- Home
- ▪
- About
- ▪
- News
- ▪
- Advanced Search
- ▪
- Mobile
- ▪
- Contact Us
- ▪
- Site Map
- ▪
- Help

1

Magnetic field generation in plasma

An equation is obtained which describes the generation of a quasi-stationary magnetic field in a weakly ionized plasma or a plasma consisting of multiply charged ions in a high-frequency electromagnetic wave. A consistent kinematic description of electron heating during bremsstrahlung absorption has made it possible to discover the effect of a substantial increase in the magnetic field rise rate dependent on the radiation intensity.

Ovchinnikov, K. N.; Silin, V. P.; Uriupin, S. A.

1991-09-01

2

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

3

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.)

4

Magnetic field generation device for magnetohydrodynamic electric power generation

International Nuclear Information System (INIS)

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

5

Magnetic field generation in curved spacetimes

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

Mahajan, Swadesh M

2011-01-01

6

A deep dynamo generating Mercury's magnetic field.

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

Christensen, Ulrich R

2006-12-21

7

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

8

The ULF Magnetic Fields Generated by Thunderstorms

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

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

2013-12-01

9

The seed magnetic field generated during recombination

Nonlinear dynamics creates vortical currents when the tight-coupling approximation between photons and baryons breaks down around the time of recombination. This generates a magnetic field at second order in cosmological perturbations, whose power spectrum is fixed by standard physics, without the need for any ad hoc assumptions. We present the fully relativistic calculation of the magnetic power spectrum, including the effects of metric perturbations, second-order velocity and the photon anisotropic stress, thus generalizing and correcting previous results. We also show that significant magnetogenesis continues to occur after recombination. The power spectrum $\\sqrt{k^3 P_B} $ behaves as $ \\propto k^4$ on large scales, and $\\propto k^{0.5}$ on small scales, down to $\\sim 1\\,$Mpc. On cluster scales, the created field has strength $\\sim 3\\times 10^{-29}$ Gauss.

Fenu, Elisa; Maartens, Roy

2010-01-01

10

Generation of Cosmic Magnetic Fields at Recombination

It is shown that the standard cosmological model predicts ab initio generation of large-scale cosmic magnetic fields at the epoch of recombination of the primeval plasma. Matter velocities dominated by coherent flows on a scale $L\\approx 50h^{-1}(1+z)^{-1}$ Mpc lead to a dipole of radiation flux in the frame of the moving matter. Thomson scattering of the radiation differentially accelerates the electrons and ions, creating large-scale coherent electric currents and magnetic fields. This process is analyzed using magnetohydrodynamic equations which include a modification of Ohm's law describing the effect of Thomson drag on the electrons. The field strength saturates near equipartition with the baryon kinetic energy density at $B\\simeq 5\\times 10^{-5}$G. Magnetic stresses significantly damp baryonic motions at the epoch of last scattering, reducing the predicted background radiation anisotropy at small angles and changing estimates of fitted cosmological parameters. The field at late times retains its large-s...

Hogan, C J

2000-01-01

11

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

12

Modelling coils system for generating homogeneous magnetic field

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

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

2014-10-01

13

High Magnetic Field Generator of Sub-Microsecond Duration

Directory of Open Access Journals (Sweden)

Full Text Available The article describes the possibility of generating a micro and sub-microsecond magnetic impulse reaching 1–10 T, investigates various configurations of microcoils and discusses the principal circuit of a magnetic field impulse generator of microsecond duration. The transient processes of current, temperature and magnetic field are calculated applying the finite element method.Article in Lithuanian

Audrius Grainys

2012-04-01

14

Visualisation of Magnetic Fields Generated by Helmholtz Coils

Directory of Open Access Journals (Sweden)

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

Tibor Frank

2006-01-01

15

Generation of magnetic fields in plasmas

Energy Technology Data Exchange (ETDEWEB)

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

Shukla, Nitin

2012-07-01

16

Improved Magnetic Field Generation Efficiency and Higher Temperature Spheromak Plasmas

Energy Technology Data Exchange (ETDEWEB)

New understanding of the mechanisms governing the observed magnetic field generation limits on the sustained spheromak physics experiment has been obtained. Extending the duration of magnetic helicity injection during the formation of a spheromak and optimizing the ratio of injected current to bias flux produce higher magnetic field plasmas with record spheromak electron temperatures. To explore magnetic field buildup efficiency limits, the confinement region geometry was varied resulting in improved field buildup efficiencies.

Wood, R D; Hill, D N; McLean, H S; Hooper, E B; Hudson, B F; Moller, J M; Romero-Talamas, C A

2008-09-15

17

Generation of whistler waves by a rotating magnetic field source

The paper discusses the generation of polarized whistler waves radiated from a rotating magnetic field source created via a novel phased orthogonal two loop antenna. The results of linear three-dimensional electron magnetohydrodynamics simulations along with experiments on the generation whistler waves by the rotating magnetic field source performed in the large plasma device are presented. Comparison of the experimental results with the simulations and linear wave properties shows good agreement. The whistler wave dispersion relation with nonzero transverse wave number and the wave structure generated by the rotating magnetic field source are also discussed. The phase velocity of the whistler waves was found to be in good agreement with the theoretical dispersion relation. The exponential decay rate of the whistler wave propagating along the ambient magnetic field is determined by Coulomb collisions. In collisionless case the rotating magnetic field source was found to be a very efficient radiation source for transferring energy along the ambient magnetic field lines.

Karavaev, A. V.; Gumerov, N. A.; Papadopoulos, K.; Shao, Xi; Sharma, A. S.; Gekelman, W.; Gigliotti, A.; Pribyl, P.; Vincena, S.

2010-01-01

18

Magnetic Helicity Generation from the Cosmic Axion Field

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Campanelli, L.; Giannotti, M.

2005-01-01

19

Giga-Gauss scale quasistatic magnetic field generation with laser

A simple setup for the generation of ultra-intense quasistatic magnetic fields is proposed and analysed. Estimations and numerical Particle-In-Cell calculations show that magnetic fields of gigagauss scale may be generated with conventional powerful relativistic lasers interacting with the appropriate targets of a special geometry. The setup may be useful for a wide range of applications, from laboratory astrophysics to magnetized ICF schemes.

Korneev, Philipp; Tikhonchuk, Vladimir

2014-01-01

20

Effects of non-linearities on magnetic field generation

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 suggest that magnetic fields of the order of 10-30- 10-27 G can be generated (although this depends on the small scale cut-off of the integral), which 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.

Nalson, Ellie; Christopherson, Adam J.; Malik, Karim A.

2014-09-01

21

The Model of Magnetic-Field Generation with Screw Dynamo

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

Tlatov, Andrey G

2013-01-01

22

The protostar merger scenario of Ap star magnetic field generation

We propose that the small fraction of stars that are magnetic can be explained if, towards the end of the formation process, a correspondingly small fraction of stars merge after they have developed substantial radiative envelopes. Magnetic A stars may result from merging stars, and owe their strong magnetism to fields generated by a dynamo mechanism as they merge. We postulate a simple dynamo that generates magnetic field from differential rotation. We limit the growth of magnetic fields by the requirement that the poloidal field stabilizes the toroidal field and vice versa. While magnetic torques dissipate the differential rotation, toroidal field is generated from poloidal field by an ? dynamo. Both poloidal and toroidal fields reach a stable configuration that is independent of the size of small initial seed fields but proportional to the initial differential rotation. We posit the hypothesis that strongly magnetic stars form from the merging of two stellar objects. Highest fields are generated when the merger introduces differential rotation that amounts to its critical break up velocity within the condensed object. Such mergers can also account for the lack of close binaries among these stars.

Lau, H. H. B.; Tout, C. A.; Wickramasinghe, D.; Ferrario, L.

2014-11-01

23

Active screening of magnetic field near power stations generator buses

Directory of Open Access Journals (Sweden)

Full Text Available An experimental study technique for a prototyping system of active screening of power-frequency magnetic field distortions near power station generator buses via controllable magnetic field sources is presented. Results of experimental research on a proto-typing active screening system with different control algorithms are given.

B.I. Kuznetsov

2013-12-01

24

Observation of a Turbulence-Generated Large Scale Magnetic Field

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.

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

2006-01-01

25

Generation of solar magnetic fields. I and II

International Nuclear Information System (INIS)

The universe poses a problem which is still very mysterious, namely, that nearly every object seems to have a magnetic field associated with it, whether one talks about planets, stars, or galaxies. Wherever there are magnetic fields, they produce activity, usually in the form of superheated gases. Although the stated topic of the next two lectures is the generation of solar magnetic fields from the motion of conducting fluids, they will be elementary lectures on magnetic fields in general because the sun is by no means an isolated body. In these lectures, the author talks about the properties of magnetic fields that allow them to destroy themselves remarkably rapidly, producing solar activity, stellar activity, geomagnetic activity, and so forth. It might be called the birth and death of magnetic fields. (Auth.)

26

Magnetic field generation and star formation in protogalaxies

International Nuclear Information System (INIS)

If the first generation of stars forms just after protogalaxies have acquired their spin, then star formation in this epoch must overcome an angular momentum barrier nearby as severe as that in our own galactic disk. This paper outlines work done in collaboration with Joseph Silk on the resolution of this problem by magnetic braking. While seed magnetic fields in the protogalactic gas can be no more than about 10-18 Gauss, we show that very high fields (10-6 Gauss) can be generated by dynamo action within one protogalactic free-fall time. The requirement is that strong cloud-cloud collisions should characterize the state of the galaxy at this time. High fields are generated in the shocked gas layers that form as a consequence of such collisions. The predictions are in agreement with the high galactic halo magnetic field strengths which have been inferred from Faraday rotation measures observed towards radio loud quasars

27

Particle Acceleration and Magnetic Field Generation in Shear-Flows

We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma by the kinetic Kelvin-Helmholtz instability for different mass ratios (mi/me = 1, 20, and 1836) and different jet Lorentz factors. We found that electron-positron cases have alternating magnetic fields instead of the DC magnetic fields found in electron-ion cases. We have also investigated particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock.

Nishikawa, K.-I.; Hardee, P.; Mizuno, Y.; Du?an, I.; Zhang, B.; Medvedev, M.; Meli, A.; Choi, E. J.; Min, K. W.; Niemiec, J.; Nordlund, Å.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Marscher, A.; Gómez, J. L.

2014-03-01

28

Generation of magnetic fields in the early Universe

International Nuclear Information System (INIS)

Nonlinear interactions between intense photon and neutrino beams and relativistically hot electron-positron-ion plasmas of the early Universe are considered. It is shown that a small fraction of ions produces large space charge electric fields in the presence of the plasma pressure gradient, relativistic photon ponderomotive force and weak nuclear driving force of neutrinos. Large space charge electric fields can separate pairs, generating the currents which are required for creating magnetic fields in plasmas. The present theory thus offers a possible clue to the origin of primordial magnetic fields in the early Universe

29

Highly Stable and Finely Tuned Magnetic Fields Generated by Permanent Magnet Assemblies

Permanent magnetic materials are the only magnetic source that can be used to generate magnetic fields without power consumption or maintenance. Such stand-alone magnets are very attractive for many scientific and engineering areas, but they suffer from poor temporal field stability, which arises from the strong sensitivity of the magnetic materials and mechanical support to temperature variation. In this work, we describe a highly efficient method useful to cancel the temperature coefficient of permanent magnet assemblies in a passive and accurate way. It is based on the combination of at least two units made of magnetic materials with different temperature coefficients arranged in such a way that the ratio of the fields generated by each unit matches the ratio of their effective temperature coefficients defined by both the magnetic and mechanical contributions. Although typically available magnetic materials have negative temperature coefficients, the cancellation is achieved by aligning the fields generated by each unit in the opposite direction. We demonstrate the performance of this approach by stabilizing the field generated by a dipolar Halbach magnet, recently proposed to achieve high field homogeneity. Both the field drift and the homogeneity are monitored via nuclear magnetic resonance spectroscopy experiments. The results demonstrate the compatibility of the thermal compensation approach with existing strategies useful to fine-tune the spatial dependence of the field generated by permanent magnet arrays.

Danieli, E.; Perlo, J.; Blümich, B.; Casanova, F.

2013-05-01

30

Magnetic field generation in fully convective rotating spheres

Magnetohydrodynamic simulations of fully convective, rotating spheres with volume heating near the center and cooling at the surface are presented. The dynamo-generated magnetic field saturates at equipartition field strength near the surface. In the interior, the field is dominated by small-scale structures, but outside the sphere by the global scale. Azimuthal averages of the field reveal a large-scale field of smaller amplitude also inside the star. The internal angular velocity shows some tendency to be constant along cylinders and is ``anti-solar'' (fastest at the poles and slowest at the equator).

Dobler, W; Brandenburg, A

2004-01-01

31

Computational Models for Creating Homogeneous Magnetic Field Generation Systems

Directory of Open Access Journals (Sweden)

Full Text Available It is increasingly common to use magnetic fields at the cellular level to assess their interaction with biological tissues. The stimulation is usually done with Helmholtz coils which generate a uniform magnetic field in the center of the system. However, assessing cellular behavior with different magnetic field characteristics can be a long and expensive process. For this, it can be used computational models to previously estimate the cellular behavior due to variety of field characteristics prior to in-vitro stimulation in a laboratory. In this paper, we present a methodology for the development of three computational models of homogeneous magnetic field generation systems for possible application in cell stimulation. The models were developed in the Ansys Workbench environment and it was evaluated the magnetic flux density behavior at different configurations. The results were validated with theoretical calculations from the Biot-Savart law. Validated models will be coupled to Ansys APDL environment in order to assess the harmonic response of the system.

Gerlys M. Villalobos-Fontalvo

2013-11-01

32

Energy confinement and magnetic field generation in the SSPX spheromak

Energy Technology Data Exchange (ETDEWEB)

The Sustained Spheromak Physics Experiment (SSPX) [E.B. Hooper, et. al., Nuclear Fusion, Vol. 39, No. 7] explores the physics of efficient magnetic field buildup and energy confinement, both essential parts of advancing the spheromak concept. Extending the spheromak formation phase increases the efficiency of magnetic field generation with the maximum edge magnetic field for a given injector current (B/I) from 0.65 T/MA previously to 0.9 T/MA. We have achieved the highest electron temperatures (T{sub e}) recorded for a spheromak with T{sub e} > 500 eV, toroidal magnetic field {approx}1 T and toroidal current ({approx}1 MA) [R.D. Wood, D.N. Hill, H.S. McLean, E.B. Hooper, B.F. Hudson, J.M. Moller, 'Improved magnetic field generation efficiency and higher temperature spheromak plasmas', submitted to Physical Review Letters]. Extending the sustainment phase to > 8 ms extends the period of low magnetic fluctuations (< 1 %) by 50%. The NIMROD 3-D resistive MHD code [C.R. Sovinec, T.A. Gianakon, E.D. Held, S.E. Kruger and D.D. Schnack, The NIMROD Team, Phys. Plasmas 10, 1727 (2003)] reproduces the observed flux amplification {Psi}{sub pol}/{Psi}{sub gun}. Successive gun pulses are demonstrated to maintain the magnetic field in a quasi-steady state against resistive decay. Initial measurements of neutral particle flux in multi-pulse operation show charge-exchange power loss < 1% of gun input power and dominantly collisional majority ion heating. The evolution of electron temperature shows a distinct and robust feature of spheromak formation: a hollow-to-peaked T{sub e}(r) associated with q {approx} 1/2.

Hudson, B; McLean, H S; Wood, R D; Hooper, E B; Hill, D N; Jayakumar, J; Moller, J; Romero-Talamas, C; Casper, T A; LoDestro, L L; Pearlstein, L D; Johnson, III, J A; Mezonlin, E

2008-02-11

33

Second order semiclassics with self-generated magnetic fields

DEFF Research Database (Denmark)

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

Erdös, Laszlo; Fournais, SØren

2012-01-01

34

Wave propagatiom and magnetic field generation in Rydberg plasmas

We call Rydberg plasma the weakly ionized gas produced in magneto-optical traps. In such a plasma, the neutral atoms can be excited in Rydberg states. Wave propagation in Rydberg plasmas, and the mutual influence of plasma dispersion and atomic dispersion is considered. New dispersion relations are established, showing new instability regimes and new cut-off frequencies. It is also shown that the ponderomotive force of a large-amplitude electromagnetic wave in Rydberg plasmas can generate quasi-stationary magnetic fields. The present result can account for the origin of seed magnetic fields in ultracold Rydberg plasmas when they are irradiated by the high-frequency electromagnetic wave.

Tercas, Hugo; Shukla, Nitin; Shukla, P. K.; Loureiro, J.; Mendonca, J. T.

2009-11-01

35

Generation of quasi-stationary magnetic fields in turbulent plasmas

We investigate quasi-stationary magnetic field generation by a high frequency electromagnetic wave in an inhomogeneous plasma using kinetic theory. A general expression for the nonlinear current is calculated which contains previous results in the collisional, cold and warm plasma regimes as special cases. In addition, the contribution of nonlinear Landau damping is studied, which appears to be significant for Langmuir turbulence. The space-time evolution of the quasi-stationary magnetic field is calculated analytically in different regimes of laser-plasma interaction.

Jovanovi?, D.; Vukovi?, S.

1984-10-01

36

Axial magnetic field generation in a nonuniform laser produced plasma

International Nuclear Information System (INIS)

Magnetic field generation in a laser produced plasma plays a vital role in inertial confinement fusion (ICF) scheme. Many transport characteristics like thermal transport inhibition, lateral plasma flow etc. which have a direct bearing over the ICF performance, are essentially determined by the self-generated magnetic field (SGMF) in the laser-produced plasma. Theoretically, a variety of mechanisms have been proposed in the last two decades that leads to generation of toroidal magnetic field. This is extensively reviewed in a recent paper by J.A. Stamper. However, not much work has been done so far as the self-generated axial magnetic field (SGAMF) is concerned. An evidence of SGAMF of 0.6 MG was shown by Briand et.al. in their experiment on a planar Al target irradiated by an intense pulse of short wave length laser. They also proposed that such SGAMF could grow from the small scale toroidal field through dynamo effect. However, Dragila argued that this could be due to ion acoustic turbulence. Another mechanism was suggested by Chakraborty et.al. which was based on the interaction between elliptically polarized standing waves. However, none of the above theories could explain the experimental results to be conducted over the wide range of parametric conditions. In the present paper we propose that an obliquely incident spatially inhomogeneous intense and longer wavelength p-polarized laser beam could generate SGAMF in a nonuniform plasma in the range of megagauss. Moiform plasma in the range of megagauss. Moreover, for lower intensity and short wavelength lasers, a field in the range of kilogauss could be produced by collisional excitation via ponderomotive effect for both the s and p-polarized beam even in a uniform plasma. (author) 5 refs., 3 figs

37

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

38

Generation and measurement of pulsed high magnetic field

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

Jana, S

2000-01-01

39

Dark matter and generation of galactic magnetic fields

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

Berezhiani, Zurab; Tkachev, I I

2013-01-01

40

A limitation of the generation of magnetic fields. [astrophysics

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

Balbus, Steven A.

1993-01-01

41

Relativistic Scott correction in self-generated magnetic fields

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 $Z \\alpha < 2/\\pi$, where $\\alpha$ denotes the fine structure constant. We are interested in the ground state energy in the simultaneous limit $Z \\rightarrow \\infty$, $\\alpha \\rightarrow 0$ such that $\\kappa=Z \\alpha$ is fixed. The leading term in the energy asymptotics is independent of $\\kappa$, it is given by the Thomas-Fermi energy of order $Z^{7/3}$ 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 $S(\\alpha Z) Z^2$. The current paper extends the result of \\cite{SSS} 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 in \\cite{SS...

Erdos, Laszlo; Solovej, Jan Philip

2011-01-01

42

dc-Magnetic-field generation in unmagnetized shear flows.

The generation of dc magnetic fields in unmagnetized electron-ion shear flows is shown to be associated to either initial thermal effects or the onset of electron-scale shear instabilities, in particular the cold Kelvin-Helmholtz instability. This mechanism, intrinsic to shear gradients on the electron scale, is described through a kinetic model that predicts the growth and the saturation of the dc field in both scenarios. The theoretical results are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long-lived magnetic fields (t~100's ?(pi)(-1)) along the full longitudinal extent of the shear layer, with a typical transverse width of ?[?(0)]c/?(pe), reaching magnitudes eB(dc)/m(e)c?(pe)~?(0)?[?(0)] for an initial sharp shear. The case of an initial smooth shear is also discussed. PMID:23863009

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

2013-07-01

43

International Nuclear Information System (INIS)

The problem of electric field generation in the Earth magnetospheric boundary layer in absence of the interplanetary magnetic field is discussed. It is supposed that the electric field is generated by the mechanism of quasiviscous solar wind interaction with magnetospheric plasma. A quantitative model of the above mechanism is suggested. A good qualitative agreement of model calculations with the data for the effective value of magnetic Reynolds number equalling 105, is obtained

44

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

International Nuclear Information System (INIS)

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

45

On Generation of magnetic field in astrophysical bodies

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Verma, Mahendra K.

