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1

Generation of helical magnetic fields from inflation  

CERN Document Server

The generation of helical magnetic fields during single field inflation due to an axial coupling of the electromagnetic field to the inflaton is discussed. We find that such a coupling always leads to a blue spectrum of magnetic fields during slow roll inflation. Though the helical magnetic fields further evolve during the inverse cascade in the radiation era after inflation, we conclude that the magnetic fields generated by such an axial coupling can not lead to observed field strength on cosmologically relevant scales.

Jain, Rajeev Kumar; Hollenstein, Lukas

2012-01-01

2

Strong and superstrong pulsed magnetic fields generation  

CERN Document Server

Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

Shneerson, German A; Krivosheev, Sergey I

2014-01-01

3

Generation of Magnetic Fields in Cosmology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Mechanisms of generation of magnetic fields in the early universe which could seed the present-day large scale galactic magnetic fields, are briefly reviewed. Three possible ways to create large scale magnetic fields are discussed: breaking of conformal invariance of electromagnetic interactions and inflationary stretching of the field wave length, first order cosmological phase transitions, and chaotic electric currents generated by turbulent flows in the primeval plasma.

Dolgov, A. D.

2001-01-01

4

Possible Generation of Self-Magnetic Fields  

International Nuclear Information System (INIS)

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

5

Magnetic field generation by coherent turbulence structures  

International Nuclear Information System (INIS)

It is thought that the small-scale magnetic fields observed in accretion discs, galaxies and galactic clusters are generated by a dynamo process in which the turbulent plasma amplifies small initial magnetic fluctuations. Numerical simulations of turbulence have revealed that turbulence consists of filament-like vortex structures superimposed on an incoherent background, which carry a considerable amount of the energy. The natural questions to ask are whether these coherent structures can generate a magnetic field and, if so, if the generated magnetic field is also filament-like. After setting up a turbulence model which consists only of vortex filaments, we show in an unambiguous way that the coherent structure can sustain kinematic dynamo action and that the magnetic field thus generated consists of relatively thick ribbons (flattened tubes) located in between vortices

6

Magnetic field generation in curved spacetimes  

CERN Document Server

Using the generally covariant magnetofluid formalism for a hot plasma, a new curvature (of space time) driven mechanism for generating seed vorticity/magnetic field is presented. The "battery" owes its origin to the interaction between gravity (epitomized in the spatial variation of the metric tensor) and the inhomogeneous plasma thermodynamics. The general relativistic drive for the seed field is evaluated in a simplified model of a hot plasma accreting around a Schwarzschild black hole. Some astrophysical applications are suggested.

Mahajan, Swadesh M

2011-01-01

7

Magnetic field generation in the Galaxy disk  

Energy Technology Data Exchange (ETDEWEB)

The process of the large-scale Galaxy magnetic field generation is determined by the values of two dimensionless dynamo numbers. The rotation curve of the Galaxy is used. The radial variations of the ionized gas layer thickness and a characteristic velocity of turbulent motions are taken into account. The dynamo mechanism acts in the main body of the galactic disk producing a non-oscillatory even azimuthal field and a quadrupolar hollow field. But in the inner part of the Galaxy oscillatory and steady fields of dipole and quadrupole symmetry are possible. The dynamo action is impossible in the 4<=r<=6 kpc interval. The space boundaries of the dynamo action region are r<=1 kpc and 8<=r<=20 kpc. The corresponding values of the magnetic field rates of growth are S<=1/(5x10/sup 7/ years) and 1/(5x10/sup 8/ years). The process of penetration of the magnetic field of the disk into a hot gaseous halo surrounding the galactic disk are discussed. Estimation of the value of the magnetic field at the auter-boundary of the halo is equal to 2x10/sup -7/ Gs.

Ruzmaikin, A.A.; Shukurov, A.M. (AN SSSR, Moscow. Inst. Prikladnoj Matematiki; Moskovskij Gosudarstvennyj Univ. (USSR). Gosudarstvennyj Astronomicheskij Inst. ' ' GAISh' ' )

8

Generation of magnetic fields in plasmas  

International Nuclear Information System (INIS)

Relativistic and non-relativistic plasma outflows are quite ubiquitous in astrophysical scenarios, as well as in laboratory plasmas. The propagation of relativistic and non- relativistic charged particle beams in background plasmas provides return currents in the opposite direction and interactions between the currents then drive several plasma instabilities involving the longitudinal (electrostatic instabilities) and trans- verse (electromagnetic instability) modes. Such instabilities have been accepted as possible mechanisms for generating spontaneous magnetic fields in extreme astrophysical environments, such as the gamma-ray bursts (GRBs), pulsar magnetosphere, active galactic nuclei (AGN), as well as in laboratory plasmas such as those in inertial confinement fusion schemes. In the present thesis, we have studied several aspects of waves and instabilities in both unmagnetized and magnetized plasmas. We have calculated the linear growth rates of the plasma instabilities that can occur in the presence of counter-propagating anisotropic plasmas (the Weibel instability/filamentation instability) in an unmagnetized plasma, due to the counter-streaming of electrons and positrons in uniform and nonuniform magnetoplasmas, and by a nonstationary ponderomotive force of an electromagnetic wave in a warm plasma. Comprehensive analytical and numerical studies of plasma instabilities have been made to understand possible mechanisms for purely growing magnetic fields in the pre purely growing magnetic fields in the presence of mobile/immobile ions and (or) cold/mildly hot electron beams. The theory has been developed for a proper understanding of fast as well as slow phenomena in plasmas by using the kinetic, fluid and magnetohydrodynamic (MHD) approaches. Specific applications are presented, including inertial confinement fusion; Gamma- rays bursts (GRBs), and pulsar magnetosphere. We have also studied new and purely growing modes in quantum-plasmas, which happen to be a rapidly growing emerging subfield of plasma physics. We have investigated an oscillatory instability involving dust acoustic-like waves due to a relative drift between the ions and the charged dust particles in quantum dusty magneto-plasma. This study can be of importance in semiconductor plasmas or in astrophysical plasmas, such as those in the cores of white dwarfs

9

Modelling coils system for generating homogeneous magnetic field  

Science.gov (United States)

Magnetometers are used for measuring the characteristics of magnetic field and magnetic properties of the material. A changeable source of a homogeneous magnetic field is necessary for verification and calibration of magnetometers. Often the Helmholtz coil is used for generating magnetic homogeneous field, but homogeneous field area generated by Helmholtz coils is confined to a small volume in the center of the coils. The paper describes result of modeling a coils system to generate a homogeneous magnetic field with increased volume in comparison to Helmholtz coils.

Ogay, V.; Baranov, P.; Stepankova, A.

2014-10-01

10

Visualisation of Magnetic Fields Generated by Helmholtz Coils  

Directory of Open Access Journals (Sweden)

Full Text Available This article deals with a method of a homogenous magnetic field generation using Helmholtz coils. There is also an experiment of a magnetic field visualisation with a digital image processing performed with a magneto-resistive sensor described. At the end of this article, there is a possibility of permeability measurement using digital images of a magnetic field shown.

Jozef Suriansky

2006-01-01

11

Generation of magnetic fields in plasmas  

Energy Technology Data Exchange (ETDEWEB)

Relativistic and non-relativistic plasma outflows are quite ubiquitous in astrophysical scenarios, as well as in laboratory plasmas. The propagation of relativistic and non- relativistic charged particle beams in background plasmas provides return currents in the opposite direction and interactions between the currents then drive several plasma instabilities involving the longitudinal (electrostatic instabilities) and trans- verse (electromagnetic instability) modes. Such instabilities have been accepted as possible mechanisms for generating spontaneous magnetic fields in extreme astrophysical environments, such as the gamma-ray bursts (GRBs), pulsar magnetosphere, active galactic nuclei (AGN), as well as in laboratory plasmas such as those in inertial confinement fusion schemes. In the present thesis, we have studied several aspects of waves and instabilities in both unmagnetized and magnetized plasmas. We have calculated the linear growth rates of the plasma instabilities that can occur in the presence of counter-propagating anisotropic plasmas (the Weibel instability/filamentation instability) in an unmagnetized plasma, due to the counter-streaming of electrons and positrons in uniform and nonuniform magnetoplasmas, and by a nonstationary ponderomotive force of an electromagnetic wave in a warm plasma. Comprehensive analytical and numerical studies of plasma instabilities have been made to understand possible mechanisms for purely growing magnetic fields in the presence of mobile/immobile ions and (or) cold/mildly hot electron beams. The theory has been developed for a proper understanding of fast as well as slow phenomena in plasmas by using the kinetic, fluid and magnetohydrodynamic (MHD) approaches. Specific applications are presented, including inertial confinement fusion; Gamma- rays bursts (GRBs), and pulsar magnetosphere. We have also studied new and purely growing modes in quantum-plasmas, which happen to be a rapidly growing emerging subfield of plasma physics. We have investigated an oscillatory instability involving dust acoustic-like waves due to a relative drift between the ions and the charged dust particles in quantum dusty magneto-plasma. This study can be of importance in semiconductor plasmas or in astrophysical plasmas, such as those in the cores of white dwarfs.

Shukla, Nitin

2012-07-01

12

Magnetic helicity generation from the cosmic axion field  

International Nuclear Information System (INIS)

The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about vertical bar HB vertical bar ?(10-20G)2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields

13

Magnetic Helicity Generation from the Cosmic Axion Field  

CERN Document Server

The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about |H_B| \\simeq (10^{-20} G)^2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields.

Campanelli, L

2005-01-01

14

Magnetic Helicity Generation from the Cosmic Axion Field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about |H_B| \\simeq (10^{-20} G)^2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the...

Campanelli, L.; Giannotti, M.

2005-01-01

15

Generation of a magnetic field in a weakly ionized plasma  

International Nuclear Information System (INIS)

A possibility of quasistationary magnetic field generation in weakly ionized plasma, present in the field of intense high-frequency radiation is investigated. It is shown that non-collinearity of electron density gradients and high-frequency field intensity appears to be the reason for magnetic field generation in one-atom gas plasma, and generation rate itself is proportional to the atom mass. Apart from this reason, magnetic field generation caused by non-collinearity of electron density gradients and molecule temperature is possible in weakly ionized plasma. In this case the higher the magnitude of the both magnetic field the share of energy lost by electron for the excitation of rotation levels of molecules

16

Numerical methods for studying compressed magnetic field generators  

International Nuclear Information System (INIS)

Explosively driven compressed magnetic field (CMF) power supplies have been used for a variety of applications. A two-dimensional MHD computational model, entitled COMAG, has been constructed to study the characteristics of helically wound CMF generators. The code combines an existing Eulerian materials response code with a two-dimensional (2D) magnetic field solver to compute the self-consistent interaction between the field and the conductors, including magnetic forces, Joule heating, and nonlinear resistive diffusion. Sample results are presented

17

The Model of Magnetic-Field Generation with Screw Dynamo  

CERN Document Server

This paper considers a possibility of magnetic-field generation by local turbulent flows at the bottom of convective zone. The cycle of magnetic-field generation in this model can be represented in the form of sequency of processes. There are vortexes with azimuth axis, similar with Taylor vortex, close to the bottom of convection zone. This leads to the generation of twisted flux tubes because of screw dynamo. The growth of magnetic field causes emersion of U- loops. During the process of emersion and extraction azimuthal field of flux tubes converts to axial field, and reaches the surface as bipolar of sunspots with U-shaped configuration. Due to differential rotation residual bipolar fields stretch out to the surface toroidal field and are shifted to the bottom of the convective zone by means of meridional flow at high latitudes. The direction of the toroidal field within the generation zone reverses its sign, and the cycle is repeated.

Tlatov, Andrey G

2013-01-01

18

RESISTIVE MAGNETIC FIELD GENERATION AT COSMIC DAWN  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Relativistic charged particles (CRs for cosmic rays) produced by supernova explosion of the first generation of massive stars that are responsible for the reionization of the universe escape into the intergalactic medium, carrying an electric current. Charge imbalance and induction give rise to a return current, ? jt , carried by the cold thermal plasma which tends to cancel the CR current. The electric field, ?E = n? jt , required to draw the collisional return current opposes the outf...

Miniati, F.; Bell, Ar

2011-01-01

19

Interstellar Turbulent Magnetic Field Generation by Plasma Instabilities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The maximum magnetic field strength generated by Weibel-type plasma instabilities is estimated for typical conditions in the interstellar medium. The relevant kinetic dispersion relations are evaluated by conducting a parameter study both for Maxwellian and for suprathermal particle distributions showing that micro Gauss magnetic fields can be generated. It is shown that, depending on the streaming velocity and the plasma temperatures, either the longitudinal or a transverse...

Tautz, R. C.; Triptow, J.

2013-01-01

20

Interstellar Turbulent Magnetic Field Generation by Plasma Instabilities  

CERN Document Server

The maximum magnetic field strength generated by Weibel-type plasma instabilities is estimated for typical conditions in the interstellar medium. The relevant kinetic dispersion relations are evaluated by conducting a parameter study both for Maxwellian and for suprathermal particle distributions showing that micro Gauss magnetic fields can be generated. It is shown that, depending on the streaming velocity and the plasma temperatures, either the longitudinal or a transverse instability will be dominant. In the presence of an ambient magnetic field, the filamentation instability is typically suppressed while the two-stream and the classic Weibel instability are retained.

Tautz, R C

2013-01-01

 
 
 
 
21

Generation of dynamo magnetic fields in thin Keplerian disks  

International Nuclear Information System (INIS)

The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation front. 36 refs

22

Generation of large scale magnetic fields at recombination epoch  

Digital Repository Infrastructure Vision for European Research (DRIVER)

It is argued that large scale cosmic magnetic field could be generated in the primeval plasma slightly before hydrogen recombination. Non-zero vorticity, necessary for that, might be created by the photon diffusion in the second order in the temperature fluctuations. The resulting seed fields at galactic scale would be only 4 orders of magnitude smaller than the observed ones and with a mild galactic dynamo amplifying the seed fields by the factor $\\sim 10^4$ an existence of...

Berezhiani, Z.; Dolgov, A. D.

2003-01-01

23

Relativistic Scott correction in self-generated magnetic fields.  

DEFF Research Database (Denmark)

We consider a large neutral molecule with total nuclear charge Z in a model with self-generated classical magnetic field and where the kinetic energy of the electrons is treated relativistically. To ensure stability, we assume that Za < 2/p, where a denotes the fine structure constant. We are interested in the ground state energy in the simultaneous limit Z ¿ 8, a ¿ 0 such that ¿ = Za is fixed. The leading term in the energy asymptotics is independent of ¿, it is given by the Thomas-Fermi energy of order Z7/3 and it is unchanged by including the self-generated magnetic field. We prove the first correction term to this energy, the so-called Scott correction of the form S(aZ)Z2. The current paper extends the result of Solovej et al. [Commun. Pure Appl. Math. LXIII, 39–118 (2010)] on the Scott correction for relativistic molecules to include a self-generated magnetic field. Furthermore, we show that the corresponding Scott correction function S, first identified by Solovej et al. [Commun. Pure Appl. Math. LXIII,39–118 (2010)], is unchanged by including a magnetic field. We also prove new Lieb-Thirring inequalities for the relativistic kinetic energy with magnetic fields.

Erdos, Laszlo; Fournais, SØren

2012-01-01

24

Second order semiclassics with self-generated magnetic fields  

DEFF Research Database (Denmark)

We consider the semiclassical asymptotics of the sum of negative eigenvalues of the three-dimensional Pauli operator with an external potential and a self-generated magnetic field B. We also add the field energy ß¿B 2 and we minimize over all magnetic fields. The parameter ß effectively determines the strength of the field. We consider the weak field regime with ßh2 = const > 0, where h is the semiclassical parameter. For smooth potentials we prove that the semiclassical asymptotics of the total energy is given by the non-magnetic Weyl term to leading order with an error bound that is smaller by a factor h 1+e , i.e. the subleading term vanishes. However for potentials with a Coulomb singularity, the subleading term does not vanish due to the non-semiclassical effect of the singularity. Combined with a multiscale technique, this refined estimate is used in the companion paper (Erdos et al. in Scott correction for large molecules with a self-generated magnetic field, Preprint, 2011) to prove the second order Scott correction to the ground state energy of large atoms and molecules.

Erdös, Laszlo; Fournais, SØren

2012-01-01

25

Generation of magnetic fields in Einstein-Aether gravity  

CERN Document Server

Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \\sim 10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in General Relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-Aether gravity model, in which the aether field can act as a new source of vector metric perturbations and thus of magnetic fields. We estimate the angular power spectra of temperature and B-mode polarization of the Cosmic Microwave Background (CMB) Anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the pow...

Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi

2013-01-01

26

Generation and measurement of pulsed high magnetic field  

CERN Document Server

Pulsed magnetic field has been generated by discharging a capacitor bank through a 5-layer air-core solenoid. The strength of the magnetic field at its peak has been measured using the voltage induced in various pick-up coils, and also from the Zeeman splitting of an ion having a known g value. Synchronizing a xenon flash at the peak of the magnetic field, this lab-made instrument has been made well suited to study the Zeeman effect, etc. at a temperature of 25 K. As an application of this setup, we have investigated the Zeeman splitting of the sup 4 I sub 9 sub / sub 2-> sup 4 G sub 5 sub / sub 2 transition of the Nd sup 3 sup + -doped CsCdCl sub 3 crystal at 7.8 T, and determined the splitting factors.

Jana, S

2000-01-01

27

On the electric and magnetic field generation in expanding plasmas  

International Nuclear Information System (INIS)

This thesis deals with the generation of electric and magnetic fields in expanding plasmas. The theoretical model used to calculate the different field quantities in such plasmas is discussed in part 1 and is in fact an analysis of Ohm's law. A general method is given that decomposes each of the forces terms in Ohm's law in a component that induces a charge separation in the plasma and in a component that can drive current. This decomposition is unambiguous and depends upon the boundary conditions for the electric potential. It is shown that in calculating the electromagnetic field quantities in a plasma that is located in the vicinity of a boundary that imposes constraints on the electric potential, Ohm's law should be analyzed instead of the so-called induction equation. Three applications of the model are presented. A description is given of the unipolar arc discharge where both plasma and sheath effects have been taken into account. Secondly a description is presented of the plasma effects of a cathode spot. The third application of the model deals with the generation of magnetic fields in laser-produced plasmas. The second part of this thesis describes the experiments on a magnetized argon plasma expanding from a cascaded arc. With the use of spectroscopic techniques the electron density, ion temperature and the rotation velocity profiles of the ion gas have been determined. The magnetic field generated by the plasma has been measured with the use of the Zeeman effect. Depending on the channel diameter of the nozzle of the cascaded arc, self-generated magnetic fields with axial components of the order of 1% of the externally applied mangetic field have been observed. From the measured ion rotation it has been concluded that this magnetic field is mainly generated by azimuthal electron currents. The corresponding azimuthal current density is of the order of 15% of the axial current density. The observed ion rotation is caused by electron-ion friction. (author). 77 refs.; 69 figs.; 1 tab

28

Generation of cosmic magnetic fields in electroweak plasma  

CERN Document Server

We study the generation of strong magnetic fields in magnetars and in the early universe. For this purpose we calculate the antisymmetric contribution to the photon polarization tensor in a medium consisting of an electron-positron plasma and a gas of neutrinos and antineutrinos, interacting within the Standard Model. Such a contribution exactly takes into account the temperature and the chemical potential of plasma as well as the photon dispersion law in this background matter. It is shown that a nonvanishing Chern-Simons parameter, which appears if there is a nonzero asymmetry between neutrinos and antineutrinos, leads to the instability of a magnetic field resulting to its growth. We apply our result to the description of the magnetic field amplification in the first second of a supernova explosion. It is suggested that this mechanism can explain strong magnetic fields of magnetars. Then we use our approach to study the cosmological magnetic field evolution. We find a lower bound on the neutrino asymmetrie...

Dvornikov, Maxim

2014-01-01

29

Raman Generated Magnetic Fields in Laser Light Speckles  

Energy Technology Data Exchange (ETDEWEB)

In modern 2D and 3D PIC simulations relevant to National Ignition Facility (NIF) parameters, the low frequency magnetic fields associated with the localized fast electron currents generated by Stimulated Raman Scatter have been identified. We consider electron plasma densities from 0.1 to 0.2 of critical density (n{sub c}) and electron plasma temperatures (T{sub e}) from a few keV to over 10 keV in simulations with space scales corresponding to a laser speckle in modeling with our massively parallel PIC code 23. These magnetic fields are {approx} 1 MG, Then the electrons accelerated by the Raman process are magnetized with their Lamor radii on the order of a speckle width. The transport of these hot electrons out of the speckle then becomes a more complex process than generally assumed.

Lasinski, B F; Still, C H; Langdon, A B; Hinkel, D E; Williams, E A

2003-09-02

30

Dark matter and generation of galactic magnetic fields  

CERN Document Server

A mechanism for creation of galactic and intergalactic magnetic fields at a recent cosmological epoch is proposed. We show that in rotating protogalaxies circular electric currents are generated by the interactions of free electrons with dark matter particles while the impact of such interactions on galactic protons is considerably weaker. Light dark matter particles can be efficient for generation of such currents if these particles have some long range interactions. In particular, millicharged warm dark matter particles or light mirror particles with the photon kinetic mixing to the usual matter are considered. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales without need for a strong dynamo amplification. On the other hand, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. We also discuss how the global motion of the ionized gas ...

Berezhiani, Zurab; Tkachev, I I

2013-01-01

31

An investigation of electromagnetic rig-generated strong magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis, two alternative solenoid designs are presented: 'Air-core' coil design and 'C-shape' coil design. The coils were designed to be capable of generating strong and static magnetic fields in various samples of magnetic materials. In the case of the first design, the sample would be placed in the central air space. In the second design, the sample would be placed in part of the 'jaws' of the 'C' shape. It was intended that the rig would be used to measure the magnetostriction strai...

Ekreem, Nasser B.

2009-01-01

32

A limitation of the generation of magnetic fields. [astrophysics  

Science.gov (United States)

Simple arguments are put forward to show that the currents produced in disks by radiative or other types of drag forces on electrons must give rise to extraordinarily small magnetic fields. The field strengths are consistent with earlier (more complex) treatments of this class of problem, but inconsistent with the claims of recent papers in the literature. The discrepancies involve the treatment of self-induction. Ion-electron inductive coupling limits the generated magnetic field to have an associated ion Larmor radius greater than or of order of the radius of the disk, a result which follows most directly from conservation of canonical ion momentum, p + eA/c. An explicit time-dependent model for the buildup of the field leads to the same conclusion. If internal velocity gradient scales are smaller than the ion Larmor radius, and the plasma is not collision dominated, standard dynamo amplification within the disk is hardly likely to be effective. But to explain the Galactic field, dynamo amplification in a collisional plasma is also likely to be problematic. The difficulties posed by the existence of ordered Galactic-scale magnetic fields are made all the more acute by the simplicity and the scope of the discussed field limitation.

Balbus, Steven A.

1993-01-01

33

On the leak width of bumpy line cusp magnetic field generated by permanent magnets  

International Nuclear Information System (INIS)

Plasma leak width of the line cusp is investigated with a bumpy cusp magnetic field generated by arrays of permanent magnets. Electron density and space potential are used to specify the leak width. It is shown that the so-called hybrid gyrodiameter is an adequate measure of the leak width even when there is a periodic variation of the magnetic field strength along the line cusp. (author)

34

High magnetic field generation for laser-plasma experiments  

International Nuclear Information System (INIS)

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

35

High Magnetic field generation for laser-plasma experiments  

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-05-01

36

Generation of local magnetic field; application to VCSEL  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract In this article, we report on the simulation and realization of a magnetic circuit allowing to apply an axial magnetic field higher than 1 T. The proposed electromagnet is used to investigate the influence of a magnetic field on the polarization behavior of a vertical-cavity-surface-emitting laser (VCSEL). A non-linear polarization behavior can be experimentally observed for currents as low as the threshold current, provided that the magnetic field is strong enough.

Gaiffe, O.; Euphrasie, S.; Cretin, B.; Vairac, P.

2009-01-01

37

Dark matter and generation of galactic magnetic fields  

International Nuclear Information System (INIS)

A new scenario for creation of galactic magnetic fields is proposed which is operative at the cosmological epoch of the galaxy formation, and which relies on unconventional properties of dark matter. Namely, it requires existence of feeble but long range interaction between the dark matter particles and electrons. In particular, millicharged dark matter particles or mirror particles with the photon kinetic mixing to the usual photon can be considered. We show that in rotating protogalaxies circular electric currents can be generated by the interactions of free electrons with dark matter particles in the halo, while the impact of such interactions on galactic protons is considerably weaker. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales with the help of moderate dynamo amplification. In addition, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. The global motion of the ionized gas could produce sufficiently large magnetic fields also in filaments and galaxy clusters. (orig.)

38

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets  

Science.gov (United States)

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), supernova remnants, and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that particle acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration' is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different spectral 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. We will review recent PIC simulations of relativistic jets and try to make a connection with observations.

Nishikawa, K.-I.; Hardee, P.; Hededal, C.; Mizuno, Yosuke; Fishman, G. Jerry; Hartmann, D. H.

2006-01-01

39

Dark matter and generation of galactic magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

A new scenario for creation of galactic magnetic fields is proposed which is operative at the cosmological epoch of the galaxy formation, and which relies on unconventional properties of dark matter. Namely, it requires existence of feeble but long range interaction between the dark matter particles and electrons. In particular, millicharged dark matter particles or mirror particles with the photon kinetic mixing to the usual photon can be considered. We show that in rotating protogalaxies circular electric currents can be generated by the interactions of free electrons with dark matter particles in the halo, while the impact of such interactions on galactic protons is considerably weaker. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales with the help of moderate dynamo amplification. In addition, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. The global motion of the ionized gas could produce sufficiently large magnetic fields also in filaments and galaxy clusters. (orig.)

Berezhiani, Zurab [Universita dell' Aquila, Dipartimento di Fisica and Chemica, Coppito, L' Aquila (Italy); Laboratori Nazionali Gran Sasso, INFN, Assergi, L' Aquila (Italy); Dolgov, A.D. [Novosibirsk State University, Novosibirsk (Russian Federation); ITEP, Moscow (Russian Federation); Universita di Ferrara, Dipartimento di Fisica, Ferrara (Italy); INFN, Sezione di Ferrara, Ferrara (Italy); Tkachev, I.I. [Novosibirsk State University, Novosibirsk (Russian Federation); Institute of Nuclear Research, Moscow (Russian Federation)

2013-10-15

40

Dark matter and generation of galactic magnetic fields  

Science.gov (United States)

A new scenario for creation of galactic magnetic fields is proposed which is operative at the cosmological epoch of the galaxy formation, and which relies on unconventional properties of dark matter. Namely, it requires existence of feeble but long range interaction between the dark matter particles and electrons. In particular, millicharged dark matter particles or mirror particles with the photon kinetic mixing to the usual photon can be considered. We show that in rotating protogalaxies circular electric currents can be generated by the interactions of free electrons with dark matter particles in the halo, while the impact of such interactions on galactic protons is considerably weaker. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales with the help of moderate dynamo amplification. In addition, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. The global motion of the ionized gas could produce sufficiently large magnetic fields also in filaments and galaxy clusters.

Berezhiani, Zurab; Dolgov, A. D.; Tkachev, I. I.

2013-10-01

 
 
 
 
41

Construction of various types of strong magnetic field generators using superconducting bulk magnets  

International Nuclear Information System (INIS)

We have succeeded in constructing a superconducting permanent magnet system capable of generating 3.2 T by melt-processed bulk superconductors. The trapped field was measured in the open gap between the magnetic poles settled face to face after the pulsed-field magnetization technique called the 'IMRA' method operated at 38 K. A novel face-to-face field generator has been composed by a pair of wide magnetic poles installed with seven bulk superconductors arranged in one plane. The magnetic pole is 150 mm in diameter. The performance of the magnetic field by the field cooling method by a 5 T conduction-cooled superconducting solenoid reached 1.4 and 0.9 T at the centre of the vacuum chamber surface and at the centre of the open space between the magnetic poles with a gap of 34 mm. The intense magnetic fields are investigated for application in various industries such as the magnetic separation technique and so on in the Iwate CREATE (Collaboration of Regional Entities for the Advancement of Technological Excellence) project supported by the Japanese government

42

Poloidal magnetic field generation in laser plasma interaction  

International Nuclear Information System (INIS)

The generation of poloidal magnetic field in an inhomogeneous cold, collisionless plasma by an elliptically polarized Gaussian laser beam is presented. It has been shown that self generated magnetic field (SGMF) of the order of mega Gauss is introduced by the laser inhomogeneity effect even for a normal incident Gaussian beam in both uniform and non-uniform plasmas and scales as I0?. Numerically it has been estimated that for homogeneous laser beam (using focal spot radius ? density scale length), I0?1020 Wm-2, ??1.06 ?m, incident angle ?0?22.5 degree, n0?5 x 1026 m-3, the poloidal SGMF (Bx)?0.115 MG, whereas for CO2 laser (??10.6 ?m) with I0?1018 Wm-2, n0?5 x 1024 m-3, the authors get a Bx?1.4 tesla. For inhomogeneous laser beam incident almost normally the authors get an induced poloidal SGMG?0.39 MG for I0?1020 Wm-2 and ??1.06 ?m which is shown as independent of the density profile structure

43

Magnetic Field Generation in Intense Laser-Matter Interactions  

Science.gov (United States)

The multi-fluid implicit plasma simulation code ANTHEM^1 has been used to study the transport of hot electrons generated by an intense (>= 3 x 10^18 W/cm^2) short pulse 1.06 ?m laser into plasma tagets over a broad range of densities (0.35 to 10^4 n_crit), as arising in the Fast Ignitor apporach to Inertial Confinement Fusion. The most intense (30 MG to 1.5 GG) magnetic fields generated in this interaction are traced to the ponderomotive push on background electrons, and tardy electron shielding. At densities slightly exceeding critical relativistic lowering of the plasma frequency results in burn-though by the laser. At higher backgound densities the stong magnetic fields focus the incident hot electron stream toward the center of the spot. They can also confine heated electrons to the neighboring surface, aiding ignition, but leading possibly to energy loss through fast ion blow off. ^1 R. J. Mason, J. Comput. Phys. 71, 429 (1987). Work supported by the USDOE.

Thomas, V. A.; Mason, R. J.; Cobble, J. A.; Tabak, M.

1997-11-01

44

The use of mirror image symmetry in coil winding, applications and advantages in magnetic field generation  

International Nuclear Information System (INIS)

In this paper, an improved method of winding inductors, transformers and motors is discovered. This invention greatly enhances the ability to generate magnetic fields with a given amount of wire. This invention may be as fundamental to the use of magnetic fields as was Nikola Tesla's use of rotating magnetic fields for the generation of alternating current

45

Rotation invariance of electromagnetic radiation generated by relativistic particles in magnetic fields  

International Nuclear Information System (INIS)

This paper deals with electromagnetic radiation generated by relativistic particles in arbitrary planar magnetic field (in undulator for example). Magnetic system producing this field is assumed to be planar consisting of permanent magnets. It is shown that there is a special class of magnetic moment rotations in such system while magnetic field is varying but spontaneous radiation spectrum generated by relativistic particles remains the same. This property of electromagnetic radiation can be used in designing new undulators

46

Projectile-power-compressed magnetic-field pulse generator  

International Nuclear Information System (INIS)

Design considerations and experimental results are presented of a compressed magnetic field pulsed energy source. A 100-mm-diameter, gun-fired projectile of approx. 2MJ kinetic energy was the input energy source. An initial magnetic field was trapped and compressed by the projectile. With a shorted load, a magajoule in a nanohenry was the design goal, i.e., 50 percent energy transformation from kinetic to magnetic. Five percent conversion was the highest recorded before gauge failure

47

Magnetic-Field Generation by Randomly Forced Shearing Waves  

CERN Document Server

A rigorous theory for the generation of a large-scale magnetic field by random nonhelically forced motions of a conducting fluid combined with a linear shear is presented in the analytically tractable limit of Rm << Re << 1. This is a minimal proof-of-concept calculation aiming to put the shear dynamo, a new effect recently reported in a number of numerical experiments, on a firm physical and analytical footing. Numerically observed scalings of the wavenumber and growth rate of the fastest growing mode, previously not understood, are derived analytically. The simplicity of the model suggests that shear dynamo may be a generic property of shear flows -- with ubiquitous relevance to astrophysical systems.

Schekochihin, A A; Kleeorin, N; Lesur, G; Mallet, A; McWilliams, J C; Rogachevskii, I; Yousef, T A

2008-01-01

48

On the problem of magnetic field generation by helical turbulence  

Science.gov (United States)

Mean-field electrodynamics, including both the -effect and the effect of Lorentz forces damping action on small-scale helical fluid motions (the latter taken in the limit of low magnetic Reynolds number values) is formulated for the electrically conducting, rotating, inviscid Boussinesq fluid. A self-consistent system of two coupled ordinary differential equations in terms of mean magnetic field intensity and helicity bulk density is derived for the case of spatial homogeneity and isotropy. The mean-field induction equation takes into account both the -effect and the effect of magnetic viscosity. The helicity balance equation contains the helicity source due to buoyant forcing and the helicity sink because of Ohmic dissipation. This system has the unique stationary solution, which is the global attractor, and describes the saturated values of mean magnetic field intensity and helicity. Possible implications to the problem of the terrestrial magnetism are discussed briefly.

Kurgansky, M. V.

49

Magnetic flux concentrations from dynamo-generated fields  

CERN Document Server

The mean-field theory of magnetized stellar convection gives rise to the two possibility of distinct instabilities: the large-scale dynamo instability, operating in the bulk of the convection zone, and a negative effective magnetic pressure instability (NEMPI) operating in the strongly stratified surface layers. The latter might be important in connection with magnetic spot formation, but the growth rate of NEMPI is suppressed with increasing rotation rates, although recent direct numerical simulations (DNS) have shown a subsequent increase in the growth rate. We examine quantitatively whether this increase in the growth rate of NEMPI can be explained by an alpha squared mean-field dynamo, and whether both NEMPI and the dynamo instability can operate at the same time. We use both DNS and mean-field simulations (MFS) to solve the underlying equations numerically either with or without an imposed horizontal field. We use the test-field method to compute relevant dynamo coefficients. DNS show that magnetic flux ...

Jabbari, Sarah; Losada, Illa R; Kleeorin, Nathan; Rogachevskii, Igor

2014-01-01

50

Self-Collimation and Magnetic Field Generation of Astrophysical Jets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A novel model for collimation and transport of electron-positron-ion jets is presented. Analytical results show that the filamentary structures can be sustained by self-induced toroidal magnetic fields permeating through the filaments, whose widths significantly expand in the pair-dominant regimes. The magnetic field strength reflects a characteristic of equipartition of excess kinetic energy of the jets. It is also shown that growth of the hoselike instability is strongly s...

Honda, Mitsuru; Honda, Yasuko S.

2002-01-01

51

The spontaneous generation of magnetic and chromomagnetic fields at high temperature in the Standard Model  

CERN Document Server

The spontaneous generation of the magnetic and chromomagnetic fields at high temperature is investigated in the Standard Model. The consistent effective potential including the one-loop and the daisy diagrams of all boson and fermion fields is calculated. The mixing of the generated fields due to the quark loop diagram is studied in detail. It is found that the quark contribution increases the magnetic and chromomagnetic field strengths as compared with the separate generation of fields. The magnetized vacuum state is stable due to the magnetic gauge field masses included in the daisy diagrams. Some applications of the results obtained are discussed.

Demchik, V I

2001-01-01

52

The spontaneous generation of magnetic and chromomagnetic fields at high temperature in the standard model  

International Nuclear Information System (INIS)

The spontaneous generation of magnetic and chromomagnetic fields at high temperature is investigated in the standard model. The consistent effective potential including the one-loop and the daisy diagrams of all boson and fermion fields is calculated. The mixing of the generated fields due to the quark loop diagram is studied in detail. It is found that the quark contribution increases the magnetic and chromomagnetic field strengths as compared with the separate generation of fields. The magnetized vacuum state is stable due to the magnetic gauge field masses included in the daisy diagrams. Some applications of the results obtained are discussed. (orig.)

53

Magnetic flux concentrations from dynamo-generated fields  

Science.gov (United States)

Context. The mean-field theory of magnetized stellar convection gives rise to two distinct instabilities: the large-scale dynamo instability, operating in the bulk of the convection zone and a negative effective magnetic pressure instability (NEMPI) operating in the strongly stratified surface layers. The latter might be important in connection with magnetic spot formation. However, as follows from theoretical analysis, the growth rate of NEMPI is suppressed with increasing rotation rates. On the other hand, recent direct numerical simulations (DNS) have shown a subsequent increase in the growth rate. Aims: We examine quantitatively whether this increase in the growth rate of NEMPI can be explained by an ?2 mean-field dynamo, and whether both NEMPI and the dynamo instability can operate at the same time. Methods: We use both DNS and mean-field simulations (MFS) to solve the underlying equations numerically either with or without an imposed horizontal field. We use the test-field method to compute relevant dynamo coefficients. Results: DNS show that magnetic flux concentrations are still possible up to rotation rates above which the large-scale dynamo effect produces mean magnetic fields. The resulting DNS growth rates are quantitatively reproduced with MFS. As expected for weak or vanishing rotation, the growth rate of NEMPI increases with increasing gravity, but there is a correction term for strong gravity and large turbulent magnetic diffusivity. Conclusions: Magnetic flux concentrations are still possible for rotation rates above which dynamo action takes over. For the solar rotation rate, the corresponding turbulent turnover time is about 5 h, with dynamo action commencing in the layers beneath.

Jabbari, S.; Brandenburg, A.; Losada, I. R.; Kleeorin, N.; Rogachevskii, I.

