WorldWideScience

Sample records for magnetic field generation

  1. Magnetic Field Generation in Stars

    CERN Document Server

    Ferrario, Lilia; Zrake, Jonathan

    2015-01-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a ...

  2. Primordial Generation of Magnetic Fields

    CERN Document Server

    Pandey, Arun Kumar

    2015-01-01

    We reexamine generation of the primordial magnetic fields, at temperature $T>80$TeV, by applying a consistent kinetic theory framework which is suitably modified to take the quantum anomaly into account. The modified kinetic equation can reproduce the known quantum field theoretic results upto the leading orders. We show that our results qualitatively matches with the earlier results obtained using heuristic arguments. The modified kinetic theory can give the instabilities responsible for generation of the magnetic field due to chiral imbalance in two distinct regimes: a) when the collisions play a dominant role and b) when the primordial plasma can be regarded as collisionless. We argue that the instability developing in the collisional regime can dominate over the instability in the collisionless regime.

  3. Generation of helical magnetic fields from inflation

    OpenAIRE

    Jain, Rajeev Kumar; Durrer, Ruth.; Hollenstein, Lukas

    2012-01-01

    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 fi...

  4. Some aspects of self generated magnetic field

    International Nuclear Information System (INIS)

    Self generated magnetic field is an important phenomenon in laser produced plasma and in astrophysical plasma. Several mechanisms for generation of axial and transverse fields are described here. Scaling laws for magnetic fields involving the laser parameters are also obtained. Detection of transverse and axial fields by measuring Faraday rotation is reported. (author). 23 refs., 3 figs

  5. Strong and superstrong pulsed magnetic fields generation

    CERN Document Server

    Shneerson, German A; Krivosheev, Sergey I

    2014-01-01

    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.

  6. Magnetic field generation in relativistic shocks

    OpenAIRE

    Wiersma, Jorrit; Achterberg, A.

    2003-01-01

    We present an analytical estimate for the magnetic field strength generated by the Weibel instability in ultra-relativistic shocks in a hydrogen plasma. We find that the Weibel instability is, by itself, not capable of converting the kinetic energy of protons penetrating the shock front into magnetic field energy. Other (nonlinear) processes must determine the magnetic field strength in the wake of the shock.

  7. Generation of magnetic fields for accelerators with permanent magnets

    International Nuclear Information System (INIS)

    Commercially available permanent magnet materials and their properties are reviewed. Advantages and disadvantages of using permanent magnets as compared to electromagnets for the generation of specific magnetic fields are discussed. Basic permanent magnet configurations in multipole magnets and insertion devices are presented. (orig.)

  8. ON THE GENERATION OF ORGANIZED MAGNETIC FIELDS

    International Nuclear Information System (INIS)

    Motivated by the problem of the origin of astrophysical magnetic fields, we introduce two concepts. The first is that of a 'system-scale dynamo', i.e., a dynamo that can organize magnetic fields on the scale of the astrophysical object. The second is that of an 'essentially nonlinear dynamo'. This is a dynamo which relies on a velocity driven by magnetic forces and/or magnetic instabilities. We construct a simple framework that can be used to study such dynamos and give examples in which the evolution is such to generate a system-scale field. We argue that this framework provides a valuable complementary approach to the more conventional studies based on kinematic mean-field dynamo theory.

  9. Induction MHD generator using alternating magnetic field

    International Nuclear Information System (INIS)

    The induction MHD generator using an alternating magnetic field is proposed. The characteristics of the machine are analyzed theoretically and also compared with those of the induction MHD generator using a traveling magnetic field. Following conclusions are obtained for the fundamental characteristics of the present machine: (1) This type of the machine is possibly operated not only as the generator but also as the pump or as the damper. (2) The optimum condition for the maximum generator efficiency exists among the relations of the frequency, the fluid velocity and the inner core radius because of the eddy current loss due to an alternating magnetic field. (3) The power ratio of the reactive power of the machine to the gross output power can be reduced to a much smaller value than that of the traveling wave MHD generator. Therefore, even in the case of the working fluid with a relative low electrical conductivity such as two-phase liquid metal flow with high void fraction, the acceptable power ratio can be expected. (4) For the working fluid with higher electrical conductivity the skin effect is also able to be reduced to the acceptable level in the present machine, while it is a serious problem in the traveling wave MHD generator. (author)

  10. A deep dynamo generating Mercury's magnetic field.

    Science.gov (United States)

    Christensen, Ulrich R

    2006-12-21

    Mercury has a global magnetic field of internal origin and it is thought that a dynamo operating in the fluid part of Mercury's large iron core is the most probable cause. However, the low intensity of Mercury's magnetic field--about 1% the strength of the Earth's field--cannot be reconciled with an Earth-like dynamo. With the common assumption that Coriolis and Lorentz forces balance in planetary dynamos, a field thirty times stronger is expected. Here I present a numerical model of a dynamo driven by thermo-compositional convection associated with inner core solidification. The thermal gradient at the core-mantle boundary is subadiabatic, and hence the outer region of the liquid core is stably stratified with the dynamo operating only at depth, where a strong field is generated. Because of the planet's slow rotation the resulting magnetic field is dominated by small-scale components that fluctuate rapidly with time. The dynamo field diffuses through the stable conducting region, where rapidly varying parts are strongly attenuated by the skin effect, while the slowly varying dipole and quadrupole components pass to some degree. The model explains the observed structure and strength of Mercury's surface magnetic field and makes predictions that are testable with space missions both presently flying and planned. PMID:17183319

  11. Error field generation of solenoid magnets

    International Nuclear Information System (INIS)

    Many applications for large solenoids and solenoidal arrays depend on the high precision of the axial field profile. In cases where requirements of ?B/B for nonaxial fields are on the order of 10-4, the actual winding techniques of the solenoid need to be considered. Whereas an ideal solenoid consisting of current loops would generate no radial fields along the axis, in reality, the actual current-carrying conductors must follow spiral or helical paths. A straightforward method for determining the radial error fields generated by coils wound with actual techniques employed in magnet fabrication has been developed. The method devised uses a computer code which models a magnet by sending a single, current-carrying filament along the same path taken by the conductor during coil winding. Helical and spiral paths are simulated using small, straight-line current segments. This technique, whose results are presented in this paper, was used to predict radial field errors for the Elmo Bumpy Torus-Proof of Principle magnet. These results include effects due to various winding methods, not only spiral/helical and layer-to-layer transitions, but also the effects caused by worst-case tolerance conditions both from the conductor and the winding form (bobbin). Contributions made by extraneous circuitry (e.g., overhead buswork and incoming leads) are also mentioned

  12. Relativistic generation of vortex and magnetic field

    International Nuclear Information System (INIS)

    The implications of the recently demonstrated relativistic mechanism for generating generalized vorticity in purely ideal dynamics [Mahajan and Yoshida, Phys. Rev. Lett. 105, 095005 (2010)] are worked out. The said mechanism has its origin in the space-time distortion caused by the demands of special relativity; these distortions break the topological constraint (conservation of generalized helicity) forbidding the emergence of magnetic field (a generalized vorticity) in an ideal nonrelativistic dynamics. After delineating the steps in the ''evolution'' of vortex dynamics, as the physical system goes from a nonrelativistic to a relativistically fast and hot plasma, a simple theory is developed to disentangle the two distinct components comprising the generalized vorticity--the magnetic field and the thermal-kinetic vorticity. The ''strength'' of the new universal mechanism is, then, estimated for a few representative cases; in particular, the level of seed fields, created in the cosmic setting of the early hot universe filled with relativistic particle-antiparticle pairs (up to the end of the electron-positron era), are computed. Possible applications of the mechanism in intense laser produced plasmas are also explored. It is suggested that highly relativistic laser plasma could provide a laboratory for testing the essence of the relativistic drive.

  13. Mean magnetic field generation in sheared rotators

    OpenAIRE

    Blackman, Eric G

    1999-01-01

    A generalized mean magnetic field induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magnetic field itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean veloc...

  14. 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

  15. 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

  16. Generation of magnetic fields on galactic scale

    OpenAIRE

    Del Sordo, Fabio

    2011-01-01

    In these pages we will go through the topic of astrophysical magnetic fields, focusing on galactic fields, their observation and the theories that have been developed for a proper understanding of the these physical phenomena.We review the main work in the study of galactic magnetic fields, often seeing how it is important to deal with problems of general validity in order to be able to point out the right elements needed for a correct interpretation of specific situations. We also aim to sum...

  17. The Generation of Magnetic Fields Through Driven Turbulence

    OpenAIRE

    Cho, Jungyeon; Vishniac, Ethan T.

    2000-01-01

    We have tested the ability of driven turbulence to generate magnetic field structure from a weak uniform field using three dimensional numerical simulations of incompressible turbulence. We used a pseudo-spectral code with a numerical resolution of up to $144^3$ collocation points. We find that the magnetic fields are amplified through field line stretching at a rate proportional to the difference between the velocity and the magnetic field strength times a constant. Equipar...

  18. Design of portable electric and magnetic field generators

    Science.gov (United States)

    Stewart, M. G.; Siew, W. H.; Campbell, L. C.; Stewart, M. G.; Siew, W. H.

    2000-11-01

    Electric and magnetic field generators capable of producing high-amplitude output are not readily available. This presents difficulties for electromagnetic compatibility testing of new measurement systems where these systems are intended to operate in a particularly hostile electromagnetic environment. A portable electric and a portable magnetic field generator having high pulsed field output are described in this paper. The output of these generators were determined using an electromagnetic-compatible measurement system. These generators allow immunity testing in the laboratory of electronic systems to very high electrical fields, as well as for functional verification of the electronic systems on site. In the longer term, the basic design of the magnetic field generator may be developed as the generator to provide the damped sinusoid magnetic field specified in IEC 61000-4-10, which is adopted in BS EN 61000-4-10.

  19. The Generation of Magnetic Fields Through Driven Turbulence

    CERN Document Server

    Cho, J; Cho, Jungyeon; Vishniac, Ethan T.

    2000-01-01

    We have tested the ability of driven turbulence to generate magnetic field structure from a weak uniform field using three dimensional numerical simulations of incompressible turbulence. We used a pseudo-spectral code with a numerical resolution of up to $144^3$ collocation points. We find that the magnetic fields are amplified through field line stretching at a rate proportional to the difference between the velocity and the magnetic field strength times a constant. Equipartition between the kinetic and magnetic energy densities occurs at a scale somewhat smaller than the kinetic energy peak. Above the equipartition scale the velocity structure is, as expected, nearly isotropic. The magnetic field structure at these scales is uncertain, but the field correlation function is very weak. At the equipartition scale the magnetic fields show only a moderate degree of anisotropy, so that the typical radius of curvature of field lines is comparable to the typical perpendicular scale for field reversal. In other word...

  20. Magnetic Helicity Generation from the Cosmic Axion Field

    OpenAIRE

    Campanelli, L.; Giannotti, M.

    2005-01-01

    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...

  1. Effects of non-linearities on magnetic field generation

    CERN Document Server

    Nalson, Ellie; Malik, Karim A

    2013-01-01

    Magnetic fields are present on all scales in the Universe. While we understand the processes which amplify the fields fairly well, we do not have a "natural" mechanism to generate the small initial seed fields. By using fully relativistic cosmological perturbation theory and going beyond the usual confines of linear theory we show analytically how magnetic fields are generated. This is the first analytical calculation of the magnetic field at second order, using gauge-invariant cosmological perturbation theory, and including all the source terms. To this end, we have rederived the full set of governing equations independently. Our results indicate that magnetic fields of the order of $10^{-29}$ G can be generated. This is largely in agreement with previous results that relied upon numerical calculations. These fields are likely too small to act as the primordial seed fields for dynamo mechanisms.

  2. RESISTIVE MAGNETIC FIELD GENERATION AT COSMIC DAWN

    OpenAIRE

    Francesco Miniati; Bell, A. R.

    2011-01-01

    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...

  3. Observation of a Turbulence-Generated Large Scale Magnetic Field

    CERN Document Server

    Spence, E J; Kendrick, R D; Nornberg, M D

    2006-01-01

    A uniform magnetic field is applied to a spherical, turbulent flow of liquid sodium. An induced magnetic dipole moment is measured which cannot be generated by the interaction of the axisymmetric mean flow with the applied field, indicating the presence of a turbulent electromotive force. It is shown that the induced dipole moment should vanish for any axisymmetric laminar flow. Also observed is the production of toroidal magnetic field from applied poloidal magnetic field (the omega-effect). Its potential role in the production of the induced dipole is discussed.

  4. Simulation of surface field THz generation in a magnetic field

    OpenAIRE

    Johnston, MB; Corchia, A; R.; McLaughlin; Davies, AG; Linfield, EH; Ritchie, DA; Whittaker, DM; Arnone, DD; Pepper, M.

    2001-01-01

    THz emission from InAs and GaAs surfaces was analyzed under magnetic field. The surfaces were excited with 1 nJ pulses of 1.57 eV photons from a mode-locked Ti:Sapphire laser. Magnetic field enhancement of terahertz (THz) power was attributed to additional charge acceleration under Lorentz force. Simulation data showed that the magnetic field dependance of saturation of emitted THz power was due to carrier-carrier scattering and the screening of internal electric fields.

  5. Magnetic field generated by shielding current in high Tc superconducting coils for NMR magnets

    International Nuclear Information System (INIS)

    Numerical electromagnetic field analyses of high Tc superconducting tape in coils were carried out to calculate the magnetic field generated by the shielding (magnetization) current in superconducting tape. The numerical model employs the power law electric field-current density characteristic and the thin strip approximation, in which the current component normal to the wide face of the tape is neglected. The shielding (magnetization) currents lead to non-uniform current distributions in the superconducting tape in the coils. The magnetic field generated by the shielding (magnetization) current can deteriorate the field quality and could be a concern in insert coils for NMR magnets using high Tc superconducting tape

  6. Theory of magnetic field generation by relativistically strong laser radiation

    International Nuclear Information System (INIS)

    We consider the interaction of subpicosecond relativistically strong short laser pulses with an underdense cold unmagnetized electron plasma. It is shown that the strong plasma inhomogeneity caused by laser pulses results in the generation of a low frequency (quasistatic) magnetic field. Since the electron density distribution is determined completely by the pump wave intensity, the generated magnetic field is negligibly small for nonrelativistic laser pulses but increases rapidly in the ultrarelativistic case. Due to the possibility of electron cavitation (complete expulsion of electrons from the central region) for narrow and intense beams, the increase in the generated magnetic field slows down as the beam intensity is increased. The structure of the magnetic field closely resembles that of the field produced by a solenoid; the field is maximum and uniform in the cavitation region, then it falls, changes polarity and vanishes. In extremely dense plasmas, highly intense laser pulses in the self-channeling regime can generate magnetic fields ?100 MG and greater. copyright 1997 The American Physical Society

  7. Megagauss magnetic field generation on Proto-II

    International Nuclear Information System (INIS)

    Results are reported for an experiment in which a peak current of 7.5 MA from the Proto-II accelerator was discharged through a small brass cylinder of 2 mm diameter, generating approximately 15 MG magnetic fields. These results are compared with those of a one-dimensional calculation of this system which suggest that at peak current the magnetic field has compressed the brass inner conductor to about 90% of its initial radius

  8. Wiggler magnetic field assisted second harmonic generation in clusters

    Science.gov (United States)

    Aggarwal, Munish; Vij, Shivani; Kant, Niti

    2015-06-01

    Wiggler magnetic field assisted second harmonic generation in clusters has been investigated theoretically. An intense short-pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls. For clusters with radius less than one tenth of the laser wavelength, the nonlinear restoration force dominates, which leads to second harmonic generation. The magnetic wiggler provides the uncompensated momentum to second harmonic photon, to make the process of harmonic generation resonant. We explore the impact of laser intensity and cluster size on the efficiency of second harmonic generation. Pulse slippage of second harmonic pulse out of the domain of fundamental laser pulse has been observed on account of group velocity mismatch between the fundamental and second harmonic pulse. Enhancement in the efficiency of the second harmonic is seen for the optimum values of wiggler magnetic field.

  9. The magnetic field gradients generation for magnetic resonance tomography; Generacja gradientow pola magnetyczbego dla tomografii MR

    Energy Technology Data Exchange (ETDEWEB)

    Jasinski, A.; Skorka, T.; Kwiecinski, S. [Institute of Nuclear Physics, Cracow (Poland)

    1994-12-31

    To obtain three-dimensional images in the computerized tomography a gradient of magnetic field should be generated. In this paper the analytical as well as computerized calculations of magnetic coils for such purposes are presented. 4 refs, 8 figs.

  10. Resistive Magnetic Field Generation at the Break of Cosmic Dawn

    CERN Document Server

    Miniati, Francesco

    2010-01-01

    A scenario is proposed in which the magnetization of cosmic space is caused by relativistic charged particles (CR for cosmic-rays) produced by Supernova explosion of the first generation of massive stars that are also responsible for the re-ionization of the Universe. Streaming of such particles through the hitherto non-magnetized intergalactic space induces return currents and, hence, electric fields in the cosmic plasma. Owing to resistivity inhomogeneities caused by temperature structure in the cosmic plasma, the electric fields possess a rotational component which sustains Faraday's induction. Magnetic fields thus grow at rate of 10^{-18}-10^{-16} Gauss/Gyr, depending on distance from the CR sources, until the temperature of the intergalactic medium is raised by cosmic reionization. After that the unstable interaction of the magnetic field with the CR currents may produce further amplification by orders of magnitude. Matter accreting onto cosmic structures such as galaxies and clusters of galaxies should ...

  11. Cosmological magnetic fields: their generation, evolution and observation

    Science.gov (United States)

    Durrer, Ruth; Neronov, Andrii

    2013-06-01

    We review the possible mechanisms for the generation of cosmological magnetic fields, discuss their evolution in an expanding Universe filled with the cosmic plasma and provide a critical review of the literature on the subject. We put special emphasis on the prospects for observational tests of the proposed cosmological magnetogenesis scenarios using radio and gamma-ray astronomy and ultra-high-energy cosmic rays. We argue that primordial magnetic fields are observationally testable. They lead to magnetic fields in the intergalactic medium with magnetic field strength and correlation length in a well defined range. We also state the unsolved questions in this fascinating open problem of cosmology and propose future observations to address them.

  12. Relativistic Scott correction in self-generated magnetic fields.

    DEFF Research Database (Denmark)

    Erdos, Laszlo; Fournais, SØren

    2012-01-01

    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.

  13. Relativistic Shocks: Particle Acceleration, Magnetic Field Generation, and Emission

    Science.gov (United States)

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

    2005-02-01

    Shock acceleration is an 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 with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. 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 non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock at the same simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale (mainly transverse) magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation of ``jitter'' radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a uniform magnetic field. 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 and other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

  14. Laser-generated magnetic fields in quasi-hohlraum geometries

    Science.gov (United States)

    Pollock, Bradley; Turnbull, David; Ross, Steven; Hazi, Andrew; Ralph, Joseph; Lepape, Sebastian; Froula, Dustin; Haberberger, Dan; Moody, John

    2014-10-01

    Laser-generated magnetic fields of 10--40 T have been produced with 100--4000 J laser drives at Omega EP and Titan. The fields are generated using the technique described by Daido et al. [Phys. Rev. Lett. 56, 846 (1986)], which works by directing a laser through a hole in one plate to strike a second plate. Hot electrons generated in the laser-produced plasma on the second plate collect on the first plate. A strap connects the two plates allowing a current of 10 s of kA to flow and generate a solenoidal magnetic field. The magnetic field is characterized using Faraday rotation, b-dot probes, and proton radiography. Further experiments to study the effect of the magnetic field on hohlraum performance are currently scheduled for Omega. This work was performed under the auspices of the United States Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA-27344.

  15. Generation of long scale magnetic field from rippled surface irregularity

    International Nuclear Information System (INIS)

    A mechanism of long scale magnetic field generation from rippled surface irregularity is given and compared with thermoelectric effect. Criteria are given for the former dominating over the latter. These criteria are accessible in the present day experiments. An experiment is done to show an implication of the above mechanism. (author)

  16. Second order semiclassics with self-generated magnetic fields

    DEFF Research Database (Denmark)

    Erdös, Laszlo; Fournais, SØren

    2012-01-01

    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.

  17. Generation of magnetic fields in Einstein-Aether gravity

    CERN Document Server

    Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi

    2013-01-01

    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...

  18. Entropy Generation in Natural Convection Under an Evanescent Magnetic Field

    International Nuclear Information System (INIS)

    We numerically study the effect of an externally-evanescent magnetic field on total entropy generation in conducting and non-reactive fluid enclosed in a square cavity. The horizontal walls of the enclosure are assumed to be insulated while the vertical walls are kept isothermal. A control volume finite element method is used to solve the conservation equations at Prandtl number of 0.71. The values of relaxation time of the magnetic field are chosen, so that the Lorentz force acts only in the transient state of entropy generation in natural convection. The total entropy generation was calculated for fixed value of irreversibility distribution ratio, different relaxation time varying from 0 to 1/5 and Grashof number equal to 105

  19. 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

  20. Dark matter and generation of galactic magnetic fields

    CERN Document Server

    Berezhiani, Zurab; Tkachev, I I

    2013-01-01

    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 ...

  1. An investigation of electromagnetic rig-generated strong magnetic fields

    OpenAIRE

    Ekreem, Nasser B.

    2009-01-01

    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...

  2. A 7 T Pulsed Magnetic Field Generator for Magnetized Laser Plasma Experiments

    International Nuclear Information System (INIS)

    A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (?230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field. (inertially confined plasma)

  3. Particle acceleration, magnetic field generation, and emission in relativistic shocks

    Science.gov (United States)

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

    2006-01-01

    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 3D relativistic electromagnetic particle code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find small differences in the results for no ambient and modest ambient magnetic fields. 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 defected 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 ?-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

  4. A 3 T magnetic field generator using melt-processed bulk superconductors as trapped field magnets and its applications

    International Nuclear Information System (INIS)

    An intense magnetic field generator yielding 3.15 T in the open space between the magnetic poles has been constructed by using a pair of melt-processed bulk superconductors as trapped field magnets. The field was measured in a 2 mm gap between the magnetic poles set face-to-face after the pulsed-field magnetization 'IMRA' method. This field generator is composed of Sm-based 123 compounds, vacuum pumps, pulsed-field coils and GM refrigerators with compressors. The system can be used in various applications. We investigated, for instance, the application to a high gradient magnetic separation system. It was found that the alpha hematite fine particles mixed in the flowing water was completely removed by this technique which was operated in the field of 1.7 T in the gap of 20 mm

  5. On Generation of magnetic field in astrophysical bodies

    OpenAIRE

    Verma, Mahendra K.

    2001-01-01

    In this letter we compute energy transfer rates from velocity field to magnetic field in MHD turbulence using field-theoretic method. The striking result of our field theoretic calculation is that there is a large energy transfer rate from the large-scale velocity field to the large-scale magnetic field. We claim that the growth of large-scale magnetic energy is primarily due to this transfer. We reached the above conclusion without any linear approximation like that in $\\al...

  6. Modeling and Measurement of Ocean Generated Magnetic Fields

    Science.gov (United States)

    Liang, R.; Avera, W. E.; Nelson, J.; Brozena, J. M.

    2011-12-01

    Motion of conductive seawater through the earth's magnetic field will produce magnetic fields. Magnetic fields from motions such as ocean waves and swells are detectable near the ocean's surface but decay rapidly with distance. Non-linear internal waves (NLIWs) generated by mechanisms such as tides over bathymetric features have been predicted to produce magnetic anomalies of .1-1 nT at altitudes of ~ 100 m above the surface (Chave, 1986) due to the large volumes of coherently moving water. An experiment was performed in 2009 by the Defense Research and Development Canada (DRDC) and the US Naval Research Laboratory (NRL) to see if magnetic signatures predicted from oceanographic measurements could be detected by airborne and ocean bottom mounted magnetometers. The test was conducted near the shelf-break off the coast of New Jersey where NLIWs have been observed. Oceanographic measurements were collected by a set of bottom-mounted ADCPs, towed C-T sensors mounted on a "SCANFISH" tow-body, and a hull-mounted ADCP. Magnetic measurements consisted of total-field magnetometers co-located with the bottom mounted ADCPs, three magnetic base-stations (total field and vector) in New Jersey for geomagnetic noise cancellation, and magnetometers aboard two aircraft ( a Canadian National Research Council Convair 580 and the NRL P-3) flown simultaneously with a 20-30 second separation ( corresponding to 2-3 km) along a repeat track over the bottom-mounted sensors. The multiple aircraft and repeat tracks were intended to remove the spatially stationary geologic component. The time-varying geomagnetic signal was extrapolated from the magnetic base-stations to the aircraft measurements. Both aircraft had high quality magnetometers and magnetic-field compensation systems based on co-located vector magnetometers and kinematic GPS. The Convair had two magnetometer and compensation systems mounted in wing-pods with a base-line of ~ 32 m that allowed the calculation of a cross-track gradient. Total-field compensated and edited data from each aircraft and the magnetic base-station data were low-pass filtered and sub-sampled to 4Hz for analysis. Data from the magnetic base-stations exhibit good coherence, as do the data from the ocean-bottom magnetometers. After correction for the geomagnetic component, the two aircraft residuals matched quite closely in both amplitude and phase in many places, but in other places the phase match was poor. This produced an overall poor coherence between the two residuals. However, cross-spectral analysis showed that there was a statistical correlation between the two aircraft residuals in the frequency band 0.02-0.05 Hz (5000-2000 m wavelength for an aircraft flying at 100 m/s). Both the amplitude (0.1-0.2 nT) and wavelength were consistent with predictions computed from the 3-D water velocities and conductivity from the ADCP using a simple model. The predicted undersea magnetic fields correlated well with the measured undersea magnetometer fields at times, but they rarely matched at the "wiggle-for-wiggle" level. More often, it was the statistics that correlated well.

  7. 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

  8. Relativistic Shocks: Particle Acceleration and Magnetic Field Generation, and Emission

    CERN Document Server

    Nishikawa, K I; Richardson, G; Preece, R; Sol, H; Fishman, G J

    2005-01-01

    Shock acceleration is an 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 with and without initial magnetic fields. 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 non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock at the same simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. The simul...

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

    CERN Document Server

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

    2004-01-01

    Shock acceleration is an 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 with and without initial magnetic fields. 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 non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock at the same simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. While so...

  10. Dirac electron in graphene under supersymmetry generated magnetic fields

    International Nuclear Information System (INIS)

    We use supersymmetry transformations to obtain new one parameter families of inhomogeneous magnetic fields B= B-tilde (x,?) e-hat z for which the massless Dirac electron possesses exact solutions. The inhomogeneity appearing in B-tilde (x,?) can be controlled by the parameter ?. The obtained magnetic fields are interpreted as deformed variants of some physically attainable well known magnetic fields. A particular example, that of a constant magnetic field being deformed, is considered to show that equidistant Landau levels exist even in the presence of an infinite number of specially designed inhomogeneous magnetic fields. (paper)

  11. 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

  12. Glutathione production using magnetic fields generated by magnets

    Directory of Open Access Journals (Sweden)

    Lucielen Oliveira dos Santos

    2012-12-01

    Full Text Available The objective of this work was to study the production of GSH by Saccharomyces cerevisiae ATCC 7754 in a fermentor (5 L using a cell recycle system with magnets. The fermentation conditions were 20°C, 500 rpm, 5% (v/v of inoculum, pHinitial 5, 1.1 vvm aeration and total fermentation time of 72 h. The time of application of MF ranged from 24, 48 or 72 h. In comparison to the control experiment, the best results were obtained with 72 h of application of MF. The cell concentration reached 19.5 g/L and GSH concentration was 271.9 mg/L that corresponded to an increase of 2.63 and 32.1% compared to the control experiment, respectively.

  13. Glutathione production using magnetic fields generated by magnets

    Scientific Electronic Library Online (English)

    Lucielen Oliveira dos, Santos; Tatiane Araujo, Gonzales; Beatriz Torsani, Úbeda; Ranulfo Monte, Alegre.

    2012-12-01

    Full Text Available The objective of this work was to study the production of GSH by Saccharomyces cerevisiae ATCC 7754 in a fermentor (5 L) using a cell recycle system with magnets. The fermentation conditions were 20°C, 500 rpm, 5% (v/v) of inoculum, pHinitial 5, 1.1 vvm aeration and total fermentation time of 72 h. [...] The time of application of MF ranged from 24, 48 or 72 h. In comparison to the control experiment, the best results were obtained with 72 h of application of MF. The cell concentration reached 19.5 g/L and GSH concentration was 271.9 mg/L that corresponded to an increase of 2.63 and 32.1% compared to the control experiment, respectively.

  14. Dark matter and generation of galactic magnetic fields

    Science.gov (United States)

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

    2013-10-01

    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.

  15. Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets

    Science.gov (United States)

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

    2006-01-01

    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.

  16. 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.)

  17. Magnetic energy dissipation and mean magnetic field generation in planar convection-driven dynamos.

    Science.gov (United States)

    Tilgner, A

    2014-07-01

    A numerical study of dynamos in rotating convecting plane layers is presented which focuses on magnetic energies and dissipation rates and the generation of mean fields (where the mean is taken over horizontal planes). The scaling of the magnetic energy with the flux Rayleigh number is different from the scaling proposed in spherical shells, whereas the same dependence of the magnetic dissipation length on the magnetic Reynolds number is found for the two geometries. Dynamos both with and without mean field exist in rapidly rotating convecting plane layers. PMID:25122366

  18. Magnetic energy dissipation and mean magnetic field generation in planar convection driven dynamos

    CERN Document Server

    Tilgner, A

    2014-01-01

    A numerical study of dynamos in rotating convecting plane layers is presented which focuses on magnetic energies and dissipation rates, and the generation of mean fields (where the mean is taken over horizontal planes). The scaling of the magnetic energy with the flux Rayleigh number is different from the scaling proposed in spherical shells, whereas the same dependence of the magnetic dissipation length on the magnetic Reynolds number is found for the two geometries. Dynamos both with and without mean field exist in rapidly rotating convecting plane layers.

  19. Internal split field generator

    Science.gov (United States)

    Thundat; Thomas George (Knoxville, TN); Van Neste, Charles W. (Kingston, TN); Vass, Arpad Alexander (Oak Ridge, TN)

    2012-01-03

    A generator includes a coil of conductive material. A stationary magnetic field source applies a stationary magnetic field to the coil. An internal magnetic field source is disposed within a cavity of the coil to apply a moving magnetic field to the coil. The stationary magnetic field interacts with the moving magnetic field to generate an electrical energy in the coil.

  20. Methods of high current magnetic field generator for transcranial magnetic stimulation application

    Science.gov (United States)

    Bouda, N. R.; Pritchard, J.; Weber, R. J.; Mina, M.

    2015-05-01

    This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ±1200 A can be generated with inputs of +/-20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG1) and MOSFET circuits (HCMFG2) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed.

  1. Compactly composed strong magnetic field generators with cryo-cooled high temperature bulk superconductors as quasi-permanent magnets

    International Nuclear Information System (INIS)

    The authors have constructed various types of strong magnetic field generators using superconducting bulk magnets in conjunction with compact refrigerators. The magnetic field in the open space outside the vacuum chamber that contains a bulk magnet has been estimated as over 3 T when activated by the static fields of a 5 T superconducting solenoid magnet. The authors have tried to extend the variation of such strong field generators which are promised to develop in the future. In the study, a novel and compact bulk magnet system with use of a compact pulse tube cryocooler has recorded the maximum trapped field of 2.78 T on the magnetic pole surface. The characteristic feature of superconducting bulk magnet is defined as a compact and strong magnetic field generator. This implies that various kinds of equipments must be successively proposed even in the very early stage of industrialization of strong magnetic field generators

  2. The magnetic field generated by a rotating charged polygon

    International Nuclear Information System (INIS)

    The magnetic field along the symmetry axis of a regular polygon carrying a uniform electric charge on its edges is calculated systematically when the polygon is rotated about this axis of symmetry. A group of circular current-carrying coils arranged concentrically about the axis of the polygon has been designed to simulate the magnetic field characteristics of the rotating charged polygon. The magnetic field of the simulated coils is measured using the PASCO magnetic field sensor. The results show that the theoretical calculation agrees well with the experimental results. (paper)

  3. 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

  4. Generation of scale invariant magnetic fields in bouncing universes

    CERN Document Server

    Sriramkumar, L; Jain, Rajeev Kumar

    2015-01-01

    We consider the generation of primordial magnetic fields in a class of bouncing models when the electromagnetic action is coupled non-minimally to a scalar field that, say, drives the background evolution. For scale factors that have the power law form at very early times and non-minimal couplings which are simple powers of the scale factor, one can easily show that scale invariant spectra for the magnetic fields can arise {\\it before the bounce} for certain values of the indices involved. It will be interesting to examine if these power spectra retain their shape {\\it after the bounce}. However, analytical solutions for the Fourier modes of the electromagnetic vector potential across the bounce are difficult to obtain. In this work, with the help of a new time variable that we introduce, which we refer to as the ${\\rm e}$-${\\cal N}$-fold, we investigate these scenarios numerically. Imposing the initial conditions on the modes in the contracting phase, we numerically evolve the modes across the bounce and eva...