2001-01-01

46

Modeling Alfven Waves Generation by a Rotating Magnetic Field Source

Recent experiments conducted in the Large Plasma Device (LAPD) located at UCLA demonstrated efficient excitation of whistler and shear Alfven waves by a Rotating Magnetic Fields (RMF) source created by a phased orthogonal loop antenna. This paper presents a combination of computational results along with the experiments that emphasize the RMF properties for generation of MHD waves. In order to understand the RMF and magnetized plasma interaction and the resultant radiation patterns in frequency regimes below the ion cyclotron frequency a three-dimensional code was developed. The time-domain code solves the linearized Maxwell equations coupled to the two fluid magnetohydrodynamics description of cold plasma. The antenna excitation is modeled as a set of external currents. A comparison of the simulation results and the experiments shows good agreement between them. The scaling laws of the induced magnetic field as a function of the RMF frequency, the plasma parameters and the spatial decay rate of magnetic field, as well as the use of RMFs as efficient radiation sources of waves in space plasmas are also discussed. This work was sponsored by ONR MURI Grant 5-28828.

Karavaev, A. V.; Gumerov, N.; Shao, X.; Sharma, A. S.; Papadopoulos, K.; Gigliotti, A. F.; Gekelman, W. N.

2009-12-01

47

Development of Bi-2212 conductors and magnets for high-magnetic-field generation

International Nuclear Information System (INIS)

Bi-2212 is a very interesting superconductor from the point of view of high-magnetic-field generation because it has an extraordinarily high upper critical field. This paper reviews recent remarkable progress on Bi-2212/Ag superconductors and their applications to high-field magnets. Bi-2212/Ag multifilamentary and multilayer tape conductors with excellent performance in high fields were developed by the application of a powder-in-tube method and a coating method, respectively. High Jc values of (1.5-3)x105A cm-2 in a field of 30 T at 4.2 K were obtained for both multifilamentary and multilayer tapes. Pancake-type magnets were fabricated with these Bi-2212 tapes. The combination of Bi-2212 magnets and an 18 T conventional superconducting magnet generated a world record of 23.4 T at 4.2 K. A Bi-2212 magnet having a practical size of clear bore of 61 mm was also fabricated. This magnet generated 3 T in a backup field of 18 T at 4.2 K with a total field of 21 T. This 21 T magnet system has been operated many times since 28 September 1998, and the magnet system is now being used for experiments such as the Jc-B measurements of superconductors. These results clearly demonstrate that a Bi-2212 conductor is very promising for high-field applications. One of the interesting applications of a high-field superconducting magnet is a high-field NMR spectrometer. The electric field versus current density (E-J) characteristics and the per density (E-J) characteristics and the persistent-current mode of magnet operation are discussed in connection with the NMR. (author)

48

High Magnetic field generation for laser-plasma experiments

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-05-01

49

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

50

Modeling and Measurement of Ocean Generated Magnetic Fields

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.

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

2011-12-01

51

Dirac electron in graphene under supersymmetry generated magnetic fields

We use supersymmetry transformations to obtain new one parameter families of inhomogeneous magnetic fields \\boldsymbol {B} = \\widetilde{ {B}}(x,\\lambda ) \\hat{e}_z for which the massless Dirac electron possesses exact solutions. The inhomogeneity appearing in \\widetilde{ {B}}(x,\\lambda ) 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.

Midya, Bikashkali; Fernández, David J.

2014-07-01

52

Glutathione production using magnetic fields generated by magnets

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

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

53

Glutathione production using magnetic fields generated by magnets

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

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

2012-12-01

54

A new proposal for generating multipole fields with permanent magnets

International Nuclear Information System (INIS)

In this paper a new proposal of multipole permanent magnets is discussed. Only radially magnetized permanent magnet segments are used in this new proposal. The required magnetic field can be produced by modulating the widths of the segments. In the 2-dimensional ideal case a pure 2N-pole magnetic field can be formed. Expressions for the spatial variation of the scalar potentials for the ideal case and for the real case are given and methods to reduce the undesirable higher harmonics in the magnetic field in the real case are also given. (orig.)

55

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.)

56

Generation and evolution of magnetic fields in the gravitomagnetic field of a Kerr Black Hole

I study the generation and evolution of magnetic fields in the plasma surrounding a rotating black hole. Attention is focused on effects of the gravitomagnetic potential. The gravitomagnetic force appears as battery term in the generalized Ohm's law. The generated magnetic field should be stronger than fields generated by the classical Biermann battery. The coupling of the gravitomagnetic potential with electric fields appears as gravitomagnetic current in Maxwell's equations. In the magnetohydrodynamic induction equation, this current re-appears as source term for the poloidal magnetic field, which can produce closed magnetic structures around an accreting black hole. In principle, even self-excited axisymmetric dynamo action is possible, which means that Cowling's anti dynamo theorem does not hold in the Kerr metric. Finally, the structure of a black hole driven current is studied.

Khanna, R

1999-01-01

57

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

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.

Tilgner, A

2014-01-01

58

Magnetic-moment field generation in the reflection region in a cold magnetized plasma

International Nuclear Information System (INIS)

Magnetization due to a magnetic moment contributes to the non-oscillating magnetic field in a plasma. The dynamics of classically bound electrons in the presence of an applied circularly polarized strong electromagnetic field in the reflection region generates this field. The special case of its resonant generation when the frequency of a right circularly polarized wave is equal to the ion gyration frequency is studied here. Another source of non-oscillating magnetization is the interaction of electromagnetic fields, including fields in the Alfven-wave frequency range, with a cold collisionless fully ionized magnetized plasma also in the reflection region. The induced field from a left circularly polarized field at Alfven-wave frequencies is paramagnetic, inversely proportional to the square of the ambient field and independent of the mass per particle of both electrons and ions. The induced field from a right circularly polarized field at Alfven-wave frequencies is diamagnetic, inversely proportional to the cube of the ambient field and depends directly on the plasma mass density. (author)

59

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

60

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

61

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

62

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

Smolyakov, M N

2000-01-01

63

Giga-Gauss scale quasistatic magnetic field generation in an 'escargot' target

A simple setup for the generation of ultra-intense quasistatic magnetic fields, based on the generation of electron currents with a predefined geometry in a curved 'escargot' target, is proposed and analysed. Particle-In-Cell simulations and qualitative estimates show that giga-Gauss scale magnetic fields may be achieved with existent laser facilities. The described mechanism of the strong magnetic field generation may be useful in a wide range of applications, from laboratory astrophysics to magnetized ICF schemes.

Korneev, Ph; Tikhonchuk, V

2014-01-01

64

Magnetic field generation by short ultraintense laser pulse in underdense plasmas

International Nuclear Information System (INIS)

The theory of magnetic field generation due to the interaction of short relativistic laser pulses with underdense plasmas has been developed. The magnetic field is generated due to the inverse Faraday effect occurring with a circularly polarized laser pulse. The spatial distribution of the magnetic field is investigated. It is shown that the magnetic field magnitude depends on the relationship between the laser beam radius and the plasma skin-depth. (Author)

65

Z: A Fast Pulsed Power Generator for Ultra-High Magnetic Field Generation

Energy Technology Data Exchange (ETDEWEB)

Advances in fast, pulsed-power technologies have resulted in the development of very high current drivers that have current rise times - 100 ns. The largest such pulsed power drive r today is the new Z accelerator located at Sandia National Laboratories in Albuquerque, New Mexico. Z is capable of delivering more than 20 MA with a time-to-peak of 105 ns to low inductance (- 1 nH)loads. Such large drivers are capable of directly generating magnetic fields approaching 3 kT in small, 1 -cm3, volumes. In addition to direct field generation, Z can be used to compress an applied, axial seed field with a plasma. Flux compression scheme~: are not new and are, in fact, the basis of all explosive flux-compression generators but we propose the use of plasma armatures rather than solid, conducting armatures. We will present experimental results from the Z accelerator in which magnetic fields - 2 kT are generated and measured with several diagnostics. Issues such as energy loss in solid conductors and dynamic response of current-carrying conductors to very large magnetic fields will be reviewed in context with Z experiments. We will describe planned flux-compression experiments that are expected to create the highest-magnitude uniform-field volumes yet attained in the laboratory.

Asay, J.R.; Bailey, J.E.; Bernard, M.A.; Hall, C.A.; McDaniel, D.H.; Spielman, R.B.; Struve, K.W.; Stygar, W.A.

1998-11-04

66

Magnetic flux concentrations from dynamo-generated fields

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

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

2014-01-01

67

Inflationary susceptibilities, duality, and large-scale magnetic field generation

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 backreaction problems. The parameter space of this magnetogenesis scenario is wider than in the case in which the susceptibilities are equal, as it happens when the inflaton or some other spectator field is solely coupled to the standard gauge kinetic term.

Giovannini, Massimo

2013-10-01

68

Inflationary susceptibilities, duality and large-scale magnetic fields generation

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 ...

Giovannini, Massimo

2013-01-01

69

Dynamo-generated magnetic fields in fast rotating single giants

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.

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

2009-01-01

70

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.

71

Effects of Self-Generated Magnetic Field on Rayleigh-Taylor Instability

Scaling of the self-generated magnetic field generated by Rayleigh-Taylor instability and a new aspect of the instability in the acceleration of the laser fusion target are presented. The scaling is derived from linear analysis and compared with the simulation result. Electron heat conduction affected by the self-generated magnetic field causes the configuration change of surface perturbation, higher mode generation and steepening of the field. The field restrains the heat flux and produces a temperature gradient nonparallel to the density gradient in plasmas. This thermoelectric current generates a magnetic field larger than the initial field with certain parameters. These phenomena are observed in the hydrodynamic simulations.

Nishiguchi, Akio

2002-01-01

72

Dynamical quark mass generation in a strong external magnetic field

We investigate the effect of a strong magnetic field on dynamical chiral symmetry breaking in quenched and unquenched QCD. To this end we apply the Ritus formalism to the coupled set of (truncated) Dyson-Schwinger equations for the quark and gluon propagator under the presence of an external constant Abelian magnetic field. We work with an approximation that is trustworthy for large fields eH >?QCD2 but is not restricted to the lowest Landau level. We confirm the linear rise of the quark condensate with a large external field previously found in other studies and observe the transition to the asymptotic power law at extremely large fields. We furthermore quantify the validity of the lowest Landau level approximation and find substantial quantitative differences to the full calculation even at very large fields. We discuss unquenching effects in the strong field propagators, condensate and the magnetic polarization of the vacuum. We find a significant weakening of magnetic catalysis caused by the backreaction of quarks on the Yang-Mills sector. Our results support explanations of the inverse magnetic catalysis found in recent lattice studies due to unquenching effects.

Mueller, Niklas; Bonnet, Jacqueline A.; Fischer, Christian S.

2014-05-01

73

Magnetic field generation in the cores of terrestrial bodies

Efforts to find some scaling law for the dipole moments of planets seem illusory for, although dynamo theory is still in a rudimentary state, once the critical magnetic Reynolds Number is exceeded it appears that the field strength is determined by the energy source, it it is permissible to treat the core as a heat engine. For this reason the lunar magnetic field is of special significance as the paleomagnetic evidence strongly suggests that the surface field was about 1 G 3.9 by diminishing exponentially to about .02 G 3.2 by ago and completely disappearing some time later.

Runcorn, S. K.

1985-01-01

74

Turbulent Generation of Flows and Magnetic Field at the Rational Magnetic Surfaces of a Tokamak

International Nuclear Information System (INIS)

Full text: Comparative analysis of generation of large-scale structures, zonal flows and streamers, by drift wave turbulence is conducted for periodic systems with magnetic shear such as a tokamak. In a strong magnetic field dynamics of quasi two-dimensional perturbations strongly depends on the value of the wave vector along the magnetic field. When the parallel wave vector is significantly large, so that the parallel phase velocity of perturbation is small compared to electron thermal velocity, the parallel electron motion results in a finite electron density perturbation. It follows the Boltzmann distribution. However, for large-scale structures with poloidal and toroidal symmetry m = n = 0, and the parallel wave vector is zero. This results in strong reduction of density perturbation for m = n = 0. This difference has profound consequences for generation of large-scale zonal flows and streamers due to different structure of the nonlinear interaction matrix. The interaction term has a structure similar to the standard convective nonlinearity for zonal flows, while for streamers it has the structure of the Hasegawa-Mima nonlinearity (which is the higher order due to a small parameter associated with a finite ion Larmor radius). Respectively, zonal flows have the larger growth rate gamma(ZF) compared to that of the streamers. It is shown that 3D electromagnetic helical perturbations will have the growth rate comparable to that of zonal flows if their symmetry coincidt of zonal flows if their symmetry coincides with the symmetry of rational magnetic surface, m = nq. The field line bending provides a stabilizing effect and thus determines the radial localization of such structures. Therefore, it is expected that three-dimensional structures of flows and magnetic field will be preferentially generated at the rational magnetic surfaces of a tokamak with a growth rate of order gamma(ZF). This theoretical result may corroborate existing experimental correlations of large-scale shear flow structures with rational magnetic surfaces of a tokamak. (author)

75

Magnetic flux concentrations from dynamo-generated fields

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

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

2014-08-01

76

Dynamical quark mass generation in a strong external magnetic field

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

Mueller, Niklas; Fischer, Christian S

2014-01-01

77

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

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

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

2014-07-01

78

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

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 generation by natural planetocentric nuclear fission reactors.

Herndon, J Marvin

2009-01-01

79

Hypervelocity impacts of meteoroids onto early planetary surfaces may have generated short-lived magnetic fields. The high specific power densities of the impacts, plasma production in the ejecta clouds, and the chemically layered targets of the meteoroids are analyzed in describing the evolution of the magnetic fields. Durations from about one millionth of a minute to one minute, as well as strengths up to 100 tesla, are posited for the impact-generated magnetic fields. The analogy of magnetic-field generation in laser-target experiments is also mentioned. The acquisition of shock remanence and thermoremanence by the ejecta and nearby rock following impact is discussed.

Srnka, L. J.

1977-01-01

80

Stochastic island generation and influence on the effective transport in stochastic magnetic fields

Digital Repository Infrastructure Vision for European Research (DRIVER)

The transport of collisional particles in stochastic magnetic fields is studied using the decorrelation trajectory method. The nonlinear effect of stochastic generation of magnetic island by magnetic line trapping is considered together with particle collisions. The running diffusion coefficient is determined for arbitrary values of the statistical parameters of the stochastic magnetic field and of the collisional velocity. The effect of the stochastic magnetic islands is an...

Vlad, M.; Spineanu, F.; Misguich, J. H.; Balescu, R.

2002-01-01

81

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

82

Geometrical generation of cosmic magnetic fields within standard electromagnetism

Scientific Electronic Library Online (English)

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

Christos G., Tsagas; Alejandra, Kandus.

83

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

The CHAMP satellite continues to provide highly accurate magnetic field measurements with decreasing orbital altitudes (<350km) at solar minimum conditions. A promising new CHAMP data product has become available, which provides the total field with one order of magnitude smaller noise amplitudes. The product is inferred from suitably merged Fluxgate and Overhauser magnetometer data. While the low-noise Fluxgate measurements are used in the short-period range (<900sec, or <6000km wavelength), we take advantage of the high stability provided by the 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.

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

2007-12-01

84

The spatial distribution and time evolution of impact-generated magnetic fields

The production of magnetic fields was revealed by laboratory hypervelocity impacts in easily vaporized targets. As quantified by pressure measurements, high frame-rate photography, and electrostatic probes, these impacts tend to produce large quantities of slightly ionized vapor, which is referred to as impact-generated plasma. Nonaligned electron density and temperature gradients within this plasma may lead to production of the observed magnetic fields. Past experiments were limited to measuring a single component of the impact-generated magnetic fields at only a few locations about the developing impact crater and consequently gave little information about the field production mechanism. To understand this mechanism, the techniques were extended to map the three components of the magnetic field both in space and time. By conducting many otherwise identical experiments with arrayed magnetic detectors, a preliminary 3-D picture was produced of impact-generated magnetic fields as they develop through time.

Crawford, D. A.; Schultz, P. H.

1991-01-01

85

Generation and evolution of stable stellar magnetic fields in young A-type stars

While the presence of magnetic fields on low-mass stars is attributed to a dynamo process that is primarily driven by convective motion, the existence of magnetic fields on intermediate-mass stars very probably has other explanations. This paper focuses on the generation of stable magnetic configurations at the early stages of stellar evolution, and presumes that the fields we detect are nearly constant in time. The convective processing of an initial magnetic field during the pre-main-sequence phase is studied in a very simple model star. Azimuthal magnetic fields are found to be typical remnants in the upcoming radiative envelope after convection has receded.

Arlt, R.

2014-11-01

86

Dynamical mass generation in strong coupling Quantum Electrodynamics with weak magnetic fields

We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of magnetic fields using Schwinger-Dyson equations. We show that, contrary to the case where the magnetic field is strong, in the weak field limit eB << m(0)^2, where m(0) is the value of the dynamically generated mass in the absence of the magnetic field, masses are generated above a critical value of the coupling and that this value is the same as in the case with no magnetic field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB)^2.

Ayala, A; Raya, A; Rojas, E; Ayala, Alejandro; Bashir, Adnan; Raya, Alfredo; Rojas, Eduardo

2006-01-01

87

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

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.

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

2014-09-01

88

Magnetic field generation and amplification in an expanding plasma

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

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

2013-01-01

89

The generation of the earth magnetic field. Pt. 1

International Nuclear Information System (INIS)

The only possibility to produce the magnetic field of the earth is the dynamo-effect of a flow in the conducting fluid core of the earth. Theoretically it is possible to construct detailed models for the geodynamo, although only first attempts are made in this direction. The first part of this paper deals with the kinematics of the dynamo problem in general and particularly with the homogenious dynamo. (orig.)

90

Wake field generation and nonlinear evolution in a magnetized electron-positron-ion plasma

Digital Repository Infrastructure Vision for European Research (DRIVER)

The nonlinear propagation of a circularly polarized electromagnetic (CPEM) wave in a strongly magnetized electron-positron-ion plasma is investigated. Two coupled equations describing the interaction between a high-frequency CPEM wave and the low-frequency electrostatic wake field are derived. It is found that the generation of the wake fields partly depends on the presence of the ion species and the external magnetic field. The wake field generation in turn leads to deceleration and frequenc...

Shukla, P. K.; Brodin, G.; Marklund, M.; Stenflo, Lennart

2008-01-01

91

International Nuclear Information System (INIS)

Experimental studies on the spontaneous generation of magnetic field associated with laser-produced plasmas from solid target have been carried out in the presence of ambient gas. The differences from the high vacuum case have become clear as for the time-dependent spatial variation of magnetic field, and the magnitude of generated magnetic field is observed to increase due to the presence of ambient gas in its rapidly expanding phase. All the experimental results thus obtained are consistent with what is called the ''magnetic field amplification''. (author)

92

Investigations of Flux Compression Energy Sources and Ultra-High Magnetic Field Generators in Vniief

Results of VNIIEF investigations in the creation of flux compression energy generators (FCG) with different geometry are considered. Calculations and experimental data are analyzed on application of these devices for pulsed formation of high voltages, generation of high-power electron beams and of ultra-high magnetic fields. Perspectives on the development of explosive generators are connected with the creation of the "Sprut" energy system and complex EMIR, intended for investigations in high-energy density physics. Experiments using ultra-high magnetic field generators created, for the first time in the world, a magnetic field of 28 MG.

Selemir, V. D.; Demidov, V. A.

2004-11-01

93

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2011-01-01

94

Dynamical mass generation in strongly coupled quantum electrodynamics with weak magnetic fields

International Nuclear Information System (INIS)

We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of weak magnetic fields using Schwinger-Dyson equations. Contrary to the case where the magnetic field is strong, in the weak field limit the coupling should exceed certain critical value in order for the generation of masses to take place, just as in the case where no magnetic field is present. The weak field limit is defined as eB2, where m(0) is the value of the dynamically generated mass in the absence of the field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB)2

95

Problems connected with the generation of continuous magnetic fields above 15 Tesla

Energy Technology Data Exchange (ETDEWEB)

A review is given about the present possibilities to generate magnetic fields beyond 15 T. Whereas it seems feasible to build purely superconducting magnets for fields up to 20 T no conductors with the required critical data are available at present which allow the generation of higher fields. Magnetic fields beyond 15 T are generally produced by resistive, water cooled coils. If fields beyond 25 T have to be generated, problems are encountered because of the large amount of power which is necessary. In order to achieve the highest continuous magnetic fields, hybrid magnets can be built which consist of an inner resistive part and an outer superconducting coil. The limits of this technique are discussed for various conditions. 14 refs.

Landwehr, G.

1981-09-01

96

Problems connected with the generation of continuous magnetic fields above 15 Tesla

International Nuclear Information System (INIS)

A review is given about the present possibilities to generate magnetic fields beyond 15 T. Whereas it seems feasible to build purely superconducting magnets for fields up to 20 T no conductors with the required critical data are available at present which allow the generation of higher fields. Magnetic fields beyond 15 T are generally produced by resistive, water cooled coils. If fields beyond 25 T have to be generated, problems are encountered because of the large amount of power which is necessary. In order to achieve the highest continuous magnetic fields, hybrid magnets can be built which consist of an inner resistive part and an outer superconducting coil. The limits of this technique are discussed for various conditions. 14 refs

97

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

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

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

2013-01-01

98

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 nea...

