Tunneling Characteristics of an Electron-Hole Trilayer in a Parallel Magnetic Field

National Research Council Canada - National Science Library

Lin, Y

2003-01-01

We have studied the tunneling properties of GaSb/AlSb/InAs/AlSb/GaSb heterostructures in which electrons- and boles accumulate in the InAs and GaSb regions respectively under a magnetic field parallel...

Parallel computation of automatic differentiation applied to magnetic field calculations

International Nuclear Information System (INIS)

Hinkins, R.L.; Lawrence Berkeley Lab., CA

1994-09-01

The author presents a parallelization of an accelerator physics application to simulate magnetic field in three dimensions. The problem involves the evaluation of high order derivatives with respect to two variables of a multivariate function. Automatic differentiation software had been used with some success, but the computation time was prohibitive. The implementation runs on several platforms, including a network of workstations using PVM, a MasPar using MPFortran, and a CM-5 using CMFortran. A careful examination of the code led to several optimizations that improved its serial performance by a factor of 8.7. The parallelization produced further improvements, especially on the MasPar with a speedup factor of 620. As a result a problem that took six days on a SPARC 10/41 now runs in minutes on the MasPar, making it feasible for physicists at Lawrence Berkeley Laboratory to simulate larger magnets

Parallel magnetic field perturbations in gyrokinetic simulations

International Nuclear Information System (INIS)

Joiner, N.; Hirose, A.; Dorland, W.

2010-01-01

At low β it is common to neglect parallel magnetic field perturbations on the basis that they are of order β 2 . This is only true if effects of order β are canceled by a term in the ∇B drift also of order β[H. L. Berk and R. R. Dominguez, J. Plasma Phys. 18, 31 (1977)]. To our knowledge this has not been rigorously tested with modern gyrokinetic codes. In this work we use the gyrokinetic code GS2[Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)] to investigate whether the compressional magnetic field perturbation B || is required for accurate gyrokinetic simulations at low β for microinstabilities commonly found in tokamaks. The kinetic ballooning mode (KBM) demonstrates the principle described by Berk and Dominguez strongly, as does the trapped electron mode, in a less dramatic way. The ion and electron temperature gradient (ETG) driven modes do not typically exhibit this behavior; the effects of B || are found to depend on the pressure gradients. The terms which are seen to cancel at long wavelength in KBM calculations can be cumulative in the ion temperature gradient case and increase with η e . The effect of B || on the ETG instability is shown to depend on the normalized pressure gradient β ' at constant β.

Experimentally attainable example of chaotic tunneling: The hydrogen atom in parallel static electric and magnetic fields

International Nuclear Information System (INIS)

Delande, Dominique; Zakrzewski, Jakub

2003-01-01

Statistics of tunneling rates in the presence of chaotic classical dynamics is discussed on a realistic example: a hydrogen atom placed in parallel, uniform, static electric, and magnetic fields, where tunneling is followed by ionization along the fields direction. Depending on the magnetic quantum number, one may observe either a standard Porter-Thomas distribution of tunneling rates or, for strong scarring by a periodic orbit parallel to the external fields, strong deviations from it. For the latter case, a simple model based on random matrix theory gives the correct distribution

Propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere

Science.gov (United States)

Huba, J. D.; Rowland, H. L.

1993-01-01

The propagation of electromagnetic waves parallel to the magnetic field in the nightside Venus ionosphere is presented in a theoretical and numerical analysis. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as that produced by lightning. Specifically addressed is wave propagation in the altitude range z = 130-160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector: 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. Parameterizations of the wave intensities, peak electron density, and Poynting flux as a function of magnetic field are presented. The waves are found to propagate most easily in conditions of low electron density and high magnetic field. The results of the model are consistent with observational data.

The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection

International Nuclear Information System (INIS)

Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L.; Aunai, N.; Karimabadi, H.; Daughton, W.

2013-01-01

We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line

Anisotropic behaviour of transmission through thin superconducting NbN film in parallel magnetic field

Czech Academy of Sciences Publication Activity Database

Šindler, Michal; Tesař, Karel; Koláček, Jan; Skrbek, L.

2017-01-01

Roč. 533, Feb (2017), s. 154-157 ISSN 0921-4534 R&D Projects: GA MŠk(CZ) LD14060 Institutional support: RVO:68378271 Keywords : far-infrared transmission * NbN * ssuperconducting film * vortices * terahertz waves * parallel magnetic field Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.404, year: 2016

Unsteady free convection MHD flow between two heated vertical parallel plates in induced magnetic field

International Nuclear Information System (INIS)

Chakraborty, S.; Borkakati, A.K.

1999-01-01

An unsteady viscous incompressible free convection flow of an electrically conducting fluid between two heated vertical parallel plates is considered in presence of a uniform magnetic field applied transversely to the flow. The approximate analytical solutions for velocity, induced field and temperature distributions are obtained for small and large magnetic Reynolds number. The skin-friction on the two plates are obtained and plotted graphically. The problem is extended for thermometric case. (author)

Two-dimensional superconducting state of monolayer Pb films grown on GaAs(110) in a strong parallel magnetic field.

Science.gov (United States)

Sekihara, Takayuki; Masutomi, Ryuichi; Okamoto, Tohru

2013-08-02

Two-dimensional (2D) superconductivity was studied by magnetotransport measurements on single-atomic-layer Pb films on a cleaved GaAs(110) surface. The superconducting transition temperature shows only a weak dependence on the parallel magnetic field up to 14T, which is higher than the Pauli paramagnetic limit. Furthermore, the perpendicular-magnetic-field dependence of the sheet resistance is almost independent of the presence of the parallel field component. These results are explained in terms of an inhomogeneous superconducting state predicted for 2D metals with a large Rashba spin splitting.

Equilibrium properties of the plasma sheath with a magnetic field parallel to the wall

International Nuclear Information System (INIS)

Krasheninnikova, Natalia S.; Tang Xianzhu

2010-01-01

Motivated by the magnetized target fusion (MTF) experiment [R. E. Siemon et al., Comments Plasma Phys. Controlled Fusion 18, 363 (1999)], a systematic investigation of the force balance and equilibrium plasma flows was carried out using analytical theory and the particle-in-cell code VPIC[K. J. Bowers et al., Phys. Plasmas 15, 055703 (2008)] for a one-dimensional plasma sheath with a magnetic field parallel to the wall. Initially uniform full Maxwellian plasma consisting of equal temperature collisionless electrons and ions is allowed to interact with a perfectly absorbing wall. The analysis of the steady-state force balance of the entire plasma as well as its individual components illuminates the roles that the hydrodynamic, magnetic, and electric forces play. In particular, when ρ thi D , the magnetic force balances the divergence of the pressure tensor. As the magnetic field is decreased, the electric force becomes prominent in areas where quasineutrality breaks, which can be a substantial part of the sheath. Its importance depends on the relation between three parameters, namely, electron and ion thermal Larmor radii and plasma Debye length: ρ the , ρ thi , and λ D . The relative importance of the electron and ion current in the magnetic or Lorentz force term can be understood through the analysis of the two-fluid force balance. It reveals that the current is carried primarily by the electrons. This is due to the direction of the electric field that helps confine the ions, but not the electrons, which are forced to carry a large current to confine themselves magnetically. In the regimes where the electric field is negligible, the ions also need the current for confinement, but in these cases the divergence of ion pressure tensor is much smaller than that of the electrons. Consequently the ion current is also smaller. The study of the electron and ion flow parallel to the wall clarifies this picture even further. In the regime of strong magnetic field, the

Dynamic and statistical thermodynamic properties of electrons in a thin quantum well in a parallel magnetic field

International Nuclear Information System (INIS)

Horing, Norman J Morgenstern; Glasser, M Lawrence; Dong Bing

2006-01-01

We carry out a theoretical analysis of quantum well electron dynamics in a parallel magnetic field of arbitrary strength, for a narrow quantum well. An explicit analytical closed-form solution is obtained for the retarded Green's function for Landau-quantized electrons in skipping states of motion between the narrow well walls, effectively involving in-plane translational motion, and hybridized with the zero-field lowest subband energy eigenstate. The dispersion relation for electron eigenstates is examined, and we find a plethora of such discrete Landau-quantized modes coupled to the subband state. In the weak field limit, we determine low magnetic field corrections to the lowest subband state energy associated with close-packing (phase averaging) of the Landau levels in the skipping states. At higher fields the discrete energy levels of the well lie between adjacent Landau levels, but they are not equally spaced, albeit undamped. Furthermore, we also examine the associated thermodynamic Green's function for Landau-quantized electrons in a thin quantum well in a parallel magnetic field and construct the (grand) thermodynamic potential (logarithm of the grand partition function) determining the statistical thermodynamics of the system

Green's function for electrons in a narrow quantum well in a parallel magnetic field

International Nuclear Information System (INIS)

Horing, Norman J. Morgenstern; Glasser, M. Lawrence; Dong Bing

2005-01-01

Electron dynamics in a narrow quantum well in a parallel magnetic field of arbitrary strength are examined here. We derive an explicit analytical closed-form solution for the Green's function of Landau-quantized electrons in skipping states of motion between the narrow well walls coupled with in-plane translational motion and hybridized with the zero-field lowest subband energy eigenstate. Such Landau-quantized modes are not uniformly spaced

Flux pinning and critical current in layered type-II superconductors in parallel magnetic fields

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We have shown, within the Ginzburg-Landau theory, that the interaction between vortices and normal-metal layers in high-T c superconductor--normal-metal superlattices can cause high critical-current densities j c . The interaction is primarily magnetic, except at very low temperatures T, where the core interaction is dominant. For a lattice of vortices commensurate with an array of normal-metal layers in a parallel magnetic field H, strong magnetic pinning is obtained, with a nonmonotonic critical-current dependence on H, and with j c of the order of 10 7 --10 8 A/cm 2

Parallel electric fields from ionospheric winds

International Nuclear Information System (INIS)

Nakada, M.P.

1987-01-01

The possible production of electric fields parallel to the magnetic field by dynamo winds in the E region is examined, using a jet stream wind model. Current return paths through the F region above the stream are examined as well as return paths through the conjugate ionosphere. The Wulf geometry with horizontal winds moving in opposite directions one above the other is also examined. Parallel electric fields are found to depend strongly on the width of current sheets at the edges of the jet stream. If these are narrow enough, appreciable parallel electric fields are produced. These appear to be sufficient to heat the electrons which reduces the conductivity and produces further increases in parallel electric fields and temperatures. Calculations indicate that high enough temperatures for optical emission can be produced in less than 0.3 s. Some properties of auroras that might be produced by dynamo winds are examined; one property is a time delay in brightening at higher and lower altitudes

Magnetic response to applied electrostatic field in external magnetic field

Energy Technology Data Exchange (ETDEWEB)

Adorno, T.C. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); University of Florida, Department of Physics, Gainesville, FL (United States); Gitman, D.M. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil); Tomsk State University, Department of Physics, Tomsk (Russian Federation); Shabad, A.E. [P. N. Lebedev Physics Institute, Moscow (Russian Federation)

2014-04-15

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

Parallel electric fields in a simulation of magnetotail reconnection and plasmoid evolution

International Nuclear Information System (INIS)

Hesse, M.; Birn, J.

1990-01-01

Properties of the electric field component parallel to the magnetic field are investigate in a 3D MHD simulation of plasmoid formation and evolution in the magnetotail, in the presence of a net dawn-dusk magnetic field component. The spatial localization of E-parallel, and the concept of a diffusion zone and the role of E-parallel in accelerating electrons are discussed. A localization of the region of enhanced E-parallel in all space directions is found, with a strong concentration in the z direction. This region is identified as the diffusion zone, which plays a crucial role in reconnection theory through the local break-down of magnetic flux conservation. 12 refs

Thermal conductivity of layered organic superconductor β-(BDA-TTP)2SbF6 in a parallel magnetic field: Anomalous effect of coreless vortices

Science.gov (United States)

Tanatar, M. A.; Ishiguro, T.; Toita, T.; Yamada, J.

2005-01-01

Thermal conductivity κ of the organic superconductor β-(BDA-TTP)2SbF6 was studied down to 0.3 K in magnetic fields H of varying orientation with respect to the superconducting plane. Anomalous plateau shape of the field dependence, κ vs H , is found for orientation of magnetic fields precisely parallel to the plane, in contrast to usual behavior observed in the perpendicular fields. We show that the lack of magnetic-field effect on the heat conduction results from coreless structure of vortices, causing both negligible scattering of phonons and constant in field electronic conduction up to the fields close to the upper critical field Hc2 . Usual behavior is recovered on approaching Hc2 and on slight field inclination from parallel direction, when normal cores are restored. This behavior points to the lack of bulk quasiparticle excitations induced by magnetic field, consistent with the conventional superconducting state.

Conductance of auroral magnetic field lines

International Nuclear Information System (INIS)

Weimer, D.R.; Gurnett, D.A.; Goertz, C.K.

1986-01-01

DE-1 high-resolution double-probe electric-field data and simultaneous magnetic-field measurements are reported for two 1981 events with large electric fields which reversed over short distances. The data are presented graphically and analyzed in detail. A field-line conductance of about 1 nmho/sq m is determined for both upward and downward currents, and the ionospheric conductivity is shown, in the short-wavelength limit, to have little effect on the relationship between the (N-S) electric and (E-W) magnetic fields above the potential drop parallel to the magnetic-field lines. The results are found to be consistent with a linear relationship between the field-aligned current density and the parallel potential drop. 14 references

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}.

Calibration of magnetic force microscopy tips by using nanoscale current-carrying parallel wires

International Nuclear Information System (INIS)

Kebe, Th.; Carl, A.

2004-01-01

Experimental results on the characterization of commercially available magnetic force microscopy (MFM) thin film tips as a function of an external magnetic field are presented. Magnetic stray fields with a definitive z-component (perpendicular to the substrate) and a magnetic field strength of up to H z =±45 Oe are produced with current carrying parallel nanowires with a thickness of t=60 nm, which are fabricated by electron-beam lithography. The magnetic fields are generated by electrical dc-currents of up to ±6 mA which are directed antiparallel through the nanowires. The geometry and the dimensions of the nanowires are systematically varied by choosing different wire widths w as well as separations b between the parallel wires for two different sets of samples. On the one hand, the wire width w is varied within 380 nm< w<2460 nm while the separation b≅450 nm between the wires is kept constant. On the other hand the separation b between the parallel wires is varied within 120 nm< b<5100 nm, while the wire width w=960 nm is kept constant. For all the geometrical configurations of parallel wires the resulting magnetic contrast is imaged by MFM at various tip lift-heights. By treating the MFM tip as a point probe, the analysis of the image contrast as a function of both the magnetic field strength and the tip lift height allows one to quantitatively determine the effective magnetic dipole and monopole moments of the tip as well as their imaginary locations within the real physical tip. Our systematic study quantitatively relates the above point-probe parameters to (i) the dimensions of the parallel wires and (ii) to the characteristic decay length of the z-component of the magnetic field of parallel wires. From this the effective tip-volume of the real thin film tip is determined which is relevant in MFM-imaging. Our results confirm the reliability of earlier tip calibration schemes for which nanofabricated current carrying rings were used instead of parallel

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

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.

Parallel critical magnetic fields of superconducting hyperthin films of vanadium and technetium

International Nuclear Information System (INIS)

Teplov, A.A.; Mikheeva, M.N.

1980-01-01

The nature of limiting parallel magnetic fields Hsub(c parallel) destroying a superconducting state in films of vanadium and technetium is found out. A dependence of Hsub(c parallel) on the thickness of films up to d approximately 60 A is studied. The |dHsub(c parallel)sup(2)/dT|sub(Tsub(c)) derivative, which increases in the region of large d with the increase of 1/d and achieves the maximum va;ue at d approximately 100 A, was determined, using the experimental data. For the most thin films this derivative tends to drop (the value of the derivative changes from 16 up to 20.00 kOe 2 /k and for technetium and from 4 up to 2100 kOe 2 /k for vanadium). Such stop at |dHsub(c11)sup(2)/ dT|sub(Tsub(c)) growth during the decrease of d is not explained in the framework of the theory taking into account only orbital effects. An account of the additional paramagnetic effect (spin effects) leads to a good agreement of the experiment with the theory in the whole range of thicknesses for vanadium. For technetium films in the d range <=110 A the value of Hsub(c parallel) exceeds several times Hsub(c parallel) calculated with provision of spin effects. For d approximately 80 A and d approximately 55 A this increase achieves the triple value. This effect is explained qualitatively by the spin-orbital scattering appearing with the increase of the atomic number

Equilibrium properties of the plasma sheath with a magnetic field parallel to the wall

International Nuclear Information System (INIS)

Krasheninnikova, Natalia S.; Tang Xianzhu

2011-01-01

Motivated by the Magnetized Target Fusion (MTF), a systematic investigation of the equilibrium properties of a 1D plasma sheath with a magnetic field parallel to the wall was carried out using analytical theory and kinetic simulations. Initially uniform full Maxwellian plasma consisting of equal temperature collisionless electrons and ions is allowed to interact with a perfectly absorbing conducting wall, which charges positively due to large ions gyro-radii. The analysis of the steady-state plasma and field profiles reveals the importance of the relation between electron and ion thermal Larmor radii and plasma Debye length. In particular, the sheath width scaling, the details of the particle flows and the break-down of force balance components exhibit different behaviors in three possible regimes. Despite our primary motivation, the results in this paper can also be applicable to the divertor and the first wall of tokamaks.

Interaction of Mutually Perpendicular Magnetic Fields in HTSC

Directory of Open Access Journals (Sweden)

Vasilyev Aleksandr Fedorovich

2015-11-01

Full Text Available In this article a problem of interaction of the crossed magnetic fields in superconductors is considered. Superconducting materials have nonlinear magnetic properties. It allows using a non-linear magnetic susceptibility for measurement of feeble magnetic fields. We place a wire of superconducting material in a constant parallel uniform magnetic field. Then we let through a wire the alternating current leak. Interaction of mutual and perpendicular variation magnetic fields, with adequate accuracy is described by Ginzburg-Landau's equations. Approximate solution of the written equations is received. The component of a magnetic field parallel to a wire contains a variable component. Frequency of a variable component of the magnetic field is equal to the doubled current frequency. Amplitude of the variable component of the magnetic field is proportional to strength of the constant magnetic field. The experimental installation for research of interaction of mutually perpendicular magnetic fields is created. The cylinder from HTSC of ceramics of the YBa2Cu3O7-x was used as a sensor. Dependence of amplitude of the second harmonica of a variation magnetic field on strength of a constant magnetic field is received.

Tripolar electric field Structure in guide field magnetic reconnection

OpenAIRE

S. Fu; S. Huang; M. Zhou; B. Ni; X. Deng

2018-01-01

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 amplit...

The influence of the magnetic field on the performance of an active magnetic regenerator (AMR)

DEFF Research Database (Denmark)

Bjørk, Rasmus; Engelbrecht, Kurt

2011-01-01

The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed...... temperature span and the maximum cooling capacity of 20–40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads...

Particle Acceleration, Magnetic Field Generation in Relativistic Shocks

Science.gov (United States)

Nishikawa, Ken-Ichi; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.

2005-01-01

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.

Pulsed critical current measurements of NbTi in perpendicular and parallel pulsed magnetic fields using the new Cryo-BI-Pulse System

International Nuclear Information System (INIS)

Stehr, V; Tan, K S; Hopkins, S C; Glowacki, B A; Keyser, A De; Bockstal, L Van; Deschagt, J

2006-01-01

Rapid transport current versus high magnetic field characterisation of high-irreversibility type II superconductors is important to maximise their critical parameters. HTS conductors are already used to produce insert coils that increase the fields of conventional magnets made from NbTi (Nb, Ta) 3 Sn and Nb 3 Al wires. There is fundamental interest in the study of HTS tapes and wires in magnetic fields higher than 21T, the current limit of superconducting magnets producing a DC field. Such fields can be obtained by using pulse techniques. High critical currents cannot be routinely measured with a continuous current applied at liquid helium, hydrogen or neon temperatures because of thermal and mechanical effects. A newly developed pulsed magnetic field and pulsed current system which allows rapid J c (B, T) measurements of the whole range of superconducting materials was tested with a multifilamentary NbTi wire in perpendicular and parallel orientations

Magnetic Field Emission Comparison for Series-Parallel and Series-Series Wireless Power Transfer to Vehicles – PART 1/2

DEFF Research Database (Denmark)

Batra, Tushar; Schaltz, Erik

2014-01-01

Resonant circuits of wireless power transfer system can be designed in four possible ways by placing the primary and secondary capacitor in a series or parallel order with respect to the corresponding inductor. The two topologies series-parallel and series-series under investigation have been...... already compared in terms of their output behavior (current or voltage source) and reflection of the secondary impedance on the primary side. In this paper it is shown that for the same power rating series-parallel topology emits lesser magnetic fields to the surroundings than its series...

Mechanism of parallel electric fields inferred from observations

International Nuclear Information System (INIS)

Yeh, H.; Hill, T.W.

1981-01-01

An analysis of satellite data from regions of upward Birkeland (magnetic-field-aligned) current shows that the typical magnetic-field-aligned potential drop in the auroral zone is larger than required to provide direct acceleration of magnetospheric electrons by the field-aligned electric field against the upward magnetic force to produce the observed upward Birkeland current. A model of simple electrostatic acceleration without anomalous resistivity predicts observable relations between parallel current and parallel potential drop and between energy deposition and parallel potential drop. The temperature, density, and species of the unaccelerated charge carriers are the relevant parameters of the model. Simultaneously measurements of electron precipitation and ion drift velocities on the satellites Atmosphere Explorere C and D were used to test these relations. In a steady state the divergence of ionospheric currents must be compensated by Birkeland currents. The model current-voltage relation was applied to predict the densities of the primary charge carriers (i.e., plasma sheet electrons above the acceleration region for upward currents). In cases involving thin arc structures, where the reliable estimation of the divergence of ionospheric current is difficult and the steady-state assumption may not apply, the precipitating energy flux versus voltage relation was used to predict the densities of the unaccelerated plasma sheet electrons. Within the experimental uncertainties, reasonable agreement is found between these predicted densities and those inferred directly from the simultaneous data of the Low-Energy Electron Experiment. These results are interpreted as indicating that anomalous resistivity is not important in determining the magnitude of the field-aligned potential drop in the auroral zone

Collisionless reconnection: magnetic field line interaction

Directory of Open Access Journals (Sweden)

R. A. Treumann

2012-10-01

Full Text Available Magnetic field lines are quantum objects carrying one quantum Φ0 = 2πh/e of magnetic flux and have finite radius λm. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.

Thomson scattering in magnetic fields. [of white dwarf stars

Science.gov (United States)

Whitney, Barbara

1989-01-01

The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

Reduction of momentum transfer rates by parallel electric fields: A two-fluid demonstration

International Nuclear Information System (INIS)

Delamere, P.A.; Stenbaek-Nielsen, H.C.; Otto, A.

2002-01-01

Momentum transfer between an ionized gas cloud moving relative to an ambient magnetized plasma is a general problem in space plasma physics. Obvious examples include the Io-Jupiter interaction, comets, and coronal mass ejections. Active plasma experiments have demonstrated that momentum transfer rates associated with Alfven wave propagation are poorly understood. Barium injection experiments from the Combined Release and Radiation Effects Satellite (CRRES) have shown that dense ionized clouds are capable of ExB drifting over large distances perpendicular to the magnetic field. The CRRES 'skidding' distances were much larger than predicted by magnetohydrodynamic theory and it has been proposed that parallel electric fields were a key component in the skidding phenomenon. A two-fluid code was used to demonstrate the role of parallel electric fields in reducing momentum transfer between two distinct plasma populations. In this study, a dense plasma was initialized moving relative to an ambient plasma and perpendicular to B. Parallel electric fields were introduced via a friction term in the electron momentum equation and the collision frequency was scaled in proportion to the field-aligned current density. The simulation results showed that parallel electric fields decreased the decelerating magnetic tension force on the plasma cloud through a magnetic diffusion/reconnection process

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....

Heat transfer and flow analysis of nanofluid flow between parallel plates in presence of variable magnetic field using HPM

Energy Technology Data Exchange (ETDEWEB)

Hatami, M., E-mail: m.hatami@tue.nl [Esfarayen University of Technology, Mechanical Engineering Department, Esfarayen, North Khorasan (Iran, Islamic Republic of); Jing, Dengwei; Song, Dongxing [International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi' an 710049 (China); Sheikholeslami, M.; Ganji, D.D. [Department of Mechanical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of)

2015-12-15

In this study, effect of variable magnetic field on nanofluid flow and heat transfer analysis between two parallel disks is investigated. By using the appropriate transformation for the velocity, temperature and concentration, the basic equations governing the flow, heat and mass transfer were reduced to a set of ordinary differential equations. These equations subjected to the associated boundary conditions were solved analytically using Homotopy perturbation method. The analytical investigation is carried out for different governing parameters namely: squeeze number, suction parameter, Hartmann number, Brownian motion parameter, thermophrotic parameter and Lewis number. Results show that Nusselt number has direct relationship with Brownian motion parameter and thermophrotic parameter but it is a decreasing function of squeeze number, suction parameter, Hartmann number and Lewis number. - Highlights: • Heat and mass transfer of nanofluids between parallel plates investigated. • A variable magnetic field is applied on the plates. • Governing equations are solved analytically. • Effects of physical parameters are discussed on the Nusselt number.

Heat transfer and flow analysis of nanofluid flow between parallel plates in presence of variable magnetic field using HPM

International Nuclear Information System (INIS)

Hatami, M.; Jing, Dengwei; Song, Dongxing; Sheikholeslami, M.; Ganji, D.D.

2015-01-01

In this study, effect of variable magnetic field on nanofluid flow and heat transfer analysis between two parallel disks is investigated. By using the appropriate transformation for the velocity, temperature and concentration, the basic equations governing the flow, heat and mass transfer were reduced to a set of ordinary differential equations. These equations subjected to the associated boundary conditions were solved analytically using Homotopy perturbation method. The analytical investigation is carried out for different governing parameters namely: squeeze number, suction parameter, Hartmann number, Brownian motion parameter, thermophrotic parameter and Lewis number. Results show that Nusselt number has direct relationship with Brownian motion parameter and thermophrotic parameter but it is a decreasing function of squeeze number, suction parameter, Hartmann number and Lewis number. - Highlights: • Heat and mass transfer of nanofluids between parallel plates investigated. • A variable magnetic field is applied on the plates. • Governing equations are solved analytically. • Effects of physical parameters are discussed on the Nusselt number

Magnetic field transfer device and method

Science.gov (United States)

Wipf, S.L.

1990-02-13

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

Induced superconductivity in Nb/InAs-hybrid structures in parallel and perpendicular magnetic fields; Induzierte Supraleitung in Nb/InAs-Hybridstrukturen in parallelen und senkrechten Magnetfeldern

Energy Technology Data Exchange (ETDEWEB)

Rohlfing, Franziska

2007-07-15

The thesis in hand investigates experimentally Josephson contacts based on Nb/InAs-hybrid structures. The experiments discussed here were done on samples of different width of the Josephson contacts (between 500 nm and 2000 nm). They were realized by means of different methods of the semiconductor technology. The length of the Josephson contacts was about 600 nm and, as superconducting material, niobium was used. Both critical current and characteristics in the resistive regime (excess-current and multiple Andreev reflection) are studied as a function of temperature and external magnetic fields. Measurements in perpendicular and parallel magnetic fields with respect to the plain of the two-dimensional electron gas, are presented. The Andreev reflection amplitude determining the supercurrent is calculated by means of the Greens functions of the two-dimensional electron gas beneath the superconductors which is modified by the proximity effect. From the fit to the data with this model, the transparency of the boundary between the superconductor and the two-dimensional electron gas can be estimated to be about 0.1. The transparency of the point contacts in the two-dimensional electrons gas can be determined independently from the Josephson junction width dependence of the normal resistance (T=10 K). This transparency amounts to about 0.8 in the examined samples. The measurements of the critical current in a magnetic field perpendicular to the two-dimensional electron gas show a Fraunhofer pattern. In order to study the transition from perpendicular orientation into parallel orientation, measurements of the critical current as a function of the magnetic field were done for different angles. In the resistive regime, the excess current measurements in the magnetic field show a very interesting behaviour: In parallel magnetic fields, the excess current becomes zero at about 2.5 T. In perpendicular magnetic field however, the excess current is strongly suppressed below 30 m

Flow of conductive fluid between parallel disks in an axial magnetic field, (2)

International Nuclear Information System (INIS)

Koike, Kazuo; Kamiyama, Shin-ichi

1981-01-01

The basic characteristics of the flow in a disc type non-equilibrium MHD power generator were studied. The flow of conductive fluid between parallel disks in an axial magnetic field was analyzed as the subsonic MHD turbulent approach flow of viscous compressible fluid, taking the electron temperature dependence of conductivity into account. The equations for the flow between disks are described by ordinary electromagnetic hydrodynamic approximation. Practical numerical calculation was performed for the non-equilibrium argon plasma seeded with potassium. The effects of the variation of characteristics of non-equilibrium plasma in main flow and boundary layer on the flow characteristics became clear. The qualitative tendency of the properties of MHD generators can be well explained. (Kato, T.)

