WorldWideScience
 
 
1

Transformer generated magnetic fields  

International Nuclear Information System (INIS)

Magnetic fields produced by both small and large apparatus are being investigated for their possible relation to human health effects. A number of studies have been done in characterizing the magnetic field generated by transmission lines, household wiring and appliances. Two other major sources of magnetic fields are motors and transformers. The magnetic field generated by power transformers has not been studied extensively. The purpose of this paper is to experimentally quantify the magnetic field of a power transformer and compare it with calculated results obtained using one of the numerical techniques.

1996-01-01

2

Magnetic field generator  

Energy Technology Data Exchange (ETDEWEB)

A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

Krienin, Frank (Shoreham, NY)

1990-01-01

3

Generation of helical magnetic fields from inflation  

CERN Multimedia

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

4

Strong and superstrong pulsed magnetic fields generation  

CERN Multimedia

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.

Dolotenko, Mikhail I; Shneerson, German A

2014-01-01

5

Magnetic field generation due to resonance absorption  

International Nuclear Information System (INIS)

[en] A detailed study of mechanism of megagauss magnetic field generation in resonant absorption of laser light is presented which takes into account effects of both dissipation and thermal motion of electrons. (auth.)

1975-07-16

6

Generation of magnetic fields for accelerators with permanent magnets  

International Nuclear Information System (INIS)

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

1994-01-26

7

Induction MHD generator using alternating magnetic field  

International Nuclear Information System (INIS)

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

1979-01-01

8

The seed magnetic field generated during recombination  

CERN Multimedia

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

Fenu, Elisa; Maartens, Roy

2010-01-01

9

Magnetic fields generated by the Rayleigh-Taylor instability  

International Nuclear Information System (INIS)

[en] In the absence of magnetic diffusion the self-generated magnetic field in a plasma is proportional to the fluid vorticity. The ratio of magnetic to fluid energy then shows that self-generated magnetic fields can only affect the Rayleigh Taylor growth rate for large kappa (wavelengths less than a few microns). (author)

1986-01-01

10

Fluorescent lamp with static magnetic field generating means  

Energy Technology Data Exchange (ETDEWEB)

A fluorescent lamp wherein magnetic field generating means (e.g., permanent magnets) are utilized to generate a static magnetic field across the respective electrode structures of the lamp such that maximum field strength is located at the electrode's filament. An increase in efficacy during operation has been observed.

Moskowitz, Philip E. (Peabody, MA); Maya, Jakob (Brookline, MA)

1987-01-01

11

VNIIEF achievements on ultra-high magnetic fields generation  

Science.gov (United States)

A brief review of the achievements on ultra-high magnetic field generation at VNIIEF is given. The cascade MC-1 generators for the 10 and 20MG magnetic field ranges are described. Investigations in ultra-high fields provided by cascade MC-1 generators are an example of extended international collaboration.

Bykov, A. I.; Dolotenko, M. I.; Kolokolchikov, N. P.; Selemir, V. D.; Tatsenko, O. M.

2001-01-01

12

High Magnetic Field Generator of Sub-Microsecond Duration  

Directory of Open Access Journals (Sweden)

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

Audrius Grainys

2012-01-01

13

Visualisation of Magnetic Fields Generated by Helmholtz Coils  

Directory of Open Access Journals (Sweden)

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

Jozef Suriansky; Tibor Frank

2006-01-01

14

Pular magnetogyro ratios and pulsar evolution. III. Magnetic field generation  

Energy Technology Data Exchange (ETDEWEB)

Evidence to support the earlier contention that the primary mechanism of magnetic field generation in short-period (P< or approx. =0.5 s) pulsars is the thermally driven, Hall field limited battery effect is presented.

Woodward, J.F.

1984-04-15

15

Dynamical mass generation in QED with weak magnetic fields  

International Nuclear Information System (INIS)

[en] 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

2006-09-25

16

The Model of Magnetic-Field Generation with Screw Dynamo  

CERN Multimedia

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

Tlatov, Andrey G

2013-01-01

17

Generation of high magnetic fields using superconducting magnets  

International Nuclear Information System (INIS)

High-field superconducting magnets have opened new frontiers for several kinds of applications, such as fusion reactors, particle accelerators, and nuclear magnetic resonance (NMR) spectrometers. The present record for the highest field in a fully superconducting state is 23.4 T. It was achieved with a combination of NbTi, Nb3Sn, and Bi-2212 conductors in 1999. Since high T c (critical temperature) superconductors (HTS) have sufficiently high critical current density even in excess of 30 T, they are promising for use as high-field superconducting magnets. However, several problems still remain to be resolved for practical applications, and the use of HTS coils will be limited to the inner part of a high-field magnet system in the near future. The required technologies to develop a high-field superconducting magnet with a field of up to 28 T have already been established. Such a magnet is certain to provide information to all leading research areas.

2006-01-01

18

Evolution of inflation-generated magnetic field through phase transitions  

CERN Multimedia

We study the evolution of an inflation-generated magnetic field, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magnetic field stays almost unchanged on large scales, while on small scales the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magnetic field generates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise.

Kahniashvili, Tina; Campanelli, Leonardo; Ratra, Bharat; Tevzadze, Alexander G

2012-01-01

19

Generation of primordial magnetic fields on linear overdensity scales.  

UK PubMed Central (United Kingdom)

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(-24) G on comoving scales ~10 kpc. 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 S; Narayan R

2013-08-01

20

Generation of primordial magnetic fields on linear overdensity scales.  

UK PubMed Central (United Kingdom)

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^{-24}??G on comoving scales ?10??kpc. 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 S; Narayan R

2013-08-01

 
 
 
 
21

Ultrafast generation of magnetic fields in a Schottky diode.  

UK PubMed Central (United Kingdom)

For the development of future magnetic data storage technologies, the ultrafast generation of local magnetic fields is essential. Subnanosecond excitation of the magnetic state has so far been achieved by launching current pulses into micro-coils and micro-striplines and by using high-energy electron beams. Local injection of a spin-polarized current through an all-metal junction has been proposed as an efficient method of switching magnetic elements, and experiments seem to confirm this. Spin injection has also been observed in hybrid ferromagnetic-semiconductor structures. Here we introduce a different scheme for the ultrafast generation of local magnetic fields in such a hybrid structure. The basis of our approach is to optically pump a Schottky diode with a focused, approximately 150-fs laser pulse. The laser pulse generates a current across the semiconductor-metal junction, which in turn gives rise to an in-plane magnetic field. This scheme combines the localization of current injection techniques with the speed of current generation at a Schottky barrier. Specific advantages include the ability to rapidly create local fields along any in-plane direction anywhere on the sample, the ability to scan the field over many magnetic elements and the ability to tune the magnitude of the field with the diode bias voltage.

Acremann Y; Buess M; Back CH; Dumm M; Bayreuther G; Pescia D

2001-11-01

22

Ultrafast generation of magnetic fields in a Schottky diode.  

Science.gov (United States)

For the development of future magnetic data storage technologies, the ultrafast generation of local magnetic fields is essential. Subnanosecond excitation of the magnetic state has so far been achieved by launching current pulses into micro-coils and micro-striplines and by using high-energy electron beams. Local injection of a spin-polarized current through an all-metal junction has been proposed as an efficient method of switching magnetic elements, and experiments seem to confirm this. Spin injection has also been observed in hybrid ferromagnetic-semiconductor structures. Here we introduce a different scheme for the ultrafast generation of local magnetic fields in such a hybrid structure. The basis of our approach is to optically pump a Schottky diode with a focused, approximately 150-fs laser pulse. The laser pulse generates a current across the semiconductor-metal junction, which in turn gives rise to an in-plane magnetic field. This scheme combines the localization of current injection techniques with the speed of current generation at a Schottky barrier. Specific advantages include the ability to rapidly create local fields along any in-plane direction anywhere on the sample, the ability to scan the field over many magnetic elements and the ability to tune the magnitude of the field with the diode bias voltage. PMID:11689938

Acremann, Y; Buess, M; Back, C H; Dumm, M; Bayreuther, G; Pescia, D

2001-11-01

23

Fluorescent lamp unit with magnetic field generating means  

Energy Technology Data Exchange (ETDEWEB)

A fluorescent lamp unit having a magnetic field generating means for improving the performance of the fluorescent lamp is disclosed. In a preferred embodiment the fluorescent lamp comprises four longitudinally extending leg portions disposed in substantially quadrangular columnar array and joined by three generally U-shaped portions disposed in different planes. In another embodiment of the invention the magnetic field generating means comprises a plurality of permanent magnets secured together to form a single columnar structure disposed within a centrally located region defined by the shape of lamp envelope.

Grossman, Mark W. (Belmont, MA); George, William A. (Rockport, MA)

1989-01-01

24

Intense transient magnetic-field generation by laser plasma  

Energy Technology Data Exchange (ETDEWEB)

In a laser system, the return current of a laser generated plasma is conducted near a target to subject that target to the magnetic field thereof. In alternate embodiments the target may be either a small non-fusion object for testing under the magnetic field or a laser-fusion pellet. In the laser-fusion embodiment, the laser-fusion pellet is irradiated during the return current flow and the intense transient magnetic field is used to control the hot electrons thereof to hinder them from striking and heating the core of the irradiated laser-fusion pellet.

Benjamin, R.F.

1981-08-18

25

Structure of magnetic fields generated in laser produced plasma  

Energy Technology Data Exchange (ETDEWEB)

A numerical model is used to interpret recent results on magnetic fields generated in laser plasma experiments. Satisfactory agreement is found between model predictions and experimental observations of the morphology of the field. The principal features of the measured density profile are also reproduced.

Boyd, T.J.M.; Humphreys-Jones, G.J.; Cooke, D. (Wales Univ., Bangor (UK))

1982-03-01

26

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-12-31

27

Seed Magnetic Fields Generated by Primordial Supernova Explosions  

CERN Multimedia

The origin of the magnetic field in galaxies is an open question in astrophysics. Several mechanisms have been proposed related, in general, with the generation of small seed fields amplified by a dynamo mechanism. In general, these mechanisms have difficulty in satisfying both the requirements of a sufficiently high strength for the magnetic field and the necessary large coherent scales. We show that the formation of dense and turbulent shells of matter, in the multiple explosion scenario of Miranda and Opher (1996, 1997) for the formation of the large-scale structures of the Universe, can naturally act as a seed for the generation of a magnetic field. During the collapse and explosion of Population III objects, a temperature gradient not parallel to a density gradient can naturally be established, producing a seed magnetic field through the Biermann battery mechanism. We show that seed magnetic fields $\\sim 10^{-12}-10^{-14}G$ can be produced in this multiple explosion scenario on scales of the order of clu...

Miranda, O D; Opher, R

1998-01-01

28

Highly stable and finely tuned magnetic fields generated by permanent magnet assemblies.  

UK PubMed Central (United Kingdom)

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

29

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

30

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. PMID:23683185

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

2013-04-30

31

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

1976-04-26

32

Generation of magnetic fields in Einstein-Aether gravity  

CERN Multimedia

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

Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi

2013-01-01

33

Second order semiclassics with self-generated magnetic fields  

DEFF Research Database (Denmark)

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

Erdös, Laszlo; Fournais, SØren

2012-01-01

34

Axial magnetic field generation in a nonuniform laser produced plasma  

International Nuclear Information System (INIS)

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

1992-07-03

35

Generation and measurement of pulsed high magnetic field  

CERN Multimedia

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

36

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

1989-01-01

37

Electron holography of magnetic field generated by a magnetic recording head.  

UK PubMed Central (United Kingdom)

The magnetic field generated by a magnetic recording head is evaluated using electron holography. A magnetic recording head, which is connected to an electric current source, is set on the specimen holder of a transmission electron microscope. Reconstructed phase images of the region around the magnetic pole show the change in the magnetic field distribution corresponding to the electric current applied to the coil of the head. A simulation of the magnetic field, which is conducted using the finite element method, reveals good agreement with the experimental observations.

Goto T; Jeong JS; Xia W; Akase Z; Shindo D; Hirata K

2013-06-01

38

Apparatus for unilateral generation of a homogeneous magnetic field  

Energy Technology Data Exchange (ETDEWEB)

This patent describes an apparatus for generating within a selected volume a magnetic field having a uniform strength to a selected tolerance, comprising: a first electromagnet coil having a first number of turns N/sub 1/ at a first radius R/sub 1/ with a center of the first coil spaced axially a first distance from the selected volume; a second electromagnet coil axially concentric with and parallel to the first coil and having a second number of turns N/sub 2/ at a second radius R/sub 2/ greater than R/sub 1/ and spaced unilateral of the volume with the first coil a second distance greater than the first distance from the selected volume. The first radius and first distance and the second radius and second distance is functionally related to enable the first and second electromagnet coils to produce first and second electromagnet coils to produce first and second magnetic fields, respectively, having substantially linear gradients within the selected volume. N/sub 1/ and N/sub 2/ are effective when energized with predetermined first and second currents, respectively, to produce equal and opposite gradients of the respective first and second magnetic fields in the unilateral volume and a net magnetic field having a strength within the selected volume effective for nuclear magnetic resonance determinations.

Fukushima, E.; Rath, A.R.; Roeder, S.B.

1988-01-26

39

Relativistic Scott correction in self-generated magnetic fields  

CERN Multimedia

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

40

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 ?0c/?pe, reaching magnitudes eBdc/mec?pe˜?0?0 for an initial sharp shear. The case of an initial smooth shear is also discussed.

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

2013-07-01

 
 
 
 
41

FLASH magnetohydrodynamic simulations of shock-generated magnetic field experiments  

Science.gov (United States)

We report the results of benchmark FLASH magnetohydrodynamic (MHD) simulations of experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. We first outline the implementation of 2D cylindrical geometry in the unsplit MHD solver in FLASH and present results of verification tests. We then describe the results of benchmark 2D cylindrical MHD simulations of the LULI experiments using FLASH that explore the impact of external fields along with the possibility of magnetic field amplification by turbulence that is associated with the shock waves and that is induced by a grid placed in the gas-filled chamber.

Tzeferacos, P.; Fatenejad, M.; Flocke, N.; Gregori, G.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Scopatz, A.; Weide, K.

2012-12-01

42

Tokamak with in situ magnetohydrodynamic generation of toroidal magnetic field  

Energy Technology Data Exchange (ETDEWEB)

A tokamak apparatus includes an electrically conductive metal pressure vessel for defining a chamber and confining liquid therein. A liner disposed within said chamber defines a toroidal space within the liner and confines gas therein. The metal vessel provides an electrically conductive path linking the toroidal space. Liquid metal is forced outwardly through the chamber outside of the toroidal space to generate electric current in the conductive path and thereby generate a toroidal magnetic field within the toroidal space. Toroidal plasma is developed within the toroidal space about the major axis thereof.

Schaffer, Michael J. (San Diego, CA)

1986-01-01

43

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

Energy Technology Data Exchange (ETDEWEB)

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

Oka, T.; Yokoyama, K.; Itoh, Y.; Yanagi, Y.; Yoshikawa, M.; Ikuta, H.; Mizutani, U.; Okada, H.; Noto, K

2003-10-15

44

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

Science.gov (United States)

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

Oka, T.; Yokoyama, K.; Itoh, Y.; Yanagi, Y.; Yoshikawa, M.; Ikuta, H.; Mizutani, U.; Okada, H.; Noto, K.

2003-10-01

45

High magnetic field generation using single-turn coils  

Energy Technology Data Exchange (ETDEWEB)

The advent of the homopolar generator has recently permitted the demonstration of a 20 T on-axis, single turn toroidal magnet. Homopolar generators are inherently high current, low-voltage machines which ideally match the requirements of single-turn coils. Magnetic field levels previously limited by the insulation's thermal and voltage breakdown capability have been surpassed. The entire coil volume is essentially occupied by high strength, high conductivity conductor. A current density of 840 MA/m[sup 2] has been achieved in a 9 cm major radius, toroidal coil with a 9.14 MA, 56 V open-current discharge (sinusoidal pulse, 150 ms). Experimental test results are presented, as well as discussion of the potential for applying this technology to solenoid-type coils. This research is funded by the Texas Atomic Energy Research Foundation.

Werst, M.D.; Ingram, S.K.; Wehrlen, D.J.; Weldon, W.F. (Univ. of Texas, Austin, TX (United States). Center for Electromechanics)

1994-07-01

46

Glutathione production using magnetic fields generated by magnets  

Directory of Open Access Journals (Sweden)

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

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

2012-01-01

47

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

Energy Technology Data Exchange (ETDEWEB)

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

Oka, T [Iwate Industrial Promotion Center, 3-35-2 Iiokashinden, Morioka, Iwate 020-0852 (Japan); Yokoyama, K [Iwate Industrial Promotion Center, 3-35-2 Iiokashinden, Morioka, Iwate 020-0852 (Japan); Noto, K [Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-0855 (Japan)

2005-02-01

48

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

Science.gov (United States)

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

Oka, T.; Yokoyama, K.; Noto, K.

2005-02-01

49

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

International Nuclear Information System (INIS)

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

2005-02-01

50

Internal split field generator  

Energy Technology Data Exchange (ETDEWEB)

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

51

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

CERN Document Server

We investigate the generation of large scale magnetic fields in the universe from quantum fluctuations 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 at the onset of the reheating stage. Second, the dilaton continues its evolution after reheating and then decays. In both cases, we come back to the usual Maxwell equations after inflation and then calculate present magnetic fields.

Zavareh, A Akhtari; Mirza, B

2007-01-01

52

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

1983-01-01

53

Projectile-power-compressed magnetic-field pulse generator  

Energy Technology Data Exchange (ETDEWEB)

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.

Barlett, R.H.; Takemori, H.T.; Chase, J.B.

1983-03-17

54

The generation and stability of magnetic fields in CP stars  

CERN Multimedia

A variety of magnetohydrodynamic mechanisms that may play a role in magnetic, chemically peculiar (mCP) stars is reviewed. These involve dynamo mechanisms in laminar flows as well as turbulent environments, and magnetic instabilities of poloidal and toroidal fields as well as combinations of the two. While the proto-stellar phase makes the survival of primordial fields difficult, the variety of magnetic field configurations on mCP stars may be an indication for that they are instability remnants, but there is no process which is clearly superior in explaining the strong fields.

Arlt, R

2008-01-01

55

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

56

Inflationary susceptibilities, duality and large-scale magnetic fields generation  

CERN Multimedia

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

Giovannini, Massimo

2013-01-01

57

Dynamo-generated magnetic fields in fast rotating single giants  

CERN Multimedia

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

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

2009-01-01

58

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-11-04

59

Magnetic field geometry of the Earth magnetosphere and generation of longitudinal generation of longitudinal currents  

International Nuclear Information System (INIS)

[en] Problem of longitudinal currents in asymmetrical plasma trap is considered. Analysis of isoline configuration of equal volume of magnetic force tubes and current lines in equatorial plane was conducted on the basis of Tsyganenko-87 and Tsyganenko-87 W geomagnetic field distribution in asymmetrical part of Earth magnetosphere corresponds to generation of magneto statistically equilibrium longitudinal currents of current system 1 of

1995-01-01

60

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.

2010-11-01

 
 
 
 
61

Low pressure arc discharge lamp apparatus with magnetic field generating means  

Energy Technology Data Exchange (ETDEWEB)

A low-pressure arc discharge apparatus having a magnetic field generating means for increasing the output of a discharge lamp is disclosed. The magnetic field generating means, which in one embodiment includes a plurality of permanent magnets, is disposed along the lamp for applying a constant transverse magnetic field over at least a portion of the positive discharge column produced in the arc discharge lamp operating at an ambient temperature greater than about 25.degree. C.

Grossman, Mark W. (Belmont, MA); George, William A. (Rockport, MA); Maya, Jakob (Brookline, MA)

1987-01-01

62

System for generating double-pulsed magnetic fields in a kicker magnet  

International Nuclear Information System (INIS)

Two bunched beams are accelerated in the 1A ring of JHF. They are extracted for meson experiments and for neutron experiments successively. Therefore, the extraction kicker magnet should generate double-pulsed magnetic fields at intervals of about 100 ?sec, with a repetition rate of 50 Hz. In order to test the feasibility of generating double pulses, we used two sets of thyratron housings and a kicker magnet for the KEK-PS-extraction system, which has an impedance of 25 ?. Using a thyratron cathode-loaded system, the first firing induces a second misfire by a rapid voltage drop of the second thyratron cathode. A thyratron anode-loaded system does not have the above-mentioned trouble, and has succeeded in generating the desired double pulses with half of the voltage required for the usual operation of JHF (? 80kV). (author).