Von Pahlen, J. Graf; Tsiklauri, D.

2014-01-01

99

Estimate of the dynamo-generated magnetic fields in late-type stars

International Nuclear Information System (INIS)

The depth of the convection zone varies significantly with spectral type in late-type stars. We study the effect of this variation on the generation of magnetic fields by dynamo processes. For this we develop a scheme for determining the magnetic field strength generated in late-type main sequence stars. This method is based upon the assumption that the fields are determined when the rise time of a magnetic flux tube due to buoyancy is equal to the e-folding amplification time for the stellar dynamo. The basic results indicate that for a given rotational period, the magnetic field increases with (B-V) color, whereas the amplification time decreases, suggesting shorter cycle periods. For M stars and for rotational periods of the order of that of the Sun the magnetic field area coverage approaches 100% of the stellar surface, suggesting small dissipation scales for the magnetic field

100

Generation and Growth of Magnetic Fields in Rayleigh-Taylor Unstable Plasmas

It has long been expected that Rayleigh-Taylor instabilities in ICF implosions can generate magnetic fields. To investigate this, a Hall-MHD model is used with the discontinuous Galerkin method in the code, WARPX (Washington Approximate Riemann Plasma). 2-D single-mode and multi-mode studies of a Rayleigh-Taylor instability are performed in a stratified two-fluid plasma. Self-generated magnetic fields are observed and these fields grow (˜10^2T) as the Rayleigh-Taylor instability progresses. The ?nex?Te term in the generalized Ohm's law is responsible for the formation of a self-generated magnetic field. In the absence of this term in Ohm's law, no magnetic field forms. Scaling studies are performed to determine the growth of the self-generated magnetic field as a function of density, gravity, and perturbation wavelength. The magnetic field increases as the wavelength decreases, and as gravity increases, which is consistent with theory. Additionally, the MHD dynamo term, v xB, is expected to further increase the magnetic field that is formed. An investigation of the coupling and growth of the MHD dynamo with the self-generated out-of-plane fields will enable us to estimate how large the fields will grow in 3-D.

Srinivasan, Bhuvana; Dimonte, Guy; Tang, Xianzhu

2011-11-01

101

International Nuclear Information System (INIS)

The effect of plasma formation limitedness on space-time evolution of the generated quasi-stationary magnetic field in a plasma is discussed. The analysis is performed using the simplest two-dimensional case of uniform circular cylinder irradiated by a converging cylindrical wave. The magnetic field generation mechanism is related to electrons trapped by the HF-field of azimuthal harmonic excited in a plasma. It is shown that space-time evolution of magnetic field and its stationary value depend essentially on electric dimensions of a plasma formation and structure of incident HF-field

102

Magnetic field generation and penetration into dense laser-produced plasma

International Nuclear Information System (INIS)

Electron magnetohydrodynamic (EMH) models have been applied to examine the generation and penetration of intense magnetic fields in plasmas of density several times critical. For plane polarized light the highly relativistic electrons produced in interactions at the edge of the overdense region play an important role. In sufficiently large numbers they are themselves the source of magnetic fields of up to 100 MG. They may also serve to advect a boundary field into the dense plasma beyond the critical density. For relativistic electrons the magnetic field can penetrate to a depth of several vacuum wavelengths. We also discuss the characteristics of thermoelectrically generated fields within the hole bored in the plasma by the laser and consider some aspects of magnetic fields generated by a circularly polarized driver. In particular, we compare predicted values of the longitudinal field produced by the inverse Faraday effect with results from 2D PIC simulations. (author)

103

Magnetic field generation and penetration into dense laser-produced plasma

Energy Technology Data Exchange (ETDEWEB)

Electron magnetohydrodynamic (EMH) models have been applied to examine the generation and penetration of intense magnetic fields in plasmas of density several times critical. For plane polarized light the highly relativistic electrons produced in interactions at the edge of the overdense region play an important role. In sufficiently large numbers they are themselves the source of magnetic fields of up to 100 MG. They may also serve to advect a boundary field into the dense plasma beyond the critical density. For relativistic electrons the magnetic field can penetrate to a depth of several vacuum wavelengths. We also discuss the characteristics of thermoelectrically generated fields within the hole bored in the plasma by the laser and consider some aspects of magnetic fields generated by a circularly polarized driver. In particular, we compare predicted values of the longitudinal field produced by the inverse Faraday effect with results from 2D PIC simulations. (author)

Boyd, T.J.M.; Tatarinov, A.; Bawa-Aneh, M.; Dyson, A. [Essex Univ., Colchester (United Kingdom). Dept. of Physics

1997-12-31

104

Generation of Primordial Magnetic Fields on Linear Over-density Scales

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

Naoz, Smadar

2013-01-01

105

Development of wire and coil designing for high-magnetic field generation

The ultimate tensile strength, and electric conductivity were investigated for Cu(Nb), Cu(Be), Cu(Cr), Cu(Ag), and Cu(Nb-Ti) wires in order to produce higher magnetic field than 50 T. The highest tensile strength is realized in Cu(Nb) wire. The Cu(Nb) and Cu(Ag) are regarded as the best materials for the nondestructive pulsed-magnetic-field generation. The coil designing was also studied to generate high magnetic field. It was found that the fiberglass reinforcement of wire layer by layer is quite effective to produce high pulsed magnetic fields. By using this technique, a 55 T field can be generated even using pure copper wire. The usage of water (ice) for solidifying the solenoid shortens considerably the cooling time of the pulsed magnet.

Kido, Giyuu

1991-05-01

106

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

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

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

2014-01-01

107

Axial magnetic field generation by intense circularly polarized laser pulses in underdense plasmas

International Nuclear Information System (INIS)

Axial magnetic field generation by intense circularly polarized laser beams in underdense plasmas has been studied with three-dimensional particle-in-cell simulations and by means of theoretical analysis. Comparisons between analytical models and simulation results have identified an inverse Faraday effect as the main mechanism of the magnetic field generation in inhomogeneous plasmas. The source of azimuthal nonlinear currents and of the axial magnetic field depends on the transverse inhomogeneities of the electron density and laser intensity. The fields reach a maximum strength of several tens of megagauss for laser pulses undergoing relativistic self-focusing and channeling in moderately relativistic regime. Ultrarelativistic laser conditions inhibit magnetic field generation by directly reducing a source term and by generating fully evacuated plasma channels.

108

International Nuclear Information System (INIS)

Complete text of publication follows. Generation of harmonic radiation is an important subject of laser plasma interaction and attracts great attention due to a wide range of applications. It has been seen that intense electromagnetic and quasi-static transverse magnetic fields are generated in laser plasma interaction. An extremely intense magnetic field (up to hundreds of MG) has been observed by experimental measurements in interaction of short laser pulses with plasma. These self-generated or applied magnetic fields affect the propagation of the laser pulses. In most laser interactions with homogeneous plasma, odd harmonics of laser frequency are generated. In this paper, we point out the possibility of even harmonics generation when a linearly polarized laser beam propagates in homogeneous plasma in the presence of a transverse magnetic field. It is shown that applying external field induces a transverse current density oscillating twice of the laser field which leds to generation of second harmonic radiation. This current density is derived using the perturbation method, and the steady state amplitude of the second harmonic obtained by solution of the wave equation. By the same procedure the current density and then the steady state amplitude of higher order harmonics are calculated. The efficiency of harmonic generation (the ratio of harmonic power to incident power) is a drastically function of the strength of external magnetic field. It is found that the efficiency of even harmonics is zero in the absence of magnetic field and increases as the magnetic field is increased. For odd harmonics, applying the external magnetic field enhances the generated harmonics as well. The conversion efficiency also increases with increase in plasma density and intensity of the laser beam.

109

3D Magnetic Field Effects in an NSC KIPT Compact Intense X-ray Generator

International Nuclear Information System (INIS)

The new generation of the intense X-rays sources based on low energy electron storage ring and Compton scattering of intense laser beam allows to produce hard X-rays with intensity up to 1014 phot/s. One of the main traits of a storage ring lattice for such generator type is using of magnetic elements with combined focusing functions such as bending magnets with quadrupole and sextupole field components. In combination with very low bending radius and dense magnetic elements setting along ring circumference it leads to increasing of 3D magnetic field effects on electron beam dynamics and can decrease generated radiation intensity drastically. The article is devoted to the investigations of the effects of 3D magnetic fields on bending magnet edges and lattice lenses interference on electron beam dynamics and parameters of produced radiation for NSC KIPT 225 MeV storage ring

110

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

von der Pahlen, J Graf

2014-01-01

111

Magnetic field generation in a relativistic plasma with high frequency waves

Energy Technology Data Exchange (ETDEWEB)

Magnetic field generation in a relativistic plasma in the presence of Langmuir or electromagnetic waves is studied theoretically. The generation is shown to occur in the form of the three simplest instabilities: anisotropic, magnetic-modulational and magnetic-transformational, or their combinations. Characteristic wave numbers and growth rates of the instabilities mentioned are found as function of the degree of plasma relativism. The growth rates are shown to attain their maxima at relativistic temperatures.

Mikhailovskii, A.B.; Suramlishvili, G.I.; Kudashev, V.R.; Tatarinov, E.G.

1984-03-01

112

Primordial magnetic fields generated by the non-adiabatic fluctuations at pre-recombination era

International Nuclear Information System (INIS)

In the pre-recombination era, cosmological density fluctuations can naturally generate magnetic fields through Thomson scatterings. In previous studies, only the magnetic field generation from the initially- adiabatic fluctuations has been considered. Here we investigate the generation of cosmological magnetic fields sourced by the primordial non-adiabatic fluctuations based on the cosmological perturbation theory, using the tight-coupling approximations between photon and baryon fluids. It is found that the magnetic fields from the non-adiabatic fluctuations can arise at the first-order expansion of the tight coupling approximation. This result is in contrast to the case of adiabatic initial fluctuations, where the magnetic fields can be generated only at the second-order. In a general case where the primordial density perturbations contain small non-adiabatic fluctuations on the top of the dominant adiabatic ones, we show that the leading source of magnetic fields is given by the second-order coupling of the adiabatic and non-adiabatic fluctuations. We calculate the power spectrum of the generated magnetic fields when the non-adiabatic fluctuations have a blue power spectrum, which has been suggested by recent cosmological observations

113

Precise Measurement of a Magnetic Field Generated by the Electromagnetic Flux Compression Technique

The precision of the values of a magnetic field generated by electromagnetic flux compression was investigated in ultra-high magnetic fields of up to 700 T. In an attempt to calibrate the magnetic field measured by pickup coils, precise Faraday rotation (FR) measurements were conducted on optical (quartz and crown) glasses. A discernible "turn-around" phenomenon was observed in the FR signal as well as the pickup coils before the end of a liner implosion. We found that the magnetic field measured by pickup coils should be corrected by taking into account the high-frequency response of the signal transmission line. Near the peak magnetic field, however, the pickup coils failed to provide reliable values, leaving the FR measurement as the only method to precisely measure an extremely high magnetic fields.

Nakamura, D; Matsuda, Y H; Takeyama, S

2013-01-01

114

Precise measurement of a magnetic field generated by the electromagnetic flux compression technique

The precision of the values of a magnetic field generated by electromagnetic flux compression was investigated in ultra-high magnetic fields of up to 700 T. In an attempt to calibrate the magnetic field measured by pickup coils, precise Faraday rotation (FR) measurements were conducted on optical (quartz and crown) glasses. A discernible "turn-around" phenomenon was observed in the FR signal as well as the pickup coils before the end of a liner implosion. We found that the magnetic field measured by pickup coils should be corrected by taking into account the high-frequency response of the signal transmission line. Near the peak magnetic field, however, the pickup coils failed to provide reliable values, leaving the FR measurement as the only method to precisely measure extremely high magnetic fields.

Nakamura, D.; Sawabe, H.; Matsuda, Y. H.; Takeyama, S.

2013-04-01

115

Algorithms for the self-consistent generation of magnetic fields in plasmas

International Nuclear Information System (INIS)

The generation, advection and diffusion of magnetic fields in cylindrically symmetric plasmas is considered. Stable and conservative numerical schemes for treating this problem within the framework of a conventional multi-celled fluid code are presented

116

Earth's Inconstant Magnetic Field

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

2007-04-27

117

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with the analytical computation of the magnetic field of a cylindrical permanent magnet linear generator. It offers an alternative solution to the magnetic field problem. A new approach to solve Poisson equation using Struve function is introduced and it offers a simple but accurate analytical estimation to the calculation of the open circuit flux density and induced voltage. The finite element analysis simulation is performed to validate the analytical calculation.

Wijono

2007-01-01

118

Generation of axial and lateral magnetic fields in laser produced plasmas

International Nuclear Information System (INIS)

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

119

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

120

We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics, in the presence of magnetic fields of arbitrary strength, by solving the Schwinger-Dyson equation (SDE) 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 \\alpha. For intense fields it is also well known that m \\propto \\sqrt eB. Our approach allows us to span all regimes of parameters \\alpha and eB. We find that m \\propto \\sqrt eB provided \\alpha is small. However, when \\alpha increases beyond the critical value \\alpha_c which marks the onslaught of dynamical fermion masses in vacuum, we find m \\propto \\Lambda, the cut-off required to regularize the ultraviolet divergences. Our method permits us to verify the results available in l...

Rojas, Eduardo; Bashir, Adnan; Raya, Alfredo

2008-01-01

121

One-dimensional models of magnetic fields generated by hypervelocity impact

International Nuclear Information System (INIS)

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

122

Energy Technology Data Exchange (ETDEWEB)

Two types of strong magnetic field generator have been newly constructed by using superconducting bulk magnets that mainly consist of rare earth 123 single domain compounds (REBa{sub 2}Cu{sub 3}O{sub y}) in conjunction with different kinds of compact cryocoolers. The magnetic flux densities in the open space outside the vacuum chambers that contain bulk magnets have reached 3.37 T and 2.78 T when a Gifford-McMahon (GM) cryocooler and a Stirling-cycle (ST) pulse tube cryocooler cooled them to 30.8 K and 62.0 K, respectively. In this study, the activation of a bulk magnet was accomplished by field cooling magnetization using the static field of a 5 T superconducting solenoid magnet. It was clarified that the trapped field distributions strongly reflect the temperature dependence of superconducting properties of the bulk magnet. The conditions for supplying intense fields in the open space are discussed to utilize them in practical applications. The most characteristic feature of superconducting bulk magnets is defined as a compact and strong magnetic field generator, which is discussed on the map from the industrial point of view.

Oka, T; Hirose, Y; Kanayama, H; Kikuchi, H; Fukui, S; Ogawa, J; Sato, T; Yamaguchi, M [Niigata University, 8050 Ikarashi-Nino-cho, Nishi-ku, Niigata 950-2181 (Japan)

2007-12-15

123

International Nuclear Information System (INIS)

Two types of strong magnetic field generator have been newly constructed by using superconducting bulk magnets that mainly consist of rare earth 123 single domain compounds (REBa2Cu3Oy) in conjunction with different kinds of compact cryocoolers. The magnetic flux densities in the open space outside the vacuum chambers that contain bulk magnets have reached 3.37 T and 2.78 T when a Gifford-McMahon (GM) cryocooler and a Stirling-cycle (ST) pulse tube cryocooler cooled them to 30.8 K and 62.0 K, respectively. In this study, the activation of a bulk magnet was accomplished by field cooling magnetization using the static field of a 5 T superconducting solenoid magnet. It was clarified that the trapped field distributions strongly reflect the temperature dependence of superconducting properties of the bulk magnet. The conditions for supplying intense fields in the open space are discussed to utilize them in practical applications. The most characteristic feature of superconducting bulk magnets is defined as a compact and strong magnetic field generator, which is discussed on the map from the industrial point of view

124

Residual fields from extinct dynamos. [magnetic fields generation in convective A star

The generation of magnetic fields in convective zones of declining vigor and/or thickness is considered, the goal being to explain the magnetic fields observed in A-stars. The investigation is restricted to kinematical dynamos in order to show some of the many possibilities, which depend on the assumed conditions of decline of the convection. The examples illustrate the quantitative detail required to describe the convection in order to extract any firm conclusions concerning specific stars. The first example treats the basic problem of diffusion from a layer of declining thickness. The second has a buoyant rise added to the field in the layer. The third deals with plane dynamo waves in a region with declining eddy diffusivity, dynamo coefficient, and large-scale shear. It is noted that the dynamo number may increase or decrease with declining convection, with an increase expected if the large-scale shear does not decline as rapidly as the eddy diffusivity. It is shown that one of the components of the field may increase without bound even when the dynamo number declines to zero.

Parker, E. N.

1981-01-01

125

Study of magnetic field expansion using a plasma generator for space radiation active protection

There are many active protecting methods including Electrostatic Fields, Confined Magnetic Field, Unconfined Magnetic Field and Plasma Shielding etc. for defending the high-energy solar particle events (SPE) and Galactic Cosmic Rays (GCR) in deep space exploration. The concept of using cold plasma to expand a magnetic field is the best one of all possible methods so far. The magnetic field expansion caused by plasma can improve its protective efficiency of space particles. One kind of plasma generator has been developed and installed into the cylindrical permanent magnet in the eccentric. A plasma stream is produced using a helical-shaped antenna driven by a radio-frequency (RF) power supply of 13.56 MHz, which exits from both sides of the magnet and makes the magnetic field expand on one side. The discharging belts phenomenon is similar to the Earth's radiation belt, but the mechanism has yet to be understood. A magnetic probe is used to measure the magnetic field expansion distributions, and the results indicate that the magnetic field intensity increases under higher increments of the discharge power.

Jia, Xiang-Hong; Jia, Shao-Xia; Xu, Feng; Bai, Yan-Qiang; Wan, Jun; Liu, Hong-Tao; Jiang, Rui; Ma, Hong-Bo; Wang, Shou-Guo

2013-09-01

126

Measurements of magnetic fields generated in underdense plasmas by intense lasers

International Nuclear Information System (INIS)

Measurements have been made of the magnetic field generated by the passage of high intensity short laser pulses through underdense plasmas. For a 30 fs, 1 J, 800 nm linearly-polarised laser pulse, an azimuthal magnetic field is observed at a radial extent of approximately 200 ?m. The field is found to exceed 2.8 MG. For a 1 ps, 40 J, 1054 nm circularly-polarised laser pulse, a solenoidal field is observed that can exceed 7 MG. This solenoidal field is absent with linear polarised light, and hence can be considered as an Inverse Faraday effect. Both types of field are found to decay on the picosecond timescale. For both the azimuthal and solenoidal fields produced by such intense lasers, the production of energetic electrons by the interaction is thought to be vital for magnetic field generation

127

Self-generated magnetic fields in direct-drive implosion experiments

Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA Laser Facility were investigated employing radiography with ˜10- to 60-MeV protons. The experiment used plastic-shell targets with imposed surface defects (glue spots, wires, and mount stalks), which enhance self-generated fields. The fields were measured during the 1-ns laser drive with an on-target intensity ˜1015 W/cm2. Proton radiographs show multiple ring-like structures produced by electric fields ˜107 V/cm and fine structures from surface defects, indicating self-generated fields up to ˜3 MG. These electric and magnetic fields show good agreement with two-dimensional magnetohydrodynamic simulations when the latter include the ?Te × ?ne source, Nernst convection, and anisotropic resistivity. The simulations predict that self-generated fields affect heat fluxes in the conduction zone and, through this, affect the growth of local perturbations.

Igumenshchev, I. V.; Zylstra, A. B.; Li, C. K.; Nilson, P. M.; Goncharov, V. N.; Petrasso, R. D.

2014-06-01

128

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

Directory of Open Access Journals (Sweden)

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.

Atef El Jery

2010-05-01

129

International Nuclear Information System (INIS)

Electrodynamic means for the control of loop antenna radiation efficiency in plasma is proposed, which can be used in the whistler frequency band. The method is based on the generation, without perturbing the plasma density, of localized ambient magnetic field irregularities in the vicinity of the antenna. In order to produce such irregularities, it is suggested to feed the antenna with additional dc current along with the rf current. Experiments performed in a large laboratory magnetoplasma showed that the generation of localized magnetic field enhancements provides the possibility of increasing the amplitude of the whistlers emitted by the loop antenna. Moreover, experiments have shown that the amplification of the whistlers' signals from the receiving loop antenna fed with additional dc current is observed when a static magnetic field enhancement is generated in the vicinity of the receiver. The experimental data are in good agreement with the theoretical results obtained for comparatively weak ambient magnetic field perturbations

130

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

Veysi, Mehdi; Capolino, Filippo

2014-01-01

131

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.

132

Evolution of magnetic field generated by the Kelvin-Helmholtz instability

The Kelvin-Helmholtz instability in an ionized plasma is considered with a focus on the generation of magnetic field via the Biermann battery mechanisms. The problem is studied through direct numerical simulations of two counter-directed flows in 2D geometry. The simulations demonstrate the formation of eddies and their further interaction resulting in a large single vortex. At early stages, the generated magnetic field evolves due to the baroclinic term in the induction equation, revealing significantly different structures from the vorticity field, despite the fact that magnetic field and vorticity obey identical equations. At later times, the magnetic field exhibits complex behavior and continues to grow even after a hydrodynamic vortex has developed.

