording medium experience field pulses from a write head during recording. In general, a short head field rise time and a square pulse shape have been viewed as optimal. This work investigates the optimum field pulse shape for microwave assisted magnetic recording on single layer and ECC media. A square pulse was found to give the best recording performance on single layer media, but an initially negative field pulse increasing at a constant rate was more suitable for ECC media.

Studies of time dependence of fields in TEVATRON superconducting dipole magnets

International Nuclear Information System (INIS)

Hanft, R.W.; Brown, B.C.; Herrup, D.A.; Lamm, M.J.; McInturff, A.D.; Syphers, M.J.

1988-01-01

The time variation in the magnetic field of a model Tevatron dipole magnet at constant excitation current has been studied. Variations in symmetry allowed harmonic components over long time ranges show a log t behavior indicative of ''flux creep.'' Both short time range and long time range behavior depend in a detailed way on the excitation history. Similar effects are seen in the remnant fields present in full-scale Tevatron dipoles following current ramping. Both magnitudes and time dependences are observed to depend on details for the ramps, such as ramp rate, flattop duration, and number of ramps. In a few magnets, variations are also seen in symmetry unallowed harmonics. 9 refs., 10 figs

Numerical analyses of a Couette-Taylor flow in the presence of a magnetic field

International Nuclear Information System (INIS)

Tagawa, T; Kaneda, M

2005-01-01

An axisymmetric Couette-Taylor flow of liquid metal in the presence of a magnetic field has been numerically studied. An inner cylinder of a coaxial container is rotating at a constant angular velocity whereas the outer cylindrical wall is at rest. An axial or a toroidal magnetic field is applied to this configuration to investigate the influence of such magnetic fields on the liquid metal Couette-Taylor flow. The toroidal magnetic field can be produced with a straight wire along the central axis in which electric current passes. The governing equations of mass conservation, momentum, Ohm's law and conservation of electric charge for an axisymmetric cylindrical coordinate system have been numerically solved with a finite difference method using the HSMAC algorithm. In the numerical analyses, since the Joule heating and the induced magnetic field are neglected, the system parameters are the Hartmann number and the Reynolds number. The numerical results reveal significant difference in the Couette-Taylor flow depending on whether the applied magnetic field is axial or toroidal as well as on the Hartmann and Reynolds numbers. The axial magnetic field damps out the secondary flow efficiently and velocity gradient in the direction of the magnetic field tends to diminish while the toroidal magnetic field does not have such an efficient damping

Magnetization measurement of single La{sub 0.67}Ca{sub 0.33}MnO{sub 3} nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator

Energy Technology Data Exchange (ETDEWEB)

Antonio, D., E-mail: dario.antonio@cab.cnea.gov.a [Comision Nacional de Energia Atomica, Centro Atomico Bariloche, (8400) S. C. de Bariloche (Argentina); Dolz, M.I.; Pastoriza, H. [Comision Nacional de Energia Atomica, Centro Atomico Bariloche, (8400) S. C. de Bariloche (Argentina)

2010-03-15

Using a silicon micromechanical resonator as a sensitive magnetometer, the authors have studied both experimentally and theoretically the magnetic behavior of two isolated ferromagnetic nanotubes of perovskite La{sub 0.67}Ca{sub 0.33}MnO{sub 3}. The article investigates the specific configuration where a magnetic field H is applied perpendicular to the magnetic easy axis of an isolated nanotube characterized by an uniaxial anisotropy constant K. In this situation, the magnetization M reduces the effective elastic constant k{sub M} of the resonator. This softening of the mechanical system is opposed to the hardening effect of M observed in a previous work, where H was applied parallel to the easy axis. Moreover, in this magnetic field configuration two distinct magnetization regimes are manifested, depending on the magnitude of H. For H>>2K/M the magnetization is almost parallel to the applied magnetic field and for H<<2K/M it is almost parallel to the easy axis of the nanotube. At a certain value of H there is a sharp transition from one regime to the other, accompanied by a peak in the energy dissipation.

Trapped field recovery of bulk superconductor magnets by static field magnetization

Science.gov (United States)

Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

2011-11-01

Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa2Cu3Oy (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

Highly versatile atomic micro traps generated by multifrequency magnetic field modulation

International Nuclear Information System (INIS)

Courteille, Ph W; Deh, B; Fortagh, J; Guenther, A; Kraft, S; Marzok, C; Slama, S; Zimmermann, C

2006-01-01

We propose the realization of custom-designed adiabatic potentials for cold atoms based on multimode radio frequency radiation in combination with static inhomogeneous magnetic fields. For example, the use of radio frequency combs gives rise to periodic potentials acting as gratings for cold atoms. In strong magnetic field gradients, the lattice constant can be well below 1 μm. By changing the frequencies of the comb in time the gratings can easily be propagated in space, which may prove useful for Bragg scattering atomic matter waves. Furthermore, almost arbitrarily shaped potentials are possible such as disordered potentials on a scale of several 100 nm or lattices with a spatially varying lattice constant. The potentials can be made state selective and, in the case of atomic mixtures, also species selective. This opens new perspectives for generating tailored quantum systems based on ultracold single atoms or degenerate atomic and molecular quantum gases

Influence of continuous magnetic field on the separation of ephedrine enantiomers by molecularly imprinted polymers.

Science.gov (United States)

Guerreiro, António R; Korkhov, Vadim; Mijangos, Irene; Piletska, Elena V; Rodins, Juris; Turner, Anthony P F; Piletsky, Sergey A

2008-02-28

A set of polymers was imprinted with (-)-ephedrine using UV initiation, under the influence of a constant external magnetic field with intensities ranging from 0 to 1.55 T. Synthesised materials were characterised by X-ray crystallography, infrared spectroscopy, swelling and surface area. Recognition properties were assessed by the ability to discriminate between (+) and (-)-ephedrine and by Scatchard analyses on chromatographic mode. It was shown that polymer morphology and recognition properties are affected by the magnetic field. This resulted in considerable improvements in the chromatographic resolution of ephedrine enantiomers by materials synthesised under the influence of magnetic field. Apparently the magnetic field improved the ordering of the polymer structure and facilitated the formation of more uniform imprinting sites.

Magnetic Field Calculator

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...

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

International Nuclear Information System (INIS)

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

2010-01-01

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.

Strong Magnetic Field Characterisation

Science.gov (United States)

2012-04-01

an advertised surface field of approximately 0.5 T were used to supply the static magnetic field source. The disc magnet had a diameter of 50 mm and... colour bar indicates the magnetic field strength set to an arbitrary 0.25 T. The white area has a field >0.25 T. The size of the arrow is proportional...9 shows the magnetic field strength along a slice in the XZ plane. The colours represent the total UNCLASSIFIED 10 UNCLASSIFIED DSTO-TR-2699

Schrödinger and Dirac operators with the Aharonov-Bohm and magnetic-solenoid fields

International Nuclear Information System (INIS)

Gitman, D M; Tyutin, I V; Voronov, B L

2012-01-01

We construct all self-adjoint Schrödinger and Dirac operators (Hamiltonians) with both the pure Aharonov-Bohm (AB) field and the so-called magnetic-solenoid field (a collinear superposition of the AB field and a constant magnetic field). We perform a spectral analysis for these operators, which includes finding spectra and spectral decompositions, or inversion formulae. In constructing the Hamiltonians and performing their spectral analysis, we follow, respectively, the von Neumann theory of self-adjoint extensions of symmetric operators and the Krein method of guiding functionals. (paper)

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

Science.gov (United States)

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

2001-01-01

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.

Model for field-induced reorientation strain in magnetic shape memory alloy with tensile and compressive loads

International Nuclear Information System (INIS)

Zhu Yuping; Dui Guansuo

2008-01-01

A model based on the micromechanical and the thermodynamic theory is presented for field-induced martensite reorientation in magnetic shape memory alloy (MSMA) single crystals. The influence of variants morphology and the material property to constitutive behavior is considered. The nonlinear and hysteretic strain and magnetization response of MSMA are investigated for two main loading cases, namely the magnetic field-induced reorientation of variants under constant compressive stress and tensile stress. The predicted results have shown that increasing tensile loading reduces the required field for actuation, while increasing compressive loads result in the required magnetic field growing considerably. It is helpful to design the intelligent composite with MSMA fibers

Generation of strong pulsed magnetic fields using a compact, short pulse generator

Science.gov (United States)

Yanuka, D.; Efimov, S.; Nitishinskiy, M.; Rososhek, A.; Krasik, Ya. E.

2016-04-01

The generation of strong magnetic fields (˜50 T) using single- or multi-turn coils immersed in water was studied. A pulse generator with stored energy of ˜3.6 kJ, discharge current amplitude of ˜220 kA, and rise time of ˜1.5 μs was used in these experiments. Using the advantage of water that it has a large Verdet constant, the magnetic field was measured using the non-disturbing method of Faraday rotation of a polarized collimated laser beam. This approach does not require the use of magnetic probes, which are sensitive to electromagnetic noise and damaged in each shot. It also avoids the possible formation of plasma by either a flashover along the conductor or gas breakdown inside the coil caused by an induced electric field. In addition, it was shown that this approach can be used successfully to investigate the interesting phenomenon of magnetic field enhanced diffusion into a conductor.

Magnetic field line Hamiltonian

International Nuclear Information System (INIS)

Boozer, A.H.

1985-02-01

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

Magnetic fluid bridge in a non-uniform magnetic field

International Nuclear Information System (INIS)

Pelevina, D.A.; Naletova, V.A.; Turkov, V.A.

2017-01-01

The shape of a magnetic fluid bridge between a horizontal ferrite rod of circular cross-section and a horizontal plate above the rod in a vertical applied uniform magnetic field is studied. Various static shapes of the bridges are obtained theoretically and experimentally for the same magnetic field value. Abrupt changes and the hysteresis of the bridge shape in alternating magnetic fields are observed experimentally. - Highlights: • Magnetic fluid bridge between rod and horizontal plate in magnetic field is studied. • Magnetic field is created by a ferrite rod in a uniform vertical magnetic field. • Various static bridge shapes for fixed field are obtained in theory and experiment. • A good agreement of experimental and theoretical results is obtained. • Hysteresis of the bridge shape in alternating field is observed experimentally.

Magnetic fluid bridge in a non-uniform magnetic field

Energy Technology Data Exchange (ETDEWEB)

Pelevina, D.A., E-mail: pelevina.daria@gmail.com; Naletova, V.A.; Turkov, V.A.

2017-06-01

The shape of a magnetic fluid bridge between a horizontal ferrite rod of circular cross-section and a horizontal plate above the rod in a vertical applied uniform magnetic field is studied. Various static shapes of the bridges are obtained theoretically and experimentally for the same magnetic field value. Abrupt changes and the hysteresis of the bridge shape in alternating magnetic fields are observed experimentally. - Highlights: • Magnetic fluid bridge between rod and horizontal plate in magnetic field is studied. • Magnetic field is created by a ferrite rod in a uniform vertical magnetic field. • Various static bridge shapes for fixed field are obtained in theory and experiment. • A good agreement of experimental and theoretical results is obtained. • Hysteresis of the bridge shape in alternating field is observed experimentally.

Dynamics of solar magnetic fields. VI. Force-free magnetic fields and motions of magnetic foot-points

International Nuclear Information System (INIS)

Low, B.C.; Nakagawa, Y.

1975-01-01

A mathematical model is developed to consider the evolution of force-free magnetic fields in relation to the displacements of their foot-points. For a magnetic field depending on only two Cartesian coordinates and time, the problem reduces to solving a nonlinear elliptic partial differential equation. As illustration of the physical process, two specific examples of evolving force-free magnetic fields are examined in detail, one evolving with rising and the other with descending field lines. It is shown that these two contrasting behaviors of the field lines correspond to sheared motions of their foot-points of quite different characters. The physical implications of these two examples of evolving force-free magnetic fields are discussed. (auth)

The Juno Magnetic Field Investigation

DEFF Research Database (Denmark)

Connerney, J. E. P.; Benn, Mathias; Bjarnø, Jonas Bækby

2017-01-01

The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor ...

Chip-Based Measurements of Brownian Relaxation of Magnetic Beads Using a Planar Hall Effect Magnetic Field Sensor

DEFF Research Database (Denmark)

Østerberg, Frederik Westergaard; Dalslet, Bjarke Thomas; Snakenborg, Detlef

2010-01-01

using only the self-field arising from the bias current applied to the sensors as excitation field. We present measurements on a suspension of magnetic beads with a nominal diameter of 250 nm vs. temperature and find that the observations are consistent with the Cole-Cole model for Brownian relaxation...... with a constant hydrodynamic bead diameter when the temperature dependence of the viscosity of water is taken into account. These measurements demonstrate the feasibility of performing measurements of the Brownian relaxation response in a lab-on-a-chip system and constitute the first step towards an integrated...... biosensor based on the detection of the dynamic response of magnetic beads....

LRS Bianchi Type II Massive String Cosmological Models with Magnetic Field in Lyra's Geometry

Directory of Open Access Journals (Sweden)

Raj Bali

2013-01-01

Full Text Available Bianchi type II massive string cosmological models with magnetic field and time dependent gauge function ( in the frame work of Lyra's geometry are investigated. The magnetic field is in -plane. To get the deterministic solution, we have assumed that the shear ( is proportional to the expansion (. This leads to , where and are metric potentials and is a constant. We find that the models start with a big bang at initial singularity and expansion decreases due to lapse of time. The anisotropy is maintained throughout but the model isotropizes when . The physical and geometrical aspects of the model in the presence and absence of magnetic field are also discussed.

The Galactic magnetic fields

International Nuclear Information System (INIS)

Han Jinlin

2006-01-01

A good progress has been made on studies of Galactic magnetic fields in last 10 years. I describe what we want to know about the Galactic magnetic fields, and then review we current knowledge about magnetic fields in the Galactic disk, the Galactic halo and the field strengths. I also listed many unsolved problems on this area

Magnetic fields in diffuse media

CERN Document Server

Pino, Elisabete; Melioli, Claudio

2015-01-01

This volume presents the current knowledge of magnetic fields in diffuse astrophysical media. Starting with an overview of 21st century instrumentation to observe astrophysical magnetic fields, the chapters cover observational techniques, origin of magnetic fields, magnetic turbulence, basic processes in magnetized fluids, the role of magnetic fields for cosmic rays, in the interstellar medium and for star formation. Written by a group of leading experts the book represents an excellent overview of the field. Nonspecialists will find sufficient background to enter the field and be able to appreciate the state of the art.

Quantum rings in magnetic fields and spin current generation.

Science.gov (United States)

Cini, Michele; Bellucci, Stefano

2014-04-09

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

Bose-Einstein condensation of a charged relativistic ideal gas in a general homogeneous magnetic field

International Nuclear Information System (INIS)

Toms, D.J.

1994-01-01

It is shown how the effective action formalism and ζ-function regularization can be used to study Bose-Einstein condensation for a relativistic charged scalar field in a general homogeneous magnetic field in a spacetime of arbitrary dimension. In the special case where the magnetic field has only one component, Bose-Einstein condensation occurs at high temperature only for D≥5 where D is the spatial dimension. When Bose-Einstein condensation does occur the ground-state expectation value of the scalar field is not constant and we determine its value. If the magnetic field has p independent nonzero components we show that the condition for Bose-Einstein condensation is D≥3+2p. In particular, Bose-Einstein condensation can never occur if the magnetic field has all of its independent components nonzero. The problem of Bose-Einstein condensation in a cylindrical box in D spatial dimensions with a uniform magnetic field directed along the axis of the cylinder is also discussed

Reversible control of magnetic interactions by electric field in a single-phase material.

Science.gov (United States)

Ryan, P J; Kim, J-W; Birol, T; Thompson, P; Lee, J-H; Ke, X; Normile, P S; Karapetrova, E; Schiffer, P; Brown, S D; Fennie, C J; Schlom, D G

2013-01-01

Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.

Behaviour of magnetic superconductors in a magnetic field

International Nuclear Information System (INIS)

Buzdin, A.I.

