WorldWideScience
1

Magnetic Field Generation in Stars  

Science.gov (United States)

Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Coherent searches for the Crab pulsar with the Laser Interferometer Gravitational Wave Observatory (LIGO) have already constrained its gravitational wave luminosity to be ?2 % of the observed spin-down luminosity, thus placing a limit of ?1016 G on the internal field. Indirect spin-down limits inferred from recycled pulsars also yield interesting gravitational-wave-related constraints. Thus we may be at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes which control the diffusive magnetic flux transport in stars.

Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

2015-03-01

2

Generation of helical magnetic fields from inflation  

CERN Document Server

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

Jain, Rajeev Kumar; Hollenstein, Lukas

2012-01-01

3

Strong and superstrong pulsed magnetic fields generation  

CERN Document Server

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

Shneerson, German A; Krivosheev, Sergey I

2014-01-01

4

The magnetic field gradients generation for magnetic resonance tomography  

International Nuclear Information System (INIS)

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

5

Generation of magnetic fields in planets  

International Nuclear Information System (INIS)

The strong and persistent magnetic fields of virtually all classes of cosmic objects are attributed to an active generation process known as the MHD dynamo. The regenerative power of dynamo fluid motions derives from the cyclonic or helical character of convection in rotating bodies. The small-scale, rapid variations in the field are a direct manifestation of the generation process, and the long-term behavior patterns carry important clues about the field's structure and dynamical state. 24 references

6

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.)

7

ON THE GENERATION OF ORGANIZED MAGNETIC FIELDS  

International Nuclear Information System (INIS)

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

8

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

9

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

10

The Model of Magnetic-Field Generation with Screw Dynamo  

OpenAIRE

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...

Tlatov, Andrey G.

2013-01-01

11

Generation of magnetic fields in plasmas  

Energy Technology Data Exchange (ETDEWEB)

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

Shukla, Nitin

2012-07-01

12

Giga-Gauss scale quasistatic magnetic field generation with laser  

OpenAIRE

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; D Humieres, Emmanuel; Tikhonchuk, Vladimir

2014-01-01

13

Effects of non-linearities on magnetic field generation  

CERN Document Server

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

Nalson, Ellie; Malik, Karim A

2013-01-01

14

Magnetic field generating thermal instability including the Nernst effect  

International Nuclear Information System (INIS)

Nernst effect is taken into account in the analysis of the magnetic field generating thermal instability. Instability condition and the growth rate ? are obtained. The Nernst effect as well as the hydrodynamic effect induces the instability in the region of nabla n0.nabla T0 < 0 and it increases the magnitude of the magnetic field especially in the overdense region. (author)

15

Magnetic Field Correlation as a Measure of Iron-Generated Magnetic Field Inhomogeneities in the Brain  

OpenAIRE

The magnetic field correlation (MFC) at an applied field level of 3 T was estimated by means of MRI in several brain regions for 21 healthy human adults and one subject with aceruloplasminemia. For healthy subjects, highly elevated MFC values compared to surrounding tissues were found within the basal ganglia. These are argued as being primarily the result of microscopic magnetic field inhomogeneities generated by non-heme brain iron. The MFC in the aceruloplasminemia subject was significantl...

Jensen, Jens H.; Szulc, Kamila; Hu, Cathy; Ramani, Anita; Lu, Hanzhang; Xuan, Liang; Falangola, Maria F.; Chandra, Ramesh; Knopp, Edmond A.; Schenck, John; Zimmerman, Earl A.; Helpren, Joseph A.

2009-01-01

16

Interstellar Turbulent Magnetic Field Generation by Plasma Instabilities  

OpenAIRE

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

Tautz, R. C.; Triptow, J.

2013-01-01

17

Electron beam therapy with coil-generated magnetic fields  

International Nuclear Information System (INIS)

This paper presents an initial study on the issues involved in the practical implementation of the use of transverse magnetic fields in electron beam therapy. By using such magnetic fields the dose delivered to the tumor region can increase significantly relative to that deposited to the healthy tissue. Initially we calculated the magnetic fields produced by the Helmholtz coil and modified Helmholtz coil configurations. These configurations, which can readily be used to generate high intensity magnetic fields, approximate the idealized magnetic fields studied in our previous publications. It was therefore of interest to perform a detailed study of the fields produced by these configurations. Electron beam dose distributions for 15 MeV electrons were calculated using the ACCEPTM code for a 3T transverse magnetic field produced by the modified Helmholtz configuration. The dose distribution was compared to those obtained with no magnetic field. The results were similar to those obtained in our previous work, where an idealized step function magnetic field was used and a 3T field was shown to be the optimal field strength. A simpler configuration was also studied in which a single external coil was used to generate the field. Electron dose distributions are also presented for a given geometry and given magnetic field strength using this configuration. The results indicate that this method is more difficult to apply to radiotherapy due to its lack of symmetry and its irreg due to its lack of symmetry and its irregularity. For the various configurations dealt with here, a major problem is the need to shield the magnetic field in the beam propagation volume, a topic that must be studied in detail

18

Generation of Primordial Magnetic Fields on Linear Overdensity Scales  

Science.gov (United States)

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 spatial power spectrum of the magnetic field. At redshifts of order a few tens, we estimate a root mean square field strength of order 10-25-10-24G on comoving scales ˜10kpc. This field, which is generated purely from linear perturbations, is expected to be amplified significantly after reionization, and to be further boosted by dynamo processes during nonlinear structure formation.

Naoz, Smadar; Narayan, Ramesh

2013-08-01

19

Cosmological magnetic fields: generation during inflation and evolution  

OpenAIRE

This paper concerns the generation and evolution of the cosmological (large-scale $\\sim Mpc$) magnetic fields in an inflationary universe. The universe during inflation is represented by de Sitter space-time. We started with the Maxwell equations in spatially flat Friedmann-Robertson-Walker (FRW) Cosmologies. Then we calculated the wave equations of the magnetic field and electric field for the evolution. We consider the input current that was produced from a massless charge...

Dai, Zuxiang

2003-01-01

20

Propagation of electromagnetically generated wake fields in inhomogeneous magnetized plasmas  

OpenAIRE

Generation of wake fields by a short electromagnetic pulse in a plasma with an inhomogeneous background magnetic field and density profile is considered, and a wave equation is derived. Transmission and reflection coefficients are calculated in a medium with sharp discontinuities. Particular attention is focused on examples where the longitudinal part of the electromagnetic field is amplified for the transmitted wave. Furthermore, it is noted that the wake field can propagat...

Servin, Martin; Brodin, Gert

2001-01-01

21

Heat diffusion and magnetic field generation  

International Nuclear Information System (INIS)

In the report of CECAM workshop in 1982 some results of heat diffusion, when the spontaneous B-field is calculated, have been given. Separately, a similar code (magneto-calo-dynamic or MCD code) has been built and it was interesting to compare them. Comparisom has been made during the workshop of October 1983

22

Relativistic Scott correction in self-generated magnetic fields.  

DEFF Research Database (Denmark)

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

Erdos, Laszlo; Fournais, SØren

2012-01-01

23

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

Science.gov (United States)

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

24

GENERATION OF MAGNETIC FIELDS BY THE STATIONARY ACCRETION SHOCK INSTABILITY  

International Nuclear Information System (INIS)

We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field, and in some cases rotation, to an initially spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. In axisymmetric simulations, we find that cycles of latitudinal flows into and radial flows out of the polar regions amplify the field parallel to the symmetry axis, typically increasing the total magnetic energy by about 2 orders of magnitude. Non-axisymmetric calculations result in fundamentally different flows and a larger magnetic energy increase: shearing associated with the SASI spiral mode contributes to a widespread and turbulent field amplification mechanism, boosting the magnetic energy by almost 4 orders of magnitude (a result which remains very sensitive to the spatial resolution of the numerical simulations). While the SASI may contribute to neutron star magnetization, these simulations do not show qualitatively new features in the global evolution of the shock as a result of SASI-induced magnetic field amplification.

25

Laser light absorption due to self-generated magnetic fields  

International Nuclear Information System (INIS)

It is shown that even normally incident laser light will be resonantly absorbed near the critical density surface when there are self-generated DC magnetic fields. Theoretical estimates for the coupling mechanism, saturation amplitudes, and absorption are given and tested in computer simulations for parameters characteristic of some recent laser-plasma experiments

26

Gravitational radiation generated by cosmological phase transition magnetic fields  

International Nuclear Information System (INIS)

We study gravitational waves generated by the cosmological magnetic fields induced via bubble collisions during the electroweak (EW) and QCD phase transitions. The magnetic field generation mechanisms considered here are based on the use of the fundamental EW minimal supersymmetric and QCD Lagrangians. The gravitational waves spectrum is computed using a magnetohydrodynamic turbulence model. We find that the gravitational wave spectrum amplitude generated by the EW phase transition peaks at a frequency of approximately 1-2 mHz, and is of the order of 10-20-10-21; thus this signal is possibly detectable by the Laser Interferometer Space Antenna (LISA). The gravitational waves generated during the QCD phase transition, however, are outside the LISA sensitivity bands.

27

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

28

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

29

Generation and measurement of pulsed high magnetic field  

CERN Document Server

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

Jana, S

2000-01-01

30

On the electric and magnetic field generation in expanding plasmas  

International Nuclear Information System (INIS)

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

31

Generation of cosmic magnetic fields in electroweak plasma  

CERN Document Server

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

Dvornikov, Maxim

2014-01-01

32

Dark matter and generation of galactic magnetic fields  

CERN Document Server

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

Berezhiani, Zurab; Tkachev, I I

2013-01-01

33

Relativistic Scott correction in self-generated magnetic fields  

CERN Document Server

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

34

dc-Magnetic-field generation in unmagnetized shear flows.  

Science.gov (United States)

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

35

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

Science.gov (United States)

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

Hu, Guangyue; Liang, Yihan; Song, Falun; Yuan, Peng; Wang, Yulin; Zhao, Bin; Zheng, Jian

2015-02-01

36

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

37

Modeling and Measurement of Ocean Generated Magnetic Fields  

Science.gov (United States)

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

38

Dynamical mass generation in QED with magnetic fields: arbitrary field strength and coupling constant  

OpenAIRE

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 mas...

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

2008-01-01

39

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets  

Science.gov (United States)

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

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

2006-01-01

40

Dark matter and generation of galactic magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-10-15

41

Laser light absorption and harmonic generation due to self-generated magnetic fields  

International Nuclear Information System (INIS)

It is shown that self-generated magnetic fields can play a significant role in laser light absorption. Even normally incident light will then be resonantly absorbed. Computer simulations and theoretical estimates for this absorption and the concomitant harmonic generation are given for parameters characteristic of some recent experiments

42

Internal split field generator  

Science.gov (United States)

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

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

2012-01-03

43

Generation of the large scale magnetic fields by coupling to curvature and dilaton field  

Directory of Open Access Journals (Sweden)

Full Text Available  We investigate the generation of large scale magnetic fields in the universe from quantum fluctuations that are produced in the inflationary stage. By coupling these quantum fluctuations to the dilaton field and Ricci scalar, we show that the magnetic fields with the strength observed today can be produced. We consider two situations. First, the evolution of dilaton ends by starting the reheating stage. Second, the dilaton continues its evolution after reheating and then decays. We here consider the first case. In both cases, we come back to the usual Maxwell equations after inflation and then calculate present magnetic fields.

A. Akhtari Zavareh

2006-06-01

44

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

International Nuclear Information System (INIS)

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

45

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

International Nuclear Information System (INIS)

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

46

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

CERN Document Server

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

47

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

48

Consistent generation of magnetic fields in axion inflation models  

CERN Document Server

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

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

2015-01-01

49

Magnetic-Field Generation by Randomly Forced Shearing Waves  

CERN Document Server

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

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

2008-01-01

50

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

International Nuclear Information System (INIS)

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

51

Dynamical mass generation in strongly coupled Quantum Electrodynamics with weak magnetic fields  

OpenAIRE

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 eB

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

2006-01-01

52

MHD turbulence developed and generation of magnetic field  

International Nuclear Information System (INIS)

Turbulence in a conducting medium presents a critical magnetic Reynolds number, as do the linear dynamos with a given velocity field. Results obtained with the EDQNM model in non linear MHD turbulence (helical or non helical) are given

53

Geometrical generation of cosmic magnetic fields within standard electromagnetism  

Scientific Electronic Library Online (English)

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

Christos G., Tsagas; Alejandra, Kandus.

1070-10-01

54

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

Science.gov (United States)

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

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

2012-04-20

55

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

Science.gov (United States)

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

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

2014-11-01

56

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1976-01-01

57

Ultra-High Intensity Magnetic Field Generation in Dense Plasma  

Energy Technology Data Exchange (ETDEWEB)

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

Fisch, Nathaniel J

2014-01-08

58

Magnetic-field generation in plasma implosions due to Nernst refrigeration  

International Nuclear Information System (INIS)

It is shown that the Nernst effect may generate a large magnetic field in a high-density plasma on a very short time scale, even in initially symmetric systems. Such a field would have implications for pellet fusion. (author)

59

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

CERN Document Server

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

60

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

Science.gov (United States)

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

61

Magnetic-field generation and amplification in an expanding plasma.  

Science.gov (United States)

Particle-in-cell simulations are used to investigate the formation of magnetic fields B in plasmas with perpendicular electron density and temperature gradients. For system sizes L comparable to the ion skin depth 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 ? ? 100), independent of L. The magnetic energy spectra below the electron Larmor radius scale are well fitted by the power law with slope -16/3, as predicted by Schekochihin et al. [Astrophys. J. Suppl. Ser. 182, 310 (2009)]. PMID:24836254

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

2014-05-01

62

Magnetic field generation and amplification in an expanding plasma  

CERN Document Server

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

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

2013-01-01

63

Magnetic-Field Generation and Amplification in an Expanding Plasma  

Science.gov (United States)

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

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

2014-05-01

64

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

65

External split field generator  

Science.gov (United States)

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

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

2012-02-21

66

Mechanism for magnetic field generation and growth in Rayleigh-Taylor unstable inertial confinement fusion plasmas  

International Nuclear Information System (INIS)

Rayleigh-Taylor instabilities (RTI) in inertial confinement fusion (ICF) implosions are expected to generate magnetic fields at the gas-ice interface and at the ice-ablator interface. The focus here is on the gas-ice interface where the temperature gradient is the largest. A Hall-MHD model is used to study the magnetic field generation and growth for 2-D single-mode and multimode RTI in a stratified two-fluid plasma, the two fluids being ions and electrons. Self-generated magnetic fields are observed and these fields grow as the RTI progresses via the ?ne×?Te term in the generalized Ohm’s law. Srinivasan et al.[Phys. Rev. Lett. 108, 165002 (2012)] present results of the magnetic field generation and growth, and some scaling studies in 2-dimensions. The results presented here study the mechanism behind the magnetic field generation and growth, which is related to fluid vorticity generation by RTI. The magnetic field wraps around the bubbles and spikes and concentrates in flux bundles at the perturbed gas-ice interface where fluid vorticity is large. Additionally, the results of Srinivasan et al.[Phys. Rev. Lett. 108, 165002 (2012)] are described in greater detail. Additional scaling studies are performed to determine the growth of the self-generated magnetic field as a function of density, acceleration, perturbation wavelength, Atwood number, and ion mass.

67

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

International Nuclear Information System (INIS)

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

68

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

OpenAIRE

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

69

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

CERN Document Server

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

Guervilly, Celine; Jones, Chris A

2015-01-01

70

Magnetic field generation and amplification in an expanding plasma  

OpenAIRE

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-produ...

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

2013-01-01

71

Generation of Primordial Magnetic Fields on Linear Over-density Scales  

CERN Document Server

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

Naoz, Smadar

2013-01-01

72

Ultra intense magnetic fields in laser plasma interaction: their generation and influence on light propagation  

International Nuclear Information System (INIS)

Extremely large, quasi-stationary magnetic fields can be generated in plasmas by high intensity laser pulses. These fields can change the plasma dynamics and the pulse propagation. Several aspects of their generation and of their effect on the plasma and on the laser pulse are discussed in the relativistic pulse amplitude regime: (a) the formation of magnetic wakes, (b) the development of longitudinal and transverse Langmuir wake wavebreaks and (c) the magnetic field generation on a thin foil, viewed as a model for overdense plasmas with sharp boundaries

73

The permanent magnet systems generating strong stray fields with large localization region  

International Nuclear Information System (INIS)

Three systems of permanent magnets, which produce strong magnetic stray fields (SFs) with H>Br=4?Mr were studied in this work. Remarkable feature of the developed systems is localization of the strong fields in large region with linear dimension ?r comparable to characteristic magnet dimension a. The first system composed of uniformly magnetized magnets generates sufficiently homogeneous strong SFs, which amounts up to 1.5 of magnets induction Br. The second system with nonuniform magnetization is represented by cylindrical and hemispheric magnets their magnetization vector directed at every point along the radius. Such distribution of magnetization is assumed to be the consequence of magnet radial crystal texture resulting in a high uniaxial anisotropy field HK. It is shown that maximal SFs can exist on the flat surface of cylindrical magnet at the distance r from its axis and their limiting value equals to 4?Mr ln(2a/r). Here, the localization region of the fields is comparable to diameter of cylindrical magnet ?r?2R. As for the hemisphere its SFs are less than corresponding SFs for the cylinder. The third so-called quasi-nonuniform system consists of uniformly magnetized cylindrical sectors their magnetization vector is directed along the sector bisectrix. The strong SFs and their localization region are calculated in details for this case. The passage to radial magnetized cylinder is consideredzed cylinder is considered

74

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

CERN Document Server

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

von der Pahlen, J Graf

2014-01-01

75

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

CERN Document Server

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

Martin, Jerome

2007-01-01

76

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

Science.gov (United States)

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

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

2006-01-01

77

Nonlinear Generation of shear flows and large scale magnetic fields by small scale  

Science.gov (United States)

EGU2009-233 Nonlinear Generation of shear flows and large scale magnetic fields by small scale turbulence in the ionosphere by G. Aburjania Contact: George Aburjania, g.aburjania@gmail.com,aburj@mymail.ge

Aburjania, G.