Modestov, Mikhail; Brodin, Gert; Marklund, Mattias; Brandenburg, Axel

2014-01-01

133

Generation of large-scale magnetic fields from inflation in teleparallelism

International Nuclear Information System (INIS)

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

134

The breakdown of dipolar magnetic field generation in planetary dynamo models (Invited)

Magnetic field measurements show that each dynamo in our solar system is distinct with field strengths that differ by many orders of magnitude and morphologies that range from titled dipoles to nearly axisymmetric dipole-quadrupoles to non-axisymmetric multipoles. The characteristics of stellar and astrophysical magnetic fields are similarly wide-ranging. Towards understanding the diversity of this dynamo zoo, we investigate the breakdown of dipole-dominated magnetic fields in a suite of planetary dynamo and otherwise identical non-magnetic simulations where the convective vigor and rotation rate are varied systematically. This survey considers models with Prandtl number Pr=1, magnetic Prandtl numbers up to Pm = 5, Ekman numbers in the range 1e-3 transition from dipolar to multipolar dynamos is observed in models with moderate to high Ekman numbers. This breakdown of the dipole happens when inertial and viscous forces become comparable and coincides with a degradation of helicity in the flow, which also occurs when no magnetic field is present. Large-scale poloidal magnetic fields in these models then appear to be generated by a viscously controlled, macro-scale alpha-effect. Our lowest Ekman number cases, however, suggest that the dynamics may be changing as the viscous force decreases. Since viscosity is expected to be negligible in planetary and stellar interiors, an extrapolation of our results implies that moderate Ekman number models may not simulate the physical mechanisms of magnetic field generation in these bodies correctly.

Soderlund, K. M.; King, E. M.; Aurnou, J. M.

2013-12-01

135

The crossed-magnetic-field effect on the demagnetization factor of stacked second generation (2G) high temperature superconducting tapes is presented. The superconducting sample was initially magnetized along the c-axis by the field cooling magnetization method and after achieving the magnetic relaxation of the sample, an extensive set of experimental measurements for different amplitudes of an applied ac magnetic field parallel to the ab-plane was performed. On the one hand, a striking reduction of the demagnetization factor compared with the reported values for superconducting bulks is reported. On the other hand, the demagnetization factor increases linearly with the amplitude of the ac transverse magnetic field confirming the universal linear behavior for the magnetic susceptibility predicted by Brandt [Phys. Rev. B 54, 4246 (1996)]. The study has been also pursued at different frequencies of the ac transverse magnetic field in order to determine the influence of this parameter on the demagnetization factor measurements. We report an even lower demagnetization factor as long as the frequency of the transverse magnetic field increases. Thus, the significant reduction on the demagnetization factor that we have found by using stacked 2G-superconducting tapes, with higher mechanical strength compared with the one of superconducting bulks, makes to this configuration a highly attractive candidate for the future development of more efficient high-power density rotating machines and strong magnet applications.

Baghdadi, M.; Ruiz, H. S.; Coombs, T. A.

2014-06-01

136

International Nuclear Information System (INIS)

We calculate the magnetic field generated during bubble collisions in a first-order electroweak phase transition that may occur for some choices of parameters in the minimal supersymmetric standard model. We derive equations of motion from the electroweak Lagrangian that couple the Higgs field and the gauge fields of the standard model sector. We show that for sufficiently gentle collisions, where the Higgs field is relatively unperturbed in the bubble overlap region, the equations of motion can be linearized so that in the absence of fermions the charged W± fields are the source of the electromagnetic current for generating the seed fields. Solutions of the equations of motion for the charged gauge fields and Maxwell's equations for the magnetic field in O(1,2) space-time symmetry are expressed in closed form by applying boundary conditions at the time of collision. Our results indicate that the magnetic fields generated by charged W± fields in the collision are comparable to those found in previous work. The magnetic fields so produced could seed galactic and extra-galactic magnetic fields observed today

137

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

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. PMID:25273750

Ju, J-C; Zhang, H; Zhang, J; Shu, T; Zhong, H-H

2014-09-01

138

Design of pulsed guiding magnetic field for high power microwave generators

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.

Ju, J.-C.; Zhang, H.; Zhang, J.; Shu, T.; Zhong, H.-H.

2014-09-01

139

Magneto-modulational instability in Kappa distributed plasmas with self-generated magnetic fields

International Nuclear Information System (INIS)

The behavior of magnetic fields generated by high-frequency transverse plasmons in Kappa distributed plasmas can be described by generalized Zakharov equations, which have considered the nonlinear wave-wave, wave-particle interactions in the kinetic regime and the effects of superthermal electrons. Modulational instability of the spontaneous magnetic fields is investigated on the basis of the equations. The effect of the superthermal electrons on the modulational instability is discussed and a comparison with previous results is presented. It is shown that the characteristic scale and maximum growth rate of the magnetic fields depend on the energy density of transverse plasmons and the superthermal index ?.

140

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-06-01

141

Theory of nonlinear particle acceleration at shocks and self-generation of the magnetic field

We present some recent developments in the theory of particle acceleration at shock fronts in the presence of dynamical reaction of the accelerated particles and self-generation of magnetic field due to streaming instability. The spectra of accelerated particles, the velocity, magnetic field and temperature profiles can be calculated in this approach anywhere in the precursor and in the downstream region. The implications for the origin of cosmic rays and for the phenomenology of supernova remnants will be discussed.

Blasi, Pasquale

2007-01-01

142

The intensity of the magnetic field of sunspots during the generation of a penumbra

International Nuclear Information System (INIS)

The maximum values of the intensity of the magnetic field of sunspots before and after the generation of a penumbra are studied. The results obtained from observations made in different periods of the solar activity cycles (1917 - 1924 and 1962 - 1970) using visual and photographic observation methods indicate that the intensity of the sunspot magnetic field does not vary continuously in the course of sunspot develop-ment, but displays discrete values. (author)

143

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dynamics of magnetic fields with amplitude of several tens of Megagauss, generated at both sides of a solid target irradiated with a high intensity (? 1019W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and ...

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

2012-01-01

144

Directory of Open Access Journals (Sweden)

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

E. D. Schmitter

2010-02-01

145

Generation of Uranus and Neptune large-scale magnetic fields by turbulent dynamo mechanism

International Nuclear Information System (INIS)

A model of generation of a large-scale magnetic field in the Uranus nucleus and ocean bottom using nonuniform rotation and mean spiraling convective movements is built. It is shown that in a thin ocean envelope there can occur the prevailing excitation of a nonaxisymmetric field resulting in a sharp slope of the total dipole momentum of the nucleus and envelope field. The minimum convective velocities required for exciting the observed field are estimated. Due to the similar structure of Uranus and Neptune the same model can be applied to the latter. Taking into account that nearly one half of the Neptune nucleus is solid a lowere convection rate and consequently less effective magnetic field generation can be expected inside the Neptune nucleus that is why the main contribution into generation of the Neptune field must be made by motions in its ocean

146

Chaotic dynamics of the magnetic field generated by dynamo action in a turbulent flow

Energy Technology Data Exchange (ETDEWEB)

We present models related to the results of a recent experiment (the 'VKS experiment') showing the generation of a magnetic field by a fully turbulent flow of liquid sodium. We first discuss the geometry of the mean magnetic field when the two coaxial impellers driving the flow counter-rotate at the same frequency. We then show how we expect this geometry to be modified when the impellers rotate at different frequencies. We also show that, in the latter case, dynamical regimes of the magnetic field can be easily understood from the interaction of modes with dipolar (respectively quadrupolar) symmetry. In particular, this interaction generates magnetic field reversals that have been observed in the experiment and display a hierarchy of timescales similar to the Earth's magnetic field: the duration of the steady phases is widely distributed, but is always much longer than the time needed to switch polarity. In addition to reversals, several other large scale features of the generated magnetic field are obtained when varying the governing parameters of the flow. These results are also understood in the framework of the same model.

Petrelis, F; Fauve, S [Laboratoire de Physique Statistique, CNRS UMR 8550, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France)], E-mail: petrelis@lps.ens.fr

2008-12-10

147

Chaotic dynamics of the magnetic field generated by dynamo action in a turbulent flow

International Nuclear Information System (INIS)

We present models related to the results of a recent experiment (the 'VKS experiment') showing the generation of a magnetic field by a fully turbulent flow of liquid sodium. We first discuss the geometry of the mean magnetic field when the two coaxial impellers driving the flow counter-rotate at the same frequency. We then show how we expect this geometry to be modified when the impellers rotate at different frequencies. We also show that, in the latter case, dynamical regimes of the magnetic field can be easily understood from the interaction of modes with dipolar (respectively quadrupolar) symmetry. In particular, this interaction generates magnetic field reversals that have been observed in the experiment and display a hierarchy of timescales similar to the Earth's magnetic field: the duration of the steady phases is widely distributed, but is always much longer than the time needed to switch polarity. In addition to reversals, several other large scale features of the generated magnetic field are obtained when varying the governing parameters of the flow. These results are also understood in the framework of the same model.

148

The experiment of generation and maintainance of a FRC by means of a rotating magnetic field

International Nuclear Information System (INIS)

An experiment in which a rotating magnetic field was used to generate and maintain a FRC is described. The FRC life time appeared to be limited by the duration of the rotating field pulse (40 ms), there was no evidence of gross instabilities

149

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.

Vu Bioengineering Ret Program

150

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

151

Directory of Open Access Journals (Sweden)

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

Ammar Ben Brahim

2011-05-01

152

International Nuclear Information System (INIS)

In design of the future fusion devises in which low activation ferritic steel is planned to use as the plasma facing material and/or the inserts for ripple reduction, the appreciation of the error field effect against the plasma as well as the optimization of ferritic plate arrangement to reduce the toroidal field ripple require calculation of magnetic field generated by ferritic steel. However iterative calculations concerning the non-linearity in B-H curve of ferritic steel disturbs high-speed calculation required as the design tool. In the strong toroidal magnetic field that is characteristic in the tokamak fusion devices, fully magnetic saturation of ferritic steel occurs. Hence a distribution of magnetic charges as magnetic field source is determined straightforward and any iteration calculation are unnecessary. Additionally objective ferritic steel geometry is limited to the thin plate and ferritic plates are installed along the toroidal magnetic field. Taking these special conditions into account, high-speed calculation code ''FEMAG'' has been developed. In this report, the formalization of 'FEMAG' code, how to use 'FEMAG', and the validity check of 'FEMAG' in comparison with a 3D FEM code, with the measurements of the magnetic field in JFT-2M are described. The presented examples are numerical results of design studies for JT-60 modification. (author)

153

Energy Technology Data Exchange (ETDEWEB)

In design of the future fusion devises in which low activation ferritic steel is planned to use as the plasma facing material and/or the inserts for ripple reduction, the appreciation of the error field effect against the plasma as well as the optimization of ferritic plate arrangement to reduce the toroidal field ripple require calculation of magnetic field generated by ferritic steel. However iterative calculations concerning the non-linearity in B-H curve of ferritic steel disturbs high-speed calculation required as the design tool. In the strong toroidal magnetic field that is characteristic in the tokamak fusion devices, fully magnetic saturation of ferritic steel occurs. Hence a distribution of magnetic charges as magnetic field source is determined straightforward and any iteration calculation are unnecessary. Additionally objective ferritic steel geometry is limited to the thin plate and ferritic plates are installed along the toroidal magnetic field. Taking these special conditions into account, high-speed calculation code ''FEMAG'' has been developed. In this report, the formalization of 'FEMAG' code, how to use 'FEMAG', and the validity check of 'FEMAG' in comparison with a 3D FEM code, with the measurements of the magnetic field in JFT-2M are described. The presented examples are numerical results of design studies for JT-60 modification. (author)

Urata, Kazuhiro [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

2003-03-01

154

Electron holographic observation of micro-magnetic fields current-generated from single carbon coil

Energy Technology Data Exchange (ETDEWEB)

A carbon coil was evaluated for use as a micro-solenoid in a small magnetic device. A single carbon coil was lifted out of the aggregate using a tungsten fine probe in a focused ion beam (FIB) system and was wired to two small electrodes in the specimen holder of a transmission electron microscope (TEM). A direct current was supplied to the single carbon coil. A micro/nano-magnetic field generated from the coil was directly observed by electron holography. A computer simulation of electron holography was also done to quantitatively analyze the magnetic field. Details on the FIB technique, the electron holographic observation and the simulation are described.

Yamamoto, Kazuo [Japan Society for the Promotion of Science (JSPS), c/o Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta, Nagoya 456-8587 (Japan)]. E-mail: kazuo.yamamoto@asu.edu; Hirayama, Tsukasa [Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta, Nagoya 456-8587 (Japan); Kusunoki, Michiko [Japan Fine Ceramics Center, 2-4-1, Mutsuno, Atsuta, Nagoya 456-8587 (Japan); Yang, Shaoming [Department of Applied Chemistry, Faculty of Engineering, Gifu University, Gifu 501-1193 (Japan); Motojima, Seiji [Department of Applied Chemistry, Faculty of Engineering, Gifu University, Gifu 501-1193 (Japan)

2006-03-15

155

Electron holographic observation of micro-magnetic fields current-generated from single carbon coil.

A carbon coil was evaluated for use as a micro-solenoid in a small magnetic device. A single carbon coil was lifted out of the aggregate using a tungsten fine probe in a focused ion beam (FIB) system and was wired to two small electrodes in the specimen holder of a transmission electron microscope (TEM). A direct current was supplied to the single carbon coil. A micro/nano-magnetic field generated from the coil was directly observed by electron holography. A computer simulation of electron holography was also done to quantitatively analyze the magnetic field. Details on the FIB technique, the electron holographic observation and the simulation are described. PMID:16338074

Yamamoto, Kazuo; Hirayama, Tsukasa; Kusunoki, Michiko; Yang, Shaoming; Motojima, Seiji

2006-03-01

156

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...

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

2014-01-01

157

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

Jung, Tae-Uk

2012-04-01

158

Magnetic fields generated by r-modes in accreting millisecond pulsars

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

Cuofano, Carmine

2009-01-01

159

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

160

Computational Study of the Strong Magnetic Field Generation in Non-Spherical Cone-Guided Implosion

International Nuclear Information System (INIS)

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

161

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

162

International Nuclear Information System (INIS)

The two-dimensional distribution of self-generated magnetic fields near the laser-plasma interaction region is observed for the first time by a very simple method of laser irradiation of audio magnetic tape. The lobe structure is a maximum at the incident angle of 10 to 15 degrees for p-polarized laser beam. The direction of the fields is perpendicular to the density gradient and to the incident p-polarization plane. Parity existence is verified by using convergent and divergent laser beams in a large cone angle case. In a small cone angle experiment, negative and positive magnetic fields across the resonance region, and the parity existence by reversing the sign of the incident angle are proved. These observations strongly support the resonance absorption as the field generation mechanism. (author)

163

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

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

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

2008-01-01

164

The magnetic field appearing as bipolar magnetic regions at the surface of the sun represents the lines of force from a general azimuthal field of the order of 100 gauss somewhere beneath the surface. The amplification time, as a consequence of the nonuniform rotation, is of the order of 10 years. But magnetic buoyancy brings the azimuthal field up through much of the convective zone in a time rather less than 10 years, raising the question of where the azimuthal field can be retained long enough to be amplified. We show that magnetic fields can be retained for long periods of time in the stable radiative region beneath the convective zone, but unfortunately the solar dynamo cannot function there because turbulent diffusion is an essential part of its operation. The only possible conclusion appears to be that the dynamo operates principally in the very lowest levels of the convective zone at depths of 150,000 km or more, where the gas density is 0.1 g/cu cm, and the fields are limited to 50 gauss.

Parker, E. N.

1975-01-01

165

International Nuclear Information System (INIS)

Based on Maxwell's equations, the electric current and voltage pulses induced in explosion driven induction generators (R/sub m/ = ?0sigmavL>>1) with plane electrodes and homogeneous external magnetic field B0 are calculated analytically for two plasma shock flows, (i) the jet flow with shock speed v(t) = v0, t> or =0, and (ii) the plane detonation flow with shock speed v(t) = (2/3)(E0/rho0)/sup 1/3/t/sup -1/3/, t> or =0. The external load circuit with resistance R0 and inductance L0 is connected either (I) to the downstream ends or (II) to the flow entrance ends of the electrodes so that the magnetic self-field B(t) of the generated current I(t) is (I) parallel and (II) antiparallel to the transverse external field B0. In both generator models I and II, the jet flow produces large current and voltage pulses, whereas the detonation flow generates considerably smaller and shorter current and voltage pulses. In all cases, the magnetic self-field B(t) of the generated current I(t) is of the order-of-magnitude of B0, but the generator with electrode wiring I (positive superposition of B and B0) produces considerably more power and energy than the generator with electrode wiring II (negative superposition of B and B0)

166

Device for generating toroidal magnetic fields in torus type thermonuclear device

International Nuclear Information System (INIS)

Purpose: To obtain a toroidal magnetic field generation device which is simple in structure, capable of accurately mounting toroidal coils and in excellent in durability. Constitution: In a device for generating toroidal magnetic field of tokamak type thermonuclear device, each of the magnet coils support frames made of non-magnetic copper or the like is firmly assembled with a lower support and an upper support and a connection member so as to support the coils withstanding the own weight of the coils, thermal stress and centripetal force, and the both of the inner sides of each support frame at the center is formed with wedge surfaces. Retention rings are firmly fitted to the projections at the lower and the upper portions of the support frames and accurately assembled into the support frames to thereby transmit the centripetal force to the wedge surfaces to receive the withstanding force. (Horiuchi, T.)

167

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

168

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

Energy Technology Data Exchange (ETDEWEB)

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

Brizard, A.J.; Murayama H.; Wurtele, J.S.

1999-11-24

169

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

Energy Technology Data Exchange (ETDEWEB)

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)

Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N; Firsov, V V [D.V. Skobel' tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2013-05-31

170

International Nuclear Information System (INIS)

Building on earlier work, we develop an equation-of-motion method for calculating magnetic seed fields generated from currents arising from charged W± fields in bubble collisions during a first-order primordial electroweak phase transition allowed in some proposed extensions of the standard model. The novel feature of our work is that it takes into account, for the first time, the dynamics of the bubble walls in such collisions. We conclude that for bubbles with sufficiently thin surfaces the magnetic seed fields may be comparable to, or larger than, those found in earlier work. Thus, our results strengthen the conclusions of previous studies that cosmic magnetic fields observed today may originate from seeds created during the electroweak phase transition, and consequently that these fields may offer a clue relevant to extensions of the standard model.

171

Second-harmonic generation in asymmetric quantum dots in the presence of a static magnetic field

International Nuclear Information System (INIS)

The second-harmonic generation (SHG) coefficient in an asymmetric quantum dot (QD) with a static magnetic field is theoretically investigated. Within the framework of the effective-mass approximation, we obtain the confined wave functions and energies of electrons in the QD. We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method. The numerical results for the typical GaAs/AlGaAs QD show that the SHG coefficient depends strongly on the magnitude of magnetic field, parameters of the asymmetric potential and the radius of the QD. The resonant peak shifts with the magnetic field or the radius of the QD changing. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

172

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)

173

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.

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

2014-06-01

174

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

175

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

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

2008-01-01

176

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

177

Generation of a strong magnetic field by intense CO/sub 2/ laser irradiation

International Nuclear Information System (INIS)

Generation of a magnetic field by intense CO/sub 2/ laser irradiation is reported. The magnetic field is observed to be greater than several hundred kilogauss. The configuration of the target and the observation system are presented. The laser-irradiated target is composed of two 50-?m thick 2-mm diam copper disks. The front side disk has a 1-mm diam hole at the center for the laser injection. A one-turn coil of 2-mm diameter with 80-?m diam copper wire is connected to the two disks. The magnetic field is measured by using the 1-mm diam search coil linked to a Tektronix 7104 oscilloscope whose bandwidth is 1 GHz. From the results of the author's study, they obtain a scaling law for the self-induced magnetic field which indicates that magnetic fields up to a few (megagauss) can be generated which are strong enough for various applications such as plasma confinement and the material sciences

178

Generation of shear Alfvén waves by a rotating magnetic field source: Three-dimensional simulations

The paper discusses the generation of polarized shear Alfvén waves radiated from a rotating magnetic field source created via a phased orthogonal two-loop antenna. A semianalytical three-dimensional cold two-fluid magnetohydrodynamics model was developed and compared with recent experiments in the University of California, Los Angeles large plasma device. Comparison of the simulation results with the experimental measurements and the linear shear Alfvén wave properties, namely, spatiotemporal wave structure, a dispersion relation with nonzero transverse wave number, the magnitude of the wave dependences on the wave frequency, show good agreement. From the simulations it was found that the energy of the Alfvén wave generated by the rotating magnetic field source is distributed between the kinetic energy of ions and electrons and the electromagnetic energy of the wave as: ˜1/2 is the energy of the electromagnetic field, ˜1/2 is the kinetic energy of the ion fluid, and ˜2.5% is the kinetic energy of electron fluid for the experiment. The wave magnetic field power calculated from the experimental data and using a fluid model differ by ˜1% and is ˜250 W for the experimental parameters. In both the experiment and the three-dimensional two-fluid magnetohydrodynamics simulations the rotating magnetic field source was found to be very efficient for generating shear Alfvén waves.