  5. Mass Generation in the Supersymmetric Nambu--Jona--Lasinio Model in an External Magnetic Field

    OpenAIRE

    Shovkovy, Igor A.

    1997-01-01

    The mass generation in the (3+1)-dimensional supersymmetric Nambu-Jona-Lasinio model in a constant magnetic field is studied. It is shown that the external magnetic field catalyzes chiral symmetry breaking.

  6. 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

  7. Consistent generation of magnetic fields in axion inflation models

    CERN Document Server

    Fujita, Tomohiro; Tada, Yuichiro; Takeda, Naoyuki; Tashiro, Hiroyuki

    2015-01-01

    There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton $\\phi$ through the characteristic term $\\phi F\\tilde F$, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. Th...

  8. Inflationary susceptibilities, duality and large-scale magnetic fields generation

    CERN Document Server

    Giovannini, Massimo

    2013-01-01

    We investigate what can be said about the interaction of scalar fields with Abelian gauge fields during a quasi-de Sitter phase of expansion and under the assumption that the electric and the magnetic susceptibilities do not coincide. The duality symmetry, transforming the magnetic susceptibility into the inverse of the electric susceptibility, exchanges the magnetic and electric power spectra. The mismatch between the two susceptibilities determines an effective refractive index affecting the evolution of the canonical fields. The constraints imposed by the duration of the inflationary phase and by the magnetogenesis requirements pin down the rate of variation of the susceptibilities that is consistent with the observations of the magnetic field strength over astrophysical and cosmological scales but avoids back-reaction problems. The parameter space of this magnetogenesis scenario is wider than in the case when the susceptibilities are equal, as it happens when the inflaton or some other spectator field is ...

  9. Magnetic flux concentrations from dynamo-generated fields

    CERN Document Server

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

    2014-01-01

    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 ...

  10. Dynamo-generated magnetic fields in fast rotating single giants

    CERN Document Server

    Konstantinova-Antova, Renada; Schröder, Klaus-Peter; Petit, Pascal

    2009-01-01

    Red giants offer a good opportunity to study the interplay of magnetic fields and stellar evolution. Using the spectro-polarimeter NARVAL of the Telescope Bernard Lyot (TBL), Pic du Midi, France and the LSD technique, we began a survey of magnetic fields in single G-K-M giants. Early results include 6 MF-detections with fast rotating giants, and for the first time a magnetic field was detected directly in an evolved M-giant: EK Boo. Our results could be explained in the terms of $\\alpha$--$\\omega$ dynamo operating in these giants.

  11. Magnetic separation technique for environmental water purification by strong magnetic field generator loading HTS bulk magnets

    International Nuclear Information System (INIS)

    The magnetic separation technique in combination with high temperature superconducting bulk magnets has been investigated to purify the ground water which has been used in the coolant system for the incinerator furnace to cool the burning gas. The experiment has been operated by means of the newly-built alternating channel type magnetic separating device. The separation ratios of ferromagnetic flocks including fine magnetite powder have been estimated by means of the high gradient magnetic separation method with small iron balls filled in the water channels. As the magnetic force acting on the magnetic particle is given by the product of a magnetization of the material and a gradient of magnetic field, and as the ferromagnetic stainless steel balls yield the steep gradient of magnetic field around them in a strong magnetic field, the system has exhibited a quite excellent performance with respect to the separation ratios. The separation ratios of the flocks which contain the magnetite powder with the values more than 50 ppm have remained over 80% for under the flow rates less than 5 L/min.

  12. Consistent generation of magnetic fields in axion inflation models

    Science.gov (United States)

    Fujita, Tomohiro; Namba, Ryo; Tada, Yuichiro; Takeda, Naoyuki; Tashiro, Hiroyuki

    2015-05-01

    There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton phi through the characteristic term phi tilde F F, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. The EM field is subsequently amplified by parametric resonance during the period of inflaton oscillation. Once the thermal plasma is formed (reheating), the produced helical magnetic fields undergo a turbulent process called inverse cascade, which shifts their peak correlation scales from smaller to larger scales. We consistently take all these effects into account within the regime where the perturbation of phi is negligible and obtain Beff ~ 10?19 G, indicating the necessity of additional mechanisms to accommodate the observations.

  13. Particle Acceleration, Magnetic Field Generation in Relativistic Shocks

    Science.gov (United States)

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

    2005-01-01

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

  14. Sixth generation lithospheric magnetic field model, MF6, from CHAMP satellite magnetic measurements

    Science.gov (United States)

    Maus, S.; Fan, Y.; Manoj, C.; Rother, M.; Rauberg, J.; Stolle, C.; Luhr, H.

    2007-12-01

    The CHAMP satellite continues to provide highly accurate magnetic field measurements with decreasing orbital altitudes (Overhauser magnetometer data. While the low-noise Fluxgate measurements are used in the short-period range (Overhauser for the longer periods. The new data set is used for generating an improved lithospheric magnetic field model (MF6). Although MF6 is still in production at the time of writing this abstract, we anticipate significant benefits in terms of resolving small- scale low-amplitude crustal features from the new data. Further improvements include a new correction for steady ocean circulation and an expansion to higher spherical harmonic degrees of the model.

  15. Geometrical generation of cosmic magnetic fields within standard electromagnetism

    Scientific Electronic Library Online (English)

    Christos G., Tsagas; Alejandra, Kandus.

    1070-10-01

    Full Text Available 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.

  16. Magnetic field generation in Rayleigh-Taylor unstable inertial confinement fusion plasmas.

    Science.gov (United States)

    Srinivasan, Bhuvana; Dimonte, Guy; Tang, Xian-Zhu

    2012-04-20

    Rayleigh-Taylor instabilities (RTI) in inertial confinement fusion implosions are expected to generate magnetic fields. A Hall-MHD model is used to study the field generation by 2D single-mode and multimode RTI in a stratified two-fluid plasma. Self-generated magnetic fields are predicted and these fields grow as the RTI progresses via the ?n(e)×?T(e) term in the generalized Ohm's law. Scaling studies are performed to determine the growth of the self-generated magnetic field as a function of density, acceleration, Atwood number, and perturbation wavelength. PMID:22680725

  17. Effect of plasma density profile inhomogeneity on the self-generated magnetic field

    Science.gov (United States)

    Vaziri (Khamedi, M.; Sohaily; Bahrampour, A. R.

    2014-11-01

    The photon orbital and/or spin angular-momentum absorption in absorbing plasma medium causes the circular motion of electrons and generate the azimuthal component of current density. The axial magnetic field generation due to the azimuthal component of generated current density is known as inverse Faraday effect. In this paper, the axial magnetic field generation in an absorbing plasma with ramped density by the propagation of linear polarized Laguerre-Gaussian beam is taken into consideration. It is shown that the positive slope of the initial electron density causes a considerable enhancement of self-generated axial magnetic field. The magnetic field enhancement depends on the twisted light vortex charge number. The rotation angle of the linearly polarized light which can be employed for measurement of the generated magnetic field, is calculated.

  18. On the theory of magnetic field generation by relativistically strong laser radiation

    International Nuclear Information System (INIS)

    The authors consider the interaction of subpicosecond relativistically strong short laser pulses with an underdense cold unmagnetized electron plasma. It is shown that the strong plasma inhomogeneity caused by laser pulses results in the generation of a low frequency (quasistatic) magnetic field. Since the electron density distribution is determined completely by the pump wave intensity, the generated magnetic field is negligibly small for nonrelativistic laser pulses but increases rapidly in the ultrarelativistic case. Due to the possibility of electron cavitation (complete expulsion of electrons from the central region) for narrow and intense beams, the increase in the generated magnetic field slows down as the beam intensity is increased. The structure of the magnetic field closely resembles that of the field produced by a solenoid; the field is maximum and uniform in the cavitation region, then it falls, changes polarity and vanishes. In extremely dense plasmas, highly intense laser pulses in the self-channeling regime can generate magnetic fields ? 100 Mg and greater

  19. Self-generation mechanisms of intense magnetic fields in laser produced plasmas on solid targets

    International Nuclear Information System (INIS)

    Mechanisms of magnetic field self-generation in laser produced plasma are presented. Magnetic field generation due to the thermoelectric sources (Vnsub(e) x VTsub(e)), resonance absorption, ponderomotive forces, some kind of instabilities (modulational, Weibel, Rayleigh-Taylor instabilities) is considered. Estimates or scaling laws for parameters typical for current experiments are given. (author)

  20. A simple mechanism for the generation of Earth's magnetic field

    OpenAIRE

    Styazhkin, Oleg. V.

    2011-01-01

    Based on the ideal gas model, the dielectric polarization of mantle is achieved, the physical-mathematical model is constructed and the estimate calculation of a dipole of Earth's magnetic field with the considering of rotation, parameters of density and temperature, potential of ionization and static dielectric constant (relative dielectric permittivity), chemical compound of substance in Earth's mantle is executed.

  1. Ultra-High Intensity Magnetic Field Generation in Dense Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Fisch, Nathaniel J

    2014-01-08

    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.

  2. Study of second-generation high-temperature superconducting magnets: the self-field screening effect

    Science.gov (United States)

    Zhang, Min; Yuan, Weijia; Hilton, David K.; Dalban Canassy, Matthieu; Trociewitz, Ulf P.

    2014-09-01

    Second-generation high-temperature superconductors (2G HTS) have high current density in very high magnetic fields. They are good candidates for high field magnets, especially when the magnetic field exceeds the critical fields of low-temperature superconductors. However, the thin and flat geometry of these conductors allows persistent screening currents (or shielding currents) to flow in the conductors. The screening currents caused by the ramping of applied current to the coil is identified as the self-field screening effect. The screening-current-induced magnetic field changes the magnetic field distribution of the magnet, and it also generates drift. This paper employs both experimental and numerical methods to study the mechanism of self-field screening currents for 2G HTS magnets. A 2G HTS magnet was constructed and tested, and a finite element model was built based on the magnet. The comparison between calculation and measurement is presented with detailed analysis. Current distributions inside the HTS magnet are calculated to illustrate the effects of screening. The screening-current-induced magnetic field is quantified by comparing the magnetic field distribution with a baseline copper model. The model is also used to explain the mechanism of the current sweep strategy, which can be used to effectively eliminate screening currents.

  3. Nature of Planetary Matter and Magnetic Field Generation in the Solar System

    OpenAIRE

    Herndon, J. Marvin

    2009-01-01

    Understanding the nature of the matter comprising the Solar System is crucial for understanding the mechanism that generates the Earth's geomagnetic field and the magnetic fields of other planets and satellites. The commonality in the Solar System of matter like that of the inside of the Earth, together with common nuclear reactor operating conditions,forms the basis for generalizing the author's concept of nuclear geomagnetic field generation to planetary magnetic field gen...

  4. Quantum rings in magnetic fields and spin current generation

    International Nuclear Information System (INIS)

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

  5. Lightning remagnetization of the Vredefort impact crater: No evidence for impact-generated magnetic fields

    OpenAIRE

    Carporzen, Laurent; Weiss, Benjamin P.; Gilder, Stuart A.; Pommier, Anne; Hart, Rodger J.

    2011-01-01

    The Vredefort impact crater in South Africa is one of the oldest and largest craters on Earth, making it a unique analog for planetary basins. Intense and randomly oriented remanent magnetization observed in surface samples at Vredefort has been attributed to impact-generated magnetic fields. This possibility has major implications for extraterrestrial paleomagnetism since impact-generated fields have been proposed as a key alternative to the dynamo hypothesis for magnetization on the Moon an...

  6. Magnetic field generation and amplification in an expanding plasma

    CERN Document Server

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

    2013-01-01

    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).

  7. Spin polarized current generation from quantum dots without magnetic fields

    OpenAIRE

    Halperin, Bertrand; Krich, Jacob

    2008-01-01

    An unpolarized charge current passing through a chaotic quantum dot with spin-orbit coupling can produce a spin polarized exit current without magnetic fields or ferromagnets. We use random matrix theory to estimate the typical spin polarization as a function of the number of channels in each lead in the limit of large spin-orbit coupling. We find rms spin polarizations up to 45% with one input channel and two output channels. Finite temperature and dephasing both suppress t...

  8. External split field generator

    Science.gov (United States)

    Thundat, Thomas George (Knoxville, TN); Van Neste, Charles W. (Kingston, TN); Vass, Arpad Alexander (Oak Ridge, TN)

    2012-02-21

    A generator includes a coil disposed about a core. A first stationary magnetic field source may be disposed on a first end portion of the core and a second stationary magnetic field source may be disposed on a second end portion of core. The first and second stationary magnetic field sources apply a stationary magnetic field to the coil. An external magnetic field source may be disposed outside the coil to apply a moving magnetic field to the coil. Electrical energy is generated in response to an interaction between the coil, the moving magnetic field, and the stationary magnetic field.

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

    CERN Document Server

    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

    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...

  10. Computational study of strong magnetic field generation in a nonspherical, cone-guided implosion

    International Nuclear Information System (INIS)

    It is known that a strong magnetic field is generated in laser plasma, especially during an asymmetric implosion such as in a cone-guided implosion used for fast ignition of nuclear fusion. As the first approximation, in this paper, the magnetic field for a nonspherical, cone-guided implosion is simulated using temporal evolution equations of the magnetic field coupled with the simulated result of a two-dimensional radiation hydrodynamic simulation for fast ignition. The results show that the magnetic field is generated by the ?Te × ?ne term, and is compressed by the implosion. In addition, we find that the magnetic field reaches 5 MG at maximum compression, which has not been investigated previously. Also, a high Hall parameter region appears between the cone tip and core plasma. This magnetic field is strong enough to affect the implosion dynamics and the hot electron transport, and should therefore be considered in simulations for fast ignition. (paper)

  11. Generation of magnetic fields by large-scale vortices in rotating convection.

    Science.gov (United States)

    Guervilly, Céline; Hughes, David W; Jones, Chris A

    2015-04-01

    We propose a self-consistent dynamo mechanism for the generation of large-scale magnetic fields in natural objects. Recent computational studies have described the formation of large-scale vortices in rotating turbulent convection. Here we demonstrate that for magnetic Reynolds numbers below the threshold for small-scale dynamo action, such turbulent flows can sustain large-scale magnetic fields, i.e., fields with a significant component on the scale of the system. PMID:25974429

  12. Generation of magnetic fields by large-scale vortices in rotating convection

    CERN Document Server

    Guervilly, Celine; Jones, Chris A

    2015-01-01

    We propose a new self-consistent dynamo mechanism for the generation of large-scale magnetic fields in natural objects. Recent computational studies have described the formation of large-scale vortices (LSVs) in rotating turbulent convection. Here we demonstrate that for magnetic Reynolds numbers below the threshold for small-scale dynamo action, such turbulent flows can sustain large-scale magnetic fields --- i.e. fields with a significant component on the scale of the system.

  13. Generation of magnetic fields by large-scale vortices in rotating convection

    Science.gov (United States)

    Guervilly, Céline; Hughes, David W.; Jones, Chris A.

    2015-04-01

    We propose a self-consistent dynamo mechanism for the generation of large-scale magnetic fields in natural objects. Recent computational studies have described the formation of large-scale vortices in rotating turbulent convection. Here we demonstrate that for magnetic Reynolds numbers below the threshold for small-scale dynamo action, such turbulent flows can sustain large-scale magnetic fields, i.e., fields with a significant component on the scale of the system.

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

    OpenAIRE

    Yuan, Kai-Jun; Bandrauk, Andre D.

    2013-01-01

    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...

  15. Generation of magnetic field on the accretion disk around a proto-first-star

    International Nuclear Information System (INIS)

    The generation process of a magnetic field around a proto-first-star is studied. Utilizing the recent numerical results of proto-first-star formation based on radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that a magnetic field of ?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 an 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 is ?10–14-10–13 G at n H = 103 cm–3, which could play an important role in the next generation star formation, as well as the seeds of the magnetic field in the present-day universe.

  16. Generation of large-scale magnetic fields by small-scale dynamo in shear flows

    CERN Document Server

    Squire, Jonathan

    2015-01-01

    We propose a new mechanism for turbulent mean-field dynamo in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the "shear-current" effect. Given the inevitable existence of non-helical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help to explain generation of large-scale magnetic fields across a wide range of astrophysical objects.

  17. Spatiotemporal structure of magnetic field and convection vortices generated in a rotating spherical shell

    International Nuclear Information System (INIS)

    Intensification mechanisms of magnetic field by thermal convection in a rotating spherical shell are investigated by the direct numerical simulation analysis of the MHD Boussinesq equation. It is found that an axial magnetic dipole field whose energy is 15 times as large as kinetic energy is generated. Anticyclonic vortices play a key role in sustaining the structure. (author)

  18. Generation of quasi static magnetic field in the relativisitic laser-plasma interactions

    OpenAIRE

    Kato, Susumu; Nakamura, Tatsufumi; Mima, Kunioki; Sentoku, Yasuhiko; Nagatomo, Hideo; Owadano, Yoshiro

    2004-01-01

    The magnetic field generation by a relativistic laser light irradiated on a thin target at the oblique incidence is investigated using a two dimensional particle-in-cell simulation. The surface magnetic field inhibits the electron transport towards the inside plasma, when an incident angle exceeds the critical angle, which depends on the laser and plasma parameters.

  19. The study of turbulence in MHD flow generated by rotating and traveling magnetic fields

    Science.gov (United States)

    Kolesnichenko, Ilya; Pavlinov, Alexander; Golbraikh, Ephim; Frick, Peter; Kapusta, Arkadii; Mikhailovich, Boris

    2015-05-01

    We consider a problem of spectral analysis of signals from electromagnetic sensors operating in a turbulent MHD flow generated by rotating and traveling magnetic fields, which create a strong electromagnetic noise. Using a wavelet-based technique for cross-correlation signal analysis and filtration, we show that at frequencies lower than the frequency of the applied magnetic field, the spectral properties of the velocity field can be clearly seen in spite of the fact that the measured fields are much weaker than the driving rotating (or traveling) magnetic field. On the basis of the proposed method, spectra of turbulent velocity fields, measured in the experiment, were studied.

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

    Science.gov (United States)

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

    2006-01-01

    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.

  1. Generation of Large-Scale Magnetic Fields in Single-Field Inflation

    CERN Document Server

    Martin, Jerome

    2007-01-01

    We consider the generation of large-scale magnetic fields in slow-roll inflation. The inflaton field is described in a supergravity framework where the conformal invariance of the electromagnetic field is generically and naturally broken. For each class of inflationary scenarios, we determine the functional dependence of the gauge coupling that is consistent with the observations on the magnetic field strength at various astrophysical scales and, at the same time, avoid a back-reaction problem. Then, we study whether the required coupling functions can naturally emerge in well-motivated, possibly string-inspired, models. We argue that this is non trivial and can be realized only for a restricted class of scenarios. This includes power-law inflation where the inflaton field is interpreted as a modulus. However, this scenario seems to be consistent only if the energy scale of inflation is low and the reheating stage prolonged. Another reasonable possibility appears to be small field models since no back-reactio...

  2. Nonlinear wave generation by laser plasma interaction in an oscillating inhomogeneous magnetic field

    International Nuclear Information System (INIS)

    The nonlinear generation of waves at combined frequencies in a thin inhomogeneous plasma layer due to interaction of waves of similar polarization (either S- or P- polarized) is analyzed. The effect of an external inhomogeneous magnetic field, oscillates at high frequency is considered (Hext = ez H (x) exp )-i wm t). wm is equal to the frequency of interacting waves or their sum. Oscillation of the magnetic field and type of polarization are found to affect, strongly, the wave generation

  3. Dynamical mass generation in QED with magnetic fields: Arbitrary field strength and coupling constant

    International Nuclear Information System (INIS)

    We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics, in the presence of magnetics fields of arbitrary strength, by solving the Schwinger-Dyson equation for the fermion self-energy in the rainbow approximation. We employ the Ritus eigenfunction formalism which provides a neat solution to the technical problem of summing over all Landau levels. It is well known that magnetic fields catalyze the generation of fermion mass m for arbitrarily small values of electromagnetic coupling ?. For intense fields it is also well known that m??(eB). Our approach allows us to span all regimes of parameters ? and eB. We find that m??(eB) provided ? is small. However, when ? increases beyond the critical value ?c which marks the onslaught of dynamical fermion masses in vacuum, we find m??, the cutoff required to regularize the ultraviolet divergences. Our method permits us to verify the results available in literature for the limiting cases of eB and ?. We also point out the relevance of our work for possible physical applications.

  4. Hall effects on the generation of field-aligned currents in three-dimensional magnetic reconnection

    Science.gov (United States)

    Ma, Z. W.; Lee, L. C.

    2001-11-01

    A three-dimensional Hall MHD simulation is carried out to study the Hall effects on the generation of field-aligned currents (FAC) and Alfvén waves by magnetic reconnection. The magnetic field is initially set up with an antiparallel component (Bz) with respect to the plane x=0. The initial current flows in the y direction. Several interesting features emerge owing to the inclusion of the Hall term in the MHD equation. In Hall MHD, the magnetic field lines are frozen in the electron fluid, but not in the ion fluid. In the presence of a Hall term, a strong electron velocity in the -y direction is usually present in the region with a high current density J in the y direction. As a result, the reconnected magnetic field lines are bent and also shifted in the -y direction. Generated FACs break the dawn-dusk symmetry, and the region of generated FACs tends to shift to the side with y1.

  5. Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection

    Directory of Open Access Journals (Sweden)

    Atef El Jery

    2010-05-01

    Full Text Available The influence of an external oriented magnetic field on entropy generation in natural convection for air and liquid gallium is numerically studied in steady-unsteady states by solving the mass, the momentum and the energy conservation equations. Entropy generation depends on five parameters which are: the Prandtl number, the irreversibility coefficients, the inclination angle of the magnetic field, the thermal Grashof and the Hartmann numbers. Effects of these parameters on total and local irreversibilities as well as on heat transfer and fluid flow are studied. It was found that the magnetic field tends to decrease the convection currents, the heat transfer and entropy generation inside the enclosure. Influence of inclination angle of the magnetic field on local irreversibility is then studied.

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

    CERN Document Server

    Veysi, Mehdi; Capolino, Filippo

    2014-01-01

    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...

  7. Evolution of the magnetic field generated by the Kelvin-Helmholtz instability

    Energy Technology Data Exchange (ETDEWEB)

    Modestov, M. [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Bychkov, V.; Brodin, G. [Department of Physics, Umeå University, SE-901 87 Umeå (Sweden); Marklund, M. [Department of Physics, Umeå University, SE-901 87 Umeå (Sweden); Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg (Sweden); Brandenburg, A. [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Department of Astronomy, Stockholm University, SE-10691 Stockholm (Sweden)

    2014-07-15

    The Kelvin-Helmholtz instability in an ionized plasma is studied with a focus on the magnetic field generation via the Biermann battery (baroclinic) mechanism. The problem is solved by using direct numerical simulations of two counter-directed flows in 2D geometry. The simulations demonstrate the formation of eddies and their further interaction and merging resulting in a large single vortex. In contrast to general belief, it is found that the instability generated magnetic field may exhibit significantly different structures from the vorticity field, despite the mathematically identical equations controlling the magnetic field and vorticity evolution. At later stages of the nonlinear instability development, the magnetic field may keep growing even after the hydrodynamic vortex strength has reached its maximum and started decaying due to dissipation.

  8. Magnetic field amplification and generation in hypervelocity meteoroid impacts with application to lunar paleomagnetism

    Science.gov (United States)

    Hood, L. L.; Vickery, A.

    1984-01-01

    A one-dimensional numerical model for the expansion of impact-produced vapor clouds is used to investigate magnetic field generation mechanisms in events such as meteor collisions with the moon. The resulting cloud properties, such as ionization fraction, electrical conductivity, radial expansion velocity, mass density, and energy density are estimated. The model is initiated with the peak shock states and pressure thresholds for incipient and complete vaporization of anorthosite lunar surface materials by iron and GA composition meteorites. The expansion of the spherical gas cloud into a vacuum was traced with a one-dimensional explicit lagrangian hydrodynamic code. The hypervelocity impact plasmas produced are found to be significant in the amplitudes and orientations of the magnetic fields generated. An ambient magnetic field could have been provided by the core dynamo, which would have interacted with the expanding plasmas and formed induced paleomagnetic fields. Several other field-contribution mechanisms are discussed and discarded as potential remanent magnetism contributors.

  9. Magnetic field amplification and generation in hypervelocity meteoroid impacts with application to lunar paleomagnetism

    International Nuclear Information System (INIS)

    A one-dimensional numerical model for the expansion of impact-produced vapor clouds is used to investigate magnetic field generation mechanisms in events such as meteor collisions with the moon. The resulting cloud properties, such as ionization fraction, electrical conductivity, radial expansion velocity, mass density, and energy density are estimated. The model is initiated with the peak shock states and pressure thresholds for incipient and complete vaporization of anorthosite lunar surface materials by iron and GA composition meteorites. The expansion of the spherical gas cloud into a vacuum was traced with a one-dimensional explicit lagrangian hydrodynamic code. The hypervelocity impact plasmas produced are found to be significant in the amplitudes and orientations of the magnetic fields generated. An ambient magnetic field could have been provided by the core dynamo, which would have interacted with the expanding plasmas and formed induced paleomagnetic fields. Several other field-contribution mechanisms are discussed and discarded as potential remanent magnetism contributors

  10. Magnetic field generation by non-Gaussian, non-random turbulent motion

    Science.gov (United States)

    Sanchez, Raul; Newman, David E.

    2013-10-01

    It is well known that a turbulent velocity field generates perturbations of the electric current and magnetic field that, under certain conditions, may generate an average,large-scale magnetic field. Such generation process is of great importance to account for the generation of large-scale magnetic fields in stars, planetary and laboratory plasmas. Traditionally, one attacks this generation process theoretically by assuming a random velocity field with near-Gaussian fluctuations. This simplifying ansatz allows to express the effective electromotive force appearing in Faraday's law in terms of a piece that is proportional to the large-scale magnetic field itself (the so-called ?-term), and a second one that is proportional to its curl (the ? term), if certain conditions regarding the symmetry of the system are met. Physically, the ?-term represents a measure of the mean helicity of the turbulent flow. The ?-term, an enhanced magnetic diffusivity. In this contribution, we depart form this traditional view and explore instead the consequences of considering Levy-distributed, Lagrangianly-correlated velocity fields, that have been currently identified as of relevance in regimes of near-marginal turbulence or in the presence of strong, stable sheared flows.

  11. 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.

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

    Science.gov (United States)

    Sheikh Amiri, M.; Szielasko, K.; Altpeter, I.; Boller, C.; Fischer, D.; Hahn, J.

    2012-02-01

    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.

  13. Uniformity design of magnetic field of magnetostrictive actuators generated by permanent magnet bias

    Science.gov (United States)

    Guan, Xin chun; Guo, Pengfei; Ou, Jin ping

    2007-07-01

    Due to possessing virtue of simple structure, small volume, fast response and good controllability, the actuator made with Terfenol-D exhibits widely potential application in the field of vibration control, precision machine and instrument, micro-driven and sonar system. One key technology for designing above devices is gain efficient and uniform bias magnetic field. In this paper, using software of ANSYS, the distribution character of magnetic field of magnetostrictive actuator was analyzed; methods to improve uniformity of magnetic field were also discussed.

  14. Magnetic field-generating device with quenching protection for superconductive coil, and quenching protection coils

    International Nuclear Information System (INIS)

    In a magnetic field-generation device having a plurality of magnetically coupled superconductive coils, superconductive coils are disposed so as to magnetically coupled with other superconductive coils more tightly. Electric current is commutated to a system which rapidly attenuates current flowing in quenched superconductive coils. When quenching is occurred in the superconductive coils, electric current flowing to the superconductive coils is commutated to the ordinary conductive coils, and the commutated current is attenuated by a current attenuating means connected in series with the ordinary conductive coils. In addition, at the same time with the occurrence of the quenching, electric power supply to the superconductive coils is stopped. Then, it is possible to make compatible between the requirement for the superconductive coils in view of operation and the assurance of the controllability for magnetic field pattern to be generated, thereby enabling to stop the device safely while controlling the entire magnetic field pattern. (N.H.)

  15. Steady mixed convective magnetohydrodynamic mass transfer flow with induced magnetic field and heat generation effects

    International Nuclear Information System (INIS)

    The study of steady heat and mass transfer by mixed convection flow from a vertical porous plate with heat generation has been made under the action of transverse magnetic field taking into account the induced magnetic field with viscous and magnetic dissipations of energy. The porous plate is subjected to a constant suction velocity as well as a uniform free stream velocity. The boundary layer equations have been transformed into dimensionless coupled nonlinear ordinary differential equations by appropriate transformations. The similarity solutions of the transformed dimensionless equations for the flow field, induced magnetic field, current density, heat and mass transfer characteristics are obtained by series solution technique and their numerical results' are presented in the form of graphs. The results show that heat generation decreases the fluid velocity when free convection currents cool the plate. The x-component of induced magnetic field is significantly affected by the magnetic field, magnetic Prandtl number and heat generation parameter. Applications of the study include laminar magneto-aerodynamics, materials processing and MHD propulsion thermo-fluid dynamics. (author)

  16. Design of pulsed guiding magnetic field for high power microwave generators

    International Nuclear Information System (INIS)

    In this paper, we present a comprehensive study on designing solenoid together with the corresponding power supply system to excite pulsed magnetic field required for high power microwave generators. Particularly, a solenoid is designed and the excited magnetic field is applied to a Ku-band overmoded Cerenkov generator. It is found in experiment that the electron beam is properly guided by the magnetic field and a 1.1 GW high power microwave is achieved at a central frequency of 13.76 GHz. Pulsed solenoid system has the advantages of compactness and low energy consumption, which are of great interest for repetitive operation. The reported studies and results can be generalized to other applications which require magnetic fields

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

    CERN Document Server

    Yuan, Kai-Jun

    2013-01-01

    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.

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

    International Nuclear Information System (INIS)

    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. (paper)

  19. Theoretical study of self generation of magnetic field due to laser plasma interaction

    International Nuclear Information System (INIS)

    Self generated high order magnetic field in the corona of Inertial Confinement Fusion Plasma plays a very important role in the design of fusion target because of its strong influence on the transport of thermal flux from the critical density region to the ablation layer. A theoretical study of the generation of megagauss magnetic field study has been presented. Out of number of causes, in this paper we have studied the role of pressure and temperatures gradient inside the fuel pellet to estimate the magnitude of the magnetic field produced. The intense pressure and temperature gradients inside the plasma caused by the lasers intensity (I > 1019 Wcm-2) short pulse (t?1 ps) giving rise to the Magnetic field. (author)

  20. Generation of quasi static magnetic field in the relativistic laser-plasma interactions

    International Nuclear Information System (INIS)

    The magnetic field generation by a relativistic laser light impinging on a thin target at oblique incidence is investigated using a two dimensional particle-in-cell simulation. We have found that the surface magnetic field inhibits the electron transport into the plasma and restricts the electron motion of the low energies at the surface for ? = 75 degrees. When the incident angle is larger than a certain critical angle, a magnetic field will restrict electron motion strongly. The existence of the critical angle, which restricts the electron transport, is well consistent with the theory. (authors)

  1. Induced polarization of electrons. Asymmetry of the angular distribution of neutrinos generated in a magnetic field

    International Nuclear Information System (INIS)

    This paper shows that there can be induced radiative polarization of electrons along a magnetic field if they are irradiated by an electromagnetic wave in resonance with the difference between the electron energy levels in the field and polarized in the plane parallel to the field. The influence of a homogeneous magnetic field on weak processes is considered. It is shown that it induces an asymmetry of the angular distribution of neutrino pairs generated in the field and modifies the angular distribution of particles in processes in which one neutrino is produced. Some possible effects of the asymmetry are pointed out

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  3. The role of rotation in the evolution of dynamo generated magnetic fields in Super Earths

    OpenAIRE

    Zuluaga, Jorge I.; Cuartas-restrepo, Pablo A.

    2011-01-01

    Planetary magnetic fields could impact the evolution of planetary atmospheres and have a role in the determination of the required conditions for the emergence and evolution of life (planetary habitability). We study here the role of rotation in the evolution of dynamo-generated magnetic fields in massive earth-like planets, Super Earths (1-10 $M_\\oplus$). Using the most recent thermal evolution models of Super Earths (Gaidos et al. 2010; Tachinami et al. 2011) and updated s...

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

    Directory of Open Access Journals (Sweden)

    E. D. Schmitter

    2010-02-01

    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.