2014-08-01

54

Dynamical quark mass generation in a strong external magnetic field  

CERN Document Server

We investigate the effect of a strong magnetic field on dynamical chiral symmetry breaking in quenched and unquenched QCD. To this end we apply the Ritus formalism to the coupled set of (truncated) Dyson-Schwinger equations for the quark and gluon propagator under the presence of an external constant Abelian magnetic field. We work with an approximation that is trustworthy for large fields eH > \\Lambda_{QCD}^2 but is not restricted to the lowest Landau level. We confirm the linear rise of the quark condensate with large external field previously found in other studies and observe the transition to the asymptotic power law at extremely large fields. We furthermore quantify the validity of the lowest Landau level approximation and find substantial quantitative differences to the full calculation even at very large fields. We discuss unquenching effects in the strong field propagators, condensate and the magnetic polarization of the vacuum. We find a significant weakening of magnetic catalysis caused by the back...

Mueller, Niklas; Fischer, Christian S

2014-01-01

55

Yukawa interactions and dynamical generation of mass in an external magnetic field  

International Nuclear Information System (INIS)

In this work we study the dynamical generation of a fermion mass induced by a constant and uniform external magnetic field in an Abelian gauge model with a Yukawa term. We show that the Yukawa coupling not only enhances the dynamical generation of the mass, but it substantially decreases the magnetic field required for the mass to be generated at temperatures comparable to the electroweak critical temperature. These results indicate that if large enough primordial magnetic fields were present during the early universe evolution, the field-induced generation of fermion masses, which in turn corresponds to the generation of fermion bound states, may play an important role in the electroweak phase transition

56

Effect of a magnetic field generated by permanent magnets on the GPD polarization sensitivity  

Science.gov (United States)

The Gas Pixel Detector (GPD) is an imaging X-ray polarimeter with a moderate spectral resolution and a very good position resolution.1, 2 The GPD derives this information from the true 2-d charge image of the photoelectron track produced in gas and collected by an ASIC CMOS chip after its drift and its multiplication. In this paper we report on the experimental results of the study of the effect of a strong magnetic field in reducing the diffusion and increasing the sensitivity for a GPD filled with one bar of He-DME 20-80. We generated a magnetic field of about 1600 Gauss by means of commercial magnets made of an alloy of Neodymium-Iron-Boron configured as one ring and one cylinder. We compared the pixel size distributions and the modulation curves with and without magnets at two different drift fields, corresponding to different nominal diffusion properties, with both polarized and unpolarized sources. The results obtained show that a not sensitive improvement is present at this fields implying that a much larger magnetic field is necessary with this mixture, albeit a shift on the position angle of the modulation curve, derived from a polarized source, is observed.

Soffitta, Paolo; Costa, Enrico; Morbidini, Alfredo; Muleri, Fabio; Rubini, Alda; Spiga, Daniele; Bellazzini, Ronaldo; Brez, Alessandro; de Ruvo, Luca; Minuti, Massimo; Pinchera, Michele; Spandre, Gloria

2014-07-01

57

Magnetic guide field generation in collisionless current sheets  

Directory of Open Access Journals (Sweden)

Full Text Available In thin (?< few ?i collisionless current sheets in a space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal fluctuation level by the action of the non-magnetic Weibel instability (Weibel, 1959. The instability is driven by the counter-streaming electron inflow from the "ion diffusion" (ion inertial Hall region into the inner current (electron inertial region after thermalisation by the two-stream instability. Under magnetospheric tail conditions it takes ~50 e-folding times (~100 s for the Weibel field to reach observable amplitudes |bW|~1 nT. In counter-streaming inflows these fields are of guide field type.

W. Baumjohann

2010-03-01

58

Parametric generation of the magnetic field and the activity in Crab nebula  

International Nuclear Information System (INIS)

The parametric generation of the magnetic field in a plasma is considered. It is shown that in the Crab Nebula plasma regions, where certain resonance conditions hold, a powerful electromagnetic wave is capable of generating a stationary magnetic field. A new mechanism of the appearance of wisps that characterize the lasting activity of the Crab Nebula is suggested

59

Generation of quasistationary magnetic fields in a plasma with non- Maxwell electron distribution  

International Nuclear Information System (INIS)

Generation of quasistationary magnetic fields in plasma with the non-Maxwellian function of electron distribution is investigated theoretically. It is shown that anisotropy of electron tempera-- ture and the presence of fast electron impurity affect considerably the generation efficiency of the quasistationary magnetic fields

60

SSWL and BWL: finite element models of compressed magnetic field current generators  

Energy Technology Data Exchange (ETDEWEB)

Documentation is presented for two new computer codes modeling the behavior of compressed magnetic field current generators. Code output results for the typical generator configurations are presented and compared to experimental results. (auth)

Tucker, T.J.; Leeman, J.E.

1976-01-01

 
 
 
 
61

Geometrical generation of cosmic magnetic fields within standard electromagnetism  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english We study the evolution of cosmological magnetic fields in FRW models with curved spatial sections and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to FRW universes with open spatial s [...] ections. We discuss the general relativistic nature of the effect and show how it modifies the adiabatic magnetic evolution by reducing the depletion rate of the field. Assuming a universe that is only marginally open today (i.e. for 1-omega0 ~ 10-2), we estimate the main features of the superadiabatically amplified residual field and find that is of astrophysical interest.

Christos G., Tsagas; Alejandra, Kandus.

1070-10-01

62

Ultra-High Intensity Magnetic Field Generation in Dense Plasma  

Energy Technology Data Exchange (ETDEWEB)

I. Grant Objective The main objective of this grant proposal was to explore the efficient generation of intense currents. Whereasthefficient generation of electric current in low-­?energy-­? density plasma has occupied the attention of the magnetic fusion community for several decades, scant attention has been paid to carrying over to high-­?energy-­? density plasma the ideas for steady-­?state current drive developed for low-­?energy-­? density plasma, or, for that matter, to inventing new methodologies for generating electric current in high-­?energy-­?density plasma. What we proposed to do was to identify new mechanisms to accomplish current generation, and to assess the operation, physics, and engineering basis of new forms of current drive in regimes appropriate for new fusion concepts.

Fisch, Nathaniel J

2014-01-08

63

Magnetic-Field Generation and Amplification in an Expanding Plasma  

Science.gov (United States)

Particle-in-cell simulations are used to investigate the formation of magnetic fields B in plasmas with perpendicular electron density and temperature gradients. For system sizes L comparable to the ion skin depth di, it is shown that B˜di/L, consistent with the Biermann battery effect. However, for large L/di, it is found that the Weibel instability (due to electron temperature anisotropy) supersedes the Biermann battery as the main producer of B. The Weibel-produced fields saturate at a finite amplitude (plasma ??100), independent of L. The magnetic energy spectra below the electron Larmor radius scale are well fitted by the power law with slope -16/3, as predicted by Schekochihin et al. [Astrophys. J. Suppl. Ser. 182, 310 (2009)].

Schoeffler, K. M.; Loureiro, N. F.; Fonseca, R. A.; Silva, L. O.

2014-05-01

64

Magnetic field generation and amplification in an expanding plasma  

CERN Document Server

Particle-in-cell simulations are used to investigate the formation of magnetic fields, B, in plasmas with perpendicular electron density and temperature gradients. For system sizes, L, comparable to the ion skin depth, d_i, it is shown that B ~ d_i/L, consistent with the Biermann battery effect. However, for large L/d_i, it is found that the Weibel instability (due to electron temperature anisotropy) supersedes the Biermann battery as the main producer of B. The Weibel-produced fields saturate at a finite amplitude (plasma \\beta \\approx 100), independent of L. The magnetic energy spectra below the electron Larmor radius scale is well fitted by power law with slope -16/3, as predicted in Schekochihin et al., Astrophys. J. Suppl. Ser 182, 310 (2009).

Schoeffler, K M; Fonseca, R A; Silva, L O

2013-01-01

65

Noninvasive Measurements of Magnetic Field Generated by Induced Current within Human Body under Exposure to Very Low Frequency Electromagnetic Fields  

Science.gov (United States)

We have developed a measurement system for a magnetic field that is generated by the induced ionic current within the human body under exposure to very low frequency electromagnetic fields, and compared the magnetic field strength obtained with those of a magnetomyogram (MMG). The developed system consists of an exposure coil, a magnetic sensor, a lock-in detector, and data acquisition. The waveform characteristics of the magnetic field of the induced current (MFIC) of the abdomen from 1 kHz to 400 Hz are obtained. Compared with the magnetic field strength of abdominal MMG, abdominal MFIC is stronger at an exposure electromagnetic field greater than the ?T order.

Tsukada, Keiji; Kiwa, Toshihiko

2005-04-01

66

Magnetic field dependence of singlet oxygen generation by nanoporous silicon  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state. This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

Amonkosolpan, Jamaree; Aliev, Gazi N.; Wolverson, Daniel; Snow, Paul A.; Davies, James John

2014-01-01

67

Magnetic field dependence of singlet oxygen generation by nanoporous silicon  

Science.gov (United States)

Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state. This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

Amonkosolpan, Jamaree; Aliev, Gazi N.; Wolverson, Daniel; Snow, Paul A.; Davies, James John

2014-07-01

68

Generation of compact torus configuration by rotating magnetic fields  

International Nuclear Information System (INIS)

Compact torus configurations can be established by rotating magnetic fields according the ''Rotamak'' concept or utilizing the ''Blevin-Thonemann End Effect'' by a linearly polarized r.f. field. Experiments were performed to investigate both configurations. The r.f. fields are produced up to a power level of 5 MW for a pulse period up to 1.5 msec at a frequency of 1 MHz. In both cases stable compact torus configurations can be maintained during the whole pulse duration. In contrast to the explanation of the ''Blevin-Thonemann End Effect'' the driven d.c. currents have direction of the diamagnetic current only in a limited density domain. On the basis of excitation of magnetoacoustic waves an explaination of these phenomena is undertaken

69

Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows  

CERN Document Server

As the ejecta from supernovae or other energetic astrophysical events stream through the interstellar media, this plasma is shaped by instabilities that generate electric and magnetic fields. Among these instabilities, the Weibel filamentation instability plays a particularly important role, as it can generate significant magnetic fields in an initially un-magnetized medium. It is theorized that these Weibel fields are responsible for the observed gamma-ray burst light curve, particle acceleration in shock waves, and for providing seed fields for larger-scale cosmological magnetic structures. While the presence of these instability-generated fields has been inferred from astrophysical observation and predicted in simulation, observation in experiments is challenging. Here we report direct observation of well-organized, large-amplitude, filamentary magnetic fields associated with the Weibel instability in a scaled laboratory experiment. The experimental images, captured with proton radiography, are shown to be...

Huntington, C M; Ross, J S; Zylstra, A B; Drake, R P; Froula, D H; Gregori, G; Kugland, N L; Kuranz, C C; Levy, M C; Li, C K; Meinecke, J; Morita, T; Petrasso, R; Plechaty, C; Remington, B A; Ryutov, D D; Sakawa, Y; Spitkovsky, A; Takabe, H; Park, H -S

2013-01-01

70

Attosecond Magnetic Field Pulse Generation by Intense Few Cycle Circularly Polarized UV Pulses  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Intense attosecond magnetic field pulses are predicted to be produced by intense few cycle circularly polarized UV pulses. Numerical solutions of the time dependent Schr\\"{o}dinger equation for H$_2^+$ are used to study the dynamical process. Spiralling attosecond circular electron wave packets are created with nanometer molecular dimensions, thus generating magnetic fields of several tens of Teslas ($10^5$ Gauss). Simulations show that the induced magnetic field is critical...

Yuan, Kai-jun; Bandrauk, Andre D.

2013-01-01

71

The spontaneous generation of magnetic fields at high temperature in a supersymmetric theory  

International Nuclear Information System (INIS)

The spontaneous generation of magnetic and chromomagnetic fields at high temperature in the minimal supersymmetric standard model is investigated. The consistent effective potential including the one-loop and the daisy diagrams of all bosons and fermions is calculated and the magnetization of the vacuum is observed. The mixing of the generated fields due to the quark and s-quark loop diagrams and the role of superpartners are studied in detail. It is found that the contribution of these diagrams increases the magnetic and chromomagnetic field strengths as compared with the case of a separate generation of fields. The magnetized vacuum state is found to be stable due to the magnetic masses of gauge fields included in the daisy diagrams. Applications of the results obtained are discussed. A comparison with the standard model case is given. (orig.)

72

The spontaneous generation of magnetic fields at high temperature in a supersymmetric theory  

CERN Document Server

The spontaneous generation of magnetic and chromomagnetic fields at high temperature in the minimal supersymmetric standard model (MSSM) is investigated. The consistent effective potential including the one-loop and the daisy diagrams of all bosons and fermions is calculated and the magnetization of the vacuum is observed. The mixing of the generated fields due to the quark and s-quark loop diagrams and the role of superpartners are studied in detail. It is found that the contribution of these diagrams increases the magnetic and chromomagnetic field strengths as compared with the case of a separate generation of fields. The magnetized vacuum state is found to be stable due to the magnetic masses of gauge fields included in the daisy diagrams. Applications of the results obtained are discussed. A comparison with the standard model case is done.

Demchik, V I

2003-01-01

73

Generation of Primordial Magnetic Fields on Linear Over-density Scales  

CERN Document Server

Magnetic fields appear to be present in all galaxies and galaxy clusters. Recent measurements indicate that a weak magnetic field may be present even in the smooth low density intergalactic medium. One explanation for these observations is that a seed magnetic field was generated by some unknown mechanism early in the life of the Universe, and was later amplified by various dynamos in nonlinear objects like galaxies and clusters. We show that a primordial magnetic field is expected to be generated in the early Universe on purely linear scales through vorticity induced by scale-dependent temperature fluctuations or equivalently, a spatially varying speed of sound of the gas. Residual free electrons left over after recombination tap into this vorticity to generate magnetic field via the Biermann battery process. Although the battery operates even in the absence of any relative velocity between dark matter and gas at the time of recombination, the presence of such a relative velocity modifies the predicted spati...

Naoz, Smadar

2013-01-01

74

A Calculation of Required Magnetic Field Strength in a Magnetohydrodynamic Supersonic Generator and Accelerator  

Science.gov (United States)

A one-dimensional supersonic CFD code was utilized to solve for the required magnetic field strength, as a function of conductivity, for fixed length and constant static enthalpy magnetohydrodynamic generator and accelerator. The inlet velocity and pressure to the generator were varied, while requiring the exit Mach number of the generator to remain at 2.0. The flow after the generator proceeded through a simple supersonic combustion process, and the bypassed energy was then used in the accelerator to increase the flow velocity. Results show that varying the conductivity between 7 and 70 mho/m and inlet velocity between 5000 and 14000 ft/s, require magnetic fields in the generator between 1 and 12 Tesla with greater magnetic field strength required at lower conductivities. It was also calculated that for the same energy and conductivity used in the accelerator, a lower magnetic field was needed.

Lang, Amy W.; Czysz, Paul

2001-11-01

75

Magnetic Field Generation in Core-sheath Jets via the Kinetic Kelvin-Helmholtz Instability  

Science.gov (United States)

We have investigated magnetic field generation in velocity shears via the kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet core and stationary plasma sheath. Our three-dimensional particle-in-cell simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15 for both electron-proton and electron-positron plasmas. For electron-proton plasmas, we find generation of strong large-scale DC currents and magnetic fields that extend over the entire shear surface and reach thicknesses of a few tens of electron skin depths. For electron-positron plasmas, we find generation of alternating currents and magnetic fields. Jet and sheath plasmas are accelerated across the shear surface in the strong magnetic fields generated by the kKHI. The mixing of jet and sheath plasmas generates a transverse structure similar to that produced by the Weibel instability.

Nishikawa, K.-I.; Hardee, P. E.; Du?an, I.; Niemiec, J.; Medvedev, M.; Mizuno, Y.; Meli, A.; Sol, H.; Zhang, B.; Pohl, M.; Hartmann, D. H.

2014-09-01

76

Magnetic Field Generation in Core-Sheath Jets via the Kinetic Kelvin-Helmholtz Instability  

CERN Document Server

We have investigated magnetic field generation in velocity shears via the kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet core and stationary plasma sheath. Our three-dimensional particle-in-cell simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15 for both electron-proton and electron-positron plasmas. For electron-proton plasmas we find generation of strong large-scale DC currents and magnetic fields which extend over the entire shear-surface and reach thicknesses of a few tens of electron skin depths. For electron-positron plasmas we find generation of alternating currents and magnetic fields. Jet and sheath plasmas are accelerated across the shear surface in the strong magnetic fields generated by the kKHI. The mixing of jet and sheath plasmas generates transverse structure similar to that produced by the Weibel instability.

Nishikawa, K -I; Dutan, I; Niemiec, J; Medvedev, M; Mizuno, Y; Meli, A; Sol, H; Zhang, B; Pohl, M; Hartmann, D H

2014-01-01

77

Generation of approximately steady magnetic fields in a plasma with a non-Maxwellian electron distribution  

International Nuclear Information System (INIS)

A theory is derived for the generation of approximately steady magnetic fields in a plasma having a non-Maxwellian electron energy distribution. An anisotropy of the electron temperature and the presence of a hot-electron component strongly affect the efficiency with which the approximately steady magnetic fields are produced

78

Generation of a static magnetic field-free line using two Maxwell coil pairs  

Science.gov (United States)

In this paper, the generation of a magnetic field-free line (FFL) along a constant direction is investigated. It is shown that an FFL gradient field can be generated by two perpendicular Maxwell coil pairs. These coils can be used for imaging distributions of superparamagnetic nanoparticles with high sensitivity applying the magnetic particle imaging technique. To this end, the FFL has to be rapidly moved back and forth while either the object or the coil assembly rotates slowly. The field quality of the proposed coil setup is assessed by manufacturing a prototype and measuring the magnetic field using a Hall-effect sensor.

Knopp, Tobias; Erbe, Marlitt; Sattel, Timo F.; Biederer, Sven; Buzug, Thorsten M.

2010-08-01

79

Octupolar out-of-plane magnetic field structure generation during collisionless magnetic reconnection in a stressed X-point collapse  

CERN Document Server

The out-of-plane magnetic field, generated by fast magnetic reconnection, during collisionless, stressed $X$-point collapse, was studied with a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code, using both closed (flux conserving) and open boundary conditions on a square grid. It was discovered that the well known quadrupolar structure in the out-of-plane magnetic field gains four additional regions of opposite magnetic polarity, emerging near the corners of the simulation box, moving towards the $X$-point. The emerging, outer, magnetic field structure has opposite polarity to the inner quadrupolar structure, leading to an overall octupolar structure. Using Ampere's law and integrating electron and ion currents, defined at grid cells, over the simulation domain, contributions to the out-of-plane magnetic field from electron and ion currents were determined. The emerging regions of opposite magnetic polarity were shown to be the result of ion currents. Magnetic octupolar struct...

von der Pahlen, J Graf

2014-01-01

80

Magnetic fields generated by hydromagnetic dynamos at the low Prandtl number in dependence on the Ekman and magnetic Prandtl numbers  

Science.gov (United States)

This article investigates the dependence of hydromagnetic dynamos on the magnetic Prandtl number at low Prandtl number. In all the investigated cases, the generated magnetic fields are dipolar and neither transition to hemispherical dynamos nor weaker magnetic fields (which are less dipole dominated) were observed, although the inertia becomes important. The magnetic field becomes weak in the polar regions (is "convected out of polar regions") only for low Prandtl numbers, when the inertia becomes important. It is a basic condition. However, whether the magnetic field gets weak in the polar regions (is "convected out of polar regions") or not depends also on the magnetic Prandtl number. The magnetic Prandtl number has to exceed a minimum value in order to sustain dynamo action. If the magnetic diffusion is small (large magnetic Prandtl numbers) then this phenomenon does not exist but if it is large (small magnetic Prandtl numbers) it exists because the strong magnetic diffusion significantly weakens the magnetic field inside the tangent cylinder. The magnetic diffusion and inertia seem to act in the same direction as to weaken the magnetic field inside the tangent cylinder.

Šimkanin, Ján; Hejda, Pavel

2013-04-01

 
 
 
 
81

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets and Supernova Remnants  

Science.gov (United States)

We performed numerical simulations of particle acceleration, magnetic field generation, and emission from shocks in order to understand the observed emission from relativistic jets and supernova remnants. The investigation involves the study of collisionless shocks, where the Weibel instability is responsible for particle acceleration as well as magnetic field generation. A 3-D relativistic particle-in-cell (RPIC) code has been used to investigate the shock processes in electron-positron plasmas. The evolution of theWeibe1 instability and its associated magnetic field generation and particle acceleration are studied with two different jet velocities (0 = 2,5 - slow, fast) corresponding to either outflows in supernova remnants or relativistic jets, such as those found in AGNs and microquasars. Slow jets have intrinsically different structures in both the generated magnetic fields and the accelerated particle spectrum. In particular, the jet head has a very weak magnetic field and the ambient electrons are strongly accelerated and dragged by the jet particles. The simulation results exhibit jitter radiation from inhomogeneous magnetic fields, generated by the Weibel instability, which has different spectral properties than standard synchrotron emission in a homogeneous magnetic field.

Nishikawa, K.-I.; Hartmann, D. H.; Hardee, P.; Hededal, C.; Mizunno, Y.; Fishman, G. J.

2006-01-01

82

Comparison of Weibel instability and magnetic field generating thermal instability  

International Nuclear Information System (INIS)

Comparison of the mechanisms of the Weibel instability and the field generating thermal instability is made on the basis of the Boltzmann equation. The case k perpendicular nabla T0 parallel nabla n0 is investigated, where k is the wave vector, T0 and n0 are the zeroth order temperature and the number density. In the collisional plasma (kl sub(m) > 1), the situation is vice versa. When the equilibrium velocity distribution function is expanded by the Legendre polynomials P sub(l) with the polar axis along nabla T0, l = 2 and l = 1 components are essential, respectively, for the Weibel instability and the thermal instability. (author)

83

Generation of axial and lateral magnetic fields in laser produced plasmas  

International Nuclear Information System (INIS)

The generation of both axial and lateral magnetic fields caused by the interaction of intense radiations with laser produced plasmas has been analytically studied. It is shown that the inverse bremsstrahlung absorption has an impact on the generation of the lateral magnetic field in laser produced plasmas, modifying the lateral thermal energy transport in the coronal region. However, the axial energy transport may remain unaffected. (author). 6 refs

84

Effect of magnetic field variation in ion source on discharge current in NT50 neutron generator  

International Nuclear Information System (INIS)

Based on the ion source discharging experiment in NT50 neutron generator, effect of magnetic field variation in Penning ion source on discharge current is studied. The relation curves of discharge current and changing magnetic fields are obtained. The data are analyzed to discover the role of ion source discharge. The prime working state and parameters of the ion source were determined to improve performance of the neutron generator. (authors)

85

Evaluation of Human Exposure to Magnetic Fields Generated by Electric Power Systems in Complex Configurations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The international growing concern for the human exposure to magnetic fields generated by electric power lines has unavoidably led to imposing legal limits. Respecting these limits, implies being able to calculate easily and accurately the generated magnetic field also in complex configurations. Twisting of phase conductors is such a case. The consolidated exact and approximated theory regarding a single-circuit twisted three-phase power cable line has been reported along with the proposal of ...

Kandia, Effrosyni

2013-01-01

86

One-dimensional models of magnetic fields generated by hypervelocity impact  

International Nuclear Information System (INIS)

One-dimensional theoretical models are obtained for magnetic fields of plasma induced by hypervelocity projectile impacting target, according to existing theories of magnetic fields about laser plasma along with the maxwell's equation and Faraday's law of electromagnetic induction. Meanwhile, Based on the partial differential equations of magnetic fields for semi-sphere plasma cloud generated by hypervelocity normal impact, the partial differential equations of magnetic fields are established for plasma cloud in the form of part of ellipsoid induced by hypervelocity oblique impact in cylindrical coordinate system. Magnetic induction intensity measurement is carried out with magnetic coils through hypervelocity impact experiment. Experimental results and model prediction show that the model can be used to describe the magnetic induction intensity induced by plasma during hypervelocity oblique impact approximately. (authors)

87

Generation of Magnetic Field on the Accretion Disk around a Proto-First-Star  

CERN Document Server

The generation process of magnetic field around a proto-first-star is studied. Utilizing the recent numerical result of proto-first-star formation based upon the radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that magnetic field of \\sim 10^{-9} G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low density regions ...

Shiromoto, Yuki; Hosokawa, Takashi

2014-01-01

88

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

CERN Document Server

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

Veysi, Mehdi; Capolino, Filippo

2014-01-01

89

Generation of large-scale magnetic fields from inflation in teleparallelism  

International Nuclear Information System (INIS)

We explore the generation of large-scale magnetic fields from inflation in teleparallelism, in which the gravitational theory is described by the torsion scalar instead of the scalar curvature in general relativity. In particular, we examine the case that the conformal invariance of the electromagnetic field during inflation is broken by a non-minimal gravitational coupling between the torsion scalar and the electromagnetic field. It is shown that for a power-law type coupling, the magnetic field on 1 Mpc scale with its strength of ? 10?9 G at the present time can be generated

90

Point Probes: a new generation of magnetic sensors for the measurement of local magnetic fields  

International Nuclear Information System (INIS)

In several magnetic Non-Destructive Testing (NDT) methods, the local measurement of the magnetic field inside the material is required. Moreover, looking at difficult part geometries, magnetic field sensors have to be small enough in order to reach the measuring position. The most-used magnetic field sensors are coils, Hall-effect sensors, flux gates and magnetoresistive sensors. However, regarding the industrial application, those sensors are often packaged and cannot be placed close enough to the measuring position. As part of an ongoing research project funded by the German Ministry of Economics and Technology (BMWi), a new kind of magnetic field sensor was developed and used in order to measure the strength of remanent magnetic field spots. This so-called 'Point Probe' is based upon a needle-shaped ferromagnetic core having a primary coil as a magnetic field source and a secondary coil as an inductive pick-up. This contribution describes the details of the sensor design and its operating principle. The sensitivity of the measured signals for local magnetic fields is described. Finally, a method for nondestructive hardness estimation of materials by using the Point Probe is presented. The results show a high correlation between hardness and a new coercivity-dependent testing parameter.

91

Instabilities of a multicomponent plasma with accelerated particles and magnetic field generation in astrophysical objects  

International Nuclear Information System (INIS)

A system of MHD equations for the description of a magnetized nonequilibrium astrophysical plasma with neutral atoms and suprathermal (in particular, relativistic) particles is formulated. The instabilities of such a plasma, which arise from the presence of neutral and relativistic components, are considered. It is shown that the presence of nonthermal particles interacting with the thermal plasma component via regular and fluctuating electromagnetic fields is responsible for the emergence of specific mechanisms of MHD wave generation. The main generation mechanisms of static and turbulent magnetic fields near shock wave fronts in the Galaxy and interplanetary space are analyzed. We discuss the application of the generation effects of long-wave magnetic fluctuations to the problems of magnetic field origin and relativistic particle acceleration in astrophysical objects of various natures. (reviews of topical problems)

92

Heat generation in agglomerated ferrite nanoparticles in an alternating magnetic field  

Science.gov (United States)

The role of agglomeration and magnetic interparticle interactions in heat generation of magnetic ferrofluids in an ac magnetic field is still unclear, with apparent discrepancy between the results presented in the literature. In this work, we measured the heat generating capability of agglomerated ferrite nanoparticles in a non-invasive ac magnetic field with f = 100 kHz and H0 = 13 kA m-1. The nanoparticles were morphologically and magnetically characterized, and the specific absorption rate (SAR) for our ac magnetic field presents a clear dependence on the diameter of the nanoparticles, with a maximum SAR = 48 W g-1 for 15 nm. Our agglomerated nanoparticles have large hydrodynamic diameters, thus the mechanical relaxation can be neglected as a heat generation mechanism. Therefore, we present a model that simulates the SAR dependence of the agglomerated samples on the diameter of the nanoparticles based on the hysteresis losses that is valid for the non-linear region (with H0 comparable to the anisotropy field). Our model takes into account the magnetic interactions among the nanoparticles in the agglomerate. For comparison, we also measured the SAR of non-agglomerated nanoparticles in a similar diameter range, in which Néel and Brown relaxations dominate the heat generation.

Lima, E., Jr.; De Biasi, E.; Vasquez Mansilla, M.; Saleta, M. E.; Granada, M.; Troiani, H. E.; Effenberger, F. B.; Rossi, L. M.; Rechenberg, H. R.; Zysler, R. D.

2013-01-01

93

Attosecond Magnetic Field Pulse Generation by Intense Few Cycle Circularly Polarized UV Pulses  

CERN Document Server

Intense attosecond magnetic field pulses are predicted to be produced by intense few cycle circularly polarized UV pulses. Numerical solutions of the time dependent Schr\\"{o}dinger equation for H$_2^+$ are used to study the dynamical process. Spiralling attosecond circular electron wave packets are created with nanometer molecular dimensions, thus generating magnetic fields of several tens of Teslas ($10^5$ Gauss). Simulations show that the induced magnetic field is critically dependent on the pulse wavelength $\\lambda$ and pulse duration $n\\tau$ ($n$ number of cycle) as predicted by a classical model. For ultrashort few cycle circularly polarized attosecond pulses, molecular orientation influences the generation of the induced magnetic fields as a result of preferential ionization perpendicular to the molecular axis.

Yuan, Kai-Jun

2013-01-01

94

3-D RPIC Simulations of Relativistic Jets: Particle Acceleration, Magnetic Field Generation, and Emission  

Science.gov (United States)

Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets into ambient plasmas show that acceleration occurs in relativistic shocks. The Weibel instability created in shocks is responsible for particle acceleration, and generation and amplification of highly inhomogeneous, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection in relativistic jets. The "jitter" radiation from deflected electrons has different properties than the synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understand the complex time evolution and spectral structure in relativistic jets and gamma-ray bursts. We will present recent PIC simulations which show particle acceleration and magnetic field generation. We will also calculate associated self-consistent emission from relativistic shocks.

Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Hededal, C. B.; Fishman, G. J.

2006-01-01

95

Magnetic field seed generation in plasmas around charged and rotating black holes  

Science.gov (United States)

Previous work by the authors introduced the possibility of generating seed magnetic fields by spacetime curvature and applied it in the vicinity of a Schwarzschild black hole. It was pointed out that it would be worthwhile to consider the effect in other background geometries and particularly in the vicinity of a rotating black hole, which is generically to be expected, astrophysically. In this paper that suggestion is followed up and we calculate generated magnetic field seed due to Reissner-Nördstrom and Kerr spacetimes. The conditions for the drive for the seed of a magnetic field is obtained for charged black holes, finding that in the horizon the drive vanishes. Also, the ?N-force produced by the Kerr black hole is obtained and its relation with the magnetic field seed is discussed, producing a more effective drive.

Qadir, Asghar; Asenjo, Felipe A.; Mahajan, Swadesh M.

2014-08-01

96

Generic estimates for magnetic fields generated during inflation including Dirac-Born-Infeld theories  

CERN Document Server

We estimate the strength of large-scale magnetic fields produced during inflation in the framework of Dirac-Born-Infeld (DBI) theories. This analysis is sufficiently general in the sense that it covers most of conformal symmetry breaking theories in which the electromagnetic field is coupled to a scalar field. In DBI theories there is an additional factor associated with the speed of sound, which allows a possibility to lead to an extra amplification of the magnetic field in a ultra-relativistic region. We clarify the conditions under which seed magnetic fields to feed the galactic dynamo mechanism at a decoupling epoch as well as present magnetic fields on galactic scales are sufficiently generated to satisfy observational bounds.

Bamba, Kazuharu; Tsujikawa, Shinji

2008-01-01

97

Magnetic field induced effects in optical second harmonic generation from iron-garnet films  

Science.gov (United States)

The magnetic field induced effects in the second harmonic generation (SHG) from epitaxially grown iron-garnet films have been studied. The magnetic field induced variations in the azimuthal angular dependences and the polarization diagrams of the SHG intensity are shown to be due to the linear Faraday effect. Enhancements in the SHG intensity were detected for (Bi,Gd,Fu) 3(Fe,Ga) 5O 12 iron-garnet films grown on (Gd,Ca) 3(Mg,Zr,Ga) 5O 12 single-crystal substrates with various orientations. This dependence of the SHG intensity on the magnetic field may be caused by magnetostriction effects.

Aktsipetrov, O. A.; Aleshkevich, V. A.; Melnikov, A. V.; Misuryaev, T. V.; Murzina, T. V.; Randoshkin, V. V.

1997-01-01

98

Generation of low-frequency electric and magnetic fields during large- scale chemical and nuclear explosions  

Energy Technology Data Exchange (ETDEWEB)

We discuss the main parameters of the electric field in the surface layer of the atmosphere and the results of the investigations of the natural electric field variations. Experimental investigations of the electromagnetic field for explosions in air are presented. Electromagnetic signals generated by underground nuclear and chemical explosions are discussed and explosions for 1976--1991 are listed. Long term anomalies of the earth`s electromagnetic field in the vicinity of underground explosions were also investigated. Study of the phenomenon of the irreversible shock magnetization showed that in the zone nearest to the explosion the quasistatic magnetic field decreases in inverse proportion to the distance.

Adushkin, V.V. [Academy of Sciences, Moscow (Russian Federation). Inst. for Dynamics of the Geospheres; Dubinya, V.A.; Karaseva, V.A.; Soloviev, S.P.; Surkov, V.V. [Lawrence Livermore National Lab., CA (United States)

1995-06-01

99

Large-scale magnetic field generation by alpha effect driven by collective neutrino-plasma interaction.  

Science.gov (United States)

We suggest a new mechanism for the generation of a large-scale magnetic field in the hot plasma of the early Universe which is based on parity violation in weak interactions and depends neither on the helicity of matter turbulence resulting in the standard alpha effect nor on general rotation. The mechanism can result in a self-excitation of an (almost) uniform cosmological magnetic field. PMID:15089594

Semikoz, V B; Sokoloff, D D

2004-04-01

100

Brief communication "Modeling tornado dynamics and the generation of infrasound, electric and magnetic fields"  

Directory of Open Access Journals (Sweden)

Full Text Available Recent observations endorse earlier measurements of time varying electric and magnetic fields generated by tornadoes and dust devils. These signals may provide a means for early warning but together with a proper modeling approach can also provide insight into geometry and dynamics of the vortices. Our model calculations show the existence of pressure resonances characterized as acoustic duct modes with well defined frequencies. These resonances not only generate infrasound but also modulate the charge density and the velocity field and in this way lead to electric and magnetic field oscillations in the 0.5–20-Hz range that can be monitored from a distance of several kilometers.

E. D. Schmitter

2010-02-01

 
 
 
 
101

Generation of Seed Magnetic Field around First Stars: the Biermann Battery Effect  

CERN Document Server

We investigate generation processes of magnetic fields around first stars. Since the first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magnetic fields are generated by effects of radiation force as well as the Biermann battery effect. We have calculated the amplitude of magnetic field generated by the effects of radiation force around the first stars in the preceding paper, in which the Biermann battery effects are not taken into account.In this paper, we calculate the generation of magnetic fields by the Biermann battery effect as well as the effects of radiation force, utilizing the radiation hydrodynamics simulations. As a result, we find that the generated magnetic field strengths are ~ 10^{-19}G-10^{-17}G at ~ 100pc-1kpc scale mainly by the Biermann battery, which is an order of magnitude larger than the results of our previous study. We also find that this result is insensitive to various physical parameters including the mass of the source star, distance be...

Doi, Kentaro

2011-01-01

102

Analysis of the Magnetic Field Effect on Entropy Generation at Thermosolutal Convection in a Square Cavity  

Directory of Open Access Journals (Sweden)

Full Text Available Thermosolutal convection in a square cavity filled with air and submitted to an inclined magnetic field is investigated numerically. The cavity is heated and cooled along the active walls with a mass gradient whereas the two other walls of the cavity are adiabatic and insulated. Entropy generation due to heat and mass transfer, fluid friction and magnetic effect has been determined in transient state for laminar flow by solving numerically the continuity, momentum energy and mass balance equations, using a Control Volume Finite—Element Method. The structure of the studied flows depends on four dimensionless parameters which are the Grashof number, the buoyancy ratio, the Hartman number and the inclination angle. The results show that the magnetic field parameter has a retarding effect on the flow in the cavity and this lead to a decrease of entropy generation, Temperature and concentration decrease with increasing value of the magnetic field parameter.

Ammar Ben Brahim

2011-05-01

103

Effect of transverse magnetic field on generation of electron beam in gas diode  

International Nuclear Information System (INIS)

One studied experimentally the effect of the transverse magnetic field (0.08 and 0.016 T) on the generation of an electron beam within a gas diode. At U=25 kV gas diode voltage and helium low pressure (45 Torr) the transverse magnetic field is shown to affect the beam current amplitude outside the foil and on its foil cross section distribution. Under the increased pressure values and at generation of an ultra short-time avalanche electron beam (UAEB) in helium, nitrogen and in air the transverse magnetic field is shown to affect negligibly the UAEB amplitude and duration outside the foil. At the generator voltage equal to hundreds of kilovolts a portion of the escaping electrons was found to arrive to the gas diode lateral walls including those from the discharge plasma in the vicinity of a cathode

104

Theory and experimental show up of axial magnetic fields self-generated in dense laser-produced plasmas  

International Nuclear Information System (INIS)

The work presented in this thesis concerns the magnetic fields generated in laser produced plasma. A summary of the theoretical and experimental studies concerning the toroidal magnetic fields and realised by different groups of research is presented. Then, we present our original contribution on the generation of axial magnetic fields by the dynamo effect. The experimental work for the detection of magnetic field is based on the Faraday rotation and Zeeman effects. The experimental diagrams are detailed and discussed. The experimental results are presented and compared to the theory. Finaly, we present some consequences of the generation of the axial magnetic fields in laser produced plasma as a discussion of the thermal conductivity

105

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

Science.gov (United States)

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

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

2005-10-01

106

Magnetic field generation by the Weibel instability at temperature gradients in collisionless plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Weibel instability could be responsible for the generation of magnetic fields in various objects such as gamma-ray bursts, jets from active galactic nuclei, and clusters of galaxies. Using numerical simulations, the development of the Weibel instability at a temperature gradient is studied. It is found that current sheets are first generated at the gradient, and then they are rounded off and turn into current filaments. During this process, return currents are generated ...