Acceleration of auroral particles by magnetic-field aligned electric fields

International Nuclear Information System (INIS)

Block, L.P.

1988-01-01

Measurements on the S3-3 and Viking satellites appear to show that at least a large fraction of magnetic field-aligned potential drops are made up of multiple double layers. Solitons and double layers in U-shaped potential structures give rise to spiky electric fields also perpendicular to the magnetic field in agreement with satellite measurements. The large scale potential structures associated with inverted V-events are built up of many similar short-lived structures on a small scale. Viking measurements indicate that electric fields parallel to the magnetic field are almost always directed upward

Improved magnetic field line design for TMX

International Nuclear Information System (INIS)

Logan, B.G.; Baldwin, D.E.; Foote, J.H.; Chargin, A.K.; Hinkle, R.E.; Hussung, R.O.; Damm, C.C.

1977-01-01

Optimization of the currents in the TMX magnet set leads to a field line configuration which has a central solenoidal region uniform in parallel B parallel to within 10 percent over a 2m length. The field design has sufficient flexibility to meet all three physics objectives of the TMX experiment

On field line resonances of hydromagnetic Alfven waves in dipole magnetic field

International Nuclear Information System (INIS)

Chen, Liu; Cowley, S.C.

1989-07-01

Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfven eigenfunctions have also been systematically derived. 11 refs

A model of the magnetosheath magnetic field during magnetic clouds

Directory of Open Access Journals (Sweden)

L. Turc

2014-02-01

Full Text Available Magnetic clouds (MCs are huge interplanetary structures which originate from the Sun and have a paramount importance in driving magnetospheric storms. Before reaching the magnetosphere, MCs interact with the Earth's bow shock. This may alter their structure and therefore modify their expected geoeffectivity. We develop a simple 3-D model of the magnetosheath adapted to MCs conditions. This model is the first to describe the interaction of MCs with the bow shock and their propagation inside the magnetosheath. We find that when the MC encounters the Earth centrally and with its axis perpendicular to the Sun–Earth line, the MC's magnetic structure remains mostly unchanged from the solar wind to the magnetosheath. In this case, the entire dayside magnetosheath is located downstream of a quasi-perpendicular bow shock. When the MC is encountered far from its centre, or when its axis has a large tilt towards the ecliptic plane, the MC's structure downstream of the bow shock differs significantly from that upstream. Moreover, the MC's structure also differs from one region of the magnetosheath to another and these differences vary with time and space as the MC passes by. In these cases, the bow shock configuration is mainly quasi-parallel. Strong magnetic field asymmetries arise in the magnetosheath; the sign of the magnetic field north–south component may change from the solar wind to some parts of the magnetosheath. We stress the importance of the Bx component. We estimate the regions where the magnetosheath and magnetospheric magnetic fields are anti-parallel at the magnetopause (i.e. favourable to reconnection. We find that the location of anti-parallel fields varies with time as the MCs move past Earth's environment, and that they may be situated near the subsolar region even for an initially northward magnetic field upstream of the bow shock. Our results point out the major role played by the bow shock configuration in modifying or keeping the

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.

Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks

Science.gov (United States)

Nishikawa, Ken-IchiI.; Hededal, C.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G.

2004-01-01

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (m) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.

Particle reflection along the magnetic field in nonlinear magnetosonic pulses

Science.gov (United States)

Ohsawa, Yukiharu

2017-11-01

Reflection of electrons and positrons in oblique, nonlinear magnetosonic pulses is theoretically analyzed. With the use of the parallel pseudo potential F, which is the integral of the parallel electric field along the magnetic field, a simple equation for reflection conditions is derived, which shows that reflection along the magnetic field is caused by two forces: one arising from the parallel pseudo potential multiplied by the particle charge and the other from the magnetic mirror effect. The two forces push electrons in the opposite directions. In compressive solitons, in which the magnetic field is intensified, electrons with large magnetic moments can be reflected by the magnetic mirror effect, whereas in rarefactive solitons, in which the magnetic field is weaker than outside, electrons with small magnetic moments can be reflected by the parallel pseudo potential. Although F is basically positive and large in shock waves, it occasionally becomes negative in some regions behind the shock front in nonstationary wave evolution. These negative spikes of F can reflect electrons. In contrast to the case of electrons, the two forces push positrons in the same direction. For this reason, compressive solitons in an electron-positron-ion plasma reflect a large fraction of positrons compared with electrons, whereas rarefactive solitons will reflect no positrons. A shock wave can reflect a majority of positrons with its large F. However, in a pure electron-positron plasma, in which F becomes zero, positron reflection will rarely occur.

Light scattering of rectangular slot antennas: parallel magnetic vector vs perpendicular electric vector

Science.gov (United States)

Lee, Dukhyung; Kim, Dai-Sik

2016-01-01

We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet’s principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet’s principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies.

Magnetic Phase Transitions of CeSb. II: Effects of Applied Magnetic Fields

DEFF Research Database (Denmark)

Meier, G.; Fischer, P.; Hälg, W.

1978-01-01

For pt.I see ibid., vol.11, p.345 (1978). The metamagnetic phase transition and the associated phase diagram of the anomalous antiferromagnet CeSb were determined in a neutron diffraction study of the magnetic ordering of CeSb single crystals in applied magnetic fields parallel to the (001...... magnetic fields. The observed magnetic structures do not correspond to the stable configurations expected from the molecular field theory of the face-centred cubic lattice. The change from a first-order transition at the Neel temperature in zero field to second-order transition at high fields points...

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.

Photoluminescence spectra of n-doped double quantum wells in a parallel magnetic field

International Nuclear Information System (INIS)

Huang, D.; Lyo, S.K.

1999-01-01

We show that the photoluminescence (PL) line shapes from tunnel-split ground sublevels of n-doped thin double quantum wells (DQW close-quote s) are sensitively modulated by an in-plane magnetic field B parallel at low temperatures (T). The modulation is caused by the B parallel -induced distortion of the electronic structure. The latter arises from the relative shift of the energy-dispersion parabolas of the two quantum wells (QW close-quote s) in rvec k space, both in the conduction and valence bands, and formation of an anticrossing gap in the conduction band. Using a self-consistent density-functional theory, the PL spectra and the band-gap narrowing are calculated as a function of B parallel , T, and the homogeneous linewidths. The PL spectra from symmetric and asymmetric DQW close-quote s are found to show strikingly different behavior. In symmetric DQW close-quote s with a high density of electrons, two PL peaks are obtained at B parallel =0, representing the interband transitions between the pair of the upper (i.e., antisymmetric) levels and that of the lower (i.e., symmetric) levels of the ground doublets. As B parallel increases, the upper PL peak develops an N-type kink, namely a maximum followed by a minimum, and merges with the lower peak, which rises monotonically as a function of B parallel due to the diamagnetic energy. When the electron density is low, however, only a single PL peak, arising from the transitions between the lower levels, is obtained. In asymmetric DQW close-quote s, the PL spectra show mainly one dominant peak at all B parallel close-quote s. In this case, the holes are localized in one of the QW close-quote s at low T and recombine only with the electrons in the same QW. At high electron densities, the upper PL peak shows an N-type kink like in symmetric DQW close-quote s. However, the lower peak is absent at low B parallel close-quote s because it arises from the inter-QW transitions. Reasonable agreement is obtained with recent

Relativistic degenerate electron plasma in an intense magnetic field

International Nuclear Information System (INIS)

Delsante, A.E.; Frankel, N.E.

1978-01-01

The dielectric response function for a dense, ultra-degenerate relativistic electron plasma in an intense uniform magnetic field is presented. Dispersion relations for plasma oscillations parallel and perpendicular to the magnetic field are obtained

Magnetic field-aligned particle precipitation

International Nuclear Information System (INIS)

Carlson, W.

1985-01-01

Magnetic field-aligned particle fluxes are a common auroral phenomenon. Precipitating field-aligned electrons are seen in the vicinity of auroral arcs as suprathermal bursts, as well as superimposed on the more isotropic inverted V electron precipitation. Electron distribution functions reveal two distinct source populations for the inverted V and field-aligned electron components, and also suggest possible acceleration mechanisms. The inverted V electrons are a hot, boundary plasma sheet population that gains the full parallel acceleration. The field-aligned component appears to originate from cold ionospheric electrons that may be distributed throughout the acceleration region. A turbulent parallel field might explain the apparent lifetime of cold electrons in the acceleration region

Streaming flows produced by oscillating interface of magnetic fluid adsorbed on a permanent magnet in alternating magnetic field

Science.gov (United States)

Sudo, S.; Ito, M.; Ishimoto, Y.; Nix, S.

2017-04-01

This paper describes microstreaming flows generated by oscillating interface of magnetic fluid adsorbed on a circular cylindrical permanent magnet in alternating magnetic field. The interface of magnetic fluid adsorbed on the NdFeB magnet responds to the external alternating magnetic flied as harmonic oscillation. The directions of alternating magnetic field are parallel and antiparallel to the magnetic field of permanent magnet. The oscillation of magnetic fluid interface generates streaming flow around the magnet-magnetic fluid element in water. Microstreaming flows are observed with a high-speed video camera analysis system. The flow pattern generated by magnetic fluid motion depends on the Keulegan-Carpenter number and the Reynolds number.

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.

Banana regime pressure anisotropy in a bumpy cylinder magnetic field

International Nuclear Information System (INIS)

Garcia-Perciante, A.L.; Callen, J.D.; Shaing, K.C.; Hegna, C.C.

2006-01-01

The pressure anisotropy is calculated for a plasma in a bumpy cylindrical magnetic field in the low collisionality (banana) regime for small magnetic-field modulations (ε≡ΔB/2B parallel is then calculated and is shown to exceed the flux-surface-averaged parallel viscous force parallel > by a factor of O(1/ε). A high-frequency limit (ω>>ν) for the pressure anisotropy is also determined and the calculation is then extended to include the full frequency dependence by using an expansion in Cordey eigenfunctions

Orbital effect for the Fulde-Ferrell-Larkin-Ovchinnikov phase in a quasi-two-dimensional superconductor in a parallel magnetic field

Science.gov (United States)

Lebed, A. G.

2018-04-01

We theoretically study the orbital destructive effect against superconductivity in a parallel magnetic field in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF) phase at zero temperature in a quasi-two-dimensional (Q2D) conductor. We demonstrate that at zero temperature a special parameter, λ =l⊥(H ) /d , is responsible for strength of the orbital effect, where l⊥(H ) is a typical "size" of the quasiclassical electron orbit in a magnetic field and d is the interplane distance. We discuss applications of our results to the existing experiments on the FFLO phase in the organic Q2D conductors κ -(ET) 2Cu (NCS) 2 and κ -(ET) 2Cu [N (CN) 2] Cl .

Orienting Paramecium with intense static magnetic fields

Science.gov (United States)

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

2004-03-01

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

Laser-induced extreme magnetic field in nanorod targets

Science.gov (United States)

Lécz, Zsolt; Andreev, Alexander

2018-03-01

The application of nano-structured target surfaces in laser-solid interaction has attracted significant attention in the last few years. Their ability to absorb significantly more laser energy promises a possible route for advancing the currently established laser ion acceleration concepts. However, it is crucial to have a better understanding of field evolution and electron dynamics during laser-matter interactions before the employment of such exotic targets. This paper focuses on the magnetic field generation in nano-forest targets consisting of parallel nanorods grown on plane surfaces. A general scaling law for the self-generated quasi-static magnetic field amplitude is given and it is shown that amplitudes up to 1 MT field are achievable with current technology. Analytical results are supported by three-dimensional particle-in-cell simulations. Non-parallel arrangements of nanorods has also been considered which result in the generation of donut-shaped azimuthal magnetic fields in a larger volume.

The approximation of anomalous magnetic field by array of magnetized rods

Science.gov (United States)

Denis, Byzov; Lev, Muravyev; Natalia, Fedorova

2017-07-01

The method for calculation the vertical component of an anomalous magnetic field from its absolute value is presented. Conversion is based on the approximation of magnetic induction module anomalies by the set of singular sources and the subsequent calculation for the vertical component of the field with the chosen distribution. The rods that are uniformly magnetized along their axis were used as a set of singular sources. Applicability analysis of different methods of nonlinear optimization for solving the given task was carried out. The algorithm is implemented using the parallel computing technology on the NVidia GPU. The approximation and calculation of vertical component is demonstrated for regional magnetic field of North Eurasia territories.

Coherent quantum states of a relativistic particle in an electromagnetic plane wave and a parallel magnetic field

International Nuclear Information System (INIS)

Colavita, E.; Hacyan, S.

2014-01-01

We analyze the solutions of the Klein–Gordon and Dirac equations describing a charged particle in an electromagnetic plane wave combined with a magnetic field parallel to the direction of propagation of the wave. It is shown that the Klein–Gordon equation admits coherent states as solutions, while the corresponding solutions of the Dirac equation are superpositions of coherent and displaced-number states. Particular attention is paid to the resonant case in which the motion of the particle is unbounded. -- Highlights: •We study a relativistic electron in a particular electromagnetic field configuration. •New exact solutions of the Klein–Gordon and Dirac equations are obtained. •Coherent and displaced number states can describe a relativistic particle

Enlargement of Tuning Range in a Ferrite-Tuned Cavity Through Superposed Orthogonal and Parallel Magnetic Bias

CERN Document Server

Vollinger, C

2013-01-01

Conventional ferrite-tuned cavities operate either with bias fields that are orthogonal or parallel to the magnetic RF-field. For a cavity that tunes rapidly over an overall frequency range around 100-400 MHz with high Q, we use ferrite garnets exposed to an innovative new biasing method consisting of a superposition of perpendicular and parallel magnetic fields. This method leads to a significant enlargement of the high-Q cavity tuning range by defining an operation point close to the magnetic saturation and thus improving ferrite material behaviour. A further advantage of this technique is the fast tuning speed resulting from the fact that tuning is carried out either with pure parallel biasing, or together with a very small change of operating point from perpendicular bias. In this paper, several scaled test models of ferrite-filled resonators are shown; measurements on the set-ups are compared and discussed.

Electron temperature in field reversed configurations and theta pinches with closed magnetic field lines

International Nuclear Information System (INIS)

Newton, A.A.

1986-01-01

Field-reversed configurations (FRC) and theta pinches with trapped reversed bias field are essentially the same magnetic confinement systems using closed magnetic field lines inside an open-ended magnetic flux tube. A simple model of joule heating and parallel electron thermal conduction along the open flux lines to an external heat sink gives the electron temperature as Tsub(e)(eV) approx.= 0.05 Bsup(2/3)(G)Lsup(1/3)(cm), where B is the magnetic field and L is the coil length. This model appears to agree with measurements from present FRC experiments and past theta-pinch experiments which cover a range of 40-900 eV. The energy balance in the model is dominated by (a) parallel electron thermal conduction along the open field lines which has a steep temperature dependence, Q is proportional to Tsub(e)sup(7/2), and (b) the assumed rapid perpendicular transport in the plasma bulk which, in experiments to date, may be due to the small number of ion gyroradii across the plasma. (author)

Sound absorption in a field of a strong electromagnetic wave in a quantizied magnetic field

International Nuclear Information System (INIS)

Chajkovskij, I.A.

1974-01-01

A coefficient of sound absorption GAMMA in a semiconductor and semi-metal in the quantized magnetic field is calculated for a system exposed to a field of strong electromagnetic radiation. The cases E parallel H and E orthogonal H are considered. Along with the already known strong oscillations of sound absorption in magnetic fields, the absorption spectrum GAMMAsub(par) and GAMMAsub(orth) shows new oscillations representing a manifestation of the quasi-energetic electron spectrum in the field of a strong electromagnetic wave. The oscillation height at E parallel H is modulated by the electromagnetic field. It is shown that the ratio GAMMAsub(par)/GAMMAsub(orth) allows the determination of the effective mass of the carriers

Measurements of electron drift and diffusion properties in a large cylindrical drift chamber (TPC) with parallel electric and magnetic fields

International Nuclear Information System (INIS)

Richstein, J.

1986-01-01

This work describes measurements on the drift of electrons in gases, using the TPC90, the prototype of the ALEPH Time Projection Chamber. Tracks which were created by UV-Laser ionization have been drifted over distances of up to 1.3 m in parallel electric and magnetic fields. Electron drift properties have been systematically measured as a function of these, in several gas mixtures. (orig./HSI)

Sidewall containment of liquid metal with horizontal alternating magnetic fields

Science.gov (United States)

Pareg, Walter F.

1990-01-01

An apparatus for confining molten metal with a horizontal alternating magnetic field. In particular, this invention employs a magnet that can produce a horizontal alternating magnetic field to confine a molten metal at the edges of parallel horizontal rollers as a solid metal sheet is cast by counter-rotation of the rollers.

Method and means for measuring the anisotropy of a plasma in a magnetic field

Science.gov (United States)

Shohet, J.L.; Greene, D.G.S.

1973-10-23

Anisotropy is measured of a free-free-bremsstrahlungradiation-generating plasma in a magnetic field by collimating the free-free bremsstrahlung radiation in a direction normal to the magnetic field and scattering the collimated free- free bremsstrahlung radiation to resolve the radiation into its vector components in a plane parallel to the electric field of the bremsstrahlung radiation. The scattered vector components are counted at particular energy levels in a direction parallel to the magnetic field and also normal to the magnetic field of the plasma to provide a measure of anisotropy of the plasma. (Official Gazette)

Investigation of magnetic drift on transport of plasma across magnetic field

International Nuclear Information System (INIS)

Hazarika, Parismita; Chakraborty, Monojit; Das, Bidyut; Bandyopadhyay, Mainak

2015-01-01

When a metallic body is inserted inside plasma chamber it is always associated with sheath which depends on plasma and wall condition. The effect of sheath formed in the magnetic drift and magnetic field direction on cross field plasma transport has been investigated in a double Plasma device (DPD). The drifts exist inside the chamber in the transverse magnetic field (TMF) region in a direction perpendicular to both magnetic field direction and axis of the DPD chamber. The sheath are formed in the magnetic drift direction in the experimental chamber is due to the insertion of two metallic plates in these directions and in the magnetic field direction sheath is formed at the surface of the TMF channels. These metallic plates are inserted in order to obstruct the magnetic drift so that we can minimised the loss of plasma along drift direction and density in the target region is expected to increase due to the obstruction. It ultimately improves the negative ion formation parameters. The formation of sheath in the transverse magnetic field region is studied by applying electric field both parallel and antiparallel to drift direction. Data are acquired by Langmuir probe in source and target region of our chamber. (author)

Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum

Science.gov (United States)

Fujiwara, Yoshihisa; Tomishige, Masahiko; Itoh, Yasuhiro; Fujiwara, Masao; Shibata, Naho; Kosaka, Toshikazu; Hosoya, Hiroshi; Tanimoto, Yoshifumi

2006-05-01

Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum was studied by using a superconducting magnet. Around a centre of a round vessel, random swimming at 0 T and aligned swimming parallel to the magnetic field (MF) of 8 T were observed. Near a wall of the vessel, however, swimming round and round along the wall at 0 T and aligned swimming of turning at right angles upon collision with the wall, which was remarkable around 1-4 T, were detected. It was experimentally revealed that the former MF-induced parallel swimming at the vessel centre was caused physicochemically by the parallel magnetic orientation of the cell itself. From magnetic field dependence of the extent of the orientation, the magnetic susceptibility anisotropy (χ ∥-χ ⊥) was first obtained to be 3.4× 10-23 emu cell-1 at 298 K for Paramecium caudatum. The orientation of the cell was considered to result from the magnetic orientation of the cell membrane. On the other hand, although mechanisms of the latter swimming near the vessel wall regardless of the absence and presence of the magnetic field are unclear at present, these experimental results indicate that whether the cell exists near the wall alters the magnetic field effect on the swimming in the horizontal magnetic field.

Shear-induced inflation of coronal magnetic fields

International Nuclear Information System (INIS)

Klimchuk, J.A.

1990-01-01

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes. 38 refs

Evaluation of pulsing magnetic field effects on paresthesia in multiple sclerosis patients, a randomized, double-blind, parallel-group clinical trial.

Science.gov (United States)

Afshari, Daryoush; Moradian, Nasrin; Khalili, Majid; Razazian, Nazanin; Bostani, Arash; Hoseini, Jamal; Moradian, Mohamad; Ghiasian, Masoud

2016-10-01

Evidence is mounting that magnet therapy could alleviate the symptoms of multiple sclerosis (MS). This study was performed to test the effects of the pulsing magnetic fields on the paresthesia in MS patients. This study has been conducted as a randomized, double-blind, parallel-group clinical trial during the April 2012 to October 2013. The subjects were selected among patients referred to MS clinic of Imam Reza Hospital; affiliated to Kermanshah University of Medical Sciences, Iran. Sixty three patients with MS were included in the study and randomly were divided into two groups, 35 patients were exposed to a magnetic pulsing field of 4mT intensity and 15-Hz frequency sinusoidal wave for 20min per session 2 times per week over a period of 2 months involving 16 sessions and 28 patients was exposed to a magnetically inactive field (placebo) for 20min per session 2 times per week over a period of 2 months involving 16 sessions. The severity of paresthesia was measured by the numerical rating scale (NRS) at 30, 60days. The study primary end point was NRS change between baseline and 60days. The secondary outcome was NRS change between baseline and 30days. Patients exposing to magnetic field showed significant paresthesia improvement compared with the group of patients exposing to placebo. According to our results pulsed magnetic therapy could alleviate paresthesia in MS patients .But trials with more patients and longer duration are mandatory to describe long-term effects. Copyright © 2016 Elsevier B.V. All rights reserved.

On the helicity of open magnetic fields

International Nuclear Information System (INIS)

Prior, C.; Yeates, A. R.

2014-01-01

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

Tempered Lévy walk of charged particles in turbulent magnetic field

International Nuclear Information System (INIS)

Sibatov, R T; Uchaikin, V V; Byzykchi, A N

2017-01-01

Recently, various diffusion regimes of ions and electrons in interplanetary magnetic field have been recognized from the data collected by different spacecrafts. Particularly for protons, superdiffusion and normal diffusion parallel to the mean magnetic field were declared, simulation also predicts transient superdiffusive behavior. We interpret parallel motion in terms of the one-dimensional tempered Lévy walk process and show that this representation is consistent with the experimental and simulated results. (paper)

Water flow patterns induced by bridge oscillation of magnetic fluid between two permanent magnets subjected to alternating magnetic field

International Nuclear Information System (INIS)

Sudo, Seiichi; Yamamoto, Kazuki; Ishimoto, Yukitaka; Nix, Stephanie

2017-01-01

This paper describes the characteristics of water flow induced by the bridge oscillation of magnetic fluid between two permanent magnets subject to an external alternating magnetic field. The magnetic fluid bridge is formed in the space between a pair of identical coaxial cylindrical permanent magnets submerged in water. The direction of alternating magnetic field is parallel /antiparallel to the magnetic field produced by two permanent magnets. The magnetic fluid bridge responds to the external alternating magnetic field with harmonic oscillation. The oscillation of magnetic fluid bridge generates water flow around the bridge. Water flow is visualized using a thin milk film at the container bottom. Water flows are observed with a high-speed video camera analysis system. The experimental results show that the flow pattern induced by the bridge oscillation depends on the Keulegan–Carpenter number.

Water flow patterns induced by bridge oscillation of magnetic fluid between two permanent magnets subjected to alternating magnetic field

Energy Technology Data Exchange (ETDEWEB)

Sudo, Seiichi, E-mail: sudo@akita-pu.ac.jp [Faculty of Systems Science and Technology, Akita Prefectural University, Ebinokuchi 84-4, Yurihonjo 015-0055 (Japan); Yamamoto, Kazuki [Graduate School of Engineering, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan); Ishimoto, Yukitaka; Nix, Stephanie [Faculty of Systems Science and Technology, Akita Prefectural University, Ebinokuchi 84-4, Yurihonjo 015-0055 (Japan)

2017-06-01

This paper describes the characteristics of water flow induced by the bridge oscillation of magnetic fluid between two permanent magnets subject to an external alternating magnetic field. The magnetic fluid bridge is formed in the space between a pair of identical coaxial cylindrical permanent magnets submerged in water. The direction of alternating magnetic field is parallel /antiparallel to the magnetic field produced by two permanent magnets. The magnetic fluid bridge responds to the external alternating magnetic field with harmonic oscillation. The oscillation of magnetic fluid bridge generates water flow around the bridge. Water flow is visualized using a thin milk film at the container bottom. Water flows are observed with a high-speed video camera analysis system. The experimental results show that the flow pattern induced by the bridge oscillation depends on the Keulegan–Carpenter number.

Magnetic fields of Jupiter and Saturn

International Nuclear Information System (INIS)

Ness, N.F.

1981-01-01

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

Magnetic field line random walk in non-axisymmetric turbulence

International Nuclear Information System (INIS)

Tautz, R.C.; Lerche, I.

2011-01-01

Including a random component of a magnetic field parallel to an ambient field introduces a mean perpendicular motion to the average field line. This effect is normally not discussed because one customarily chooses at the outset to ignore such a field component in discussing random walk and diffusion of field lines. A discussion of the basic effect is given, indicating that any random magnetic field with a non-zero helicity will lead to such a non-zero perpendicular mean motion. Several exact analytic illustrations are given of the effect as well as a simple numerical illustration. -- Highlights: → For magnetic field line random walk all magnetic field components are important. → Non-vanishing magnetic helicity leads to mean perpendicular motion. → Analytically exact stream functions illustrate that the novel transverse effect exists.

MAGNETICALLY DOMINATED PARALLEL INTERSTELLAR FILAMENTS IN THE INFRARED DARK CLOUD G14.225-0.506

International Nuclear Information System (INIS)

Santos, Fábio P.; Busquet, Gemma; Girart, Josep Miquel; Franco, Gabriel A. P.; Zhang, Qizhou

2016-01-01

The infrared dark cloud G14.225-0.506 (IRDC G14.2) displays a remarkable complex of parallel dense molecular filaments projected on the plane of the sky. Previous studies of dust emission and molecular lines have speculated whether magnetic fields could have played an important role in the formation of such elongated structures, which are hosts to numerous young stellar sources. In this work we have conducted a vast polarimetric survey at optical and near-infrared wavelengths in order to study the morphology of magnetic field lines in IRDC G14.2 through the observation of background stars. The orientation of interstellar polarization, which traces magnetic field lines, is perpendicular to most of the filamentary features within the cloud. Additionally, the larger-scale molecular cloud as a whole exhibits an elongated shape also perpendicular to magnetic fields. Estimates of magnetic field strengths indicate values in the range 320–550 μ G, which allow sub-alfvénic conditions, but do not prevent the gravitational collapse of hub–filament structures, which in general are close to the critical state. These characteristics suggest that magnetic fields played the main role in regulating the collapse from large to small scales, leading to the formation of series of parallel elongated structures. The morphology is also consistent with numerical simulations that show how gravitational instabilities develop when subjected to strong magnetic fields. Finally, the results corroborate the hypothesis that strong support from internal magnetic fields might explain why the cloud seems to be contracting on a timescale 2–3 times longer than what is expected from a free-fall collapse.

MAGNETICALLY DOMINATED PARALLEL INTERSTELLAR FILAMENTS IN THE INFRARED DARK CLOUD G14.225-0.506

Energy Technology Data Exchange (ETDEWEB)

Santos, Fábio P. [Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Busquet, Gemma; Girart, Josep Miquel [Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, S/N E-08193 Bellaterra, Catalunya (Spain); Franco, Gabriel A. P. [Departamento de Física—ICEx—UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte, MG (Brazil); Zhang, Qizhou, E-mail: fabiops@northwestern.edu, E-mail: busquet@ice.cat, E-mail: girart@ice.cat, E-mail: franco@fisica.ufmg.br, E-mail: qzhang@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60, Garden Street, Cambridge, MA 02138 (United States)

2016-12-01

The infrared dark cloud G14.225-0.506 (IRDC G14.2) displays a remarkable complex of parallel dense molecular filaments projected on the plane of the sky. Previous studies of dust emission and molecular lines have speculated whether magnetic fields could have played an important role in the formation of such elongated structures, which are hosts to numerous young stellar sources. In this work we have conducted a vast polarimetric survey at optical and near-infrared wavelengths in order to study the morphology of magnetic field lines in IRDC G14.2 through the observation of background stars. The orientation of interstellar polarization, which traces magnetic field lines, is perpendicular to most of the filamentary features within the cloud. Additionally, the larger-scale molecular cloud as a whole exhibits an elongated shape also perpendicular to magnetic fields. Estimates of magnetic field strengths indicate values in the range 320–550 μ G, which allow sub-alfvénic conditions, but do not prevent the gravitational collapse of hub–filament structures, which in general are close to the critical state. These characteristics suggest that magnetic fields played the main role in regulating the collapse from large to small scales, leading to the formation of series of parallel elongated structures. The morphology is also consistent with numerical simulations that show how gravitational instabilities develop when subjected to strong magnetic fields. Finally, the results corroborate the hypothesis that strong support from internal magnetic fields might explain why the cloud seems to be contracting on a timescale 2–3 times longer than what is expected from a free-fall collapse.

