WorldWideScience
 
 
1

Octupole magnet for soft X ray magnetic dichroism experiments: Design and performance  

International Nuclear Information System (INIS)

An octupole magnet endstation for soft x-ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x-ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x-ray incidence while keeping the relative orientation of magnetic field and sample fixed

2003-08-25

2

Octupole Magnet For Soft X Ray Magnetic Dichroism Experiments: Design and Performance  

International Nuclear Information System (INIS)

An octupole magnet endstation for soft x ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x ray incidence while keeping the relative orientation of magnetic field and sample fixed

2004-05-12

3

Octupole magnet for soft X ray magnetic dichroism experiments: Design and performance  

Energy Technology Data Exchange (ETDEWEB)

An octupole magnet endstation for soft x-ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x-ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x-ray incidence while keeping the relative orientation of magnetic field and sample fixed.

Arenholz, Elke; Prestemon, Soren O.

2003-08-24

4

Octupole Magnet For Soft X Ray Magnetic Dichroism Experiments: Design and Performance  

Science.gov (United States)

An octupole magnet endstation for soft x ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x ray incidence while keeping the relative orientation of magnetic field and sample fixed.

Arenholz, Elke; Prestemon, Soren O.

2004-05-01

5

Magnetic octupole strength in rare-earth nuclei: A sum-rule approach  

International Nuclear Information System (INIS)

We use linear energy-weighted sum rules within the proton-neutron interacting boson model to deduce a relationship between magnetic dipole and magnetic octupole transition probabilities. We then obtain a first estimate of the summed magnetic octupole strength to be expected in rare-earth nuclei

1995-06-01

6

Spectroscopy on a single trapped 137Ba+ ion for nuclear magnetic octupole moment determination  

CERN Document Server

We present precision measurements of the hyperfine splittings in the 5D3/2 manifold of a single trapped Barium ion, 137Ba+ . Measurements of the hyperfine splittings are made between mF = 0 sublevels over a range of magnetic fields allowing us to interpolate to the zero field splittings with an accuracy below 10 Hz. Our results, in conjunction with theoretical calculations, allow the determination of the hyperfine coupling constant, C, with an accuracy below 0.1 Hz. This gives a subsequent determination of the nuclear magnetic octupole moment with an uncertainty limited almost completely by the accuracy of theoretical calculations.

Lewty, Nicholas C; Cazan, Radu; Barrett, M D

2012-01-01

7

Modified octupoles for damping coherent instabilities  

International Nuclear Information System (INIS)

The introduction tune spread in circular e"+e"- accelerators with modified octupoles to reduce the loss of dynamic aperture is discussed. The new magnet design features an octupole of field component on-axis and a tapered field structure off-axis to minimize loss of dynamic aperture. Tracking studies show that the modified octupoles can produce the desired tune spread in SPEAR without compromising confinement of the beam. The technique for designing such magnets is presented, together with an example of magnets that give the required field distribution. 7 refs., 7 figs

1991-05-06

8

Octupole deformation for Ba isotopes in a reflection-asymmetric relativistic mean-field approach  

CERN Multimedia

The potential energy surfaces of even-even $^{142-156}$Ba are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, $^{142}$Ba is near spherical,$^{156}$Ba well quadrupole-deformed, and in between $^{144-154}$Ba octupole deformed. In particular, the nuclei $^{148,150}$Ba with $N=92,94$ have the largest octupole deformations. By including the octupole degree of freedom, energy gaps $N=88$, $N=94$ and $Z=56$ near Fermi surfaces for the single-particle levels in $^{148}$Ba with $\\beta_2\\sim 0.26$ and $\\beta_3\\sim 0.17$ are found. Furthermore, the performance of the octupole deformation driving pairs ($\

Zhang, W; Zhang, S Q

2010-01-01

9

Octupole deformation properties of actinide isotopes within a mean field approach  

CERN Document Server

We discuss the octupole deformation properties of many even-even actinide isotopes. The analysis is carried out in the mean field framework (Hartree-Fock-Bogoliubov approximation) by using the axially symmetric octupole moment as a constraint. A one-dimensional octupole collective Hamiltonian is used to obtain properties like excitation energies or $E1$ and $E3$ transition probabilities of the negative parity band-heads associated to the lowest lying $1^{-}$ and $3^{-}$ states. The evolution of these values with neutron number is discussed and a comparison with available experimental data is made. In order to minimize the uncertainties associated to the energy density functional used, the calculations have been carried out for an assorted set ranging from the BCP1 functional to the finite range Gogny interaction with the D1S, D1N and D1M parametrization.

Robledo, L M; 10.1088/0954-3899/39/10/105103

2012-01-01

10

Octupole degree of freedom for nuclei near 152Sm in a reflection-asymmetric relativistic mean-field approach  

International Nuclear Information System (INIS)

The potential energy surfaces of even-even isotopes near 152Sm are investigated within the constrained reflection-asymmetric relativistic mean-field approach using parameter sets PK1 and NL3. It is shown that the critical-point candidate nucleus 152Sm marks the shape/phase transition not only from U(5) to SU(3) symmetry, but also from the octupole deformed ground state in 150Sm to the quadrupole deformed ground state in 154Sm. The important role of the octupole deformation driving pair (?2f7/2, ?1i13/2) is demonstrated based on the components of the single-particle levels near the Fermi surface. In addition, the patterns of both the proton and the neutron octupole deformation driving pairs (?2f7/2, ?1i13/2) and (?2d5/2, ?1h11/2) are investigated.

2011-09-23

11

Measuring the Nuclear Magnetic Octupole Moment of a Single Trapped Barium-137 Ion  

Science.gov (United States)

Recent measurements of hyperfine structure in the cesium-133 atom resolved a nuclear magnetic octupole moment ? much larger than expected from the nuclear shell model[1]. To explore this issue further, we are undertaking an experiment to measure the hyperfine structure in the 5D manifold of a single trapped barium-137 ion which, together with reliable calculations in alkali-like Ba^+, should resolve ? with sensitivity better than the shell model value [2]. We use a TmHo:YLF laser tuned to 2051 nm and a fiber laser tuned to 1762 nm to drive the 6S1/2 to 5D3/2 and 6S1/2 to 5D5/2 electric quadrupole transitions. These lasers allow us to selectively populate any hyperfine sub-level in the 5D manifold. We will then perform RF spectroscopy on the 5D states to make a precision measurement of the hyperfine frequency intervals. We report on the development of the laser and RF spectroscopy systems. [1] V. Gerginov, A. Derevianko, and C. E. Tanner, Phys. Rev. Lett. 91, 072501 [2] K. Beloy, A. Derevianko, V. A. Dzuba, G. T. Howell, B. B. Blinov, E. N. Fortson, arXiv:0804.4317v1 [physics.atom-ph] 28 Apr 2008

Kleczewski, Adam; Fortson, Norval; Blinov, Boris

2009-05-01

12

Octupole correlation effects in nuclei  

Energy Technology Data Exchange (ETDEWEB)

Octupole correlation effects in nuclei are discussed from the point of view of many-body wavefunctions as well as mean-field methods. The light actinides, where octupole effects are largest, are considered in detail. Comparisons of theory and experiment are made for energy splittings of parity doublets; E1 transition matrix elements and one-nucleon transfer reactions.

Chasman, R.R.

1992-08-01

13

Octupole correlation effects in nuclei  

Energy Technology Data Exchange (ETDEWEB)

Octupole correlation effects in nuclei are discussed from the point of view of many-body wavefunctions as well as mean-field methods. The light actinides, where octupole effects are largest, are considered in detail. Comparisons of theory and experiment are made for energy splittings of parity doublets; E1 transition matrix elements and one-nucleon transfer reactions.

Chasman, R.R.

1992-01-01

14

Octupole Ordering Model for the Phase IV of CexLa1-xB6  

CERN Multimedia

An octupole ordering model is studied by the mean field theory, and its relevance to the phase IV of CexLa1-xB6 is discussed. The observed lattice distortion along the [111] direction is interpreted in terms of the \\Gamma_{5g}-type ferro-quadrupole moment induced by an antiferro-octupole ordered state with \\Gamma_{5u} symmetry. The octupole model also accounts for the cusp in the magnetization as in the N\\'{e}el transition, and the softening of the elastic constant C_{44} below the ordering temperature. However, the internal magnetic field due to the octupole moment is smaller than the observed one by an order of magnitude. Also discussed is the possibility of a pressure induced antiferromagnetic moment in the octupole-ordered state.

Kubo, K; Kubo, Katsunori; Kuramoto, Yoshio

2003-01-01

15

Quadrupole magnet field mapping for FRIB  

Energy Technology Data Exchange (ETDEWEB)

Extensive magnetic field map measurements have been done on a newly built superconducting quadrupole triplet with sextupole and octupole coils nested within every quadrupole. The magnetic field multipole composition and fringe field distributions have been analyzed and an improved parameterization of the field has been developed within the beam transport simulation framework. Parameter fits yielding standard deviations as low as 0.3% between measured and modeled values are reported here.

Portillo, M., E-mail: portillo@frib.msu.edu [Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI (United States); Amthor, A.M.; Chouhan, S. [Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI (United States); Cooper, K.; Gehring, A. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI (United States); Hausmann, M. [Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI (United States); Hitchcock, S.; Kwarsick, J. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI (United States); Manikonda, S. [Argonne National Laboratory, Argonne, IL (United States); Sumithrarachchi, C. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI (United States)

2013-12-15

16

Relaxed plasmas in external magnetic fields  

International Nuclear Information System (INIS)

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

1994-09-01

17

Cross field diffusion and fluctuation spectra in a levitated octupole in the presence of a toroidal field  

Energy Technology Data Exchange (ETDEWEB)

The diffusion coefficient, D/sub perpendicular to/, for a collisionless hydrogen plasma was measured in the Levitated Octupole when a weak toroidal field was added. A 20-fold decrease in the anomalous diffusion was observed with B/sub T//B/sub P/ approx. 0.1. Since the plasma is collisionless locally trapped particles in the poloidal field mirrors allows the convective cell activity (f < 600 Hz) to persist even when toroidal field was added. A shift in the k/sub perpendicular to/ spectrum to shorter wavelengths was noted. Measurements and calculations indicate that the higher frequency portion of the spectrum (f > 600 Hz) cannot be responsible for the observed diffusion.

Ehrhardt, A. B.; Garner, H. R.; Navratil, G. A.; Post, R. S.

1980-11-01

18

Magnetic fields for transporting charged beams  

International Nuclear Information System (INIS)

The transport of charged particle beams requires magnetic fields that must be shaped correctly and very accurately. During the last 20 years or so, many studies have been made, both analytically and through the use of computer programs, of various magnetic shapes that have proved to be useful. Many of the results for magnetic field shapes can be applied equally well to electric field shapes. A report is given which gathers together the results that have more general significance and would be useful in designing a configuration to produce a desired magnetic field shape. The field shapes studied include the fields in dipoles, quadrupoles, sextupoles, octupoles, septum magnets, combined-function magnets, and electrostatic septums. Where possible, empirical formulas are proposed, based on computer and analytical studies and on magnetic field measurements. These empirical formulas are often easier to use than analytical formulas and often include effects that are difficult to compute analytically. In addition, results given in the form of tables and graphs serve as illustrative examples. The field shapes studied include uniform fields produced by window-frame magnets, C-magnets, H-magnets, and cosine magnets; linear fields produced by various types of quadrupoles; quadratic and cubic fields produced by sextupoles and octupoles; combinations of uniform and linear fields; and septum fields with sharp boundaries

1976-01-01

19

Octupole degree of freedom for the critical-point candidate nucleus $^{152}$Sm in a reflection-asymmetric relativistic mean-field approach  

CERN Document Server

The potential energy surfaces of even-even $^{146-156}$Sm are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that the critical-point candidate nucleus $^{152}$Sm marks the shape/phase transition not only from U(5) to SU(3) symmetry, but also from the octupole-deformed ground state in $^{150}$Sm to the quadrupole-deformed ground state in $^{154}$Sm. By including the octupole degree of freedom, an energy gap near the Fermi surface for single-particle levels in $^{152}$Sm with $\\beta_2 = 0.14 \\sim 0.26$ is found, and the important role of the octupole deformation driving pair $\

Zhang, W; Zhang, S Q; Meng, J; 10.1103/PhysRevC.81.034302

2010-01-01

20

Interference corrections of the second Born approximation to the elastic scattering cross section of electron by the nuclei with magnetic octupole moment  

International Nuclear Information System (INIS)

The correction of the second Born approximation to the cross section of elastic back scattering of electrons (TyETA=?) by nuclei possessing electric quadrupole and magnetic dipole and octupole moments taking into account the interference contributions between charged and magnetic scatterings. The correction behaviour is investigated in the case of 1p-shell ("9Be, "1"1B) nuclei. Analytic expressions are obtained for corrections in the limits of not very high energies of incident electrons

1981-11-01

 
 
 
 
21

Interference corrections of the second Born approximation to the elastic scattering cross section of electron by the nuclei with magnetic octupole moment  

Energy Technology Data Exchange (ETDEWEB)

The correction of the second Born approximation to the cross section of elastic back scattering of electrons (TyETA=..pi..) by nuclei possessing electric quadrupole and magnetic dipole and octupole moments taking into account the interference contributions between charged and magnetic scatterings. The correction behaviour is investigated in the case of 1p-shell (/sup 9/Be, /sup 11/B) nuclei. Analytic expressions are obtained for corrections in the limits of not very high energies of incident electrons.

Kerimov, B.K.; Ehl' gavkhari, A.I.; Ganiev, A.G. (Moskovskij Gosudarstvennyj Univ. (USSR))

1981-11-01

22

Lattice Distortion and Octupole Ordering Model in CexLa1-xB6  

CERN Document Server

Possible order parameters of the phase IV in CexLa1-xB6 are discussed with special attention to the lattice distortion recently observed. A \\Gamma_{5u}-type octupole order with finite wave number is proposed as the origin of the distortion along the [111] direction. The \\Gamma_8 crystalline electric field (CEF) level splits into three levels by a mean field with the \\Gamma_{5u} symmetry. The ground and highest singlets have the same quadrupole moment, while the intermediate doublet has an opposite sign. It is shown that any collinear order of \\Gamma_{5u}-type octupole moment accompanies the \\Gamma_{5g}-type ferro-quadrupole order, and the coupling of the quadrupole moment with the lattice induces the distortion. The cusp in the magnetization at the phase transition is reproduced, but the internal magnetic field due to the octupole moment is smaller than the observed one by an order of magnitude.

Kubo, K; Kubo, Katsunori; Kuramoto, Yoshio

2003-01-01

23

New Results on Octupole Collectivity  

International Nuclear Information System (INIS)

Octupole correlations play an important role in determining the level structure of nuclei throughout the periodic chart. Microscopically, octupole correlations are the result of the long-range, octupole-octupole interaction between nucleons occupying pairs of orbitals which differ in both orbital and total angular momentum by 3 units. A review of some of the most recent findings on octupole correlations is given. Emphasis is placed on new results from the actinide region, where two distinct collective modes have long been identified: octupole vibration and octupole deformation. These new results include negative-parity structures which appear to evolve from an octupole vibration into a static octupole deformed mode. In addition, newly observed rotational structures built on an excited 0+ state have been tentatively associated with a double-octupole phonon excitation. These newly observed properties can be successively described by calculations based on the concept of rotational-aligned octupole phonon condensation.

2011-09-23

24

Zonal harmonic model of Saturn's magnetic field from Voyager 1 and 2 observations  

International Nuclear Information System (INIS)

An axisymmetric octupole model of Saturn's planetary magnetic field is proposed. This three parameter model is extremely efficient in representing the main magnetic field of Saturn and reconciling the in situ magnetic field observations obtained by Pioneer 11 with those obtained by the Voyager 1 and 2 space-craft. Saturn's unique field configuration is thus not that of a simple displaced dipole but rather appears to be the axisymmetric part of a complex dynamo field. (author)

1982-07-01

25

The main magnetic field of Jupiter  

International Nuclear Information System (INIS)

The main magnetic field of Jupiter has been measured by the Goddard Space Flight Center flux gate magnetometer on Pioneer 11, and analysis of the data yields a more detailed model than that obtained from Pioneer 10 results. In a spherical harmonic octupole representation the dipole term (with opposite polarity to earth's) has a magnitude of 4.28 G R/sub j/ 3 at a tilt angle of 9.6degree and a system III longitude of 232degree. The quadrupole and octupole moments are significant, 24% and 21% of the dipole, respectively. This leads to a significant deviation of the planetary magnetic field from a simple offset dipole topology at distances of <3R/sub j/. The north polar field strength is 14 G, and in the northern hemisphere the 'footprint' of the lo associated flux tube traverses the magnetic polar region. Associated L shell splitting in the radiation belts, warping of the charged particle equatorial planes, and enhanced absorption effects due to the satellites Amalthea and lo are expected as a result of the field complexity

1976-06-01

26

Octupole correlations at superdeformed shape in the Hg-Pb region - including nonaxial components  

International Nuclear Information System (INIS)

We investigate octupole correlations at strongly elongated (axis ratio close to 2:1) quadrupole shapes in the Hg-Pb region including nonaxial components of the octupole mean field. Within the cranked Strutinsky method we find the variation of octupole stiffness with rotational frequency and with the aid of cranking mass parameters we estimate octupole vibration frequencies. The strongest octupole effects are predicted due to the ?=0 and 2 components of the octupole tensor, the estimated oscillation frequencies ranging from 1.1 to 1.6 MeV. (orig.)