Karavaev, A. V.; Gumerov, N. A.; Papadopoulos, K.; Shao, Xi; Sharma, A. S.; Gekelman, W.; Wang, Y.; Van Compernolle, B.; Pribyl, P.; Vincena, S.

2011-03-01

179

International Nuclear Information System (INIS)

An 18mm period, 0.54 Tesla, 8mm gap superconducting undulator with both horizontal and vertical focusing has been built and tested. This magnet, which is fabricated in 25 cm length sections, is being tested for use in the radiator section (total magnet length of 1.5 m) of the Harmonic Generation Free Electron Laser experiment at the National Synchrotron Light Source - Accelerator Test Facility at Brookhaven National Lab., in collaboration with Grumman Corp. The measurement system is outlined, sources and estimates of errors are described, and some magnetic field data are presented and discussed

180

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

181

Simulations of magnetic field generation in unmagnetized plasmas via beat-wave current drive.

This work describes the scientific basis and associated simulation results for the magnetization of an unmagnetized plasma via beat-wave current drive. Two-dimensional electromagnetic particle-in-cell simulations have been performed for a variety of angles between the injected waves to demonstrate beat-wave generation in agreement with theoretical predictions of the beat-wave wave vector and saturation time, revealing new 2D effects. The simulations clearly demonstrate electron acceleration by the beat waves and resultant current drive and magnetic field generation. The basic process depends entirely on the angle between the parent waves and the ratio of the beat-wave phase velocity to the electron thermal velocity. The wave to magnetic energy conversion efficiency of the cases examined is as high as 0.2%. The technique could enable novel plasma experiments in which the use of magnetic coils is infeasible. PMID:23368130

Welch, D R; Genoni, T C; Thoma, C; Bruner, N; Rose, D V; Hsu, S C

2012-11-30

182

Injection of whistler waves into Earth's inner radiation belt to enhance precipitation of energetic electrons has been an active research area, and is referred to as RB Remediation (RBR). Most mechanisms of pitch angle scattering of energetic particles are based on gyro-resonant wave-particle interaction. Recent experiments and simulations show that Rotating Magnetic Field (RMF) antennas in plasmas can be efficient radiation sources of MHD and whistler waves. In experiments conducted in the Large Plasma Device (LAPD) at UCLA, poly-phased current loops drove the RMF antenna. These experiments, as well as simulations show that 75-85% of the radiation generated by the RMF antenna is in guided propagation. The whistler and MHD waves have non-local magnetic field gradients in the transverse direction and these provide ways to break the adiabatic invariants of electrons and precipitate them via a non-resonant scattering. In this paper simulations of non-resonant pitch angle scattering of energetic particles by waves generated by RMF sources are presented. Three-dimensional EMHD simulations are used to model whistlers and the resultant 3D electromagnetic fields are used in particle tracing codes to study pitch angle scattering. The simulations are carried out for a wide range of magnetic fields produced by RMF sources, including fields much larger than the ambient magnetic field in space plasma environments. This work was sponsored by ONR MURI Grant 5-28828

Shao, X.; Karavaev, A. V.; Sharma, A. S.; Papadopoulos, K.; Gumerov, N.; Gigliotti, A. F.; Gekelman, W. N.

2009-12-01

183

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

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

2014-03-01

184

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

DEFF Research Database (Denmark)

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.

VennerstrØm, Susanne

2006-01-01

185

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

International Nuclear Information System (INIS)

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

186

Energy Technology Data Exchange (ETDEWEB)

A formalism is presented that enables the calculation of atomic charge and current densities in Russel-Saunders states of free atoms and ions in terms of scalar and vector spherical harmonics. The electric and magnetic fields generated by the multipole components of charge and current distributions are easily calculated. They are found to have the same multipolarity as their generating sources and Maxwell's equations are satisfied component by component. Calculations of these fields for hydrogen-like atoms and specific transition-metal and rare-earth ions are presented using realistic analytic radial wave functions.

Ayuel, K., E-mail: ayuel_2000@yahoo.co [Department of Physics, University of Juba, P.O. Box 321/1, Khartoum (Sudan); Chatel, P.F. de, E-mail: pdechatel@gmail.co [Chinese Academy of Sciences, Institute of Metal Research, 72 Wenhua Road, Shenyang 110016 (China)

2009-05-01

187

Thermally generated magnetic fields in laser-driven compressions and explosions

The evolution of thermally generated magnetic fields in a plasma undergoing a nearly spherically symmetric adiabatic compression or expansion is calculated. The analysis is applied to obtain approximate results for the development of magnetic fields in laser-driven compression and explosion of a pellet of nuclear fuel. Localized sources, such as those occurring at composition boundaries in structured pellets or at shock fronts, give stronger fields than those deriving from smoothly distributed asymmetries. Although these fields may approach 10 million G in the late stages of compression, this is not expected to present difficulties for the compression process. Assuming ignition of a nuclear explosion occurs, the sources become much stronger, and values of approximately 10 billion G are obtained at tamper boundaries assuming a 20% departure from spherical symmetry during the explosion.

Tidman, D. A.

1975-01-01

188

Uniform magnetic fields generated by circular current-carrying coils. [for spacecraft

The study described was carried out to evaluate known systems of circular coils with a view toward their application on board the space probes Ranger 1, Ranger 2, and Explorer 10. Particular attention is given to a new method, developed during the investigation, for determining the constants of systems composed of 6 to 8 coils. Such systems were found to generate magnetic fields of very high uniformity. By using advanced computational techniques, it proved possible to evaluate the field uniformity of various systems without recourse to complex analytical methods. Means of evaluating the influence of coil dimensions on the uniformity of the field of any system are described.

Williams, V. L.; Cain, J. C.

1975-01-01

189

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

Kunze, Kerstin E

2013-01-01

190

International Nuclear Information System (INIS)

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

191

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

International Nuclear Information System (INIS)

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

192

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

Energy Technology Data Exchange (ETDEWEB)

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

Boulware, Jeffrey C., E-mail: j.c.boulware@aggiemail.usu.ed [Department of Mechanical and Aerospace Engineering, Utah State University, 4130 Old Main Hill, Logan, UT 84322-4130 (United States); Ban, Heng, E-mail: hban@engineering.usu.ed [Department of Mechanical and Aerospace Engineering, Utah State University, 4130 Old Main Hill, Logan, UT 84322-4130 (United States); Jensen, Scott, E-mail: sjensen@sdl.usu.ed [Space Dynamics Laboratory, Utah State University Research Foundation, 1695 North Research Park Way, North Logan, UT 84341 (United States); Wassom, Steve, E-mail: swassom@sdl.usu.ed [Space Dynamics Laboratory, Utah State University Research Foundation, 1695 North Research Park Way, North Logan, UT 84341 (United States)

2010-07-15

193

Fluid theory for quasistatic magnetic field generation in intense laser plasma interaction

International Nuclear Information System (INIS)

Based on the ten-moment Grad system of hydrodynamic equations, a self-consistent fluid model is presented for the generation of quasistatic magnetic fields in relativistic intense laser plasma interaction. In this model, the nondiagonal stress tensor is taken into account and the generalized vorticity is proved to be not conserved, which are different from previous ideal fluid models. In the quasistatic approximation, where the low-frequency phase speed vp is much smaller than the electron thermal speed vte, the axial magnetic field Bz and the azimuthal one B? are derived. It is found that the condition vp>>vte used as the cold fluid approximation by previous papers is improper, where the derived Bz is incomplete and one magnetization current for Bz associated with the electron thermal motion does not appear. The profiles of both Bz and B? are analyzed. Their dependence on the laser intensity is discussed

194

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

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 tine 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.

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

2005-01-01

195

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

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

Gigliotti, A.; Gekelman, W.; Pribyl, P.; Vincena, S.; Karavaev, A.; Shao, X.; Sharma, A. Surjalal; Papadopoulos, D.

2009-09-01

196

Directory of Open Access Journals (Sweden)

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

Roberto De Luca

2011-10-01

197

Performance results of a 300 MWth generator at high magnetic field

The High Performance Demonstration Experiment (HPDE) in progress at AEDC has as its objective a 300 MW thermal input open-cycle MHD system has been assembled. Testing with the channel configured in the Faraday mode was initiated in late 1979. Experimental results have been obtained at a magnetic field strength from 1.5 to 3.8 Tesla (T). A maximum Faraday power of 35.5 MW has been generated, which represents an enthalpy extraction of 11.6 percent.

Christensen, L. S.; Whitehead, G. L.; Felderman, E. J.

1983-01-01

198

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

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.

Asenjo, Felipe A; Qadir, Asghar

2012-01-01

199

New mechanism of generation of large-scale magnetic field in a sheared turbulent plasma

A review of recent studies on a new mechanism of generation of large-scale magnetic field in a sheared turbulent plasma is presented. This mechanism is associated with the shear-current effect which is related to the W x J-term in the mean electromotive force. This effect causes the generation of the large-scale magnetic field even in a nonrotating and nonhelical homogeneous sheared turbulent convection whereby the alpha effect vanishes. It is found that turbulent convection promotes the shear-current dynamo instability, i.e., the heat flux causes positive contribution to the shear-current effect. However, there is no dynamo action due to the shear-current effect for small hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if the spatial scaling for the turbulent correlation time is k^{-2}, where k is the small-scale wave number. We discuss here also the nonlinear mean-field dynamo due to the shear-current effect and take into account the transport of magnetic helicity as a dynamical n...

Kleeorin, N

2007-01-01

200

Energy Technology Data Exchange (ETDEWEB)

The relative locations and characteristics of the distribution lines feeding 434 residences in the Denver metropolitan area were recorded and classified according to the Wertheimer-Leeper code (WL code) as a part of an epidemiological study of the incidence of childhood cancer. The WL code was found to place the mean values of the fields in rank order. However, the standard deviations were approximately the same size as the means. Theoretical calculations indicate that a significant fraction of the low-power magnetic fields can be generated by the distribution lines, especially in the cases where the distribution lines are within 50 feet of the residence. Thus, the wiring code was shown to be a useful method for making a first-order approximation to predict long-term, low-level magnetic fields in residences.

Barnes, F.; Wachtel, H.; Savitz, D.; Fuller, J.

1989-01-01

201

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.

Khordad, R.; Bahramiyan, H.

2014-08-01

202

Recent experiments conducted in the Large Plasma Device (LAPD) located at UCLA demonstrated efficient excitation of whistler and shear Alfven waves by a Rotating Magnetic Field (RMF) source. We present analytical theory, computational modeling and experimental results of the shear Alfven wave excitation by RMF source created by a phased orthogonal two-loop antenna in a plasma. An analytical theory and simulations using a three-dimensional cold two-fluid model of Alfven wave excitation were developed and compared with experiments. These comparisons show good agreement on linear shear Alfven wave properties, namely, spatio-temporal wave structure, dispersion relation, and the dependence of wave magnitude on the wave frequency. From the simulations it was found that the energy of the Alfven wave generated by the rotating magnetic field source is distributed among the kinetic energies of ions and electrons and the electromagnetic energy of the wave. The wave magnetic field power calculated from the experimental data and using a fluid model agrees within 1 percent. The RMF source is thus very efficient in generating shear Alfven waves. Work supported by ONR MURI grant.

Shao, X.; Karavaev, A. V.; Gumerov, N.; Sharma, A. S.; Papadopoulos, K.; Gekelman, W. N.; Wang, Y.; Vincena, S. T.; Pribyl, P.

2010-12-01

203

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

DEFF Research Database (Denmark)

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.

Erdös, Laszlo; Fournais, SØren

2012-01-01

204

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

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. PMID:24440895

Karimi, Ebrahim; Grillo, Vincenzo; Boyd, Robert W; Santamato, Enrico

2014-03-01

205

Magnetic fields generated by r-modes in accreting millisecond pulsars

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

Cuofano, Carmine

2009-01-01

206

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

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

2012-01-01

207

Significance of self magnetic field in long-distance collimation of laser-generated electron beams

Long-distance collimation of fast electron beams generated by laser-metallic-wire targets has been observed in recent experiments, while the mechanism behind this phenomenon remains unclear. In this work, we investigate in detail the laser-wire interaction processes with a simplified model and Classical Trajectory Monte Carlo simulations, and demonstrate the significance of the self magnetic fields of the beams in the long-distance collimation. Good agreements of simulated image plate patterns with various experiments and detailed analysis of electron trajectories show that the self magnetic fields provide restoring force that is critical for the beam collimation. By studying the wire-length dependence of beam divergence in certain experiments, we clarify that the role of the metallic wire is to balance the space-charge effect and thus maintain the collimation.

Chen, Shi; Niu, Yifei; Dan, Jiakun; Chen, Ziyu; Li, Jianfeng

2014-01-01

208

Generation of a spin-polarized electron beam by multipoles magnetic fields

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 these analysis could prove useful in the design of improved electron microscope.

Karimi, Ebrahim; Boyd, Robert W; Santamato, Enrico

2013-01-01

209

Pitch Angle Scattering of Electrons by Alfven Waves Generated with Rotating Magnetic Field Source

The pitch angle scattering by large amplitude whistler and Alfven waves is an attractive mechanism for the precipitation of electrons in the radiation belt. Recent experiments in LAPD/UCLA have shown rapid loss of energetic electrons in the presence of waves and this is studied in detail using simulations with experimental parameters. The Alfven waves generated by a Rotating Magnetic Field (RMF) antenna in LAPD have sharp gradients in the transverse direction. These rapidly varying magnetic fields leads to the breaking of the adiabatic invariant of electrons and precipitate them to the loss cone via non-resonant scattering. The generation of Alfven waves by the RMF antenna is simulated with a two fluid code and the resulting fields are used in a particle tracing code to study the pitch angle scattering of electrons. It is found that the pitch angle diffusion coefficient for the non-resonant scattering scales as the square of the ratio of the electron Larmor radius to the transverse wavelength. Further, the fluctuations generated by the two loop RMF source fills the plasma volume more effectively and is more effective in pitch angle scattering the electrons than using one loop antenna Work supported by ONR MURI grant.

Karavaev, A. V.; Shao, X.; Gumerov, N.; Sharma, A. S.; Papadopoulos, K.; Gekelman, W. N.; Pribyl, P.; Wang, Y.; van Compernolle, B.

2010-12-01

210

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

International Nuclear Information System (INIS)

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

211

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.

212

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-02-15

213

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

Fan Ya Jun; Qiu Aici

2002-01-01

214

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

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

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

2013-02-01

215

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Enqvist, Kari

1994-01-01

216

Three dimensional structure of the magnetic field generated by counter-streaming electron beams

The Weibel instability is an electromagnetic plasma mode that can transform the thermal energy of an anisotropic plasma into magnetic field energy. In the field of laser plasma interactions a similar type of instability has been considered as the cause of the current filamentation and magnetic field generation that occurs in the wake of an ultra-intense, ultra-short laser pulse propagating in an underdense plasma [1]. Recently, much attention has been paid to this instability also in overdense plasma regimes [2] where current filaments are observed in large scale 3D PIC numerical simulations and large ordered magnetic fields can contribute to the energetic electron transport. Here we study the evolution of this instability in a 3D fluid (relativistic) regime, in the case of a plasma where the anisotropy is due two counter-streaming electron beams, with the aim of understanding the typical magnetic structures that are to be expected as a consequence of the development of this instability. We present the initial phase of the nonlinear instability regime, where kinetic effects are not yet dominant, and stress the differences with respect to the 2D results where the system is supposed to remain homogeneous along the beam direction. The applicability of these results to the interpretation of the simulation results in the overdense laser-plasma regime is also discussed. [1] G.A.Askar'an, S.V. Bulanov, F. Pegoraro, A.M. Pukhov, Physics Reports 21, 835 (1995) [2] M. Honda, J. Meyer-ter-Vehn, and A. Pukhov, Plasma Phys. Rev. Lett. 85, 2128 (2000)

Califano, F.; Pegoraro, F.; Bulanov, S.

2002-11-01

217

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Baryshevsky, Vladimir G.

1999-01-01

218

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

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

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

2011-12-16

219

3D magnetic field effects in the NSC KIPT compact intense x-ray generator

International Nuclear Information System (INIS)

The paper is devoted to studying the 3D magnetic field effects on bending magnet edges and lattice lens interference on the electron beam dynamics and parameters of produced radiation for the NSC KIPT 225 MeV storage ring

220

It is shown that a dynamo can operate in an Active Galactic Nuclei accretion disk due to the Keplerian shear and due to the helical motions of expanding and twisting plumes of plasma heated by many star passages through the disk. Each plume rotates a fraction of the toroidal flux into poloidal flux, always in the same direction, through a finite angle, and proportional to its diameter. The predicted growth rate of poloidal magnetic flux, based upon two analytic approaches and numerical simulations, leads to a rapid exponentiation of a seed field, \\sim 0.1 to \\sim 0.01 per Keplerian period of the inner part of the disk. The initial value of the seed field may therefore be arbitrarily small yet reach, through dynamo gain, saturation very early in the disk history. Because of tidal disruption of stars close to the black hole, the maximum growth rate occurs at a radius of about 100 gravitational radii from the central object. The generated mean magnetic field, a quadrupole field, has predominantly even parity so ...

Pariev, V I; Finn, J M; Pariev, Vladimir I.; Colgate, Stirling A.; Finn, John M.

2006-01-01

221

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

222

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

International Nuclear Information System (INIS)

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

223

The energy conversion processes occurring in three-dimensional driven reconnection is analyzed. In particular, the energy conversion processes during localized reconnection in a taillike magnetic configuration are studied. It is found that three-dimensional driven reconnection is a powerful energy converter which transforms magnetic energy into plasma bulk flow and thermal energy. Three-dimensional driven reconnection is an even more powerful energy converter than two-dimensional reconnection, because in the three-dimensional case, plasmas were drawn into the reconnection region from the sides as well as from the top and bottom. Field-aligned currents are generated by three-dimensional driven reconnection. The physical mechanism responsible for these currents which flow from the tail toward the ionosphere on the dawnside of the reconnection region and from the ionosphere toward the tail on the duskside is identified. The field-aligned currents form as the neutral sheet current is diverted through the slow shocks which form on the outer edge of the reconnected field lines (outer edge of the plasma sheet).

Sato, T.; Walker, R. J.; Ashour-Abdalla, M.

1984-01-01

224

International Nuclear Information System (INIS)

The authors investigated possible alterations in the enzyme activity of catalase and isozyme MB-creatin kinase induced by prolonged exposure of laboratory rodents to a static magnetic field generated by a 0.5 T Magnetic Resonance unit. The results seems to exclude any alterations in the activity of catalase and MB-CK after exposure. However some homeostatic mechanism peculiar to multi cellular organisms might act 'in vivo' to adapt to the effects of the static magnetic field during exposure

225

Nonequilibrium current carrier generation in strong electric field in magnetic EuO semiconductor

International Nuclear Information System (INIS)

The processes of heating the magnon subsystem by current carriers and time alterations of resistance and magnetization in magnetic semiconductor EuO in a strong electric field, are considered. It is shown that the heating of magnetic subsystem increases the energy of donor activation, creates nonequilibrium concentration of current carriers in the conductivity zone. The temperature increase of magnous corresponds to decrease in magnetization and increase in resistance

226

International Nuclear Information System (INIS)

We investigate the effects of magnetic field on the entropy generation during fluid flow and heat transfer due to the radially stretching surface. The partial differential equations governing the flow and heat transfer phenomenon are transformed into nonlinear ordinary differential equations by using suitable similarity transformations. These equations are then solved by the homotopy analysis method and the shooting technique. The effects of the magnetic field parameter M and the Prandtl number Pr on velocity and the temperature profiles are presented. Moreover, influence of the magnetic field parameter M and the group parameter Br/? on the local entropy generation number Ns as well as the Bejan number Be are inspected. It is observed that the magnetic field is a strong source of entropy production in the considered problem

227

Generation of zonal flows and large-scale magnetic fields by drift-Alfven turbulence

International Nuclear Information System (INIS)

The possibility of generating zonal perturbations by drift-Alfven turbulence in a plasma with a finite pressure (1 > ? > me /mi) is investigated. A set of coupled equations is derived that includes the equation for the spectral function of the turbulence and the averaged equations for zonal perturbations. It is shown that, in particular cases, the equation for the spectral function possesses action invariants; i.e., it takes the form of a conservation law for some quantities that are proportional to the spectral function of turbulence. Two types of instability of the zonal perturbations are revealed. The first type of instability generates only a zonal flow. Two regimes of this instability--resonant and hydrodynamic regimes--are examined, and the corresponding instability growth rates are determined. The second type of instability takes place when the resonant interaction of drift-Alfven waves with electrons is taken into account. Because of this instability, the generation of a zonal magnetic field is inevitably accompanied by the generation of a zonal flow. It is found that the growth rate of the second type of instability is slower than that of the first type

228

Impossibility of the strong magnetic fields generation in an electron-positron plasma

We examine the issue of whether a magnetic field can be amplified in a background matter consisting of electrons and positrons self-interacting within the Fermi model. For this purpose, we compute the antisymmetric contribution to the photon polarization tensor in this matter having nonzero temperature and chemical potential. It is shown that this contribution is vanishing in the static limit. Then we study a particular case of a degenerate relativistic electron gas present in a magnetar. We demonstrate that a seed magnetic field is attenuated in this case. Thus, contrary to the recent claim, we show that there is no magnetic field instability in such a system, which can lead to the magnetic field growth. Therefore, the recently proposed mechanism cannot be used for the explanation of strong magnetic fields of magnetars.