1991-01-01

63

On a mechanism of magnetic field generation in pulsars  

Energy Technology Data Exchange (ETDEWEB)

Consideration is given to a two-component superfluid neutron-proton Fermi liquid in the npe phase of a neutron star. Equations are obtained for the thermal Green functions and the anomalous expectation values of the two-component Fermi liquid. The Green functions are used to obtain an expression for the superconducting proton current and an equation for the magnetic field within the star. It is shown that the rotation leads to the occurrence of proton vortex filaments at the positions of neutron vortex filaments. In addition, rotation leads to the occurrence of a weak homogeneous static magnetic field.

Sedrakian, D.M.; Shakhabasian, K.M.

1981-04-01

64

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

UK PubMed Central (United Kingdom)

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.

Srinivasan B; Dimonte G; Tang XZ

2012-04-01

65

Magnetic field generation in first order phase transition bubble collisions  

Science.gov (United States)

We consider the formation of a ring-like magnetic field in collisions of bubbles of broken phase in an Abelian Higgs model. Particular attention is paid to multiple collisions. The small collision velocity limit, appropriate to the electroweak phase transition, is discussed. Assuming the relevant features of the Abelian Higgs model are appropriate also to the electroweak case, we argue that after the completion of the electroweak phase transition, when averaged over nucleation center distances, there exists a mean magnetic field B~=2.0×1020 G with a coherence length 9.1×103 GeV-1 (for mH=68 GeV). Because of the ring-like nature of B, the volume average behaves as B~1/L. Taking into account the turbulent enhancement of the field by inverse cascade, we estimate that colliding electroweak bubbles would give rise to a mean field Brms~=10-21 G at 10 Mpc comoving scale today.

Ahonen, Jarkko; Enqvist, Kari

1998-01-01

66

The influence of self-generated magnetic fields on the Rayleigh-Taylor instability  

International Nuclear Information System (INIS)

[en] In the absence of magnetic diffusion the self-generated magnetic field in a plasma is proportional to the fluid vorticity. The ratio of magnetic to fluid energy then shows that self-generated magnetic fields can only affect the Rayleigh-Taylor growth rate for large k(wavelengths less than a few microns). Reduction of the plasma thermal conductivity on the other hand is more important for small k,i.e. long wavelength modes. (author)

1986-01-01

67

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

CERN Multimedia

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

Maeda, Satoshi; Ichiki, Kiyotomo

2011-01-01

68

Apparatus for unilateral generation of a homogeneous magnetic field  

Science.gov (United States)

An apparatus for unilaterally producing a substantially homogeneous magnetic field. The apparatus includes two circular electromagnet coils, a small coil and a large coil, which are coaxial with one another and which are separated by a distance equal to one-half the difference in the radius of the two coils. By appropriate selection of electrical currents, which are passed through the coil in opposite directions, a region of homogeneous magnetic field is formed. This region is centered on the common axis of the two coils, at a point on the axis which is at a distance from the small coil equal to one-half the radius of the small coil, and which is on the opposite side of the small coil from the large coil. The apparatus has particular application in the field of diagnostic medical NMR and other NMR applications.

Fukushima, Eiichi (Los Alamos, NM); Rath, Alan R. (San Diego, CA); Roeder, Stephen B. W. (La Mesa, CA)

1988-01-01

69

Geometrical generation of cosmic magnetic fields within standard electromagnetism  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english We study the evolution of cosmological magnetic fields in FRW models with curved spatial sections and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to FRW universes with open spatial sections. 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. Assumin (more) g 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.

Tsagas, Christos G.; Kandus, Alejandra

2005-12-01

70

Spontaneous Generation of Magnetic Field in Three Dimensional QED at Finite Temperature  

CERN Document Server

We investigate the effects of thermal fluctuations on the spontaneous magnetic condensate in three dimensional QED coupled with P-odd Dirac fermions. Our results show that the phenomenon of the spontaneous generation of the constant background magnetic field survives to the thermal corrections even at infinite temperature. We also study the thermal corrections to the fermionic condensate in presence of the magnetic field.

Cea, P; Cea, Paolo; Tedesco, Luigi

1998-01-01

71

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

International Nuclear Information System (INIS)

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

1982-01-01

72

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

Energy Technology Data Exchange (ETDEWEB)

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

Lominadze, D.G.; Tsikarishvili, E.G.; Chedia, O.V. (AN Gruzinskoj SSR, Abastumani. Abastumanskaya Astrofizicheskaya Observatoriya)

1982-04-01

73

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

CERN Document Server

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

Arlt, Rainer

2013-01-01

74

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

CERN Multimedia

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

75

External split field generator  

Energy Technology Data Exchange (ETDEWEB)

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

76

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

Science.gov (United States)

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

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

2004-11-01

77

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

CERN Multimedia

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

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

2013-01-01

78

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

Science.gov (United States)

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.

Nagatomo, H.; Johzaki, T.; Sunahara, A.; Sakagami, H.; Mima, K.; Shiraga, H.; Azechi, H.

2013-06-01

79

Completing magnetic field generation from gravitationally coupled electrodynamics with the curvaton mechanism  

CERN Multimedia

Primordial magnetic fields of cosmologically interesting field strengths can be generated from gravitationally coupled electrodynamics during inflation. As the cosmological constraints require this to be power law inflation it is not possible to generate at the same time the curvature perturbation from inflation. Therefore here a completion is considered whereby the large scale magnetic field is generated during inflation and the primordial curvature mode in a subsequent era from a curvaton field. It is found that constraints on the model to obtain strong magnetic fields and those to suppress the amplitude of the curvature perturbation generated during inflation can be simultaneously satisfied for magnetic seed fields $B_s\\stackrel{>}{\\sim}10^{-30}$ G.

Kunze, Kerstin E

2012-01-01

80

Generation of Primordial Magnetic Fields on Linear Over-density Scales  

CERN Multimedia

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

 
 
 
 
81

Magnetic Seed Field Generation from Electroweak Bubble Collisions, with Bubble Walls of Finite Thickness  

CERN Document Server

Several papers have proposed mechanisms by which the observed galactic and extra-galactic magnetic fields could have evolved from magnetic seed fields created during the electroweak phase transition. Here we develop an equation-of-motion method for calculating the magnetic fields arising from currents generated in bubble collisions by the charged $W^\\pm$-fields of the Standard Model, taking into account, for the first time, the dynamics of the bubble walls. We conclude that for bubbles with thin surfaces magnetic fields may be comparable to, or larger than, those found in earlier work. Thus, our results support the conclusions of previous studies that magnetic fields created during the electroweak phase transition could be the seeds for present-day observations of cosmic magnetic fields.

Stevens, Trevor

2009-01-01

82

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

Energy Technology Data Exchange (ETDEWEB)

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

Aliev, Y.M.; Bychenkov, V.Y.; Frolov, A.A.

1982-01-01

83

The generation of the earth magnetic field. Pt. 1  

International Nuclear Information System (INIS)

[en] The only possibility to produce the magnetic field of the earth is the dynamo-effect of a flow in the conducting fluid core of the earth. Theoretically it is possible to construct detailed models for the geodynamo, although only first attempts are made in this direction. The first part of this paper deals with the kinematics of the dynamo problem in general and particularly with the homogenious dynamo. (orig.)[de] Die Dynamowirkung von Stroemungen im elektrisch leitenden, fluessigen Kern der Erde stellt die einzige Moeglichkeit der Erzeugung des Erdmagnetfeldes dar. Es ist theoretisch moeglich, wenn auch erst in Ansaetzen realisiert, detaillierte hydromagnetische Modelle fuer den Geodynamo zu konstruieren. Der erste Teil der Arbeit befasst sich mit dem kinematischen Dynamoproblem allgemein und speziell mit dem homogenem Dynamo. (orig.)

1976-01-01

84

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

Science.gov (United States)

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

Šimkanin, Ján; Hejda, Pavel

2013-04-01

85

Magnetic field simulation of magnetic phase detection sensor for steam generator tube in nuclear power plants  

Science.gov (United States)

Magnetic phases and defects are partly produced in steam generator tubes by stress and heat, because steam generator tubes in nuclear power plants are used under high temperature, high pressure, and radioactivity. The magnetic phases induce an error in the detection of the defects in steam generator tubes by the conventional eddy current method. So a new method is needed for detecting the magnetic phases in the steam generator tubes. We designed a new U-type yoke which has two kinds of coils and simulated the signal by the magnetic phases and defects in the Inconnel 600 tube.

Ryu, Kwon-Sang; Son, Derac; Park, Duck-Gun; Kim, Yong-Il

2010-05-01

86

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

CERN Document Server

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

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

2013-01-01

87

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

UK PubMed Central (United Kingdom)

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

Nakamura D; Sawabe H; Matsuda YH; Takeyama S

2013-04-01

88

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

89

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; H. Arof

2007-01-01

90

An analytic solution of the Boltzmann equation in the presence of self-generated magnetic fields in astrophysical plasmas  

CERN Multimedia

Through relating a self-generated magnetic field to the regular motion of free electrons that is responsible for the magnetic field generation in astrophysical plasmas, we solve the Boltzmann kinetic equation in the presence of the self-generated magnetic fields to obtain a steady-state, collisional invariant analytic solution of the equation.

Li, L H

1998-01-01

91

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

International Nuclear Information System (INIS)

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

2009-01-01

92

Generation of axial and lateral magnetic fields in laser produced plasmas  

International Nuclear Information System (INIS)

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

1989-01-01

93

One-dimensional models of magnetic fields generated by hypervelocity impact  

International Nuclear Information System (INIS)

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

2011-01-01

94

Relation between Weibel instability and magnetic field generating thermal instability  

International Nuclear Information System (INIS)

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

1980-01-01

95

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; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

2010-01-01

96

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

International Nuclear Information System (INIS)

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

1984-11-15

97

Generation of large-scale magnetic fields from inflation in teleparallelism  

CERN Multimedia

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

Bamba, Kazuharu; Luo, Ling-Wei

2012-01-01

98

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Vredefort impact crater in South Africa is one of the oldest and largest craters on Earth, making it a unique analog for planetary basins. Intense and randomly oriented remanent magnetization observed in surface samples at Vredefort has been attributed to impact-generated magnetic fields. This p...

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

99

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 earthâs magnetic field on a compass. Students see the connection that the compass simply responds to the earthâs magnetic field since it is the closest, strongest field, and therefore the compass will respond 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

100

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

CERN Multimedia

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

Bamba, Kazuharu; Tsujikawa, Shinji

2008-01-01

 
 
 
 
101

Self-Generated Magnetic Field Effects in National Ignition Facility Capsule Simulations  

Science.gov (United States)

The self generated magnetic field effects for the National Ignition Facility tritium-hydrogen-deuterium (THD) capsule design are simulated in 2D using the multiphysics code HYDRA. In the simulation the magnetic field is generated through the curl of the electron pressure gradient initiated through the Rayleigh-Taylor instability and evolved due to magnetic diffusion, and advection. The calculation accounts for the magnetic field to determine anisotropic thermal electron and ion conduction as well as effects on the alpha particles in the burn phase. Transport coefficients are calculated using the Epperlein-Haines coefficients with Lee-More degeneracy corrections. Maximum field magnitudes in excess of 30 MG are observed in the simulations. Comparisons for capsule designs with and without perturbations on the CH ablator/DT ice layers and radiation source are performed.

Koning, Joseph

2012-10-01

102

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

103

Heat generation in agglomerated ferrite nanoparticles in an alternating magnetic field  

International Nuclear Information System (INIS)

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

2013-01-30

104

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

105

Magnetic-field generation and electron acceleration in relativistic laser channel  

International Nuclear Information System (INIS)

The interaction between energetic electrons and a circularly polarized laser pulse inside an ion channel is studied. Laser radiation can be resonantly absorbed by electrons executing betatron oscillations in the ion channel and absorbing angular momentum from the laser. The absorbed angular momentum manifests itself as a strong axial magnetic field (inverse Faraday effect). The magnitude of this magnetic field is calculated and related to the amount of the absorbed energy. Absorbed energy and generated magnetic field are estimated for the small and large energy gain regimes. Qualitative comparisons with recent experiments are also made.

2002-01-01

106

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

CERN Document Server

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

Blasi, Pasquale

2007-01-01

107

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

2010-01-01

108

The effect of an applied magnetic field on ion generation processes in a rarefied gas  

Energy Technology Data Exchange (ETDEWEB)

An equilibrium under which ions' escape from a generated plasma due to their own electric field occurs in the presence of an external uniform magnetic field is studied analytically. It is found that for an arbitrary source of ionization there is a limiting value (threshold) of the magnetic field after which no balance between birth and collisionless escape of ions is possible and, therefore, no stationary process of ion generation can exist. An experimental setup allowing the observation of the threshold is discussed.

Kuperman, V.Y.; Friedman, G. (Department of Electrical Engineering and Computer Science, University of Illinois at Chicago, Chicago, Illinois 60680-4348 (United States))

1993-05-01

109

Self-Generated Magnetic Field Measurements in TEA-CO sub 2 Laser Produced Plasmas on Different Targets.  

Science.gov (United States)

Results of self-generated magnetic field measurements using differential inductive probes in TEA-CO sub 2 laser produced plasmas on different metallic targets are presented. Dependences of the magnetic field strengths on the incident laser energy, the tar...

E. Cojocaru V. Draganescu M. Ganciu-Petcu I. M. Popescu

1983-01-01

110

Numerical modeling of compressed magnetic field generators loaded with a spherical mesh-initiator  

International Nuclear Information System (INIS)

Initiation of a spherical thin film of explosive with an electrically exploded etched spherical copper mesh loaded by a compressed magnetic field generator (CMF) is an idea spherical wave generator for use in many purposes. The design of this device is greatly facilitated by use of numerical modeling. This paper describes the authors' numerical work.

1990-01-01

111

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

112

On stimulated generation of the neutrinos by nucleons in a magnetic field  

International Nuclear Information System (INIS)

Complete probabilities of n?n+?+?-bar and p?n+e++?e processes in the magnetic field are calculated. n?n+?+?-bar process contribution into neutrino generation is evaluated as compared to conventional ?-decay. In case of p?n+e++?e decay the produced neutrino spins will be oriented against the field. It is shown that in fields with B0 ?3x1017 Gs induction, stationary proton decay is prohibited and its lifetime decreases rapidly with the field increase, which may sufficiently effect n-p balance of magnetic neutron stars.

1986-01-01

113

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

International Nuclear Information System (INIS)

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

2010-02-02

114

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

Science.gov (United States)

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

Lancia, L.; Fourment, C.; Nakatsutsumi, M.; Hulin, S.; Bastiani-Ceccotti, S.; Santos, J. J.; Gauthier, M.; Le Gloahec, M.; Feugeas, J.-L.; Nicolaï, Ph.; Schurtz, G.; Audebert, P.; Fuchs, J.; Migliorati, M.

2010-02-01

115

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

Energy Technology Data Exchange (ETDEWEB)

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.

Yanagi, Y. [IMRA Material R and D Co., Ltd., 5-50 Hachiken-cho, Kariya, Aichi 448-0021 (Japan)]. E-mail: yanagi@ai-i.aisin.co.jp; Matsuda, T. [E and X-ray Co., Ltd, 66 Yotsuya-cho, Kasugai, Aichi 486-0909 (Japan); Hazama, H. [Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yokouchi, K. [Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yoshikawa, M. [IMRA Material R and D Co., Ltd., 5-50 Hachiken-cho, Kariya, Aichi 448-0021 (Japan); Itoh, Y. [IMRA Material R and D Co., Ltd., 5-50 Hachiken-cho, Kariya, Aichi 448-0021 (Japan); Oka, T. [IMRA Material R and D Co., Ltd., 5-50 Hachiken-cho, Kariya, Aichi 448-0021 (Japan); Ikuta, H. [Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Mizutani, U. [Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

2005-10-01

116

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.

1975-01-01

117

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

Energy Technology Data Exchange (ETDEWEB)

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

G. Shvets; N.J. Fisch; J.-M. Rax

2002-01-18

118

Large-scale Magnetic Field Generation via the Kinetic Kelvin-Helmholtz Instability in Unmagnetized Scenarios  

Science.gov (United States)

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 B /epsilon 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 presence of velocity shears.

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

2012-02-01

119

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.

2009-10-15

120

Heavy-ion source using a laser-generated plasma transported through an axial magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Results of transporting a laser-generated plasma through magnetic fields are reported. Plasma plumes have been generated in strong magnetic fields, in directions both transverse and parallel to the field. Collective effects are demonstrated by the plasma while in the high-density state near the laser target. The formation of the plasma and its transport through an axial magnetic field enhances the relative amount of highest charge states and the lowest charge states. The focusing properties of the magnetic field near the extractor gap can prove useful in enhancing ion density at the anode aperture of the extractor gap. It is suggested that the duty cycle of laser ion sources can be extended by simply increasing the ion flight time through the magnetic field from the laser target to the extractor gap without appreciable loss of ions. Further, it is suggested that energy spread in a given ion species can be made small by using an extractor potential programmed to increase in time relative to the laser fire time.

Gray, L.G.; Hughes, R.H.; Anderson, R.J.

1982-10-01

 
 
 
 
121

Dynamical Generation of the Primordial Magnetic Field by Ferromagnetic Domain Walls  

CERN Multimedia

The spontaneous generation of uniform magnetic condensate in $QED_3$ gives rise to ferromagnetic domain walls at the electroweak phase transition. These ferromagnetic domain walls are caracterized by vanishing effective surface energy density avoiding, thus, the domain wall problem. Moreover we find that the domain walls generate a magnetic field $B \\simeq 10^{24} Gauss$ at the electroweak scale which account for the seed field in the so called dynamo mechanism for the cosmological primordial magnetic field. We find that the annihilation processes of walls with size $R \\simeq 10^5 Km$ could release an energy of order $10^{52} erg$ indicating the invisible ferromagnetic walls as possible compact sources of Gamma Ray Bursts.

Cea, P; Cea, Paolo; Tedesco, Luigi

1999-01-01

122

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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. ...

E. D. Schmitter

123

Effect of Superstrong Magnetic Fields on Nuclear Energy Generation Rate in the Crust of Neutron Stars  

International Nuclear Information System (INIS)

This paper shows that superstrong magnetic fields (such as those of magnetars) can increase the energy generation rate many times in the crust of neutron stars. This result undoubtedly not only influences the cooling of neutron stars and the X-ray luminosity observed of neutron stars but also the evolution of neutron stars

2008-04-15

124

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

International Nuclear Information System (INIS)

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

1992-01-01

125

Magnetic Fields  

Science.gov (United States)

This page and its annex describes, in trivial terms, the physics of magnetic fields and the history of its discovery. Included is the work of Halley, Oersted, Ampere and Maxwell. It also describes a way of demonstrating it in the classroom, using a vu-graph projector. Later sections #5, #5a and #6 extend this to magnetic field lines and electromagnetism.

Stern, David

2005-01-04

126

Field-cooled measurements of harmonic generation in magnetization of high-Tc superconductors  

International Nuclear Information System (INIS)

[en] We present measurements of harmonic generation in the magnetization of sintered pellets of YBa2Cu3O7 and Bisub(1.7)Pbsub(0.3)Sr2Ca2Cu3O10 as a function of DC field. The DC field is applied in the field-cooled mode. Measurements are made at 77 K for various values of the AC field amplitude. A comparison is made with calculations done within the critical state model. (author). 18 refs., 11 figs

1993-01-01

127

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

128

Magnetic field of pulsars  

Energy Technology Data Exchange (ETDEWEB)

The generation of the magnetic field in pulsars is considered. It is shown that the currents associated with drag of protons by rotating neutrons produce a mean magnetic field of order 10 to the 13th G. Within the star, this field has a vortex structure with density of order 3 x 10 to the 19th per sq cm. The almost homogeneous magnetic field produces a magnetic moment of order 10 to the 31st G cu cm. 8 references.