1992-01-02

27

Octupole correlations at superdeformed shape in the Hg-Pb region - including nonaxial components  

Energy Technology Data Exchange (ETDEWEB)

We investigate octupole correlations at strongly elongated (axis ratio close to 2:1) quadrupole shapes in the Hg-Pb region including nonaxial components of the octupole mean field. Within the cranked Strutinsky method we find the variation of octupole stiffness with rotational frequency and with the aid of cranking mass parameters we estimate octupole vibration frequencies. The strongest octupole effects are predicted due to the {mu}=0 and 2 components of the octupole tensor, the estimated oscillation frequencies ranging from 1.1 to 1.6 MeV. (orig.).

Skalski, J. (Physique Nucleaire Theorique et Physique Mathematique, Univ. Libre, Brussels (Belgium))

1992-01-02

28

Measurement of octupole induced decoherence at CESR  

International Nuclear Information System (INIS)

The Landau damping of the transverse oscillations of a relativistic bunch can be enhanced by creating an amplitude-dependent betatron tune spread in the bunch. This tune spread can be created by introducing octupole magnets into the lattice. In order to further their understanding of this mechanism the authors have conducted experiments in CESR where the tune spread of the beam has been measured via measurements of the damping of the centroid motion of the beam after the beam has been kicked. The turn-by-turn transient response of the transverse motion to excitation by injection kickers is measured as a function of octupole current and excitation amplitude. The experimental data is shown to be in good agreement with particle tracking results and the theory of octupole induced decoherence

1991-05-06

29

A novel structure of multipole field magnets and their applications in uniformizing beam spot at target  

International Nuclear Information System (INIS)

A novel structure of multipole field magnets is proposed, and it can provide any order either symmetric or anti-symmetric field distribution within a good-field region in a flat rectangular shape with relative field errors of about 1%. Some of these field distributions cannot be obtained by standard multipole magnets but are quite useful in some applications, thanks to the decoupling of the two halves of the magnets by a pair of shielding plates. In addition, the simplified structure compared with the standard one makes the magnet fabrication easier and cost effective. Two-dimensional magnetic field calculations for anti-symmetric sextupole, octupole, decapole and dodecapole fields show that the new types of multipole magnets have good field quality. Three-dimensional magnetic field calculations have confirmed the validity of the two-dimensional calculations. Symmetric field distributions by the simplified multipole field magnets have also been confirmed by two-dimensional field calculations. Two application examples by using numerical simulations are also given to show the effectiveness of simplified multipole field magnets in producing uniform-like beam spots at two different targets with different beam inputs. It is also shown that combinations of the lower order anti-symmetric field magnets – a merit of this magnet structure – are more advantageous than the traditional combination of octupole and dodecapole magnets in beam spot uniformization, besides with cheaper construction and operation costs. The applications of non-standard field distributions such as anti-symmetric sextupole and symmetric octupole field distributions in synchrotrons are to be exploited in the future.

2012-11-01

30

Explaining Mercury's peculiar magnetic field  

Science.gov (United States)

MESSENGER magnetometer data revealed that Mercury's magnetic field is not only particularly weak but also has a peculiar geometry. The MESSENGER team finds that the location of the magnetic equator always lies significantly north of the geographic equator, is largely independent of the distance to the planet, and also varies only weakly with longitude. The field is best described by an axial dipole that is offset to the north by about 20% of the planetary radius. In terms of classical Gauss coefficients, this translates into a low axial dipole component of g10= -190 nT but a relatively large axial quadrupole contribution that amounts to roughly 40% of this value. The axial octupole is also sizable while higher harmonic contributions are much weaker. Very remarkable is also the fact that the equatorial dipole contribution is very small, consistent with a dipole tilt below 0.8 degree, and this is also true for the other non-axisymmetic field contributions. We analyze several numerical dynamos concerning their capability of explaining Mercury's magnetic field. Classical schemes geared to model the geomagnetic field typically show a much weaker quadrupole component and thus a smaller offset. The onset only becomes larger when the dynamo operates in the multipolar regime at higher Rayleigh numbers. However, since the more complex dynamics generally promotes all higher multipole contributions the location of the magnetic equator varies strongly with longitude and distance to the planet. The situation improves when introducing a stably stratified outer layer in the dynamo region, representing either a rigid FeS layer or a sub-adiabatic core-mantle boundary heat flux. This layer filters out the higher harmonic contributions and the field not only becomes sufficiently weak but also assumes a Mercury like offset geometry during a few percent of the simulation time. To increase the likelihood for the offset configuration, the north-south symmetry must be permanently broken and we explore two scenarios. Increasing the heat flux through the northern hemisphere of the core-mantle boundary is an obvious choice but is not supported by current models for Mercury's mantle. We find that a combination of internal rather than bottom driving and an increased heat flux through the equatorial region of the core-mantle boundary also promotes the required symmetry breaking and results in very Mercury like fields. The reason is that the imposed heat flux pattern, though being equatorially symmetric, lowers the critical Rayleigh number for the onset of equatorially anti-symmetric convection modes. In both scenarios, a stably stratified layer or a feedback coupling to the magnetospheric field is required for lowering the field strength to Mercury-like values.

Wicht, Johannes; Cao, Hao; Heyner, Daniel; Dietrich, Wieland; Christensen, Ulrich R.

2014-05-01

31

Plasma resistivity measurements in the Wisconsin levitated octupole  

International Nuclear Information System (INIS)

Resistivity measurements parallel to the magnetic field were made on gun injected plasmas ranging in density from 10"9cm"-"3 to 10"1parallelcm"-"3 in the Wisconsin levitated octupole with toroidal and poloidal magnetic fields. The 10"9cm"-"3 plasma was collisionless with lambda/sub mfp/ > 100 mirror lengths, had T/sub e/ = 10 eV, T/sub i/ = 30 eV and was found to have anomalous resistivity scaling like eta = ?T/sub e//n/sub e/ when E/sub parallel/ > E/su c/ is the Dreicer critical field. The 10"1"2cm"-"3 plasma was collisional with lambda/sub mfp/ < mirror length, had T/sub e/ = T/sub i/ approx. = .2 eV and was found to have Spitzer resistivity when E/sub parallel/ < E/sub c/

1980-01-01

32

Plasma resistivity measurements in the Wisconsin levitated octupole  

Energy Technology Data Exchange (ETDEWEB)

Resistivity measurements parallel to the magnetic field were made on gun injected plasmas ranging in density from 10/sup 9/cm/sup -3/ to 10/sup 1/parallelcm/sup -3/ in the Wisconsin levitated octupole with toroidal and poloidal magnetic fields. The 10/sup 9/cm/sup -3/ plasma was collisionless with lambda/sub mfp/ > 100 mirror lengths, had T/sub e/ = 10 eV, T/sub i/ = 30 eV and was found to have anomalous resistivity scaling like eta = ..sqrt..T/sub e//n/sub e/ when E/sub parallel/ > E/su c/ is the Dreicer critical field. The 10/sup 12/cm/sup -3/ plasma was collisional with lambda/sub mfp/ < mirror length, had T/sub e/ = T/sub i/ approx. = .2 eV and was found to have Spitzer resistivity when E/sub parallel/ < E/sub c/.

Brouchous, D. A.

1980-11-01

33

Octupole effects in the lanthanides  

International Nuclear Information System (INIS)

Arrays of Anti-Compton Spectrometer enabled systematic investigations of octupole correlations in the neutron-rich lanthanides. The studies mostly confirm the theoretical expectations of moderate octupole deformation at medium spins in nuclei from this region but in some cases predictions deviate from the experiment. In cesium isotopes strong octupole effects are predicted but not observed and new measurements for 139Xe suggest octupole effects stronger than expected. Systematics of excitation energy of the 31 states excitations, updated in the present work for Xe isotopes, indicates the N=85 and Z=54 lines as borders for strong octupole correlations. Systematic of electric dipole moment, upgraded in the present work for Ca and Ce isotopes confirms the Z=54 limit and adds new information about local canceling of electric dipole moment at the N=90 neutron number

1999-07-02

34

Neutron star deformation due to multipolar magnetic fields  

Science.gov (United States)

Certain multiwavelength observations of neutron stars, such as intermittent radio emissions from rotation-powered pulsars beyond the pair-cascade death line, the pulse profile of the magnetar SGR 1900+14 after its 1998 August 27 giant flare and X-ray spectral features of PSR J0821-4300 and SGR 0418+5729, suggest that the magnetic fields of non-accreting neutron stars are not purely dipolar and may contain higher order multipoles. Here, we calculate the ellipticity of a non-barotropic neutron star with (i) a quadrupole poloidal-toroidal field, and (ii) a purely poloidal field containing arbitrary multipoles, deriving the relation between the ellipticity and the multipole amplitudes. We present, as a worked example, a purely poloidal field comprising dipole, quadrupole and octupole components. We show the correlation between field energy and ellipticity for each multipole, that the l = 4 multipole has the lowest energy, and that l = 5 has the lowest ellipticity. We show how a mixed multipolar field creates an observationally testable mismatch between the principal axes of inertia (to be inferred from gravitational wave data) and the magnetic inclination angle. Strong quadrupole and octupole components (with amplitudes ˜102 times higher than the dipole) in SGR 0418+5729 still yield ellipticity ˜10-8, consistent with current gravitational wave upper limits. The existence of higher multipoles in fast-rotating objects (e.g. newborn magnetars) has interesting implications for the braking law and hence phase tracking during coherent gravitational wave searches.

Mastrano, A.; Lasky, P. D.; Melatos, A.

2013-09-01

35

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

36

Multi-dimensional potential energy surfaces and non-axial octupole correlations in actinide and transfermium nuclei from relativistic mean field models  

CERN Document Server

We have developed multi-dimensional constrained covariant density functional theories (MDC-CDFT) for finite nuclei in which the shape degrees of freedom \\beta_{\\lambda\\mu} with even \\mu, e.g., \\beta_{20}, \\beta_{22}, \\beta_{30}, \\beta_{32}, \\beta_{40}, etc., can be described simultaneously. The functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the non-linear or density-dependent couplings. For the pp channel, either the BCS approach or the Bogoliubov transformation is implemented. The MDC-CDFTs with the BCS approach for the pairing (in the following labelled as MDC-RMF models with RMF standing for "relativistic mean field") have been applied to investigate multi-dimensional potential energy surfaces and the non-axial octupole $Y_{32}$-correlations in N=150 isotones. In this contribution we present briefly the formalism of MDC-RMF models and some results from these models. The potential energy surfaces with and without triaxial deformatio...

Lu, Bing-Nan; Zhao, En-Guang; Zhou, Shan-Gui

2013-01-01

37

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 report contains a general overview of the Earth's magnetic field. The different sources that contribute to the total magnetic field are presented and the diverse variations in the field are describ...

Edda Lína Gunnarsdóttir 1988

2012-01-01

38

The Declining Magnetic Field  

Science.gov (United States)

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

39

Lower hybrid heating associated with mode conversion on the Wisconsin octupole  

Energy Technology Data Exchange (ETDEWEB)

This thesis addresses the following key issues in the lower hybrid frequency range: 1. What are the importent physics aspects of wave propagation and heating in an experimental situation. 2. How effective is plasma heating in the complex magnetic field configuration of the octupole. Experimental work is accomplished by launching 1-10ms pulses of up to 40kW of radio frequency power at 140MHz corresponding to the hot plasma lower hybrid resonance in the octupole. A diploe antenna which is moveable radially and is also rotatable couples wave power to the plasma. Coupling efficiencies greater than 95% are achieved by proper antenna placement near the edge of the plasma radial density profile.

Owens, T.L.

1979-08-01

40

Octupole Deformed Nuclei in the Actinide Region  

CERN Multimedia

% IS322 \\\\ \\\\ The aim of the present study is to investigate the limits of the "island" of octupole deformation in the mass region A=225. It is of particular importance to demonstrate experimentally the sudden disappearance of the stable octupole deformation in the presence of a well developed quadrupole field. \\\\ \\\\In order to establish the upper border line the $\\beta$ decay chains of $^{227}$Rn $\\rightarrow ^{227}$Fr $\\rightarrow ^{227}$Ra and $^{231}$Fr $\\rightarrow ^{231}$Ra $\\rightarrow ^{231}$Ac were studied at PSB-ISOLDE using advanced fast timing and $\\gamma$-ray spectroscopy techniques. The lifetimes of the excited states have been measured in the picosecond range using the time-delayed $\\beta\\gamma\\gamma$(t) method.

Thorsteinsen, T; Rubio barroso, B; Simpson, J; Gulda, K; Sanchez-vega, M; Cocks, J; Nybo, K; Garcia borge, M; Aas, A; Fogelberg, B; Honsi, J; Smith, G; Naumann, R; Grant, I

2002-01-01

 
 
 
 
41

PHOTODETACHMENT IN MAGNETIC FIELDS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The behavior of the photodetachment cross section, near threshold, for atomic negative ions in a magnetic field is described and illustrated with data on photodetachment of electrons from negative sulfur ions. The effect of the final state interaction is discussed and the photodetachment of atomic negative ions in a magnetic field is compared to photoionization of neutral atoms in a magnetic field. New data on the photodetachment cross section of a molecular negative ion, SeH-, in a magnetic ...

1982-01-01

42

Magnetic fields in galaxies  

CERN Multimedia

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

43

Experimental tests for stable octupole deformation in actinium-227  

Energy Technology Data Exchange (ETDEWEB)

The question of intrinsic reflection asymmetry or stable-octupole deformation in /sup 227/Ac was studied by the single-proton stripping reactions /sup 226/Ra(/sup 3/He,d)/sup 227/Ac with E/sub 3He/ = 30 MeV and /sup 226/Ra(..cap alpha..,t)/sup 227/Ac with E/sub ..cap alpha../ = 30 MeV and by measuring the magnetic moment of the first excited 3/2/sup +/ state at 27.38 keV by a differential perturbed angular correlation (DPAC) experiment. Theoretical differential cross sections were determined using calculated nuclear structure factors with and without octupole-deformed Woods-Saxon model wave functions. Theoretical values for the magnetic moments of the ground state and first excited state with and without octupole deformation were determined using calculated intrinsic g-factors from folded Yukawa model wave functions. The results of the proton-stripping cross sections are inconclusive. No how comparison of the measured values for the magnetic moment of the first excited state with a previous measurement for the ground state seems to support stable octupole deformation in /sup 227/Ac. Therefore, the energy ordering of orbitals and the magnetic moment results are consistent and they seem to support a stable-octupole deformed shape for the ground state parity doublet in /sup 227/Ac. Furthermore, the results are consistent with the branching ratio determination of the magnetic moment of the first excited state in /sup 227/Ac which is in agreement with the stable-octupole model prediction.

Martz, H.E. Jr.

1986-01-01

44

Experimental tests for stable octupole deformation in actinium-227  

International Nuclear Information System (INIS)

The question of intrinsic reflection asymmetry or stable-octupole deformation in "2"2"7Ac was studied by the single-proton stripping reactions "2"2"6Ra("3He,d)"2"2"7Ac with E/sub 3He/ = 30 MeV and "2"2"6Ra(?,t)"2"2"7Ac with E/sub ?/ = 30 MeV and by measuring the magnetic moment of the first excited 3/2"+ state at 27.38 keV by a differential perturbed angular correlation (DPAC) experiment. Theoretical differential cross sections were determined using calculated nuclear structure factors with and without octupole-deformed Woods-Saxon model wave functions. Theoretical values for the magnetic moments of the ground state and first excited state with and without octupole deformation were determined using calculated intrinsic g-factors from folded Yukawa model wave functions. The results of the proton-stripping cross sections are inconclusive. No how comparison of the measured values for the magnetic moment of the first excited state with a previous measurement for the ground state seems to support stable octupole deformation in "2"2"7Ac. Therefore, the energy ordering of orbitals and the magnetic moment results are consistent and they seem to support a stable-octupole deformed shape for the ground state parity doublet in "2"2"7Ac. Furthermore, the results are consistent with the branching ratio determination of the magnetic moment of the first excited state in "2"2"7Ac which is in agreement with the stable-octupole model prediction

1986-01-01

45

Voyager 1 assessment of Jupiter's planetary magnetic field  

International Nuclear Information System (INIS)

A new estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with spherical harmonic model of the planetary field with both sets of parameters determined simulataneously by using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r>20 R/sub j/). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octupole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as is appropriate for centrifugal loading of the magnetosphere by a cold plasma. No statistically significant evidence is found for secular change of the equivalent dipole estimated from Pioneer 11 (1974.9) and Voyager 1 (1979.2) data

1982-05-01

46

Magnetic field measuring device  

International Nuclear Information System (INIS)

A coil is disposed to a beam secured at one end thereof for measuring magnetic fields at peripheries of reactor core plasmas. Electric current is supplied to the coil to cause electromagnetic force in magnetic fields to be measured, and the deformation amount of the beam is measured to determine low frequency components of the magnetic fields. High frequency components of the magnetic fields are measured based on output signals of a pick-up coil, and the two magnetic field components are synthesized to form one magnetic signal. Namely, the electromagnetic force acts as a bending moment of the beam, the beam is deformed, and the deformation amount is in proportion to the bending moment. Therefore, if a resistance wire is disposed to one end of the beam so that the resistance wire shrinks by the deformation of the beam and the resistance value is changed, the magnetic field can be determined based on the changing amount of the resistance value. Since magnetic fields free from a drift ingredient of an integrator can be measured, magnetic fields can be measured for a long period of time at a predetermined accuracy, and since a semiconductor sensor is not used, magnetic fields having excellent radiation resistance can be provided. (N.H.)