Magnetic-field inversion in vortices in multilayers

International Nuclear Information System (INIS)

Theodorakis, S.; Leontidis, E.

1997-01-01

We present a description of very dense vortex lattices in highly anisotropic multilayers, for high fields parallel to the layers. We show that a magnetic-field inversion can occur away from the center of a vortex, provided the layers are sufficiently far apart. copyright 1997 The American Physical Society

Effects of a vertical magnetic field on particle confinement in a magnetized plasma torus.

Science.gov (United States)

Müller, S H; Fasoli, A; Labit, B; McGrath, M; Podestà, M; Poli, F M

2004-10-15

The particle confinement in a magnetized plasma torus with superimposed vertical magnetic field is modeled and measured experimentally. The formation of an equilibrium characterized by a parallel plasma current canceling out the grad B and curvature drifts is described using a two-fluid model. Characteristic response frequencies and relaxation rates are calculated. The predictions for the particle confinement time as a function of the vertical magnetic field are verified in a systematic experimental study on the TORPEX device, including the existence of an optimal vertical field and the anticorrelation between confinement time and density.

A fast parallel code for calculating energies and oscillator strengths of many-electron atoms at neutron star magnetic field strengths in adiabatic approximation

Science.gov (United States)

Engel, D.; Klews, M.; Wunner, G.

2009-02-01

We have developed a new method for the fast computation of wavelengths and oscillator strengths for medium-Z atoms and ions, up to iron, at neutron star magnetic field strengths. The method is a parallelized Hartree-Fock approach in adiabatic approximation based on finite-element and B-spline techniques. It turns out that typically 15-20 finite elements are sufficient to calculate energies to within a relative accuracy of 10-5 in 4 or 5 iteration steps using B-splines of 6th order, with parallelization speed-ups of 20 on a 26-processor machine. Results have been obtained for the energies of the ground states and excited levels and for the transition strengths of astrophysically relevant atoms and ions in the range Z=2…26 in different ionization stages. Catalogue identifier: AECC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 3845 No. of bytes in distributed program, including test data, etc.: 27 989 Distribution format: tar.gz Programming language: MPI/Fortran 95 and Python Computer: Cluster of 1-26 HP Compaq dc5750 Operating system: Fedora 7 Has the code been vectorised or parallelized?: Yes RAM: 1 GByte Classification: 2.1 External routines: MPI/GFortran, LAPACK, PyLab/Matplotlib Nature of problem: Calculations of synthetic spectra [1] of strongly magnetized neutron stars are bedevilled by the lack of data for atoms in intense magnetic fields. While the behaviour of hydrogen and helium has been investigated in detail (see, e.g., [2]), complete and reliable data for heavier elements, in particular iron, are still missing. Since neutron stars are formed by the collapse of the iron cores of massive stars, it may be assumed that their atmospheres contain an iron plasma. Our objective is to fill the gap

Parallel magnetic resonance imaging

International Nuclear Information System (INIS)

Larkman, David J; Nunes, Rita G

2007-01-01

Parallel imaging has been the single biggest innovation in magnetic resonance imaging in the last decade. The use of multiple receiver coils to augment the time consuming Fourier encoding has reduced acquisition times significantly. This increase in speed comes at a time when other approaches to acquisition time reduction were reaching engineering and human limits. A brief summary of spatial encoding in MRI is followed by an introduction to the problem parallel imaging is designed to solve. There are a large number of parallel reconstruction algorithms; this article reviews a cross-section, SENSE, SMASH, g-SMASH and GRAPPA, selected to demonstrate the different approaches. Theoretical (the g-factor) and practical (coil design) limits to acquisition speed are reviewed. The practical implementation of parallel imaging is also discussed, in particular coil calibration. How to recognize potential failure modes and their associated artefacts are shown. Well-established applications including angiography, cardiac imaging and applications using echo planar imaging are reviewed and we discuss what makes a good application for parallel imaging. Finally, active research areas where parallel imaging is being used to improve data quality by repairing artefacted images are also reviewed. (invited topical review)

Effects of magnetic field on the pseudogap in the Kondo semiconductor CeRhAs

International Nuclear Information System (INIS)

Yoshii, S.; Kindo, K.; Sasakawa, T.; Suemitsu, T.; Takabatake, T.

2004-01-01

The magnetization and magnetoresistance of single-crystalline CeRhAs, which is the so-called Kondo semiconductor with an energygap of ∼280 K, have been measured in pulsed magnetic field up to 55 T. At 1.3 K, the slopes of the magnetization M for H parallel b and H parallel c decrease slightly at around 16 and 13 T, respectively, while M(H parallel a) shows monotonous dependence. Weak anisotropy is observed on the whole, M b (H)>M c (H)>M a (H). M b (H) reaches only to 0.07 μ B /f.u. at 55 T, which indicates the non-magnetic state being stable even in the high magnetic field. Strongly anisotropic behaviors are observed in the magnetoresistance. The longitudinal magnetoresistance (LMR) along the b- and c-axis show characteristic structures partly associated with the anomalies of the magnetizations, while the LMR along the a-axis shows only a broad maximum. The transverse magnetoresistances (TMR) for I parallel b and I parallel c follow the relation Δρ(H)/ρ(0)∝H α (α=1.5-1.7) below 5 T, whereas TMR for I parallel a exhibits only the weak field dependence. These results suggest the existence of a narrow and anisotropic structure within the wide pseudogap structure in the density of states

Theorem on magnet fringe field

International Nuclear Information System (INIS)

Wei, Jie; Talman, R.

1995-01-01

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

Analysis of PM Magnetization Field Effects on the Unbalanced Magnetic Forces due to Rotor Eccentricity in BLDC Motors

Directory of Open Access Journals (Sweden)

S. Mahdiuon-Rad

2013-08-01

Full Text Available This paper investigates both static and dynamic eccentricities in single phase brushless DC (BLDC motors and analyzes the effect of the PM magnetization field on unbalanced magnetic forces acting on the rotor. Three common types of PM magnetization field patterns including radial, parallel and sinusoidal magnetizations are considered. In both static and dynamic eccentricities, harmonic components of the unbalanced magnetic forces on the rotor are extracted and analyzed. Based on simulation results, the magnetization fields that produce the lowest and highest unbalanced magnetic forces are determined in rotor eccentricity conditions.

Human Exposure to Electromagnetic Fields from Parallel Wireless Power Transfer Systems.

Science.gov (United States)

Wen, Feng; Huang, Xueliang

2017-02-08

The scenario of multiple wireless power transfer (WPT) systems working closely, synchronously or asynchronously with phase difference often occurs in power supply for household appliances and electric vehicles in parking lots. Magnetic field leakage from the WPT systems is also varied due to unpredictable asynchronous working conditions. In this study, the magnetic field leakage from parallel WPT systems working with phase difference is predicted, and the induced electric field and specific absorption rate (SAR) in a human body standing in the vicinity are also evaluated. Computational results are compared with the restrictions prescribed in the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs). The results show that the middle region between the two WPT coils is safer for the two WPT systems working in-phase, and the peripheral regions are safer around the WPT systems working anti-phase. Thin metallic plates larger than the WPT coils can shield the magnetic field leakage well, while smaller ones may worsen the situation. The orientation of the human body will influence the maximum magnitude of induced electric field and its distribution within the human body. The induced electric field centralizes in the trunk, groin, and genitals with only one exception: when the human body is standing right at the middle of the two WPT coils working in-phase, the induced electric field focuses on lower limbs. The SAR value in the lungs always seems to be greater than in other organs, while the value in the liver is minimal. Human exposure to EMFs meets the guidelines of the International Committee on Non-Ionizing Radiation Protection (ICNIRP), specifically reference levels with respect to magnetic field and basic restrictions on induced electric fields and SAR, as the charging power is lower than 3.1 kW and 55.5 kW, respectively. These results are positive with respect to the safe applications of parallel WPT systems working

Human Exposure to Electromagnetic Fields from Parallel Wireless Power Transfer Systems

Science.gov (United States)

Wen, Feng; Huang, Xueliang

2017-01-01

The scenario of multiple wireless power transfer (WPT) systems working closely, synchronously or asynchronously with phase difference often occurs in power supply for household appliances and electric vehicles in parking lots. Magnetic field leakage from the WPT systems is also varied due to unpredictable asynchronous working conditions. In this study, the magnetic field leakage from parallel WPT systems working with phase difference is predicted, and the induced electric field and specific absorption rate (SAR) in a human body standing in the vicinity are also evaluated. Computational results are compared with the restrictions prescribed in the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs). The results show that the middle region between the two WPT coils is safer for the two WPT systems working in-phase, and the peripheral regions are safer around the WPT systems working anti-phase. Thin metallic plates larger than the WPT coils can shield the magnetic field leakage well, while smaller ones may worsen the situation. The orientation of the human body will influence the maximum magnitude of induced electric field and its distribution within the human body. The induced electric field centralizes in the trunk, groin, and genitals with only one exception: when the human body is standing right at the middle of the two WPT coils working in-phase, the induced electric field focuses on lower limbs. The SAR value in the lungs always seems to be greater than in other organs, while the value in the liver is minimal. Human exposure to EMFs meets the guidelines of the International Committee on Non-Ionizing Radiation Protection (ICNIRP), specifically reference levels with respect to magnetic field and basic restrictions on induced electric fields and SAR, as the charging power is lower than 3.1 kW and 55.5 kW, respectively. These results are positive with respect to the safe applications of parallel WPT systems working

Human Exposure to Electromagnetic Fields from Parallel Wireless Power Transfer Systems

Directory of Open Access Journals (Sweden)

Feng Wen

2017-02-01

Full Text Available The scenario of multiple wireless power transfer (WPT systems working closely, synchronously or asynchronously with phase difference often occurs in power supply for household appliances and electric vehicles in parking lots. Magnetic field leakage from the WPT systems is also varied due to unpredictable asynchronous working conditions. In this study, the magnetic field leakage from parallel WPT systems working with phase difference is predicted, and the induced electric field and specific absorption rate (SAR in a human body standing in the vicinity are also evaluated. Computational results are compared with the restrictions prescribed in the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs. The results show that the middle region between the two WPT coils is safer for the two WPT systems working in-phase, and the peripheral regions are safer around the WPT systems working anti-phase. Thin metallic plates larger than the WPT coils can shield the magnetic field leakage well, while smaller ones may worsen the situation. The orientation of the human body will influence the maximum magnitude of induced electric field and its distribution within the human body. The induced electric field centralizes in the trunk, groin, and genitals with only one exception: when the human body is standing right at the middle of the two WPT coils working in-phase, the induced electric field focuses on lower limbs. The SAR value in the lungs always seems to be greater than in other organs, while the value in the liver is minimal. Human exposure to EMFs meets the guidelines of the International Committee on Non-Ionizing Radiation Protection (ICNIRP, specifically reference levels with respect to magnetic field and basic restrictions on induced electric fields and SAR, as the charging power is lower than 3.1 kW and 55.5 kW, respectively. These results are positive with respect to the safe applications of parallel WPT systems

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

MHD shear flows with non-constant transverse magnetic field

International Nuclear Information System (INIS)

Núñez, Manuel

2012-01-01

Viscous conducting flows parallel to a fixed plate are studied. In contrast with the Hartmann setting, the problem is not linearized near a fixed transverse magnetic field, although the field tends to be transversal far from the wall. While general solutions may be formally obtained for all cases, their behavior is far more clear when the magnetic Prandtl number equals one. We consider two different instances: a fixed magnetic field at the wall, or an insulating sheet. The evolution of the flow and the magnetic field both near the plate and far from it are detailed, analyzing the possibility of reverse flow and instability of the solutions. -- Highlights: ► A conducting shear flow does not leave a transverse magnetic field invariant. ► Solutions are found for all cases, but these are more useful when kinetic and magnetic diffusivities coincide. ► Dirichlet and Neumann conditions on the magnetic field are studied. ► Reverse flow, and eventual instability, are possible.

Experimental verification of the role of electron pressure in fast magnetic reconnection with a guide field

International Nuclear Information System (INIS)

Fox, W.; Sciortino, F.; Stechow, A. von; Jara-Almonte, J.

2017-01-01

We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. Furthermore, these results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models of the importance of electron pressure gradients for obtaining fast magnetic reconnection.

Self-Generated Magnetic Fields in Stagnation-Phase ICF Implosions

Science.gov (United States)

Walsh, Christopher; Chittenden, Jeremy; McGlinchey, Kristopher; Niasse, Nicolas

2016-10-01

3-D extended-MHD simulations of the stagnation phase of an ICF implosion are presented, showing significant self-generated magnetic fields (1000-5000T) due to the Biermann Battery effect. Perturbed hot-spots generate magnetic fields at their edges, as the extremities of hot bubbles are rapidly cooled by the surrounding low temperature fuel, giving non-parallel electron pressure and density gradients. Larger amplitude and higher mode-number perturbations lead to an increased hot-spot surface area and more heat flow, developing greater non-parallel gradients and therefore larger magnetic fields. Due to this, largely perturbed hot-spots can be affected more by magnetic fields, although the accelerated cooling associated with greater deviations from symmetry lowers magnetisation. The Nernst effect advects magnetic field down temperature gradients towards the outer region of the hot-spot, which can also lower the magnetisation of the plasma. In some regions, however, the Nernst velocity is convergent, magnetising the tips of cold fuel spikes, resulting in anisotropic heat-flow and an improvement in energy containment. Low-mode and multi-high-mode simulations are shown, with magnetisations reaching sufficiently high levels in some regions of the hot-spot to suppress thermal conduction to lower than 50% of the unmagnetised case. A quantitative analysis of how this affects the hot-spot energy balance is included.

An explanation for parallel electric field pulses observed over thunderstorms

Science.gov (United States)

Kelley, M. C.; Barnum, B. H.

2009-10-01

Every electric field instrument flown on sounding rockets over a thunderstorm has detected pulses of electric fields parallel to the Earth's magnetic field associated with every strike. This paper describes the ionospheric signatures found during a flight from Wallops Island, Virginia, on 2 September 1995. The electric field results in a drifting Maxwellian corresponding to energies up to 1 eV. The distribution function relaxes because of elastic and inelastic collisions, resulting in electron heating up to 4000-5000 K and potentially observable red line emissions and enhanced ISR electron temperatures. The field strength scales with the current in cloud-to-ground strikes and falls off as r -1 with distance. Pulses of both polarities are found, although most electric fields are downward, parallel to the magnetic field. The pulse may be the reaction of ambient plasma to a current pulse carried at the whistler packet's highest group velocity. The charge source required to produce the electric field is very likely electrons of a few keV traveling at the packet velocity. We conjecture that the current source is the divergence of the current flowing at mesospheric heights, the phenomenon called an elve. The whistler packet's effective radiated power is as high as 25 mW at ionospheric heights, comparable to some ionospheric heater transmissions. Comparing the Poynting flux at the base of the ionosphere with flux an equal distance away along the ground, some 30 db are lost in the mesosphere. Another 10 db are lost in the transition from free space to the whistler mode.

Numerical Study of a Crossed Loop Coil Array for Parallel Magnetic Resonance Imaging

International Nuclear Information System (INIS)

Hernandez, J.; Solis, S. E.; Rodriguez, A. O.

2008-01-01

A coil design has been recently proposed by Temnikov (Instrum Exp Tech. 2005;48;636-637), with higher experimental signal-to-noise ratio than that of the birdcage coil. It is also claimed that it is possible to individually tune it with a single chip capacitor. This coil design shows a great resemble to the gradiometer coil. These results motivated us to numerically simulate a three-coil array for parallel magnetic resonance imaging and in vivo magnetic resonance spectroscopy with multi nuclear capability. The magnetic field was numerical simulated by solving Maxwell's equations with the finite element method. Uniformity profiles were calculated at the midsection for one single coil and showed a good agreement with the experimental data. Then, two more coils were added to form two different coil arrays: coil elements were equally distributed by an angle of a 30 deg. angle. Then, uniformity profiles were calculated again for all cases at the midsection. Despite the strong interaction among all coil elements, very good field uniformity can be achieved. These numerical results indicate that this coil array may be a good choice for magnetic resonance imaging parallel imaging

Magnetic field of Mercury

International Nuclear Information System (INIS)

Jackson, D.J.; Beard, D.B.

1977-01-01

The geomagnetic field, suitably scaled down and parameterized, is shown to give a very good fit to the magnetic field measurements taken on the first and third passes of the Mariner 10 space probe past Mercury. The excellence of the fit to a reliable planetary magnetospheric model is good evidence that the Mercury magnetosphere is formed by a simple, permanent, intrinsic planetary magnetic field distorted by the effects of the solar wind. The parameters used for a best fit to all the data are (depending slightly on the choice of data) 2.44--2.55 for the ratio of Mercury's magnetic field strength at the subsolar point to that of the earth's subsolar point field (this results in a dipole moment of 170 γR/sub M/ 3 (R/sub M/ is Mercury Radius), i.e., 2.41 x 10 22 G cm 3 in the same direction as the earth's dipole), approx.-113 γR/sub M/ 4 for the planetary quadrupole moment parallel to the dipole moment, 10degree--17degree for the tilt of the planet dipole toward the sun, 4.5degree for the tilt of the dipole toward dawn, and 2.5degree--7.6degree aberration angle for the shift in the tail axis from the planet-sun direction because of the planet's orbital velocity. The rms deviation overall for the entire data set compared with the theoretical fitted model for the magnetic field strength was 17 γ (approx.4% of the maximum field measured). If the data from the first pass that show presumed strong time variations are excluded, the overall rms deviation for the field magnitude is only 10 γ

Transverse magnetic scattering by parallel conducting elliptic cylinders

Science.gov (United States)

Sebak, A.

1991-10-01

A boundary value solution to the problem of transverse magnetic multiple scattering by M parallel perfectly conducting elliptic cylinders is presented. The solution is an exact one and based on the separation-of-variables technique and the addition theorem for Mathieu functions. It is expressed in terms of a system of simultaneous linear equations of infinite order, which is then truncated for numerical computations. Representative numerical results for the scattered field by two cylinders are then generated, for some selected sizes and orientations parameters, and presented.

Parallel inhomogeneity and the Alfven resonance. 1: Open field lines

Science.gov (United States)

Hansen, P. J.; Harrold, B. G.

1994-01-01

In light of a recent demonstration of the general nonexistence of a singularity at the Alfven resonance in cold, ideal, linearized magnetohydrodynamics, we examine the effect of a small density gradient parallel to uniform, open ambient magnetic field lines. To lowest order, energy deposition is quantitatively unaffected but occurs continuously over a thickened layer. This effect is illustrated in a numerical analysis of a plasma sheet boundary layer model with perfectly absorbing boundary conditions. Consequences of the results are discussed, both for the open field line approximation and for the ensuing closed field line analysis.

Simulations of Magnetic Fields in Tidally Disrupted Stars

Energy Technology Data Exchange (ETDEWEB)

Guillochon, James [Harvard-Smithsonian Center for Astrophysics, The Institute for Theory and Computation, 60 Garden Street, Cambridge, MA 02138 (United States); McCourt, Michael, E-mail: jguillochon@cfa.harvard.edu [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

2017-01-10

We perform the first magnetohydrodynamical simulations of tidal disruptions of stars by supermassive black holes. We consider stars with both tangled and ordered magnetic fields, for both grazing and deeply disruptive encounters. When the star survives disruption, we find its magnetic field amplifies by a factor of up to 20, but see no evidence for a self-sustaining dynamo that would yield arbitrary field growth. For stars that do not survive, and within the tidal debris streams produced in partial disruptions, we find that the component of the magnetic field parallel to the direction of stretching along the debris stream only decreases slightly with time, eventually resulting in a stream where the magnetic pressure is in equipartition with the gas. Our results suggest that the returning gas in most (if not all) stellar tidal disruptions is already highly magnetized by the time it returns to the black hole.

Topology in SU(2) lattice gauge theory and parallelization of functional magnetic resonance imaging

Energy Technology Data Exchange (ETDEWEB)

Solbrig, Stefan

2008-07-01

In this thesis, I discuss topological properties of quenched SU(2) lattice gauge fields. In particular, clusters of topological charge density exhibit a power-law. The exponent of that power-law can be used to validate models for lattice gauge fields. Instead of working with fixed cutoffs of the topological charge density, using the notion of a ''watermark'' is more convenient. Furthermore, I discuss how a parallel computer, originally designed for lattice gauge field simulations, can be used for functional magnetic resonance imaging. Multi parameter fits can be parallelized to achieve almost real-time evaluation of fMRI data. (orig.)

Topology in SU(2) lattice gauge theory and parallelization of functional magnetic resonance imaging

International Nuclear Information System (INIS)

Solbrig, Stefan

2008-01-01

In this thesis, I discuss topological properties of quenched SU(2) lattice gauge fields. In particular, clusters of topological charge density exhibit a power-law. The exponent of that power-law can be used to validate models for lattice gauge fields. Instead of working with fixed cutoffs of the topological charge density, using the notion of a ''watermark'' is more convenient. Furthermore, I discuss how a parallel computer, originally designed for lattice gauge field simulations, can be used for functional magnetic resonance imaging. Multi parameter fits can be parallelized to achieve almost real-time evaluation of fMRI data. (orig.)

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.

Distribution of local magnetic field of vortex lattice near anisotropic superconductor surface in inclined external fields

International Nuclear Information System (INIS)

Efremova, S.A.; Tsarevskij, S.L.

1997-01-01

Magnetic field distribution in a unit cell of the Abrikosov vortex lattice near the surface of monoaxial anisotropic type-ii superconductors in inclined external magnetic field has been found in the framework of London model for the cases when the symmetry axis is perpendicular and parallel to the superconductor surface interface. Distribution of local magnetic field as a function of the distance from the superconductor interface surface and external field inclination angle has been obtained. Using high-Tc superconductor Y-Ba-Cu-O by way of examples, it has been shown that the study of local magnetic field distribution function, depending on external magnetic field inclination angle towards the superconductor symmetry axis and towards the superconductor surface, can provide important data on anisotropic properties of the superconductor [ru

Measurement of time series variation of thermal diffusivity of magnetic fluid under magnetic field by forced Rayleigh scattering method

Energy Technology Data Exchange (ETDEWEB)

Motozawa, Masaaki, E-mail: motozawa.masaaki@shizuoka.ac.jp [Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu-shi, Shizuoka 432-8561 (Japan); Muraoka, Takashi [Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu-shi, Shizuoka 432-8561 (Japan); Motosuke, Masahiro, E-mail: mot@rs.tus.ac.jp [Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585 (Japan); Fukuta, Mitsuhiro, E-mail: fukuta.mitsuhiro@shizuoka.ac.jp [Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu-shi, Shizuoka 432-8561 (Japan)

2017-04-15

It can be expected that the thermal diffusivity of a magnetic fluid varies from time to time after applying a magnetic field because of the growth of the inner structure of a magnetic fluid such as chain-like clusters. In this study, time series variation of the thermal diffusivity of a magnetic fluid caused by applying a magnetic field was investigated experimentally. For the measurement of time series variation of thermal diffusivity, we attempted to apply the forced Rayleigh scattering method (FRSM), which has high temporal and high spatial resolution. We set up an optical system for the FRSM and measured the thermal diffusivity. A magnetic field was applied to a magnetic fluid in parallel and perpendicular to the heat flux direction, and the magnetic field intensity was 70 mT. The FRSM was successfully applied to measurement of the time series variation of the magnetic fluid from applying a magnetic field. The results show that a characteristic configuration in the time series variation of the thermal diffusivity of magnetic fluid was obtained in the case of applying a magnetic field parallel to the heat flux direction. In contrast, in the case of applying a magnetic field perpendicular to the heat flux, the thermal diffusivity of the magnetic fluid hardly changed during measurement. - Highlights: • Thermal diffusivity was measured by forced Rayleigh scattering method (FRSM). • FRSM has high temporal and high spatial resolutions for measurement. • We attempted to apply FRSM to magnetic fluid (MF). • Time series variation of thermal diffusivity of MF was successfully measured by FRSM. • Anisotropic thermal diffusivity of magnetic fluid was also successfully confirmed.

Magnetic field screens

International Nuclear Information System (INIS)

Mansfield, P.; Turner, R.; Chapman, B.L.W.; Bowley, R.M.

1990-01-01

A screen for a magnetic coil, for producing, for example, a homogeneous, gradient or RF field in nuclear magnetic resonance imaging, is described. It is provided by surround the coil with a set of electrical conductors. The currents within the conductors are controlled in such a manner that the field is neutralised in a specific region of space. The current distribution within the conductors is determined by calculating the current within a hypothetical superconductive shield which would have the effect of neutralising the field, the current through the conductors thereby being a substitute for the superconductive shield. The conductors may be evenly spaced and connected in parallel, their resistances being determined by thickness or composition to provide the desired current, or they may carry equal currents but be differently spaced. A further set or sets of controlled conductors outside the first set may ensure that the first set does not upset the field from the NMR coil. The shield may selectively reflect certain fields while transmitting others and may prevent acoustic vibration e.g. when switching gradient fields. An RF coil arrangement may consist of two orthogonal coils, one coil within the other for use as a transmit/receive set or as a double resonance transmitter; a shield between the coils is in series with, and formed from the same winding as, the inner coil. (author)

Approximate Integrals of rf-driven Particle Motion in Magnetic Field

International Nuclear Information System (INIS)

Dodin, I.Y.; Fisch, N.J.

2004-01-01

For a particle moving in nonuniform magnetic field under the action of an rf wave, ponderomotive effects result from rf-driven oscillations nonlinearly coupled with Larmor rotation. Using Lagrangian and Hamiltonian formalism, we show how, despite this coupling, two independent integrals of the particle motion are approximately conserved. Those are the magnetic moment of free Larmor rotation and the quasi-energy of the guiding center motion parallel to the magnetic field. Under the assumption of non-resonant interaction of the particle with the rf field, these integrals represent adiabatic invariants of the particle motion

Efficient Analysis of Simulations of the Sun's Magnetic Field

Science.gov (United States)

Scarborough, C. W.; Martínez-Sykora, J.

2014-12-01

Dynamics in the solar atmosphere, including solar flares, coronal mass ejections, micro-flares and different types of jets, are powered by the evolution of the sun's intense magnetic field. 3D Radiative Magnetohydrodnamics (MHD) computer simulations have furthered our understanding of the processes involved: When non aligned magnetic field lines reconnect, the alteration of the magnetic topology causes stored magnetic energy to be converted into thermal and kinetic energy. Detailed analysis of this evolution entails tracing magnetic field lines, an operation which is not time-efficient on a single processor. By utilizing a graphics card (GPU) to trace lines in parallel, conducting such analysis is made feasible. We applied our GPU implementation to the most advanced 3D Radiative-MHD simulations (Bifrost, Gudicksen et al. 2011) of the solar atmosphere in order to better understand the evolution of the modeled field lines.

Stable magnetization of iron filled carbon nanotube MFM probes in external magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Wolny, Franziska; Weissker, Uhland; Muehl, Thomas; Lutz, Matthias U; Mueller, Christian; Leonhardt, Albrecht; Buechner, Bernd, E-mail: f.wolny@ifw-dresden.d [Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany)

2010-01-01

We present results on the application of an iron filled carbon nanotube (Fe-CNT) as a probe for magnetic force microscopy (MFM) in an external magnetic field. If an external field is applied parallel to the sample surface, conventional ferromagnetically coated MFM probes often have the disadvantage that the magnetization of the coating turns towards the direction of the applied field. Then it is difficult to distinguish the effect of the external field on the sample from those on the MFM probe. The Fe-CNT MFM probe has a large shape anisotropy due to the high aspect ratio of the enclosed iron nanowire. Thanks to this the direction of the magnetization stays mainly oriented along the long nanotube axis in in-plane fields up to our experimental limit of 250 mT. Thus, the quality of the MFM images remains unchanged. Apart from this, it is shown that Fe-CNT MFM probe yields a very good magnetic resolution of about 25 nm due to the small diameter of the iron filling.

Magnetic anisotropy of thin sputtered MgB2 films on MgO substrates in high magnetic fields

Directory of Open Access Journals (Sweden)

Savio Fabretti

2014-03-01

Full Text Available We investigated the magnetic anisotropy ratio of thin sputtered polycrystalline MgB2 films on MgO substrates. Using high magnetic field measurements, we estimated an anisotropy ratio of 1.35 for T = 0 K with an upper critical field of 31.74 T in the parallel case and 23.5 T in the perpendicular case. Direct measurements of a magnetic-field sweep at 4.2 K show a linear behavior, confirmed by a linear fit for magnetic fields perpendicular to the film plane. Furthermore, we observed a change of up to 12% of the anisotropy ratio in dependence of the film thickness.