Sedrakian, D.M.

1983-01-01

129

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

Energy Technology Data Exchange (ETDEWEB)

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

Slough, J. T. [Redmond Plasma Physics Laboratory, University of Washington, Seattle, Washington 98195 (United States); Miller, K. E. [Redmond Plasma Physics Laboratory, University of Washington, Seattle, Washington 98195 (United States)

2000-05-01

130

Multipole expansions: Magnetic and electric fields generated by electrons bound in spin-orbit eigenstates  

International Nuclear Information System (INIS)

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

2009-05-01

131

Multipole expansions: Magnetic and electric fields generated by electrons bound in spin-orbit eigenstates  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-05-01

132

Cosmological Magnetic Fields  

CERN Document Server

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

Kunze, Kerstin E

2013-01-01

133

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

International Nuclear Information System (INIS)

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

2010-01-01

134

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%.

2010-01-01

135

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

International Nuclear Information System (INIS)

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

1992-01-01

136

Harmonic generation FEL magnets: measured B-fields compared to 3D simulation  

Energy Technology Data Exchange (ETDEWEB)

The Harmonic Generation Free Electron Laser is a Trim Coil short period, high-gain amplifier FEL configured as an optical klystron. It is designed to lase at 3.47 {mu}m using a 30 MeV electron beam at the Accelerator Test Facility at BNL. Each of the three superconducting wiggler magnet sections (modulator, dispersion, radiator) has been built and the magnetic fields have been measured. This paper compares the measurement results with three-dimensional nonlinear computer models created with the TOSCA code.

Graves, W.S.; Solomon, L.

1996-12-01

137

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

138

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

139

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

International Nuclear Information System (INIS)

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

2011-01-01

140

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

1994-11-04

 
 
 
 
141

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

Energy Technology Data Exchange (ETDEWEB)

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 (Al{sub 2}O{sub 3}) 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. (author)

Ishikawa, M.; Koshiba, Y.; Matsushita, T. [University of Tsukuba (Japan). Institute of Engineering Mechanics and Systems

2004-03-01

142

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.

2004-01-01

143

Construction of a 2-5 T class superconducting magnetic field generator with use of an Sm123 bulk superconductor and its application to high-magnetic field demanding devices  

Science.gov (United States)

Superconducting permanent magnet systems generating magnetic fields of 2-5 T have been constructed for the first time in the world by c-axis oriented Sm-Ba-Cu-O bulk superconductors fabricated through the melt processing as trapped field magnets. The trapped magnetic fields of 3.8 and 6.7 T have been produced on the bulk surface at 30 K by the pulsed field magnetization (PFM) and field cooling (FC) methods, respectively. The magnetic field in the open space outside the vacuum vessel exceeds 2.0 and 3.2 T when magnetized by the PFM and FC modes, respectively. It was found that the iteratively magnetizing pulsed-field operation with reducing amplitudes (IMRA method) is very effective in magnetizing high Jc bulk superconductors. This implies the superconducting permanent magnets can be used as high magnetic field generators in various practical applications.

Oka, T.; Itoh, Y.; Yanagi, Y.; Yoshikawa, M.; Ikuta, H.; Mizutani, U.

2000-06-01

144

Missile generation due to electrical arcing in high field fusion magnets  

International Nuclear Information System (INIS)

[en] Large amounts of energy (10 /sup 10/-10/sup 11/ J) are stored in the magnetic field of superconducting magnet systems used in conceptual fusion-reactor designs. If only part of this energy is released accidentally, damage to the magnet and to other rector subsystems may result. In fusion-reactor environments it may lead to the evaporation of activated material and to the generation of energetic missiles, involving interference with sources of radioaactive material in the plant. Results from a Runge-Kutta routine have been obtained for FINTOR, a minimum size Tokamak DT experimental reactor, indicating that missiles of about 20 kg weight may reach velocities in the order of 100 m/s

1981-10-29

145

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

International Nuclear Information System (INIS)

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 to1010-1011Oe2/cm. Estimations of extremely achievable fields and their gradients are made.

2004-01-01

146

Explosive generation of high magnetic fields in large volumes and solid state applications  

Energy Technology Data Exchange (ETDEWEB)

Various methods of producing ultra-high magnetic fields by explosive flux compression are described. A survey is made of the kinds of high magnetic field solid state data obtained in such fields by various groups. Preliminary results are given for the magnetic phase boundary that separates the spin-flop and paramagnetic regions of MnF/sub 2/.

Fowler, C.M.; Caird, R.S.; Erickson, D.J.; Freeman, B.L.; Garn, W.B.

1980-01-01

147

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

CERN Multimedia

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

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

2013-01-01

148

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

149

The generation and application of megagauss fields at the Humboldt High Magnetic Field Center  

International Nuclear Information System (INIS)

A new multi-megagauss generator has been constructed which produces 239 and 311T with a pulse duration of 5 ?s in single turn coil with an inner diameter of 10 and 5mm, respectively. Prominent features of the installation are the vertical coil orientation, a stripline-based lightweight/low inductance discharge circuit in modular arrangement and the galvanic separation of control panels and high-voltage units. The installation is designed as a scientific instrument including suitable cryostats, fast data acquisition systems and basic setups for spectroscopical investigations. The design and performance of the field generator as well as the supplementary equipment are discussed and demonstrated in connection with cyclotron resonance measurements at temperatures down to 5K

1998-01-01

150

Magnetic fields in galaxies  

CERN Document Server

Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic fie...

Beck, Rainer

2013-01-01

151

Suprathermal electron transport and self-generated magnetic field in laser-target interaction  

International Nuclear Information System (INIS)

Recent laser-target experiment at laser intensities greater than 10/sup 14/W/cm/sup 2/ have reported the occurrence of a gigantic laser driven return current (-- 1 MA) from a small target (? 1cm/sup 2/ x1mm) with current rising time less than -- 1 ns. These results generate optimism for the prospects of achieving ultrastrong magnetic fields of up to 10/sup 3/ T as well as extremely intensive power pulses, and opening up a new era for the scientific areas such as thermonuclear confinement, solid state physics, and many other critical technologies. A strong toroidal magnetic field is produced in laser-target interaction by a rapid expansion of suprathermal electrons. The toroidal magnetic field is calculated self-consistently. In this calculation, the motion of suprathermal electrons emitted at radii the beam axis is calculated exactly, and the motion of the electrons at radii away from the beam axis is approximated by a guiding center model.

1987-01-01

152

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

Science.gov (United States)

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

Yuan, X. H.; Robinson, A. P. L.; Quinn, M. N.; Carroll, D. C.; Borghesi, M.; Clarke, R. J.; Evans, R. G.; Fuchs, J.; Gallegos, P.; Lancia, L.; Neely, D.; Quinn, K.; Romagnani, L.; Sarri, G.; Wilson, P. A.; McKenna, P.

2010-06-01

153

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

Energy Technology Data Exchange (ETDEWEB)

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

Yuan, X H; Quinn, M N; Carroll, D C; Gallegos, P; McKenna, P [SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Robinson, A P L; Clarke, R J; Evans, R G; Neely, D [Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX (United Kingdom); Borghesi, M; Quinn, K; Romagnani, L; Sarri, G; Wilson, P A [School of Mathematics and Physics, Queen' s University Belfast, Belfast BT7 1NN (United Kingdom); Fuchs, J; Lancia, L, E-mail: p.mckenna@phys.strath.ac.u [Laboratoire pour l' Utilisation des Lasers Intenses, Ecole Polytechnique, 91128 Palaiseau (France)

2010-06-15

154

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

International Nuclear Information System (INIS)

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

2010-01-01

155

Self focusing of laser beams and its effect in the generation of magnetic field in laser-produced plasma  

Energy Technology Data Exchange (ETDEWEB)

The present work deals with the generation of magnetic field in a plasma due to self focusing effects of laser beam. Spontaneously generated magnetic fields of the order of several kilogauss have been investigated and the cause for the generation of B-field has been attributed to the time dependent ponderomotive force of a self focused inhomogeneous gaussian shaped laser beam. The magnitude of the magnetic field is found to increase with self focusing effect of the laser beam. It can be shown that for high-frequency laser (viz. Nd-glass laser having the wavelength ({lambda}) = 1.06 {mu}m and amplitude of E-field (E{sub 00}) = 3.9 x 10{sup 11} V/m), the magnitude of B-field is found to be in better agreement with the experiment. B-field varies inversely with temperature which has not been taken care in earlier reports. (author)

Ghimire, A. [Kathmandu Univ., Dhulikhel (Nepal); Jha, L.N.

1997-12-31

156

Self focusing of laser beams and its effect in the generation of magnetic field in laser-produced plasma  

International Nuclear Information System (INIS)

The present work deals with the generation of magnetic field in a plasma due to self focusing effects of laser beam. Spontaneously generated magnetic fields of the order of several kilogauss have been investigated and the cause for the generation of B-field has been attributed to the time dependent ponderomotive force of a self focused inhomogeneous gaussian shaped laser beam. The magnitude of the magnetic field is found to increase with self focusing effect of the laser beam. It can be shown that for high-frequency laser (viz. Nd-glass laser having the wavelength (?) = 1.06 ?m and amplitude of E-field (E00) = 3.9 x 1011 V/m), the magnitude of B-field is found to be in better agreement with the experiment. B-field varies inversely with temperature which has not been taken care in earlier reports. (author)

1997-01-01

157

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

International Nuclear Information System (INIS)

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.

2013-01-01

158

Large-Scale Magnetic Field Re-generation by Resonant MHD Wave Interactions  

CERN Multimedia

We investigate numerically the long-time behavior of balanced Alfven wave turbulence forced at intermediate scales. Whereas the usual constant-flux solution is found at the smallest scales, two new scalings are obtained at the forcing scales and at the largest scales of the system. In the latter case we show, in particular, that the spectrum evolves first to a state determined by Loitsyansky invariant and later a state close to the thermodynamic equipartition solution predicted by wave turbulence. The astrophysical implications for galactic magnetic field generation are discussed.

Galtier, S

2007-01-01

159

FLASH hydrodynamic simulations of experiments to explore the generation of cosmological magnetic fields  

Science.gov (United States)

We report the results of FLASH hydrodynamic simulations of the experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. The simulations show that the result of the laser illuminating the target is a series of complex hydrodynamic phenomena.

Scopatz, A.; Fatenejad, M.; Flocke, N.; Gregori, G.; Koenig, M.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Ravasio, A.; Tzeferacos, P.; Weide, K.; Yurchak, R.

2013-03-01

160

Behavioral effects on rats of high strength magnetic fields generated by a resistive electromagnet.  

UK PubMed Central (United Kingdom)

It has been reported previously that exposure to static high magnetic fields of 7 T or above in superconducting magnets has behavioral effects on rats. In particular, magnetic field exposure acutely but transiently suppressed rearing and induced walking in tight circles; the direction of circular locomotion was dependent on the rats' orientation within the magnet. Furthermore, when magnet exposure was paired with consumption of a palatable, novel solution, rats acquired a persistent taste aversion. In order to confirm these results under more controlled conditions, we exposed rats to static magnetic fields of 4 to 19.4 T in a 189 mm bore, 20 T resistive magnet. By using a resistive magnet, field strengths could be arbitrary varied from -19.4 to 19.4 T within the same bore. Rearing was suppressed after exposure to 4 T and above; circling was observed after 7 T and above. Conditioned taste aversion was acquired after 14 T and above. The effects of the magnetic fields were dependent on orientation. Exposure to +14 T induced counter-clockwise circling, while exposure to -14 T induced clockwise circling. Exposure with the rostral-caudal axis of the rat perpendicular to the magnetic field produced an attenuated behavioral response compared to exposure with the rostral-caudal axis parallel to the field. These results in a single resistive magnet confirm and extend our earlier findings using multiple superconducting magnets. They demonstrate that the behavioral effects of exposure within large magnets are dependent on the magnetic field, and not on non-magnetic properties of the machinery. Finally, the effects of exposure to 4 T are clinically relevant, as 4 T magnetic fields are commonly used in functional MRI assays.

Houpt TA; Pittman DW; Riccardi C; Cassell JA; Lockwood DR; Barranco JM; Kwon B; Smith JC

2005-10-01

 
 
 
 
161

Theory of Magnetic Seed-Field Theory of Magnetic Seed-Field Generation during the Cosmological First-Order Electroweak Phase Transition  

CERN Multimedia

We present a theory of the generation of magnetic seed fields in bubble collisions during a first-order electroweak phase transition (EWPT) possible for some choices of parameters in the minimal supersymmetric Standard Model. The theory extends earlier work and is formulated to assess the importance of surface dynamics in such collisions. We are led to linearized equations of motion with O(3) symmetry appropriate for examining collisions in which the Higgs field is relatively unperturbed from its mean value in the collision volume. Coherent evolution of the charged $W$ fields within the bubbles is the main source of the electromagnetic current for generating the seed fields, with fermions also contributing through the conductivity terms. We present numerical simulations within this formulation to quantify the role of the surface of the colliding bubbles, particularly the thickness of the surface, and to show how conclusions drawn from earlier work are modified. The main sensitivity arises such that the steepe...

Stevens, Trevor

2010-01-01

162

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.

1999-01-01

163

Primordial magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Full text: Magnetic fields are found throughout the cosmos, and models of mechanisms that generate these fields in the present Universe cannot explain all its forms. The fields are detected in the radiation emitted by galaxies, galaxy clusters and superclusters that display patterns of a known phenomena: Zeeman Effect (splitting of the molecular energy lines), Synchrotron Radiation (emitted by relativistic electrons in a magnetic field); Faraday Effect (rotation of the radiation plane of polarization by a magnetic field parallel to its propagation). Such magnetic fields can arise from the Primordial Universe; if it preceded the Cosmic Microwave Background (CMB) radiation, it could be observed today. The wavelengths of the fields found sweep a large region of the spectrum: from nanometers to the size of megaparsec. Its intensity is also quite varied, ranging from micro-Gauss to a few Gauss. We make perturbations in the primordial plasma before the Era of Recombination. In such plasma, the efficient collision between its constituents generates a relative velocity between electrons and protons, creating a magnetic field. In such a way that makes it possible to generate fields of the order of 10{sup -18} G for scales of 1Mpc and 10{sup -14} of 10kpc. The perturbations are made in viscous cosmological model, using Inflation theory. As the disturbance of the density of matter and the generation of gravitational waves behave differently from the magnetic fields produced in the primordial era, we can distinguish them in the power spectrum of current observations. It is possible and interesting to compare the model of primordial magnetic fields with its evolution in nucleosynthesis (which would limit the elements formed) and at CMB radiation. Developed the model and determined its parameters, we determine its limitations with the current observational data. So we are able to speculate the formation of magnetic fields that today fill the Universe within the capability of our model. (author)

Goncalves, Sergio Vitorino de Borba; Scardua, A.C. [Universidade Federal do Espirito Santo (UFES), ES (Brazil)

2011-07-01

164

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

International Nuclear Information System (INIS)

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

1994-01-01

165

A study by computer simulation of the generation and evolution of the Earth`s magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Until recently very little has been known about the maintenance of the Earth`s magnetic field. The general consensus was that some type of convective motion edits in the Earth`s liquid iron alloy core that is affected by rotational forces in a way that continually generates new magnetic field to replace that which diffuses away. Magnetic-field reversals and secular variation have long been measured but no theory existed to explain these phenomena. To gain an understanding of the basic physical mechanisms of the ``geodynamo,`` we produced the first self-consistent computer simulation of convection and magnetic field generation in a rotating three-dimensional spherical fluid shell as an anologue to the Earth`s convective dynamo. This is a final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL).

Glatzmaier, G.A.; Hollerbach, R.; Roberts, P.H.

1995-12-31

166

Cosmological magnetic fields  

CERN Document Server

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-alpha systems. In principle, these fields could play an important role in structure formation and also affect the anisotropies in the cosmic microwave background radiation (CMB). The study of cosmological magnetic fields aims not only to quantify these effects on large-scale structure and the CMB, but also to answer one of the outstanding puzzles of modern cosmology: when and how do magnetic fields originate? They are either primordial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.

Maartens, R

2000-01-01

167

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

Directory of Open Access Journals (Sweden)

Full Text Available On the basis of the spontaneous fast reconnection model, three-dimensional magnetic field profiles associated with a large-scale plasmoid propagating along the antiparallel magnetic fields are studied in the general sheared current sheet system. The plasmoid is generated ahead of the fast reconnection jet as a result of distinct compression of the magnetized plasma. Inside the plasmoid, the sheared (east-west) field component has the peak value at the plasmoid center located at x=XC, where the north-south field component changes its sign. The plasmoid center corresponds to the so-called contact discontinuity that bounds the reconnected field lines in xfield lines without reconnection in x>XC. Hence, contray to the conventional prediction, the reconnected sheared field lines in xfield lines in x>XC. It is demonstrated that the resulting profiles of magnetic field components inside the plasmoid are, in principle, consistent with satellite observations. In the ambient magnetic field region outside the plasmoid too, the magnetic field profiles are in good agreement with the well-known observations of traveling compression regions (TCRs).

M. Ugai

2010-01-01

168

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

Energy Technology Data Exchange (ETDEWEB)

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.

Aliev, Y.M.; Bychenkov, V.Y.; Frolov, A.A.

1982-11-01

169

Electron fluid equations and magnetic field generation in laser-irradiated collisional plasmas  

International Nuclear Information System (INIS)

[en] The results of a previous paper are used for deriving the electron fluid equations of laser-irradiated collisional plasmas as well as the equations which govern the magnetic field generation in these media. It is shown that these equations involve various collisional contributions which can be exactly calculated at each order for any electron-ion interaction law, and that they enable us to recover, as special cases, the results given in other works. These methods provide a self-consistent theory of transport phenomena in high Z plasmas, in which the background state is generally non-Maxwellian and evolves on a slow time scale determined by the electron heating process. The full calculations are given for the Coulomb law in a particular case, and the results so obtained are compared to those derived from the Krook model. (orig.)

1987-01-01

170

Self-generated magnetic field in CO2 laser produced plasma  

International Nuclear Information System (INIS)

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

1979-01-01

171

Generation of depth-perception information in stereoscopic nuclear magnetic resonance imaging by non-linear magnetic field gradients.  

Science.gov (United States)

Stereoscopic NMR images have been produced in the past. However, because of the gradients are linear, only isometric projections can be produced, i.e., they do not carry correct depth-perception information. The resulting stereoscopic image will not have correct relative sizes at different depths. This paper gives an analysis of what perception information is needed and shows that it can be produced by a non-linear magnetic field gradient. The concept is exemplified by simulations and its implementation is demonstrated successfully by experiments. The depth-encoding gradient can be generated by static steel pieces or by current loops. The procedure can be incorporated into any existing hardware and pulse sequences, and has potential application in surgery. PMID:9665551

Chen, C N

1998-05-01

172

Analyzing the uniformity of the generated magnetic field by a practical one-dimensional Helmholtz coils system.  

UK PubMed Central (United Kingdom)

Using the Helmholtz coils system is one of the most suitable approaches which have been introduced for generating uniform magnetic fields. In this paper, uniformity of the generated magnetic field by a practical one-dimensional (1D) Helmholtz coils system has been analyzed, mathematically. For this purpose, relationships between the magnetic field uniformity and different practical unavoidable mismatches have been extracted. The theoretical analysis clearly demonstrates the effect of assembly misalignments and manufacturing mismatches on the magnetic field achieved by a practical 1D Helmholtz coils system. The given analyses have been confirmed by the experimental results which are in good agreement with the calculated values. This analysis and the experimental results illustrate that to achieve a very high uniform magnetic field, practical assembly misalignments, and manufacturing mismatches must be as small as possible, and the background magnetic field distortion must be avoided, too. The results of this work are important in the design of instruments and systems where Helmholtz coils are used.