1996-06-17

47

Construction and Operational Experience with a Superconducting Octupole Used to Trap Antihydrogen  

Energy Technology Data Exchange (ETDEWEB)

A superconducting octupole magnet has seen extensive service as part of the ALPHA experiment at CERN. ALPHA has trapped antihydrogen, a crucial step towards performing precision measurements of anti-atoms. The octupole was made at the Direct Wind facility by the Superconducting Magnet Division at Brookhaven National Laboratory. The magnet was wound with a six-around-one NbTi cable about 1 mm in diameter. It is about 300 mm long, with a radius of 25 mm and a peak field at the conductor of 4.04 T. Specific features of the magnet, including a minimal amount of material in the coil and coil ends with low multipole content, were advantageous to its use in ALPHA. The magnet was operated for six months a year for five years. During this time it underwent about 900 thermal cycles (between 4K and 100K). A novel operational feature is that during the course of data-taking the magnet was repeatedly shut off from its 950 A operating current. The magnet quenches during the shutoff, with a decay constant of 9 ms. Over the course of the five years, the magnet was deliberately quenched many thousands of times. It still performs well.

Wanderer P.; Escallier, J.; Marone, A.; Parker, B.

2011-09-06

48

Magnetic Field Example 1  

Science.gov (United States)

Clicking on the different links below will produce different magnetic fields in the box above. The wires (perpendicular to the screen) or coils (in and out of the screen) are not visible, but you can determine what they are from the field. You can also click on a point to read off the magnetic field at that place.

Christian, Wolfgang; Belloni, Mario

2008-02-19

49

Magnetic Fields of Stars  

Science.gov (United States)

Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

Bychkov, V. D.; Bychkova, L. V.; Madej, J.

50

The Earth's Magnetic Field  

Science.gov (United States)

The magnetic field of the Earth is contained in a region called the magnetosphere. The magnetosphere prevents most of the particles from the sun, carried in solar wind, from hitting the Earth. This site, produced by the University Corporation for Atmospheric Research (UCAR), uses text, scientific illustrations,and remote imagery to explain the occurrence and nature of planetary magnetic fields and magnetospheres, how these fields interact with the solar wind to produce phenomena like auroras, and how magnetic fields of the earth and other planets can be detected and measured by satellite-borne magnetometers.

51

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

International Nuclear Information System (INIS)

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

2012-04-01

52

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

53

Magnetic fields at Neptune  

International Nuclear Information System (INIS)

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

1989-12-15

54

Hall Attractor in Axially Symmetric Magnetic Fields in Neutron Star Crusts  

Science.gov (United States)

We find an attractor for an axially symmetric magnetic field evolving under the Hall effect and subdominant Ohmic dissipation, resolving the question of the long-term fate of the magnetic field in neutron star crusts. The electron fluid is in isorotation, analogous to Ferraro's law, with its angular velocity being approximately proportional to the poloidal magnetic flux, ? ??. This equilibrium is the long-term configuration of a magnetic field evolving because of the Hall effect and Ohmic dissipation. For an initial dipole-dominated field, the attractor consists mainly of a dipole and an octupole component accompanied by an energetically negligible quadrupole toroidal field. The field dissipates in a self-similar way: Although higher multipoles should decay faster, the toroidal field mediates transfer of energy into them from the lower ones, leading to an advection diffusion equilibrium and keeping the ratio of the poloidal multipoles almost constant. This has implications for the structure of the intermediate-age neutron stars, suggesting that their poloidal field should consist of a dipole and an octupole component accompanied by a very weak toroidal quadrupole. For initial conditions that have a higher multipole ? structure, the attractor consists mainly of ? and ?+2 poloidal components.

Gourgouliatos, Konstantinos N.; Cumming, Andrew

2014-05-01

55

Mapping Magnetic Field Lines  

Science.gov (United States)

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

56

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

57

The Heliospheric Magnetic Field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as ...

2013-01-01

58

Magnetic field control device  

International Nuclear Information System (INIS)

The device of the present invention enables PID control to provide high speed response upon conducting feedback control of magnetic fields for confining plasmas of a thermonuclear device. That is, the device of the present invention receives a detection signal VB from a detection coil which is in proportion to a differentiated value of magnetic fields, together with a measured value Bdf for magnetic fields as an input. A signal prepared by intaking VB in the form of negative feedback control to a PI control signal obtained by proportionating/integration of a deviation between the Bdf and an aimed magnetic field value Brf, is defined as a control signal. The control signal is outputted to an electromagnet coil power source. D control, which has not be realized in the existent device, can be attained in the present invention, in addition to PI control. As a result, response speed of the magnetic field device can be improved compared with the prior art. (I.S.)

1991-02-04

59

Superconducting film magnetization in weak magnetic fields  

International Nuclear Information System (INIS)

A study is made on dependences of M magnetization on H magnetic field intensity (H2Cu3O7-? films in magnetic field, perpendicular to film plane. Correlation of hysteresis curves of film and massive sample magnetization was conducted. It is shown that M(H) dependences of films differ sufficiently from corresponding curves of massive samples

1990-01-01

60

ISR Radial Field Magnet  

CERN Multimedia

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

1983-01-01

 
 
 
 
61

Cosmic magnetic fields  

CERN Multimedia

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

62

Magnetic Field and Life  

Science.gov (United States)

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

63

Solar Magnetic Fields  

CERN Multimedia

This review provides an introduction to the generation and evolution of the Sun's magnetic field, summarising both observational evidence and theoretical models. The eleven year solar cycle, which is well known from a variety of observed quantities, strongly supports the idea of a large-scale solar dynamo. Current theoretical ideas on the location and mechanism of this dynamo are presented. The solar cycle influences the behaviour of the global coronal magnetic field and it is the eruptions of this field that can impact on the Earth's environment. These global coronal variations can be modelled to a surprising degree of accuracy. Recent high resolution observations of the Sun's magnetic field in quiet regions, away from sunspots, show that there is a continual evolution of a small-scale magnetic field, presumably produced by small-scale dynamo action in the solar interior. Sunspots, a natural consequence of the large-scale dynamo, emerge, evolve and disperse over a period of several days. Numerical simulation...

Hood, Alan W

2011-01-01

64

A review of experimental evidence for octupole deformation  

International Nuclear Information System (INIS)

Experimental evidence for octupole correlations, which lead to octupole instability and octupole deformation of some nuclei, is illustrated through typical examples. Data are considered for both the 220 < A < 230 region and for a few medium mass nuclei

1986-01-01

65

Nuclear magnetic resonance and earth magnetic field  

International Nuclear Information System (INIS)

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

1998-03-01

66

High field superconducting magnets  

Science.gov (United States)

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

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

2011-01-01

67

Cryogenically cooled octupole ion trap for spectroscopy of biomolecular ions  

Science.gov (United States)

We present here the design of a linear octupole ion trap, suitable for collisional cryogenic cooling and spectroscopy of large ions. The performance of this trap has been assessed using ultraviolet (UV) photofragmentation spectroscopy of protonated dipeptides. At the trap temperature of 6.1 K, the vibrational temperature of the ions reaches 9.1 K, although their estimated translational temperature is ˜150 K. This observation suggests that, despite the significant translational heating by radio-frequency electrical field, vibrational cooling of heavy ions in the octupole is at least as efficient as in the 22-pole ion traps previously used in our laboratory. In contrast to the 22-pole traps, excellent radial confinement of ions in the octupole makes it convenient for laser spectroscopy and boosts the dissociation yield of the stored ions to 30%. Overlap of the entire ion cloud by the laser beam in the octupole also allows for efficient UV depletion spectroscopy of ion-He clusters. The measured electronic spectra of the dipeptides and the clusters differ drastically, complicating a use of UV tagging spectroscopy for structural determination of large species.

Boyarkin, Oleg V.; Kopysov, Vladimir

2014-03-01

68

Nuclear Magnetic Resonance and Magnetic Field Measurements  

Science.gov (United States)

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

2012-01-04

69

The earth's magnetic field  

International Nuclear Information System (INIS)

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

1983-01-01

70

Magnetic fields and stellar evolution  

International Nuclear Information System (INIS)

The author reviews the present state of knowledge regarding magnetic fields and stellar evolution. Two explanations of stellar magnetic fields are discussed: contemporary dynamo action maintaining the magnetic field and, a slowly decaying relic of either the galactic field pervading the gas from which the star formed, or of dynamo action in an earlier epoch in the star's life. (Auth.)

1980-07-25

71

Magnetic Fields, Flares & Forecasts  

Science.gov (United States)

A 2D wavelet transform modulus maxima (WTMM) method is used to characterise the complexity of the distribution of the photospheric magnetic field of active regions. The WTMM method offers increased accuracy and reliability over previous fractal and multifractal methods. The multifractal spectrum of both quiet Sun and active region magnetic features are presented. It is shown that the multifractal nature of the quiet Sun is significantly different from that of an active region. As such, a method is proposed to seperate the information corresponding to the multifractal spectrum of an active region from the surrounding quite Sun texture. The WTMM method and segmentation procedure are shown to detect the internal restructuring of active region magnetic features prior to flaring. We detect two thresholds (Haussdorf dimension > 1.2 and Holder Exponent > -0.7) as possible indicators for conditions favourable to flaring.

Conlon, Paul A.; Kestener, P.; McAteer, R.; Gallagher, P.

2009-05-01

72

Octupole correlations in the heavy elements  

Energy Technology Data Exchange (ETDEWEB)

The effects of octupole correlations on the nuclear structure of the heavy elements are discussed. The cluster model description of the heavy elements is analyzed. The relevance of 2/sup 6/-pole deformation and fast El transitions to an octupole model is considered. 30 refs., 21 figs., 1 tab.

Chasman, R.R.

1986-01-01

73

Octupole correlations in the heavy elements  

International Nuclear Information System (INIS)

The effects of octupole correlations on the nuclear structure of the heavy elements are discussed. The cluster model description of the heavy elements is analyzed. The relevance of 26-pole deformation and fast El transitions to an octupole model is considered. 30 refs., 21 figs., 1 tab

1986-06-05

74

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

75

Octupole softness of 146 Nd  

International Nuclear Information System (INIS)

The nucleus 146 Nd was studied through the reaction 136 Xe (13 C, 3 n?) at a beam-energy of 54 MeV. The experiment was carried out at NBI, Denmark, with the NORDBALL detector array and a cryogenic target. The use of the large NORDBALL detector array enabled us to obtain good statistics, a total number of ? 100 million ?-? coincidence events being recorded. The ?-? coincidence data were analyzed and for most transitions a DCO ratio was obtained. The level scheme presents relatively long chains of intraband E1 ?-rays linking sequences of stretched E2 gammas, generally observed in the region. The enhanced E1 transition rates in nuclei from the Ba - Sm region was theoretically predicted to be a consequence of the octupole instability (or octupole softness). In this respect, the measured B(E1)/B(E2) branching ratios, related to B(E2) values taken from systematics, indicate a large average value of D0 ? 0.20 efm for the intrinsic dipole moment of medium spins. (Author)

1992-09-21

76

The Galactic Magnetic Field  

CERN Multimedia

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

77

Magnetic Field Topology in Jets  

Science.gov (United States)

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

Gardiner, T. A.; Frank, A.

2000-01-01

78

Low field magnetic resonance imaging  

Science.gov (United States)

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

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

2010-07-13

79

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

80

Magnetic fields in galactic haloes  

CERN Document Server

Magnetic fields on a range of scales play a large role in the ecosystems of galaxies, both in the galactic disk and in the extended layers of gas away from the plane. Observing magnetic field strength, structure and orientation is complex, and necessarily indirect. Observational data of magnetic fields in the halo of the Milky Way are scarce, and non-conclusive about the large-scale structure of the field. In external galaxies, various large-scale configurations of magnetic fields are measured, but many uncertainties about exact configurations and their origin remain. There is a strong interaction between magnetic fields and other components in the interstellar medium such as ionized and neutral gas and cosmic rays. The energy densities of these components are comparable on large scales, indicating that magnetic fields are not passive tracers but that magnetic field feedback on the other interstellar medium components needs to be taken into account.

Haverkorn, Marijke

2011-01-01

 
 
 
 
81

Low Cost Magnetic Field Controller  

CERN Document Server

The Physics Institute of the University of São Paulo (IFUSP) is building a continuous wave (cw) racetrack microtron. This machine has several dipole magnets, like the first and second stage recirculators, and a number of smaller ones in the transport line. These magnets must produce very stable magnetic fields to allow the beam to recirculate along very precise orbits and paths. Furthermore, the fields must be reproducible with great accuracy to allow an easier setup of the machine, though the effects of hysteresis tend to jeopardize the reproducibility. If the magnetic field is chosen by setting the current in the coils, temperature effects over the magnet and power supply tend to change the field. This work describes an inexpensive magnetic field controller that allows a direct measure of the magnetic field through an Hall probe. It includes a microcontroller running a feedback algorithm to control the power supply, in order to keep the field stable and reproducible. The controller can also execu...

Malafronte, Alexandre A

2005-01-01

82

Octupole vibrations at high angular momenta  

CERN Document Server

Properties of octupole vibrations in rapidly rotating nuclei are discussed. Microscopic RPA calculations based on the cranked shell model are performed to investigate the interplay between rotation and vibrations. The ability of this model to describe the properties of collective vibrations built on the ground bands in rare-earth and actinide nuclei is demonstrated at high angular momentum. The octupole vibrational states in even-even superdeformed Hg nuclei are also predicted and compared with available experimental data. A new interpretation of the observed excited superdeformed bands invoking these octupole bands is proposed.

Nakatsukasa, T

1995-01-01

83

Poloidal magnetic field fluctuations  

International Nuclear Information System (INIS)

Elementary non-linear tearing-mode theory in a two-dimensional cylindrical geometry is used to predict accurately the amplitude of the m=2 poloidal-magnetic-field fluctuations (Mirnov oscillations) at the limiter of a tokamak. The input required is the electron temperature radial profile from which the safety factor profile can be inferred. The saturation amplitude of the m=2 tearing mode is calculated from the safety factor profile using a non-linear ?' analysis. This gives an absolute result (no arbitrary factors) for the amplitude of the perturbation in the poloidal magnetic field everywhere and, in particular, at the limiter. An analysis of ORMAK and T-4 safety factor profiles (inferred from electron temperature profiles) gives results that are in agreement with the experimental data. - A study of a general profile shows that, as a function of the safety factor at the limiter, a maximum occurs in the amplitude of the Mirnov oscillation. The magnitude of the maximum increases with a decrease in temperature near the limiter. (author)

1979-01-01

84

The Heliospheric Magnetic Field  

Directory of Open Access Journals (Sweden)

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

Mathew J. Owens

2013-11-01

85

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

86

Photonic Magnetic Field Sensor  

Science.gov (United States)

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

Wyntjes, Geert

2002-02-01

87

Voyager 1 assessment of Jupiter's planetary magnetic field  

Energy Technology Data Exchange (ETDEWEB)

A new estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with spherical harmonic model of the planetary field with both sets of parameters determined simulataneously by using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r>20 R/sub j/). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octupole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as is appropriate for centrifugal loading of the magnetosphere by a cold plasma. No statistically significant evidence is found for secular change of the equivalent dipole estimated from Pioneer 11 (1974.9) and Voyager 1 (1979.2) data.

Connerney, J.E.P.; Acuna, M.H.; Ness, N.F.