Dvornikov, Maxim

2014-08-01

229

Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth.

Gao, L.; Nilson, P. M.; Igumenschev, I. V.; Fiksel, G.; Yan, R.; Davies, J. R.; Martinez, D.; Smalyuk, V.; Haines, M. G.; Blackman, E. G.; Froula, D. H.; Betti, R.; Meyerhofer, D. D.

2013-05-01

230

Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, Jc. To minimize such grain boundary obstacles, HTS conductors such as REBa2Cu3O7-x and (Bi, Pb)2Sr2Ca2Cu3O10-x are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi2Sr2CaCu2O8-x (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high Jc of 2,500 A mm-2 at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high Jc can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries.

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

2014-04-01

231

Directory of Open Access Journals (Sweden)

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*=X_{C}, 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*<*X*_{C} and the field lines without reconnection in *x*>*X*_{C}. Hence, contray to the conventional prediction, the reconnected sheared field lines in *x*<*X*_{C} are not spiral or helical, since they cannot be topologically connected to the field lines in *x*>*X*_{C}. 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.

M. Ugai

2010-08-01

232

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)

233

Magnetic fields generated by an induction heating (IH) cook top do not cause genotoxicity in vitro.

The use of induction heater (IH) cook tops in homes has become widespread, especially in Japan, but there are concerns about the safety of intermediate frequency (IF) electromagnetic fields associated with these cooking appliances. Since the cellular genotoxicity of IF magnetic fields has not been examined in cultured cells, we examined the effects of these fields at a magnetic flux density of 532 +/- 20 microT at 23 kHz, using an exposure unit with a built-in CO2 incubator. Exposure to the IF magnetic field at 532 microT for 2 h did not affect the growth of CHO-K1 cells and caused no mutagenic effects in bacterial mutation assays. Exposure to the IF magnetic field for 2 h induced neither single nor double DNA strand breaks in comet assays, and caused no significant change in the mutation frequency at the HPRT locus compared to sham exposure. The magnetic field used in this study is more than 80 times higher than the level recommended as safe in the International Commission on Non-ionizing Radiation Protection (ICNIRP) guidelines. From these results, we suggest that exposure to an IF magnetic field for 2 h does not cause cellular genotoxicity in bacteria and in Chinese hamster cells. However, the possibility of effects on other cellular functions remains, and further studies on the cellular effects of IF magnetic fields are required. PMID:17492656

Miyakoshi, Junji; Horiuchi, Emi; Nakahara, Takehisa; Sakurai, Tomonori

2007-10-01

234

Magnetic Propeller for Uniform Magnetic Field Levitation

Digital Repository Infrastructure Vision for European Research (DRIVER)

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external fie...

Krinker, Mark; Bolonkin, Alexander

2008-01-01

235

Effect of laser flux on magnetic field generated thermal instability in a laser produced plasma

International Nuclear Information System (INIS)

In the underdense region of a laser produced plasma, density and temperature gradients are aligned parallel to each other. The magnetic field generates an off diagonal component of thermal conductivity tensor leading to a component of heat flow in the direction of k-vector and hence to the growth of the original perturbation. However, the temperature perturbation also modifies the ac conductivity of the plasma (?/sub ac/?T/sup -3/2/) leading to a slower rate of energy deposition from the laser in the regions of higher T/sub 1/ and hence tending to stabilize the instability. For typical parameters, the instability is suppressed at power density of the order of 10/sup 15/ W/cm/sup 2/ of a Nd: Glass laser. A self consistent analysis of the instability is developed

236

International Nuclear Information System (INIS)

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

237

Diffusion and Stochastic Island Generation in the Magnetic Field Line Random Walk

The cross-field diffusion of field lines in stochastic magnetic fields described by the 2D+slab model is studied using a semi-analytic statistical approach, the decorrelation trajectory method. We show that field line trapping and the associated stochastic magnetic islands strongly influence the diffusion coefficients, leading to dependences on the parameters that are different from the quasilinear and Bohm regimes. A strong amplification of the diffusion is produced by a small slab field in the presence of trapping. The diffusion regimes are determined and the corresponding physical processes are identified.

Vlad, M.; Spineanu, F.

2014-08-01

238

Self-generated magnetic field in CO2 laser produced plasma

International Nuclear Information System (INIS)

Measurements have been made of an azimuthal magnetic field spontaneously associated with plasmas produced by the irradiation of an 80 ns CO2 laser pulse to a CD2 target. The magnetic field diffuses from an initial source into an ambient nitrogen plasma. Extrapolation of measured data to the initial target surface shows a field intensity of --0.6 MG. The diffusion coefficient calculated from the ambient plasma parameters is in accordance with direct experimental data. The diffused field is followed by the expanding laser target plasma. For sufficiently high ambient gas pressure, the field direction is reversed. (author)

239

Self-generated magnetic fields of an air-breakdown plasma produced by two sequential laser pulses

International Nuclear Information System (INIS)

The spatial and temporal distribution of the self-generated magnetic fields were measured in a laser spark produced by double pulses in air. When an atmospheric air breakdown is produced by two sequential laser pulses a resonance-like phenomenon occurs which can be used for the study of the dependence of the amplitude of self-generated magnetic field on the time separation. The results are compared with those obtained when plasma in air was ignited on metal and dielectric targets. (D.Gy.)

240

Steady magnetic-field generation via surface-plasma-wave excitation

International Nuclear Information System (INIS)

The possibility of inducing a magnetic field via surface plasma-wave excitation is investigated with a simple nonrelativistic hydrodynamic model. A static magnetic field is predicted at the plasma surface, scaling with the square of the surface-wave field amplitude, and the influence of the electron plasma density is studied. In the case of resonant surface-wave excitation by laser this result can be applied to low intensities such that the electron quiver velocity in the field of the surface wave is less than its thermal velocity.

241

Magnetization dynamics using ultrashort magnetic field pulses

Digital Repository Infrastructure Vision for European Research (DRIVER)

Very short and well shaped magnetic field pulses can be generated using ultra-relativistic electron bunches at Stanford Linear Accelerator. These fields of several Tesla with duration of several picoseconds are used to study the response of magnetic materials to a very short excitation. Precession of a magnetic moment by 90 degrees in a field of 1 Tesla takes about 10 picoseconds, so we explore the range of fast switching of the magnetization by precession.

Tudosa, Ioan

2005-01-01

242

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

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

2014-04-01

243

Hamilton flow generated by field lines near a toroidal magnetic surface

Energy Technology Data Exchange (ETDEWEB)

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

Skovoroda, A. A., E-mail: skovorod@nfi.kiae.ru [National Research Center Kurchatov Institute (Russian Federation)

2013-07-15

244

Hamilton flow generated by field lines near a toroidal magnetic surface

International Nuclear Information System (INIS)

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

245

Hamilton flow generated by field lines near a toroidal magnetic surface

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

Skovoroda, A. A.

2013-07-01

246

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

Ichiki, Kiyotomo; Sugiyama, Naoshi

2011-01-01

247

International Nuclear Information System (INIS)

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

248

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

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

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

2008-06-01

249

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

International Nuclear Information System (INIS)

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

250

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-05-10

251

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

International Nuclear Information System (INIS)

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

252

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 (ÃŽÂ¸Ã¢ÂˆÂž)...

Al-nimr, Moh D. A.; Damseh, Renhe A.; Al-odat, Mohammed Q.

2004-01-01

253

The aim of this study was to evaluate effects of intermediate frequency magnetic fields (IFMF) generated by a wireless power transmission (WPT) based on magnetic resonance from the perspective of cellular genotoxicity on cultured human lens epithelial cells (HLECs). We evaluated the effects of exposure to 90?kHz magnetic fields at 93.36?µT on cellular genotoxicity in vitro for 2 and 4?h. The magnetic flux density is approximately 3.5 times higher than the reference level recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. For assessment of genotoxicity, we studied cellular proliferation, apoptosis and DNA damage by Cell Counting Kit-8 (CCK-8) assay, flow cytometry analysis, alkaline comet assay and phosphorylated histone H2AX (?H2AX) foci formation test. We did not detect any effect of a 90?kHz IFMF generated by WPT based on magnetic resonance on cell proliferation, apoptosis, comet assay, and ?H2AX foci formation test. Our results indicated that exposure to 90?kHz IFMF generated by WPT based on magnetic resonance at 93.36?µT for 2 and 4?h does not cause detectable cellular genotoxicity. Bioelectromagnetics. 35:512-518, 2014. © 2014 Wiley Periodicals, Inc. PMID:25196478

Shi, Dejing; Zhu, Chunbo; Lu, Rengui; Mao, Shitong; Qi, Yanhua

2014-10-01

254

The generation of large-scale magnetic fields in inflationary cosmology is explored, in particular, in a kind of moduli inflation motivated by racetrack inflation in the context of the Type IIB string theory. In this model, the conformal invariance of the hypercharge electromagnetic fields is broken thanks to the coupling of both the scalar and pseudoscalar fields to the hypercharge electromagnetic fields. The following three cosmological observable quantities are first evaluated: The current magnetic field strength on the Hubble horizon scale, which is much smaller than the upper limit from the back reaction problem, the local non-Gaussianity of the curvature perturbations due to the existence of the massive gauge fields, and the tensor-to-scalar ratio. It is explicitly demonstrated that the resultant values of the local non-Gaussianity and the tensor-to-scalar ratio are consistent with the Planck data.

Bamba, Kazuharu

2014-01-01

255

International Nuclear Information System (INIS)

The self generated magnetic field of megagauss order is reported to play a crucial role in ICF target designs because of its strong influence on the transport of energy from the critical density region to the ablation layer. The inhibition of the thermal flux due to such a field, thus, affects the whole of the other phenomenon of ICF. The knowledge of the proper variation of the magnetic field may help in assigning the existing controversial value of flux limit, f. Many papers dealing with the spatial variation of such a field exist and are well documented but the study on the variation of self generated field with time is rare. Here, the spatial variation of the megagauss field generated in the corona of a wire target irradiated by a laser as well as a model to study the temporal nature of the B-field at the peak have been obtained by solving the self inhibited diffusion which is regarded as the most dominant mechanism by which the thermal transport is influenced. The field exists for about ten nanoseconds even after the laser is switched off. The ratio of the two components of the thermal conductivity is also plotted against time and shows the inhibition. So, a track on the B-field variation both in space and time is necessary to keep for at least a few nanoseconds for computation of f. (author). 19 refs, 4 figs

256

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

257

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

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

2007-01-01

258

Generation of the sheared radial electric field by a magnetic island structure

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of the presence of a magnetic island structure on the am bipolar radial electric field is studied in the context of the belt island model. It is shown that the sheared radial electric field region exists on the island position. Depending on the model parameters, the single (ion root) or multiple (one ion and two electron roots) solutions for the radial electric field are obtained at different radial positions. The radially non-local treatment is developed proposing the steady-state...

Man?i? Ana; Maluckov Aleksandra; Masayoshi Yokoyama; Masao Okamoto

2004-01-01

259

International Nuclear Information System (INIS)

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

260

International Nuclear Information System (INIS)

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

261

Generation of the sheared radial electric field by a magnetic island structure

Directory of Open Access Journals (Sweden)

Full Text Available The effect of the presence of a magnetic island structure on the am bipolar radial electric field is studied in the context of the belt island model. It is shown that the sheared radial electric field region exists on the island position. Depending on the model parameters, the single (ion root or multiple (one ion and two electron roots solutions for the radial electric field are obtained at different radial positions. The radially non-local treatment is developed proposing the steady-state plasma conditions. The numerical calculations show that the diffusion of the radial electric field is significant only near the island boundaries. As a result the discontinuities in the am bipolar electric field profile are smoothed.

Man?i? Ana

2004-01-01

262

Super ferromagnetic field generation device

International Nuclear Information System (INIS)

In a super ferromagnetic field generation device, initial magnetic fields are generated and highly electroconductive liquid metals are atomized into spray-like fluidized particles and jetted in the initial magnetic fields for freezing magnetic fluxes. The frozen spray-like fluidized particles are shrinked by optical pressure of pulse laser beams and explosive shrinkage caused by molten plasma on the surface of the particles upon laser irradiation. Further, the device comprises a liquid metal containing vessel, a blanket as a ferromagnetic field generation vessel, superconductive magnets, a nozzle for jetting the liquid metals as spray-like fluidized particles in the blacket and a pair of laser beam sources for irradiating pulsed laser beams to the fluidized particles which freeze the magnetic fluxes. Then, super ferromagnetic fields of several 105 teslas to several 1010 teslas can be obtained as continuous pulses. (N.H.)

263

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 numberRec 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."

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

2014-10-01

264

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

265

Effect of the magnetic field curvature on the generation of zonal flows by drift-Alfven waves

International Nuclear Information System (INIS)

One makes studies into the generation of the zonal flows by the drift-Alfven waves modified by the magnetic field curvature effects. The mentioned effects are simulated by the gravity. The equations of vorticity, of the Ohm's longitudinal law, of the continuity relating the electrostatic potential, the vector potential and the disturbed density are used as the source plasma-and-dynamic equations. The mentioned equations are analyzed in the parametric formalism terms. One has revealed a new class of the instabilities of the zonal flows being the analog of the linear theory two-beam instabilities. One points out that the zonal flows may be generated both in case of the magnetic hill and in case of the magnetic well. In the first case, the instabilities of the zonal flows are similar to the linear theory negative mass type instabilities, while in the second case - to the two-beam instabilities

266

International Nuclear Information System (INIS)

The efficiency of laser overdense plasma coupling via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed over a wide range of laser pulse intensity from 1015 to 1020 W cm-2?m2 with electron density ranging from 25 to 100nc to describe the laser interaction with a grating target where a surface plasma wave excitation condition is fulfilled. The numerical studies confirm an efficient coupling with an enhancement of the laser absorption up to 75%. The simulations also show the presence of a localized, quasi-static magnetic field at the plasma surface. Two interaction regimes are identified for low (I?2 17 W cm-2?m2) and high (I?2 > 1017 W cm-2?m2) laser pulse intensities. At ''relativistic'' laser intensity, steady magnetic fields as high as ?580 MG ?m/?0 at 7 x 1019 W cm-2?m2 are obtained in the simulations.

267

Directory of Open Access Journals (Sweden)

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

Ammar Ben Brahim

2011-11-01

268

International Nuclear Information System (INIS)

It is conceivable that the periodic reversal of the Sun's large-scale magnetic field and the concentration of the field in strong thin flux tubes on small scales could both result from the following likely processes near the base of the convection zone. It is likely that in a base layer of thickness 105 km near the base of the convection zone a small part (approximately 0.4 percent) of the energy flux from below goes into an azimuthal magnetoaccoustic oscillation and once in approximately 11y or so such an oscillation reaches a critical amplitude approximately 104 (cm s-1) when it undergoes a 'shock transition' to a cellular (azimuthal) convective mode. The shock transition will involve creation of electric current sheaths and magnetic flux sheaths of field intensity approximately 104G and thickness approximately 102 km each near the 'nodal' meridian planes. The electric current sheaths would provide the 'reversed' magnetic field on one side and the magnetic flux sheaths would eventually degenerate into 'clusters' of thousands of flux tubes of fluxes 1018Mx each. (author)

269

International Nuclear Information System (INIS)

The Weibel instability is an electromagnetic instability that can generate a quasi-static magnetic field in the wake of an ultra-intense, ultra-short laser pulse propagating in an underdense plasma. Recently, attention has been paid to this instability also in the overdense plasma regime where current filaments are observed in large scale PIC numerical simulations. Here we study the evolution of the Weibel instability in the 3D fluid, relativistic, collisionless limit in the case of two initially counterstreaming electron beams. The aim is to understand the typical magnetic structures that can be expected to form as a consequence of the development of the Weibel instability. (Author)

270

An expression is obtained which relates the maximum magnitude of a quasi-stationary magnetic field generated during the resonance interaction between electromagnetic radiation and a plasma to the intensity of incident radiation, with allowance made for the striction deformation of the plasma density profile. For the cases of weak and strong deformation, analytical estimates of this relationship are obtained and verified by computer calculations.

Kochetov, A. V.; Litvak, A. G.; Feigin, A. M.; Khimich, A. V.

1986-07-01

271

Pulsed Magnetic Field Induced Fast Drug Release from Magneto Liposomes via Ultrasound Generation.

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

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

2014-10-01

272

International Nuclear Information System (INIS)

An analytical fluid model is proposed for artificially collimating fast electron beams produced in the interaction of ultraintense laser pulses with specially engineered low-density-core-high-density-cladding structure targets. Since this theory clearly predicts the characteristics of the spontaneously generated magnetic field and its dependence on the plasma parameters of the targets transporting fast electrons, it is of substantial relevance to the target design for fast ignition. The theory also reveals that the rapid changing of the flow velocity of the background electrons in a transverse direction (perpendicular to the flow velocity) caused by the density jump dominates the generation of a spontaneous interface magnetic field for these kinds of targets. It is found that the spontaneously generated magnetic field reaches as high as 100 MG, which is large enough to collimate fast electron transport in overdense plasmas. This theory is also supported by numerical simulations performed using a two-dimensional particle-in-cell code. It is found that the simulation results agree well with the theoretical analysis.

273

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

274

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha, Eckert number (Ec, Prandtl number (Pr, Joule heating parameter (R and the free stream temperature parameter (ÃŽÂ¸Ã¢ÂˆÂž 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 ÃŽÂ¸Ã¢ÂˆÂž=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation.

Moh'd A. Al-Nimr

2004-06-01

275

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

International Nuclear Information System (INIS)

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

276

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

International Nuclear Information System (INIS)

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

277

Generation of ultrasonic waves by ac magnetic fields in the mixed state of high-Tc superconductors

International Nuclear Information System (INIS)

We discuss the interaction of a vortex array in a superconductor with sound oscillations, taking into account pinning forces between vortices and crystal displacements. The generation of ultrasound by an ac electromagnetic field acting on the vortex array is considered. We find that at low temperatures and in the linear regime the amplitude of the induced sound wave is proportional to the applied dc magnetic field and independent of pinning strength. We show how the subsequent multiple echo amplitudes allow one to obtain information on the Magnus force and viscosity of the vortex array

278

Effects of metallurgical microstructure of armatures on compressed magnetic field generators

International Nuclear Information System (INIS)

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

279

Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability

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

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

2007-01-01

280

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

VU Bioengineering RET Program, School of Engineering,

281

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

International Nuclear Information System (INIS)

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

282

Resonant magnetic fields from inflation

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the ...

Byrnes, Christian T.; Hollenstein, Lukas; Jain, Rajeev Kumar; Urban, Federico R.

2011-01-01

283

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.

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

2014-03-01

284

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-12-15

285

Visualizing Magnetic Field Lines

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

VU Bioengineering RET Program, School of Engineering,

286

International Nuclear Information System (INIS)

The results of high power ion beam (HPIB) generation and plasma formation processes in the magnetically insulated diode (MID) installed at 3.1010W nanosecond accelerator are given. The possibility of efficient HPIB ballistic focusing using the preformed plasma in the HPIB transport region is demonstrated. Several new diagnostics (spring pendulum and acoustic probe) were used to measure the plasma ablation pressure during the impact of the HPIB with the target. The plasma formation and its behavior in the diode gap were studied by high voltage probe, array of collimated Faradey cups, streak image converter. The dominant role in the MID impedance behavior played the electron losses at the anode. The application of the active plasma source provided the control on the HPIB characteristics and MID impedance behavior

287

Resonant magnetic fields from inflation

International Nuclear Information System (INIS)

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

288

The CHAMP satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes (<350 km) at solar minimum conditions. Using the latest 4 years (2004-2007) of readings from the CHAMP fluxgate magnetometer, including an improved scalar data product, we have estimated the lithospheric magnetic field to spherical harmonic degree 120, corresponding to 333 km wavelength resolution. The data were found to be sensitive to crustal field variations up to degree 150 (down to 266 km wavelength), but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120. This new MF6 model is the first satellite-based magnetic model to resolve the direction of oceanic magnetic lineations, revealing the age structure of oceanic crust.

Maus, S.; Yin, F.; Lühr, H.; Manoj, C.; Rother, M.; Rauberg, J.; Michaelis, I.; Stolle, C.; Müller, R. D.