Beiranvand R

2013-07-01

173

Generation of electromagnetic oscillations by electrons which are rotating in cylindrical resonator with radial electric and longitudinal magnetic fields  

International Nuclear Information System (INIS)

[en] Generation of electromagnetic waves by electrons which are rotating in crossed radial electrostatic and axial magnetic fields in a cylindric resonator is studied theoretically. Dispersion equations which describe electron-wave interaction are obtained. It was shown that wave generation by plasma or Cherenkov resonances. Wave frequencies and increments are found for mentioned resonances in a homogeneous plasma layer. The advantages and disadvantages of wave generation under different conditions are noted. 5 refs

1997-01-01

174

Three-magnetic fields  

CERN Document Server

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

Koivisto, Tomi S

2011-01-01

175

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

Energy Technology Data Exchange (ETDEWEB)

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

Pettini, Marco; Torricelli-Ciamponi, Guidetta

1988-12-01

176

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

International Nuclear Information System (INIS)

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

1988-01-01

177

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-04-01

178

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

International Nuclear Information System (INIS)

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

1994-01-01

179

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

International Nuclear Information System (INIS)

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

1975-11-17

180

Limits for primordial magnetic fields  

CERN Multimedia

A possible explanation for the origin of the magnetic fields observed today in matter structures is that they were generated in the primordial universe. After briefly revising the model of a primordial stochastic magnetic field and sketching the main features of its time evolution in the primordial plasma, we illustrate the current upper bounds on the magnetic field amplitude and spectral index from Cosmic Microwave Background observations and gravitational wave production. We conclude that a primordial magnetic field generated by a non-causal process such as inflation with a red spectrum seems to be favoured as a seed for the magnetic fields observed today in structures.

Caprini, Chiara

2011-01-01

 
 
 
 
181

NOAA/NGDC candidate models for the 11th generation International Geomagnetic Reference Field and the concurrent release of the 6th generation Pomme magnetic model  

Science.gov (United States)

The International Geomagnetic Reference Field (IGRF) is updated every five years based on candidate model submissions by research institutions worldwide. In the call for the 11th generation of IGRF, candidates were requested for the definitive main field in 2005, the predicted main field in 2010, and the predicted secular variation from 2010 to 2015. The NOAA/NGDC candidate models for IGRF-11 were produced from parent models parameterized in the same way as the 6th generation of our Pomme magnetic model. All models were based on CHAMP satellite measurements, while Ørsted satellite measurements were used for model validation. The internal field in Pomme-6 is described by a 2nd degree Taylor time series of spherical harmonic expansion coefficients of a scalar magnetic potential. Magnetic fields of ionospheric origin are avoided by careful data selection. Instead of co-estimating magnetospheric fields, we subtract a magnetospheric field model estimated previously from a more extensive data set covering all local times. From comparison with Örsted measurements and general considerations of magnetic field predictability, we attribute a root mean square (RMS) uncertainty of 1.3 nT to our candidate model for the main field in 2005, 2.5 nT to the predicted main field in 2010 and 26 nT/a to the predicted secular variation from 2010 to 2015.

Maus, S.; Manoj, C.; Rauberg, J.; Michaelis, I.; Lühr, H.

2010-10-01

182

Experimental Observation of Optical Rotation Generated in Vacuum by a Magnetic Field  

International Nuclear Information System (INIS)

We report the experimental observation of a light polarization rotation in vacuum in the presence of a transverse magnetic field. Assuming that data distribution is Gaussian, the average measured rotation is (3.9±0.5)x10-12 rad/pass, at 5 T with 44 000 passes through a 1 m long magnet, with ?=1064 nm. The relevance of this result in terms of the existence of a light, neutral, spin-zero particle is discussed.

2006-03-24

183

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

Energy Technology Data Exchange (ETDEWEB)

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.

Friedman, M.; Serlin, V.

1985-07-08

184

Could the rotation of the Earth's inner core be the cause of a dipolar magnetic field generation?  

Energy Technology Data Exchange (ETDEWEB)

Beginning with the comment of S. Marinov article, the authors studied two processes that could generate a dipolar magnetic field: the electron inertia in metals and the Barnet effect, and calculated the field generated by such processes. Then, they solved analytically the hydrodynamic problem of the fluid motion in the spherical shell when the inner and outer spheres rotate with different angular velocities and considered an analogue model for the liquid outer core of the Earth. Putting this solution into the kinematics equation of the dynamo theory, they discussed about the solution and about the possibility of modifying and amplifying the dipolar field by the fluid motion.

Duka, B. [Tirana Univ. (Albania). Faculty of Natural Sciences, Dept. of Physics

1999-04-01

185

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

Science.gov (United States)

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

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

2011-02-01

186

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).

1997-01-01

187

Magnetic field coils  

Energy Technology Data Exchange (ETDEWEB)

The patent concerns magnetic field coils, particularly coils designed to produce a defined field in at least one volume, e.g. for NMR spectroscopy. The coils are formed by conductors located on a surface. The positions of the conductors are determined by the calculation of the continuous current density required on that surface to generate the required magnetic field on a specific target surface (or at specified points). The distribution of conductors that provides a good approximation to the current density is then calculated and the conductors are then wound onto the surface into the calculated positions. (U.K.).

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

1988-02-03

188

Temporal behaviour of self generated magnetic field and its influence on inhibition of thermal flux in ICF plasma  

International Nuclear Information System (INIS)

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

1989-01-01

189

Heat generation ability in AC magnetic field and their computer simulation for Ti tube filled with ferrite powder  

International Nuclear Information System (INIS)

The heat generation ability of needle-type materials was studied for the application of thermal coagulation therapy in an AC magnetic field. Although the Ti tube without the MgFe2O4 powder or Ti rod showed poor heat generation abilities in an AC magnetic field, the temperature was significantly increased by the presence of ferrite powder in the Ti tube. We confirmed using a computer simulation that the eddy loss of the Ti tube was increased by the enhanced magnetic flux density due to the ferrite powder in the Ti tube. The heat generation of the ferrite filled Ti tube was increased by utilization of the quenched MgFe2O4 powder from elevated temperature. The relative magnetic permeability of the quenched ferrite was enhanced with the decrease in the inverse ratio of the cubic spinel structure. The heat generation ability was increased with the increase in the relative magnetic permeability of the Ti tube with ferrite powder. The calculated joule loss based on the experimental results showed an agreement with those using the computer simulation.

2011-01-01

190

Generation of 1.5-kW, 1-THz coherent radiation from a gyrotron with a pulsed magnetic field.  

Science.gov (United States)

To cover a so-called terahertz gap in available sources of coherent electromagnetic radiation, the gyrotron with a pulsed solenoid producing up to a 40 T magnetic field has been designed, manufactured, and tested. At a 38.5 T magnetic field, the gyrotron generated coherent radiation at 1.022 THz frequency in 50 musec pulses. The microwave power and energy per pulse were about 1.5 kW and 75 mJ, respectively. Details of the gyrotron design, manufacturing, operation and measurements of output radiation are given. PMID:18232780

Glyavin, M Yu; Luchinin, A G; Golubiatnikov, G Yu

2008-01-11

191

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

International Nuclear Information System (INIS)

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

1988-01-01

192

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

Energy Technology Data Exchange (ETDEWEB)

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

Rizzato, F.B.

1988-10-01

193

Generation of 1.5-kW, 1-THz coherent radiation from a gyrotron with a pulsed magnetic field.  

UK PubMed Central (United Kingdom)

To cover a so-called terahertz gap in available sources of coherent electromagnetic radiation, the gyrotron with a pulsed solenoid producing up to a 40 T magnetic field has been designed, manufactured, and tested. At a 38.5 T magnetic field, the gyrotron generated coherent radiation at 1.022 THz frequency in 50 musec pulses. The microwave power and energy per pulse were about 1.5 kW and 75 mJ, respectively. Details of the gyrotron design, manufacturing, operation and measurements of output radiation are given.

Glyavin MY; Luchinin AG; Golubiatnikov GY

2008-01-01

194

The second-harmonic generation of anisotropic quantum disks in the presence of a tilted magnetic field  

Science.gov (United States)

We theoretically investigate the second-harmonic generation (SHG) coefficient of anisotropic quantum disks in the presence of a tilted magnetic field. Within the framework of the effective-mass approximation, we obtain the confined wave functions and energies of electrons of anisotropic quantum disks. We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method. The numerical results for the typical GaAs/AlGaAs anisotropic quantum disks show that the SHG coefficient depends strongly on the anisotropy and the magnetic field direction ?. And we find that the maximum value of SHG coefficient is occurring at maximum ?.

Li, Xuechao; Zhang, Chaojin

2013-10-01

195

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

Science.gov (United States)

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-? (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 direction at a temperature of 77 K. The persistent screen, incorporating a single layer of superconducting film, can attenuate an external magnetic field of up to 5 mT by more than an order of magnitude. For comparison purposes, another type of screen which incorporates low critical temperature quasipersistent joints was also built. The shielding technique we describe here appears to be especially promising for the realization of large scale high-Tc superconducting screens.

Fagnard, J. F.; Dirickx, M.; Levin, G. A.; Barnes, P. N.; Vanderheyden, B.; Vanderbemden, P.

2010-07-01

196

New repetitive X-ray generator using magnetic field controlled POS  

International Nuclear Information System (INIS)

[en] The paper represents new results in repetitive pulsed power production using inductive storage and Plasma Opening Switch operating in applied magnetic field. A design of new compact X-ray production facility capable of producing 4-5 MV pulsed electron beam is proposed. The facility is intended for radiation sterilization technology , food and wastes decontamination

1231-01-00

197

Anisotropic distributions of the fast electron and the spontaneous magnetic field generated during laser interaction with foil targets  

International Nuclear Information System (INIS)

An anisotropic distribution of fast electrons from the interaction of femtosecond laser with foil targets has been measured. The result shows that the fast electron emission is mainly along the direction of reflection laser and of 60 degree with incidence laser,, which is due to the accelerated mechanisms of the reflection laser and the resonance absorption. The spontaneous magnetic field generated during laser interactions with foil targets are calculated by the 2 ? spectra which was obtained by using an OMA spectrometer. It is found that the magnetic field is affected by the distributions of fast electrons. The electric current density induced by the fast electron beam have been estimated roughly to is 1010-11 Acm-2, which is better consistent with other one PIC simulation. This huge electric current may be responsible principally for the production of spontaneous magnetic field. (authors)

2011-01-01

198

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

International Nuclear Information System (INIS)

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

1990-01-01

199

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

200

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

1993-01-01

 
 
 
 
201

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

Directory of Open Access Journals (Sweden)

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

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

2004-01-01

202

Photon echoes generated by reversing magnetic field gradients in a rubidium vapor.  

Science.gov (United States)

We propose a photon echo quantum memory scheme using detuned Raman coupling to long-lived ground states. In contrast to previous three-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 vapor 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. PMID:18923610

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

2008-10-15

203

Magnetic Fields in Galaxies  

Science.gov (United States)

Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized emission traces turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular or anisotropic random, generated from isotropic random fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. 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 generated by a mean-field dynamo. However, in most spiral galaxies observed so far the field structure is more complicated. 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. Future observations of polarized emission at high frequencies, with the EVLA, the SKA and its precursors, will trace galactic magnetic fields in unprecedented detail. Low-frequency telescopes (e.g. LOFAR and MWA) are ideal to search for diffuse emission and small RMs from weak interstellar and intergalactic fields.

Beck, Rainer

2012-05-01

204

Origin of magnetic field enhancement in the generation of terahertz radiation from semiconductor surfaces.  

UK PubMed Central (United Kingdom)

We present a theory of the magnetic field enhancement of terahertz (THz) emission from photogenerated carriers in the surface depletion region of a semiconductor. A combination of the Drude-Lorentz model for the carrier dynamics with an appropriate solution of the radiation problem is sufficient to explain the strong B -field enhancement in THz radiation that has been observed experimentally. The effect arises primarily from the increased radiation efficiency of transient currents flowing in the plane of the surface. The model provides quantitative agreement with experiment for the pronounced angular dependence of the enhancement and predicts the correct trend for the enhancement in a variety of materials.

Shan J; Weiss C; Wallenstein R; Beigang R; Heinz TF

2001-06-01

205

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.

2010-05-17

206

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.

Nejib Hidouri; Mounir Bouabid; Mourad Magherbi; Ammar Ben Brahim

2011-01-01

207

Effect of self-generated magnetic field on the two-plasmon decay instability in a laser-produced plasma  

International Nuclear Information System (INIS)

In this paper we have made a theoretical investigation on the two-plasmon decay instability of laser radiation in the presence of the self-generated magnetic field at the quarter-critical density region in a laser-produced plasma. The Vlasov equation in terms of guiding centre coordinates has been employed to obtain the non-linear response of electrons in the plasma. The threshold power density of the incident laser radiation for the two-plasmon decay instability is always exceeded in currently employed power densities in laser-target experiments and above the threshold the growth rate of the instability is quite large. It is also noticed that the self-generated magnetic field enhances the threshold to a large extent, thus drastically reducing the growth rate of the instability. (author)

1985-01-01

208

Generation of enhanced-scalelength plasmas and zeeman study of magnetic fields. Memorandum report  

Energy Technology Data Exchange (ETDEWEB)

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

Stamper, J.A.; McLean, E.A.; Obenschain, S.P.; Griem, H.R.; Manka, C.K.

1983-03-31

209

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.

Mohammed Q. Al-Odat; Renhe A. Damseh; Moh'd A. Al-Nimr

2004-01-01

210

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

211

Magnetic field line Hamiltonian  

Energy Technology Data Exchange (ETDEWEB)

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

Boozer, A.H.

1985-02-01

212

Numerical investigations on influence of B-dependent flow resistivity on third harmonics of generated magnetic field  

Energy Technology Data Exchange (ETDEWEB)

The numerical code for simulating the time evolution of the shielding current density in the high-temperature superconductor has been developed on the basis of the element-free Galerkin method. The magnetic flux density generated by the shielding current density is calculated by use of the code and its spectral analysis is performed. The results of computations show that an increase in the amplitude of the applied ac magnetic field will cause the appearance of the third harmonics of the magnetic flux density. Furthermore, it is found that the rapid growth of the third harmonics arises not from the B-dependence of the critical current density but from that of the flow resistivity.

Kamitani, Atsushi; Saitoh, Ayumu; Ikuno, Soichiro

2004-10-01

213

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

214

Generation and focusing of high power ion beam in magnetically insulated diode with applied b - field  

International Nuclear Information System (INIS)

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

1989-01-01

215

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

1984-01-01

216

Zeeman ratchets: pure spin current generation in mesoscopic conductors with non-uniform magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

We consider the possibility to employ a quantum wire realized in a two-dimensional electron gas (2DEG) as a spin ratchet. We show that a net spin current without accompanying net charge transport can be induced in the nonlinear regime by an unbiased external driving via an ac voltage applied between the contacts at the ends of the quantum wire. To achieve this, we make use of the coupling of the electron spin to inhomogeneous magnetic fields created by ferromagnetic stripes patterned on the semiconductor heterostructure that harbors the 2DEG. Using recursive Green function techniques, we numerically study two different set-ups, consisting of one and two ferromagnetic stripes, respectively.

Scheid, Matthias [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Bercioux, Dario [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Richter, Klaus [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany)

2007-11-15

217

Linear Magnetic Motor/Generator.  

Science.gov (United States)

A linear magnetic motor/generator is disclosed which uses magnetic flux to provide mechanical motion or electrical energy. The linear magnetic motor/generator includes an axially movable actuator mechanism. A permament magnet mechanism defines a first mag...

P. A. Studer

1982-01-01

218

Biexciton in magnetic fields  

International Nuclear Information System (INIS)

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

2010-01-01

219

Flexible magnetic field therapy mat  

UK PubMed Central (United Kingdom)

Devices for performing magnetic field therapy employ rigid field excitation coils for attachment or application onto the body of a patient, and this partially delimits the range of action of the therapeutically active field lines. The novel, flexible magnetic field therapy mat is to permit optimum utilization of the field in the entire body region coupled with extreme comfort on use. In a double-walled textile or plastic mat (1) which can surround a human body from the armpits to the thighs, coils (2) which are wound onto flat iron cores and are connected in series are excited via an adjustable direct current pulse generator for periodic, polarised formation of magnetic fields. Direct application of all coil rods on the body and the "coil core position" of the patient in the mat result in an optimum therapeutic effect of all the force lines of the therapy field. Magnetic field therapy in the ELF field.

KASCHIK GERHARD

220

The earth's magnetic field  

International Nuclear Information System (INIS)

[en] 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)

1983-01-01

 
 
 
 
221

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

International Nuclear Information System (INIS)

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

2005-01-01

222

Laser-driven shock experiments in pre-compressed water: Implications for magnetic field generation in Icy Giant planets  

Energy Technology Data Exchange (ETDEWEB)

Laser-driven shock compression of pre-compressed water (up to 1 GPa precompression) produces high-pressure, -temperature conditions in the water inducing two optical phenomena: opacity and reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semi-conductor to electronic conductor transition in water and is found at pressures above {approx}130 GPa for single-shocked samples pre-compressed to 1 GPa. This electronic conduction provides an additional contribution to the conductivity required for magnetic field generation in Icy Giant planets like Uranus and Neptune.

Lee, K; Benedetti, L R; Jeanloz, R; Celliers, P M; Eggert, J H; Hicks, D G; Moon, S J; Mackinnon, A; Henry, E; Koenig, M; Benuzzi-Mounaix, A; Collins, G W

2005-11-10

223

Magnetic Propeller for Uniform Magnetic Field Levitation  

CERN Multimedia

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

224

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

Energy Technology Data Exchange (ETDEWEB)

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 line of best fit were 0.87 and 0.07 {mu}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.

Renew, D C [National Grid Transco plc, 1-3 Strand, London WC2N 5EH (United Kingdom); Cook, R F [Formerly National Grid Company plc, Kelvin Avenue, Leatherhead, Surrey KT22 7ST (United Kingdom); Ball, M C [Formerly National Grid Company plc, Kelvin Avenue, Leatherhead, Surrey KT22 7ST (United Kingdom)

2003-09-01

225

METHOD FOR DESIGNING COIL SYSTEMS FOR GENERATION OF MAGNETIC FIELDS OF DESIRED GEOMETRY, A MAGNETIC RESONANCE IMAGING OR MAGNETOENCEPHALOGRAPHY APPARATUS WITH A COIL ASSEMBLY AND A COMPUTER PROGRAM  

UK PubMed Central (United Kingdom)

The present invention introduces a method, apparatus and computer program for magnetic resonance imaging or magnetoencephalography applications in order to control currents of a coil assembly (20), and thus achieving desired magnetic fields precisely in the measuring volume (21). The approach is an algebraic method where a field vector is generated for the test currents of each coil (20). Vector and matrix algebra is applied and a linear set of equations is formed. Field components and their derivatives up to the desired order can be taken into account. Principal component analysis or independent component analysis can be applied for determination of the dominant external interference components. By checking the condition value for the matrix (33, 45), it is possible to investigate whether a reasonable solution of currents for desired magnetic fields is possible to achieve. Finally, solved currents can be installed into a current supply unit (29) feeding the coils of the assembly (20). The invention can be applied as an active compensation feature for different interference shapes in the MEG application (25), or for the precise creation of the fields and gradients in the MRI application (24).

SIMOLA JUHA; TAULU SAMU

226

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

1979-06-20

227

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

International Nuclear Information System (INIS)

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

1990-01-01

228

Stellar magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

Strong evidence of magnetic fields is shown by white dwarves, chemically peculiar stars, and late-type dwarves. The magnetic data available, for CP stars agree with the oblique rotator model. The distribution of the magnetic axis inclination could be random or a mixture of low and high obliquities. The data are consistent with rotational braking on the main sequence and with field decay. Moreover, they show an anti-correlation between the magnetic field strength and the rotational velocity.

Didelon, P. (Observatoire de Strasbourg, 67 (France))

1984-01-01

229

A «tidal» magnetic field?  

Directory of Open Access Journals (Sweden)

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

F. Bocchio

1997-01-01

230

Chaotic magnetic field reversals in turbulent dynamos  

CERN Document Server

We present direct numerical simulations of reversals of the magnetic field generated by swirling flows in a spherical domain. In agreement with a recent model, we observe that coupling dipolar and quadrupolar magnetic modes by an asymmetric forcing of the flow generates field reversals. In addition, we show that this mechanism strongly depends on the value of the magnetic Prandtl number.