  5. Spontaneous generation of toroidal magnetic field during spheromak formation in a conical Theta-pinch

    International Nuclear Information System (INIS)

    Spheromaks have been generated in conical Theta-pinches in a similar manner to FRC generation in straight reversed-field Theta-pinches. The essential difference is that when a conical Theta-pinch coil is used, a toroidal component to the magnetic field spontaneously appears. The poloidal component is generated by quickly reversing the current in the coil after an initial bias field is embedded in the preionized plasma. The toroidal component is generated through a much more subtle physical process. Numerical calculations have shown that the Hall term can lead to the generation of toroidal magnetic fields during the formation of an FRC; however for a straight coil, symmetry demands equal and opposite fields at each end, so no net toroidal flux or helicity can be generated. A simple analysis shows that even for a conical coil, the Hall term by itself cannot generate significant toroidal magnetic flux or helicity. They will show that a combination of the Hall term with the plasma resistivity can result in toroidal fields of comparable magnitude to experimental observation

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

    Directory of Open Access Journals (Sweden)

    Ammar Ben Brahim

    2011-05-01

    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.

  7. 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

  8. 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

  9. Encouragement of Enzyme Reaction Utilizing Heat Generation from Ferromagnetic Particles Subjected to an AC Magnetic Field

    Science.gov (United States)

    Suzuki, Masashi; Aki, Atsushi; Mizuki, Toru; Maekawa, Toru; Usami, Ron; Morimoto, Hisao

    2015-01-01

    We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize ?-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when ?-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which ?-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, ?-amylase on the particles is heated up and activated. We next prepare a solution, in which ?-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of ?-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only ?-amylase immobilized on the particles is selectively activated due to heat generation from the particles. PMID:25993268

  10. Generation of a spin-polarized electron beam by multipole magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Karimi, Ebrahim, E-mail: ekarimi@uottawa.ca [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Grillo, Vincenzo [CNR-Istituto Nanoscienze, Centro S3, Via G Campi 213/a, I-41125 Modena (Italy); Boyd, Robert W. [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Institute of Optics, University of Rochester, Rochester, NY 14627 (United States); Santamato, Enrico [Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, 80126 Napoli (Italy); Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Napoli (Italy)

    2014-03-01

    The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin–magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope. - Highlights: • Theory of generating spin-polarized electron beams. • Interacting electron vortex beams with space-variant magnetic fields. • Bohr–Pauli impossibility of generating spin-polarized free electrons.

  11. Magnetic Fields

    Science.gov (United States)

    VU Bioengineering RET Program,

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

  12. Generation of Electric and Magnetic Fields During Detonation of High Explosive Charges in Boreholes

    Energy Technology Data Exchange (ETDEWEB)

    Soloviev, S; Sweeney, J

    2004-06-04

    We present experimental results of a study of electromagnetic field generation during underground detonation of high explosive charges in holes bored in sandy loam and granite. Test conditions and physico-mechanical properties of the soil exert significant influence on the parameters of electromagnetic signals generated by underground TNT charges with masses of 2 - 200 kg. The electric and magnetic field experimental data are satisfactorily described by an electric dipole model with the source embedded in a layered media.

  13. Measurements of Self-Generated Magnetic Fields Influence on Electron Heat Conduction in Dense Plasmas

    International Nuclear Information System (INIS)

    Proton radiography measurements of self generated magnetic fields developing in long pulse (ns), high-power laser plasma interactions were employed to investigate the influence of these fields on the propagation of heat flow in dense plasmas. During the experiments, the heat wave propagation speed was measured simultaneously with the fields. These two coupled measurements could give an insight on the limitations of current numerical models of heat transport. They suggest that non locality of heat transport and diffusion of magnetic fields are important to model correctly the interaction.

  14. A numerical model of resistive generation of intergalactic magnetic field at cosmic dawn

    OpenAIRE

    Miniati, Francesco; Bell, A. R.

    2011-01-01

    Miniati and Bell (2011) proposed a mechanism for the generation of magnetic seeds that is based the finite resistivity of the low temperature IGM in the high redshift universe. In this model, cosmic-ray protons generated by the first generation of galaxies, escape into the intergalactic medium carrying an electric current that induces return currents, $j_t$, and associated electric fields, $\\vec E=\\eta\\vec j_t$ there. Because the resistivity, $\\eta$, depends on the IGM tempe...

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

    Science.gov (United States)

    Huntington, C. M.; Fiuza, F.; 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.

    2015-02-01

    Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability efficiently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. This result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts.

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

    CERN Document Server

    Alves, E P; Fonseca, R A; Silva, L O

    2014-01-01

    Strong shear flow regions found in astrophysical jets are shown to be important dissipation regions, where the shear flow kinetic energy is converted into electric and magnetic field energy via shear instabilities. The emergence of these self-consistent fields make shear flows significant sites for radiation emission and particle acceleration. We focus on electron-scale instabilities, namely the collisionless, unmagnetized Kelvin-Helmholtz instability (KHI) 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 outburst of active galactic nuclei and gamma-ray bursters. We show that the KHI 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 KHI, performed with OSIRIS, reveal the emergen...

  17. Generation of entangled photons by trapped ions in microcavities under a magnetic field gradient

    International Nuclear Information System (INIS)

    We propose a potential scheme to generate entangled photons by manipulating trapped ions embedded in two-mode microcavities assisted by a magnetic field gradient. By means of the spin-spin coupling due to the magnetic field gradient and the Coulomb repulsion between the ions, we show how to efficiently generate entangled photons by detecting the internal states of the trapped ions. We emphasize that our scheme is advantageous to create complete sets of entangled multiphoton states. The requirements and the experimental feasibility of our proposal are discussed in detail

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

    International Nuclear Information System (INIS)

    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

  19. Attosecond-magnetic-field-pulse generation by coherent circular molecular electron wave packets

    Science.gov (United States)

    Yuan, Kai-Jun; Bandrauk, André D.

    2015-04-01

    Attosecond-magnetic-field-pulse generation is investigated using numerical solutions of the time-dependent Schrödinger equation for oriented H2 + excited and ionized by intense 2 ×1016 W /cm2 circularly polarized attosecond UV pulses. The results show that localized attosecond-magnetic-field pulses B at the molecular center (r =0 ) decrease in intensity with increasing attosecond-pulse wavelength, following a classical model. Magnetic-field minima are obtained at a specific laser-pulse wavelength ? =55 nm, which is attributed to ionization suppression. It is found that spatially localized coherent circular electron currents and wave packets are created and induce magnetic-field minima. At ? =55 nm, coherent excitation between the ground state and Rydberg states is created, giving rise to partial Rabi oscillations in population and doublets in molecular above-threshold-ionization photoelectron energy spectra. Pulse intensities are shown to influence these effects on the attosecond time scale through population variations.

  20. Magnetic field generation and evolution in high-energy-density plasmas

    Science.gov (United States)

    Moissard, C.; Deng, W.; Fox, W.; Bhattacharjee, A.

    2014-10-01

    Magnetic reconnection has been proposed to account for many astrophysical phenomena and is inferred to play an important role in fusion. Recent experiments have studied magnetic reconnection in high-energy-density (HED) plasmas at the Vulcan, Omega and Shenguang laser facilities. Plasma bubbles are created by laser irradiation of solid targets. These bubbles self-generate MG-scale magnetic fields, and the collision of pairs of bubbles drives reconnection of this magnetic field. 2D first principles particle-in-cell (PIC) simulations with a collision operator have been used to study the evolution of the magnetic field in these experiments. The ablation of the target is modeled by a Gaussian heating function acting on an initially cold, high density plasma. It is shown that the Biermann battery effect (?T × ?n in generalized Ohm's law) can account quantitatively for the magnetic field produced. However, special attention must be given to the temperature, which can no longer be considered as a scalar in the regime of the experiments. In simulations with a collision operator, the evolution of the magnetic field is compared to Braginskii's transport theory. Results of 3D simulations of magnetic reconnection with the self-consistent Biermann effect will be reported.

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

    Energy Technology Data Exchange (ETDEWEB)

    Avino, F., E-mail: fabio.avino@epfl.ch; Fasoli, A.; Furno, I. [Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne (Switzerland)

    2014-03-15

    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.

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

    Science.gov (United States)

    Avino, F; Fasoli, A; Furno, I

    2014-03-01

    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. PMID:24689584

  3. 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

  4. 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

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

    Science.gov (United States)

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

    2008-01-01

    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.

  6. Control of generation regimes of ring chip laser under the action of the stationary magnetic field

    International Nuclear Information System (INIS)

    We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)

  7. The rotamak: a compact torus configuration generated by a rotating magnetic field

    International Nuclear Information System (INIS)

    In the Rotamak concept, a rotating magnetic field is used to drive the toroidal current in a compact torus device. A Rotamak device is described and initial experimental results are presented. Toroidal currents in the range 6 - 10 kA have been produced. Magnetic probe and power measurements, together with zero-dimensional, time-dependent plasma model calculations, indicate that a compact torus configuration has been generated for which the ohmic power input is balanced by line radiation

  8. The Effect of an Electrically Conducting Lower Mantle on Dynamo Generated Planetary Magnetic Fields

    Science.gov (United States)

    Vilim, R.; Stanley, S.

    2012-12-01

    Recent studies have shown that the lower mantles of Earth[1], Mercury[2], and large terrestrial exoplanets[3, 4] may be good conductors of electricity. This raises questions about the effect of an electrically conducting lower mantle on magnetic field generation in these planets. A core dynamo generated magnetic field can interact with an electrically conducting mantle in two ways. First, magnetic fields lines can be be frozen into the solid mantle. The flows in the core can then stretch the magnetic field lines at the core mantle boundary increasing their strength. Second, any field observed at the surface will be attenuated due to the screening effect, which preferentially attenuates the components of the magnetic field that vary quickest in time. We use a numerical dynamo model to investigate the effect of a conducting mantle on dynamo generated planetary magnetic fields. [1] Ohta, K., Cohen, R. E., Hirose, K., Haule, K., Shimizu, K., and Ohishi, Y. (2012). Experimental and Theoretical Evidence for Pressure-Induced Metallization in FeO with Rocksalt-Type Structure. PRL, 108, 026403 [2] Smith, D. E., Zuber, M. T., Phillips, R. J., Solomon, S. C., Hauck, S. A. II, Lemoine, F. G., Mazarico, E., Neumann, G.A., Peale, S.J., Margot, J.L., Johnson C.L., Torrence, M.H., Perry, M.E., Rowlands D.D., Goossens, S., Head, J.W., Taylor, A.H. (2012). Gravity Field and Internal Structure of Mercury from MESSENGER. Science [3] Nellis, W. J. (2011). Metallic liquid hydrogen and likely Al2O3 metallic glass. The European Physical Journal Special Topics, 196, 121-130 [4] Tsuchiya, T. (2011). Prediction of a hexagonal SiO2 phase affecting stabilities of MgSiO3 and CaSiO3 at multimegabar pressures. PNAS, 108, 1252-1255

  9. 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

  10. Study of two medium size 'C' core electromagnets generating low magnetic fields

    International Nuclear Information System (INIS)

    Magnetic field requirements of laboratories may impose constraints that often call for a variety of non-standard designs. The designer has to fulfil these demands without letting the design to become too inefficient. Since no ready design procedures are available he has to resort to intuition calculation and modelling. In spite of this there may be wide discrepancy between the design values and the actual results. This report describes the experience gained on two 'C' core electromagnets being used by authors. These magnets generate low magnetic fields over reasonably large volumes, a requirement that runs opposite to that of most other magnets. The study reveals the dependence of overall performance efficiency, field uniformity etc. on the design parameters. 31 figures. (author)

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

    Science.gov (United States)

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

    2008-01-01

    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.

  12. Impact-generated magnetic fields on the Moon : a magnetohydrodynamic numerical investigation

    Science.gov (United States)

    Oran, Rona; Shprits, Yuri; Weiss, Benjamin; Gombosi, Tamas

    2015-04-01

    Natural remanent magnetization has been identified in lunar rocks, the lunar crust, and a diversity of meteorites. Much of this magnetization is thought to have been produced by cooling a core dynamo mag-netic field. However, the identification of lunar crustal magnetic anomalies at the antipodes of four of the five youngest large (>600 km diameter) impact basins has motivated the alternative hypothesis that the lunar crust could have been magnetized by the impacts. In particular, it has been proposed that highly conducting ionized vapor produced by a basin-forming impact interacts with the ambient solar wind plasma surrounding the Moon to amplify the ambient solar wind magnetic field or any core dynamo field. In this picture, as the ionized vapor cloud expands around the Moon, it pushes and compresses the solar wind plasma into a small region at the antipodal point. The conservation of magnetic flux then leads to an enhanced magnetic field in the compressed plasma. This field can then be recorded as shock remanent magnetization by crustal materials at the antipodal point following the impact of converging basin ejecta. A key requirement for the impact-generated fields hypothesis is that the compressed field be suffi-ciently strong to explain the lunar paleointensities (at least tens of ?T) and maintained at the antipodal point for a sufficiently long time (several hours) for the ejecta to arrive and impact the surface. Previous simulations of the expansion of the vapor cloud found that the enhanced field will be strong enough (per-haps reaching hundreds of ?T) and will remain at the antipodal site for a sufficiently long time (>1 day) for the arrival of incoming ejecta. However, these studies did not include an explicit calculation of the interaction of the magnetized solar wind plasma with the vapor cloud. Rather, the cloud evolution under the lunar gravity was simulated in the purely hydrodynamic regime. The vapor cloud structure at certain times was used to derive a simplified picture of what the effects would be on an ambient magnetized plasma using general magnetohydrodynamic (MHD) arguments. The solar wind drag acting on the cloud, as well as MHD effects such as field lines stretching and magnetic reconnection were not taken into ac-count. With the advances made in computational MHD models in recent years, we can now revisit these ear-lier important models. Our goal is to perform the first MHD simulations of an impact-generated vapor cloud expanding in the solar wind around the Moon, using BATSRUS, a 3D highly-parallelized versatile MHD code developed at the University of Michigan, in order to self-consistently test the previous estima-tions of the strength and duration of the magnetic field enhancement at the antipodal points. We will con-sider different MHD processes, such as: 1) the finite resistivity of the lunar mantle 2) magnetic diffusion between the solar wind and the initially non-magnetized cloud, 3) magnetic reconnection at the antipode, and 4) viscous drag and the transport of magnetic flux due to solar wind motion, and 4) MHD instabili-ties. This will allow us to systematically examine whether impact-generated fields can indeed be respon-sible for the formation of crustal field enhancements on the Moon.

  13. 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

  14. Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability

    Directory of Open Access Journals (Sweden)

    K.-I. Nishikawa

    2013-09-01

    Full Text Available We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic jet and an unmagnetized sheath plasma. We have examined the strong magnetic fields generated by kinetic shear (Kelvin–Helmholtz instabilities. Compared to the previous studies using counter-streaming performed by Alves et al. (2012, the structure of the kinetic Kelvin–Helmholtz instability (KKHI of our jet-sheath configuration is slightly different, even for the global evolution of the strong transverse magnetic field. In our simulations the major components of growing modes are the electric field Ez, perpendicular to the flow boundary, and the magnetic field By, transverse to the flow direction. After the By component is excited, an induced electric field Ex, parallel to the flow direction, becomes significant. However, other field components remain small. We find that the structure and growth rate of KKHI with mass ratios mi/me = 1836 and mi/me = 20 are similar. In our simulations saturation in the nonlinear stage is not as clear as in counter-streaming cases. The growth rate for a mildly-relativistic jet case (?j = 1.5 is larger than for a relativistic jet case (?j = 15.

  15. Toroidal magnetic field generation during compact toroid formation in a field-reversed theta pinch and a conical theta pinch

    International Nuclear Information System (INIS)

    The influence that the Hall and delP/sub e/ terms, in a generalized Ohm's law, have on the formation of a compact toroid in a field-reversed theta pinch and a conical theta pinch has been examined. The inclusion of these terms leads to the spontaneous generation of toroidal magnetic fields and toroidal velocities. The toroidal fields in the end regions reach peak values of almost 50% of the external poloidal field during the early stages of formation. When the coil geometry is the same at each end of the theta pinch, equal and opposite toroidal fields are generated by the Hall effect, so that no net toroidal flux is generated. When the geometry is not the same at each end, the Hall effect can lead to a net toroidal flux. Calculations for both a conical theta pinch experiment and a field-reversed configuration translation experiment demonstrate the generation of net toroidal flux, as observed experimentally

  16. Laser-driven platform for generation and characterization of strong quasi-static magnetic fields

    CERN Document Server

    Santos, J J; Giuffrida, L; Forestier-Colleoni, P; Fujioka, S; Zhang, Z; Korneev, Ph; Bouillaud, R; Dorard, S; Batani, D; Chevrot, M; Cross, J; Crowston, R; Dubois, J -L; Gazave, J; Gregori, G; d'Humières, E; Hulin, S; Ishihara, K; Kojima, S; Loyez, E; Marquès, J -R; Morace, A; Nicolaï, Ph; Peyrusse, O; Poyé, A; Raffestin, D; Ribolzi, J; Roth, M; Schaumann, G; Serres, F; Tikhonchuk, V T; Vacar, Ph; Woolsey, N

    2015-01-01

    Quasi-static magnetic-fields up to $800\\,$T are generated in the interaction of intense laser pulses (500J, 1ns, 10^{17}W/cm^2) with capacitor-coil targets of different materials. The reproducible magnetic-field was consistently measured by three independent diagnostics: GHz-bandwidth inductor pickup coils (B-dot probes), Faraday rotation of polarized optical laser light and proton beam-deflectometry. The field rise time is consistent with the laser pulse duration, and it has a dipole-like distribution over a characteristic volume of 1mm^3, which is coherent with theoretical expectations. These results demonstrate a very efficient conversion of the laser energy into magnetic fields, thus establishing a robust laser-driven platform for reproducible, well characterized, generation of quasi-static magnetic fields at the kT-level, as well as for magnetization and accurate probing of high-energy-density samples driven by secondary powerful laser or particle beams.

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

    OpenAIRE

    E. D. Schmitter

    2010-01-01

    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 ...

  18. Study of buoyancy-driven flows and magnetic-field generation in rotating spherical shells

    International Nuclear Information System (INIS)

    The bifurcation-sequence approach is used to tackle the full nonlinear magnetohydrodynamic (MHD) problem of the generation of planetary magnetic fields by convection. The analysis proceeds in four steps. First, the problem of the thermal instability without magnetic fields is solved. In the second step, the solutions of finite-amplitude convection are calculated and the three-dimensional instability of nonlinear convection is analyzed. The convective flow obtained from the second step is then used to compute the growing magnetic field without including the feedback of the Lorentz force. This third step determines the critical magnetic Prandtl number and the most rapidly growing mode of the magnetic field. The coupled nonlinear magnetohydrodynamic problem including the Lorentz force and the associated instability analysis are considered in the fourth step. Three distinct fundamental modes are found as a function of the Taylor number T at the onset of convection. Two different kinds of transition between the modes are discovered. The magnetic fields of dipolar and quadrupolar symmetries are found to have nearly the same chances to be realized. There is no clear preference of symmetry in the MHD solutions

  19. 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

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

    OpenAIRE

    Veysi, Mehdi; Guclu, Caner; Capolino, Filippo

    2014-01-01

    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 si...

  1. Magnetic Field Generation and Particle Energization at Relativistic Shear Boundaries in Collisionless Electron-Positron Plasmas

    OpenAIRE

    Liang, Edison; Boettcher, Markus; Smith, Ian

    2011-01-01

    Using 2.5-dimensional Particle-in-Cell simulations, we study the kinetic physics of relativistic shear flow boundary in collisionless electron-positron (e+e-) plasmas. We find efficient magnetic field generation and particle energization at the shear boundary, driven by streaming instabilities across the shear interface and sustained by the shear flow. Nonthermal, anisotropic high-energy particles are accelerated across field lines to produce a power-law tail, truncated at e...

  2. Symplectic integrator for s-dependent static magnetic fields based on mixed-variable generating functions

    International Nuclear Information System (INIS)

    We describe a technique for constructing a symplectic transfer map for a charged particle moving through an accelerator component with arbitrary three-dimensional static magnetic field. The transfer map is constructed by symplectic integration; by representing the map at each step of the integration by a mixed-variable generating function, exact symplecticity is ensured. By using an appropriate integration algorithm, there is no necessity to make the paraxial approximation. The technique is illustrated by application (in one degree of freedom) to a quadrupole magnet with strong octupole component and fringe field.

  3. Impact of magnetic field parameters and iron oxide nanoparticle properties on heat generation for use in magnetic hyperthermia

    Science.gov (United States)

    Shah, Rhythm R.; Davis, Todd P.; Glover, Amanda L.; Nikles, David E.; Brazel, Christopher S.

    2015-08-01

    Heating of nanoparticles (NPs) using an AC magnetic field depends on several factors, and optimization of these parameters can improve the efficiency of heat generation for effective cancer therapy while administering a low NP treatment dose. This study investigated magnetic field strength and frequency, NP size, NP concentration, and solution viscosity as important parameters that impact the heating efficiency of iron oxide NPs with magnetite (Fe3O4) and maghemite (?-Fe2O3) crystal structures. Heating efficiencies were determined for each experimental setting, with specific absorption rates (SARs) ranging from 3.7 to 325.9 W/g Fe. Magnetic heating was conducted on iron oxide NPs synthesized in our laboratories (with average core sizes of 8, 11, 13, and 18 nm), as well as commercially-available iron oxides (with average core sizes of 8, 9, and 16 nm). The experimental magnetic coil system made it possible to isolate the effect of magnetic field parameters and independently study the effect on heat generation. The highest SAR values were found for the 18 nm synthesized particles and the maghemite nanopowder. Magnetic field strengths were applied in the range of 15.1-47.7 kA/m, with field frequencies ranging from 123 to 430 kHz. The best heating was observed for the highest field strengths and frequencies tested, with results following trends predicted by the Rosensweig equation. An increase in solution viscosity led to lower heating rates in nanoparticle solutions, which can have significant implications for the application of magnetic fluid hyperthermia in vivo.

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

    International Nuclear Information System (INIS)

    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. (paper)

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

    Science.gov (United States)

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

    2014-03-01

    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.

  6. Analytical analysis of magnetic field and back electromotive force calculation of an axial-flux permanent magnet synchronous generator with coreless stator

    OpenAIRE

    Virtic?, Peter; Pis?ek, Peter; Marc?ic?, Tine; Hadz?iselimovic?, Miralem; S?tumberger, Bojan

    2012-01-01

    This paper presents the analytical analysis of magnetic field and back electromotive force (back EMF) calculation in an axial flux permanent magnet synchronous generator (AFPMSG) without stator core. For the verification, the numerical analysis [finite element method (FEM)] of magnetic field is accomplished and comparison between analytical and numerical solution of magnetic field is presented. Both analytical and numerical solutions are obtained via magnetic vector potential, respectively. T...

  7. 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

  8. Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks

    CERN Document Server

    Nishikawa, K I; Richardson, G; Preece, R; Sol, H; Fishman, G J

    2003-01-01

    Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The `...

  9. Generation of a symmetric magnetic field by thermal convection in a plane rotating layer

    CERN Document Server

    Zheligovsky, V

    2010-01-01

    We investigate numerically magnetic field generation by thermal convection with square periodicity cells in a rotating horizontal layer of electrically-conducting fluid with stress-free electrically perfectly conducting boundaries for Rayleigh numbers in the interval 5100\\le R\\le 5800. Dynamos of three kinds, apparently not encountered before, are presented: 1) Steady and time-periodic regimes, where the flow and magnetic field are symmetric about a vertical axis. In regimes with this symmetry, the global alpha-effect is insignificant, and the complex structure of the system of amplitude equations controlling weakly nonlinear stability of the system to perturbations with large spatial and temporal scales suggests that the perturbations are likely to exhibit uncommon complex patterns of behaviour, to be studied in the future work. 2) Periodic in time regimes, where magnetic field is always concentrated in the interior of the convective layer, in contrast to the behaviour first observed by St Pierre (1993) and ...

  10. Modeling and analysis of solar wind generated contributions to the near-Earth magnetic field

    DEFF Research Database (Denmark)

    VennerstrØm, Susanne; Moretto, T.

    2006-01-01

    Solar wind generated magnetic disturbances are currently one of the major obstacles for improving the accuracy in the determination of the magnetic field due to sources internal to the Earth. In the present study a global MHD model of solar wind magnetosphere interaction is used to obtain a physically consistent, divergence-free model of ionospheric, field-aligned and magnetospheric currents in a realistic magnetospheric geometry. The magnetic field near the Earth due to these currents is analyzed by estimating and comparing the contributions from the various parts of the system, with the aim of identifying the most important aspects of the solar wind disturbances in an internal field modeling context. The contribution from the distant magnetospheric currents is found to consist of two, mainly opposing, contributions from respectively the dayside magnetopause currents and the cross-tail current. At high latitudes the field-aligned component is of partidular interest in connection with internal field-modelling. In the attitude regime of 400-800 km (typical for low Earth orbit satellites) the ionospheric currents are found to contribute significantly to the disturbancance, and account for more than 90% of the field-aligned disturbance. The magnetic disturbance field from field-aligned currents (FACs) is basically transverse to the main field, and they therefore contribute with less than 2% to the disturbance in total field intensity. Inhomogeneity in ionospheric conductance is identified as the main cause of main-field disturbance in the field-aligned direction. These disturbances are associated with the ionospheric Pedersen currents, and may introduce systematic errors in internal field models.

  11. 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

  12. 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

  13. 3-D Rpic Simulations of Relativistic Jets: Particle Acceleration, Magnetic Field Generation, and Emission

    Science.gov (United States)

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

    2007-01-01

    We have applied numerical simulations and modeling to the particle acceleration, magnetic field generation, and emission from relativistic shocks. We investigate the nonlinear stage of theWeibel instability and compare our simulations with the observed gamma-ray burst emission. In collisionless shocks, plasma waves and their associated instabilities (e.g., the Weibel, Buneman and other two-stream instabilities) are responsible for particle (electron, positron, and ion) acceleration and magnetic field generation. 3-D relativistic electromagnetic particle (REMP) simulations with three different electron-positron jet velocity distributions and also with an electron-ion plasma have been performed and show shock processes including spatial and temporal evolution of shocks in unmagnetized ambient plasmas. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions. 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-positron shocks are larger for smaller jet Lorentz factor. This comes from the fact that the growth time of the Weibel instability is proportional to the square of the jet Lorentz factor. We have performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which is assumed to be created by photon annihilation. Simulation results with this broad distribution show that the Weibel instability is excited continuously by the wide-range of jet Lorentz factor from lower to higher values. In all simulations the Weibel instability is responsible for generating and amplifying magnetic fields perpendicular to the jet propagation direction, and contributes to the electron’s (positron’s) transverse deflection behind the jet head. This small scale magnetic field structure contributes to the generation of “jitter” radiation from deflected electrons (positrons), which is different from synchrotron radiation in uniform magnetic fields. 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. The detailed studies of shock microscopic process evolution may provide some insights into early and later GRB afterglows.

  14. Magnetic Field

    DEFF Research Database (Denmark)

    Olsen, Nils

    2015-01-01

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

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

    CERN Document Server

    de Andrade, Garcia

    2011-01-01

    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...

  16. External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator

    Science.gov (United States)

    Niedra, Janis M.; Geng, Steven M.

    2013-01-01

    Linear alternators coupled to high efficiency Stirling engines are strong candidates for thermal-to-electric power conversion in space. However, the magnetic field emissions, both AC and DC, of these permanent magnet excited alternators can interfere with sensitive instrumentation onboard a spacecraft. Effective methods to mitigate the AC and DC electromagnetic interference (EMI) from solenoidal type linear alternators (like that used in the Advanced Stirling Convertor) have been developed for potential use in the Advanced Stirling Radioisotope Generator. The methods developed avoid the complexity and extra mass inherent in data extraction from multiple sensors or the use of shielding. This paper discusses these methods, and also provides experimental data obtained during breadboard testing of both AC and DC external magnetic field devices.

  17. Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

    Science.gov (United States)

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

    2005-04-01

    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 three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New 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. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron's (positron's) transverse deflection behind the jet head. This small-scale magnetic field structure is appropriate to the generation of ``jitter'' radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a uniform magnetic field. 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.

  18. Nonlinear second harmonic generation by light wave-plasma interaction in oscillating magnetic field

    International Nuclear Information System (INIS)

    The nonlinear generation of second harmonic electromagnetic waves in a thin inhomogeneous (dense and rarefied) plasma layer (of length d) by obliquely and normal incidence of light wave is analyzed. We consider the effect of external time- dependent magnetic field on the generation and amplification of waves. Two cases are considered, when the magnetic field oscillates at frequency: (i) equal, and (ii) double of that of the incident wave. For normal incidence, waves are not radiated in case (i), while in case (ii) the second harmonics are radiated equally from the plasma boundaries at x = o and x = d. For rarefied plasma, the second harmonics are radiated with equal amplitudes in both cases. (author). 3 refs

  19. Back-reactions of dynamo-generated magnetic fields: Torsional oscillations and variations in meridional circulation

    CERN Document Server

    Choudhuri, Arnab Rai

    2011-01-01

    The periodically varying Lorentz force of the periodic solar magnetic field generated by the solar dynamo can induce two kinds of motions: torsional oscillations and periodic variations in the meridional circulation. Observational evidence now exists for both these kinds of motions. We discuss our ongoing effort in theoretically studying the variations of the meridional circulation. Then we present our theoretical model of torsional oscillations, which addresses the question why these oscillations start before sunspot cycles at latitudes higher than where sunspots are seen.

  20. Generating vorticity and magnetic fields in plasmas in general relativity: spacetime curvature drive

    CERN Document Server

    Asenjo, Felipe A; Qadir, Asghar

    2012-01-01

    Using the generally covariant magnetofluid formalism for a hot plasma, a new spacetime curvature driven mechanism for generating seed vorticity/magnetic field is presented. The ``battery'' owes its origin to the interaction between gravity 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.

  1. Electronic and Optical Properties of a Lens Shaped Quantum Dot under Magnetic Field: Second and Third-Harmonic Generation

    International Nuclear Information System (INIS)

    In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method (FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation (SHG) and third-harmonic generation (THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

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

    CERN Document Server

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

    2011-01-01

    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...

  3. Particle Acceleration and Radiation Associated with Magnetic Field Generation from Relativistic Collisionless Shocks

    Science.gov (United States)

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

    2004-09-01

    Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

  4. 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)

  5. 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

  6. Scott Correction for Large Atoms and Molecules in a Self-Generated Magnetic Field

    DEFF Research Database (Denmark)

    Erdös, Laszlo; Fournais, SØren

    2012-01-01

    We consider a large neutral molecule with total nuclear charge Z in non-relativistic quantum mechanics with a self-generated classical electromagnetic field. To ensure stability, we assume that Za2 = ¿0 for a sufficiently small ¿0, where a denotes the fine structure constant. We show that, in the simultaneous limit Z ¿ 8, a ¿ 0 such that ¿ = Za2 is fixed, the ground state energy of the system is given by a two term expansion c1Z7/3 + c2(¿) Z2 + o(Z2). The leading term is given by the non-magnetic Thomas-Fermi theory. Our result shows that the magnetic field affects only the second (so-called Scott) term in the expansion.

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

    CERN Document Server

    Nishikawa, K -I; Fishiman, G J; Hardee, P

    2008-01-01

    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 ra...

  8. Weibel Instability Driven by Relativistic Pair Jets: Particle Acceleration, Magnetic Field Generation, and Emission

    Science.gov (United States)

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

    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 of the Weibel instability in electron-positron jets are not affected by the (electron-positron or electron-ion) ambient plasmas. However, the amplitudes of generated local magnetic fields in the electron-ion ambient plasma are significantly larger than those in the electron-positron ambient plasma. 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 angle deflected electrons may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts and other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

  9. 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.

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

    Science.gov (United States)

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

    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 (electron-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is an 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 electrons' transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties to synchrotron radiation which assumes 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.

  11. Phenomenon of the time-reversal violating magnetic field generation by a static electric field in a medium and vacuum

    OpenAIRE

    Baryshevsky, Vladimir G.

    1999-01-01

    It is shown that the T- and P-odd weak interactions yield to the existence of both electric field and magnetic (directed along the electric field) field around an electric charge. Similarly the assotiated magnetic field is directed along the vector of strength of stationary gravitational field.

  12. Helicity Balance and Steady-State Strength of the Dynamo Generated Galactic Magnetic Field

    OpenAIRE

    Kleeorin, N.; Moss, D.; Rogachevskii, I.; Sokoloff, D.

    2002-01-01

    We demonstrate that the inclusion of the helicity flux in the magnetic helicity balance in the nonlinear stage of galactic dynamo action results in a radical change in the magnetic field dynamics. The equilibrium value of the large-scale magnetic field is then approximately the equipartition level. This is in contrast to the situation without the flux of helicity, when the magnetic helicity is conserved locally, which leads to substantially subequipartition values for the eq...