1984-01-01

The behaviour of magnetic superconductors with close ferromagnetic and superconducting transition temperatures in a magnetic field is considered. It is shown that on lowering of the temperature the superconducting transition changes from a second to first order transition. The respective critical fields and dependence of the magnetization on the magnetic field and temperature are found. The magnetization discontinuity in the vortex core in magnetic superconductors is noted. Due to this property and the relatively large scattering cross section, magnetic superconductors are convenient for studying the superconducting vortex lattice by neutron diffraction techniques

Two-phase regime in the magnetic field-temperature phase diagram of a type-II superconductor

International Nuclear Information System (INIS)

Adams, L.L.A.; Halterman, Klaus; Valls, Oriol T.; Goldman, A.M.

2004-01-01

The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V 3 Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius-Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases

Two-phase regime in the magnetic field-temperature phase diagram of a type-II superconductor

Energy Technology Data Exchange (ETDEWEB)

Adams, L.L.A.; Halterman, Klaus; Valls, Oriol T.; Goldman, A.M

2004-01-01

The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V{sub 3}Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius-Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases.

Effect of a magnetic field on the fluorescence produced in irradiated anthracene solutions

International Nuclear Information System (INIS)

Dixon, R.S.; Sargent, F.P.; Lopata, V.J.; Gardy, E.M.; Brocklehurst, B.

1977-01-01

The effect of an applied magnetic field on the fluorescence from radiolytic ion recombination has been studied for anthracene in some hydrocarbon solvents. In pulse-irradiated anthracene in squalane, the fluorescence intensity following the pulse increases as a function of applied magnetic field in the range studied. At a constant magnetic field strength, the field-induced enhancement of the fluorescence intensity varies with time after the pulse. At high field strengths the enhancement reaches a maximum about 50 ns after the pulse. Similar effects are observed in cyclohexane but the enhancement is smaller than that in squalane. In benzene solutions the effect is extremely small. These findings are confirmed by observations in continuously gamma-irradiated solutions. 9,10-Dimethylanthracene gives a larger enhancement and anthracene-d 10 a smaller enhancement than the parent anthracene at high fields. The results are in general agreement with recent theoretical predictions based on the effect of a magnetic field on the loss of spin correlation of geminate ions pairs prior to recombination

Method of regulating magnetic field of magnetic pole center

International Nuclear Information System (INIS)

Watanabe, Masao; Yamada, Teruo; Kato, Norihiko; Toda, Yojiro; Kaneda, Yasumasa.

1978-01-01

Purpose: To provide the subject method comprising using a plurality of magnetic metal pieces having different thicknesses, regulating very easily symmetry of the field of the magnetic pole center depending upon the combination of said metal pieces, thereby obtaining a magnetic field of high precision. Method: The regulation of magnetic field at the central part of the magnetic field is not depending only upon processing of the center plug, axial movement of trim coil and ion source but by providing a magnetic metal piece such as an iron ring, primary higher harmonics of the field at the center of the magnetic field can be regulated simply while the position of the ion source slit is on the equipotential surface in the field. (Yoshihara, H.)

Magnetization reversal in ultrashort magnetic field pulses

International Nuclear Information System (INIS)

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

2000-01-01

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

Magnetic fields at Neptune

International Nuclear Information System (INIS)

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

1989-01-01

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10 -5 gauss) was observed near closest approach, at a distance of 1.18 R N . The planetary magnetic field between 4 and 15 R 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 N and inclined by 47 degrees with respect to the rotation axis. Within 4 R 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

Magnetic field stabilization in THe-Trap

Energy Technology Data Exchange (ETDEWEB)

Streubel, Sebastian; Eronen, Tommi; Hoecker, Martin; Ketter, Jochen; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA (United States)

2012-07-01

THe-Trap is a Penning trap mass spectrometer dedicated to measure the {sup 3}H to {sup 3}He mass ratio aiming to a relative mass uncertainty better than 10{sup -11}. The most vital prerequisite for this measurement is a stable magnetic field: The relative temporal fluctuations during a measurement cycle of typically 1 hour, should be better than 10{sup -11}. The 5.26 T field is provided by a superconducting magnet. Unfortunately, the materials within the cryostat have a temperature-dependent susceptibility which necessitates a temperature stabilization. The stabilization is achieved by controlling the liquid helium level above the traps, and by keeping the pressure of the liquid helium constant. An important part of the system is the pressure reference, which is stable at a 0.04 Pa level. In addition to the stabilization of the field fluctuations within the cryostat itself, a system to cancel external fluctuations is set up consisting of a passive coil with a shielding factor of up to 180 build into the cryostat. Furthermore, a Helmholtz coil pair is placed around the cryostat. The compensation signal is provided by a custom-built flux-gate magnetometer. Technical details about the stabilization systems are given.

Flux quantization and quantum mechanics on Riemann surfaces in an external magnetic field

International Nuclear Information System (INIS)

Bolte, J.; Steiner, F.

1990-10-01

We investigate the possibility to apply an external constant magnetic field to a quantum mechanical system consisting of a particle moving on a compact or non-compact two-dimensional manifold of constant negative Gaussian curvature and of finite volume. For the motion on compact Riemann surfaces we find that a consistent formulation is only possible if the magnetic flux is quantized, as it is proportional to the (integrated) first Chern class of a certain complex line bundle over the manifold. In the case of non-compact surfaces of finite volume we obtain the striking result that the magnetic flux has to vanish identically due to the theorem that any holomorphic line bundle over a non-compact Riemann surface is holomorphically trivial. (orig.)

Superposition of DC magnetic fields by cascading multiple magnets in magnetic loops

Directory of Open Access Journals (Sweden)

Fei Sun

2015-09-01

Full Text Available A novel method that can effectively collect the DC magnetic field produced by multiple separated magnets is proposed. With the proposed idea of a magnetic loop, the DC magnetic field produced by these separated magnets can be effectively superimposed together. The separated magnets can be cascaded in series or in parallel. A novel nested magnetic loop is also proposed to achieve a higher DC magnetic field in the common air region without increasing the DC magnetic field in each magnetic loop. The magnetic loop can be made by a magnetic hose, which is designed by transformation optics and can be realized by the combination of super-conductors and ferromagnetic materials.

Particle-confinement criteria for axisymmetric field-reversed magnetic configurations

International Nuclear Information System (INIS)

Hsiao, M.Y.; Miley, G.H.

1984-01-01

Based on two constants of motion, H and Psub(theta), where H is the total energy of a particle and Psub(theta) is its canonical angular momentum, particle confinement criteria are derived which impose constraints on H and Psub(theta). With no electric field at the ends of field-reversed magnetic configurations, confinement criteria for closed-field and absolute confinements are obtained explicitly, including both lower and upper bounds of Psub(theta)/q, where q is the charge of the species considered, for a class of Hill's vortex field-reversed magnetic configurations. The commonly used criterion for the Hamiltonian, H 0 Psub(theta), where ω 0 is identical to qB 0 /mc, is deduced from a more general form as a special case. In this special case, it is found necessary to impose a new criterion, -B 0 R 2 sub(w)/2c 0 is the vacuum field, which reduces the confinement region in (H,Psub(theta)) space. With the presence of electric fields at the ends of field-reversed magnetic configurations, confinement criteria are obtained for two interesting cases. In addition to lower and upper bounds of H, both lower and upper bounds of Psub(theta)/q are found. For axially confined particles, the lower bound of Psub(theta)/q reduces the confinement region in (H,Psub(theta)) space and represents a new criterion. These results can be applied to calculations for field-reversed mirrors and field-reversed theta pinches. (author)

Calculations of atomic magnetic nuclear shielding constants based on the two-component normalized elimination of the small component method

Science.gov (United States)

Yoshizawa, Terutaka; Zou, Wenli; Cremer, Dieter

2017-04-01

A new method for calculating nuclear magnetic resonance shielding constants of relativistic atoms based on the two-component (2c), spin-orbit coupling including Dirac-exact NESC (Normalized Elimination of the Small Component) approach is developed where each term of the diamagnetic and paramagnetic contribution to the isotropic shielding constant σi s o is expressed in terms of analytical energy derivatives with regard to the magnetic field B and the nuclear magnetic moment 𝝁 . The picture change caused by renormalization of the wave function is correctly described. 2c-NESC/HF (Hartree-Fock) results for the σiso values of 13 atoms with a closed shell ground state reveal a deviation from 4c-DHF (Dirac-HF) values by 0.01%-0.76%. Since the 2-electron part is effectively calculated using a modified screened nuclear shielding approach, the calculation is efficient and based on a series of matrix manipulations scaling with (2M)3 (M: number of basis functions).

Electronic Properties of SiNTs Under External Electric and Magnetic Fields Using the Tight-Binding Method

Science.gov (United States)

Chegel, Raad; Behzad, Somayeh

2014-02-01

We investigated the electronic properties of silicon nanotubes (SiNTs) under external transverse electric fields and axial magnetic fields using the tight-binding approximation. It was found that, after switching on the electric and magnetic fields, band modifications such as distortion of degeneracy, change in energy dispersion and subband spacing, and bandgap size reduction occur. The bandgap of silicon gear-like nanotubes (Si g-NTs) decreases linearly with increasing electric field strength, but the bandgap for silicon hexagonal nanotubes (Si h-NTs) first increases and then decreases (metallic) or first remains constant and then decreases (semiconducting). Our results show that the bandgap of Si h-NTs is very sensitive to both electric and magnetic fields, unlike Si g-NTs, which are more sensitive to electric than magnetic fields.

On the motion of the field of a permanent magnet

Energy Technology Data Exchange (ETDEWEB)

Leus, Vladimir [Sobolev Institute of Mathematics, Novosibirsk (Russian Federation); Taylor, Stephen, E-mail: s.taylor@liv.ac.uk [Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ (United Kingdom)

2011-09-15

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

Polarization of electron-positron vacuum by strong magnetic field in theory with fundamental mass

International Nuclear Information System (INIS)

Kadyshevskij, V.G.; ); Rodionov, V.N.

2003-01-01

The exact Lagrangian function of the intensive constant magnetic field, replacing the Heisenberg-Euler Lagrangian in the traditional quantum electrodynamics, is calculated within the frames of the theory with the fundamental mass in the single-loop approximation. It is established that the obtained generalization of the Lagrangian function is substantial by arbitrary values of the magnetic field. The calculated Lagrangian in the weak field coincides with the known Heisenberg-Euler formula. The Lagrangian dependence on the field in the extremely strong fields completely disappears and it tends in this area to the threshold value, which is determined by the fundamental and lepton mass ratio [ru

Magnetic resonance of field-frozen and zero-field-frozen magnetic fluids

International Nuclear Information System (INIS)

Pereira, A.R.; Pelegrini, F.; Neto, K. Skeff; Buske, N.; Morais, P.C.

2004-01-01

In this study magnetic resonance was used to investigate magnetic fluid samples frozen under zero and non-zero (15 kG) external fields. The magnetite-based sample containing 2x10 17 particle/cm 3 was investigated from 100 to 400 K. Analysis of the temperature dependence of the resonance field revealed bigger magnetic structures in the frozen state than in the liquid phase. Also, differences in the mesoscopic organization in the frozen state may explain the data obtained from samples frozen under zero and non-zero fields

Dipolar local field in homogeneously magnetized quasi-two-dimensional crystals

International Nuclear Information System (INIS)

Leon, H; Estevez-Rams, E

2009-01-01

A formalism to calculate the dipolar local field in homogeneously magnetized quasi-two-dimensional (Q2D) crystals is comprehensively presented. Two fundamental tests for this formalism are accomplished: the transition from the Q2D quantities to the corresponding 3D ones; and the recovering of the macroscopic quantities of the 3D continuum theory. The additive separation between lattice and shape contributions to the local field allows an unambiguous interpretation of the respective effects. Calculated demagnetization tensors for square and circular lateral geometries of dipole layers show that for a single crystal layer an extremely thin film, but still with a finite thickness, is a better physical representation than a strictly 2D plane. Distinct close-packed structures are simulated and calculations of the local field at the nodes of the stacked 2D lattices allow one to establish the number of significantly coupled dipole layers, depending on the ratio between the interlayer distance and the 2D lattice constant. The conclusions drawn are of interest for the study of the dipolar interaction in magnetic ultrathin films and other nanostructured materials, where magnetic nanoparticles are embedded in non-magnetic matrices.

Electron Raman scattering in semiconductor quantum wire in an external magnetic field

International Nuclear Information System (INIS)

Betancourt-Riera, Ri; Nieto Jalil, J M; Riera, R; Betancourt-Riera, Re; Rosas, R

2008-01-01

The differential cross-section for an electron Raman scattering process in a semiconductor quantum wire in the presence of an external magnetic field perpendicular to the plane of confinement is calculated. We assume a single parabolic conduction band. The emission spectra for different scattering configurations and the selection rules for the processes are studied. Singularities in the spectra are found and interpreted. The electron Raman scattering studied here can be used to provide direct information about the electron band and subband structure of these confinement systems. The magnetic field distribution is considered constant with value B 0 inside the wire and zero outside

Self-generation of magnetic fields

International Nuclear Information System (INIS)

Dolan, T.J.

2000-01-01

The stars generate self-magnetic fields on large spatial scales and long time scales,and laser-produced plasmas generate intense self-magnetic fields on very short spatial and time scales. Two questions are posed : (1) Could a self-magnetic field be generated in a laboratory plasma with intermediate spatial and time scales? (2) If a self-magnetic field were generated,would it evolve towards a minimum energy state? If the answers turned out to be affirmative,then self-magnetic fields could possibly have interesting applications

Generation of high magnetic fields using superconducting magnets

International Nuclear Information System (INIS)

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

2006-01-01

High-field superconducting magnets have opened new frontiers for several kinds of applications, such as fusion reactors, particle accelerators, and nuclear magnetic resonance (NMR) spectrometers. The present record for the highest field in a fully superconducting state is 23.4 T. It was achieved with a combination of NbTi, Nb 3 Sn, and Bi-2212 conductors in 1999. Since high T c (critical temperature) superconductors (HTS) have sufficiently high critical current density even in excess of 30 T, they are promising for use as high-field superconducting magnets. However, several problems still remain to be resolved for practical applications, and the use of HTS coils will be limited to the inner part of a high-field magnet system in the near future. The required technologies to develop a high-field superconducting magnet with a field of up to 28 T have already been established. Such a magnet is certain to provide information to all leading research areas

Artificial magnetic-field quenches in synthetic dimensions

Science.gov (United States)

Yılmaz, F.; Oktel, M. Ö.

2018-02-01

Recent cold atom experiments have realized models where each hyperfine state at an optical lattice site can be regarded as a separate site in a synthetic dimension. In such synthetic ribbon configurations, manipulation of the transitions between the hyperfine levels provide direct control of the hopping in the synthetic dimension. This effect was used to simulate a magnetic field through the ribbon. Precise control over the hopping matrix elements in the synthetic dimension makes it possible to change this artificial magnetic field much faster than the time scales associated with atomic motion in the lattice. In this paper, we consider such a magnetic-flux quench scenario in synthetic dimensions. Sudden changes have not been considered for real magnetic fields as such changes in a conducting system would result in large induced currents. Hence we first study the difference between a time varying real magnetic field and an artificial magnetic field using a minimal six-site model. This minimal model clearly shows the connection between gauge dependence and the lack of on-site induced scalar potential terms. We then investigate the dynamics of a wave packet in an infinite two- or three-leg ladder following a flux quench and find that the gauge choice has a dramatic effect on the packet dynamics. Specifically, a wave packet splits into a number of smaller packets moving with different velocities. Both the weights and the number of packets depend on the implemented gauge. If an initial packet, prepared under zero flux in an n -leg ladder, is quenched to Hamiltonian with a vector potential parallel to the ladder, it splits into at most n smaller wave packets. The same initial wave packet splits into up to n2 packets if the vector potential is implemented to be along the rungs. Even a trivial difference in the gauge choice such as the addition of a constant to the vector potential produces observable effects. We also calculate the packet weights for arbitrary initial and

Pumping behavior of ion pump elements at high and misaligned magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Hseuh, H. C.; Jiang, W. S.; Mapes, M.