Fujita, Yutaka; Kato, Tsunehiko N.; Okabe, Nobuhiro

2006-01-01

107

Study of the primary process for plasma generation in strong magnetic field using laser light  

International Nuclear Information System (INIS)

Ionization and dissociation processes in gaseous molecules absorbed higher energies above ionization energy were precisely measured in strong magnetic fields above 10T using a multiple resonance method with variable wavelength pulsed laser. Pulsed molecular beams were generated in a narrow gap of a superconducting magnet, and molecules in the beams were cooled down to a few degrees Kelvin. Landau levels of the gaseous molecules were succeeded in the first observation in the world. All energy levels of the Landau levels were identified from the calculation of semi- classical quantum theory. A new ion detector working in strong magnetic fields without loss of sensitivity was developed. (Y. Kazumata)

108

Electromagnetic design analysis and performance improvement of axial field permanent magnet generator for small wind turbine  

Science.gov (United States)

Axial field permanent magnet (AFPM) generators are widely applied for the small wind turbine. The output power of conventional AFPM generator, AFER-NS (Axial Field External Rotor-Non Slotted) generator, is limited by the large reluctance by the long air-gap flux paths. In this paper, the novel structure of AFPM generator, AFIR-S (Axial Field Inner Rotor-Slotted) generator, is suggested to improve the output characteristics. The electromagnetic design analysis and the design improvement of the suggested AFIR-S generator are studied. Firstly, the electromagnetic design analysis was done to increase the power density. Secondly, the design optimizations of the rotor pole-arc ratio and skew angle to increase the output power and to reduce the cogging torque. Finally, the output performances of AFER-NS and AFIR-S generator are compared with each other.

Jung, Tae-Uk

2012-04-01

109

Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles  

CERN Document Server

The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.

Shvets, G

2002-01-01

110

Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks  

International Nuclear Information System (INIS)

A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a thick astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed. 30 references

111

Generation of synchronous AC power through magnetic field compression  

International Nuclear Information System (INIS)

This paper presents conceptual analytical design picture for the MHD-synchronous AC generator using an accelerated plasma from the divertor of the fusion reactor plant. The exhaust plasma of the fusion reactor usually at low level in pressure and velocity will be accelerated through the action of any model of the linear induction accelerators. Structural components of the synchronous-MHD generator comprises co-axial perfectly conducting cylinders with the inner cylinder having a set of lateral tangential blades whose function is to impart the rotor with the desired mechanical velocity for synchronous operation, from the impinging plasma. Electric AC power will be developed through induction in a sinusoidally distributed three phase conventional winding close to the inner cylinder. Magneto-fluid interaction solutions as well as electro-mechanical outcome power expressions have been secured for actual concept design. (Auth.)

112

Computational study of the strong magnetic field generation in non-spherical cone-guided implosion  

International Nuclear Information System (INIS)

The magnetic field in non-spherical cone-guided implosion is simulated using temporal evolution equations of the magnetic field coupled with simulated result of 2-D radiation hydrodynamic simulation for Fast Ignition as the first attempt. We have found that the magnetic field is generated by ?Te x ?ne term, and it is compressed by the implosion. In the result, it reaches 5 MG at maximum compression, which was not considered before. Also, high Hall parameter region is appeared between cone tip and core plasma. This magnetic field is strong enough to affect the implosion dynamic and hot electron transport, therefore it should be paid attention in these simulations for Fast Ignition. (author)

113

The new TORPEX in-vessel toroidal conductor for the generation of a poloidal magnetic field  

International Nuclear Information System (INIS)

TORoidal Plasma EXperiment (TORPEX) is a Simple Magnetized Torus featuring open helical magnetic field lines obtained from the superposition of a small vertical component on the main toroidal field. This work introduces the experimental setup developed to include a poloidal magnetic field. The toroidal and poloidal fields generate a rotational transform, making the magnetic geometry of TORPEX closer to that of a tokamak. This upgrade opens the possibility to deal with closed and open flux surfaces, as well as with the transition region across the last closed flux surface. The main technical solutions are discussed together with the physical considerations at the basis of the system design. Selected examples of the magnetic configurations accessible with the set of magnetic field coils available on TORPEX are discussed, ranging from single-null X-points to magnetic snowflakes. The simplest magnetic configuration of quasi-circular concentric flux surfaces is tested experimentally. Measurements of the two-dimensional electron plasma density profiles and the particle confinement time are presented, together with the first steps towards the understanding of plasma production mechanisms

114

Magnetic Fields  

CERN Document Server

In this chapter, we give a brief introduction into the use of the Zeeman effect in astronomy and the general detection of magnetic fields in stars, concentrating on the use of FORS2 for longitudinal magnetic field measurements.

Schöller, Markus

2015-01-01

115

Calculations of self-generated magnetic fields in parylene disc experiments  

International Nuclear Information System (INIS)

Experiments have been planned at Livermore to measure self-generated magnetic fields using the Faraday Rotation of frequency quadrupled 1.1 ?m laser light. The LASNEX code was used during the planning of these experiments and has provided valuable information in establishing the conditions under which the thermoelectric fields expected can be measured. Suspected thermoelectric fields have been inferred from experiments that have been carried out at NRL

116

Waves in plasmas generated by a rotating magnetic field and implications to radiation belts  

Science.gov (United States)

The interaction of rotating magnetic fields (RMF) with magnetized plasmas is a fundamental plasma physics problem with implications to a wide range of areas, including laboratory and space plasma physics. Despite the importance of the topic the basic physics of the phenomenon remains unexplored. An important application of a RMF is its potential use as an efficient radiation source of low frequency waves in space plasmas, including whistler and shear Alfvéen waves (SAW) for controlled remediation of energetic particles in the Earth's radiation belts. In this dissertation the RMF waves generated in magnetized plasma are studied using numerical simulations with a semi-analytical three-dimensional magneto-hydrodynamic (MHD) model and experiments on the generation of whistler and magnetohydrodynamic waves conducted in UCLA's Large Plasma Device. Comparisons of the simulation results with the experimental measurements, namely, measured spatiotemporal wave structures, dispersion relation with finite transverse wave number, wave amplitude dependence on plasma and RMF source parameters, show good agreement in both the whistler and MHD wave regimes. In both the experiments and the 3D MHD simulations a RMF source was found to be very efficient in the generation of MHD and whistler waves with arbitrary polarizations. The RMF source drives significant field aligned plasma currents confined by the ambient magnetic field for both the whistler and MHD wave regimes, resulting in efficient transport of wave energy along the ambient magnetic field. The efficient transfer of the wave energy results in slow decay rates of the wave amplitude along the ambient magnetic field. The circular polarization of the waves generated by the RMF source, slow amplitude decay rate along the ambient magnetic field and nonzero transverse wave number determined by the RMF source size lead to nonlocal gradients of the wave magnetic field in the direction perpendicular to the ambient magnetic field. A RMF can be generated by a system of polyphase alternating currents or by a rotating permanent or superconducting magnet. For the magnetospheric plasma rotating permanent or superconducting magnets are suitable for injection of very low frequency (VLF) shear Alfven and magnetosonic waves. The generation of whistler waves in the magnetosphere plasma requires frequencies of the order of kHz, so in order to inject whistler waves generated by a RMF it is necessary to use an antenna with polyphase alternating currents. The interactions of the waves generated by a RMF source with highly energetic electron population were investigated in LAPD experiment and by test-particle simulations of non-resonant pitch angle scattering of trapped energetic electrons using the electromagnetic fields calculated using the 3D model. It was found in both the experiment and test-particle simulations that waves generated by a RMF source are, indeed, very efficient in pitch angle scattering of trapped hot electrons due to the creation of magnetic field gradients in the direction perpendicular to the ambient magnetic field. Different scenarios for the applications to the precipitation of highly energetic electrons in the magnetosphere are presented.

Karavaev, Alexey V.

117

Performance of a Cylindrical Hall-Effect Thruster with Magnetic Field Generated by Permanent Magnets  

Science.gov (United States)

While Hall thrusters can operate at high efficiency at kW power levels, it is difficult to construct one that operates over a broad envelope down to 100W while maintaining an efficiency of 45- 55%. Scaling to low power while holding the main dimensionless parameters constant requires a decrease in the thruster channel size and an increase in the magnetic field strength. Increasing the magnetic field becomes technically challenging since the field can saturate the miniaturized inner components of the magnetic circuit and scaling down the magnetic circuit leaves very little room for magnetic pole pieces and heat shields. An alternative approach is to employ a cylindrical Hall thruster (CHT) geometry. Laboratory model CHTs have operated at power levels ranging from the order of 50 Watts up to 1 kW. These thrusters exhibit performance characteristics which are comparable to conventional, annular Hall thrusters of similar size. Compared to the annular Hall thruster, the CHT has a lower insulator surface area to discharge chamber volume ratio. Consequently, there is the potential for reduced wall losses in the channel of a CHT, and any reduction in wall losses should translate into lower channel heating rates and reduced erosion. This makes the CHT geometry promising for low-power applications. Recently, a CHT that uses permanent magnets to produce the magnetic field topology was tested. This thruster has the promise of reduced power consumption over previous CHT iterations that employed electromagnets. Data are presented for two purposes: to expose the effect different controllable parameters have on the discharge and to summarize performance measurements (thrust, Isp, efficiency) obtained using a thrust stand. These data are used to gain insight into the thruster's operation and to allow for quantitative comparisons between the permanent magnet CHT and the electromagnet CHT.

Polzin, Kurt A.; Raitses, Yevgeny; Fisch, Nathaniel J.

2008-01-01

118

Generation of high magnetic field 11 T by large scale superconducting coils  

International Nuclear Information System (INIS)

In May, 1984, in Japan Atomic Energy Research Institute, a high magnetic field of 11 T was successfully generated with the large scale superconducting coils for a nuclear fusion reactor. It was the highest magnetic field in the world. The generation of this high magnetic field was achieved by installing CBC coils in the coils installed before, in the setup simulating toroidal coil arrangement called cluster test apparatus. In this paper, the outline of the power-augmenting works for the cluster test apparatus related to the installation of CBC coils is discussed. For the development of large scale superconducting coils, as the technical subjects, the development of large current superconductors acting in a high magnetic field, the countermeasures to strong electromagnetic force, the solution of the electric, magnetic and mechanical problems caused by pulsed magnetic field, the development of large helium-liquefying refrigerators and their peripheral equipment, and the development of synthetic technology systematizing those are enumerated. The development of high voltage, large current leads is in progress. (Kako, I.)

119

Magnetic field generation from Self-Consistent collective neutrino-plasma interactions  

International Nuclear Information System (INIS)

A new Lagrangian formalism for self-consistent collective neutrino-plasma interactions is presented in which each neutrino species is described as a classical ideal fluid. The neutrino-plasma fluid equations are derived from a covariant relativistic variational principle in which finite-temperature effects are retained. This new formalism is then used to investigate the generation of magnetic fields and the production of magnetic helicity as a result of collective neutrino-plasma interactions

120

Magnetic Field Generation from Self-Consistent Collective Neutrino-Plasma Interactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new Lagrangian formalism for self-consistent collective neutrino-plasma interactions is presented in which each neutrino species is described as a classical ideal fluid. The neutrino-plasma fluid equations are derived from a covariant relativistic variational principle in which finite-temperature effects are retained. This new formalism is then used to investigate the generation of magnetic fields and the production of magnetic helicity as a result of collective neutrino-p...

Brizard, Alain J.; Murayama, Hitoshi; Wurtele, Jonathan S.

1999-01-01

 
 
 
 
121

Magnetic fields in cosmology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Different mechanisms which may possibly explain existence of magnetic fields on astronomically large scales are described. A recently suggested model of magnetic fields generation slightly before hydrogen recombination is discussed in more detail.

Dolgov, A. D.

2003-01-01

122

High Magnetic Field Superconducting Magnets Fabricated In Budker Inp For Sr Generation  

CERN Document Server

BESSY operates a 3-rd generation synchrotron light source in VUV to XUV region at Berlin-Adlershof. The main radiation sources in storage ring are special magnetic elements as undulators and wigglers. 3 superconducting shifters and one multipole superconducting wiggler are operating giving enhanced photon flux for 10-25 keV X-ray region. As the superconducting elements presently are located in straight sections, BESSY intends to exchange 4 of conventional room-temperature bending magnets by superconducting ones.The report contains brief description of 9 Tesla superbend prototype as a candidate for replacing of conventional magnets of BESSY-2, which was designed, fabricated and tested at Budker INP and was commissioned at BESSY in June 2004.Main parameters of 9 Tesla superconducting bending magnet prototype as well as testing results are presented.

Zolotarev, K V; Khruschev, S V; Krämer, Dietrich; Kulipanov, G N; Lev, V H; Mezentsev, N A; Miginsky, E G; Shkaruba, V A; Syrovatin, V M; Tsukanov, V M; Zjurba, V K

2004-01-01

123

Field generated within the SSC magnets due to persistant currents in the superconductor  

International Nuclear Information System (INIS)

This report presents the results of a number of computer studies of the magnetic fields generated by persistent circulating currents in the superconductor of superconducting dipoles. These magnetic fields are referred to as residual fields throughout this report. Since the field generated by persistent currents have a hysteric behavior, they are analagous to the residual filed found in iron bound conventional solenoids. The residual field calculations presented in this report were done using the LBL SCMAG4 computer code. This code has not been well tested against measured data, but a comparison with measured CBA data given in this report suggests that good agreement is possible. The residual fields generated by persistent superconducting currents are rich in higher multipoles. This is of concern to the accelerator designer for SSC. This report shows the effect of various superconductor parameters and coil parameters on the magnitude and structure of the residual fields. The effect of the magnet charging history on residual fields is aldo discussed. 14 references

124

Octupolar out-of-plane magnetic field structure generation during collisionless magnetic reconnection in a stressed X-point collapse  

International Nuclear Information System (INIS)

The out-of-plane magnetic field, generated by fast magnetic reconnection, during collisionless, stressed X-point collapse, was studied with a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code, using both closed (flux conserving) and open boundary conditions on a square grid. It was discovered that the well known quadrupolar structure in the out-of-plane magnetic field gains four additional regions of opposite magnetic polarity, emerging near the corners of the simulation box, moving towards the X-point. The emerging, outer, magnetic field structure has opposite polarity to the inner quadrupolar structure, leading to an overall octupolar structure. Using Ampere's law and integrating electron and ion currents, defined at grid cells, over the simulation domain, contributions to the out-of-plane magnetic field from electron and ion currents were determined. The emerging regions of opposite magnetic polarity were shown to be the result of ion currents. Magnetic octupolar structure is found to be a signature of X-point collapse, rather than tearing mode, and factors relating to potential discoveries in experimental scenarios or space-craft observations are discussed

125

Efficient gradient field generation providing a multi-dimensional arbitrary shifted field-free point for magnetic particle imaging  

Energy Technology Data Exchange (ETDEWEB)

Magnetic Particle Imaging (MPI) is a tomographic imaging modality capable to visualize tracers using magnetic fields. A high magnetic gradient strength is mandatory, to achieve a reasonable image quality. Therefore, a power optimization of the coil configuration is essential. In order to realize a multi-dimensional efficient gradient field generator, the following improvements compared to conventionally used Maxwell coil configurations are proposed: (i) curved rectangular coils, (ii) interleaved coils, and (iii) multi-layered coils. Combining these adaptions results in total power reduction of three orders of magnitude, which is an essential step for the feasibility of building full-body human MPI scanners.

Kaethner, Christian, E-mail: kaethner@imt.uni-luebeck.de; Ahlborg, Mandy; Buzug, Thorsten M., E-mail: buzug@imt.uni-luebeck.de [Institute of Medical Engineering, Universität zu Lübeck, 23562 Lübeck (Germany); Knopp, Tobias [Thorlabs GmbH, 23562 Lübeck (Germany); Sattel, Timo F. [Philips Medical Systems DMC GmbH, 22335 Hamburg (Germany)

2014-01-28

126

Efficient gradient field generation providing a multi-dimensional arbitrary shifted field-free point for magnetic particle imaging  

Science.gov (United States)

Magnetic Particle Imaging (MPI) is a tomographic imaging modality capable to visualize tracers using magnetic fields. A high magnetic gradient strength is mandatory, to achieve a reasonable image quality. Therefore, a power optimization of the coil configuration is essential. In order to realize a multi-dimensional efficient gradient field generator, the following improvements compared to conventionally used Maxwell coil configurations are proposed: (i) curved rectangular coils, (ii) interleaved coils, and (iii) multi-layered coils. Combining these adaptions results in total power reduction of three orders of magnitude, which is an essential step for the feasibility of building full-body human MPI scanners.

Kaethner, Christian; Ahlborg, Mandy; Knopp, Tobias; Sattel, Timo F.; Buzug, Thorsten M.

2014-01-01

127

Efficient gradient field generation providing a multi-dimensional arbitrary shifted field-free point for magnetic particle imaging  

International Nuclear Information System (INIS)

Magnetic Particle Imaging (MPI) is a tomographic imaging modality capable to visualize tracers using magnetic fields. A high magnetic gradient strength is mandatory, to achieve a reasonable image quality. Therefore, a power optimization of the coil configuration is essential. In order to realize a multi-dimensional efficient gradient field generator, the following improvements compared to conventionally used Maxwell coil configurations are proposed: (i) curved rectangular coils, (ii) interleaved coils, and (iii) multi-layered coils. Combining these adaptions results in total power reduction of three orders of magnitude, which is an essential step for the feasibility of building full-body human MPI scanners

128

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

Science.gov (United States)

The performance of a low-power cylindrical Hall thruster, which more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster, was measured using a planar plasma probe and a thrust stand. The field in the cylindrical thruster was produced using permanent magnets, promising a power reduction over previous cylindrical thruster iterations that employed electromagnets to generate the required magnetic field topology. Two sets of ring-shaped permanent magnets are used, and two different field configurations can be produced by reorienting the poles of one magnet relative to the other. A plasma probe measuring ion flux in the plume is used to estimate the current utilization for the two magnetic configurations. The measurements indicate that electron transport is impeded much more effectively in one configuration, implying a higher thrust efficiency. Preliminary thruster performance measurements on this configuration were obtained over a power range of 100-250 W. The thrust levels over this power range were 3.5-6.5 mN, with anode efficiencies and specific impulses spanning 14-19% and 875- 1425 s, respectively. The magnetic field in the thruster was lower for the thrust measurements than the plasma probe measurements due to heating and weakening of the permanent magnets, reducing the maximum field strength from 2 kG to roughly 750-800 G. The discharge current levels observed during thrust stand testing were anomalously high compared to those levels measured in previous experiments with this thruster.

Polzin, K. A.; Raitses, Y.; Merino, E.; Fisch, N. J.

2008-01-01

129

Study on magnetic field generation and electron collimation in overdense plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An analytical fluid model is proposed for artificially collimating fast electron beams produced in interaction of ultraintense laser pulses with specially engineered sandwich structure targets. The theory reveals that in low-density-core structure targets, the magnetic field is generated by the rapid change of the flow velocity of the background electrons in transverse direction (perpendicular to the flow velocity) caused by the density jump. It is found that the spontaneously generated magne...

Cai Hongbo; Zhu Shaoping; He X.T.; Mima K.

2013-01-01

130

Nonlinear mechanism for electromagnetic field generation in modulation-unstable magnetized plasma media  

International Nuclear Information System (INIS)

A modulation instability process in a plasma medium is considered in a strong constant magnetic field. The plasmon condensate is modulated not by a low-frequency ionic sound as is usually done, but by the beating of two high-frequency transverse electromagnetic waves propagating along the external magnetic field. Conditions in which aperiodic instability occurs are found and its increment is defined. Instability leads to a decrease of the scale of Langmuir turbulence along the external magnetic field and to the generation of electromagnetic fields. Dissipative property of the medium increases an amplitude threshold of the pumping waves. It is shown that for sufficiently large amplitudes of pumping waves the effect described in the Letter is the defining nonlinear process

131

Magnetic field produced by a thin sheet inductor of a superconducting generator  

International Nuclear Information System (INIS)

A 3D calculation of the magnetic field produced in the air by a thin sheet model of a superconducting generator's horse saddle type winding is presented in this paper. To be able to calculate the field everywhere in space, including on the winding, analytical expressions consisting in elliptic integrals, as also adapted numerical methods were derived, permitting a new time-saving efficient computation algorithm

132

Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets  

Science.gov (United States)

Strong shear flow regions found in astrophysical jets are shown to be important dissipation regions, where the shear flow kinetic energy flow is converted into electric and magnetic field energy via shear instabilities. The emergence of these self-consistent fields makes shear flows significant sites for radiation emission and particle acceleration. We focus on electron-scale instabilities, namely the collisionless, unmagnetized electron-scale Kelvin-Helmholtz instability (ESKHI) and a large-scale DC magnetic field generation mechanism on the electron scales. We show that these processes are important candidates to generate magnetic fields in the presence of strong velocity shears, which may naturally originate in energetic matter outbursts of active galactic nuclei and gamma-ray bursters. We show that the ESKHI is robust to density jumps between shearing flows, thus operating in various scenarios with different density contrasts. Multidimensional particle-in-cell (PIC) simulations of the ESKHI, performed with OSIRIS, reveal the emergence of a strong and large-scale DC magnetic field component, which is not captured by the standard linear fluid theory. This DC component arises from kinetic effects associated with the thermal expansion of electrons of one flow into the other across the shear layer, whilst ions remain unperturbed due to their inertia. The electron expansion forms DC current sheets, which induce a DC magnetic field. Our results indicate that most of the electromagnetic energy developed in the ESKHI is stored in the DC component, reaching values of equipartition on the order of 10-3 in the electron time-scale, and persists longer than the proton time-scale. Particle scattering/acceleration in the self-generated fields of these shear flow instabilities is also analyzed.

Alves, E. P.; Grismayer, T.; Fonseca, R. A.; Silva, L. O.

2014-03-01

133

Magnetic Field Effect on Natural Convection Flow with Internal Heat Generation using Fast ? – ? Method  

Directory of Open Access Journals (Sweden)

Full Text Available The magnetic field effect on laminar natural convection flow is investigated in a filled enclosure with internal heat generation using two-dimensional numerical simulation. The enclosure is heated by a uniform volumetric heat density and walls have constant temperature. A fixed magnetic field is applied to the enclosure. The dimensionless governing equations are solved numerically for the stream function, vorticity and temperature using finite difference method for various Rayleigh (Ra and Hartmann (Ha numbers in MATLAB software. The stream function equation is solved using fast Poisson's equation solver on a rectangular grid (POICALC function in MATLAB, voricity and temperature equations are solved using red-black Gauss-Seidel and bi-conjugate gradient stabilized (BiCGSTAB methods respectively. The results show that the strength of the magnetic field has significant effects on the flow and temperature fields. For the square cavity, the maximum temperature reduces with increasing Ra number. It is also observed that at low Ra number, location of the maximum temperature is at the centre of the cavity and it shifts upwards with increase in Ra number. Circulation inside the enclosure and therefore the convection becomes stronger as the Ra number increases while the magnetic field suppresses the convective flow and the heat transfer rate. The ratio of the Lorentz force to the buoyancy force (Ha2/Ra is as an index to compare the contribution of natural convection and magnetic field strength on heat transfer.

M.A. Taghikhani

2015-01-01

134

The ULF magnetic fields generated by thunderstorms: A source of ULF geomagnetic pulsations?  

Science.gov (United States)

It has long been known that thunderstorms produce strong electric field fluctuations in their immediate vicinity, but it has been little recognized that these storms can also be a source of strong ULF magnetic field fluctuations (ULF; frequencies less than 5 Hz). Some characteristics of these magnetic field fluctuations were documented for a thunderstorm occurring in 1990. We now describe further measurements of these magnetic field changes for a well-defined and comparatively intense thunderstorm that passed over the San Francisco Bay area on 8-9 September 1999. The thunderstorm is further characterized by measurements of its associated lightning by the National Lightning Detection Network. As compared with the results reported for the 1990 thunderstorm, the new measurements were made by two independent systems and more components of the magnetic field changes are measured. Given the possibility that the thunderstorm-related ULF magnetic field changes can stimulate ULF hydromagnetic waves in the ionosphere, these measurements suggest, once again, that thunderstorms may be a source of ULF energy in the magnetosphere that can, in turn, lead to the generation of some of the ULF geomagnetic pulsations commonly observed on the ground. In addition, it may also be significant that the frequencies associated with these hydromagnetic waves in the magnetosphere are ideally suited for them to interact with some populations of the protons and ions in the radiation belts, potentially inducing them to precipitate into the atmosphere.

Fraser-Smith, Antony C.; Kjono, Sandra N.

2014-12-01

135

Generation of high magnetic fields using a gas-puff Z pinch  

International Nuclear Information System (INIS)

The imploding plasma column of a gas-puff Z pinch was used to compress an embedded axial magnetic field. Field compression ratios up to 180 times and peak compressed fields up to 1.6 MG were measured by Faraday rotation. Field compression by this method has the advantage of high repetition rate for applications in the controlled production of high-energy densities, solid-state studies, generation of short-wavelength radiation, reducing the ignition threshold for fusion, and particle acceleration

136

Magnetic field generation by the Weibel instability at temperature gradients in collisionless plasmas  

International Nuclear Information System (INIS)

The Weibel instability could be responsible for the generation of magnetic fields in various objects such as gamma-ray bursts, jets from active galactic nuclei, and clusters of galaxies. Using numerical simulations, the development of the Weibel instability at a temperature gradient is studied. It is found that current sheets are first generated at the gradient, and then they are rounded off and turn into current filaments. During this process, return currents are generated around the filaments and they prevent filaments from the merger. The magnetic fields around the filaments persist at least until t?8000/?p, where ?p is the plasma frequency, and it is very likely that they survive for a much longer time

137

Self-generated magnetic fields and energy transport by ultra-intense laser-plasma interaction  

International Nuclear Information System (INIS)

The electromagnetic instability (Weibel instability) and its mechanism in ultra-intense laser-plasma interactions are studied by using three-dimensional particle-in-cell simulations. The transport of energy in electron thermal conduction is analyzed by the Spitzer-Harm theory, and the election's vertical pyrogenation phenomenon that resulted from anisotropic heating of laser is observed. The results indicate that the strong magnetic field excited by Weibel instability makes the electron beam deposit its energy within a very short distance, and it restrains the electron thermal flux formed when the laser ponderomotive force bursts through the electron. With the increase of the self-generated magnetic field, the electron will be seized by the wave of magnetic field, and the transport of heat will be restricted. (authors)

138

Self focussing effects of a gaussian laser beam on magnetic field generation in laser produced plasmas  

International Nuclear Information System (INIS)

In the present paper, the authors calculated the magnetic field generated in a plasma due to irradiation of a self focussed Gaussian laser beam. They write the momentum equation for the plasma in the presence of such a laser field and resolve it into a slowly oscillating component and a rapidly varying component. After a certain transient period, neglecting the pressure gradient term they obtain a balance equation containing the Lorentz force term and the ponderomotive force term. Making use of the Ampere's law they get an equation for the generation of magnetic field. In particular they consider a Nd-glass laser having ?. 1.06 ?m, whose intensity is in the range of 10/sup 12/-10/sup 16/ W/cm/sup 2/ and beam width r/sub o/ ? 15 ?m, and calculate the magnetic field as a function of its radial coordinate for different points of beam along its direction of propagation, they find that the magnetic field is reduced appreciably and is comparable to measured values i.e. the order of a few megagauss

139

Magnetic-field generation and particle acceleration in relativistic shear layers  

Science.gov (United States)

Both observational evidence and theoretical considerations suggest that the relativistic jets of AGN and GRBs are likely to be cylindrically stratified with a fast, inner spine and a slower, outer sheath. The resulting relativistic shear layer is expected to be a site of self-generation of magnetic fields due to the Weibel instability, and of relativistic particle acceleration. We here present first results of particle-in-cell (PIC) simulations of relativistic shear layers in both electron-proton and electron-positron jets. We demonstrate that magnetic fields close to equipartition can be self-generated in initially unmagnetized flows, and strong electric fields and MHD turbulence in the shear layer lead to the acceleration of highly anisotropic particle distributions. The resulting highly beamed synchrotron and Compton emission, in addition to beaming due to the bulk motion of the plasma, may offer a solution to the Lorentz factor crisis for AGN jets.

Böttcher, Markus; Liang, Edison P.; Smith, Ian A.; Roustazadeh, Parisa

2012-12-01

140

Generation of polarized shear Alfven waves by a rotating magnetic field source  

International Nuclear Information System (INIS)

Experiments are performed in the Large Plasma Device at the University of California, Los Angeles to study the propagation of field-aligned, polarized kinetic shear Alfven waves radiated from a rotating magnetic field source created via a novel phased orthogonal loop antenna. Both right and left hand circular polarizations are generated at a wide range of frequencies from 0.21??/?ci<0.93. Propagation parallel to the background magnetic field near the Alfven velocity is observed along with a small parallel wave magnetic field component implying a shear mode. The peak-to-peak magnitude of the wave magnetic field, 33 cm away from the antenna, is on the order of 0.8% of the background field and drops off in the far field. The full width at half maximum of the wave energy changes little over a distance of 2.5 parallel wavelengths while the exponential decrease in wave energy as a function of distance can be attributed to collisional damping. Evidence of electron heating and ionization is observed during the pulse.

 
 
 
 
141

Effect of collisions on dc magnetic-field generation in a plasma by resonance absorption of light  

International Nuclear Information System (INIS)

The importance of collisional ponderomotive effects on dc magnetic field generation is stressed. Computer simulations show that a weak rate of collision is sufficient to completely modify dc magnetic field generation in the resonant absorption of light, as compared with previous collisionless simulations. The agreement with theoretical predictions is shown

142

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

International Nuclear Information System (INIS)

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

143

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

International Nuclear Information System (INIS)

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

144

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

Science.gov (United States)

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

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

2005-05-01

145

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-10-01

146

The interrelation between the generation of large-scale electric fields and that of large-scale magnetic fields during inflation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The interrelation between the generation of large-scale electric fields and that of large-scale magnetic fields due to the breaking of the conformal invariance of the electromagnetic field in inflationary cosmology is studied. It is shown that if large-scale magnetic fields with a sufficiently large amplitude are generated during inflation, the generation of large-scale electric fields is suppressed, and vice versa. Furthermore, a physical interpretation of the result and it...

Bamba, Kazuharu

2007-01-01

147

Photon mass new limits from strong photon-torsion coupling generation of primordial magnetic fields  

CERN Document Server

Recently Adelberger et al [Phys Rev Lett 98: 010402, (2007)] have placed a limit to photon mass by investigating the primordial magnetic fields. Earlier Bertolami et al [Phys Lett \\textbf{B} 455, 96(1999)] showed that massive photons in a spontaneous Lorentz breaking may generate primordial magnetic fields consistent with galactic dynamo seeds. Torsion coupling constant of order $10^{-5}$, much higher than the previously obtained by de Sabbata and Sivaram of $10^{-24}$, leads to strong amplification of magnetic field able to seed galactic dynamo at recombination era contrary to what happens in general relativistic dynamos. This results in $B\\sim{10^{-5}{\\beta}G}$ where ${\\beta}$ is the massive photon-torsion coupling. Thus in order to obtain the observed galaxy field of $B_{G}\\sim{{\\mu}G}$ one should have a coupling $\\beta\\sim{10^{-1}}$, never observed in the universe. Thus we may conclude that the weaker couplings for torsion to e.m fields shall only produce magnetic fields without dynamos starting from extr...

de Andrade, Garcia

2011-01-01

148

Magnetic Field  

DEFF Research Database (Denmark)

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 observations.

Olsen, Nils

2015-01-01

149

Flux generation and sustainment of a field reversed configuration with rotating magnetic field current drive  

International Nuclear Information System (INIS)

A new experimental device has been constructed to study the flux build-up and sustainment of a field reversed configuration (FRC) with a rotating magnetic field (RMF). Even though complete penetration was expected from RMF theory, the RMF field was observed to penetrate only a few centimeters inside the FRC separatrix. Despite the limited penetration, significantly larger toroidal currents (40 kA) were driven than in previous experiments (?2 kA) with the same RMF field. The high currents and lack of deep penetration allowed the axial field to be the dominant field throughout the FRC. The radially inward pondermotive force arising from axial screening currents at the FRC edge had a significant influence on energy and particle confinement, reducing convective losses to the limit of observability. With only ohmic heating, the measured low ion temperatures (2 eV) left the ions unmagnetized while the electrons (?40 eV) were well magnetized. No destructive instability was observed for the RMF driven FRC despite the lack of a strong kinetic ion component. (c) 2000 American Institute of Physics

150

Flux generation and sustainment of a field reversed configuration with rotating magnetic field current drive  

Science.gov (United States)

A new experimental device has been constructed to study the flux build-up and sustainment of a field reversed configuration (FRC) with a rotating magnetic field (RMF). Even though complete penetration was expected from RMF theory, the RMF field was observed to penetrate only a few centimeters inside the FRC separatrix. Despite the limited penetration, significantly larger toroidal currents (40 kA) were driven than in previous experiments (˜2 kA) with the same RMF field. The high currents and lack of deep penetration allowed the axial field to be the dominant field throughout the FRC. The radially inward pondermotive force arising from axial screening currents at the FRC edge had a significant influence on energy and particle confinement, reducing convective losses to the limit of observability. With only ohmic heating, the measured low ion temperatures (2 eV) left the ions unmagnetized while the electrons (˜40 eV) were well magnetized. No destructive instability was observed for the RMF driven FRC despite the lack of a strong kinetic ion component.

Slough, J. T.; Miller, K. E.

2000-05-01

151

Generation of strong radial magnetic insulation fields in high power ion diodes in extraction geometrie  

International Nuclear Information System (INIS)

The efficient conversion of the electromagnetic energy delivered by the TW pulsed power generator KALIF into a high power ion beam requires a strong externally applied magnetic field which suppresses the electron flow. This pulsed insulating magnetic field is produced by two coils concentric to the beam axis and placed on the cathode side of the ion beam diode of the extraction type used in these experiments. Operating this diode with ratios of Vcrit to Vdiode >3, a field strength near the anode surface of 3 T typically had to be generated by coil currents peaking around 50 kA. With the dimensions of the coils fixed by the diodes emitting area this resulted in hoop forces up to 300 kN acting on the inner coil of just 10 cm outer diameter. The technologies developed and applied to solve the resulting mechanical, high voltage, thermal, vacuum and shock wave problems will be described. Furthermore the generated field with respect to its strength, symmetry and time response is compared to calculations. Finally the influence of the insulation field strength on the ion production efficiency is discussed, along with the design of future field coils for higher accelerating voltages

152

The First Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and duri...

Davies, George; Widrow, Lawrence M.

2011-01-01

153

Experimental studies of the pressures generated by a liquid oxygen slug in a magnetic field  

International Nuclear Information System (INIS)

The strong paramagnetic susceptibility of liquid oxygen (LOX) has established it as a good candidate for a cryogenic magnetic fluid system. While its properties have been known for several decades, a fundamental understanding of the behavior of LOX in a magnetically controlled fluid system is needed for the development of a suitable space application that can operate reliably and efficiently. This study conducted quantitative experiments on the dynamics of a LOX slug in a tube when subjected to electrically-induced magnetic fields within a solenoid. The experiments used a quartz tube with an inner diameter of 1.9 mm and LOX slugs of 0.6, 1.3, 1.9, 2.5, and 3.2 mm length at various initial positions relative to the solenoid. The pressures generated by the motion of the LOX slug under the magnetic force were recorded to characterize the pressure differential generated and the breakdown of the slug. The highest attainable pressure differential was found to be 1.45 kPa, which correlated well to theoretical predictions once the analysis accounted for the resistance heating of the solenoid. The noted differences between experimental results and theory could also be attributed to impeded slug motion from shear and mass forces. Within the workable pressure range, however, an optimal slug length was found which appropriately balances the pressure, shear, and magnetic forces in the system. This paper presents the experimental data on the dynamics and the maximum pressure differe dynamics and the maximum pressure differential generated by a LOX slug in a magnetic field and discusses the viability of LOX in a magnetic fluid management system intended for space applications.

154

Study on magnetic field generation and electron collimation in overdense plasmas  

International Nuclear Information System (INIS)

An analytical fluid model is proposed for artificially collimating fast electron beams produced in interaction of ultra intense laser pulses with specially engineered sandwich structure targets. The theory reveals that in low-density-core structure targets, the magnetic field is generated by the rapid change of the flow velocity of the background electrons in transverse direction (perpendicular to the flow velocity) caused by the density jump. It is found that the spontaneously generated magnetic field reaches as high as 100 MG, which is large enough to collimate fast electron transport in overdense plasmas. This theory is also supported by numerical simulations performed using a two-dimensional particle-in-cell code. It is found that the simulation results agree well with the theoretical analysis. (authors)

155

Study on magnetic field generation and electron collimation in overdense plasmas  

Directory of Open Access Journals (Sweden)

Full Text Available An analytical fluid model is proposed for artificially collimating fast electron beams produced in interaction of ultraintense laser pulses with specially engineered sandwich structure targets. The theory reveals that in low-density-core structure targets, the magnetic field is generated by the rapid change of the flow velocity of the background electrons in transverse direction (perpendicular to the flow velocity caused by the density jump. It is found that the spontaneously generated magnetic field reaches as high as 100?MG, which is large enough to collimate fast electron transport in overdense plasmas. This theory is also supported by numerical simulations performed using a two-dimensional particle-in-cell code. It is found that the simulation results agree well with the theoretical analysis.

Cai Hongbo

2013-11-01

156

Magnetic fields generated by r-modes in accreting millisecond pulsars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In rotating neutron stars the existence of the Coriolis force allows the presence of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. Here, for the first time, we introduce the magnetic damping rate in the evolution equations of r-modes. We show that r-modes can generate very strong toroidal fields in the core of accreting millisecond pulsars by inducing differential rotation. We shortly discuss the instabilities o...