  13. Magnetic Field Generation on Super-Earths and Sub-Earths

    Science.gov (United States)

    Stamenkovic, Vlada; Breuer, Doris

    2010-05-01

    The last 15 years of astronomical observation have revealed a universe filled with planets. The observational techniques still limit the possibility to detect smaller, Earth-sized planets. New missions such as Kepler and Corot, next generation telescopes such as Darwin and TPF, and improved techniques in radial velocity measurements will lower this limit and make it possible to even detect Earth-sized planets in the near future. We study the ability of planets with different masses to generate a magnetic dynamo. For this we [1] investigate the thermal evolution and convection of planets with Earth-like composition and structure of sizes ranging from 0.1 to 10 Earth masses (Mearth). Important is that we include the pressure dependence of viscosity into our parameterized 1D boundary layer and spherical 2D/3D models, with the scope to understand how the pressure-viscosity coupling changes the convection in the mantles of Super-Earths, and less massive planets, which we termed Sub-Earths. We then look how this influences magnetic dynamos on those planets. We observe that the pressure dependence of viscosity becomes an important factor for the mantle convection of planets with masses larger than 1Mearth - resulting in a sluggish convection regime in the lower mantle for Earth-sized planets. Depending on activation volume we observe with growing planetary mass the formation of a conductive lid over the core mantle boundary (CMB), termed low-lid, where convection velocities cease and where heat transport is only due to conduction. The sluggish convection and the formation of the low-lid reduce the convective vigour throughout the mantle. This leads to much lower core cooling in comparison to non-pressure-dependent viscosity models. We find using our parameterized 1D convection models that the low-lid insulates the core and thus affects the potential growth of an inner core and the ratio of CMB heat flux to critical heat flux. This on the other hand influences the generation of a magnetic dynamo, thermally and compositionally. The results, in particular for the compositional dynamo, depend on the melting curve, which can differ strongly in magnitude if different approaches are followed ([2], [3]). But we can show that thermodynamic constraints lead to the exclusion of [2] and therefore leave [3] as the most reliable melting curve at high pressures. In our model the scaling of thermodynamic core properties is tightly connected to the Grüneisen parameter. Assuming an initially molten core as the consequence of accretion and core formation, we find that in the early evolution the low-lid reduces strongly the heat flow through the core-mantle-boundary, even though the melting temperatures (and thus the initial core temperatures), can be very high - up to 20'000K for 10-Earth-mass planets with pressures above 1200 GPa. Our results show that the thermally induced magnetic field generation is highly suppressed on Super-Earths, for plate tectonics and stagnant lid planets, as critical heat fluxes grow much faster that effective CMB heat fluxes. Compositional dynamos might also be suppressed as the inner core growth rate might become only very small, and the associated power is possibly even not strong enough to overcome ohmic dissipation thus inducing only small surface magnetic fields or no fields at all. We show that the mass-richer the planet, the more difficult it is to generate strong magnetic fields. References [1] Stamenkovic, V., L. Noack, T. Spohn and D. Breuer (2010), to be submitted to EPSL [2] Boehler, R. (1993) Nature, 363, 534-536 [3] Stacey, F.D and Davies, P.M. (2004) PEPI, 142, 137-184

  14. 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

  15. Particle acceleration, magnetic field generation, and emission in relativistic pair jets

    Science.gov (United States)

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

    2005-05-01

    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 of Weibel instability are proportional to the Lorentz factors of jets. 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.

  16. Particle acceleration, magnetic field generation, and emission in relativistic pair jets

    International Nuclear Information System (INIS)

    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 far 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 of Weibel instability are proportional to the Lorentz factors of jets. 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 tram small scale magnetic field structures may be important far understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks

  17. 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

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

    Science.gov (United States)

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

    2009-10-13

    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.

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

    Science.gov (United States)

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

    2009-01-01

    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.

  20. Effect of the plasma-generated magnetic field on relativistic electron transport.

    Science.gov (United States)

    Nicolaï, Ph; Feugeas, J-L; Regan, C; Olazabal-Loumé, M; Breil, J; Dubroca, B; Morreeuw, J-P; Tikhonchuk, V

    2011-07-01

    In the fast-ignition scheme, relativistic electrons transport energy from the laser deposition zone to the dense part of the target where the fusion reactions can be ignited. The magnetic fields and electron collisions play an important role in the collimation or defocusing of this electron beam. Detailed description of these effects requires large-scale kinetic calculations and is limited to short time intervals. In this paper, a reduced kinetic model of fast electron transport coupled to the radiation hydrodynamic code is presented. It opens the possibility to carry on hybrid simulations in a time scale of tens of picoseconds or more. It is shown with this code that plasma-generated magnetic fields induced by noncollinear temperature and density gradients may strongly modify electron transport in a time scale of a few picoseconds. These fields tend to defocus the electron beam, reducing the coupling efficiency to the target. This effect, that was not seen before in shorter time simulations, has to be accounted for in any ignition design using electrons as a driver. PMID:21867317

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

    Energy Technology Data Exchange (ETDEWEB)

    Mitrofanov, K. N., E-mail: mitrofan@triniti.ru [Troitsk Institute for Innovaiton and Fusion Research (Russian Federation); Krauz, V. I., E-mail: krauz_vi@nrcki.ru; Myalton, V. V.; Velikhov, E. P.; Vinogradov, V. P.; Vinogradova, Yu. V. [National Research Centre Kurchatov Institute (Russian Federation)

    2014-11-15

    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.

  2. Generation of RF plasma assisted high power pulsed sputtering glow discharge without using a magnetic field

    International Nuclear Information System (INIS)

    High power pulsed sputtering plasma is an emerging technology used to modify the surfaces of industrial components and biomedical parts. The characteristic feature of the plasma is that metallic species are highly ionized and charged particles are magnetized. In order to use the plasma source in a variety of material processing applications, it is desirable that the glow is generated without a magnetic field. In this paper, a sputtering of metallic species is enhanced by a pulsed dc voltage applied to a pair of electrodes immersed in an RF plasma. Sputtered metallic species are ionized as follows: first, a 200 kHz-RF (radio frequency, output voltage: 3 kV and duration: 200 ?s) argon plasma is generated. Then, a pulsed dc (direct current) voltage is applied to a pair of electrodes (of 60 mm diameter and 75 mm long) set in the RF plasma to accelerate argon ions toward the cathode (sputter target). The applied voltage ranges from 0.8 to 1.4 kV with negative polarity. The argon gas pressure is 2.7 Pa. The pulse width is 60 ?s. In a typical example, the induced current through the electrode is 45 A with a voltage of 1000 V. The instantaneous consumed power of 45 kW and the energy consumed per pulse is 2.7 J, corresponding to an average power of 216 W at a repetition rate of 80 Hz.

  3. Magnetic field measurements of the harmonic generation FEL superconducting undulator at BNL-NSLS

    International Nuclear Information System (INIS)

    A three stage superconducting undulator (modulator, dispersive section, and radiator) is under construction at Brookhaven National Laboratory. Sections of the radiator, consisting of 25cm long steel yokes, each with 18mm period, 0.54 Tesla field, and 8.6mm gap are under test. The magnetic measurements and operational characteristics of the magnet are discussed. Measurement results and analysis are presented, with emphasis on the integrated field quality. The magnet winding and the effects of the various trims are discussed

  4. Magnetic field enhancement of generation-recombination and shot noise in organic light emitting diodes

    Science.gov (United States)

    Djidjou, T. K.; Chen, Ying; Basel, Tek; Shinar, J.; Rogachev, A.

    2015-03-01

    We have studied the effect of magnetic field on noise in series of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene-based organic light emitting diodes with dominant hole injection, dominant electron injection, and balanced electron and hole injection. The noise spectra of the balanced devices revealed the generation-recombination (g-r) noise term, which we associated with bimolecular electron-hole recombination. The presence of the g-r noise term is correlated with the strong organic magnetoresistance (up to 25%) observed in the balanced devices. The noise spectra also have the shot noise contribution with the Fano factor 0.25-0.4. We found that time constant of the g-r term decreases and the magnitude of shot noise increases when magnetic field is applied. This behavior can be consistently explained within the polaron-polaron model of organic magnetoresistance. We have not found any evidence that the magnetoresistance in studied devices is affected by traps.

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

    International Nuclear Information System (INIS)

    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. (paper)

  6. Generation of excited coherent states for a charged particle in a uniform magnetic field

    Science.gov (United States)

    Mojaveri, B.; Dehghani, A.

    2015-04-01

    We introduce excited coherent states, |? , ? ; n| ? a† n | ? , ?|, where n is an integer and states |? , ?| denote the coherent states of a charged particle in a uniform magnetic field. States |? , ?| minimize the Schrödinger-Robertson uncertainty relation while having the nonclassical properties. It has been shown that the resolution of identity condition is realized with respect to an appropriate measure on the complex plane. Some of the nonclassical features such as sub-Poissonian statistics and quadrature squeezing of these states are investigated. Our results are compared with similar Agarwal's type photon added coherent states (PACSs) and it is shown that, while photon-counting statistics of |? , ? , n| are the same as PACSs, their squeezing properties are different. It is also shown that for large values of |?|, while they are squeezed, they minimize the uncertainty condition. Additionally, it has been demonstrated that by changing the magnitude of the external magnetic field, Bext, the squeezing effect is transferred from one component to another. Finally, a new scheme is proposed to generate states |beta; , ? ; n| in cavities.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zibold, A F, E-mail: zibold@mail.donbass.com [Artiom str., 127/54, Donetsk, Ukraine, 83001 (Ukraine)

    2015-02-01

    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. (paper)

  8. Magnetic field structure of large-scale plasmoid generated by the fast reconnection mechanism in a sheared current sheet

    Directory of Open Access Journals (Sweden)

    M. Ugai

    2010-08-01

    Full Text Available On the basis of the spontaneous fast reconnection model, three-dimensional magnetic field profiles associated with a large-scale plasmoid propagating along the antiparallel magnetic fields are studied in the general sheared current sheet system. The plasmoid is generated ahead of the fast reconnection jet as a result of distinct compression of the magnetized plasma. Inside the plasmoid, the sheared (east-west field component has the peak value at the plasmoid center located at x=XC, where the north-south field component changes its sign. The plasmoid center corresponds to the so-called contact discontinuity that bounds the reconnected field lines in x<XC and the field lines without reconnection in x>XC. Hence, contray to the conventional prediction, the reconnected sheared field lines in x<XC are not spiral or helical, since they cannot be topologically connected to the field lines in x>XC. It is demonstrated that the resulting profiles of magnetic field components inside the plasmoid are, in principle, consistent with satellite observations. In the ambient magnetic field region outside the plasmoid too, the magnetic field profiles are in good agreement with the well-known observations of traveling compression regions (TCRs.

  9. 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)

  10. Generation and Application of Ultra-High-Intensity Magnetic Field Gradient Pulses for NMR Spectroscopy

    Science.gov (United States)

    Galvosas, Petrik; Stallmach, Frank; Seiffert, Günter; Kärger, Jörg; Kaess, Udo; Majer, Günter

    2001-08-01

    Two different concepts of gradient current power supplies are introduced, which are suitable for the generation of ultra-high intensity pulsed magnetic field gradients of alternating polarity. The first system consists of a directly binary coded current source (DBCCS). It yields current pulses of up to ±120 A and a maximum voltage across the gradient coil of ±400 V. The second system consists of two TECHRON 8606 power supplies in push-pull configuration (PSPPC). It yields current pulses of up to ±100 A and a maximum voltage across the gradient coil of ±300 V. In combination with actively shielded anti-Helmholtz gradient coils, both systems are used routinely in NMR diffusion studies with unipolar pulsed field gradients of up to 35 T/m. Until now, alternating pulsed field gradient experiments were successfully performed with gradient intensities of up to ±25 T/m (DBCCS) and ±35 T/m (PSPPC), respectively. Based on the observation of the NMR spin echo in the presence of a small read gradient, procedures to test the stability and the matching of such ultra-high pulsed field gradient intensities as well as an automated routine for the compensation of possible mismatches are introduced. The results of these procedures are reported for the PSPPC system.

  11. Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers

    KAUST Repository

    Kim, J.

    2014-12-04

    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.

  12. Weibel Instability Driven by Relativistic Pair Jets: Particle Acceleration, Magnetic Field Generation, and Emission

    CERN Document Server

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

    2005-01-01

    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 of the Weibel instability in electron-positron jets are not affected by the (electron-positron or electron-ion) ambient plasmas. However, the amplitudes of generated local magnetic fields in the electron-ion ambient plasma are significantly larger than those in the electron-positron ambient plasma.

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

    CERN Document Server

    Ballardini, Mario; Paoletti, Daniela

    2014-01-01

    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)$.

  14. Stimulated Brillouin backscattering and magnetic field generation in laser-produced plasmas

    International Nuclear Information System (INIS)

    This thesis is concerned with aspects of laser-plasma interactions related to fusion reactions; in particular thermoelectric magnetic field generation around a hole dug in plasma by intense laser beams, and stimulated Brillouin back scattering (SBBS) from plasmas containing hot spots. A hole, of the size of the laser focal spot, is dug in the plasma when illuminated by intense laser if the laser pressure exceeds the plasma thermal pressure. This hole is found to have steep, radial density gradients. My first concern arose from the prediction that magnetic fields might be generated around the hole-plasma interface in places where the steep density gradients overlap with the non-aligned temperature gradients. When a high-power laser beam is focused on a solid pellet, plasma is formed at the surface. In order to create conditions for thermonuclear reactions in the interior of the pellet, an effective deposition of the laser energy to thermal energy of the pellet via laser-plasma coupling is necessary. When light irradiates a plasma collective processes occur, which can either enhance or reduce the light absorption. For a better understanding of the fusion problem a knowledge of the nature of these collective processes and of the fraction of light reflected from the plasma modes is required. Local hot spots seen experimentally lead to higher gain levels of scattered light. These local temperature inhomogeneities could lead to non-equilibrium distributions, which result inequilibrium distributions, which result in a free energy leading to some interesting phenomena in plasma. In the second part of the thesis stimulated Brillouin back scattering from an ion acoustic mode in a hot spot is studied. Temperature inhomogeneities lead to an ion acoustic instability, and to higher levels of SBBS gain, which leads to lower thresholds for the same electron to ion temperature ratios. This could be the answer for the observed high levels of scattering from hot spots. (author)

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

    OpenAIRE

    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

    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.

  16. Magnetic fields from inflation?

    OpenAIRE

    Demozzi, Vittoria; Mukhanov, Viatcheslav; Rubinstein, Hector

    2009-01-01

    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 sma...

  17. Fabrication program of NbTi and Nb3Sn superconducting magnets for mineral separation and high magnetic field generation

    International Nuclear Information System (INIS)

    This paper describes the design of two superconducting magnets for industrial and laboratory use: a 7T NbTi split-pair type magnet, 168 mm of clear bore and 350 KJ of stored energy to be operated in parallel and opposition current modes of ruse as a High Gradient Magnetic Separation (HGMS) system and as a Helical Channel Magnetic Separation (HCMS), respectively; and a 12T mixed type magnet composed of one Nb3Sn inner coil and one NbTi outer coil with 75 mm of clear bore, field homogeneity of 1% in a D.S.V. of 50 mm. This configuration causes the reduction of cost due to the use of graded conductors according to the magnetic field which they are exposed

  18. Observation of Self-Similarity in the Magnetic Fields Generated by the Ablative Nonlinear Rayleigh-Taylor Instability

    Science.gov (United States)

    Gao, Lan

    2014-10-01

    The Rayleigh-Taylor (RT) instability has been extensively studied because of its relevance to ignition target designs in inertial confinement fusion, material strength studies in high energy density physics, and astrophysical systems. This talk presents the first measurements of magnetic field generation by the nonlinear RT instability in laser-accelerated planar foils using ultrafast proton radiography at the OMEGA EP Laser System. Thin plastic foils were irradiated with 4-kJ, 2.5-ns laser pulses at focused laser intensities of ~1014 W /cm2. Target modulations were seeded by laser nonuniformities and amplified during the target-acceleration phase by the RT instability growth. A high-energy proton beam tracked the hydrodynamic evolution of the target and mapped the magnetic field spatial distribution with high spatial and temporal resolution. The experimental data show self-similar behavior in the growing cellular magnetic field structures. The calculated magnetic cell-merging rate is consistent with the value determined by earlier x-ray measurements, linking the cellular magnetic field structures with the RT bubble and spike growth. The results are consistent with two-dimensional magnetohydrodynamic simulations, showing MG-level magnetic field generation in the laser-driven foil. The work could benefit the understanding of magnetic-seed-field generation in high energy density plasmas and the flow-driven processes that induce global magnetic structures prior to their turbulent amplification by the dynamo process. The Rayleigh-Taylor (RT) instability has been extensively studied because of its relevance to ignition target designs in inertial confinement fusion, material strength studies in high energy density physics, and astrophysical systems. This talk presents the first measurements of magnetic field generation by the nonlinear RT instability in laser-accelerated planar foils using ultrafast proton radiography at the OMEGA EP Laser System. Thin plastic foils were irradiated with 4-kJ, 2.5-ns laser pulses at focused laser intensities of ~1014 W /cm2. Target modulations were seeded by laser nonuniformities and amplified during the target-acceleration phase by the RT instability growth. A high-energy proton beam tracked the hydrodynamic evolution of the target and mapped the magnetic field spatial distribution with high spatial and temporal resolution. The experimental data show self-similar behavior in the growing cellular magnetic field structures. The calculated magnetic cell-merging rate is consistent with the value determined by earlier x-ray measurements, linking the cellular magnetic field structures with the RT bubble and spike growth. The results are consistent with two-dimensional magnetohydrodynamic simulations, showing MG-level magnetic field generation in the laser-driven foil. The work could benefit the understanding of magnetic-seed-field generation in high energy density plasmas and the flow-driven processes that induce global magnetic structures prior to their turbulent amplification by the dynamo process. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  19. 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)

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

    Science.gov (United States)

    Zibold, A. F.

    2015-02-01

    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.

  1. 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)

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

    Science.gov (United States)

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

    2008-06-01

    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.

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

    Science.gov (United States)

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

    2014-08-01

    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

  4. Laser beat wave terahertz generation in a clustered plasma in an azimuthal magnetic field

    International Nuclear Information System (INIS)

    Laser beat wave excitation of terahertz radiation in a rippled density clustered plasma, in the presence of an azimuthal magnetic field, is investigated. The lasers exert a beat ponderomotive force on cluster electrons, imparting them an oscillatory velocity with a significant transverse component due to the azimuthal magnetic field. The oscillatory velocity beats with the cluster density ripple and produces a nonlinear current, driving terahertz radiation. The terahertz field turns out to have ring shaped distribution. Its amplitude is enhanced by the cluster plasma resonance when (4?/3)nc0rc03ne/(?2-?pe2/3)>n0/?2.

  5. The effects of ion mass variation and domain size on octupolar out-of-plane magnetic field generation in collisionless magnetic reconnection

    Science.gov (United States)

    Graf von der Pahlen, J.; Tsiklauri, D.

    2015-03-01

    Graf von der Pahlen and Tsiklauri [Phys. Plasmas 21, 060705 (2014)] established that the generation of octupolar out-of-plane magnetic field structure in a stressed X-point collapse is due to ion currents. The field has a central region, comprising of the well-known quadrupolar field (quadrupolar components), as well as four additional poles of reversed polarity closer to the corners of the domain (octupolar components). In this extended work, the dependence of the octupolar structure on domain size and ion mass variation is investigated. Simulations show that the strength and spatial structure of the generated octupolar magnetic field is independent of ion to electron mass ratio; thus showing that ion currents play a significant role in out-of-plane magnetic structure generation in physically realistic scenarios. Simulations of different system sizes show that the width of the octupolar structure remains the same and has a spacial extent of the order of the ion inertial length. The width of the structure thus appears to be independent on boundary condition effects. The length of the octupolar structure, however, increases for greater domain sizes, prescribed by the external system size. This was found to be a consequence of the structure of the in-plane magnetic field in the outflow region halting the particle flow and thus terminating the in-plane currents that generate the out-of-plane field. The generation of octupolar magnetic field structure is also established in a tearing-mode reconnection scenario. The differences in the generation of the octupolar field and resulting qualitative differences between X-point collapse and tearing-mode are discussed.

  6. Generation of a modulated IREB (intense relativistic electron beam) with a frequency tunable by a magnetic field

    International Nuclear Information System (INIS)

    The present invention comprises a device for generating a modulated intense relativistic beam (IREB) with an electronically tunable frequency, comprising: a longitudinally running drift tube; a plurality of gaps in the drift tube including first gap and a second gap, disposed with a predetermined distance therebetween; and a plurality of cavities, with a first cavity disposed around the drift tube at the location of the first gap, and a second cavity disposed around the drift tube at the location of the second gap. These first and second cavities are provided with volumes and a geometry such as to excite a predetermined frequency band below the plasma frequency for the device. A circuit is provided for generating an IREB and injecting this IREB to propagate within the drift tube with a predetermined-plasma frequency. Additionally, a main magnetic field generating means is provided for generating an IREB and injecting this IREB to a desired beam diameter. The frequency tuning is obtained by providing an auxiliary magnetic field running parallel to and within the drift tube and located only along a predetermined length between the first and second gaps, with this auxiliary magnetic field running parallel to and within the drift tube and located along a predetermined length between first and second gaps, with this auxiliary magnetic field being tunable to thereby tune the frequencies of excitations in the first and second gaps. Finally, a means is provided at one end of the drift tube for converting the kinetic energy of the IREB into electrical energy

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

    OpenAIRE

    E. D. Schmitter

    2010-01-01

    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 ...

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

    CERN Document Server

    Wiersma, J

    2004-01-01

    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-proton plasmas than in pair plasmas. We find this estimate by modelling the plasma in the shock transition zone with a waterbag momentum distribution for the protons and with a background of hot electrons. For ultra-relativistic shocks we find that the wavelength of the most efficient mode for magnetic field generation equals the electron skin depth, that the relevant nonlinear stabilization mechanism is magnetic trapping, and that the presence of the hot electrons limits the typical magnetic field strength generated by this mode so that ...

  9. Investigation of magnetic field generation by non-Gaussian, non-Markovian velocity fluctuations using meshless, Lagrangian numerical schemes

    Science.gov (United States)

    Sanchez, Raul; Newman, David

    2014-10-01

    Turbulent velocity fields can generate perturbations of the electric current and magnetic field that, under certain conditions, may generate an average, large-scale magnetic field. Such generation is important to understand the behavior of stars, planetary and laboratory plasmas. This generation is traditionally studied by assuming near-Gaussian, random velocity fluctuations. This simplification allows to exprese the effective electromotive force in Faraday's law in terms of a piece proportional to the large-scale magnetic field itself (the ?-term) and another proportional to its curl (the ? term) assuming certain symmetry conditions are met. Physically, the ?-term is a measure of the mean helicity of the flow and drives the dynamo process. In a previous contribution, we examined theoretically what consequences would follow from assuming instead Levy-distributed, Lagrangianly-correlated velocity fields, that have been recently identified as of relevance in regimes of near-marginal turbulence or in the presence of a strong, stable sheared flow. Here, we will discuss and extend these results numerically by implementing the kinematic dynamo equation using a Lagrangian, meshless numerical method inspired by the SPH schemes frequently used in hydrodynamics.

  10. Magnetic Field Solver

    Science.gov (United States)

    Ilin, Andrew V.

    2006-01-01

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

  11. Magnetic field dependence of the harmonic generation in sintered pellets of YBaCuO. The history effects

    International Nuclear Information System (INIS)

    Results are presented for a detailed study of harmonic generation in the magnetization of a sintered YBa2Cu3O7 pellet subjected to various combinations of AC and DC magnetic field. On cooling the sample below Tc in zero field, a large hysteresis is observed between HDC increasing and decreasing cases. General features of this observation can be understood in terms of the hysteretic properties of the weak-linked intergrain region mediated by trapped flux inside the grains. However, there remain some finer aspects which do not have a simple explanation within this model. (orig.)

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

    Science.gov (United States)

    Béghin, Christian

    2015-02-01

    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.

  13. 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%

  14. Absolute measuremens of magnetic field generated by different coils in the center of EGYPTOR tokamak.

    Czech Academy of Sciences Publication Activity Database

    Hegazy, H.; Žá?ek, František

    2006-01-01

    Ro?. 25, 1-2 (2006), s. 115-120. ISSN 0164-0313 Institutional research plan: CEZ:AV0Z20430508 Keywords : small tokamaks * EGYPTOR tokamak * pickup coil * magnetic field Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.381, year: 2006

  15. 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

  16. 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

  17. Measuring of magnetic susceptibility of dielectrics by means of the cryogenic generator on a field effect transistor

    International Nuclear Information System (INIS)

    A facility for measuring magnetic susceptibility of magnetodielectrics within 1.6-50 K temperature range and in magnetic fields up to 50 kOe is described. The measuring process comprises measuring frequency of a RF-generator with an empty coil of the circuit and with a sample lead into it. The design of the cryogenic part of the facility and the block-diagram of the main measuring circuits are presented. The RF-generator is connected with the capacitive feedback circuits. The measured signal is fed to wide-band amplifier and then to the frequency-meter and control oscillograph. The facility sensitivity equals to 10-6, its relative accuracy is 2%. The facility has been used in investigation of magnetic properties of garnet structure compounds

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

    Science.gov (United States)

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

    2014-10-01

    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

  19. 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)

    Ammar Ben Brahim

    2011-11-01

    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.

  20. Magnetic Field Grid Calculator

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

  1. Magnetic Field Calculator

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

  2. Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

    CERN Document Server

    Nishikawa, K I; Richardson, G; Preece, R; Sol, H; Fishman, G J

    2004-01-01

    Shock acceleration is an 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 electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. 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 non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and ...

  3. Calculation of Magnetic Near-Field Generated by the Contact Discharge of an ESD-gun

    Science.gov (United States)

    Fujiwara, Osamu; Mori, Ikuko; Ishigami, Shinobu; Yamanaka, Yukio

    An ESD (electrostatic discharge) testing is specified in the IEC 61000-4-2, in which the detailed waveform of the discharge current injected by an ESD-gun is prescribed. However, due to lack of understanding of the discharge process, it is difficult to confirm whether or not such the IEC current waveform be injected onto actual equipment. We thus previously proposed an equivalent circuit model for the ESD-gun based on its geometrical structure, and showed decisive factors for the discharge current. In this study, in order to confirm the feasibility of the above equivalent circuit model, we measured with a 6-GHz wide-band digital oscilloscope the discharge current through an SMA connector and the resultant magnetic near-field for the contact discharge of an ESD-gun. As a result, we found that both the measured waveforms approximately agree with those calculated from our equivalent circuit model. We then measured with respect to charge voltages the magnetic near-fields for the contact discharge of the ESD-gun to the ground, which showed that the measured waveform around the first peak fairly agrees with the calculated one. Furthermore, we also found that the magnetic field peak increases with increasing the charge voltage, whose dependence can be predicted from our equivalent model.

  4. Multiwavelength Magnetic Field Modeling

    Science.gov (United States)

    Jaffe, T. R.

    2015-03-01

    We model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.

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

    Directory of Open Access Journals (Sweden)

    Moh'd A. Al-Nimr

    2004-06-01

    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.

  6. Ocean circulation generated magnetic signals

    DEFF Research Database (Denmark)

    Manoj, C.; Kuvshinov, A.

    2006-01-01

    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.

  7. 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

  8. AN IRON FREE ASYNCHRONOUS PULSED GENERATOR FOR THE PRODUCTION OF PULSED HIGH MAGNETIC FIELDS

    OpenAIRE

    Sultanem, F.; Bleijs, C.; Postel, C.; Askenazy, S.; Marquez, J.

    1984-01-01

    The production of long pulsed high fields (> 500 kgaus with ? > 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.

  9. ANALYSIS OF LOW TEMPERATURE PLASMA FLOW IN DISC-TYPE MHD GENERATOR IN STRONG MAGNETIC FIELD WITH EXTRATHERMAL IONIZATION

    Directory of Open Access Journals (Sweden)

    Józef Kunc

    1971-01-01

    Full Text Available Basing on the given flow model, low temperature plasma flow equations in disc-type MHD Generator in strong magnetic field are educed, taking into consideration the Hall's Component of Electrical Current. The He-Cs plasma ionization is considered as extrathermal ("electron heating" according to Kerrbrock's Model.The solutions of flow equations for low Mach numbers and numeral calculations based on the given parameters are presented also.The most typical functions for the MHD Generator theory are shown in the form of diagrams.

  10. Exploring Magnetic Field Lines

    Science.gov (United States)

    2012-06-26

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

  11. Evaluation of human exposure to complex waveform magnetic fields generated by arc-welding equipment according to European safety standards.

    Science.gov (United States)

    Zoppetti, Nicola; Bogi, Andrea; Pinto, Iole; Andreuccetti, Daniele

    2015-02-01

    In this paper, a procedure is described for the assessment of human exposure to magnetic fields with complex waveforms generated by arc-welding equipment. The work moves from the analysis of relevant guidelines and technical standards, underlining their strengths and their limits. Then, the procedure is described with particular attention to the techniques used to treat complex waveform fields. Finally, the procedure is applied to concrete cases encountered in the workplace. The discussion of the results highlights the critical points in the procedure, as well as those related to the evolution of the technical and exposure standards. PMID:24936022

  12. Evaluation of human exposure to complex waveform magnetic fields generated by arc-welding equipment according to european safety standards

    International Nuclear Information System (INIS)

    In this paper, a procedure is described for the assessment of human exposure to magnetic fields with complex waveforms generated by arc-welding equipment. The work moves from the analysis of relevant guidelines and technical standards, underlining their strengths and their limits. Then, the procedure is described with particular attention to the techniques used to treat complex waveform fields. Finally, the procedure is applied to concrete cases encountered in the workplace. The discussion of the results highlights the critical points in the procedure, as well as those related to the evolution of the technical and exposure standards. (authors)

  13. On the problem of large-scale magnetic field generation in rotating compressible convection

    CERN Document Server

    Favier, Benjamin

    2013-01-01

    Mean-field dynamo theory suggests that turbulent convection in a rotating layer of electrically-conducting fluid produces a significant alpha-effect, which is one of the key ingredients in any mean-field dynamo model. Provided that this alpha-effect operates more efficiently than (turbulent) magnetic diffusion, such a system should be capable of sustaining a large-scale dynamo. However, in the Boussinesq model that was considered by Cattaneo&Hughes (2006) the dynamo produced small-scale, intermittent magnetic fields with no significant large-scale component. In this paper, we consider the compressible analogue of the rotating convective layer that was considered by Cattaneo&Hughes (2006). Varying the horizontal scale of the computational domain, we investigate the dependence of the dynamo upon the rotation rate. Our simulations indicate that these turbulent compressible flows can drive a small-scale dynamo but, even when the layer is rotating very rapidly (with a mid-layer Taylor number of Ta=10^8), w...

  14. The effects of ion mass variation and domain size on octupolar out-of-plane magnetic field generation in collisionless magnetic reconnection

    CERN Document Server

    von der Pahlen, Jan Graf

    2015-01-01

    J. Graf von der Pahlen and D. Tsiklauri, Phys. Plas. 21, 060705 (2014), established that the generation of octupolar out-of-plane magnetic field structure in a stressed $X$-point collapse is due to ion currents. The field has a central region, comprising of the well-known qaudrupolar field (quadrupolar components), as well as four additional poles of reversed polarity closer to the corners of the domain (octupolar components). In this extended work, the dependence of the octupolar structure on domain size and ion mass variation is investigated. Simulations show that the strength and spatial structure of the generated octupolar magnetic field is independent of ion to electron mass ratio. Thus showing that ion currents play a significant role in out-of-plane magnetic structure generation in physically realistic scenarios. Simulations of different system sizes show that the width of the octupolar structure remains the same and has a spacial extent of the order of the ion inertial length. The width of the structu...

  15. Exploring Magnetic Fields

    Science.gov (United States)

    2012-08-03

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

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

    Science.gov (United States)

    Babouri, A; Hedjeidj, A

    2007-01-01

    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

  17. Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability

    Science.gov (United States)

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

    2007-01-01

    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.

  18. Magnetic field effect on the third harmonic generation in quantum well wires with triangular cross-section

    Science.gov (United States)

    Niculescu, E. C.; Cristea, M.; Radu, A.

    2014-03-01

    The conduction subband structure of a triangular cross-section GaAs/AlGaAs quantum well wire under magnetic field is theoretically investigated by taking into account a finite confining potential and two orientations of the field relative to the wire axis. The calculation of the subband energy levels is based on a two-dimensional finite element method within the effective mass approximation. It is shown that the magnetic field could be used for tuning the intersubband transitions: in the transverse field there is an obvious augment of the energy levels, whereas an axial field induces blueshifts/redshifts on the subband energies, depending on the azimuthal quantum number. We found that an axial orientation of the field allows the third harmonic generation and this process is enhanced for a particular polarization of the incident light and a proper field strength. A third-order nonlinear susceptibility with a peak value of 10-13 ( is predicted when the triple resonance condition is achieved.