1982-05-01

88

Magnetic Fields in Stellar Jets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Although several lines of evidence suggest that jets from young stars are driven magnetically from accretion disks, existing observations of field strengths in the bow shocks of these flows imply that magnetic fields play only a minor role in the dynamics at these locations. To investigate this apparent discrepancy we performed numerical simulations of expanding magnetized jets with stochastically variable input velocities with the AstroBEAR MHD code. Because the magnetic fi...

Hartigan, P.; Frank, A.; Varniere, P.; Blackman, E.

2007-01-01

89

Scattering by magnetic fields  

CERN Multimedia

Consider the scattering amplitude $s(\\omega,\\omega^\\prime;\\lambda)$, $\\omega,\\omega^\\prime\\in{\\Bbb S}^{d-1}$, $\\lambda > 0$, corresponding to an arbitrary short-range magnetic field $B(x)$, $x\\in{\\Bbb R}^d$. This is a smooth function of $\\omega$ and $\\omega^\\prime$ away from the diagonal $\\omega=\\omega^\\prime$ but it may be singular on the diagonal. If $d=2$, then the singular part of the scattering amplitude (for example, in the transversal gauge) is a linear combination of the Dirac function and of a singular denominator. Such structure is typical for long-range scattering. We refer to this phenomenon as to the long-range Aharonov-Bohm effect. On the contrary, for $d=3$ scattering is essentially of short-range nature although, for example, the magnetic potential $A^{(tr)}(x)$ such that ${\\rm curl} A^{(tr)}(x)=B(x)$ and $=0$ decays at infinity as $|x|^{-1}$ only. To be more precise, we show that, up to the diagonal Dirac function (times an explicit function of $\\omega$), the scattering amplitude has only a w...

Yafaev, D R

2005-01-01

90

Solar magnetic fields and activity  

International Nuclear Information System (INIS)

The author summarizes the experience of a solar observer dealing with the dynamics of solar background magnetic fields formation, including the development of new active regions magnetic fluxes. Single active regions occurrences, complexes of activity and proton-flare region related large-scale regular magnetic patterns growths are investigated. The meaning and importance of magnetic active longitudes are indicated. The physical background of magnetic fields generation in connection with convection, differential rotation and especially with the photospheric surface kinematics of the background fields is discussed. (Auth.)

1982-01-01

91

Design of multi-element corrector magnet for NewSUBARU  

International Nuclear Information System (INIS)

An octupole-base corrector magnet of multi-elements was designed. The new corrector magnets will be installed in the electron storage ring NewSUBARU in place of vertical steering (dipole) magnets in 2010. The new magnet will have coil windings to produce skew quadrupole, skew sextupole, normal octupole, and the skew dipole field. The skew dipole element will work as a vertical steering. The skew quadrupole and the skew sextupole elements are for the resonance correction. The normal octupole element will be use to control the higher order dispersion function and the higher order momentum compaction factor of the ring. In designing the magnet, a consideration to a field interference with the neighboring magnet was an important issue, because the yoke length, space between the yokes and the bore diameter are comparable. The field interference was calculated using OPERA-3D. (author)

2009-08-05

92

Primordial Magnetic Fields in Cosmology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Brown, Iain A.

2008-01-01

93

Status of the Production of the LHC Superconducting Corrector Magnets  

CERN Document Server

The Large Hadron Collider (LHC) will be equipped with a large number (6400) of superconducting corrector magnets. These magnets are powerful, with typical peak fields of 3-4 T on the coils, but at the same time compact and of low cost. There are many types: sextupoles, octupoles and decapoles to correct the main dipole field, dipoles, quadrupoles, sextupoles and octupoles to condition the proton beams and several nested correctors from dipole to dodecapole in the inner triplets. The sizes vary from 6 kg, 110 mm long, nested decapole-octupole spool pieces to 1800 kg, 1.4m long, trim quadrupoles. The fabrication of the 11 different types of magnets is assured by 10 contracts placed at 6 firms, two of which are in India. A number of magnets are now in series production, others in their pre-series production. The paper describes the present state of the fabrication and the testing of these magnets.

Allitt, M; Karppinen, M; Mazet, J; Wolf, R

2004-01-01

94

Atoms in high magnetic fields  

International Nuclear Information System (INIS)

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

1977-01-01

95

Theory of fossil magnetic field  

CERN Document Server

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

Dudorov, Alexander E

2014-01-01

96

On the unique structure of the magnetic fields of Uranus and Neptune  

Science.gov (United States)

The magnetic fields of Uranus and Neptune, which have comparable dipole, quadrupole, and octupole harmonics, are unique in the present-day solar system, but they resemble the geomagnetic field at the epochs of excursions and reversals known from paleomagnetic data. The precession dynamo model, in which the dominant role in the generation of the planetary magnetic fields is played by external gravitational forces, allows us to propose two scenarios for the formation of the unique topology of the magnetic fields of Uranus and Neptune. In the first case, tidal flows in the 'oceans' of these two planets extend down to the depths where the matter has a noticeable electric conductivity and velocity. A hydromagnetic interaction of the moving conducting fluid with the planetary magnetic field outside the generation region results in the deformation of the field and the deceleration of the motion under the action of the radial magnetic field. In the second case, the deformation of the field facilitates drastic changes in cyclonic cells within the generation region causing instabilities that result in a multi-polar field structure, excursions, and inversions. This paper considers this problem in greater detail by using the Neptune-Triton system as an example.

Dolginov, Sh. SH.

1993-01-01

97

Multipactor discharges in magnetic fields  

International Nuclear Information System (INIS)

In the high frequency electric field in vacuum, discharge occurs at a small electric field which does not cause discharge in the case of DC. This is because the number of electrons is doubled due to the emission of secondary electrons from an electrode synchronizing with the high frequency electric field, and it is called multipactor discharge. The multipactor discharge occurs also in nuclear fusion experimental apparatuses, and has drawn attention. The research on the multipactor discharge when a magnetic field exists is few. The authors carried out the experiment on the multipactor discharge in 100 MHz zone in the statical magnetic field up to about 0.08 T, and the theoretical analysis on the voltage at which discharge begins in a vertical magnetic field corresponding to [Angular frequency of electron cyclotron ?(c)]/(Angular frequency of high frequency field ?) < 1. The experimental result and the theoretical analysis result agreed qualitatively. Moreover, the simple theoretical analysis on the monopole multipactor discharge in a vertical magnetic field was carried out. Accompanying the application of a vertical magnetic field, the region where both-pole multipactor discharge is possible moved in the direction of large voltage and f1(f: frequency, 1: distance between electrodes). Both-pole multipactor discharge is cut off at a certain magnetic flux density of a vertical magnetic field. (Kako, I.)

1986-01-01

98

Magnetic field-effect transistor  

International Nuclear Information System (INIS)

The magnetic control of the filamentary current flow during avalanche breakdown in a semiconductor at low temperatures represents an interesting new principle of a magnetic field-effect transistor. The power losses in such a device are minimized by using superconducting lines for the generation of the magnetic control field and for the interconnections. For such a hybrid concept, implementing semiconducting and superconducting components, the important performance characteristics are evaluated

1986-09-01

99

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

100

Design for the magnetic field requirements of the tandem mirror experiment  

International Nuclear Information System (INIS)

The tandem mirror magnetic geometry is described, followed by an analysis of the magnet set designed to meet the requirements of the TMX experiment. The final magnet line-up is composed of a baseball coil with two C coils for each plug, six solenoidal coils for the central cell, and two RC coils plus one octupole coil for each transition

1977-10-29

 
 
 
 
101

Resonant magnetic fields from inflation  

CERN Document Server

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

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

2012-01-01

102

Magnetic fields of the Sun  

International Nuclear Information System (INIS)

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

1986-11-01

103

Magnetic fields and scintillator performance  

International Nuclear Information System (INIS)

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

1995-01-01

104

Electrons in superstrong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Interaction of an electron moving in a superstrong magnetic field Hsub(c) is considered. To describe such quantum phemomena in Hsub(c) as dependence of radiative corrections to the ground state of the electron on H/Hsub(c) ratio, synchrotron radiation, anomalous magnetic moment of the electron, distortion of the Coulomb potential due to polarization of the electron vacuum, Dirac quantum mechanics is used. The state of the electron in the magnetic field of high intensity is described by the wave function which is the solution of the Dirac equation in which electron and field interaction is accurately taken into account.

Ternov, I.M.; Khalilov, V.R. (Moskovskij Gosudarstvennyj Univ. (USSR))

1983-05-01

105

Magnetic Field Effect Transistors.  

Science.gov (United States)

It has been demonstrated that magnetic Cr02 can be selectively deposited on semiconductor substrates and polymide resin plastics with feature resolution smaller than micron. In addition, hard coatings have been fabricated to protect active devices as well...

J. T. Spencer P. A. Dowben

1990-01-01

106

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

1984-02-13

107

Nuclear magnetic octupole moment and the hyperfine structure of the $5D_{3/2,5/2}$ states of the Ba$^+$ ion  

CERN Document Server

The hyperfine structure of the long-lived $5D_{3/2}$ and $5D_{5/2}$ levels of Ba$^+$ ion is analyzed. A procedure for extracting relatively unexplored nuclear magnetic moments $\\Omega$ is presented. The relevant electronic matrix elements are computed in the framework of the ab initio relativistic many-body perturbation theory. Both the first- and the second-order (in the hyperfine interaction) corrections to the energy levels are analyzed. It is shown that a simultaneous measurement of the hyperfine structure of the entire $5D_J$ fine-structure manifold allows one to extract $\\Omega$ without contamination from the second-order corrections. Measurements to the required accuracy should be possible with a single trapped barium ion using sensitive techniques already demonstrated in Ba$^+$ experiments.

Beloy, K; Dzuba, V A; Howell, G T; Blinov, B B; Fortson, E N

2008-01-01

108

N-flationary magnetic fields  

CERN Multimedia

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

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

2007-01-01

109

Solenoid magnet with homogeneous magnet field  

International Nuclear Information System (INIS)

This is preferably used in NMR imaging. It includes several attached coils, preferably Bitter coils, and some parameters such as coil length, coil spire thickness and outer diameter are chosen to get the field homogeneity and to optimize the product power-mass of the magnet

1984-12-14

110

ISR split-field magnet  

CERN Multimedia

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

1975-01-01

111

Toroidal magnetic field generation device  

International Nuclear Information System (INIS)

Purpose: To facilitate the assembly work and improve the reliability by disposing the main body of a toroidal magnetic field generation device to the inside of a vacuum container. Constitution: Surfaces of a coil container, a feedwater heater and each of the components exposed in vacuum are made of such material and configuration as suitable to the use in superhigh vacuum, and a toroidal electromagnet is cooled by water from outside of the vacuum container. Toroidal magnetic field can be formed in the vacuum by the toroidal magnetic field generation device main body disposed in the vacuum container, whereby complicated steps such as the assembly of the main body of the toroidal magnetic field generation device crossing to the outer circumferential surface of doughnut-shaped pipes can be saved. (Horiuchi, T.)

1981-01-01

112

ISR split-field magnet  

CERN Multimedia

The Split-Field-Magnet at the ISR with arrays of multiwire proportional chambers installed in its large aperture. The detection system is now in full action for experiments and the first results have been reported.

1974-01-01

113

Magnetic field effect on capillary rise of magnetic fluids  

International Nuclear Information System (INIS)

The objective of this work is to study the effect of the external uniform magnetic field on the height and dynamics of magnetic fluid ascension into a vertical cylindrical capillary. Due to demagnetization effects in the magnetic fluid, the height of ascension increases in the magnetic field longitudinal to the capillary and decreases in the transverse field, proportionally to the square of the magnetic fluid magnetization. Magnetic fluid ascension decelerates strongly in the transverse field

2005-03-01

114

Rigidity for periodic magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the motion of a charge on a conformally flat Riemannian torus in the presence of magnetic field. We prove that for any non-zero magnetic field there always exist orbits of this motion which have conjugate points. We conjecture that the restriction of conformal flatness of the metric is not essential for this result. This would provide a ``twisted'' version of the recent generalisation of Hopf's rigidity result obtained by Burago and Ivanov.

Bialy, M. L.

1999-01-01

115

Magnetic fields on the Sun  

International Nuclear Information System (INIS)

Synoptic observations of solar magnetic fields are discussed. Seen in long-term averages, the magnetic fields of the Sun show distinctive behavior. The active-region latitudes are characterized by magnetic fields of preceding polarity. The flow of following polarity fields to make up the polar fields is episodic, not continuous. This field motion is a directed poleward flow and is not due to diffusion. The total magnetic flux on the solar surface, which is related linearly to the calcium emission in integrated sunlight, varies from activity minimum to maximum by a factor of 2 or 3. Nearly all this flux is seen at active-region latitudes-only about 1% is at the poles. The total flux of the Sun disappears from the surface at a very rapid rate and is replaced by new flux. All the field and flux patterns that we see originate in active-region latitudes. The polar magnetic fields of the Sun were observed to change polarity recently. The variations of the full-disk solar flux are shown to lead to the proper rotation rate of the Sun, but the phase of the variations is constant for only a year or two at most

1981-01-01

116

Theorem on magnet fringe field  

International Nuclear Information System (INIS)

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 (bn) and skew (an) multipoles, By + iBx = summation(bn + ian)(x + iy)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 BL ? ? B(x,y,z)dz where the integration range starts well before the magnet and ends well after it. For bar an, bar bn, bar Bx, and bar By 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 |?p?|, the transverse deflection produced by the ion-gitudinal component of the fringe field at one magnet end relative to |?p0|, 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 Bx from the vicinity of one magnet end since, along a path parallel to the magnet axis such as path BC

1995-10-15

117

Field measurements for PETRA magnets  

International Nuclear Information System (INIS)

Two fast measuring machines have been built for measuring the great series of dipoles and focussing magnets for PETRA. The measuring system consists of a machine with a long moving integrating coil for measuring the dipoles and of a rotating coil system for an integral measurement of quadrupoles, sextupoles and other higher multipoles. Both machines are computer controlled. Results of field measurements for the first part of the series magnets are presented. The measurements show the profile of the integral field and the improvements due to end-field corrections. Magnets of the same type are compared as to integral field for gradient. The effect of different energizing cycles on the reproducibility of field setting is described. (author)

1977-09-02

118

Microscopic analysis of the octupole phase transition in Th isotopes  

CERN Document Server

A shape phase transition between stable octupole deformation and octupole vibrations in Th nuclei is analyzed in a microscopic framework based on nuclear density functional theory. The relativistic functional DD-PC1 is used to calculate axially-symmetric quadrupole-octupole constrained energy surfaces. Observables related to order parameters are computed using an interacting-boson Hamiltonian, with parameters determined by mapping the microscopic energy surfaces to the expectation value of the Hamiltonian in the boson condensate. The systematics of constrained energy surfaces and low-energy excitation spectra point to the occurrence of a phase transition between octupole-deformed shapes and shapes characterized by octupole-soft potentials.

Nomura, K; Lu, B -N

2013-01-01

119

To picosecond magnetic fields (abstract)  

Energy Technology Data Exchange (ETDEWEB)

The magnetic reversal mechanism in perpendicularly oriented, premagnetized Co based thin film alloys, induced by ultra short magnetic field exposure of a few picoseconds duration has been studied. Field pulses with a magnitude of several thousand Tesla were generated by the 50 GeV final focus electron beam at the Stanford Linear Accelerator Center (SLAC). Characteristic remanent domain patterns are observed in these films long after field exposure using polar Kerr microscopy. Complete reversal of the magnetization is found to occur during a single spin precession event of 6.0 ps duration where the inplane-field amplitude is greater or equal to the macroscopically determined perpendicular anisotropy field. Further, a wide transition range, dividing the reversed and nonreversed regions is observed which is broken into a quasi periodic stripe domain structure with stripe-width 0.3 {mu}m. As a main result of this experimental study we find that magnetization reversal on this time scale is solely governed by the intrinsic effective field, i.e., anisotropy- and demagnetization-field contributions, rather then by complex curling and buckling mechanisms. Unique insight into fundamental spin reversal mechanisms and their ultimate speed in thin magnetic recording films is provided by these experiments. {copyright} {ital 1996 American Institute of Physics.}

Heidmann, J. [IBM Storage Systems Division, 5600 Cottle Road, San Jose, California 95193 (United States); Weller, D. [IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Siegmann, H.C. [Swiss Federal Institute of Technology, Zurich (Switzerland); Garwin, E.L. [Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States)

1996-04-01

120

Mapping of confinement magnetic field  

International Nuclear Information System (INIS)

The present magnetic field confinement device for high temperature plasma consists of torus, and its representative tokamak basically has axisymmetry, but the symmetry is broken by various causes such as the errors in the devices and MHD instability. In asymmetric magnetic fields, the lines of magnetic force present chaotic state locally in the vicinity of the resonance magnetic surface due to the nonlinearity. In the study, for helical torus magnetic fields, the method of deriving approximately scalar potential and flux function (Hamiltonian) by double Fourier development method is proposed, and the example of application is shown. By this Hamiltonian, the information required for the design of devices can be obtained, and the chaotic state can be examined. The derivation of toroidal helical magnetic field is described. Toroidal helical flux function along the lines of magnetic force is shown. The example of the calculated helical pinch plasma is shown. The state of the tracks by the approximated Hamiltonian in the vicinity of the separatrix was examined by separatrix mapping. The results of having carried out the separatrix mapping 10,000 times are shown. (K.I.)