2009-04-01

78

Open Circuit Field Distribution and Induced Voltage of a Cylindrical Permanent Magnet Linear Generator  

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

79

Open Circuit Field Distribution and Induced Voltage of a Cylindrical Permanent Magnet Linear Generator  

OpenAIRE

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; Arof, H.

2007-01-01

80

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

OpenAIRE

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 ir...

Atef El Jery; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

2010-01-01

81

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

82

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

International Nuclear Information System (INIS)

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

83

Dynamical mass generation in QED with magnetic fields: arbitrary field strength and coupling constant  

CERN Document Server

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

84

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

CERN Document Server

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

Shiromoto, Yuki; Hosokawa, Takashi

2014-01-01

85

Self-generated magnetic fields in direct-drive implosion experiments  

Science.gov (United States)

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

86

Self-generated magnetic fields in direct-drive implosion experiments  

International Nuclear Information System (INIS)

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

87

Generation of Magnetic Fields and Jitter Radiation in GRBs. I. Kinetic Theory  

OpenAIRE

We present a theory of generation of strong (sub-equipartition) magnetic fields in relativistic collisionless GRB shocks. These fields produced by the kinetic two-stream instability are tangled on very small spatial scales. This has a clear signature in the otherwise synchrotron(-self-Compton) $\\gamma$-ray spectrum. Second, we present an analytical theory of jitter radiation, which is emitted when the correlation length of the magnetic field is smaller then the gyration (Lar...

Medvedev, Mikhail V.

2001-01-01

88

Effect of magnetic field on the plasma generated during a sliding contact  

Science.gov (United States)

The triboelectrically generated plasma discharge generated in the gap behind a sliding contact is thought to be one of the main causes of the unexplained serious tribological problems met recently in the development of advanced technologies. To solve the tribological problems arising from the triboplasma, it is essential to develop a triboplasma control technology. In this report, the effect of magnetic field on triboplasma generation is investigated as a method for developing a control technology using the Lorenz force, which acts on moving charged particles in the plasma under the influence of an applied magnetic field. Photographs of the photons emitted from the sliding contact and its vicinity were obtained with an ICCD camera while sliding a diamond pin along a sapphire disk in ambient air. By applying a magnetic field, both the distribution and intensity of the tribo-plasma changed greatly, demonstrating that a triboplasma can be controlled by applying a magnetic field.

Nakayama, K.

2011-06-01

89

Effect of magnetic field on the plasma generated during a sliding contact  

Energy Technology Data Exchange (ETDEWEB)

The triboelectrically generated plasma discharge generated in the gap behind a sliding contact is thought to be one of the main causes of the unexplained serious tribological problems met recently in the development of advanced technologies. To solve the tribological problems arising from the triboplasma, it is essential to develop a triboplasma control technology. In this report, the effect of magnetic field on triboplasma generation is investigated as a method for developing a control technology using the Lorenz force, which acts on moving charged particles in the plasma under the influence of an applied magnetic field. Photographs of the photons emitted from the sliding contact and its vicinity were obtained with an ICCD camera while sliding a diamond pin along a sapphire disk in ambient air. By applying a magnetic field, both the distribution and intensity of the tribo-plasma changed greatly, demonstrating that a triboplasma can be controlled by applying a magnetic field.

Nakayama, K, E-mail: Keiji.nakayama@it-chiba.ac.jp [Advanced Research Institute, Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba 275-0016 (Japan)

2011-06-23

90

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

91

Effect of magnetic field on the plasma generated during a sliding contact  

International Nuclear Information System (INIS)

The triboelectrically generated plasma discharge generated in the gap behind a sliding contact is thought to be one of the main causes of the unexplained serious tribological problems met recently in the development of advanced technologies. To solve the tribological problems arising from the triboplasma, it is essential to develop a triboplasma control technology. In this report, the effect of magnetic field on triboplasma generation is investigated as a method for developing a control technology using the Lorenz force, which acts on moving charged particles in the plasma under the influence of an applied magnetic field. Photographs of the photons emitted from the sliding contact and its vicinity were obtained with an ICCD camera while sliding a diamond pin along a sapphire disk in ambient air. By applying a magnetic field, both the distribution and intensity of the tribo-plasma changed greatly, demonstrating that a triboplasma can be controlled by applying a magnetic field.

92

Manufacturing method for coil conductors to generate strong magnetic field  

International Nuclear Information System (INIS)

A cylindrical member comprising copper/chromium alloy steel is formed. A central hole is perforated at the center of the cylindrical member for passing coolants. A wedge is attached to the central hole and struck by a static pressure press to extend the central hole. In this case, pressing force of the wedge is applied to the inner surface of the central hole of the cylindrical member, by which the central hole undergoes cold working to provide a metal tissues with large intramolecular density, and the inner surface of the central hole is hardened. Mechanical fabrication and electric discharge machining are applied to the outer surface of the cylindrical member and the wall surface of the central hole. Subsequently, spiral grooves are formed on the surface of the cylindrical member. A durability in view of strength is increased by hardening the inner surface of the central hole of the coil conductor, the coil conductor has sufficient resistance against strong magnetic fields if occur. (I.N.)

93

Nonlinear generation mechanism for the vortical electric field in magnetized plasma media  

Science.gov (United States)

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

Aburjania, G. D.

2007-10-01

94

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

International Nuclear Information System (INIS)

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

95

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-07-15

96

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

Science.gov (United States)

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

Modestov, M.; Bychkov, V.; Brodin, G.; Marklund, M.; Brandenburg, A.

2014-07-01

97

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

Science.gov (United States)

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

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

2006-01-01

98

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

International Nuclear Information System (INIS)

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

99

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

CERN Document Server

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

Yuan, Kai-Jun

2013-01-01

100

Design of pulsed guiding magnetic field for high power microwave generators  

Energy Technology Data Exchange (ETDEWEB)

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., E-mail: jujinchuan@126.com; Zhang, H.; Zhang, J.; Shu, T.; Zhong, H.-H. [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-09-15

101

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

Science.gov (United States)

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

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

2014-08-01

102

Design of pulsed guiding magnetic field for high power microwave generators  

International Nuclear Information System (INIS)

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

103

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-06-01

104

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

OpenAIRE

Recently Adelberger et al [Phys Rev Lett 98: 010402, (2007)] have placed a limit to photon mass by investigating the primordial magnetic fields. Earlier Bertolami et al [Phys Lett \\textbf{B} 455, 96(1999)] showed that massive photons in a spontaneous Lorentz breaking may generate primordial magnetic fields consistent with galactic dynamo seeds. Torsion coupling constant of order $10^{-5}$, much higher than the previously obtained by de Sabbata and Sivaram of $10^{-24}$, lead...

Andrade, Garcia

2011-01-01

105

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

Directory of Open Access Journals (Sweden)

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

E. D. Schmitter

2010-02-01

106

GENERATION OF A SEED MAGNETIC FIELD AROUND FIRST STARS: THE BIERMANN BATTERY EFFECT  

International Nuclear Information System (INIS)

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

107

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

Science.gov (United States)

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

Doi, Kentaro; Susa, Hajime

2011-11-01

108

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

CERN Document Server

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

Doi, Kentaro

2011-01-01

109

Self-generated magnetic fields due to laser-plasma resonance absorption  

International Nuclear Information System (INIS)

A simple and effective diagnostic method of using magnetic tapes was studied. The two-dimensional distribution of the self-generated magnetic field near the resonance region was observed. A magnetic tape was dipped in a magnetic tape developer, and the field distribution can be observed with a microscope. The magnetic tape developer contained the iron particles having diameter range from 1 to 2.5 micrometer suspended in trichlorotrifluoroethane. The field polarity was measured with a small bar magnet. After the developer was evaporated, the dry pattern was obtained. The ferromagnetic film of a tape was irradiated by divergent laser beam. The pattern was obtained, and the lobe structure was registered in the dry pattern. The explanation of patterns are given. If the resonance absorption is the generation mechanism, the parity of the self-generated magnetic fields must exist. The experiment was made with convergent laser beam, and the result showed the parity existence in the observed polarities of N and S poles in comparison with those in the divergent laser case. (Kato, T.)

110

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

Directory of Open Access Journals (Sweden)

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

Ammar Ben Brahim

2011-05-01

111

Magnetic Fields  

Science.gov (United States)

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,

112

Experimental and theoretical study of helical explosive electrical current generators with magnetic field compression  

International Nuclear Information System (INIS)

A generator of electrical energy in which magnetic field compression is achieved by a solid explosive is described. The magnetic flux losses have been calculated for generators of various configurations by the skin depth concept. Calculations take the Joule heating of conductors into account. In helical generators the magnetic flux losses are higher than those calculated by considering diffusion only. Additional losses approximately as important as diffusion losses have already been observed elsewhere on similar devices. Detailed calculations of the motion of the explosively driven inner conductor show that losses come from the jumps encountered by sliding contact moving along the helix. The jumps are caused by little geometrical defects and the consequence on losses is strongly dependent on current intensity. The jumps decrease when the pitch of helix increases. The jumps are detrimental to the efficient use of the explosive energy. With helical generators only 5% of the energy is transferred into magnetic energy

113

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-01

114

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

International Nuclear Information System (INIS)

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

115

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

International Nuclear Information System (INIS)

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

116

Generation of static magnetic fields by a test charge in a plasma with anisotropic electron temperature  

International Nuclear Information System (INIS)

Structure of electomagnetic field generated with a charge in a plasma with anisotropic electron temperature has been studied. Unlike a hydrodynamical approach to study on the magnetic field qeneration with a test charge a kinetic theory describing spatial distribution of both magnetic and electrostatic components of charge field was constructed. Such theory results permit to investigate the charge field structure both at distances larger than length of free electron path and not exceeding it. The developed theory can serve as the basis for development of new methods for anisotropic plasma diagnostics

117

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

International Nuclear Information System (INIS)

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

118

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

International Nuclear Information System (INIS)

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

119

Development of FEMAG. Calculation code of magnetic field generated by ferritic plates in the tokamak devices  

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

120

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

Science.gov (United States)

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

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

2015-02-01

121

Gap generation for Dirac fermions on Lobachevsky plane in a magnetic field  

International Nuclear Information System (INIS)

We study symmetry breaking and gap generation for fermions in the 2D space of constant negative curvature (the Lobachevsky plane) in an external covariantly constant magnetic field in a four-fermion model. It is shown that due to the magnetic and negative curvature catalyses phenomena the critical coupling constant is zero and there is a symmetry breaking condensate in the chiral limit even in free theory. We analyze solutions of the gap equation in the cases of zero, weak, and strong magnetic fields. As a byproduct, we calculate the density of states and the Hall conductivity for noninteracting fermions that may be relevant for studies of graphene

122

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

CERN Document Server

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

123

Magnetic field generation by the Rayleigh-Taylor instability in laser-driven planar plastic targets.  

Science.gov (United States)

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with ?4-kJ, 2.5-ns laser pulses focused to an intensity of ?10(14)??W/cm(2) on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations. PMID:23005637

Gao, L; Nilson, P M; Igumenschev, I V; Hu, S X; Davies, J R; Stoeckl, C; Haines, M G; Froula, D H; Betti, R; Meyerhofer, D D

2012-09-14

124

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

International Nuclear Information System (INIS)

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

125

Two-dimensional distribution of laser-plasma self-generated magnetic fields by a magnetic tape method  

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)

126

LARGE-SCALE MAGNETIC FIELD GENERATION VIA THE KINETIC KELVIN-HELMHOLTZ INSTABILITY IN UNMAGNETIZED SCENARIOS  

Energy Technology Data Exchange (ETDEWEB)

Collisionless plasma instabilities are fundamental in magnetic field generation in astrophysical scenarios, but their role has been addressed in scenarios where velocity shear is absent. In this work we show that velocity shears must be considered when studying realistic astrophysical scenarios, since these trigger the collisionless Kelvin-Helmholtz instability (KHI). We present the first self-consistent three-dimensional particle-in-cell simulations of the KHI in conditions relevant for unmagnetized relativistic outflows with velocity shear, such as active galactic nuclei and gamma-ray bursts. We show the generation of a strong large-scale DC magnetic field, which extends over the entire shear-surface, reaching thicknesses of a few tens of electron skin depths, and persisting on timescales much longer than the electron timescale. This DC magnetic field is not captured by magnetohydrodynamic models since it arises from intrinsically kinetic effects. Our results indicate that the KHI can generate intense magnetic fields yielding equipartition values up to {epsilon}{sub B}/{epsilon}{sub p} {approx_equal} 10{sup -3}-10{sup -2} in the electron timescale. The KHI-induced magnetic fields have a characteristic structure that will lead to a distinct radiation signature and can seed the turbulent dynamo amplification process. The dynamics of the KHI are relevant for non-thermal radiation modeling and can also have a strong impact on the formation of relativistic shocks in presence of velocity shears.

Alves, E. P.; Grismayer, T.; Martins, S. F.; Fiuza, F.; Fonseca, R. A.; Silva, L. O. [GoLP/Instituto de Plasmas e Fusao Nuclear-Laboratorio Associado, Instituto Superior Tecnico, Lisbon (Portugal)

2012-02-20

127

LARGE-SCALE MAGNETIC FIELD GENERATION VIA THE KINETIC KELVIN-HELMHOLTZ INSTABILITY IN UNMAGNETIZED SCENARIOS  

International Nuclear Information System (INIS)

Collisionless plasma instabilities are fundamental in magnetic field generation in astrophysical scenarios, but their role has been addressed in scenarios where velocity shear is absent. In this work we show that velocity shears must be considered when studying realistic astrophysical scenarios, since these trigger the collisionless Kelvin-Helmholtz instability (KHI). We present the first self-consistent three-dimensional particle-in-cell simulations of the KHI in conditions relevant for unmagnetized relativistic outflows with velocity shear, such as active galactic nuclei and gamma-ray bursts. We show the generation of a strong large-scale DC magnetic field, which extends over the entire shear-surface, reaching thicknesses of a few tens of electron skin depths, and persisting on timescales much longer than the electron timescale. This DC magnetic field is not captured by magnetohydrodynamic models since it arises from intrinsically kinetic effects. Our results indicate that the KHI can generate intense magnetic fields yielding equipartition values up to ?B/?p ? 10–3-10–2 in the electron timescale. The KHI-induced magnetic fields have a characteristic structure that will lead to a distinct radiation signature and can seed the turbulent dynamo amplification process. The dynamics of the KHI are relevant for non-thermal radiation modeling and can also have a strong impact on the formation of relativistic shocks in preseon of relativistic shocks in presence of velocity shears.

128

Interpenetrating plasma shells: near-equipartition magnetic field generation and non-thermal particle acceleration  

OpenAIRE

We present the first three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations of the collision of two interpenetrating plasma shells. The highly accurate plasma-kinetic "particle-in-cell" (with the total of $10^8$ particles) parallel code OSIRIS has been used. Our simulations show: (i) the generation of long-lived near-equipartition (electro)magnetic fields, (ii) non-thermal particle acceleration, and (iii) short-scale to long-scale magnetic ...

Silva, L. O.; Fonseca, R. A.; Tonge, J.; Dawson, J. M.; Mori, W. B.; Medvedev, M. V.

2003-01-01

129

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

130

Large-scale magnetic field generation by randomly forced shearing waves  

OpenAIRE

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 experim...

Heinemann, T.; Mcwilliams, Jc; Schekochihin, Aa

2011-01-01

131

Gap generation for Dirac fermions on Lobachevsky plane in a magnetic field  

OpenAIRE

We study symmetry breaking and gap generation for fermions in the 2D space of constant negative curvature (the Lobachevsky plane) in an external covariantly constant magnetic field in a four-fermion model. It is shown that due to the magnetic and negative curvature catalysis phenomena the critical coupling constant is zero and there is a symmetry breaking condensate in the chiral limit even in free theory. We analyze solutions of the gap equation in the cases of zero, weak, ...

Gorbar, E. V.; Gusynin, V. P.