  19. Magnetic Fields Matter

    Science.gov (United States)

    VU Bioengineering RET Program, School of Engineering,

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

  20. Visualizing Magnetic Field Lines

    Science.gov (United States)

    VU Bioengineering RET Program, School of Engineering,

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

  1. What are Magnetic Fields?

    Science.gov (United States)

    This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

  2. Magnetic field line Hamiltonian

    International Nuclear Information System (INIS)

    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

  3. Generating Long Scale-Length Plasma Jets Embedded in a Uniform, Multi-Tesla Magnetic-Field

    Science.gov (United States)

    Manuel, Mario; Kuranz, Carolyn; Rasmus, Alex; Klein, Sallee; Fein, Jeff; Belancourt, Patrick; Drake, R. P.; Pollock, Brad; Hazi, Andrew; Park, Jaebum; Williams, Jackson; Chen, Hui

    2013-10-01

    Collimated plasma jets emerge in many classes of astrophysical objects and are of great interest to explore in the laboratory. In many cases, these astrophysical jets exist within a background magnetic field where the magnetic pressure approaches the plasma pressure. Recent experiments performed at the Jupiter Laser Facility utilized a custom-designed solenoid to generate the multi-tesla fields necessary to achieve proper magnetization of the plasma. Time-gated interferometry, Schlieren imaging, and proton radiography were used to characterize jet evolution and collimation under varying degrees of magnetization. Experimental results will be presented and discussed. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, by the National Laser User Facility Program, grant number DE-NA0000850, by the Predictive Sciences Academic Alliances Program in NNSA-ASC, grant number DEFC52-08NA28616, and by NASA through Einstein Postdoctoral Fellowship grant number PF3-140111 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060.

  4. Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: Optimization of corrections and quantitative characterization of magnet/gradient systems

    OpenAIRE

    Boesch, C.; Gruetter, R.; Martin, E.

    1991-01-01

    We propose methods for the spatial and temporal characterization of time-dependent magnetic fields generated by eddy currents after switching gradients. For an on-line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift ??B(z)(t) and of a decay constant k(t). This procedure allows us to optimize interactively the multiexponential pre-emphasis as well as any spectral ...

  5. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Mark, J. Abraham Hudson, E-mail: a.john.peter@gmail.com; Peter, A. John, E-mail: a.john.peter@gmail.com [Dept. of Physics, SSM Institute of Engineering and Technology, Dindigul-624002 (India)

    2014-04-24

    Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  6. Determination of self generated magnetic field and the plasma density using Cotton Mouton polarimetry with two color probes

    Directory of Open Access Journals (Sweden)

    Joshi A.S.

    2013-11-01

    Full Text Available Self generated magnetic fields (SGMF in laser produced plasmas are conventionally determined by measuring the Faraday rotation angle of a linearly polarized laser probe beam passing through the plasma along with the interferogram for obtaining plasma density. In this paper, we propose a new method to obtain the plasma density and the SGMF distribution from two simultaneous measurements of Cotton Mouton polarimetry of two linearly polarized probe beams of different colors that pass through plasma in a direction normal to the planar target. It is shown that this technique allows us to determine the distribution of SGMF and the plasma density without doing interferometry of laser produced plasmas.

  7. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    International Nuclear Information System (INIS)

    Third order susceptibility of third order harmonic generation is investigated in a Zn0.1Mg0.9Se/Zn0.8Mg0.2Se/Zn0.1Mg0.9Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems

  8. Shocks in unmagnetized plasma with a shear flow: Stability and magnetic field generation

    CERN Document Server

    Dieckmann, M E; Ahmed, H; Doria, D; Sarri, G; Ynnerman, A; Borghesi, M

    2015-01-01

    A pair of curved shocks in a collisionless plasma is examined with a two-dimensional particle-in-cell (PIC) simulation. The shocks are created by the collision of two electron-ion clouds at a speed that exceeds everywhere the threshold speed for shock formation. A variation of the collision speed along the initially planar collision boundary, which is comparable to the ion acoustic speed, yields a curvature of the shock that increases with time. The spatially varying Mach number of the shocks results in a variation of the downstream density in the direction along the shock boundary. This variation is eventually equilibrated by the thermal diffusion of ions. The pair of shocks is stable for tens of inverse ion plasma frequencies. The angle between the mean flow velocity vector of the inflowing upstream plasma and the shock's electrostatic field increases steadily during this time. The disalignment of both vectors gives rise to a rotational electron flow, which yields the growth of magnetic field patches that a...

  9. 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)

  10. Mapping Magnetic Fields

    Science.gov (United States)

    2012-08-03

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

  11. 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)

  12. 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

  13. The Earth's Magnetic Field

    OpenAIRE

    Edda Lína Gunnarsdóttir 1988

    2012-01-01

    The Earth's magnetic field is essential for life on Earth, as we know it, to exist. It forms a magnetic shield around the planet, protecting it from high energy particles and radiation from the Sun, which can cause damage to life, power systems, orbiting satellites, astronauts and spacecrafts. This report contains a general overview of the Earth's magnetic field. The different sources that contribute to the total magnetic field are presented and the diverse variations in the field are describ...

  14. The Declining Magnetic Field

    Science.gov (United States)

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

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

    CERN Document Server

    Garai, Jozsef

    2007-01-01

    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.

  16. 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

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

    Czech Academy of Sciences Publication Activity Database

    Šimkanin, Ján; Hejda, Pavel

    2013-01-01

    Ro?. 217, April (2013), s. 22-30. ISSN 0031-9201 R&D Projects: GA AV ?R IAA300120704 Institutional support: RVO:67985530 Keywords : hydromagnetic dynamo * Prandtl number * magnetic Prandtl number * inertia l forces Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 2.398, year: 2013

  18. Generation of magnetic field by the current-driven instability near cosmic-ray modified shocks

    International Nuclear Information System (INIS)

    We study the non-linear properties of the current-driven instability predicted by Bell (2004). In the first part, we combine an analytical modeling plus particle-in-cell (PIC) simulations to make a one-dimensional study of the waves as they were isolated plane waves subject to a constant cosmic ray (CR) current. In the second part, we relax these conditions by including multidimensional effects and also the back-reaction on the CRs. In the idealistic case, we find that the current-driven waves can grow exponentially until the Alfven velocity of the plasma, Va, becomes comparable to the drift velocity of the CRs, Vcr. We also find that, in the exponential growth regime, the current-driven waves will move the plasma along the direction of propagation of the CRs at a speed ?Va2/Vcr. Also, they will induce transversal plasma motions of about the '' transversal Alfven speed '', which is the Alfven speed calculated only with the fields perpendicular to the CR current. The multidimensional evolution of the instability is studied making use of two- and three-dimensional simulations. First, we find that a condition for the growth of the instability is that Vcr(Ncr/Ni) << Vai, where Ncr and Ni are the density of CR and background ions, respectively, and Vai is the initial Alfven velocity of the plasma. If this condition is not met, the instability will be suppressed by the formation of strong plasma filaments of the scale of the ions skin depth. We also find that, even if the current-driven waves can grow, they will produce significant density fluctuations in the plasma shortly after they become non-linear, which confirm previous numerical MHD studies. The formation of these fluctuations will decrease the growth rate of the instability and will enlarge its dominant wavelengths. We also study the effect of the back-reaction on CR. We find that, if the Larmor radii of the CR become comparable to the size of the magnetic fluctuations, the deflection of the CR can saturate the instability before the regime Va ? Vcr is reached. We discuss applications of this instability to both relativistic and non-relativistic shock environments. (author)

  19. Magnetic Field Problem

    Science.gov (United States)

    Wolfgang Christian

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

  20. 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%

  1. Study of the magnetic fields and soft X-ray emission generated in the implosion of double wire arrays

    International Nuclear Information System (INIS)

    Results are presented from measurements of the azimuthal magnetic field generated during the implosion of double (nested) tungsten wire arrays in the Angara-5-1 facility at currents of ?3 MA. It is found that the inner array affects the current distribution in the interarray space and that there is an optimal mass (an optimal number of wires) of the inner array at which the full width at half-maximum of the soft X-ray pulse (in the photon energy range of >100 eV) is minimal. On the average, double wire arrays provide a better reproductibility, higher power, and shorter duration of the soft X-ray pulse in comparison to single arrays

  2. Mapping Magnetic Field Lines

    Science.gov (United States)

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

  3. Magnetic fields from second-order interactions

    OpenAIRE

    Osano, Bob

    2014-01-01

    It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a c...

  4. Ferromagnetic Domain Wall and Primeval Magnetic Field

    OpenAIRE

    Iwazaki, Aiichi

    1996-01-01

    We show that coherent magnetic field is generated spontaneously when a large domain wall is created in the early universe. It is caused by two dimensional massless fermions bounded to the domain wall soliton. We point out that the magnetic field is a candidate of primordial magnetic field.

  5. Pre-ionization and spectroscopic diagnostic of plasma generated and confined by magnetic fields

    International Nuclear Information System (INIS)

    A ?-pinch system has been constructed with pre-heating devices with a total energy of 2 kJ. During this experiment a He Plasma was studied using the following three different diagnostics. a) Magnetic Probes b) Visible Spectroscopy using the Optical Multichannel Analyser - OMA c) Image Converter Camera. The experimental results have been checked with existing theoretical models. The electrical characteristics of the system were determined with the magnetic probe. The Doppler and Stark broadening effects of the ?o = 4686 (angstrom) (HeII) have been used to determine the ionic temperature and electronic density respectively. The time evolution of these parameters was obtained using the OMA. The dynamics of the plasma were observed by high speed photography. Instabilities in the plasma columm have been observed. Good agreement between the experimental and theoretical values was obtained. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-05-15

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

  7. 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)

  8. Field free line magnetic particle imaging

    CERN Document Server

    Erbe, Marlitt

    2014-01-01

    Marlitt Erbe provides a detailed introduction into the young research field of Magnetic Particle Imaging (MPI) and field free line (FFL) imaging in particular. She derives a mathematical description of magnetic field generation for FFL imaging in MPI. To substantiate the simulation studies on magnetic FFL generation with a proof-of-concept, the author introduces the FFL field demonstrator, which provides the world's first experimentally generated rotated and translated magnetic FFL field complying with the requirements for FFL reconstruction. Furthermore, she proposes a scanner design of consi

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

    Science.gov (United States)

    Sheikholeslami, Mohsen; Ganji, Davood Domiri

    2015-01-01

    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.

  10. Magnetic field line Hamiltonian

    International Nuclear Information System (INIS)

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

  11. Magnetic field line Hamiltonian

    Energy Technology Data Exchange (ETDEWEB)

    Boozer, A.H.

    1984-03-01

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

  12. The outer magnetic field

    Science.gov (United States)

    Hoeksema, J. T.; Suess, S. T.

    1990-01-01

    The magnetic field of the sun extends outward through the photosphere into the corona. The resulting coronal and interplanetary magnetic fields therefore respond to and evolve with the solar cycle, as well as on shorter and longer time scales. These fields are modeled using photospheric magnetic field observations under the assumption that the coronal field is current free, becomes radial at a 'source surface' placed at 2.5 solar radii from the center of the sun, and is passively advected by the solar wind beyond the source surface. This review covers the computation of such models and their applications to characterize the morphology, evolution, and rotation of coronal and interplanetary magnetic fields using data collected between 1976 and the present at the Wilcox Solar Observatory.

  13. Magnet Free Generators - 3rd Generation Wind Turbine Generators

    DEFF Research Database (Denmark)

    Jensen, Bogi Bech; Mijatovic, Nenad

    2013-01-01

    This paper presents an introduction to superconducting wind turbine generators, which are often referred to as 3rd generation wind turbine generators. Advantages and challenges of superconducting generators are presented with particular focus on possible weight and efficiency improvements. A comparison of the rare earth usage in different topologies of permanent magnet generators and superconducting generators is also presented.

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

    CERN Document Server

    Modica, Frank; Zhiglo, Andrey

    2013-01-01

    (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)...

  15. Magnetic fields at Neptune

    International Nuclear Information System (INIS)

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

  16. Passive Magnetic Shielding in Gradient Fields

    CERN Document Server

    Bidinosti, C P

    2013-01-01

    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...

  17. Energy transfer and magnetic field generation via ion-beam driven instabilities in an electron-ion plasma

    International Nuclear Information System (INIS)

    Whether an efficient collisionless temperature equilibration mechanism exists for a two-temperature ion-electron plasma, with Ti>Te, is important for understanding astrophysical phenomena such as two-temperature accretion flows and collisionless shocks in supernova remnants or gamma-ray bursts. In this paper, counter-streaming ion beam-driven two-stream, Weibel (or filamentation), and oblique instabilities are studied using two-dimensional (2D) particle-in-cell (PIC) simulations as a possible plasma instability that could operate in such astrophysical objects. The PIC simulations show interplay among these instabilities and that distinct stages with different dominant modes occur during the nonlinear evolution period. Although the 2D results show stronger electron-ion coupling than the one-dimensional (1D) instabilities, it is still too weak to rule out existing two-temperature accretion solutions. The nonrelativistic quasilinear equations for the 1D Weibel plus 1D two-stream modes are numerically solved to compare the results with the 2D PIC simulations and qualitative similarities were found. The equations also show that the magnetic fields generated by the Weibel instability decay to zero in the end.

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

    Directory of Open Access Journals (Sweden)

    Imbert-Gérard Lise-Marie

    2011-11-01

    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].

  19. Magnetic Resonance Imaging of time-varying magnetic fields from therapeutic devices

    OpenAIRE

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

    2013-01-01

    While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields, such as those generated by transcranial magnetic stimulators or radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this work. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by...

  20. Mapping Magnetic Field Lines

    Science.gov (United States)

    2012-08-03

    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.

  1. Transient anisotropic magnetic field calculation

    International Nuclear Information System (INIS)

    For anisotropic magnetic material, nonlinear magnetic characteristics of the material are described with magnetization curves for different magnetization directions. The paper presents transient finite element calculation of the magnetic field in the anisotropic magnetic material based on the measured magnetization curves for different magnetization directions. For the verification of the calculation method some results of the calculation are compared with the measurement

  2. Optimum Magnets for MHD Generators

    International Nuclear Information System (INIS)

    One of the more critical aspects in the design of MHD power generation systems for specific applications concerns the proper selection of a magnet for the generator. The advent of superconducting (low weight, zero power) magnets will allow of the realization of MHD systems which are competitive with conventional power generators. Nevertheless, resistive or permanent magnets may prove superior to superconducting magnets for certain types of MHD generation systems. The purpose of this study is to define the areas of applicability for permanent, conventionally cooled resistive, cryogenically cooled resistive, and superconducting magnets to open cycle MHD power generation systems. Combustion driven MHD generators utilizing continuous electrode Faraday and Hall configurations are investigated. In all cases, typical values of gas scalar conductivity, gas velocity, and Hall coefficient are used. Operation of such generators is considered over the range of net power output 100 kW to 1000 MW for durations of 1 ms to one year. For each generator case considered, magnet characteristics are calculated for systems optimized on the basis of either total system cost or total system weight by computer analysis. Magnets and refrigerator systems are assumed to be operated with power generated by the MHD process. The cost, weight, and power requirements of magnet cooling systems are calculated and included in the magnet design criteria. The net power produced by the generator must be computed taking into consideration the proper efficiency factors and losses represented by Joule heating in the resistive magnets and refrigeration losses in superconducting magnets. Coolant tankage weights are also considered for aerospace systems. The type or types of magnets most applicable to the given operating situation for the two types of generators are then selected. The selection of magnet types for stationary and mobile systems as well as for short and long duration systems is made. The results of the investigation are presented in summary form for two types of MHD generators. These results are plotted on power duration and net power output co-ordinates to show the economical operating regimes of the various types of magnets. Both a weight and cost optimum regime are shown for the entire MHD generator operating range. The most significant result of the analysis is that high-purity aluminium magnets cooled with liquid hydrogen exhibit a wide range of application from both a cost and weight standpoint. (author)

  3. Control of chaotic magnetic fields in tokamaks

    Scientific Electronic Library Online (English)

    I. L., Caldas; R. L., Viana; M. S. T., Araujo; A., Vannucci; E. C. da, Silva; K., Ullmann; M. V. A. P., Heller.

    2002-12-01

    Full Text Available Chaotic magnetic field lines play an important role in plasma confinement by tokamaks. They can either be generated in the plasma as a result of natural instabilities or artifficially produced by external conductors, like resonant helical windings and ergodic magnetic limiters. This is a review of w [...] orks carried out at the Universidade de São Paulo and Universidade Federal do Paraná on theoretical and experimental aspects of generation and control of chaotic magnetic field lines in tokamaks.

  4. Electric Field Feature of Moving Magnetic Field

    Science.gov (United States)

    Chen, You Jun

    2001-05-01

    A new fundamental relationship of electric field with magnetic field has been inferred from the fundamental experimental laws and theories of classical electromagnetics. It can be described as moving magnetic field has or gives electric feature. When a field with magnetic induction of B moves in the velocity of V, it will show electric field character, the electric field intensity E is E = B x V and the direction of E is in the direction of the vector B x V. It is improper to use the time-varying electromagnetics theories as the fundamental theory of the electromagnetics and group the electromagnetic field into static kind and time-varying kind for the static is relative to motional not only time-varying. The relationship of time variation of magnetic field induction or magnetic flux with electric field caused by magnetic field is fellowship not causality. Thus time-varying magnetic field can cause electric field is not a nature principle. Sometime the time variation of magnetic flux is equal to the negative electromotive force or the time variation of magnetic field induction is equal to the negative curl of electric field caused by magnetic field motion, but not always. And not all motion of magnetic field can cause time variation of magnetic field. Therefore Faraday-Lenz`s law can only be used as mathematics tool to calculate the quantity relation of the electricity with the magnetism in some case like the magnetic field moving in uniform medium. Faraday-Lenz`s law is unsuitable to be used in moving uniform magnetic field or there is magnetic shield. Key word: Motional magnetic field, Magnetic induction, Electric field intensity, Velocity, Faraday-Lenz’s law

  5. Magnetic field spectrum at cosmological recombination revisited

    Science.gov (United States)

    Saga, Shohei; Ichiki, Kiyotomo; Takahashi, Keitaro; Sugiyama, Naoshi

    2015-06-01

    If vector type perturbations are present in the primordial plasma before recombination, the generation of magnetic fields is known to be inevitable through the Harrison mechanism. In the context of the standard cosmological perturbation theory, nonlinear couplings of first-order scalar perturbations create second-order vector perturbations, which generate magnetic fields. Here we reinvestigate the generation of magnetic fields at second-order in cosmological perturbations on the basis of our previous study, and extend it by newly taking into account the time evolution of purely second-order vector perturbations with a newly developed second-order Boltzmann code. We confirm that the amplitude of magnetic fields from the product-terms of the first-order scalar modes is consistent with the result in our previous study. However, we find, both numerically and analytically, that the magnetic fields from the purely second-order vector perturbations partially cancel out the magnetic fields from one of the product-terms of the first-order scalar modes, in the tight coupling regime in the radiation dominated era. Therefore, the amplitude of the magnetic fields on small scales, k ?10 h Mpc-1 , is smaller than the previous estimates. The amplitude of the generated magnetic fields at cosmological recombination is about Brec=5.0 ×10-24 Gauss on k =5.0 ×10-1 h Mpc-1 . Finally, we discuss the reason for the discrepancies that exist in estimates of the amplitude of magnetic fields among other authors.

  6. Emission of magnetic fields from distribution lines

    International Nuclear Information System (INIS)

    Ontario Hydro performed a study of emission of magnetic fields from distribution lines. Comprehensive calculations were performed to evaluate magnetic fields by varying standard pole framings, voltages, typical currents, very high currents near transformers and distribution stations, perfectly balanced, and 10% unbalanced lines. All tests computed magnetic flux under the distribution line at 1 m exposure above ground. The magnetic fields measured ranged from 1.2-22 ?Tesla. These values relate very closely to magnetic fields generated by household appliances. The most effective reduction of magnetic fields occurs when the following conditions are met: reverse phasing arrangement on double-phase lines; transportation of 3-phase lines; replacement of crossarm pole framing with armless pole framing; conversion of single phase to 3-phase lines; and balancing lines as best as possible. Field strengths are compared to those found with naturally occurring magnetic fields, household appliances, transportation, security systems, industrial processes, and medical practices. 2 refs., 1 fig., 5 tabs

  7. Assessment of Foetal Exposure to the Homogeneous Magnetic Field Harmonic Spectrum Generated by Electricity Transmission and Distribution Networks

    Science.gov (United States)

    Fiocchi, Serena; Liorni, Ilaria; Parazzini, Marta; Ravazzani, Paolo

    2015-01-01

    During the last decades studies addressing the effects of exposure to Extremely Low Frequency Electromagnetic Fields (ELF-EMF) have pointed out a possible link between those fields emitted by power lines and childhood leukaemia. They have also stressed the importance of also including in the assessment the contribution of frequency components, namely harmonics, other than the fundamental one. Based on the spectrum of supply voltage networks allowed by the European standard for electricity quality assessment, in this study the exposure of high-resolution three-dimensional models of foetuses to the whole harmonic content of a uniform magnetic field with a fundamental frequency of 50 Hz, was assessed. The results show that the main contribution in terms of induced electric fields to the foetal exposure is given by the fundamental frequency component. The harmonic components add some contributions to the overall level of electric fields, however, due to the extremely low permitted amplitude of the harmonic components with respect to the fundamental, their amplitudes are low. The level of the induced electric field is also much lower than the limits suggested by the guidelines for general public exposure, when the amplitude of the incident magnetic field is set at the maximum permitted level. PMID:25837346

  8. Assessment of Foetal Exposure to the Homogeneous Magnetic Field Harmonic Spectrum Generated by Electricity Transmission and Distribution Networks

    Directory of Open Access Journals (Sweden)

    Serena Fiocchi

    2015-04-01

    Full Text Available During the last decades studies addressing the effects of exposure to Extremely Low Frequency Electromagnetic Fields (ELF-EMF have pointed out a possible link between those fields emitted by power lines and childhood leukaemia. They have also stressed the importance of also including in the assessment the contribution of frequency components, namely harmonics, other than the fundamental one. Based on the spectrum of supply voltage networks allowed by the European standard for electricity quality assessment, in this study the exposure of high-resolution three-dimensional models of foetuses to the whole harmonic content of a uniform magnetic field with a fundamental frequency of 50 Hz, was assessed. The results show that the main contribution in terms of induced electric fields to the foetal exposure is given by the fundamental frequency component. The harmonic components add some contributions to the overall level of electric fields, however, due to the extremely low permitted amplitude of the harmonic components with respect to the fundamental, their amplitudes are low. The level of the induced electric field is also much lower than the limits suggested by the guidelines for general public exposure, when the amplitude of the incident magnetic field is set at the maximum permitted level.

  9. Indoor localization using magnetic fields

    Science.gov (United States)

    Pathapati Subbu, Kalyan Sasidhar

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

  10. 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.

  11. ISR Radial Field Magnet

    CERN Multimedia

    1983-01-01

    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

  12. Noncommutativity in space and primordial magnetic field

    International Nuclear Information System (INIS)

    In this paper we show that noncommutativity in spatial coordinates can generate magnetic field in the early Universe on a horizon scale. The strength of such a magnetic field depends on tin number density of massive charged particles present at a given moment. This allows us to trace back the temperature dependence of the noncommutativity scale from the bounds on primordial magnetic field coming from nucleosynthesis. (author)

  13. Noncommutativity in Space and Primordial Magnetic Field

    OpenAIRE

    Mazumdar, Anupam; M Sheikh-jabbari, Mohammad

    2000-01-01

    In this paper we show that noncommutativity in spatial coordinates can generate magnetic field in the early Universe on a horizon scale. The strength of such a magnetic field depends on the number density of massive charged particles present at a given moment. This allows us to trace back the temperature dependence of the noncommutativity scale from the bounds on primordial magnetic field coming from nucleosynthesis.

  14. HMI Magnetic Field Products

    Science.gov (United States)

    Hoeksema, Jon T.; HMI Magnetic Field Team

    2013-07-01

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

  15. Proton probing measurement of electric and magnetic fields generated by ns and ps laser-matter interactions

    International Nuclear Information System (INIS)

    The use of laser-accelerated protons as a particle probe for the detection of electric fields in plasmas has led in recent years to a wealth of novel information regarding the ultrafast plasma dynamics following high intensity laser-matter interactions. The high spatial quality and short duration of the beams have been essential to this purpose. We will discuss some of the most recent results obtained with this diagnostic at the Rutherford Appleton Laboratory (UK) and at LULI - Ecole Polytechnique (France), also applied to conditions of interest to conventional Inertial Confinement Fusion. In particular, the technique has been used to measure electric fields responsible for proton acceleration from solid targets irradiated with ps pulses, magnetic fields formed by ns pulse irradiation of solid targets, and electric fields associated with the ponderomotive channelling of ps laser pulses in under-dense plasmas. (author)

  16. High magnetic fields science and technology

    CERN Document Server

    Miura, Noboru

    2003-01-01

    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

  17. 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)

    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

    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.

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

    OpenAIRE

    Porselvi Thayumanavan; Ranganath Muthu; Jeyasudha Sankararaman

    2014-01-01

    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...

  19. High field superconducting magnets

    Science.gov (United States)

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

    2011-01-01

    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.

  20. Magnetic fields in the sun

    Science.gov (United States)

    Mullan, D. J.

    1974-01-01

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

  1. Relaxed plasmas in external magnetic fields

    International Nuclear Information System (INIS)

    The extension of the theory of relaxed plasmas to external magnetic fields whose field lines intersect the wall is concisely formulated and then applied to the Extrap experiment [J. R. Drake, Plasma Phys. Controlled Fusion 26, 387 (1984)]. It is found that the external octupole field, though not affecting the phenomenon of current saturation, inhibits field reversal at parts of the wall if it is sufficiently strong to generate magnetic x points within the plasma

  2. Optical generation of intense ultrashort magnetic pulses at the nanoscale

    International Nuclear Information System (INIS)

    Generating, controlling and sensing strong magnetic fields at ever shorter time and length scales is important for both fundamental solid-state physics and technological applications such as magnetic data recording. Here, we propose a scheme for producing strong ultrashort magnetic pulses localized at the nanoscale. We show that a bimetallic nanoring illuminated by femtosecond laser pulses responds with transient thermoelectric currents of picosecond duration, which in turn induce Tesla-scale magnetic fields in the ring cavity. Our method provides a practical way of generating intense nanoscale magnetic fields with great potential for materials characterization, terahertz radiation generation and data storage applications. (paper)

  3. Focus on Materials Analysis and Processing in Magnetic Fields

    OpenAIRE

    Yoshio Sakka, Noriyuki Hirota

    2009-01-01

    Recently, interest in the applications of feeble (diamagnetic and paramagnetic) magnetic materials has grown, whereas the popularity of ferromagnetic materials remains steady and high. This trend is due to the progress of superconducting magnet technology, particularly liquid-helium-free superconducting magnets that can generate magnetic fields of 10 T and higher. As the magnetic energy is proportional to the square of the applied magnetic field, the magnetic energy of such 10 T magnets is in...

  4. Magnetic fields in diffuse media

    CERN Document Server

    Pino, Elisabete; Melioli, Claudio

    2015-01-01

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

  5. Study of the magnetic fields and soft X-ray emission generated in the implosion of double wire arrays

    International Nuclear Information System (INIS)

    One discusses the results of the measurements of azimuth magnetic fields at implosion of double (inserted into one another) tungsten wire arrays at the Angara-5-1 plant under ? 3 MA current. One revealed the effect of the internal array on current distribution in gap between the arrays. It is shown that there is the number optimum of wires (mass) in the internal array relevant to the minimum of soft X-ray radiation pulse duration. On the average, the inserted arrays ensure the best frequency, higher power and shorter duration of pulse in contrast to single ones

  6. Magnetic fields in the cosmos

    International Nuclear Information System (INIS)

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

  7. The rotation-magnetic field relation

    CERN Document Server

    Reiners, A; Eislöffel, J; Hallinan, G; Berger, E; Browning, M; Irwin, J; Küker, M; Matt, S

    2008-01-01

    Today, the generation of magnetic fields in solar-type stars and its relation to activity and rotation can coherently be explained, although it is certainly not understood in its entirety. Rotation facilitates the generation of magnetic flux that couples to the stellar wind, slowing down the star. There are still many open questions, particularly at early phases (young age), and at very low mass. It is vexing that rotational braking becomes inefficient at the threshold to fully convective interiors, although no threshold in magnetic activity is seen, and the generation of large scale magnetic fields is still possible for fully convective stars. This article briefly outlines our current understanding of the rotation-magnetic field relation.

  8. The rotation-magnetic field relation

    Science.gov (United States)

    Reiners, Ansgar; Scholz, Alexander; Eislöffel, Jochen; Hallinan, Gregg; Berger, Edo; Browning, Matthew; Irwin, Jonathan; Küker, Manfred; Matt, Sean

    2009-02-01

    Today, the generation of magnetic fields in solar-type stars and its relation to activity and rotation can coherently be explained, although it is certainly not understood in its entirety. Rotation facilitates the generation of magnetic flux that couples to the stellar wind, slowing down the star. There are still many open questions, particularly at early phases (young age), and at very low mass. It is vexing that rotational braking becomes inefficient at the threshold to fully convective interiors, although no threshold in magnetic activity is seen, and the generation of large scale magnetic fields is still possible for fully convective stars. This article briefly outlines our current understanding of the rotation-magnetic field relation.

  9. Measuring the Earth's Magnetic Field in a Laboratory

    Science.gov (United States)

    Cartacci, A.; Straulino, S.

    2008-01-01

    Two methods for measuring the Earth's magnetic field are described. In the former, according to Gauss, the Earth's magnetic field is compared with that of a permanent magnet; in the latter, a well-known method, the comparison is made with the magnetic field generated by a current. As all the used instruments are available off the shelf, both…

  10. Magnetic Field Problem: Current and Magnets

    Science.gov (United States)

    Wolfgang Christian

    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.

  11. Magnetic Field Topology in Jets

    Science.gov (United States)

    Gardiner, T. A.; Frank, A.

    2000-01-01

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

  12. Low field magnetic resonance imaging

    Science.gov (United States)

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

    2010-07-13

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

  13. Five years of magnetic field management

    International Nuclear Information System (INIS)

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

  14. Probing Magnetic Fields With SNRs

    Science.gov (United States)

    Kothes, Roland

    2015-03-01

    As supernova remnants (SNRs) expand, their shock waves freeze in and compress magnetic field lines they encounter; consequently we can use SNRs as magnifying glasses for interstellar magnetic fields. A simple model is used to derive polarization and rotation measure (RM) signatures of SNRs. This model is exploited to gain knowledge about the large-scale magnetic field in the Milky Way. Three examples are given which indicate a magnetic anomaly, an azimuthal large-scale magnetic field towards the anti-centre, and a chimney that releases magnetic energy from the plane into the halo.

  15. 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

  16. 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)

  17. The National High Magnetic Field Laboratory

    International Nuclear Information System (INIS)

    The National High Magnetic Field Laboratory, established in 1990 with support from the National Science Foundation, State of Florida, and the US Department of Energy, is a facility open to external users around the world. The experimental capabilities are distributed in three campuses. In Tallahassee, Florida, continuous magnetic fields are produced by means of superconducting and resistive magnets reaching fields of up to 33T (resistive), and 45T (hybrid). EMR, ICR, and a 900MHz wide bore NMR magnet are also available. The facility in Gainesville, Florida, is devoted to generating extremely low temperatures in the presence of external magnetic fields (15T, down to 0.4mK), and large MRI imaging capabilities. In Los Alamos, New Mexico, a 9 kV-capable capacitor bank and a number of different liquid Nitrogen-cooled resistive magnets produce repetitive pulses up to 75 T and now a single-shot pulsed up to 300T

  18. The National High Magnetic Field Laboratory

    Science.gov (United States)

    Jaime, M.; Lacerda, A.; Takano, Y.; Boebinger, G. S.

    2006-11-01

    The National High Magnetic Field Laboratory, established in 1990 with support from the National Science Foundation, the State of Florida, and the US Department of Energy, is a facility open to external users around the world. The experimental capabilities are distributed in three campuses. In Tallahassee, Florida, continuous magnetic fields are produced by means of superconducting and resistive magnets reaching fields of up to 33T (resistive), and 45T (hybrid). EMR, ICR, and a 900MHz wide bore NMR magnet are also available. The facility in Gainesville, Florida, is devoted to generating extremely low temperatures in the presence of external magnetic fields (15T, down to 0.4mK), and large MRI imaging capabilities. In Los Alamos, New Mexico, a 9 kV-capable capacitor bank and a number of different liquid Nitrogen-cooled resistive magnets produce repetitive pulses up to 75 T and now a single-shot pulsed up to 300T.