1994-11-01

The pumping speeds of several diode type ion pump elements with cell radii of 5 mm, 5.5 mm, 6 mm, 9 mm and 12 mm were measured while being subjected to a magnetic field B, ranging from 500 Gauss up to 15 KG, and misalignment angles (angles between the direction of B and the anode axis) from 0 to 13 degrees. The pumping speeds of elements with the 9 mm and 12 mm cells peaked around 1--2 KG, then dropped off rapidly with an increasing magnetic field. The pumping speeds of the smaller cell elements remained constant with an increasing magnetic field. The pumping speeds of all the elements decreased with increasing misalignment. The measured pumping speeds from this study are 3--4 times lower than the calculated pumping, speeds using previously reported empirical formulae.

Pumping behavior of ion pump elements at high and misaligned magnetic fields

International Nuclear Information System (INIS)

Hseuh, H.C.; Jiang, W.S.; Mapes, M.

1994-01-01

The pumping speeds of several diode type ion pump elements with cell radii of 5 mm, 5.5 mm, 6 mm, 9 mm and 12 mm were measured while being subjected to a magnetic field B, ranging from 500 Gauss up to 15 KG, and misalignment angles (angles between the direction of B and the anode axis) from 0 to 13 degrees. The pumping speeds of elements with the 9 mm and 12 mm cells peaked around 1--2 KG, then dropped off rapidly with an increasing magnetic field. The pumping speeds of the smaller cell elements remained constant with an increasing magnetic field. The pumping speeds of all the elements decreased with increasing misalignment. The measured pumping speeds from this study are 3--4 times lower than the calculated pumping, speeds using previously reported empirical formulae

Numerical simulation on the energy spectrum of the electron beam generated by low-impedance diode and the influence of external magnetic field on diode impedance

International Nuclear Information System (INIS)

Liu Guozhi

2003-01-01

The energy spectrum of the electron beam generated by low-impedance diode and the influence of external magnetic field on the impedance of diode are studied numerically in this paper. The results show that the beam generated by the diode has an energy spread, even with constant applied voltage. Additionally, external magnetic field has great but reverse influence on the impedance of low-impedance diode, which is, according to the author's analysis, the result of the change of the electron's track due to external magnetic field. If the beam current is less than the critical one for self-pinch, the impedance will be constant with the variation of external magnetic field

Theoretical study of in-plane response of magnetic field sensor to magnetic beads magnetized by the sensor self-field

DEFF Research Database (Denmark)

Hansen, Troels Borum Grave; Damsgaard, Christian Danvad; Dalslet, Bjarke Thomas

2010-01-01

We present a theoretical study of the spatially averaged in-plane magnetic field on square and rectangular magnetic field sensors from a single magnetic bead, a monolayer of magnetic beads, and a half-space filled with magnetic beads being magnetized by the magnetic self-field due to the applied...... bias current through the sensor. The analysis of the single bead response shows that beads always contribute positively to the average magnetic field as opposed to the case for an applied homogeneous magnetic field where the sign of the signal depends on the bead position. General expressions...... and analytical approximations are derived for the sensor response to beads as function of the bead distribution, the bias current, the geometry and size of the sensor, and the bead characteristics. Consequences for the sensor design are exemplified and it is described how the contribution from the self...

Representations of currents and magnetic fields in anisotropic magnetohydrostatic plasma. 2. General theory and examples

International Nuclear Information System (INIS)

Heinemann, M.; Pontius, D.H. Jr.

1991-01-01

The authors develop a general treatment of field-aligned currents in quasi-static adiabatic plasma. The formalism is an extension of an earlier analysis (Heinemann, 1990) to include electric and gravitational fields. The assumption that the particle motions are adiabatic along the magnetic field leads to an expression for the total current density that is a generalization of expressions given by Grad (1964) and Vasyliunas (1970). The current density is a vector function of the gradients of the field line constants characterizing the plasma and the gradients of field line integrals of the partial derivations of the parallel pressure with respect to the constants. The use of the expression as the current source in Ampere's law leads to an equation governing the equilibrium of the system of plasma and magnetic field. Examples based on bi-Maxwellian distribution functions suggest that the effects of thermal anisotropy can be about as large as the currents due to isotropic plasma and that the effects of parallel electric field are of the same order of magnitude

Neutral and charged scalar mesons, pseudoscalar mesons, and diquarks in magnetic fields

Science.gov (United States)

Liu, Hao; Wang, Xinyang; Yu, Lang; Huang, Mei

2018-04-01

We investigate both (pseudo)scalar mesons and diquarks in the presence of external magnetic field in the framework of the two-flavored Nambu-Jona-Lasinio (NJL) model, where mesons and diquarks are constructed by infinite sum of quark-loop chains by using random phase approximation. The polarization function of the quark-loop is calculated to the leading order of 1 /Nc expansion by taking the quark propagator in the Landau level representation. We systematically investigate the masses behaviors of scalar σ meson, neutral and charged pions as well as the scalar diquarks, with respect to the magnetic field strength at finite temperature and chemical potential. It is shown that the numerical results of both neutral and charged pions are consistent with the lattice QCD simulations. The mass of the charge neutral pion keeps almost a constant under the magnetic field, which is preserved by the remnant symmetry of QCD ×QED in the vacuum. The mass of the charge neutral scalar σ is around two times quark mass and increases with the magnetic field due to the magnetic catalysis effect, which is an typical example showing that the polarized internal quark structure cannot be neglected when we consider the meson properties under magnetic field. For the charged particles, the one quark-antiquark loop contribution to the charged π± increases essentially with the increase of magnetic fields due to the magnetic catalysis of the polarized quarks. However, the one quark-quark loop contribution to the scalar diquark mass is negative comparing with the point-particle result and the loop effect is small.

Harmonic current layer method for the design of superconducting quadrupole magnetic field

International Nuclear Information System (INIS)

Zizek, F.

1977-01-01

The magnetic field of a superconducting quadrupole is investigated by the method of harmonic current layers of cylindrical shape. The superconducting winding is replaced by a system of thin current layers with a harmonically distributed density of the surface current along the circumference. The effect of the outer ferromagnetic circuit with an arbitrary constant permeability over the cross section is replaced analogically. The resultant magnetic field is then given by the superposition of the contributions from the individual current layers. The calculation method can be modified for the selection of the geometry of the winding for the latter to meet the demand for the high homogeneity of the gradient of magnetic induction in the working space of the superconducting quadrupole. (author)

The influence of magnetic fields on crude oils viscosity

Energy Technology Data Exchange (ETDEWEB)

Goncalves, Jose L.; Bombard, Antonio J. F. [Universidade Federal de Itajuba (UNIFEI), Itajuba, MG (Brazil). Instituto de Ciencias Exatas. Lab. de Reologia

2009-07-01

The crystallization of paraffin causes serious problems in the process of transportation of petroleum. This phenomenon increases the crude oil viscosity and implies an organic resin accumulation on pipeline wall, resulting in a reduced flux area or totally blocked pipes. One of the most challenging tasks for pipeline maintenance is solving this problem at low cost. Therefore, a method that inhibits the crystallization of paraffin and reduces the viscosity of crude oil could have many useful applications within the petroleum industry. Recent studies showed that magnetic fields reduce the Wax Appearance Temperature (WAT) and the viscosity of paraffin-based crude oil. For better understanding of this discovery, a series of tests was performed. This paper will show the influence of a DC magnetic field on rheological proprieties of three crude oils with different paraffin concentrations: a crude oil sample with 11 % p/p of paraffin concentration (sample 1); a crude oil sample with 6 % p/p of paraffin concentration (sample 2); a mixture of paraffin plus light crude oil with a total of 11 % p/p of paraffin concentration. These samples were placed in an electromagnet that generates a magnetic field of 1.3 Tesla. The samples' temperatures were conditioned around their Wax Appearance Temperature (WAT), and they were exposed to the field. As the viscosity of crude oil is very sensitive to the changes in temperature, it was ensured that the temperature has remained constant throughout the process. The sample 1 revealed a considerable reduction of viscosity: its original viscosity was 66 cP before magnetic field exposure, after that its viscosity was reduced to 39 cP. The other samples showed the same viscosity, before and after the magnetic field exposure. Since the samples 1 and 3 have the same paraffin concentrations, the viscosity reduction is not due only to the presence of paraffin; there must be other factors responsible for the interaction of sample 1 with the

The measurement system of birefringence and Verdet constant of optical fiber

Science.gov (United States)

Huang, Yi; Chen, Li; Guo, Qiang; Pang, Fufei; Wen, Jianxiang; Shang, Yana; Wang, Tingyun

2013-12-01

The Faraday magneto-optical effect of optical fiber has many applications in monitoring magnetic field and electric current. When a linearly polarized light propagates in the direction of a magnetic field, the plane of polarization will rotate linearly proportional to the strength of the applied magnetic field, which following the relationship of θF =VBl. θF is the Faraday rotation angle, which is proportional to the magnetic flux density B and the Verdet constant V . However, when the optical fiber contains the effect of linear birefringence, the detection of Faraday rotation angle will depend on the line birefringence. In order to determine the Verdet constant of an optical fiber under a linear birefringence, the fiber birefringence needs to be accurately measured. In this work, a model is applied to analyze the polarization properties of an optical fiber by using the Jones matrix method. A measurement system based on the lock-in amplifier technology is designed to test the Verdet constant and the birefringence of optical fiber. The magnetic field is produced by a solenoid with a DC current. A tunable laser is intensity modulated with a motorized rotating chopper. The actuator supplies a signal as the phase-locked synchronization reference to the signal of the lock-in amplifier. The measurement accuracy is analyzed and the sensitivity of the system is optimized. In this measurement system, the Verdet constant of the SMF-28 fiber was measured to be 0.56±0.02 rad/T·m at 1550nm. This setup is well suitable for measuring the high signal-to-noise ratio (SNR) sensitivity for lock-in amplifier at a low magnetic field strength.

Design and test of a flat-top magnetic field system driven by capacitor banks.

Science.gov (United States)

Jiang, Fan; Peng, Tao; Xiao, Houxiu; Zhao, Jianlong; Pan, Yuan; Herlach, Fritz; Li, Liang

2014-04-01

An innovative method for generating a flat-top pulsed magnetic field by means of capacitor banks is developed at the Wuhan National High Magnetic Field Center (WHMFC). The system consists of two capacitor banks as they are normally used to generate a pulsed field. The two discharge circuits (the magnet circuit and the auxiliary circuit) are coupled by a pulse transformer such that the electromotive force (EMF) induced via the transformer in the magnet circuit containing the magnet coil is opposed to the EMF of the capacitor bank. At a certain point before the current pulse in the coil reaches its peak, the auxiliary circuit is triggered. With optimized parameters for charging voltage and trigger delay, the current in the magnet circuit can be approximately kept constant to obtain a flat-top. A prototype was developed at the WHMFC; the magnet circuit was energized by seven 1 MJ (3.2 mF/25 kV) capacitor modules and the auxiliary circuit by four 1 MJ modules. Fields up to 41 T with 6 ms flat-top have been obtained with a conventional user magnet used at the WHMFC.

About the Toroidal Magnetic Field of a Tokamak Burning Plasma Experiment with Superconducting Coils

International Nuclear Information System (INIS)

Mazzucato, E.

2002-01-01

In tokamaks, the strong dependence on the toroidal magnetic field of both plasma pressure and energy confinement is what makes possible the construction of small and relatively inexpensive burning plasma experiments using high-field resistive coils. On the other hand, the toroidal magnetic field of tokamaks using superconducting coils is limited by the critical field of superconductivity. In this article, we examine the relative merit of raising the magnetic field of a tokamak plasma by increasing its aspect ratio at a constant value of the peak field in the toroidal magnet. Taking ITER-FEAT as an example, we find that it is possible to reach thermonuclear ignition using an aspect ratio of approximately 4.5 and a toroidal magnetic field of 7.3 T. Under these conditions, fusion power density and neutron wall loading are the same as in ITER [International Thermonuclear Experimental Reactor], but the normalized plasma beta is substantially smaller. Furthermore, such a tokamak would be able to reach an energy gain of approximately 15 even with the deterioration in plasma confinement that is known to occur near the density limit where ITER is forced to operate

Magnetic fields for transporting charged beams

International Nuclear Information System (INIS)

Parzen, G.

1976-01-01

The transport of charged particle beams requires magnetic fields that must be shaped correctly and very accurately. During the last 20 years or so, many studies have been made, both analytically and through the use of computer programs, of various magnetic shapes that have proved to be useful. Many of the results for magnetic field shapes can be applied equally well to electric field shapes. A report is given which gathers together the results that have more general significance and would be useful in designing a configuration to produce a desired magnetic field shape. The field shapes studied include the fields in dipoles, quadrupoles, sextupoles, octupoles, septum magnets, combined-function magnets, and electrostatic septums. Where possible, empirical formulas are proposed, based on computer and analytical studies and on magnetic field measurements. These empirical formulas are often easier to use than analytical formulas and often include effects that are difficult to compute analytically. In addition, results given in the form of tables and graphs serve as illustrative examples. The field shapes studied include uniform fields produced by window-frame magnets, C-magnets, H-magnets, and cosine magnets; linear fields produced by various types of quadrupoles; quadratic and cubic fields produced by sextupoles and octupoles; combinations of uniform and linear fields; and septum fields with sharp boundaries

Perturbative versus Schwinger-propagator method for the calculation of amplitudes in a magnetic field

International Nuclear Information System (INIS)

Nieves, Jose F.; Pal, Palash B.

2006-01-01

We consider the calculation of amplitudes for processes that take place in a constant background magnetic field, first using the standard method for the calculation of an amplitude in an external field, and second utilizing the Schwinger propagator for charged particles in a magnetic field. We show that there are processes for which the Schwinger-propagator method does not yield the total amplitude. We explain why the two methods yield equivalent results in some cases and indicate when we can expect the equivalence to hold. We show these results in fairly general terms and illustrate them with specific examples as well

Plasma opening switch with extrinsic magnetic field

CERN Document Server

Dolgachev, G; Maslennikov, D

2001-01-01

Summary form only given, as follows. We have demonstrated in series of experiments that plasma opening switch (POS) switching voltage (UPOS) is defined by energy density (w) deposited in the POS plasma. If we then consider a plasma erosion mainly responsible for the effect of POS switching (the erosion effect could be described by Hall or Child-Langmuir models) the energy density (w) could be measured as a function of a system "macro-parameter" such as the initial charging voltage of the capacity storage system (the Marx pulsed voltage generator) UMarx. The POS voltage in this case could be given by UPOS"aw=aUMarx4/7, where a is a constant. This report demonstrates that for the high-impedance POS which has limited charge density transferred through the POS plasma a"2.5 (MV3/7) with no external magnetic field applied. The use of the extrinsic magnetic field allows to increase a up to 3.6 (MV3/7) and to achieve higher voltages at the opening phase - UPOS=3.6UMarx4/7. To verify this approach set of experimental ...

Controlled and spontaneous magnetic field generation in a gun-driven spheromak

International Nuclear Information System (INIS)

Woodruff, S.; Cohen, B.I.; Hooper, E.B.; Mclean, H.S.; Stallard, B.W.; Hill, D.N.; Holcomb, C.T.; Romero-Talamas, C.; Wood, R.D.; Cone, G.; Sovinec, C.R.