Topology in SU(2) lattice gauge theory and parallelization of functional magnetic resonance imaging

Energy Technology Data Exchange (ETDEWEB)

Solbrig, Stefan

2008-07-01

In this thesis, I discuss topological properties of quenched SU(2) lattice gauge fields. In particular, clusters of topological charge density exhibit a power-law. The exponent of that power-law can be used to validate models for lattice gauge fields. Instead of working with fixed cutoffs of the topological charge density, using the notion of a ''watermark'' is more convenient. Furthermore, I discuss how a parallel computer, originally designed for lattice gauge field simulations, can be used for functional magnetic resonance imaging. Multi parameter fits can be parallelized to achieve almost real-time evaluation of fMRI data. (orig.)

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.

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

Directory of Open Access Journals (Sweden)

Paulo Roberto Eckert

2014-07-01

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

Influence of segmentation of ring-shaped NdFeB magnets with parallel magnetization on cylindrical actuators.

Science.gov (United States)

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

2014-07-21

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

Remagnetization of bulk high-temperature superconductors subjected to crossed and rotating magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Vanderbemden, P [SUPRATECS and Department of Electrical Engineering and Computer Science B28, Sart-Tilman, B-4000 Liege (Belgium); Hong, Z [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Coombs, T A [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Ausloos, M [SUPRATECS and Department of Physics B5, Sart-Tilman, B-4000 Liege (Belgium); Babu, N Hari [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Cardwell, D A [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Campbell, A M [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom)

2007-09-15

Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample.

Remagnetization of bulk high-temperature superconductors subjected to crossed and rotating magnetic fields

International Nuclear Information System (INIS)

Vanderbemden, P; Hong, Z; Coombs, T A; Ausloos, M; Babu, N Hari; Cardwell, D A; Campbell, A M

2007-01-01

Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample

Anisotropy of magnetoresistance on trapping magnetic fields in granular HTSC

CERN Document Server

Sukhanov, A A

2003-01-01

The features of magnetoresistance in Bi (Pb)-HTSC ceramics with the magnetic fields trapped are investigated. It is found that on trapping magnetic flux the magnetoresistance in granular HTSC becomes anisotropic. Moreover, for magnetic fields H parallel and currents perpendicular to field H sub i which induces the trapping the magnetoresistance field dependence DELTA R(H) is nonmonotonic and the magnetoresistance is negative for small fields H < Hinv. The effect of trapped field and transport current and their orientations on the dependence DELTA R(H) is investigated. In particular, it is found that the field of magnetoresistance sign inversion Hinv almost linearly grows with increase of the effective trapped magnetic fields. Hinv decreases down to zero as the angle between fields H and H sub i increases up to pi/2 and slightly decreases with increasing transport current. The results are treated in terms of the model of magnetic flux trapping in superconducting grains or 'loops' embedded in a matrix of wea...

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.

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

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

International Nuclear Information System (INIS)

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

2001-01-01

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

Sidewall containment of liquid metal with horizontal alternating magnetic fields

International Nuclear Information System (INIS)

Pareg, W.F.

1990-01-01

This patent describes an apparatus for confining molten metal. It comprises: containment means having an open side; a magnet capable of generating a mainly horizontal alternating magnetic field. The the magnet is located adjacent to the open side of the containment means whereby the field generated by the magnet is capable of inducing eddy currents in a thin layer at the surface of the molten metal which interact with the magnetic field producing a force that can contain the molten metal within the containment means; wherein the magnet includes: magnetic poles located adjacent to the open side of the confinement means; a core connecting the poles; a coil encircling the core, the coil capable of being responsive to a current source; whereby an alternating magnetic field can be generated between the poles and parallel to the open side of the containment means so that a molten metal can be confined within the confinement means

Alfven-wave current drive and magnetic field stochasticity

International Nuclear Information System (INIS)

Litwin, C.; Hegna, C.C.

1993-01-01

Propagating Alfven waves can generate parallel current through an alpha effect. In resistive MHD however, the dynamo field is proportional to resistivity and as such cannot drive significant currents for realistic parameters. In the search for an enhancement of this effect the authors investigate the role of magnetic field stochasticity. They show that the presence of a stochastic magnetic field, either spontaneously generated by instabilities or induced externally, can enhance the alpha effect of the wave. This enhancement is caused by an increased wave dissipation due to both current diffusion and filamentation. For the range of parameters of current drive experiments at Phaedrus-T tokamak, a moderate field stochasticity leads to significant modifications in the loop voltage

Mathematical model of voltage-current characteristics of Bi(2223)/Ag magnets under an external magnetic field

CERN Document Server

Pitel, J; Lehtonen, J; Kovács, P

2002-01-01

We have developed a mathematical model, which enables us to predict the voltage-current V(I) characteristics of a solenoidal high-temperature superconductor (HTS) magnet subjected to an external magnetic field parallel to the magnet axis. The model takes into account the anisotropy in the critical current-magnetic field (I sub c (B)) characteristic and the n-value of Bi(2223)Ag multifilamentary tape at 20 K. From the power law between the electric field and the ratio of the operating and critical currents, the voltage on the magnet terminals is calculated by integrating the contributions of individual turns. The critical current of each turn, at given values of operating current and external magnetic field, is obtained by simple linear interpolation between the two suitable points of the I sub c (B) characteristic, which corresponds to the angle alpha between the vector of the resulting magnetic flux density and the broad tape face. In fact, the model is valid for any value and orientation of external magneti...

Magnetic bead micromixer: Influence of magnetic element geometry and field amplitude

DEFF Research Database (Denmark)

Lund-Olesen, Torsten; Buus, Bjarke B.; Howalt, Jakob

2008-01-01

A scheme for the silicon microfabrication of lab-on-a-chip systems with mixing based on dynamic plugs of magnetic beads is presented. The systems consist of a microfluidic channel integrated with a number of soft magnetic elements by the sides of the channel. The elements are magnetized by a homo......A scheme for the silicon microfabrication of lab-on-a-chip systems with mixing based on dynamic plugs of magnetic beads is presented. The systems consist of a microfluidic channel integrated with a number of soft magnetic elements by the sides of the channel. The elements are magnetized...... by a homogeneous external ac magnetic field. The systems are scalable with respect to the number of magnetic bead plugs and number of parallel channels, and thus they have high potential for use in biological separation using functionalized magnetic beads. The mixing efficiency is characterized for two different...

Dielectric response of a relativistic degenerate electron plasma in a strong magnetic field

International Nuclear Information System (INIS)

Delsante, A.E.; Frankel, N.E.

1979-01-01

The longitudinal dielectric response of a relativistic ultradegenerate electron plasma in a strong magnetic field is obtained via a relativistic generalization of the Hartree self-consistent field method. Dispersion relations and damping conditions for plasma oscillations both parallel and perpendicular to the magnetic field are obtained. Detailed results for the zero-field case, and applications to white dwarf stars and pulsars are given

Fast magnetic field penetration into an intense neutralized ion beam

International Nuclear Information System (INIS)

Armale, R.

1992-06-01

Experiments involving propagation of neutralized ion beams across a magnetic field indicate a magnetic field penetration time determined by the Hall resistivity rather than the Spitzer or Pedersen resistivity. In magnetohydrodynamics the Hall current is negligible because electrons and ions drift together in response to an electric field perpendicular to the magnetic field. For a propagating neutralized ion beam, the ion orbits are completely different from the electron orbits and the Hall current must be considered. There would be no effect unless there is a component of magnetic field normal to the surface which would usually be absent for a good conductor. It is necessary to consider electron inertia and the consequent penetration of the normal component to a depth c/ω p . In addition it is essential to consider a component of magnetic field parallel to the velocity of the beam which may be initially absent, but is generated by the Hall effect. The penetration time is determined by whistler waves rather than diffusion

Self-balanced modulation and magnetic rebalancing method for parallel multilevel inverters

Science.gov (United States)

Li, Hui; Shi, Yanjun

2017-11-28

A self-balanced modulation method and a closed-loop magnetic flux rebalancing control method for parallel multilevel inverters. The combination of the two methods provides for balancing of the magnetic flux of the inter-cell transformers (ICTs) of the parallel multilevel inverters without deteriorating the quality of the output voltage. In various embodiments a parallel multi-level inverter modulator is provide including a multi-channel comparator to generate a multiplexed digitized ideal waveform for a parallel multi-level inverter and a finite state machine (FSM) module coupled to the parallel multi-channel comparator, the FSM module to receive the multiplexed digitized ideal waveform and to generate a pulse width modulated gate-drive signal for each switching device of the parallel multi-level inverter. The system and method provides for optimization of the output voltage spectrum without influence the magnetic balancing.

Anisotropic transport properties of quasiballistic InAs nanowires under high magnetic field

Science.gov (United States)

Vigneau, Florian; Zeng, Zaiping; Escoffier, Walter; Caroff, Philippe; Leturcq, Renaud; Niquet, Yann-Michel; Raquet, Bertrand; Goiran, Michel

2018-03-01

The magnetoconductance of a long channel InAs nanowire based field effect transistor in the quasiballistic regime under large magnetic field is investigated. The quasi-1D nanowire is fully characterized by a bias voltage spectroscopy and measurements under magnetic field up to 50 T applied either perpendicular or parallel to the nanowire axis lifting the spin and orbital degeneracies of the subbands. Under normal magnetic field, the conductance shows quantized steps due to the backscattering reduction and a decrease due to depopulation of the 1D modes. Under axial magnetic field, a quasioscillatory behavior is evidenced due to the coupling of the magnetic field with the angular momentum of the wave function. In addition the formation of cyclotron orbits is highlighted under high magnetic field. The experimental results are compared with theoretical calculation of the 1D band structure and related parameters.

Stability analysis of perpendicular magnetic trilayers with a field-like spin torque

International Nuclear Information System (INIS)

Wang, Ri-Xing; Zhao, Jing-Li; He, Peng-Bin; Gu, Guan-Nan; Li, Zai-Dong; Pan, An-Lian; Liu, Quan-Hui

2013-01-01

We have analytically studied the magnetization dynamics in magnetic trilayers with perpendicular anisotropy for both free and pinned layers. By linear stability analysis, we obtain the phase diagram parameterized by the current, magnetic field and relative strength of the field-like spin torque to Slonczewski torque. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out-of-plane precession, and bistable states can be realized. The precession frequency can be expressed as a function of the current and external magnetic field. In addition, the presence of field-like spin torque can change the switching current and precession frequency. - Highlights: ► The phase diagram is obtained by linear stability analysis. ► The precession frequency can be controlled by the current and magnetic field. ► Field-like spin torque can change instability current and precession frequency.

Magnetic field manipulation of spin current in a single-molecule magnet tunnel junction with two-electron Coulomb interaction

Science.gov (United States)

Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, Jiu-Qing; Niu, Peng-Bin

2018-04-01

In this work, we study the generation of spin-current in a single-molecule magnet (SMM) tunnel junction with Coulomb interaction of transport electrons and external magnetic field. In the absence of field the spin-up and -down currents are symmetric with respect to the initial polarizations of molecule. The existence of magnetic field breaks the time-reversal symmetry, which leads to unsymmetrical spin currents of parallel and antiparallel polarizations. Both the amplitude and polarization direction of spin current can be controlled by the applied magnetic field. Particularly when the magnetic field increases to a certain value the spin-current with antiparallel polarization is reversed along with the magnetization reversal of the SMM. The two-electron occupation indeed enhances the transport current compared with the single-electron process. However the increase of Coulomb interaction results in the suppression of spin-current amplitude at the electron-hole symmetry point. We propose a scheme to compensate the suppression with the magnetic field.

Magnetic field generation device for magnetohydrodynamic electric power generation

International Nuclear Information System (INIS)

Kuriyama, Yoshihiko.

1993-01-01

An existent magnetic field generation device for magnetohydrodynamic electric power generation comprises at least a pair of permanent magnets disposed to an inner circumferential surface of a yoke having such a cross sectional area that two pairs of parallel sides are present, in which different magnetic poles are opposed while interposing a flow channel for a conductive fluid therebetween. Then, first permanent magnets which generate main magnetic fields are disposed each at a gap sandwiching a plane surface including a center axis of a flow channel for the conductive fluid. Second permanent magnets which generate auxiliary magnetic fields are disposed to an inner circumferential surface of a yoke intersecting the yoke to which the first permanent magnets are disposed. The magnetic poles on the side of the flow channel for the second permanent magnets have identical polarity with that of the magnetic poles of the adjacent first permanent magnets. As a result, a magnetic flux density in the flow channel for the conductive fluid can be kept homogeneous and at a high level from a position of the axial line of the flow channel to the outer circumference, thereby enabling to remarkably improve a power generation efficiency. (N.H.)

Magnetic Field Effects and Electromagnetic Wave Propagation in Highly Collisional Plasmas.

Science.gov (United States)

Bozeman, Steven Paul

The homogeneity and size of radio frequency (RF) and microwave driven plasmas are often limited by insufficient penetration of the electromagnetic radiation. To investigate increasing the skin depth of the radiation, we consider the propagation of electromagnetic waves in a weakly ionized plasma immersed in a steady magnetic field where the dominant collision processes are electron-neutral and ion-neutral collisions. Retaining both the electron and ion dynamics, we have adapted the theory for cold collisionless plasmas to include the effects of these collisions and obtained the dispersion relation at arbitrary frequency omega for plane waves propagating at arbitrary angles with respect to the magnetic field. We discuss in particular the cases of magnetic field enhanced wave penetration for parallel and perpendicular propagation, examining the experimental parameters which lead to electromagnetic wave propagation beyond the collisional skin depth. Our theory predicts that the most favorable scaling of skin depth with magnetic field occurs for waves propagating nearly parallel to B and for omega << Omega_{rm e} where Omega_{rm e} is the electron cyclotron frequency. The scaling is less favorable for propagation perpendicular to B, but the skin depth does increase for this case as well. Still, to achieve optimal wave penetration, we find that one must design the plasma configuration and antenna geometry so that one generates primarily the appropriate angles of propagation. We have measured plasma wave amplitudes and phases using an RF magnetic probe and densities using Stark line broadening. These measurements were performed in inductively coupled plasmas (ICP's) driven with a standard helical coil, a reverse turn (Stix) coil, and a flat spiral coil. Density measurements were also made in a microwave generated plasma. The RF magnetic probe measurements of wave propagation in a conventional ICP with wave propagation approximately perpendicular to B show an increase in

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

Science.gov (United States)

Mai, Chuhong; Desch, Steven J.; Boley, Aaron C.; Weiss, Benjamin P.

2018-04-01

Recent laboratory efforts have constrained the remanent magnetizations of chondrules and the magnetic field strengths to which the chondrules were exposed as they cooled below their Curie points. An outstanding question is whether the inferred paleofields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values for two proposed chondrule formation mechanisms, large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks, the magnetic field parallel to the shock front is amplified by factors of ∼10–30, regardless of the magnetic diffusivity. Therefore, chondrules melted in these shocks probably recorded an amplified magnetic field. Behind planetary bow shocks, the field amplification is sensitive to the magnetic diffusivity. We compute the gas properties behind a bow shock around a 3000 km radius planetary embryo, with and without atmospheres, using hydrodynamics models. We calculate the ionization state of the hot, shocked gas, including thermionic emission from dust, thermal ionization of gas-phase potassium atoms, and the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We find that the diffusivity is sufficiently large that magnetic fields have already relaxed to background values in the shock downstream where chondrules acquire magnetizations, and that these locations are sufficiently far from the planetary embryos that chondrules should not have recorded a significant putative dynamo field generated on these bodies. We conclude that, if melted in planetary bow shocks, chondrules probably recorded the background nebular field.

Magnetic-Field-Orientation Dependent Magnetoelectric Effect in FeBSiC/PZT/FeBSiC Composites

Directory of Open Access Journals (Sweden)

Jun-Xian Ye

2014-01-01

Full Text Available We investigate the magnetic-field-orientation dependent magnetoelectric (ME effect in the FeBSiC/Pb(Zr,TiO3(PZT/FeBSiC laminates. It is shown that, by only using the bias-magnetic-field dependent ME response measured with the magnetic-field parallel to the surface plane of PZT slab, the magnetic-field-orientation dependent ME coefficient upon magnetic-fields of various amplitudes can be obtained via computer simulations. The simulation results match well the experimental measurements, demonstrating the applicability of the ME laminates-based sensors in detecting magnetic-fields with uncertain amplitudes and/or orientations in environment.

Magnetic Fields in the Massive Dense Cores of the DR21 Filament: Weakly Magnetized Cores in a Strongly Magnetized Filament

Energy Technology Data Exchange (ETDEWEB)

Ching, Tao-Chung; Lai, Shih-Ping [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Zhang, Qizhou; Girart, Josep M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 (China); Liu, Hauyu B., E-mail: chingtaochung@gmail.com [European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

2017-04-01

We present Submillimeter Array 880 μ m dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields a plane-of-sky magnetic field strength of 0.4–1.7 mG for the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that the gravitational energy in the filament dominates magnetic and kinematic energies, while the kinematic energy dominates in the cores. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores.

The Effect of External Magnetic Field on Dielectric Permeability of Multiphase Ferrofluids

Science.gov (United States)

Dotsenko, O. A.; Pavlova, A. A.; Dotsenko, V. S.

2018-03-01

Nowadays, ferrofluids are applied in various fields of science and technology, namely space, medicine, geology, biology, automobile production, etc. In order to investigate the feasibility of applying ferrofluids in magnetic field sensors, the paper presents research into the influence of the external magnetic field on dielectric permeability of ferrofluids comprising magnetite nanopowder, multiwall carbon nanotubes, propanetriol and deionized water. The real and imaginary parts of the dielectric permeability change respectively by 3.7 and 0.5% when applying the magnetic field parallel to the electric. The findings suggest that the considered ferrofluid can be used as a magnetic level gauge or in design of variable capacitors.

Dependence of Fe/Cr superlattice magnetoresistance on orientation of external magnetic field

International Nuclear Information System (INIS)

Ustinov, V.V.; Romashev, L.N.; Minin, V.I.; Semerikov, A.V.; Del', A.R.

1995-01-01

The paper presents the results of investigations into giant magnetoresistance of [Fe/Cr] 30 /MgO superlattices obtained using molecular-beam epitaxy under various orientations of magnetic field relatively to the layers of superlattice and to the direction of current flow. Theory of orientation dependence of superlattice magnetoresistance enabling to describe satisfactorily behaviour of magnetoresistance at arbitrary direction of magnetic field on the ground of results of magnetoresistance measurements in magnetic field parallel and perpendicular to plane of layers, is elaborated. It is pointed out that it is possible to obtain field dependence of superlattice magnetization on the ground of measurement results. 9 refs., 6 figs

MAGNETIC FIELD OF THE VELA C MOLECULAR CLOUD

Energy Technology Data Exchange (ETDEWEB)

Kusune, Takayoshi; Sugitani, Koji [Graduate School of Natural Sciences, Nagoya City University, Mizuho-ku, Nagoya, Aichi 467-8501 (Japan); Nakamura, Fumitaka; Tamura, Motohide [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Watanabe, Makoto [Department of Applied Physics, Okayama University of Science, 1-1 Ridai-cho, Okayama-city, Okayama 700-0005 (Japan); Kwon, Jungmi [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yohinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Sato, Shuji, E-mail: t_kusune@nsc.nagoya-cu.ac.jp [Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan)

2016-10-20

We have performed extensive near-infrared ( JHK {sub s}) imaging polarimetry toward the Vela C molecular cloud, which covers the five high-density sub-regions (North, Centre-Ridge, Centre-Nest, South-Ridge, and South-Nest) with distinct morphological characteristics. The obtained polarization vector map shows that three of these sub-regions have distinct plane-of-the-sky (POS) magnetic-field characteristics according to the morphological characteristics. (1) In the Centre-Ridge sub-region, a dominating ridge, the POS magnetic field is mostly perpendicular to the ridge. (2) In the Centre-Nest sub-region, a structure having a slightly extended nest of filaments, the POS magnetic field is nearly parallel to its global elongation. (3) In the South-Nest sub-region, which has a network of small filaments, the POS magnetic field appears to be chaotic. By applying the Chandrasekhar–Fermi method, we derived the POS magnetic field strength as ∼70–310 μ G in the Centre-Ridge, Centre-Nest, and South-Ridge sub-regions. In the South-Nest sub-region, the dispersion of polarization angles is too large to apply the C-F method. Because the velocity dispersion in this sub-region is not greater than those in the other sub-regions, we suggest that the magnetic field in this sub-region is weaker than those in other sub-regions. We also discuss the relationship between the POS magnetic field (configuration and strength) and the cloud structure of each sub-region.

MAGNETIC FIELD OF THE VELA C MOLECULAR CLOUD

International Nuclear Information System (INIS)

Kusune, Takayoshi; Sugitani, Koji; Nakamura, Fumitaka; Tamura, Motohide; Watanabe, Makoto; Kwon, Jungmi; Sato, Shuji

2016-01-01

We have performed extensive near-infrared ( JHK s ) imaging polarimetry toward the Vela C molecular cloud, which covers the five high-density sub-regions (North, Centre-Ridge, Centre-Nest, South-Ridge, and South-Nest) with distinct morphological characteristics. The obtained polarization vector map shows that three of these sub-regions have distinct plane-of-the-sky (POS) magnetic-field characteristics according to the morphological characteristics. (1) In the Centre-Ridge sub-region, a dominating ridge, the POS magnetic field is mostly perpendicular to the ridge. (2) In the Centre-Nest sub-region, a structure having a slightly extended nest of filaments, the POS magnetic field is nearly parallel to its global elongation. (3) In the South-Nest sub-region, which has a network of small filaments, the POS magnetic field appears to be chaotic. By applying the Chandrasekhar–Fermi method, we derived the POS magnetic field strength as ∼70–310 μ G in the Centre-Ridge, Centre-Nest, and South-Ridge sub-regions. In the South-Nest sub-region, the dispersion of polarization angles is too large to apply the C-F method. Because the velocity dispersion in this sub-region is not greater than those in the other sub-regions, we suggest that the magnetic field in this sub-region is weaker than those in other sub-regions. We also discuss the relationship between the POS magnetic field (configuration and strength) and the cloud structure of each sub-region.

Generation of macroscopic magnetic-field-aligned electric fields by the convection surge ion acceleratiom mechanism

International Nuclear Information System (INIS)

Mauk, B.H.

1989-01-01

The ''convection surge'' computer model presented previously (concerning the dramatic, nonadiabatic, magnetic-field-aligned energization of ions near the Earth's geosynchronous orbit in the presence of strong, transient, magnetic-field-perpendicular inductive electric fields) has been extended to include the self-consistent generation of magnetic-field-aligned electric fields. The field-aligned electric potential is obtained by imposing the quasi-neutrality condition using approximated electron distribution forms. The ions are forced to respond self-consistently to this potential. It is found that field-aligned potential drops up to 1 to 10 kV can be generated depending on electron temperatures and on the mass species of the ions. During transient periods of the process, these large potential drops can be confined to a few degrees of magnetic latitude at positions close to the magnetic equator. Anomalous, sometimes dramatic, additional magnetic-field-aligned ion acceleration also occurs in part as a result of a quasi-resonance between the parallel velocities of some ions and the propagating electric potential fronts. It is speculated that the convection surge mechanism could be a key player in the transient, field-aligned electromagnetic processes observed to operate within the middle (e.g., geosynchronous) magnetosphere. copyright American Geophysical Union 1989

Influence of Non-Uniform Magnetic Field on Quantum Teleportation in Heisenberg XY Model

Institute of Scientific and Technical Information of China (English)

SHAO Bin; YANG Tie-jian; ZHAO Yue-hong; ZOU Jian

2007-01-01

By considering the intrinsic decoherence, the validity of quantum teleportation of a two-qubit 1D Heisenberg XY chain in a non-uniform external magnetic field is studied. The fidelity as the measurement of a possible quantum teleportation is calculated and the effects of the non-uniform magnetic field and the intrinsic decoherence are discussed. It is found that anti-parallel magnetic field is more favorable for teleportation and the fidelity is suppressed by the intrinsic decoherence.

Hybridization of electron states in a step quantum well in a magnetic field

International Nuclear Information System (INIS)

Barseghyan, M.G.; Kirakosyan, A.A.

2005-01-01

The quantum states and energy levels of an electrion in a rectangular step quantum well in a magnetic field parallel to the plane of two-dimentional electron gas are investigated. It is shown that the joint effect of the magnetic field and confining potential of the quantum well results in redical change of the electron spectrum. The dependence of the electron energy levels on the quantum well parameters, magnetic field induction and projection of the wave-vector along the magnetic field induction are calculated. Numerical calculations are carried out for a AlAs/GaAlAs/GaAs/AlAs step quantum well

Stochastic field-line wandering in magnetic turbulence with shear. II. Decorrelation trajectory method

Science.gov (United States)

Negrea, M.; Petrisor, I.; Shalchi, A.

2017-11-01

We study the diffusion of magnetic field lines in turbulence with magnetic shear. In the first part of the series, we developed a quasi-linear theory for this type of scenario. In this article, we employ the so-called DeCorrelation Trajectory method in order to compute the diffusion coefficients of stochastic magnetic field lines. The magnetic field configuration used here contains fluctuating terms which are described by the dimensionless functions bi(X, Y, Z), i = (x, y) and they are assumed to be Gaussian processes and are perpendicular with respect to the main magnetic field B0. Furthermore, there is also a z-component of the magnetic field depending on radial coordinate x (representing the gradient of the magnetic field) and a poloidal average component. We calculate the diffusion coefficients for magnetic field lines for different values of the magnetic Kubo number K, the dimensionless inhomogeneous magnetic parallel and perpendicular Kubo numbers KB∥, KB⊥ , as well as Ka v=bya vKB∥/KB⊥ .

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.

Confinement of plasma along shaped open magnetic fields from the centrifugal force of supersonic plasma rotation.

Science.gov (United States)

Teodorescu, C; Young, W C; Swan, G W S; Ellis, R F; Hassam, A B; Romero-Talamas, C A

2010-08-20

Interferometric density measurements in plasmas rotating in shaped, open magnetic fields demonstrate strong confinement of plasma parallel to the magnetic field, with density drops of more than a factor of 10. Taken together with spectroscopic measurements of supersonic E × B rotation of sonic Mach 2, these measurements are in agreement with ideal MHD theory which predicts large parallel pressure drops balanced by centrifugal forces in supersonically rotating plasmas.

Numerical analysis of magnetic field effects on hydro-thermal behavior of a magnetic nanofluid in a double pipe heat exchanger

Energy Technology Data Exchange (ETDEWEB)

Shakiba, Ali, E-mail: Shakiba7858@yahoo.com [Department of Mechanical Engineering, Mazandaran Institute of Technology, Babol (Iran, Islamic Republic of); Vahedi, Khodadad, E-mail: Khvahedi@ihu.ac.ir [Department of Mechanical Engineering, Imam Hossein University, Tehran (Iran, Islamic Republic of)

2016-03-15

This study attempts to numerically investigate the hydro-thermal characteristics of a ferrofluid (water and 4 vol% Fe{sub 3}O{sub 4}) in a counter-current horizontal double pipe heat exchanger, which is exposed to a non-uniform transverse magnetic field with different intensities. The magnetic field is generated by an electric current going through a wire located parallel to the inner tube and between two pipes. The single phase model and the control volume technique have been used to study the flow. The effects of magnetic field have been added to momentum equation by applying C++ codes in Ansys Fluent 14. The results show that applying this kind of magnetic field causes kelvin force to be produced perpendicular to the ferrofluid flow, changing axial velocity profile and creating a pair of vortices which leads to an increase in Nusselt number, friction factor and pressure drop. Comparing the enhancement percentage of Nusselt number, friction factor and pressure drop demonstrates that the optimum value of magnetic number for Re{sub ff}=50 is between Mn=1.33×10{sup 6} and Mn=2.37×10{sup 6}. So applying non-uniform transverse magnetic field can control the flow of ferrofluid and improve heat transfer process of double pipe heat exchanger. - Highlights: • Effect of applying non-uniform transverse magnetic field on a ferrofluid for enhancing the cooling process in a double pipe heat exchanger is investigated. • Heat exchanger is exposed to a non-uniform transverse magnetic field with different intensities. • The magnetic field is generated by an electric current going through a wire located parallel to inner tube and between two pipes. • Applying this field produces kelvin force to change axial velocity profile and creating a pair of vortices increasing Nusselt number, friction factor and pressure drop.

The role of magnetic-field-aligned electric fields in auroral acceleration

International Nuclear Information System (INIS)

Block, L.P.; Faelthammar, C.G.