2007-01-01

132

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

International Nuclear Information System (INIS)

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

133

Magnetic seed field generation from electroweak bubble collisions with bubble walls of finite thickness  

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.

134

Large-scale magnetic field generation via the Kelvin-Helmholtz instability  

CERN Document Server

We present the first self-consistent three-dimensional particle-in-cell simulations of the Kelvin-Helmholtz instability (KHI) in an unmagnetized scenario. We discuss the main features, including density structure formation, and magnetic field generation, its evolution and saturation on the electron time-scale. The linear theory of the longitudinal KHI dynamics is presented, including arbitrary density jumps between shearing flows, showing that the onset of the instability is robust to this asymmetry. Simulations provide new insights into the evolution of the KHI in three dimensions, revealing the formation of complex structures due to the transverse dynamics of the instability and the emergence of a strong and large-scale DC magnetic field component which is not captured by the standard linear fluid theory. Our results indicate that the KHI can generate magnetic fields up to \\epsilon_B/\\epsilon_p ~ 10^-3 in the electron time-scale.

Alves, E P; Martins, S F; Fiúza, F; Fonseca, R A; Silva, L O

2011-01-01

135

Interpenetrating plasma shells: near-equipartition magnetic field generation and non-thermal particle acceleration  

CERN Document Server

We present the first three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations of the collision of two interpenetrating plasma shells. The highly accurate plasma-kinetic "particle-in-cell" (with the total of $10^8$ particles) parallel code OSIRIS has been used. Our simulations show: (i) the generation of long-lived near-equipartition (electro)magnetic fields, (ii) non-thermal particle acceleration, and (iii) short-scale to long-scale magnetic field evolution, in the collision region. Our results provide new insights into the magnetic field generation and particle acceleration in relativistic and sub-relativistic colliding streams of particles, which are present in gamma-ray bursters, supernova remnants, relativistic jets, pulsar winds, etc..

Silva, L O; Tonge, J; Dawson, J M; Mori, W B; Medvedev, M V

2003-01-01

136

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

CERN Document Server

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

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

2004-01-01

137

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

Science.gov (United States)

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

Vilim, R.; Stanley, S.

2012-12-01

138

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)

139

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

International Nuclear Information System (INIS)

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

140

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

Science.gov (United States)

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

141

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

International Nuclear Information System (INIS)

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

142

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

Energy Technology Data Exchange (ETDEWEB)

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.

Graf von der Pahlen, J.; Tsiklauri, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom)

2014-06-15

143

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-28

144

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

Science.gov (United States)

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

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

2008-01-01

145

Magnetic structure of the reconnection layer and core field generation in plasmoids  

Science.gov (United States)

Plasmoids/flux ropes have been observed both at Earth's magnetopause as well as in the magnetotail. Magnetic field measurements of such structures often reveal that rather than a minimum in field strength at their centers as expected from a simple O-type neutral line picture, they exhibit a strong core field. To address this issue, two-dimensional (2-D) and 3-D hybrid simulations are used to investigate the magnetic structure of reconnection layer in general and the formation of the core field within plasmoids in particular. The reconnection layer in the magnetotail is found to be unstable to the fire hose instability. As a result, the region between the lobe and the central plasma sheet is nearly at the marginal fire hose condition. The magnetic signatures of single and multiple X line geometries are contrasted, and it is shown that the interaction of outflowing jets from neighboring X lines leads in general to a highly complex magnetic structure within a plasmoid. The large observed core fields are explained in terms of Hall-generated currents which can naturally lead to core field strengths that even exceed the ambient lobe field in magnitude. Ion beta and the presence of a preexisting guide field are two important factors controlling the Hall-generated fields. In particular, it is shown that the presence of the small ubiquitous cross-tail field component in the magnetotail can under certain conditions lead to a strong unipolar plasmoid core field. There exist significant differences between core fields associated with plasmoids at the magnetopause and those in the tail. This is due to (1) high plasma beta in the magnetosheath and (2) the asymmetry in plasma density across the magnetopause. The former leads to smaller core fields at the magnetopause, whereas the latter leads to differences in the polarity and structure of core fields within magnetopause and magnetotail plasmoids. Such differences are illustrated through examples.

Karimabadi, H.; Krauss-Varban, D.; Omidi, N.; Vu, H. X.

1999-06-01

146

Self-generation of magnetic fields by sheared flows in weakly ionized plasmas  

International Nuclear Information System (INIS)

A sheared, relative ion--neutral flow can generate a magnetic field in an unmagnetized, weakly ionized plasma. The field generation term is ?B/?t=(mec/e)?x?en(Vi-Vn) where ?en is the electron--neutral collision frequency, Vi is the ion fluid velocity, and Vn is the neutral fluid velocity. The time period over which the field grows is limited by diffusion, convection, or collisional relaxation of the relative drift. Since the field generation term scales as ?en/?e relative to the other terms in the field induction equation, the maximum field generated is found from ?e congruent few ?en so that Bmax congruent few (mec/e)?en. Both analytical and numerical results are presented. The computational results are based upon a two-dimensional (2-D) magnetohydrodynamic (MHD) code which includes the following terms: ion--neutral drag, gravity, resistivity, recombination, the Hall term, and the shear-driven source term. The theory is applied to the generation of magnetic fields in an unmagnetized planetary ionosphere, such as Venus, and to cometary plasmas

147

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

Directory of Open Access Journals (Sweden)

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

K.-I. Nishikawa

2013-09-01

148

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

International Nuclear Information System (INIS)

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

149

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

Science.gov (United States)

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

Aburjania, G.; Machabeli, G.; Kharshiladze, O.

2006-03-01

150

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

OpenAIRE

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

Liang, Edison; Boettcher, Markus; Smith, Ian

2011-01-01

151

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

OpenAIRE

A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the axis of propagation such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre-Gaussian beams carrying orbital angular momentum. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between si...

Veysi, Mehdi; Guclu, Caner; Capolino, Filippo

2014-01-01

152

Self-generated magnetic fields in direct-drive implosion experiments  

Energy Technology Data Exchange (ETDEWEB)

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 ?10{sup 15}?W/cm{sup 2}. Proton radiographs show multiple ring-like structures produced by electric fields ?10{sup 7}?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 ?T{sub e}?×??n{sub e} 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.; Nilson, P. M.; Goncharov, V. N. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Zylstra, A. B.; Li, C. K.; Petrasso, R. D. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2014-06-15

153

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; Moretto, T.

2006-01-01

154

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-10-01

155

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

International Nuclear Information System (INIS)

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

156

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

International Nuclear Information System (INIS)

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

157

Magnetic Field  

DEFF Research Database (Denmark)

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

Olsen, Nils

2015-01-01

158

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

CERN Document Server

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

de Andrade, Garcia

2011-01-01

159

External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator  

Science.gov (United States)

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

Niedra, Janis M.; Geng, Steven M.

2013-01-01

160

Study on magnetic field generation and electron collimation in overdense plasmas  

Science.gov (United States)

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

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

2013-11-01

161

A high power Ka band millimeter wave generator with low guiding magnetic field  

International Nuclear Information System (INIS)

A slow wave type gigawatt millimeter wave generator is proposed in this paper. In order to increase power capacity, overmoded slow wave structures (SWSs) with larger diameter have been used. Taking advantage of the ''surface wave'' property of overmoded SWSs, the TM01 mode can be selected to be the operating mode. Calculations have also been carried out to choose a proper low operating magnetic field strength, and it agrees with particle in cell (PIC) simulations. Main structure parameters of the device are optimized by PIC simulations. A typical simulation result is that, at the beam parameters of 600 keV and 5.05 kA, and guiding magnetic field of 0.85 T, a Ka band millimeter wave with an output power of 1.05 GW is generated, yielding a conversion efficiency of about 35%.

162

Study on magnetic field generation and electron collimation in overdense plasmas  

Directory of Open Access Journals (Sweden)

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

Cai Hongbo

2013-11-01

163

Development status of next-generating high magnetic field superconducting proton therapy systems  

International Nuclear Information System (INIS)

Mevion Medical Systems has designed a high magnetic field synchrocyclotron for cancer treatment that has dramatically reduced the size and complexity of proton acceleration. The enabling technology is super-conducting technology. The key technology is the TriNiobium (Nb3Sn) magnet wire. The compact super-conducting accelerator uses two rings in the accelerator. This revolutionary proton accelerator is only 6 ft (1.8 m) in diameter, and can generate 250 MeV protons capable of reaching targets as deep as 32 cm in an equivalent water medium. This system has an accelerator mounted in the outer gantry. (author)

164

Large-scale magnetic field generation via the kinetic Kelvin-Helmholtz instability in unmagnetized scenarios  

OpenAIRE

Collisionless plasma instabilities are fundamental in magnetic field generation in astrophysical scenarios, but their role has been addressed in scenarios where velocity shear is absent. In this work we show that velocity shears must be considered when studying realistic astrophysical scenarios, since these trigger the collisionless Kelvin-Helmholtz instability (KHI). We present the first self-consistent three-dimensional particle-in-cell simulations of the KHI in conditions relevant for unma...

Alves, E. P.; Grismayer, T.; Martins, S. F.; Fiuza, F.; Fonseca, R. A.; Silva, L. O.

2012-01-01

165

Magnetic field generation by Biermann battery and Weibel instability in laboratory shock waves  

Science.gov (United States)

Magnetic field generation in the Universe is still an open problem. Possible mechanisms involve the Weibel instability, due to anisotropic phase-space distributions, as well as the Biermann battery, due to misaligned density and temperature gradients. These mechanisms can be reproduced in scaled laboratory experiments. In this contribution we estimate the relative importance of these two processes and explore the laser-energy requirements for producing Weibel dominated shocks.

Gregori, G.; Miniati, F.; Reville, B.; Drake, R. P.

2012-02-01

166

Toy model of the "fountain effect" for magnetic field generation in intense laser-solid interactions  

CERN Document Server

A very simple "geometrical" model of a fountain is analyzed to evaluate the net flow on the ground resulting from the superposition of the source and the falling streams. On this basis we suggest a scaling for the magnetic field generated at the rear surface of high-intensity laser-irradiated solid targets due to the "fountain effect" related to fast electrons escaping in vacuum.

Macchi, Andrea

2012-01-01

167

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

CERN Document Server

Miniati and Bell (2011) proposed a mechanism for the generation of magnetic seeds that is based the finite resistivity of the low temperature IGM in the high redshift universe. In this model, cosmic-ray protons generated by the first generation of galaxies, escape into the intergalactic medium carrying an electric current that induces return currents, $j_t$, and associated electric fields, $\\vec E=\\eta\\vec j_t$ there. Because the resistivity, $\\eta$, depends on the IGM temperature, which is highly inhomogeneous due to adiabatic contraction and shocks produced by structure formation, a non-vanishing curl of the electric field exists which sustains the growth of magnetic field. In this contribution we have developed an approximate numerical model for this process by implementing the source terms of the resistive mechanism in the cosmological code CHARM. Our numerical estimates substantiate the earlier analysis in Miniati and Bell (2011) which found magnetic seeds between 10$^{-18}$ and 10$^{-16}$ Gauss througho...

Miniati, Francesco

2011-01-01

168

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

CERN Document Server

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

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

2011-01-01

169

High-magnetic-field MHD-generator program. Quarterly report, January 1, 1981-March 31, 1981  

Energy Technology Data Exchange (ETDEWEB)

Progress in an experimental and theoretical program designed to investigate MHD channel phenomena which are important at high magnetic fields is reported. The areas of research include nonuniformity effects, boundary layers, Hall field breakdown, the effects of electrode configuration and current concentrations, and studies of steady-state combustion disk and linear channels in an existing 6 Tesla magnet of small dimensions. In the study of the effects of nonuniformities, experiments have been performed to test a multi-channel, fiber optics diagnostic system that yields time-resolved temperature profiles in an MHD channel. For the study of magneto-acoustic fluctuation phenomena, a one-dimensional model has been developed to describe the performance of a non-ideal MHD generator with a generalized electrical configuration. The installation of the hardware for the data acquisition and reduction of the laser Doppler velocimeter data, to be used in the study of turbulence suppression in a magnetic field, has been nearly completed. A two-dimensional MHD computer code has been developed which predicts the dependence on electrode and insulator dimensions of the onset of interelectrode Hall field breakdown. Calculations have been performed of the effects of nonuniformities on the flow and electrical behavior of baseload-sized disk generators.

None

1981-04-01

170

The First Magnetic Fields  

CERN Document Server

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early genera...

Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

2011-01-01

171

High-Resolution SQUID imaging of Magnetic Fields Generated by Propagating Cardiac Action Currents  

Science.gov (United States)

The heart's magnetic field is exquisitely sensitive to anisotropy ratios in the cardiac bidomain model; Therefore, magnetic imaging of cardiac action currents is an ideally suited technique for testing the accuracy of cardiac models and elucidating the effects of anisotropy in the spread of stimulus and action currents. We mapped the magnetocardiogram (MCG) as a function of position over a 10mm x 10mm area of the left ventricle of a Langendorff perfused isolated rabbit heart using high-resolution scanning SQUID microscopy and epi-fluorescent imaging with a high speed CCD camera and the transmembrane voltage sensitive dye di-4-ANEPPS. The combination of these two methods allowed us to map the transmembrane potential, the magnetic field, and consequently the total current, over the same area. The MCGs were combined to produce a time series of 2D field maps that show a clear octupolar pattern during the cathodal current injection, a similar pattern with a reversal of currents immediately after terminating the stimulus, and the generation and propagation of an elliptical action current wave front. The observed patterns are in agreement with predictions using a bidomain model. Our high-resolution SQUID images have confirmed that unequal anisotropies in the intra- and extracellular spaces must be considered to explain the magnetic field associated with action current propagation However, a realistic cardiac bidomain model incorporating fiber rotation, cleavage planes, and tissue heterogeneities are required to reproduce the complete experimental observations.

Holzer, Jenny R.; Sidorov, Veniamin; Fong, Luis; Peters, Nicholas; Baudenbacher, Petra; Baudenbacher, Franz

2004-03-01

172

Influence of ionization 'aureole' of ambient gas to laser-plasma generation of magnetic fields and currents over irradiating target  

International Nuclear Information System (INIS)

A new way of magnetic field amplification outside laser plasma and new method of laser-plasma generation of currents in an outer circuit are proposed. Considerable amplification (1000 times) of magnetic fields outside laser plume, e.g. in the region behind the irradiating target (magnetic field splash) and significant currents (? 100 A) over conductive target have been observed for the first time under production of asymmetric contact of plasma ionization aureole with target surface. (author). 7 refs, 4 figs

173

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

International Nuclear Information System (INIS)

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

174

Laser generated hot electron transport in an externally applied magnetic field  

International Nuclear Information System (INIS)

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

175

Generation of strong inhomogeneous stray fields by high-anisotropy permanent magnets  

Energy Technology Data Exchange (ETDEWEB)

Magnetic stray fields for systems of permanent magnets with high magnetic anisotropy are calculated and measured. It is shown that intensity of these fields exceeds value of an induction of a material of magnets in some time. Besides, these fields are characterized by high gradients, and size H-bar H can reach values up to10{sup 10}-10{sup 11}Oe{sup 2}/cm. Estimations of extremely achievable fields and their gradients are made.

Samofalov, V.N. [National Technical University Kharkov Polytechnical Institute, 21 Frunze St., 61002 Kharkov (Ukraine)]. E-mail: samofalov@kpi.kharkov.ua; Ravlik, A.G. [National Technical University Kharkov Polytechnical Institute, 21 Frunze St., 61002 Kharkov (Ukraine); Belozorov, D.P. [National Scientific Center Kharkov Institute of Physics and Techonology, NAS of Ukraine, 1 Akademicheskaja St., 61108 Kharkov (Ukraine); Avramenko, B.A. [National Technical University Kharkov Polytechnical Institute, 21 Frunze St., 61002 Kharkov (Ukraine)

2004-10-01

176

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

CERN Document Server

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

177

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

178

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

CERN Document Server

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

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

2012-01-01

179

Terahertz Generation by Polar Nanowires Subjected to a Perpendicular Magnetic Field  

Science.gov (United States)

Experiment and theory have indicated the generation of coherent terahertz (THz) radiation in III-V semiconductors electronically biased so that charge carriers enter a streaming distribution. [1] Under such conditions, the large polar optical phonon scattering rate of these materials allows for phonon emission assisted transit-time resonance (TTR). Since acoustic phonon scattering acts to de-phase TTR current oscillations, generation typically occurs at low temperatures (TTR based THz generation at higher temperatures. A possible mechanism for such a reduction may be found using III-V nanowires which are subjected to a perpendicular magnetic field. The field would allow transport in skipping orbits along the nanowire edges with suppressed acoustic phonon backscattering.[2] To investigate such an effect, Monte Carlo simulations of carrier transport are employed. The effect of an applied magnetic field is accounted for within the confined electronic sub-band energy levels. Charge carrier scattering by confined and surface phonons are considered. [1] L. E. Vorob'ev et al., JETP Lett. 73, 219 (2001); P. Shiktorov et al., Acta Phys. Polonica A 113, 795 (2008) [3] A. Svizhenko et al., Phys. Rev. B 57, 4687 (1998)

Pennington, Gary

2010-03-01

180

Generation of magnetic field fluctuations in relativistic electron-positron magnetoplasmas  

International Nuclear Information System (INIS)

It is shown that magnetic field aligned equilibrium relativistic plasmas flows can excite electromagnetic fluctuations in a magnetized electron-positron (e-p) plasma. For this purpose, a new dispersion relation is derived by using a relativistic two-fluid model and the Maxwell equations. The dispersion relation admits purely growing instabilities of electromagnetic perturbations across the ambient magnetic field direction. The results have relevance for understanding the origin of magnetic field fluctuations in cosmological and laser-produced plasmas

181

Occupational exposure to magnetic fields in relation to mortality from brain cancer among electricity generation and transmission workers.  