2005-01-01

In the Sustained Spheromak Physics Experiment, SSPX [E. B. Hooper, D. Pearlstein, and D. D. Ryutov, Nucl. Fusion 39, 863 (1999)], progress has been made in understanding the mechanisms that generate fields by helicity injection. SSPX injects helicity (linked magnetic flux) from 1 m diameter magnetized coaxial electrodes into a flux-conserving confinement region. Control of magnetic fluctuations (δB/B∼1% on the midplane edge) yields T e profiles peaked at >200 eV. Trends indicate a limiting beta (β e ∼4%-6%), and so we have been motivated to increase T e by operating with stronger magnetic field. Two new operating modes are observed to increase the magnetic field: (A) Operation with constant current and spontaneous gun voltage fluctuations. In this case, the gun is operated continuously at the threshold for ejection of plasma from the gun: stored magnetic energy of the spheromak increases gradually with δB/B∼2% and large voltage fluctuations (δV∼1 kV), giving a 50% increase in current amplification, I tor /I gun . (B) Operation with controlled current pulses. In this case, spheromak magnetic energy increases in a stepwise fashion by pulsing the gun, giving the highest magnetic fields observed for SSPX (∼0.7 T along the geometric axis). By increasing the time between pulses, a quasisteady sustainment is produced (with periodic good confinement), comparing well with resistive magnetohydrodynamic simulations. In each case, the processes that transport the helicity into the spheromak are inductive and exhibit a scaling of field with current that exceeds those previously obtained. We use our newly found scaling to suggest how to achieve higher temperatures with a series of pulses

Controlled and Spontaneous Magnetic Field Generation in a Gun-Driven Spheromak

International Nuclear Information System (INIS)

Woodruff, S; Cohen, B I; Hooper, E B; McLean, H S; Stallard, B W; Hill, D N; Holcomb, C T; Romero-Talamas, C; Wood, R D; Cone, G; Sovinec, C R

2005-04-01

In the Sustained Spheromak Physics Experiment, SSPX, progress has been made in understanding the mechanisms that generate fields by helicity injection. SSPX injects helicity (linked magnetic flux) from 1-m diameter magnetized coaxial electrodes into a flux-conserving confinement region. Control of magnetic fluctuations ((delta)B/B∼1% on the midplane edge) yields T e profiles peaked at > 200eV. Trends indicate a limiting beta (β e ∼ 4-6%), and so we have been motivated to increase T e by operating with stronger magnetic field. Two new operating modes are observed to increase the magnetic field: (A) Operation with constant current and spontaneous gun voltage fluctuations. In this case, the gun is operated continuously at the threshold for ejection of plasma from the gun: stored magnetic energy of the spheromak increases gradually with (delta)B/B ∼2% and large voltage fluctuations ((delta)V ∼ 1kV), giving a 50% increase in current amplification, I tor /I gun . (B) Operation with controlled current pulses. In this case, spheromak magnetic energy increases in a stepwise fashion by pulsing the gun, giving the highest magnetic fields observed for SSPX (∼0.7T along the geometric axis). By increasing the time between pulses, a quasi-steady sustainment is produced (with periodic good confinement), comparing well with resistive MHD simulations. In each case, the processes that transport the helicity into the spheromak are inductive and exhibit a scaling of field with current that exceeds those previously obtained. We use our newly found scaling to suggest how to achieve higher temperatures with a series of pulses

Magnetic field driven domain-wall propagation in magnetic nanowires

International Nuclear Information System (INIS)

Wang, X.R.; Yan, P.; Lu, J.; He, C.

2009-01-01

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

Cosmological magnetic fields - V

Indian Academy of Sciences (India)

Magnetic fields seem to be everywhere that we can look in the universe, from our own ... The field tensor is observer-independent, while the electric and magnetic .... based on string theory [11], in which vacuum fluctuations of the field are ...

Weak nonlinear analysis of magneto–convection under magnetic field modulation

International Nuclear Information System (INIS)

Bhadauria, B S; Kiran, Palle

2014-01-01

An analytic study of heat transport in an electrically conducting fluid layer is performed under a non-uniform time-dependent magnetic field. The applied vertical magnetic field consists of two parts: a constant part and a time-dependent periodic part, which varies sinusoidally with time. A weakly nonlinear theory has been considered to investigate heat transfer in the fluid layer. The heat transfer coefficient is obtained by deriving the non-autonomous Ginzburg–Landau equation for an amplitude of convection. This amplitude of convection is derived by using NDSolve Mathematica 8, and the results are verified using Runge–Kutta–Fehlberg method. The Nusselt number is obtained in terms of various system parameters and the effect of each parameter on heat transport is reported in detail. The effect of magnetic Prandtl number Pm, amplitude of modulation δ is to enhance the heat transfer. The Chandrasekhar number Q, modulation frequency ω is to stabilize the system. Further, it is found that magnetic modulation can be used effectively in either enhancing the heat transfer or diminishing it. (paper)

High-field superferric MR magnet

International Nuclear Information System (INIS)

Huson, F.R.; Carcagno, R.; Colvin, J.

1987-01-01

Current large-bore (>20 cm), high-field (2-T) MR magnets have major implementation disadvantages, mostly related to the extensive stray field of traditional air-core superconducting magnets. To circumvent this problem, the authors designed, constructed, and tested a 30-cm prototype superconducting, self-shielded, high field magnet. This unshimmed superferric magnet can operate between 0.5 and 4 T with a field quality of about one part per million over one quarter of its aperture. The magnet can be ramped from one field strength to another in approximately 10 minutes. The 5-Gauss line extends less than 1 meter outside the magnet structure. Further details, including MR measurements and images, are demonstrated, as well as 1-meter bore scale-up projections

Magnetic field and magnetic isotope effects on photochemical reactions

International Nuclear Information System (INIS)

Wakasa, Masanobu

1999-01-01

By at present exact experiments and the theoretical analysis, it was clear that the magnetic field less than 2 T affected a radical pair reaction and biradical reaction. The radical pair life and the dissipative radical yield showed the magnetic field effects on chemical reactions. The radical pair mechanism and the triplet mechanism were known as the mechanism of magnetic field effects. The radical pair mechanism consists of four mechanisms such as the homogeneous hyperfine interaction (HFC), the delta-g mechanism, the relaxation mechanism and the level cross mechanism. In order to observe the magnetic effects of the radical pair mechanism, two conditions need, namely, the recombination rate of singlet radical pair > the dissipation rate and the spin exchange rate > the dissipation rate. A nanosecond laser photo-decomposition equipment can observe the magnetic field effects. The inversion phenomena of magnetic field effect, isolation of the relaxation mechanism and the delta-g mechanism, the magnetic field effect of heavy metal radical reaction, the magnetic field effect in homogeneous solvent, saturation of delta-g mechanism are explained. The succeeded examples of isotope concentration by the magnetic isotope effect are 17 O, 19 Si, 33 S, 73 Ge and 235 U. (S.Y.)

Determination of microturbulence enhanced electron collisionality in magnetized coaxial accelerator channels by direct magnetic field measurement

International Nuclear Information System (INIS)

Black, D.C.; Mayo, R.M.; Caress, R.W.

1997-01-01

A miniature magnetic probe array, consisting of 10 spatially separated coils, has been used to obtain profile information on the time varying magnetic field within the 2.54 cm wide flow channel of the coaxial plasma source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)]. The magnetic field data have been used, together with a resistive, Hall magnetohydrodynamic (MHD) model of applied field distortion by the flowing plasma, to obtain estimates of the microturbulent enhancement to electron collisionality within the CPS-1 flow channel. These measurements provide direct experimental evidence of anomalous electron collisionality, a previously predicted effect in these devices. The anomaly parameter, a=ν an /ν cl , determined both from the distortion of contours of constant magnetic flux, and from local B θ and B z measurements scales with the classical electron magnetization parameter (Ω cl =ω ce /ν e cl ), indicating that collisionality plays a strong role in determining the level of anomalous transport in the plasma. When this anomaly parameter scaling is cast in terms of the ratio ν e cl /ω lh , it is found that the resistivity enhancement scales with ν e cl /ω lh , and becomes significant at ν e cl /ω lh ≤1, suggesting that a lower hybrid drift instability may be the responsible mechanism for enhanced transport. copyright 1997 American Institute of Physics

The Capacitive Magnetic Field Sensor

Science.gov (United States)

Zyatkov, D. O.; Yurchenko, A. V.; Balashov, V. B.; Yurchenko, V. I.

2016-01-01

The results of a study of sensitive element magnetic field sensor are represented in this paper. The sensor is based on the change of the capacitance with an active dielectric (ferrofluid) due to the magnitude of magnetic field. To prepare the ferrofluid magnetic particles are used, which have a followingdispersion equal to 50 brand 5BDSR. The dependence of the sensitivity of the capacitive element from the ferrofluid with different dispersion of magnetic particles is considered. The threshold of sensitivity and sensitivity of a measuring cell with ferrofluid by a magnetic field was determined. The experimental graphs of capacitance change of the magnitude of magnetic field are presented.

High magnetic field MRI system

International Nuclear Information System (INIS)

Maeda, Hideaki; Urata, Masami; Satoh, Kozo

1990-01-01

A high field superconducting magnet, 4-5 T in central magnetic field, is required for magnetic resonance spectroscopic imaging (MRSI) on 31 P, essential nuclei for energy metabolism of human body. This paper reviews superconducting magnets for high field MRSI systems. Examples of the cross-sectional image and the spectrum of living animals are shown in the paper. (author)

Magnetic resonance imaging: effects of magnetic field strength

International Nuclear Information System (INIS)

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

1984-01-01

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

Magnetic Field Grid Calculator

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...

Spin polarized semimagnetic exciton-polariton condensate in magnetic field.

Science.gov (United States)

Król, Mateusz; Mirek, Rafał; Lekenta, Katarzyna; Rousset, Jean-Guy; Stephan, Daniel; Nawrocki, Michał; Matuszewski, Michał; Szczytko, Jacek; Pacuski, Wojciech; Piętka, Barbara

2018-04-27

Owing to their integer spin, exciton-polaritons in microcavities can be used for observation of non-equilibrium Bose-Einstein condensation in solid state. However, spin-related phenomena of such condensates are difficult to explore due to the relatively small Zeeman effect of standard semiconductor microcavity systems and the strong tendency to sustain an equal population of two spin components, which precludes the observation of condensates with a well defined spin projection along the axis of the system. The enhancement of the Zeeman splitting can be achieved by introducing magnetic ions to the quantum wells, and consequently forming semimagnetic polaritons. In this system, increasing magnetic field can induce polariton condensation at constant excitation power. Here we evidence the spin polarization of a semimagnetic polaritons condensate exhibiting a circularly polarized emission over 95% even in a moderate magnetic field of about 3 T. Furthermore, we show that unlike nonmagnetic polaritons, an increase on excitation power results in an increase of the semimagnetic polaritons condensate spin polarization. These properties open new possibilities for testing theoretically predicted phenomena of spin polarized condensate.

Influence of constant, alternating and cyclotron low-intensity electromagnetic fields on fibroblast proliferative activity in vitro.

Science.gov (United States)

Afinogenov, Gennadi; Afinogenova, Anna; Kalinin, Andrey

2009-12-16

Available data allow assuming the presence of stimulation of reparative processes under influence of low-intensity electromagnetic field, commensurable with a magnetic field of the Earth. Research of effects of low-intensity electromagnetic fields on fibroblast proliferative activity in human lungs in cell culture was performed.The influence of a constant electromagnetic field, an alternating electromagnetic field by frequency of 50 Hz and cyclotron electromagnetic field with identical intensity for all kinds of fields - 80 mcTl - on value of cellular mass and a correlation of live and dead cells in culture is investigated in three series of experiments. We used the universal electromagnetic radiator generating all three kinds of fields and supplied by a magnetometer which allows measuring the intensity of accurate within 0.1 mcTl including taking into account the Earth's magnetic field intensity.The peak value for stimulation cellular proliferation in the present experiences was two-hour influence by any of the specified kinds of electromagnetic fields. The irradiation by cyclotron electromagnetic field conducts positive dynamics in growth of live cells (up to 206+/-22%) and decreases the number of dead cells (down to 31+/-6%). Application of cyclotron magnetic fields promoted creation of optimum conditions for proliferation. As a result of researches we observed the reliable 30% increase of nitro-tetrazolium index (in nitro-tetrazolium blue test) after irradiation by cyclotron electromagnetic field in experience that testifies to strengthening of the cell breathing of living cells.In our opinion, it is necessary to pay attention not only to a pure gain of cells, but also to reduction of number dead cells that can be criterion of creation of optimum conditions for their specific development and valuable functioning.

On the interaction between the external magnetic field and nanofluid inside a vertical square duct

Directory of Open Access Journals (Sweden)

Kashif Ali

2015-10-01

Full Text Available In this paper, we numerically study how the external magnetic field influences the flow and thermal characteristics of nanofluid inside a vertical square duct. The flow is considered to be laminar and hydrodynamically as well as thermally developed, whereas the thermal boundary condition of constant heat flux per unit axial length with constant peripheral temperature at any cross section, is assumed. The governing equations are solved using the spectral method and the finite difference method. Excellent comparison is noted in the numerical results given by the two methods but the spectral method is found to be superior in terms of both efficiency and accuracy. We have noted that the flow reversal due to high Raleigh number may be controlled by applying an external magnetic field of suitable strength. Moreover, the Nusselt number is found to be almost a linear function of the nanoparticle volume fraction parameter, for different values of the Raleigh number and the magnetic parameter.

In-plane magnetic anisotropy and temperature dependence of switching field in (Ga, Mn) as ferromagnetic semiconductors.

Science.gov (United States)

Kamara, S; Terki, F; Dumas, R; Dehbaoui, M; Sadowski, J; Galéra, R M; Tran, Q-H; Charar, S

2012-06-01

We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.

Magnetic fields in cosmology

International Nuclear Information System (INIS)

Madsen, M.S.

1989-01-01

The possible role of a large-scale relic magnetic field in the history of the Universe is considered. The perturbation of the cosmic microwave back-ground radiation on large angular scales due to a homogeneous magnetic field is estimated in a simple relativistic model. This allows corresponding limits to be placed on the magnitude of any such large-scale relic magnetic field at the present time. These limits are essentially the strongest which can be set on the largest scales. A corresponding bound is obtained by use of the requirement that the field should not spoil the predictions of primordial nucleosynthesis. It is noted that the existence of large-scale cosmic magnetic fields would circumvent the limits previously set - also on the basis of nucleosynthesis considerations - on the large-scale anisotropy now present in the Universe. (author)

Structure and magnetic field of periodic permanent magnetic focusing system with open magnetic rings

International Nuclear Information System (INIS)

Peng Long; Li Lezhong; Yang Dingyu; Zhu Xinghua; Li Yuanxun

2011-01-01

The magnetic field along the central axis for an axially magnetized permanent magnetic ring was investigated by analytical and finite element methods. For open magnetic rings, both calculated and measured results show that the existence of the radial magnetic field creates a remarkable cosine distribution field along the central axis. A new structure of periodic permanent magnet focusing system with open magnetic rings is proposed. The structure provides a satisfactory magnetic field with a stable peak value of 120 mT for a traveling wave tube system. - Research highlights: → For open magnetic rings, both calculated and measured results show that the existence of the radial magnetic field creates a remarkable cosine distribution field along the central axis. → A new structure of periodic permanent magnet (PPM) focusing system with open magnetic rings is proposed. → The new PPM focusing system with open magnetic rings meets the requirements for TWT system.

Investigations about the effects of magnetic fields on QGP in heavy ion collisions

Energy Technology Data Exchange (ETDEWEB)

Inghirami, Gabriele; Bleicher, Marcus [FIAS, Frankfurt am Main (Germany); Goethe Universitaet, Frankfurt am Main (Germany); Del Zanna, Luca [Universita degli Studi di Firenze, Firenze (Italy); Osservatorio Astrofisico di Arcetri - INAF, Firenze (Italy); INFN, Sezione di Firenze (Italy); Haddadi, Mohsen [Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Becattini, Francesco [Universita degli Studi di Firenze, Firenze (Italy); INFN, Sezione di Firenze (Italy); Beraudo, Andrea [INFN, Sezione di Torino (Italy); Rolando, Valentina [Universita degli Studi di Ferrara, Ferrara (Italy); INFN, Sezione di Ferrara (Italy)

2016-07-01

Numerical hydrodynamic simulations of heavy ion collisions are constantly refined through the addition of effects that may significantly improve the matching with experimental data, like viscosity or fluctuating initial conditions, but, so far, electromagnetic interactions have been almost completely neglected. However, recent lattice QCD computations and classical electrodynamics estimates both suggest that the magnetic fields produced immediately after the collisions between nuclei may live long enough and with a strength sufficient to produce measurable effects. We would like to present the results of some preliminary investigations about the influence on the properties of the medium due the presence of a strong magnetic field.