1990-01-01

Electric field measurements on the Swedish satellite Viking have confirmed and extended earlier observations on S3-3 and provided further evidence of the role of dc electric fields in auroral acceleration processes. On auroral magnetic field lines the electric field is strongly fluctuating both transverse and parallel to the magnetic field. The significance of these fluctuations for the auroral acceleration process is discussed. A definition of dc electric fields is given in terms of their effects on charged particles. Fluctuations below several hertz are experienced as dc by typical auroral electrons if the acceleration length is a few thousand kilometers. For ions the same is true below about 0.1 Hz. The magnetic-field-aligned (as well as the transverse) component of the electric field fluctuations has a maximum below 1 Hz, in a frequency range that appears as dc to the electrons but not to the ions. This allows it to cause a selective acceleration, which may be important in explaining some of the observed characteristics of auroral particle distributions. The electric field observations on Viking support the conclusion that magnetic-field-aligned potential drops play an important role in auroral acceleration, in good agreement with particle observations boht on Viking and on the DE satellites. They also show that a large part, or even all, of the accelerating potential drop may be accounted for by numerous weak (about a volt) electric double layers, in agreement with earlier observations on the S3-3 satellite and with an early theoretical suggestion by L. Block

Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

Science.gov (United States)

Lu, San; Artemyev, A. V.; Angelopoulos, V.

2017-11-01

Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at 18 - 25 RE to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature, leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling, causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.

MRI-related static magnetic stray fields and postural body sway: a double-blind randomized crossover study.

Science.gov (United States)

van Nierop, Lotte E; Slottje, Pauline; Kingma, Herman; Kromhout, Hans

2013-07-01

We assessed postural body sway performance after exposure to movement induced time-varying magnetic fields in the static magnetic stray field in front of a 7 Tesla (T) magnetic resonance imaging scanner. Using a double blind randomized crossover design, 30 healthy volunteers performed two balance tasks (i.e., standing with eyes closed and feet in parallel and then in tandem position) after standardized head movements in a sham, low exposure (on average 0.24 T static magnetic stray field and 0.49 T·s(-1) time-varying magnetic field) and high exposure condition (0.37 T and 0.70 T·s(-1)). Personal exposure to static magnetic stray fields and time-varying magnetic fields was measured with a personal dosimeter. Postural body sway was expressed in sway path, area, and velocity. Mixed-effects model regression analysis showed that postural body sway in the parallel task was negatively affected (P < 0.05) by exposure on all three measures. The tandem task revealed the same trend, but did not reach statistical significance. Further studies are needed to investigate the possibility of independent or synergetic effects of static magnetic stray field and time-varying magnetic field exposure. In addition, practical safety implications of these findings, e.g., for surgeons and others working near magnetic resonance imaging scanners need to be investigated. Copyright © 2012 Wiley Periodicals, Inc.

Technical Note: Response measurement for select radiation detectors in magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Reynolds, M., E-mail: michaelreynolds@ualberta.net [Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada); Fallone, B. G. [Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada and Departments of Oncology and Physics, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada); Rathee, S. [Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada and Department of Oncology, Medical Physics Division,University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada)

2015-06-15

Purpose: Dose response to applied magnetic fields for ion chambers and solid state detectors has been investigated previously for the anticipated use in linear accelerator–magnetic resonance devices. In this investigation, the authors present the measured response of selected radiation detectors when the magnetic field is applied in the same direction as the radiation beam, i.e., a longitudinal magnetic field, to verify previous simulation only data. Methods: The dose response of a PR06C ion chamber, PTW60003 diamond detector, and IBA PFD diode detector is measured in a longitudinal magnetic field. The detectors are irradiated with buildup caps and their long axes either parallel or perpendicular to the incident photon beam. In each case, the magnetic field dose response is reported as the ratio of detector signals with to that without an applied longitudinal magnetic field. The magnetic field dose response for each unique orientation as a function of magnetic field strength was then compared to the previous simulation only studies. Results: The measured dose response of each detector in longitudinal magnetic fields shows no discernable response up to near 0.21 T. This result was expected and matches the previously published simulation only results, showing no appreciable dose response with magnetic field. Conclusions: Low field longitudinal magnetic fields have been shown to have little or no effect on the dose response of the detectors investigated and further lend credibility to previous simulation only studies.

The Permanent Magnet Operating Mechanism of Double Coil Parallel Driven at a High Speed

Directory of Open Access Journals (Sweden)

WEI Xau-Lao

2017-02-01

Full Text Available Abstract:Operating mechanism is the main part of breaker，and the quality of breaker will directly influence the safe operation of power system. Because of the continuous improvement requirements of switch，in order to mak this actuator faster and more powerful closing，this paper proposes a double coil parallel driven permanent magnet actuator at a high speed. This paper expounds the working principle of single and double coil parallel driven permanent magnet actuator. It uses Ansoft building model and contrasts test results. In prance we designed and produced the single and double coil parallel driven permanent magnet actuator for experimental study. The simulation and experiment results show that double coil parallel driven permanent magnet actuator，compared with single coil parallel driven permanent magnet actuator，has a better and faster action performance. Thus，the double coil parallel driven permanent magnet actuator achieves a kind of optimization.

Effects of an external magnetic field in pulsed laser deposition

Science.gov (United States)

García, T.; de Posada, E.; Villagrán, M.; Ll, J. L. Sánchez; Bartolo-Pérez, P.; Peña, J. L.

2008-12-01

Thin films were grown by pulsed laser deposition, PLD, on Si (1 0 0) substrates by the ablation of a sintered ceramic SrFe 12O 19 target with and without the presence of a nonhomogeneous magnetic field of μ0H = 0.4 T perpendicular to substrate plane and parallel to the plasma expansion axis. The field was produced by a rectangular-shaped Nd-Fe-B permanent magnet and the substrate was just placed on the magnet surface (Aurora method). An appreciable increment of optical emission due to the presence of the magnetic field was observed, but no film composition change or thickness increment was obtained. It suggests that the increment of the optical emission is due mainly to the electron confinement rather than confinement of ionic species.

Effects of an external magnetic field in pulsed laser deposition

Energy Technology Data Exchange (ETDEWEB)

Garcia, T. [Universidad Autonoma de la Ciudad de Mexico (UACM), Prolongacion San Isidro 151, Col. San Lorenzo Tezonco, C.P. 09790, Mexico DF (Mexico)], E-mail: tupacgarcia@yahoo.com; Posada, E. de [CINVESTAV-IPN Unidad Merida, Applied Physics Department, A.P. 73, Cordemex, C.P. 97130 Merida, Yuc. (Mexico); Villagran, M. [CCADET, Universidad Nacional Autonoma de Mexico (UNAM), A.P. 70-186, C.P. 04510, Mexico DF (Mexico); Ll, J.L. Sanchez [Laboratorio de Magnetismo, Facultad de Fisica-IMRE, Universidad de La Habana, La Habana 10400 (Cuba); Bartolo-Perez, P.; Pena, J.L. [CINVESTAV-IPN Unidad Merida, Applied Physics Department, A.P. 73, Cordemex, C.P. 97130 Merida, Yuc. (Mexico)

2008-12-30

Thin films were grown by pulsed laser deposition, PLD, on Si (1 0 0) substrates by the ablation of a sintered ceramic SrFe{sub 12}O{sub 19} target with and without the presence of a nonhomogeneous magnetic field of {mu}{sub 0}H = 0.4 T perpendicular to substrate plane and parallel to the plasma expansion axis. The field was produced by a rectangular-shaped Nd-Fe-B permanent magnet and the substrate was just placed on the magnet surface (Aurora method). An appreciable increment of optical emission due to the presence of the magnetic field was observed, but no film composition change or thickness increment was obtained. It suggests that the increment of the optical emission is due mainly to the electron confinement rather than confinement of ionic species.

Motion and magnetic field structure of the Earth's magnetic tail near 30 R/sub E/

International Nuclear Information System (INIS)

Bowling, S.B.

1975-01-01

The analysis of data taken by the NASA-GSFC magnetometer experiment on the Explorer 34 spacecraft has shown that the diurnal wobble of the geomagnetic dipole axis measurably influences the position of the magnetotail near 30 R/sub E/ (earth radii). Viewed in the solar-ecliptic coordinate system, the dipole wobble resolves into components of motion perpendicular and parallel to the earth-sun line. The perpendicular component exerts a torque on the magnetotail and causes the neutral sheet (the midplane of the magnetotail) to pivot about an axis approximately parallel to the solar-wind flow direction. The parallel component encourages the neutral sheet to move above and below the solar-magnetospheric equatorial plane with an amplitude of 1 R/sub E/, as if the neutral sheet were hinged at a geocentric distance of 5.25 R/sub E/. The motion of the neutral sheet is also characterized by a random flapping in the solar-ecliptic Z-direction at a velocity of 100 km/sec and an amplitude of +- 2 R/sub E/. Results suggest the existence of a layer of nearly uniform cross-tail electric current that is about 2.3 R/sub E/ thick and envelops the neutral sheet. The magnetic field, whose average geometry resembles a flattened and extended dipole, gradually reverses direction within this current layer. The field is perpendicular to the neutral sheet where it has a value of 2 γ (1γ = 10 -5 Gauss). The analysis does not suggest a strong dependence of the magnetic-field configuration on the geomagnetic index Kp, although the field may intermittently disrupt into localized and short-lived magnetic loops during periods of enhanced geomagnetic activity

UNDERSTANDING THE GEOMETRY OF ASTROPHYSICAL MAGNETIC FIELDS

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada); Blandford, Roger D., E-mail: aeb@cita.utoronto.c [Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Rd., Menlo Park, CA 94309 (United States)

2010-08-01

Faraday rotation measurements have provided an invaluable technique for probing the properties of astrophysical magnetized plasmas. Unfortunately, typical observations provide information only about the density-weighted average of the magnetic field component parallel to the line of sight. As a result, the magnetic field geometry along the line of sight, and in many cases even the location of the rotating material, is poorly constrained. Frequently, interpretations of Faraday rotation observations are dependent upon underlying models of the magnetic field being probed (e.g., uniform, turbulent, equipartition). However, we show that at sufficiently low frequencies, specifically below roughly 13(RM/1 rad m{sup -2}){sup 1/4}(B/1 G){sup 1/2} MHz, the character of Faraday rotation changes, entering what we term the 'super-adiabatic regime' in which the rotation measure (RM) is proportional to the integrated absolute value of the line-of-sight component of the field. As a consequence, comparing RMs at high frequencies with those in this new regime provides direct information about the geometry of the magnetic field along the line of sight. Furthermore, the frequency defining the transition to this new regime, {nu}{sub SA}, depends directly upon the local electron density and magnetic field strength where the magnetic field is perpendicular to the line of sight, allowing the unambiguous distinction between Faraday rotation within and in front of the emission region. Typical values of {nu}{sub SA} range from 10 kHz (below the ionospheric cutoff, but above the heliospheric cutoff) to 10 GHz, depending upon the details of the Faraday rotating environment. In particular, for resolved active galactic nuclei, including the black holes at the center of the Milky Way (Sgr A*) and M81, {nu}{sub SA} ranges from roughly 10 MHz to 10 GHz, and thus can be probed via existing and up-coming ground-based radio observatories.

UNDERSTANDING THE GEOMETRY OF ASTROPHYSICAL MAGNETIC FIELDS

International Nuclear Information System (INIS)

Broderick, Avery E.; Blandford, Roger D.

2010-01-01

Faraday rotation measurements have provided an invaluable technique for probing the properties of astrophysical magnetized plasmas. Unfortunately, typical observations provide information only about the density-weighted average of the magnetic field component parallel to the line of sight. As a result, the magnetic field geometry along the line of sight, and in many cases even the location of the rotating material, is poorly constrained. Frequently, interpretations of Faraday rotation observations are dependent upon underlying models of the magnetic field being probed (e.g., uniform, turbulent, equipartition). However, we show that at sufficiently low frequencies, specifically below roughly 13(RM/1 rad m -2 ) 1/4 (B/1 G) 1/2 MHz, the character of Faraday rotation changes, entering what we term the 'super-adiabatic regime' in which the rotation measure (RM) is proportional to the integrated absolute value of the line-of-sight component of the field. As a consequence, comparing RMs at high frequencies with those in this new regime provides direct information about the geometry of the magnetic field along the line of sight. Furthermore, the frequency defining the transition to this new regime, ν SA , depends directly upon the local electron density and magnetic field strength where the magnetic field is perpendicular to the line of sight, allowing the unambiguous distinction between Faraday rotation within and in front of the emission region. Typical values of ν SA range from 10 kHz (below the ionospheric cutoff, but above the heliospheric cutoff) to 10 GHz, depending upon the details of the Faraday rotating environment. In particular, for resolved active galactic nuclei, including the black holes at the center of the Milky Way (Sgr A*) and M81, ν SA ranges from roughly 10 MHz to 10 GHz, and thus can be probed via existing and up-coming ground-based radio observatories.

Liquid-metal flow in a rectangular duct with a non-uniform magnetic field

International Nuclear Information System (INIS)

Walker, J.S.

1986-04-01

This paper treats liquid-metal flow in rectangular ducts with thin conducting walls. A transverse magnetic field changes from a uniform strength upstream to a weaker uniform strength downstream. The Hartmann number and the interaction parameter are assumed to be large, while the magnetic Reynolds number is assumed to be small. If the magnetic field changes gradually over a long duct length, the velocity and pressure are nearly uniform in each cross section and the flow differs slightly from locally fully developed flow. If the magnetic field changes more abruptly over a shorter duct length, the velocity and pressure are much larger near the walls parallel to the magnetic field than in the central part of duct. Solutions for the pressure drops due to the magnetic field change are presented

Magnetic field effects on the open circuit potential of ferromagnetic electrodes in corroding solutions.

Science.gov (United States)

Dass, Amala; Counsil, Joseph A; Gao, Xuerong; Leventis, Nicholas

2005-06-02

Magnetic fields shift the open circuit potential (OCP) of ferromagnetic electrodes (Fe, Co, and Ni) in corroding solutions. The OCP changes we observe (a) follow the series Fe>Co>Ni; (b) increase with the magnetic flux density; (c) reach a maximum with disk electrodes approximately 1 mm in diameter; and (d) depend on the orientation of the electrode. We report that when the surface of the electrode is oriented parallel (theta = 90 degrees) or perpendicular (theta = 0 degrees) to the magnetic field, the open circuit potential moves in opposite directions (positive and negative, respectively) with the largest changes occurring when the electrode surface is parallel to the magnetic field. Nonconvective sleeve electrodes produce the same behavior. The overall experimental evidence suggests that the magnetic field changes the OCP by modifying the surface concentrations of the paramagnetic participants in the corrosion process of the ferromagnetic electrode by species in solution; this in turn is accomplished by imposing a field-gradient driven mode of mass transfer upon paramagnetic species in solution (magnetophoresis). Simulations of the magnetic field around the ferromagnetic electrode at the two extreme orientations considered here show that in one case (theta = 90 degrees) field gradients actually repel, while in the other case (theta = 0 degrees) they attract paramagnetic species in the vicinity of the electrode.

Magnetic fields and proper motions of sunspots. 1

International Nuclear Information System (INIS)

Kalman, B.

1976-01-01

Determining relation between magnetic fields and intrinsic motions of the Sun spots is considered. Based on daily maps of the longitudinal H 1 and transverse H 2 constituents of the magnetic field and a series of photographs of the Sun a comparison was made of motion of shadow nuclei and semishadow fibres with the structure of the magnetic field in the Sun spot group from 7 till 14 of June, 1969. It was found that the spots moved both along and across the direction of the transverse magnetic field. During the movement of spots changes in the structure of H 2 occurred which in the most cases corresponded to reorientation of lines of force along the trajectory behind the moving spot. However, in some cases the structure of the transverse field behind the moving spot became close to the perpendicular one to the trajectory of the past spot, although it could be almost parallel to the trajectory in front of the spot. The best coincidence of orientations of the spot trajectories with the H 2 structure was obtained near the zero line of the longitudinal field. The orientation of fibres of semishadows along H 2 was observed when the group was near the central meridian

Novel computational approaches for the analysis of cosmic magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Saveliev, Andrey [Universitaet Hamburg, Hamburg (Germany); Keldysh Institut, Moskau (Russian Federation)

2016-07-01

In order to give a consistent picture of cosmic, i.e. galactic and extragalactic, magnetic fields, different approaches are possible and often even necessary. Here we present three of them: First, a semianalytic analysis of the time evolution of primordial magnetic fields from which their properties and, subsequently, the nature of present-day intergalactic magnetic fields may be deduced. Second, the use of high-performance computing infrastructure by developing powerful algorithms for (magneto-)hydrodynamic simulations and applying them to astrophysical problems. We are currently developing a code which applies kinetic schemes in massive parallel computing on high performance multiprocessor systems in a new way to calculate both hydro- and electrodynamic quantities. Finally, as a third approach, astroparticle physics might be used as magnetic fields leave imprints of their properties on charged particles transversing them. Here we focus on electromagnetic cascades by developing a software based on CRPropa which simulates the propagation of particles from such cascades through the intergalactic medium in three dimensions. This may in particular be used to obtain information about the helicity of extragalactic magnetic fields.

Statistical Study of the Magnetic Field Orientation in Solar Filaments

Science.gov (United States)

Hanaoka, Yoichiro; Sakurai, Takashi

2017-12-01

We have carried out a statistical study of the average orientation of the magnetic field in solar filaments with respect to their axes for more than 400 samples, based on data taken with daily full-Sun, full-Stokes spectropolarimetric observations using the He I 1083.0 nm line. The major part of the samples are the filaments in the quiet areas, but those in the active areas are included as well. The average orientation of the magnetic field in filaments shows a systematic property depending on the hemisphere; the direction of the magnetic field in filaments in the northern (southern) hemisphere mostly deviates clockwise (counterclockwise) from their axes, which run along the magnetic polarity inversion line. The deviation angles of the magnetic field from the axes are concentrated between 10° and 30°. This hemispheric pattern is consistent with that revealed for chirality of filament barbs, filament channels, and for other solar features found to possess chirality. For some filaments, it was confirmed that their magnetic field direction is locally parallel to their structure seen in Hα images. Our results for the first time confirmed this hemispheric pattern with the direct observation of the magnetic field in filaments. Interestingly, the filaments which show the opposite magnetic field deviation to the hemispheric pattern, are in many cases found above the polarity inversion line whose ambient photospheric magnetic field has the polarity alignment being opposite to that of active regions following the Hale–Nicholson law.

The interaction of vacuum arcs with magnetic fields and applications

International Nuclear Information System (INIS)

Gorman, J.G.; Kimblin, C.W.; Slade, P.G.; Voshall, R.E.; Wien, R.E.

1983-01-01

Vacuum arc/magnetic field interactions are reviewed and extended. An axial magnetic field (parallel to current flow) produces a stable and diffuse vacuum arc. These properties have been used to build a reliable dc switch for the Tokamak Fusion Test Reactor at Princeton. The switching duty for this Ohmic Heating Interrupter involves repetitive interruption of 24kA dc against a 27kV recovery voltage. A transverse magnetic field (perpendicular to current flow) produces an unstable arc with an ensuing high arc voltage. This property has been used to complete a metallic return transfer breaker for the Pacific HVDC Intertie, here the switching duty involves interruption of currents up to 2200A dc against an 80kV recovery voltage

effect of brinkman number and magnetic field on laminar convection ...

African Journals Online (AJOL)

Joseph et al.

Science World Journal Vol 12(No 4) 2017 ... Joule heating on the fully developed MHD flow with heat transfer .... fluid in a vertical parallel – plate with effect of magnetic field and ..... Plates Channel, Proceedings of the 2013 International.

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.

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.

Spin polarization of a non-magnetic high g-factor semiconductor at low magnetic field

International Nuclear Information System (INIS)

Lee, J.; Back, J.; Kim, K.H.; Kim, S.U.; Joo, S.; Rhie, K.; Hong, J.; Shin, K.; Lee, B.C.; Kim, T.

2007-01-01

We have studied the spin polarization of HgCdTe by measuring Shubnikov-de Haas oscillations. The magnetic field have been applied in parallel and perpendicular to the current. Relatively long spin relaxation time was observed since only spin conserved transition is allowed by selection rules. The electronic spin is completely polarized when the applied magnetic field is larger than 0.5 Tesla, which can be easily generated by micromagnets deposited on the surface of the specimen. Thus, the spin-manipulation such as spin up/down junction can be realized with this semiconductor. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

The exotic molecular ion H43+ in a strong magnetic field

International Nuclear Information System (INIS)

Olivares P, H.

2006-01-01

Using the variational method, a detailed study of the lowest m = 0, -1 electronic states of the exotic molecular ion H3+ 4 in a strong magnetic field, in the linear symmetric configuration parallel to the direction of the magnetic field is carried out. A extended study of the 1σg ground state (J.C. Lopez and A.Turbiner, Phys. Rev A 62, 022510, 2000) was performed obtaining that the potential energy curve displays a sufficiently deep minimum for finite internuclear distances, indicating the possible existence of the molecular ion H 4 3+ , for magnetic fields of strength B > ∼ 3 x 10 13 G. It is demonstrated that the excited state 1π u , can exist for a magnetic field B = 4.414 x 10 13 G corresponding to the limit of applicability of the non-relativistic theory. (Author)

Theoretical predictions for spatially-focused heating of magnetic nanoparticles guided by magnetic particle imaging field gradients

Energy Technology Data Exchange (ETDEWEB)

Dhavalikar, Rohan [Department of Chemical Engineering, University of Florida, 1030 Center Drive, Gainesville, FL 32611 (United States); Rinaldi, Carlos, E-mail: carlos.rinaldi@bme.ufl.edu [Department of Chemical Engineering, University of Florida, 1030 Center Drive, Gainesville, FL 32611 (United States); J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, 1275 Center Drive, Gainesville, FL 32611 (United States)

2016-12-01

Magnetic nanoparticles in alternating magnetic fields (AMFs) transfer some of the field's energy to their surroundings in the form of heat, a property that has attracted significant attention for use in cancer treatment through hyperthermia and in developing magnetic drug carriers that can be actuated to release their cargo externally using magnetic fields. To date, most work in this field has focused on the use of AMFs that actuate heat release by nanoparticles over large regions, without the ability to select specific nanoparticle-loaded regions for heating while leaving other nanoparticle-loaded regions unaffected. In parallel, magnetic particle imaging (MPI) has emerged as a promising approach to image the distribution of magnetic nanoparticle tracers in vivo, with sub-millimeter spatial resolution. The underlying principle in MPI is the application of a selection magnetic field gradient, which defines a small region of low bias field, superimposed with an AMF (of lower frequency and amplitude than those normally used to actuate heating by the nanoparticles) to obtain a signal which is proportional to the concentration of particles in the region of low bias field. Here we extend previous models for estimating the energy dissipation rates of magnetic nanoparticles in uniform AMFs to provide theoretical predictions of how the selection magnetic field gradient used in MPI can be used to selectively actuate heating by magnetic nanoparticles in the low bias field region of the selection magnetic field gradient. Theoretical predictions are given for the spatial decay in energy dissipation rate under magnetic field gradients representative of those that can be achieved with current MPI technology. These results underscore the potential of combining MPI and higher amplitude/frequency actuation AMFs to achieve selective magnetic fluid hyperthermia (MFH) guided by MPI. - Highlights: • SAR predictions based on a field-dependent magnetization relaxation model. �

Designing magnets with prescribed magnetic fields

International Nuclear Information System (INIS)

Liu Liping

2011-01-01

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

Can primordial magnetic fields seeded by electroweak strings cause an alignment of quasar axes on cosmological scales?

Science.gov (United States)

Poltis, Robert; Stojkovic, Dejan

2010-10-15

The decay of nontopological electroweak strings may leave an observable imprint in the Universe today in the form of primordial magnetic fields. Protogalaxies preferentially tend to form with their axis of rotation parallel to an external magnetic field, and, moreover, an external magnetic field produces torque which tends to align the galaxy axis with the magnetic field. We demonstrate that the shape of a magnetic field left over from two looped electroweak strings can explain the observed nontrivial alignment of quasar polarization vectors and make predictions for future observations.

On Multiple Hall-Like Electron Currents and Tripolar Guide Magnetic Field Perturbations During Kelvin-Helmholtz Waves

Science.gov (United States)

Sturner, Andrew P.; Eriksson, Stefan; Nakamura, Takuma; Gershman, Daniel J.; Plaschke, Ferdinand; Ergun, Robert E.; Wilder, Frederick D.; Giles, Barbara; Pollock, Craig; Paterson, William R.; Strangeway, Robert J.; Baumjohann, Wolfgang; Burch, James L.

2018-02-01

Two magnetopause current sheet crossings with tripolar guide magnetic field signatures were observed by multiple Magnetosphere Multiscale (MMS) spacecraft during Kelvin-Helmholtz wave activity. The two out-of-plane magnetic field depressions of the tripolar guide magnetic field are largely supported by the observed in-plane electron currents, which are reminiscent of two clockwise Hall current loop systems. A comparison with a three-dimensional kinetic simulation of Kelvin-Helmholtz waves and vortex-induced reconnection suggests that MMS likely encountered the two Hall magnetic field depressions on either side of a magnetic reconnection X-line. Moreover, MMS observed an out-of-plane current reversal and a corresponding in-plane magnetic field rotation at the center of one of the current sheets, suggesting the presence of two adjacent flux ropes. The region inside one of the ion-scale flux ropes was characterized by an observed decrease of the total magnetic field, a strong axial current, and significant enhancements of electron density and parallel electron temperature. The flux rope boundary was characterized by currents opposite this axial current, strong in-plane and converging electric fields, parallel electric fields, and weak electron-frame Joule dissipation. These return current region observations may reflect a need to support the axial current rather than representing local reconnection signatures in the absence of any exhausts.

Specific heat of heavy-fermion CePd2Si2 in high magnetic fields

International Nuclear Information System (INIS)

Sheikin, I.; Wang, Y.; Bouquet, F.; Junod, A.; Lejay, P.

2002-01-01

We report specific heat measurements on the heavy-fermion compound CePd 2 Si 2 in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp peak in the specific heat signals the antiferromagnetic transition at T N ∼ 9.3 K in zero field. The transition is found to shift to lower temperatures when a magnetic field is applied along the crystallographic a-axis, while a field applied parallel to the tetragonal c-axis does not affect the transition. The magnetic contribution to the specific heat below T N is well described by a sum of a linear electronic term and an antiferromagnetic spin-wave contribution. Just below T N , an additional positive curvature, especially at high fields, arises most probably due to thermal fluctuations. The field dependence of the coefficient of the low-temperature linear term, γ 0 , extracted from the fits shows a maximum at about 6 T, at the point where an anomaly was detected in susceptibility measurements. The relative field dependences of both T N and the magnetic entropy at T N scale as [1-(B/B 0 ) 2 ] for B parallel a, suggesting the disappearance of antiferromagnetism at B 0 ∼42 T. The expected suppression of the antiferromagnetic transition temperature to zero makes the existence of a magnetic quantum critical point possible. (author). Letter-to-the-editor

Linear Analysis of Converging Richtmyer-Meshkov Instability in the Presence of an Azimuthal Magnetic Field

KAUST Repository

Bakhsh, Abeer; Samtaney, Ravindra

2017-01-01

We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.

Linear Analysis of Converging Richtmyer-Meshkov Instability in the Presence of an Azimuthal Magnetic Field

KAUST Repository

Bakhsh, Abeer

2017-11-17

We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.

Dirac particles in the field of magnetic monopoles and of strong electric charges

International Nuclear Information System (INIS)

Schafer, A.; Muller, B.; Greiner, W.

1985-01-01

The field of a magnetic pointlike monopole acts in a similar way on a charged Dirac particle as the field of a very strong electric point charge. To explore this parallel it is constructed a field solution for an extended magnetic-charge distribution. In contrast to what is found for extended electric charges, the Hamiltonian remains nonself-adjoint for an extended magnetic monopole. This suggests that there exist a fundamental difference between the two cases. In particular, the appearance of undefined states for point monopoles is not a consequence of the mere strength of the magnetic-monopole charge, which has a minimum value fixed by Dirac's quantization condition

Diffusion of charged particles in strong large-scale random and regular magnetic fields

International Nuclear Information System (INIS)

Mel'nikov, Yu.P.