1994-04-01

 
 
 
 
121

Fabrication of multi-element corrector magnet for NewSUBARU  

International Nuclear Information System (INIS)

Multi-element octupole-base corrector magnets will be installed in the electron storage ring NewSUBARU in place of vertical steering (skew dipole) magnets. The new magnets use coil windings to produce the skew quadrupole, skew sextupole, normal octupole, and skew dipole fields. The skew dipole element is used to achieve vertical steering. We made six magnets. The yoke is a laminated core composed of 0.5 mm thick silicon steel plates. The number of coil turns for the dipole winding was changed from the calculation (129t and 92t) to 126t and 92t because of the space requirement. (author)

2010-08-04

122

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

123

Magnetic fields in neutron stars  

Science.gov (United States)

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

Viganò, Daniele

2013-09-01

124

MAGNETICALLY CONTROLLED ACCRETION FLOWS ONTO YOUNG STELLAR OBJECTS  

Energy Technology Data Exchange (ETDEWEB)

Accretion from disks onto young stars is thought to follow magnetic field lines from the inner disk edge to the stellar surface. The accretion flow thus depends on the geometry of the magnetic field. This paper extends previous work by constructing a collection of orthogonal coordinate systems, including the corresponding differential operators, where one coordinate traces the magnetic field lines. This formalism allows for an (essentially) analytic description of the geometry and the conditions required for the flow to pass through sonic points. Using this approach, we revisit the problem of magnetically controlled accretion flow in a dipole geometry, and then generalize the treatment to consider magnetic fields with multiple components, including dipole, octupole, and split monopole contributions. This approach can be generalized further to consider more complex magnetic field configurations. Observations indicate that accreting young stars have substantial dipole and octupole components, and that accretion flow is transonic. If the effective equation of state for the fluid is too stiff, however, the flow cannot pass smoothly through the sonic points in steady state. For a multipole field of order l, we derive a general constraint on the polytropic index, n > l + 3/2, required for steady transonic flow to reach free-fall velocities. For octupole fields, inferred on surfaces of T Tauri stars, the index n > 9/2, so that the flow must be close to isothermal. The inclusion of octupole field components produces higher densities at the stellar surface and smaller areas for the hot spots, which occur at higher latitudes; the magnetic truncation radius is smaller (larger) for octupole components that are aligned (anti-aligned) with the stellar dipole. This contribution thus increases our understanding of magnetically controlled accretion for young stellar objects and can be applied to a variety of additional astrophysical problems.

Adams, Fred C. [Michigan Center for Theoretical Physics, Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States); Gregory, Scott G. [Department of Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)

2012-01-01

125

Magnetic fields of neutron stars  

CERN Document Server

Neutron stars contain the strongest magnetic fields known in the Universe. In this paper, I discuss briefly how these magnetic fields are inferred from observations, as well as the evidence for their time-evolution. I show how these extremely strong fields are actually weak in terms of their effects on the stellar structure, as is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes. I propose a scenario in which a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) is established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, becau...

Reisenegger, Andreas

2013-01-01

126

Magnetic field tomography, helical magnetic fields and Faraday depolarization  

Science.gov (United States)

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

Horellou, C.; Fletcher, A.

2014-07-01

127

Reconnection of magnetic field lines  

International Nuclear Information System (INIS)

Magnetic field line diffusion in a plasma is studied on the basis of the non-linear boundary layer equations of dissipative, incompressible magnetohydrodynamics. Non-linear steady state solutions for a class of plasma parameters have been obtained which are consistent with the boundary conditions appropriate for reconnection. The solutions are self-consistent in connecting a stagnation point flow of a plasma with reconnecting magnetic field lines. The range of the validity of the solutions, their relation to other fluid models of reconnection, and their possible applications to space plasma configurations are pointed out. (Author)

1990-07-16

128

Statistics of Magnetic Fields for OB Stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on an analysis of the catalog of magnetic fields, we have investigated the statistical properties of the mean magnetic fields for OB stars. We show that the mean effective magnetic field ${\\cal B}$ of a star can be used as a statistically significant characteristic of its magnetic field. No correlation has been found between the mean magnetic field strength ${\\cal B}$ and projected rotational velocity of OB stars, which is consistent with the hypothesis about a fossil ...

Kholtygin, A. F.; Fabrika, S. N.; Drake, N. A.; Bychkov, V. D.; Bychkova, L. V.; Chountonov, G. A.; Burlakova, T. E.; Valyavin, G. G.

2010-01-01

129

Simulations of magnetic fields in filaments  

CERN Multimedia

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

130

Magnetically Controlled Accretion Flows onto Young Stellar Objects  

CERN Multimedia

(abridged) Accretion from disks onto young stars is thought to follow magnetic field lines from the inner disk edge to the stellar surface. The accretion flow thus depends on the geometry of the magnetic field. This paper extends previous work by constructing a collection of orthogonal coordinate systems, including the corresponding differential operators, where one coordinate traces the magnetic field lines. This formalism allows for an (essentially) analytic description of the geometry and the conditions required for the flow to pass through sonic points. Using this approach, we revisit the problem of magnetically controlled accretion flow in a dipole geometry, and then generalize the treatment to consider magnetic fields with multiple components, including dipole, octupole, and split monopole contributions. This approach can be generalized further to consider more complex magnetic field configurations. Observations indicate that accreting young stars have substantial dipole and octupole components, and tha...

Adams, Fred C

2011-01-01

131

ATLAS Cavern Magnetic Field Calculations  

CERN Document Server

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

132

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

133

Lithium in strong magnetic fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic structure of the lithium atom in a strong magnetic field 0 <= gamma <= 10 is investigated. Our computational approach is a full configuration interaction method based on a set of anisotropic Gaussian orbitals that is nonlinearly optimized for each field strength. Accurate results for the total energies and one-electron ionization energies for the ground and several excited states for each of the symmetries ^20^+, ^2(-1)^+, ^4(-1)^+, ^4(-1)^-, ^2(-2)^+, ^4(-2)^...

Al-hujaj, O. -a; Schmelcher, P.

2004-01-01

134

Perturbation analysis of octupoles in circular accelerators  

International Nuclear Information System (INIS)

The octupole effects in a circular accelerator are analyzed using a first-order canonical perturbation theory. It is shown that, to the first order, the nonlinear amplitude-dependent tune shifts due to an octupole are composed of two types: terms of second order and terms of fourth order in betatron-oscillation amplitudes. The fourth-order part of tune shifts is expressed in terms of distortion functions. Distortion functions are also expanded in harmonics to express the higher-order tune shifts in harmonically expanded form. Finally, the results are applied to an accelerator and compared with the results of numerical tracking of particles. Laskar's algorithm for numerical analysis of the fundamental frequency is used to determine tunes from the tracking data, in which the error becomes inversely proportional to the cube of the number of data points. (author)

1998-06-01

135

Perturbation analysis of octupoles in circular accelerators  

Energy Technology Data Exchange (ETDEWEB)

The octupole effects in a circular accelerator are analyzed using a first-order canonical perturbation theory. It is shown that, to the first order, the nonlinear amplitude-dependent tune shifts due to an octupole are composed of two types: terms of second order and terms of fourth order in betatron-oscillation amplitudes. The fourth-order part of tune shifts is expressed in terms of distortion functions. Distortion functions are also expanded in harmonics to express the higher-order tune shifts in harmonically expanded form. Finally, the results are applied to an accelerator and compared with the results of numerical tracking of particles. Laskar`s algorithm for numerical analysis of the fundamental frequency is used to determine tunes from the tracking data, in which the error becomes inversely proportional to the cube of the number of data points. (author)

Moohyun Yoon [Dept. of Physics, Pohang Univ. of Science and Technology (POSTECH), Pohang (Korea, Republic of)

1998-06-01

136

Galactic and Extragalactic Magnetic Fields  

CERN Document Server

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

Beck, Rainer

2008-01-01

137

Majorana neutrinos and magnetic fields  

International Nuclear Information System (INIS)

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

138

Chiral transition with magnetic fields  

CERN Multimedia

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses, taken as functions of the order parameter, can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling const...

Ayala, Alejandro; Mizher, Ana Julia; Rojas, Juan Cristobal; Villavicencio, Cristian

2014-01-01

139

A Fiber Magnetic Field Sensor  

International Nuclear Information System (INIS)

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

2008-08-25

140

Transverse Magnetic Field Propellant Isolator  

Science.gov (United States)

An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

Foster, John E.

2000-01-01

 
 
 
 
141

Octupole softness of superdeformed sup 194 Pb  

Energy Technology Data Exchange (ETDEWEB)

Using parity projection and the generator-coordinate method we investigate the left-right-asymmetric softness of the superdeformed minimum of {sup 194}Pb. The collective wave functions exhibit large octupole dipsersions. Our calculation suggests that above the ground-state superdeformed band there should exist a negative-parity band of similar quadrupole deformation with an excitation energy close to 2 MeV.

Bonche, P.; Krieger, S.J.; Weiss, M.S. (Department of Physics, Lawrence Livermore National Laboratory, Livermore, California 94550 (USA)); Dobaczewski, J. (Institute of Theoretical Physics, Warsaw University, Hoza 69, PL-00681 Warsaw (Poland)); Flocard, H. (Division de Physique Theorique, Institut de Physique Nucleaire, 91406 Orsay CEDEX (France)); Heenen, P. (Service de Physique Nucleaire Theorique, Universite Libre de Bruxelles, CP229, 1050 Bruxelles (Belgium))

1991-02-18

142

Deuteron electric quadrupole and octupole polarizabilities  

CERN Document Server

The direct transition-matrix approach to determination of the electric polarizabilities of quantum bound systems developed in my recent work is applied to study the electric multipole polarizabilities of a two-particle bound complex with a central interaction between the particles. Expressions for the electric quadrupole and octupole polarizabilities of the deuteron are derived and their values in the case of the S-wave separable interaction potential are calculated.

Kharchenko, V F

2012-01-01

143

Magnetic field source for dark mode spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper is focused on the study of two-dimensional magnetic field distribution used for the analysis of the samples containing magnetically active films by means of dark mode spectroscopy (DMS). The design of proposed electromagnet for in-plane magneto-optic configuration and the magnetic field model computation are presented together with the results obtained from magnetic field distribution measurement.

Frantisek Stanek; Jaromir Pistora; Michal Lesnak

2010-01-01

144

Magnetic pumping in spatially inhomogeneous magnetic fields  

International Nuclear Information System (INIS)

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

1975-01-01

145

Separation of magnetic field lines  

Energy Technology Data Exchange (ETDEWEB)

The field lines of magnetic fields that depend on three spatial coordinates are shown to have a fundamentally different behavior from those that depend on two coordinates. Unlike two-coordinate cases, a flux tube in a magnetic field that depends on all three spatial coordinates that has a circular cross section at one location along the tube characteristically has a highly distorted cross section at other locations. In an ideal evolution of a magnetic field, the current densities typically increase. Crudely stated, if the current densities increase by a factor {sigma}, the ratio of the long to the short distance across a cross section of a flux tube characteristically increases by e{sup 2{sigma}}, and the ratio of the longer distance to the initial radius increases as e{sup {sigma}}. Electron inertia prevents a plasma from isolating two magnetic field structures on a distance scale shorter than c/{omega}{sub pe}, which is about 10 cm in the solar corona, and reconnection must be triggered if {sigma} becomes sufficiently large. The radius of the sun, R{sub Circled-Dot-Operator }=7 Multiplication-Sign 10{sup 10}cm is about e{sup 23} times larger, so when {sigma} Greater-Than-Or-Equivalent-To 23, two lines separated by c/{omega}{sub pe} at one location can be separated by the full scale of any magnetic structures in the corona at another. The conditions for achieving a large exponentiation, {sigma}, are derived, and the importance of exponentiation is discussed.

Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2012-11-15

146

The Magnetic Fields of the Quiet Sun  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work reviews our understanding of the magnetic fields observed in the quiet Sun. The subject has undergone a major change during the last decade (quiet revolution), and it will remain changing since the techniques of diagnostic employed so far are known to be severely biased. Keeping these caveats in mind, our work covers the main observational properties of the quiet Sun magnetic fields: magnetic field strengths, unsigned magnetic flux densities, magnetic field inclina...

Almeida, J. Sanchez; Gonzalez, M. Martinez

2011-01-01

147

Neutrinos in Strong Magnetic Fields  

CERN Multimedia

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

148

Electron dynamics in inhomogeneous magnetic fields  

International Nuclear Information System (INIS)

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation. (topical review)

2010-06-30

149

Instability of ferrofluid magnetic drops under magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Bacri, J. C.; Salin, D.

1982-01-01

150

Zeeman tomography of magnetic white dwarfs II. The quadrupole-dominated magnetic field of HE 1045-0908  

CERN Multimedia

We report time-resolved optical flux and circular polarization spectroscopy of the magnetic DA white dwarf HE 1045-0908 obtained with FORS1 at the ESO VLT. Considering published results, we estimate a likely rotational period of Prot ~ 2.7 h, but cannot exclude values as high as about 9 h. Our detailed Zeeman tomographic analysis reveals a field structure which is dominated by a quadrupole and contains additional dipole and octupole contributions, and which does not depend strongly on the assumed value of the period. A good fit to the Zeeman flux and polarization spectra is obtained if all field components are centred and inclinations of their magnetic axes with respect to each other are allowed for. The fit can be slightly improved if an offset from the centre of the star is included. The prevailing surface field strength is 16 MG, but values between 10 and ~75MG do occur. We derive an effective photospheric temperature of HE 1045-0908 of Teff = 10000 +/- 1000 K. The tomographic code makes use of an extensiv...

Euchner, F; Jordan, S; Beuermann, K; Gänsicke, B T

2005-01-01

151

Magnetic field properties of SSC model dipole magnets.  

Science.gov (United States)

SSC 1.5m model dipole magnets were built and tested at Fermilab. Magnetic field properties were studied in term of transfer function variation and multipole components. The results were satisfactory. Observation of periodicity of remanent field along the ...

M. Wake R. Bossert J. Carson S. Delchamps T. S. Jaffery

1992-01-01

152

Magnetic fields and halos in spiral galaxies  

CERN Document Server

Radio continuum observations allow to reveal the magnetic field structure in the disk and halo of nearby spiral galaxies, their magnetic field strength and vertical scale heights. The spiral galaxies studied so far show a similar magnetic field pattern which is of spiral shape along the disk plane and X-shaped in the halo, sometimes accompanied by strong vertical fields above and below the central region of the disk. The strength of the halo field is comparable to that of the disk. The total and turbulent magnetic field strength is (weakly) increasing with the star formation. There are, however, indications that stronger star formation reduces the magnetic field regularity globally. The magnetic field in spiral galaxies is generally thought to be amplified and maintained by dynamo action. During the galaxy's formation and evolution the turbulent dynamo amplifies the field strength to energy equipartition with the turbulent gas, while the large-scale (mean-field) dynamo mainly orders the magnetic field. Hence,...

Krause, Marita

2014-01-01

153

Generation of magnetic fields for accelerators with permanent magnets  

International Nuclear Information System (INIS)

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

1994-01-26

154

Simulation Outside Magnetic Field of the Sun  

Directory of Open Access Journals (Sweden)

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

Zhiliang Yang

2011-06-01

155

QED in inhomogeneous magnetic fields  

CERN Document Server

A lower bound is placed on the fermionic determinant of Euclidean quantum electrodynamics in three dimensions in the presence of a smooth, finite--flux, static, unidirectional magnetic field \\mathbf{B}(\\mathbf{r})=(0,0,B(\\mathbf{r})), where B(\\mathbf{r})\\geq 0 or B(\\mathbf{r})\\leq 0 and \\mathbf r is a point in the xy\\mbox{-plane}. Bounds are also obtained for the induced spin for 2+1 dimensional QED in the presence of \\mathbf{B}(\\mathbf{r}). An upper bound is placed on the fermionic determinant of Euclidean QED in four dimensions in the presence of a strong, static, directionally-varying, square-integrable magnetic field \\mathbf{B}(\\mathbf{r}) on \\R^3 .