Organic magnetic field sensor

Energy Technology Data Exchange (ETDEWEB)

McCamey, Dane; Boehme, Christoph

2017-01-24

An organic, spin-dependent magnetic field sensor (10) includes an active stack (12) having an organic material with a spin-dependence. The sensor (10) also includes a back electrical contact (14) electrically coupled to a back of the active stack (12) and a front electrical contact (16) electrically coupled to a front of the active stack (12). A magnetic field generator (18) is oriented so as to provide an oscillating magnetic field which penetrates the active stack (12).

Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation.

Science.gov (United States)

Titenko, Anatoliy; Demchenko, Lesya

2016-12-01

The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed.

On the origin of cosmic magnetic fields

Science.gov (United States)

Kulsrud, Russell M.; Zweibel, Ellen G.

2008-04-01

and most popular mechanism is the α-Ω mean field dynamo theory developed by a number of people in the late sixties. This theory and its application to galactic magnetic fields is discussed in considerable detail in this review. We point out certain difficulties with this theory that make it seem unlikely that this is the whole story. The main difficulty with this as the only such amplification mechanism is rooted in the fact that, on galactic scales, flux is constant and is frozen in the interstellar medium. This implies that flux must be removed from the galactic discs, as is well recognized by the standard theory. For our Galaxy this turns out to be a major problem, since unless the flux and the interstellar mass are somehow separated, some interstellar mass must also be removed from the deep galactic gravitational well. This is very difficult. It is pointed out that unless the field has a substantial field strength, much larger than that of the seed fields, this separation can hardly happen. And of course, it must if the α-Ω dynamo is to start from the ultra weak seed field. (It is our philosophy, expressed in this review, that if an origin theory is unable to create the magnetic field in our Galaxy it is essentially incomplete.) Thus, it is more reasonable for the first and largest amplification to occur before the Galaxy forms, and the matter embedded in the field is gravitationally trapped. Two such mechanisms are discussed for such a pregalactic origin; (1) they are generated in the turbulence of the protogalaxy and (2) the fields come from giant radio jets. Several arguments against a primordial origin are also discussed, as are ways around them. Our conclusion as to the most likely origin of cosmic magnetic fields is that they are first produced at moderate field strengths by primordial mechanisms and then changed and their strength increased to their present value and structure by a galactic disc dynamo. The primordial mechanisms have not yet been

Axial magnetic field produced by axially and radially magnetized permanent rings

International Nuclear Information System (INIS)

Peng, Q.L.; McMurry, S.M.; Coey, J.M.D.

2004-01-01

Axial magnetic fields produced by axially and radially magnetized permanent magnet rings were studied. First, the axial magnetic field produced by a current loop is introduced, from which the axial field generated by an infinitely thin solenoid and by an infinitely thin current disk can be derived. Then the axial fields produced by axially and by radially magnetized permanent magnet rings can be obtained. An analytic formula for the axial fields produced by two axially magnetized rings is given. A permanent magnet with a high axial gradient field is fabricated, the measured results agree with the theoretical calculation very well. As an example, the axial periodic field produced by an arrangement of alternating axially and radially magnetized rings has been discussed

Heat transfer enhancement of Fe{sub 3}O{sub 4} ferrofluids in the presence of magnetic field

Energy Technology Data Exchange (ETDEWEB)

Fadaei, Farzad; Shahrokhi, Mohammad; Molaei Dehkordi, Asghar, E-mail: amolaeid@sharif.edu; Abbasi, Zeinab

2017-05-01

In this article, three-dimensional (3D) forced-convection heat transfer of magnetic nanofluids in a pipe subject to constant wall heat flux in the presence of single or double permanent magnet(s) or current-carrying wire has been investigated and compared. In this regard, laminar fluid flow and equilibrium magnetization for the ferrofluid were considered. In addition, variations of magnetic field in different media were taken into account and the assumption of having a linear relationship of magnetization with applied magnetic field intensity was also relaxed. Effects of magnetic field intensity, nanoparticle volume fraction, Reynolds number value, and the type of magnetic field source (i.e., a permanent magnet or current-carrying wire) on the forced-convection heat transfer of magnetic nanofluids were carefully investigated. It was found that by applying the magnetic field, the fluid mixing could be intensified that leads to an increase in the Nusselt number value along the pipe length. Moreover, the obtained simulation results indicate that applying the magnetic field induced by two permanent magnets with a magnetization of 3×10{sup 5} (A/m) (for each one), the fully developed Nusselt number value can be increased by 196%. - Highlights: • 3D forced-convection heat transfer of magnetic nanofluids is investigated. • Effects of single or double permanent magnet on the heat transfer are studied. • Influences of magnetic field induced by a current-carrying wire are studied. • Effects of magnetic field intensity and Reynolds number value are studied. • Variations of magnetic field in different media are taken into account.

Magnetic field and dielectric environment effects on an exciton trapped by an ionized donor in a spherical quantum dot

Science.gov (United States)

Aghoutane, N.; Feddi, E.; El-Yadri, M.; Bosch Bailach, J.; Dujardin, F.; Duque, C. A.

2017-11-01

Magnetic field and host dielectric environment effects on the binding energy of an exciton trapped by an ionized donor in spherical quantum dot are investigated. In the framework of the effective mass approximation and by using a variational method, the calculations have been performed by developing a robust ten-terms wave function taking into account the different inter-particles correlations and the distortion of symmetry induced by the orientation of the applied magnetic field. The binding and the localization energies are determined as functions of dot size and magnetic field strength. It appears that the variation of magnetic shift obeys a quadratic law for low magnetic fields regime while, for strong magnetic fields, this shift tends to be linear versus the magnetic field strength. The stability of this complex subjected to a magnetic field is also discussed according to the electron-hole ratio and the dielectric constant of the surrounding medium. A last point to highlight is that the Haynes' rule remains valid even in the presence of an applied magnetic field.

On the origin of cosmic magnetic fields

International Nuclear Information System (INIS)

Kulsrud, Russell M; Zweibel, Ellen G

2008-01-01

and most popular mechanism is the α-Ω mean field dynamo theory developed by a number of people in the late sixties. This theory and its application to galactic magnetic fields is discussed in considerable detail in this review. We point out certain difficulties with this theory that make it seem unlikely that this is the whole story. The main difficulty with this as the only such amplification mechanism is rooted in the fact that, on galactic scales, flux is constant and is frozen in the interstellar medium. This implies that flux must be removed from the galactic discs, as is well recognized by the standard theory. For our Galaxy this turns out to be a major problem, since unless the flux and the interstellar mass are somehow separated, some interstellar mass must also be removed from the deep galactic gravitational well. This is very difficult. It is pointed out that unless the field has a substantial field strength, much larger than that of the seed fields, this separation can hardly happen. And of course, it must if the α-Ω dynamo is to start from the ultra weak seed field. (It is our philosophy, expressed in this review, that if an origin theory is unable to create the magnetic field in our Galaxy it is essentially incomplete.) Thus, it is more reasonable for the first and largest amplification to occur before the Galaxy forms, and the matter embedded in the field is gravitationally trapped. Two such mechanisms are discussed for such a pregalactic origin; (1) they are generated in the turbulence of the protogalaxy and (2) the fields come from giant radio jets. Several arguments against a primordial origin are also discussed, as are ways around them. Our conclusion as to the most likely origin of cosmic magnetic fields is that they are first produced at moderate field strengths by primordial mechanisms and then changed and their strength increased to their present value and structure by a galactic disc dynamo. The primordial mechanisms have not yet been

Magnetic field dependent atomic tunneling in non-magnetic glasses

International Nuclear Information System (INIS)

Ludwig, S.; Enss, C.; Hunklinger, S.

2003-01-01

The low-temperature properties of insulating glasses are governed by atomic tunneling systems (TSs). Recently, strong magnetic field effects in the dielectric susceptibility have been discovered in glasses at audio frequencies at very low temperatures. Moreover, it has been found that the amplitude of two-pulse polarization echoes generated in non-magnetic multi-component glasses at radio frequencies and at very low temperatures shows a surprising non-monotonic magnetic field dependence. The magnitude of the latter effect indicates that virtually all TSs are affected by the magnetic field, not only a small subset of systems. We have studied the variation of the magnetic field dependence of the echo amplitude as a function of the delay time between the two excitation pulses and at different frequencies. Our results indicate that the evolution of the phase of resonant TSs is changed by the magnetic field

Magnetic field dependent atomic tunneling in non-magnetic glasses

Science.gov (United States)

Ludwig, S.; Enss, C.; Hunklinger, S.

2003-05-01

The low-temperature properties of insulating glasses are governed by atomic tunneling systems (TSs). Recently, strong magnetic field effects in the dielectric susceptibility have been discovered in glasses at audio frequencies at very low temperatures. Moreover, it has been found that the amplitude of two-pulse polarization echoes generated in non-magnetic multi-component glasses at radio frequencies and at very low temperatures shows a surprising non-monotonic magnetic field dependence. The magnitude of the latter effect indicates that virtually all TSs are affected by the magnetic field, not only a small subset of systems. We have studied the variation of the magnetic field dependence of the echo amplitude as a function of the delay time between the two excitation pulses and at different frequencies. Our results indicate that the evolution of the phase of resonant TSs is changed by the magnetic field.

Anisotropic magnetism in field-structured composites

International Nuclear Information System (INIS)

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

2000-01-01

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 chainlike particle structures, and a biaxial field produces sheetlike 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. (c) 2000 The American Physical Society

Magnetic Field Topology in Jets

Science.gov (United States)

Gardiner, T. A.; Frank, A.

2000-01-01

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.

POPULATION SYNTHESIS OF YOUNG ISOLATED NEUTRON STARS: THE EFFECT OF FALLBACK DISK ACCRETION AND MAGNETIC FIELD EVOLUTION

International Nuclear Information System (INIS)

Fu, Lei; Li, Xiang-Dong

2013-01-01

The spin evolution of isolated neutron stars (NSs) is dominated by their magnetic fields. The measured braking indices of young NSs show that the spin-down mechanism due to magnetic dipole radiation with constant magnetic fields is inadequate. Assuming that the NS magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we carry out a Monte Carlo simulation of the evolution of young NSs, and show that most of the pulsars have braking indices ranging from –1 to 3. The results are compatible with the observational data of NSs associated with supernova remnants. They also suggest that the initial spin periods of NSs might occupy a relatively wide range

The dressed nonrelativistic electron in a magnetic field

International Nuclear Information System (INIS)

Amour, L.; Grebert, B.; Guillot, J.C.

2005-01-01

We consider a nonrelativistic electron interacting with a classical magnetic field pointing along the x 3 -axis and with a quantized electromagnetic field. Because of the translation invariance along the x 3 -axis, we consider the reduced Hamiltonian associated with the total momentum along the x 3 -axis and, after introducing an ultraviolet cutoff and an infrared regularization, we prove that the reduced Hamiltonian has a ground state if the coupling constant and the total momentum along the x 3 -axis are sufficiently small. Finally, we determine the absolutely continuous spectrum of the reduced Hamiltonian and we prove that the renormalized mass of the electron is greater than its bare one. (authors)

Steady state magnetic field configurations for the earth's magnetotail

International Nuclear Information System (INIS)

Hau, L.N.; Wolf, R.A.; Voigt, G.H.; Wu, C.C.

1989-01-01

The authors present a two-dimensional, force-balanced magnetic field model in which flux tubes have constant pVγ throughout an extended region of the nightside plasma sheet, between approximately 36 R E geocentric distance and the region of the inner edge of the plasma sheet. They have thus demonstrated the theoretical existence of a steady state magnetic field configuration that is force-balanced and also consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD (isotropic pressure, perfect conductivity). The numerical solution was constructed for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The primary characteristics of the steady state convection solution are (1) a pressure maximum just tailward of the inner edge of the plasma sheet and (2) a deep, broad minimum in equatorial magnetic field strength B ze , also just tailward of the inner edge. The results are consistent with Erickson's (1985) convection time sequences, which exhibited analogous pressure peaks and B ze minima. Observations do not indicate the existence of a B ze minimum, on the average. They suggest that the configurations with such deep minima in B ze may be tearing-mode unstable, thus leading to substorm onset in the inner plasma sheet

Electron dynamics in inhomogeneous magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Nogaret, Alain, E-mail: A.R.Nogaret@bath.ac.u [Department of Physics, University of Bath, Bath BA2 7AY (United Kingdom)

2010-06-30

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. (topical review)

The Juno Magnetic Field Investigation

Science.gov (United States)

Connerney, J. E. P.; Benn, M.; Bjarno, J. B.; Denver, T.; Espley, J.; Jorgensen, J. L.; Jorgensen, P. S.; Lawton, P.; Malinnikova, A.; Merayo, J. M.; Murphy, S.; Odom, J.; Oliversen, R.; Schnurr, R.; Sheppard, D.; Smith, E. J.

2017-11-01

The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ˜20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 106 nT per axis) with a resolution of ˜0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of

Low field magnetic resonance imaging

Science.gov (United States)

Pines, Alexander; Sakellariou, Dimitrios; Meriles, Carlos A.; Trabesinger, Andreas H.

2010-07-13

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.

Magnetic field measurements of the superEBIS superconducting magnet

International Nuclear Information System (INIS)

Herschcovitch, A.; Kponou, A.; Clipperton, R.; Hensel, W.; Usack, F.

1994-01-01

SuperEBIS was designed to have a solenoidal magnetic field of a 5 Tesla strength with a 120 cm long bore. The field was specified to be straight within 1 part in 10000 within the bore, and uniform to within 1 part in 1000 within the central 90 cm. Magnetic field measurements were performed with a computerized magnetic field measuring setup that was borrowed from W. Sampson's group. A preliminary test was made of a scheme to determine if the magnetic and mechanical axes of the solenoid coincided, and, if not, by how much

Calculation of the Magnetic Fields of the Electric Power Line

Directory of Open Access Journals (Sweden)

Patsiuk V.

2016-12-01

Full Text Available The task of calculation of per unit length parameters of multi-conductor electrical overhead transmission lines has been treated in the paper. The calculation of distribution of electric and magnetic fields has been performed by means of the finite volume method for entire span of the line. The theoretical justification of the method for calculation the parameters of electromagnetic field taking into account the change of the vector of magnetic potential along the line has been given. The problems of electrostatic and magnetostatic for a single electric conductor and unlimited long conductor with current have been solved. For the inner and total inductivities of a single conductor under the current have been obtained relationships and drawn dependences. Dependence between the speeds of light and of electromagnetic wave’s propagation has been presented. Based on the characteristics of distribution of electric and magnetic fields of multi-conductor lines has been provided the method of calculation of the matrix of own and mutual capacitances and inductivities the calculated values of per unit length parameters of compact 110 kV electric line which is in concordance with one of basic physical constant – the speed of light.

Multiple constant multiplication optimizations for field programmable gate arrays

CERN Document Server

Kumm, Martin

2016-01-01

This work covers field programmable gate array (FPGA)-specific optimizations of circuits computing the multiplication of a variable by several constants, commonly denoted as multiple constant multiplication (MCM). These optimizations focus on low resource usage but high performance. They comprise the use of fast carry-chains in adder-based constant multiplications including ternary (3-input) adders as well as the integration of look-up table-based constant multipliers and embedded multipliers to get the optimal mapping to modern FPGAs. The proposed methods can be used for the efficient implementation of digital filters, discrete transforms and many other circuits in the domain of digital signal processing, communication and image processing. Contents Heuristic and ILP-Based Optimal Solutions for the Pipelined Multiple Constant Multiplication Problem Methods to Integrate Embedded Multipliers, LUT-Based Constant Multipliers and Ternary (3-Input) Adders An Optimized Multiple Constant Multiplication Architecture ...

Dynamic shielding of the magnetic fields

Directory of Open Access Journals (Sweden)

RAU, M.