  19. Generation of zonal flow and magnetic field by coupled Rossby–Alfvén–Khantadze waves in the Earth's ionospheric E-layer

    International Nuclear Information System (INIS)

    It is shown that in the Earth's weakly ionized ionospheric E-layer with the dominant Hall conductivity, a new type of coupled Rossby–Alfvén–Khantadze (CRAK) electromagnetic (EM) planetary waves, attributable by the latitudinal inhomogeneity of both the Earth's Coriolis parameter and the geomagnetic field, can exist. Under such coupling, a new type of dispersive Alfvén waves is revealed. The generation of a sheared zonal flow and a magnetic field by CRAK EM planetary waves is investigated. The nonlinear mechanism of the instability is based on the parametric excitation of a zonal flow by interacting four waves, leading to the inverse energy cascade in the direction of a longer wavelength. A three-dimensional (3D) set of coupled equations describing the nonlinear interaction of pumping CRAK waves and zonal flow is derived. The growth rate of the corresponding instability and the conditions for driving them are determined. It is found that the growth rate is mainly stipulated by Rossby waves but the generation of the intense mean magnetic field is caused by Alfvén waves. (paper)

  20. Magnetic nanoparticle motion in external magnetic field

    Science.gov (United States)

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

    2015-07-01

    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 magnetization vector and the director that is parallel the particle easy anisotropy axis. These modes differ significantly in the precession frequency. For the high-frequency mode the director points approximately along the external magnetic field, whereas the frequency and the characteristic relaxation time of the precession of the unit magnetization vector are close to the corresponding values for conventional ferromagnetic resonance. On the other hand, for the low-frequency modes the unit magnetization vector and the director are nearly parallel and rotate in unison around the external magnetic field. The characteristic relaxation time for the low-frequency modes is remarkably long. This means that in a rare assembly of magnetic nanoparticles there is a possibility of additional resonant absorption of the energy of alternating magnetic field at a frequency that is much smaller compared to conventional ferromagnetic resonance frequency. The scattering of a beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic field is also considered taking into account the precession of the unit magnetization vector and director.

  1. Shear angle of magnetic fields.

    Science.gov (United States)

    Yanping, Lü; Wang, Jingxiu; Wang, Huaning

    1993-11-01

    The authors introduce a new parameter, the shear angle of vector magnetic fields, ??, to describe the non-potentiality of magnetic fields in active regions, which is defined as the angle between the observed vector magnetic field and its corresponding current-free field. In the case of highly inclined field configurations, this angle is approximately equal to the "angular shear", ??, defined by Hagyard et al. (1984). ?? can be considered as the projection of the shear angle, ??, on the photosphere. For the active region studied, the shear angle, ??, seems to have a better and neater correspondence with flare activity than does ??. It gives a clearer explanation of the non-potentiality of magnetic fields. It is a better measure of the deviation of the observed magnetic field from a potential field, and is directly related to the magnetic free energy stored in non-potential fields.

  2. Dynamical Symmetry Breaking on a Cylinder in Magnetic Field

    OpenAIRE

    Gamayun, A. V.; Gorbar, E. V.

    2004-01-01

    We study dynamical symmetry breaking on a cylinder in external magnetic field parallel to the axis of cylinder when magnetic field affects the dynamics of fermions only through the Aharonov-Bohm phase. We find that unlike other previously studied cases magnetic field in our case counteracts the generation of dynamical fermion mass which decreases with magnetic field. There exists also a purely kinematical contribution to the fermion gap which grows linearly with magnetic fie...

  3. 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

  4. Comparison of adjustable permanent magnetic field sources

    DEFF Research Database (Denmark)

    BjØrk, Rasmus; Bahl, Christian Robert Haffenden

    2010-01-01

    A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generated magnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magnetic field are measured and compared with numerical simulation and a good agrement is found.

  5. Skyrmion Motion Driven by Oscillating Magnetic Field

    OpenAIRE

    Moon, Kyoung-Woong; Kim, Duck-Ho; Je, Soong-Geun; Chun, Byong Sun; Kim, Wondong; Z. Q. Qiu; Choe, Sug-Bong; Hwang, Chanyong

    2015-01-01

    Magnetic skyrmion motion induced by an electric current has drawn much interest because of its application potential in next-generation magnetic memory devices. Recently, unidirectional skyrmion motion driven by an oscillating magnetic field was also demonstrated on large (20 micrometer) bubble domains with skyrmion topology. At smaller length scale which is more relevant to high-density memory devices, we here show by numerical simulation that a skyrmion of a few tens of na...

  6. Integral magnetic field measurement of dipole magnets

    International Nuclear Information System (INIS)

    This article presents the basic principle of dipole integral magnetic field measurement. The integral coil which has the same radius with the dipole magnets was used to measure the integral magnetic field of different magnets in Cooler Storage Ring (HIRFL-CSR). The article also generally introduced the software and hardware systems of the automatic measurement device. According to the repetitive experiments, a suit of better measurement got to be summarized. On the other hand, the article recommends the way of the data processing which were decided by the measuring instrument and environment influence. The practical measured results proved the measurement system is reliable and stable

  7. Magnetic Field in Supernovae

    CERN Document Server

    Akiyama, S; Akiyama, Shizuka

    2002-01-01

    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...

  8. Improved efficiency of heat generation in magnetic nanoparticle hyperthermia

    OpenAIRE

    Racz, J.; de Chatel, P. F.; Szabo, I. A.; Szunyogh, L; Nandori, I.

    2015-01-01

    The deterministic Landau-Lifshitz-Gilbert equation has been used to investigate the nonlinear dynamics of magnetization and the specific loss power in magnetic nanoparticles with uniaxial anisotropy driven by a rotating magnetic field. We show that a more efficient heat generation by magnetic nanoparticles is possible if the direction of the rotating external field changes periodically and we suggest its possible experimental realization in cancer therapy which requires the ...

  9. Helical magnetic fields via baryon asymmetry

    CERN Document Server

    Piratova, Eduard F; Hortúa, Héctor J

    2014-01-01

    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 $\

  10. 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)

    T. RajaRani

    2012-01-01

    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.

  11. High magnetic field ohmically decoupled non-contact technology

    Science.gov (United States)

    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

    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.

  12. Magnetic monopole field exposed by electrons

    CERN Document Server

    Béché, A; Van Tendeloo, G; Verbeeck, J

    2013-01-01

    Magnetic monopoles have provided a rich field of study, leading to a wide area of research in particle physics, solid state physics, ultra-cold gases, superconductors, cosmology, and gauge theory. So far, no true magnetic monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the central results of quantum physics, shows however, that an effective monopole field can be produced. Understanding the effects of such a monopole field on its surroundings is crucial to its observation and provides a better grasp of fundamental physical theory. We realize the diffraction of fast electrons at a magnetic monopole field generated by a nanoscopic magnetized ferromagnetic needle. Previous studies have been limited to theoretical semiclassical optical calculations of the motion of electrons in such a monopole field. Solid state systems like the recently studied 'spin ice' provide a constrained system to study similar fields, but make it impossible to separate the monopole from the material. Free space ...

  13. Magnetic field dependent impact ionization in InSb

    OpenAIRE

    Hong, Jinki; Kim, Taeyueb; Joo, Sungjung; Song, Jin Dong; Han, Suk Hee; Shin, Kyung-ho; Chang, Joonyeon

    2012-01-01

    Carrier generation by impact ionization and subsequent recombination under the influence of magnetic field has been studied for InSb slab. A simple analytic expression for threshold electric field as a function of magnetic field is proposed. Impact ionization is suppressed by magnetic field. However, surface recombination is dependent on the polarity of magnetic field: strengthened in one direction and suppressed on the opposite direction. The former contributes quadratic in...

  14. 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.)

  15. The external magnetic field environment

    Science.gov (United States)

    1977-01-01

    Calculations were made to predict magnetic field intensities surrounding an aircraft following a lightning strike. Aircraft design and aircraft structural geometry were considered in the computations. A wire grid aircraft model was used to aid in magnetic flux estimation.

  16. Plasma diffusion through multi dipole magnetic fields

    International Nuclear Information System (INIS)

    The diffusion of a cold plasma through multi dipole fields of a magnetic picket fence is presented. The ion diffusion and trapping is determined by electric potentials inside the multi dipole fields. The electron diffusion is regulated by an anomalous transport process driven by low frequency fluctuations inside the magnetic sheath. Particles drifting with velocities above the ion acoustic speed generates high amplitude turbulent waves responsible for an anomalous diffusion process. (author)

  17. Fast superconducting magnetic field switch

    International Nuclear Information System (INIS)

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs

  18. 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.

  19. Evolution of twisted magnetic fields

    International Nuclear Information System (INIS)

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

  20. Magnetic Field Spectrum at Cosmological Recombination Revisited

    CERN Document Server

    Saga, Shohei; Takahashi, Keitaro; Sugiyama, Naoshi

    2015-01-01

    If vector type perturbations are present in the primordial plasma before recombination, the generation of magnetic fields is known to be inevitable through the Harrison mechanism. In the context of the standard cosmological perturbation theory, non-linear couplings of first-order scalar perturbations create second-order vector perturbations, which generate magnetic fields. Here we reinvestigate the generation of magnetic fields at second-order in cosmological perturbations on the basis of our previous study, and extend it by newly taking into account the time evolution of purely second-order vector perturbations with a newly developed second-order Boltzmann code. We confirm that the amplitude of magnetic fields from the product-terms of the first-order scalar modes is consistent with the result in our previous study. However, we find, both numerically and analytically, that the magnetic fields from the purely second-order vector perturbations partially cancel out the magnetic fields from one of the product-te...

  1. Cyclical magnetic field flow fractionation

    Science.gov (United States)

    Tasci, T. O.; Johnson, W. P.; Gale, B. K.

    2012-04-01

    In this study, a new magnetic field flow fractionation (FFF) system was designed and modeled by using finite element simulations. Other than current magnetic FFF systems, which use static magnetic fields, our system uses cyclical magnetic fields. Results of the simulations show that our cyclical magnetic FFF system can be used effectively for the separation of magnetic nanoparticles. Cyclical magnetic FFF system is composed of a microfluidic channel (length = 5 cm, height = 30 ?m) and 2 coils. Square wave currents of 1 Hz (with 90 deg of phase difference) were applied to the coils. By using Comsol Multiphysics 3.5a, magnetic field profile and corresponding magnetic force exerted on the magnetite nanoparticles were calculated. The magnetic force data were exported from Comsol to Matlab. In Matlab, a parabolic flow profile with maximum flow speed of 0.4 mL/h was defined. Particle trajectories were obtained by the calculation of the particle speeds resulted from both magnetic and hydrodynamic forces. Particle trajectories of the particles with sizes ranging from 10 to 50 nm were simulated and elution times of the particles were calculated. Results show that there is a significant difference between the elution times of the particles so that baseline separation of the particles can be obtained. In this work, it is shown that by the application of cyclical magnetic fields, the separation of magnetic nanoparticles can be done efficiently.

  2. The magnetic field structure of Rotamak discharges

    International Nuclear Information System (INIS)

    This thesis describes an experimental study of a field-reversed compact torus configuration which is generated and sustained by a rotating magnetic field. Earlier studies of this so-called 'rotamak' concept used rotating magnetic fields of limited duration (?15 ?s). The present work extends these studies to a longer timescale (?60 ?s). The rotating magnetic field is produced by feeding RF currents, dephased by 90 deg., through two orthogonal Helmholtz coils which are wound around the outside of a spherical Pyrex vacuum vessel. Line generators are used to supply the RF current pulses. The experiments are performed using an argon plasma. From measurements of the driven toroidal current, two rotamak operating modes are identified. Detailed poloidal flux contour measurements prove that these modes are associated with either a closed magnetic field line, compact torus configuration or an open magnetic field line, mirror-like structure. In the compact torus configuration the driven toroidal current is shown to vary linearly with the magnitude of the externally applied equilibrium field. For the same initial conditions of filling pressure and externally applied equilibrium field, the plasma discharges are highly reproducible. The magnetic structures of the discharges are studied in detail for three such sets of initial conditions. In particular, poloidal flux contours are derived for each of the three conditions. Although no toroidal magnetic field is externally imposed in these experiments, under certain conditions a toroidal field is observed to be present. The toroidal field is in opposite directions in the upper and lower halves of the minor cross section. Measurements of the input power into the plasma show that this power is largely determined by the characteristics of the line-generators. The variation of this input power with time can explain all the features observed in the plasma discharges. The effects of a conducting 'shell' around the vacuum vessel are also investigated. 97 refs., 72 figs., ills

  3. 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)

  4. Rapid generation of angular momentum in bounded magnetized plasma

    CERN Document Server

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

    2010-01-01

    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.

  5. Magnetic-field-controlled reconfigurable semiconductor logic.

    Science.gov (United States)

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

    2013-02-01

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

  6. International Geomagnetic Reference Field : The eleventh generation

    DEFF Research Database (Denmark)

    Finlay, Chris; Maus, S.

    2010-01-01

    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.

  7. PERMANENT-MAGNET INDUCTION GENERATORS: AN OVERVIEW

    Directory of Open Access Journals (Sweden)

    K. S. S. RAMAKRISHNAN

    2011-06-01

    Full Text Available The advantage of using a permanent-magnet induction generator (PMIG instead of a conventional induction generator is its ability to suppress inrush current during system linking when synchronous input is performed. Induction machines excited with permanent-magnet (PM are called permanent-magnet induction generators. This paper presents an exhaustive survey of the literature discussing the classification of permanent-magnet machines, process of permanent-magnet excitation and voltage build-up, modelling, steady-state and performance analysis of the permanent-magnet induction generators.

  8. Review: Magnetic fields of O stars

    CERN Document Server

    Wade, G A

    2014-01-01

    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.

  9. Theory of fossil magnetic field

    OpenAIRE

    Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

    2014-01-01

    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.

  10. Characteristics of magnetic field induction inside a module of a magnetic separator ?????????????? ???????? ???? ? ?????? ?????????? ??????????

    Directory of Open Access Journals (Sweden)

    Sandulyak Anna Aleksandrovna

    2013-05-01

    Full Text Available Characteristics of magnetic separators are analyzed in the article. Magnetic separators are used to treat various construction materials. Unfortunately, the nature of the magnetic field, generated in their operating zone, is generally not taken into account by their designers. Academic publications fail to provide any detailed basic characteristics of the field induction emitted by magnetic separators in the course of their operation.Magnetic systems of any magnetic separator have a modular structure; they consist of several modules. Single and opposite magnetic elements are usually integrated into one module within a system having permanent magnets. If opposite magnetic elements are used, magnetic field intensity inside the module increases.In this study, characteristics of magnetic induction for single magnetic elements inside various modules of magnetic separators were assessed in a laboratory experiment. Similar characteristics of magnetic induction for single and twin (opposite magnetic elements were compared. In the module consisting of two opposed magnetic elements, the magnetic field becomes stronger compared to the field of a single magnetic element. Magnetic induction in the module recedes as the distance between magnetic elements increases, because of the isolation of the field generated by the opposed magnetic elements.The authors have proven the feasibility and expediency of employment of the superposition principle used to obtain the resulting characteristics. It may be employed to substitute modeling by calculations.???????????????? ???????? ?????????????? ???????? ?????????? ???? ??? ????????? ????????? ? ????????? ??????? ????????? ???????????. ???????????? ?????????????? ???????? ?????????? ???? ??? ????????? ? ????????? ????????? ????????? ??????. ? ??????, ????????? ? ???? ?????????????? ????????? ?????????, ???? ??????????? ?? ????????? ? ????? ?????????? ?????????? ????????, ???? ?? ???? ?????????? ???????????? ?????????? ??????? ???????? ? ?????? ????????? ?? ???? ??? ???????? «??????????» ????????? ?????, ??????????? ??????????????? ?????????? ??????????.???????? ??????????? ? ???????????? ???????????????? ????????????? ???????? ???????????? ??? ???????????? ?????????????? ?????????????? ???????? ???? ????? ??????????????? ?????????? ?????????? ??? ?????? ????????? ????????????? ?????????.

  11. High field superconducting sextupole magnets

    Energy Technology Data Exchange (ETDEWEB)

    Isaeva, L.G.; Lazarenko, B.A.; Mishnev, S.I.; Nikolenko, D.M.; Popov, S.G.; Rachek, I.A.; Shestakov, Yu.V.; Toporkov, D.K.; Vesnovsky, D.K.; Zevakov, S.A. [Rossijskaya Akademiya Nauk, Novosibirsk (Russian Federation). Inst. Yadernoj Fiziki

    1998-07-11

    A magnet system for cryogenic atomic beam source (ABS) having five superconducting sextupoles has been designed, manufactured and tested to get high intensity of polarized hydrogen/deuterium atomic beams. The beams will be used to fill the storage cell of the internal polarized target at the VEPP-3 electron storage ring in Novosibirsk. The geometry of the magnet system, results of the computations and measurements of the magnetic field are presented. A 4.8 T pole tip magnetic field has been measured for the magnet with an aperture of 44 mm. (orig.)

  12. 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

  13. Inflation and late-time cosmic acceleration in non-minimal Maxwell-F(R) gravity and the generation of large-scale magnetic fields

    International Nuclear Information System (INIS)

    We study inflation and late-time acceleration in the expansion of the universe in non-minimal electromagnetism, in which the electromagnetic field couples to the scalar curvature function. It is shown that power-law inflation can be realized due to the non-minimal gravitational coupling of the electromagnetic field, and that large-scale magnetic fields can be generated due to the breaking of the conformal invariance of the electromagnetic field through its non-minimal gravitational coupling. Furthermore, it is demonstrated that both inflation and the late-time acceleration of the universe can be realized in a modified Maxwell-F(R) gravity which is consistent with solar-system tests and cosmological bounds and free of instabilities. At small curvature typical for the current universe the standard Maxwell theory is recovered. We also consider the classically equivalent form of non-minimal Maxwell-F(R) gravity, and propose the origin of the non-minimal gravitational coupling function based on renormalization-group considerations

  14. Discontinuities in the Magnetic Field near Enceladus

    Science.gov (United States)

    Simon, S.; Saur, J.; van Treeck, S.; Kriegel, H.; Dougherty, M. K.

    2014-12-01

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

  15. 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

  16. Generation of non-equilibrium thermal quantum discord and entanglement in a three-spin XX chain by multi-spin interaction and an external magnetic field

    International Nuclear Information System (INIS)

    The generation of non-equilibrium thermal quantum discord and entanglement is investigated in a three-spin chain whose two end spins are respectively coupled to two thermal reservoirs at different temperatures. We show that the spin chain can be decoupled from the thermal reservoirs by homogeneously applying a magnetic field and including a strong three-spin interaction, and then the maximal steady-state quantum discord and entanglement in the two end spins can always be created. In addition, the present investigation may provide a useful approach to control coupling between a quantum system and its environment. -- Highlights: ? Spin chain decoupled from thermal reservoirs. ? Thermal excitation depressed. ? Maximal quantum correlations created.

  17. Generation of Alfven Waves by Magnetic Reconnection

    OpenAIRE

    Kigure, Hiromitsu; Takahashi, Kunio; Shibata, Kazunari; Yokoyama, Takaaki; Nozawa, Satoshi

    2010-01-01

    In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except...

  18. Magnetic Field Analysis of Superconducting Undulators with Variable Field Polarization

    CERN Document Server

    Kim, Suk H

    2005-01-01

    An undulator with double-helix coils on a cylindrical beam tube is the classical method of producing a helical magnetic field. This type of device, however, can produce only circularly polarized radiation and has limited horizontal aperture for beam injection. A planar superconducting undulator SCU) unit of helical field, which generates horizontal and vertical fields perpendicular to the beam direction, is inserted in between the magnetic poles of a vertical-field unit. This paper analyzes the magnetic fields and a scaling law of the SCU. The angle of the coil windings for the inserted unit is analyzed to maximize the horizontal field Bx. The range of the optimum rotation angle, for the range of gap/period ratio 0.1 - 0.6, is calculated to 30 - 40 degrees.

  19. Fully relativistic self-consistent field under a magnetic field.

    Science.gov (United States)

    Reynolds, Ryan D; Shiozaki, Toru

    2015-05-27

    We present a gauge-invariant implementation of the four-component Dirac-Hartree-Fock method for simulating the electronic structure of heavy element complexes in magnetic fields. The additional cost associated with the magnetic field is shown to be only 10-13% of that at zero field. The Dirac-Hartree-Fock wave function is constructed from gauge-including atomic orbitals. The so-called restricted magnetic balance is used to generate 2-spinor basis functions for the small component. The molecular integrals for the Coulomb and Gaunt interactions are computed using density fitting. Our efficient, parallel implementation allows for simulating the electronic structure of molecules containing more than 100 atoms with a few heavy elements under magnetic fields. PMID:25310527

  20. Saturn's magnetic field and dynamo theory

    International Nuclear Information System (INIS)

    Observations have shown that Saturn's magnetic field is remarkably axisymmetric and strongly dipolar. On reviewing three possible explanations for the field generation process we view a Braginskii nearly axisymmetric dynamo model as compatible with both the tilt angle and power requirements in a large Saturnian core. If the core is sufficiently small then a mean field dynamo becomes a more likely candidate, whereas if both these models fail an axisymmetric dynamo based on compressible flow may be possible

  1. The formation of regular interarm magnetic fields in spiral galaxies

    OpenAIRE

    Moss, David; Stepanov, Rodion; Krause, Marita; Beck, Rainer; Sokoloff, Dmitri

    2015-01-01

    Observations of several nearby galaxies of regular magnetic fields reveal magnetic arms situated between the material arms. The nature of these magnetic arms is a topic of active debate. Previously we found a hint that taking into account the effects of injections of small-scale magnetic fields generated, e.g., by turbulent dynamo action, into the large-scale galactic dynamo can result in magnetic arm formation. We now investigate the joint roles of an arm/interarm turbulent...

  2. Large scale magnetic field phenomena

    International Nuclear Information System (INIS)

    This study group had interests ranging from coronal mass ejections and magnetic modelling to active region heating and post-flare loops. Two main areas of discussion were concerned with the results from two major observing campaigns, namely the Coronal Mass Ejection Onset Programme (CMEOP) and the Coronal Magnetic Structures Observing Campaign (CoMStOC), and several theoretical experts were on hand to address the consequences of these programmes. The following report is divided into three sections: Coronal Mass Ejections; Large Scale Coronal Magnetic Fields and Flare Activity in Relation to Coronal Magnetic Fields. (author)

  3. Magnetic Field Amplification in Young Galaxies

    CERN Document Server

    Schober, Jennifer; Klessen, Ralf S

    2013-01-01

    The Universe at present is highly magnetized, with fields of the order of a few 10^-5 G and coherence lengths larger than 10 kpc in typical galaxies like the Milky Way. We propose that the magnetic field was amplified to this values already during the formation and the early evolution of the galaxies. Turbulence in young galaxies is driven by accretion as well as by supernova (SN) explosions of the first generation of stars. The small-scale dynamo can convert the turbulent kinetic energy into magnetic energy and amplify very weak primordial magnetic seed fields on short timescales. The amplification takes place in two phases: in the kinematic phase the magnetic field grows exponentially, with the largest growth on the smallest non-resistive scale. In the following non-linear phase the magnetic energy is shifted towards larger scales until the dynamo saturates on the turbulent forcing scale. To describe the amplification of the magnetic field quantitatively we model the microphysics in the interstellar medium ...

  4. The origin, evolution and signatures of primordial magnetic fields

    CERN Document Server

    Subramanian, Kandaswamy

    2015-01-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak $\\sim 10^{-16}$ Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and other phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, ...

  5. Collision echo in magnetic field

    International Nuclear Information System (INIS)

    The effects of the longitudinal magnetic field on the collision photon echo, which is formed by two laser pulses with orthogonal polarizations on the transition with the angular momentum change Ja = 0 ? Jb = 1 and arises due to the action of the elastic depolarizing collisions, are studied theoretically. It is shown that weak magnetic field acts to diminish the intensity of the collision echo up to zero, providing the tools for measuring the relaxation rates due to such collisions. With the further increase of the magnetic field strength the echo intensity reveals almost pure harmonic oscillations, though in strong magnetic field the echo appears not due to the action of collisions but mainly due to the action of the magnetic field, so it becomes not collision but conventional photon echo. However the comparison of the amplitudes of the collision echo in zero magnetic field with the maximum echo amplitude in strong magnetic field yields one more way to measure the relaxation rates due to elastic depolarizing collisions

  6. Thermal instability and magnetic field generated by a large heat flow in a plasma, especially under laser-fusion conditions

    International Nuclear Information System (INIS)

    Representing a large heat flow in a plasma as a flow of hot relatively collisionless electrons balanced by an opposing current of cold collisional electrons, it can be shown that an electrothermal instability can be induced in the cold resistive plasma when the heat flow exceeds about 3% of the free-streaming limit. This is nonconvective if the cold plasma is less than 0.2 n/sup 1/4//sub e/Z/sup 1/2/ 0K (n/sub e/m-3). The instability will lead to filamentary magnetic structures with a typical growth time of a few picoseconds and wavelength about 10 ?m

  7. Low-magnetic-field magnetars

    CERN Document Server

    Turolla, R

    2013-01-01

    It is now widely accepted that soft gamma repeaters and anomalous X-ray pulsars are the observational manifestations of magnetars, i.e. sources powered by their own magnetic energy. This view was supported by the fact that these `magnetar candidates' exhibited, without exception, a surface dipole magnetic field (as inferred from the spin-down rate) in excess of the electron critical field (~4.4E+13 G). The recent discovery of fully-qualified magnetars, SGR 0418+5729 and Swift J1822.3-1606, with dipole magnetic field well in the range of ordinary radio pulsars posed a challenge to the standard picture, showing that a very strong field is not necessary for the onset of magnetar activity (chiefly bursts and outbursts). Here we summarize the observational status of the low-magnetic-field magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.

  8. Plasma separation from magnetic field lines in a magnetic nozzle

    Science.gov (United States)

    Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.

    1993-01-01

    This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.

  9. Magnetic fields of the Sun

    International Nuclear Information System (INIS)

    Magnetic fields of the Sun are considered. Medium, large-scale Sun magnetic field exists. Its axial-symmetric poloidal component is characterised by the intensity of the order of 1 Gs and by dipole-type space mode, oriented along rotation axis. Furthermore, a weak non-axial-symmetric field (about 0.5 Gs), corresponding to dipole and (or) quadrupole, the axes of which are found in the solar equator plane. Magnetic field of the Sun does not remain unchangeable. Small-scale fields change in an irregular, random way. The field non-axial-symmetric component changes approximately with the period of the Sun rotation around its axis. 22-year axial-symmetric field cycle is well known

  10. Magnetic field analysis of high gradient magnetic separator via finite element analysis

    Science.gov (United States)

    Baik, S. K.; Ha, D. W.; Ko, R. K.; Kwon, J. M.

    2012-10-01

    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. The magnetic force generated by the field gradient is several thousand times larger than that by the magnetic flux density alone. So the HGMS shows excellent performance compared with other magnetic separators. These matrices 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 matrices 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. Magnetic field is calculated in 3 dimensions by using Finite Element Method (FEM) and also compared with results obtained from 2 dimensional analysis.

  11. Neutron scattering in magnetic fields

    OpenAIRE

    Koehler, W. C.

    1984-01-01

    The use of magnetic fields in neutron scattering experimentation is reviewed briefly. Two general areas of application can be distinguished. In one the field acts to change the properties of the scattering sample ; in the second the field acts on the neutron itself. Several examples are discussed. Precautions necessary for high precision polarized beam measurements are reviewed.

  12. Neutron scattering in magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Koehler, W.C.

    1984-01-01

    The use of magnetic fields in neutron scattering experimentation is reviewed briefly. Two general areas of application can be distinguished. In one the field acts to change the properties of the scattering sample; in the second the field acts on the neutron itself. Several examples are discussed. Precautions necessary for high precision polarized beam measurements are reviewed. 33 references.

  13. LOCAL MAGNETIC FIELD DATA PROCESSING

    Directory of Open Access Journals (Sweden)

    Ivan Ostroumov

    2015-04-01

    Full Text Available The article represents the methodology for estimation of the Earth’s magnetic field characteristics for a particular area. It is proposed to use a group of sensors inside of a tablet or a cell phone as a measurement device. We used typical sensors raw data like pitch, roll, yaw (from gyros; components of magnetic field intensity vectors (from magnetometers; latitude, longitude, altitude (from global positioning sensor. We represent the result of intensity vector components estimation for particular area. It is stated that the most important characteristics of magnetic fieldare horizontal and vertical components of intensity vector and inclination and declination angles. In addition, we compared the received results with magnetic field forecast, according to the world magnetic model.

  14. Influence of magnetic field on turbomolecular pumps

    International Nuclear Information System (INIS)

    Because Magnetically suspended turbo-molecular pumps (TMPs) with dry backing pumps are very preferable to achieve and maintain UHV without oil contamination, recently they have been widely used in nuclear fusion devices and sometimes in particle accelerators. In order to use them in these fields some researches have been published into the influence of the magnetic fields on TMPs. However, these evaluations were carried out under some ambiguous magnetic fields and only about the special type of TMPs. Thus, we have intended to establish the standard for dealing with the influence of magnetic field on TMPs. First of all, the influence has been exactly investigated for two parts: one is due to the vertical magnetic field, and the other due to the parallel component. A solenoid of diameter 500 mm and length 1500 mm has been newly constructed to examine the TMPs in the uniform magnetic fields. This solenoid has 1493 turns per m, therefore, letting a current of about 9.0A flow leads to generate the axial magnetic field of 100 gauss in the central region. The axial magnetic field is uniform with the deviation less than 0.5% in the cylindrical region of 400 mm in a diameter and 280 mm long at the center. The radial component is only about 0.5% of the axial one. We have studied the influence of the magnetic field on the TMPs of Osaka vacuum Products Co., Ltd. This TMP has not only the magnetic suspension bearing but the spirally grooved rotor, which endures such high backing pd rotor, which endures such high backing pressures as 500 Pa. The TMP is set on the table made of Al and the direction to the axis of solenoid was adjusted by the support attached to the table. We have measured the rotating speed, power for driving the rotor, and the rotor temperature as a function of the magnetic fields. In the field vertical to the rotating axis, both the rotor temperature and the driving power clearly increased even at 10 Gauss. On the other hand, they had no changes at 100 Gauss in a parallel field. In this paper the experimental results are shown in detail. (author)

  15. Nonlinear propagation of electromagnetic waves in strong magnetic fields

    International Nuclear Information System (INIS)

    The propagation of plane electromagnetic waves in strong constant magnetic fields is studied. It exhibits nonlinear effects (the generation of the second harmonics, field-dependent modification of the phase of the wave) due to the vacuum polarization. (author)

  16. Preface: Cosmic magnetic fields

    Science.gov (United States)

    Kosovichev, Alexander

    2015-02-01

    Recent advances in observations and modeling have opened new perspectives for the understanding of fundamental dynamical processes of cosmic magnetism, and associated magnetic activity on the Sun, stars and galaxies. The goal of the Special Issue is to discuss the progress in solar physics and astrophysics, similarities and differences in phenomenology and physics of magnetic phenomena on the Sun and other stars. Space observatories, ground-based telescopes, and new observational methods have provided tremendous amount of data that need to be analyzed and understood. The solar observations discovered multi-scale organization of solar activity, dramatically changing current paradigms of solar variability. On the other side, stellar observations discovered new regimes of dynamics and magnetism that are different from the corresponding solar phenomena, but described by the same physics. Stars represent an astrophysical laboratory for studying the dynamical, magnetic and radiation processes across a broad range of stellar masses and ages. These studies allow us to look at the origin and evolution of our Sun, whereas detailed investigations of the solar magnetism give us a fundamental basis for interpretation and understanding of unresolved stellar data.

  17. Generation of Gaussian Density Fields

    OpenAIRE

    Martel, Hugo

    2005-01-01

    This document describes analytical and numerical techniques for the generation of Gaussian density fields, which represent cosmological density perturbations. The mathematical techniques involved in the generation of density harmonics in k-space, the filtering of the density fields, and the normalization of the power spectrum to the measured temperature fluctuations of the Cosmic Microwave Background, are presented in details. These techniques are well-known amongst experts,...

  18. Measuring Earth's Magnetic Field Simply.

    Science.gov (United States)

    Stewart, Gay B.

    2000-01-01

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

  19. ISR split-field magnet

    CERN Multimedia

    1975-01-01

    The experimental apparatus used at intersection 4 around the Split-Field Magnet by the CERN-Bologna Collaboration (experiment R406). The plastic scintillator telescopes are used for precise pulse-height and time-of-flight measurements.

  20. Compensation of Gradient-Induced Magnetic Field Perturbations

    OpenAIRE

    Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L; de Graaf, Robin A.

    2008-01-01

    Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical ...

  1. High-Field Accelerator Magnets

    CERN Document Server

    de Rijk, G

    2014-01-01

    In this lecture an overview is given of the present technology for high field accelerator magnets. We indicate how to get high fields and what are the most important parameters. The available conductors and their limitations are presented followed by the most relevant types of coils and support structures. We conclude by showing a number of recent examples of development magnets which are either pure R&D objects or models for the LHC luminosity upgrade.