2000-01-01

The nonlinear collision integral for the Green's function averaged over a random magnetic field is transformed using an iteration procedure taking account of the strong random scattering of particles on the correlation length of the random magnetic field. Under this transformation the regular magnetic field is assumed to be uniform at distances of the order of the correlation length. The single-particle Green's functions of the scattered particles in the presence of a regular magnetic field are investigated. The transport coefficients are calculated taking account of the broadening of the cyclotron and Cherenkov resonances as a result of strong random scattering. The mean-free path lengths parallel and perpendicular to the regular magnetic field are found for a power-law spectrum of the random field. The analytical results obtained are compared with the experimental data on the transport ranges of solar and galactic cosmic rays in the interplanetary magnetic field. As a result, the conditions for the propagation of cosmic rays in the interplanetary space and a more accurate idea of the structure of the interplanetary magnetic field are determined

One phonon resonant Raman scattering in semiconductor quantum wires: Magnetic field effect

Energy Technology Data Exchange (ETDEWEB)

Betancourt-Riera, Re., E-mail: rbriera@posgrado.cifus.uson.mx [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonor, (Mexico); Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico); Betancourt-Riera, Ri. [Instituto Tecnologico de Hermosillo, Avenida Tecnologico S/N, Colonia Sahuaro, C.P. 83170, Hermosillo, Sonora (Mexico); Nieto Jalil, J.M. [Tecnologico de Monterrey-Campus Sonora Norte, Bulevar Enrique Mazon Lopez No. 965, C.P. 83000, Hermosillo, Sonora (Mexico); Riera, R. [Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-088, C.P. 83190, Hermosillo, Sonora (Mexico)

2013-02-01

We have developed a theory of one phonon resonant Raman scattering in a semiconductor quantum wire of cylindrical geometry in the presence of an external magnetic field distribution, parallel to the cylinder axis. The effect of the magnetic field in the electron and hole states, and in the Raman scattering efficiency, is determinate. We consider the electron-phonon interaction using a Froehlich-type Hamiltonian, deduced for the case of complete confinement phonon modes by Comas and his collaborators. We also assume T=0 K, a single parabolic conduction and valence bands. The spectra are discussed for different magnetic field values and the selection rules for the processes are also studied.

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...

Single-shot imaging with higher-dimensional encoding using magnetic field monitoring and concomitant field correction.

Science.gov (United States)

Testud, Frederik; Gallichan, Daniel; Layton, Kelvin J; Barmet, Christoph; Welz, Anna M; Dewdney, Andrew; Cocosco, Chris A; Pruessmann, Klaas P; Hennig, Jürgen; Zaitsev, Maxim

2015-03-01

PatLoc (Parallel Imaging Technique using Localized Gradients) accelerates imaging and introduces a resolution variation across the field-of-view. Higher-dimensional encoding employs more spatial encoding magnetic fields (SEMs) than the corresponding image dimensionality requires, e.g. by applying two quadratic and two linear spatial encoding magnetic fields to reconstruct a 2D image. Images acquired with higher-dimensional single-shot trajectories can exhibit strong artifacts and geometric distortions. In this work, the source of these artifacts is analyzed and a reliable correction strategy is derived. A dynamic field camera was built for encoding field calibration. Concomitant fields of linear and nonlinear spatial encoding magnetic fields were analyzed. A combined basis consisting of spherical harmonics and concomitant terms was proposed and used for encoding field calibration and image reconstruction. A good agreement between the analytical solution for the concomitant fields and the magnetic field simulations of the custom-built PatLoc SEM coil was observed. Substantial image quality improvements were obtained using a dynamic field camera for encoding field calibration combined with the proposed combined basis. The importance of trajectory calibration for single-shot higher-dimensional encoding is demonstrated using the combined basis including spherical harmonics and concomitant terms, which treats the concomitant fields as an integral part of the encoding. © 2014 Wiley Periodicals, Inc.

Quark pair creation in color electric fields and effects of magnetic fields

International Nuclear Information System (INIS)

Tanji, Noato

2010-01-01

The time evolution of a system where a uniform and classical SU(3) color electric field and quantum fields of quarks interact with each other is studied focusing on non-perturbative pair creation and its back reaction. We characterize a color direction of an electric field in a gauge invariant way, and investigate its dependence. Momentum distributions of created quarks show plasma oscillation as well as quantum effects such as the Pauli blocking and interference. Pressure of the system is also calculated, and we show that pair creation moderates degree of anisotropy of pressure. Furthermore, enhancement of pair creation and induction of chiral charge under a color magnetic field which is parallel to an electric field are discussed.

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.

Enhancement of grain size and crystallinity of thin layers of pentacene grown under magnetic field

Energy Technology Data Exchange (ETDEWEB)

Tabata, Kenichi [Division of Materials Science, Faculty of pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Yamamoto, Yohei, E-mail: yamamoto@ims.tsukuba.ac.jp [Division of Materials Science, Faculty of pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), Faculty of pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Center for Integrated Research in Fundamental Science and Technology (CiRfSE), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571 (Japan)

2016-03-31

Field-effect mobilities (μ) of pentacene films, prepared by a thermal deposition under a magnetic field (H-field), were largely enhanced, in comparison with that prepared without an H-field. Under a perpendicular H-field with respect to the substrate surface, the crystallinity of the edge-on pentacene orientation is enhanced, resulting in the 9-fold enhancement of μ. Furthermore, under parallel H-field with respect to the substrate surface, μ of the pentacene films were 23-fold greater than that prepared without the H-field. The surface morphology studies by atomic force microscopy of the ultra thin films of pentacene clarified that the grain size of the pentacene at the interface with the substrate is larger for films under parallel H-field than that prepared without an H-field. The simple and effective method for enhancing the semiconducting properties of the organic thin films gives high technological impact in its application to organic electronics. - Highlights: • Magnetic-field effect on the crystallinity of pentacene thin films • Magnetic-field effect on the morphology of pentacene thin films • Enhanced field-effect charge carrier mobility of pentacene thin films.

Enhancement of grain size and crystallinity of thin layers of pentacene grown under magnetic field

International Nuclear Information System (INIS)

Tabata, Kenichi; Yamamoto, Yohei

2016-01-01

Field-effect mobilities (μ) of pentacene films, prepared by a thermal deposition under a magnetic field (H-field), were largely enhanced, in comparison with that prepared without an H-field. Under a perpendicular H-field with respect to the substrate surface, the crystallinity of the edge-on pentacene orientation is enhanced, resulting in the 9-fold enhancement of μ. Furthermore, under parallel H-field with respect to the substrate surface, μ of the pentacene films were 23-fold greater than that prepared without the H-field. The surface morphology studies by atomic force microscopy of the ultra thin films of pentacene clarified that the grain size of the pentacene at the interface with the substrate is larger for films under parallel H-field than that prepared without an H-field. The simple and effective method for enhancing the semiconducting properties of the organic thin films gives high technological impact in its application to organic electronics. - Highlights: • Magnetic-field effect on the crystallinity of pentacene thin films • Magnetic-field effect on the morphology of pentacene thin films • Enhanced field-effect charge carrier mobility of pentacene thin films

Influence of the magnetic field on tadpole metamorphosis

International Nuclear Information System (INIS)

Grimaldi, S.; Lisi, A.; Rieti, S.; Manni, V.; Ravagnan, G.; Eremenko, T.; Volpe, P.; Pozzi, D.; Giuliani, L.; Volpe, P.

2000-01-01

This investigation showed the effect of 2 mT magnetic field AC at 50 Hz on populations of Xenopus laevis tadpoles. In the course of 65-day exposure to this field, while their survival showed small but significant decrease (P<0.0002), striking parallel 6-day shift in their maturation frequency and heavy impairment of their metamorphosis were observed. The metamorphosis was successful for 85% of individuals in the unirradiated tadpole population and for 45% of individuals in the irradiated one

Foucault imaging and small-angle electron diffraction in controlled external magnetic fields.

Science.gov (United States)

Nakajima, Hiroshi; Kotani, Atsuhiro; Harada, Ken; Ishii, Yui; Mori, Shigeo

2016-12-01

We report a method for acquiring Foucault images and small-angle electron diffraction patterns in external magnetic fields using a conventional transmission electron microscope without any modification. In the electron optical system that we have constructed, external magnetic fields parallel to the optical axis can be controlled using the objective lens pole piece under weak excitation conditions in the Foucault mode and the diffraction mode. We observe two ferromagnetic perovskite-type manganese oxides, La 0.7 Sr 0.3 MnO 3 (LSMO) and Nd 0.5 Sr 0.5 MnO 3 , in order to visualize magnetic domains and their magnetic responses to external magnetic fields. In rhombohedral-structured LSMO, pinning of magnetic domain walls at crystallographic twin boundaries was found to have a strong influence on the generation of new magnetic domains in external applied magnetic fields. © The Author 2016. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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

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

Parametric instabilities in an electron beam-plasma system: magnetic field effects

International Nuclear Information System (INIS)

Gell, Y.; Levush, B.; Nakach, R.

1981-09-01

The effects of a magnetic field on the excitation of low-frequency parametric instabilities in a beam-plasma system are considered. The dispersion relation of the three-dimensional beamless configuration, is analytically evaluated for an electrostatic pump wave having a finite wave-vector parallel to the magnetic field. The results of this analysis serve as a guide to the numerical study of the stability of the involved system including the beam. As for the one-dimensional case, one finds that two low-frequency electrostatic instability branches having different growth rates may exist simultaneously. The effects of the magnetic field on these instabilities could be summarized as follows: the small growth rate instability is negligibly small when the electron gyrofrequency is about equal to the pump wave frequency. This instability is magnetic field independent for high enough values of the field. When the plasma electron Debye length is greater than the beam electron Debye length, a large growth rate instability is excited and appears to be weakly dependent on the magnetic field, while the two instability branches are quite sensitive to change of the magnetic field, when the two Debye lengths are equal. Other characteristics of this system are also discussed

The plasma-wall transition layers in the presence of collisions with a magnetic field parallel to the wall

Science.gov (United States)

Moritz, J.; Faudot, E.; Devaux, S.; Heuraux, S.

2018-01-01

The plasma-wall transition is studied by means of a particle-in-cell (PIC) simulation in the configuration of a parallel to the wall magnetic field (B), with collisions between charged particles vs. neutral atoms taken into account. The investigated system consists of a plasma bounded by two absorbing walls separated by 200 electron Debye lengths (λd). The strength of the magnetic field is chosen such as the ratio λ d / r l , with rl being the electron Larmor radius, is smaller or larger than unity. Collisions are modelled with a simple operator that reorients randomly ion or electron velocity, keeping constant the total kinetic energy of both the neutral atom (target) and the incident charged particle. The PIC simulations show that the plasma-wall transition consists in a quasi-neutral region (pre-sheath), from the center of the plasma towards the walls, where the electric potential or electric field profiles are well described by an ambipolar diffusion model, and in a second region at the vicinity of the walls, called the sheath, where the quasi-neutrality breaks down. In this peculiar geometry of B and for a certain range of the mean-free-path, the sheath is found to be composed of two charged layers: the positive one, close to the walls, and the negative one, towards the plasma and before the neutral pre-sheath. Depending on the amplitude of B, the spatial variation of the electric potential can be non-monotonic and presents a maximum within the sheath region. More generally, the sheath extent as well as the potential drop within the sheath and the pre-sheath is studied with respect to B, the mean-free-path, and the ion and electron temperatures.

Influence of magnetic field on thermohydraulic and corrosion in the case of the water-cooled blanket concept

International Nuclear Information System (INIS)

Flament, T.; Terlain, A.; Sannier, J.; Labbe, P.

1990-01-01

Two CELIMENE modules have been operated during 3000 hours at the same maximum temperature (450 deg C) but the first one without magnetic field and the second one in the presence of a 1.4 T magnetic field. Comparison of dissolution and deposition rates obtained in parallel and perpendicular directions evidences that the magnetic field induces a dissymmetry for these two phenomena. Moreover the results obtained in the two CELIMENE tests show that the corrosion rate appears to be increased by the magnetic field

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.

SU-F-J-147: Magnetic Field Dose Response Considerations for a Linac Monitor Chamber

Energy Technology Data Exchange (ETDEWEB)

Reynolds, M; Fallone, B [Cross Cancer Institute, Edmonton, AB (Canada)

2016-06-15

Purpose: The impact of magnetic fields on the readings of a linac monitor chamber have not yet been investigated. Herein we examine the total dose response as well as any deviations in the beam parameters of flatness and symmetry when a Varian monitor chamber is irradiated within an applied magnetic field. This work has direct application to the development of Linac-MR systems worldwide. Methods: A Varian monitor chamber was modeled in the Monte Carlo code PENELOPE and irradiated in the presence of a magnetic field with a phase space generated from a model of a Linac-MR prototype system. The magnetic field strength was stepped from 0 to 3.0T in both parallel and perpendicular directions with respect to the normal surface of the phase space. Dose to each of the four regions in the monitor chamber were scored separately for every magnetic field adaptation to evaluate the effect of the magnetic field on flatness and symmetry. Results: When the magnetic field is perpendicular to the phase space normal we see a change in dose response with a maximal deviation (10–25% depending on the chamber region) near 0.75T. In the direction of electron deflection we expectedly see opposite responses in chamber regions leading to a measured asymmetry. With a magnetic field parallel to the phase space normal we see no measured asymmetries, however there is a monotonic rise in dose response leveling off at about +12% near 2.5T. Conclusion: Attention must be given to correct for the strength and direction of the magnetic field at the location of the linac monitor chamber in hybrid Linac-MR devices. Elsewise the dose sampled by these chambers may not represent the actual dose expected at isocentre; additionally there may be a need to correct for the symmetry of the beam recorded by the monitor chamber. Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi-planar linac MR for commercialization).

Electrostatic ion-cyclotron waves in a nonuniform magnetic field

International Nuclear Information System (INIS)

Cartier, S.L.; D'Angelo, N.; Merlino, R.L.

1985-01-01

The properties of electrostatic ion-cyclotron waves excited in a single-ended cesium Q machine with a nonuniform magnetic field are described. The electrostatic ion-cyclotron waves are generated in the usual manner by drawing an electron current to a small exciter disk immersed in the plasma column. The parallel and perpendicular (to B) wavelengths and phase velocities are determined by mapping out two-dimensional wave phase contours. The wave frequency f depends on the location of the exciter disk in the nonuniform magnetic field, and propagating waves are only observed in the region where f> or approx. =f/sub c/i, where f/sub c/i is the local ion-cyclotron frequency. The parallel phase velocity is in the direction of the electron drift. From measurements of the plasma properties along the axis, it is inferred that the electron drift velocity is not uniform along the entire current channel. The evidence suggests that the waves begin being excited at that axial position where the critical drift velocity is first exceeded, consistent with a current-driven excitation mechanism

Improved modelling of a parallel plate active magnetic regenerator

International Nuclear Information System (INIS)

Engelbrecht, K; Nielsen, K K; Bahl, C R H; Tušek, J; Kitanovski, A; Poredoš, A

2013-01-01

Much of the active magnetic regenerator (AMR) modelling presented in the literature considers only the solid and fluid domains of the regenerator and ignores other physical effects that have been shown to be important, such as demagnetizing fields in the regenerator, parasitic heat losses and fluid flow maldistribution in the regenerator. This paper studies the effects of these loss mechanisms and compares theoretical results with experimental results obtained on an experimental AMR device. Three parallel plate regenerators were tested, each having different demagnetizing field characteristics and fluid flow maldistributions. It was shown that when these loss mechanisms are ignored, the model significantly over predicts experimental results. Including the loss mechanisms can significantly change the model predictions, depending on the operating conditions and construction of the regenerator. The model is compared with experimental results for a range of fluid flow rates and cooling loads. (paper)

Donor impurity binding energies of coaxial GaAs / Alx Ga1 - x As cylindrical quantum wires in a parallel applied magnetic field

Science.gov (United States)

Tshipa, M.; Winkoun, D. P.; Nijegorodov, N.; Masale, M.

2018-04-01

Theoretical investigations are carried out of binding energies of a donor charge assumed to be located exactly at the center of symmetry of two concentric cylindrical quantum wires. The intrinsic confinement potential in the region of the inner cylinder is modeled in any one of the three profiles: simple parabolic, shifted parabolic or the polynomial potential. The potential inside the shell is taken to be a potential step or potential barrier of a finite height. Additional confinement of the charge carriers is due to the vector potential of the axial applied magnetic field. It is found that the binding energies attain maxima in their variations with the radius of the inner cylinder irrespective of the particular intrinsic confinement of the inner cylinder. As the radius of the inner cylinder is increased further, the binding energies corresponding to either the parabolic or the polynomial potentials attain minima at some critical core-radius. Finally, as anticipated, the binding energies increase with the increase of the parallel applied magnetic field. This behaviour of the binding energies is irrespective of the particular electric potential of the nanostructure or its specific dimensions.

Estimate of an environmental magnetic field of fast radio bursts

International Nuclear Information System (INIS)

Lin, Wei-Li; Dai, Zi-Gao

2016-01-01

Fast radio bursts (FRBs) are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown distances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method. Starting with dispersion measures and rotation measures (RMs), we try to obtain the parallel magnetic field component B-bar ‖ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifts are now unavailable, we demonstrate the dependence of B-bar ‖ on these two separate quantities. This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB. (paper)

Magnetic phase diagrams of UNiGe

International Nuclear Information System (INIS)

Nakotte, H.; Hagmusa, I.H.; Klaasse, J.C.P.; Hagmusa, I.H.; Klaasse, J.C.P.

1997-01-01

UNiGe undergoes two magnetic transitions in zero field. Here, the magnetic diagrams of UNiGe for B parallel b and B parallel c are reported. We performed temperatures scans of the magnetization in static magnetic fields up to 19.5T applied along the b and c axes. For both orientations 3 magnetic phases have been identified in the B-T diagrams. We confirmed the previously reported phase boundaries for B parallel c, and in addition we determined the location of the phase boundaries for B parallel b. We discuss a possible relationship of the two zero-field antiferromagnetic phases (commensurate: T<42K; incommensurate: 42K< T<50K) and the field-induced phase, which, at low temperatures, occurs between 18 and 25T or 4 and 10T for B parallel b or B parallel c, respectively. Finally, we discuss the field dependence of the electronic contribution γ to the specific heat for B parallel c up to 17.5T, and we find that its field dependence is similar to the one found in more itinerant uranium compounds

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.

Magnetic field profiles during turbulent heating in a toroidal hydrogen plasma

International Nuclear Information System (INIS)

Kalfsbeek, H.W.

1978-12-01

A description is given of the measurements of both poloidal and toroidal magnetic field components as functions of radius and time in a small turbulently heated tokamak. These measurements have been carried out with an array of miniature pick-up coils, enclosed in a quartz tube which is inserted into the plasma. The electric fields inside the plasma, as well as the parallel resistivity profiles are deduced from the measured magnetic fields. The ohmically dissipated energy is determined from the field distributions and compared with the total input energy. The experimental results are compared with the outcome of a numerical model. The consistency with information obtained from other diagnostic measurements is checked. (Auth.)

A video-image study of electrolytic flow structure in parallel electric-magnetic fields

International Nuclear Information System (INIS)

Gu, Z.H.; Fahidy, T.Z.

1987-01-01

The structure of free convective flow propagating from a vertical cathode into the electrolyte bulk has been studied via video-imaging. The enhancing effect of imposed horizontal uniform magnetic fields is manifest by vortex propagation and bifurcating flow

Anisotropic temperature relaxation of plasmas in an external magnetic field

International Nuclear Information System (INIS)

Hassan, M.H.A.

1977-01-01

The magnetized kinetic equation derived in an earlier paper (Hassan and Watson, 1977) is used to study the problem of relaxation of anisotropic electron and ion temperatures in a magnetized plasma. In the case of anisotropic electron temperature relaxation, it is shown that for small anisotropies the exchange of energy within the electrons between the components parallel and perpendicular to the magnetic field direction determine the relaxation rate. For anisotropic ion temperature relaxation it is shown that the essential mechanism for relaxation is provided by energy transfer between ions and electrons, and that the expression for the relaxation rate perpendicular to the magnetic field contains a significant term proportional to ln eta 0 ln (msub(e)/msub(i)) (where eta 0 = Ωsub(e)/ksub(D)Vsub(e perpendicular to)), in addition to the term proportional to the Coulomb logarithm. (author)

Directed Magnetic Particle Transport above Artificial Magnetic Domains Due to Dynamic Magnetic Potential Energy Landscape Transformation.

Science.gov (United States)

Holzinger, Dennis; Koch, Iris; Burgard, Stefan; Ehresmann, Arno

2015-07-28

An approach for a remotely controllable transport of magnetic micro- and/or nanoparticles above a topographically flat exchange-bias (EB) thin film system, magnetically patterned into parallel stripe domains, is presented where the particle manipulation is achieved by sub-mT external magnetic field pulses. Superparamagnetic core-shell particles are moved stepwise by the dynamic transformation of the particles' magnetic potential energy landscape due to the external magnetic field pulses without affecting the magnetic state of the thin film system. The magnetic particle velocity is adjustable in the range of 1-100 μm/s by the design of the substrate's magnetic field landscape (MFL), the particle-substrate distance, and the magnitude of the applied external magnetic field pulses. The agglomeration of magnetic particles is avoided by the intrinsic magnetostatic repulsion of particles due to the parallel alignment of the particles' magnetic moments perpendicular to the transport direction and parallel to the surface normal of the substrate during the particle motion. The transport mechanism is modeled by a quantitative theory based on the precise knowledge of the sample's MFL and the particle-substrate distance.

6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni-Mn-Ga

International Nuclear Information System (INIS)

Murray, S. J.; Marioni, M.; Allen, S. M.; O'Handley, R. C.; Lograsso, T. A.

2000-01-01

Field-induced strains of 6% are reported in ferromagnetic Ni-Mn-Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities. (c) 2000 American Institute of Physics

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)

What are we learning from the relative orientation between density structures and the magnetic field in molecular clouds?

Science.gov (United States)

Soler, J. D.; Hennebelle, P.

2017-10-01

>⟨Bˆ⊥⟩-> being mostly parallel at low NH to mostly perpendicular at the highest NH, is related to the magnetic field strength and constitutes a crucial piece of information for determining the role of the magnetic field in the dynamics of MCs.

Nonthermal ions and associated magnetic field behavior at a quasi-parallel earth's bow shock

Science.gov (United States)

Wilkinson, W. P.; Pardaens, A. K.; Schwartz, S. J.; Burgess, D.; Luehr, H.; Kessel, R. L.; Dunlop, M.; Farrugia, C. J.

1993-01-01

Attention is given to ion and magnetic field measurements at the earth's bow shock from the AMPTE-UKS and -IRM spacecraft, which were examined in high time resolution during a 45-min interval when the field remained closely aligned with the model bow shock normal. Dense ion beams were detected almost exclusively in the midst of short-duration periods of turbulent magnetic field wave activity. Many examples of propagation at large elevation angles relative to the ecliptic plane, which is inconsistent with reflection in the standard model shock configuration, were discovered. The associated waves are elliptically polarized and are preferentially left-handed in the observer's frame of reference, but are less confined to the maximum variance plane than other previously studied foreshock waves. The association of the wave activity with the ion beams suggests that the former may be triggered by an ion-driven instability, and possible candidates are discussed.

Steady state models for filamentary plasma structures associated with force free magnetic fields

International Nuclear Information System (INIS)

Marklund, G.

1978-05-01

This paper presents a model for filamentary plasma structures associated with force-free magnetic fields. A homogenous electric field parallel to the symmetry axis of the magnetic field is assumed. Under the influence of these fields, the plasma will drift radially inwards resulting in an accumulation of plasma in the central region. We assume recombination losses to keep the central plasma density at a finite value, and the recombined plasma i.e. the neutrals to diffuse radially outwards. Plasma density and some neutral gas density distributions for a steady state situation are calculated for various cases

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.)

Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

Science.gov (United States)

Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

2015-11-01

Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

Raman backscattering of circularly polarized electromagnetic waves propagating along a magnetic field

International Nuclear Information System (INIS)

Maraghechi, B.; Willett, J.e.

1979-01-01

The stimulated Raman backscattering of an intense electromagnetic wave propagating in the extraordinary mode along a uniform, static magnetic field is considered. The dispersion relation for a homogeneous magnetized plasma in the presence of the circularly polarized pump waves is developed in the cold-plasma approximation with the pump frequency above the plasma frequency. Formulas are derived for the threshold νsub(OT) of the parametric instability and for the growth rate γ of the backscattered extraordinary wave and Langmuir wave. The effects of the magnetic field parallel to the direction of propagation on νsub(0T) and γ are studied numerically. (author)

Magnetic Field Emission Comparison for Series-Parallel and Series-Series Wireless Power Transfer to Vehicles – PART 2/2

DEFF Research Database (Denmark)

Batra, Tushar; Schaltz, Erik

2014-01-01

Series-series and series-parallel topologies are the most favored topologies for design of wireless power transfer system for vehicle applications. The series-series topology has the advantage of reflecting only the resistive part on the primary side. On the other hand, the current source output...... characteristics of the series-parallel topology are more suited for the battery of the vehicle. This paper compares the two topologies in terms of magnetic emissions to the surroundings for the same input power, primary current, quality factor and inductors. Theoretical and simulation results show that the series...

Plasmas fluxes to surfaces for an oblique magnetic field

International Nuclear Information System (INIS)

Pitcher, C.S.; Stangeby, P.C.; Elder, J.D.; Bell, M.G.; Kilpatrick, S.J.; Manos, D.M.; Medley, S.S.; Owens, D.K.; Ramsey, A.T.; Ulrickson, M.

1992-07-01

The poloidal and toroidal spatial distributions of D α , He I and C II emission have been obtained in the vicinity of the TFTR bumper limiter and are compared with models of ion flow to the surface. The distributions are found not to agree with a model (the ''Cosine'' model) which determines the incident flux density using only the parallel fluxes in the scrape-off layer and the projected area of the surface perpendicular to the field lines. In particular, the Cosine model is not able to explain the significant fluxes observed at locations on the surface which are oblique to the magnetic field. It is further shown that these fluxes cannot be explained by the finite Larmor radius of impinging ions. Finally, it is demonstrated, with the use of Monte Carlo codes, that the distributions can be explained by including both parallel and cross-field transport onto the limiter surface

AC magnetization loss characteristics of HTS coated-conductors with magnetic substrates

International Nuclear Information System (INIS)

Tsukamoto, O.; Liu, M.; Odaka, S.; Miyagi, D.; Ohmatsu, K.

2007-01-01

AC magnetization loss characteristics of an HTS coated tape conductor with magnetic substrate subjected to an external AC magnetic field were investigated. The external magnetic field was perpendicular or parallel to the wide face of the tape conductor. Magnetization losses in the conductor and in the magnetic substrate itself without the superconductor layer, were measured by electric and calorimetric methods. The influence of the magnetic property of the substrate was strongly dependent on the direction of the external magnetic field. When the external magnetic field was perpendicular, magnetic property of the substrate did not affect the magnetization loss characteristics. This result suggests that the magnetization losses can be reduced by subdivisions of the superconducting layers even in the case of magnetic substrate conductors. When the external magnetic field was parallel, the magnetization losses were dominated by the losses in the magnetic substrate. Therefore, to reduce the magnetization losses in this case, reduction of magnetization losses in the substrate is necessary

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 field dependence of the current flowing in the spin-coated chlorophyll thin films

Science.gov (United States)

Aji, J. R. P.; Kusumandari; Purnama, B.

2018-03-01

The magnetic dependence of the current flowing in the spin coated chlorophyll films on a patterned Cu PCB substrate has been presented. Chlorophyll was isolated from Spirulina sp and deposited by spin coated methods. The reducing of current by the change of magnetic field (magneto conductance effect) was performed by inducing the magnetic field parallel to the inplane of film at room temp. The magnetoconductance ratio decreases as the increase of voltage. It was indicated that the origin of carrier charge in chlorophyll films should be different with the carrier charge injection (electron).

Heisenberg spin-1/2 XXZ chain in the presence of electric and magnetic fields

Science.gov (United States)

Thakur, Pradeep; Durganandini, P.

2018-02-01

We study the interplay of electric and magnetic order in the one-dimensional Heisenberg spin-1/2 XXZ chain with large Ising anisotropy in the presence of the Dzyaloshinskii-Moriya (DM) interaction and with longitudinal and transverse magnetic fields, interpreting the DM interaction as a coupling between the local electric polarization and an external electric field. We obtain the ground state phase diagram using the density matrix renormalization group method and compute various ground state quantities like the magnetization, staggered magnetization, electric polarization and spin correlation functions, etc. In the presence of both longitudinal and transverse magnetic fields, there are three different phases corresponding to a gapped Néel phase with antiferromagnetic (AF) order, gapped saturated phase, and a critical incommensurate gapless phase. The external electric field modifies the phase boundaries but does not lead to any new phases. Both external magnetic fields and electric fields can be used to tune between the phases. We also show that the transverse magnetic field induces a vector chiral order in the Néel phase (even in the absence of an electric field) which can be interpreted as an electric polarization in a direction parallel to the AF order.

Potential of the test particle in the magnetic field. I

International Nuclear Information System (INIS)

Sestak, B.

1980-01-01

The problem of the test particle potential in an external homogeneous magnetic field is solved in an unmagnetized plasma. It is shown that for the case when the parallel velocity component of the test particle is greater than the thermal velocity of the background particles, the potential is of a Coulomb character while for the case where the parallel velocity component is less than the thermal velocity the potential is of a Debye character. The Larmor radius of the test particle appears as an additional parameter in these potentials. (author)

Self running actuators moving in the same direction as the exciting magnetic field

International Nuclear Information System (INIS)

Enokizono, M.; Todaka, T.; Goto, K.