2010-11-01

Full Text Available The paper presents a comparative study of the methods used to control and compensate the direct and alternative magnetic fields. Two frequently used methods in the electromagnetic compatibility of the complex biomagnetism installations were analyzed. The two methods refer to the use of inductive magnetic field sensors (only for alternative fields and of fluxgate magnetometers as active transducers which measures both the direct and alternative components of the magnetic field. The applications of the dynamic control of the magnetic field are: control of the magnetic field of the military ships, control of parasite magnetic field produced by power transformers and the electrical networks, protection of the mass spectrometers, electronic microscopes, SQUID and optical pumping magnetometers for applications in biomagnetism.

Generating the optimal magnetic field for magnetic refrigeration

DEFF Research Database (Denmark)

Bjørk, Rasmus; Insinga, Andrea Roberto; Smith, Anders

2016-01-01

In a magnetic refrigeration device the magnet is the single most expensive component, and therefore it is crucially important to ensure that an effective magnetic field as possible is generated using the least amount of permanent magnets. Here we present a method for calculating the optimal...... remanence distribution for any desired magnetic field. The method is based on the reciprocity theorem, which through the use of virtual magnets can be used to calculate the optimal remanence distribution. Furthermore, we present a method for segmenting a given magnet design that always results...... in the optimal segmentation, for any number of segments specified. These two methods are used to determine the optimal magnet design of a 12-piece, two-pole concentric cylindrical magnet for use in a continuously rotating magnetic refrigeration device....

Earth magnetism a guided tour through magnetic fields

CERN Document Server

Campbell, Wallace H

2001-01-01

An introductory guide to global magnetic field properties, Earth Magnetism addresses, in non-technical prose, many of the frequently asked questions about Earth''s magnetic field. Magnetism surrounds and penetrates our Earth in ways basic science courses can rarely address. It affects navigation, communication, and even the growth of crystals. As we observe and experience an 11-year solar maximum, we may witness spectacular satellite-destroying solar storms as they interact with our magnetic field. Written by an acknowledged expert in the field, this book will enrich courses in earth science, atmospheric science, geology, meteorology, geomagnetism, and geophysics. Contains nearly 200 original illustrations and eight pages of full-color plates.* Largely mathematics-free and with a wide breadth of material suitable for general readers* Integrates material from geomagnetism, paleomagnetism, and solar-terrestrial space physics.* Features nearly 200 original illustrations and 4 pages of colour plates

Split-Field Magnet facility upgraded

CERN Multimedia

CERN PhotoLab

1977-01-01

The Split Field Magnet (SFM) was the largest spectrometer for particles from beam-beam collisions in the ISR. It could determine particle momenta in a large solid angle, but was designed mainly for the analysis of forward travelling particles.As the magnet was working on the ISR circulating beams, its magnetic field had to be such as to restore the correct proton orbit.The SFM, therefore, produced zero field at the crossing point and fields of opposite signs upstream and downstream of it and was completed by 2 large and 2 small compensator magnets. The gradient effects were corrected by magnetic channels equipped with movable flaps. The useful magnetic field volume was 28 m3, the induction in the median plane 1.14 T, the gap heigth 1.1 m, the length 10.5 m, the weight about 1000 ton. Concerning the detectors, the SFM was the first massive application of multiwire proportional chambers (about 70000 wires) which filled the main and the large compensator magnets. In 1976 an improved programme was started with tw...

A high pulsed power supply system designed for pulsed high magnetic field

International Nuclear Information System (INIS)

Liu Kefu; Wang Shaorong; Zhong Heqing; Xu Yan; Pan Yuan

2008-01-01

This paper introduces the design of high pulsed power supply system for producing pulsed high magnetic field up to 70 T. This system consists of 58 sets of 55 μF of capacitor bank which provides 1.0 MJ energy storage. A set of vacuum closing switch is chosen as main switch for energy discharge into magnetic coil. A crowbar circuit with high power diodes in series with resistor is used to absorb the redundant energy and adjust pulse width. The resistance of magnetic coil changing with current is deduced by energy balance equations. A capacitor-charging power supply using a series-resonant, constant on-time variable frequency control, and zero-current switching charges the capacitor bank in one minute time with high efficiency. The pulsed power supply provides adjustable current and pulse width with 30 kA peak and 30 ms maximum. The primary experiments demonstrate the system reliability. This work provides an engineering guidance for future development of pulsed high magnetic field. (authors)

Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields.

Science.gov (United States)

Maranville, Brian B; Kirby, Brian J; Grutter, Alexander J; Kienzle, Paul A; Majkrzak, Charles F; Liu, Yaohua; Dennis, Cindi L

2016-08-01

The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region. When there is non-collinear magnetization in the sample, however, there will be significant scattering from one spin state into the other, and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. The theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement.

Cosmic magnetic fields

CERN Document Server

Kronberg, Philipp P

2016-01-01

Magnetic fields are important in the Universe and their effects contain the key to many astrophysical phenomena that are otherwise impossible to understand. This book presents an up-to-date overview of this fast-growing topic and its interconnections to plasma processes, astroparticle physics, high energy astrophysics, and cosmic evolution. The phenomenology and impact of magnetic fields are described in diverse astrophysical contexts within the Universe, from galaxies to the filaments and voids of the intergalactic medium, and out to the largest redshifts. The presentation of mathematical formulae is accessible and is designed to add insight into the broad range of topics discussed. Written for graduate students and researchers in astrophysics and related disciplines, this volume will inspire readers to devise new ways of thinking about magnetic fields in space on galaxy scales and beyond.

Controlling magnetic field profiles

International Nuclear Information System (INIS)

Freeman, J.R.

1979-04-01

A method for designing solenoid magnets with controlled field profiles is discussed. The method, originated by D.B. Montgomery, minimizes both the field errors and the power consumption. An NOS time-sharing computer program for the CDC-6600, entitled MAGCOR, was constructed to provide an interactive magnet design capability. Results obtained during the design of magnets for a radial line electron accelerator are presented. 9 figures

Polymethyl methacrylate (PMMA)-bismuth ferrite (BFO) nanocomposite: low loss and high dielectric constant materials with perceptible magnetic properties.

Science.gov (United States)

Tamboli, Mohaseen S; Palei, Prakash K; Patil, Santosh S; Kulkarni, Milind V; Maldar, Noormahmad N; Kale, Bharat B

2014-09-21

Herein, poly(methyl methacrylate)-bismuth ferrite (PMMA-BFO) nanocomposites were successfully prepared by an in situ polymerization method for the first time. Initially, the as prepared bismuth ferrite (BFO) nanoparticles were dispersed in the monomer, (methyl methacrylate) by sonication. Benzoyl peroxide was used to initiate the polymerization reaction in ethyl acetate medium. The nanocomposite films were subjected to X-ray diffraction analysis (XRD), (1)H NMR, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), infrared spectroscopy (IR), dielectric and magnetic characterizations. The dielectric measurement of the nanocomposites was investigated at a frequency range of 10 Hz to 1 MHz. It was found that the nanocomposites not only showed a significantly increased value of the dielectric constant with an increase in the loading percentage of BFO as compared to pure PMMA, but also exhibited low dielectric loss values over a wide range of frequencies. The values of the dielectric constant and dielectric loss of the PMMA-BFO5 (5% BFO loading) sample at 1 kHz frequency was found be ~14 and 0.037. The variation of the ferromagnetic response of the nanocomposite was consistent with the varying volume percentage of the nanoparticles. The remnant magnetization (Mr) and saturation magnetization (Ms) values of the composites were found to be enhanced by increasing the loading percentage of BFO. The value of Ms for PMMA-BFO5 was found to be ~6 emu g(-1). The prima facie observations suggest that the nanocomposite is a potential candidate for application in high dielectric constant capacitors. Significantly, based on its magnetic properties the composite will also be useful for use in hard disk components.

A nonlinear eigenvalue problem for self-similar spherical force-free magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Lerche, I. [Institut für Geowissenschaften, Naturwissenschaftliche Fakultät III, Martin-Luther Universität, D-06099 Halle (Germany); Low, B. C. [High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80307 (United States)

2014-10-15

An axisymmetric force-free magnetic field B(r, θ) in spherical coordinates is defined by a function r sin θB{sub φ}=Q(A) relating its azimuthal component to its poloidal flux-function A. The power law r sin θB{sub φ}=aA|A|{sup 1/n}, n a positive constant, admits separable fields with A=(A{sub n}(θ))/(r{sup n}) , posing a nonlinear boundary-value problem for the constant parameter a as an eigenvalue and A{sub n}(θ) as its eigenfunction [B. C. Low and Y. Q Lou, Astrophys. J. 352, 343 (1990)]. A complete analysis is presented of the eigenvalue spectrum for a given n, providing a unified understanding of the eigenfunctions and the physical relationship between the field's degree of multi-polarity and rate of radial decay via the parameter n. These force-free fields, self-similar on spheres of constant r, have basic astrophysical applications. As explicit solutions they have, over the years, served as standard benchmarks for testing 3D numerical codes developed to compute general force-free fields in the solar corona. The study presented includes a set of illustrative multipolar field solutions to address the magnetohydrodynamics (MHD) issues underlying the observation that the solar corona has a statistical preference for negative and positive magnetic helicities in its northern and southern hemispheres, respectively; a hemispherical effect, unchanging as the Sun's global field reverses polarity in successive eleven-year cycles. Generalizing these force-free fields to the separable form B=(H(θ,φ))/(r{sup n+2}) promises field solutions of even richer topological varieties but allowing for φ-dependence greatly complicates the governing equations that have remained intractable. The axisymmetric results obtained are discussed in relation to this generalization and the Parker Magnetostatic Theorem. The axisymmetric solutions are mathematically related to a family of 3D time-dependent ideal MHD solutions for a polytropic fluid of index γ = 4

Two-dimensional frustrated spin systems in high magnetic fields

International Nuclear Information System (INIS)

Schmidt, B; Shannon, N; Thalmeier, P

2006-01-01

We discuss our numerical results on the properties of the S = 1/2 frustrated J 1 -J 2 Heisenberg model on a square lattice as a function of temperature and frustration angle φ = tan -1 (J 2 /J 1 ) in an applied magnetic field. We cover the full phase diagram of the model in the range π ≤ φ ≤ π. The discussion includes the parameter dependence of the saturation field itself, and addresses the instabilities associated with it. We also discuss the magnetocaloric effect of the model and show how it can be used to uniquely determine the effective interaction constants of the compounds which were investigated experimentally

Field dependent shape variation of magnetic fluid droplets on magnetic dots

International Nuclear Information System (INIS)

Lee, Chiun-Peng; Yang, Shu-Ting; Wei, Zung-Hang

2012-01-01

The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet. - Highlights: ► Morphology of ferrofluid droplets on magnetic thin film dots was studied experimentally. ► Aspect ratio of ferrofluid droplets was found to increase with increasing of magnetic field. ► Liquid–solid contact angle of ferrofluid droplets was found to vary with magnetic field. ► Relationship between magnetic field and the liquid–solid interfacial tension was modeled.

Surface magnetic field measurement with magnetic shielding

Czech Academy of Sciences Publication Activity Database

Perevertov, Oleksiy

2010-01-01

Roč. 61, č. 7 (2010), 66-68 ISSN 1335-3632 Grant - others:AVČR(CZ) M100100906 Institutional research plan: CEZ:AV0Z10100520 Keywords : magnetic hysteresis * magnetic field measurement * magnetic shielding * extrapolation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.270, year: 2010

Using axial magnetized permanent rings to build axial gradient magnetic field

International Nuclear Information System (INIS)

Peng Quanling

2003-01-01

Axial field produced by an axially magnetized permanent ring was studied. For two permanent magnet rings, if they are magnetized in the same direction, a nearly uniform axial field can be produced; if they are magnetized in opposite direction, an axial gradient field can be produced in the region between the two permanent rings, with the field strength changing from -B 0 to B 0 . A high gradient axial magnetic field has been built by using two axially magnetized permanent rings, the measured field results agree with the PANDIRA calculation very well. It is desirable that the field gradient can be varied to match various requirements. A method to produce the variable gradient field is presented. Axial gradient field can also be used as a beam focusing facility for linear accelerator if axial periodic field can be produced. Its magnetic field is similar to that of a solenoid, in which, large stray field will leak to the outside environment. A method for shielding the outside stray field is discussed

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

Energy Technology Data Exchange (ETDEWEB)

Sudo, Seiichi, E-mail: sudo@akita-pu.ac.j [Faculty of Systems Science and Technology, Akita Prefectural University, Ebinokuchi 84-4, Yurihonjo 015-0055 (Japan); Asano, Daisaku [Faculty of Systems Science and Technology, Akita Prefectural University, Ebinokuchi 84-4, Yurihonjo 015-0055 (Japan); Takana, Hidemasa; Nishiyama, Hideya [Institute of Fluid Science, Tohoku University, Katahira 2-1-1, Aobaku, Sendai 980-8577 (Japan)

2011-05-15

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed. - Research Highlights: Magnetic fluid of the system responds to alternating magnetic field with higher frequencies. Large-amplitude surface motions of magnetic fluid occur at the specific frequencies of the external field. Capillary jets of magnetic fluid are generated at the natural frequency of the system.

TFTR magnetic field design analyses

International Nuclear Information System (INIS)

Davies, K.; Iwinski, E.; McWhirter, J.M.

1975-11-01

The three main magnetic field windings for the TFTR are the toroidal field (TF) windings, the ohmic heating (OH) winding, and the equilibrium field (EF) winding. The following information is provided for these windings: (1) descriptions, (2) functions, (3) magnetic designs, e.g., number and location of turns, (4) design methods, and (5) descriptions of resulting magnetic fields. This report does not deal with the thermal, mechanical support, or construction details of the windings

Investigations on magnetic field induced optical transparency in magnetic nanofluids

Science.gov (United States)

Mohapatra, Dillip Kumar; Philip, John

2018-02-01

We study the magnetic field induced optical transparency and its origin in magnetic nanoemulsion of droplets of average size ∼200 nm containing superparamagnetic iron oxide nanoparticles. Beyond a certain volume fraction (Φ > 0.0021) of magnetic nanoemulsion and a critical magnetic field (Hc1), the transmitted light intensity increases drastically and reaches a maximum at another critical magnetic field (Hc2), beyond which the transmitted light intensity decreases and reaches a plateau. Interestingly, the transmitted light intensity at Hc2 is found to increase linearly with Φ and the critical magnetic fields Hc1 and Hc2 follow power law decay with Φ (i.e. Hc ∼ Φ-x), with exponents 0.48 and 0.27, respectively. The light intensity recovers to its initial value when the magnetic field is switched off, indicating the perfect reversibility of the field induced transparency process. The observed straight line scattered patterns above Hc2, on a screen placed perpendicular to the incident beam, confirms the formation of rod like anisotropic nanostructures perpendicular to the direction of light propagation. The magneto-optical measurements in the emulsion confirm that the observed field induced transparency in magnetic emulsions for Φ > 0.0021 is due to the optical birefringence caused by the rod like nanostructures. The reduced birefringence is found to be proportional to the square of the applied magnetic field. This finding offers several possibilities in using magnetic nanofluids in tunable optical devices.

Nonlinear effects in parallel magnetic fields in vanadyl and iron (111) ions solutions

International Nuclear Information System (INIS)

Ryzhov, V.A.; Fomichev, V.N.

1983-01-01

Nonlinear effects (NE) in vanadyl (VOSO 4 ) and iron (FeCl 3 x6H 2 O) solutions are investigated experimentally in the 268-323 K temperature range in parallel constant and variable linearly polarized magnetic fields, including conditions when EPR spectra are lacking due to strong resonance transition widening. It is shown that nonlinear effects are specified, on the one side, by the effect of a variable field on the relaxation processes and, on the other side, by resonance transitions in parallel fields. The relaxation and resonance effects contribute to different phase components of the second harmonic of magnetization, recorded in the experiment, at low frequences of a variable field (as compared to characteristic frequences of lattice motion). Therefore, separate analysis of the effects is possible. The presence of NE effects under conditions, when the EPR signal is not observed, and the possibility of the inverse problem solution using the variation technique on the base of simple models reveal that NE in parallel magnetic fields may be used for the investigation of paramagnets with a large EPR resonance transitions width

Cosmic Rays in Intermittent Magnetic Fields

International Nuclear Information System (INIS)

Shukurov, Anvar; Seta, Amit; Bushby, Paul J.; Wood, Toby S.; Snodin, Andrew P.