Carmine Cuofanouniversity Of Ferrara And Infn Sez Ferrara, Italy; Alessandro Dragouniversity Of Ferrara And Infn Sez Ferrara, Italy

2014-01-01

157

Electromotive Force Generation with Hydrogen Release by Salt Water Flow under a Transverse Magnetic Field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

By considering an electrolyte solution in motion in a duct under a transverse magnetic field, we notice that a so called Faraday voltage arises because of the Lorentz force acting on anions and cations in the fluid. When salt water is considered, hydrogen production takes place at one of the electrodes if an electric current, generated by Faraday voltage, flows in an external circuit. The maximum amount of hydrogen production rate is calculated by basic electrochemical concepts.

Roberto De Luca

2011-01-01

158

Electromotive Force Generation with Hydrogen Release by Salt Water Flow under a Transverse Magnetic Field  

Directory of Open Access Journals (Sweden)

Full Text Available By considering an electrolyte solution in motion in a duct under a transverse magnetic field, we notice that a so called Faraday voltage arises because of the Lorentz force acting on anions and cations in the fluid. When salt water is considered, hydrogen production takes place at one of the electrodes if an electric current, generated by Faraday voltage, flows in an external circuit. The maximum amount of hydrogen production rate is calculated by basic electrochemical concepts.

Roberto De Luca

2011-10-01

159

Cosmological Magnetic Fields  

CERN Document Server

Magnetic fields are observed on nearly all scales in the universe, from stars and galaxies upto galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early universe and might therefore be able to tell us whether cosmic magnetic fields are of primordial, cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.

Kunze, Kerstin E

2013-01-01

160

Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic field generation in shear flows  

CERN Document Server

The nature of dynamo action in shear flows prone to magnetohydrodynamic instabilities is investigated using the magnetorotational dynamo in Keplerian shear flow as a prototype problem. Using direct numerical simulations and Newton's method, we compute an exact time-periodic magnetorotational dynamo solution to the three-dimensional dissipative incompressible magnetohydrodynamic equations with rotation and shear. We discuss the physical mechanism behind the cycle and show that it results from a combination of linear and nonlinear interactions between a large-scale axisymmetric toroidal magnetic field and non-axisymmetric perturbations amplified by the magnetorotational instability. We demonstrate that this large scale dynamo mechanism is overall intrinsically nonlinear and not reducible to the standard mean-field dynamo formalism. Our results therefore provide clear evidence for a generic nonlinear generation mechanism of time-dependent coherent large-scale magnetic fields in shear flows and call for new theor...

Herault, J; Cossu, C; Lesur, G; Ogilvie, G I; Longaretti, P -Y

2011-01-01

 
 
 
 
161

Mathematical and numerical analysis of the resistive magnetohydrodynamics system with self-generated magnetic field terms  

International Nuclear Information System (INIS)

This work is devoted to the construction of numerical methods that allow the accurate simulation of inertial confinement fusion (ICF) implosion processes by taking self-generated magnetic field terms into account. In the sequel, we first derive a two-temperature resistive magnetohydrodynamics model and describe the considered closure relations. The resulting system of equations is then split in several subsystems according to the nature of the underlying mathematical operator. Adequate numerical methods are then proposed for each of these subsystems. Particular attention is paid to the development of finite volume schemes for the hyperbolic operator which actually is the hydrodynamics or ideal magnetohydrodynamics system depending on whether magnetic fields are considered or not. More precisely, a new class of high-order accurate dimensionally split schemes for structured meshes is proposed using the Lagrange re-map formalism. One of these schemes' most innovative features is that they have been designed in order to take advantage of modern massively parallel computer architectures. This property can for example be illustrated by the dimensionally split approach or the use of artificial viscosity techniques and is practically highlighted by sequential performance and parallel efficiency figures. Hyperbolic schemes are then combined with finite volume methods for dealing with the thermal and resistive conduction operators and taking magnetic field generation into account. In order to study the characteristics and effects of self-generated magnetic field terms, simulation results are finally proposed with the complete two-temperature resistive magnetohydrodynamics model on a test problem that represents the state of an ICF capsule at the beginning of the deceleration phase. (author)

162

Generation of long prolate volumes of uniform magnetic field in cylindrical saddle-shaped coils  

Science.gov (United States)

We investigate the uniformity of the magnetic flux density (referred to as the field uniformity) within a series of coils designed to provide a prolate volume of field uniformity. Computational modelling of two cylindrical coil systems which have a sinusoidal current density distributed on the surface of the cylinder, shows the extent of prolate field uniformity along the cylindrical axis, with height and width of the magnetic volume limited by the radius of the cylinder. The first coil system consists of a cos ? coil--a series of saddle-shaped filament loops spaced uniformly with respect to cos ? on the curved cylindrical surface, where ? is the angle between the radius of the cylinder and the horizontal radial axis (assuming a horizontal cylinder). The second coil system, named the ‘ELFcage’ coil, consists of saddle-shaped filament loops spaced uniformly with respect to a fixed ??, on the cylindrical surface. The volume of field uniformity is also compared with volumes generated by circular Helmholtz and Barker coil designs. For coil diameters of 2 m, the Helmholtz and Barker coils generate a volume of field uniformity within 1% to 3% of the field at the centre that extends ˜0.8 m and ˜1.4 m respectively along the axis of symmetry. This compares to an extent of 3 m and 6 m for both the cos ? and ELFcage coils wound on a 2 m diameter cylinder (8 m length), for 1% and 3% field uniformity respectively. Importantly, the ELFcage coil shows significantly greater field uniformity along the radial axis compared to the cos ? coil. An array of triaxial magnetometers was used to measure the volume of field uniformity within the cos ? coil system, consisting of two sets of orthogonal cos ? windings to generate radial fields and a solenoid winding to generate an axial field. These measurements confirmed the results obtained from computational modelling. The cos ? coil system is currently in use for calibration of magnetometers and for measuring the magnetic signatures of bulky prolate objects.

Dinale, Justin; Vrbancich, Julian

2014-03-01

163

Generation of a dynamo magnetic field in a protoplanetary accretion disk  

International Nuclear Information System (INIS)

A new computational technique is developed that allows realistic calculations of dynamo magnetic field generation in disk geometries corresponding to protoplanetary and protostellar accretion disks. The approach is of sufficient generality to allow, in the future, a wide class of accretion disk problems to be solved. Here, basic modes of a disk dynamo are calculated. Spatially localized oscillatory states are found to occur in Keplerain disks. A physical interpretation is given that argues that spatially localized fields of the type found in these calculations constitute the basic modes of a Keplerian disk dynamo

164

Effects of induced magnetic field on large scale pulsed MHD generator with two phase flow  

International Nuclear Information System (INIS)

A large pulsed MHD generator 'SAKHALIN' was constructed in Russia (the former Soviet-Union) and operated with solid fuels. The 'SAKHALIN' with the channel length of 4.5 m could demonstrate the electric power output of 510 MW. The effects of induced magnetic field and two phase flow on the shock wave within the 'SAKHALIN' generator have been studied by time dependent, one dimensional analyses. It has been shown that the magnetic Reynolds number is about 0.58 for Run No. 1, and the induced magnetic flux density is about 20% at the entrance and exit of the MHD channel. The shock wave becomes stronger when the induced magnetic field is taken into account, when the operation voltage becomes low. The working gas plasma contains about 40% of liquid particles (Al2O3) in weight, and the present analysis treats the liquid particles as another gas. In the case of mono-phase flow, the sharp shock wave is induced when the load voltage becomes small such as 500 V with larger Lorentz force, whereas in the case of two phase flow, the shock wave becomes less sharp because of the interaction with liquid particles

165

Laser generated hot electron transport in an externally applied magnetic field  

International Nuclear Information System (INIS)

The authors have investigated the effect of an externally applied DC magnetic field on the generation and transport of hot electrons in CO/sub 2/ laser irradiation of cylindrical targets. The targets used in these studies were 6.3 mm diameter metal rods through which a pulsed current was driven from an external capacitor. Magnetic fields up to 150 kgauss were produced at the target surface. The CO/sub 2/ laser was focused with an f/5 lens resulting in a laser intensity of ?3 x 10/sup 14/ W/cm/sup 2/ in a 100 ?m diameter focal spot. The effect of the external magnetic field on the generation and inward transport of superhot (? 100 keV) electrons was studied. Principal diagnostics included a six channel hard x-ray spectrometer, a high energy x-ray pinhole camera, a LiF Laue x-ray spectrograph and a Ross-filtered (W-Ta) pair of x-ray detectors. The latter two diagnostics were designed to detect Au K? /sub emission at 68.2 keV

166

Dynamics of self-generated, large amplitude magnetic fields following high-intensity laser matter interaction  

International Nuclear Information System (INIS)

The dynamics of magnetic fields with an amplitude of several tens of megagauss, generated at both sides of a solid target irradiated with a high-intensity (? 1019) W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets. (authors)

167

Magnetic fields generated by r-modes in accreting millisecond pulsars  

International Nuclear Information System (INIS)

In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting from a donor whose mass is smaller than 1 Mo-dot. Here we show that the r-mode instabilities can generate strong toroidal magnetic fields by inducing differential rotation. In this way we also provide an alternative scenario for the origin of the magnetars.

168

Magnetic fields generated by r-modes in accreting millisecond pulsars  

Energy Technology Data Exchange (ETDEWEB)

In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting from a donor whose mass is smaller than 1 M{sub o-dot}. Here we show that the r-mode instabilities can generate strong toroidal magnetic fields by inducing differential rotation. In this way we also provide an alternative scenario for the origin of the magnetars.

Cuofano, Carmine; Drago, Alessandro, E-mail: cuofano@fe.infn.i [Dipartimento di Fisica, Universita di Ferrara and INFN sezione di Ferrara, 44100 Ferrara (Italy)

2009-05-01

169

Magnetic fields generated by r-modes in accreting millisecond pulsars  

CERN Document Server

In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting from a donor whose mass is smaller than 1 $M_\\odot$. Here we show that the r-mode instabilities can generate strong toroidal magnetic fields by inducing differential rotation. In this way we also provide an alternative scenario for the origin of the magnetars.

Cuofano, Carmine

2009-01-01

170

Dynamics of self-generated, large amplitude magnetic fields following high-intensity laser matter interaction  

CERN Document Server

The dynamics of magnetic fields with amplitude of several tens of Megagauss, generated at both sides of a solid target irradiated with a high intensity (? 1019W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets.

Sarri, G; Cecchetti, C A; Kar, S; Liseykina, T V; Yang, X H; Dieckmann, M E; Fuchs, J; Galimberti, M; Gizzi, L A; Jung, R; Kourakis, I; Osterholz, J; Pegoraro, F; Robinson, A P L; Romagnani, L; Willi, O; Borghesi, M

2012-01-01

171

Magnetic Field Generation in High-Intensity-Laser endash Matter Interactions  

International Nuclear Information System (INIS)

A multifluid implicit plasma simulation code has been used to study the transport of hot electrons generated by an intense (?3x101 8 W/cm 2) short-pulse 1.06?m laser into plasma targets over a broad range of densities [(0.35-200)ncrit], as arising in the Fast Ignitor approach to inertial confinement fusion. The most intense (16-250MG) magnetic fields generated in this interaction are traced to the ponderomotive push on background electrons, and tardy electron shielding. These fields can focus the heated electrons toward the axis of the beam, while impeding the direct return flow of background electrons. copyright 1998 The American Physical Society

172

Microwave generation from a cusptron device with a rotating electron beam through a magnetic cusp field  

International Nuclear Information System (INIS)

At the University of Maryland, high-power microwave generation experiments have been conducted with a relativistic rotating electron beam of 2 MeV, 12 kA, and 10 ns. Radiation is produced via the negative mass instability at various harmonics of the electron cyclotron frequency determined by the interaction of the rotating beam cyclotron modes and the modes of the conducting boundary system. Using a magnetron-type conducting boundary in the beam-wave interaction region, we are able to exercise effective mode control. This kind of device holds promise as a tunable, high-frequency microwave tube with low magnetic fields. A table-top experiment with a non-relativistic electron beam (-6 (I/V /sup 3/2/ ). Passing through a magnetic cusp field, the beam becomes a welldefined rotating hollow beam with 3 cm diameter and 0.2 cm thickness. The name ''cusptron'' is originated from the cusp and the magnetron. The beam dimensions are independent of the beam energy and also of the magnetic field strength

173

Effect of self-generated magnetic fields on fast-electron beam divergence in solid targets  

International Nuclear Information System (INIS)

The collimating effect of self-generated magnetic fields on fast-electron transport in solid aluminium targets irradiated by ultra-intense, picosecond laser pulses is investigated in this study. As the target thickness is varied in the range of 25 ?m to 1.4 mm, the maximum energies of protons accelerated from the rear surface are measured to infer changes in the fast-electron density and therefore the divergence of the fast-electron beam transported through the target. Purely ballistic spreading of the fast-electrons would result in a much faster decrease in the maximum proton energy with increasing target thickness than that measured. This implies that some degree of 'global' magnetic pinching of the fast-electrons occurs, particularly for thick (>400 ?m) targets. Numerical simulations of electron transport are in good agreement with the experimental data and show that the pinching effect of the magnetic field in thin targets is significantly reduced due to disruption of the field growth by refluxing fast-electrons.

174

Particle Acceleration, Magnetic Field Generation and Associated Emission in Collisionless Relativistic Jets  

Science.gov (United States)

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields 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.

Nishikawa, K. I.; Ramirez-Ruiz, E.; Hardee, P.; Mizuno, Y.; Fishman. G. J.

2007-01-01

175

Generating vorticity and magnetic fields in plasmas in general relativity: Spacetime curvature drive  

Energy Technology Data Exchange (ETDEWEB)

Using the generally covariant magnetofluid formalism for a hot plasma, a spacetime curvature driven mechanism for generating seed vorticity/magnetic field is presented. The 'battery' owes its origin to the interaction between the gravity modified Lorentz factor of the fluid element and the inhomogeneous plasma thermodynamics. The general relativistic drive is evaluated for two simple cases: seed formation in a simplified model of a hot plasma accreting in stable orbits around a Schwarzschild black hole and for particles in free fall near the horizon. Some astrophysical applications are suggested.

Asenjo, Felipe A.; Mahajan, Swadesh M. [Institute for Fusion Studies, University of Texas at Austin, Texas 78712 (United States); Qadir, Asghar [Centre for Advanced Mathematics and Physics, National University of Sciences and Technology, H12, Islamabad 4400 (Pakistan)

2013-02-15

176

Experimental study on hard X-ray generation of relativistic electron beams in azimuthal magnetic field  

CERN Document Server

Experimental study on hard X-ray generation was carried out on Flash 2 accelerator, with the method of relativistic electron beams transported in a low pressure gas via azimuthal magnetic field and interacted with Ta target. At 47 cm transporting distance, the measured areal integral of hard X-ray dose rate was 2.1 x 10 sup 1 sup 0 Gy centre dot cm sup 2 /s, total areal integral of hard X-ray dose was 1843 Gy centre dot cm sup 2 , and X-ray convert rate was 108 Gy centre dot cm sup 2 /kJ

Fan Ya Jun; Qiu Aici

2002-01-01

177

Large-scale magnetic field generation by randomly forced shearing waves.  

Science.gov (United States)

A rigorous theory for the generation of a large-scale magnetic field by random nonhelically forced motions of a conducting fluid combined with a linear shear is presented in the analytically tractable limit of low magnetic Reynolds number (Rm) and weak shear. The dynamo is kinematic and due to fluctuations in the net (volume-averaged) electromotive force. This is a minimal proof-of-concept quasilinear calculation aiming to put the shear dynamo, a new effect recently found in numerical experiments, on a firm theoretical footing. Numerically observed scalings of the wave number and growth rate of the fastest-growing mode, previously not understood, are derived analytically. The simplicity of the model suggests that shear dynamo action may be a generic property of sheared magnetohydrodynamic turbulence. PMID:22243085

Heinemann, T; McWilliams, J C; Schekochihin, A A

2011-12-16

178

On Primordial Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A primordial magnetic field could be responsible for the observed magnetic fields of the galaxies. One possibility is that such a primordial field is generated at the electroweak phase transition because of the fluctuations in the Higgs field gradients. I describe a statistical averaging procedure which gives rise to a field of a correct magnitude. Another possibility, where the Yang-Mills vacuum itself is ferrromagnetic, is also discussed.

Enqvist, Kari

1994-01-01

179

Three-dimensional model for generation of the mean solar magnetic field  

International Nuclear Information System (INIS)

A three-dimensional (non-axisymmetric) model for the solar mean magnetic field generation is studied. The sources of generation are the differential rotation and mean helicity in the convective shell. The system is described by two equations of the first order in time and the fourth order in space coordinates. The solution is sought for in the form of expansion over the spherical functions Y/sub n//sup m/. The modes of different m are separated. A finite-difference scheme similar to the Peaceman-Rachford scheme is constructed so to find coefficients of the expansion depending on the time and radial coordinates. It is shown that a mode with a smaller azimuthal number m is primarily excited. The axisymmetric mode m = 0 describes the 22 year solar cycle oscillations. The modes of m 0 have no such periodicity, they oscillate with a period of rotation of the low boundary of the solar convective shell. The solutions which are symmetric relative to the equator plane are excited more easily compared with the antisymmetrical ones. The results obtained are confronted to the observational picture of the non-axisymmetric large-scale solar magnetic fields. (author)

180

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

Science.gov (United States)

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless 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 into an ambient plasma. We find that the growth times depend on the Lorenz factors of jets. The jets with larger Lorenz factors grow slower. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The small scale magnetic field structure generated by the Weibel instability is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Nishikawa, K. I.; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.

2004-01-01

 
 
 
 
181

Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites  

Science.gov (United States)

Of the terrestrial planets, Earth and Mercury have self-sustained fields while Mars and Venus do not. Magnetic field data recorded at Ganymede have been interpreted as evidence of a self-generated magnetic field. The other icy Galilean satellites have magnetic fields induced in their subsurface oceans while Io and the Saturnian satellite Titan apparently are lacking magnetic fields of internal origin altogether. Parts of the lunar crust are remanently magnetized as are parts of the crust of Mars. While it is widely accepted that the magnetization of the Martian crust has been caused by an early magnetic field, for the Moon alternative explanations link the magnetization to plasma generated by large impacts. The necessary conditions for a dynamo in the terrestrial planets and satellites are the existence of an iron-rich core that is undergoing intense fluid motion. It is widely accepted that the fluid motion is caused by convection driven either by thermal buoyancy or by chemical buoyancy or by both. The chemical buoyancy is released upon the growth of an inner core. The latter requires a light alloying element in the core that is enriched in the outer core as the solid inner core grows. In most models, the light alloying element is assumed to be sulfur, but other elements such as, e.g., oxygen, silicon, and hydrogen are possible. The existence of cores in the terrestrial planets is either proven beyond reasonable doubt (Earth, Mars, and Mercury) or the case for a core is compelling as for Venus and the Moon. The Galilean satellites Io and Ganymede are likely to have cores judging from Galileo radio tracking data of the gravity fields of these satellites. The case is less clear cut for Europa. Callisto is widely taken as undifferentiated or only partially differentiated, thereby lacking an iron-rich core. Whether or not Titan has a core is not known at the present time. The terrestrial planets that do have magnetic fields either have a well-established inner core with known radius and density such as Earth or are widely agreed to have an inner core such as Mercury. The absence of an inner core in Venus, Mars, and the Moon (terrestrial bodies that lack fields) is not as well established although considered likely. The composition of the Martian core may be close to the Fe-FeS eutectic which would prevent an inner core to grow as long as the core has not cooled to temperatures around 1500 Kelvin. Venus may be on the verge of growing an inner core in which case a chemical dynamo may begin to operate in the geologically near future. The remanent magnetization of the Martian and the lunar crust is evidence for a dynamo in Mars’ and possibly the Moon’s early evolution and suggests that powerful thermally driven dynamos are possible. Both the thermally and the chemically driven dynamo require that the core is cooled at a sufficient rate by the mantle. For the thermally driven dynamo, the heat flow from the core into the mantle must by larger than the heat conducted along the core adiabat to allow a convecting core. This threshold is a few mW m-2 for small planets such as Mercury, Ganymede, and the Moon but can be as large as a few tens mW m-2 for Earth and Venus. The buoyancy for both dynamos must be sufficiently strong to overcome Ohmic dissipation. On Earth, plate tectonics and mantle convection cool the core efficiently. Stagnant lid convection on Mars and Venus are less efficient to cool the core but it is possible and has been suggested that Mars had plate tectonics in its early evolution and that Venus has experienced episodic resurfacing and mantle turnover. Both may have had profound implications for the evolution of the cores of these planets. It is even possible that inner cores started to grow in Mars and Venus but that the growth was frustrated as the mantles heated following the cessation of plate tectonics and resurfacing. The generation of Ganymede’s magnetic field is widely debated. Models range from magneto-hydrodynamic convection in which case the field will not be self-sustained to chemical and thermally

Breuer, Doris; Labrosse, Stephane; Spohn, Tilman

2010-05-01

182

Plasma circuit breaker in a magnetic field as a high-power ion flux generator  

International Nuclear Information System (INIS)

It is ascertained that plasma circuit breaker (PCB) in the external magnetic field of acute-anguled geometry in the mode when PCB serves as inductive storage loading is a natural magnetoizolated diode. Using PCB as an ion emitter and as a high-voltage generator it proved possible in case of full electron magnetiuzation to attain the maximum efficiency of the storage. The density of ion current evaluated by the measured energy density for 30 J/cm2 thermocouple and by the energy of 1.5 MeV constitutes 100 A/cm2. The given method of ion generation is very effective when high ion currents with a high energy are required

183

Nonlinear mechanism for the generation of electromagnetic fields in a magnetized plasma by the beatings of waves  

International Nuclear Information System (INIS)

One studies the modulation instability in a plasma medium within a strong constant magnetic field. One uses beating of two high-frequency transverse electromagnetic waves propagating along the magnetic field to modulate condensate of plasmons in place of the conventional low-frequency ion sound. One determined the conditions of evolution and the increment of aperiodic instability resulting in scale reduction of the Langmuir turbulence along the external magnetic field and in generation of electromagnetic fields. It is shown that for rather high amplitudes of the excitation waves the effect described here may be the governing nonlinear process

184

Apparatus and method for generating a magnetic field by rotation of a charge holding object  

Science.gov (United States)

A device and a method for the production of a magnetic field using a Charge Holding Object that is mechanically rotated. In a preferred embodiment, a Charge Holding Object surrounding a sample rotates and subjects the sample to one or more magnetic fields. The one or more magnetic fields are used by NMR Electronics connected to an NMR Conductor positioned within the Charge Holding Object to perform NMR analysis of the sample.

Gerald, II, Rex E. (Brookfield, IL); Vukovic, Lela (Westchester, IL); Rathke, Jerome W. (Homer Glenn, IL)

2009-10-13

185

Shock Structure and Magnetic Fields Generation Associated with Relativistic Jets Unmagnetized Pair Plasma  

Science.gov (United States)

Using 3D and 2D particle-in-cell simulations we investigate a shock structure, magnetic field generation, and particle acceleration associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized pair plasma. The simulations use long computational grids which allow to study the formation and dynamics of the system in a spatial and temporal way. We find for the first time a relativistic shock system comparable to a predicted magnetohydrodynamic shock structure consisting of leading and trailing shocks separated by a contact discontinuity. Strong electromagnetic fields resulting from the Weibel two-stream instability are generated in the trailing shock where jet matter is thermalized and decelerated. We analyze the formation and nonlinear development through saturation and dissipation of those fields and associated particle acceleration. In the AGN context the trailing shock corresponds to the jet shock at the head of a relativistic astrophysical jet. In the GRB context this trailing shock can be identified with the bow shock driven by relativistic ejecta. The strong electromagnetic field region in the trailing shock provides the emission site for the hot spot at the leading edge of AGN jets and for afterglow emission from GRBs.

Niemiec, J.; Nishikawa, K.-I.; Hardee, P.; Pohl, M.; Medvedev, M.; Mizuno, Y.; Zhang, B.; Oka, M.; Sol, H.; Hartmann, D.

2009-01-01

186

Formation of current filaments and magnetic field generation in a quantum current-carrying plasma  

International Nuclear Information System (INIS)

The nonlinear dynamics of filamentation instability and magnetic field in a current-carrying plasma is investigated in the presence of quantum effects using the quantum hydrodynamic model. A new nonlinear partial differential equation is obtained for the spatiotemporal evolution of the magnetic field in the diffusion regime. This equation is solved by applying the Adomian decomposition method, and then the profiles of magnetic field and electron density are plotted. It is shown that the saturation time of filamentation instability increases and, consequently, the instability growth rate and the magnetic field amplitude decrease in the presence of quantum effects

187

High magnetic field MHD generator program. Final report, July 1, 1976-December 31, 1979  

Energy Technology Data Exchange (ETDEWEB)

A theoretical and experimental program was undertaken to investigate MHD channel phenomena which are important at high magnetic fields. The areas studied were inhomogeneity effects, boundary layers, Hall field breakdown and electrode configuration and current concentrations. In addition, a program was undertaken to study steady-state combustion disk and linear channels in an existing 6 Tesla magnet of small dimensions. The structure of the inhomogeneities in the Stanford M-2 was characterized and compared with theoretical results from a linearized perturbation analysis. General agreement was obtained and the analysis was used to compute stability regions for large size generators. The Faraday electrical connection was found to be more stable than the Hall or diagonal wall connections. Boundary layer profile measurements were compared with theoretical calculations with good agreement. Extrapolation of the calculations to pilot scale MHD channels indicates that Hartmann effects are important in the analysis of the sidewall, and Joule heating is important in calculating heat transfer and voltage drops for the electrode wall. Hall field breakdown was shown to occur both in the plasma and through the interelectrode insulator with the insulator breakdown threshold voltage lower than the plasma value. The threshold voltage was shown to depend on the interelectrode gap but was relatively independent of plasma conditions. Experiments were performed at 5.5 Tesla with both disk and linear MHD channels.

Eustis, R. H.; Kruger, C. H.; Mitchner, M.; Self, S. A.; Koester, J. K.; Nakamura, T.

1980-04-01

188

Increase of energy transfer efficiency in the electromagnetic flux compression technique generating ultra-high magnetic field  

International Nuclear Information System (INIS)

Magnetic fields of over 100 T can be generated only through the use of a destructive pulsed magnet. Electro-magnetic flux compression (EMFC) is an efficient method to generate such ultra-high magnetic fields. The EMFC system at Institute for Solid State Physics holds the world record for the highest magnetic field produced in-doors. This system has been used for various sorts of measurements applied to matters under ultrahigh magnetic fields. Recently, we successfully improved the coil system to generate a higher field using less energy injection and more simplified preparation processes. The new system increased the electro-magnetic energy transfer efficiency to at least twice that of the previously employed system. Our new primary coil using a copper current guide has the advantage of shallower high-frequency current skin depth and less contact impedance than previous ones. Therefore the discharge current spark is completely avoided. The improved skin depth resulted in a symmetric implosion of the liner coil with less influence of the feed gap. A high degree of cylindrical liner symmetry was observed during implosion. A fast liner speed of 2.4 km/s was achieved, and 350 T could be generated by 1 MJ and 470 T by 2 MJ

189

Magnetic field generation and open-quotes Weibel resonanceclose quotes in inhomogeneous plasmas  

International Nuclear Information System (INIS)

The Weibel instability is an effective general mechanism of magnetic field generation in anisotropic plasmas. Recently, it has been invoked in order to explain the magnetic field wake observed in PIC simulations of the interaction of ultrashort ultraintense laser pulses with an underdense plasma. In this case the Weibel instability is thought to arise because of the formation in the plasma of two opposite streams of electrons. When the electric currents carried by these streams are displaced one respect to the other by a transversal disturbance, a magnetic field is produced that grows because the repulsion of the oppositely directed currents reinforces the initial displacement. The evolution of this instability can be described, before wavebreaking takes place, within the framework of the (relativistic) EMHD equations where the ions axe considered to be at rest and the electrons are described as a (relativistic) fluid. (1) If the plasma is inhomogeneous and/or if the two electron streams are spatially localized, the EMHD equations show the presence of a singularity which is reminiscent of the Alfven resonance, found for Shear-Alfven waves. (2) In the simple case of two symmetric streams, this open-quotes Weibel resonanceclose quotes occurs where ?2= 2v2 where ? is the normalized growth rate and v the local value of the normalized electron velocity. As a result, a resonant mode localized around the singularity develops from an initial perturbatirity develops from an initial perturbation at a rate which depends on the characteristic gradient of the electron velocities. (3) The growth rate of this mode is nearly independent of the initial wavelength of the perturbation and is comparable to the growth rate that would be obtained with homogeneous electron velocities equal to their maximum value in the inhomogeneous case

190

Generation of liquid metal structures of high aspect ratio by application of an ac magnetic field  

Science.gov (United States)

We study how the shape of parts obtained through the LASER cladding process can be controlled by application of an ac magnetic field by means of two simple physical models: a numerical and an experimental one. More specifically, we show that straight metallic joints of high aspect ratio can be obtained by using inductors of triangular cross-section that concentrate electromagnetic forces at the bottom of the joint. The effect is first demonstrated on a numerical model for an infinitely long joint such as: we illustrate how the joint shape can be controlled by varying the inclination of the inductor and for a magnetic Bond number Bom=60 (which measures the ratio of electromagnetic to capillary forces), we obtain a joint of aspect ratio up to 7.2. We further find that inductor angles in the range 15°-25° lead to joint side faces that are close to vertical. These findings are then verified experimentally by placing a liquid metal drop in a purpose built inductor of triangular cross-section. We find a good agreement between the theoretical prediction of our two-dimensional model and the real three-dimensional drop. For the highest magnetic Bond number our generator could deliver, Bom=20.19, we achieved a drop aspect ratio of 2.73.

Andreev, Oleg; Pothérat, Alban; Thess, André

2010-06-01

191

Magnetic field distribution in the plasma flow generated by a plasma focus discharge  

International Nuclear Information System (INIS)

The magnetic field in the plasma jet propagating from the plasma pinch region along the axis of the chamber in a megajoule PF-3 plasma focus facility is studied. The dynamics of plasma with a trapped magnetic flow is analyzed. The spatial sizes of the plasma jet region in which the magnetic field concentrates are determined in the radial and axial directions. The magnetic field configuration in the plasma jet is investigated: the radial distribution of the azimuthal component of the magnetic field inside the jet is determined. It is shown that the magnetic induction vector at a given point in space can change its direction during the plasma flight. Conclusions regarding the symmetry of the plasma flow propagation relative to the chamber axis are drawn

192

Effect of external magnetic field on the generation and transport of hot electrons in laser-target irradiation  

International Nuclear Information System (INIS)

The effect of an externally applied magnetic field on the generation and transport of hot electrons in CO2 laser irradiation of cylindrical targets has been investigated. It is observed that an external magnetic field of 100 kG increases the energy coupled into the target by superhot (>100 keV) electrons by more than an order of magnitude. The transport of these electrons through a Mylar layer at solid density however is strongly inhibited by the presence of an imbedded magnetic field

193

Self-generated magnetic field measurements in TEA-CO2 laser produced plasmas on different targets  

International Nuclear Information System (INIS)

Results of self-generated magnetic field measurements using differential inductive probes in TEA-CO2 laser produced plasmas on different metallic targets are presented. Dependences of the magnetic field strengths on the incident laser energy, the target material, the target-focus distance and the coordinates of probe position are investigated. The results are correlated to those of some other complementary X-ray emission and ion collection measurements perfopmed in the same reproducible experimental conditions. (authors)

194

A numerical study of the generation of an azimuthal current in a plasma cylinder using a transverse rotating magnetic field  

International Nuclear Information System (INIS)

The generation of a steady azimuthal current in a cylindrical plasma column using a rotating magnetic field is numerically investigated. The mixed initial-boundary-value problem is solved using a finite difference method. It is shown that substantial azimuthal current can be driven provided that the amplitude of the rotating magnetic field is greater than a certain threshold value which depends on the plasma resistivity

195

An Impulse Induction MHD Generator Having a Magnetic Field with a Radial Component  

International Nuclear Information System (INIS)

An impulse induction MHD generator with a cylindrical channel has been theoretically and experimentally investigated. Given certain assumptions, it is possible to write the general system of the partial differential equations, which describes the behaviour of the generator. The mean spatial values of the physical quantities are calculated under certain simplifying conditions and a system of the common differential equations is obtained. After separation the common differential equations of the third order for the velocity and the current are found. These equations are homogeneous with constant and identical coefficients. The solution of these equations is not too complicated and information about their time dependence is obtained. The expressions for the power generated and the generator efficiency are found in the usual way. The equation of the volt-ampere characteristic is also obtained and the characteristic of the generator is found not to be, in general, linear. The equations for the case of open-circuit current and short-circuit voltage are derived. These equations are the common differential equations of the second order and their solutions give the possibility of determining two of the parameters of the plasma clusters. The theoretical conclusions are verified experimentally. A plasma gun is the source of the plasma clusters. The pressure is varied over 1.4 x 10-2 to 2 x 10-1 Torr. The magnetic field is 2 x 10-2 T. The electrical conductivity and the mass of the clusters is calculated from the expressions for the open-circuit voltage and short-circuit current. The results of the theoretical and experimental calculations are in acceptable agreement. It is possible to say that the generator will operate and could, after refinement, be used for diagnostics of plasma clusters. (author)

196

Ultrafast generation of pseudo-magnetic field for valley excitons in WSe? monolayers.  

Science.gov (United States)

The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K' valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications. PMID:25477455

Kim, Jonghwan; Hong, Xiaoping; Jin, Chenhao; Shi, Su-Fei; Chang, Chih-Yuan S; Chiu, Ming-Hui; Li, Lain-Jong; Wang, Feng

2014-12-01

197

CMB anisotropies generated by a stochastic background of primordial magnetic fields with non-zero helicity  

CERN Document Server

We consider the impact of a stochastic background of primordial magnetic fields with non-vanishing helicity on CMB anisotropies in temperature and polarization. We compute the exact expressions for the scalar, vector and tensor part of the energy-momentum tensor including the helical contribution, by assuming a power-law dependence for the spectra and a comoving cutoff which mimics the damping due to viscosity. We also compute the parity-odd correlator between the helical and non-helical contribution which generate the TB and EB cross-correlation in the CMB pattern. We finally show the impact of including the helical term on the power spectra of CMB anisotropies up to multipoles with ell ~ O(10^3)$.

Ballardini, Mario; Paoletti, Daniela

2014-01-01

198

Magnetic Weibel field generation in thin collisionless current sheets in reconnection in space plasma  

CERN Document Server

In collisionless reconnection in space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal level by the action of the non-magnetic Weibel instability driven in thin ($\\Delta<$ few $\\lambda_i$) current layers by the counter-streaming electron inflow from the `ion diffusion' (ion inertial Hall) region into the inner current (electron inertial) region from where the ambient magnetic fields are excluded when released by the inflowing electrons which become non-magnetic on scales $<$ few $\\lambda_e$. It is shown that under magnetospheric tail conditions it takes $\\sim 40$ e-folding times ($\\sim 20$ s) for the Weibel field to reach observable amplitudes $|{\\bf b}_{\\rm W}|\\sim 1$ nT. In counter-streaming inflows these fields are predominantly of guide field type. In non-symmetric inflows the field may possess a component normal to the current which would be capable of initiating reconnection onset.

Treumann, R A

2009-01-01

199

Virtual cathode microwave generation using inhomogeneous magnetic field and wave guide wall configuration  

International Nuclear Information System (INIS)

Microwave generation from a virtual cathode system is investigated using two-dimensional particle-in-cell simulation. In the typical virtual cathode geometry, the electron beam diode is separated from the output waveguide by a ground plane which is a thin foil or screen. By lowering the diode impedance sufficiently, it is possible to form a virtual cathode in the waveguide region a short distance from the ground plane. In this configuration two mechanisms can lead to microwave generation: 1) electron bunching due to reflection between the real and virtual cathode and 2) electron bunching due to virtual cathode oscillation. Both mechanisms are typically present, but it appears possible to make one mechanism dominant by adjusting the output waveguide radius. Although such a configuration might generate 1-10 GW output, electron deposition into the ground plane, waveguide wall, and output window causes breakdown. To overcome these disadvantages, the authors have investigated a configuration with no ground plane coupled with the use of an inhomogeneous external magnetic field and waveguide wall

200

Role of phase difference between superposing lasers and magnetic field for efficient terahertz radiation generation by tunnel ionization  

Science.gov (United States)

The generation of terahertz (THz) radiation is an active field of research due to its applications in THz spectroscopy, material characterization, imaging, topography, etc. Since plasma can sustain high field and it is a nonlinear medium, the plasma based schemes are very attractive techniques for the THz radiation generation. In the present work, we make use of tunnel ionization, where quick ionization is achieved with the help of two femtosecond lasers having a phase difference. Then the generated plasma cylinder is caused to oscillate and radiate at the frequency in the THz range. An application of DC magnetic field on the plasma cylinder helps getting a directional THz radiation emission. The role of phase difference and the magnetic field for efficient THz radiation generation and a control on the emission of radiation are discussed. The conversion efficiency of the present scheme is ˜10-3 and it supersedes several other schemes.

Malik, Anil Kumar; Malik, Hitendra K.