OpenAIRE

OBJECTIVE: To investigate whether the risks of mortality from brain cancer are related to occupational exposure to magnetic fields. METHODS: A total of 112 cases of primary brain cancer (1972-91) were identified from a cohort of 84,018 male and female employees of the (then) Central Electricity Generating Board and its privatised successor companies. Individual cumulative occupational exposures to magnetic fields were estimated by linking available computerised job history data with magnetic ...

Harrington, J. M.; Mcbride, D. I.; Sorahan, T.; Paddle, G. M.; Tongeren, M.

1997-01-01

182

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

Science.gov (United States)

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

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

2007-01-01

183

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

184

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

CERN Document Server

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

Fan Ya Jun; Qiu Aici

2002-01-01

185

N-body + Magnetohydrodynamical Simulations of Merging Clusters of Galaxies: Characteristic Magnetic Field Structures Generated by Bulk Flow Motion  

CERN Document Server

We present results from N-body + magnetohydrodynamical simulations of merging clusters of galaxies. We find that cluster mergers cause various characteristic magnetic field structures because of the strong bulk flows in the intracluster medium. The moving substructures result in cool regions surrounded by the magnetic field. These will be recognized as magnetized cold fronts in the observational point of view. A relatively ordered magnetic field structure is generated just behind the moving substructure. Eddy-like field configurations are also formed by Kelvin-Helmholtz instabilities. These features are similarly seen even in off-center mergers though the detailed structures change slightly. The above-mentioned characteristic magnetic field structures are partly recognized in Faraday rotation measure maps. The higher absolute values of the rotation measure are expected when observed along the collision axis, because of the elongated density distribution and relatively ordered field structure along the axis. T...

Takizawa, Motokazu

2008-01-01

186

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

187

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

Science.gov (United States)

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

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

2009-10-13

188

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

Science.gov (United States)

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

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

2009-01-01

189

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

190

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

International Nuclear Information System (INIS)

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

191

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

Science.gov (United States)

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

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

2011-07-01

192

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-04-01

193

Biological effects from a static magnetic field generated by a 0.5 T Magnetic Resonance system on the enzyme activity of catalase and creatin kinase in rodents  

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

194

Magnetic field measuring device  

International Nuclear Information System (INIS)

In order to directly measure the magnetic fields in the vicinity of plasmas in a thermonuclear device, electric current is supplied to a conductor intersecting magnetic fields, and the position of the conductor is changed by generated electromagnetic forces, and the positional change of the conductor is measured to determine the magnetic fields. Namely, if electric current is supplied to the conductor crossing the magnetic fields, electromagnetic forces directly in proportion to the magnetic fields exert on the object. If the forces are measured, magnetic fields can be determined directly without using an integrator. If springs are attached to the conductor undergoing electromagnetic forces, as a method of measuring electromagnetic forces, since the distortion is in proportion to the electromagnetic forces, magnetic fields can be determined, for example, by changing the position of a contact of a variable resistor interlocking with the positional change of the spring. Since a semiconductor device which is sensitive to radiation is not necessary and the magnetic fields can be measured directly in this method for the measurement of the magnetic fields, the measurement can be conducted at a constant accuracy even in a long period of time. The device of the present invention can measure magnetic fields with no drift components of the integrator, has excellent radiation-resistance and can improve the plant safety. (N.H.)

195

Magnetic field measuring device  

International Nuclear Information System (INIS)

If signal voltages are integrated with lapse of time in a thermonuclear device, erroneous voltages are also integrated with lapse of time thereby resulting in occurrence of measuring errors increased with lapse of time, and continuous measurement for magnetic fields at high accuracy for a long period of time has been difficult. Then, a movable coil is disposed in the magnetic fields to be measured in order to directly measure the magnetic fields at the periphery of the plasmas, and electric current is supplied to the coil and resulted electromagnetic force is measured to obtain a magnetic field. If electric current is supplied to the coil in the magnetic fields, electromagnetic force (rotational torque) directly in proportion to the magnetic fields is generated. If the electromagnetic force is measured, magnetic fields can be determined directly without using an integrator. If a resistor wire is disposed on one end of the coil so that the resistor wire extends/shrinks by the electromagnetic force and changes the resistance value, the electromagnetic force can be determined from the magnetic fields based on the change of the resistance values. Since the measurement using magnetic fields does not require semiconductor devices which are sensitive to radiation, and the magnetic fields can be measured directly, the measurement can be conducted at a constant accuracy even for a long period of time. (N.H.)

196

Diffraction-biased shear wave fields generated with longitudinal magnetic resonance elastography drivers.  

Science.gov (United States)

Magnetic resonance elastography (MRE) is a technique for quantifying the acoustic response of biological tissues to propagating waves applied at low frequencies in order to evaluate mechanical properties. Application-specific MRE drivers are typically required to effectively deliver shear waves within the tissue of interest. Surface MRE drivers with transversely oriented vibrations have often been used to directly generate shear waves. These drivers may have disadvantages in certain applications, such as poor penetration depth and inflexible orientation. Therefore, surface MRE drivers with longitudinally oriented vibrations are used in some situations. The purpose of this work was to investigate and optimize a longitudinal driver system for MRE applications. A cone-like hemispherical distribution of shear waves being generated by these drivers and the wave propagation being governed by diffraction in the near field are shown. Using MRE visualization of the vector displacement field, we studied the properties of the shear wave field created by longitudinal MRE drivers of various sizes to identify optimum shear wave imaging planes. The results offer insights and improvements in both experimental design and imaging plane selection for 2-D MRE data acquisition. PMID:18467059

Yin, Meng; Rouvière, Olivier; Glaser, Kevin J; Ehman, Richard L

2008-07-01

197

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-11-15

198

Effects of Magnetic Field on Entropy Generation in Flow and Heat Transfer due to a Radially Stretching Surface  

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

199

Exploring the role of a basal magma ocean in generating Earth's ancient magnetic field (Invited)  

Science.gov (United States)

Observations of Earth's magnetic field extending back to 3.45 billion years ago indicate that generation by a core dynamo must be sustained over most of Earth's history. However, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo throughout Earth history by convective core cooling alone. Here we explore the geomagnetic consequences of a basal magma ocean layer in the lowermost mantle, hypothesized to exist in the early Earth and surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. We consider a range of possible electrical conductivities and find that for the highest electrical conductivities considered, a long-lived basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4 Ga-present within a quasi-adiabatic core that includes a solidifying inner core.

Ziegler, L. B.; Stegman, D. R.

2013-12-01

200

Implications of a long-lived basal magma ocean in generating Earth's ancient magnetic field  

Science.gov (United States)

Observations of Earth's magnetic field extending back to 3.45 billion years ago indicate that generation by a core dynamo must be sustained over most of Earth's history. However, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly three times larger than previously thought, exacerbating difficulties for driving a core dynamo throughout Earth history by convective core cooling alone. Here, we explore the geomagnetic consequences of a basal magma ocean layer in the lowermost mantle, hypothesized to exist in the early Earth and perhaps surviving until well after the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. We consider a range of possible electrical conductivities and find that for the highest electrical conductivities considered, a long-lived basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5 to 2.45 Ga within a basal magma ocean, from 2.25 to 0.4 Ga within a superadiabatically cooled liquid core, and from 0.4 Ga to present within a quasi-adiabatic core that includes a solidifying inner core.

Ziegler, L. B.; Stegman, D. R.

2013-11-01

201

Exploring the role of a basal magma ocean in generating Earth's ancient magnetic field  

Science.gov (United States)

Observations of Earth's magnetic field extending back to 3.45 billion years ago indicate that generation by a core dynamo must be sustained over most of Earth's history. However, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core.

Ziegler, Leah; Stegman, Dave

2014-05-01

202

Observation of self-similarity in the magnetic fields generated by the ablative nonlinear Rayleigh-Taylor instability.  

Science.gov (United States)

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. PMID:23683208

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

203

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

International Nuclear Information System (INIS)

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

204

Laboratory measurements of 0.7 GG magnetic fields generated during high-intensity laser interactions with dense plasmas  

International Nuclear Information System (INIS)

We report measurements of ultrahigh magnetic fields produced during intense (?1020 Wcm-2 ?m2) laser interaction experiments with solids. We show that polarization measurements of high-order vuv laser harmonics generated during the interaction (up to the 15th order) suggest the existence of magnetic field strengths of 0.7±0.1 GG in the overdense plasma. Measurements using higher order harmonics indicate that denser regions of the plasma can be probed. This technique may be useful for measurements of multi-GG level magnetic fields which are predicted to occur at even higher intensities

205

Generation of strong quasistatic magnetic fields in interactions of ultraintense and short laser pulses with overdense plasma targets.  

Science.gov (United States)

An analytical fluid model is proposed for the generation of strong quasistatic magnetic fields during normal incidence of a short ultraintense Gaussian laser pulse with a finite spot size on an overdense plasma. The steepening of the electron density profile in the originally homogeneous overdense plasma and the formation of electron cavitation as the electrons are pushed inward by the laser are included self-consistently. It is shown that the appearance of the cavitation plays an important role in the generation of quasistatic magnetic fields: the strong plasma inhomogeneities caused by the formation of the electron cavitation lead to the generation of a strong axial quasistatic magnetic field Bz. In the overdense regime, the generated quasistatic magnetic field increases with increasing laser intensity, while it decreases with increasing plasma density. It is also found that, in a moderately overdense plasma, highly intense laser pulses can generate magnetic fields approximately 100 MG and greater due to the transverse linear mode conversion process. PMID:17930347

Cai, Hong-bo; Yu, Wei; Zhu, Shao-ping; Zhou, Cang-tao

2007-09-01

206

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)

207

Generation of static magnetic fields by a test charge in a plasma with an electron temperature anisotropy  

International Nuclear Information System (INIS)

A kinetic theory is derived for the generation of a magnetic field by a test charge in a plasma with an anisotropic temperature. The spatial structure of both the magnetostatic and electrostatic components of the field of the charge is studied

208

Steady current generation by RF travelling field in a magnetized toroidal plasma  

International Nuclear Information System (INIS)

There are two factors to control the currents driven by RF fields travelling along a toroidal plasma; one is the penetration depth of the RF magnetic field into the plasma, and the other is the ratio of the RF magnetic field to the static toroidal magnetic field Bsub(t). The currents are observed to increase with Bsub(t), since the skin depth for the RF fields increases. There is an optimum toroidal magnetic field to hold a maximum toroidal current, and at higher Bsub(t), the toroidal currents decrease as more strongly than Bsub(t)sup(-1). The toroidal current can also be excited by a local assembly of RF coils. (auth.)

209

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

CERN Document Server

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

Ballardini, Mario; Paoletti, Daniela

2014-01-01

210

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

Science.gov (United States)

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

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

2014-12-01

211

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

Science.gov (United States)

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

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

2014-12-01

212

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

KAUST Repository

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

Kim, J.

2014-12-04

213

Magnetic Propeller for Uniform Magnetic Field Levitation  

OpenAIRE

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

214

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

International Nuclear Information System (INIS)

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

215

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

Science.gov (United States)

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

Malik, Anil Kumar; Malik, Hitendra K.

2011-11-01

216

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

CERN Document Server

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

Caprioli, D; Amato, E; Vietri, M

2008-01-01

217

Studies on the wall conditioning with microwave-generated plasmas in a toroidal magnetic field  

International Nuclear Information System (INIS)

One main problem for the use of the controlled fusion as possible energy source for the future is the interaction between of the hot fusion plasma with the surrounding wall components of the vacuum vessel. To reduce these negative effects it is indispensable to condition the vessel walls regular by deposition of thin, oxygen gettering layers using reactive gases like silane (SiH4) or diborane (B2H6) and to remove accumulated impurities. These methods have been mainly developed at the experimental device TEXTOR at the research centre Juelich and are successfully practised at many fusion devices by using glow discharges. The implementation of superconducting field coils in future fusion devices will lead to significant extended discharge duration but will also require new techniques for the wall conditioning, because glow discharges are not compatible with the permanent magnetic fields. Therefore, this thesis is dedicated to the investigation of microwave generated plasmas in a toroidal magnetic field. In the first part the discharge is characterised in dependence on the selectable parameters magnetic field strength, neutral gas pressure and microwave input power. Spatial measurements of the electron density and temperature were done for different process gases to allow an extrapolation of the results on the plasma parameter during the layer deposition in reactive gaseous like methane (CH4) or acetylene (C2H2) or acetylene (C2H2). As a result of the application of various diagnostics the spatial distribution of the film thickness on the wall of the vacuum vessel could be distinguished. Further on the composition of the layers by carbon and hydrogen could by analysed and the thermal stability of the films was investigated ex-situ. The results of these measurements leads to an improved understanding on the mechanism of the film growth and the influence of neutral radicals and charged hydrocarbons on it. In addition the erosion of the deposited layers by discharges in hydrogen, deuterium and oxygen has been characterised by mass spectrometry and investigation of the layer thickness by interference colour analysis. (orig.)

218

The Effect of Lower Mantle Metallization on Magnetic Field Generation in Rocky Exoplanets  

CERN Document Server

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 d...

Vilim, Ryan; Elkins-Tanton, Linda

2013-01-01

219

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

Science.gov (United States)

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

Zibold, A. F.

2015-02-01

220

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

Science.gov (United States)

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

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

2008-06-01

221

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

Science.gov (United States)

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

Stepinski, Tomasz F.

1994-01-01

222

The magnetic field effect on electron beam generation in magnetron injection guns with secondary-emission cathodes  

International Nuclear Information System (INIS)

The experiments have shown that a variation in the magnetic field can give rise to space charge oscillations in the interelectrode (anode-cathode) gap of the magnetron gun.These effects observed during beam generation and transport must be taken into account when using a magnetron gun in high-power microwave devices

223

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

International Nuclear Information System (INIS)

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

224

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

International Nuclear Information System (INIS)

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

225

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

226

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-07-01

227

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

Science.gov (United States)

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

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

2015-03-01

228

Use of second generation coated conductors for efficient shielding of DC magnetic fields  

OpenAIRE

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO) coated conductors. Since effective screening of the axial DC magnetic field requires the unimpeded flow of an azimuthal persistent current, we demonstrate a configuration of a screening shell made out of standard YBCO coated conductor capable to accomplish that. The screen allows the persistent current to flow in the predominantly azimuthal dire...

Fagnard, Jean-francois; Dirickx, Michel; Levin, G. A.; Barnes, P. N.; Vanderheyden, Benoi?t; Vanderbemden, Philippe

2010-01-01

229

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

OpenAIRE

Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha), Eckert number (Ec), Prandtl number (Pr), Joule heating parameter (R) and the free stream temperature parameter (θ∞)...

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

2004-01-01

230

The dynamics of current channels with large self-generated magnetic fields  

International Nuclear Information System (INIS)

In a series of experiments a single of two parallel current channels are drawn through a collisionless magnetoplasma produced by an barium oxide-coated cathode, DC discharge. In the first series of experiments two cylindrical current channels are launched and their behavior is tracked in space and time using detailed maps of Bvector(rvector, t). The three dimensional currents are evaluated (Jvector = ?o-1 rot Bvector. The columns are observed to merge and twist about each other but are free from kink or sausage instabilities. In a second series of experiments a single cylindrical current channel is established in a background plasma. Using a repidly swept Langmuir probe the plasma potential, density and temperature are evaluated in the current channel and its surroundings. A self-generated radial electric field is observed. The column also twists about itself. The relative magnetic helicity is evaluated in the volumen probed and is found to jump after the current formation occurs. (author). 12 refs.; 14 figs

231

Intermediate frequency magnetic field generated by a wireless power transmission device does not cause genotoxicity in vitro.  