Gissinger, Christophe; Fauve, Stephan

2009-01-01

231

Primordial Magnetic Fields in Cosmology  

CERN Multimedia

Magnetic fields have been observed in galaxies, clusters of galaxies and probably in superclusters. While mechanisms exist to generate these in the late universe, it is possible that magnetic fields have existed since very early times. This thesis is concerned with methods to predict the form of such imprints. We review in detail a standard, linearised cosmology before introducing an electromagnetic field. We then consider the intrinsic statistics of the magnetic stresses in two ways, analytically and via static realisations. We construct the power spectra, some of which we present for the first time. At the one- and three-point level we find significant intrinsic non-Gaussianities. Finally we turn to the observable impacts a primordial magnetic field. Assuming coherence, the statistics of the source can be mapped onto the CMB in a simple manner. We demonstrate that our approach is valid by reproducing the signals for Gaussian power law fields on the microwave sky. [ABRIDGED

Brown, Iain A

2008-01-01

232

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

International Nuclear Information System (INIS)

[en] 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)

2012-01-01

233

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.

2010-10-15

234

Primordial magnetic field limits from cosmological data  

CERN Multimedia

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.

Kahniashvili, Tina; Sethi, Shiv K; Pandey, Kanhaiya; Ratra, Bharat

2010-01-01

235

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

International Nuclear Information System (INIS)

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

1980-01-01

236

Heat Generation Ability in AC Magnetic Field for Y3Fe5O12-based Garnet Ferrite  

International Nuclear Information System (INIS)

The Y3Fe5O12-based ferrite, i.e., Y3-XGdXFe5O12 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 Y3Fe5O12-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 (?T = 40-63deg. C, 370kHz, 1.77kA/m) was obtained for the powder materials sintered at 1100 deg. C for the Y3-XGdXFe5O12 system. The particle growth with the formation of the cubic single phase strongly influenced to the heat generation.

2011-10-29

237

Cosmological magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

Observations indicate that magnetic fields are associated with most structures in the universe. Upto now the origin of large scale primordial magnetic fields is an open problem. Two mechanisms in particular, taking place during inflation in the very early universe are reviewed.

Kunze, Kerstin E, E-mail: kkunze@usal.e [Departamento de Fisica Fundamental, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain)

2009-10-01

238

Magnetic field on board  

International Nuclear Information System (INIS)

[en] Here, the calculation of the magnetic field on board ships is performed, using matrix calculus, in a similar way as when the magnetic field in matter is studied. Thus the final formulas are written in a more compact form and they are obtained through a simpler way, more suitable for the university education. (Author)

1995-01-01

239

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

240

Spontaneous magnetic fields in spherical laser targets  

International Nuclear Information System (INIS)

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

1985-01-01

 
 
 
 
241

Large-Scale Filamentary Structures in Laser-Produced Plasmas as a Sign of Strong Magnetic Field Generation  

Science.gov (United States)

The method [1] of multilevel dynamical contrasting is applied to available database from experiments on interaction of a powerful short-pulsed laser beam with a flat target. It was found from processing the soft X-ray images that the expanding plasma produces a dynamical filamentary structures, a long-living ones as compared to inertial lifetimes of plasma inhomogeneities in laser-produced plasmas. Such a structuring appears to be similar to the networking of filamented electric currents in high-current gaseous discharges (dense Z-pinch [1] and plasma focus [2]). The structuring disclosed suggests a view into the role of electric current filamentation in the following phenomena in laser-produced plasmas: (i) generation of a strong magnetic field by the strong filamentary electric currents; (ii) formation of closed electric currents and large-scale closed magnetic configurations; (iii) axial stratification of the emerging dense Z-pinch; (iv) formation of long-range bonds between the core and the periphery of expanding plasma. [1] Kukushkin A.B., Rantsev-Kartinov V.A., Laser and Particle Beams, 16(3) 1998 (to be published). [2] Kukushkin A.B., Rantsev-Kartinov V.A., Terentiev A.R., Fusion Technology, 32 (1997) 83.

Kukushkin, A. B.; Rantsev-Kartinov, V. A.

1998-11-01

242

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

CERN Multimedia

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

Yarmohammadi Satri, M

2013-01-01

243

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

CERN Multimedia

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

244

Magnetic Field Created by Tile Permanent Magnets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper presents the analytical calculation of the three components of the magnetic field created by tile permanent magnets whose magnetization is either radial or axial. The calculations are based on the coulombian model of permanent magnets. The magnetic field is directly calculated, without th...

Ravaud, Romain; Lemarquand, Guy; Lemarquand, Valérie

245

Primordial magnetic fields from pseudo Goldstone bosons  

Energy Technology Data Exchange (ETDEWEB)

The existence of large-scale magnetic fields in galaxies is well established, but there is no accepted mechanism for generating a primordial field which could grow into what is observed today. We discuss a model which attempts to account for the necessary primordial field by invoking a pseudo Goldstone boson coupled to electromagnetism. The evolution of this boson during inflation generates a magnetic field; however, it seems difficult on rather general grounds to obtain fields of sufficient strength on astrophysically interesting scales.

Garretson, W.D.; Field, G.B.; Carroll, S.M. (Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States))

1992-12-15

246

The Earth's Magnetic Field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Earth's magnetic field is essential for life on Earth, as we know it, to exist. It forms a magnetic shield around the planet, protecting it from high energy particles and radiation from the Sun, which can cause damage to life, power systems, orbiting satellites, astronauts and spacecrafts. This ...

Edda Lína Gunnarsdóttir 1988

247

Magnetic field dosimeter development  

Energy Technology Data Exchange (ETDEWEB)

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.

Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

1980-09-01

248

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

1980-01-01

249

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

CERN Multimedia

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

Modica, Frank; Zhiglo, Andrey

2013-01-01

250

Magnetic field line reconnection  

Energy Technology Data Exchange (ETDEWEB)

The term 'magnetic field line reconnection' has arisen in the physics of rarefied plasmas with very high conductivity. When such a plasma is in motion, the remarkable property of field line 'freezing in' of the plasma manifests itself. However, situations sometimes occur in real plasma motion where this condition is violated. The process of reconnection results in a marked change in the field line topology and is accompanied by the formation of current layers and the conversion of magnetic energy into kinetic and thermal plasma energies. Magnetic field line reconnection plays a key role in many processes in the near-Earth, space and laboratory fusion plasmas.

Kadomtsev, B.B.

1987-02-01

251

Principles in power system magnetic field reduction  

Energy Technology Data Exchange (ETDEWEB)

The basic principles of generation of magnetic fields are identified, analyzed and synthesized for reduction of power system magnetic fields, notably from transmission lines. The field reduction methods studied are phase-split arrangements, passive shielding with and without series compensation, and configuration twist. A novel unorthodox four-conductor arrangement is presented. 3 refs, 8 figs

Pettersson, Per [Vattenfall Utveckling AB, Vaellingby (Sweden)

1995-12-01

252

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

Energy Technology Data Exchange (ETDEWEB)

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. E-mail: mfam2000@yahoo.com

2004-03-01

253

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

International Nuclear Information System (INIS)

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

2004-01-01

254

Observations of Cool-Star Magnetic Fields  

CERN Multimedia

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 me...

Reiners, Ansgar

2012-01-01

255

Magnetic field structure effect on the spatial flow in a supersonic MHD generator with boundary layer separation  

International Nuclear Information System (INIS)

Calculational experiment for evaluating the role of the inhomogeneous two-component magnetic field constants in the MHD-channel is carried out. Difference of the medium-integral magnetic induction from the values on the axis is within the range of 2 up 4%. It is shown that availability of additional component of the magnetic field in the electrode direction in the channel cross sections intensifies the secondary flows and thereby increases the danger of the boundary layers break-off. The negative effect of the additional component by the beginning of the break-off regime is surpassed by stabilizing effect from decrease in the basic component to electrodes. By developed break-off flow the effects related to the availability of the additional component are prevailing

1999-01-01

256

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 Gene...

Harrington, J M; McBride, D I; Sorahan, T; Paddle, G M; van Tongeren, M

257

Damping of cosmic magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

We examine the evolution of magnetic fields in an expanding fluid composed of matter and radiation with particular interest in the evolution of cosmic magnetic fields. We derive the propagation velocities and damping rates for relativistic and non-relativistic fast and slow magnetosonic and Alfv{acute e}n waves in the presence of viscous and heat conducting processes. The analysis covers all magnetohydrodynamics modes in the radiation diffusion and the free-streaming regimes. When our results are applied to the evolution of magnetic fields in the early universe, we find that cosmic magnetic fields are damped from prior to the epoch of neutrino decoupling up to recombination. Similar to the case of sound waves propagating in a demagnetized plasma, fast magnetosonic waves are damped by radiation diffusion on all scales smaller than the radiation diffusion length. The characteristic damping scales are the horizon scale at neutrino decoupling (M{sub {nu}}{approx}10{sup {minus}4}M{sub {circle_dot}} in baryons) and the Silk mass at recombination (M{sub {gamma}}{approx}10{sup 13}M{sub {circle_dot}} in baryons). In contrast, the oscillations of slow magnetosonic and Alfv{acute e}n waves get overdamped in the radiation diffusion regime, resulting in frozen-in magnetic field perturbations. Further damping of these perturbations is possible only if before recombination the wave enters a regime in which radiation free-streams on the scale of the perturbation. The maximum damping scale of slow magnetosonic and Alfv{acute e}n modes is always smaller than or equal to the damping scale of fast magnetosonic waves, and depends on the magnetic field strength and its direction relative to the wave vector. Our findings have multifold implications for cosmology. The dissipation of magnetic field energy into heat during the epoch of neutrino decoupling ensures that most magnetic field configurations generated in the very early universe satisfy big bang nucleosynthesis constraints. Further dissipation before recombination constrains models in which primordial magnetic fields give rise to galactic magnetic fields or density perturbations. Finally, the survival of Alfv{acute e}n and slow magnetosonic modes on scales well below the Silk mass may be of significance for the formation of structure on small scales. {copyright} {ital 1998} {ital The American Physical Society}

Jedamzik, K. [Max-Planck-Institut fuer Astrophysik, 85748 Garching bei Muenchen (Germany); Katalinic, V.; Olinto, A.V. [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave., Chicago, Illinois 60637 (United States)

1998-03-01

258

ISR Radial Field Magnet  

CERN Document Server

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

259

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)

[en] 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)

2008-11-12

260

Control of chaotic magnetic fields in tokamaks  

Scientific Electronic Library Online (English)

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

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

2002-12-01

 
 
 
 
261

Permanent magnet edge-field quadrupole  

Energy Technology Data Exchange (ETDEWEB)

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

Tatchyn, Roman O. (Mountain View, CA)

1997-01-01

262

Control of chaotic magnetic fields in tokamaks  

Directory of Open Access Journals (Sweden)

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

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

2002-01-01

263

Cosmic magnetic fields  

CERN Document Server

Magnetic fields are important in the Universe and their effects contain the key to many astrophysical phenomena that are otherwise impossible to understand. This book presents an up-to-date overview of this fast-growing topic and its interconnections to plasma processes, astroparticle physics, high energy astrophysics, and cosmic evolution. The phenomenology and impact of magnetic fields are described in diverse astrophysical contexts within the Universe, from galaxies to the filaments and voids of the intergalactic medium, and out to the largest redshifts. The presentation of mathematical formulae is accessible and is designed to add insight into the broad range of topics discussed. Written for graduate students and researchers in astrophysics and related disciplines, this volume will inspire readers to devise new ways of thinking about magnetic fields in space on galaxy scales and beyond.

Kronberg, Philipp P

2013-01-01

264

Trapped field internal dipole superconducting motor generator  

Energy Technology Data Exchange (ETDEWEB)

A motor generator including a high temperature superconductor rotor and an internally disposed coil assembly. The motor generator superconductor rotor is constructed of a plurality of superconductor elements magnetized to produce a dipole field. The coil assembly can be either a conventional conductor or a high temperature superconductor. The superconductor rotor elements include a magnetization direction and c-axis for the crystals of the elements and which is oriented along the magnetization direction.

Hull, John R. (Downers Grove, IL)

2001-01-01

265

Effects of interstimulus interval on somatosensory evoked magnetic fields (SEFs): a hypothesis concerning SEF generation at the primary sensorimotor cortex.  

UK PubMed Central (United Kingdom)

Cerebral responses evoked by peripheral stimuli are known to depend critically on the interstimulus interval (ISI). Here we report on the effects of ISI on somatosensory evoked magnetic fields (SEFs) to right median nerve stimulation, obtained in 9 healthy adults with ISIs of 0.15 0.3, 1,3 and 5 s. At the contralateral (left) primary sensorimotor cortex (SMI), the first cortical response, N20m, was stable between the ISIs 0.3 and 5 s, but slightly attenuated at the shortest ISI of 0.15 s. In contrast, the P35m and P60m deflections were very sensitive to changes of the ISI, declining steadily with shortening of the ISI throughout the entire range. These deflections were frequently undetectable at the shortest ISI of 0.15 s. Concomitant with the reductions of P35m and P60m, an N45m deflection was enhanced toward the short ISIs. Responses from second somatosensory cortex (SII) and posterior parietal cortex (PPC) were seen only with ISIs of 1 s or greater, being strongest at the 5 s ISI. Based on known effects of the ISI on intracellular evoked potentials, we present the following tentative model for the generation mechanism of the SMI response: N20m represents early excitatory postsynaptic potentials (EPSPs), P35m early inhibitory postsynaptic potentials (IPSPs), N45m secondary EPSPs and P60m late IPSPs in pyramidal neurones of area 3b. For practical purposes, SEFs from SMI can be obtained with short ISIs, while responses from SII and PPC require an ISI of at least 1 s.

Wikström H; Huttunen J; Korvenoja A; Virtanen J; Salonen O; Aronen H; Ilmoniemi RJ

1996-11-01

266

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.).

1986-01-01

267

Generation mechanism of slow-time-scale magnetic fields and electron acceleration by the field in an underdense relativistic Vlasov plasma  

International Nuclear Information System (INIS)

Slow-time-scale magnetic fields driven by fast-time-scale electromagnetic waves or plasma waves are unitarily discussed in a relativistic Vlasov plasma. Such a field is a result of the difference beat of wave-wave, which drives a solenoidal current, and the interaction of wave-particle. The magnitude of the slow-time-scale magnetic field proposed here can be as high as about 20 MS on the critical surface for the laser intensity I = 1018 W/cm2 at laser wavelength ? = 1.06?m. (authors)

2000-01-01

268

Magnetic Field from Loops Model  

Science.gov (United States)

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

Christian, Wolfgang; Hwang, Fu-Kwun

2008-11-17

269

Noncommutativity in Space and Primordial Magnetic Field  

International Nuclear Information System (INIS)

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

2001-07-02

270

Noncommutativity in Space and Primordial Magnetic Field  

CERN Document Server

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

Mazumdar, A

2001-01-01

271

Noncommutativity in space and primordial magnetic field  

International Nuclear Information System (INIS)

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

2001-01-01

272

Nuclear magnetic resonance and earth magnetic field  

International Nuclear Information System (INIS)

[en] Nuclear magnetic resonance concerns nuclei whose spin is different from 0. These nuclei exposed to a magnetic field is comparable to a peg top spinning around its axis while being moved by a precession movement called Larmor precession. This article presents an experiment whose aim is to reveal nuclear magnetism of nuclei by observing Larmor precession phenomena due to the earth magnetic field. The earth magnetic field being too weak, it is necessary to increase the magnetization of the sample during a polarization phase. First the sample is submitted to a magnetic field B perpendicular to the earth magnetic field B0, then B is cut off and the nuclei move back to their equilibrium position by executing a precession movement due to B0 field. (A.C.)

1998-01-01

273

Spin torque-generated magnetic droplet solitons.  

UK PubMed Central (United Kingdom)

Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.

Mohseni SM; Sani SR; Persson J; Nguyen TN; Chung S; Pogoryelov Y; Muduli PK; Iacocca E; Eklund A; Dumas RK; Bonetti S; Deac A; Hoefer MA; Akerman J

2013-03-01

274

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

International Nuclear Information System (INIS)

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

2012-01-01

275

Magnetic Fields in the Solar Convection Zone  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Active regions on the solar surface are generally thought to originate from a strong toroidal magnetic field generated by a deep seated solar dynamo mechanism operating at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach th...

Yuhong Fan

276

The Humboldt High Magnetic Field Center  

International Nuclear Information System (INIS)

The Humboldt High Magnetic Field Center has moved to a new campus with improved conditions. The three basic kinds of magnetic field generators are DC-superconducting solenoids up to 20 T, nondestructive coils for pulsed fields up to 60 T, and semidestructive/nondestructive single-turn coils up to more than 300/40 T, respectively. The latter variant is especially suitable for repetitive experiments with high dB/dt>107 T/s. The magnetic fields generated, allow, combined with the sophisticated supporting equipment, a great variety of solid-state experiments.

2004-04-30

277

Second harmonic generation in magnetic nanoparticles with vortex magnetic state  

Science.gov (United States)

Nonlinear optical properties of a regular array of triangular-shaped vortex magnetic nanoparticles is studied using the optical second harmonic generation (SHG) technique. We demonstrate that the SHG azimuthal anisotropy is consistent with the 3m symmetry of individual Co nanodots placed in a square surface lattice. Qualitatively different SHG magnetic hysteresis loops are obtained for circular and linear polarizations of the fundamental radiation. In the first case, a wide SHG hysteresis at zero DC magnetic field H is observed, which is attributed to a macroscopic magnetic toroid moment in Co nanodots induced by a noncentrosymmetric distribution of the magnetization. On the contrary, for the linear pump polarization the SHG loop is similar to observed commonly in linear magnetooptics for vortex magnetic structures and reveals a rather narrow width at H=0. A phenomenological SHG description based on the introduction of the SHG polarization induced by a magnetic toroid moment in vortex magnetic nanostructures is presented.

Krutyanskiy, V. L.; Kolmychek, I. A.; Gribkov, B. A.; Karashtin, E. A.; Skorohodov, E. V.; Murzina, T. V.

2013-09-01

278

Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization  

Energy Technology Data Exchange (ETDEWEB)

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

279

The Heliospheric Magnetic Field  

Science.gov (United States)

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper.

Balogh, André; Erdõs, Géza

2013-06-01

280

Magnetic field optimization of permanent magnet undulators for arbitrary polarization  

Energy Technology Data Exchange (ETDEWEB)

Techniques for improving the magnetic field quality of APPLE II undulators are discussed. Individual block characterization including the inhomogeneities of the magnetization permits a precise prediction of field integrals as required for sorting. Specific shimming procedures adapted to the magnetic design of APPLE II undulators have to be employed in order to meet the stringent requirements of insertion devices in third generation synchrotron radiation sources as demonstrated for BESSY.

Bahrdt, J. E-mail: bahrdt@bessy.de; Frentrup, W.; Gaupp, A.; Scheer, M.; Englisch, U

2004-01-11

 
 
 
 
281

A Fiber Magnetic Field Sensor  

International Nuclear Information System (INIS)

[en] A Fabry-Perot interferometer-based fiber optic sensor that uses magnetostrictive Terfenol-D (Tb0,3Dy0,7Fe1,92) rod as a sensor gauge for measuring DC magnetic fields was designed. A single mode fiber was placed in front of the one of the polished circular face of Terfenol-D rod with 48 mm long and 6 mm in diameter, acts as a reflector, thereby creating an air gap that acts as a Fabry-Perot cavity. A solenoid was used to generate magnetic field and the sensor was inserted inside the coil. The detectable minimum magnetic field level is 8 kA/m (?100 Oe). Up to 45 kA/m magnetic field was measured by using the sensor. Also the obtained results were compared with the theoretical results. A single mode diode laser was used as a light source with 660 nm wavelength and the data acquisition was made with ADC with a simple program written in Labview 8.0

2008-01-01

282

Magnetic fields and cancer  

Energy Technology Data Exchange (ETDEWEB)

This letter is a response to an article by Savitz and Kaune, EHP 101:76-80. W-L wire code was applied to data from a 1988 Denver study, and an association was reported between high W-L wire code and childhood cancer. This author discusses several studies and provides explanations which weakens the argument that classification error resulted in an appreciable reduction in the association between W-L high wire code and childhood cancer. In conclusion, the fact that new wire code is only weakly correlated with magnetic field measurements (in the same manner as the original W-L wire code) suggests that the newly reported stronger association with childhood cancer is likely due to factors other than magnetic fields. Differential residential mobility and differential residential age are two possible explanations and are suggestive that the reported association may be false.