  2. Laboratory Measurements of Astrophysical Magnetic Fields

    Science.gov (United States)

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

    2010-11-01

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

  3. Quench limits in the next generation of magnets

    OpenAIRE

    Todesco, E.

    2014-01-01

    Several projects around the planet aim at building a new generation of superconducting magnets for particle accelerators, relying on Nb3Sn conductor, with peak fields in the range of 10-15 T. In this paper we give an overview of the main challenges for protecting this new generation of magnets. The cases of isolated short magnets, in which the energy can be extracted on an external dump resistor, and chain of long magnets, which have to absorb their stored energy and have to...

  4. Nonlinear dynamics of magnetic island interacting with external helical magnetic field

    International Nuclear Information System (INIS)

    Full text: The control of magnetic islands is one of important issues for magnetically confined fusion plasmas. Magnetic islands strongly affect the achievable ?''-value by modifying transports, equilibrium fields (i.e. radial profiles of electric current, pressure and electric field) and the stability of plasmas. The induction of resonant helical magnetic fields, which interact with magnetic islands, is an effective method to control the dynamics of magnetic islands. In the Large Helical Device (LHD), magnetic islands are excited by the external magnetic, and the generation of equilibrium poloidal E x B flows by magnetic islands is observed. On the other hand, the external helical magnetic fields have been used to control the poloidal rotation and the stability of magnetic islands in tokamak plasmas. The error field, which is caused by the misalignment of toroidal magnetic coil, plays a similar role to the external helical magnetic field. The locking of the rotation of magnetic islands by error field triggers the disruption in tokamak plasmas. Thus, it is important to understand the basic mechanism of the interaction between magnetic islands and external helical magnetic fields. In this study, nonlinear simulation of drift tearing mode is performed using a set of reduced two-fluid equations, and the detailed study of the interaction between magnetic islands with external helical magnetic fields is reported. The external helical field associated with magnetic islands is imposed by means of finite amplitude of perturbed magnetic flux (vector potential) at edge boundary. In our simulation, the locking (stop) of the rotation of magnetic islands is observed. The rotation of magnetic island is basically driven by the diamagnetic drift flow and E x B flow. It is found that contributions of these flows approximately cancel each other inside the separatrix of magnetic island in the locking phase. The detailed mechanism of the locking of magnetic island rotation is discussed in the presentation. (author)

  5. Distortion of magnetic field and magnetic force of a brushless dc motor due to deformed rubber magnet

    Science.gov (United States)

    Lee, C. J.; Jang, G. H.

    2008-04-01

    This paper investigates the distortion of magnetic field of a brushless dc (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force is calculated by using the Maxwell stress tensor. When the rubber magnet is globally or locally deformed, the unbalanced magnetic force has the frequencies with the first harmonic and the harmonics of slot number ±1. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry.

  6. Magnetic nanoparticles for applications in oscillating magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Peeraphatdit, Chorthip

    2010-12-15

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

  7. Magnetic field induced dynamical chaos

    International Nuclear Information System (INIS)

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

  8. Modeling Magnetic Field Amplification in Nonlinear Diffusive Shock Acceleration

    CERN Document Server

    Vladimirov, Andrey

    2009-01-01

    This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of ...

  9. Studying the magnetic fields of cool stars

    Science.gov (United States)

    Lynch, Christene Rene

    Magnetic fields are prevalent in a wide variety of low mass stellar systems and play an important role in their evolution. Yet the process through which these fields are generated is not well understood. To understand how such systems can generate strong field structures characterization of these fields is required. Radio emission traces the fields directly and the properties of this emission can be modeled leading to constraints on the field geometry and magnetic parameters. The new Karl Jansky Very Large Array (VLA) provides highly sensitive radio observations. My thesis involves combining VLA observations with the development of magnetospheric emission models in order to characterize the magnetic fields in two fully convective cool star systems: (1) Young Stellar Objects (YSOs); (2) Ultracool dwarf stars. I conducted multi epoch observations of DG Tau, a YSO with a highly active, collimated outflow. The radio emission observed from this source was found to be optically thick thermal emission with no indication of the magnetic activity observed in X-rays. I determined that the outflow is highly collimated very close to the central source, in agreement with jet launching models. Additionally, I constrained the mass loss of the ionized component of the jet and found that close to the central source the majority of mass is lost through this component. Using lower angular resolution observations, I detected shock formations in the extended jet of DG Tau and modeled their evolution with time. Taking full advantage of the upgraded bandwidth on the VLA, I made wideband observations of two UCDs, TVLM513-46 and 2M 0746+20. Combining these observations with previously published and archival VLA observations I was able to fully characterize the spectral and temporal properties of the radio emission. I found that the emission is dominated by a mildly polarized, non-thermal quiescent component with periodic strongly polarized flare emission. The spectral energy distribution and polarization of the quiescent emission is well modeled using gyrosynchrotron emission with a mean field B ˜100 G, mildly relativistic power-law electrons with a density ne ˜ 105-6 cm-3, and source size of R ˜ 2R*. We were able to model the pulsed emission by coherent electron cyclotron radiation from a small number of isolated loops of high magnetic field (2-3 kG) with scale heights˜1.2-2.7 stellar radii. The loops are well-separated in magnetic longitude, and are not part of a single dipolar magnetosphere. The overall magnetic configuration of both stars appears to confirm recent suggestions that radio over-luminous UCD's have `weak field' non-axisymmetric topologies, but with isolated regions of high magnetic field.

  10. On the relationship between quadrupolar magnetic field and collisionless reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Smets, R., E-mail: roch.smets@lpp.polytechnique.fr; Belmont, G. [LPP, University P. and M. Curie, CNRS, Ecole Polytechnique, F-91128 Palaiseau (France); Aunai, N. [IRAP, University Paul Sabatier, F-31028 Toulouse (France); Boniface, C. [CEA/DAM, DIF, F-91297 Arpajon (France); Fuchs, J. [LULI, Ecole Polytechnique, CNRS, CEA, University P. and M. Curie, F-91128 Palaiseau (France)

    2014-06-15

    Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed.

  11. Magnetic fields and coronal heating

    Science.gov (United States)

    Golub, L.; Maxson, C.; Rosner, R.; Vaiana, G. S.; Serio, S.

    1980-01-01

    General considerations concerning the scaling properties of magnetic-field-related coronal heating mechanisms are used to build a two-parameter model for the heating of closed coronal regions. The model predicts the way in which coronal temperature and electron density are related to photospheric magnetic field strength and the size of the region, using the additional constraint provided by the scaling law of Rosner, Tucker, and Vaiana. The model duplicates the observed scaling of total thermal energy content with total longitudinal flux; it also predicts a relation between the coronal energy density (or pressure) and the longitudinal field strength modified by the region scale size.

  12. Magnetic fields in neutron stars

    Science.gov (United States)

    Viganò, Daniele

    2013-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Malik, Anil K., E-mail: anilkmalik@gmail.com [Department of Physics, Multani Mal Modi College Modinagar, C.C.S. University, Meerut, Uttar Pradesh 201204 (India); Singh, Kunwar Pal [Singh Simutech Pvt. Ltd., Bharatpur, Rajasthan 321201 (India); Sajal, V. [Jaypee Institute of Information Technology, Noida 201307 (India)

    2014-07-15

    A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ?{sub 1}, ?{sub 2} and wave numbers k{sub 1}, k{sub 2} in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ?{sup ?}=?{sub 1}??{sub 2} and wave number k{sup ?}=k{sub 1}?k{sub 2} 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 ?{sub UH}=?((?{sub p}{sup 2}+?{sub c}{sup 2})) (where ?{sub 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.

  14. Transformation Optics for Controlling DC Magnetic Field

    OpenAIRE

    Sun, Fei

    2014-01-01

    Based on the form-invariant of Maxwell’s equations under coordinate transformations, we extend the theoryof transformation optics to transformation magneto-statics, which can design magnets through coordinatetransformations. Some novel DC magnetic field illusions created by magnets (e.g. rescaling magnets,cancelling magnets and overlapping magnets) are designed and verified by numerical simulations. Ourresearch will open a new door to designing magnets and controlling DC magnetic fields.

  15. Satellite to study earth's magnetic field

    Science.gov (United States)

    1979-01-01

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

  16. NMR system and method having a permanent magnet providing a rotating magnetic field

    Science.gov (United States)

    Schlueter, Ross D [Berkeley, CA; Budinger, Thomas F [Berkeley, CA

    2009-05-19

    Disclosed herein are systems and methods for generating a rotating magnetic field. The rotating magnetic field can be used to obtain rotating-field NMR spectra, such as magic angle spinning spectra, without having to physically rotate the sample. This result allows magic angle spinning NMR to be conducted on biological samples such as live animals, including humans.

  17. Separation of magnetic field lines

    International Nuclear Information System (INIS)

    The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor ?, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e2?, and the ratio of the longer distance to the initial radius increases as e?. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/?pe, which is about 10 cm in the solar corona, and reconnection must be triggered if ? becomes sufficiently large. The radius of the sun, R?=7×1010cm is about e23 times larger, so when ??23, two lines separated by c/?pe at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, ?, are derived, and the importance of exponentiation is discussed.

  18. Large scale magnetic fields and their dissipation in GRB fireballs

    OpenAIRE

    Spruit, H.C.; Daigne, F.; Drenkhahn, G.

    2000-01-01

    We consider possible geometries of magnetic fields in GRB outflows, and their evolution with distance from the source. For magnetically driven outflows, with an assumed ratio of magnetic to kinetic energy density of order unity, the field strengths are sufficient for efficient production of gamma-rays by synchrotron emission in the standard internal shock scenario, without the need for local generation of small scale fields. In these conditions, the MHD approximation is vali...

  19. Temperature compensated current sensor using reference magnetic field

    Science.gov (United States)

    Yakymyshyn, Christopher Paul (Seminole, FL); Brubaker, Michael Allen (Loveland, CO); Yakymyshyn, Pamela Jane (Seminole, FL)

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by a separate but identical magnetic field sensor and is used to correct variations in the output signal due to temperature variations and aging.

  20. Magnetic fields in early-type stars

    CERN Document Server

    Grunhut, Jason H

    2015-01-01

    For several decades we have been cognizant of the presence of magnetic fields in early-type stars, but our understanding of their magnetic properties has recently (over the last decade) expanded due to the new generation of high-resolution spectropolarimeters (ESPaDOnS at CFHT, Narval at TBL, HARPSpol at ESO). The most detailed surface magnetic field maps of intermediate-mass stars have been obtained through Doppler imaging techniques, allowing us to probe the small-scale structure of these stars. Thanks to the effort of large programmes (e.g. the MiMeS project), we have, for the first time, addressed key issues regarding our understanding of the magnetic properties of massive (M > 8 M_sun) stars, whose magnetic fields were only first detected about fifteen years ago. In this proceedings article we review the spectropolarimetric observations and statistics derived in recent years that have formed our general understanding of stellar magnetism in early-type stars. We also discuss how these observations have fu...

  1. Magnetic Field Limits on SGRs

    CERN Document Server

    Rothschild, R E; Lingenfelter, R E

    1999-01-01

    We measure the period and spin-down rate for SGR 1900+14 during the quiescient period two years before the recent interval of renewed burst activity. We find that the spin-down rate doubled during the burst activity which is inconsistent with both mangetic dipole driven spin down and a magnetic field energy source for the bursts. We also show that SGRs 1900+14 and 1806-20 have braking indices of $\\sim$1 which indicate that the spin-down is due to wind torques and not magnetic dipole radiation. We further show that a combination of dipole radiation, and wind luminosity, coupled with estimated ages and present spin parameters, imply that the magnetic fields of SGRs 1900+14 and 1806-20 are less than the critical field of 4$\\times10^{13}$ G and that the efficiency for conversion of wind luminosity to x-ray luminosity is <2%.

  2. Magnetic Forces and Field Line Density

    Science.gov (United States)

    2012-08-03

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

  3. Magnetic Fields of the Earth and Sun

    Science.gov (United States)

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

  4. Magnetic fields of neutron stars

    CERN Document Server

    Reisenegger, Andreas

    2013-01-01

    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 scenario in which a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) is established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, becau...

  5. Quench limits in the next generation of magnets

    CERN Document Server

    Todesco, E

    2013-01-01

    Several projects around the planet aim at building a new generation of superconducting magnets for particle accelerators, relying on Nb3Sn conductor, with peak fields in the range of 10-15 T. In this paper we give an overview of the main challenges for protecting this new generation of magnets. The cases of isolated short magnets, in which the energy can be extracted on an external dump resistor, and chain of long magnets, which have to absorb their stored energy and have to rely on quench heaters, are discussed. We show that this new generation of magnets can pose special challenges, related to both the large current density and to the energy densities.

  6. Magnetic field tomography, helical magnetic fields and Faraday depolarization

    Science.gov (United States)

    Horellou, C.; Fletcher, A.

    2014-07-01

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

  7. Linear magnetic motor/generator. [to generate electric energy using magnetic flux for spacecraft power supply

    Science.gov (United States)

    Studer, P. A. (inventor)

    1982-01-01

    A linear magnetic motor/generator is disclosed which uses magnetic flux to provide mechanical motion or electrical energy. The linear magnetic motor/generator includes an axially movable actuator mechanism. A permament magnet mechanism defines a first magnetic flux path which passes through a first end portion of the actuator mechanism. Another permament magnet mechanism defines a second magnetic flux path which passes through a second end portion of the actuator mechanism. A drive coil defines a third magnetic flux path passing through a third central portion of the actuator mechanism. A drive coil selectively adds magnetic flux to and subtracts magnetic flux from magnetic flux flowing in the first and second magnetic flux path.

  8. A simple mechanism for the reversals of Earth's magnetic field

    OpenAIRE

    Petrelis, F.; Fauve, S.; Dormy, E.; Valet, J. P.

    2008-01-01

    We show that a model, recently used to describe all the dynamical regimes of the magnetic field generated by the dynamo effect in the VKS experiment [1], also provides a simple explanation of the reversals of Earth's magnetic field, despite strong differences between both systems.

  9. Bosonic Casimir effect in external magnetic field

    OpenAIRE

    Cougo-Pinto, M. V.; Farina, C; Negrao, M. R.; Tort, A. C

    1998-01-01

    We compute the influence of an external magnetic field on the Casimir energy of a massive charged scalar field confined between two parallel infinite plates. For this case the obtained result shows that the magnetic field inhibits the Casimir effect.

  10. Focus on Materials Analysis and Processing in Magnetic Fields

    Directory of Open Access Journals (Sweden)

    Yoshio Sakka, Noriyuki Hirota, Shigeru Horii and Tsutomu Ando

    2009-01-01

    Full Text Available Recently, interest in the applications of feeble (diamagnetic and paramagnetic magnetic materials has grown, whereas the popularity of ferromagnetic materials remains steady and high. This trend is due to the progress of superconducting magnet technology, particularly liquid-helium-free superconducting magnets that can generate magnetic fields of 10 T and higher. As the magnetic energy is proportional to the square of the applied magnetic field, the magnetic energy of such 10 T magnets is in excess of 10 000 times that of conventional 0.1 T permanent magnets. Consequently, many interesting phenomena have been observed over the last decade, such as the Moses effect, magnetic levitation and the alignment of feeble magnetic materials. Researchers in this area are widely spread around the world, but their number in Japan is relatively high, which might explain the success of magnetic field science and technology in Japan.Processing in magnetic fields is a rapidly expanding research area with a wide range of promising applications in materials science. The 3rd International Workshop on Materials Analysis and Processing in Magnetic Fields (MAP3, which was held on 14–16 May 2008 at the University of Tokyo, Japan, focused on various topics including magnetic field effects on chemical, physical, biological, electrochemical, thermodynamic and hydrodynamic phenomena; magnetic field effects on the crystal growth and processing of materials; diamagnetic levitation, the magneto-Archimedes effect, spin chemistry, magnetic orientation, control of structure by magnetic fields, magnetic separation and purification, magnetic-field-induced phase transitions, properties of materials in high magnetic fields, the development of NMR and MRI, medical applications of magnetic fields, novel magnetic phenomena, physical property measurement by magnetic fields, and the generation of high magnetic fields.This focus issue compiles 13 key papers selected from the proceedings of MAP3. Other papers of the proceedings are published in Journal of Physics: Conference Series. Tournier and Beaugnon review experimental texturing in metallic melts by cooling in magnetic fields, which is modeled in detail in a study by Tournier. Wang et al provide further experimental results on the solidification of Mn-90.4 wt % Sb alloy in magnetic fields. The orientations of grains and particles induced by magnetic fields is reported by Horii et al (rare-earth-doped cuprates, Tanaka et al (barium-bismuth titanate ceramics, Liu and Schwartz (Bi2Sr2CaCu2Ox/AgMg wires and Tsuda and Sakka (carbon nanotubes. Gielen et al present a model of how to quantify a molecular alignment using magnetic birefringence, and Ando et al simulate the movement of feeble particles in magnetic fields. Hirota et al report the experimental control of the lattice constant in a triangular lattice of feeble magnetic particles. The size separation of diamagnetic particles by magnetic fields is experimentally studied by Tarn et al and theoretically studied by Fukui et al. A setup measuring x-ray diffraction patterns in magnetic fields up to 5 T and temperatures above 200 oC has been developed by Mitsui et al.We hope that this focus issue will help readers to understand several aspects of materials analysis and processing in magnetic fields at the frontier of the science.

  11. How to Draw Magnetic Fields - I

    Science.gov (United States)

    This is an activity about depicting magnetic fields. Learners will observe two provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines for both orientations. This is the third activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

  12. ATLAS cavern magnetic field calculations

    International Nuclear Information System (INIS)

    A new approach has been adopted in an attempt to produce a complete ATLAS cavern B-field map using a more precise methodological approach (variable magnetisation, depending on the external field) and the latest design taking into account of the structural elements. The basic idea was to produce a dedicated basic TOSCA model and then to insert a series of ferromagnetic structure elements to monitor the perturbative effect on the basic field map. Eventually, it was found: the bedplate field perturbation is an order of magnitude above the permissible level; manufacturing of the bedplates from nonmagnetic material or careful evaluation of their field contribution in the event reconstruction codes is required; the field value at the rack positions is higher than the permissible one; the final position of racks should be chosen taking into account the detailed magnetic field distribution

  13. New Magnetic Susceptibility and Magnetic Field Tools for Wireline Logging

    Science.gov (United States)

    Williams, T.; Evans, H.; Robinson, S.; Goldberg, D.; Tool Design Team

    2008-12-01

    Two new tools are being developed to provide downhole magnetic measurements for the Integrated Ocean Drilling Program (IODP) and other scientific drilling programs. The Magnetic Susceptibility Sonde (MSS) is built and has been run successfully in land boreholes, and the Multi-sensor Magnetometer Module (MMM) is at the design stage. Magnetic susceptibility is one of the best measurements for investigating stratigraphic changes in marine sediments, because the measurement is quick, repeatable, and non-destructive, and because different lithologies often have strongly contrasting susceptibilities. The MSS includes a Bartington sensor with a 12-cm vertical resolution, sufficient to resolve thin beds and track astronomical cyclicity for paleoceanographic studies, together with a deep-reading sensor that is minimally affected by tool standoff from the borehole wall. These downhole susceptibility measurements will complement the susceptibility measured on core and be invaluable for core-log integration. We have proposed to build a new magnetometer tool, the MMM, to measure the magnetic field in the borehole, from which we can calculate the magnetization and polarity of the rocks surrounding the borehole. The combination of a three-axis fluxgate magnetometer, an accurate Overhauser effect total-field magnetometer, and optical gyroscope orientation in a single tool will provide the capability to measure a wide range of rock types, from highly magnetic basalts to more weakly magnetized unlithified sediments. The magnetization of the igneous ocean crust is a fundamental subject in marine geophysics, and downhole measurements offer the advantages of oriented paleomagnetic data and continuous coverage in these difficult-to-recover rocks. The tool will also be able to provide downhole magnetostratigraphy in marine sediment sequences, as demonstrated with the previous generation of IODP downhole magnetometer (a commercial tool, no longer available). Both these new tools will run in-line with the standard Schlumberger tools used in IODP, a major advance in integration over previous third-party tools that will save operational time.

  14. Magnetic pumping in spatially inhomogeneous magnetic fields

    International Nuclear Information System (INIS)

    A method is described for fast radial toroidal plasma column acceleration in an average ion-ion collision time or less back and forth in the plane of the closed containment means of the ATC described in U. S. Pat. No. 3,702,163, irreversibly to heat the plasma column. In accordance with this invention, current is flowed through the toroidal and poloidal coil means of the ATC and these coils are distributed to provide an unbalanced biasing force on the toroidal, current carrying, plasma column by means of a shaped magnetic field having an unstable region between spaced apart stable regions. By modulating the shaped field the plasma column is pushed back and forth between the two stable regions. In another embodiment, the plasma current is modulated to the same end. (U.S.)

  15. Experimental Study on Current Decay Characteristics of Persistent Current HTS Magnet by Alternating Magnetic Field

    Science.gov (United States)

    Park, Young Gun; Lee, Chang Young; Hwang, Young Jin; Lee, Woo Seung; Lee, Jiho; Jo, Hyun Chul; Chung, Yoon Do; Ko, Tae Kuk

    This paper deals with a current decay characteristics of a high temperature superconducting (HTS) magnet operated in persistent current mode (PCM). In superconducting synchronous machine applications such as linear synchronous motor (LSM), the superconducting coil is designed to operate in the PCM to obtain steady magnetic field with DC transport current. This superconducting magnet operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the magnet is subjected to an external time-varying magnetic field, it is possible to result in a decay of the current in PCM system due to AC loss. In this research, a PCM system with armature coil which generates time-varying magnetic field was fabricated to verify current decay characteristics by external alternating magnetic field. The current decay rate was measured by using a hall sensor as functions of amplitude and frequency of armature coil.

  16. Nuclear Georeactor Generation of Earth's Geomagnetic Field

    CERN Document Server

    Herndon, J Marvin

    2007-01-01

    The purpose of this communication is to suggest that the mechanism for generating the geomagnetic field and the energy source for powering it are one and the same, a nuclear georeactor at the center of the Earth. Toward this end, I: i) Present evidence that the nuclear georeactor fission-product sub-shell is fluid; ii)Suggest that the geomagnetic field is generated within the georeactor sub-shell, rather than within Earth's iron-alloy fluid core; iii) Describe why convection appears more feasible within the georeactor sub-shell than within the iron-alloy core; iv) Disclose additional relative physical advantages for georeactor sub-shell dynamo operation; and, v) Outline briefly the research that should be conducted to advance the state of knowledge of georeactor-geomagnetic field generation. The concept of geomagnetic field production by the nuclear georeactor is presented specifically for the Earth. The concepts and principles, however, are generally applicable to planetary magnetic field production.

  17. Baryon onset in a magnetic field

    OpenAIRE

    Haber, Alexander; Preis, Florian; Schmitt, Andreas

    2014-01-01

    The critical baryon chemical potential for the onset of nuclear matter is a function of the vacuum mass and the binding energy. Both quantities are affected by an external magnetic field. We show within two relativistic mean-field models - including magnetic catalysis, but omitting the anomalous magnetic moment - that a magnetic field increases both the vacuum mass and the binding energy. For sufficiently large magnetic fields, the effect on the vacuum mass dominates and as ...

  18. Instability of ferrofluid magnetic drops under magnetic field

    OpenAIRE

    Bacri, J. C.; Salin, D.

    1982-01-01

    We have followed the evolution of the shape of ferrofluid magnetic drops in presence of a magnetic field. The prolate ellipsoid shape of the drop becomes unstable for a certain magnetic field threshold : the drop jumps from a slightly elongated shape to a much more elongated shape. When decreasing the magnetic field the same feature occurs for a smaller threshold. This instability is simply understood from a balance between magnetic energy and interfacial tension energy.

  19. Magnetic monopole and the nature of the static magnetic field

    OpenAIRE

    Huang, Xiuqing

    2008-01-01

    We investigate the factuality of the hypothetical magnetic monopole and the nature of the static magnetic field. It is shown from many aspects that the concept of the massive magnetic monopoles clearly is physically untrue. We argue that the static magnetic field of a bar magnet, in fact, is the static electric field of the periodically quasi-one-dimensional electric-dipole superlattice, which can be well established in some transition metals with the localized d-electron. T...

  20. Molecular collisions in magnetic fields

    International Nuclear Information System (INIS)

    The control of atom-atom interactions using magnetic fields has been crucial to recent advances in atomic physics. Similar control should be possible for atom-molecule and molecule-molecule collisions. We have generalized the BOUND and MOLSCAT packages to allow calculations in magnetic fields, initially for collisions of molecules in multiplet Sigma states with structureless atoms. We have used the new capability to carry out bound-state and scattering calculations on 3He+NH and 4He+NH as a function of magnetic field. Following the bound-state energies to the point where they cross thresholds gives very precise predictions of the magnetic fields at which zero-energy Feshbach resonances occur. We have located and characterized two very narrow zero-energy Feshbach resonances in 4He+NH. One resonance shows a pole in the scattering length as usually observed for atomic collisions, but for the second resonance the pole in the scattering length is dramatically suppressed and the cross sections show relatively small peaks. The suppression of the pole in the scattering length is due to inelastic scattering. This is a general result, applicable to both atomic and molecular collisions. In general, poles will be strongly suppressed whenever the resonant state is coupled with comparable strength to the elastic and inelastic channels

  1. Strong horizontal photospheric magnetic field in a surface dynamo simulation

    OpenAIRE

    Schuessler, M.; Voegler, A.

    2008-01-01

    Observations with the Hinode spectro-polarimeter have revealed strong horizontal internetwork magnetic fields in the quiet solar photosphere. We aim at interpreting the observations by means of results from numerical simulations. Radiative MHD simulations of dynamo action by near-surface convection are analyzed with respect to the relation between vertical and horizontal magnetic field components. The dynamo-generated fields show a clear dominance of the horizontal field in ...

  2. HMI Measurements Of The Solar Magnetic Field

    Science.gov (United States)

    Hoeksema, Jon Todd; HMI Magnetic Field Team

    2011-05-01

    The Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory (SDO) routinely produces a comprehensive array of magnetic field data products including 45-second line-of-sight magnetograms, synoptic maps and synchronic frames, 12-minute vector field time series in HMI Active Region Patches (HARPs), model calculations of the coronal field and solar wind, and near-real-time parameters for space weather. Other products, such as surface flow maps, can be produced on demand or on request. We present examples of data products generated during the first year of operations and compare some of these with measurements from other observatories, including the now-dormant MDI. The HMI Team is sponsored by NASA.

  3. SQUID-detected magnetic resonance imaging in microtesla magnetic fields

    International Nuclear Information System (INIS)

    We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (?1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a 31P nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and 31P nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mmr using slice selection, again with 1-mm resolution. In further experiments we demonstrate T1-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T1. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging

  4. Evolution of primordial magnetic fields in mean-field approximation

    CERN Document Server

    Campanelli, Leonardo

    2013-01-01

    We study the evolution of phase-transition-generated cosmic magnetic fields coupled to the primeval cosmic plasma in turbulent and viscous free-streaming regimes. The evolution laws for the magnetic energy density and correlation length, both in helical and non-helical cases, are found by solving the autoinduction and Navier-Stokes equations in mean-field approximation. Analytical results are derived in Minkowski spacetime and then extended to the case of a Friedmann universe with zero spatial curvature, both in radiation and matter dominated eras. The three possible viscous free-streaming phases are characterized by a drag term in the Navier-Stokes equation which depends on the free-steaming properties of neutrinos, photons, or hydrogen atoms, respectively. In the case of non-helical magnetic fields, the magnetic intensity $B$ and the magnetic correlation length $\\xi_B$ evolve asymptotically with the temperature $T$ as $B(T) \\simeq \\kappa_B (N_i v_i)^{\\varrho_1} (T/T_i)^{\\varrho_2}$ and $\\xi_B(T) \\simeq \\kap...

  5. Progress on chiral symmetry breaking in a strong magnetic field

    OpenAIRE

    Wang, S. -y

    2007-01-01

    The problem of chiral symmetry breaking in QED in a strong magnetic field is briefly reviewed. Recent progress on issues regarding the gauge fixing independence of the dynamically generated fermion mass is discussed.

  6. Measurements of the Magnetic Field Induced by a Turbulent Flow of Liquid Metal

    CERN Document Server

    Nornberg, M D; Kendrick, R D; Forest, C B

    2005-01-01

    Initial results from the Madison Dynamo Experiment provide details of the inductive response of a turbulent flow of liquid sodium to an applied magnetic field. The magnetic field is reconstructed from measurements both outside and within the flow. Differential rotation of the fluid generates a large mean toroidal magnetic field from an externally-generated axial field through the omega-effect. Mean poloidal magnetic flux is expelled from the fluid by the poloidal flow. Small-scale, time-varying magnetic field structures are generated by turbulence in the flow. The resulting magnetic power spectrum exhibits the characteristic power-law scalings expected from Kolmogorov-like turbulence with an apparent knee at the resistive dissipation scale. Large-scale velocity fluctuations create dynamic flow profiles that generate intermittent bursts of non-axisymmetric magnetic fields indicating that the transition from damped magnetic fields to growing magnetic fields is not smooth for a turbulent flow.

  7. Galaxy cluster magnetic fields from radio polarized emission

    CERN Document Server

    Bonafede, A; Murgia, M; Govoni, F; Giovannini, G; Vacca, V

    2010-01-01

    The presence of magnetic fields in the intra-cluster medium of galaxy clusters is now well estabilished. It is directly revealed by the presence of cluster-wide radio sources: radio halos and radio relics. In the last years increasing attention has been devoted to the intra cluster magnetic field through the study of polarized radio emission of radio galaxies, radio halos and radio relics. Recent radio observations have revealed important features of the intra-cluster magnetic field, allowing us to constrain its main properties and to understand the physical processes taking place in the intra-cluster medium. I will review the newest results on galaxy cluster magnetic fields, both focusing on single objects and aimed at describing the magnetic field general properties. The up-coming generation of radio telescopes, EVLA and LOFAR, will shed light on several problematics regarding the cluster magnetic fields and the related non-thermal emission.

  8. High-magnetic-field research collaborations

    International Nuclear Information System (INIS)

    This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The purpose of this project was to develop collaborations with the academic community to exploit scientific research potential of the pulsed magnetic fields that might be possible with electrically pulsed devices, as well as magneto-cumulative generators. The author started with a campaign of experiments using high-explosive-driven flux compression generators. The campaign's objective was to explore completely novel ideas in condensed-matter physics and chemistry. The initiative was very successful in pulling together top researchers from around the world

  9. Magnetic field of the Earth

    Science.gov (United States)

    Popov, Aleksey

    2013-04-01

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

  10. A Vorticity-Magnetic Field Dynamo Instability

    OpenAIRE

    Blackman, Eric G; Chou, Tom

    1997-01-01

    We generalize the mean field magnetic dynamo to include local evolution of the mean vorticity in addition to the mean magnetic field. The coupled equations exhibit a general mean field dynamo instability that enables the transfer of turbulent energy to the magnetic field and vorticity on larger scales. The growth of the vorticity and magnetic field both require helical turbulence which can be supplied by an underlying global rotation. The dynamo coefficients are derived incl...

  11. Dense matter is strong magnetic fields

    OpenAIRE

    Sinha, Monika

    2012-01-01

    Compact stars having strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10^14-10^15 G, the implied internal field strength being several orders larger. We study the equation of state and composition of hypernuclear matter and quark matter - two forms of dense matter in strong magnetic fields. We find that the magnetic field has substantial influence on the properties of hypernuclear matter and quark matter for ...

  12. Galactic and intergalactic magnetic fields

    CERN Document Server

    Klein, Ulrich

    2014-01-01

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible.In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later c

  13. On the origin of the Earth's magnetic field

    OpenAIRE

    Ryskin, Gregory(Robert R. McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, United States)

    2003-01-01

    It is thought that the magnetic field of the Earth is generated by the hydromagnetic dynamo action in the Earth's liquid outer core, consisting mainly of iron (the standard model). Here I propose that the magnetic field of the Earth is generated by dynamo action in the world ocean at the Earth's surface. This hypothesis is free of the problems of the standard model; in particular, it explains the close temporal correlation between geomagnetic reversals and the stratigraphic ...

  14. Magnetic field variations and the seismicity of solar active regions

    OpenAIRE

    Martinez-Oliveros, J. C.; Donea, A. -C.

    2009-01-01

    Dynamical changes in the solar corona have proven to be very important in inducing seismic waves into the photosphere. Different mechanisms for their generation have been proposed. In this work, we explore the magnetic field forces as plausible mechanisms to generate sunquakes as proposed by Hudson, Fisher and Welsch. We present a spatial and temporal analysis of the line-of-sight magnetic field variations induced by the seismically active 2003 October 29 and 2005 January 15...