2011-11-01

 
 
 
 
201

Dynamo generation of magnetic fields in three-dimensional space: Solar cycle main flux tube formation and reversals  

International Nuclear Information System (INIS)

Dynamo processes as a magnetic field generation mechanism in astrophysics can be described essentially by movement and deformation of magnetic field lines due to plasma fluid motions. A basic element of the processes is a kinematic problem. As an important prototype of these processes, we investigate the case of the solar magnetic cycle. To follow the movement and deformation, we solve magnetohydrodynamic (MHD) equations by a numerical method with a prescribed velocity field. A simple combination of differential rotation and global convection, given by a linear analysis of fluid dynamics in a rotating sphere, can perpetually create and reverse great magnetic flux tubes encircling the Sun. We call them the main flux tubes of the solar cycle. They are progenitors of small-scale flux ropes of the solar activity. This shows that magnetic field generation by fluid motions is, in fact, possible and that MHD equations have a new type of oscillatory solution. The solar cycle can be identified with one of such oscillatory solutions. This means that we can follow detailed stages of the field generation and reversal processes of the dynamo by continuously observing the Sun. It is proposed that the magnetic flux tube formation by streaming plasma flows exemplified here could be a universal mechanism of flux tube formation in astrophysics

202

Effects of self-generated electric and magnetic fields in laser-generated fast electron propagation in solid materials: Electric inhibition and beam pinching  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present some experimental results which demonstrate the presence of electric inhibition in the propagation of relativistic electrons generated by intense laser pulses, depending on target conductivity. The use of transparent targets and shadowgraphic techniques has made it possible to evidence electron jets moving at the speed of light, an indication of the presence of self-generated strong magnetic fields.

Bernardinello, A.; Batani, D.; Antonicci, A.; Pisani, F.; Koenig, M.; Gremillet, L.; Amiranoff, F.; Baton, S.; Martinolli, E.; Rousseaux, C.; Hall, Ta; Norreys, P.; Djaoui, A.

2001-01-01

203

Recent Results from and proposed changes to the TCS Rotating magnetic Field FRC Generation Experiment  

Science.gov (United States)

FRCs have been generated and sustained in steady state from preionized gas fills using Rotating Magnetic Fields (RMF) in the TCS device. These FRCs are limited to sub 100 eV temperatures by at least several percent impurity content. Hot FRCs have also been translated and expanded into TCS from the LSX/mod theta pinch. These FRCs reflected off the end mirrors of TCS and their high supersonic directed energies were rethermalized to close to the original formation temperatures, but at less than one tenth the density (RMF applied to these FRCs altered the internal field B_z(r) profiles and could stabilize the n=2 rotational instability, but could not sustain the flux due to a surrounding layer of ionized quartz vapor ablated from the quartz tube walls. Ablation was caused by lack of centering of the reflected FRCs and the resultant vapor absorbed most of the RMF power and significantly reduced its amplitude. A modification to the TCS device will add internal metal flux conserving rings to shield the quartz wall from hot plasma. Also multipole fields will be provided to better center the translated FRC. In addition, discharge cleaning and wall conditioning will be added to minimize impurity production.

Guo, H. Y.; Hoffman, A. L.; Pietrzyk, Z. A.; Brooks, R. D.; Grossnickle, J. A.; Miller, K. E.; Peter, A. M.; Votroubek, G. R.

2002-11-01

204

New performance in harmonic analysis device generation used for magnetic fields measurements  

International Nuclear Information System (INIS)

In particle accelerator, correcting high multipole components of magnets are of high importance for quality magnet: to get a pure quadrupole to within 10-4, we have to know the field quality to 10-5 through the 30. order. Our laboratory needed such a very sharp device to find small harmonic components of magnetic field. For harmonic analysis of magnetic field, we adopted the standard method, i.e. a rotating coil connected to a flux integrator. Nowadays, coils measuring azimuthal component of magnetic field are used. In order to obtain correct and accurate measurements, we were guided by two imperatives: first, optimisation of construction constraints and second, comparison of azimuthal and radial component measurements. With this background, this article describes both new technological solutions adopted and new performance obtained. We also discuss the most suitable geometric structure for the coils. We obtained a noiseless signal, a repeatability of 10-5 and a sensitivity up to 10-8 Weber for both types of coils. Our device is able to find and measure main component, normal and skew multipole components up to the 32. order, when simulating local defects. The magnetic axis is located within 5 ?m. The central gradient is also measured and magnetic length deduced. Complementary functions of two types of coils were noticed in detecting local defects of magnetic structure. (authors)

205

New performance in harmonic analysis device generation used for magnetic fields measurements  

Energy Technology Data Exchange (ETDEWEB)

In particle accelerator, correcting high multipole components of magnets are of high importance for quality magnet: to get a pure quadrupole to within 10{sup -4}, we have to know the field quality to 10{sup -5} through the 30. order. Our laboratory needed such a very sharp device to find small harmonic components of magnetic field. For harmonic analysis of magnetic field, we adopted the standard method, i.e. a rotating coil connected to a flux integrator. Nowadays, coils measuring azimuthal component of magnetic field are used. In order to obtain correct and accurate measurements, we were guided by two imperatives: first, optimisation of construction constraints and second, comparison of azimuthal and radial component measurements. With this background, this article describes both new technological solutions adopted and new performance obtained. We also discuss the most suitable geometric structure for the coils. We obtained a noiseless signal, a repeatability of 10{sup -5} and a sensitivity up to 10{sup -8} Weber for both types of coils. Our device is able to find and measure main component, normal and skew multipole components up to the 32. order, when simulating local defects. The magnetic axis is located within 5 {mu}m. The central gradient is also measured and magnetic length deduced. Complementary functions of two types of coils were noticed in detecting local defects of magnetic structure. (authors).

Evesque, C.; Tkatchenko, M.

1996-12-31

206

Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T.  

Science.gov (United States)

Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, J(c). To minimize such grain boundary obstacles, HTS conductors such as REBa2Cu3O(7-x) and (Bi, Pb)2Sr2Ca2Cu3O(10-x) are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi2Sr2CaCu2O(8-x) (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high J(c) of 2,500 A mm(-2) at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high Jc can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries. PMID:24608141

Larbalestier, D C; Jiang, J; Trociewitz, U P; Kametani, F; Scheuerlein, C; Dalban-Canassy, M; Matras, M; Chen, P; Craig, N C; Lee, P J; Hellstrom, E E

2014-04-01

207

Hydrodynamic structures generated by a rotating magnetic field in a cylindrical vessel  

Science.gov (United States)

The hydrodynamic structures arising in a cylinder under the influence of a rotating magnetic field were considered, and the stability of a primary stationary flow in an infinitely long cylinder was investigated by linear approximation. The curves of neutral stability were obtained for a wide range of flow parameters and the calculations generated a single-vortex (in the radial direction) structure of Taylor’s vortices. The flow stability in the infinitely long cylinder was evaluated based on energy balance. The problem of three-dimensional stationary flow of a viscous incompressible conducting liquid induced by a rotating magnetic field in a cylindrical vessel of limited length was solved using an iteration method. The values of the parameters were found for which the iterative process still converges. Numerical experiment made it possible to investigate the arising spatial flow patterns and to track their evolution with changes in the flow parameters. Results of modelling showed the appearance of a three-dimensional structure of Taylor-type vortices in the middle portion of a sufficiently long vessel. The appearance of a double laminar boundary layer was demonstrated under certain conditions of azimuthal velocity distribution along the vessel height at the location of the end-wave vortex. This article was accepted for publication in Fluid Dynamics Research 2014 Vol 46, No 4; which was a special issue consisting of papers from the 5th International Symposium on Bifurcations in Fluid Dynamics. Due to an unfortunate error on the part of the journal, this article was not published with the other articles from this issue.

Zibold, A. F.

2015-02-01

208

Constraint on the primordial vector mode and its magnetic field generation from seven-year Wilkinson Microwave Anisotropy Probe Observations  

CERN Document Server

A primordial vector mode and its associated magnetic field generation are investigated. Firstly, we put an observational constraint on the amount of the primordial vector mode from the seven-year WMAP data. The constraint is found as $r_v \\lesssim -\\frac{r}{40}+0.012$, where $r_v$ and $r$ are the amounts of vector and tensor perturbation amplitudes with respect to the scalar one, respectively. Secondly, we calculate the spectrum of magnetic fields inevitably created from the primordial vector mode, given the constraint on $r_v$. It is found that the maximum amount of magnetic fields generated from the vector mode is given by $B\\lesssim 10^{-22}{\\rm G} (\\frac{r_v}{0.012})^{1/2} (\\frac{k}{0.002})^{(n_v+1)/2}$ with $n_v$ being a spectral index of the vector mode. We find a non-trivial cancellation of the magnetic field generation in the radiation dominated era, which creates a characteristic cut off in the magnetic field spectrum around $k\\approx 1.0$ Mpc$^{-1}$.

Ichiki, Kiyotomo; Sugiyama, Naoshi

2011-01-01

209

Hamilton flow generated by field lines near a toroidal magnetic surface  

Science.gov (United States)

A method is described for obtaining the Hamiltonian of a vacuum magnetic field in a given 3D toroidal magnetic surface (superconducting shell). This method is used to derive the expression for the integrable surface Hamiltonian in the form of the expansion of a rotational transform of field lines on embedded near-boundary magnetic surfaces into a Taylor series in the distance from the boundary. This expansion contains the value of the rotational transform and its shear at the boundary surface. It is shown that these quantities are related to the components of the first and second quadratic forms of the boundary surface.

Skovoroda, A. A.

2013-07-01

210

Stochastic magnetic field generation in MHD resistive instabilities: validity limits of linear stability analysis  

International Nuclear Information System (INIS)

The validity limits of a linear analysis for a resistive instability are determined. The effects of mode-coupling on the magnetic field structure are investigated in the reconnecting layer. Given an equilibrium magnetic field and a perturbation field, the conditions are found under which the equations for the magnetic field lines of force can be expressed in Hamiltonian form. These conditions can be fulfilled by a resistive instability. Consequently, in a simple equilibrium magnetic field the resistive eigenmodes have been analytically derived. This result is used to give an explicit expression of the Hamiltonian for field-line equations when two resistive eigenmodes are taken into account. The analytical form of the resulting Hamiltonian coincides with the so-called paradigm Hamiltonian (1.5 degrees of freedom) for which the Escande-Doveil renormalization procedure leads to an explicit expression for the global stochasticity threshold. Thus it can be shown that any pair of modes - in a suitable range of parameters - yields spatial stochasticity of magnetic field lines when the perturbation amplitude is still very low. Hence a limit of validity of the linear theory can be found. The linear phase of the resistive instability turns out to be relevant only to describe the onset of the instability itself. (author)

211

Microwave generation from an axially extracted virtual cathode oscillator with a guide magnetic field  

Energy Technology Data Exchange (ETDEWEB)

The operation of a virtual cathode oscillator (vircator) with strong axial magnetic field has been experimentally studied. Depending on the cathode--anode gap and cathode diameter, the operating voltage varies from 200 kV up to 480 kV with 2--7 kA diode current. Microwave emission is produced by the oscillating virtual cathode. The central microwave frequency follows the beam plasma frequency. It varies by 11.5 GHz up to 22 GHz, depending on the current density. The oscillation frequency does not depend on the guide magnetic field magnitude. A maximal output power of 15[plus minus]5 MW in asymmetric transverse magnetic (TM) modes is achieved by the axially extracted vircator. Variation of the magnetic field intensity in a range of 0--40 kG has an insignificant effect upon the emitted microwave power. An electron beam power to microwave power conversion efficiency of approximately 1% is obtained.

Kostov, K.G.; Nikolov, N.A. (Department of General Physics, Sofia University, Sofia 1126 (Bulgaria))

1994-04-01

212

Magnetic field generation in relativistic shocks - An early end of the exponential Weibel instability in electron-proton plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss magnetic field generation by the proton Weibel instability in relativistic shocks, a situation that applies to the external shocks in the fireball model for Gamma-ray Bursts, and possibly also to internal shocks. Our analytical estimates show that the linear phase of the instability ends well before it has converted a significant fraction of the energy in the proton beam into magnetic energy: the conversion efficiency is much smaller (of order m_e/m_p) in electron...

Wiersma, J.; Achterberg, A.

2004-01-01

213

Evidence from numerical experiments for a feedback dynamo generating Mercury's magnetic field.  

Science.gov (United States)

The observed weakness of Mercury's magnetic field poses a long-standing puzzle to dynamo theory. Using numerical dynamo simulations, we show that it could be explained by a negative feedback between the magnetospheric and the internal magnetic fields. Without feedback, a small internal field was amplified by the dynamo process up to Earth-like values. With feedback, the field strength saturated at a much lower level, compatible with the observations at Mercury. The classical saturation mechanism via the Lorentz force was replaced by the external field impact. The resulting surface field was dominated by uneven harmonic components. This will allow the feedback model to be distinguished from other models once a more accurate field model is constructed from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and BepiColombo data. PMID:22194574

Heyner, Daniel; Wicht, Johannes; Gómez-Pérez, Natalia; Schmitt, Dieter; Auster, Hans-Ulrich; Glassmeier, Karl-Heinz

2011-12-23

214

Magnetic fields from reionisation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a complementary study to a new model for generating magnetic fields of cosmological interest. The driving mechanism is the photoionisation process by photons provided by the first luminous sources. Investigating the transient regime at the onset of inhomogeneous reionisation, we show that magnetic field amplitudes as high as $2 \\times 10^{-16}$ Gauss can be obtained within a source lifetime. Photons with energies above the ionisation threshold accelerate electrons...

Langer, Mathieu; Aghanim, Nabila; Puget, Jean-loup

2005-01-01

215

Effect of a transverse magnetic field on the generation of electron beams in the gas-filled diode  

Science.gov (United States)

The effect of a transverse magnetic field (0.080 and 0.016 T) on generation of an electron beam in the gas-filled diode is experimentally investigated. It is shown that, at voltage U = 25 kV across the diode and a low helium pressure (45 Torr), the transverse magnetic field influences the beam current amplitude behind a foil and its distribution over the foil cross section. At elevated pressures and under the conditions of ultrashort avalanche electron beam formation in helium, nitrogen, and air, the transverse magnetic field (0.080 and 0.016 T) has a minor effect on the amplitude and duration of the beam behind the foil. It is established that, when the voltage of the pulse generator reaches several hundreds of kilovolts, some runaway electrons (including the electrons from the discharge plasma near the cathode) are incident on the side walls of the diode.

Baksht, E. H.; Burachenko, A. G.; Erofeev, M. V.; Kostyrya, I. D.; Lomaev, M. I.; Rybka, D. V.; Tarasenko, V. F.

2008-06-01

216

Directing assembly of DNA-coated colloids with magnetic fields to generate rigid, semiflexible, and flexible chains.  

Science.gov (United States)

We report the formation of colloidal macromolecules consisting of chains of micron-sized paramagnetic particles assembled using a magnetic field and linked with DNA. The interparticle spacing and chain flexibility were controlled by varying the magnetic field strength and the linker spring constant. Variations in the DNA lengths allowed for the generation of chains with an improved range of flexibility as compared to previous studies. These chains adopted the rigid-rod, semiflexible, and flexible conformations that are characteristic of linear polymer systems. These assembly techniques were investigated to determine the effects of the nanoscale DNA linker properties on the properties of the microscale colloidal chains. With stiff DNA linkers (564 base pairs) the chains were only stable at moderate to high field strengths and produced rigid chains. For flexible DNA linkers (8000 base pairs), high magnetic field strengths caused the linkers to be excluded from the gap between the particles, leading to a transition from very flexible chains at low field strengths to semiflexible chains at high field strengths. In the intermediate range of linker sizes, the chains exhibited predictable behavior, demonstrating increased flexibility with longer DNA linker length or smaller linking field strengths. This study provides insight into the process of directed assembly using magnetic fields and DNA by precisely tuning the components to generate colloidal analogues of linear macromolecular chains. PMID:25052952

Byrom, Julie; Han, Patric; Savory, Michael; Biswal, Sibani Lisa

2014-08-01

217

Energy system for the generation of divertor magnetic fields in the PDX fusion research device  

Energy Technology Data Exchange (ETDEWEB)

One of the major problems encountered in the development of Tokamak type fusion reactors is the presence of impurities in the plasma. The PDX device is designed to study the operation of poloidal magnetic field divertors and consequent magnetic limiters for controlling and reducing the amount of impurities. A system of coils placed at specific locations produces a required field configuration for the poloidal divertor. This paper describes the system of energy supplies required and the interrelations of field coil currents during plasma current initiation, growth and steady state.

Turitzin, N. M.

1976-05-01

218

Nonlinear generation of sheared flows and zonal magnetic fields by electron whistlers in plasmas  

Energy Technology Data Exchange (ETDEWEB)

The nonlinear generation of shear field and flow in whistler waves is considered. It is shown that a coherent parametric process leads to modulational instability of four waves whistler interaction. Growth rates for the flow/field are compared with published simulation results. -- Highlights: ? The mechanisms of self-generated flow and field has been done in EMHD plasma. ? A parametric process leads to modulational instability. ? The growth rate matches with simulation results.

Chakrabarti, Nikhil, E-mail: nikhil.chakrabarti@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700 064 (India); Shukla, Padma K., E-mail: profshukla@yahoo.de [Institute for Theoretical Physics, International Centre for Advanced Studies in Physical Sciences, Ruhr University Bochum, D-44780 Bochum (Germany)

2011-10-24

219

Nonlinear generation of sheared flows and zonal magnetic fields by electron whistlers in plasmas  

International Nuclear Information System (INIS)

The nonlinear generation of shear field and flow in whistler waves is considered. It is shown that a coherent parametric process leads to modulational instability of four waves whistler interaction. Growth rates for the flow/field are compared with published simulation results. -- Highlights: ? The mechanisms of self-generated flow and field has been done in EMHD plasma. ? A parametric process leads to modulational instability. ? The growth rate matches with simulation results.

220

Three-magnetic fields  

CERN Document Server

A completely new mechanism to generate the observed amount of large-scale cosmological magnetic fields is introduced in the context of three-form inflation. The amplification of the fields occurs via fourth order dynamics of the vector perturbations and avoids the backreaction problem that plagues most previously introduced mechanisms.

Koivisto, Tomi S

2011-01-01

 
 
 
 
221

Evolution of dynamo-generated magnetic fields in accretion disks around compact and young stars  

Science.gov (United States)

Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized objects because the accreted matter, whether it comes from the companion star (binaries) or from a collapsing molecular cloud core (single young stars), carries an embedded magnetic field. In addition, most accretion disks are hot and turbulent, thus meeting the condition for the MHD turbulent dynamo to maintain and amplify any seed field magnetic field. In fact, for a disk's magnetic field to persist long enough in comparison with the disk viscous time it must be contemporaneously regenerated because the characteristic diffusion time of a magnetic field is typically much shorter than a disk's viscous time. This is true for most thin accretion disks. Consequently, studying magentic fields in thin disks is usually synonymous with studying magnetic dynamos, a fact that is not commonly recognized in the literature. Progress in studying the structure of many accretion disks was achieved mainly because most disks can be regarded as two-dimensional flows in which vertical and radial structures are largely decoupled. By analogy, in a thin disk, one may expect that vertical and radial structures of the magnetic field are decoupled because the magnetic field diffuses more rapidly to the vertical boundary of the disk than along the radius. Thus, an asymptotic method, called an adiabatic approximation, can be applied to accretion disk dynamo. We can represent the solution to the dynamo equation in the form B = Q(r)b(r,z), where Q(r) describes the field distribution along the radius, while the field distribution across the disk is included in the vector function b, which parametrically depends on r and is normalized by the condition max (b(z)) = 1. The field distribution across the disk is established rapidly, while the radial distribution Q(r) evolves on a considerably longer timescale. It is this evolution that is the subject of this paper.

Stepinski, Tomasz F.

1994-01-01

222

THE EFFECT OF LOWER MANTLE METALLIZATION ON MAGNETIC FIELD GENERATION IN ROCKY EXOPLANETS  

International Nuclear Information System (INIS)

Recent theoretical and experimental evidence indicates that many of the materials that are thought to exist in the mantles of terrestrial exoplanets will metallize and become good conductors of electricity at mantle pressures. This allows for strong electromagnetic coupling of the core and the mantle in these planets. We use a numerical dynamo model to study the effect of a metallized lower mantle on the dynamos of terrestrial exoplanets using several inner core sizes and mantle conductivities. We find that the addition of an electrically conducting mantle results in stronger core-mantle boundary fields because of the increase in magnetic field stretching. We also find that a metallized mantle destabilizes the dynamo resulting in less dipolar, less axisymmetric poloidal magnetic fields at the core-mantle boundary. The conducting mantle efficiently screens these fields to produce weaker surface fields. We conclude that a conducting mantle will make the detection of extrasolar terrestrial magnetic fields more difficult while making the magnetic fields in the dynamo region stronger.

223

THE EFFECT OF LOWER MANTLE METALLIZATION ON MAGNETIC FIELD GENERATION IN ROCKY EXOPLANETS  

Energy Technology Data Exchange (ETDEWEB)

Recent theoretical and experimental evidence indicates that many of the materials that are thought to exist in the mantles of terrestrial exoplanets will metallize and become good conductors of electricity at mantle pressures. This allows for strong electromagnetic coupling of the core and the mantle in these planets. We use a numerical dynamo model to study the effect of a metallized lower mantle on the dynamos of terrestrial exoplanets using several inner core sizes and mantle conductivities. We find that the addition of an electrically conducting mantle results in stronger core-mantle boundary fields because of the increase in magnetic field stretching. We also find that a metallized mantle destabilizes the dynamo resulting in less dipolar, less axisymmetric poloidal magnetic fields at the core-mantle boundary. The conducting mantle efficiently screens these fields to produce weaker surface fields. We conclude that a conducting mantle will make the detection of extrasolar terrestrial magnetic fields more difficult while making the magnetic fields in the dynamo region stronger.

Vilim, R.; Stanley, S. [Department of Physics, University of Toronto, Toronto, Ontario (Canada); Elkins-Tanton, L., E-mail: rvilim@physics.utoronto.ca [Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC (United States)

2013-05-10

224

Dynamical Feedback of Self-generated Magnetic Fields in Cosmic Rays Modified Shocks  

Energy Technology Data Exchange (ETDEWEB)

We present a semi-analytical kinetic calculation of the process of non-linear diffusive shock acceleration (NLDSA) which includes magnetic field amplification due to cosmic ray induced streaming instability, the dynamical reaction of the amplified magnetic field and the possible effects of turbulent heating. This kinetic calculation allows us to show that the net effect of the amplified magnetic field is to enhance the maximum momentum of accelerated particles while reducing the concavity of the spectra, with respect to the standard predictions of NLDSA. This is mainly due to the dynamical reaction of the amplified field on the shock, which smoothens the shock precursor. The total compression factors which are obtained for parameters typical of supernova remnants are R{sub tot} {approx} 7-10, in good agreement with the values inferred from observations. The strength of the magnetic field produced through excitation of streaming instability is found in good agreement with the values inferred for several remnants if the thickness of the X-ray rims are interpreted as due to severe synchrotron losses of high energy electrons. We also discuss the relative role of turbulent heating and magnetic dynamical reaction in smoothening the shock precursor.

Caprioli, D.; /Pisa, Scuola Normale Superiore; Blasi, P.; /Arcetri Observ. /Fermilab; Amato, E.; /Arcetri Observ.; Vietri, M.; /Pisa, Scuola Normale Superiore

2008-07-01

225

The role of a dynamo generated magnetic field in accretion disk models  

International Nuclear Information System (INIS)

The authors stress the role of magnetic energy production by dynamo action in accretion disks around compact objects of stellar size and supermassive black holes to explain the strong X-ray luminosity of galactic and extragalactic sources respectively. The basic point is that magnetic field intensification by differential rotation is essentially sustained by angular momentum transfer associated with mass accretion. Magnetic energy is then dissipated in a coronal-like disk envelope. Therefore it is suggested that conversion of gravitational energy into X-ray radiated thermal energy in accretion disks occurs via a magnetic field based dynamo mechanism. An expression for the X-ray luminosity is derived in terms of the basic parameters, namely the disk size, its angular velocity and the mass accretion rate. (Auth.)

226

Cosmological magnetic field survival  

CERN Document Server

It is widely believed that primordial magnetic fields are dramatically diluted by the expansion of the universe. As a result, cosmological magnetic fields with residual strengths of astrophysical relevance are generally sought by going outside standard cosmology, or by extending conventional electromagnetic theory. Nevertheless, the survival of strong B-fields of primordial origin is possible in spatially open Friedmann universes without changing conventional electromagnetism. The reason is the hyperbolic geometry of these spacetimes, which slows down the adiabatic magnetic decay-rate and leads to their superadiabatic amplification on large scales. So far, the effect has been found to operate on Friedmannian backgrounds containing either radiation or a slow-rolling scalar field. We show here that the superadiabatic amplification of large-scale magnetic fields, generated by quantum fluctuations during inflation, is essentially independent of the type of matter that fills the universe and appears to be a generi...

Barrow, John D

2011-01-01

227

Thermal convection and generation of large-scale magnetic fields in the inner regions of accretion discs around black holes  

International Nuclear Information System (INIS)

The theory of thermal convection in the inner region of an accretion disc (IRAD) is investigated. The characteristic time of development of the convective instability is determined, which, at the optimal configuration of the convective cells, proved to be of the order of the disc's revolution time. The effect of the differential rotation and azimuthal magnetic field on this instability is studied. The following quantities are estimated with the use of the equations of the turbulent dynamo in the disc: growth time of the large-scale magnetic field, the relations between the components of this field, and the maximum value-scale magnetic field, which can be generated in the inner region of the accretion disc in the framework of our model

228

Photon echoes generated by reversing magnetic field gradients in a rubidium vapour  

CERN Document Server

We propose a photon echo quantum memory scheme using detuned Raman coupling to long lived ground states. In contrast to previous 3-level schemes based on controlled reversible inhomogeneous broadening that use sequences of $\\pi$-pulses, the scheme does not require accurate control of the coupling dynamics to the ground states. We present a proof of principle experimental realization of our proposal using rubidium atoms in a warm vapour cell. The Raman resonance line is broadened using a magnetic field that varies linearly along the direction of light propagation. Inverting the magnetic field gradient rephases the atomic dipoles and re-emits the light pulse in the forward direction.

Hétet, G; Sparkes, B; Oblak, D; Lam, P K; Buchler, B C

2008-01-01

229

Chaotic signal generation in low-voltage vircator with electron source shielded from external magnetic field  

Science.gov (United States)

The effect of shielding an electron source from a homogeneous external magnetic field of the drift chamber on the nonlinear dynamics of the electron beam with a virtual cathode (VC) and on the characteristics of output microwave radiation in a low-voltage vircator have been numerically simulated within the framework of a two-dimensional model. It is established that the increased degree of shielding of the electron source from the external magnetic field leads to the complication of the VC dynamics in the system and the corresponding chaotization of the output microwave radiation. Physical processes that account for the observed effect of shielding are analyzed.

Kurkin, S. A.; Hramov, A. E.; Koronovskii, A. A.

2011-02-01

230

Dynamo generation of magnetic field in the white dwarf GD 358  

Science.gov (United States)

On the basis of Whole Earth Telescope observations of the g-mode oscillation spectrum of the white dwarf GD 358, Winget et al. find evidence for significant differential rotation and for a time-varying magnetic field concentrated in the surface layers of this star. Here we argue on theoretical grounds that this magnetic field is produced by an alpha omega dynamo operating in the lower part of a surface convection zone in GD 358. Our argument is based on numerical solutions of the nonlinear, local dynamo equations of Robinson & Durney, with specific parameters based on our detailed models of white-dwarf convective envelopes, and universal constants determined by a calibration with the the Sun's dynamo. The calculations suggest a dynamo cycle period of about 6 years for the fundamental mode, and periods as short as 1 year for the higher-order modes that are expected to dominate in view of the large dynamo number we estimate for GD 358. These dynamo periods are consistent with the changes in the magnetic field of GD 358 over the span of 1 month inferred by Winget et. al. from their observations. Our calculations also suggest a peak dynamo magnetic field strength at the base of the surface convection zone of about 1800 G, which is consistent with the field strength inferred from the observations.

Markiel, J. Andrew; Thomas, John H.; Van Horn, H. M.

1994-01-01

231

Weak nonlinear electromagnetic waves and low-frequency magnetic-field generation in electron-positron-ion plasmas  

International Nuclear Information System (INIS)

The weakly nonlinear localization of obliquely modulated high-frequency electromagnetic waves in an electron-positron-ion plasma is considered. It is shown that the amplitude of the wave turns out to be a strongly dependent function of the angle between the slow modulations and the fast spatial variations and that the possibility appears of spontaneous generation of low-frequency magnetic fields. These magnetic fields are also functions of this angle and of the high-frequency wave polarization. The analysis of colinear modulation in electron-positron plasmas shows that some restriction must be made regarding the validity of previous calculations. (author)

232

Diode with magnetic insulation and Br field as a generator of power microsecond ion beam  

International Nuclear Information System (INIS)

Results of investigations into the generation of microsecond duration high-power ion beam in a plane magnetoisolated diode with an external isolating field with radial distribution are presented. The investigations are conducted using a microsecond generator operating in the regime of generating positive high-voltage ?600 kV amplitude pulses. Ring-type cross section ion beam consisting mainly of H+ and C+ ions is studied. The energy range occupied by the major part of the ions generated makes up 300-500 keV. The complete energy store of the beam extracted from the diode makes up 10 kJ, the generation efficiency is 60%

233

Self-consistent modeling of induced magnetic field in Titan's atmosphere accounting for the generation of Schumann resonance  

Science.gov (United States)

This model is worked out in the frame of physical mechanisms proposed in previous studies accounting for the generation and the observation of an atypical Schumann Resonance (SR) during the descent of the Huygens Probe in the Titan's atmosphere on 14 January 2005. While Titan is staying inside the subsonic co-rotating magnetosphere of Saturn, a secondary magnetic field carrying an Extremely Low Frequency (ELF) modulation is shown to be generated through ion-acoustic instabilities of the Pedersen current sheets induced at the interface region between the impacting magnetospheric plasma and Titan's ionosphere. The stronger induced magnetic field components are focused within field-aligned arcs-like structures hanging down the current sheets, with minimum amplitude of about 0.3 nT throughout the ramside hemisphere from the ionopause down to the Moon surface, including the icy crust and its interface with a conductive water ocean. The deep penetration of the modulated magnetic field in the atmosphere is thought to be allowed thanks to the force balance between the average temporal variations of thermal and magnetic pressures within the field-aligned arcs. However, there is a first cause of diffusion of the ELF magnetic components, probably due to feeding one, or eventually several SR eigenmodes. A second leakage source is ascribed to a system of eddy-Foucault currents assumed to be induced through the buried water ocean. The amplitude spectrum distribution of the induced ELF magnetic field components inside the SR cavity is found fully consistent with the measurements of the Huygens wave-field strength. Waiting for expected future in-situ exploration of Titan's lower atmosphere and the surface, the Huygens data are the only experimental means available to date for constraining the proposed model.

Béghin, Christian

2015-02-01

234

Magnetic flux generation and sawteeth in the MST reversed-field pinch  

International Nuclear Information System (INIS)

The Madison Symmetric Torus (MST) is a reversed-field pinch (RFP) which began operation in June 1988 (major radius of 1.50 m and minor radius of 0.52 m). Since its initial operation, discrete magnetic disturbances have been observed which result in an increase in the average toroidal magnetic flux and a decrease in the toroidal field at the wall. These disturbances are well correlated with events on other diagnostics: a sharp drop in soft x-ray signals (similar to the tokamak sawteeth), a decrease in the line averaged density, an increase in the edge density, and an increase in wall interactions as seen by spectroscopic signals. The plasma column also experiences a sudden inward shift as seen by magnetic pickup coils

235

Analysis of ruby luminescence R-line wavelength shift upon isentropic compression by MC-generator ultrahigh magnetic field pressure  

International Nuclear Information System (INIS)

The method of isentropic material compression by MC-generator ultrahigh magnetic field pressure has been developed. One of the problems arising from analysis of material equation of state in megabar pressure range is the lack of reliable method for pulsed pressure measurement. To determine the static pressure, produced in diamond anvils, the shift of ruby luminescence R-line length is used. The works analyzing the ruby optical spectrum by shock-wave compression have become available. This paper considers the possible use of ruby pickup to measure the pulsed pressure, generated by ultrahigh magnetic field in MC-1 generator. Furthermore, spectroscopic studies carried out in conditions of isentropic compression are of interest to understand the effect of dynamic compression on material properties at the atomic-molecular level

236

Magnetic fields from inflation?  

International Nuclear Information System (INIS)

We consider the possibility of generation of the primordial magnetic field on inflation and show that the effect of the back reaction of this field can be very important. Assuming that the back reaction does not spoil inflation we find a rather strong restriction on the amplitude of the primordial field which could be generated on inflation. Namely, this amplitude recalculated to the present epoch cannot exceed 10?32G in Mpc scales. This field seems to be too small to be amplified to the observable values by a possible dynamo mechanism

237

Study and realization of a power circuit of a superconducting dipole generator of a magnetic field  

International Nuclear Information System (INIS)

The project of experimental reactor building on controlled fusion (I.T.E.R) needed the development of a superconducting cable made of niobium-tin. Tested with a current of fifty kilo amperes under a twelve tesla constant field, this cable has to be tested under a variable field. The installation of the power circuit of the dipole field generator, consisted to the study and realization of the four following points: an important power cable; a tension protection organ of the dipole, under a seventeen milli Henrys inductance and four kilo amperes; a current regulating system given by the generator; a complete pilot system of the test station

238

Ubiquity of chaotic magnetic-field lines generated by three-dimensionally crossed wires in modern electric circuits.  

Science.gov (United States)

We investigate simple three-dimensionally crossed wires carrying electric currents which generate chaotic magnetic-field lines (CMFLs). As such wire systems, cross-ring and perturbed parallel-ring wires are studied, since topologically equivalent configurations to these systems can often be found in contemporary electric and integrated circuits. For realistic fundamental wire configurations, the conditions for wire dimensions (size) and current values to generate CMFLs are numerically explored under the presence of the weak but inevitable geomagnetic field. As a result, it is concluded that CMFLs can exist everywhere; i.e., they are ubiquitous in the modern technological world. PMID:20365304

Hosoda, M; Miyaguchi, T; Imagawa, K; Nakamura, K

2009-12-01

239

The mean electromotive force generated by random Alfven waves in a collisionless plasma under a non-uniform mean magnetic field  

International Nuclear Information System (INIS)

The mean electromotive force generated by random Alfven waves in a collisionless plasma is evaluated taking into account magnetic field gradients. It is shown that the mean electromotive force associated with a magnetic shear of the mean field and the helicity spectrum function of the random velocity field exists and has a component parallel to the mean magnetic field when it is generated by random waves propagating along the mean magnetic field and by statistically anisotropic random waves propagating in arbitrary directions. The results are applied to the magnetospheric substorms. (author)

240

Simulation Study of Magnetic Fields generated by the Electromagnetic Filamentation Instability driven by Pair Loading  

Science.gov (United States)

Using a 3-D relativistic particle-in-cell (RPIC) code, we have investigated particle acceleration associated with a relativistic electron-positron (cold) jet propagating into ambient electron-positron and electron-ion plasmas without initial magnetic fields in order to investigate the nonlinear stage of the Weibel instability. We have also performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which are assumed to be created by the photon annihilation. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions and ambient plasma. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities, currents, electric, and magnetic fields in the electron-ion ambient plasma are larger than those in the electron-positron ambient plasma. We have shown that plasma instabilities driven by these streaming electron-positron pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. These fields maintain a strong saturated level on timescales much longer than the electron skin depth at least for the duration of the simulations. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between electron-positron pairs and ions, and may help explain the origin of large upstream fields in GRB shock.

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

2007-01-01

 
 
 
 
241

A magnetically isolated diode with B?-field as a generator of high-power microsecond ion beam  

International Nuclear Information System (INIS)

The results of a study of the generation of a high-power microsecond ion beam in a planar magnetically isolated diode with external radially distributed isolating field are presented. A ring cross-section ion beam consisting mainly of H+ and C+ ions was studied. The energy range of most of the generated ions is 300-500 keV. The total energy stored in the beam extracted from the diode is 10 kJ and the generation efficiency reaches 60%. 5 refs., 4 figs

242

High heat generation ability in AC magnetic field for nano-sized magnetic Y3Fe5O12 powder prepared by bead milling  

International Nuclear Information System (INIS)

Nano-sized magnetic Y3Fe5O12 ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 ?m in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y3Fe5O12 ferrites. The highest heat ability in the AC magnetic field was for the fine Y3Fe5O12 powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y3Fe5O12 samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g?1) was estimated using a 3.58×10?4 fH2 frequency (f/kHz) and the magnetic field (H/kA m?1), which is the highest reported value of superparamagnetic materials. - Highlights: ? The nano-sized Y3Fe5O12 powder prepared by bead-milling has the highest heat generag has the highest heat generation ability in an AC magnetic field. ? The heat generation properties are ascribed to an increase in the Néel relaxation of the superparamagnetic material. ? The heat ability (W g?1) can be estimated using 3.58×10?4 fH2 (f=kHz, H=kA m?1). ? This is an expectable material for use in a drug delivery system for the thermal coagulation therapy of cancer tumors.

243

Influence of the Backreaction of Streaming Cosmic Rays on Magnetic Field Generation and Thermal Instability  

Science.gov (United States)

Using a multifluid approach, we investigate streaming and thermal instabilities of the electron-ion plasma with homogeneous cold cosmic rays propagating perpendicular to the background magnetic field. Perturbations are also considered to be across the magnetic field. The backreaction of cosmic rays resulting in strong streaming instabilities is taken into account. It is shown that, for sufficiently short wavelength perturbations, the growth rates can exceed the growth rate of cosmic-ray streaming instability along the magnetic field, found by Nekrasov & Shadmehri, which is in turn considerably larger than the growth rate of the Bell instability. The thermal instability is shown not to be subject to the action of cosmic rays in the model under consideration. The dispersion relation for the thermal instability has been derived, which includes sound velocities of plasma and cosmic rays and Alfvén and cosmic-ray streaming velocities. The relation between these parameters determines the kind of thermal instability ranging from the Parker to the Field instabilities. The results obtained can be useful for a more detailed investigation of electron-ion astrophysical objects, such as supernova remnant shocks, galaxy clusters, and others, including the dynamics of streaming cosmic rays.