Jones, T.L.

1993-10-01

283

Distributed generation induction and permanent magnet generators  

CERN Document Server

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

Lai, Loi Lei

2008-01-01

284

Generation of Alfven Waves by Magnetic Reconnection  

CERN Multimedia

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

285

End fields of CBA superconducting magnets  

International Nuclear Information System (INIS)

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

1983-01-01

286

Magnetic fields in the cosmos  

Energy Technology Data Exchange (ETDEWEB)

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

Parker, E.N.

1983-08-01

287

Acupressure device for developing and applying acupressure on e.g. spine, has sharp sections designed such that length of sharp sections from housing is adjustable, and permanent magnets generating magnetic fields at sharp sections  

UK PubMed Central (United Kingdom)

The device (100) has two sharp sections (102) projecting from an end of a housing (112). Permanent magnets (106) generate magnetic fields at the sections. The sections are designed such that the length of the sections from the housing is adjustable. A germanium-tourmaline-silver mixture (116) is arranged on the end of the housing to discharge infrared beam and to ionize surrounding medium. The magnets are formed from neodymium-iron-boron. A snap clip is formed as a holder of the housing. A germanium-tourmaline-silver mixture silicone is provided as an adhesive agent in the device.

KWON HYORK-SOON

288

The LHC Magnetic Field Model  

CERN Document Server

The compensation of the field changes during the beam injection and acceleration in the LHC requires an accurate forecast and an active control of the magnetic field in the accelerator. The LHC Magnetic Field Model is the core of this magnetic prediction system. The model will provide the desired field components at a given time, magnet operating current, magnet ramp rate, magnet temperature and magnet powering history to the required precision. The model is based on the identification and physical decomposition of the effects that contribute to the total field in the magnet aperture of the LHC dipoles. Each effect is quantified using data obtained from series measurements, and modeled theoretically or empirically depending on the complexity of the physical phenomena involved. This paper presents the developments of the new finely tuned magnetic field model and evaluates its accuracy and predictive capabilities over a sector of the machine.

Sammut, Nicholas J; Micallef, Joseph

2005-01-01

289

Skewed magnetic field lines reconnection  

International Nuclear Information System (INIS)

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

1986-01-01

290

Low field magnetic resonance imaging  

Energy Technology Data Exchange (ETDEWEB)

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

291

Observations of magnetic fields in hot stars  

CERN Multimedia

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

Petit, V

2010-01-01

292

Magnetization reversal in ultrashort magnetic field pulses  

Science.gov (United States)

We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization reversal process. Comparing the case of perpendicular anisotropy with different kinds of in-plane anisotropies, a principal difference is found due to the symmetry of the shape anisotropy with respect to the anisotropy in question.

Bauer, M.; Lopusnik, R.; Fassbender, J.; Hillebrands, B.

2000-08-01

293

A Linear Magnetic Motor/Generator.  

Science.gov (United States)

A linear magnetic motor/generator is described which uses magnetic flux to provide mechanical motion or electrical energy. The linear magnetic motor/generator includes an axially movable actuator mechanism. A permanent magnet mechanism defines a first mag...

P. A. Studer

1980-01-01

294

Small generators of function fields  

CERN Document Server

Let $K/k$ be a finite extension of a global field. Such an extension can be generated over $k$ by a single element. The aim of this article is to prove the existence of a "small" generator in the function field case. This answers the function field version of a question of Ruppert on small generators of number fields.

Widmer, Martin

2012-01-01

295

The Galactic Magnetic Field  

CERN Document Server

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

Jansson, Ronnie

2012-01-01

296

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

2012-01-01

297

The rotation-magnetic field relation  

CERN Multimedia

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

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

2008-01-01

298

Magnetic Field Problem: Current and Magnets  

Science.gov (United States)

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

299

Evolution of Primordial Magnetic Fields from Phase Transitions  

CERN Multimedia

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

300

Generating highly uniform electromagnetic field characteristics  

Energy Technology Data Exchange (ETDEWEB)

An apparatus and method for generating homogenous 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 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.

Crow, James T. (Albuquerque, NM)

1998-01-01

 
 
 
 
301

Generating highly uniform electromagnetic field characteristics  

Energy Technology Data Exchange (ETDEWEB)

An apparatus and method for generating homogenous 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 cancelling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set.

Crow, James T. (Albuquerque, NM)

1997-01-01

302

Generating highly uniform electromagnetic field characteristics  

Energy Technology Data Exchange (ETDEWEB)

An apparatus and method for generating homogenous 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.

Crow, James Terry (Albuquerque, NM)

1998-01-01

303

Generation and focusing of high-power ion beams in a magnetically insulated diode with applied B field  

International Nuclear Information System (INIS)

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

1991-01-01

304

Nanosystem magnetization via magnetic field rotation  

CERN Multimedia

We study the magnetization in systems of uniaxial ferromagnetic nanoparticles which is induced by the rotating magnetic field and enhanced by thermal fluctuations. We clarify the nature of this effect, develop an effective method for its description, calculate within this method the frequency dependence of the magnetization, and reveal the role of the magnetic dipolar interaction. The feasibility and desirability of experimental investigation of this phenomenon are argued.

Denisov, S I; Hänggi, P

2006-01-01

305

Fast superconducting magnetic field switch  

Energy Technology Data Exchange (ETDEWEB)

The superconducting magnetic switch or fast kicker magnet is employed with an electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater than the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

306

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

2005-01-01

307

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

1991-01-01

308

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

309

Organic Superconductors at Extremely High Magnetic Fields  

Energy Technology Data Exchange (ETDEWEB)

Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures {approx}13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.

Mielke, Charles H. (LANL and National High Magnetic Field Laboratory)

2002-02-27

310

Comparison of adjustable permanent magnetic field sources  

Energy Technology Data Exchange (ETDEWEB)

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.

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

2010-11-15

311

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

312

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

313

Leptogenesis and Primordial Magnetic Fields  

CERN Multimedia

The anomalous conversion of leptons into baryons during leptogenesis is shown to produce a right-handed helical magnetic field; in contrast, the magnetic field produced during electroweak baryogenesis is known to be left-handed. If the cosmological medium is turbulent, the magnetic field evolves to have a present day coherence scale and field strength that are of astrophysical interest. Observations of the amplitude, coherence scale, and helicity of the intergalactic magnetic field promise to provide a powerful probe of physics beyond the Standard Model and the very early universe.

Long, Andrew J; Vachaspati, Tanmay

2013-01-01

314

Fast superconducting magnetic field switch  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-01-01

315

Spontaneous generation of voltage in Gd5(SixGe4-x) during a first-order phase transition induced by temperature or magnetic field  

International Nuclear Information System (INIS)

[en] The spontaneous generation of voltage has been observed during the first-order magnetic-Martensitic phase transition process in Gd5(SixGe4-x) alloys regardless of whether the transformation is triggered by temperature or magnetic field. Based on various experimental data we show that thermoelectric power is a major contributor to the observed voltage. The characteristics of the simultaneously recorded spontaneous voltage and the signal from a differential thermocouple attached to the sample are quite complex, indicating that thermal effects arising in this class of materials during the first-order phase transition are nontrivial. The unusual dynamics of both the heat release and absorption during the phase transformations in Gd5(SixGe4-x) result in the appearance of temperature gradients and, therefore, thermoelectricity

2001-05-01

316

Magnetic monopole field exposed by electrons  

CERN Multimedia

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

317

Reconnection of Magnetic Fields  

Science.gov (United States)

Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

Birn, J.; Priest, E. R.

2007-01-01

318

High magnetic field ohmically decoupled non-contact technology  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-05-19

319

Plasma diffusion through multi dipole magnetic fields  

International Nuclear Information System (INIS)

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

1992-01-01

320

Magnetic fields in Local Group dwarf irregulars  

CERN Multimedia

We clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and what is the role of dwarf galaxies in the magnetization of the Universe. We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100m Effelsberg telescope at 2.64 and 4.85GHz. Magnetic fields in LG dwarfs are three times weaker than in the normal spirals (6muG) are observed only in dwarfs of extreme characteristics while typical LG dwarfs are not suitable objects for efficient supply of magnetic fields to the intergalactic medium.

Chyzy, Krzysztof T; Beck, Rainer; Bomans, Dominik J

2011-01-01

 
 
 
 
321

A next-generation, flow-diverting implant used to treat brain aneurysms: in vitro evaluation of magnetic field interactions, heating and artifacts at 3-T.  

UK PubMed Central (United Kingdom)

BACKGROUND AND PURPOSE: Fine-mesh braided, stent-like structures (flow diverters) have been proposed for treatment of brain aneurysms. To date, the safety of performing magnetic resonance imaging (MRI) in patients with these implants is unknown. Therefore, the purpose of this study was to evaluate MRI issues at 3-T for a new flow-diverting implant used to treat brain aneurysms. METHODS: The Surpass NeuroEndoGraft (Surpass Medical, Ltd., Tel Aviv, Israel) underwent evaluation for magnetic field interactions, MRI-related heating and artifacts using standardized techniques. Magnetic field interactions were assessed for this implant with regard to translational attraction (i.e., using the deflection angle technique) and torque (qualitative assessment method). MRI-related heating was evaluated by placing the implant in a gelled-saline-filled, head/torso phantom and performing MRI using a transmit/receive radiofrequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 min. Artifacts were characterized using T1-weighted, spin echo (SE) and gradient echo (GRE) pulse sequences. RESULTS: The Surpass NeuroEndoGraft exhibited minor magnetic field interactions (21° deflection angle and no torque), which were acceptable from a safety consideration. Heating was not substantial, with the highest temperature change being 2.3°C (background temperature rise without the implant was 1.5°C). Artifacts may create issues if the area of interest is in the same area or close to this implant. CONCLUSIONS: The findings demonstrated that it would be acceptable for patients with this next-generation, flow-diverting implant to undergo MRI at 3-T or less.

Karacozoff AM; Shellock FG; Wakhloo AK

2013-01-01

322

Source of the earth's magnetic field  

International Nuclear Information System (INIS)

[en] 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

1979-01-01

323

Magnetic Fields in the Solar Convection Zone  

Directory of Open Access Journals (Sweden)

Full Text Available Recent studies of the dynamic evolution of magnetic flux tubes in the solar convection zone are reviewed with focus on emerging flux tubes responsible for the formation of solar active regions. The current prevailing picture is that active regions on the solar surface originate from strong toroidal magnetic fields generated by the solar dynamo mechanism at the thin tachocline layer at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. This review discusses results with regard to the following major topics: 1. the equilibrium properties of the toroidal magnetic fields stored in the stable overshoot region at the base of the convection zone, 2. the buoyancy instability associated with the toroidal magnetic fields and the formation of buoyant magnetic flux tubes, 3. the rise of emerging flux loops through the solar convective envelope as modeled by the thin flux tube calculations which infer that the field strength of the toroidal magnetic fields at the base of the solar convection zone is significantly higher than the value in equipartition with convection, 4. the minimum twist needed for maintaining cohesion of the rising flux tubes, 5. the rise of highly twisted kink unstable flux tubes as a possible origin of d -sunspots, 6. the evolution of buoyant magnetic flux tubes in 3D stratified convection, 7. turbulent pumping of magnetic flux by penetrative compressible convection, 8. an alternative mechanism for intensifying toroidal magnetic fields to significantly super-equipartition field strengths by conversion of the potential energy associated with the superadiabatic stratification of the solar convection zone, and finally 9. a brief overview of our current understanding of flux emergence at the surface and post-emergence evolution of the subsurface magnetic fields.

Fan Yuhong

2004-01-01

324

Generation of magnetic fields over 21 T in a 61 mm clear bore using low copper ratio (Nb,Ti){sub 3}Sn conductors  

Energy Technology Data Exchange (ETDEWEB)

A 21 T superconducting magnet system has been developed and improved at the National Research Institute for Metals in Japan. As the steady progress of high-Tc superconducting coils required a larger bore for testing their performance, a new innermost coil has been developed. The authors increased the available bore from 50 mm to 61 mm. The new coil employed three kinds of rectangular (Nb,Ti){sub 3}Sn conductors. External copper stabilized these conductors, with a Cu:SC ratio of only 0.25. The new coil operated in a 160 mm diameter clear bore with a background field of 18 T in saturated superfluid helium, generating a central field of 21.5 T without any training behavior. A double walled dewar, the outer diameter of which was 60 mm, was also developed. With this dewar, the new system provides a temperature-variable bore of 50 mm.

Kiyoshi, T.; Kosuge, M.; Inoue, K.; Maeda, H. [National Research Inst. for Metals, Tsukuba, Ibaraki (Japan). Tsukuba Magnet Labs.

1996-07-01

325

Recurrent flux emergence from dynamo-generated fields  

CERN Multimedia

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

Warnecke, Jörn

2010-01-01

326

Magnetic-field-controlled reconfigurable semiconductor logic.  

UK PubMed Central (United Kingdom)

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.

Joo S; Kim T; Shin SH; Lim JY; Hong J; Song JD; Chang J; Lee HW; Rhie K; Han SH; Shin KH; Johnson M

2013-02-01

327

Three generation magnetized orbifold models  

Energy Technology Data Exchange (ETDEWEB)

We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super-Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown.

Abe, Hiroyuki [Department of Physics, Tohoku University, Sendai 980-8578 (Japan)], E-mail: abe@tuhep.phys.tohoku.ac.jp; Choi, Kang-Sin [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)], E-mail: kschoi@gauge.scphys.kyoto-u.ac.jp; Kobayashi, Tatsuo [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)], E-mail: kobayash@gauge.scphys.kyoto-u.ac.jp; Ohki, Hiroshi [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)], E-mail: ohki@scphys.kyoto-u.ac.jp

2009-06-11

328

Three generation magnetized orbifold models  

International Nuclear Information System (INIS)

We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super-Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown

2009-06-11

329

Three generation magnetized orbifold models  

CERN Document Server

We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown.

Abe, Hiroyuki; Kobayashi, Tatsuo; Ohki, Hiroshi

2008-01-01

330

Charge in Magnetic Field Model  

Science.gov (United States)

The EJS Charge In B-Field model allows the user to simulate moving charged particles in two identical magnetic field regions separated by a zero magnetic field gap. The Charge in B Field Model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ntnu_em_ChargeInBField.jar file will run the program if Java is installed.

Hwang, Fu-Kwun

2009-05-19

331

Measurements of magnetic field alignment  

Energy Technology Data Exchange (ETDEWEB)

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.

Kuchnir, M.; Schmidt, E.E.

1987-11-06

332

Origin of cosmic magnetic fields.  

UK PubMed Central (United Kingdom)

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.

Campanelli L

2013-08-01

333

Origin of cosmic magnetic fields.  

UK PubMed Central (United Kingdom)

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.

Campanelli L

2013-08-01

334

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×10-12G if the energy scale of inflation is few×1016GeV. Such a field accounts for galactic and galaxy cluster magnetic fields.

Campanelli, Leonardo

2013-08-01

335

Interplanetary electric and magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

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

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

1982-08-01

336

Magnetic fields in O stars  

CERN Multimedia

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

Naze, Yael

2013-01-01

337

International Geomagnetic Reference Field : The eleventh generation  

DEFF Research Database (Denmark)

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

Finlay, Chris; Maus, S.

2010-01-01

338

Nonlocal pseudopotentials and magnetic fields  

CERN Multimedia

We show how to describe the coupling of electrons to non-uniform magnetic fields in the framework of the widely used norm-conserving pseudopotential appro ximation for electronic structure calculations. Our derivation applies to magnetic fields that are smooth on the scale of the core region. The method is validated by application to the calculation of the magnetic susceptibility of molecules. Our results are compared with high quality all electron quantum chemical results, and another recently proposed formalism.

Pickard, C J; Pickard, Chris J.; Mauri, Francesco

2003-01-01

339

Magnetic Fields in the Early Universe  

CERN Multimedia

This review concerns the origin and the possible effects of magnetic fields in the early Universe. We start by providing to the reader with a short overview of the current state of art of observations of cosmic magnetic fields. We then illustrate the arguments in favour of a primordial origin of magnetic fields in the galaxies and in the clusters of galaxies. We argue that the most promising way to test this hypothesis is to look for possible imprints of magnetic fields on the temperature and polarization anisotropies of the cosmic microwave background radiation (CMBR). With this purpose in mind, we provide a review of the most relevant effects of magnetic fields on the CMBR. A long chapter of this review is dedicated to particle physics inspired models which predict the generation of magnetic fields during the early Universe evolution. Although it is still unclear if any of these models can really explain the origin of galactic and intergalactic magnetic fields, we show that interesting effects may arise any...

Grasso, D; Grasso, D

2001-01-01

340

Multi-coil magnetic field modeling.  

UK PubMed Central (United Kingdom)

The performance of multi-coil (MC) magnetic field modeling is compared to dedicated wire patterns for the generation of spherical harmonic (SH) shapes as these are the workhorse for spatial encoding and magnetic field homogenization in MR imaging and spectroscopy. To this end, an example 48 channel MC setup is analyzed and shown to be capable of generating all first through fourth order SH shapes over small and large regions-of-interest relevant for MR investigations. The MC efficiency for the generation of linear gradient fields shares the same order of magnitude with classic and state-of-the-art SH gradient coils. MC field modeling becomes progressively more efficient with the synthesis of more complex field shapes that require the combination of multiple SH terms. The possibility of a region-specific optimization of both magnetic field shapes and generation performance with the MC approach are discussed with emphasis on the possible trade-off between the field accuracy and generation efficiency. MC shimming has been shown previously to outperform current SH shimming. Along with the efficiency gains of MC shimming shown here, the MC concept has the potential to (1) replace conventional shim systems that are based on sets of dedicated SH coils and (2) allow optimal object-specific shim solutions similar to object-specific RF coils.

Juchem C; Green D; de Graaf RA

2013-09-01

 
 
 
 
341

Power generation tests of the improved shaped B-field-type MHD generator  

Energy Technology Data Exchange (ETDEWEB)

Ozawa and Kayukawa (1975) have proposed the design of an MHD generator employing the Shaped B-Field Configuration (SFC), in which the applied magnetic field is greatly diminished near the electrode walls by keeping the core magnetic field at approximately the same level as the conventional MHD generator. Attention is presently given to the experimental results obtained for an SFC MHD generator incorporating an improved magnetic field design, under shock tube operating conditions. These results are compared with those for a previous SFC MHD device and a conventional MHD generator with uniform B-field configuration. 5 references.

Kayukawa, N.

1985-08-01

342

Dynamo generated field emergence through recurrent plasmoid ejections  

CERN Multimedia

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

Warnecke, Jörn

2010-01-01

343

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

UK PubMed Central (United Kingdom)

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.

Guzdar PN; Kleva RG; Das A; Kaw PK

2001-07-01

344

Preflare magnetic and velocity fields  

International Nuclear Information System (INIS)

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares.

1983-01-24

345

Low-magnetic-field magnetars  

CERN Document Server

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

Turolla, R

2013-01-01

346

Magnetic fields and scintillator performance  

Energy Technology Data Exchange (ETDEWEB)

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.

Green, D.; Ronzhin, A. [Fermi National Accelerator Lab., Batavia, IL (United States); Hagopian, V. [Florida State Univ., Tallahasse, FL (United States)

1995-06-01

347

Magnetic field observations of low-mass stars  

CERN Multimedia

Direct measurements of magnetic fields in low-mass stars of spectral class M have become available during the last years. This contribution summarizes the data available on direct magnetic measurements in M dwarfs from Zeeman analysis in integrated and polarized light. Strong magnetic fields at kilo-Gauss strength are found throughout the whole M spectral range, and so far all field M dwarfs of spectral type M6 and later show strong magnetic fields. Zeeman Doppler images from polarized light find weaker fields, which may carry important information on magnetic field generation in partially and fully convective stars.