2017-01-01

The propagation of cosmic rays in turbulent magnetic fields is a diffusive process driven by the scattering of the charged particles by random magnetic fluctuations. Such fields are usually highly intermittent, consisting of intense magnetic filaments and ribbons surrounded by weaker, unstructured fluctuations. Studies of cosmic-ray propagation have largely overlooked intermittency, instead adopting Gaussian random magnetic fields. Using test particle simulations, we calculate cosmic-ray diffusivity in intermittent, dynamo-generated magnetic fields. The results are compared with those obtained from non-intermittent magnetic fields having identical power spectra. The presence of magnetic intermittency significantly enhances cosmic-ray diffusion over a wide range of particle energies. We demonstrate that the results can be interpreted in terms of a correlated random walk.

Cosmic Rays in Intermittent Magnetic Fields

Energy Technology Data Exchange (ETDEWEB)

Shukurov, Anvar; Seta, Amit; Bushby, Paul J.; Wood, Toby S. [School of Mathematics and Statistics, Newcastle University, Newcastle Upon Tyne NE1 7RU (United Kingdom); Snodin, Andrew P., E-mail: a.seta1@ncl.ac.uk, E-mail: amitseta90@gmail.com [Department of Mathematics, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Bangkok 10800 (Thailand)

2017-04-10

The propagation of cosmic rays in turbulent magnetic fields is a diffusive process driven by the scattering of the charged particles by random magnetic fluctuations. Such fields are usually highly intermittent, consisting of intense magnetic filaments and ribbons surrounded by weaker, unstructured fluctuations. Studies of cosmic-ray propagation have largely overlooked intermittency, instead adopting Gaussian random magnetic fields. Using test particle simulations, we calculate cosmic-ray diffusivity in intermittent, dynamo-generated magnetic fields. The results are compared with those obtained from non-intermittent magnetic fields having identical power spectra. The presence of magnetic intermittency significantly enhances cosmic-ray diffusion over a wide range of particle energies. We demonstrate that the results can be interpreted in terms of a correlated random walk.

Experimental study on viscosity of spinel-type manganese ferrite nanofluid in attendance of magnetic field

Energy Technology Data Exchange (ETDEWEB)

Amani, Mohammad, E-mail: m_amani@sbu.ac.ir [Mechanical and Energy Engineering Department, Shahid Beheshti University, Tehran (Iran, Islamic Republic of); Amani, Pouria, E-mail: pouria.amani@ut.ac.ir [Department of Chemical Engineering, Faculty of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Kasaeian, Alibakhsh, E-mail: akasa@ut.ac.ir [Department of Renewable Energies, Faculty of New Science & Technologies, University of Tehran, Tehran (Iran, Islamic Republic of); Mahian, Omid, E-mail: omid.mahian@mshdiau.ac.ir [Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad (Iran, Islamic Republic of); Kasaeian, Fazel, E-mail: f.kasa92@student.sharif.edu [Faculty of Material Science and Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Wongwises, Somchai, E-mail: somchai.won@kmutt.ac.th [Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut' s University of Technology Thonburi (KMUTT), Bangmod, Bangkok (Thailand)

2017-04-15

In this paper, an experimental evaluation on the viscosity of water-based manganese ferrite nanofluid with and without magnetic field with 100, 200, 300, and 400 G intensities has been conducted. The Brookfield DV-I PRIME viscometer is implemented to measure the MnFe{sub 2}O{sub 4}/water nanofluid viscosity and to evaluate the influence of different volume concentrations (from 0.25% to 3%) and various temperatures (from 20 to 60 °C) on the viscosity. According to the measurements, viscosity incrementally increases with the augmentation of nanoparticles concentration while it remarkably decreases at higher temperatures under absence and attendance of magnetic field. The maximum viscosity ratio of 1.14 is achieved at 3 vol% of nanoparticles and 20 °C under no magnetic field, whereas it increments to maximum viscosity ratio of 1.75 at 3 vol% of nanoparticles and 40 °C under 400 G magnetic field. Furthermore, new correlation is proposed for determination of viscosity of MnFe{sub 2}O{sub 4}/water nanofluids in terms of magnetic field intensity, volume concentration and temperature. - Highlights: • Viscosity of spinel-type manganese ferrite nanofluids is measured. • Effect of a constant magnetic field on the viscosity is investigated. • A novel correlation is proposed for estimation of the measured viscosity.

Experimental study on viscosity of spinel-type manganese ferrite nanofluid in attendance of magnetic field

International Nuclear Information System (INIS)

Amani, Mohammad; Amani, Pouria; Kasaeian, Alibakhsh; Mahian, Omid; Kasaeian, Fazel; Wongwises, Somchai

2017-01-01

In this paper, an experimental evaluation on the viscosity of water-based manganese ferrite nanofluid with and without magnetic field with 100, 200, 300, and 400 G intensities has been conducted. The Brookfield DV-I PRIME viscometer is implemented to measure the MnFe 2 O 4 /water nanofluid viscosity and to evaluate the influence of different volume concentrations (from 0.25% to 3%) and various temperatures (from 20 to 60 °C) on the viscosity. According to the measurements, viscosity incrementally increases with the augmentation of nanoparticles concentration while it remarkably decreases at higher temperatures under absence and attendance of magnetic field. The maximum viscosity ratio of 1.14 is achieved at 3 vol% of nanoparticles and 20 °C under no magnetic field, whereas it increments to maximum viscosity ratio of 1.75 at 3 vol% of nanoparticles and 40 °C under 400 G magnetic field. Furthermore, new correlation is proposed for determination of viscosity of MnFe 2 O 4 /water nanofluids in terms of magnetic field intensity, volume concentration and temperature. - Highlights: • Viscosity of spinel-type manganese ferrite nanofluids is measured. • Effect of a constant magnetic field on the viscosity is investigated. • A novel correlation is proposed for estimation of the measured viscosity.

Satellite to study earth's magnetic field

Science.gov (United States)

1979-01-01

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.

Demagnetizing fields in active magnetic regenerators

DEFF Research Database (Denmark)

Nielsen, Kaspar Kirstein; Bahl, Christian R.H.; Smith, Anders

2014-01-01

A magnetic material in an externally applied magnetic field will in general experience a spatially varying internal magnetic field due to demagnetizing effects. When the performance of active magnetic regenerators (AMRs) is evaluated using numerical models the internal field is often assumed...... is in general both a function of the overall shape of the regenerator and its morphology (packed particles, parallel plates etc.) as well as the magnetization of the material. Due to the pronounced temperature dependence of the magnetization near the Curie temperature, the demagnetization field is also...... temperature dependent. We propose a relatively straightforward method to correct sufficiently for the demagnetizing field in AMR models. We discuss how the demagnetizing field behaves in regenerators made of packed spheres under realistic operation conditions....

Modeling stretched solitary waves along magnetic field lines

Directory of Open Access Journals (Sweden)

L. Muschietti

2002-01-01

Full Text Available A model is presented for a new type of fast solitary waves which is observed in downward current regions of the auroral zone. The three-dimensional, coherent structures are electrostatic, have a positive potential, and move along the magnetic field lines with speeds on the order of the electron drift. Their parallel potential profile is flattened and cannot fit to the Gaussian shape used in previous work. We develop a detailed BGK model which includes a flattened potential and an assumed cylindrical symmetry around a centric magnetic field line. The model envisions concentric shells of trapped electrons slowly drifting azimuthally while bouncing back and forth in the parallel direction. The electron dynamics is analysed in terms of three basic motions that occur on different time scales characterized by the cyclotron frequency We , the bounce frequency wb , and the azimuthal drift frequency wg. The ordering We >> wb >> wg is required. Self-consistent distribution functions are calculated in terms of approximate constants of motion. Constraints on the parameters characterizing the amplitude and shape of the stretched solitary wave are discussed.

Observing Interstellar and Intergalactic Magnetic Fields

Science.gov (United States)

Han, J. L.

2017-08-01

Observational results of interstellar and intergalactic magnetic fields are reviewed, including the fields in supernova remnants and loops, interstellar filaments and clouds, Hii regions and bubbles, the Milky Way and nearby galaxies, galaxy clusters, and the cosmic web. A variety of approaches are used to investigate these fields. The orientations of magnetic fields in interstellar filaments and molecular clouds are traced by polarized thermal dust emission and starlight polarization. The field strengths and directions along the line of sight in dense clouds and cores are measured by Zeeman splitting of emission or absorption lines. The large-scale magnetic fields in the Milky Way have been best probed by Faraday rotation measures of a large number of pulsars and extragalactic radio sources. The coherent Galactic magnetic fields are found to follow the spiral arms and have their direction reversals in arms and interarm regions in the disk. The azimuthal fields in the halo reverse their directions below and above the Galactic plane. The orientations of organized magnetic fields in nearby galaxies have been observed through polarized synchrotron emission. Magnetic fields in the intracluster medium have been indicated by diffuse radio halos, polarized radio relics, and Faraday rotations of embedded radio galaxies and background sources. Sparse evidence for very weak magnetic fields in the cosmic web is the detection of the faint radio bridge between the Coma cluster and A1367. Future observations should aim at the 3D tomography of the large-scale coherent magnetic fields in our Galaxy and nearby galaxies, a better description of intracluster field properties, and firm detections of intergalactic magnetic fields in the cosmic web.

Five years of magnetic field management

International Nuclear Information System (INIS)

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

1995-01-01

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

The symmetric quartic map for trajectories of magnetic field lines in elongated divertor tokamak plasmas

Science.gov (United States)

Jones, Morgin; Wadi, Hasina; Ali, Halima; Punjabi, Alkesh

2009-04-01

The coordinates of the area-preserving map equations for integration of magnetic field line trajectories in divertor tokamaks can be any coordinates for which a transformation to (ψt,θ,φ) coordinates exists [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. ψt is toroidal magnetic flux, θ is poloidal angle, and φ is toroidal angle. This freedom is exploited to construct the symmetric quartic map such that the only parameter that determines magnetic geometry is the elongation of the separatrix surface. The poloidal flux inside the separatrix, the safety factor as a function of normalized minor radius, and the magnetic perturbation from the symplectic discretization are all held constant, and only the elongation is κ varied. The width of stochastic layer, the area, and the fractal dimension of the magnetic footprint and the average radial diffusion coefficient of magnetic field lines from the stochastic layer; and how these quantities scale with κ is calculated. The symmetric quartic map gives the correct scalings which are consistent with the scalings of coordinates with κ. The effects of m =1, n =±1 internal perturbation with the amplitude that is expected to occur in tokamaks are calculated by adding a term [H. Ali, A. Punjabi, A. H. Boozer, and T. Evans, Phys. Plasmas 11, 1908 (2004)] to the symmetric quartic map. In this case, the width of stochastic layer scales as 0.35 power of κ. The area of the footprint is roughly constant. The average radial diffusion coefficient of field lines near the X-point scales linearly with κ. The low mn perturbation changes the quasisymmetric structure of the footprint, and reorganizes it into a single, large scale, asymmetric structure. The symmetric quartic map is combined with the dipole map [A. Punjabi, H. Ali, and A. H. Boozer, Phys. Plasmas 10, 3992 (2003)] to calculate the effects of magnetic perturbation from a current carrying coil. The coil position and coil current coil are

The symmetric quartic map for trajectories of magnetic field lines in elongated divertor tokamak plasmas

International Nuclear Information System (INIS)

Jones, Morgin; Wadi, Hasina; Ali, Halima; Punjabi, Alkesh

2009-01-01

The coordinates of the area-preserving map equations for integration of magnetic field line trajectories in divertor tokamaks can be any coordinates for which a transformation to (ψ t ,θ,φ) coordinates exists [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. ψ t is toroidal magnetic flux, θ is poloidal angle, and φ is toroidal angle. This freedom is exploited to construct the symmetric quartic map such that the only parameter that determines magnetic geometry is the elongation of the separatrix surface. The poloidal flux inside the separatrix, the safety factor as a function of normalized minor radius, and the magnetic perturbation from the symplectic discretization are all held constant, and only the elongation is κ varied. The width of stochastic layer, the area, and the fractal dimension of the magnetic footprint and the average radial diffusion coefficient of magnetic field lines from the stochastic layer; and how these quantities scale with κ is calculated. The symmetric quartic map gives the correct scalings which are consistent with the scalings of coordinates with κ. The effects of m=1, n=±1 internal perturbation with the amplitude that is expected to occur in tokamaks are calculated by adding a term [H. Ali, A. Punjabi, A. H. Boozer, and T. Evans, Phys. Plasmas 11, 1908 (2004)] to the symmetric quartic map. In this case, the width of stochastic layer scales as 0.35 power of κ. The area of the footprint is roughly constant. The average radial diffusion coefficient of field lines near the X-point scales linearly with κ. The low mn perturbation changes the quasisymmetric structure of the footprint, and reorganizes it into a single, large scale, asymmetric structure. The symmetric quartic map is combined with the dipole map [A. Punjabi, H. Ali, and A. H. Boozer, Phys. Plasmas 10, 3992 (2003)] to calculate the effects of magnetic perturbation from a current carrying coil. The coil position and coil current coil are

Magnetic field line Hamiltonian

International Nuclear Information System (INIS)

Boozer, A.H.

1984-03-01

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

Tripolar electric field Structure in guide field magnetic reconnection

Science.gov (United States)

Fu, Song; Huang, Shiyong; Zhou, Meng; Ni, Binbin; Deng, Xiaohua

2018-03-01

It has been shown that the guide field substantially modifies the structure of the reconnection layer. For instance, the Hall magnetic and electric fields are distorted in guide field reconnection compared to reconnection without guide fields (i.e., anti-parallel reconnection). In this paper, we performed 2.5-D electromagnetic full particle simulation to study the electric field structures in magnetic reconnection under different initial guide fields (Bg). Once the amplitude of a guide field exceeds 0.3 times the asymptotic magnetic field B0, the traditional bipolar Hall electric field is clearly replaced by a tripolar electric field, which consists of a newly emerged electric field and the bipolar Hall electric field. The newly emerged electric field is a convective electric field about one ion inertial length away from the neutral sheet. It arises from the disappearance of the Hall electric field due to the substantial modification of the magnetic field and electric current by the imposed guide field. The peak magnitude of this new electric field increases linearly with the increment of guide field strength. Possible applications of these results to space observations are also discussed.

Tripolar electric field Structure in guide field magnetic reconnection

Directory of Open Access Journals (Sweden)

S. Fu

2018-03-01

Full Text Available It has been shown that the guide field substantially modifies the structure of the reconnection layer. For instance, the Hall magnetic and electric fields are distorted in guide field reconnection compared to reconnection without guide fields (i.e., anti-parallel reconnection. In this paper, we performed 2.5-D electromagnetic full particle simulation to study the electric field structures in magnetic reconnection under different initial guide fields (Bg. Once the amplitude of a guide field exceeds 0.3 times the asymptotic magnetic field B0, the traditional bipolar Hall electric field is clearly replaced by a tripolar electric field, which consists of a newly emerged electric field and the bipolar Hall electric field. The newly emerged electric field is a convective electric field about one ion inertial length away from the neutral sheet. It arises from the disappearance of the Hall electric field due to the substantial modification of the magnetic field and electric current by the imposed guide field. The peak magnitude of this new electric field increases linearly with the increment of guide field strength. Possible applications of these results to space observations are also discussed.