Fry, M P

1996-01-01

156

Cluster Magnetic Fields from Galactic Outflows  

CERN Document Server

We performed cosmological, magneto-hydrodynamical simulations to follow the evolution of magnetic fields in galaxy clusters, exploring the possibility that the origin of the magnetic seed fields are galactic outflows during the star-burst phase of galactic evolution. To do this we coupled a semi-analytical model for magnetized galactic winds as suggested by Bertone et.al. (2006) to our cosmological simulation. We find that the strength and structure of magnetic fields observed in galaxy clusters are well reproduced for a wide range of model parameters for the magnetized, galactic winds and do only weakly depend on the exact magnetic structure within the assumed galactic outflows. Although the evolution of a primordial magnetic seed field shows no significant differences to that of galaxy clusters fields from previous studies, we find that the magnetic field pollution in the diffuse medium within filaments is below the level predicted by scenarios with pure primordial magnetic seed field. We therefore conclude...

Donnert, J; Lesch, H; Müller, E

2008-01-01

157

Tunneling in a magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum tunneling between two potential wells in a magnetic field can be strongly increased when the potential barrier varies in the direction perpendicular to the line connecting the two wells and remains constant along this line. An oscillatory structure of the wave function is formed in the direction joining the wells. The resulting motion can be coherent like motion in a conventional narrow band periodic structure. A particle penetrates the barrier over a long distance w...

Ivlev, B.

2005-01-01

158

Passive Magnetic Shielding in Gradient Fields  

CERN Multimedia

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

Bidinosti, C P

2013-01-01

159

Studies on Somatosensory Evoked Magnetic Fields.  

Science.gov (United States)

Spatiotemporal patterns of somatosensory evoked magnetic fields to stimulation of upper and lower limb nerves were examined in healthy humans. The studies summarized here provide the first magnetic field maps over the primary foot projection area after li...

J. Huttunen

1987-01-01

160

Statistics of Magnetic Fields for OB Stars  

CERN Document Server

Based on an analysis of the catalog of magnetic fields, we have investigated the statistical properties of the mean magnetic fields for OB stars. We show that the mean effective magnetic field ${\\cal B}$ of a star can be used as a statistically significant characteristic of its magnetic field. No correlation has been found between the mean magnetic field strength ${\\cal B}$ and projected rotational velocity of OB stars, which is consistent with the hypothesis about a fossil origin of the magnetic field. We have constructed the magnetic field distribution function for B stars, $F({\\cal B})$, that has a power-law dependence on ${\\cal B}$ with an exponent of $\\approx -1.82$. We have found a sharp decrease in the function $F({\\cal B})$F for ${\\cal B}\\lem 400 G$ that may be related to rapid dissipation of weak stellar surface magnetic fields.

Kholtygin, A F; Drake, N A; Bychkov, V D; Bychkova, L V; Chountonov, G A; Burlakova, T E; Valyavin, G G

2010-01-01

 
 
 
 
161

Topological constraints in magnetic field relaxation  

CERN Document Server

Stability and reconnection of magnetic fields play a fundamental role in natural and man-made plasma. In these applications the field's topology determines the stability of the magnetic field. Here I will describe the importance of one topology quantifier, the magnetic helicity, which impedes any free decay of the magnetic energy. Further constraints come from the fixed point index which hinders the field to relax into the Taylor state.

Candelaresi, Simon

2013-01-01

162

Magnetic measurements of the correction and adjustment magnets of the main ring  

International Nuclear Information System (INIS)

Correction magnets correct the field imperfections and alignment errors of the main quadrupole and bend magnets. For reducing and controlling chromaticity there are 186 sextupoles and 78 octupoles, while for suppressing various resonances there are 12 normal and 18 skew sextupoles and 24 normal and 19 skew quadrupoles. Beam positions are individually controlled by 108 horizontal and 108 skew dipoles. This report includes results of the all Main Ring correction and adjustment magnet harmonic measurements. The measurement principle and basic equations are described

1986-01-01

163

"Magnetic Gradient" edge magnetoplasmons in non-uniform magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

It is shown that laterally inhomogeneous strong magnetic field applied to otherwise spatially homogeneous two-dimensional electron system (2DES) allows "magnetic gradient" or special magnetic-edge magnetoplasmons (MEMPs). This mechanism is different from usual "density gradient" edge magnetoplasmons. Symmetric and antisymmetric families of MEMPs are obtained. They are localized at magnetic field inhomogeneity (magnetic-edge). Both symmetric and antisymmetric MEMPs have the modes of opposite c...

Balev, O. G.; Larkin, Ivan

2013-01-01

164

Plastic scintillators in magnetic fields  

International Nuclear Information System (INIS)

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

1991-01-01

165

Superconducting vibrator with a trapped magnetic field  

International Nuclear Information System (INIS)

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

2000-06-01

166

Magnetic field quality analysis using ANSYS.  

Science.gov (United States)

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results...

D. Dell'Orco Y. Chen

1991-01-01

167

Magnetic field instability correction method  

International Nuclear Information System (INIS)

The gradient-echo methods, especially when long echo times are used, are more sensitive to magnetic field fluctuations than the pulse-echo methods. Such fluctuations can alter the phase of a gradient echo and cause artifacts in the images. The authors have developed a method, called echo-phase correction (EPC), which can considerably reduce these artifacts. In the EPC method the phase of the echo can be corrected by using the information about a special secondary echo. A low-field strength (400 G) MR imager was installed in an environment where strong external-field fluctuations exist. Very long gradient-echo times (up to 80 msec) could be used. Without phase correction, severe artifacts frequently appeared, but with the EPC method these artifacts were considerably reduced

1989-12-01

168

Solenoid magnet with homogeneous magnetic field  

International Nuclear Information System (INIS)

This resistive magnet is used noticeably for NMR imaging. It includes many coils, preferably Bitter coils; and some parameters as coil length, distances between coils, their outer diameter are chosen to optimize the product power-mass of the magnet

1984-12-14

169

Critical magnetic field ratio of anisotropic magnetic superconductors  

Energy Technology Data Exchange (ETDEWEB)

The upper critical field, the lower critical field and the critical magnetic field ratio of anisotropic magnetic superconductors are calculated by Ginzburg-Landau theory analytically. The effect of the Ginzburg-Landau parameter ({kappa}{sub 0}), magnetic susceptibility ({chi}) and magnetic-to-anisotropic parameter ratio ({theta}) on the critical field ratio are considered. We find that the value of critical field ratio increases with increasing {kappa}{sub 0} and {theta}, and decreases with increasing {chi}. The highest and the lowest value of critical field ratio is found in the diamagnetic superconductors and the ferromagnetic superconductors, respectively.

Changjan, A. [Prasarnmit Physics Research Unit, Department of Physics, Faculty of Science, Srinakharinwirot University, Bangkok 10110 (Thailand); Thailand Center of Excellence in Physics, Si Ayutthaya Road, Bangkok 10400 (Thailand); Department of Mathematics and Basic Science, Faculty of Science and Technology, Phathumwan Institute of Technology, Bangkok 10330 (Thailand); Udomsamuthirun, P., E-mail: udomsamut55@yahoo.co [Prasarnmit Physics Research Unit, Department of Physics, Faculty of Science, Srinakharinwirot University, Bangkok 10110 (Thailand); Thailand Center of Excellence in Physics, Si Ayutthaya Road, Bangkok 10400 (Thailand)

2011-01-15

170

Magnetic Helicity and Large Scale Magnetic Fields: A Primer  

CERN Document Server

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

Blackman, Eric G

2014-01-01

171

Graphene in high magnetic fields  

Science.gov (United States)

Carbon-based nano-materials, such as graphene and carbon nanotubes, represent a fascinating research area aiming at exploring their remarkable physical and electronic properties. These materials not only constitute a playground for physicists, they are also very promising for practical applications and are envisioned as elementary bricks of the future of the nano-electronics. As for graphene, its potential already lies in the domain of opto-electronics where its unique electronic and optical properties can be fully exploited. Indeed, recent technological advances have demonstrated its effectiveness in the fabrication of solar cells and ultra-fast lasers, as well as touch-screens and sensitive photo-detectors. Although the photo-voltaic technology is now dominated by silicon-based devices, the use of graphene could very well provide higher efficiency. However, before the applied research to take place, one must first demonstrates the operativeness of carbon-based nano-materials, and this is where the fundamental research comes into play. In this context, the use of magnetic field has been proven extremely useful for addressing their fundamental properties as it provides an external and adjustable parameter which drastically modifies their electronic band structure. In order to induce some significant changes, very high magnetic fields are required and can be provided using both DC and pulsed technology, depending of the experimental constraints. In this article, we review some of the challenging experiments on single nano-objects performed in high magnetic and low temperature. We shall mainly focus on the high-field magneto-optical and magneto-transport experiments which provided comprehensive understanding of the peculiar Landau level quantization of the Dirac-type charge carriers in graphene and thin graphite.

Orlita, Milan; Escoffier, Walter; Plochocka, Paulina; Raquet, Bertrand; Zeitler, Uli

2013-01-01

172

Effective magnetic moment of neutrinos in strong magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

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

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

2002-07-01

173

Quark Antiscreening at Strong Magnetic Field and Inverse Magnetic Catalysis  

CERN Document Server

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

Ferrer, E J; Wen, X J

2014-01-01

174

PROCESS OF PLANETS’ MAGNETIC FIELDS FORMATION  

Directory of Open Access Journals (Sweden)

Full Text Available Heated melt of the cores of the Sun and the planets is the basis of their permanent magnetic fields that, in interaction with the large-scale magnetic field of the Galaxy, condition on the action of their dynamo mechanisms which, on the basis of the speed of the Sun and the planets axial rotation in the galactic magnetic space, provide formation of variable magnetic fields of the Solar System planets.

E.V. Savich

2013-06-01

175

Aligned electric and magnetic Weyl fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the spacetimes admitting a direction for which the relative electric and magnetic Weyl fields are aligned. We give an invariant characterization of these metrics and study the properties of its Debever null vectors. The directions 'observing' aligned electric and magnetic Weyl fields are obtained for every Petrov type. The results on the no existence of purely magnetic solutions are extended to the wider class having homothetic electric and magnetic Weyl fields.

Sa?ez, Joan Josep Ferrando Juan Antonio

2003-01-01

176

HIGH MAGNETIC FIELD SPECTROSCOPY IN ASTROPHYSICS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The discovery of very large magnetic fields in white dwarf stars and neutron stars has stimulated interest in the spectroscopy of free atoms in high magnetic fields. We review the discovery of continuum polarization in certain white dwarf stars. We discuss the interpretation of the spectra of the magnetic white dwarfs and the confirmation of the presence of large fields. We describe recent investigations on a class of magnetic white dwarf binary stars (AM Herculis stars). Finally we mention t...

Garstang, R.

1982-01-01

177

Emission of magnetic fields from distribution lines  

International Nuclear Information System (INIS)

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

1988-01-01

178

Octupole focusing in transport and acceleration systems  

International Nuclear Information System (INIS)

The radio-frequency quadrupole (RFQ) linac is capable of accelerating high-current, low-velocity RFQ and higher velocity accelerating structures, the current bottleneck still typically occurs within the FRQ. This limiting current is quite high in most cases, but linacs with even higher currents may be required in the future. We have begun a study of higher multipole systems to determine their capability for focusing and accelerating very high currents. We have chosen first to examine a radio-frequency octupole (RFO) transport system, and have developed a smooth-approximation analytical description that includes the conditions for input radial matching of a zero space-charge beam. Further, we have constructed a multiparticle beam-dynamics simulation program that accepts the low-current matched beam and gradually increases the beam current as it is transported. This results in a matched high-current beam, and the procedure can be used to determine the saturation-current limit of a periodic octupole system. As expected, at high currents the beam develops a hollow radial distribution that reduces the space-charge defocusing; initial results show that high currents can be transported. For acceleration, we have formulated the design parameters for a section of RFO linac, including the potential function, acceleration, and focusing efficiencies, and the geometry of the radially modulated pole tips

1982-02-01

179

Persistence of octupole correlations in $^{231}/Ra$  

CERN Multimedia

The structure of /sup 231/Ra, the heaviest odd Ra nucleus currently accessible for detailed spectroscopic investigation, has been studied in the beta /sup -/ decay of /sup 231/Fr. The main purpose has been to verify whether fast B(E1) rates and significant octupole correlations recently established in /sup 229/Ra persist in /sup 231 /Ra, The excited states in /sup 231/Ra have been determined for the first time. Spins and parities have been deduced from conversion electron measurements, while level half-lives in the ps and ns ranges have been measured with the Advanced Time Delayed beta gamma gamma (t) method. The moderately fast B(E1) rates found for transitions connecting the lowest-lying K/sup pi /=5/2/sup +or-/ and K/sup pi /=1 /2/sup +or-/ bands, reveal the persistence of octupole collective effects in /sup 231/Ra, although the B(E1) rates are lower than in /sup 229/Ra. These findings reinforce the differences in the B(E1) systematics between isotonic Ra and Th nuclei. (42 refs).

Fraile-Prieto, L M; Mach, H; Boutami, R; Aas, A J; Fogelberg, B; Gracía-Raffi, L M; Grant, I S; Gulda, K; Hagebø, E; Kurcewicz, W; Kvasil, J; López, M J; Løvhøiden, G; Martínez, T; Rubio, B; Taín, J L; Tengblad, O

2001-01-01

180

Near-Field Magnetic Dipole Moment Analysis  

Science.gov (United States)

This paper describes the data analysis technique used for magnetic testing at the NASA Goddard Space Flight Center (GSFC). Excellent results have been obtained using this technique to convert a spacecraft s measured magnetic field data into its respective magnetic dipole moment model. The model is most accurate with the earth s geomagnetic field cancelled in a spherical region bounded by the measurement magnetometers with a minimum radius large enough to enclose the magnetic source. Considerably enhanced spacecraft magnetic testing is offered by using this technique in conjunction with a computer-controlled magnetic field measurement system. Such a system, with real-time magnetic field display capabilities, has been incorporated into other existing magnetic measurement facilities and is also used at remote locations where transport to a magnetics test facility is impractical.

Harris, Patrick K.

2003-01-01

 
 
 
 
181

Quark stars under strong magnetic fields  

CERN Document Server

Within the confined-isospin-density-dependent-quark-mass model, we study the properties of strange quark matter (SQM) and quark stars (QSs) under strong magnetic fields. The equation of state of SQM under a constant magnetic field is obtained self-consistently and the pressure perpendicular to the magnetic field is shown to be larger than that parallel to the magnetic field, implying that the properties of magnetized QSs generally depend on both the strength and the orientation of the magnetic fields distributed inside the stars. Using a density-dependent magnetic field profile which is introduced to mimic the magnetic field strength distribution in a star, we study the properties of static spherical QSs by assuming two extreme cases for the magnetic field orientation in the stars, i.e., the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial direction. Our r...

Chu, Peng-Cheng; Wang, Xin

2014-01-01

182

Neutron star deformation due to arbitrary-order multipolar magnetic fields  

CERN Document Server

Certain multi-wavelength observations of neutron stars, such as intermittent radio emissions from rotation-powered pulsars beyond the pair-cascade death line, the pulse profile of the magnetar SGR 1900+14 after its 1998 August 27 giant flare, and X-ray spectral features of PSR J0821-4300 and SGR 0418+5729, suggest that the magnetic fields of non-accreting neutron stars are not purely dipolar and may contain higher-order multipoles. Here, we calculate the ellipticity of a non-barotropic neutron star with (i) a quadrupole poloidal-toroidal field, and (ii) a purely poloidal field containing arbitrary multipoles, deriving the relation between the ellipticity and the multipole amplitudes. We present, as a worked example, a purely poloidal field comprising dipole, quadrupole, and octupole components. We show the correlation between field energy and ellipticity for each multipole, that the l=4 multipole has the lowest energy, and that l=5 has the lowest ellipticity. We show how a mixed multipolar field creates an ob...

Mastrano, Alpha; Melatos, Andrew

2013-01-01

183

Magnetization reversal of ferromagnetic nanoparticles under inhomogeneous magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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

Chang, Joonyeon [Nano Device Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of)]. E-mail: presto@kist.re.kr; Yi, Hyunjung [Nano Device Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Cheol Koo, Hyun [Nano Device Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Mironov, V.L. [Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod (Russian Federation); Gribkov, B.A. [Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod (Russian Federation); Fraerman, A.A. [Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod (Russian Federation); Gusev, S.A. [Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod (Russian Federation); Vdovichev, S.N. [Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod (Russian Federation)

2007-02-15

184

Preparation of pyrolytic magnetic carbon under magnetic field  

International Nuclear Information System (INIS)

We have prepared pyrolytic carbon samples from triethylamine and investigated their magnetic properties. A ferromagnetic sample was obtained from the pyrolysis products even at room temperature, with spontaneous magnetization of 5 x 10-1 emu/g at 300 K. The magnetization was decreased with increasing temperature up to 500 K, but increased above 550 K. After this measurement, it was found that the magnetization at 300 K was changed to 6 x 10-1 emu/g. Another ferromagnetic sample has been also prepared by pyrolysis under high magnetic field of 2 Tesla. The spontaneous magnetization of this field-pyrolysis sample is 1.3 emu/g, which is twice as large as that of the above-mentioned sample prepared without magnetic field. Therefore, the magnetic field may help to form a ferromagnetic structure in pyrolytic carbon.