Reiners, Ansgar

2009-01-01

348

Neutron scattering in magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Koehler, W.C.

349

Neutron scattering in magnetic fields  

International Nuclear Information System (INIS)

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

1984-01-01

350

Magnetic field structure of Mercury  

Science.gov (United States)

Recently planet Mercury—an unexplored territory in our solar system—has been of much interest to the scientific community due to recent flybys of the spacecraft MESSENGER that discovered its intrinsic stationary and large-scale dipole like magnetic field structure with an intensity of ˜300nT confirming Mariner 10 observations. In the present study, with the observed constraint of Mercury's atmospheric magnetic field structure, internal magnetic field structure is modeled as a solution of magnetic diffusion equation. In this study, Mercury's internal structure mainly consists of a stable stratified fluid core and the convective mantle. For simplicity, magnetic diffusivity in both parts of the structure is considered to be uniform and constant with a value represented by a suitable averages. It is further assumed that vigorous convection in the mantle disposes of the electric currents leading to a very high diffusivity in that region. Thus, in order to satisfy observed atmospheric magnetic field structure, Mercury's most likely magnetic field structure consists of a solution of MHD diffusion equation in the core and a combined multipolar (dipole and quadrupole like magnetic field structures embedded in the uniform field) solution of a current free like magnetic field structure in the mantle and in the atmosphere. With imposition of appropriate boundary conditions at the core-mantle boundary for the first two diffusion eigen modes, in order to satisfy the observed field structure, present study puts the constraint on Mercury's core radius to be ˜2000km.From the estimated magnetic diffusivity and the core radius, it is also possible to estimate the two diffusion eigen modes with their diffusion time scales of ˜8.6 and 3.7 billion years respectively suggesting that the planet inherits its present-day magnetic field structure from the solar Nebula. It is proposed that permanency of such a large-scale magnetic field structure of the planet is attained during Mercury's early evolutionary history of heavy bombardments by the asteroids and comets supporting the giant impact hypothesis for the formation of Mercury.

Hiremath, K. M.

2012-04-01

351

Magnetic field transfer device and method  

Energy Technology Data Exchange (ETDEWEB)

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

Wipf, Stefan L. (Hamburg, DE)

1990-01-01

352

Field of the Magnetic Monopole  

CERN Multimedia

This paper shows that based upon the Helmholtz decomposition theorem the field of a stationary magnetic monopole, assuming it exists, cannot be represented by a vector potential. Persisting to use vector potential in monopole representation violates fundamentals of mathematics. The importance of this finding is that the vector potential representation was crucial to the original prediction of the quantized value for a magnetic charge.

Hadjesfandiari, A R

2007-01-01

353

Simple mechanism for reversals of earth's magnetic field.  

UK PubMed Central (United Kingdom)

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 Kármán 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.

Pétrélis F; Fauve S; Dormy E; Valet JP

2009-04-01

354

Simple Mechanism for Reversals of Earth's Magnetic Field  

International Nuclear Information System (INIS)

[en] 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

2009-04-10

355

Magnetic field processing of polymers  

Energy Technology Data Exchange (ETDEWEB)

Hydroxypropyl cellulose (HPC) of degree of substitution three and average molecular weight of 100,000 was processed in a magnetic field of 1.2T. Films of HPC were cast from water, methanol, ethyl methyl ketone and 1,1,2,2-tetrachloroethane solutions in a magnetic field using {open_quotes}static{close_quotes} and {open_quotes}dynamic{close_quotes} casting techniques. The dynamic casting technique involved a shear radiant effect in addition to the magnetic field effect during the formation of the film. The processed films were evaluated for tensile strength, elastic modules, microhardness, thermal properties and molecular chain alignment by wide angle x-ray diffraction and polarized infrared. The films cast in a magnetic field, using the {open_quotes}dynamic{close_quotes} casting technique, showed no increase in the elastic modulus, a 106% increase in the tensile strength and a 21% increase in the microhardness and were dichroic.

Liepins, R.; Jahn, R.K.; Elliott, N.E.; Hubbard, K.M. [Los Alamos National Laboratory, NM (United States)

1993-12-31

356

Stellar and interstellar magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

It is noted that the stellar and interstellar magnetic fields are revealed directly by the splitting of the spectral lines caused by the Zeeman effect and indirectly by the polarization of radiation. The methods used in obtaining information on the interstellar magnetic field are discussed. These are (1) the optical polarization of starlight, (2) the rotation measure of radio sources, (3) the Zeeman effect at the 21-cm line, (4) the pulsar rotation measure, combined with the pulsar dispersion measure, and (5) radio polarization data on the continuum emission from the galaxy. Attention is also given to methods for measuring the stellar fields. The characteristics of the magnetic fields in chemically peculiar stars are discussed, as are magnetic white dwarfs and neutron stars.

Hack, M.

1982-01-01

357

Sidewall containment of liquid metal with horizontal alternating magnetic fields  

International Nuclear Information System (INIS)

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

1988-11-17

358

NMR in pulsed magnetic fields  

International Nuclear Information System (INIS)

The first observation of NMR in the pulsed high magnetic field at the Hochfeldmagnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf (FZD) is reported. The new spectrometer that operates at up to 3.0 GHz is described, as well as its implementation in the pulsed field facility. Free induction decays and spin echo experiments on 1H and 63,65Cu in various magnets are described and discussed in terms of sensitivity and resolution.

2010-01-01

359

Theorem on magnet fringe field  

Energy Technology Data Exchange (ETDEWEB)

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

Wei, Jie [Brookhaven National Lab., Upton, NY (United States); Talman, R. [Cornell Univ., Ithaca, NY (United States). Lab. of Nuclear Studies

1995-12-31

360

EARTH MAGNETIC-FIELD AUGMENTERS  

UK PubMed Central (United Kingdom)

Magnetic-field-augmented beds (10, 246, 258, 366, 388, 406, 424, 426), mattresses (330, 352), box springs (408), seating furniture (490), desks (542, 572), carrells (278, 514) rooms (168, 202, 216A, 216B), and buildings (156, 164, 192, 230, 472) include magnetic-field augmenters (18, 40, 46, 56, 154, 162, 172, 198, 210, 224A, 224B, 230, 254, 260, 282, 308, 334, 362, 380, 386, 412, 430, 442, 446, 456, 476, 492, 524, 550) that, when connected to a source (70) of electrical power, provide a healthful magnetic field for entire bodies of human beings or other living things in living spaces. In still another embodiment, a magnetic-field augmenter (444) is hung on a wall (446), and in another embodiment, a magnetic-field augmenter (456) is arranged on a floor (456) around seating furniture (462). Included among the various types of magnetic-field augmenters are bundled augmenter coils (390, 414, 476), dual-axis augmenters (492, 550), open-sided augmenters (524, 550), and dual-axis open-sided augmenters (550). An electrical-circuit protector (594) protects against loose connections and shorts.

MILLER Wendell E.; SOUTH Robert E.; SOUTH Michael R.

 
 
 
 
361

PERMANENT-MAGNET INDUCTION GENERATORS: AN OVERVIEW  

Directory of Open Access Journals (Sweden)

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

PAWAN SHARMA; T. S. BHATTI; K. S. S. RAMAKRISHNAN

2011-01-01

362

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

363

Magnetic field properties of the ISABELLE Project superconducting dipole magnets  

International Nuclear Information System (INIS)

A series of prototype superconducting dipole magnets have been constructed and tested as part of the ISABELLE Project research and development program. Results of magnetic field measurements are presented with emphasis placed on the DC and AC components of the main field. Magnetization and the effects of the magnetic fields at the ends of the magnet are displayed

1981-03-13

364

Field-flow fractionation of magnetic particles in a cyclic magnetic field.  

UK PubMed Central (United Kingdom)

Although magnetic field-flow fractionation (MgFFF) is emerging as a promising technique for characterizing magnetic particles, it still suffers from limitations such as low separation efficiency due to irreversible adsorption of magnetic particles on separation channel. Here we report a novel approach based on the use of a cyclic magnetic field to overcome the particle entrapment in MgFFF. This cyclic field is generated by rotating a magnet on the top of the spiral separation channel so that magnetic and opposing gravitational forces alternately act on the magnetic particles suspended in the fluid flow. As a result, the particles migrate transversely between the channel walls and their adsorption at internal channel surface is prevented due to short residence time which is controlled by the rotation frequency. With recycling of the catch-release process, the particles follow saw-tooth-like downstream migration trajectories and exit the separation channel at velocities corresponding to their sedimentation coefficients. A retention model has been developed on the basis of the combined effects of magnetic, gravitational fields and hydrodynamic flow on particle migration. Two types of core-shell structured magnetic microspheres with diameters of 6.04- and 9.40-?m were synthesized and used as standard particles to test the proposed retention theory under varying conditions. The retention ratios of these two types of particles were measured as a function of magnet rotation frequency, the gap between the magnet and separation channel, carrier flow rate, and sample loading. The data obtained confirm that optimum separation of magnetic particles with improved separation efficiency can be achieved by tuning rotation frequency, magnetic field gradient, and carrier flow rate. In view of the widespread applications of magnetic microspheres in separation of biological molecules, virus, and cells, this new method might be extended to separate magnetically labeled proteins or organisms for multiplex analyte identification and purification.

Bi Y; Pan X; Chen L; Wan QH

2011-06-01

365

Measurements of magnetic field alignment  

International Nuclear Information System (INIS)

[en] 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

1987-01-01

366

Evaluation of magnetic field distribution of superconducting bulk magnets with the same pole arrangement  

International Nuclear Information System (INIS)

We study on the construction of superconducting permanent magnets by RE123 bulk materials and the investigation of these industrial applications such as a magnetic separation. The bulk magnets can generate strong magnetic field in comparison with common permanent magnets and iron-cored electromagnets. In order to propagate an industrial application of bulk magnet in the feature, it is necessary to form various shape of magnetic field, as well as its strength is enlarged. In this paper, the strong magnetic field in the radial direction has been constructed by a pair of bulk magnets. Two Gd123 bulk materials are magnetized by the IMRA method and these are arranged face-to-face with the same pole facing each other. When the radial component of magnetic fields, Bx, is measured in the open space between the magnetic poles with a gap of 50 mm, the area of |Bx| > 0.5 T increases to 148% compared with the single pole.

2008-09-15

367

Evaluation of magnetic field distribution of superconducting bulk magnets with the same pole arrangement  

Science.gov (United States)

We study on the construction of superconducting permanent magnets by RE123 bulk materials and the investigation of these industrial applications such as a magnetic separation. The bulk magnets can generate strong magnetic field in comparison with common permanent magnets and iron-cored electromagnets. In order to propagate an industrial application of bulk magnet in the feature, it is necessary to form various shape of magnetic field, as well as its strength is enlarged. In this paper, the strong magnetic field in the radial direction has been constructed by a pair of bulk magnets. Two Gd123 bulk materials are magnetized by the IMRA method and these are arranged face-to-face with the same pole facing each other. When the radial component of magnetic fields, Bx, is measured in the open space between the magnetic poles with a gap of 50 mm, the area of |Bx| > 0.5 T increases to 148% compared with the single pole.

Yokoyama, K.; Oka, T.; Noto, K.

2008-09-01

368

Reconnection in magnetic field lines  

International Nuclear Information System (INIS)

Magnetic surfaces are described for MHD equilibrium plasma with central hole plasma current density, confined in large aspect-ratio tokamaks, perturbed by external helical windings. The integrable case is first considered, where reconnection phenomenon is described for the field lines. A toroidal correction causes the integrability loss, leading to the onset of chaotic field lines. (author). 7 refs, 4 figs

1994-11-04

369

Magnetic field distributions of superconducting MRI magnet in insert dewar  

Energy Technology Data Exchange (ETDEWEB)

This paper describes the test results of magnetic field distributions of superconducting MRI magnet in an insert dewar. To get a very high homogeneous magnetic field, various shim coils are installed besides the main magnet. The operating currents of each shim coils are obtained from the exact measurements of the magnetic field. In this paper, we report the test results of the magnetic field distribution measurements with various shim coils. (author). 2 refs., 8 figs., 1 tab.

Jin, H.B.; Oh, B.H.; Kwon, Y.G.; Oh, S.S.; Cho, J.W.; Ha, D.W.; Lee, E.Y.; Ryu, K.W.; Ryu, K.S.; Hahn, I.Y. [Korea Electrotechonology Research Institute (Korea, Republic of); Nah, W. [Sungkwunkwan University (Korea, Republic of)

1995-07-01

370

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS  

International Nuclear Information System (INIS)

Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

2004-01-01

371

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.  

Energy Technology Data Exchange (ETDEWEB)

Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS. R.; WANDERER, P.

2004-10-03

372

Magnetic Fields in Molecular Clouds  

CERN Document Server

Magnetic fields are believed to play an important role in the evolution of molecular clouds, from their large scale structure to dense cores, protostellar envelopes, and protoplanetary disks. How important is unclear, and whether magnetic fields are the dominant force driving star formation at any scale is also unclear. In this review we examine the observational data which address these questions, with particular emphasis on high angular resolution observations. Unfortunately the data do not clarify the situation. It is clear that the fields are important, but to what degree we don't yet know. Observations to date have been limited by the sensitivity of available telescopes and instrumentation. In the future ALMA and the SKA in particular should provide great advances in observational studies of magnetic fields, and we discuss which observations are most desirable when they become available.

Goodman, T L B A A

2004-01-01

373

Magnetic nanoparticles for applications in oscillating magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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

Peeraphatdit, Chorthip

2010-12-15

374

Magnetic field draping about coronal mass ejecta  

Energy Technology Data Exchange (ETDEWEB)

Fast coronal mass ejecta (CMEs) accelerate and deflect the slower moving solar wind plasma which piles up ahead of them as they propagate out through the heliosphere. This acceleration and deflection, in turn, causes the interplanetary magnetic field (IMF) imbedded in the upstream solar wind to drape about the ejecta. Draping should cause substantial out-of-the-ecliptic magnetic fields at some locations ahead of CMEs, and radial fields behind and along the flanks. At the Earth, draping can be an important factor in the generation of some magnetic storms and substorms, while in the outer heliosphere draping may produce very large magnetotail-like configurations, somewhat analogous to those observed behind Venus and comets. 17 refs.

McComas, D.J.; Gosling, J.T.

1987-01-01

375

Magnetic fields a comprehensive theoretical treatise for practical use  

CERN Document Server

A unique resource for physicists and engineers working with magnetic fieldsAn understanding of magnetic phenomena is essential for anyone working on the practical application of electromagnetic theory. Magnetic Fields: A Comprehensive Theoretical Treatise for Practical Use provides physicists and engineers with a thorough treatment of the magnetic aspects of classical electromagnetic theory, focusing on key issues and problems arising in the generation and application of magnetic fields. From magnetic potentials and diffusion phenomena to magnetohydrodynamics and properties of matter-topics are carefully selected for their relevance to the theoretical framework as well as current technologies

Knoepfel, Heinz E

2000-01-01

376

Ultrafast time domain demonstration of bulk magnetization precession at zero magnetic field ferromagnetic resonance induced by terahertz magnetic field.  

Science.gov (United States)

We report the first observation of sub-terahertz bulk-magnetization precession, using terahertz time-domain spectroscopy. The magnetization precession in gallium-substituted epsilon-iron oxide nano-ferromagnets under zero magnetic field is induced by the impulsive magnetic field of the THz wave through the gyromagnetic effect. Just at the resonance frequency, the linear to circular polarized wave conversion is realized. This is understood as the free induction decay signal radiated from a rotating magnetic dipole corresponding to the natural resonance. Furthermore, this demonstration reveals that the series of gallium-substituted epsilon-iron oxide nano-ferromagnets is very prospective for magneto-optic devices, which work at room temperature without external magnetic field, in next-generation wireless communication. PMID:20721218

Nakajima, M; Namai, A; Ohkoshi, S; Suemoto, T

2010-08-16

377

Ultrafast time domain demonstration of bulk magnetization precession at zero magnetic field ferromagnetic resonance induced by terahertz magnetic field.  

UK PubMed Central (United Kingdom)

We report the first observation of sub-terahertz bulk-magnetization precession, using terahertz time-domain spectroscopy. The magnetization precession in gallium-substituted epsilon-iron oxide nano-ferromagnets under zero magnetic field is induced by the impulsive magnetic field of the THz wave through the gyromagnetic effect. Just at the resonance frequency, the linear to circular polarized wave conversion is realized. This is understood as the free induction decay signal radiated from a rotating magnetic dipole corresponding to the natural resonance. Furthermore, this demonstration reveals that the series of gallium-substituted epsilon-iron oxide nano-ferromagnets is very prospective for magneto-optic devices, which work at room temperature without external magnetic field, in next-generation wireless communication.

Nakajima M; Namai A; Ohkoshi S; Suemoto T

2010-08-01

378

Prototype development to expose bacterial cultures to magnetic fields  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic and electromagnetic fields are widely used in our environment. However, their effects on living tissues are quite unknown, and the existing results obtained from former researches are not conclusive. Objective: To develop a prototype that allows an evaluation of the bacterial culture exposed to magnetic fields generated by two ferrite magnets attracted to each other. Methods: The prototype was built with acrylic plates of different sizes and formats. Two circular ferrite magnets were fixed to the plates, attracted to each other, in order to generate a magnetic field of 100 ± 5 mT. Test tubes were adapted in the prototype to allow bacterial growth in broth under stimulation. Results: Inthe present pilot study, the prototype was effective in exposing bacterial cultures to a magnetic field. Conclusion: The developed prototype served to the purpose of the study and made possible to expose bacterial cultures to a static magnetic field.

Lucienne Miranda ULBRICH; Paulo Henrique TOMAZINHO; Melany Glaser RUPOLLO; Marcela Costa FRANÇOSO; Andressa NETZEL; Caroline PONTAROLLI; Tonivan VANIN; Marcelo FILIETAZ

2010-01-01

379

Magnetic resonance imaging of time-varying magnetic fields from therapeutic devices.  

UK PubMed Central (United Kingdom)

While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields such as those generated by transcranial magnetic stimulators and radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this study. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by a figure-eight coil inside simple phantoms over a range of frequencies and intensities using a 7T small animal MRI scanner. The method was able to reconstruct the three-dimensional components of the oscillating magnetic field vector.

Hernandez-Garcia L; Bhatia V; Prem-Kumar K; Ulfarsson M

2013-06-01

380

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

Science.gov (United States)

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

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

2008-04-01

 
 
 
 
381

The Protogalactic Origin for Cosmic Magnetic Fields  

CERN Document Server

It is demonstrated that strong magnetic fields are produced from a zero initial magnetic field during the pregalactic era, when galaxies are first forming. Their development proceeds in three phases. In the first phase, weak magnetic fields are created by the Biermann battery mechanism, acting in shocked parts of the intergalactic medium where caustics form and intersect. In the second phase, these weak magnetic fields are amplified to strong magnetic fields by the Kolmogoroff turbulence endemic to gravitational structure formation of galaxies. During this second phase, the magnetic fields reach saturation with the turbulent power, but they are coherent only on the scale of the smallest eddy. In the third phase, the magnetic field strength increases to equipartition with the turbulent energy, and the coherence length of the magnetic fields increases to the scale of the largest turbulent eddy, comparable to the scale of the entire galaxy. The resulting magnetic field represents a galactic magnetic field of pri...

Kulsrud, R M; Ostriker, J P; Ryu, D; Kulsrud, Russell M.; Cen, Renyue; Ostriker, Jeremiah P.; Ryu, Dongsu

1996-01-01

382

Simulations of magnetic fields in filaments  

CERN Document Server

The intergalactic magnetic field within filaments should be less polluted by magnetised outflows from active galaxies than magnetic fields in clusters. Therefore, filaments may be a better laboratory to study magnetic field amplification by structure formation than galaxy clusters which typically host many more active galaxies. We present highly resolved cosmological AMR simulations of magnetic fields in the cosmos and make predictions about the evolution and structure of magnetic fields in filaments. Comparing our results to observational evidence for magnetic fields in filaments suggests that amplification of seed fields by gravitational collapse is not sufficient to produce IGM fields. Finally, implications for cosmic ray transport are discussed.