Study on magnetic field mapping within cylindrical center volume of general magnet

Energy Technology Data Exchange (ETDEWEB)

Huang, Li; Lee, Sang Jin [Uiduk University, Gyeongju (Korea, Republic of)

2016-06-15

For the magnetic field analysis or design, it is important to know the behavior of the magnetic field in an interesting space. Magnetic field mapping becomes a useful tool for the study of magnetic field. In this paper, a numerical way for mapping the magnetic field within the cylindrical center volume of magnet is presented, based on the solution of the Laplace's equation in the cylindrical coordinate system. The expression of the magnetic field can be obtained by the magnetic flux density, which measured in the mapped volume. According to the form of the expression, the measurement points are arranged with the parallel cylindrical line (PCL) method. As example, the magnetic flux density generated by an electron cyclotron resonance ion source (ECRIS) magnet and a quadrupole magnet were mapped using the PCL method, respectively. The mapping results show the PCL arrangement method is feasible and convenience to map the magnetic field within a cylindrical center volume generated by the general magnet.

Dynamic rheological properties of viscoelastic magnetic fluids in uniform magnetic fields

International Nuclear Information System (INIS)

Yamaguchi, Hiroshi; Niu Xiaodong; Ye Xiaojiang; Li Mingjun; Iwamoto, Yuhiro

2012-01-01

The dynamic rheological properties of viscoelastic magnetic fluids in externally applied uniform magnetic fields are investigated by a laboratory-made cone-plate rheometer in this study. In particular, the effects of the magnetic field on the viscoelastic properties (the complex dynamic modulus) of the viscoelastic magnetic fluids are studied. In the investigation, three viscoelastic magnetic fluids are made by mixing a magnetic fluid and a viscoelastic fluid with different mass ratios. As a supplementation to the experimental investigation, a theoretical analysis is also presented. The present study shows that the viscosity and elasticity of the viscoelastic magnetic fluids are significantly influenced by the magnetic field and the concentrations of the magnetic particles in the test fluids. Theoretical analysis qualitatively explains the present findings. - Highlights: ► The dynamic rheological properties of the viscoelastic magnetic fluids in uniform magnetic fields are investigated. ► Both the magnetic field strength and the concentration of the magnetic particles in the fluids have significant effects on the viscosity and elasticity of the viscoelastic magnetic fluids. ► Theoretical prediction and analysis qualitatively explains the present findings.

On the role of magnetic field intensity for better micro-structural characterization during Barkhausen Noise analysis

Science.gov (United States)

Yusufzai, Mohd Zaheer Khan; Vashista, M.

2018-04-01

Barkhausen Noise analysis is a popular and preferred technique for micro-structural characterization. The root mean square value and peak value of Barkhausen Noise burst are important parameters to assess the micro-hardness and residual stress. Barkhausen Noise burst can be enveloped using a curve known as Barkhausen Noise profile. Peak position of profile changes with change in micro-structure. In the present work, raw signal of Barkhausen Noise burst was obtained from Ni based sample at various magnetic field intensity to observe the effect of variation in field intensity on Barkhausen Noise burst. Raw signal was opened using MATLAB to further process for microstructure analysis. Barkhausen Noise analysis parameters such as magnetizing frequency, number of burst, high pass and low pass filter frequency were kept constant and magnetizing field was varied in wide range between 200 Oe to 1200 Oe. The processed profiles of Barkhausen Noise burst obtained at various magnetizing field intensity clearly reveals requirement of optimum magnetic field strength for better characterization of micro-structure.

Hypernuclear matter in strong magnetic field

Energy Technology Data Exchange (ETDEWEB)

Sinha, Monika [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany); Indian Institute of Technology Rajasthan, Old Residency Road, Ratanada, Jodhpur 342011 (India); Mukhopadhyay, Banibrata [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Sedrakian, Armen, E-mail: sedrakian@th.physik.uni-frankfurt.de [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany)

2013-01-17

Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10{sup 14}–10{sup 15} G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta–Bodmer–Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B⩾10{sup 17} G, in particular the matter properties become anisotropic. Moreover, for the central fields B⩾10{sup 18} G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value B{sub cr}≃10{sup 19} G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value B{sub cr}.

Mercury's magnetic field and interior

International Nuclear Information System (INIS)

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

1988-01-01

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

Magnetic monopole plasma oscillations and the survival of Galactic magnetic fields

International Nuclear Information System (INIS)

Parker, E.N.

1987-01-01

This paper explores the general nature of magnetic-monopole plasma oscillations as a theoretical possibility for the observed Galactic magnetic field in the presence of a high abundance of magnetic monopoles. The modification of the hydromagnetic induction equation by the monopole oscillations produces the half-velocity effect, in which the magnetic field is transported bodily with a velocity midway between the motion of the conducting fluid and the monopole plasma. Observational studies of the magnetic field in the Galaxy, and in other galaxies, exclude the half-velocity effect, indicating that the magnetic fields is not associated with monopole oscillations. In any case the phase mixing would destroy the oscillations in less than 100 Myr. The conclusion is that magnetic monopole oscillations do not play a significant role in the galactic magnetic fields. Hence the existence of galactic magnetic fields places a low limit on the monopole flux, so that their detection - if they exist at all - requires a collecting area at least as large as a football field. 47 references

Effect of the low magnetic field on the electrodeposition of Co{sub x}Ni{sub 100−x} alloys

Energy Technology Data Exchange (ETDEWEB)

Olvera, S. [Instituto Politécnico Nacional, ESIQIE, Departamento de Ingeniería en Metalurgia y Materiales, 07738 México, D.F., México (Mexico); Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química-Física Aplicada, 28049 Madrid (Spain); Arce Estrada, E.M. [Instituto Politécnico Nacional, ESIQIE, Departamento de Ingeniería en Metalurgia y Materiales, 07738 México, D.F., México (Mexico); Sanchez-Marcos, J. [Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química-Física Aplicada, 28049 Madrid (Spain); Palomares, F.J.; Vazquez, L. [Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, Cantoblanco, 28049 Madrid (Spain); Herrasti, P., E-mail: pilar.herrasti@uam.es [Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química-Física Aplicada, 28049 Madrid (Spain)

2015-07-15

Magnetic, chemical and structural properties of electrosynthesized Co{sub x}Ni{sub 100−x} have been studied. The electrodeposition has been conducted both in the presence and absence of a low magnetic field. The application of a perpendicular magnetic field during the synthesis modified slightly the morphology of the alloys. These changes depend more on the film composition than on the applied field, as demonstrated by AFM images. In the absence of magnetic field, the Co{sub x}Ni{sub 100−x} film grows along the (200) direction. However, when the magnetic field was applied, a preferential orientation along the (111) direction was observed. No important magnetic changes are induced by the presence of the magnetic field during the growth. Based on X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) experiments, the chemical composition of the films was preserved during preparation regardless of whether or not magnetic field is applied. There has been observed an increase in deposition rate in the presence of field even at these low magnetic fields. - Highlights: • CoNi alloys were electrosynthesized in the absence and presence of a low magnetic field. • Application of a magnetic field produced an orientation in the (111) plane of the alloy. • An external field changes the voltammetric curves reducing the energy required for the alloy formation. • The composition and magnetic properties were constant in the absence and presence of magnetic field.

Laboratory experiments on the magnetic field and neutral density limits on CIV interaction

International Nuclear Information System (INIS)

Axnaes, I.; Brenning, N.

1990-03-01

Laboratory experiments are reported which determine the magnetic field and neutral density limit for Critical Ionization Velocity (CIV) interaction in the impact configuration. A combination of microwave interferometry and spectroscopy has been used to measure how the electron energy distribution varies with the neutral density and the magnetic field strength. The efficiency of the CIV process is evaluated in terms of the efficiency factor η of energy transfer to the electron. This efficiency is studied as function of the ratio V A /V 0 between the Alfven velocity and the plasma stream velocity and the ratio ν i /ω gi between the ionization frequency and the ion gyro frequency. With other parameters kept constant, V A /V 0 is proportional to the square root of the magnetic field, while ν i /ω gi is proportional to the neutral density. We have found that these two dimensionless parameters are coupled in such a fashion that a stronger magnetic field can compensate for a lower neutral density. For our strongest magnetic field, corresponding to V A /V 0 = 4, CIV interaction is found to occur for a comparatively low value ν i /ω gi ∼ 0.1. For V A /V 0 = 1, we found a clear absence of CIV interaction even for ν i /ω gi approaching unity. (authors)

Si:P as a laboratory analogue for hydrogen on high magnetic field white dwarf stars.

Science.gov (United States)

Murdin, B N; Li, Juerong; Pang, M L Y; Bowyer, E T; Litvinenko, K L; Clowes, S K; Engelkamp, H; Pidgeon, C R; Galbraith, I; Abrosimov, N V; Riemann, H; Pavlov, S G; Hübers, H-W; Murdin, P G

2013-01-01

Laboratory spectroscopy of atomic hydrogen in a magnetic flux density of 10(5) T (1 gigagauss), the maximum observed on high-field magnetic white dwarfs, is impossible because practically available fields are about a thousand times less. In this regime, the cyclotron and binding energies become equal. Here we demonstrate Lyman series spectra for phosphorus impurities in silicon up to the equivalent field, which is scaled to 32.8 T by the effective mass and dielectric constant. The spectra reproduce the high-field theory for free hydrogen, with quadratic Zeeman splitting and strong mixing of spherical harmonics. They show the way for experiments on He and H(2) analogues, and for investigation of He(2), a bound molecule predicted under extreme field conditions.

Spin structure factors of Heisenberg spin chain in the presence of anisotropy and magnetic field

Energy Technology Data Exchange (ETDEWEB)

Rezania, H., E-mail: rezania.hamed@gmail.com

2017-02-01

We have theoretically studied the spin structure factors of spin chain in the presence of longitudinal field and transverse anisotropy. The possible effects of easy axis magnetization are investigated in terms of anisotropy in the Heisenberg interactions. This anisotropy is considered for exchange coupling constants perpendicular to magnetic field direction. The original spin model hamiltonian is mapped to a bosonic model via a hard core bosonic transformation where an infinite hard core repulsion is imposed to constrain one boson occupation per site. Using Green's function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the position of peak in the longitudinal structure factor at fixed value for anisotropy moves to higher frequency with magnetic field. Also the intensity of dynamical structure factor decreases with magnetic field. A small dependence of longitudinal dynamical spin structure factor on the anisotropy is observed for fixed value of magnetic field. Our results show longitudinal static structure factor is found to be monotonically increasing with magnetic field due to increase of spins aligning along magnetic field. Furthermore the dispersion behaviors of static longitudinal and transverse structure factors for different magnetic fields and anisotropy parameters are addressed. - Highlights: • Theoretical calculation of spin structure factors of Heisenberg chain. • The investigation of the effect of anisotropy spin structure factors of Heisenberg chain. • The investigation of the effect of magnetic field on spin structure factors of Heisenberg chain.

Spin structure factors of Heisenberg spin chain in the presence of anisotropy and magnetic field

International Nuclear Information System (INIS)

Rezania, H.

2017-01-01

We have theoretically studied the spin structure factors of spin chain in the presence of longitudinal field and transverse anisotropy. The possible effects of easy axis magnetization are investigated in terms of anisotropy in the Heisenberg interactions. This anisotropy is considered for exchange coupling constants perpendicular to magnetic field direction. The original spin model hamiltonian is mapped to a bosonic model via a hard core bosonic transformation where an infinite hard core repulsion is imposed to constrain one boson occupation per site. Using Green's function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the position of peak in the longitudinal structure factor at fixed value for anisotropy moves to higher frequency with magnetic field. Also the intensity of dynamical structure factor decreases with magnetic field. A small dependence of longitudinal dynamical spin structure factor on the anisotropy is observed for fixed value of magnetic field. Our results show longitudinal static structure factor is found to be monotonically increasing with magnetic field due to increase of spins aligning along magnetic field. Furthermore the dispersion behaviors of static longitudinal and transverse structure factors for different magnetic fields and anisotropy parameters are addressed. - Highlights: • Theoretical calculation of spin structure factors of Heisenberg chain. • The investigation of the effect of anisotropy spin structure factors of Heisenberg chain. • The investigation of the effect of magnetic field on spin structure factors of Heisenberg chain.

Magnetic properties of mixed Ni–Cu ferrites calculated using mean field approach

Energy Technology Data Exchange (ETDEWEB)

Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63, 46000 Safi (Morocco); LMPHE, URAC 12, Faculté des Sciences, Université Mohamed V-Agdal, Rabat (Morocco); Hamedoun, M. [Institute for Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE, URAC 12, Faculté des Sciences, Université Mohamed V-Agdal, Rabat (Morocco); Institute for Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Academie Hassan II des Sciences et Techniques, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble cedex 9 (France)

2014-08-01

The magnetic properties of spinel ferrites [Fe{sub 1−(1−x)y}{sup 3+}Cu{sub (1−x)y}{sup 2+}]{sub A}[Ni{sub x}{sup 2+}Cu{sub (1−x)(1−y)}{sup 2+}Fe{sub 1+(1−x)y}{sup 3+}]{sub B}O{sub 4} have been studied by the mean field theory (MFT) and high temperature series expansions (HTSEs) combined with the Padé approximants. The critical temperature, the saturation magnetisation (M{sub S}) and the intra-sublattice exchanges interactions (J{sub AA}(x,y), J{sub BB}(x,y) and J{sub AB}(x,y)) are obtained by using a probability distribution law. The critical exponents associate with the magnetic susceptibility have been obtained. The effect of copper doping on the magnetic properties of nickel ferrites has been examined. - Highlights: • The exchange and constants interactions of CuFe{sub 2}O{sub 4} material are obtained. • The saturation magnetisation, the critical temperature, the Curie Weiss temperature and the Curie constant of CuFe{sub 2}O{sub 4} are obtained. • The critical exponent associated with the magnetic susceptibility is given.

3D study in modelling in static regime of a bi facial polycrystalline solar cell under intense light and under a constant magnetic field

International Nuclear Information System (INIS)

ZOUNGRANA Martial

2010-01-01

In this work we propose a three-dimensional (3D) study of magnetic field, light concentration and electron gradient concentration electric field respective influences on bi facial polycrystalline silicon solar cell behaviour. The hold account of these parameters in our study leads to the new expressions of continuity equations, electric and electronic parameters. On the basis of these equations, grain size, grain boundary recombination velocity, magnetic field and light intensity effects on carriers density, photocurrent, photovoltage, electric and electronic parameters are analysed. We finally propose an equivalent electric model of bi facial polycrystalline silicon solar cell under magnetic field. According to this model, electric parameters expressions was established (shunt and series resistances, space charge zone capacity ) and we study magnetic field, grain size, grain boundary recombination velocity and light concentration influences on these parameters.(Author) [fr

Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength.

Science.gov (United States)

Raaijmakers, A J E; Raaymakers, B W; Lagendijk, J J W

2008-02-21

Several institutes are currently working on the development of a radiotherapy treatment system with online MR imaging (MRI) modality. The main difference between their designs is the magnetic field strength of the MRI system. While we have chosen a 1.5 Tesla (T) magnetic field strength, the Cross Cancer Institute in Edmonton will be using a 0.2 T MRI scanner and the company Viewray aims to use 0.3 T. The magnetic field strength will affect the severity of magnetic field dose effects, such as the electron return effect (ERE): considerable dose increase at tissue air boundaries due to returning electrons. This paper has investigated how the ERE dose increase depends on the magnetic field strength. Therefore, four situations where the ERE occurs have been simulated: ERE at the distal side of the beam, the lateral ERE, ERE in cylindrical air cavities and ERE in the lungs. The magnetic field comparison values were 0.2, 0.75, 1.5 and 3 T. Results show that, in general, magnetic field dose effects are reduced at lower magnetic field strengths. At the distal side, the ERE dose increase is largest for B = 0.75 T and depends on the irradiation field size for B = 0.2 T. The lateral ERE is strongest for B = 3 T but shows no effect for B = 0.2 T. Around cylindrical air cavities, dose inhomogeneities disappear if the radius of the cavity becomes small relative to the in-air radius of the secondary electron trajectories. At larger cavities (r > 1 cm), dose inhomogeneities exist for all magnetic field strengths. In water-lung-water phantoms, the ERE dose increase takes place at the water-lung transition and the dose decreases at the lung-water transition, but these effects are minimal for B = 0.2 T. These results will contribute to evaluating the trade-off between magnetic field dose effects and image quality of MR-guided radiotherapy systems.