2010-01-01

185

Magnetization reversal of ferromagnetic nanoparticles under inhomogeneous magnetic field  

International Nuclear Information System (INIS)

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

2007-02-01

186

Pulsed field magnets at the US NHMFL  

International Nuclear Information System (INIS)

The pulsed field facility of the National High Magnetic Field Laboratory (NHMFL) consists of four components. Now available are (1) explosive flux compression, (2) capacitor-driven magnets, and (3) a 20 T superconducting magnet. The fourth component, a 60 T quasi-continuous magnet, has been designed and is scheduled for installation in early 1995. All magnets have He-4 cryostats giving temperatures from room temperature (RT) to 2.2-1.5 K. Dilution refrigerators for the superconducting 20 T magnet and the 50 T pulsed magnet will be installed by early 1994. A wide range of experiments have been completed within the past year. ((orig.))

1993-11-10

187

Magnetic field effects on microwave absorbing materials  

Science.gov (United States)

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.

1991-01-01

188

Magnetic field waves at Uranus  

Science.gov (United States)

The research efforts funded by the Uranus Data Analysis Program (UDAP) grant to the Bartol Research Institute (BRI) involved the study of magnetic field waves associated with the Uranian bow shock. Upstream wave studies are motivated as a study of the physics of collisionless shocks. Collisionless shocks in plasmas are capable of 'reflecting' a fraction of the incoming thermal particle distribution and directing the resulting energetic particle motion back into the upstream region. Once within the upstream region, the backward streaming energetic particles convey information of the approaching shock to the supersonic flow. This particle population is responsible for the generation of upstream magnetic and electrostatic fluctuations known as 'upstream waves', for slowing the incoming wind prior to the formation of the shock ramp, and for heating of the upstream plasma. The waves produced at Uranus not only differed in several regards from the observations at other planetary bow shocks, but also gave new information regarding the nature of the reflected particle populations which were largely unmeasurable by the particle instruments. Four distinct magnetic field wave types were observed upstream of the Uranian bow shock: low-frequency Alfven or fast magnetosonic waves excited by energetic protons originating at or behind the bow shock; whistler wave bursts driven by gyrating ion distributions within the shock ramp; and two whistler wave types simultaneously observed upstream of the flanks of the shock and argued to arise from resonance with energetic electrons. In addition, observations of energetic particle distributions by the LECP experiment, thermal particle populations observed by the PLS experiment, and electron plasma oscillations recorded by the PWS experiment proved instrumental to this study and are included to some degree in the papers and presentations supported by this grant.

Smith, Charles W.; Goldstein, Melvyn L.; Lepping, Ronald P.; Mish, William H.; Wong, Hung K.

1994-01-01

189

Magnetic Gradient edge magnetoplasmons in non-uniform magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have theoretically studied two-dimensional electron gas placed in a strong laterally non-uniform magnetic field, which appears due to ferromagnetic film . We have found, that in this case 2DEG experiences static charge redistribution that strongly depends on presence and configuration of the gates on the surface of a heterostructure. Also, it is shown that lateral inhomogeneity of a strong magnetic field allows itself “magnetic gradient” or “magnetic-edge” magnetoplasmons due ...

Larkin, Ivan; Balev, O. G.

2012-01-01

190

Magnetic field properties of SSC model dipole magnets  

International Nuclear Information System (INIS)

SSC 1.5 m model dipole magnets were built and tested at Fermilab. Magnetic field properties were studied in term of transfer function variation and multipole components. The results were satisfactory. Observation of periodicity of remanent field along the axis is also reported. Based on the model magnet experience, Fermilab has already built two successful full scale magnets. (author) 12 refs.; 3 figs.; 3 tabs

1992-01-01

191

Electrolytic tiltmeters inside magnetic fields: Some observations  

International Nuclear Information System (INIS)

We present observations of the electrolytic clinometers behaviour inside magnetic field environments introducing phenomenological expressions to account for the measured output voltage variations as functions of field gradients and field strengths

2007-04-21

192

Electrolytic tiltmeters inside magnetic fields: Some observations  

Energy Technology Data Exchange (ETDEWEB)

We present observations of the electrolytic clinometers behaviour inside magnetic field environments introducing phenomenological expressions to account for the measured output voltage variations as functions of field gradients and field strengths.

Alberdi, J. [CIEMAT, Madrid (Spain); Arce, P. [CIEMAT, Madrid (Spain); Barcala, J.M. [CIEMAT, Madrid (Spain); Calvo, E. [CIEMAT, Madrid (Spain); Ferrando, A. [CIEMAT, Madrid (Spain)]. E-mail: antonio.ferrando@ciemat.es; Josa, M.I. [CIEMAT, Madrid (Spain); Luque, J.M. [CIEMAT, Madrid (Spain); Molinero, A. [CIEMAT, Madrid (Spain); Navarrete, J. [CIEMAT, Madrid (Spain); Oller, J.C. [CIEMAT, Madrid (Spain); Yuste, C. [CIEMAT, Madrid (Spain); Calderon, A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Garcia-Moral, L.A. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gomez, G. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Gonzalez-Sanchez, F.J. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Martinez-Rivero, C. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Matorras, F. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Rodrigo, T. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Ruiz-Arbol, P. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Scodellaro, L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Sobron, M. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Vila, I. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain); Virto, A.L. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander (Spain)

2007-04-21

193

Inertial fusion reactors and magnetic fields  

International Nuclear Information System (INIS)

The application of magnetic fields of simple configurations and modest strengths to direct target debris ions out of cavities can alleviate recognized shortcomings of several classes of inertial confinement fusion (ICF) reactors. Complex fringes of the strong magnetic fields of heavy-ion fusion (HIF) focusing magnets may intrude into reactor cavities and significantly affect the trajectories of target debris ions. The results of an assessment of potential benefits from the use of magnetic fields in ICF reactors and of potential problems with focusing-magnet fields in HIF reactors conducted to set priorities for continuing studies are reported. Computational tools are described and some preliminary results are presented

1985-03-03

194

Baking a magnetic-field display  

Science.gov (United States)

Copy machine developer powder is an alternative for creating permanent displays of magnetic fields. A thin layer of developer powder on a sheet of paper placed over a magnet can be baked in the oven, producing a lasting image of a magnetic field.

Cavanaugh, Terence; Cavanaugh, Catherine

1998-02-01

195

Electromagnetic showers in a strong magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the results concerning the main shower characteristics in a strong magnetic field obtained through shower simulation. The processes of magnetic bremsstrahlung and pair production were taken into account for values of the parameter $\\chi \\gg 1$. We compare our simulation results with a recently developed cascade theory in a strong magnetic field.

Anguelov, V.; Vankov, H.

2000-01-01

196

Asymmetric Diffusion of Magnetic Field Lines  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Stochasticity of magnetic field lines is important for particle transport properties. Magnetic field lines separate faster than diffusively in turbulent plasma, which is called superdiffusion. We discovered that this superdiffusion is pronouncedly asymmetric, so that the separation of field lines along the magnetic field direction is different from the separation in the opposite direction. While the symmetry of the flow is broken by the so-called imbalance or cross-helicity,...

Beresnyak, Andrey

2013-01-01

197

On Primordial Magnetic Fields of Electroweak Origin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider Vachaspati's primordial magnetic field which is generated at the electroweak phase transition. Assuming that either the gradients of the Higgs field or, alternatively, the magnetic field itself are stochastic variables with a normal distribution, we find that the resulting magnetic field has an {\\em rms} value in the present-day universe which is fully consistent with what is required for the galactic dynamo mechanism.

Enqvist, K.; Olesen, P.

1993-01-01

198

Quench antennas for RHIC quadrupole magnets  

Energy Technology Data Exchange (ETDEWEB)

Quench antennas for RHIC quadrupole magnets are being developed jointly by KEK and BNL. A quench antenna is a device to localize a quench origin using arrays of pick-up coils lined up along the magnet bore. Each array contains four pick-up coils: sensitive to normal sextupole, skew sextupole, normal octupole, and skew octupole field. This array configuration allows an azimuthal localization of a quench front while a series of arrays gives an axial localization and a quench propagation velocity. Several antennas have been developed for RHIC magnets and they are now routinely used for quench tests of production magnets. The paper discusses the description of the method and introduces a measured example using an antenna designed for quadrupole magnets.

Ogitsu, T.; Terashima, A.; Tsuchiya, K. [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan); Ganetis, G.; Muratore, J.; Wanderer, P. [Brookhaven National Lab., Upton, NY (United States)

1995-05-01

199

Birefringence of magnetic liquid in electric and magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

This paper studies birefringence under simultaneous application of electric and magnetic fields on a liquid. The anisotropy of the refractive index of colloids in the electric and magnetic fields is examined. The samples with magnetic liquid were low-concentration magnetite colloids in kerosene and transformer oil with oleic acid. It was found that, upon addition of the oleic acid, the birefringence of these dispersed media in the electric and magnetic fields is smaller by 6-7 orders of magnitude than in the magnetic colloid.

Chekanov, V.V.; Kozevnikov, V.M.; Padalka, V.V.; Skibin, Y.N.

1985-10-01

200

MR imaging at high magnetic fields  

International Nuclear Information System (INIS)

Recently, more investigators have been applying higher magnetic field strengths (3-4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the same set of imaging parameters at lower magnetic field strengths would provide differences in signal or contrast to noise ratios at 3 T or higher. Therefore, an outcome of the combined effect of all these factors should be considered to estimate the change in usefulness at different magnetic fields. The objective of this article is to illustrate the practical scientific applications, focusing on MR imaging, of higher magnetic field strength. First, we will discuss previous literature and our experiments to demonstrate several changes that lead to a number of practical applications in MR imaging, e.g. in relaxation times, effects of contrast agent, design of RF coils, maintaining a safety profile and in switching magnetic field strength. Second, we discuss what will be required to gain the maximum benefit of high magnetic field when the current magnetic field (?1.5 T) is switched to 3 or 4 T. In addition, we discuss MR microscopy, which is one of the anticipated applications of high magnetic field strength to understand the quantitative estimation of the gain benefit and other considerations to help establish a practically available imaging protocol

2003-04-01

 
 
 
 
201

Studies of a poloidal divertor reversed field pinch  

International Nuclear Information System (INIS)

Several attempts have been made to form a reversed field pinch (RFP) in a four-node, poloidal divertor configuration which positions the plasma far from a conducting wall. In this configuration, the plasma is localized within a magnetic separatrix formed by the combination of toroidal currents in the plasma and four, internal, conducting rings. These experiments were conducted on three devices: Tokapole II, the Wisconsin Levitated Octupole, and the modified Octupole with smaller conducting rings. Transient, RFP-like equilibria were obtained on Tokapole II and the Wisconsin Levitated Octupole. RFP-like equilibria with field reversal duration /approximately/1 msec were obtained in the small ring Octupole. None of these plasmas was sustained against resistive magnetic diffusion. Local, internal measurements of the magnetic field in Tokapole II plasmas indicated the plasma current and density were mostly confined to the region inside the magnetic separatrix. The sharp drop in plasma pressure near the separatrix generated a large diamagnetic current in that region. Large magnetic perturbations observed in the startup phase of these plasmas. On the small ring Octupole, the perturbation was measured to have a dominant poloidal mode number of m = 1 and toroidal mode numbers n /approximately/ /minus/5, i.e., internally resonant or nonresonant modes. This perturbation was stationary and was phase-locked to a magnetic field error. If the tenuous plasma region outside the separatrix is ''vacuum-like,'' then this behavior might represent current-driven instability owing to the lack of nearly, stabilizing boundary. Such instability is consistent with linear magnetohydrodynamic stability calculations and nonlinear simulations of a cylindrical REP plasma bounded by a large vacuum region and a distant conducting wall. 53 refs., 48 figs

1988-01-01

202

Dynamic shielding of the magnetic fields  

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents a comparative study of the methods used to control and compensate the direct and alternative magnetic fields. Two frequently used methods in the electromagnetic compatibility of the complex biomagnetism installations were analyzed. The two methods refer to the use of inductive magnetic field sensors (only for alternative fields and of fluxgate magnetometers as active transducers which measures both the direct and alternative components of the magnetic field. The applications of the dynamic control of the magnetic field are: control of the magnetic field of the military ships, control of parasite magnetic field produced by power transformers and the electrical networks, protection of the mass spectrometers, electronic microscopes, SQUID and optical pumping magnetometers for applications in biomagnetism.

RAU, M.

2010-11-01

203

Field free line magnetic particle imaging  

CERN Document Server

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

Erbe, Marlitt

2014-01-01

204

Magnetic field measurements of the superEBIS superconducting magnet  

International Nuclear Information System (INIS)

SuperEBIS was designed to have a solenoidal magnetic field of a 5 Tesla strength with a 120 cm long bore. The field was specified to be straight within 1 part in 10000 within the bore, and uniform to within 1 part in 1000 within the central 90 cm. Magnetic field measurements were performed with a computerized magnetic field measuring setup that was borrowed from W. Sampson's group. A preliminary test was made of a scheme to determine if the magnetic and mechanical axes of the solenoid coincided, and, if not, by how much

1994-01-01

205

Relativistic stars with purely toroidal magnetic fields  

CERN Document Server

We investigate the effects of the purely toroidal magnetic field on the equilibrium structures of the relativistic stars. The master equations for obtaining equilibrium solutions of relativistic rotating stars containing purely toroidal magnetic fields are derived for the first time. To solve these master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for calculating relativistic rotating stars containing no magnetic field to incorporate the effects of the purely toroidal magnetic fields. By using the numerical scheme, we then calculate a large number of the equilibrium configurations for a particular distribution of the magnetic field in order to explore the equilibrium properties. We also construct the equilibrium sequences of the constant baryon mass and/or the constant magnetic flux, which model the evolution of an isolated neutron star as it loses angular momentum via the gravitational waves. Important properties of the equilibrium configurations of the magnetized stars obtained in th...

Kiuchi, Kenta

2008-01-01

206

Nonlinear physics of twisted magnetic field lines  

Energy Technology Data Exchange (ETDEWEB)

Twisted magnetic field lines appear commonly in many different plasma systems, such as magnetic ropes created through interactions between the magnetosphere and the solar wind, magnetic clouds in the solar wind, solar corona, galactic jets, accretion discs, as well as fusion plasma devices. In this paper, we study the topological characterization of twisted magnetic fields, nonlinear effect induced by the Lorentz back reaction, length-scale bounds, and statistical distributions. (author)

Yoshida, Zensho [Department of Quantum Engineering, University of Tokyo, Tokyo (Japan)

1998-08-01

207

Tuning permanent magnets with adjustable field clamps  

International Nuclear Information System (INIS)

The effective length of a permanent-magnet assembly can be varied by adjusting the geometrical parameters of a field clamp. This paper presents measurements on a representative dipole and quadrupole as the field clamp is withdrawn axially or radially. The detailed behavior depends upon the magnet multipolarity and geometry. As a rule-of-thumb, a 3-mm-thick iron plate placed at one end plane of the magnet shortens the length by one-third of the magnet bore radius

1987-03-16

208

Observations of Cool-Star Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2012-01-01

209

Simultaneous quadrupole and octupole shape phase transitions in Thorium  

Energy Technology Data Exchange (ETDEWEB)

The evolution of quadrupole and octupole shapes in Th isotopes is studied in the framework of nuclear Density Functional Theory. Constrained energy maps and observables calculated with microscopic collective Hamiltonians indicate the occurrence of a simultaneous quantum shape phase transition between spherical and quadrupole-deformed prolate shapes, and between non-octupole and octupole-deformed shapes, as functions of the neutron number. The nucleus {sup 224}Th is closest to the critical point of a double phase transition. A microscopic mechanism of this phenomenon is discussed in terms of the evolution of single-nucleon orbitals with deformation.