2008-07-01

289

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

International Nuclear Information System (INIS)

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

290

Steady-state electric fields and post-lightning quasi-electrostatic fields generated in different atmospheric regions above thunderstorms play an important role as drivers of a diversity of processes and events caused by electron heating in the middle atmosphere. Such are some of the transient luminous events: red sprites, halos, blue jets, etc. Recent investigations of these electric fields and related phenomena allowed better understanding of the electrical coupling of atmospheric regions and showed their importance. Nevertheless, little is done to study the problem whether the electric fields by a thunderstorm can penetrate into its magnetically conjugated region, and what effects can they cause there. Some observations in the mesosphere could be explained as such effects, as indicated in some papers. For example, these are the large (1 V/m and more) quasi-electrostatic fields which have been observed at mesospheric altitudes for decades. Also, red sprites with no causative thunderstorm were observed and were explained by some authors as a result of lightning occurring in the conjugated region. We propose a 2D numerical model for the generation of quasi-static electric fields due to thunderstorms with lightning discharges in the magnetically conjugated region. The model is based on the Maxwell's equations for quasi-static conditions, which take place in the mesosphere and at higher altitudes above a thunderstorm. Our first results show that in the mesosphere these fields can be as large as few tenths of V/m, but in specific cases they can be even significantly larger.

Velinov, Peter; Tonev, Peter

291

The differential rotation induced by the r-mode instability can generate very strong toroidal fields in the core of accreting, millisecond spinning neutron stars. We introduce explicitly the magnetic damping term in the evolution equations of the r-modes and solve them numerically, to follow the development and growth of the internal magnetic field. We show that the strength of the latter can reach large values, $\\sim 10^{14}$ G, in the core of the fastest accreting neutron stars. This is strong enough to induce a significant quadrupole moment of the neutron star mass distribution, corresponding to an ellipticity $\\epsilon_{B} \\sim 10^{-8}$. If the symmetry axis of the induced magnetic field is not aligned with the spin axis, the neutron star radiates gravitational waves. We suggest that this mechanism may explain the upper limit of the spin frequencies observed in accreting neutron stars in Low Mass X-Ray Binaries. In the end we discuss the relevance of our results for the search of gravitational waves.

Cuofano, Carmine; Drago, Alessandro; Stella, Luigi

2012-01-01

292

Energy Technology Data Exchange (ETDEWEB)

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.

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

293

Directory of Open Access Journals (Sweden)

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.

Joshi A.S.

2013-11-01

294

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

295

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

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

2012-11-01

296

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

International Nuclear Information System (INIS)

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

297

Magnetic Propeller for Uniform Magnetic Field Levitation

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.

Krinker, Mark

2008-01-01

298

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Edda Lína Gunnarsdóttir 1988

2012-01-01

299

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.

300

A relativistic short laser pulse is modeled having amplitude modulation in time and Gaussian profile of intensity distribution transverse to the direction of laser propagation. The relativistic laser exerts a ponderomotive force on the electrons imparting them an oscillatory velocity. When the plasma has a density gradient perpendicular to this ponderomotive force, a quasistatic magnetic field is produced. The magnetic field lasts for duration of the laser pulse. At plasma resonance (?p approx ?/2), the magnetic field is enhanced significantly.

Kumar, Asheel

2005-01-01

301

Miniature linear permanent magnet generators

International Nuclear Information System (INIS)

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

302

Well-posedness of some initial-boundary-value problems for dynamo-generated poloidal magnetic fields

Given a bounded domain $G \\subset \\R^d$, $d\\geq 3$, we study smooth solutions of a linear parabolic equation with non-constant coefficients in $G$, which at the boundary have to $C^1$-match with some harmonic function in $\\R^d \\setminus \\ov{G}$ vanishing at spatial infinity. This problem arises in the framework of magnetohydrodynamics if certain dynamo-generated magnetic fields are considered: For example, in the case of axisymmetry or for non-radial flow fields, the poloidal scalar of the magnetic field solves the above problem. We first investigate the Poisson problem in $G$ with the above described boundary condition as well as the associated eigenvalue problem and prove the existence of smooth solutions. As a by-product we obtain the completeness of the well-known poloidal "free decay modes" in $\\R^3$ if $G$ is a ball. Smooth solutions of the evolution problem are then obtained by Galerkin approximation based on these eigenfunctions.

Kaiser, Ralf

2012-01-01

303

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

Vu Bioengineering Ret Program

304

Magnetism—the force that deflects the needle of a compass—and magnetic fields have been found in some hundreds of stars during the past 50 yr. Magnetic fields have been detected in T Tauri stars and other pre-main-sequence stars, several types of main sequence stars, white dwarfs and neutron stars. We now know a number of methods by which such magnetic fields may be detected, we are in the proces...

Landstreet, J.; Murdin, P.

2000-11-01

305

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

306

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.

Christian, Wolfgang; Belloni, Mario

2007-03-03

307

Directory of Open Access Journals (Sweden)

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

F. Bocchio

1997-06-01

308

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

Howard, R.

1972-01-01

309

Simulation Outside Magnetic Field of the Sun

Directory of Open Access Journals (Sweden)

Full Text Available We derive the viscous current in the fully ionized two-fluid plasma to generate the solar magnetic field. The global magnetic field of the Sun can be simulated by the viscous current from the differential rotation inside the Sun. The field presents a structure with 6-polar. As the viscous current is very weak, the magnetic field intensity is only about G, which could be considered as the background field of the Sun. The theory is a start for the generation of solar magnetic field. The local strong magnetic field of the Sun is not considered in the paper.

Zhiliang Yang

2011-06-01

310

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%.

Ling, Junpu; He, Juntao; Zhang, Jiande; Jiang, Tao; Hu, Yi

2014-09-01

311

Magnetic Fields from Phase Transitions

The generation of primordial magnetic fields from cosmological phase transitions is discussed, paying particular attention to the electroweak transition and to the various definitions of the `average' field that have been put forward. It is emphasised that only the volume average has dynamical significance as a seed for galactic dynamos. On rather general grounds of causality and energy conservation, it is shown that, in the absence of MHD effects that transfer power in the magnetic field from small to large scales, processes occurring at the electroweak transition cannot generate fields stronger than $10^{-20}$ Gauss on a scale of 0.5 Mpc. However, it is implausible that this upper bound could ever be reached, as it would require all the energy in the Universe to be turned into a magnetic field coherent at the horizon scale. Non-linear MHD effects seem therefore to be necessary if the electroweak transition is to create a primordial seed field.

Hindmarsh, M B; Hindmarsh, Mark; Everett, Allen

1998-01-01

312

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.

313

International Nuclear Information System (INIS)

The understanding of low to high (L-H) transition in tokamaks has been an important area of investigation for more than a decade. Recent 3D finite ? simulations of drift-resistive ballooning modes in a flux tube geometry by Rogers et al.[Phys.Rev.Lett.81, 4396 (1998)] have provided a unique parametrization of the transition in a two-dimensional phase space. Comparison of the threshold curve in this phase space with data from ASDEX and C-MOD has shown very good agreement. In this Letter we provide a simple theory, based on the generation of zonal flow and zonal magnetic field in a finite-beta plasma, which explains this threshold curve for L-H transition in tokamaks

314

Neutral atoms may be trapped via the interaction of their magnetic dipole moment with magnetic field gradients. One of the possible schemes is the cloverleaf trap. It is often desirable to have at hand a fast and precise technique for measuring the magnetic field distribution. We introduce a novel diagnostic tool for instantaneous imaging the equipotential lines of a magnetic field within a region of space (the vacuum recipient) that is not accessible to massive probes. Our technique is based on spatially resolved observation of the fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of resonant laser light within the magnetic field region to be investigated. The inhomogeneous magnetic field spatially modulates the resonance condition between the Zeeman-shifted hyperfine sublevels and the laser light and therefore the amount of scattered photons. We demonstrate this technique by mapping the field of our cloverleaf trap in three dimensions under various conditions.

Courteille, P W; Magalhães, K; Kaiser, R; Marcassa, L G; Bagnato, V S; Courteille, Ph. W.

2001-01-01

315

International Nuclear Information System (INIS)

The effects of cutoff of plasma current on the performance of superconducting toroidal field windings in tokamaks is studied from a theoretical viewpoint. Electromagnetic energy losses and power are calculated in various components of the superconducting toroidal field windings during plasma current cutoff. Heating of the superconducting lead of the superconducting toroidal field windings is calculated during cutoff of plasma current as a function of various structural parameters of the superconducting windings

316

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Enqvist, Kari

1998-01-01

317

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)

318

Generation of zonal flows and large-scale magnetic fields by drift Alfven turbulence

International Nuclear Information System (INIS)

One studied possibility of generation of zonal flows by drift Alfven turbulence in final pressure plasma. One derived system of associated equations covering equation for spectral function of turbulence and averaged equations for zonal disturbances. It is shown that in special cases equation for spectral function has action invariants. One determined two types of instabilities of zonal disturbances. First type instability results in generation of zonal flow only. Another type instability occurs when accounting for resonance interaction of drift Alfven waves with electrons

319

We discuss the evolution of cosmological magnetic fields from the early universe to the present. We review different scenarios for magnetogenesis in the early universe and follow the subsequent evolution of these fields as the universe recombines. We then focus on the role primordial fields play after recombination in the seeding of stellar and galactic fields and the formation of structure. Cosmological magnetic fields in the intergalactic medium trace the turbulent history of the universe and may contain fossils of the early universe. We conclude by discussing observational probes of cosmological magnetic fields including the study of extragalactic cosmic rays.

Olinto, A V

1998-01-01

320

Spontaneous magnetic fields in spherical laser targets

International Nuclear Information System (INIS)

Results of theoretical investigation into generation effect of spontaneous magnetic fields as applied to laser target contraction under conditions of ''contractile'' shell are presented. Two approaches were used: a) qualitative description of a problem construction of simple physical models; b) numerical solution of equations of two-dimensional gas dynamics together with equation of generation of spontaneous magnetic fields. Results of investigation of magnetic field generation in corona of laser targets, fields generated due to development of the Rayleigh-Taylor instability; fields conditioned with appearance of crossed density and temperature gradients during target contraction are given. Experimental methods for investigating spontaneous magnetic fields in laser plasma are described in short. It is shown that in contractile targets 10MGs magnetic fields are generated at absorbed laser energy of up to 10 kJ and up to 100 MGs at absorbed energy above 100 kJ. In this case fields will significantly affect energy transfer with charged particles

321

Field free line magnetic particle imaging

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

Erbe, Marlitt

2014-01-01

322

Wakefield generation in magnetized plasmas.

We consider wakefield generation in plasmas by electromagnetic pulses propagating perpendicular to a strong magnetic field, in the regime where the electron cyclotron frequency is equal to or larger than the plasma frequency. Particle-in-cell simulations reveal that for moderate magnetic field strengths previous results are reproduced, and the wakefield wave number spectrum has a clear peak at the inverse skin depth. However, when the cyclotron frequency is significantly larger than the plasma frequency, the wakefield spectrum becomes broadband, and simultaneously the loss rate of the driving pulse is much enhanced. A set of equations for the scalar and vector potentials reproducing these results are derived, using only the assumption of a weakly nonlinear interaction. PMID:22060515

Holkundkar, Amol; Brodin, Gert; Marklund, Mattias

2011-09-01

323

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

324

Magnetic field line Hamiltonian

Energy Technology Data Exchange (ETDEWEB)

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.

Boozer, A.H.

1984-03-01

325

Generation of compression jumps in non-equilibrium plasma flux at interaction with magnetic field

International Nuclear Information System (INIS)

One studied a flow in a linearly expansible perfectly sectioned shorted MHD channel. One classified MHD flows based on the principle of continuous flows-flows with MHD deceleration jumps in ionization-homogeneous and ionization-inhomogeneous plasma. One revealed peculiarities of generation and position of a stationary deceleration jumps depending on the Stuart parameter. MHD deceleration jump in ionization-inhomogeneous plasma was found to occur at lower values of the MHD interaction parameter in contrast to that in homogeneous plasma. One revealed non-identified type of instability occurring at gas and dynamic gaps

326

There is increasing interest in the role played by pseudo Nambu-Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the produced fields are maximally helical, inverse cascade processes in the primordial plasma increase significantly their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the observed cosmological magnetic fields. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.

Anber, M M; Anber, Mohamed M.; Sorbo, Lorenzo

2007-01-01

327

Stability of Magnetic Fluids in Magnetic Fields

Directory of Open Access Journals (Sweden)

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

I.M. Arefyev

2014-07-01

328

The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyagers 1 and 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that most of the magnetic energy is released and most of this energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The energy gain of the most energetic ions results from their reflection from the ends of contracting magnetic islands, a first order Fermi process. The energy gain of the ions in contracting islands increases their parallel (to the magnetic field ${\\bf B}$) pressure $p_\\parallel$ until the marginal firehose condi...

Drake, J F; Swisdak, M; Chamoun, J N

2009-01-01

329

Axial magnetic field lens with permanent magnet

International Nuclear Information System (INIS)

A compact Permanent Magnet Symmetric (PMS) lens which produces the axial magnetic field is studied. The proposed lens has no iron pole piece except for the return poles on both ends. It can produce the magnetic field on the axis more than the remanent field of the magnet material by the perpendicular field superimposition

330

Interplanetary Magnetic Field Lines

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

Stern, David

2005-04-27

331

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

Golebiowski, J.; Milcarz, Sz

2014-04-01

332

Cosmological magnetic field survival

Digital Repository Infrastructure Vision for European Research (DRIVER)

It is widely believed that primordial magnetic fields are dramatically diluted by the expansion of the universe. As a result, cosmological magnetic fields with residual strengths of astrophysical relevance are generally sought by going outside standard cosmology, or by extending conventional electromagnetic theory. Nevertheless, the survival of strong B-fields of primordial origin is possible in spatially open Friedmann universes without changing conventional electromagnetis...

Barrow, John D.; Tsagas, Christos G.

2011-01-01

333

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 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

334

Magnetic-field effects on the decay kinetics of chain-linked triradicals have been investigated in acetonitrile at 293 K. The decay rate of the triradical linked by an 8-methylene chain was 1×10 7 s -1 under zero field and decreased with increasing field to attain a constant value of 2×10 6 s -1 at 2-10 T. These values were one order larger than those of the corresponding ketyl-diphenylmethyl biradical.

Mori, Yukie; Sakaguchi, Yoshio; Hayashi, Hisaharu

1999-02-01

335

There exists a substantial disagreement between computer simulation results and high-energy density laboratory experiments of the Rayleigh-Taylor instability [1]. Motivated by the observed discrepancies in morphology and growth rates, we attempt to bring simulations and experiments into better agreement by extending the classic purely hydrodynamic model to include self-generation of magnetic fields and anisotropic thermal conduction.

Modica, Frank; Plewa, Tomasz; Zhiglo, Andrey

2013-12-01

336

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

Modica, Frank; Zhiglo, Andrey

2013-01-01

337

Passive Magnetic Shielding in Gradient Fields

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

Bidinosti, C P

2013-01-01

338

The basis is laid out for a theory relating various phenomena in the solar atmosphere, including localized concentrations of magnetic field at the bases of coronal magnetic arches, chromospheric spicules, twisted coronal magnetic flux tubes, and flows of energy carried by Alfvén waves propagating upward into the corona. The structure of photospheric currents localized in the vicinity of supergranule boundaries and excited by convective motions is studied. These currents exist primarily in a "dynamo layer" of sharply enhanced transverse conductivity, which forms in the weakly ionized thermal photospheric plasma located in the solar gravitational field. The motions of the electrons and ions in this layer have appreciably different characters: the ions are collisionly driven by the flows of neutral atoms, while the electrons drift in the crossed electric and magnetic fields. The electric field supporting the current arises due to the polarization of the electrons and ions. This field also gives rise to Alfvén perturbations that propagate upward into the corona, together with their associated longitudinal currents. The character of this "loading" makes the system of fields and currents uniquely defined. Moreover, the momentum flux carried by these Alfvén waves should be transferred to the cool chromospheric gas, facilitating the vertical ejection of this gas in the form of spicules, as was first proposed in 1992 by Haerendel.

Kropotkin, A. P.

2011-12-01

339

Using a multi-fluid approach, we investigate streaming and thermal instabilities of the electron-ion plasma with homogeneous cold cosmic rays propagating perpendicular to the background magnetic field. Perturbations are considered to be also across the magnetic field. The back-reaction of cosmic rays resulting in strong streaming instabilities is taken into account. It is shown that for sufficiently short wavelength perturbations, the growth rates can exceed the growth rate of cosmic-ray streaming instability along the magnetic field found by Nekrasov & Shadmehri (2012), which is in its turn considerably larger than the growth rate of the Bell instability (2004). The thermal instability is shown not to be subject to the action of cosmic rays in the model under consideration. The dispersion relation for the thermal instability has been derived which includes sound velocities of plasma and cosmic rays, Alfv\\'{e}n and cosmic-ray streaming velocities. The relation between these parameters determines the kind ...

Nekrasov, Anatoly K

2014-01-01

340

Magnet Free Generators - 3rd Generation Wind Turbine Generators

DEFF Research Database (Denmark)

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.

Jensen, Bogi Bech; Mijatovic, Nenad

2013-01-01

341

Energy Technology Data Exchange (ETDEWEB)

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

Caprini, Chiara; Servant, Géraldine [CEA, IPhT and CNRS, URA 2306, F-91191 Gif-sur-Yvette (France); Durrer, Ruth, E-mail: chiara.caprini@cea.fr, E-mail: ruth.durrer@unige.ch, E-mail: geraldine.servant@cern.ch [Département de Physique Théorique, Université de Genève, 24 Quai E. Ansermet, CH-1211 Genève (Switzerland)

2009-12-01

342

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.

Park, Jaehong; Ren, Chuang; Blackman, Eric G.; Kong, Xianglong

2010-02-01

343

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.

344

International Nuclear Information System (INIS)

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

345

Magnetic fields of Sun-like stars

Magnetic fields play an important role at all stages of stellar evolution. In Sun-like stars, they are generated in the outer convective layers. Studying the large-scale magnetic fields of these stars enlightens our understanding of the field properties and gives us observational constraints for the field generation models. In this review, I summarise the current observational picture of the large-scale magnetic fields of Sun-like stars, in particular solar-twins and planet-host stars. I discuss the observations of large-scale magnetic cycles, and compare these cycles to the solar cycle.

Fares, R

2013-01-01

346

Magnetic field dosimeter development

International Nuclear Information System (INIS)

In recent years there has been increased concern over potential health hazards related to exposure of personnel to magnetic fields. If exposure standards are to be established, then a means for measuring magnetic field dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation

347

Magnetic field induced superconductivity

International Nuclear Information System (INIS)

The electrical resistance R and magnetic susceptibility chi of the pressure induced superconductors Sn/sub x/Eu/sub 1.2-x/Mo6S8 have been investigated as a function of magnetic field H up to 17 T and at pressures up to 18 kbar. Anomalous behavior is observed both in R versus H and chi versus H. The resistive behavior at p = 14 kbar at low temperatures is consistent with field enhanced superconductivity resulting from a large exchange field that compensates the applied field

348

The problem of the excitation of quasi-stationary electromagnetic fields by a moving magnetic dipole is solved within the framework of the kinetic equation for collisionless plasma using methods of the linear theory of particle emission. A multipole representation is obtained for fields at small and large distances from the dipole. The quasi-stationary electromagnetic fields excited by a dipole are pressed against the dipole, plasma currents shield the dipole field, and an anomalous skin region with a characteristic scale is formed.

Gubchenko, V. M.

1988-03-01

349

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

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

2006-01-01

350

A laboratory experiment on modeling the magnetospheric generator of the field-aligned currents and the Earth's transpolar potential in the absence of IMF is illustrated. The measurements of the total field-aligned current in the generator shorted mode and the transpolar potential in the circuit disconnection mode made it possible to determine the generator internal resistance. A model that explains the saturation current and internal resistance by the feedback between the field-aligned current and plasma flank motions has been proposed. This feedback is described through the effective resistance, which is proportional to the flow rate and the ratio of the boundary layer to the dimension of the magnetosphere. For the experimental conditions, the calculated generator resistance was in good agreement with the measured value. The estimates for the Earth's magnetosphere indicate that the MHD generator internal resistance in the boundary layer is usually much lower than the reverse integral conductivity of the ionosphere.

Shaikhislamov, I. F.; Antonov, V. M.; Zakharov, Yu. P.; Boyarintsev, E. L.; Melekhov, A. V.; Posukh, V. G.; Ponomarenko, A. G.

2014-07-01

351

On the influence of the plasma generated by comet Shoemaker-Levy 9 on Jupiter`s magnetic field

Energy Technology Data Exchange (ETDEWEB)

The impact of comet Shoemaker-Levy 9 with Jupiter has created a variety of magnetospheric plasmas which were detected by their electromagnetic emissions. By means of the Dessler-Parker-Sckopke relation we estimate the perturbation of Jupiter`s magnetic field. It appears that the produced plasma may explain the observed decrease of UV lines in Io`s torus.