Nekrasov, Anatoly K.; Shadmehri, Mohsen

2014-06-01

244

Topologies of velocity-field stagnation points generated by a single pair of magnets in free-surface electromagnetic experiments.  

Science.gov (United States)

The velocity fields generated by a static pair of magnets in free-surface electromagnetically forced flows are analyzed for different magnet attitudes, ionic currents, and brine depths. A wide range of laminar velocity fields is obtained despite the forcing simplicity. The velocity fields are classified according to their temporal mean flow topology, which strongly depends on the forcing geometry but barely on its strength, even through the bifurcation to unsteady regimes. The mean flow topology possesses a major influence on the critical Reynolds number Rec under which the steady velocity fields remain stable. The qualitative comparison of the dependence of Rec on the topology is in agreement with previous works. The unsteady configurations evidence the advection of smaller flow structures by the largest scales, commonly known as "sweeping." PMID:25375588

de la Cruz, J M García; Vassilicos, J C; Rossi, L

2014-10-01

245

Magnetic fields from inflation?  

CERN Document Server

We consider the possibility of generation of the seeds of primordial magnetic field on inflation and show that the effect of the back reaction of this field can be very important. Assuming that back reaction does not spoil inflation we find a rather strong restriction on the amplitude of the primordial seeds which could be generated on inflation. Namely, this amplitude recalculated to the present epoch cannot exceed $10^{-32}G$ in $Mpc$ scales. This field seems to be too small to be amplified to the observable values by galactic dynamo mechanism.

Demozzi, Vittoria; Rubinstein, Hector

2009-01-01

246

Wakefield generation in magnetized plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider wakefield generation in plasmas by electromagnetic pulses propagating perpendicular to a strong magnetic field, in the regime where the electron cyclotron frequency is equal to or larger than the plasma frequency. PIC-simulations reveal that for moderate magnetic field strengths previous results are re-produced, and the wakefield wavenumber spectrum has a clear peak at the inverse skin depth. However, when the cyclotron frequency is significantly larger than the ...

Holkundkar, A.; Brodin, G.; Marklund, M.

2011-01-01

247

Effects of Radiation Heat Transfer on Entropy Generation at Thermosolutal Convection in a Square Cavity Subjected to a Magnetic Field  

Directory of Open Access Journals (Sweden)

Full Text Available Thermosolutal convection in a square cavity filled with a binary perfect gas mixture and submitted to an oriented magnetic field taking into account the effect of radiation heat transfer is numerically investigated. The cavity is heated and cooled along the active walls whereas the two other walls are adiabatic and insulated. Entropy generation due to heat and mass transfer, fluid friction and magnetic effect has been determined for laminar flow by solving numerically: The continuity, momentum energy and mass balance equations, using a Control Volume Finite-Element Method. The structure of the studied flows depends on five dimensionless parameters which are: The Grashof number, the buoyancy ratio, the Hartman number, the inclination angle of the magnetic field and the radiation parameter.

Ammar Ben Brahim

2011-11-01

248

Pulsed magnetic field induced fast drug release from magneto liposomes via ultrasound generation.  

Science.gov (United States)

Fast drug delivery is very important to utilize drug molecules that are short-lived under physiological conditions. Techniques that can release model molecules under physiological conditions could play an important role to discover the pharmacokinetics of short-lived substances in the body. Here an experimental method is developed for the fast release of the liposomes' payload without a significant increase in (local) temperatures. This goal is achieved by using short magnetic pulses to disrupt the lipid bilayer of liposomes loaded with magnetic nanoparticles. The drug release has been tested by two independent assays. The first assay relies on the AC impedance measurements of MgSO4 released from the magnetic liposomes. The second standard release assay is based on the increase of the fluorescence signal from 5(6)-carboxyfluorescein dye when the dye is released from the magneto liposomes. The efficiency of drug release ranges from a few percent to up to 40% in the case of the MgSO4. The experiments also indicate that the magnetic nanoparticles generate ultrasound, which is assumed to have a role in the release of the model drugs from the magneto liposomes. PMID:25110807

Podaru, George; Ogden, Saralyn; Baxter, Amanda; Shrestha, Tej; Ren, Shenqiang; Thapa, Prem; Dani, Raj Kumar; Wang, Hongwang; Basel, Matthew T; Prakash, Punit; Bossmann, Stefan H; Chikan, Viktor

2014-10-01

249

An iron free asynchronous pulsed generator for the production of pulsed high magnetic fields  

International Nuclear Information System (INIS)

The production of long pulsed high fields (> 500 kgaus) with (tau > 1 s) with cryogenic coils requires an initial energy source of several megajoules. Iron free asynchronous pulsed generators are particulary well adapted to this application as they are able to produce this energy at a very competitive price

250

Effect of Magnetic Field on Entropy Generation Due to Laminar Forced Convection Past a Horizontal Flat Plate  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha, Eckert number (Ec, Prandtl number (Pr, Joule heating parameter (R and the free stream temperature parameter (θ∞ on the entropy generation characteristics is analyzed. The dimensionless governing equations in Cartesian coordinate were solved by an implicit finite difference technique. The solutions were carried out for Ha2=0.5-3, Ec=0.01-0.05, Pr=1-5 and θ∞=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation.

Moh'd A. Al-Nimr

2004-06-01

251

Magnetic Field and Life  

Science.gov (United States)

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

252

Generation of enhanced-scalelength plasmas and Zeeman study of magnetic fields  

International Nuclear Information System (INIS)

Using nonuniform laser illumination on flat targets, with moderate laser energies (200 J), we have produced enhanced density scalelengths; e.g., in excess of 0.5 mm at 0.1 of critical density. These enhanced scalelengths are of interest in simulating large, high-gain pellets, and investigating the potential impact of longer scalelengths on a variety of convective plasma instabilities. The nonuniform laser irradiation also affects the spontaneous magnetic fields. These fields were measured for the first time using the Zeeman effect. Space-and-time-resolved measurements, for both polarizations, were made of the 2271-2278 A CV triplets (2s3S1 - 2p3P2,1,0) emission. A comparison with theory gave fields around 200 kG

253

Cosmological magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic fields are observed on nearly all scales in the universe, from stars and galaxies upto galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field w...

Olinto, Angela V.

2000-01-01

254

Ocean circulation generated magnetic signals  

DEFF Research Database (Denmark)

Conducting ocean water, as it flows through the Earth's magnetic field, generates secondary electric and magnetic fields. An assessment of the ocean-generated magnetic fields and their detectability may be of importance for geomagnetism and oceanography. Motivated by the clear identification of ocean tidal signatures in the CHAMP magnetic field data we estimate the ocean magnetic signals of steady flow using a global 3-D EM numerical solution. The required velocity data are from the ECCO ocean circulation experiment and alternatively from the OCCAM model for higher resolution. We assume an Earth's conductivity model with a surface thin shell of variable conductance with a realistic ID mantle underneath. Simulations using both models predict an amplitude range of +/-2 nT at Swarm altitude (430 km). However at sea level, the higher resolution simulation predicts a higher strength of the magnetic field, as compared to the ECCO simulation. Besides the expected signatures of the global circulation patterns, we find significant seasonal variability of ocean magnetic signals in the Indian and Western Pacific Oceans. Compared to seasonal variation, interannual variations produce weaker signals.

Manoj, C.; Kuvshinov, A.

2006-01-01

255

Magnetic properties of Sm-doped Bi-2223 superconductor studied by low field local Hall generator ac susceptibility  

International Nuclear Information System (INIS)

We studied the grain boundary properties of Sm doped Bi(Pb)SrCaCuO using the Hall generator ac susceptibility (? = ?' + i?''). Hall generator is a convenient tool to investigate the shielding effect of superconductors under extremely low magnetic fields. Using a Hall generator system, we have investigated diamagnetic shielding behavior of Bi1.6Pb0.4Sr2Ca2-xSmxCu3Oy samples with x = 0.0, 0.0005, 0.001, 0.005, 0.01 and 0.1. The susceptibility measurements were carried out for ac field amplitudes of 47, 94, 141, 188 and 235 A/m with the frequency of 20 Hz. The critical temperatures were estimated from the temperature dependence of the ac susceptibility curves. We have also employed X-ray diffraction, energy dispersive X-ray fluorescent and scanning electron microscopy techniques to investigate the effect of Sm doping

256

Permanent magnet devices for generation of initial current in spiral explosion-magnetic generators  

International Nuclear Information System (INIS)

Principles are considered of operation of explosion-magnetic generators for generation of superstrong currents and magnetic fields. Different designs are described of magnetic systems on the base of permanent magnets, which produce high magnetic fluxes and initial currents within spirals of the explosion-magnetic generators. The magnetic flux from 1.3 to 1.8 mWb were obtained by means of the developed magnetic systems on the base of permanent magnets for the spiral explosion-magnetic generators with the diameter of 40 mm and winding step of 2.1 mm. 6 refs., 8 figs

257

Spectral modification of laser-accelerated proton beams by self-generated magnetic fields  

International Nuclear Information System (INIS)

Target normal measurements of proton energy spectra from ultra-thin (50-200 nm) planar foil targets irradiated by 1019 W cm-2 40 fs laser pulses exhibit broad maxima that are not present in the energy spectra from micron thickness targets (6 ?m). The proton flux in the peak is considerably greater than the proton flux observed in the same energy range in thicker targets. Numerical modelling of the experiment indicates that this spectral modification in thin targets is caused by magnetic fields that grow at the rear of the target during the laser-target interaction.

258

Magnetic fields generated by r-modes in accreting millisecond pulsars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside Low Mass X-ray Binaries (LMXBs), systems in which a neutron star (or a black hole) is accreting fro...

Cuofano, Carmine; Drago, Alessandro

2009-01-01

259

Effects of metallurgical microstructure of armatures on compressed magnetic field generators  

International Nuclear Information System (INIS)

Methods for improving uniform expansion behavior of compressed magnetic field device armatures were studied. Initial microstructure of the copper tubes was altered in a controlled manner by using different forming techniques and alloying. Results show a 25 to 50% improvement in uniform explosive expansion radius for electroformed and spun copper armatures compared to standard armatures machined from drawn tubing. Expansion improvement has been correlated with changes in the mechanical texture due to forming. The smoother expansion, however, did not result in a significantly higher electrical efficiency with the armature parameters tested

260

In vitro investigation of eddy current effect on pacemaker operation generated by low frequency magnetic field.  

Science.gov (United States)

This paper presents in vitro investigation of the eddy current induction effects to the cardiac pacemaker exposed to low frequency magnetic fields. The method used in this study is based to the interaction by inductive coupling through the loop formed by the pacemaker and its leads and the surrounding medium. This interaction results in an induced electromotive force between the terminals of the pacemaker which can potentially disturb the operation of this last. In this article we present experimental results, analytical calculations and numerical simulations using the finite element method. PMID:18003302

Babouri, A; Hedjeidj, A

2007-01-01

 
 
 
 
261

Ultrafast Generation of Pseudo-magnetic Field for Valley Excitons in WSe2 Monolayers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new degree of freedom, the valley pseudospin, emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2) and has attracted great scientific interest. The capability to manipulate the valley pseudospin, in analogy to the control of spin in spintronics, can open up exciting opportunities in valleytronics. Here we demonstrate that an ultrafast and ultrahigh valley pseudomagnetic field can be generated using circularly polarized femtosecond pulses to sel...

Kim, Jonghwan; Hong, Xiaoping; Jin, Chenhao; Shi, Su-fei; Chang, Chih-yuan S.; Chiu, Ming-hui; Li, Lain-jong; Wang, Feng

2014-01-01

262

Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability  

Science.gov (United States)

We have investigated the effects of plasma instabilities driven by rapid e(sup plus or minus) pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of the original spectrum. The injection of e(sup plus or minus) pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming e(sup plus or minus) pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between e(sup plus or minus) pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

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

2007-01-01

263

Second harmonic generation in laser-plasma interactions in the present of a wiggler magnetic field by using of photonic crystal theory  

International Nuclear Information System (INIS)

Interaction of a ultra short laser pulse with nonmagnetic isotropic plasma produce many nonlinear phenomena such as generation of odd harmonics. In the presence of a magnetic field, anisotropic plasma is converted to a non isotropic plasma and leads to generate even harmonics. In nonlinear optical processes such as second harmonic generation, the phase matching condition, which is an important character to obtain a large output, is given by the conservation of the momentum. In order to providing phase-matching condition, it is exerting a spatial periodic magnetic field (Wiggler magnetic field) in order to create a structure such as photonic crystal.

264

Magnetic Field Generation and Energy Confinement with Te> 500 eV in the SSPX Spheromak  

Science.gov (United States)

The understanding of confinement and energy transport in spheromaks is key the understanding the physics of spheromak formation and self-organization as well as addressing the feasibility of the concept as a reactor scenario. In the Sustained Spheromak Physics eXperiment (SSPX), increased understanding of the physics in building and sustaining self-organized magnetic equilibria has resulted in record electron temperatures Te> 500 eV and plasma currents of ˜ 1 MA on the magnetic axis. We find that the highest edge magnetic field magnitudes (and correspondingly high Te) is achieved when ?=?0Igun ?gun is near (but slightly below) the Kruskal-Shafranov instability limit ?KS2?L12.6,-1 where L is the length of the flux-conserver (0.5 m). Building on previously reported results, power-balance analysis has shown levels of electron thermal transport ?eindicating good confinement and closed flux surfaces. With the addition of a modular capacitor bank we are able to highly tailor the gun current to take advantage of the sensitive dependence of spheromak performance on the plasma ?. When in this optimum operating range we also find that the efficiency of field build-up (defined as the ratio of edge poloidal magnetic field to gun current) is increased 20% over prior results, to ˜1.0 T/MA. Additionally this brings the efficiency of spheromak formation into numerical agreement with results from the NIMROD 3-D MHD code. Plasma energy evolution has been studied by taking time-resolved measurements of Te(r) and ne(r) indicating a distinct and robust feature of spheromak formation; a hollow-to-peaked temperature transition with an inverse relationship to the electron density. This feature, as well as sub-microsecond transport, is being studied with the upgrade of the Thomson scattering diagnostic to double-pulse operation. We also present recent results of the impact of charge-exchange losses on overall power balance and estimates of the plasma ion temperature as measured with a neutral particle analyzer.

Hudson, B.

2007-11-01

265

Health effects of magnetic fields generated from power lines: new clues for an old puzzle  

International Nuclear Information System (INIS)

Thirty years ago, Nancy Wertheimer and Ed Leeper published the first report on the association between childhood cancer and electrical current configuration of houses in Denver, Colorado. In 2001 the International Agency for Research on Cancer defined 50-60 Hz magnetic fields as possibly carcinogenic to humans because of the limited evidence of carcinogenicity of residential exposure relatively to childhood leukemia. With respect to health effects other than cancer, namely neuro degenerative disorders, miscarriage, subtle differences in the timing of melatonin release, altered autonomic control of the heart, and changes in the number of natural killer cells, some open questions still remain. Several authors recommended further investigation of the possible long-term effects of magnetic fields, focussing on populations experiencing high exposure levels. In this frame a research team of ISS searched for a suitable location to implement an epidemiological study aimed at a wide range of outcomes for which a priori hypotheses could be formulated. The recently published findings of this project showed an increase of primary and secondary malignant neoplasms, ischaemic disease and haematological diseases. Future studies should thus address the most exposed sectors of the population, take into account different outcomes (all neoplasms, neuro degenerative diseases, immunological disorders, specific cardiovascular effects) and follow research protocols that enable subsequent posearch protocols that enable subsequent pooled analyses. A precautionary approach may provide the frame for decision making where the available resources for environmental remediation be prioritatively allocated to worst-off situations.

266

Study of self-generated magnetic fields in laser produced plasmas using a three-channel polaro-interferometer.  

Science.gov (United States)

Self-generated magnetic fields produced in laser plasmas at moderate laser intensities have been measured using a three-channel polaro-interferometer. The main elements of this device are two birefringent calcite wedges placed between two crossed polarizers. Using this device, the spatial profiles of (a) the rotation angle (polarometry), (b) the electron density (interferometry), and (c) the transmitted probe beam intensity (shadowgraphy) are recorded simultaneously using a digital camera with a large format CCD in a single laser shot. Magnetic fields of 2-4 MG had been estimated in aluminum plasma at laser intensities ~10(13) W/cm(2). It is also possible to use this device in other configurations to get time resolved information. PMID:22225217

Prasad, Y B S R; Barnwal, S; Bolkhovitinov, E A; Naik, P A; Kamath, M P; Joshi, A S; Kumbhare, S R; Rupasov, A A; Gupta, P D

2011-12-01

267

Study of self-generated magnetic fields in laser produced plasmas using a three-channel polaro-interferometer  

Energy Technology Data Exchange (ETDEWEB)

Self-generated magnetic fields produced in laser plasmas at moderate laser intensities have been measured using a three-channel polaro-interferometer. The main elements of this device are two birefringent calcite wedges placed between two crossed polarizers. Using this device, the spatial profiles of (a) the rotation angle (polarometry), (b) the electron density (interferometry), and (c) the transmitted probe beam intensity (shadowgraphy) are recorded simultaneously using a digital camera with a large format CCD in a single laser shot. Magnetic fields of 2-4 MG had been estimated in aluminum plasma at laser intensities {approx}10{sup 13} W/cm{sup 2}. It is also possible to use this device in other configurations to get time resolved information.

Prasad, Y. B. S. R.; Barnwal, S.; Naik, P. A.; Kamath, M. P.; Joshi, A. S.; Kumbhare, S. R.; Gupta, P. D. [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Bolkhovitinov, E. A.; Rupasov, A. A. [Laboratory of Plasma Diagnostics, P.N. Lebedev Physical Institute, 53 Leninsky Prospekt, Moscow 117924 (Russian Federation)

2011-12-15

268

Study of self-generated magnetic fields in laser produced plasmas using a three-channel polaro-interferometer  

International Nuclear Information System (INIS)

Self-generated magnetic fields produced in laser plasmas at moderate laser intensities have been measured using a three-channel polaro-interferometer. The main elements of this device are two birefringent calcite wedges placed between two crossed polarizers. Using this device, the spatial profiles of (a) the rotation angle (polarometry), (b) the electron density (interferometry), and (c) the transmitted probe beam intensity (shadowgraphy) are recorded simultaneously using a digital camera with a large format CCD in a single laser shot. Magnetic fields of 2-4 MG had been estimated in aluminum plasma at laser intensities ?1013 W/cm2. It is also possible to use this device in other configurations to get time resolved information.

269

Magnetic Fields in Galaxies  

Science.gov (United States)

The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field ? -? dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos around edge-on galaxies out to large distances from the plane, with X-shaped patterns. In the outflow cone above a starburst region of NGC 253, RM data indicate a helical magnetic field.

Beck, Rainer

270

Resonant magnetic fields from inflation  

CERN Document Server

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of ${\\cal O}(10^{-15}\\, \\Gauss)$ today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.

Byrnes, Christian T; Jain, Rajeev Kumar; Urban, Federico R

2012-01-01

271

Wide-angle optics with strong magnetic fields for efficient generation of secondary-particle beams  

International Nuclear Information System (INIS)

Optimization of the conditions for producing beams of secondary particles (positrons, antiproton, ?-mesons) has led to the development of projects at the Institute of Nuclear Physics of the Siberian Branch of the USSR Academy of Sciences aimed at creating optical devices with strong (50 to 300 kOE) pulsed magnetic fields and with a wide range of parameters determined by the type of secondary particles, their energy and the requirements for the beam characteristics. This theme encompasses two areas: the development of so-called parabolic lenses consisting of thin-walled shells of revolution about which current flows and which, by assigning the appropriate shape, facilitate aberration-free focusing of the particles for practically any collection angles, and of cylindrical lenses made of light metal (lithium, sodium) with cross-sectionally uniform current-density distribution for short focusing of beams

272

Magnetic field line Hamiltonian  

Energy Technology Data Exchange (ETDEWEB)

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

Boozer, A.H.

1985-02-01

273

Neutron Emission Generated in the Collision of Plasma Flows in the Presence of an External Magnetic Field  

International Nuclear Information System (INIS)

Results are presented from experimental studies of the neutron emission generated in the collision of deuterium plasma flows produced in discharges in crossed E x H fields and propagating in opposite directions in a neutral gas across an external magnetic field. It is shown that the interaction of oppositely propagating deuterium plasma flows gives rise to the generation of soft X-ray emission and neutron emission from the dd reaction (dd ? 3He + n) and is accompanied by an almost complete depolarization of the flows and rapid variations in the magnetic field (at a rate of ?1011 G/s). The measurements were performed at energies and velocities of the flows of up to 600 J and 3.5 x 107 cm/s, respectively. The plasma density in each flow was ?1015 cm-3. The upper estimates for the astrophysical S factor and the effective cross sections of the dd reaction obtained from our measurements are compared to theoretical calculations and to the results of experiments performed in the MIG high-current accelerator (Institute of High-Current Electronics, Russian Academy of Sciences, Tomsk)

274

Study of the U-25B MHD generator system in strong electric and magnetic fields  

International Nuclear Information System (INIS)

The third and fourth tests of the U-25B facility have demonstrated that the MHD flow train has operated for over 50 h with little difficulty. Review of the data reveals no significant problems associated with vibration, stress, or fluctuation of the electrical and gasdynamic parameters of the system components. In Test 3, the MHD generator produced a maximum power of 575 kW, a maximum Hall voltage of 4240 V, and a maximum Hall field of 2100 V/m. Inverter loading characteristics indicated that the upstream portion of the channel operated at low conductivity compared to the two downstream sections. During Test 4, at a lower mass flow rate but with cesium seed and oxygen enrichment to 60%, a power level of about 400 kW was generated. Because of inadvertent water and air leakage into the combustion chamber, however, combustion temperatures were lower in Test 4 that anticipated. These factors had a detrimental effect on the generator performance. Analysis of the data obtained from Tests 3 and Test 4 illustrates that in order to increase the power of the U-25B channel, a number of steps should be taken to increase the effective plasma conductivity and channel mass flow. For example, increasing the mass flow rate to 5 kg/s and achieving a K/sub sigma/ of 0.7 to 0.8, a channel inlet temperature about 2950 K may produce an electrical power output up to 1.3 MW. Steps are being taken to increase the preheat temperature in the facility, as well as to eliminate all water and air leakage into the combustor and decrease other thermal losses in the combustor nozzle and generator

275

Influence of the magnetic field on the velocity of the ion component of the particle beam generated during a nanosecond vacuum dielectric flashover  

Science.gov (United States)

Results of experimental investigations into the influence of the direction of magnetic field of 0.06 T on the velocity of ion component of particle flux generated during anode surface flashover of dielectrics in vacuum with voltage pulses of 230 kV are presented. It is demonstrated that the magnetic field applied in the plane of the sample surface decelerates the ion particle beam generated by the discharge. If the [ E × B] vector is collinear with the external normal to the sample surface, the beam is decelerated less than in the case of the opposite orientation of the magnetic field.

Gilev, A. S.; Morozov, P. A.; Emlin, R. V.; Punanov, I. F.; Cholakh, S. O.

2012-11-01

276

Energy transfer from a homopolar generator to a single turn coil toroidal field magnet  

International Nuclear Information System (INIS)

The designs of busbars and switches to efficiently transfer energy to the IGNITEX (Texas Fusion Ignition Experiment), single-turn tokamak and to the IGNITEX Technology Demonstrator (ITD) are presented. The IGNITEX machine should produce and control an ignited plasma with ohmic heating alone. A proposed homopolar generator (HPG) power supply formed by 12, 1-GJ HPGs will power the toroidal field (TF) of the full-scale IGNITEX device. The objective of the ITD is to test the design, fabrication procedures, and operation of a single turn, 20 T, TF coil. The ITD will be driven by an existing 60 MJ, 9 MA power supply consisting of six, 10-MJ HPGs located at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Busbsar design considerations include physical integration, thermal and electromechanical stresses, material properties in liquid nitrogen, effects on circuit response, and resistive and inductive energy dissipation

277

Semi-analytical study of AC losses in an infinitely long superconducting cylinder surrounded by a metallic sheath: magnetic field dependent critical current density and generation of harmonics  

International Nuclear Information System (INIS)

We study the AC losses in an infinitely long cylinder made of a superconducting core surrounded by a non-magnetic metallic sheath and subjected to an axial magnetic field. The losses are computed by assuming the Bean–Kim model for the superconductor and Ohmic dissipation for the metal. The time varying magnetic flux crossing the superconductor induces eddy currents in the metal sheath and, due to the nonlinear response of the superconducting material, generates harmonics in the metal current density. In turn, these currents generate distorted magnetic fields acting back on the superconductor. This coupling mechanism is sensitive to the magnetic constitutive law of the superconductor and affects both the waveform of the fields and the total losses. In this paper, we study the importance of the harmonics in the metal on the total losses, as well as their sensitivity to a field dependent critical current density following Kim’s law. (paper)

278

Biexciton in magnetic fields  

International Nuclear Information System (INIS)

The binding energy and structure of biexcitons in strong magnetic field is investigated using the stochastic variational method. The magnetic field confines the electrons and positrons in a small volume leading to Wigner-crystal like states of particles. (author)

279

Global coupling at 660 km is proposed to explain plate tectonics and the generation of the earth's magnetic field  

CERN Document Server

The presence of low viscosity layers in the mantle is supported by line of geological and geophysical observations. Recent high pressure and temperature investigations indicated that partial carbonate melt should exist at the bottom of the lithosphere and at 660 km. The presence of few percent carbonate melt reduces the viscosity by several order of magnitude. The globally existing 660 km very low viscosity layer allows the development of differential rotation between the upper and lower mantle. This differential rotation between the 660 km outer shell and the rest of the earth offers a plausible explanation for plate tectonics and for the generation of the earth's magnetic field. Simple dynamo model is proposed, which able to reproduce all of the features of the contemporary and, within reasonable uncertainty, the paleomagnetic field. The model is also consistent with geological and geophysical observations.

Garai, Jozsef

2007-01-01

280

Miniature linear permanent magnet generators  

International Nuclear Information System (INIS)

This paper discusses the advantages of linear permanent magnet generators for many applications which require the provision of relatively low levels of electrical power. The utility of linear generators, and a number of salient features of their design synthesis are illustrated by means of two design studies. In both cases, the design studies encompass the development of field calculation techniques for the accurate prediction of the complex field distributions within the devices, the design optimisation of the devices including considerations such as bearings and power conditioning electronics, and the construction and experimental characterisation of prototype devices. (orig.)

 
 
 
 
281

Miniature linear permanent magnet generators  

Energy Technology Data Exchange (ETDEWEB)

This paper discusses the advantages of linear permanent magnet generators for many applications which require the provision of relatively low levels of electrical power. The utility of linear generators, and a number of salient features of their design synthesis are illustrated by means of two design studies. In both cases, the design studies encompass the development of field calculation techniques for the accurate prediction of the complex field distributions within the devices, the design optimisation of the devices including considerations such as bearings and power conditioning electronics, and the construction and experimental characterisation of prototype devices. (orig.)

Wang, J.; Wang, W.; Jewell, G.W.; Howe, D. [Sheffield Univ. (United Kingdom). Dept. of Electronic and Electrical Engineering

1998-07-01

282

An enhanced firing generator design for the TFTR magnetic field coil power supplies  

International Nuclear Information System (INIS)

This paper presents an enhanced firing generator designed for TFTR. The existing firing generators, which control the rectifiers powering the TFTR coil system, will undergo a major overhaul to be upgraded to the new enhanced firing generator design. The new design makes maximum use of digital processing to improve the firing generator accuracy, maintainability and reliability. Additional functional enhancements have been included

283

Applications of the computer codes FLUX2D and PHI3D for the electromagnetic analysis of compressed magnetic field generators and power flow channels  

International Nuclear Information System (INIS)

The authors present the results of three electromagnetic field problems for compressed magnetic field generators and their associated power flow channels. The first problem is the computation of the transient magnetic field in a two-dimensional model of a helical generator during loading. The second problem is the three-dimensional eddy current patterns in a section of an armature beneath a bifurcation point of a helical winding. The authors' third problem is the calculation of the three-dimensional electrostatic fields in a region known as the post-hole convolute in which a rod connects the inner and outer walls of a system of three concentric cylinders through a hole in the middle cylinder. While analytic solutions exist for many electromagnetic filed problems in cases of special and ideal geometries, the solution of these and similar problems for the proper analysis and design of compressed magnetic field generators and their related hardware require computer simulations

284

Electricity and Magnetic Fields  

Science.gov (United States)

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magnetic field off. Through the accompanying activity students explore the nature of an electrically induced magnetic field and its applicability to the needed magnet.

Vu Bioengineering Ret Program

285

Drawing Magnetic Fields  

Science.gov (United States)

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

2014-09-18

286

Magnetic properties of Sm-doped Bi-2223 superconductor studied by low field local Hall generator ac susceptibility  

Energy Technology Data Exchange (ETDEWEB)

We studied the grain boundary properties of Sm doped Bi(Pb)SrCaCuO using the Hall generator ac susceptibility ({chi} = {chi}' + i{chi}''). Hall generator is a convenient tool to investigate the shielding effect of superconductors under extremely low magnetic fields. Using a Hall generator system, we have investigated diamagnetic shielding behavior of Bi{sub 1.6}Pb{sub 0.4}Sr{sub 2}Ca{sub 2-x}Sm{sub x}Cu{sub 3}O{sub y} samples with x = 0.0, 0.0005, 0.001, 0.005, 0.01 and 0.1. The susceptibility measurements were carried out for ac field amplitudes of 47, 94, 141, 188 and 235 A/m with the frequency of 20 Hz. The critical temperatures were estimated from the temperature dependence of the ac susceptibility curves. We have also employed X-ray diffraction, energy dispersive X-ray fluorescent and scanning electron microscopy techniques to investigate the effect of Sm doping.

Yegen, D. [Faculty of Arts and Sciences, Department of Physics, Abant Izzet Baysal University, 14280 Bolu (Turkey)], E-mail: yegen_d@ibu.edu.tr; Varilci, A. [Faculty of Arts and Sciences, Department of Physics, Abant Izzet Baysal University, 14280 Bolu (Turkey); Yilmazlar, M. [Faculty of Education, Sakarya University, 54300 Hendek, Sakarya (Turkey); Terzioglu, C.; Belenli, I. [Faculty of Arts and Sciences, Department of Physics, Abant Izzet Baysal University, 14280 Bolu (Turkey)

2007-11-01

287

Circuits and Magnetic Fields  

Science.gov (United States)

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

Vu Bioengineering Ret Program

288

Improved foilless Ku-band transit-time oscillator for generating gigawatt level microwave with low guiding magnetic field  

International Nuclear Information System (INIS)

An improved foilless Ku-band transit-time oscillator with low guiding magnetic field is proposed and investigated in this paper. With a non-uniform buncher and a coaxial TM02 mode dual-resonant reflector, this improved device can output gigawatt level Ku-band microwave with relatively compact radial dimensions. Besides the above virtue, this novel reflector also has the merits of high TEM reflectance, being more suitable for pre-modulating the electron beam and enhancing the conversion efficiency. Moreover, in order to further increase the conversion efficiency and lower the power saturation time, a depth-tunable coaxial collector and a resonant cavity located before the extractor are employed in our device. Main structure parameters of the device are optimized by particle in cell simulations. The typical simulation result is that, with a 380?kV, 8.2?kA beam guided by a magnetic field of about 0.6?T, 1.15?GW microwave pulse at 14.25?GHz is generated, yielding a conversion efficiency of about 37%

289

Improved foilless Ku-band transit-time oscillator for generating gigawatt level microwave with low guiding magnetic field  

Energy Technology Data Exchange (ETDEWEB)

An improved foilless Ku-band transit-time oscillator with low guiding magnetic field is proposed and investigated in this paper. With a non-uniform buncher and a coaxial TM{sub 02} mode dual-resonant reflector, this improved device can output gigawatt level Ku-band microwave with relatively compact radial dimensions. Besides the above virtue, this novel reflector also has the merits of high TEM reflectance, being more suitable for pre-modulating the electron beam and enhancing the conversion efficiency. Moreover, in order to further increase the conversion efficiency and lower the power saturation time, a depth-tunable coaxial collector and a resonant cavity located before the extractor are employed in our device. Main structure parameters of the device are optimized by particle in cell simulations. The typical simulation result is that, with a 380?kV, 8.2?kA beam guided by a magnetic field of about 0.6?T, 1.15?GW microwave pulse at 14.25?GHz is generated, yielding a conversion efficiency of about 37%.

Ling, Junpu; He, Juntao, E-mail: hejuntao12@163.com; Zhang, Jiande; Jiang, Tao; Hu, Yi [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-09-15

290

A «tidal» magnetic field?  

Directory of Open Access Journals (Sweden)

Full Text Available t is shown that on the magnetization axis of a uniformly magnetized body of constant density the magnetic field intensity displays a «tidal» structure,i.e. the ratios among the differential magnetic field intensity in three orthogonal directions are the same as the ratios among the gravitational gradient tensor components pertaining to the same directions; it is also seen that the same characteristic ratios occur, both locally and non-locally, among the components of the magnetic field intensity and among the components of the gradient tensors of the two fields.

F. Bocchio

1997-06-01

291

Simulation of Electric Quadrupole and Magnetic Dipole Transition Efficiencies in Optical Near Fields Generated by a Subwavelength Slit Array  

Science.gov (United States)

We calculate optical near fields generated by a periodically structured 50-nm-wide slit array of a 50-nm-thick gold film with a finite difference time domain method. Efficiencies of the electric quadrupole (E2) and magnetic dipole (M1) transitions, which are associated with the space derivative of the excitation light field, are evaluated for the calculated optical fields. The E2 transition efficiency is largely enhanced in the case where the polarization of the incident light is perpendicular to the slit direction, while such an enhancement is not expected for the M1 transition for this polarization. The large enhancement of the E2 transition efficiency originates not only from the field enhancement but also from its localization near the slit edge. The slit period dependence of the enhancement of the E2 transition efficiency suggests the enhancement to be affected by surface plasmon resonance. In the case where the polarization of the incident light is parallel to the slit, a small enhancement is obtained for the E2 and M1 transitions, the value of which corresponds to (1/k0d)2, where k0 is the wave number of the homogenously propagating light in vacuum and d is the slit width.

Deguchi, Kazuhiro; Okuda, Michihiro; Iwamae, Atsushi; Nakamura, Hiroaki; Sawada, Keiji; Hasuo, Masahiro

2009-02-01

292

A technical note about Phidel: A new software for evaluating magnetic induction field generated by power lines  

International Nuclear Information System (INIS)

The Regional Environment Protection Agency of Friuli Venezia Giulia (ARPA FVG, Italy) has performed an analysis on existing software designed to calculate magnetic induction field generated by power lines. As far as the agency's requirements are concerned the tested programs display some difficulties in the immediate processing of electrical and geometrical data supplied by plant owners, and in certain cases turn out to be inadequate in representing complex configurations of power lines. Phidel, an innovative software, tackles and works out all the above-mentioned problems. Therefore, the obtained results, when compared with those of other programs, are the closest to experimental measurements. The output data can be employed both in the GIS and Excel environments, allowing the immediate overlaying of digital cartography and the determining of the 3 and 10 ?T bands, in compliance with the Italian Decree of the President of the Council of Ministers of 8 July 2003. (authors)

293

Electroweak Origin of Cosmological Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic fields may have been generated in the electroweak phase transition through spontaneous symmetry breaking or through the subsequent dynamical evolution of semiclassical field configurations. Here I demonstrate explicitly how magnetic fields emerge spontaneously in the phase transition also when no gradients of the Higgs field are present. Using a simple model, I show that no magnetic fields are generated, at least initially, from classical two-bubble collisions in a ...

Tornkvist, Ola

1997-01-01

294

Macro-scale matter wave generation in charged particle dynamics in a magnetic field, a consequence of quantum entanglement  

International Nuclear Information System (INIS)

Matter wave interference effects on the macro-scale predicted by the author in charged particle dynamics in a magnetic field [R.K. Varma, Phys. Rev. E 64, 036608 (2001)], and observed subsequently [R.K. Varma, A.M. Punithavelu, S.B. Banerjee, Phys. Rev. E 65, 026503 (2002); R.K. Varma, S.B. Banerjee, Phys. Scr. 75, 19 (2007)] have been shown here to be an interesting consequence of quantum entanglement between the parallel and perpendicular degrees of freedom of the particle. Treating the problem in the framework of the inelastic scattering theory, it is shown that these macro-scale matter waves are generated in the 'parallel' degree of freedom as a modulation of the plane wave state of the particle along the field concomitantly with the excitation of Landau levels in the perpendicular degree of freedom in an inelastic scattering episode. We highlight here the role of quantum entanglement leading to the generation of this macro-scale quantum entity which has been shown to exhibit observable consequences. This case also exemplifies a situation exhibiting quantum entanglement on the macro-scale. (author)

295

Macro-scale matter wave generation in charged particle dynamics in a magnetic field, a consequence of quantum entanglement  

Science.gov (United States)

Matter wave interference effects on the macro-scale predicted by the author in charged particle dynamics in a magnetic field [R.K. Varma, Phys. Rev. E 64, 036608 (2001)], and observed subsequently [R.K. Varma, A.M. Punithavelu, S.B. Banerjee, Phys. Rev. E 65, 026503 (2002); R.K. Varma, S.B. Banerjee, Phys. Scr. 75, 19 (2007)] have been shown here to be an interesting consequence of quantum entanglement between the parallel and perpendicular degrees of freedom of the particle. Treating the problem in the framework of the inelastic scattering theory, it is shown that these macro-scale matter waves are generated in the `parallel' degree of freedom as a modulation of the plane wave state of the particle along the field concomitantly with the excitation of Landau levels in the perpendicular degree of freedom in an inelastic scattering episode. We highlight here the role of quantum entanglement leading to the generation of this macro-scale quantum entity which has been shown to exhibit observable consequences. This case also exemplifies a situation exhibiting quantum entanglement on the macro-scale.

Varma, R. K.