  15. Extragalactic magnetic fields rule out electroweak phase transition magnetogenesis

    CERN Document Server

    Wagstaff, Jacques M

    2014-01-01

    In this letter we show that magnetic fields generated at the electroweak phase transition must have helicity in order to explain the void magnetic fields apparently observed today. In the most optimistic case, the helicity fraction must be at least of order $10^{-11}$. We show that the helicity naturally produced in conjunction with the baryon asymmetry is too small to explain observations, and therefore new mechanisms to generate primordial helicity are required.

  16. Magnetic field tomography, helical magnetic fields and Faraday depolarization

    OpenAIRE

    Horellou, Cathy; Fletcher, Andrew

    2014-01-01

    Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three-dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along the wave's propagation path to the observer). In order to proceed, reliable methods are required for inverting the signals obs...

  17. Effect of magnetic field on ball milled hard magnetic particles

    Science.gov (United States)

    Altuncevahir, B.; Poudyal, N.; Chakka, V. M.; Chen, K. H.; Black, T. D.; Liu, T. D.

    2004-03-01

    In this investigation, the powder particles of NdFeB and SmCo based alloys prepared by the ball milling in a uniform magnetic field are compared to those milled without an applied magnetic field. The ball milling was carried out for a total of 100 hours, and the powders were sampled every 25 hours. The particle size after 100 hours of milling was around 100 nm and the grain size in the particles was below 20 nm. The particles were then aligned in a magnetic field in hardening epoxy. It was found that the remanence ratios of the samples milled in an applied magnetic field were remarkably higher than those milled without field. XRD patterns also showed that the powder milled in magnetic field has better alignment than those milled without magnetic field. This technique is a novel approach to preparing anisotropic magnetic nanoparticles and has potential for producing high energy-product nanocomposite permanent magnets.

  18. Displacement current and the generation of parallel electric fields.

    Science.gov (United States)

    Song, Yan; Lysak, Robert L

    2006-04-14

    We show for the first time the dynamical relationship between the generation of magnetic field-aligned electric field (E||) and the temporal changes and spatial gradients of magnetic and velocity shears, and the plasma density in Earth's magnetosphere. We predict that the signatures of reconnection and auroral particle acceleration should have a correlation with low plasma density, and a localized voltage drop (V||) should often be associated with a localized magnetic stress concentration. Previous interpretations of the E|| generation are mostly based on the generalized Ohm's law, causing serious confusion in understanding the nature of reconnection and auroral acceleration. PMID:16712084

  19. Graphene-enhanced, internal-magnetic-field-generated Rabi oscillations in metal-coated Si-SiO2 photoconductive detectors

    CERN Document Server

    Nalla, Venkatram; Loh, Kian Ping; Ji, Wei

    2013-01-01

    We report our demonstration of Rabi oscillations in Si-SiO2-Al photoconductive devices with nanosecond laser pulses of a few nJ at room temperature without external magnetic fields. Zeeman splitting of spin quantum states of dopants in silicon is achieved with internal magnetic fields produced by the Al film under excitation of laser pulses. Rabi oscillation frequency is 15 MHz and 25 MHz when photocurrent direction is perpendicular and parallel, respectively, to the propagation direction of linearly-polarized, 532-nm, 7-ns laser pulses. Insertion of graphene buffer layer between Al and SiO2 provides a three-fold enhancement in Rabi oscillation amplitude. This simple-structured, low-cost device operated at room temperature should open a new avenue for future spin-based electronics and optoelectronics.

  20. Revivals, collapses and magnetic-pulse generation in quantum rings

    OpenAIRE

    Moskalenko, A. S.; Matos-abiague, A.; Berakdar, J.

    2006-01-01

    Using a microscopic theory based on the density matrix formalism we investigate quantum revivals and collapses of the charge polarization and charge current dynamics in mesoscopic rings driven by short asymmetric electromagnetic pulses. The collapsed state is utilized for sub-picosecond switching of the current and associated magnetization, enabling thus the generation of pulsed magnetic fields with a tunable time structure and shape asymmetry which provides a new tool to st...

  1. The magnetic field of pulsars and the gravito-magnetic theory

    CERN Document Server

    Biemond, J

    2004-01-01

    Many authors have considered a gravitational origin of the magnetic field of celestial bodies. Especially, the so-called Wilson-Blackett formula has been investigated, both theoretically and observationally. It appeared possible to deduce this formula from general relativity, e. g., by application of a special interpretation of gravito-magnetic theory. More consequences of the latter theory for pulsars will be considered in this work. As an example, the standard quadrupolar charge density for pulsars can be deduced from the gravito-magnetic theory. Moreover, a new magnetic dipole moment from electromagnetic origin is found, generated in the basic magnetic field from gravito-magnetic origin. In general, for thirteen accreting, slowly rotating, binary pulsars the agreement between the observed magnetic field and the gravito-magnetic prediction is better than between the observed value and the value from the standard magnetic dipole radiation model. At present, an analogous comparison for five isolated pulsars a...

  2. Measurement of instant magnetic fields

    International Nuclear Information System (INIS)

    A two-channel Hall magnetometer, which is designed to measure the distribution of pulsed magnetic fields and their gradients in space and time, has been developed. A sampler containing a Hall transducer is connected with the main circuit by a cable 10 m long. The magnetic fields measured range from 102 to 2.5x104 oe. The instrument measures with an accuracy of 0.1%. The hall transducer is fed by stable pulses (< 10 musec) of current up to 1.0 A. Because the feeding current is characterized by amplitudes 10 to 20 times as high as the dc amplitude, the Hall transducer sensitively is improved and the input circuit induction is significantly reduced. The use in the magnetometer of modern integral operational amplifiers with the differential input has made it possible to obtain wide-band, stable, and linear measuring channels. The block diagram of one of the measuring channels is presented. The 'instantaneousness' of measurement of fields is less than 1 musec. The instrument is calibrated in magnetic fields using an NMR-magnetometer

  3. Diagnostics of vector magnetic fields

    Science.gov (United States)

    Stenflo, J. O.

    1985-01-01

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

  4. The Magnetism of Meteorites and Early Solar System Magnetic Fields

    Science.gov (United States)

    Collinson, D. W.

    1994-11-01

    The characteristics of the remanent magnetization of chondrite, achondrite and shergottite, nakhlite and chassignite (SNC) meteorites are described, and interpretation in terms of magnetizing fields in the ancient Solar System discussed. The magnetism of ordinary chondrites is commonly scattered in direction within samples, implying magnetization of constituent fragments before accumulation. The magnetic history of these meteorites is uncertain because of lack of knowledge of the origin and properties of tetrataenite, an ordered FeNi alloy often carrying the bulk of the magnetization. Achondrites also often possess scattered magnetization, the primary component probably being acquired during cooling after differentiation of the parent body. A magnetizing field of internal origin is possible. Estimates of magnetizing field strength are in the approximate range 5-100 ? T, with carbonaceous chondrites showing the highest values. The SNC meteorites, probably originating on Mars, provide evidence for a weak, ancient Martian magnetic field of the order 1 ? T.

  5. Analysis of brushless DC generator incorporating an axial field coil

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Hassan, E-mail: H_moradi@sbu.ac.i [Department of Electrical and Computer Engineering, Shahid Beheshti University, GC, Tehran (Iran, Islamic Republic of); Afjei, E. [Department of Electrical and Computer Engineering, Shahid Beheshti University, GC, Tehran (Iran, Islamic Republic of)

    2011-07-15

    Highlights: {yields} Magnetic analysis and experiment of a three-phase field assisted BLDC generator. {yields} Confirm the accuracy of the predicted flux-linkage by 2-D FE analysis. {yields} Confirm the accuracy of the FE analysis results by coupling the FE and BE method. {yields} Control the output voltage to a desired level by control the amplitude of the I{sub f}. {yields} Compatible with any application that requires variable speed operation. -- Abstract: This paper describes the magnetic analysis and experiment of a three-phase field assisted brushless DC (BLDC) generator. Unlike conventional BLDC generators, the permanent magnet is replaced with an assisted field winding. The stator and rotor are constructed with two dependent magnetically sets, in which each stator set includes nine salient poles with coil windings, and the rotor comprises of six salient poles. Other pole combinations also are possible. This construction is similar to a homopolar inductor alternator. The DC current in the assisted field winding produces axial flux which makes the rotor magnetically polarized at its ends. The magnetic field flows axially through the rotor shaft and closes through the stator teeth and the machine housing. To evaluate the generator performance, two types of analysis, namely the numerical technique and the experimental study have been utilized. In the numerical analysis, 2-D finite element (FE) analysis has been carried out using a MagNet CAD package (Infolytica Corporation Ltd.), to confirm the accuracy of the predicted flux-linkage characteristics, whereas in the experimental study, a prototype BLDC generator was constructed for verifying the actual performance. Furthermore, the evaluation method based on a hybrid numerical method coupling the finite element (FE) analysis and boundary element (BE) method, has been carried out to confirm the accuracy of the 2-D FE analysis simulation results. It provides not only confirmations of the investigation in results but also exact illustration for magnetic field distribution for this complex generator geometry.

  6. Analysis of brushless DC generator incorporating an axial field coil

    International Nuclear Information System (INIS)

    Highlights: ? Magnetic analysis and experiment of a three-phase field assisted BLDC generator. ? Confirm the accuracy of the predicted flux-linkage by 2-D FE analysis. ? Confirm the accuracy of the FE analysis results by coupling the FE and BE method. ? Control the output voltage to a desired level by control the amplitude of the If. ? Compatible with any application that requires variable speed operation. -- Abstract: This paper describes the magnetic analysis and experiment of a three-phase field assisted brushless DC (BLDC) generator. Unlike conventional BLDC generators, the permanent magnet is replaced with an assisted field winding. The stator and rotor are constructed with two dependent magnetically sets, in which each stator set includes nine salient poles with coil windings, and the rotor comprises of six salient poles. Other pole combinations also are possible. This construction is similar to a homopolar inductor alternator. The DC current in the assisted field winding produces axial flux which makes the rotor magnetically polarized at its ends. The magnetic field flows axially through the rotor shaft and closes through the stator teeth and the machine housing. To evaluate the generator performance, two types of analysis, namely the numerical technique and the experimental study have been utilized. In the numerical analysis, 2-D finite element (FE) analysis has been carried out using a MagNet CAD package (Infolytica Corporation Ltd.), to nfolytica Corporation Ltd.), to confirm the accuracy of the predicted flux-linkage characteristics, whereas in the experimental study, a prototype BLDC generator was constructed for verifying the actual performance. Furthermore, the evaluation method based on a hybrid numerical method coupling the finite element (FE) analysis and boundary element (BE) method, has been carried out to confirm the accuracy of the 2-D FE analysis simulation results. It provides not only confirmations of the investigation in results but also exact illustration for magnetic field distribution for this complex generator geometry.

  7. Anisotropic magnetism in field-structured composites

    International Nuclear Information System (INIS)

    Magnetic field-structured composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g., rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chainlike particle structures, and a biaxial field produces sheetlike particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCs of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material. (c) 2000 The American Physical Society

  8. Energy of Alfven waves generated during magnetic reconnection

    CERN Document Server

    Wang, L C; Ma, Z W; Zhang, X; Lee, L C

    2015-01-01

    A new method for the determination of the Alfven wave energy generated during magnetic reconnection is introduced and used to analyze the results from two-dimensional MHD simulations. It is found that the regions with strong Alfven wave perturbations almost coincide with that where both magnetic-field lines and flow-stream lines are bent, suggesting that this method is reliable for identifying Alfven waves. The magnetic energy during magnetic reconnection is mainly transformed into the thermal energy. The conversion rate to Alfven wave energy from the magnetic energy is strongly correlated to the magnetic reconnection rate. The maximum conversion rate at the time with the peak reconnection rate is found to be only about 4% for the cases with the plasma beta=0.01,0.1, and 1.0.

  9. Floating and flying ferrofluid bridges induced by external magnetic fields

    Science.gov (United States)

    Ma, Rongchao; Zhou, Yixin; Liu, Jing

    2015-04-01

    A ferrofluid is a mixture that exhibits both magnetism and fluidity. This merit enables the ferrofluid to be used in a wide variety of areas. Here we show that a floating ferrofluid bridge can be induced between two separated boards under a balanced external magnetic field generated by two magnets, while a flying ferrofluid bridge can be induced under an unbalanced external magnetic field generated by only one magnet. The mechanisms of the ferrofluid bridges were discussed and the corresponding mathematical equations were also established to describe the interacting magnetic force between the ferro particles inside the ferrofluid. This work answered a basic question that, except for the well-known floating water bridges that are related to electricity, one can also build up a liquid bridge that is related to magnetism.

  10. Magnetic field effects in chemical systems

    OpenAIRE

    Rodgers, Christopher T.; Hore, P. J.; Timmel, Christiane R

    2007-01-01

    Magnetic fields influence the rate and/or yield of chemical reactions that proceed via spin correlated radical pair intermediates. The field of spin chemistry centres around the study of such magnetic field effects (MFEs). This thesis is particularly concerned with the effects of the weak magnetic fields B? ~ 1mT relevant in the ongoing debates on the mechanism by which animals sense the geomagnetic field and on the putative health effects of environmental electromagnetic fields. Relatively f...

  11. Magnetic field effect for cellulose nanofiber alignment

    Science.gov (United States)

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

    2008-11-01

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

  12. Superconducting vibrator with a trapped magnetic field

    International Nuclear Information System (INIS)

    Paper offers a design of a superconducting vibrator for flexural oscillations. Dependence of the vibrator proper frequency on the magnetic field is estimated. The proper frequency of the proposed design is shown to be tens times more sensitive to the magnetic field in contrast to all those used earlier. It is proposed to use such a resonator to study magnetic field penetration into superconductors

  13. Quarkyonic Chiral Spirals in a Magnetic Field

    OpenAIRE

    Ferrer, Efrain J.; La Incera, Vivian; Sanchez, Angel

    2012-01-01

    We discuss the formation of quarkyonic chiral spirals in the presence of a magnetic field. The explicit breaking of the rotational symmetry by the external magnetic field gives rise to an additional chiral spiral that varies along the field direction and rotates in the chiral space between pion and magnetic moment components.

  14. Spin echo without an external permanent magnetic field

    OpenAIRE

    Bergli, Joakim; Glazman, Leonid

    2006-01-01

    The spin echo techniques aim at the elimination of the effect of a random magnetic field on the spin evolution. These techniques conventionally utlize the application of a permanent field which is much stronger than the random one. The strong field, however, may also modify the magnetic response of the medium containing the spins, thus altering their ``natural'' dynamics. We suggest an iterative scheme for generating a sequence of pulses which create an echo without an exter...

  15. Recombination era magnetic fields from axion dark matter

    CERN Document Server

    Banik, Nilanjan

    2015-01-01

    We introduce a new mechanism for generating magnetic fields in the recombination era. This Harrison-like mechanism utilizes vorticity in baryons that is sourced through the Bose-Einstein condensate of axions via gravitational interactions. The magnetic fields generated are on the galactic scales $\\sim 10\\,{\\rm kpc}$ and have a magnitude of the order of $B\\sim10^{-23}\\,{\\rm G}$ today. The field has a greater magnitude than those generated from other mechanisms relying on second order perturbation theory, and is sufficient to provide a seed for battery mechanisms.

  16. Magnetic-Field-Tunable Superconducting Rectifier

    Science.gov (United States)

    Sadleir, John E.

    2009-01-01

    Superconducting electronic components have been developed that provide current rectification that is tunable by design and with an externally applied magnetic field to the circuit component. The superconducting material used in the device is relatively free of pinning sites with its critical current determined by a geometric energy barrier to vortex entry. The ability of the vortices to move freely inside the device means this innovation does not suffer from magnetic hysteresis effects changing the state of the superconductor. The invention requires a superconductor geometry with opposite edges along the direction of current flow. In order for the critical current asymmetry effect to occur, the device must have different vortex nucleation conditions at opposite edges. Alternative embodiments producing the necessary conditions include edges being held at different temperatures, at different local magnetic fields, with different current-injection geometries, and structural differences between opposite edges causing changes in the size of the geometric energy barrier. An edge fabricated with indentations of the order of the coherence length will significantly lower the geometric energy barrier to vortex entry, meaning vortex passage across the device at lower currents causing resistive dissipation. The existing prototype is a two-terminal device consisting of a thin-film su - perconducting strip operating at a temperature below its superconducting transition temperature (Tc). Opposite ends of the strip are connected to electrical leads made of a higher Tc superconductor. The thin-film lithographic process provides an easy means to alter edge-structures, current-injection geo - metries, and magnetic-field conditions at the edges. The edge-field conditions can be altered by using local field(s) generated from dedicated higher Tc leads or even using the device s own higher Tc superconducting leads.

  17. Enhancement of magnetic fields arising from galactic encounters

    CERN Document Server

    Moss, David; Beck, Rainer; Krause, Marita

    2014-01-01

    Galactic encounters are usually marked by a substantial increase of synchrotron emission of the interacting galaxies compared to the typical emission from similar isolated galaxies. This is believed to be associated with an increase of the star formation rate and the associated turbulent magnetic fields. The regular magnetic field is usually believed to decrease. We consider a simple, however rather realistic, mean-field galactic dynamo model where the effects of small-scale generation are represented by random injections of magnetic field from star forming regions. We represent an encounter by the introduction of large-scale streaming velocities and by an increase in small-scale magnetic field injections. The latter describes the effect of an increase of the star formation rate caused by the encounter. We demonstrate that large-scale streaming, with associated deviations in the rotation curve, can result in an enhancement of the anisotropic turbulent (ordered) magnetic field strength, mainly along the azimut...

  18. Bats respond to very weak magnetic fields.

    Science.gov (United States)

    Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang

    2015-01-01

    How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 ?T; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 ?T), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944

  19. Magnetic Helicity and Large Scale Magnetic Fields: A Primer

    CERN Document Server

    Blackman, Eric G

    2014-01-01

    Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. H...

  20. Magnetic field depression within electron holes

    Science.gov (United States)

    Vasko, I. Y.; Agapitov, O. V.; Mozer, F.; Artemyev, A. V.; Jovanovic, D.

    2015-04-01

    We analyze electron holes that are spikes of the electrostatic field (up to 500 mV/m) observed by Van Allen Probes in the outer radiation belt. The unexpected feature is the magnetic field depression of about several tens of picotesla within many of the spikes. The earlier observations showed amplification or negligible perturbations of the magnetic field within the electron holes. We suggest that the observed magnetic field depression is due to the diamagnetic current of hot and highly anisotropic population of electrons trapped within the electron holes. The required trapped population should have a density up to 65% of the background plasma density, a temperature up to several keV, and a temperature anisotropy T?/T?˜2. We argue that the observed electron holes could be generated due to injections of highly anisotropic plasma sheet electrons into the outer radiation belt. These electron holes may present a source of the seed population due to transport of trapped electrons to higher latitudes and can be potentially used for distant probing of plasma properties in their source region.

  1. Strong Langmuir turbulence in a magnetic field

    Science.gov (United States)

    Rowland, H. L.

    1985-01-01

    A series of computer simulations, using both particle and fluid codes, is reported on the strong turbulence evolution of Langmuir waves in an ambient magnetic field. For an initial spectrum of Langmuir waves with a small transverse spread, such as would be generated by the kinetic-beam plasma instability, the strong turbulence is initially one-dimensional and compresses the field into localized structures in the direction parallel to the initial waves, thus forming planar solitons. In two dimensions with no parallel magnetic field, the growth of transverse instabilities causes Langmuir collapse, with the energy being absorbed in heavily damped short wavelength modes. In the simulation with a single initial wave, the parallel magnetic field leads to more pancake-shaped solitons by reducing the shortest unstable mode, but has minor effects on the transverse collapse. For an initial wave packet, if the shortest unstable mode is less than the k-perpendicular gradient, the transverse perturbations are stabilized and the collapse does not take place.

  2. Effective magnetic moment of neutrinos in strong magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Perez M, A.; Perez R, H. [Instituto de Matematica Cibernetica y Fisica, Calle E Esq. a 15, No. 309. Vedado, C. Habana (Cuba); Masood, S.S. [Phys. Dept. Quaid-i-Azam University, Islamabad (Pakistan); Gaitan, R.; Rodriguez R, S. [Centro de Investigaciones Teoricas, Facultad de Estudios Superiores, Universidad Nacional Autonoma de Mexico, Apdo. Post. 142, Cuautitlan-Izcalli, Estado de Mexico (Mexico)

    2002-07-01

    In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)

  3. The Experimental Characterization of the Magnetic Field Effect on a Liquid Sodium Flow

    International Nuclear Information System (INIS)

    A liquid sodium coolant is used for a LMR such as KALIMER and a magnetic field is generated in the electromagnetic pump or flowmeter. The magnetic field has an effect on the electrically conducting metal flow by a generation of an electromagnetic pressure drop. Therefore, in the present study, a theoretical calculation is carried out for the effect of an external magnetic field and the magnetic field is measured over the electromagnet system manufactured for the magnetohydrodynamic experiments

  4. The magnetic field measurements of the booster synchrotron magnet

    International Nuclear Information System (INIS)

    The magnetic field properties of the booster synchrotron magnet are investigated. Method of the field measurement, magnetic field measuring system, its data acquisition system and procedure of data processing are described in detail, with a special emphasis on the accuracy in the measurement. The excitation dependences and distributions of the field strength, field gradient, multipole fields and their effective lengths are given and analyzed. The betatron tune and chromaticity are discussed by taking account of the effect of the fringing field as well as the multipole fields of focussing and defocussing sectors. (auth.)

  5. Hypernuclear matter in strong magnetic field

    International Nuclear Information System (INIS)

    Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 1014–1015 G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta–Bodmer–Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B?1017 G, in particular the matter properties become anisotropic. Moreover, for the central fields B?1018 G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value Bcr?1019 G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value Bcr

  6. Plastic scintillators in magnetic fields

    International Nuclear Information System (INIS)

    The dependence of the light yield and the transmission on magnetic fields has been measured with different methods up to 0.45 T for the plastic scintillators NE-102A, SCSN-38 and Polivar. The scintillators were excited by 25 MeV protons, 5.9 keV X-rays and UV light. When excited with ionizing radiation and increase of light yield is observed. For SCSN-38 of 2.6 mm thickness it amounts to 0.3%, 0.9%, 1.1%, and 3.3% at 1, 10, 100 and 450 mT, respectively. NE-102A behaves similar, whereas an acrylic scintillator shows a stronger field dependence. The effect is independent of the direction of the field but increases for the acrylic scintillator with its thickness. No change in the decay time of the scintillator has been observed. The response of the scintillators did not change when excited by UV light in a magnetic field. (orig.)

  7. Quark Antiscreening at Strong Magnetic Field and Inverse Magnetic Catalysis

    CERN Document Server

    Ferrer, E J; Wen, X J

    2014-01-01

    The dependence of the QCD coupling constant with a strong magnetic field and the implications for the critical temperature of the chiral phase transition are investigated. It is found that the coupling constant becomes anisotropic in a strong magnetic field, and that the quarks, confined by the field to the LLL, produce an antiscreening effect. These results lead to inverse magnetic catalysis, providing a natural explanation for the behavior of the critical temperature in the strong field region.

  8. Contactless dielectrophoretic manipulation of biological cells using pulsed magnetic fields.

    Science.gov (United States)

    Novickij, Vitalij; Grainys, Audrius; Novickij, Jurij

    2014-06-01

    Contactless method for manipulation of polar or polarisable micro and nanoscale particles based on the dielectrophoresis force exerted by the induced electric field in high pulsed magnetic field is presented in this study. Finite element method analysis of the magnetic and resulting induced electric fields is carried out. The structure of the magnetic field generator that was based on a controlled frequency spark gap, and the structure of the coil that was used as a load are described. Experimental data showing positive dielectrophoresis on the Jurkat T-lymphoblasts is presented. The study discusses further developments of the technique, its limitations and possible applications. PMID:25014083

  9. A magnetic minirobot with anchoring and drilling ability in tubular environments actuated by external magnetic fields

    Science.gov (United States)

    Choi, K.; Jeon, S. M.; Nam, J. K.; Jang, G. H.

    2015-05-01

    We propose a magnetic minirobot with anchoring and drilling ability (MMAD) controlled by an external magnetic field. The proposed MMAD can navigate through a tubular environment, such as human blood vessels, actuated by a magnetic gradient and uniform rotating magnetic field. It can also generate an anchoring motion, which stably holds the position of the MMAD under pulsatile flow, in order to drill and unclog obstructed blood vessels. The operating conditions of the MMAD were examined by investigating the magnetic torques, and the holding force of the MMAD was measured by a force sensing resistor. Finally, we performed various experiments in a tubular environment to verify the validity of the proposed MMAD.

  10. The formation of regular interarm magnetic fields in spiral galaxies

    CERN Document Server

    Moss, David; Krause, Marita; Beck, Rainer; Sokoloff, Dmitri

    2015-01-01

    Observations of several nearby galaxies of regular magnetic fields reveal magnetic arms situated between the material arms. The nature of these magnetic arms is a topic of active debate. Previously we found a hint that taking into account the effects of injections of small-scale magnetic fields generated, e.g., by turbulent dynamo action, into the large-scale galactic dynamo can result in magnetic arm formation. We now investigate the joint roles of an arm/interarm turbulent diffusivity contrast and injections of small-scale magnetic field on the formation of large-scale magnetic field ("magnetic arms") in the interarm region. We use the relatively simple "no-$z$" model for the galactic dynamo. This involves projection on to the galactic equatorial plane of the azimuthal and radial magnetic field components; the field component orthogonal to the galactic plane is estimated from the solenoidality condition. We find that addition of diffusivity gradients to the effect of magnetic field injections makes the magn...

  11. How to Draw Magnetic Fields - II

    Science.gov (United States)

    This is an activity about depicting magnetic polarity. Learners will observe several provided drawings of magnetic field line patterns for bar magnets in simple orientations of like and unlike polarities and carefully draw the field lines and depict the polarities for several orientations, including an arrangement of six magnetic poles. This is the fourth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

  12. Biotropic parameters of magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Shishlo, M.A.

    The use of magnetic fields (MF) in biology and medicine to control biological systems has led to appearance of the term, biotropic parameters of MF. They include the physical characteristics of MF, which determine the primary biologically significant physicochemical mechanisms of field action causing formation of corresponding reactions on the level of the integral organism. These parameters include MF intensity, gradient, vector, pulse frequency and shape, and duration of exposure. Factors that elicit responses by the biological system include such parameter of MF interaction with the integral organism as localization of exposure and volume of tissues interacting with the field, as well as the initial state of the organism. In essence, the findings of experimental studies of biotropic parameters of MF make it possible to control physiological processes and will aid in optimizing methods of MF therapy.

  13. The effective potential of composite fields in weakly coupled QED in a uniform external magnetic field

    CERN Document Server

    Lee, D S; Ng, Y J; Shovkovy, I A

    1999-01-01

    The effective potential for the composite fields responsible for chiral symmetry breaking in weakly coupled QED in a magnetic field is derived. The global minimum of the effective potential is found to acquire a non-vanishing expectation value of the composite fields that leads to generating the dynamical fermion mass by an external magnetic field. The results are compared with those for the Nambu-Jona-Lasinio model.

  14. Bats Respond to Very Weak Magnetic Fields

    Science.gov (United States)

    Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang

    2015-01-01

    How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 ?T; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 ?T), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (Pmagnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944

  15. The levitation characteristics of the magnetic substances using trapped HTS bulk annuli with various magnetic field distributions

    International Nuclear Information System (INIS)

    Highlights: •The spherical solenoid magnet can make a various magnetic field distributions. •We generated a large magnetic gradient at inner space of HTS bulks. •The levitation height of samples was improved by the reapplied field method. •The levitation height depends on the variation rate of magnetic field gradient. -- Abstract: We have been investigating the levitation system without any mechanical contact which is composed of a field-cooled ring-shaped high temperature superconducting (HTS) bulks [1]. In this proposed levitation system, the trapped magnetic field distributions of stacked HTS bulk are very important. In this paper, the spherical solenoid magnet composed of seven solenoid coils with different inner and outer diameters was designed and fabricated as a new magnetic source. The fabricated spherical solenoid magnet can easily make a homogeneous and various magnetic field distributions in inner space of stacked HTS bulk annuli by controlling the emerging currents of each coil. By using this spherical solenoid magnet, we tried to make a large magnetic field gradient in inner space of HTS bulk annuli, and it is very important on the levitation of magnetic substances. In order to improve the levitation properties of magnetic substances with various sizes, the external fields were reapplied to the initially trapped HTS bulk magnets. We could generate a large magnetic field gradient along the axial direction in inner space of HTS bulk annuli, and obtain the improved levitation height of samples by the proposed reapplied field method

  16. Hypernuclear matter in strong magnetic field

    CERN Document Server

    Sinha, Monika; Sedrakian, Armen

    2012-01-01

    Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10^{14}-10^{15} G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta-Bodmer-Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B \\ge 10^{17} G, in particular the matter properties become anisotropic. Moreover, for the central fields B_{\\rm cr} \\ge 10^{19} G, the magnetized hypernuclear matter becomes unstable, which limits the range of admissible fields in magnetars to fields below the critical value B_{\\rm cr}.

  17. An Intergalactic Magnetic Field from Quasar Outflows

    OpenAIRE

    Furlanetto, Steven; Loeb, Abraham

    2001-01-01

    Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function magnetic field strength at different redshifts. We find that by a redshift z ~ 3, about 5-80% of the IGM volume is filled by magnetic fields with an energy density > 10% of the mean thermal e...

  18. Magnetization reversal of ferromagnetic nanoparticles under inhomogeneous magnetic field

    International Nuclear Information System (INIS)

    We investigated remagnetization processes in ferromagnetic nanoparticles under inhomogeneous magnetic field induced by the tip of magnetic force microscope (MFM) in both theoretical and empirical ways. Systematic MFM observations were carried out on arrays of submicron-sized elliptical ferromagnetic particles of Co and FeCr with different sizes and periods. It clearly reveals the distribution of remanent magnetization and processes of local remagnetization of individual ferromagnetic particles. Modeling of remagnetization processes in ferromagnetic nanoparticles under magnetic field induced by MFM probe was performed on the base of Landau-Lifshitz-Gilbert equation for magnetization. MFM-induced inhomogeneous magnetic field is very effective to control the magnetic state of individual ferromagnetic nanoparticles as well as to create different distribution of magnetic field in array of ferromagnetic nanoparticles

  19. Model for charged dust expansion across a magnetic field

    International Nuclear Information System (INIS)

    Plasma fluctuations arise in the boundary region between charged dust clouds and background plasmas. A self-consistent computational model is developed to study expansion of a charged dust cloud across a magnetic field, creation of the inhomogeneous boundary layer and associated processes. The charging of the dust particulates produces a boundary layer and associated ambipolar electric field. This ambipolar field provides a source for low frequency dust acoustic waves in unmagnetized plasmas. A background magnetic field if sufficiently strong, may impact the dust acoustic wave evolution and dust density structures due to E×B and diamagnetic current generation. The dust acoustic density fluctuation generation across a strong magnetic field (?pe/?ce?1) may be suppressed as compared to an unmagnetized dusty plasma, which will be discussed. Fluctuations generated at longer timescales propagating along the dust boundary layer will also be investigated in the lower hybrid and dust lower hybrid frequency range. Applications to space and laboratory plasmas are discussed

  20. Stray field magnetic resonance imaging

    International Nuclear Information System (INIS)

    Magnetic resonance imaging (MRI) is well known in a clinical context as a technique capable of delivering highly detailed anatomical images, particularly of soft tissue. The MRI method is completely non-invasive and allows spatial resolution down to a few micrometres in three dimensions. Image contrast is governed by one of several nuclear magnetic resonance parameters and might reflect water mobility, chemical potential, self-diffusion coefficient, coherent flow or temperature, depending upon the exact form of the MRI measurement. Less widely realized is the enormous potential for the use of MRI in materials science. The flexibility that makes MRI such a valuable clinical tool is equally applicable in a non-medical scenario, but the greater technical difficulties associated with MRI in solid materials have hitherto limited the development of the technique in this area. This review describes in detail one approach to MRI in solid materials which is currently benefiting from rapidly increasing application: stray field (magnetic resonance) imaging (STRAFI). An introduction to the phenomenon of nuclear magnetic resonance and particularly its detection in solids is followed by a description of the steps necessary for its use as an imaging modality. The limits of MRI spatial resolution in liquids and solids are briefly discussed. STRAFI is placed in context throughout this introduction. The STRAFI technique is then described in detail, in terms of its merits relative to otail, in terms of its merits relative to other approaches to solids MRI and the subtleties of its implementation. The principal areas of current STRAFI application are reviewed and developments with which STRAFI advancement is closely linked, are also described. In conclusion, some consideration is given to the promising future of stray field MRI as a widely accepted research tool in materials science and to the development of the technique itself. (author)