Stabile, F.; Zimbardo, G. [Arcavacata di Rende, Cosenza, Univ. della Calabria (Italy). Dipt. di Fisica

1997-11-01

352

International Nuclear Information System (INIS)

.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 ?T respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer

353

International Nuclear Information System (INIS)

The effect of a magnetic field on the photocurrent generated by a bulk heterojunction solar cell made from poly-3-hexylthiophene (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is investigated. At the operating voltage, increases in photocurrent of ?9% can be obtained at magnetic fields of less than 100 mT. This increase in photocurrent is attributed to an increase in the rate of intersystem crossing, between the singlet and triplet states, leading to a higher net efficiency of exciton dissociation. Close to the open-circuit voltage, an increase of more than two orders of magnitude in the photocurrent could be obtained under applied magnetic field. (fast track communication)

354

Magnetic Field Problem: Current

A cross section of a circular wire loop carrying an unknown current is shown above. 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 can double-click in the animation to add magnetic field lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.

Christian, Wolfgang; Belloni, Mario

2007-03-03

355

Permanent magnet edge-field quadrupole

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

356

Eruptive solar magnetic fields

International Nuclear Information System (INIS)

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

357

Indoor localization using magnetic fields

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

Pathapati Subbu, Kalyan Sasidhar

358

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

359

Effect of the magnetic field curvature on the generation of zonal flows by drift-Alfven waves

International Nuclear Information System (INIS)

The generation of zonal flows by drift-Alfven waves is studied with allowance for magnetic curvature effects. The basic plasmadynamic equations relating the electrostatic potential, vector potential, and perturbed plasma density are the vorticity equation, longitudinal Ohm's law, and continuity equation. The basic equations are analyzed by applying a parametric formalism similar to that used in the theory of the generation of convective cells. In contrast to most previous investigations on the subject, consideration is given to primary modes having an arbitrary spectrum rather than to an individual monochromatic wave packet. The parametric approach so modified makes it possible to reveal a new class of instabilities of zonal flows that are analogous to two-stream instabilities in linear theory. It is shown that, in the standard theory of zonal flows, the zonal components of the vector potential and perturbed density are not excited. It is pointed out that zonal flows can be generated both in the case of a magnetic hill and in the case of a magnetic well. In the first case, the instabilities of zonal flows are analogous to negative-mass instabilities in linear theory, and, in the second case, they are analogous to two-stream instabilities

360

Distributed generation induction and permanent magnet generators

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

Lai, Loi Lei

2008-01-01

361

International Nuclear Information System (INIS)

A simple formulation for calculating the magnetic field external to an extended nonpermeable conducting body due to thermal current fluctuations within the body is developed, and is applied to a recent experimental search for the atomic electric-dipole moment (EDM) of 199Hg. It is shown that the thermal fluctuation field is only slightly smaller in magnitude than other noise sources in that experiment. The formulation is extended to permeable bodies, and the implications for general EDM experiments are discussed. copyright 1999 The American Physical Society

362

Magnetic Field from Loops Model

The EJSMagnetic Field from Loops model computes the B-field created by an electric current through a straight wire, a closed loop, and a solenoid. Users can adjust the vertical position of the slice through the 3D field. The Magnetic Field from Loops model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ntnu_MagneticFielfFromLoops.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Hwang, Fu-Kwun

2008-11-17

363

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 these 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. (authors)

364

Energy Technology Data Exchange (ETDEWEB)

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 these 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. (authors)

Romagnania, L.; Borghesia, M.; Cecchettia, C.A.; Kara, S.; Wilsona, P.A. [School of Mathematics and Physics, The Queen' s University of Belfast, Belfast (United Kingdom); Antici, P.; Audebert, P.; Fuchs, J. [Laboratoire pour l' Utilisation des Lasers Intenses (LULI), UMR 7605 CNRS-CEA-Ecole Polytechnique-University, 91 - Palaiseau (France); Bandhoupadjay, S.; Heathcote, R.; Neely, D.; Notley, M. [Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Didcot (United Kingdom); Ceccherini, F.; Liseykin, T.V.; Macchi, A. [Dipartimento di Fisica -E. Fermi, Universita di Pisa, Pisa (Italy); Cowan, T. [Physics Department, MS-220, University of Nevada, Reno Nevada (United States); Galimberti, M.; Gizzi, L.A. [Intense Laser Irradiation Laboratory, IPCF-CNR, Pisa (Italy); Grismayer, T.; Mora, P. [Centre de Physique Theorique, UMR 7644, CNRS-Ecole Polytechnique, 91 - Palaiseau (France); Schurtz, G. [Centre d' Etudes des Lasers Intenses et Applications, UMR 5107 Universtity of Bordeaux I-CNRS-CEA, 33 (France); Macchi, A. [PolyLAB, CNR-INFM, Pisa (Italy); Jung, R.; Osterholtz, J.; Pipahl, C.A.; Pretzler, G.; Toncian, T.; Willi, O. [Institut fur Laser und Plasma Physik, Heinrich-Heine-Universitat Dusseldorf (Germany); Antici, A.; Schiavi, A. [Dipartimento di Energetica, Universita di Roma, La Sapienza, Roma (Italy)

2008-07-01

365

Chiral near fields generated from plasmonic lattices

Plasmonic fields are usually considered non-chiral because of the transverse magnetic polarization of surface plasmon modes. We however show here that plasmonic lattices built from coherent superpositions of surface plasmons can generate optical chirality in the interfering near field. We reveal in particular the emergence of plasmonic potentials relevant to the generation of near-field chiral forces. This draws promising perspectives for performing enantiomeric separation schemes within the near field.

Canaguier-Durand, Antoine

2014-01-01

366

High field superconducting magnets

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

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

2011-01-01

367

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

Kim, Dae-Hyun; Suh, Tae-Suk; Kang, Young Nam; Yoo, Seung Hoon; Pae, Ki-Hong; Shin, Dongho; Lee, Se Byeong

2013-01-01

368

High magnetic fields science and technology

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

Miura, Noboru

2003-01-01

369

Lattice Planar QED in external magnetic field

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

Cea, P.; Cosmai, L.; Giudice, P.; Papa, A.

370

Lattice Planar QED in external magnetic field

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

Cea, Paolo; Giudice, Pietro; Papa, Alessandro

2011-01-01

371

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization

In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.

Doughty, Frank C. (Plano, TX); Spencer, John E. (Plano, TX)

2000-12-19

372

Nuclear Magnetic Resonance and Magnetic Field Measurements

This laboratory is designed for students to become familiar with the principles and detection techniques of Nuclear Magnetic Resonance (NMR), examine the relationship between current and magnetic field in an electromagnet, and gain experience in the use of magnetic field measurement techniques.

2012-01-04

373

Steady high magnetic field facilities at ASIPP

International Nuclear Information System (INIS)

Steady magnetic fields up to 20 T have been generated at the Institute of Plasma Physics, Academia Sinica (ASIPP), by a hybrid magnet consisting of an outer NbTi superconducting coil and an inner water-cooled Bitter coil in support of the research in high magnetic fields. This hybrid magnet with the other laboratory magnets, i.e. the water-cooled magnets with fields up to 14 T and the superconducting magnets capable of producing 8.0 T in different bores have been opened to the scientific community since 1992 and extensive studies on high Tc superconductors, semi-conductors, magnetic materials low-dimensional organic conductors as well as the chemical and biological effects of the high magnetic fields etc. have been conducted. To cope with the increasing demand for high fields and more magnet time, the 20 T hybrid magnet is ready to upgrade to 23 T. Based on the use of 40 MW fly-wheel generator power a future plan for constructing a 45T, 2 s flat-top quasisteady magnet has been proposed for creating new scientific opportunities at higher fields

374

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-06-15

375

Ninth generation international geomagnetic reference field released

The coefficients for the new 9th Generation International Geomagnetic Reference Field (IGRF) were finalized at the XXIII General Assembly of the International Union of Geophysics and Geodesy (IUGG), held in Sapporo, Japan, in July 2003. The IGRF is widely used as a mathematical representation for the Earth's magnetic field in studies of the Earth's deep interior, crust, and ionosphere and magnetosphere. It is the product of a collaborative effort between magnetic field modelers and the institutes involved in collecting and disseminating magnetic field data from observatories and surveys around the world and from satellites.

Macmillan, S.; Maus, S.; Bondar, T.; Chambodut, A.; Golovkov, V.; Holme, R.; Langlais, B.; Lesur, V.; Lowes, F.; Lühr, H.; Mai, W.; Mandea, M.; Olsen, N.; Rother, M.; Sabaka, T.; Thomson, A.; Wardinski, I.

376

On magnetic field ``reconstruction''

Context: Solanki and colleagues have presented intriguing 3D “reconstructions” of magnetic fields from the vector polarimetry of the He I 1083 nm multiplet. Aims: In this Research Note I re-examine the reconstruction technique used. Methods: Using a simple dipole field, I examine the reconstruction technique as applied to the theoretical fields. I assume that the He line forms in two locations, (1) along the magnetic loops and (2) in a horizontal plane. Results: The planar interpretation can account for all aspects of the data, but the loop interpretation has geometrical and physical problems. Conclusions: The data by themselves are not sufficient to determine which picture is more applicable. Nevertheless I argue that the planar interpretation makes more physical sense and that the early reconstructions lead to spurious results. I suggest additional tests that might help constrain the problem further.

Judge, P. G.

2009-01-01

377

We studied the statistical properties of the magnetic fields of OB stars based on the recent measurements. As the statistically significant characteristic of the magnetic field we use the rms magnetic field of the star ${\\cal B}$ . The distribution functions f( ${\\cal B}$ ) of magnetic fields of OB stars are evaluated. The function f( ${\\cal B}$ ) has a power-law dependence on the ${\\cal B}$ with an index of about 2-3 and a fast drop below ${\\cal B}$ = 100 - 300 G. We proposed that the compact regions with strong local magnetic fields can contribute to the global magnetic field of O stars.

Kholtygin, A. F.; Hubrig, S.; Drake, N. A.; Sudnik, N.; Dushin, V.

2014-08-01

378

Magnetic fields in diffuse media

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

Pino, Elisabete; Melioli, Claudio

2015-01-01

379

Magnetic helicity and cosmological magnetic field

Digital Repository Infrastructure Vision for European Research (DRIVER)

The magnetic helicity has paramount significance in nonlinear saturation of galactic dynamo. We argue that the magnetic helicity conservation is violated at the lepton stage in the evolution of early Universe. As a result, a cosmological magnetic field which can be a seed for the galactic dynamo obtains from the beginning a substantial magnetic helicity which has to be taken into account in the magnetic helicity balance at the later stage of galactic dynamo.

Semikoz, V. B.; Sokoloff, D. D.

2004-01-01

380

End fields of CBA superconducting magnets

International Nuclear Information System (INIS)

Measurements of the two dimensional harmonic content of the end fields generated by the Brookhaven CBA dipole and quadrupole superconducting magnets are presented. Both the local longitudinal structure and the integrated end effects are examined

381

Focus on Materials Analysis and Processing in Magnetic Fields

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Yoshio Sakka, Noriyuki Hirota

2009-01-01

382

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)

383

Human provocation studies that investigate the effects of Global System for Mobiles (GSM) communication systems on the brain have focused on Radio Frequency (RF) exposure. We wish to further extend such study by investigating the effect of both RF and Extremely Low Frequency (ELF) field exposure, the latter generated by the GSM handset's battery switching. The use of a commercial handset as an exposure source for such investigations is problematic for a number of reasons and therefore a simulated exposure source, capable of producing both RF and ELF components of exposure, is desirable. As a first step in developing such a source, we have quantified and characterized the ELF field from several commercial handsets (the RF characteristics being already well understood). Through experimental measurement we deduce that these fields can be sufficiently simulated by a 9 mm radius loop residing 10 mm beneath the front surface of the handset device and carrying enough current to generate peak fields of 25 microT at the surface of the handset. PMID:18946983

Perentos, N; Iskra, S; McKenzie, R J; Cosi, I

2008-09-01

384

Nonlinear dynamics of coupled internal-gravity (IG) and alfven electromagnetic planetary waves in the weakly ionized ionospheric E-layer is investigated. Under such coupling new type of alfven waves is revealed. It is shown that such short wavelength turbulence of IG and alfvén waves is unstable with respect to the excitation of low-frequency and large-scale perturbations of the zonal flow and magnetic field. A set of coupled equations describing the nonlinear interaction of coupled IG and alfven waves with zonal flows is derived. The nonlinear mechanism of the instability is driven by the advection of vorticity and is based on the parametric excitation of convective cells by finite-amplitude coupled IG and alfven waves leading to the inverse energy cascade toward the longer wavelength. The growth rates of the corresponding instability and the conditions for driving them are determined. The possibility of generation of the intense mean magnetic field is shown.

Kaladze, Tamaz; Kahlon, Laila

385

International Nuclear Information System (INIS)

The fundamental principles of particle acceleration by magnetic reconnection in cosmic plasmas are reviewed. The history of reconnection models is traced, and consideration is given to the Kelvin-Helmholtz theorem, the frozen-field theorem, the application of the Kelvin-Helmholtz theorem to a collisionless plasma, solutions to specific reconnection problems, and configurational instability. Diagrams and graphs are provided, and the objections raised by critics of the reconnection theory and/or its astrophysical applications are discussed. 42 references

386

International Nuclear Information System (INIS)

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

387

Skewed magnetic field lines reconnection

International Nuclear Information System (INIS)

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

388

International Nuclear Information System (INIS)

The results of high-power ion beam (HPIB) generation and in the magnetically insulated diode (MID) installed on a 3 x 1010-W nanosecond accelerator are given. The possibility of efficient HPIB ballistic focusing with the use of the preformed plasma in the HPIB transport region was demonstrated. Several new diagnostics (spring pendulum and acoustic probe) were used to measure the plasma ablation pressure during the impact of the HPIB with the target. The highest degree of HPIB focusing attained during the experiments with spherical geometries of the diode electrodes was equal to 60. The ablation average pressures measured by the spring pendulum gave several kilobars for 8-10 kA/cm2 of HPIB density. The peak pressure measured by accoustic probes attained tens of kilobars for the same HPIB current amplitudes. (author)

389

The rotation-magnetic field relation

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.

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

2009-02-01

390

The rotation-magnetic field relation

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.

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

2008-01-01

391

Magnetic Field Topology in Jets

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

Gardiner, T. A.; Frank, A.

2000-01-01

392

Measuring the Earth's Magnetic Field in a Laboratory

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…

Cartacci, A.; Straulino, S.

2008-01-01

393

International Nuclear Information System (INIS)

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

394

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-12-10

395

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

Jansson, Ronnie

2012-01-01

396

International Nuclear Information System (INIS)

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

397

Measuring nuclear magnetization in strong magnetic fields

International Nuclear Information System (INIS)

Al nuclear magnetization has been measured in magnetic fields up to 100 kOe, by use of a capacitive Faraday magnetometer installed in a dilution refrigerator. The sample employed was an Al0.98Si0.02 alloy prepared from high purity (6N) elements. The Si doping was essential in suppressing the de Haas-van Alphen oscillations of conduction electrons. Fine Curie's law was observed at temperatures below 3 K down to ?60 mK, in several magnetic fields in the range 30-100 kOe. The measurement opens a new route towards primary thermometry at low temperature and high magnetic field region

398

NMR provides outstanding information in chemistry and in medicine. But the equipment is expensive as high-field magnets are employed. Low-field NMR works with inexpensive permanent magnets. Until recently these did not provide fields sufficiently homogeneous for spectroscopy and were mostly used for relaxation measurements. Relaxation can also be measured outside the magnet, and small mobile NMR devices have been developed for non-destructive testing of large objects. Today small stray-field magnets and small magnets with homogeneous fields are available for relaxation analysis, imaging, and spectroscopy. Their availability is believed to be essential for shifting NMR analysis from a specialist's tool to a convenience tool.

Blümich, Bernhard; Casanova, Federico; Appelt, Stephan

2009-08-01

399

The interaction of ultrafast intense terawatt laser pulses with clusters can create high density plasmas with temperatures much greater than 1 keV. The neutron yield from cigar-shape deuterium fusion plasmas is believed to be limited by the fast expansion time ( 100 T) could limit the radial transport, increasing the fusion time and neutron yield considerably. We present initial tests of the prototype magnetic field generator intended to produce 50 T (upgradeable to 200 T). The device consists of two 100 kV capacitors that can deliver 500 kA through 12 coaxial cables into a conical transmission line. A destructible double coil of 1 cm diameter is connected at the center of the line to create a high magnetic field in a mirror configuration for 1 ?s. We will use a cryogenically cooled gas jet to produce 10 nm deuterium clusters as the laser target. The jet will be irradiated initially by a 20 TW laser beam propagating on the axis of the 200 T magnetic field. The experiment will be conducted later using petawatt-class lasers.

Wisher, M.; Quevedo, H. J.; McCormick, M.; Bengtson, R. D.; Ditmire, T.; Struve, K. W.; Stoltzfus, B. S.; Rovang, D. C.; Savage, M.; Porter, J. L.

2010-11-01

400

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)

401

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

Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

2014-01-01

402

International Nuclear Information System (INIS)

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

403

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-06

404

Extended Magnetization of Superconducting Pellets in Highly Inhomogeneous Magnetic Field

The magnetization of superconducting pellets is a worth point in the development of trapped flux superconducting motors. Experimental and simulated data have been reported extensively according to the framework of one or several pulses of a homogeneous magnetizing field applied to a pellet or a set of pellets. In case of cylindrical rotors of low power motors with radial excitation, however, the use of the copper coils to produce the starting magnetization of the pellets produces a highly inhomogeneous magnetic field which cannot be reduced to a 2D standard model. In this work we present an analysis of the magnetization of the superconducting cylindrical rotor of a small motor by using a commercial FEM program, being the rotor magnetized by the working copper coils of the motor. The aim of the study is a report of the magnetization obtained and theheat generated in the HTSC pellets.

Maynou, R.; López, J.; Granados, X.; Torres, R.; Bosch, R.

405

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

406

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

Katayama, Ryuichi

2014-09-01

407

Comparison of adjustable permanent magnetic field sources

DEFF Research Database (Denmark)

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.

BjØrk, Rasmus; Bahl, Christian Robert Haffenden

2010-01-01

408

Comparison of adjustable permanent magnetic field sources

International Nuclear Information System (INIS)

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.

409

Comparison of adjustable permanent magnetic field sources

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.

Bjørk, R.; Bahl, C. R. H.; Smith, A.; Pryds, N.

2010-11-01

410

Comparison of adjustable permanent magnetic field sources

Energy Technology Data Exchange (ETDEWEB)

Bjork, R., E-mail: rabj@risoe.dtu.d [Fuel Cells and Solid State Chemistry Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark - DTU, Frederiksborgvej 399, DK-4000 Roskilde (Denmark); Bahl, C.R.H.; Smith, A.; Pryds, N. [Fuel Cells and Solid State Chemistry Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark - DTU, Frederiksborgvej 399, DK-4000 Roskilde (Denmark)

2010-11-15

411

Comparison of adjustable permanent magnetic field sources

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 agreement is found.

Bjørk, R; Smith, A; Pryds, N

2014-01-01

412

Magnetic Fields: Visible and Permanent.

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

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

413

The Heliospheric Magnetic Field

Directory of Open Access Journals (Sweden)

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

Mathew J. Owens

2013-11-01

414

Comparison of various shapes of superconducting magnets for MHD generators

International Nuclear Information System (INIS)

Some shapes of cross-sections of magnet coils designed for a magnetohydrodynamic generator are given and the evaluation is made of eight types of magnetic systems producing a magnetic field as homogeneous as possible in the working space of a rectangular section. The assesment is made using the example of a magnet for a MHD generator with heat input of about 500 MW. (author)

415

Directory of Open Access Journals (Sweden)

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

T. RajaRani

2012-01-01

416

Understanding the Chromospheric Magnetic Field

The chromospheric magnetic field is an important and essential component for understanding solar atmospheric fields. Due to the problems of polarization radiation transfer in the chromosphere and the low detective sensitivity of chromospheric spectrum lines, observations of chromospheric magnetic fields are very difficult, so studies of chromospheric fields are infrequent. However, the understanding of chromospheric fields is evolving. In this report, we summarize our current empirical knowledge and basic physical understanding of chromospheric fields. We concentrate on the comparison of magnetic fields in the photosphere and chromosphere, and then display their difference.

Jin, C. L.; Harvey, J. W.; Pietarila, A.

2014-10-01

417

Helical magnetic fields via baryon asymmetry

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

Piratova, Eduard F; Hortúa, Héctor J

2014-01-01

418

Magnetic monopole field exposed by electrons

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 ...

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

2013-01-01

419

Evolution of twisted magnetic fields

International Nuclear Information System (INIS)

The magnetic field of the solar corona evolves quasi-statically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. It is shown that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, the equilibrium of a thin magnetic flux tube with small twist per unit length was calculated. 22 references

420

Jet Collimation by Small-Scale Magnetic Fields

A popular model for jet collimation is associated with the presence of a large-scale and predominantly toroidal magnetic field originating from the central engine (a star, a black hole, or an accretion disk). Besides the problem of how such a large-scale magnetic field is generated, in this model the jet suffers from the fatal long-wave mode kink magnetohydrodynamic instability. In this paper we explore an alternative model: jet collimation by small-scale magnetic fields. These magnetic fields are assumed to be local, chaotic, and tangled, but are dominated by toroidal components. Just as in the case of a large-sca