2012-02-01

296

Cyclic Magnetic Field Reconnection  

Science.gov (United States)

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

Karlický, Marian

2009-02-01

297

Primordial Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The explanation of the observed galactic magnetic fields may require the existence of a primordial magnetic field. Such a field may arise during the early cosmological phase transitions, or because of other particle physics related phenomena in the very early universe reviewed here. The turbulent evolution of the initial, randomly fluctuating microscopic field to a large-scale macroscopic field can be described in terms of a shell model, which provides an approximation to th...

Giovannini, Massimo

1998-01-01

298

Entropy generation of nanofluid in presence of magnetic field using Lattice Boltzmann Method  

Science.gov (United States)

In this paper magnetohydrodynamic free convection flow of CuO-water nanofluid in a square enclosure with a rectangular heated body is investigated numerically using Lattice Boltzmann Method (LBM) scheme. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo-Kleinstreuer-Li) correlation. The influence of pertinent parameters such as Hartmann number, nanoparticle volume fraction and Rayleigh number on the flow, heat transfer and entropy generation have been examined. The results show that the heat transfer rate and Dimensionless entropy generation number increase with increase of the Rayleigh number and nanoparticle volume fraction but it decreases with increase of the Hartmann number.

Sheikholeslami, Mohsen; Ganji, Davood Domiri

2015-01-01

299

Numerical study and modeling of hydrodynamic instabilities in the context of inertial confinement fusion in the presence of self-generated magnetic fields  

International Nuclear Information System (INIS)

In the context of inertial confinement fusion we investigate effects of magnetic fields on the development in the linear regime of two hydrodynamic instabilities: Richtmyer-Meshkov instability using ideal magnetohydrodynamics and ablative Rayleigh-Taylor instability in both acceleration and deceleration stages. Direct numerical simulations with a linear perturbation code enable us to confirm the stabilizing effect of the component of the magnetic field along the perturbations wave vector. The amplitude doesn't grow linearly in time but experiences oscillations instead. The compressibility taken into account in the code does not affect predictions given by an already existing impulsive and incompressible model. As far as Rayleigh-Taylor instability is concerned we study the effects of self-generated magnetic fields that arise from the development of the instability itself. In the acceleration stage we perform two dimensional simulations in planar geometry. We show that magnetic fields of about 1 T can be generated and that the instability growth transits more rapidly into nonlinear growth with the enhancement of the development of the third harmonic. We also propose an adaptation of an existing model that aims at studying thermal conductivity anisotropy effects, to take into account the effects of the self-generated magnetic fields on the Rayleigh-Taylor instability growth rate. Finally, in the deceleration stage, we perform two dimensional simulations in cylindrical geometry that take into account self-generation of magnetic fields due to the instability development. It reveals magnetic fields of about several thousands of Teslas that are not strong enough though to affect the instability behavior. (author)

300

Primordial magnetic field limits from cosmological data  

International Nuclear Information System (INIS)

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

 
 
 
 
301

Shaped angular dependence of the spin transfer torque and microwave generation without magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The generation of oscillations in the microwave frequency range is one of the most important applications expected from spintronics devices exploiting the spin transfer phenomenon. We report transport and microwave power measurements on specially designed nanopillars for which a non-standard angular dependence of the spin transfer torque (wavy variation) is predicted by theoretical models. We observe a new kind of current-induced dynamics that is characterized by large angle...

Boulle, O.; Cros, V.; Grollier, J.; Pereira, L. G.; Deranlot, C.; Petroff, F.; Faini, G.; Barnas, J.; Fert, A.

2007-01-01

302

Effect Of The LEBT Solenoid Magnetic Field On The Beam Generation For Particle Tracking  

CERN Document Server

Linac4 is a 160 MeV H- linear accelerator which will replace the 50 MeV proton Linac2 for upgrade of the LHC injectors with higher intensity and eventually an increase of the LHC luminosity. Linac4 structure is a source, a 45 keV low energy beam transport line (LEBT) with two solenoids, a 3 MeV Radiofrequency Quadrupole (RFQ), a Medium Energy Beam Transport line (MEBT), a 50 Mev DTL, a 100 Mev CCDTL and PIMS up to 160 Mev. We use Travel v4.07 and PathManager code for simulation. Firstly, we need to a file as a source and defining the beginning point (last point in tracking back) of simulation. We recognise the starting point base on the solenoid magnetic property of LEBT.

Yarmohammadi Satri, M; CERN. Geneva. ATS Department

2013-01-01

303

Numerical simulation of Czochralski crystal growth under the influence of a traveling magnetic field generated by an internal heater-magnet module (HMM)  

Science.gov (United States)

We present numerical simulations of vapor pressure controlled (VCz) and liquid encapsulated Czochralski (LEC) crystal growth of GaAs under the influence of a traveling magnetic field (TMF) with melt diameters of approximately 6 in and melt heights of approximately 1.8 in. The TMF is generated by an internal heater-magnet module (HMM) inside the pressure chamber in the growth arrangement and has been developed within the project KRIST MAG˜, see http://www.kristmag.com. For the global simulation, i.e. for the computation in the entire pressure chamber, the software WIAS-HiTNIHS is used. We validate this software by comparing measured and simulated Lorentz forces. Furthermore, we discuss how to account for effects of non-axisymmetric parts of the growth configuration during the axisymmetric computations performed by WIAS-HiTNIHS. Results computed by stationary global simulations are used as input data for transient local simulations of the melt. For the local simulations, we use the code NAVIER to solve the Navier-Stokes equations with the Boussinesq approximation together with the energy equation in an axisymmetric setting. Numerical simulations of the melt in an LEC configuration with an HMM are presented, showing that the Lorentz force generated by a TMF induced from the HMM can damp the temperature oscillations in the Taylor cell below the crystal.

Klein, Olaf; Lechner, Christiane; Druet, Pierre-Étienne; Philip, Peter; Sprekels, Jürgen; Frank-Rotsch, Christiane; Kießling, Frank-M.; Miller, Wolfram; Rehse, Uwe; Rudolph, Peter

2008-04-01

304

Wakefield generation in magnetized plasmas  

International Nuclear Information System (INIS)

We consider wakefield generation in plasmas by electromagnetic pulses propagating perpendicular to a strong magnetic field, in the regime where the electron cyclotron frequency is equal to or larger than the plasma frequency. Particle-in-cell simulations reveal that for moderate magnetic field strengths previous results are reproduced, and the wakefield wave number spectrum has a clear peak at the inverse skin depth. However, when the cyclotron frequency is significantly larger than the plasma frequency, the wakefield spectrum becomes broadband, and simultaneously the loss rate of the driving pulse is much enhanced. A set of equations for the scalar and vector potentials reproducing these results are derived, using only the assumption of a weakly nonlinear interaction.

305

Cosmological Magnetic Fields from Primordial Helicity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Primordial magnetic fields may account for all or part of the fields observed in galaxies. We consider the evolution of the magnetic fields created by pseudoscalar effects in the early universe. Such processes can create force-free fields of maximal helicity; we show that for such a field magnetic energy inverse cascades to larger scales than it would have solely by flux freezing and cosmic expansion. For fields generated at the electroweak phase transition, we find that the...

Field, George B.; Carroll, Sean M.

1998-01-01

306

On Cosmic Magnetic Fields  

Science.gov (United States)

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

Florido, E.; Battaner, E.

2010-12-01

307

Design and Modelling of a Silicon Optical MEMS Switch Controlled by Magnetic Field Generated by a Plain Coil  

Science.gov (United States)

Optical switches can be made as a silicon cantilever with a magnetic layer. Such a structure is placed in a magnetic field of a planar coil. There is a torque deflecting the silicon beam with NiFe layer depending on a flux density of the magnetic field. The study shows an analysis of ferromagnetic layer parameters, beam's dimensions on optical switch characteristics. Different constructions of the beams were simulated for a range of values of magnetic field strength from 100 to 1000 A/m. An influence of the actuators parameters on characteristics was analysed. The loss of stiffness of the beam caused by specific constructions effected in displacements reaching 85 nm. Comsol Multiphysics 4.3b was used for the simulations.

Golebiowski, J.; Milcarz, Sz

2014-04-01

308

Transmission line magnetic fields  

International Nuclear Information System (INIS)

Recent controversy over 60 Hz magnetic fields has heightened public awareness of overhead transmission lines. As a result, there is increasing motivation to study the magnetic fields form transmission lines. The most cost effective means to conduct research into transmission line magnetic fields is with computer or reduced-scale line models. However, from the standpoint of public perception and acceptance, it is first necessary to demonstrate that the model being used correlates well with actual operating lines. This paper presents results that compare the calculated and measured magnetic field profiles of both an operating 230 kV line and a 4:1 reduced-scale test span. In both cases the phase currents and shield wire currents were measured simultaneously with the magnetic field measurements, and the profiles were studied to distances well beyond a typical edge of right-of-way

309

Stability of Magnetic Fluids in Magnetic Fields  

Directory of Open Access Journals (Sweden)

Full Text Available Stability of magnetic fluids in magnetic fields is one of the major factors determining the possibility of their practical use and resource of their exploitation. This paper examines the stability of magnetic fluids based on kerosene in constant and variable magnetic fields. It is shown that the synthesized magnetic fluids are stable during long-term exposure to magnetic fields and can be used as the working fluid in a number of magnetic fluid devices.

I.M. Arefyev

2014-07-01

310

Stability of Magnetic Fluids in Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Stability of magnetic fluids in magnetic fields is one of the major factors determining the possibility of their practical use and resource of their exploitation. This paper examines the stability of magnetic fluids based on kerosene in constant and variable magnetic fields. It is shown that the synthesized magnetic fluids are stable during long-term exposure to magnetic fields and can be used as the working fluid in a number of magnetic fluid devices.

 arefyev, I. M.;  arefyeva, T. A.

2014-01-01

311

Primordial magnetic fields from inflation?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The hot plasma above the electroweak scale contains (hyper) charged scalar particles which are coupled to Abelian gauge fields. Scalars may interact with gravity in a non-conformally invariant way and thus their fluctuations can be amplified during inflation. These fluctuations lead to creation of electric currents and produce inhomogeneous distribution of charge density, resulting in the generation of cosmological magnetic fields. We address the question whether these field...

Giovannini, Massimo; Shaposhnikov, Mikhail E.

2000-01-01

312

Cosmic solutions in the Einstein-Weinberg-Salam theory and the generation of large electric and magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

In the SU(2){sub L} x U(1){sub Y} standard electroweak theory coupled with the Einstein gravity, new topological configurations naturally emerge, if the spatial section of the universe is globally a three-sphere (S{sup 3}) with a small radius. The SU(2){sub L} gauge fields wrap the space nontrivially, producing homogeneous but anisotropic space. As the universe expands, large electric and magnetic fields are produced. The electromagnetic field configuration is characterized by the Hopf map.

Hosotani, Yutaka; Emoto, Hiroki; Kubota, Takahiro

2003-04-01

313

Cosmic Solutions in the Einstein-Weinberg-Salam Theory and the Generation of Large Electric and Magnetic Fields  

CERN Document Server

In the SU(2)_L x U(1)_Y standard electroweak theory coupled with the Einstein gravity, new topological configurations naturally emerge, if the spatial section of the universe is globally a three-sphere (S^3) with a small radius. The SU(2)_L gauge fields wrap the space nontrivially, producing homogeneous but anisotropic space. As the universe expands, large electric and magnetic fields are produced. The electromagnetic field configuration is characterized by the Hopf map.

Hosotani, Y; Kubota, T; Hosotani, Yutaka; Emoto, Hiroki; Kubota, Takahiro

2002-01-01

314

The Braginskii model of the Rayleigh-Taylor instability. I. Effects of self-generated magnetic fields and thermal conduction in two dimensions  

CERN Document Server

(abridged) There exists a substantial disagreement between computer simulation results and high-energy density laboratory experiments of the Rayleigh-Taylor instability Kuranz et al. (2010). We adopt the Braginskii formulation for transport in hot, dense plasma, implement and verify the additional physics modules, and conduct a computational study of a single-mode RTI in two dimensions with various combinations of the newly implemented modules. We find that magnetic fields reach levels on the order of 11 MG in the absence of thermal conduction. We observe denting of the RT spike tip and generation of additional higher order modes as a result of these fields. Contrary to interpretation presented in earlier work Nishiguchi (2002), the additional mode is not generated due to modified anisotropic heat transport effects but due to dynamical effect of self-generated magnetic fields. The main effects of thermal conduction are a reduction of the RT instability growth rate (by about 20% for conditions considered here)...

Modica, Frank; Zhiglo, Andrey

2013-01-01

315

Conservative numerical methods for a two-temperature resistive MHD model with self-generated magnetic field term  

Directory of Open Access Journals (Sweden)

Full Text Available We propose numerical methods on Cartesian meshes for solving the 2-D axisymmetric two-temperature resistivive magnetohydrodynamics equations with self-generated magnetic field and Braginskii’s [1] closures. These rely on a splitting of the complete system in several subsystems according to the nature of the underlying mathematical operator. The hyperbolic part is solved using conservative high-order dimensionally split Lagrange-remap schemes whereas semi-implicit diffusion operators have been developed for the thermal and resistive conduction equations. Source terms are treated explictly. Numerical results on the deceleration phase of an ICF implosion test problem are proposed, a benchmark which was initially proposed in [2]. Nous proposons dans cet article des méthodes numériques pour les équations de la magnétohydrodynamique résistive à deux températures avec champ magnétique auto-généré et relations de fermeture de Braginskii [1] en géométrie 2-D axisymétrique sur maillage cartésien. Celles-ci sont basées sur une décomposition du système complet selon la nature des opérateurs mathématiques sous-jacents. La partie hyperbolique est résolue par des schémas conservatifs Lagrange-projection d’ordre élevé en directions alternées tandis que des opérateurs de diffusion semi-implicites ont été développés pour les équations de conduction thermique et résistive. Les termes sources sont traités de manière explicite. Des résultats numériques sur un cas-test simulant la phase de décélération d’une implosion de capsule FCI sont proposés, ce benchmark ayant été initialement présenté dans [2].

Imbert-Gérard Lise-Marie

2011-11-01

316

The stochastic gravitational wave background from turbulence and magnetic fields generated by a first-order phase transition  

International Nuclear Information System (INIS)

We analytically derive the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition. In contrast to previous studies, we take into account the fact that turbulence and magnetic fields act as sources of gravitational waves for many Hubble times after the phase transition is completed. This modifies the gravitational wave spectrum at large scales. We also model the initial stirring phase preceding the Kolmogorov cascade, while earlier works assume that the Kolmogorov spectrum sets in instantaneously. The continuity in time of the source is relevant for a correct determination of the peak position of the gravitational wave spectrum. We discuss how the results depend on assumptions about the unequal-time correlation of the source and motivate a realistic choice for it. Our treatment gives a similar peak frequency as previous analyses but the amplitude of the signal is reduced due to the use of a more realistic power spectrum for the magneto-hydrodynamical turbulence. For a strongly first-order electroweak phase transition, the signal is observable with the space interferometer LISA

317

Low-inductive pulse current generators on the base of connection elements with a volume structure magnetic field  

International Nuclear Information System (INIS)

Problems for design of a low-inductive pulse current generator (PCG) in power supply systems of electrophysical devices are considered. The structure of a flat bus capacitive PCG of W=106 J power for the voltage U=50 kV with the inductance L=0.4 nH is analyzed. Its optimum geometry is determined. The structure of modulus, connecting assemblies, commutator and cable collector with volume structure magnetic field is developed. Inductance of a section in the regime of short circuit is 5 nH. Transverse dimension of the section is 100 mm. The section is designed for solenoid power supply with the current of 4 MA from a battery with W=106 J and U=10 kV. It is shown, that parameter ?=LW/U is the value, characterizing the inner structure of PCG. It is also shown, that in the PCG structure connection elements with stable inductance - current leads, the minimum inductance of which is limited, play a ignificant role

318

Magnetic fields in cosmology  

International Nuclear Information System (INIS)

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

319

Passive Magnetic Shielding in Gradient Fields  

CERN Document Server

The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied. It is found that for concentric cylindrical or spherical shells of high permeability material, higher order multipoles in the magnetic field are shielded progressively better, by a factor related to the order of the multipole. In regard to the design of internal coil systems for the generation of uniform internal fields, we show how one can take advantage of the coupling of the coils to the innermost magnetic shield to further optimize the uniformity of the field. These results demonstrate quantitatively a phenomenon that was previously well-known qualitatively: that the resultant magnetic field within a passively magnetically shielded region can be much more uniform than the applied magnetic field itself. Furthermore we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields clos...

Bidinosti, C P

2013-01-01

320

Detecting Exoplanetary Magnetic Fields  

Science.gov (United States)

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

Llama, Joe

2015-01-01

 
 
 
 
321

Mapping Magnetic Field Lines  

Science.gov (United States)

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

2012-08-03

322

Linear electric field frequency shift (important for next generation electric dipole moment searches) induced in confined gases by a magnetic field gradient  

CERN Document Server

The search for particle electric dipole moments (edm) represents a most promising way to search for physics beyond the standard model. A number of groups are planning a new generation of experiments using stored gases of various kinds. In order to achieve the target sensitivities it will be necessary to deal with the systematic error resulting from the interaction of the well-known $\\overrightarrow{v}\\times \\overrightarrow{E}$ field with magnetic field gradients (often referred to as the geometric phase effect (Commins, ED; Am. J. Phys. \\QTR{bf}{59}, 1077 (1991), Pendlebury, JM \\QTR{em}{et al;} Phys. Rev. \\QTR{bf}{A70}, 032102 (2004)). This interaction produces a frequency shift linear in the electric field, mimicking an edm. In this work we introduce an analytic form for the velocity auto-correlation function which determines the velocity-position correlation function which in turn determines the behavior of the frequency shift (Lamoreaux, SK and Golub, R; Phys. Rev \\QTR{bf}{A71}, 032104 (2005)) and show how...

Barabanov, A A L; Lamoreaux, S K; Barabanov, Authors A.L.

2006-01-01

323

Cluster Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic fields in galaxy clusters have been measured using a variety of techniques, including: studies of synchrotron relic and halo radio sources within clusters, studies of inverse Compton X-ray emission from clusters, surveys of Faraday rotation measures of polarized radio sources both within and behind clusters, and studies of Cluster Cold Fronts in X-ray images. These measurements imply that most cluster atmospheres are substantially magnetized, with typical field stre...

Carilli, C. L.; Taylor, G. B.

2001-01-01

324

FIREX Project and Effects of Self-generated Electric and Magnetic Fields on Electron Driven Fast Ignition  

International Nuclear Information System (INIS)

The fast ignition is a new scheme in laser fusion, in which higher energy gain is expected with smaller laser pulse energy. The cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, the laser with 4 beams and the total output of 10kJ/ps: LFEX has been built and we have started the integrated experiments. The experiments showed that the coupling efficiency is degraded because of the laser pre-pulse. Namely, the main pulse is absorbed in a long scale pre-plasma produced by the pre-pulse and hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is long. So, we are exploring how to overcome the pre-pulse effects on the cone target. The next series of experiments is planned for this fall. In these experiments, the LFEX pre-pulse level will be reduced and advanced targets for mitigating the pre-pulse effects will be introduced.In this paper, it is proposed that a thin foil cover the laser entrance of a cone to mitigate the pre-plasma and a double cone reduce loss of high energy electrons from the side wall of the cone. The simulations indicate that higher coupling efficiency is expected for the double cone target with a thin foil on the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electro-magnetic fields generated on the surface of the inner cone will confine high energy electrons. The goal of the next series of experrons. The goal of the next series of experiments will be high coupling efficiency to heat a compressed plasma to temperatures higher than 2 keV.

325

Permanent magnet edge-field quadrupole  

International Nuclear Information System (INIS)

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

326

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

Science.gov (United States)

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

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

2010-06-01

327

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

International Nuclear Information System (INIS)

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 magnhreshold. We will present the trapped magnetic characteristics and the technique to generate the controlled pulsed field.

328

Eruptive solar magnetic fields  

International Nuclear Information System (INIS)

This paper considers the quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes. Special interest is taken in the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates has been treated previously, and we extend it to a field which is not force free but in static equilibrium with plasma pressure and gravity. The basic physics is illustrated by the evolution of a loop-shaped electric current sheet enclosing a potential bipolar field with footpoints rooted in the photosphere. A free-boundary problem is posed and solved for the equilibrium configuration of the current sheet in a hydrostatically supported isothermal atmosphere. As the footpoints move appart to spread a constant photospheric magnetic flux over a larger region, the equilibria available extend the field to increasingly great heights. Two basic behaviors are possible, depending on the ratio of the total magnetic flux to an equivalent flux constructed dimensionally from the pressure difference across the current sheet and the density scale height. For a small, total magnetic flux, nonequilibrium can set in with the appearance of a marginally stable equilibriu, as demonstrated previously for the frece-free fields. For a total magnetic flux exceeding a certain critical value, the field lines rise high enough for gravity to play a significant role. The sequence of equilibria in this case . The sequence of equilibria in this case suggests that nonequilibrium can set in with the opening of the field lines by magnetic buoyancy. This eruption can also take place with a prominence filament and may be the origin of the white light coronal transient

329

Observations of Cool-Star Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cool stars like the Sun harbor convection zones capable of producing substantial surface magnetic fields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magnetic fields are keys for our understanding of low-mass stellar dynamos, the solar dynamo, and also for other large-scale and pla...

Ansgar Reiners

2012-01-01

330

Distributed generation induction and permanent magnet generators  

CERN Document Server

Distributed power generation is a technology that could help to enable efficient, renewable energy production both in the developed and developing world. It includes all use of small electric power generators, whether located on the utility system, at the site of a utility customer, or at an isolated site not connected to the power grid. Induction generator (IG) is the most commonly used and cheapest technology, compatible with renewable energy resources. Permanent magnet (PM) generators have traditionally been avoided due to high fabrication costs; however, compared with IGs they are more rel

Lai, Loi Lei

2008-01-01

331

Generation of 24 T at 4.2 K using a layer-wound GdBCO insert coil with Nb3Sn and Nb–Ti external magnetic field coils  

International Nuclear Information System (INIS)

High-temperature superconducting (HTS) magnets are believed to be a practical option in the development of high field nuclear magnetic resonance (NMR) systems. The development of a 600 MHz NMR system that uses an HTS magnet and a probe with an HTS radio frequency coil is underway. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. The tolerance to high tensile stress is expected for HTS conductors in order to reduce the magnet in volume. A layer-wound Gd–Ba–Cu–O (GdBCO) insert coil was fabricated in order to investigate its properties under a high electromagnetic force in a high magnetic field. The GdBCO insert coil was successfully operated at a current of up to 321 A and an electromagnetic force BJR of 408 MPa in an external magnetic field generated by Nb3Sn and Nb–Ti low-temperature superconducting coils. The GdBCO insert coil also managed to generate a magnetic field of 6.8 T at the center of the coil in an external magnetic field of 17.2 T. The superconducting magnet consisting of GdBCO, Nb3Sn and Nb–Ti coils successfully generated a magnetic field of 24.0 T at 4.2 K, which represents a new record for a superconducting magnet. (paper)

332

Indoor localization using magnetic fields  

Science.gov (United States)

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

Pathapati Subbu, Kalyan Sasidhar

333

ISR Radial Field Magnet  

CERN Multimedia

There were 37 (normal) + 3 (special) Radial Field magnets in the ISR to adjust vertically the closed orbit. Gap heights and strengths were 200 mm and .12 Tm in the normal magnets, 220 mm and .18 Tm in the special ones. The core length was 430 mm in both types. Due to their small length as compared to the gap heights the end fringe field errors were very important and had to be compensated by suitably shaping the poles. In order to save on cables, as these magnets were located very far from their power supplies, the coils of the normal type magnets were formed by many turns of solid cpper conductor with some interleaved layers of hollow conductor directly cooled by circulating water

1983-01-01

334

The Sun and Magnetic Fields  

Science.gov (United States)

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

335

MIXED CONVECTION OVER AN ISOTHERMAL VERTICAL FLAT PLATE EMBEDDED IN A POROUS MEDIUM WITH MAGNETIC FIELD, RADIATION AND VARIABLE VISCOSITY WITH HEAT GENERATION  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper focuses on the numerical solutions of the effects of magnetic field, radiation, variable viscosity and heat generation on similarity solutions of mixed convection adjacent to an isothermal vertical plate which is embedded in a porous medium. A similarity transformation is used to reduce the partial differential equations governing the problem into ordinary differential equations and the equations are solved numerically subject to appropriate boundary conditions by the use of Runge-...

Rajarani, T.; Rao, C. N. B.

2012-01-01

336

Magnetotransport in inhomogeneous magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum transport in inhomogeneous magnetic fields is investigated numerically in two-dimensional systems using the equation of motion method. In particular, the diffusion of electrons in random magnetic fields in the presence of additional weak uniform magnetic fields is examined. It is found that the conductivity is strongly suppressed by the additional uniform magnetic field and saturates when the uniform magnetic field becomes on the order of the fluctuation of the rando...

Kawarabayashi, Tohru; Ohtsuki, Tomi

2004-01-01

337

Nuclear magnetic resonance and earth magnetic field  

International Nuclear Information System (INIS)

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 B0, then B is cut off and the nuclei move back to their equilibrium position by executing a precession movement due to B0 field. (A.C.)

338

Parametric study of a variable-magnetic-field-based energy-selection system for generating a spread-out Bragg peak with a laser-accelerated proton beam  

International Nuclear Information System (INIS)

Laser-based proton beam acceleration, which produces broad energy spectra, is unsuitable for direct clinical use. Thus, employing an energy selection system is necessary. The purpose of the present study was to investigate a method whereby a variable magnetic field could be employed with an energy selection system to generate a spread-out Bragg peak (SOBP). For energy selection, particle transport and dosimetric property measurements, the Geant4 toolkit was implemented. The energy spectrum of the laser-accelerated proton beam was acquired using a particle-in-cell simulation. The hole size and the position of the energy selection collimator were varied in order to determine the effects of those parameters on the dosimetric properties. To generate an SOBP, we changed the magnetic field in the energy selection system for each beam weighting factor during beam irradiation. The overall results of this study suggest that the use of an energy selection system with a variable magnetic field can effectively generate an SOBP suitable for proton radiation therapy applications.

339

Field-free line formation in a magnetic field  

International Nuclear Information System (INIS)

In this communication, the theory of field-free line (FFL) formation in a magnetic field is investigated. It is shown that an FFL can be generated by only three Maxwell coil pairs. By varying the applied currents, the FFL can be arbitrarily rotated, while keeping the coils static in space. For translation, additional Helmholtz coil pairs can be used. These findings enable efficient realization of a field generating unit for a recently developed imaging method named magnetic particle imaging. (fast track communication)

340

Field-free line formation in a magnetic field  

Energy Technology Data Exchange (ETDEWEB)

In this communication, the theory of field-free line (FFL) formation in a magnetic field is investigated. It is shown that an FFL can be generated by only three Maxwell coil pairs. By varying the applied currents, the FFL can be arbitrarily rotated, while keeping the coils static in space. For translation, additional Helmholtz coil pairs can be used. These findings enable efficient realization of a field generating unit for a recently developed imaging method named magnetic particle imaging. (fast track communication)

Knopp, T; Sattel, T F; Biederer, S; Buzug, T M [Institute of Medical Engineering, University of Luebeck, Luebeck (Germany)], E-mail: knopp@imt.uni-luebeck.de

2010-01-08

 
 
 
 
341

Research on the dq coordinate transform in the six-phase double star windings shifted by 30° synchronous generators with axial magnetic field  

Science.gov (United States)

As an intermediate frequency power source, the double star windings shifted by 30° synchronous generator with axial magnetic field (DSWAMF) is widely used in the different areas. Using the generalized inverse, the transformation matrix of double windings synchronous generators with two Y-connected 3-phase symmetrical windings displaced in turn by 30° from rotating to stationary axes is proposed. With the transformation matrix, the state-space model of the generators is established. Obtained the relation of interconnection, and optimize the parameter. The kind of machine is simulated by finite element method (FEM), mutual inductance of the simulation is similar to theory. The generator mathematical model is established, the internal parameter of this kind of generator can be obtained easily with transformation matrix.

Bian, Xiangnan; Ma, Qishuang

2006-11-01

342

High magnetic fields science and technology  

CERN Document Server

This three-volume book provides a comprehensive review of experiments in very strong magnetic fields that can only be generated with very special magnets. The first volume is entirely devoted to the technology of laboratory magnets: permanent, superconducting, high-power water-cooled and hybrid; pulsed magnets, both nondestructive and destructive (megagauss fields). Volumes 2 and 3 contain reviews of the different areas of research where strong magnetic fields are an essential research tool. These volumes deal primarily with solid-state physics; other research areas covered are biological syst

Miura, Noboru

2003-01-01

343

Sensor-less Field Oriented Control of Wind Turbine Driven Permanent Magnet Synchronous Generator Using Flux Linkage and Back EMF Estimation Methods  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The study aims at the speed control of the wind turbine driven Permanent Magnet Synchronous Generator (PMSG) by sensor-less Field Oriented Control (FOC) method. Two methods of sensor-less FOC are proposed to control the speed and torque of the PMSG. The PMSG and the full-scale converter have an increasing market share in variable speed Wind Energy Conversion System (WECS). When compared to the Induction Generators (IGs), the PMSGs are smaller, easier to control and more efficient. In addition...

Porselvi Thayumanavan; Ranganath Muthu; Jeyasudha Sankararaman

2014-01-01

344

High field superconducting magnets  

Science.gov (United States)

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

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

2011-01-01

345

High heat generation ability in AC magnetic field for nano-sized magnetic Y{sub 3}Fe{sub 5}O{sub 12} powder prepared by bead milling  

Energy Technology Data Exchange (ETDEWEB)

Nano-sized magnetic Y{sub 3}Fe{sub 5}O{sub 12} ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 {mu}m in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y{sub 3}Fe{sub 5}O{sub 12} ferrites. The highest heat ability in the AC magnetic field was for the fine Y{sub 3}Fe{sub 5}O{sub 12} powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm{phi} beads). The heat generation ability of the excessively milled Y{sub 3}Fe{sub 5}O{sub 12} samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Neel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm{phi} beads, the heat generation ability (W g{sup -1}) was estimated using a 3.58 Multiplication-Sign 10{sup -4} fH{sup 2} frequency (f/kHz) and the magnetic field (H/kA m{sup -1}), which is the highest reported value of superparamagnetic materials. - Highlights: Black-Right-Pointing-Pointer The nano-sized Y{sub 3}Fe{sub 5}O{sub 12} powder prepared by bead-milling has the highest heat generation ability in an AC magnetic field. Black-Right-Pointing-Pointer The heat generation properties are ascribed to an increase in the Neel relaxation of the superparamagnetic material. Black-Right-Pointing-Pointer The heat ability (W g{sup -1}) can be estimated using 3.58 Multiplication-Sign 10{sup -4} fH{sup 2} (f=kHz, H=kA m{sup -1}). Black-Right-Pointing-Pointer This is an expectable material for use in a drug delivery system for the thermal coagulation therapy of cancer tumors.

Aono, Hiromichi, E-mail: aono.hiromichi.mf@ehime-u.ac.jp [Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577 (Japan); Ebara, Hiroki; Senba, Ryota; Naohara, Takashi; Maehara, Tsunehiro [Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577 (Japan); Hirazawa, Hideyuki [Department of Environmental Materials Engineering, Niihama National College of Technology, Niihama 792-8580 (Japan); Watanabe, Yuji [Department of Surgery, Graduate School of Medicine, Ehime University, Toon 791-0295 (Japan)

2012-06-15

346

Occupational exposure assessment of magnetic fields generated by induction heating equipment-the role of spatial averaging.  

Science.gov (United States)

Induction heating equipment is a source of strong and nonhomogeneous magnetic fields, which can exceed occupational reference levels. We investigated a case of an induction tempering tunnel furnace. Measurements of the emitted magnetic flux density (B) were performed during its operation and used to validate a numerical model of the furnace. This model was used to compute the values of B and the induced in situ electric field (E) for 15 different body positions relative to the source. For each body position, the computed B values were used to determine their maximum and average values, using six spatial averaging schemes (9-285 averaging points) and two averaging algorithms (arithmetic mean and quadratic mean). Maximum and average B values were compared to the ICNIRP reference level, and E values to the ICNIRP basic restriction. Our results show that in nonhomogeneous fields, the maximum B is an overly conservative predictor of overexposure, as it yields many false positives. The average B yielded fewer false positives, but as the number of averaging points increased, false negatives emerged. The most reliable averaging schemes were obtained for averaging over the torso with quadratic averaging, with no false negatives even for the maximum number of averaging points investigated. PMID:22964714

Kos, Bor; Vali?, Blaž; Kotnik, Tadej; Gajšek, Peter

2012-10-01

347

Occupational exposure assessment of magnetic fields generated by induction heating equipment—the role of spatial averaging  

Science.gov (United States)

Induction heating equipment is a source of strong and nonhomogeneous magnetic fields, which can exceed occupational reference levels. We investigated a case of an induction tempering tunnel furnace. Measurements of the emitted magnetic flux density (B) were performed during its operation and used to validate a numerical model of the furnace. This model was used to compute the values of B and the induced in situ electric field (E) for 15 different body positions relative to the source. For each body position, the computed B values were used to determine their maximum and average values, using six spatial averaging schemes (9-285 averaging points) and two averaging algorithms (arithmetic mean and quadratic mean). Maximum and average B values were compared to the ICNIRP reference level, and E values to the ICNIRP basic restriction. Our results show that in nonhomogeneous fields, the maximum B is an overly conservative predictor of overexposure, as it yields many false positives. The average B yielded fewer false positives, but as the number of averaging points increased, false negatives emerged. The most reliable averaging schemes were obtained for averaging over the torso with quadratic averaging, with no false negatives even for the maximum number of averaging points investigated.

Kos, Bor; Vali?, Blaž; Kotnik, Tadej; Gajšek, Peter

2012-10-01

348

Occupational exposure assessment of magnetic fields generated by induction heating equipment—the role of spatial averaging  

International Nuclear Information System (INIS)

Induction heating equipment is a source of strong and nonhomogeneous magnetic fields, which can exceed occupational reference levels. We investigated a case of an induction tempering tunnel furnace. Measurements of the emitted magnetic flux density (B) were performed during its operation and used to validate a numerical model of the furnace. This model was used to compute the values of B and the induced in situ electric field (E) for 15 different body positions relative to the source. For each body position, the computed B values were used to determine their maximum and average values, using six spatial averaging schemes (9–285 averaging points) and two averaging algorithms (arithmetic mean and quadratic mean). Maximum and average B values were compared to the ICNIRP reference level, and E values to the ICNIRP basic restriction. Our results show that in nonhomogeneous fields, the maximum B is an overly conservative predictor of overexposure, as it yields many false positives. The average B yielded fewer false positives, but as the number of averaging points increased, false negatives emerged. The most reliable averaging schemes were obtained for averaging over the torso with quadratic averaging, with no false negatives even for the maximum number of averaging points investigated. (paper)

349

Fields from a relativistic magnetic explosion  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Following Prendergast we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that...

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

2008-01-01

350

Galactic and Extragalactic Magnetic Fields  

CERN Document Server

The strength of the total magnetic field in our Milky Way from radio Zeeman and synchrotron measurements is about 6 muG near the Sun and several mG in dense clouds, pulsar wind nebulae, and filaments near the Galactic Center. Diffuse polarized radio emission and Faraday rotation of the polarized emission from pulsars and background sources show many small-scale magnetic features, but the overall field structure in our Galaxy is still under debate. -- Radio synchrotron observations of nearby galaxies reveal dynamically important magnetic fields of 10-30 muG total strength in the spiral arms. Fields with random orientations are concentrated in spiral arms, while ordered fields (observed in radio polarization) are strongest in interarm regions and follow the orientation of the adjacent gas spiral arms. Faraday rotation of the diffuse polarized radio emission from the disks of spiral galaxies sometimes reveals large-scale patterns which are signatures of coherent fields generated by dynamos, but in most galaxies ...

Beck, Rainer

2008-01-01

351

Electrostatic wave heating and possible formation of self-generated high electric fields in a magnetized plasma  

Science.gov (United States)

A plasma reactor operates at the Laboratori Nazionali del Sud of INFN, Catania, and it has been used as a test-bench for the investigation of innovative mechanisms of plasma ignition based on electrostatic waves (ES-W), obtained via the inner plasma EM-to-ES wave conversion. Evidences of Bernstein wave (BW) generation will be shown. The Langmuir probe measurements have revealed a strong increase of the ion saturation current, where the BW are generated or absorbed, this being a signature of possible high energy ion flows. The results are interpreted through the Bernstein wave heating theory, which predicts the formation of high speed rotating layers of the plasma (a dense plasma ring is in fact observed). High intensity inner plasma self-generated electric fields (on the order of several tens of kV/cm) come out by our calculations.

Mascali, D.; Celona, L.; Gammino, S.; Miracoli, R.; Castro, G.; Gambino, N.; Ciavola, G.

2011-10-01

352

Magnetic fields in diffuse media  

CERN Document Server

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.