1998-01-01

This paper presents two kinds of drive units whose rotation axes are parallel to the exciting outer magnetic field. One is a hard-material-type that uses permanent magnets and silicon steel sheets to obtain the radial components of the field strength, and the other is a soft-material-type that uses the vibration of an amorphous ribbon to induce a rotational force. These drive units were developed to improve the freedom of movement of sensing devices. By combining the developed units with conventional ones, it will be possible to control the movement of devices freely by means of the outer magnetic field. In this paper, the basic characteristics of the drive units and their applicability are discussed. (author)

The Influence of magnetic field on the separation of droplets from ferrofluid jet

Science.gov (United States)

Fabian, M.; Burda, P.; Šviková, M.; Huňady, R.

2017-06-01

The influence of parallel and perpendicular homogenous magnetic field on the ferrofluid drop formation in dripping regime is studied experimentally. Experimental images are obtained using high-speed video camera with frame rate up to 25,000 fps. The detachment of a drop from the nozzle occurs via the formation of a neck which quickly narrows down until the drop pinches off. The formation of micro-thread from the primary neck is observed before the drop separation. Details of the shape and dynamics of the liquid neck are studied with regard to magnetic field. It is shown that near the detachment point scaled profiles exhibit self-similarity which is not affected by applied magnetic field.

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.

Electric Mars: A large trans-terminator electric potential drop on closed magnetic field lines above Utopia Planitia

Science.gov (United States)

Collinson, Glyn; Mitchell, David; Xu, Shaosui; Glocer, Alex; Grebowsky, Joseph; Hara, Takuya; Lillis, Robert; Espley, Jared; Mazelle, Christian; Sauvaud, Jean-André; Fedorov, Andrey; Liemohn, Mike; Andersson, Laila; Jakosky, Bruce

2017-02-01

Parallel electric fields and their associated electric potential structures play a crucial role in ionospheric-magnetospheric interactions at any planet. Although there is abundant evidence that parallel electric fields play key roles in Martian ionospheric outflow and auroral electron acceleration, the fields themselves are challenging to directly measure due to their relatively weak nature. Using measurements by the Solar Wind Electron Analyzer instrument aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars Scout, we present the discovery and measurement of a substantial (ΦMars=7.7 ± 0.6 V) parallel electric potential drop on closed magnetic field lines spanning the terminator from day to night above the great impact basin of Utopia Planitia, a region largely free of crustal magnetic fields. A survey of the previous 26 orbits passing over a range of longitudes revealed similar signatures on seven orbits, with a mean potential drop (ΦMars) of 10.9 ± 0.8 V, suggestive that although trans-terminator electric fields of comparable strength are not ubiquitous, they may be common, at least at these northerly latitudes.

Electric Mars: A Large Trans-Terminator Electric Potential Drop on Closed Magnetic Field Lines Above Utopia Planitia

Science.gov (United States)

Collinson, Glyn; Mitchell, David; Xu, Shaosui; Glocer, Alex; Grebowsky, Joseph; Hara, Takuya; Lillis, Robert; Espley, Jared; Mazelle, Christian; Sauvaud, Jean-Andre

2017-01-01

Abstract Parallel electric fields and their associated electric potential structures play a crucial role inionospheric-magnetospheric interactions at any planet. Although there is abundant evidence that parallel electric fields play key roles in Martian ionospheric outflow and auroral electron acceleration, the fields themselves are challenging to directly measure due to their relatively weak nature. Using measurements by the Solar Wind Electron Analyzer instrument aboard the NASA Mars Atmosphere and Volatile EvolutioN(MAVEN) Mars Scout, we present the discovery and measurement of a substantial (Phi) Mars 7.7 +/-0.6 V) parallel electric potential drop on closed magnetic field lines spanning the terminator from day to night above the great impact basin of Utopia Planitia, a region largely free of crustal magnetic fields. A survey of the previous 26 orbits passing over a range of longitudes revealed similar signatures on seven orbits, with a mean potential drop (Phi) Mars of 10.9 +/- 0.8 V, suggestive that although trans-terminator electric fields of comparable strength are not ubiquitous, they may be common, at least at these northerly latitudes.

Magnetic fields with photon beams: Use of circular current loops

International Nuclear Information System (INIS)

Jette, David

2001-01-01

Strong transverse magnetic fields can produce very large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. Through EGS4 Monte Carlo simulations, we have examined the effects of applying a magnetic field produced by a pair of circular current loops to a photon beam penetrating a water phantom of finite thickness. We have indeed found very substantial localized dose enhancements, albeit with no corresponding dose reduction just distal to the region of dose enhancement. (However, dose reduction does occur near the distal end of the phantom.) We have also observed two phenomena to be concerned with, for this configuration: significant broadening of the penumbra close to the current loop, and narrowness of the enhanced dose region in a plane parallel to the planes of the loops. We have also examined the use of a single current loop to produce the magnetic field, and have found great asymmetry in the dose distribution; this asymmetry appears to make it impossible to treat with a single circular magnet a tumor of large dimension extending below the application surface

Toroidal equilibrium states with reversed magnetic shear and parallel flow in connection with the formation of Internal Transport Barriers

Science.gov (United States)

Kuiroukidis, Ap.; Throumoulopoulos, G. N.

2015-08-01

We construct nonlinear toroidal equilibria of fixed diverted boundary shaping with reversed magnetic shear and flows parallel to the magnetic field. The equilibria have hole-like current density and the reversed magnetic shear increases as the equilibrium nonlinearity becomes stronger. Also, application of a sufficient condition for linear stability implies that the stability is improved as the equilibrium nonlinearity correlated to the reversed magnetic shear gets stronger with a weaker stabilizing contribution from the flow. These results indicate synergetic stabilizing effects of reversed magnetic shear, equilibrium nonlinearity and flow in the establishment of Internal Transport Barriers (ITBs).

dc properties of series-parallel arrays of Josephson junctions in an external magnetic field

International Nuclear Information System (INIS)

Lewandowski, S.J.

1991-01-01

A detailed dc theory of superconducting multijunction interferometers has previously been developed by several authors for the case of parallel junction arrays. The theory is now extended to cover the case of a loop containing several junctions connected in series. The problem is closely associated with high-T c superconductors and their clusters of intrinsic Josephson junctions. These materials exhibit spontaneous interferometric effects, and there is no reason to assume that the intrinsic junctions form only parallel arrays. A simple formalism of phase states is developed in order to express the superconducting phase differences across the junctions forming a series array as functions of the phase difference across the weakest junction of the system, and to relate the differences in critical currents of the junctions to gaps in the allowed ranges of their phase functions. This formalism is used to investigate the energy states of the array, which in the case of different junctions are split and separated by energy barriers of height depending on the phase gaps. Modifications of the washboard model of a single junction are shown. Next a superconducting inductive loop containing a series array of two junctions is considered, and this model is used to demonstrate the transitions between phase states and the associated instabilities. Finally, the critical current of a parallel connection of two series arrays is analyzed and shown to be a multivalued function of the externally applied magnetic flux. The instabilities caused by the presence of intrinsic serial junctions in granular high-T c materials are pointed out as a potential source of additional noise

Many-Body Mean-Field Equations: Parallel implementation

International Nuclear Information System (INIS)

Vallieres, M.; Umar, S.; Chinn, C.; Strayer, M.

1993-01-01

We describe the implementation of Hartree-Fock Many-Body Mean-Field Equations on a Parallel Intel iPSC/860 hypercube. We first discuss the Nuclear Mean-Field approach in physical terms. Then we describe our parallel implementation of this approach on the Intel iPSC/860 hypercube. We discuss and compare the advantages and disadvantages of the domain partition versus the Hilbert space partition for this problem. We conclude by discussing some timing experiments on various computing platforms

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.

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.

Computation of demagnetizing fields and particle distribution in magnetic fluid with inhomogeneous density

International Nuclear Information System (INIS)

Pshenichnikov, A.F.

2012-01-01

A new algorithm for calculating magnetic fields in a concentrated magnetic fluid with inhomogeneous density is proposed. Inhomogeneity of the fluid is caused by magnetophoresis. In this case, the diffusion and magnetostatic parts of the problem are tightly linked together and are solved jointly. The dynamic diffusion equation is solved by the finite volume method and, to calculate the magnetic field inside the fluid, an iterative process is performed in parallel. The solution to the problem is sought in Cartesian coordinates, and the computational domain is decomposed into rectangular elements. This technique eliminates the need to solve the related boundary-value problem for magnetic fields, accelerates computations and eliminates the error caused by the finite sizes of the outer region. Formulas describing the contribution of the rectangular element to the field intensity in the case of a plane problem are given. Magnetic and concentration fields inside the magnetic fluid filling a rectangular cavity generated under the action of the uniform external filed are calculated. - Highlights: ▶ New algorithm for calculating magnetic field intense magnetic fluid with account of magnetophoresis and diffusion of particles. ▶ We do not need to solve boundary-value problem, but we accelerate computations and eliminate some errors. ▶ We solve nonlinear flow equation by the finite volume method and calculate magnetic and focus fields in the fluid for plane case.

Fast magnetic field computation in fusion technology using GPU technology

Energy Technology Data Exchange (ETDEWEB)

Chiariello, Andrea Gaetano [Ass. EURATOM/ENEA/CREATE, Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, Via Roma 29, Aversa (CE) (Italy); Formisano, Alessandro, E-mail: Alessandro.Formisano@unina2.it [Ass. EURATOM/ENEA/CREATE, Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, Via Roma 29, Aversa (CE) (Italy); Martone, Raffaele [Ass. EURATOM/ENEA/CREATE, Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, Via Roma 29, Aversa (CE) (Italy)

2013-10-15

Highlights: ► The paper deals with high accuracy numerical simulations of high field magnets. ► The porting of existing codes of High Performance Computing architectures allowed to obtain a relevant speedup while not reducing computational accuracy. ► Some examples of applications, referred to ITER-like magnets, are reported. -- Abstract: One of the main issues in the simulation of Tokamaks functioning is the reliable and accurate computation of actual field maps in the plasma chamber. In this paper a tool able to accurately compute magnetic field maps produced by active coils of any 3D shape, wound with high number of conductors, is presented. Under linearity assumption, the coil winding is modeled by means of “sticks”, following each conductor's shape, and the contribution of each stick is computed using high speed Graphic Computing Units (GPU's). Relevant speed enhancements with respect to standard parallel computing environment are achieved in this way.

Tuning Bacterial Hydrodynamics with Magnetic Fields: A Path to Bacterial Robotics

Science.gov (United States)

Pierce, Christopher; Mumper, Eric; Brangham, Jack; Wijesinghe, Hiran; Lower, Stephen; Lower, Brian; Yang, Fengyuan; Sooryakumar, Ratnasingham

Magnetotactic Bacteria (MTB) are a group of motile prokaryotes that synthesize chains of lipid-bound, magnetic nano-particles. In this study, the innate magnetism of these flagellated swimmers is exploited to explore their hydrodynamics near confining surfaces, using the magnetic field as a tuning parameter. With weak (Gauss), uniform, external, magnetic ?elds and the field gradients arising from micro-magnetic surface patterns, the relative strength of hydrodynamic, magnetic and ?agellar force components is tuned through magnetic control of the bacteria's orientation and position. In addition to direct measurement of several hydrodynamic quantities related to the motility of individual cells, their tunable dynamics reveal a number of novel, highly controllable swimming behaviors with potential value in micro-robotics applications. Specifically, the experiments permit the MTB cells to be directed along parallel or divergent trajectories, suppress their flagellar forces through magnetic means, and induce transitions between planar, circulating trajectories and drifting, vertically oriented ``top-like'' motion. The implications of the work for fundamental hydrodynamics research as well as bacterially driven robotics applications will be discussed.

Experimental and modelling results of a parallel-plate based active magnetic regenerator

DEFF Research Database (Denmark)

Tura, A.; Nielsen, Kaspar Kirstein; Rowe, A.

2012-01-01

The performance of a permanent magnet magnetic refrigerator (PMMR) using gadolinium parallel plates is described. The configuration and operating parameters are described in detail. Experimental results are compared to simulations using an established twodimensional model of an active magnetic...

Natural convection and boiling heat transfer of a liquid metal in a magnetic field

International Nuclear Information System (INIS)

Seki, Masahiro; Kawamura, Hiroshi

1983-02-01

A liquid metal is often assumed as a coolant and a breeding material of a Tokamak fusion reactor. However, many problems on the thermo-hydraulics of a liquid metal in a magnetic field are still remained to be studied. In the present report, natural convection and boiling of a liquid metal in a strong magnetic field are studied to examine a fundamental feasibility of a fusion reactor cooled by a liquid metal. In the experimental study of the natural convection, the circulation of a liquid metal was found to be surpressed even by a magnetic field parallel to the gravity. A numerical study has confirmed the conclusion drawn by the experiment. In the study of boiling heat transfer, stable boiling of a liquid metal has been found also in a strong magnetic field. The burnout heat flux hardly affected by the magnetic field. These indicate a fundamental feasibility of the liquid-metal cooling for a Tokamak fusion reactor. (author)

Laboratory observation of magnetic field growth driven by shear flow

Energy Technology Data Exchange (ETDEWEB)

Intrator, T. P., E-mail: intrator@lanl.gov; Feng, Y.; Sears, J.; Weber, T. [Los Alamos National Laboratory, M.S. E526, Los Alamos, New Mexico 87545 (United States); Dorf, L. [Applied Materials, Inc., Santa Clara, CA 95054 (United States); Sun, X. [University of Science and Technology, Hefei (China)

2014-04-15

Two magnetic flux ropes that collide and bounce have been characterized in the laboratory. We find screw pinch profiles that include ion flow v{sub i}, magnetic field B, current density J, and plasma pressure. The electron flow v{sub e} can be inferred, allowing the evaluation of the Hall J×B term in a two fluid magnetohydrodynamic Ohm's Law. Flux ropes that are initially cylindrical are mutually attracted and compress each other, which distorts the cylindrical symmetry. Magnetic field is created via the ∇×v{sub e}×B induction term in Ohm's Law where in-plane (perpendicular) shear of parallel flow (along the flux rope) is the dominant feature, along with some dissipation and magnetic reconnection. We predict and measure the growth of a quadrupole out-of-plane magnetic field δB{sub z}. This is a simple and coherent example of a shear flow driven dynamo. There is some similarity with two dimensional reconnection scenarios, which induce a current sheet and thus out-of-plane flow in the third dimension, despite the customary picture that considers flows only in the reconnection plane. These data illustrate a general and deterministic mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence.

Specific heat of heavy-fermion CePd{sub 2}Si{sub 2} in high magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Sheikin, I. [University of Geneva, DPMC, Geneva (Switzerland)]. E-mail: Ilya.Sheikin@physics.unige.ch; Wang, Y.; Bouquet, F.; Junod, A. [University of Geneva, DPMC, Geneva (Switzerland); Lejay, P. [CRTBT, CNRS, Grenoble (France)

2002-07-22

We report specific heat measurements on the heavy-fermion compound CePd{sub 2}Si{sub 2} in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp peak in the specific heat signals the antiferromagnetic transition at T{sub N} {approx} 9.3 K in zero field. The transition is found to shift to lower temperatures when a magnetic field is applied along the crystallographic a-axis, while a field applied parallel to the tetragonal c-axis does not affect the transition. The magnetic contribution to the specific heat below T{sub N} is well described by a sum of a linear electronic term and an antiferromagnetic spin-wave contribution. Just below T{sub N}, an additional positive curvature, especially at high fields, arises most probably due to thermal fluctuations. The field dependence of the coefficient of the low-temperature linear term, {gamma}{sub 0}, extracted from the fits shows a maximum at about 6 T, at the point where an anomaly was detected in susceptibility measurements. The relative field dependences of both T{sub N} and the magnetic entropy at T{sub N} scale as [1-(B/B{sub 0}){sup 2}] for B parallel a, suggesting the disappearance of antiferromagnetism at B{sub 0}{approx}42 T. The expected suppression of the antiferromagnetic transition temperature to zero makes the existence of a magnetic quantum critical point possible. (author). Letter-to-the-editor.

Periodic magnetic field as a polarized and focusing thermal neutron spectrometer and monochromator

Energy Technology Data Exchange (ETDEWEB)

Cremer, J. T.; Williams, D. L.; Fuller, M. J.; Gary, C. K.; Piestrup, M. A. [Adelphi Technology, Inc., 2003 East Bayshore Rd., Redwood City, California 94063 (United States); Pantell, R. H.; Feinstein, J. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Flocchini, R. G.; Boussoufi, M.; Egbert, H. P.; Kloh, M. D.; Walker, R. B. [Davis McClellan Nuclear Radiation Center, University of California, McClellan, California 95652 (United States)

2010-01-15

A novel periodic magnetic field (PMF) optic is shown to act as a prism, lens, and polarizer for neutrons and particles with a magnetic dipole moment. The PMF has a two-dimensional field in the axial direction of neutron propagation. The PMF alternating magnetic field polarity provides strong gradients that cause separation of neutrons by wavelength axially and by spin state transversely. The spin-up neutrons exit the PMF with their magnetic spins aligned parallel to the PMF magnetic field, and are deflected upward and line focus at a fixed vertical height, proportional to the PMF period, at a downstream focal distance that increases with neutron energy. The PMF has no attenuation by absorption or scatter, as with material prisms or crystal monochromators. Embodiments of the PMF include neutron spectrometer or monochromator, and applications include neutron small angle scattering, crystallography, residual stress analysis, cross section measurements, and reflectometry. Presented are theory, experimental results, computer simulation, applications of the PMF, and comparison of its performance to Stern-Gerlach gradient devices and compound material and magnetic refractive prisms.

Periodic magnetic field as a polarized and focusing thermal neutron spectrometer and monochromator.

Science.gov (United States)

Cremer, J T; Williams, D L; Fuller, M J; Gary, C K; Piestrup, M A; Pantell, R H; Feinstein, J; Flocchini, R G; Boussoufi, M; Egbert, H P; Kloh, M D; Walker, R B

2010-01-01

A novel periodic magnetic field (PMF) optic is shown to act as a prism, lens, and polarizer for neutrons and particles with a magnetic dipole moment. The PMF has a two-dimensional field in the axial direction of neutron propagation. The PMF alternating magnetic field polarity provides strong gradients that cause separation of neutrons by wavelength axially and by spin state transversely. The spin-up neutrons exit the PMF with their magnetic spins aligned parallel to the PMF magnetic field, and are deflected upward and line focus at a fixed vertical height, proportional to the PMF period, at a downstream focal distance that increases with neutron energy. The PMF has no attenuation by absorption or scatter, as with material prisms or crystal monochromators. Embodiments of the PMF include neutron spectrometer or monochromator, and applications include neutron small angle scattering, crystallography, residual stress analysis, cross section measurements, and reflectometry. Presented are theory, experimental results, computer simulation, applications of the PMF, and comparison of its performance to Stern-Gerlach gradient devices and compound material and magnetic refractive prisms.

Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel

Science.gov (United States)

Jha, B. K.; Aina, B.

2017-08-01

The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.

An in situ Comparison of Electron Acceleration at Collisionless Shocks under Differing Upstream Magnetic Field Orientations

Energy Technology Data Exchange (ETDEWEB)

Masters, A.; Dougherty, M. K. [The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom); Sulaiman, A. H. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); Stawarz, Ł. [Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow (Poland); Reville, B. [School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN (United Kingdom); Sergis, N. [Office of Space Research and Technology, Academy of Athens, Soranou Efesiou 4, 11527 Athens (Greece); Fujimoto, M. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Burgess, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom); Coates, A. J., E-mail: a.masters@imperial.ac.uk [Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom)

2017-07-10

A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn’s bow shock have revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream–downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ∼100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures.

Momentum-energy transport from turbulence driven by parallel flow shear

International Nuclear Information System (INIS)

Dong, J.Q.; Horton, W.; Bengtson, R.D.; Li, G.X.

1994-04-01

The low frequency E x B turbulence driven by the shear in the mass flow velocity parallel to the magnetic field is studied using the fluid theory in a slab configuration with magnetic shear. Ion temperature gradient effects are taken into account. The eigenfunctions of the linear instability are asymmetric about the mode rational surfaces. Quasilinear Reynolds stress induced by such asymmetric fluctuations produces momentum and energy transport across the magnetic field. Analytic formulas for the parallel and perpendicular Reynolds stress, viscosity and energy transport coefficients are given. Experimental observations of the parallel and poloidal plasma flows on TEXT-U are presented and compared with the theoretical models

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

The effects of a magnetic field on the morphologies of nickel and copper deposits: the concept of “effective overpotential”

Directory of Open Access Journals (Sweden)

NEBOJSA D. NIKOLIC

2007-08-01

Full Text Available The morphologies of nickel and copper deposits obtained without applied magnetic fields, and with both parallel and perpendicular applied magnetic fields were examined by the scanning electron microscopy (SEM technique. Changes in the morphologies of the metals caused by the effect of the magnetic fields are explained by the concept of “effective overpotential”. The morphologies of the nickel and copper deposits obtained under parallelly oriented magnetic fields were similar to those obtained at some lower cathodic potentials without an applied magnetic field. The magnetic field with a perpendicular orientation to the electrode surface increased the dispersity of the nickel and copper deposits. Nickel and copper deposits obtained under this orientation of the magnetic field were similar to those obtained at some higher cathodic potentials without an applied magnetic field.

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.

TRACING THE MAGNETIC FIELD MORPHOLOGY OF THE LUPUS I MOLECULAR CLOUD

Energy Technology Data Exchange (ETDEWEB)

Franco, G. A. P. [Departamento de Física—ICEx—UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte (Brazil); Alves, F. O., E-mail: franco@fisica.ufmg.br, E-mail: falves@mpe.mpg.de [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr. 1, D-85748 Garching (Germany)

2015-07-01

Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales.

TRACING THE MAGNETIC FIELD MORPHOLOGY OF THE LUPUS I MOLECULAR CLOUD

International Nuclear Information System (INIS)

Franco, G. A. P.; Alves, F. O.

2015-01-01

Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales

Quantum capacitance of an ultrathin topological insulator film in a magnetic field

KAUST Repository

Tahir, M.; Sabeeh, K.; Schwingenschlö gl, Udo

2013-01-01

We present a theoretical study of the quantum magnetocapacitance of an ultrathin topological insulator film in an external magnetic field. The study is undertaken to investigate the interplay of the Zeeman interaction with the hybridization between the upper and lower surfaces of the thin film. Determining the density of states, we find that the electron-hole symmetry is broken when the Zeeman and hybridization energies are varied relative to each other. This leads to a change in the character of the magnetocapacitance at the charge neutrality point. We further show that in the presence of both Zeeman interaction and hybridization the magnetocapacitance exhibits beating at low and splitting of the Shubnikov de Haas oscillations at high perpendicular magnetic field. In addition, we address the crossover from perpendicular to parallel magnetic field and find consistency with recent experimental data.

Quantum capacitance of an ultrathin topological insulator film in a magnetic field

KAUST Repository

Tahir, M.

2013-02-12

We present a theoretical study of the quantum magnetocapacitance of an ultrathin topological insulator film in an external magnetic field. The study is undertaken to investigate the interplay of the Zeeman interaction with the hybridization between the upper and lower surfaces of the thin film. Determining the density of states, we find that the electron-hole symmetry is broken when the Zeeman and hybridization energies are varied relative to each other. This leads to a change in the character of the magnetocapacitance at the charge neutrality point. We further show that in the presence of both Zeeman interaction and hybridization the magnetocapacitance exhibits beating at low and splitting of the Shubnikov de Haas oscillations at high perpendicular magnetic field. In addition, we address the crossover from perpendicular to parallel magnetic field and find consistency with recent experimental data.

Energization of electrons in a plasma beam entering a curved magnetic field

International Nuclear Information System (INIS)

Brenning, N.; Lindberg, L.; Eriksson, A.

1980-09-01

Earlier experiments have indicated that suprathermal electrons appear when a collisionless plasma flowing along a magnetic field enters a region where the magnetic field is curved. In the present investigation newly developed methods of He-spectroscopy based on the absolute intensities of the He I 3889 A and He II 4686 A lines are utilized to study the electron temperature and to estimate the population of non-thermal electrons. The density of helium added for the diagnostic purpose is so low that the flow is not disturbed. It is found that the intrusion of the plasma into a curved or transverse field gives rise to a slight increase (15-20%) in the electron temperature and a remarkable increase in the fraction of non-thermal (>100 eV) electrons from below 1% to as much as 20-25% of the total electron population. There are also indications that the energization of electrons is particularly efficient on that side of the plasma beam which becomes polarized to a positive potential when entering the curved field. The experiments are confined to the case of weak magnetic field, i.e. only the electrons are magnetically confined. New details of the electric field and potential structure are presented and discussed. Electric field components parallel to the magnetic field are likely to energize the electrons, probably through the run-away phenomenon. (Auth.)

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

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.

Influence of magnetostatic interactions on the magnetization reversal of patterned magnetic elements

International Nuclear Information System (INIS)

Yin Xioalu; Liou, S. H.; Adeyeye, A. O.; Jain, S.; Han Baoshan

2011-01-01

The magnetization reversal in patterned thin-film arrays of elliptical submicron permalloy elements has been investigated by magnetic-force microscopy and micro-magneto-optic Kerr effect. Three different spatial arrangements of chains are considered, namely chains aligned parallel to the long axis of the ellipse, chains aligned parallel to the short axis of the ellipse, and arrays with roughly equal element-to-element spacings in both directions. Comparison of the hysteresis loops in an in-plane field perpendicular to the ellipses' long axes shows that the magnetization reversibility is highest for chains along the long axis. This is due to the nearly coherent magnetization rotation in the applied magnetic field and to the formation of a head-to-tail domain arrangement. Other arrangements, such as chains of ellipses aligned parallel to short axis, yield flux-closure domains as the applied magnetic field is changed.

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

Mapping the magnetic field generated by a supercurrent in a ring of YBa2Cu3O7-δ

Science.gov (United States)

Sulca, P. D.; Gómez, R. W.

2017-11-01

We design and construct a device to map the magnetic field generated by a supercurrent in a rectangular cross section ring of YBa2Cu3O7-δ . For the measurements of the magnetic field, we develop a Gaussmeter based on a commercial Hall effect sensor coupled to an Arduino microprocessor. Our results show an asymmetric distribution of the magnetic field intensity measured at a certain distance along a plane parallel to the ring surface. The behavior of the magnetic field intensity with distance along the ring axis is closely related to what is expected for a toroid. Using the Biot-Savart law and the measured magnetic field values, the induced supercurrent is determined.

Rapid characterization of superconducting wires and tapes in strong pulsed magnetic fields

International Nuclear Information System (INIS)

Bockstal, L. van; Keyser, A. de; Deschagt, J.; Hopkins, S.C.; Glowacki, B.A.

2007-01-01

A new measurement system for rapid characterization of superconducting wires and tapes is developed. The CryoPulse-BI is a system to provide a direct measurement of critical material parameters for superconducting materials when high long pulsed magnetic fields and strong currents are applied. In the experiments, synchronized magnetic fields up to 30 T and current pulses up to 5 kA are generated with adjustable timing. Varying the magnetic field strength, the current through the sample and the BI timing allows for a thorough characterization of the sample and the determination of critical currents. The rapid cycle time of the experiments yields a rapid and thorough determination of the critical parameters. The method has been tested on low T c as well as high T c materials with the field parallel or perpendicular to the current. The discussion covers the current state of the art including a comparison of our results to classical DC characterization measurements

Creation of Magnetic Fields by Electrostatic and Thermal Fluctuations

International Nuclear Information System (INIS)

Saleem, Hamid

2009-01-01

It is pointed out that the electrostatic and thermal fluctuations are the main source of magnetic fields in unmagnetized inhomogeneous plasmas. The unmagnetized inhomogeneous plasmas can support a low frequency electromagnetic ion wave as a normal mode like Alfven wave of magnetized plasmas. But this is a coupled mode produced by the mixing of longitudinal and transverse components of perturbed electric field due to density inhomogeneity. The ion acoustic wave does not remain electrostatic in non-uniform plasmas. On the other hand, a low frequency electrostatic wave can also exist in the pure electron plasmas and it couples with ion acoustic wave when ions are dynamic. These waves can become unstable when density and temperature gradients are parallel to each other as can be the case of laser plasmas and is the common situation in stellar cores. The main instability condition for the electrostatic and electromagnetic modes is the same (2/3)κ n T (where κ n and κ T are inverse of the scale lengths of gradients of density and electron temperature, respectively). This indicates that the electrostatic and magnetic field fluctuations are strongly coupled in unmagnetized nonuniform plasmas.

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)

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

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 ...

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.

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

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

Magnetohydrodynamic flow in a rectangular duct under a uniform transverse magnetic field at high Hartmann number

International Nuclear Information System (INIS)

Temperley, D.J.