Science.gov (United States)

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. PMID:25196478

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

2014-10-01

232

Generation of large-scale magnetic fields, non-Gaussianity, and primordial gravitational waves in inflationary cosmology  

CERN Document Server

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

233

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

CERN Document Server

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

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

2008-01-01

234

Effects of the axial magnetic field on RF plasma generation mechanism using a spiral antenna  

Energy Technology Data Exchange (ETDEWEB)

Characteristics of the RF produced plasma using a planar, spiral antenna are investigated. In order to understand electron heating process in inductively coupled plasma, skin depth of the evanescent wave and antenna loading resistance are measured at various collision frequency. These results show that a collisionless (collisional) heating mechanism exists in the low (high) collisionality region. In addition, with an applied magnetic field, observed spatial profiles of excited magnetic fields and the dispersion relation show that helicon wave with a dominant azimuthal mode number of m=0 can be excited. (author)

Takechi, S.; Shinohara, S.; Kawai, Y. [Kyushu Univ., Fukuoka (Japan)

1997-12-31

235

Effects of the axial magnetic field on RF plasma generation mechanism using a spiral antenna  

International Nuclear Information System (INIS)

Characteristics of the RF produced plasma using a planar, spiral antenna are investigated. In order to understand electron heating process in inductively coupled plasma, skin depth of the evanescent wave and antenna loading resistance are measured at various collision frequency. These results show that a collisionless (collisional) heating mechanism exists in the low (high) collisionality region. In addition, with an applied magnetic field, observed spatial profiles of excited magnetic fields and the dispersion relation show that helicon wave with a dominant azimuthal mode number of m=0 can be excited. (author)

236

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

International Nuclear Information System (INIS)

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

237

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

Science.gov (United States)

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

Béghin, Christian

2015-02-01

238

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

OpenAIRE

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 larg...

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

2014-01-01

239

Gap generation in the XXZ model in a transverse magnetic field  

OpenAIRE

The ground state phase diagram of the 1D XXZ model in transverse magnetic field is obtained. It consists of the gapped phases with different types of long range order (LRO) and critical lines at which the gap and the LRO vanish. Using scaling estimations and a mean-field approach as well as numerical results we found critical indices of the gap and the LRO in the vicinity of all critical lines.

Dmitriev, D. V.; Krivnov, V. Ya; Ovchinnikov, A. A.

2001-01-01

240

Interaction of an SCT with an Externally Generated Diamagnetic Magnetic Field Structure  

Science.gov (United States)

It is clear that an efficient tokamak-based fusion reactor will require high plasma beta. In the high poloidal beta regime (?p > 1), the internal poloidal currents of the tokamak discharge serve to cancel the vacuum toroidal field created by the external TF coils. Since the zeroth order stopping mechanism of the Spheromak-like Compact Toroid (SCT) is the displacement energy of the toroidal field, the diamagnetic effect can produce new physics issues for SCT penetration. We have added a pair of external coils on the vessel of our Davis diverted Torus (DDT) tokamak at the injection location. We will excite an opposite magnetic field using these external coils to artificially create a diamagnetic field region where the SCT enters the tokamak. The major radial dependence of the local coils is substantially different than the oversized toroidal field coil structure. In addition to the interaction studies, we will measure the effect of the field gradient on SCT penetration. Several diagnostics will be used to observe the behavior of the SCT translating into the DDT field region including magnetic probes to measure the rotation of the SCT in the DDT field structure.

Hwang, D. Q.

1998-11-01

241

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

242

General coil-shape in superconducting quadrupole magnets for generating the perfect field  

International Nuclear Information System (INIS)

It is well-known that a constant current in a coil configuration generated by two perpendicular intersecting ellipses produces the perfect quadrupole field. We have found that an ideal quadrupole field can be obtained with a variety of coil shapes and the intersecting ellipse shape is only a special form in that class. We have given the general form of the coil shape for generating the ideal quadrupole field. The shape parameters of the coil can be optimized to obtain the maximum possible gradient for a given coil cross-section and aperture

243

Experimental investigation of a Ka band high power millimeter wave generator operated at low guiding magnetic field  

International Nuclear Information System (INIS)

An overmoded slow wave type Ka band generator is investigated experimentally to produce high power millimeter waves in this paper. The experiments were carried out at the TORCH-01 accelerator. The produced microwave frequency was measured by dispersive line method, and the power was estimated by integrating over the radiation pattern at far field. With relatively low guiding magnetic field of 0.8 T and diode voltage and beam current of 590 kV and 5.2 kA, respectively, a 33.56 GHz millimeter wave with an output power of 320 MW was generated, and the microwave mode was quasi-TM01 mode.

244

Generation of Magnetic Field by Combined Action of Turbulence and Shear  

CERN Document Server

The possibility of a mean-field dynamo in nonhelical turbulence with superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of magnetic field at scales much larger than the outer scale of the turbulence is found. The charateristic scale of the field is ~ S^{-1/2} and growth rate is gamma ~ S, where S is the shearing rate. This newly discovered form of large-scale dynamo action may have an extremely broad range of applications to astrophysical systems with spatially coherent mean flows.

Yousef, T A; Schekochihin, A A; Kleeorin, N; Rogachevskii, I; Iskakov, A B; Cowley, S C; McWilliams, J C

2007-01-01

245

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

International Nuclear Information System (INIS)

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

246

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

International Nuclear Information System (INIS)

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

247

Simulations of Magnetic Field Generation in Unmagnetized Plasmas via Beat Wave Current Drive  

OpenAIRE

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 elect...

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

2012-01-01

248

Multi-megajoule pulsed power generation from a reusable compressed magnetic field device  

International Nuclear Information System (INIS)

A pulsed power system is described which is potentially capable of producing multimegajoule pulses with millisecond rise time and repetition rates of more than one per second. A metallic piston is driven by gas combustion through axially aligned coils which are originally energized with relatively small magnetic energy. Experimental results are presented for a pulse generator of this kind which utilized a piston of 20 MJ kinetic energy, and comparison is made with predictions of a numerical model

249

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

Science.gov (United States)

The velocity fields generated by a static pair of magnets in free-surface electromagnetically forced flows are analyzed for different magnet attitudes, ionic currents, and brine depths. A wide range of laminar velocity fields is obtained despite the forcing simplicity. The velocity fields are classified according to their temporal mean flow topology, which strongly depends on the forcing geometry but barely on its strength, even through the bifurcation to unsteady regimes. The mean flow topology possesses a major influence on the critical Reynolds 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

250

Mechanism for the generation of 109 G magnetic fields in the interaction of ultraintense short laser pulse with an overdense plasma target  

International Nuclear Information System (INIS)

The physical mechanism for the generation of very high ''dc'' magnetic fields in the interaction of ultraintense short laser pulse with an overdense plasma target originates in the spatial gradients and nonstationary character of the ponderomotive force. A set of model equations to determine the evolution of the ''dc'' fields is derived and it is shown that the ''dc'' magnetic field is of the same order of magnitude as the high frequency laser magnetic field

251

Efficient laser-overdense plasma coupling via surface plasma waves and steady magnetic field generation  

Science.gov (United States)

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 1017 W cm-2 ?m2) laser pulse intensities. At "relativistic" laser intensity, steady magnetic fields as high as ˜580 MG ?m/?0 at 7 × 1019 W cm-2 ?m2 are obtained in the simulations.

Bigongiari, A.; Raynaud, M.; Riconda, C.; Héron, A.; Macchi, A.

2011-10-01

252

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

Directory of Open Access Journals (Sweden)

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

Ammar Ben Brahim

2011-11-01

253

Generation of zonal magnetic fields by drift waves in a current carrying nonuniform magnetoplasma  

International Nuclear Information System (INIS)

It is shown that zonal magnetic fields (ZMFs) can be nonlinearly excited by incoherent drift waves (DWs) in a current carrying nonuniform magnetoplasma. The dynamics of incoherent DWs in the presence of ZMFs is governed by a wave-kinetic equation. The governing equation for ZMFs in the presence of nonlinear advection force of the DWs is obtained from the parallel component of the electron momentum equation and the Faraday law. Standard techniques are used to derive a nonlinear dispersion relation, which depicts instability via which ZMFs are excited in plasmas. ZMFs may inhibit the turbulent cross-field particle and energy transport in a nonuniform magnetoplasma.

254

Magnetic field generation by circularly polarized laser light and inertial plasma confinement in a miniature 'Magnetic Bottle' induced by circularly polarized laser light  

International Nuclear Information System (INIS)

A new concept of hot plasma confinement in a miniature magnetic bottle induced by circularly polarized laser light is suggested in this work. Magnetic fields generated by circularly polarized laser light may be of the order of megagauss. In this configuration the circularly polarized laser light is used to get confinement of a plasma contained in a good conductor vessel. The poloidal magnetic field induced by the circularly polarized laser and the efficiency of laser absorption by the plasma are calculated in this work. The confinement in this scheme is supported by the magnetic forces and the Lawson criterion for a DT plasma might be achieved for number density n=5*1021 cm-3 and confinement time ?= 20 nsec. The laser and the plasma parameters required to get an energetic gain are calculated. (authors)

255

Magnetophoretic velocimetry of manganese(II) in a single microdroplet in a flow system under a high gradient magnetic field generated with a superconducting magnet.  

Science.gov (United States)

An experimental system for magnetophoretic velocimetry, which could determine the volume magnetic susceptibility of a single particle dispersed in a liquid phase from a magnetophoretic velocity, has been developed. A micrometer-sized high-gradient magnetic field could be generated in a capillary by a pair of iron pole pieces in a superconducting magnet (10 T). The magnetophoretic behavior of a single particle in a capillary flow system was investigated under the inhomogeneous magnetic field. From the magnetophoretic velocity of a polystyrene latex particle dispersed in a MnCl2 aqueous solution, the product of the magnetic flux density and the gradient, B(dB/dx), was determined as a function of the position along the capillary. The maximum value of B(dB/dx) was 4.7 x 10(4) T2 m(-1), which was approximately 100 times higher than that obtained by two Nd-Fe-B permanent magnets (0.4 T). Organic droplets extracting manganese(II) with 2-thenoyltrifluoroacetone and tri-n-octylphosphine oxide from MnCl2 solution were used as test samples. The difference of the volume magnetic susceptibility between the droplet and the medium could be determined from the magnetophoretic velocity. This method allowed us to continuously measure a volume magnetic susceptibility of 10-6 level for a picoliter droplet and to determine manganese(II) in the single droplet at the attomole level. PMID:12380826

Suwa, Masayori; Watarai, Hitoshi

2002-10-01

256

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

Directory of Open Access Journals (Sweden)

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

Moh'd A. Al-Nimr

2004-06-01

257

The saturation of the electron beam filamentation instability by the self-generated magnetic field and magnetic pressure gradient-driven electric field  

CERN Document Server

Two counter-propagating cool and equally dense electron beams are modelled with particle-in-cell (PIC) simulations. The electron beam filamentation instability is examined in one spatial dimension. The box length resolves one pair of current filaments. A small, a medium-sized and a large filament are considered and compared. The magnetic field amplitude at the saturation time of the filamentation instability is proportional to the filament size. It is demonstrated, that the force on the electrons imposed by the electrostatic field, which develops during the nonlinear stage of the instability, oscillates around a mean value that equals the magnetic pressure gradient force. The forces acting on the electrons due to the electrostatic and the magnetic field have a similar strength. The electrostatic field reduces the confining force close to the stable equilibrium of each filament and increases it farther away. The confining potential is not sinusoidal, as assumed by the magnetic trapping model, and it permits an...

Dieckmann, M E; Kourakis, I; Borghesi, M

2008-01-01

258

Generation and transfer of polarized radiation in the solar atmosphere: Physical mechanisms and magnetic-field diagnostics  

Science.gov (United States)

The main physical mechanisms responsible for the generation and transfer of polarized radiation in the solar atmosphere can be classified in a suitable bidimensional diagram with an indicator of the magnetic field strength on its vertical axis and an indicator of the radiation field anisotropy on its horizontal axis. The various polarimetric observations performed on solar spectral lines are interpreted with different theoretical schemes according to their classification in the diagram and to the optical depths involved. These theoretical schemes, and the associated diagnostic tools for inferring the magnetic field vector from observations are reviewed. In particular, the role of magneto-optical effects in determining the direction of the observed linear polarization in active regions is discussed in some detail.

Deglinnocenti, E. L.

1985-01-01

259

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

Directory of Open Access Journals (Sweden)

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

Józef Kunc

1971-01-01

260

Exploring Magnetic Field Lines  

Science.gov (United States)

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

2012-06-26

261

Magnetic field sensor  

Science.gov (United States)

Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.

Silva, Nicolas

2012-09-01

262

Ocean circulation generated magnetic signals  

DEFF Research Database (Denmark)

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

Manoj, C.; Kuvshinov, A.

2006-01-01

263

Magnetoresistance Generated by Combination of Spin-Orbit Interaction and Applied Magnetic Field in Bipolar Conductors  

Science.gov (United States)

We have theoretically studied the magnetotransport properties in bipolar conductors under consideration of the simultaneous presence of an external magnetic field, left-right asymmetric carrier scattering due to spin-orbit interactions, and spin-polarized holes/electrons, predicting both positive and negative transverse magnetoresistance (TMR) terms, the mechanisms of which are completely different from the conventional mechanism in bipolar conductors. The positive TMR term is predicted only for the asymmetric carrier scattering case, the sign of which is the same (negative) between a hole and an electron. The other case of asymmetric scattering, the sign of which is opposite between a hole and an electron, was also determined to always show a negative TMR. Our proposed TMR was experimentally evidenced from the magnetotransport and magnetization measurements of a compensated metal, YH2. Also, application to logic gates is discussed on the basis of our proposed mechanism.

Sakai, Masamichi; Kodama, Daisuke; Okano, Yoshihisa; Sakuraba, Takahito; Honda, Zentaro; Kitajima, Akira; Oshima, Akihiro; Higuchi, Koji; Hasegawa, Shigehiko; Nakamura, Osamu

2013-09-01

264

CAVMA3 - an IBM 360/75 code for calculating axial and radial components of the magnetic field generated by a finite-dimensions axially symmetrical coil; application to the experiment of magnetic scattering in nuclear reactor  

CERN Document Server

CAVMA3 - an IBM 360/75 code for calculating axial and radial components of the magnetic field generated by a finite-dimensions axially symmetrical coil; application to the experiment of magnetic scattering in nuclear reactor

Franco, F; Pedretti, E no 1; Franco, F no 1

1973-01-01

265

Instability of relativistic electron layer rotating in crossed radial electrostatic and axial magnetic fields due to generation by high frequency radiation  

International Nuclear Information System (INIS)

Mechanisms of electromagnetic oscillation generation by a thin cylindric layer of relativistic electrons in crossed radial electrostatic and axial magnetic fields in a cylindric oscillator are studied theoretically. Dispersion equations which describe electron-wave interaction are obtained. It was shown that wave generation is possible by plasma or Cherenkov resonances. The advantages and disadvantages of different generation mechanisms are discussed. Dependence of the obtained results on relativistic factor and magnetic field is studied. 7 refs

266

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

CERN Document Server

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

Favier, Benjamin

2013-01-01

267

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

268

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

Science.gov (United States)

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

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

2015-02-01

269

Novel modes of vacuum discharges in magnetic field as the base for effective ion generation  

International Nuclear Information System (INIS)

New properties of vacuum discharges in magnetic field with unconventional discharge gaps at low pressure up to high vacuum are briefly described. Both single- and multi-charge ion sources may be developed on basis of such new discharge modes. Such ion sources may have advantages in comparison with conventional ones. The main advantages are the long lifetime due to the absence of filaments and arc spots, high energy and gas efficiency due to high plasma electron temperature. The development of the discharge research and recent results are discussed.

270

Exploring Magnetic Fields  

Science.gov (United States)

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

2012-08-03

271

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

CERN Document Server

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

von der Pahlen, Jan Graf

2015-01-01

272

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

International Nuclear Information System (INIS)

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

273

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

OpenAIRE

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

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

2014-01-01

274

Simulation Study of Magnetic Fields Generated by the Electromagnetic Filamentation Instability  

Science.gov (United States)

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

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

2007-01-01

275

Efficient laser-overdense plasma coupling via surface plasma waves and steady magnetic field generation  

Energy Technology Data Exchange (ETDEWEB)

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 10{sup 15} to 10{sup 20} W cm{sup -2}{mu}m{sup 2} with electron density ranging from 25 to 100n{sub c} 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{lambda}{sup 2} < 10{sup 17} W cm{sup -2}{mu}m{sup 2}) and high (I{lambda}{sup 2} > 10{sup 17} W cm{sup -2}{mu}m{sup 2}) laser pulse intensities. At ''relativistic'' laser intensity, steady magnetic fields as high as {approx}580 MG {mu}m/{lambda}{sub 0} at 7 x 10{sup 19} W cm{sup -2}{mu}m{sup 2} are obtained in the simulations.

Bigongiari, A. [CEA/DSM/LSI, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); TIPS/LULI, Universite Paris 6, CNRS, CEA, Ecole Polytechnique, 3, rue Galilee 94200, Ivry-sur-Seine (France); Raynaud, M. [CEA/DSM/LSI, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Riconda, C. [TIPS/LULI, Universite Paris 6, CNRS, CEA, Ecole Polytechnique, 3, rue Galilee 94200, Ivry-sur-Seine (France); Heron, A. [CPHT, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Macchi, A. [Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica (CNR/INO), Dipartimento di Fisica ' ' E. Fermi' ' , Largo B. Pontecorvo 3, 56127 Pisa (Italy)

2011-10-15

276

Magnetic Fields Matter  

Science.gov (United States)

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,

277

Visualizing Magnetic Field Lines  

Science.gov (United States)

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,

278

What are Magnetic Fields?  