Brüggen, M; Simionescu, A; Hoeft, M; Vecchia, C D

2005-01-01

383

Origin of solar magnetic fields  

International Nuclear Information System (INIS)

Turbulent-dynamo theories of the solar cycle are criticized, and an alternative theory is proposed.The critique of dynamo theory focuses on attempts to justify the theory's basic physical and mathematical assumptions. It is argued that the theory's fundamental equation, the dynamo equation, is not a mathematically valid or physically plausible approximation to the exact equation governing the mean field; that there is no known physical or mathematical basis for the assumption that fluid turbulence enhances the diffusion of weak magnetic fields, as required by dynamo theories; and that mathematical models of ?? dynamos are internally inconsistent. Dynamo theories also encounter serious observational dificulties. The absence of strong surface fields for extended periods (70 years in the case of the Maunder minimum) is difficult to reconcile with theoretical expectations.The alternative theory invokes a nonregenerated, irregular magnetic field largely confined to the nonconvective core. The genesis of this field during the Hayashi phase of pre-main-sequence evolution and its role in the spin-down of the proto-Sun are discussed in qualitative terms. It is argued that the submerged field interacts with differential rotation mainly in a narrow layer at the base of the convection zone. This interaction drives a t torsional hydromagnetic oscillation which produces the reversing toroidal field in the manner originally suggested by Cowling (1953). This picture accounts qualitatively for the observed ocrrelations among the duration, intensity, and rise time of the magnetic cycle, as well as for the existence of extended periods of surface inactivity

1979-05-01

384

Random Fields Generated by Dilution in Zero External Field  

Energy Technology Data Exchange (ETDEWEB)

It is shown that arbitrarily small amounts of bond or site dilution generate (in zero magnetic field) effects in some Ising antiferromagnets much like random fields and are, therefore, not covered by the criterion of Harris. All antiferromagnets on f.c.c. lattices as well as antiferromagnets of type-II in b.c.c. lattice suffer this effect. We argue that the cross-over exponent into the impurity-dominated regime fulfills in any dimensionality, and that an Ising model is unstable against any small site or bond dilution. Numerical results for strips, obtained by the transfer matrix method confirm this picture.

Fernandez, J.F.

1988-01-01

385

Hall field limitations in MHD generators  

Energy Technology Data Exchange (ETDEWEB)

An experimental and theoretical study of Hall field limitations in clean fuel combustion-driven MHD generators has been completed. The purpose of this study has been to understand the processes leading up to both insulator and plasma initiated interelectrode breakdown. The present work has been most concerned with insulator initiated breakdown as a result of the lower breakdown thresholds for this breakdown mode as compared to the plasma initiated breakdown mode. The experimental work consisted of two sets of experiments. In the first set, several interelectrode insulator cooling techniques were studied for the purpose of extending the insulator initiated breakdown threshold to higher voltages. The second set of experiments dealt with the dependence of the Hall field behavior on generator parameters such as magnetic field, insulator size and transverse current density. The theoretical work consisted of developing a computer program to model the processes leading up to both insulator and plasma initiated breakdown. The program has been used to explain the trends observed in the experiments and also to predict the dependence of the Hall field behavior on generator parameters for both an experimental scale and a large scale generator. The results of the research demonstrate the effectiveness of several interelectrode insulator cooling techniques in preventing insulator initiated breakdown. Experimental and theoretical results have also been obtained that indicate the dependence of the Hall behavior on several generator parameters.

Hermina, W.L.

1982-01-01

386

Hall-field limitations in MHD generators  

Energy Technology Data Exchange (ETDEWEB)

An experimental and theoretical study of Hall field limitations in clean fuel combustion-driven MHD generators has been completed. The purpose of this study has been to understand the processes leading up to both insulator and plasma initiated interelectrode breakdown. The present work has been most concerned with insulator initiated breakdown as a result of the lower breakdown thresholds for this breakdown mode as compared to the plasma initiated breakdown mode. The experimental work consisted of two sets of experiments. In the first set, several interelectrode insulator cooling techniques were studied for the purpose of extending the insulator initiated breakdown threshold to higher voltages. The second set of experiments dealt with the dependence of the Hall field behavior on generator parameters such as magnetic field, insulator size and transverse current density. The theoretical work consisted of developing a computer program to model the processes leading up to both insulator and plasma initiated breakdown. The program has been used to explain the trends observed in the experiments and also to predict the dependence of the Hall field behavior on generator parameters for both an experimental scale and a large scale generator. The results of the research demonstrate the effectiveness of several interelectrode insulator cooling techniques in preventing insulator initiated breakdown. Experimental and theoretical results have also been obtained that indicate the dependence of the Hall behavior on several generator parameters.

Hermina, W.L.

1982-04-01

387

Temperature compensated current sensor using reference magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-10-09

388

ATLAS cavern magnetic field calculations  

International Nuclear Information System (INIS)

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

2000-01-01

389

ATLAS Cavern Magnetic Field Calculations  

CERN Multimedia

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

Vorojtsov, S B; Butin, F; Price, M

2000-01-01

390

Force Free Magnetic Fields and Solar Activity.  

Science.gov (United States)

This report concerning the prediction of solar flares, centers on devising methods for calculating magnetic field structures in the solar atmosphere. Force-free fields comprise an important class of magnetic-field structures which may be calculated by rel...

P. A. Sturrock C. W. Barnes

1974-01-01

391

Can the observed large scale magnetic fields be seeded by helical primordial fields?  

CERN Multimedia

Gravitational wave production induces a strong constraint on the amplitude of a primordial magnetic field. It has been shown that the nucleosynthesis bound for a stochastic gravitational wave background implies that causally generated fields cannot have enough power on large scales to provide the seeds necessary for the observed magnetic fields in galaxies and clusters, even by the most optimistic dynamo amplification. Magnetic fields generated at inflation can have high enough amplitude only if their spectrum is very red. Here we show that helicity, which leads to an inverse cascade, can mitigate these limits. In particular, we find that helical fields generated at the QCD phase transition or at inflation with red spectrum are possible seeds for the dynamo. Helical fields generated at the electroweak phase transition are instead excluded as seeds at large scales. We also calculate the spectrum of gravitational waves generated by helical magnetic fields.

Caprini, Chiara; Fenu, Elisa

2009-01-01

392

Magnetic Fields in Protoplanetary Disks  

CERN Document Server

Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary disks. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface. Magnetically-driven mixing has implications for disk chemistry and evolution of the grain population, and the effective viscous response of the disk determines whether planets migrate inwards or outwards. However, the weak ionisation of protoplanetary disks means that magnetic fields may not be able to effectively couple to the matter. I examine the magnetic diffusivity in a minimum solar nebula model and present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to supress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few mic...

Wardle, Mark

2007-01-01

393

Magnetic fields in neutron stars  

CERN Multimedia

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

Viganò, Daniele

2013-01-01

394

Hybrid permanent magnet and variable reluctance generator  

Energy Technology Data Exchange (ETDEWEB)

This patent describes a hybrid electrical generator. It comprises: a permanent magnet generator having a permanent magnet rotor mounted on a shaft, the permanent magnet generator providing an output voltage over an operating range which falls in response to an increasing electrical load; a variable reluctance generator having a rotor mounted on the shaft with excitation of a stator of the variable reluctance generator being provided from the permanent magnet generator, the variable reluctance generator providing an output voltage which varies in response to an increasing electrical load over an operating range; and a voltage regulator, responsive to combined output voltages of the generators, for controlling the output voltage provided by the variable reluctance generator.

Vaidya, J.; Belanger, D.J.

1990-09-25

395

Applied magnetic field design for the field reversed configuration compression heating experiment.  

UK PubMed Central (United Kingdom)

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.

Domonkos MT; Amdahl D; Camacho JF; Coffey SK; Degnan JH; Delaney R; Frese M; Gale D; Grabowski TC; Gribble R; Intrator TP; McCullough J; Montano N; Robinson PR; Wurden G

2013-04-01

396

Applied magnetic field design for the field reversed configuration compression heating experiment  

Science.gov (United States)

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics®. In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.

Domonkos, M. T.; Amdahl, D.; Camacho, J. F.; Coffey, S. K.; Degnan, J. H.; Delaney, R.; Frese, M.; Gale, D.; Grabowski, T. C.; Gribble, R.; Intrator, T. P.; McCullough, J.; Montano, N.; Robinson, P. R.; Wurden, G.

2013-04-01

397

Magnetic Fields in the Solar Convection Zone  

Directory of Open Access Journals (Sweden)

Full Text Available Active regions on the solar surface are generally thought to originate from a strong toroidal magnetic field generated by a deep seated solar dynamo mechanism operating at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. Understanding this process of active region flux emergence is therefore a crucial component for the study of the solar cycle dynamo. This article reviews studies with regard to the formation and rise of active region scale magnetic flux tubes in the solar convection zone and their emergence into the solar atmosphere as active regions.

Yuhong Fan

2009-01-01

398

Majorana neutrinos and magnetic fields  

International Nuclear Information System (INIS)

[en] It is stressed that if neutrinos are massive they are probably of Majorana type. This implies that their magnetic moment form factor vanishes identically so that the previously discussed phenomenon of spin rotation in a magnetic field would not appear to take place. It is pointed out that Majorana neutrinos can, however, have transition moments. This enables an inhomogeneous magnetic field to rotate both spin and flavor of a neutrino. In this case the spin rotation changes particle to anti-particle. The spin-flavor rotation effect is worked out in detail. The parameterization and calculation of the electromagnetic form factors of Majorana neutrinos are discussed, taking into account the somewhat unusual quantum theory of massive Majorana particles

1981-01-01

399

Magnetic field exposure of commercial airline pilots.  

UK PubMed Central (United Kingdom)

PURPOSE: Airline pilots are exposed to magnetic fields generated by the aircraft's electrical and electronic systems. The purpose of this study was to directly measure the flight deck magnetic fields to which commercial airline pilots are exposed when flying on different aircraft types over a 75-hour flight-duty month.METHODS: Magentic field measurements were taken using personal dosimeters capable of measuring magnetic fields in the 40-800 Hz frequency range. Dosimeters were carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. The data were analyzed by aircraft type, with statistics based on block hours. Block hours begin when the aircraft departs the gate prior to take off and end when the aircraft returns to the gate after landing.RESULTS: Approximately 1008 block hours were recorded at a sampling rate of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200.CONCLUSIONS: Measured flight deck magnetic field levels were substantially above the 0.8 to 1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.

Hood W; Nicholas J; Butler G; Lackland D; Hoel D; Mohr L

2000-10-01

400

Magnetic field measurement of RIKEN IRC sector magnets  

International Nuclear Information System (INIS)

Magnetic field measurements of the RIKEN IRC sector magnets were made with a newly constructed field mapping system. Using mapping data of the base and trim coil fields for several field levels, production of the isochronous field for a typical ion beam was attempted and the measured field was compared with the expected one

2001-12-12

 
 
 
 
401

Control of the fields due to superconductor magnetization in the SSC (Superconducting Super Collider) magnets  

Energy Technology Data Exchange (ETDEWEB)

Field uniformity of better than one part in 10,000 is required for the dipole magnets for the Superconducting Super Collider (SSC). The high field dipole and quaddrupole magnets proposed for the SSC generate higher multipole components of field due to magnetization (persistent currents) in the superconductor. When the superconductor filament diameter is of the order of 20..mu..m, the sextupole term alone is about 17 parts in 10,000 at an injection induction of 0.3 tesla in the SSC dipole magnets at a radius of 1 cm. This paper shows calculations of the magnetization phenomena which agree very well with magnetic measurement. Several passive methods for removing the sextupole component and higher components of the field generated by magnetization of the superconductor in the SSC dipole magnets are presented in the paper.

Green, M.A.

1986-09-01

402

GRB: magnetic fields, cosmic rays, and emission from first principles?  

CERN Multimedia

We describe a scenario for large-scale magnetic field generation and particle acceleration in a collisionless collision of cold plasma clouds. A first-principle (i.e. using particles) numerical simulation of this process might be possible. Our scenario is essentially 3D. We argue that {\\it large-scale} magnetic fields are not generated in 2D, even in collisionless plasma. We calculate and numerically simulate magnetic field generation by relativistic collisionless Kelvin-Helmholtz instability in 2D. Collisionless tangential discontinuity might be more important than collisionless shock, because tangential discontinuity remains unstable even in the hydro limit, when the shock stabilizes.

Gruzinov, Andrei

2008-01-01

403

Heterotic String in a Constant Magnetic Field  

CERN Multimedia

When a charged heterotic string is placed in a constant magnetic field B, we show that this system can be solved exactly by using the cyclotron frequency. We then calculate anomalies of the super Virasoro algebra, and give the corresponding spectrum-generating algebra for this system. They differ from the free case by the cyclotron frequency. It is remarkable that our system is equivalent to the completely free system when B takes integral values.

Kokado, Akira; Saito, Takesi

2009-01-01

404

Neutrinos in Strong Magnetic Fields  

CERN Document Server

We compute the dispersion relations for neutrinos propagating in an electroweak plasma, in the presence of very strong magnetic fields. The neutrino self-energy is calculated in the one-loop approximation. We consider only contributions of the first Landau level to the propagator of the W-bosons, and distinguish between motion parallel or perpendicular to the external magnetic field. We find that the neutrino soup just below the phase transition at the maximal field value $B\\le M_W^2/e$ exhibits spontaneous symmetry breakdown of translational invariance, i.e. superfluidity. Our results seem to validate the idea that the early universe is theoretically similar to the fractional quantum Hall effect.

Pérez-Martínez, A; Agüero, D O; Pérez-Rojas, Hugo Celso; Romo, S R

1997-01-01

405

Gluon Vortices and Induced Magnetic Field in Compact Stars  

International Nuclear Information System (INIS)

The natural candidates for the realization of color superconductivity are the extremely dense cores of compact stars, many of which have very large magnetic fields, especially the so called magnetars. In this paper we discuss how a color superconducting core can serve to generate and enhance the stellar magnetic field without appealing to a magnetohydrodynamic dynamo mechanism

2007-10-26

406

Adiabatic compression and radiative compression of magnetic fields  

International Nuclear Information System (INIS)

Flux is conserved during mechanical compression of magnetic fields for both nonrelativistic and relativistic compressors. However, the relativistic compressor generates radiation, which can carry up to twice the energy content of the magnetic field compressed adiabatically. The radiation may be either confined or allowed to escape

1980-01-01

407

Magnetic field of the Earth  

Science.gov (United States)

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

Popov, Aleksey

2013-04-01

408

Evolution of primordial magnetic fields in mean-field approximation  

CERN Multimedia

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

Campanelli, Leonardo

2013-01-01

409

Nuclear Georeactor Generation of Earth's Geomagnetic Field  

CERN Document Server

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

Herndon, J Marvin

2007-01-01

410

Unique Topological Characterization of Braided Magnetic Fields  

CERN Multimedia

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of the magnetic field, and measures the average poloidal magnetic flux around any given field line. Moreover, its integral over the cross-section yields the relative magnetic helicity. Using the fact that the flux function is also an action in the Hamiltonian formulation of the field line equations, we prove that it uniquely characterizes the field line mapping and hence the magnetic topology.

Yeates, A R

2012-01-01

411

Decay of Magnetic Fields in the Early Universe  

CERN Multimedia

We study the evolution of a stochastic helical magnetic field generated in the early Universe after the electroweak phase transition, using standard magnetohydrodynamics (MHD). We find how the coherence length xi, magnetic energy E_M and magnetic helicity H evolve with time. We show that the self-similarity of the magnetic power spectrum alone implies that xi ~ t^{1/2}. This in turn implies that magnetic helicity decays as H ~ t^{-2s}, and that the magnetic energy decays as E_M ~ t^{-0.5-2s}, where s is inversely proportional to the magnetic Reynolds number Re_M. These laws improve on several previous estimates.

Hindmarsh, M; Brandenburg, A; Hindmarsh, Mark

2003-01-01

412

Establishment of magnetic coordinates for a given magnetic field  

International Nuclear Information System (INIS)

A method is given for expressing the magnetic field strength in magnetic coordinates for a given field. This expression is central to the study of equilibrium, stability, and transport in asymmetric plasmas

1981-01-01

413

The production of Ganymede's magnetic field  

Science.gov (United States)

One of the great discoveries of NASA's Galileo mission was the presence of an intrinsically produced magnetic field at Ganymede. Generation of the relatively strong (750 nT) field likely requires dynamo action in Ganymede's metallic core, but how such a dynamo has been maintained into the present epoch remains uncertain. Using a one-dimensional, three layer thermal model of Ganymede, we find that magnetic field generation can only occur if the sulfur mass fraction in Ganymede's core is very low (?3%) or very high (?21%), and the silicate mantle can cool rapidly (i.e. it has a viscosity like wet olivine). However, these requirements are not necessarily compatible with cosmochemical and physical models of the satellite. We therefore investigate an alternative scenario for producing Ganymede's magnetic field in which passage through an eccentricity pumping Laplace-like resonance in Ganymede's past enables present day dynamo action in the metallic core. If sufficient tidal dissipation occurs in Ganymede's silicate mantle during resonance passage, silicate temperatures can undergo a runaway which prevents the core from cooling until the resonance passage ends. The rapid silicate and core cooling that follows resonance escape triggers dynamo action via thermal and/or compositional convection. To test the feasibility of this mechanism we couple our thermal model with an orbital evolution model to examine the effects of resonance passage on Ganymede's silicate mantle and metallic core. We find that, contrary to expectations, there are no physically plausible scenarios in which tidal heating in the silicates is sufficient to cause the thermal runaway necessary to prevent core cooling. These findings are robust to variations in the silicate rheology, tidal dissipation factor of Jupiter (Q), structure of the ice shell, and the inclusion of partial melting in the silicate mantle. Resonance passage therefore appears unlikely to explain Ganymede's magnetic field and we must appeal to the special conditions described above to explain the presence of the field.

Bland, Michael T.; Showman, Adam P.; Tobie, Gabriel

2008-12-01

414

Flight deck magnetic fields in commercial aircraft.  

UK PubMed Central (United Kingdom)

BACKGROUND: Airline pilots are exposed to magnetic fields generated by the aircraft's electrical system. The objectives of this study were (1) to directly measure flight deck magnetic fields in terms of personal exposure to the pilots when flying on different aircraft types over a 75-hour flight-duty month, and (2) to compare magnetic field exposures across flight deck types and job titles. METHODS: Measurements were taken using personal dosimeters carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. RESULTS: Approximately 1,008 block hours were recorded at a sampling frequency of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200. CONCLUSIONS: Measured flight deck magnetic field levels were substantially above the 0.8-1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.

Nicholas JS; Butler GC; Lackland DT; Hood WC Jr; Hoel DG; Mohr LC Jr

2000-11-01

415

Constraining the central magnetic field of magnetars  

CERN Multimedia

The magnetars are believed to be highly magnetized neutron stars having surface magnetic field 10^{14} - 10^{15} G. It is believed that at the center, the magnetic field may be higher than that at the surface. We study the effect of the magnetic field on the neutron star matter. We model the nuclear matter with the relativistic mean field approach considering the possibility of appearance of hyperons at higher density. We find that the effect of magnetic field on the matter of neutron stars and hence on the mass-radius relation is important, when the central magnetic field is atleast of the order of 10^{17} G. Very importantly, the effect of strong magnetic field reveals anisotropy to the system. Moreover, if the central field approaches 10^{19} G, then the matter becomes unstable which limits the maximum magnetic field at the center of magnetars.

Mukhopadhyay, Banibrata

2013-01-01

416

SQUID-detected magnetic resonance imaging in microtesla magnetic fields  

International Nuclear Information System (INIS)

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

2003-11-26

417

Magnetic field reversals and galactic dynamos  

CERN Multimedia

We argue that global magnetic field reversals similar to those observed in the Milky Way occur quite frequently in mean-field galactic dynamo models that have relatively strong, random, seed magnetic fields that are localized in discrete regions. The number of reversals decreases to zero with reduction of the seed strength, efficiency of the galactic dynamo and size of the spots of the seed field. A systematic observational search for magnetic field reversals in a representative sample of spi