1976-01-01

In this paper we consider fully developed, laminar, unidirectional flow of uniformly conducting, incompressible fluid through a rectangular duct of uniform cross-section. An externally applied magnetic field acts parallel to one pair of opposite walls and induced velocity and magnetic fields are generated in a direction parallel to the axis of the duct. The governing equations and boundary conditions for the latter fields are introduced and study is then concentrated on the special case of a duct having all walls non-conducting. For values of the Hartmann number M>>1, classical asymptotic analysis reveals the leading terms in the expansions of the induced fields in all key regions, with the exception of certain boundary layers near the corners of the duct. The order of magnitude of the affect of the latter layers on the flow-rate is discussed and closed-form solutions are obtained for the induced fields near the corners of the duct. Attempts were made to formulate a concise Principle of Minimum Singularity to enable the correct choice of eigen functions for the various field components in the boundary layers on the walls parallel to the applied field. It was found, however, that these components are best found by taking the outer expansion of the closed-form solution in those boundary-layers near the corners of the duct where classical asymptotic analysis is not applicable. (author)

Formaldehyde sensor based on Ni-doped tetrapod-shaped ZnO nanopowder induced by external magnetic field

Science.gov (United States)

Bai, Zikui; Xie, Changsheng; Hu, Mulin; Zhang, Shunping

2008-12-01

The sensors based on Ni-doped ZnO nanopowder with tetrapod-shape (T-ZnO) were fabricated by screen-printing technique with external magnetic field in different direction. The morphologies and crystal structures of the thick film were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. Gas-sensing property of sensors responded to 100 ppm formaldehyde was also detected. The results show that the direction of magnetic field has crucial effect on the sensor sensitivity. The sensors based on 5 wt% Ni-doped T-ZnO induced by magnetic field in parallel direction to the thick film surface, has the optimization sensitivity, the shortest response and recovery time, which are 10.6, 16 and 15 s, respectively. The magnetic-field induction model and the gas-sensing mechanism of the Ni-doped T-ZnO are proposed.

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

A surface acoustic wave passive and wireless sensor for magnetic fields, temperature, and humidity

KAUST Repository

Li, Bodong; Yassine, Omar; Kosel, Jü rgen

2015-01-01

In this paper, we report an integrated single-chip surface acoustic wave sensor with the capability of measuring magnetic field, temperature, and humidity. The sensor is fabricated using a thermally sensitive LiNbO3 substrate, a humidity sensitive hydrogel coating, and a magnetic field sensitive impedance load. The sensor response to individually and simultaneously changing magnetic field, temperature and humidity is characterized by connecting a network analyzer directly to the sensor. Analytical models for each measurand are derived and used to compensate noise due to cross sensitivities. The results show that all three measurands can be monitored in parallel with sensitivities of 75 ppm/°C, 0.13 dB/%R.H. (at 50%R.H.), 0.18 dB/Oe and resolutions of 0.1 °C, 0.4%R.H., 1 Oe for temperature, humidity and magnetic field, respectively. A passive wireless measurement is also conducted on a current line using, which shows the sensors capability to measure both temperature and current signals simultaneously.

Ulysses Observations of Tripolar Guide-Magnetic Field Perturbations Across Solar Wind Reconnection Exhausts

Science.gov (United States)

Eriksson, S.; Peng, B.; Markidis, S.; Gosling, J. T.; McComas, D. J.; Lapenta, G.; Newman, D. L.

2014-12-01

We report observations from 15 solar wind reconnection exhausts encountered along the Ulysses orbit beyond 4 AU in 1996-1999 and 2002-2005. The events, which lasted between 17 and 45 min, were found at heliospheric latitudes between -36o and 21o with one event detected as high as 58o. All events shared a common characteristic of a tripolar guide-magnetic field perturbation being detected across the observed exhausts. The signature consists of an enhanced guide field magnitude within the exhaust center and two regions of significantly depressed guide-fields adjacent to the center region. The events displayed magnetic field shear angles as low as 37o with a mean of 89o. This corresponds to a strong external guide field relative to the anti-parallel reconnecting component of the magnetic field with a mean ratio of 1.3 and a maximum ratio of 3.1. A 2-D kinetic reconnection simulation for realistic solar wind conditions reveals that tripolar guide fields form at current sheets in the presence of multiple X-lines as two magnetic islands interact with one another for such strong guide fields. The Ulysses observations are also compared with the results of a 3-D kinetic simulation of multiple flux ropes in a strong guide field.

TU-H-BRA-02: The Physics of Magnetic Field Isolation in a Novel Compact Linear Accelerator Based MRI-Guided Radiation Therapy System

Energy Technology Data Exchange (ETDEWEB)

Low, D [UCLA, Los Angeles, CA (United States); Mutic, S [Washington University School of Medicine, Saint Louis, MO (United States); Shvartsman, S; Chmielewski, T; Fought, G; Sharma, A; Dempsey, J [ViewRay, Inc., Oakwood Village, OH (United States)

2016-06-15

Purpose: To develop a method for isolating the MRI magnetic field from field-sensitive linear accelerator components at distances close to isocenter. Methods: A MRI-guided radiation therapy system has been designed that integrates a linear accelerator with simultaneous MR imaging. In order to accomplish this, the magnetron, port circulator, radiofrequency waveguide, gun driver, and linear accelerator needed to be placed in locations with low magnetic fields. The system was also required to be compact, so moving these components far from the main magnetic field and isocenter was not an option. The magnetic field sensitive components (exclusive of the waveguide) were placed in coaxial steel sleeves that were electrically and mechanically isolated and whose thickness and placement were optimized using E&M modeling software. Six sets of sleeves were placed 60° apart, 85 cm from isocenter. The Faraday effect occurs when the direction of propagation is parallel to the magnetic RF field component, rotating the RF polarization, subsequently diminishing RF power. The Faraday effect was avoided by orienting the waveguides such that the magnetic field RF component was parallel to the magnetic field. Results: The magnetic field within the shields was measured to be less than 40 Gauss, significantly below the amount needed for the magnetron and port circulator. Additional mu-metal was employed to reduce the magnetic field at the linear accelerator to less than 1 Gauss. The orientation of the RF waveguides allowed the RT transport with minimal loss and reflection. Conclusion: One of the major challenges in designing a compact linear accelerator based MRI-guided radiation therapy system, that of creating low magnetic field environments for the magnetic-field sensitive components, has been solved. The measured magnetic fields are sufficiently small to enable system integration. This work supported by ViewRay, Inc.

TU-H-BRA-02: The Physics of Magnetic Field Isolation in a Novel Compact Linear Accelerator Based MRI-Guided Radiation Therapy System

International Nuclear Information System (INIS)

Low, D; Mutic, S; Shvartsman, S; Chmielewski, T; Fought, G; Sharma, A; Dempsey, J

2016-01-01

Purpose: To develop a method for isolating the MRI magnetic field from field-sensitive linear accelerator components at distances close to isocenter. Methods: A MRI-guided radiation therapy system has been designed that integrates a linear accelerator with simultaneous MR imaging. In order to accomplish this, the magnetron, port circulator, radiofrequency waveguide, gun driver, and linear accelerator needed to be placed in locations with low magnetic fields. The system was also required to be compact, so moving these components far from the main magnetic field and isocenter was not an option. The magnetic field sensitive components (exclusive of the waveguide) were placed in coaxial steel sleeves that were electrically and mechanically isolated and whose thickness and placement were optimized using E&M modeling software. Six sets of sleeves were placed 60° apart, 85 cm from isocenter. The Faraday effect occurs when the direction of propagation is parallel to the magnetic RF field component, rotating the RF polarization, subsequently diminishing RF power. The Faraday effect was avoided by orienting the waveguides such that the magnetic field RF component was parallel to the magnetic field. Results: The magnetic field within the shields was measured to be less than 40 Gauss, significantly below the amount needed for the magnetron and port circulator. Additional mu-metal was employed to reduce the magnetic field at the linear accelerator to less than 1 Gauss. The orientation of the RF waveguides allowed the RT transport with minimal loss and reflection. Conclusion: One of the major challenges in designing a compact linear accelerator based MRI-guided radiation therapy system, that of creating low magnetic field environments for the magnetic-field sensitive components, has been solved. The measured magnetic fields are sufficiently small to enable system integration. This work supported by ViewRay, Inc.

Mapping the magnetic field generated by a supercurrent in a ring of YBa2Cu3O7−δ

International Nuclear Information System (INIS)

Sulca, P D; Gómez, R W

2017-01-01

We design and construct a device to map the magnetic field generated by a supercurrent in a rectangular cross section ring of YBa 2 Cu 3 O 7−δ . For the measurements of the magnetic field, we develop a Gaussmeter based on a commercial Hall effect sensor coupled to an Arduino microprocessor. Our results show an asymmetric distribution of the magnetic field intensity measured at a certain distance along a plane parallel to the ring surface. The behavior of the magnetic field intensity with distance along the ring axis is closely related to what is expected for a toroid. Using the Biot–Savart law and the measured magnetic field values, the induced supercurrent is determined. (paper)

Gauge field governing parallel transport along mixed states

International Nuclear Information System (INIS)

Uhlmann, A.

1990-01-01

At first a short account is given of some basic notations and results on parallel transport along mixed states. A new connection form (gauge field) is introduced to give a geometric meaning to the concept of parallelity in the theory of density operators. (Author) 11 refs

Thermomechanic equations for magnetic fluids of equilibrium magnetization

International Nuclear Information System (INIS)

Bashtovoy, V.G.; Berkovsky, B.M.; Vislovich, A.N.

1988-01-01

The main physical prerequisite for the existence of equilibrium magnetization is the assumption that nothing, except thermal motion, hinders the orientation of elementary magnetic moments along the field and that the mean value of magnetization is achieved instantaneously, i.e., within the times much shorter than the characteristic times of macroscopic processes (hydrodynamic, thermal, electromagnetic, etc.). This assumption makes it possible to consider the fluid magnetization vector M-vector at a given instant to be parallel to the vector of magnetic field intensity H-vector, which in the general form may be related as M-vector = (M/H)H-vector. Magnetization M is determined by the fluid temperature and density and by field intensity: M = M(T,rho,H). It is natural that it decreases with rising temperature and increases with the field intensity. The condition for the vectors M-vector and H-vector to be parallel is realized in a MF only for certain colloid characteristics. Nevertheless, for a wide range of problems this condition may be regarded as fulfilled and enables one to study those effects in a MF which are caused to occur by the volume magnetic force due to the interaction between equilibrium magnetization and the magnetic field

Neutron diffraction study of antiferromagnetic ErNi3Ga9 in magnetic fields

Science.gov (United States)

Ninomiya, Hiroki; Sato, Takaaki; Matsumoto, Yuji; Moyoshi, Taketo; Nakao, Akiko; Ohishi, Kazuki; Kousaka, Yusuke; Akimitsu, Jun; Inoue, Katsuya; Ohara, Shigeo

2018-05-01

We report specific heat, magnetization, magnetoresistance, and neutron diffraction measurements of single crystals of ErNi3Ga9. This compound crystalizes in a chiral structure with space group R 32 . The erbium ions form a two-dimensional honeycomb structure. ErNi3Ga9 displays antiferromagnetic order below 6.4 K. We determined that the magnetic structure is slightly amplitude-modulated as well as antiferromagnetic with q = (0 , 0 , 0.5) . The magnetic properties are described by an Ising-like model in which the magnetic moment is always along the c-axis owing to the large uniaxial anisotropy caused by the crystalline electric field effect in the low temperature region. When the magnetic field is applied along the c-axis, a metamagnetic transition is observed around 12 kOe at 2 K. ErNi3Ga9 possesses crystal chirality, but the antisymmetric magnetic interaction, the so-called Dzyaloshinskii-Moriya (DM) interaction, does not contribute to the magnetic structure, because the magnetic moments are parallel to the DM-vector.

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

Shear flow effect on ion temperature gradient vortices in plasmas with sheared magnetic field

DEFF Research Database (Denmark)

Chakrabarti, N.; Juul Rasmussen, J.

1999-01-01

The effect of velocity shear on ion temperature gradient (ITG) driven vortices in a nonuniform plasma in a curved, sheared magnetic field is investigated. In absence of parallel ion dynamics, vortex solutions for the ITG mode are studied analytically. It is shown that under certain conditions...... and ultimately lead to a dominating monopolar form. The effects of magnetic shear indicate it may destroy these structures. (C) 1999 American Institute of Physics....

Effects of a static inhomogeneous magnetic field acting on a laser-produced carbon plasma plume

Directory of Open Access Journals (Sweden)

M. Favre

2017-08-01

Full Text Available We present time- and space-resolved observations of the dynamics of a laser-produced carbon plasma, propagating in a sub-Tesla inhomogeneous magnetic field, with both, axial and radial field gradients. An Nd:YAG laser pulse, 340 mJ, 3.5 ns, at 1.06 μm, with a fluence of 7 J/cm2, is used to generate the plasma from a solid graphite target, in vacuum. The magnetic field is produced using two coaxial sets of two NeFeB ring magnets, parallel to the laser target surface. The diagnostics include plasma imaging with 50 ns time resolution, spatially resolved optical emission spectroscopy and Faraday cup. Based on our observations, evidence of radial and axial plasma confinement due to magnetic field gradients is presented. Formation of C2 molecules, previously observed in the presence of a low pressure neutral gas background, and enhanced on-axis ion flux, are ascribed to finite Larmor radius effects and reduced radial transport due to the presence of the magnetic field.

Electromagnetic fluctuation spectra of collective oscillations in magnetized Maxwellian plasmas for parallel wave vectors

Science.gov (United States)

Vafin, S.; Schlickeiser, R.; Yoon, P. H.

2016-05-01

The general electromagnetic fluctuation theory for magnetized plasmas is used to calculate the steady-state wave number spectra and total electromagnetic field strength of low-frequency collective weakly damped eigenmodes with parallel wavevectors in a Maxwellian electron-proton plasma. These result from the equilibrium of spontaneous emission and collisionless damping, and they represent the minimum electromagnetic fluctuations guaranteed in quiet thermal space plasmas, including the interstellar and interplanetary medium. Depending on the plasma beta, the ratio of |δB |/B0 can be as high as 10-12 .

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

THE MAGNETIC FIELD IN TAURUS PROBED BY INFRARED POLARIZATION

International Nuclear Information System (INIS)

Chapman, Nicholas L.; Goldsmith, Paul F.; Pineda, Jorge L.; Li Di; Clemens, D. P.; Krco, Marko

2011-01-01

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

Experimental study on heat transfer enhancement of laminar ferrofluid flow in horizontal tube partially filled porous media under fixed parallel magnet bars

Energy Technology Data Exchange (ETDEWEB)

Sheikhnejad, Yahya; Hosseini, Reza, E-mail: hoseinir@aut.ac.ir; Saffar Avval, Majid

2017-02-15

In this study, steady state laminar ferroconvection through circular horizontal tube partially filled with porous media under constant heat flux is experimentally investigated. Transverse magnetic fields were applied on ferrofluid flow by two fixed parallel magnet bar positioned on a certain distance from beginning of the test section. The results show promising notable enhancement in heat transfer as a consequence of partially filled porous media and magnetic field, up to 2.2 and 1.4 fold enhancement were observed in heat transfer coefficient respectively. It was found that presence of both porous media and magnetic field simultaneously can highly improve heat transfer up to 2.4 fold. Porous media of course plays a major role in this configuration. Virtually, application of Magnetic field and porous media also insert higher pressure loss along the pipe which again porous media contribution is higher that magnetic field. - Highlights: • Porous media can improve the coefficient of heat transfer up to 2.2 fold. • Both porous media and Nano particles have undesired pressure drop effect. • Application of both porous media and magnetic field in ferrofluid flow will result in significant enhancement in heat transfer up to 2.4 fold. • Magnet bar effect is mainly restricted to approximately one fourth of the test section. • Diluted Ferrofluids 2%, results in over 1.4 fold enhancement in heat transfer coefficient.

Ionospheric plasma escape by high-altitude electric fields: Magnetic moment ''pumping''

International Nuclear Information System (INIS)

Lundin, R.; Hultqvist, B.

1989-01-01

Measurements of electric fields and the composition of upward flowing ionospheric ions by the Viking spacecraft have provided further insight into the mass dependent plasma escape process taking place in the upper ionosphere. The Viking results of the temperature and mass-composition of individual ion beams suggest that upward flowing ion beams can be generated by a magnetic moment ''pumping'' mechanism caused by low-frequency transverse electric field fluctuations, in addition to a field aligned ''quasi-electrostatic'' acceleration process. Magnetic moment ''pumping'' within transverse electric field gradients can be described as a conversion of electric drift velocity to cyclotron velocity by the inertial drift in time-dependent electric field. This gives an equal cyclotron velocity gain for all plasma species, irrespective of mass. Oxygen ions thus gain 16 times as much transverse energy as protons. In addition to a transverse energy gain above the escape energy, a field-aligned quasi-electrostatic acceleration is considered primarily responsible for the collimated upward flow of ions. The field-aligned acceleration adds a constant parallel energy to escaping ionospheric ions. Thus, ion beams at high altitudes can be explained by a bimodal acceleration from both a transverse (equal velocity) and a parallel (equal energy) acceleration process. The Viking observations also show that the thermal energy of ion beams, and the ion beam width are mass dependent. The average O + /H + ''temperature ratio has been found to be 4.0 from the Viking observations. This is less than the factor of 16 anticipated from a coherent transverse electric field acceleration but greater than the factor of 1 (or even less than 1) expected from a turbulent acceleration process. copyright American Geophysical Union 1989

Influence of deposition field on the magnetic anisotropy in epitaxial Co70Fe30 films on GaAs(001)

International Nuclear Information System (INIS)

Hindmarch, A.T.; Arena, D.; Dempsey, K.J.; Henini, M.; Marrows, C.H.

2010-01-01

The effect of the application of a magnetic field during deposition of epitaxial Co 70 Fe 30 onto GaAs(001) is shown; we find an initially counterintuitive result. For field applied along the interfacial uniaxial hard axis the relative effective uniaxial magnetic anisotropy is increased by a factor of two in comparison to both field along the uniaxial easy axis, or no field; usually, application of a deposition field results in a uniaxial easy axis parallel to this field direction. We show that the deposition field changes the maximal projection of the atomic orbital magnetic moments onto the easy axis, which corresponds to a deposition field induced shift in the Helmholtz free-energy landscape of the system.

Effect of alignment of easy axes on dynamic magnetization of immobilized magnetic nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Yoshida, Takashi, E-mail: t_yoshi@ees.kyushu-u.ac.jp [Department of Electrical and Electronic Engineering, Kyushu University, Fukuoka 819-0395 (Japan); Matsugi, Yuki; Tsujimura, Naotaka; Sasayama, Teruyoshi; Enpuku, Keiji [Department of Electrical and Electronic Engineering, Kyushu University, Fukuoka 819-0395 (Japan); Viereck, Thilo; Schilling, Meinhard; Ludwig, Frank [Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig 38106 (Germany)

2017-04-01

In some biomedical applications of magnetic nanoparticles (MNPs), the particles are physically immobilized. In this study, we explore the effect of the alignment of the magnetic easy axes on the dynamic magnetization of immobilized MNPs under an AC excitation field. We prepared three immobilized MNP samples: (1) a sample in which easy axes are randomly oriented, (2) a parallel-aligned sample in which easy axes are parallel to the AC field, and (3) an orthogonally aligned sample in which easy axes are perpendicular to the AC field. First, we show that the parallel-aligned sample has the largest hysteresis in the magnetization curve and the largest harmonic magnetization spectra, followed by the randomly oriented and orthogonally aligned samples. For example, 1.6-fold increase was observed in the area of the hysteresis loop of the parallel-aligned sample compared to that of the randomly oriented sample. To quantitatively discuss the experimental results, we perform a numerical simulation based on a Fokker-Planck equation, in which probability distributions for the directions of the easy axes are taken into account in simulating the prepared MNP samples. We obtained quantitative agreement between experiment and simulation. These results indicate that the dynamic magnetization of immobilized MNPs is significantly affected by the alignment of the easy axes. - Highlights: • We clarify how the alignment of easy axis of MNP affects the AC magnetization. • Parallel-aligned immobilized MNPs exhibit the largest AC hysteresis loop. • Parallel-aligned immobilized MNPs exhibit the largest harmonic magnetization spectra. • The AC magnetization is strongly affected by the alignment of the easy axes.

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...

An optimization of a GPU-based parallel wind field module

International Nuclear Information System (INIS)

Pinheiro, André L.S.; Shirru, Roberto

2017-01-01

Atmospheric radionuclide dispersion systems (ARDS) are important tools to predict the impact of radioactive releases from Nuclear Power Plants and guide people evacuation from affected areas. Four modules comprise ARDS: Source Term, Wind Field, Plume Dispersion and Doses Calculations. The slowest is the Wind Field Module that was previously parallelized using the CUDA C language. The statement purpose of this work is to show the speedup gain with the optimization of the already parallel code of the GPU-based Wind Field module, based in WEST model (Extrapolated from Stability and Terrain). Due to the parallelization done in the wind field module, it was observed that some CUDA processors became idle, thus contributing to a reduction in speedup. It was proposed in this work a way of allocating these idle CUDA processors in order to increase the speedup. An acceleration of about 4 times can be seen in the comparative case study between the regular CUDA code and the optimized CUDA code. These results are quite motivating and point out that even after a parallelization of code, a parallel code optimization should be taken into account. (author)

An optimization of a GPU-based parallel wind field module

Energy Technology Data Exchange (ETDEWEB)

Pinheiro, André L.S.; Shirru, Roberto [Coordenacao de Pos-Graduacao e Pesquisa de Engenharia (PEN/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Pereira, Cláudio M.N.A., E-mail: apinheiro99@gmail.com, E-mail: schirru@lmp.ufrj.br, E-mail: cmnap@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

2017-07-01

Atmospheric radionuclide dispersion systems (ARDS) are important tools to predict the impact of radioactive releases from Nuclear Power Plants and guide people evacuation from affected areas. Four modules comprise ARDS: Source Term, Wind Field, Plume Dispersion and Doses Calculations. The slowest is the Wind Field Module that was previously parallelized using the CUDA C language. The statement purpose of this work is to show the speedup gain with the optimization of the already parallel code of the GPU-based Wind Field module, based in WEST model (Extrapolated from Stability and Terrain). Due to the parallelization done in the wind field module, it was observed that some CUDA processors became idle, thus contributing to a reduction in speedup. It was proposed in this work a way of allocating these idle CUDA processors in order to increase the speedup. An acceleration of about 4 times can be seen in the comparative case study between the regular CUDA code and the optimized CUDA code. These results are quite motivating and point out that even after a parallelization of code, a parallel code optimization should be taken into account. (author)

Development of low temperature and high magnetic field X-ray diffraction facility

Energy Technology Data Exchange (ETDEWEB)

Shahee, Aga; Sharma, Shivani; Singh, K.; Lalla, N. P., E-mail: nplallaiuc82@gmail.com; Chaddah, P. [UGC-DAE Consortium for Scientific Research, University campus, Khandwa Road, Indore-452001 (India)

2015-06-24

The current progress of materials science regarding multifunctional materials (MFM) has put forward the challenges to understand the microscopic origin of their properties. Most of such MFMs have magneto-elastic correlations. To investigate the underlying mechanism it is therefore essential to investigate the structural properties in the presence of magnetic field. Keeping this in view low temperature and high magnetic field (LTHM) powder x-ray diffraction (XRD), a unique state-of-art facility in the country has been developed at CSR Indore. This setup works on symmetric Bragg Brentano geometry using a parallel incident x-ray beam from a rotating anode source working at 17 kW. Using this one can do structural studies at non-ambient conditions i.e. at low- temperatures (2-300 K) and high magnetic field (+8 to −8 T). The available scattering angle ranges from 5° to 115° 2θ with a resolution better than 0.1°. The proper functioning of the setup has been checked using Si sample. The effect of magnetic field on the structural properties has been demonstrated on Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} sample. Clear effect of field induced phase transition has been observed. Moreover, the effect of zero field cooled and field cooled conditions is also observed.

Stochastic electron dynamics due to drift waves in a sheared magnetic field and other drift motion problems

International Nuclear Information System (INIS)

Robertson, J.A.

1986-12-01

Electron motion in a single electrostatic wave in a sheared magnetic field is shown to become stochastic in the presence of a second wave at an amplitude well below that obtained from the overlapping pendulum resonance approximation. The enhanced stochasticity occurs for low parallel velocity electrons for which the parallel trapping motion from eE/sub parallel//m interacts strongly with the E x B trapping motion due to the presence of magnetic shear. The guiding-center equations for single particle electron orbits in given fields are investigated using both analytical and numerical techniques. The model assumes a slab magnetic field geometry with shear and two electrostatic plane waves propagating at an angle with respect to each other. Collisions and the self-consistent effect of the electron motion upon the fields are ignored. The guiding-center motion in an inertial reference frame moving in phase with the two waves is given by a two degree-of-freedom, autonomous Hamiltonian system. The single wave particle motion may be reduced to a two parameter family of one degree-of-freedom Hamiltonians which bifurcate from a pendulum phase space to a topology with three chains of elliptic and hyperbolic fixed points separated in radius about the mode-rational surface. In the presence of a perturbing wave with a different helicity, electrons in the small parallel velocity regime become stochastic at an amplitude scaling as the fourth root of the wave potential. The results obtained for stochastic motion apply directly to the problem of electron diffusion in drift waves occurring in toroidal fusion confinement devices. The effect of an adiabatically changing radial electric field upon guiding-center orbits in tokamaks is also investigated. This perturbation causes a radial polarization drift of trapped particle tokamak orbits

The Effect of a Guide Field on the Structures of Magnetic Islands: 2D PIC Simulations

Science.gov (United States)

Huang, C.; Lu, Q.; Lu, S.; Wang, P.; Wang, S.

2014-12-01

Magnetic island plays an important role in magnetic reconnection. Using a series of 2D PIC simulations, we investigate the magnetic structures of a magnetic island formed during multiple X-line magnetic reconnection, considering the effects of the guide field in symmetric and asymmetric current sheets. In a symmetric current sheet, the current in the direction forms a tripolar structure inside a magnetic island during anti-parallel reconnection, which results in a quadrupole structure of the out-of-plane magnetic field. With the increase of the guide field, the symmetry of both the current system and out-of-plane magnetic field inside the magnetic island is distorted. When the guide field is sufficiently strong, the current forms a ring along the magnetic field lines inside magnetic island. At the same time, the current carried by the energetic electrons accelerated in the vicinity of the X lines forms another ring at the edge of the magnetic island. Such a dual-ring current system enhance the out-of-plane magnetic field inside the magnetic island with a dip in the center of the magnetic island. In an asymmetric current sheet, when there is no guide field, electrons flows toward the X lines along the separatrices from the side with a higher density, and are then directed away from the X lines along the separatrices to the side with a lower density. The formed current results in the enhancement of the out-of-plane magnetic field at one end of the magnetic island, and the attenuation at the other end. With the increase of the guide field, the structures of both the current system and the out-of-plane magnetic field are distorted.

Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Pair Jets

Science.gov (United States)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Mizuno, Y.

2005-01-01

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created by relativistic pair jets are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma with and without initial magnetic fields. The growth rates of the Weibel instability depends on the distribution of pair jets. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Acceleration of the charged particles due to chaotic scattering in the combined black hole gravitational field and asymptotically uniform magnetic field

International Nuclear Information System (INIS)

Stuchlik, Zdenek; Kolos, Martin

2016-01-01

To test the role of large-scale magnetic fields in accretion processes, we study the dynamics of the charged test particles in the vicinity of a black hole immersed into an asymptotically uniform magnetic field. Using the Hamiltonian formalism of the charged particle dynamics, we examine chaotic scattering in the effective potential related to the black hole gravitational field combined with the uniform magnetic field. Energy interchange between the translational and oscillatory modes of the charged particle dynamics provides a mechanism for charged particle acceleration along the magnetic field lines. This energy transmutation is an attribute of the chaotic charged particle dynamics in the combined gravitational and magnetic fields only, the black hole rotation is not necessary for such charged particle acceleration. The chaotic scatter can cause a transition to the motion along the magnetic field lines with small radius of the Larmor motion or vanishing Larmor radius, when the speed of the particle translational motion is largest and it can be ultra-relativistic. We discuss the consequences of the model of ionization of test particles forming a neutral accretion disc, or heavy ions following off-equatorial circular orbits, and we explore the fate of heavy charged test particles after ionization where no kick of heavy ions is assumed and only the switch-on effect of the magnetic field is relevant. We demonstrate that acceleration and escape of the ionized particles can be efficient along the Kerr black hole symmetry axis parallel to the magnetic field lines. We show that a strong acceleration of the ionized particles to ultra-relativistic velocities is preferred in the direction close to the magnetic field lines. Therefore, the process of ionization of Keplerian discs around the Kerr black holes can serve as a model of relativistic jets. (orig.)