Science.gov (United States)

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

279

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

280

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

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

281

A method for assessing occupational exposure to power-frequency magnetic fields for electricity generation and transmission workers  

International Nuclear Information System (INIS)

A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the lin.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

282

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

283

Mapping Magnetic Fields  

Science.gov (United States)

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

2012-08-03

284

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

International Nuclear Information System (INIS)

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

285

Magnetic Propeller for Uniform Magnetic Field Levitation  

CERN Document Server

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

286

The earth's magnetic field  

International Nuclear Information System (INIS)

After a historical introduction in Chapter 1, the more traditional aspects of geomagnetism relating to the present field and historical observations are presented in Chapter 2. The various methods and techniques and theoretical background of palaeomagnetism are given in Chapter 3. Chapters 4, 5 and 6 present the results of palaeomagnetic and archaeomagnetic studies in three topics. Chapter 4 relates to studies of the geomagnetic field roughly back to about 50,000 years ago. Chapter 5 is about reversals of the geomagnetic field and Chapter 6 presents studies of the field for times older than 50,000 years and on the geological time scale of millions or hundreds of millions of years. Chapters 7, 8 and 9 provide insight into dynamo theory. Chapter 7 is essentially a non-mathematical attempt to explain the physical basis of dynamo theories to palaeomagnetists. This is followed in Chapter 8 by a more advanced theoretical treatment. Chapter 9 explains theoretical aspects of secular variation and the origin of reversals of the geomagnetic field. Chapter 10 is our attempt to relate theory to experiment and vice versa. The final two chapters consider the magnetic fields of the moon, sun, planets and meteorites, in an attempt to determine the necessary and sufficient conditions for magnetic field generation in large solar system bodies. (author)

287

The Earth's Magnetic Field  

OpenAIRE

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

288

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

International Nuclear Information System (INIS)

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

289

Drawing Magnetic Fields  

Science.gov (United States)

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

VU Bioengineering RET Program,

290

The Magnetic Field  

Science.gov (United States)

This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

Jeffrey Barker

291

Circuits and Magnetic Fields  

Science.gov (United States)

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

VU Bioengineering RET Program,

292

Time-reversal violating generation of static magnetic and electric fields and a problem of electric dipole moment measurement  

OpenAIRE

It is shown that in the experiments for search of the EDM of an electron (atom, molecule) the T-odd magnetic moment induced by an electric field and the T-odd electric dipole moment induced by a magnetic field will be also measured. It is discussed how to distinguish these contributions.

Baryshevsky, Vladimir G.

2003-01-01

293

Magnetic Field Problem  

Science.gov (United States)

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. 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.

Wolfgang Christian

294

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-15

295

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

International Nuclear Information System (INIS)

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

296

A new mechanism for the generation of primordial seeds for the cosmic magnetic fields  

CERN Document Server

We discuss the inflationary production of magnetic seeds for the galactic dynamo through the photon-graviphoton mixing typical of extended models of local supersymmetry. An analisys of the allowed region in parameter space shows that such a mechanism is compatible with existing phenomenological bounds on the vector mass and on the mixing parameter.

Gasperini, M

2001-01-01

297

Mapping Magnetic Field Lines  

Science.gov (United States)

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

298

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

International Nuclear Information System (INIS)

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

299

The Magnetic Field  

Science.gov (United States)

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

Windows to the Universe

1997-12-03

300

Primordial magnetic field limits from cosmological data  

International Nuclear Information System (INIS)

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

301

Magnetic Field Measurements in Beam Guiding Magnets  

CERN Document Server

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as well as the recently developed method of beam based alignment. References of historical nature as well as citations of recent work are given. The present commercial availability of the different sensors and asso-ciated equipment is indicated. Finally we shall try to analyze possible future needs for developments in those fields.

Henrichsen, K N

1998-01-01

302

Field free line magnetic particle imaging  

CERN Document Server

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

303

A high-field superferric NMR magnet.  

Science.gov (United States)

Strong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4-T, whole-body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4-T, 30-cm-bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along the z axis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spectroscopy. PMID:8419740

Huson, F R; Bryan, R N; MacKay, W W; Herrick, R C; Colvin, J; Ford, J J; Pissanetzky, S; Plishker, G A; Rocha, R; Schmidt, W

1993-01-01

304

Controlling magnetic field profiles  

International Nuclear Information System (INIS)

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

305

Dissipation of the sectored heliospheric magnetic field near the heliopause: a mechanism for the generation of anomalous cosmic rays  

CERN Document Server

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

306

Generation of strong magnetic fields via the small-scale dynamo during the formation of the first stars  

CERN Document Server

Here we summarize our recent results of high-resolution computer simulations on the turbulent amplification of weak magnetic seed fields showing that such fields will be exponentially amplified also during the gravitational collapse reminiscent to the situation during primordial star formation. The exponential magnetic field amplification is driven by the turbulent small-scale dynamo that can be only observed in computer simulations if the turbulent motions in the central core are sufficiently resolved. We find that the Jeans length, which determines the central core region, has to be resolved by at least 30 grid cells to capture the dynamo activity. We conclude from our studies that strong magnetic fields will be unavoidably created already during the formation of the first stars in the Universe, potentially influencing their evolution and mass distribution.

Banerjee, Robi; Federrath, Christoph; Schleicher, Dominik R G; Klessen, Ralf S

2012-01-01

307

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

308

On the possibility of generating and/or sustaining the reversed field pinch configurations by means of a transverse rotating magnetic field  

International Nuclear Information System (INIS)

The generation of plasma currents using rotating fields is examined. Numerical studies show that, provided the amplitude of the applied rotating field exceeds some value, it completely penetrates the plasma and sets the electrons rotating. An experiment is described which uses this technique to generate a reversed field configuration. Attention is drawn to the usefulness of the technique in generating the equilibrium currents appropriate to a variety of plasma-field configurations

309

Passive Magnetic Shielding in Gradient Fields  

CERN Document Server

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

Bidinosti, C P

2013-01-01

310

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

International Nuclear Information System (INIS)

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

311

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

International Nuclear Information System (INIS)

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

312

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

Directory of Open Access Journals (Sweden)

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

Imbert-Gérard Lise-Marie

2011-11-01

313

Influence of the back-reaction of streaming cosmic rays on magnetic field generation and thermal instability  

CERN Document Server

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

314

Detecting Exoplanetary Magnetic Fields  

Science.gov (United States)

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

Llama, Joe

2015-01-01

315

Magnetic fields in the early universe  

CERN Document Server

We give a pedagogical introduction to two aspects of magnetic fields in the early universe. We first focus on how to formulate electrodynamics in curved space time, defining appropriate magnetic and electric fields and writing Maxwell equations in terms of these fields. We then specialize to the case of magnetohydrodynamics in the expanding universe. We emphasize the usefulness of tetrads in this context. We then review the generation of magnetic fields during the inflationary era, deriving in detail the predicted magnetic and electric spectra for some models. We discuss potential problems arising from back reaction effects and from the large variation of the coupling constants required for such field generation.

Subramanian, Kandaswamy

2009-01-01

316

Combined effect of internal heat generation and magnetic field on free convection and mass transfer flow in a micropolar fluid with constant suction  

Science.gov (United States)

This paper studied the problem of free convection with mass transfer flow for a micropolar fluid bounded by a vertical infinite surface with an exponentially decaying heat generation, under the action of a transverse magnetic field. Numerical calculations are carried out for the various parameters entering into the problem. The numerical values of the skin friction, the wall couple stress, the rate of heat transfer, the concentration gradient at the wall and the boundary layer thickness are shown graphically as functions of the magnetic field parameter.

El-Amin, M. F.

2004-03-01

317

Generation of nuclear magnetic resonance images  

International Nuclear Information System (INIS)

Two generation techniques of nuclear magnetic resonance images, the retro-projection and the direct transformation method are studied these techniques are based on the acquisition of NMR signals which phases and frequency components are codified in space by application of magnetic field gradients. The construction of magnet coils is discussed, in particular a suitable magnet geometry with polar pieces and air gap. The obtention of image contrast by T1 and T2 relaxation times reconstructed from generated signals using sequences such as spin-echo, inversion-recovery and stimulated echo, is discussed. The mathematical formalism of matrix solution for Bloch equations is also presented. (M.C.K.)

318

Field-aligned currents and magnetospheric generator in experiments on a laser-produced plasma flowing around a magnetic dipole  

Science.gov (United States)

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

319

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

320

The effect of applied magnetic field on photocurrent generation in poly-3-hexylthiophene:[6,6]-phenyl C61-butyric acid methyl ester photovoltaic devices  

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)

321

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

Science.gov (United States)

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

Mima, Kunioki; Sunahara, A.; Shiraga, Hiroyuki; Nishimura, H.; Azechi, H.; Johzaki, T.; Nagatomo, H.; Garcia, C.; Veralde, P.

2010-11-01

322

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

Directory of Open Access Journals (Sweden)

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

Serena Fiocchi

2015-04-01

323

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

324

ISR Radial Field Magnet  

CERN Multimedia

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

1983-01-01

325

Isotope separation by magnetic fields  

International Nuclear Information System (INIS)

One of the isotopes of an element having several isotopes can be separated from the others in a dense, neutral plasma. Thus initially a neutral plasma is prepared including the element in question. This may consist of positive ions and negative electrons or alternatively of positive and negative ions, or else of a mixture of positive ions, negative ions and electrons. The plasma may then be injected into a magnetic field or may be generated in the field where more energy is imparted to a selected isotope than to the others. Finally, the isotopes are separated from each other on the basis of their differential energies. For example, the selected isotope may be given more energy than the others by stimulating it within the plasma at its resonant frequency which may be close to the cyclotron frequency, either by an electric field or by a magnetic field. In order to excite the other isotope, a different resonant frequency is required which depends on the plasma density, the relative concentration of electrons if the plasma contains electrons, the strength of the magnetic field, the ratio of charge to mass of the isotope, and possibly on the physical parameters of the plasma apparatus itself, such as the ratio of the length of the plasma column to its radius. The more energetic isotope may be separated by energy dependent chemical reactions, it may be collected by a positively biased probe or else the isotopes may be separated from each other by magnetic fields or in various other ways

326

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

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

327

Generation of Alfven Waves by Magnetic Reconnection  

CERN Document Server

In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except for the current sheet region. Alfven waves are generated at the reconnection point and propagate along the reconnected field line. The energy fluxes of the Alfven waves and sound waves generated by the magnetic reconnection are measured. Each flux shows the similar time evolution independent of theta. The percentage of the energies (time integral of energy fluxes) carried by the Alfven waves and sound waves to the released magnetic energy are calculated. The Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at the...

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

2010-01-01

328

Non-destructive evaluation of stream generator tubes and pressure tubes from the PHWR reactors, using the rotating magnetic field method  

International Nuclear Information System (INIS)

This work presents a new type of eddy current transducer with a rotating magnetic field devoted to the inspection of steam generator tubes and pressure tubes from the PHWR reactors. A theoretical model has been developed that permits the calculations of the emf induced in the reception coils in the presence of the copper or magnetite deposits, anti-vibration railing and garter springs. (authors)

329

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

OpenAIRE

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

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

2012-01-01

330

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

Science.gov (United States)

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

331

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

Energy Technology Data Exchange (ETDEWEB)

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 [The Catholic University of Korea, Seoul (Korea, Republic of); Kang, Young-Nam [Seoul St. Mary' s Hospital, The Catholic University of Korea, Seoul (Korea, Republic of); Yoo, Seung-Hoon [CHA Bundang Medical Center, CHA University, Seongnam (Korea, Republic of); Pae, Ki-Hong [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Shin, Dong-Ho; Lee, Se-Byeong [National Cancer Center, Goyang (Korea, Republic of)

2013-01-15

332

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

International Nuclear Information System (INIS)

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

333

Literature review on permanent magnet generators design and dynamic behavior  

Energy Technology Data Exchange (ETDEWEB)

This paper is a literature review which describes the construction of state of the art of permanent magnet generators and motors constructing and discusses the current and possible application of these machines in industry. Permanent magnet machines are a well-know class of rotating and linear electric machines used for many years in industrial applications. A particular interest for permanent magnet generators is connected with wind mills, which seem to be becoming increasingly popular nowadays. Geared and direct-driven permanent magnet generators are described. A classification of direct-driven permanent magnet generators is given. Design aspects of permanent magnet generators are presented. Permanent magnet generators for wind turbines designs are highlighted. Dynamics and vibration problems of permanent magnet generators covered in literature are presented. The application of the Finite Element Method for mechanical problems solution in the field of permanent magnet generators is discussed. (orig.)

Aleksashkin, A; Mikkola, A.

2008-07-01

334

High field superconducting magnets  

Science.gov (United States)

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

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

2011-01-01

335

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization  

Science.gov (United States)

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

336

"Electromaglev" ("active-maglev") - magnetic levitation of a superconducting disk with a DC field generated by electromagnets. Part 4: theoretical and experimental results on supercurrent distributions in field-cooled YBCO disks  

Science.gov (United States)

We present Part 4 results of a comprehensive theoretical study of an "electromaglev" system, in which a high-temperature superconducting bulk YBCO sample is levitated stably in a DC magnetic field generated by magnet system underneath the floating object. An electromagnetic analysis, based on a three-dimensional finite element technique (FEM) applied to the current vector potential method, has been developed to determine the supercurrent distribution in a field-cooled (and hence trapped-flux) YBCO disk that levitates stably in a magnetic field generated by the magnet system. The supercurrent distribution thus determined was in turn used to compute trapped-flux-induced field profiles of the disk and predict a "levitation current" in the magnet system at which the disk, initially resting on a support plate, begins to levitate. Agreement between computed field profiles and levitation currents and those measured in the experiment was excellent, validating the analysis itself and the method used to derive solutions. The analysis demonstrates that the supercurrent distribution within a trapped-flux disk is far more complicated than that derived from the Bean model for a long cylinder under a uniform axial magnetic field. It is used for a parametric study of the effects of disk dimensions (radius, thickness, radius/thickness ratio) and trapped-flux strength on supercurrent distribution and lift-to-weight ratio. The magnitude of the Br component generated by the magnet system is very important for lift and it is shown that thinner disks rather than thicker disks can improve lift-to-weight ratio. Because accuracy of the analysis is disk-size independent, small disks are time-efficient for performing the analysis.

Tsuda, Makoto; Lee, Haigun; Noguchi, So; Iwasa, Yukikazu

337

`Electromaglev' (`active-maglev')—magnetic levitation of a superconducting disk with a DC field generated by electromagnets: Part 3. Theoretical results on levitation height and stability  

Science.gov (United States)

We present Part 3 results of a comprehensive theoretical study of an `electromaglev' (`active-maglev') system, in which a high-temperature superconducting bulk YBCO sample is levitated stably in a DC magnetic field generated by a magnet system. Field solutions have been obtained numerically to compute levitation height and define stability criteria for the superconducting disk sample. Our analysis assumes that the disk, which otherwise obeys the Bean critical-state model, traps flux when cooled in the presence of a field from the normal state to the superconducting state. Indeed it is shown that the trapped flux makes subtle and crucial changes in field distribution (and thus current density distribution) in the disk, which differ from those in a disk strictly obeying the Bean model used in the zeroth-order theory. The analysis confirms a key experimental finding that the trapped flux is another essential element for determining levitation height and ensuring tilt-free stable levitation. For stability, trapped flux is in addition to at least two degrees of freedom for spatial supercurrent flow and the profile conditions imposed on the field generated by the magnet system. Procedures to produce stable, tilt-free levitation are described. Agreement between experiment and analysis on dependence of levitation height on magnet current is quite good. The analysis also shows that to achieve stable levitation, a YBCO ring sample requires a radial build that is sufficiently thick to permit the supercurrent to flow in the radial direction. The minimum radial build required, ? Rmin, for a YBCO ring of outside radius 12.5 mm operating at 77 K is typically ˜50 ?m. An analytical expression that gives approximate values of ? Rmin has also been derived; ? Rmin depends inversely on the square of the critical current density of the superconductor.