Pino, Elisabete; Melioli, Claudio

2015-01-01

353

Magnetic field dependent atomic tunneling in non-magnetic glasses  

International Nuclear Information System (INIS)

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

354

Magnetic Fields in the Solar Convection Zone  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Yuhong Fan

2009-01-01

355

Measurement of electric and magnetic fields  

International Nuclear Information System (INIS)

A project was initiated to study power frequency electric and magnetic fields that exist in Canada. The main objective of the study was to produce a compendium of electric and magnetic field levels that exist in Canada, and to characterize and classify the sources of electric and magnetic fields. Typical electric and magnetic field levels were measured around generating plants, substations, transmission lines, distribution lines, residences and workplaces. Protocols were developed so that a consistent set of data could be collected, and so that sufficient detail could be captured for a thorough analysis. Generating plants were found to exhibit the widest range of magnetic field levels, from 0.02 to 250 microtesla, however had low electric field levels. Electric fields tend to be highest in substations, due to lower clearances of energized bus-work to the ground. Transmission lines had higher magnetic fields than substations and distribution lines. Characterization of distribution lines was difficult due to a wide range of configurations, however in general magnetic fields are lower than near transmission lines. A wide range of magnetic fields were found in residences, but tended to be lower than those found in workplaces. Appendices describe data collection protocols and database structure. Eight separate abstracts have been prepared for this report. 4 refs., 29 figs

356

Heat generation ability in AC magnetic field of nano MgFe2O4-based ferrite powder prepared by bead milling  

International Nuclear Information System (INIS)

Nanosized MgFe2O4-based ferrite powder having heat generation ability in an AC magnetic field was prepared by bead milling and studied for thermal coagulation therapy applications. The crystal size and the particle size significantly decreased by bead milling. The heat generation ability in an AC magnetic field improved with the milling time, i.e. a decrease in crystal size. However, the heat generation ability decreased for excessively milled samples with crystal sizes of less than 5.5 nm. The highest heat ability (?T=34 oC) in the AC magnetic field (370 kHz, 1.77 kA/m) was obtained for fine MgFe2O4 powder having a ca. 6 nm crystal size (the samples were milled for 6-8 h using 0.1 mm ? beads). The heat generation of the samples was closely related to hysteresis loss, a B-H magnetic property. The reason for the high heat generation properties of the samples milled for 6-8 h using 0.1 mm ? beads was ascribed to the increase in hysteresis loss by the formation of a single domain. Moreover, the improvement in heating ability was obtained by calcination of the bead-milled sample at low temperature. In this case, the maximum heat generation (?T=41 oC) ability was obtained for a ca. 11 nm crystal size sample was prepared by crystal growth during the sample calcination. On the other hand, the ?T value for Mg0.5Ca0.5Fe2O4 was synthesized using a reverse precipitasynthesized using a reverse precipitation method decreased by bead milling. - Research Highlights: ?The crystal and particle size for MgFe2O4 based ferrite were decreased by bead milling. ?The highest heat ability was obtained for MgFe2O4 having a ca. 6 nm crystal size. ?This high heat generation ability was ascribed to the increase in hysteresis loss. ?Hysteresis loss was increased by the formation of a single domain.

357

Helical magnetic fields via baryon asymmetry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

There is strong observational evidence for the presence of large-scale magnetic fields MF in galaxies and clusters, with strength $\\sim \\mu$G and coherence lenght on the order of Kpc. However its origin remains as an outstanding problem. One of the possible explanations is that they have been generated in the early universe. Recently, it has been proposed that helical primordial magnetic fields PMFs, could be generated during the EW or QCD phase transitions, parity-violating...

Piratova, Eduard F.; Reyes, Edilson A.; Hortu?a, He?ctor J.

2014-01-01

358

Crustal Magnetic Fields  

Science.gov (United States)

Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

Taylor, Patrick T.; Ravat, D.; Frawley, James J.

1999-01-01

359

Magnetic Fields of Neutron Stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Neutron stars contain the strongest magnetic fields known in the Universe. In this paper, I discuss briefly how these magnetic fields are inferred from observations, as well as the evidence for their time-evolution. I show how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes. I propose a scena...

Konar, Sushan; Bhattacharya, Dipankar

1999-01-01

360

Skewed magnetic field lines reconnection  

International Nuclear Information System (INIS)

Three-dimensional time-dependent reconnection of skewed magnetic field lines is studied. Reconnection is shown to be possible only in the limited oval-shaped part of the current sheet, which was called the reconnection zone. The size of the reconnection zone is defined by the reconnection line length, the behaviour of the electric field in the diffusion region as well as by the angle between the reconnecting fields. Reconnected magnetic flux has the same direction as it has in the Petschek's model near the reconnection line (normal flux), but it changes its sign in the rest of the reconnection zone (anomalous flux). The magnetic energy is converted into the kinetic one in the normal flux region, and the reverse process occurs in the anomalous flux region, so the energy balance is fulfilled within the reconnection region. An electric double layer emerges along the reconnection zone, which emits Alfven waves, these carryin away the energy released in the reconnection process. The solution obtained may be useful in various problems of cosmic plasma physics, e.g. MHD waves generation on the Sun, carrying magnetic flux away from its surface, origin of solar cosmic rays, etc

 
 
 
 
361

Observations of Cool-Star Magnetic Fields  

Directory of Open Access Journals (Sweden)

Full Text Available Cool stars like the Sun harbor convection zones capable of producing substantial surface magnetic fields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magnetic fields are keys for our understanding of low-mass stellar dynamos, the solar dynamo, and also for other large-scale and planetary dynamos. Our observational picture of cool-star magnetic fields has improved tremendously over the last years. Sophisticated methods were developed to search for the subtle effects of magnetism, which are difficult to detect particularly in cool stars. With an emphasis on the assumptions and capabilities of modern methods used to measure magnetism in cool stars, I review the different techniques available for magnetic field measurements. I collect the analyses on cool-star magnetic fields and try to compare results from different methods, and I review empirical evidence that led to our current picture of magnetic fields and their generation in cool stars and brown dwarfs.

Ansgar Reiners

2012-02-01

362

Matter in Strong Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The properties of matter are significantly modified by strong magnetic fields, $B>>2.35\\times 10^9$ Gauss ($1 G =10^{-4} Tesla$), as are typically found on the surfaces of neutron stars. In such strong magnetic fields, the Coulomb force on an electron acts as a small perturbation compared to the magnetic force. The strong field condition can also be mimicked in laboratory semiconductors. Because of the strong magnetic confinement of electrons perpendicular to the field, atom...

Lai, Dong

2000-01-01

363

Technique for calculation of three-dimensional magnetic fields in the saddle-shaped superconducting systems of mhd generators with account of frontal part effects  

International Nuclear Information System (INIS)

The calculation technique for determining the components of a three-dimensional magnetic field formed by a finite-length dipole magnetic system with an allowance for butt-end faces is described. The components of the magnetic field, induced by an ellipse arc, at an arbitraty point in space are determined from equations obtained on the basis of the Biot-Savart law. The algorithm of calculation of the relative values of the magnetic field components at an arbitrary point of the three-dimensional space, including the current region of the winding, is presented. An analysis of the calculation results shows that the inhomogeneity of the magnetic field in the linear part of the magnetic system does not exceed 7%. In the butt-end zones the magnetic field on the system axis reduces by 5 times. It should be noted that near the butt-end parts there are regions in which the direction of the magnetic field is opposite to that of the magnetic field in the working region of the system. The fringing fields of the dipole magnetic system at a distance less than 2R(R is the inner radius of the dipole magnetic system) may be compared with the field at the centre of the system and are 20-40% of the magnetic field strength at the system centre

364

Optimization of superconductivity properties in MgB2 Wires and tapes to generate high magnetic fields  

International Nuclear Information System (INIS)

We present, in this work, a study of the effects of doping, heat treatments and mechanisms of deformation, over the microstructure and superconducting properties of powder in tube (PIT) MgB2 wires and tapes.We observed that nano-SiC doping improves the critical current density (Jc) and the upper critical field (Hc2).The combined use of doping and Hot Isostatic Pressing (HIPing), produces samples with high density and improves Jc s.We studied the influence of number and temperature of intermediate heat treatments (TTI), during the fabrication of wires and tapes.We observed that TTI made at low temperature (oC), results in wires and tapes with better microstructure than those made at high temperature.Moreover, the increment of the heat treatments numbers at high temperature, decreases the quality of microstructure and Jc.In the study of sheaths materials, we observed that the Jc values measured by magnetization in Ti sheath samples are two order of magnitude larger than the values measured by transport, which indicates macroscopic fracture problems.On other hand, we fabricated tapes with excellent Jc values (104A/cm2 at 4K and 7T), which are similar to those of samples made with HIPing.This tape presents some degree of grains alignment, as a consequence of rolling.We observed Jc anisotropy in both transport and magnetization measurements in a range between 4 and 26K, and the same effect in Hc2.The anisotropy factor in Jc increase with applied field, while the anisotropy in Hc2 is constant with temperature (Hc2 parallel Hc2 perpendicular ?1.2).Finally, we observed that carbon nanotubes doping improves Hc2 and this effects is most important at temperatures below 5K.This increase in Hc2 was predicted by Gurevich [45], as an effect of modification in scattering coefficient between electronics bands of MgB2 by doping

365

Magnetic Field Topology in Jets  

Science.gov (United States)

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

Gardiner, T. A.; Frank, A.

2000-01-01

366

Low field magnetic resonance imaging  

Science.gov (United States)

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

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

2010-07-13

367

Evolution of Primordial Magnetic Fields from Phase Transitions  

CERN Document Server

We consider the evolution of primordial magnetic fields generated during cosmological, electroweak or QCD, phase transitions. We assume that the magnetic field generation can be described as an injection of magnetic energy to cosmological plasma at a given scale determined by the moment of magnetic field generation. A high Reynolds number ensures strong coupling between magnetic field and fluid motions. The subsequent evolution of the magnetic field is governed by decaying hydromagnetic turbulence. Both our numerical simulations and a phenomenological description allow us to recover "universal" laws for the decay of magnetic energy and the growth of magnetic correlation length in the turbulent (low viscosity) regime. In particular, we show that during the radiation dominated epoch, energy and correlation length of non-helical magnetic fields scale as conformal time to the powers -1/2 and +1/2, respectively. For helical magnetic fields, energy and correlation length scale as conformal time to the powers -1/3 a...

Kahniashvili, Tina; Brandenburg, Axel; Neronov, Andrii

2012-01-01

368

Magnetic Field Problem: Current and Magnets  

Science.gov (United States)

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

369

Effects of MHD slow shocks propagating along magnetic flux tubes in a dipole magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Variations of the plasma pressure in a magnetic flux tube can produce MHD waves evolving into shocks. In the case of a low plasma beta, plasma pressure pulses in the magnetic flux tube generate MHD slow shocks propagating along the tube. For converging magnetic field lines, such as in a dipole magnetic field, the cross section of the magnetic flux tube decreases enormously with increasing magnetic field strength. In such a case, the propagation of MHD waves along magnetic flux tubes is...

Erkaev, N. V.; Shaidurov, V. A.; Semenov, V. S.; Biernat, H. K.

2002-01-01

370

Augmentation of natural convective heat transfer in square cavity by utilizing nano-fluids in the presence of magnetic field and uniform heat generation/absorption  

International Nuclear Information System (INIS)

Natural convection in a square cavity filled with different nano-fluids is studied numerically. Both upper and lower surfaces are being insulated, whilst a uniform magnetic field is applied in a horizontal direction. Constant different temperatures are imposed along the vertical walls of the enclosure, steady state laminar regime is considered. The transport equations for continuity, momentum, energy are solved. The numerical results are reported for the effect of Rayleigh number, solid volume fraction and both Hartmann number and heat generation or absorption coefficient on the iso-contours of streamline and temperature. In addition, the predicted results for average Nusselt are presented for various parametric conditions. This study was done for 103 ? Ra ? 107, 0 ? Ha ? 60, 0 ? ? ? 0.06 and -10 ? q ? 10 while the Prandtl number represent water is kept constant at 6.2. The results show that for weak magnetic field; the addition of nano-particles is necessary to enhance the heat transfer but for strong magnetic field there is no need for nano-particles because the heat transfer will decrease. On the other hand to augment the heat transfer; nano-particles volume fraction must be increased but with a small value of heat absorption coefficient (q < 0) at constant Hartmann and Rayleigh numbers. (authors)

371

A low-power magnetic-field-assisted plasma jet generated by dielectric-barrier discharge enhanced direct-current glow discharge at atmospheric pressure  

Energy Technology Data Exchange (ETDEWEB)

A magnetic field is introduced to the dielectric-barrier discharge enhanced direct-current glow discharge for efficient plasma generation, with the discharge power of 2.7?W and total energy consumption reduced to 34% of the original. By spatially examining the emission spectra and plasma temperature, it is found that their peaks shift from edges to the center and the negative and anode glows merge into the positive column and disappear, accompanied by improvement of uniformity and chemical activity of the enlarged plasma. This lies in the enhancement of ionization in the curved and lengthened electron path and the dispersion of discharge domains.

Jiang, Weiman; Tang, Jie, E-mail: tangjie1979@opt.ac.cn; Wang, Yishan; Zhao, Wei [State Key Laboratory of Transient Optics and Photonics, Xi' an Institute of Optics and Precision Mechanics of CAS, Xi' an 710119 (China); Duan, Yixiang [State Key Laboratory of Transient Optics and Photonics, Xi' an Institute of Optics and Precision Mechanics of CAS, Xi' an 710119 (China); Research Center of Analytical Instrumentation, Sichuan University, Chengdu 610064 (China)

2014-01-06

372

A low-power magnetic-field-assisted plasma jet generated by dielectric-barrier discharge enhanced direct-current glow discharge at atmospheric pressure  

International Nuclear Information System (INIS)

A magnetic field is introduced to the dielectric-barrier discharge enhanced direct-current glow discharge for efficient plasma generation, with the discharge power of 2.7?W and total energy consumption reduced to 34% of the original. By spatially examining the emission spectra and plasma temperature, it is found that their peaks shift from edges to the center and the negative and anode glows merge into the positive column and disappear, accompanied by improvement of uniformity and chemical activity of the enlarged plasma. This lies in the enhancement of ionization in the curved and lengthened electron path and the dispersion of discharge domains

373

Magnetic nanoparticle traveling in external magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A set of equations describing the motion of a free magnetic nanoparticle in an external magnetic field in a vacuum, or in a medium with negligibly small friction forces is postulated. The conservation of the total particle momentum, i.e. the sum of the mechanical and the total spin momentum of the nanoparticle is taken into account explicitly. It is shown that for the motion of a nanoparticle in uniform magnetic field there are three different modes of precession of the unit...

Usov, N. A.; Liubimov, B. Ya

2014-01-01

374

Simulation on near-field light generated by metal nano-dot on GaAs substrate for heat source of heat-assisted magnetic recording  

Science.gov (United States)

Heat-assisted magnetic recording (HAMR) is promising for achieving more than 1 Tb/inch2 recording density. A near-field transducer (NFT), which forms a hot spot of 10-100 nm in diameter on a recording medium, is necessary in HAMR. In this study, localized surface plasmons generated by a metal nano-dot in a novel device for a heat source of heat-assisted magnetic recording were analyzed using a simple model in which a metal hemisphere was formed on a GaAs substrate and a quasi-electrostatic approximation. The scattering and absorption efficiencies as well as the enhancement factor were investigated for several kinds of metal. As a result, their dependence on the wavelength and the polarization direction of the incident light was clarified.

Katayama, Ryuichi

2014-09-01

375

Galactic magnetic fields as a consequence of inflation.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The generation of a magnetic field in the Early Universe is considered, due to the gravitational production of the Z-boson field during inflation. Scaled to the epoch of galaxy formation this magnetic field suffices to trigger the galactic dynamo and explain the observed galactic magnetic fields. The mechanism is independent of the inflationary model.

Dimopoulos, Konstantinos

2002-01-01

376

The magnetic field of rotating bodies  

International Nuclear Information System (INIS)

The paper discusses the possibility of interpreting the magnetic fields of astronomical bodies in the framework of a unified field theory. Using one of the solutions of the generalized field theory, a direct relation between the polar magnetic field, the angular velocity and the gravitational potential of the body considered, is obtained. The model used for applications has spherical symmetry. The predictions of the theoretical formula, obtained from the model, are compared with available observational data, and with the empirical relation of Blackett. The theoretical formula gives a possible interpretation of a seed magnetic field which will develop and produce the largescale magnetic field observed for celestial objects. The formula shows that the field may be generated as a result of the rotation of the massive object. (author). 24 refs, 3 figs, 1 tab

377

Fields from a relativistic magnetic explosion  

CERN Document Server

Following Prendergast we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magnetic field is crucial, as short time-scales lead to strong radiant fields. Assuming a magnetic field of $10^{13}Gauss$ emerging from a magnetosphere of $10^{9}cm$ we end with a jet when confined by a pressure environment that falls more slowly than $r^{-4}$. The jet carries energy of $10^{51}erg$, which is mostly due to differential rotation at the base.

Gourgouliatos, K N

2008-01-01

378

The origin of large scale magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic fields correlated on several kiloparsec scales are seen in spiral galaxies. Their origin could be due to the winding up of a primordial cosmological field or due to amplification of a small seed field by a turbulent galactic dynamo. Both options have difficulties: There is no known battery mechanism for producing the required primordial field. Equally the turbulent dynamo may self destruct before being able to produce the large scale field, due to excess generation ...

Subramanian, K.

1996-01-01

379

Magnetic Field in Supernovae  

CERN Document Server

A relatively modest value of the initial rotation of the iron core, a period of ~ 6-31 s, will give a very rapidly rotating protoneutron star and hence strong differential rotation with respect to the infalling matter. Under these conditions, a seed field is expected to be amplified by the MRI and to grow exponentially. Exponential growth of the field on the time scale Omega^{-1} by the magnetorotational instability (MRI) will dominate the linear growth process of field line "wrapping" with the same characteristic time. The shear is strongest at the boundary of the newly formed protoneutron star. Modest initial rotation velocities of the iron core result in sub-Keplerian rotation and a sub-equipartition magnetic field that nevertheless produce substantial MHD luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G develop ~ 300 msec after bounce with an associated MHD luminosity of ~ 10^{49} - 10^{53} erg s^{-1}. Bi-polar flows driven by this MHD power can affect or even cause the explosi...

Akiyama, S; Akiyama, Shizuka

2002-01-01

380

Dynamically Generated Anomalous Magnetic Moment in Massless QED  

CERN Document Server

In this paper we investigate the non-perturbative generation of an anomalous magnetic moment for massless fermions in the presence of an external magnetic field. In the context of massless QED in a magnetic field, we prove that the phenomenon of magnetic catalysis of chiral symmetry breaking, which has been associated in the literature with dynamical mass generation, is also responsible for the generation of a dynamical anomalous magnetic moment. As a consequence, the degenerate energy of electrons in Landau levels higher than zero exhibits Zeeman splitting. We explicitly report the splitting for the first Landau level and find the non-perturbative Lande $\\textit{g}$-factor and Bohr magneton. We anticipate that a dynamically generated anomalous magnetic moment will be a universal feature of theories with magnetic catalysis. Our findings can be important for condensed planar systems as graphene, as well as for highly magnetized dense systems as those forming the core of compact stars.

Ferrer, Efrain J

2009-01-01

 
 
 
 
381

Observations of magnetic fields in hot stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The presence of magnetic fields at the surfaces of many massive stars has been suspected for decades, to explain the observed properties and activity of OB stars. However, very few genuine high-mass stars had been identified as magnetic before the advent of a new generation of powerful spectropolarimeters that has resulted in a rapid burst of precise information about the magnetic properties of massive stars. During this talk, I will briefly review modern methods used to dia...

Petit, V.

2010-01-01

382

MIXED CONVECTION OVER AN ISOTHERMAL VERTICAL FLAT PLATE EMBEDDED IN A POROUS MEDIUM WITH MAGNETIC FIELD, RADIATION AND VARIABLE VISCOSITY WITH HEAT GENERATION  

Directory of Open Access Journals (Sweden)

Full Text Available This paper focuses on the numerical solutions of the effects of magnetic field, radiation, variable viscosity and heat generation on similarity solutions of mixed convection adjacent to an isothermal vertical plate which is embedded in a porous medium. A similarity transformation is used to reduce the partial differential equations governing the problem into ordinary differential equations and the equations are solved numerically subject to appropriate boundary conditions by the use of Runge-Kutta-Gill method together with a shooting technique. The flow and heat transfer quantities of similarity equations are found to be the functions of C,Rd, ,Q ? ? and RP where C is the magnetic interaction parameter, Rd is the radiation parameter, ? ? is viscosity variation coefficient, Q is the heat generation/absorption parameter and RP is the mixed convection parameter which is the ratio of Rayleigh to pe?clet numbers. In the present work the cases of assisting and opposing flows are discussed. It has been found that in opposing flow case, dual solutions exist for negative values of RP and boundary layer separation occurs. It is observed that depending on the values of RP there exists no solution, a unique solution or dual solutions and also the temperature decreases significantly with increase in Q and C. Skin friction, heat transfer coefficient, velocity and temperature fields are studied and discussed with the help of a table and graphs.

T. RajaRani

2012-01-01

383

SCUPOL Magnetic Field Analysis  

CERN Document Server

We present an extensive analysis of the 850 microns polarization maps of the SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-to-mean magnetic field ratio of each region. Similar sets of parameters are calculated from 2D synthetic maps of dust emission polarization produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and DR21 molecular clouds polarization maps. For these specific regions the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfv\\`en and sonic Mach numbers, are consistent within a factor 1 to 2 with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher (1999). Constraints on the values of the inclination angle of the mean magnetic field with respect to the LOS are also given. The values obtained from th...

Poidevin, Frederick; Kowal, Grzegorz; Pino, Elisabete de Gouveia Dal; Magalhaes, Antonio-Mario

2013-01-01

384

Photonic Magnetic Field Sensor  

Science.gov (United States)

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

Wyntjes, Geert

2002-02-01

385

Magnetized microdischarge plasma generation at low pressure  

International Nuclear Information System (INIS)

A magnetized microdischarge plasma is generated at low pressure with planar electrodes and a non-uniform magnetic field configuration causing closed E x B electron drift. Stable generation with a 1 mm electrode gap has been achieved in 0.5-55 Torr of argon. The breakdown voltage curve is found to have two local minima, the lower of which is believed to be caused by strong electron magnetization, as supported by simple Monte Carlo simulations. The current-voltage curves show strong variations between operation at 10 Torr and lower pressures. The plasma confinement, as inferred from the luminous emission of the annular-shape discharge, appears to be stronger at low pressures. Optical emission is used to infer electron excitation temperatures, which are estimated to be about 1 eV

386

Magnetized microdischarge plasma generation at low pressure  

Energy Technology Data Exchange (ETDEWEB)

A magnetized microdischarge plasma is generated at low pressure with planar electrodes and a non-uniform magnetic field configuration causing closed E x B electron drift. Stable generation with a 1 mm electrode gap has been achieved in 0.5-55 Torr of argon. The breakdown voltage curve is found to have two local minima, the lower of which is believed to be caused by strong electron magnetization, as supported by simple Monte Carlo simulations. The current-voltage curves show strong variations between operation at 10 Torr and lower pressures. The plasma confinement, as inferred from the luminous emission of the annular-shape discharge, appears to be stronger at low pressures. Optical emission is used to infer electron excitation temperatures, which are estimated to be about 1 eV.

Ito, Tsuyohito [Frontier Research Base for Global Young Researchers, Frontier Research Center, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)], E-mail: tsuyohito@wakate.frc.eng.osaka-u.ac.jp; Kobayashi, Kazunobu; Hamaguchi, Satoshi [Center for Atomic and Molecular Technologies, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Cappelli, Mark A. [Mechanical Engineering Department, Stanford University, Stanford, CA 94305-3032 (United States)

2008-08-01

387

Helical magnetic fields via baryon asymmetry  

CERN Document Server

There is strong observational evidence for the presence of large-scale magnetic fields MF in galaxies and clusters, with strength $\\sim \\mu$G and coherence lenght on the order of Kpc. However its origin remains as an outstanding problem. One of the possible explanations is that they have been generated in the early universe. Recently, it has been proposed that helical primordial magnetic fields PMFs, could be generated during the EW or QCD phase transitions, parity-violating processes and predicted by GUT or string theory. Here we concentrate on the study of two mechanisms to generate PMFs, the first one is the $\

Piratova, Eduard F; Hortúa, Héctor J

2014-01-01

388

Origin of neutron star magnetic fields  

CERN Document Server

Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritance is not sufficient to explain the fields of magnetars. Energetic considerations point to differential rotation in the final stages of core collapse process as the most likely source of field generation, at least for magnetars. A runaway phase of exponential growth is needed to achieve sufficient field amplification during relevant phase of core collapse; it can probably be provided by a some form of magnetorotational instability. Once formed in core collapse, the field is in danger of decaying again by magnetic instabilities. The evolution of a magnetic field in a newly formed neutron star is discussed, with emphasis on the existence of stable equilibrium configurations as end products of this evolution, and the role of magnetic helicity in their existence.

Spruit, H C

2007-01-01

389

Fast superconducting magnetic field switch  

Science.gov (United States)

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

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

1996-01-01

390

Relaxed plasmas in external magnetic fields  

International Nuclear Information System (INIS)

The well-known theory of relaxed plasmas (Taylor states) is extended to external magnetic fields whose field lines intersect the conducting toroidal boundary. Application to an axially symmetric, large-aspect-ratio torus with circular cross section shows that the maximum pinch ratio, and hence the phenomenon of current saturation, is independent of the external field. The relaxed state is explicitly given for an external octupole field. In this case, field reversal is inhibited near parts of the boundary if the octupole generates magnetic x-points within the plasma. (orig.)

391

Recurrent flux emergence from dynamo-generated fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the emergence of a large-scale magnetic field. This field is dynamo-generated by turbulence driven with a helical forcing function. Twisted arcade-like field structures are found to emerge in the exterior above the turbulence zone. Time series of the magnetic field structure show recurrent plasmoid ejections.

Warnecke, Jo?rn; Brandenburg, Axel

2010-01-01

392

Adaptable controller of magnetic field homogeneity  

International Nuclear Information System (INIS)

The electrical wiring is described of an adaptable controller of the magnetic field homogeneity. The controller is designed for search and maintenance of the optimal magnetic field homogeneity using a correction system. The system comprises an electronic voltage-to-frequency converter, a clock pulse generator, bidirectional counters, and digital-to-analog converters. The controller is especially suitable for use in NMR spectrometers. (J.B.)

393

High magnetic field ohmically decoupled non-contact technology  

Science.gov (United States)

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

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

2009-05-19

394

Magnetic fields in massive stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

Hubrig, S.

2007-01-01

395

Dynamo generated field emergence through recurrent plasmoid ejections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic buoyancy is believed to drive the transport of magnetic flux tubes from the convection zone to the surface of the Sun. The magnetic fields form twisted loop-like structures in the solar atmosphere. In this paper we use helical forcing to produce a large-scale dynamo-generated magnetic field, which rises even without magnetic buoyancy. A two layer system is used as computational domain where the upper part represents the solar atmosphere. Here, the evolution of the m...

Warnecke, Jo?rn; Brandenburg, Axel

2010-01-01

396

International Geomagnetic Reference Field : The eleventh generation  

DEFF Research Database (Denmark)

The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V?MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined.

Finlay, Chris; Maus, S.

2010-01-01

397

Magnetic field and gradient analysis around matrix for HGMS  

International Nuclear Information System (INIS)

A High Gradient Magnetic Separator (HGMS) uses matrix to make high magnetic field gradient so that ferro- or para-magnetic particles can be attracted to them by high magnetic force. These matrixes are usually composed of stainless wires having high magnetization characteristics. This paper deals with superconducting HGMS which is aimed for purifying wastewater by using stainless steel matrix. Background magnetic field up to 6 T is generated by a superconducting solenoid and the stainless steel matrix are arranged inside of the solenoid. In order to calculate magnetic forces exerting on magnetic particles in wastewater, it is important to calculate magnetic field and magnetic field gradient those are proportional to the magnetic force acting on the particle. So we presents magnetic field distribution analysis result and estimates how many times of magnetic force will act on a particle when the matrix are arranged or not.

398

Protein detection with magnetic nanoparticles in a rotating magnetic field  

Science.gov (United States)

A detection scheme based on magnetic nanoparticle (MNP) dynamics in a rotating magnetic field for a quantitative and easy-to-perform detection of proteins is illustrated. For the measurements, a fluxgate-based setup was applied, which measures the MNP dynamics, while a rotating magnetic field is generated. The MNPs exhibit single iron oxide cores of 25 nm and 40 nm diameter, respectively, as well as a protein G functionalized shell. IgG antibodies were utilized as binding target molecules for the physical proof-of-concept. The measurement results were fitted with a theoretical model describing the magnetization dynamics in a rotating magnetic field. The established detection scheme allows quantitative determination of proteins even at a concentration lower than of the particles. The observed differences between the two MNP types are discussed on the basis of logistic functions.

Dieckhoff, Jan; Lak, Aidin; Schilling, Meinhard; Ludwig, Frank

2014-01-01

399

Magnetic Fields on Cool Stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic fields are an important ingredient to cool star physics, and there is great interest in measuring fields and their geometry in order to understand stellar dynamos and their influence on star formation and stellar evolution. During the last few years, a large number of magnetic field measurements became available. Two main approaches are being followed to measure the Zeeman effect in cool stars; 1) the measurement of polarized light, for example to produce magnetic m...

Reiners, Ansgar

2010-01-01

400

GZK horizon and magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss some aspects of the propagation of high-energy cosmic rays (CRs) in turbulent magnetic fields, and propose a formula for the diffusion coefficient based on accurate simulations in a wide energy range. We discuss the transition between ballistic and diffusive regimes and the magnetic horizon of CR sources, showing how magnetic fields of a few nG could modify the shape of the GZK feature. Such fields would roughly be in equipartition with the extragalactic CRs, and ...

Parizot, Etienne

2004-01-01

 
 
 
 
401

Atoms in high magnetic fields  

International Nuclear Information System (INIS)

High magnetic fields have been of interest for some time in solid-state physics. Recent spectroscopic experiments on highly excited barium atoms and the discovery of very large magnetic fields in white dwarf stars and neutron stars have stimulated renewed interest in the spectroscopy of free atoms in high magnetic fields. The various spectroscopic regimes ranging from the low-field Zeeman effect to the high-field Landau regime are reviewed and calculations of the energy levels of hydrogen, helium and the isoelectronic ions in fields of any strength are surveyed. Observations of the quadratic Zeeman effect in the alkalis and high-field effects in the neutral barium spectrum are described. Finally, recent discoveries of continuum polarization in white dwarf stars, its interpretation in terms of the presence of high magnetic fields, and confirmation of such fields spectroscopically, and some remaining mysteries in these remarkable stellar spectra, are reviewed. (author)

402

Optimization of Cryogenic and Superconducting Magnetic Systems for MHD Generators  

International Nuclear Information System (INIS)

Increasing the strength of the magnetic field within the working volume of an MHD generator results in a considerable increase in the power density and consequently a reduction in the weight of the generator and in the unit power cost. Strong magnetic fields can be obtained by means of iron-free magnetic systems in which either super pure metals or superconducting alloys cooled by liquid gases are used in the windings. The best windings cross-section for producing a uniform magnetic field in the rectangular working region is chosen. With an iron-free magnetic system incorporating windings of such configuration the weight can be reduced to a minimum. The authors present the calculations for producing uniform magnetic fields of high intensity in the working volume of the MHD duct by means of iron-free magnetic systems. The properties of these systems are compared in the paper. (author)

403

Study of the effects of magnetic volume forces generated by a high magnetic field on yield stress fluids - opportunities of solide-gel transition  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Yield stress fluids have amazing mechanical properties: below a particular shear stress, called yield stress, the fluid behaves like a solid. Once the yield stress is exceeded, they flow like a viscous fluid or a gel. This thesis deals with the effects of magnetic volume forces on these fluids. We study the opportunity of the solid--gel transition from magnetic volume forces created by various magnetic devices. These fluids have no special magnetic properties. It is therefore necessary to cre...

Heyrendt, Laurent

2012-01-01

404

Generation and manipulation of monodispersed ferrofluid emulsions: The effect of a uniform magnetic field in flow-focusing and T-junction configurations  

Science.gov (United States)

This paper demonstrates the use of magnetically controlled microfluidic devices to produce monodispersed ferrofluid emulsions. By applying a uniform magnetic field on flow-focusing and T-junction configurations, the size of the ferrofluid emulsions can be actively controlled. The influences of the flow rates, the orientation, and the polarity of the magnetic field on the size of ferrofluid emulsions produced in both flow-focusing and T-junction configurations are compared and discussed.

Tan, Say Hwa; Nguyen, Nam-Trung

2011-09-01

405

Rapid generation of angular momentum in bounded magnetized plasma  

CERN Document Server

Direct numerical simulations of two-dimensional decaying MHD turbulence in bounded domains show the rapid generation of angular momentum in nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this mechanism. On a larger time scale, the generation of a magnetic angular momentum, or angular field, is observed. For axisymmetric geometries, the generation of angular momentum is absent; nevertheless, a weak magnetic field can be observed. The derived evolution equations for both the angular momentum and angular field yield possible explanations for the observed behavior.

Bos, Wouter J T; Schneider, Kai; 10.1103/PhysRevLett.101.235003

2010-01-01

406

Magnetic response to applied electrostatic field in external magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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.)

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

407

Dynamo generated field emergence through recurrent plasmoid ejections  

CERN Document Server

Magnetic buoyancy is believed to drive the transport of magnetic flux tubes from the convection zone to the surface of the Sun. The magnetic fields form twisted loop-like structures in the solar atmosphere. In this paper we use helical forcing to produce a large-scale dynamo-generated magnetic field, which rises even without magnetic buoyancy. A two layer system is used as computational domain where the upper part represents the solar atmosphere. Here, the evolution of the magnetic field is solved with the stress--and--relax method. Below this region a magnetic field is produced by a helical forcing function in the momentum equation, which leads to dynamo action. We find twisted magnetic fields emerging frequently to the outer layer, forming arch-like structures. In addition, recurrent plasmoid ejections can be found by looking at space--time diagrams of the magnetic field. Recent simulations in spherical coordinates show similar results.

Warnecke, Jörn

2010-01-01

408

Theory of fossil magnetic field  

CERN Document Server

Theory of fossil magnetic field is based on the observations, analytical estimations and numerical simulations of magnetic flux evolution during star formation in the magnetized cores of molecular clouds. Basic goals, main features of the theory and manifestations of MHD effects in young stellar objects are discussed.

Dudorov, Alexander E

2014-01-01

409

Review: Magnetic fields of O stars  

CERN Document Server

Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this paper I will review the characteristics of the inferred fields of individual stars, as well as the overall population. I will discuss the extension of the 'magnetic desert', first inferred among the A-type stars, to O stars up to 60 solar masses. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating complex 'dynamical magnetosphere' structures detected in optical and UV lines, and in X-ray lines and continuum. Finally, I will discuss the detection of a small number of variable O stars in the LMC and SMC that exhibit spectral characteristics analogous to the known Galactic magnetic stars, and that almost certainly represent the first known examples of extra-Galactic magnetic stars.

Wade, G A

2014-01-01

410

Cosmic Magnetic Fields - An Overview  

Science.gov (United States)

Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

Wielebinski, Richard; Beck, Rainer

411

Protogalactic evolution and magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that the relatively strong magnetic fields ($\\ge 1 \\mu$G) in high redshift objects can be explained by the combined action of an evolving protogalactic fluctuation and electrodynamic processes providing the magnetic seed fields. Three different seed field mechanisms are reviewed and incorporated into a spherical "top-hat" model and tidal torque theory for the fate of a forming galaxy in an expanding universe. Very weak fields $10^{-19} \\sim 10^{-23}$G created in an e...

Lesch, Harald; Chiba, Masashi

1994-01-01

412

Torsion, neutrinos, and intergalactic magnetic field  

International Nuclear Information System (INIS)

It is suggested that in the early universe neutrinos with magnetic moment M aligned to generate an ubiquitous magnetic field B. Their alignment was spurred by torsion. With an iterative procedure it was found a relation connecting M to B at any epoch. This result does not depend on the value of the initial torsion, all was needed is an initial torsion no matter how small. With M = 10-44 erg/gauss one finds B =10-9 gauss at the present epoch. This value explains the observed mean galactic magnetic field

413

Origin of cosmic magnetic fields.  

Science.gov (United States)

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

Campanelli, Leonardo

2013-08-01

414

Measurements of magnetic field alignment  

International Nuclear Information System (INIS)

The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs

415

Highly focused and efficient terahertz radiation generation by photo-mixing of lasers in plasma in the presence of magnetic field  

International Nuclear Information System (INIS)

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ?1, ?2 and wave numbers k1, k2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ??=?1??2 and wave number k?=k1?k2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ?UH=?((?p2+?c2)) (where ?c is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field

416

Biological effects of magnetic fields  

International Nuclear Information System (INIS)

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

417

Magnetic fields in O stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Over the last decade, large-scale, organized (generally dipolar) magnetic fields with a strength between 0.1 and 20 kG were detected in dozens of OB stars. This contribution reviews the impact of such magnetic fields on the stellar winds of O-stars, with emphasis on variability and X-ray emission.

Naze?, Yae?l

2013-01-01

418

Split-field magnet (SFM)  

CERN Multimedia

The split-field magnet (SFM) completely assembled and undergoing power tests in its assembly hall. On the gallery at the far right is one of the large compensator magnets which restore ISR beams to their orbits after deviation by the SFM's field.

1972-01-01

419

Interplanetary electric and magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

A kinematic model of the stationary electromagnetic fields in interplanetary space with finite conductivity is considered. The electrodynamic problem is solved for a medium with uniform conductivity and radial plasma outflow from a spherical source. Simple analytical formulae are obtained for electric and magnetic fields, currents and charges in the case of a uniformly-magnetized rotating sphere.

Alexeev, I.I.; Kropotkin, A.P.; Veselovsky, I.S. (Moskovskij Gosudarstvennyj Univ. (USSR). Nauchno-Issledovatel' skij Inst. Yadernoj Fiziki)

1982-08-01

420

Magnetic fields in laser heated plasmas  

International Nuclear Information System (INIS)

With a fixed-ion code for the study of self-generated magentic fields in laser heated plasmas, the inhibition of thermal transport and the effect of the Nernst term are modeled for a KrF laser. For various values of the flux limiter, the response of a foil to a focused laser is calculated without a magnetic field and compared with the response calculated with a magnetic field. The results are: The Nernst term convects the magnetic field to densities above critical as found by Nishiguchi et al. (1984), but the field does not strongly inhibit transport into the foil. The field is also transported to sub-critical densities, where it inhibits thermal diffusion and enhance lateral transport by convection