Tsuda, Makoto; Lee, Haigun; Iwasa, Yikikazu

338

Galactic magnetic fields and magnetic monopoles  

International Nuclear Information System (INIS)

This chapter proposes that the existence of the galactic field implies that the flux of magnetic monopoles is not in excess of 10-15 monopoles cm-2 s-1 unless the monopole mass is much larger than 1016 GeV or that the field of the galaxy is a manifestation of magnetic monopole plasma oscillations. Methods of avoiding excessive Landsu damping and phase mixing are given. Topics considered include the acceleration of magnetic monopoles and magnetic monopole plasma oscillations

339

Optical generation of intense ultrashort magnetic pulses at the nanoscale  

Science.gov (United States)

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

Tsiatmas, Anagnostis; Atmatzakis, Evangelos; Papasimakis, Nikitas; Fedotov, Vassili; Luk'yanchuk, Boris; Zheludev, Nikolay I.; García de Abajo, F. Javier

2013-11-01

340

Focus on Materials Analysis and Processing in Magnetic Fields  

OpenAIRE

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

341

Generation of zonal flow and magnetic field by coupled internal-gravity and alfvén waves in the ionospheric E-layer  

Science.gov (United States)

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

342

High magnetic fields in chemistry  

OpenAIRE

Recent applications of large (? 1 T ? 30 T) magnetic fields in modern chemical research are reviewed. Magnetic field effects of chemical relevance appear on the levels of quantum mechanics, thermodynamics, and macroscopic forces. Quantum mechanical magnetic field effects are governed by the Zeeman interaction and are borne out as static and dynamic effects in spectroscopy and in chemical kinetics. Magnetic circular dichroism (MCD) spectroscopy and magnetic fluorescence quenching in the ...

Steiner, Ulrich; Gilch, Peter

2003-01-01

343

Magnetic field distribution controlled by anisotropic inter-pole and reduction of fringing field  

International Nuclear Information System (INIS)

A novel method to generate a gradient field in a constant gapped magnet is devised with use of inter-pole made of anisotropic magnet material. This magnet can have not only constant gap but also smaller fringing field compared with a conventional one. This technique should widen the recipe to design a magnet with a complex magnetic field distribution. (author)

344

Electrically silent magnetic fields.  

OpenAIRE

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical poten...

Roth, B. J.; Wikswo, J. P.

1986-01-01

345

The rotation-magnetic field relation  

Science.gov (United States)

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

346

Observations of Cool-Star Magnetic Fields  

Directory of Open Access Journals (Sweden)

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

Ansgar Reiners

2012-02-01

347

Observations of Interstellar Magnetic Fields  

Science.gov (United States)

This article describes how interstellar magnetic fields are detected, measured, and mapped, the results of such observations, and the role played by interstellar magnetic fields in the physics of the interstellar medium. A goal of the observations is the measurement of the morphology and strengths of the uniform (Bu) and random (Br) components of magnetic fields. Observational techniques probe either the component of B parallel to the line of sight (B_parallel) or in the plane of the sky (B_?). Tracers of B_parallel are Faraday rotation of the position angle of linearly polarized radiation and Zeeman splitting of spectral lines. Tracers of B_? are the strength of synchrotron radiation and linear polarization of syn chrotron radiation and of emission or absorption from dust and spectral lines. Starlight polarization shows that on large spatial scales the Galactic magnetic field is not heavily tangled (B_u/B_r ? 0.7 - 1.0), that the field is generally parallel to the Galactic plane near the plane, that the local field points approximately along the local spiral arm (pitch angle 9.4(°) , center of curvature 7.8 kpc distant towards ? ? -15.4(°) ), and that off the Galactic plane there is considerable small-scale structure to the field. Galactic synchrotron emission shows magnetic spiral arms with a total strength B_t ? 6 #55G and B_u ? 4 #55G. Pulsar data show evidence for reversals of the field direction with Galactic radius and yield B_r ? 5 #55G and B_u ? 1.5 #55G; the morphology of the large-scale mean field is consistent with dynamo generation. H I Zeeman detections for diffuse clouds yield B_parallel char 126 5 - 20 #55G with many limits B_parallel #55G. A recent survey of Galactic H I in absorption against extragalactic sources confirms the result that the fields in diffuse clouds are often quite weak. The critical parameter for evaluating the importance of magnetic fields in star formation is the ratio of the mass to the magnetic flux, M/Phi_B; observations focus on measuring both this quantity and the morphology of fields in dense regions. Zeeman observations of molecular lines are consistent with B propto sigma_v sqrt{n}, which is the theoretical prediction for flattened cores supported by a combination of a uniform magnetic field pressure and turbulence. In cores, motions are approximately Alfvénic, and M/Phi_B$ has a critical to slightly supercritical value. The ratio of Br/Bu appears to decline with density. In some molecular cores there is evidence for the "hourglass" pinch that would be produced by cloud contraction with the magnetic field frozen into the matter.

Crutcher, R.; Heiles, C.; Troland, T.

348

Measuring the Earth's Magnetic Field in a Laboratory  

Science.gov (United States)

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

349

Generating highly uniform electromagnetic field characteristics  

Energy Technology Data Exchange (ETDEWEB)

An apparatus and method are disclosed for generating homogeneous electromagnetic fields within a volume. The homogeneity provided may be for magnetic and/or electric fields, and for field magnitude, radial gradient, or higher order radial derivative. The invention comprises conductive pathways oriented mirror symmetrically about a desired region of homogeneity. A corresponding apparatus and method is provided for substantially canceling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set. 26 figs.

Crow, J.T.

1997-06-24

350

Low field magnetic resonance imaging  

Science.gov (United States)

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

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

2010-07-13

351

Evolution of Primordial Magnetic Fields from Phase Transitions  

CERN Document Server

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

Kahniashvili, Tina; Brandenburg, Axel; Neronov, Andrii

2012-01-01

352

Magnetic Field Problem: Current and Magnets  

Science.gov (United States)

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

Wolfgang Christian

353

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

International Nuclear Information System (INIS)

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

354

Magnetic-field transfer of water molecules  

Science.gov (United States)

Thermal agitation induces the rotational motion of the two positively charged hydrogens around the oxygen nucleus in a water molecule, which forms an electric current with a short duration, generating a Lorentz force in a uniform static magnetic field. Since the center of gravity of a water molecule is approximately located at the oxygen nucleus, the Lorentz force has two components that rotate the hydrogens and push the oxygen nucleus. The component of the Lorentz force that pushes the oxygen nucleus parallel to the magnetic field has a strength that is half that of the component that pushes the oxygen nucleus perpendicular to the magnetic field. Since the Lorentz force causes water molecules to carry out a random walk, magnetic-field transfer, that is, a cumulative effect of random walks, is expected. The ratio of the diffusional coefficient for the magnetic-field transfer of D2O to that of H2O is 4:1 because the ratio of the interval between each random walk of D2O to that of H2O, which is also the ratio of the duration of one rotation, is 2:1. The diffusional displacement of the magnetic-field transfer is proportional to the magnetic field and reaches 0.62 Å/day for liquid water at 37 °C in a magnetic field of 2.0 T. Magnetic-field transfer is predicted to occur in polarized molecules with rotational freedom and restricted translational freedom.

Osuga, Toshiaki; Tatsuoka, Hozumi

2009-11-01

355

Five years of magnetic field management  

International Nuclear Information System (INIS)

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

356

Magnetic field evolution in interacting galaxies  

Science.gov (United States)

Aims: Violent gravitational interactions can change the morphologies of galaxies and, by means of merging, transform them into elliptical galaxies. We aim to investigate how they affect the evolution of galactic magnetic fields. Methods: We selected 16 systems of interacting galaxies with available VLA archive radio data at 4.86 and 1.4 GHz and compared their radio emission and estimated magnetic field strengths with their star-forming activity, far-infrared emission, and the stage of tidal interaction. Results: The estimated mean of total magnetic field strength for our sample of interacting galaxies is 14 ± 5 ?G, which is larger than for the non-interacting objects. The field regularity (of 0.27 ± 0.09) is lower than in typical spirals and indicates enhanced production of random magnetic fields in the interacting objects. We find a general evolution of magnetic fields: for weak interactions the strength of magnetic field is almost constant (10-15 ?G) as interaction advances, then it increases up to 2× , peaks at the nuclear coalescence (25 ?G), and decreases again, down to 5-6 ?G, for the post-merger remnants. The main production of magnetic fields in colliding galaxies thus terminates somewhere close to the nuclear coalescence, after which magnetic field diffuses. The magnetic field strength for whole galaxies is weakly affected by the star formation rate (SFR), while the dependence is higher for galactic centres. We show that the morphological distortions visible in the radio total and polarized emission do not depend statistically on the global or local SFRs, while they do increase (especially in the polarization) with the advance of interaction. The constructed radio-far-infrared relations for interacting and non-interacting galaxies display a similar balance between the generation of cosmic rays, magnetic fields, and the production of the thermal energy and dust radiation. Conclusions: The regular magnetic fields are much more sensitive to morphological distortions induced by tidal interactions than are the random fields. As a result the polarized emission could be yet another indicator of an ongoing merging process. The found evolution of magnetic field with advancing interaction would definitely imply a stronger effect of magnetic fields on the galaxy surroundings in the earlier cosmological epochs. The process of strong gravitational interactions can efficiently magnetize the merger's surroundings, having a similar magnetizing effect on intergalactic medium as supernova explosions or galactic winds. If interacting galaxies generate some ultra-high energy cosmic rays (UHECRs), the disk or magnetized outflows can deflect them (up to 23°), and make an association of the observed UHECRs with the sites of their origin very uncertain.

Drzazga, R. T.; Chy?y, K. T.; Jurusik, W.; Wiórkiewicz, K.

2011-09-01

357

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

International Nuclear Information System (INIS)

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

358

Magnetic nanoparticle traveling in external magnetic field  

OpenAIRE

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

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

2014-01-01

359

Leukaemia mortality in relation to magnetic field exposure: findings from a study of United Kingdom electricity generation and transmission workers, 1973-97  

OpenAIRE

OBJECTIVE—To investigate whether risks of leukaemia are related to occupational exposure to magnetic fields.?METHODS—The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All employees were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calc...

Harrington, J.; Nichols, L.; Sorahan, T.; Tongeren, M.

2001-01-01

360

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-06

361

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

International Nuclear Information System (INIS)

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

362

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

363

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

364

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.

365

Comparison of adjustable permanent magnetic field sources  

Science.gov (United States)

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

366

Comparison of adjustable permanent magnetic field sources  

CERN Document Server

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

367

Magnetic response to applied electrostatic field in external magnetic field  

OpenAIRE

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an app...

Adorno, T. C. Instituto Fi?sica; Gitman, D. M.; Shabad, A. E.

2013-01-01

368

Magnetic field therapy: a review.  

Science.gov (United States)

There is increasing interest in using permanent magnets for therapeutic purposes encouraged by basic science publications and clinical reports. Magnetotherapy provides a non invasive, safe, and easy method to directly treat the site of injury, the source of pain and inflammation, and other types of disease. The physiological bases for the use of magnetic fields for tissue repair as well as physical principles of dosimetry and application of various magnetic fields are subjects of this review. Analysis of the magnetic and electromagnetic stimulation is followed by a discussion of the advantage of magnetic field stimulation compared with electric current and electric field stimulation. PMID:17454079

Markov, Marko S

2007-01-01

369

Biermann Mechanism in Primordial Supernova Remnant and Seed Magnetic Fields  

Science.gov (United States)

We study the generation of magnetic fields by the Biermann mechanism in the supernova explosions of the first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We perform a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the magnetic fields that are produced. We find that magnetic fields with amplitude 10-14 to 10-17 G are generated inside the bubble, although the amount of magnetic field generated depends on the specific values of the initial conditions. This corresponds to magnetic fields of 1028-1031 ergs for each supernova remnant, which is strong enough to be the seed magnetic field for a galactic and/or interstellar dynamo.

Hanayama, Hidekazu; Takahashi, Keitaro; Kotake, Kei; Oguri, Masamune; Ichiki, Kiyotomo; Ohno, Hiroshi

2005-11-01

370

Biermann mechanism in primordial supernova remnants and seed magnetic fields  

Science.gov (United States)

We have studied the generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of the first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We have performed a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the produced magnetic fields. We find that magnetic fields with amplitude 10-14-10-17 G are generated inside the bubble, though the amount of magnetic fields generated depend on specific values of initial conditions. This corresponds to magnetic fields with total energy of 1028-1031 erg per each supernova remnant, which is strong enough to be the seed magnetic field for a galactic and/or interstellar dynamo.

Hanayama, H.; Takahashi, K.; Kotake, K.; Oguri, M.; Ichiki, K.; Ohno, H.

2006-06-01

371

Polar Magnetic Field Experiment  

Science.gov (United States)

This grant covers the initial data reduction and analysis of the magnetic field measurements of the Polar spacecraft. At this writing data for the first three years of the mission have been processed and deposited in the key parameter database. These data are also available in a variety of time resolutions and coordinate systems via a webserver at UCLA that provides both plots and digital data. The flight software has twice been reprogrammed: once to remove a glitch in the data where there were rare collisions between commands in the central processing unit and once to provide burst mode data at 100 samples per second on a regular basis. The instrument continues to function as described in the instrument paper (1.1 in the bibliography attached below). The early observations were compared with observations on the same field lines at lower altitude. The polar magnetic measurements also proved to be most useful for testing the accuracy of MHD models. WE also made important contributions to study of waves and turbulence.

Russell, C. T.

1999-01-01

372

SCUPOL Magnetic Field Analysis  

CERN Document Server

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

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

2013-01-01

373

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

Directory of Open Access Journals (Sweden)

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

T. RajaRani

2012-01-01

374

Helical magnetic fields via baryon asymmetry  

CERN Document Server

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

Piratova, Eduard F; Hortúa, Héctor J

2014-01-01

375

Magnetic monopole field exposed by electrons  

CERN Document Server

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

376

Magnetic Branes Supported by Nonlinear Electromagnetic Field  

OpenAIRE

Considering the nonlinear electromagnetic field coupled to Einstein gravity in the presence of cosmological constant, we obtain a new class of $d$-dimensional magnetic brane solutions. This class of solutions yields a spacetime with a longitudinal nonlinear magnetic field generated by a static source. These solutions have no curvature singularity and no horizons but have a conic geometry with a deficit angle $\\delta \\phi$. We investigate the effects of nonlinearity on the me...

Hendi, Seyed Hossein

2010-01-01

377

Evolution of twisted magnetic fields  

International Nuclear Information System (INIS)

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

378

Magnetic Field Spectrum at Cosmological Recombination Revisited  

CERN Document Server

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

Saga, Shohei; Takahashi, Keitaro; Sugiyama, Naoshi

2015-01-01

379

Protein detection with magnetic nanoparticles in a rotating magnetic field  

Science.gov (United States)

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

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

2014-01-01

380

The magnetic field structure of Rotamak discharges  

International Nuclear Information System (INIS)

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

381

Source of the earth's magnetic field  

International Nuclear Information System (INIS)

The structure and dynamics of the earth's magnetic field are described. The structure and electric, mechanical, and gravitational forces generated in the core and their effects on this field as well as various dynamical models, particularly the heat-driven and the gravitationally powered dynamos, are discussed

382

Magnetic Fields on Cool Stars  

OpenAIRE

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

Reiners, Ansgar

2010-01-01

383

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition  

International Nuclear Information System (INIS)

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. A cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, a laser with four beams and a total output of 10 kJ ps-1, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Namely, the main pulse is absorbed in the long-scale pre-plasma produced by the pre-pulse and the hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is large. Hence, we are exploring how to overcome the pre-pulse effects on the cone target. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high-energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electromagnetic fields generated on the surface of the inner cone will confine high-energy electrons.

384

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition  

Energy Technology Data Exchange (ETDEWEB)

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. A cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, a laser with four beams and a total output of 10 kJ ps{sup -1}, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Namely, the main pulse is absorbed in the long-scale pre-plasma produced by the pre-pulse and the hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is large. Hence, we are exploring how to overcome the pre-pulse effects on the cone target. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high-energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electromagnetic fields generated on the surface of the inner cone will confine high-energy electrons.

Mima, Kunioki; Sunahara, A; Shiraga, Hiroyuki; Nishimura, H; Azechi, H; Nakamura, T; Johzaki, T; Nagatomo, H [Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871 (Japan); Garcia, C; Veralde, P [Institute of Nuclear Fusion, University Politecnica de Madrid, C/Jose Gutierrez Abascal, 2, 28006 Madrid (Spain)

2010-12-15

385

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition  

Science.gov (United States)

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. A cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, a laser with four beams and a total output of 10 kJ ps-1, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Namely, the main pulse is absorbed in the long-scale pre-plasma produced by the pre-pulse and the hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is large. Hence, we are exploring how to overcome the pre-pulse effects on the cone target. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high-energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electromagnetic fields generated on the surface of the inner cone will confine high-energy electrons.

Mima, Kunioki; Sunahara, A.; Shiraga, Hiroyuki; Nishimura, H.; Azechi, H.; Nakamura, T.; Johzaki, T.; Nagatomo, H.; Garcia, C.; Velarde, P.

2010-12-01

386

Magnetic fields of the magnetosheath  

International Nuclear Information System (INIS)

The magnetic field of the magnetosheath is most naturally discussed in terms of its steady state and its fluctuating components. The theory of the steady state field is quite well developed, and its essential features have been confirmed by observations. The interplanetary field is convected through the bow shock where its magnitude is increased and its direction changed by the minimal amount necessary to preserve the normal component across the shock. Convection within the magnetosheath usually increases the magnitude still further near the subsolar point and further distorts the direction until the field is aligned approximately tangent to the magnetopause. Fluctuations of the magnetosheath field are very complex, variable, and not well understood. Power spectra of the field typically vary as 1/f or 1/f2 below and 1/f3 above the proton gyrofrequency. Spectral peaks are common features which occur at different frequencies at various times. Transverse waves are often dominant at frequencies less than or equal to 0.002 Hz, and compressional waves are often dominant at somewhat higher frequencies. Perturbation vectors of hydromagnetic waves tend to be aligned with the shock and magnetopause surfaces. Magnetosheath waves may be generated upstream, within the magnetosheath, at the bow shock, or at the magnetopause, but the relative importance of these sources is not known. 83 references

387

Magnetic fields from heterotic cosmic strings  

International Nuclear Information System (INIS)

Large-scale magnetic fields are observed today to be coherent on galactic scales. While there exists an explanation for their amplification and their specific configuration in spiral galaxies--the dynamo mechanism--a satisfying explanation for the original seed fields required is still lacking. Cosmic strings are compelling candidates because of their scaling properties, which would guarantee the coherence on cosmological scales of any resultant magnetic fields at the time of galaxy formation. We present a mechanism for the production of primordial seed magnetic fields from heterotic cosmic strings arising from M theory. More specifically, we make use of heterotic cosmic strings stemming from M5-branes wrapped around four of the compact internal dimensions. These objects are stable on cosmological time scales and carry charged zero modes. Therefore a scaling solution of such defects will generate seed magnetic fields which are coherent on galactic scales today.

388

Magnetic-field-controlled reconfigurable semiconductor logic.  

Science.gov (United States)

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

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

2013-02-01

389

Magnetic response to applied electrostatic field in external magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-04-15

390

Magnetic response to applied electrostatic field in external magnetic field  

International Nuclear Information System (INIS)

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

391

Theory of fossil magnetic field  

Science.gov (United States)

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

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

392

Theory of fossil magnetic field  

OpenAIRE

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

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2014-01-01

393

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

International Nuclear Information System (INIS)

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

394

Origin of cosmic magnetic fields  

CERN Document Server

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

Campanelli, Leonardo

2013-01-01

395

Origin of cosmic magnetic fields.  

Science.gov (United States)

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

Campanelli, Leonardo

2013-08-01

396

Measurements of magnetic field alignment  

International Nuclear Information System (INIS)

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

397

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

International Nuclear Information System (INIS)

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

398

Zonal flow and zonal magnetic field generation by finite beta drift waves: a theory for low to high transitions in tokamaks.  

Science.gov (United States)

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 beta 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. PMID:11461469

Guzdar, P N; Kleva, R G; Das, A; Kaw, P K

2001-07-01

399

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

Directory of Open Access Journals (Sweden)

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

Sandulyak Anna Aleksandrovna

2013-05-01

400

Magnetic Field Analysis of Superconducting Undulators with Variable Field Polarization  

CERN Document Server

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

Kim, Suk H

2005-01-01

401

SEED BANKS FOR MAGNETIC FLUX COMPRESSION GENERATORS  

Energy Technology Data Exchange (ETDEWEB)

In recent years the Lawrence Livermore National Laboratory (LLNL) has been conducting experiments that require pulsed high currents to be delivered into inductive loads. The loads fall into two categories (1) pulsed high field magnets and (2) the input stage of Magnetic Flux Compression Generators (MFCG). Three capacitor banks of increasing energy storage and controls sophistication have been designed and constructed to drive these loads. One bank was developed for the magnet driving application (20kV {approx} 30kJ maximum stored energy.) Two banks where constructed as MFCG seed banks (12kV {approx} 43kJ and 26kV {approx} 450kJ). This paper will describe the design of each bank including switching, controls, circuit protection and safety.

Fulkerson, E S

2008-05-14

402

Compact low field magnetic resonance imaging magnet: Design and optimization  

Science.gov (United States)

Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80-100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These "dedicated" apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.

Sciandrone, M.; Placidi, G.; Testa, L.; Sotgiu, A.

2000-03-01

403

Heat Generation Ability in AC Magnetic Field for Y{sub 3}Fe{sub 5}O{sub 12}-based Garnet Ferrite  

Energy Technology Data Exchange (ETDEWEB)

The Y{sub 3}Fe{sub 5}O{sub 12}-based ferrite, i.e., Y{sub 3-X}Gd{sub X}Fe{sub 5}O{sub 12} system was synthesized using a reverse coprecipitation method for application of new thermal coagulation therapy using an AC magnetic field for the treatment of cancerous tissues. The mixed phase of the Y{sub 3}Fe{sub 5}O{sub 12}-type orthorhombic and cubic materials without any impurities were obtained for this systems calcined at low temperature in XRD results. However the orthorhombic phase almost disappeared by the calcination at 1150 deg. C or higher temperature for all the X samples. The calcination temperature strongly influenced the heat generation ability. The maximum heat generation ability ({Delta}T = 40-63deg. C, 370kHz, 1.77kA/m) was obtained for the powder materials sintered at 1100 deg. C for the Y{sub 3-X}Gd{sub X}Fe{sub 5}O{sub 12} system. The particle growth with the formation of the cubic single phase strongly influenced to the heat generation.

Hirazawa, H [Department of Environmental Materials Engineering, Niihama National College of Technology, 7-1, Yagumo-tyo, Niihama, Ehime (Japan); Aono, H; Moritani, K; Naohara, T; Maehara, T [Graduate school of Science and Engineering, Ehime University, 3, Bunkyo-tyo, Matsuyama, Ehime (Japan); Watanabe, Y, E-mail: hirazawa@mat.niihama-nct.ac.jp [Department of Organ Regenerative Suegery, Graduate School of Medicine, Ehime University, Shitsukawa, Toon, Ehime (Japan)

2011-10-29

404

Magnetic field homogeneity perturbations in finite Halbach dipole magnets  

Science.gov (United States)

Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z) - Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm.

Turek, Krzysztof; Liszkowski, Piotr

2014-01-01

405

Rotating superconductor magnet for producing rotating lobed magnetic field lines  

International Nuclear Information System (INIS)

A rotating superconductor magnet is described for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet

406

Venus magnetic field and magnetosphere  

International Nuclear Information System (INIS)

Magnetic field investigations have been conducted in the distance of 1500-3000 km and 1-6Rsub(?) from the Venus, where Rsub(?) - is the Venus radius. Magnetic field complex topology, observed at the Venus night side form ''Venera-9,10'' satellites is explained by the Venus having its own weak magnetic field and the action of outer source fields. There is a magnetic stub on the planet night side, in which 2 bunches of lines of force, devided by neutral layer, are directed from the planet (to the north of equator) and to the planet (to the south of equator). The magnetic stub narrows at approaching to the planet and is located inside the planet geometric shade near the planet. The planet magnetic field effects but slightly the character of the planet flow-around by the sun wind. The stub topology depends on the polarity mark and force of field in the planet transfer zone. The ''overuniting'' processes of magnetospheric field and fields of outer sources present permanent process in the Venus magnetosphere. Notwithstanding the weakness of the Venus field, it is similar to geomagnetic one in a model way, provided the planet rotation peculiarities are taken into account

407

Preprocessing Magnetic Fields with Chromospheric Longitudinal Fields  

Science.gov (United States)

Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

Yamamoto, Tetsuya T.; Kusano, K.

2012-06-01

408

Simple Mechanism for Reversals of Earth's Magnetic Field  

International Nuclear Information System (INIS)

We show that a model, recently used to describe all the dynamical regimes of the magnetic field generated by the dynamo effect in the von Karman sodium experiment, also provides a simple explanation of the reversals of Earth's magnetic field, despite strong differences between both systems. The validity of the model relies on the smallness of the magnetic Prandtl number

409

Primordial magnetic fields from self-ordering scalar fields  

Science.gov (United States)

A symmetry-breaking phase transition in the early universe could have led to the formation of cosmic defects. Because these defects dynamically excite not only scalar and tensor type cosmological perturbations but also vector type ones, they may serve as a source of primordial magnetic fields. In this study, we calculate the time evolution and the spectrum of magnetic fields that are generated by a type of cosmic defects, called global textures, using the non-linear sigma (NLSM) model. Based on the standard cosmological perturbation theory, we show, both analytically and numerically, that a vector-mode relative velocity between photon and baryon fluids is induced by textures, which inevitably leads to the generation of magnetic fields over a wide range of scales. We find that the amplitude of the magnetic fields is given by B~10?9((1+z)/103)?2.5(v/mpl)2(k/Mpc?1)3.5/?N Gauss in the radiation dominated era for klesssim 1 Mpc?1, with v being the vacuum expectation value of the O(N) symmetric scalar fields. By extrapolating our numerical result toward smaller scales, we expect that B~ 10?14.5((1+z)/103)1/2(v/mpl)2(k/Mpc?1)1/2/?N Gauss on scales of kgtrsim 1 Mpc?1 at redshift 0zgtrsim 110. This might be a seed of the magnetic fields observed on large scales today.

Horiguchi, Kouichirou; Ichiki, Kiyotomo; Sekiguchi, Toyokazu; Sugiyama, Naoshi

2015-04-01

410

Axial anomaly in 3He-A: Simulation of baryogenesis and generation of primordial magnetic field in Manchester and Helsinki  

OpenAIRE

The gapless fermionic excitations in superfluid 3He-A have a "relativistic" spectrum close to the gap nodes. They are the counterpart of the chiral particles (left-handed and right-handed) in high energy physics above the electroweak transition. We discuss the effective gravity and effective gauge fields, induced by these massless fermions in the low-energy corner. The interaction of the chiral fermions with the gauge field in 3He-A is discussed in detail. It gives rise to t...

Volovik, G. E.

1998-01-01

411

Magnetic fields and scintillator performance  

International Nuclear Information System (INIS)

Experimental data have shown that the light output of a scintillator depends on the magnitude of the externally applied magnetic fields, and that this variation can affect the calorimeter calibration and possibly resolution. The goal of the measurements presented here is to study the light yield of scintillators in high magnetic fields in conditions that are similar to those anticipated for the LHC CMS detector. Two independent measurements were performed, the first at Fermilab and the second at the National High Magnetic Field Laboratory at Florida State University

412

Streamer propagation in magnetic field  

CERN Document Server

The propagation of a streamer near an insulating surface under the influence of a transverse magnetic field is theoretically investigated. In the weak magnetic field limit it is shown that the trajectory of the streamer has a circular form with a radius that is much larger than the cyclotron radius of an electron. The charge distribution within the streamer head is strongly polarized by the Lorentz force exerted perpendicualr to the streamer velocity. A critical magnetic field for the branching of a streamer is estimated. Our results are in good agreement with available experimental data.

Zhuravlev, V N; Vagner, I D; Wyder, P

1997-01-01

413

Measuring the Earth's magnetic field in a laboratory  

International Nuclear Information System (INIS)

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 methods are cheap. With some attention to the procedure, both methods give accurate results

414

The origin, evolution and signatures of primordial magnetic fields  

CERN Document Server

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

Subramanian, Kandaswamy

2015-01-01

415

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

OpenAIRE

We report our demonstration of Rabi oscillations in Si-SiO2-Al photoconductive devices with nanosecond laser pulses of a few nJ at room temperature without external magnetic fields. Zeeman splitting of spin quantum states of dopants in silicon is achieved with internal magnetic fields produced by the Al film under excitation of laser pulses. Rabi oscillation frequency is 15 MHz and 25 MHz when photocurrent direction is perpendicular and parallel, respectively, to the propaga...

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

2013-01-01

416

The National High magnetic Field Laboratory Pulsed Field Facility. An overview of high field magnet operations and scientific techniques  

Science.gov (United States)

The National High magnetic Field Laboratory -- Pulsed Field Facility (NHMFL-PFF) is the home to the pulsed field user facility which routinely delivers 85T pulses for user science using a 1.4GW motor generator. The facility also houses a 60T shaped waveform magnet, 65T short pulse and 50T mid pulse capacitor driven magnets. Many techniques are available to users including, Transport, magnetization, calorimeter and cantilever techniques. I will describe the facilities and the measurement techniques available to users.

Betts, Jon

2011-03-01

417

Preface: Cosmic magnetic fields  

Science.gov (United States)

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

Kosovichev, Alexander

2015-02-01

418

Lightning Magnetic Field Measurements around Langmuir Laboratory  

Science.gov (United States)

In the absence of artificial conductors, underground lightning transients are produced by diffusion of the horizontal surface magnetic field of a return stroke vertically downward into the conducting earth. The changing magnetic flux produces an orthogonal horizontal electric field, generating a dispersive, lossy transverse electromagnetic wave that penetrates a hundred meters or more into the ground according to the skin depth of the medium. In turn, the electric field produces currents that flow toward or away from the channel to ground depending on the stroke polarity. The underground transients can produce large radial horizontal potential gradients depending on the distance from the discharge and depth below the surface. In this study we focus on the surface excitation field. The goal of the work is to compare measurements of surface magnetic field waveforms B(t) at different distances from natural lightning discharges with simple and detailed models of the return stroke fields. In addition to providing input to the diffusion mechanism, the results should aid in further understanding return stroke field generation processes. The observational data are to be obtained using orthogonal sets of straightened Rogowski coils to measure magnetic field waveforms in N-S and E-W directions. The waveforms are sampled at 500 kS/s over 1.024 second time intervals and recorded directly onto secure digital cards. The instrument operates off of battery power for several days or weeks at a time in remote, unattended locations and measures magnetic field strengths of up to several tens of amperes/meter. The observations are being made in conjunction with collocated slow electric field change measurements and under good 3-D lightning mapping array (LMA) and fast electric field change coverage.

Stock, M.; Krehbiel, P. R.; Rison, W.; Aulich, G. D.; Edens, H. E.; Sonnenfeld, R. G.

2010-12-01

419

Cosmic Magnetic Fields: Observations and Prospects  

Science.gov (United States)

Synchrotron emission, its polarization and its Faraday rotation at radio frequencies of 0.2-10 GHz are powerful tools to study the strength and structure of cosmic magnetic fields. Unpolarized emission traces turbulent fields which are strongest in galactic spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular (uni-directional) or anisotropic random (generated from isotropic random fields by compression or shear). Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. The strongest ordered (mostly regular) fields of 10-15 ?G strength are generally found in galactic interarm regions and follow the orientation of adjacent gas spiral arms. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several spiral galaxies reveal large-scale patterns, which are signatures of regular fields probably generated by a mean-field dynamo. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Ordered magnetic fields are also observed in radio halos around edge-on galaxies, out to large distances from the plane, with X-shaped patterns.--The strength of the total magnetic field in our Milky Way is about 6 ?G near the solar radius, but several mG in dense clouds, pulsar wind nebulae, and filaments near the Galactic Center. Diffuse polarized radio emission and Faraday rotation data from pulsars and background sources show spiral fields with large-scale reversals, but the overall field structure in our Galaxy is still under debate.--Diffuse radio emission from the halos of galaxy clusters is mostly unpolarized because intracluster magnetic fields are turbulent, while cluster ``relics'', probably shock fronts by cluster mergers, can have degrees of polarization of up to 60% and extents of up to 2 Mpc. The IGM magnetic field strength is >=3 10-16 G with a filling factor of at least 60%, derived from the combination of data from the HESS and FERMI telescopes.--Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of cosmic magnetic fields and will help to understand their origin. At low frequencies, LOFAR (10-250 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies and galaxy clusters. Small Faraday rotation measures can also be best measured at low frequencies. Polarization at higher frequencies (1-10 GHz), as observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of nearby galaxies in unprecedented detail. The SKA pulsar survey will find many new pulsars; their RMs will map the Milky Way's magnetic field with high precision. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with the SKA and its precursor telescope ASKAP are dedicated to measure magnetic fields in distant intervening galaxies, galaxy clusters and intergalactic filaments, and will be used to model the overall structure and strength of the magnetic field in the Milky Way. With the SKA, ordered fields in distant galaxies and cluster relics can be measured to redshifts of z~=0.5, turbulent fields in starburst galaxies or cluster halos to z~=3 and regular fields in intervening galaxies towards QSOs to z~=5.

Beck, Rainer

2011-09-01

420

`Electromaglev' (`Active-Maglev') — magnetic levitation of a superconducting disk with a DC field generated by electromagnets: Part 2 Theoretical and experimental results on lift-to-weight ratio and lateral stiffness  

Science.gov (United States)

We present Part 2 results of a comprehensive study, both theoretical and experimental, of an electromaglev (`active-maglev') system, in which a YBCO bulk sample is levitated stably in a DC magnetic field generated by a magnet system located underneath the floating sample. The 0th-order theory presented in Part 1 is used to interpret experimental results of levitation stability, lift-to-weight ratio, and lateral stiffness for four YBCO samples: 1) disk; 2) annulus; 3) the same annulus with a permanent magnet disk placed in the hole; and 4) ring. Also presented is a procedure to induce in a sample a trapped flux that is shown experimentally to be essential for the sample to levitate tilt-free. Trapped flux is another requirement for levitation stablity; it is in addition to at least two degrees of freedom required on spatial supercurrent flow and certain spatial profiles imposed on the field generated by the magnet system.

Lee, Haigun; Tsuda, Makoto; Iwasa, Yukikazu