Li, Z.P.; Song, B.Y.; Yao, J.M. [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China); Vretenar, D. [Physics Department, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia); Kavli Institute for Theoretical Physics China, CAS, Beijing 100190 (China); Meng, J., E-mail: mengj@pku.edu.cn [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Department of Physics, University of Stellenbosch, Stellenbosch (South Africa)

2013-11-04

210

Two-octupole-phonon states in 146,148Gd  

International Nuclear Information System (INIS)

Recently the multi-octupole-phonon states have been observed in 146,148Gd and the relevant B(E3) values have been measured. We give a report of our microscopic calculations on the collective multi-octupole-phonon-excited states in these nuclei by using the Dyson boson mapping method. It has been clarified that not only the strong collectivity in the octupole modes in these nuclei but also the coupling with the single-particle modes work together to bring about the highly enhanced B(E3) values in 148Gd. (author)

1995-03-01

211

FLINESH computer code for magnetic fields calculation  

International Nuclear Information System (INIS)

This paper describes the 'FLINESH' computer code for magnetic fields calculation developed for the simulation of field configurations in plasma magnetic confinement devices. The expressions for the poloidal field and flux, the program structure and the input parameters description are presented, and also the analysis of the graphic output possibilities. (L.C.J.A.). 12 refs, 14 figs, 2 tabs

1994-01-01

212

Damping of cosmic magnetic fields  

CERN Multimedia

We study the evolution of magnetic fields in an expanding plasma composed of relativistic and non-relativistic particles. We derive the dispersion relations for the propagating MHD modes---fast and slow magnetosonic, sonic, and Alfv\\'en waves---in the presence of viscosity and heat conductivity. We find that all four modes are damped on scales up to the particle diffusion length. The calculated dispersion relations and damping scales can be applied to any viscous plasma in which the pressure is dominated by relativistic particles. In particular, we examine the propagation of MHD modes in the early universe by deriving the appropriate sources of viscosity due to the decoupling of neutrinos and photons. Neutrino diffusion damps all modes on mass scales inside the horizon at the time of neutrino decoupling, M_{d\

Jedamzik, K; Olinto, A V

1998-01-01

213

Tunneling in a magnetic field  

CERN Multimedia

Quantum tunneling between two potential wells in a magnetic field can be strongly increased when the potential barrier varies in the direction perpendicular to the line connecting the two wells and remains constant along this line. An oscillatory structure of the wave function is formed in the direction joining the wells. The resulting motion can be coherent like motion in a conventional narrow band periodic structure. A particle penetrates the barrier over a long distance which strongly contrasts to WKB-like tunneling. The whole problem is stationary. A not very small tunneling transparency can be set between two quantum wires with real physical parameters and separated by a long potential barrier. The phenomenon is connected to Euclidean resonance.

Ivlev, B I

2005-01-01

214

Synchrotron Applications of High Magnetic Fields  

International Nuclear Information System (INIS)

This workshop aims at discussing the scientific potential of X-ray diffraction and spectroscopy in magnetic fields above 30 T. Pulsed magnetic fields in the range of 30 to 40 T have recently become available at Spring-8 and the ESRF (European synchrotron radiation facility). This document gathers the transparencies of the 6 following presentations: 1) pulsed magnetic fields at ESRF: first results; 2) X-ray spectroscopy and diffraction experiments by using mini-coils: applications to valence state transition and frustrated magnet; 3) R5(SixGe1-x)4: an ideal system to be studied in X-ray under high magnetic field?; 4) high field studies at the Advanced Photon Source: present status and future plans; 5) synchrotron X-ray diffraction studies under extreme conditions; and 6) projects for pulsed and steady high magnetic fields at the ESRF

2006-11-16

215

Static uniform magnetic fields and amoebae  

Energy Technology Data Exchange (ETDEWEB)

Three species of potentially pathogenic amoebae were exposed to 71 and 106.5 mT from constant homogeneous magnetic fields and examined for inhibition of population growth. The number of amoebae for three species was significantly less than controls after a 72 h exposure to the magnetic fields when the temperature was 20 C or above. Axenic cultures, i.e., cultures grown without bacteria, were significantly affected after only 24 h. In 20 of 21 tests using the three species, the magnetic field significantly inhibited the growth of amoebae. In one test in which the temperature was 20 C for 48 h, exposure to the magnetic field was not inhibitory. Final numbers of magnetic field-exposed amoebae ranged from 9 to 72% lower than the final numbers of unexposed controls, depending on the species. This research may lead to disinfection strategies utilizing magnetic fields for surfaces on which pathogenic amoebae may proliferate.

Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A. [Tennessee Technological Univ., Cookeville, TN (United States)

1997-03-01

216

Synchrotron Applications of High Magnetic Fields  

Energy Technology Data Exchange (ETDEWEB)

This workshop aims at discussing the scientific potential of X-ray diffraction and spectroscopy in magnetic fields above 30 T. Pulsed magnetic fields in the range of 30 to 40 T have recently become available at Spring-8 and the ESRF (European synchrotron radiation facility). This document gathers the transparencies of the 6 following presentations: 1) pulsed magnetic fields at ESRF: first results; 2) X-ray spectroscopy and diffraction experiments by using mini-coils: applications to valence state transition and frustrated magnet; 3) R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}: an ideal system to be studied in X-ray under high magnetic field?; 4) high field studies at the Advanced Photon Source: present status and future plans; 5) synchrotron X-ray diffraction studies under extreme conditions; and 6) projects for pulsed and steady high magnetic fields at the ESRF.

NONE

2006-07-01

217

Dirac neutrinos and primordial magnetic fields  

International Nuclear Information System (INIS)

We consider random primordial magnetic fields and discuss their dissipation, coherence length L0, scaling behaviour and constraints implied by the primordial nucleosynthesis. Such magnetic fields could excite the right-helicity states of Dirac neutrinos, with adverse consequences for nucleosynthesis. We present solutions to the spin kinetic equation of a Dirac neutrino traversing a random magnetic field in the cases of large and small L0, taking also into account elastic collisions. Depending on the scaling behaviour and on the magnetic coherence length, the lower limit on the neutrino magnetic moment thus obtained could be as severe as 10-20?B. ((orig.))

1995-02-20

218

High magnetic fields science and technology  

CERN Document Server

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

Miura, Noboru

2003-01-01

219

On the octupole excitation in 236U  

International Nuclear Information System (INIS)

Measurements of the K, Lsub(I), Lsub(II) and Msub(I) conversion lines of the 687.7 keV transition in 236U are evaluated within the electron penetration formalism. The spin-parity assignment of the octupole-band-head is found to be 1- in accordance with reaction data, and an assignment of 2- to the 687.7 keV state is ruled out. The penetration matrix element vertical strokeetavertical stroke has the value of 13.5 for the K-shell and increases slightly for higher main shells. An estimate of the anomalous amplitudes is compared with values reported for transitions in the odd even actinide nuclei. Furthermore electron conversion data for the 1-->2+ and 1-->4+ transitions are given. Radioactivity 236U from 235U(n,e-); measured: conversion electron decay; deduced: conversion coefficients from K, L and M shells; evaluated: dynamic matrix elements. (orig.)

1983-10-01

220

Fast nuclear rotation and octupole deformation  

CERN Document Server

The 150Sm nucleus has been studied to high spins in a measurement of gamma radiation following the 136Xe(18O,4n)150Sm, compound-nucleus reaction at beam energy of 76 MeV. The measurement was performed at NBI Riso using the NORDBALL array. Alternating parity, s=+1 band in 150Sm has been observed up to spin I=22. This band is crossed by two aligned bands, corresponding to a reflection-symmetric shape. After the second crossing the s=+1 band ends abruptly, suggesting that the octupole shape vanishes in 150Sm above spin I=22, as predicted by calculations. Other explanations, assuming continuation of the s=+1 band past the two alignments are also discussed.

Urban, W; Nyberg, J

2001-01-01

 
 
 
 
221

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

International Nuclear Information System (INIS)

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

2010-06-01

222

Rydberg molecule in a magnetic field  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Rydberg states of the NO molecule have been probed by two-color resonantly enhanced multiphoton ionization in a magnetic field of 0.93 T. Penetrating s and d states show strong interactions with the intramolecular field while nonpenetrating f states show stronger interactions with the external magnetic field. Competition between the molecular core anisotropy and the external field anisotropy leads to a greater variety of situations than in a Rydberg atom, ranging from a “weak field” regi...

Shafizadeh, N.; Raoult, M.; Horani, M.; Guizard, S.; Gauyacq, D.

1992-01-01

223

Evolution of superhigh magnetic fields of magnetars  

CERN Document Server

In this paper, we consider the effect of Landau levels on the decay of superhigh magnetic fields of magnetars. Applying ${}^3P_2$ anisotropic neutron superfluid theory yield a second-order differential equation for a superhigh magnetic field $B$ and its evolutionary timescale $t$. The superhigh magnetic fields may evolve on timescales $\\sim (10^{6}-10^{7})$ yrs for common magnetars. According to our model, the activity of a magnetar may originate from instability caused by the high electron Fermi energy.

Gao, Z F; Yuan, J P; Jiang, L; Song, D L; Qiao, E L

2013-01-01

224

Magnetic field effects on plasma ionization balance  

Energy Technology Data Exchange (ETDEWEB)

Magnetic fields give rise to several phenomena that can significantly affect ionization balance in a plasma. Theoretical models commonly used to determine the charge state distribution (viz., ) of ions in non-magnetized plasmas are reviewed first, for both equilibrium and non-equilibrium situations. Then, after a brief survey of laboratory and cosmic plasmas with strong fields, B > 10{sup 6} Gauss, some of the ways such magnetic fields influence are highlighted. Most key problems have yet to be tackled.

Weisheit, J.C.

1995-12-31

225

Stellarators with doublet configuration of magnetic field  

International Nuclear Information System (INIS)

The vacuum magnetic configurations of stellarators differing from the conventional ones only in possissing an additional quadrupole magnetic field uniform along the longitudinal coordinate are analytically studied. It is shown that by means of this field three-axes doublet configurations can be obtained in the stellarators. Their geometric and magnetic characteristics have been calculated. The systems with helical fields of different multipolarities are compared. 21 refs.; 4 figs

1989-01-01

226

Transient Magnetic Field in a Conducting Cylinder  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the paper we determine the transient magnetic field in a conducting cylinder placed in external longitudinal sine-shaped magnetic field using the solution of Bessell equation in cylindrical co-ordinates, and also applying integral Laplace transformations, attenuation and diffusion of the magnetic field strength in the cylinder. The resulting equations can be used to describe volume density of the power lost in the cylinder and to determine substitute parameters of the inductor-cylindrical ...

Zygmunt Piatek

2004-01-01

227

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

228

Electrons in an ultrastrong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Effects associated with the behavior of electrons in an ultrastrong magnetic field are examined on the basis of solutions of the Dirac equation, with precise allowance for electron-field interaction. Attention is given to electromagnetic emission from the electrons, radiative corrections in an ultrastrong field, and the modification of Coulomb's law in an ultrastrong field. As an example, an analysis is presented of the behavior of an electron in a superposition of magnetic and Coulomb fields, a problem that arises in the study of the properties of simple quantum-mechanical systems (a hydrogen atom or positronium) in the ultrastrong magnetic field of a pulsar.

Ternov, I.M.; Khalilov, V.R.

1983-05-01

229

Horizontal magnetic fields in the solar photosphere  

Science.gov (United States)

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI ?1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of ? 5 = 1( ? 5 denotes ? at ? = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3-6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.

Sheminova, V. A.

2009-05-01

230

Domestic magnetic fields. Protocols, measurements and results  

International Nuclear Information System (INIS)

The quantification of magnetic field exposure has been the subject of considerable debate. A number of surrogates have been used including, spot measurements, wire coding and 24 hour averages. The quantification of domestic magnetic fields including the identification of sources is important if any mitigation is required. The State Electricity Commission of Victoria has developed recording instrumentation and measurement protocols for the survey of domestic magnetic field strengths in the Melbourne area. A range of domestic locations in the Melbourne metropolitan area is chosen to test the influence of external installations and the effect of appliance usage and energy consumption on the domestic magnetic field environment. (author)

1992-05-17

231

Magnetic Fields in the Milky Way  

CERN Document Server

This chapter presents a review of observational studies to determine the magnetic field in the Milky Way, both in the disk and in the halo, focused on recent developments and on magnetic fields in the diffuse interstellar medium. I discuss some terminology which is confusingly or inconsistently used and try to summarize current status of our knowledge on magnetic field configurations and strengths in the Milky Way. Although many open questions still exist, more and more conclusions can be drawn on the large-scale and small-scale components of the Galactic magnetic field. The chapter is concluded with a brief outlook to observational projects in the near future.

Haverkorn, Marijke

2014-01-01

232

Flow Transitions in a Rotating Magnetic Field  

Science.gov (United States)

Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

Volz, M. P.; Mazuruk, K.

1996-01-01

233

Principles of power frequency magnetic field management  

International Nuclear Information System (INIS)

At the most general level, magnetic field management is the creation, elimination, or modification of sources in order to alter the spatial distribution of magnetic fields over some region of space. The two main options for magnetic field management are source modification (elimination or modification of original sources) and cancellation (creation of new sources). Source modification includes any changes in the layout or location of field sources, elimination of ground paths, or any options that increase the distance between sources and regions of interest. Cancellation involves the creation of new magnetic field sources, passive and/or active that produce magnetic fields that are opposite to the original fields in the region of interest. Shielding using materials of high conductivity and/or high permeability falls under the cancellation option. Strategies for magnetic field management, whether they are source modification or cancellation, typically vary on a case to case basis depending on the regions of interest, the types of sources and resulting complexity of the field structure, the field levels, and the attenuation requirements. This paper gives an overview of magnetic field management based on fundamental concepts. Low field design principles are described, followed by a structured discussion of cancellation and shielding. The two basic material shielding mechanisms, induced current shielding, and flux-shunting are discussed

1995-04-18

234

Reducing Field Distortion in Magnetic Resonance Imaging  

Science.gov (United States)

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob

2010-01-01

235

Magnetic field helicity in a coaxial discharge  

International Nuclear Information System (INIS)

The behavior of the dynamic sheath was studied for 4.4 kJ coaxial electrode discharge device operated with hydrogen gas at a pressure of 0.85 Torr. In normal mode operation, i.e. Without external magnetic field, it has been found that an induced axial magnetic field along the coaxial electrodes is created. With the application of 3.6 kg external axial magnetic field along the coaxial electrodes, both the plasma sheath current in the azimuthal direction, and the axial magnetic field, increased by about 2 times; during the first half cycle of discharge. For the second half cycle, results indicated that the self induced field is less than the applied axial magnetic field along the coaxial electrode. The applied field increase the rotating sheath current by 1.2 times. The experimental results of the azimuthal component of magnetic field B 0 along the axial electrodes indicated that ; the application of external magnetic field causes a decrease of B 0 to about 90%. Magnetic field helicity in a coaxial discharge. 4 figs

1994-01-01

236

An Intergalactic Magnetic Field from Quasar Outflows  

CERN Document Server

Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function magnetic field strength at different redshifts. We find that by a redshift z ~ 3, about 5-80% of the IGM volume is filled by magnetic fields with an energy density > 10% of the mean thermal energy density of a photo-ionized IGM (at ~ 10^4 K). As massive galaxies and X-ray clusters condense out of the magnetized IGM, the adiabatic compression of the magnetic field could result in the fields observed in these systems without a need for further dynamo amplification.

Furlanetto, S; Furlanetto, Steven; Loeb, Abraham

2001-01-01

237

Measuring Magnetic Fields in the Solar Atmosphere  

CERN Multimedia

Since the discovery by Hale in the early 1900s that sunspots harbor strong magnetic field, magnetism has become increasingly important in our understanding of processes on the Sun and in the Heliosphere. Many current and planned instruments are capable of diagnosing magnetic field in the solar atmosphere. Photospheric magnetometry is now well-established. However, many challenges remain. For instance, the diagnosis of magnetic field in the chromosphere and corona is difficult, and interpretation of measurements is harder still. As a result only very few measurements have been made so far, yet it is clear that if we are to understand the outer solar atmosphere we must study the magnetic field. I will review the history of solar magnetic field measurements, describe and discuss the three types of magnetometry, and close with an outlook on the future.

de Wijn, A G

2012-01-01

238

Solar Force-free Magnetic Fields  

Directory of Open Access Journals (Sweden)

Full Text Available The structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces like plasma pressure gradient and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishes. This can be obtained by either vanishing electric currents (leading to potential fields or the currents are co-aligned with the magnetic field lines. First we discuss a mathematically simpler approach that the magnetic field and currents are proportional with one global constant, the so-called linear force-free field approximation. In the generic case, however, the relation between magnetic fields and electric currents is nonlinear and analytic solutions have been only found for special cases, like 1D or 2D configurations. For constructing realistic nonlinear force-free coronal magnetic field models in 3D, sophisticated numerical computations are required and boundary conditions must be obtained from measurements of the magnetic field vector in the solar photosphere. This approach is currently of large interests, as accurate measurements of the photospheric field become available from ground-based (for example SOLIS and space-born (for example Hinode and SDO instruments. If we can obtain accurate force-free coronal magnetic field models we can calculate the free magnetic energy in the corona, a quantity which is important for the prediction of flares and coronal mass ejections. Knowledge of the 3D structure of magnetic field lines also help us to interpret other coronal observations, e.g., EUV images of the radiating coronal plasma.

Thomas Wiegelmann

2012-09-01

239

Magnetic field properties of SSC model dipole magnets  

International Nuclear Information System (INIS)

SSC 1.5m model dipole magnets were built and tested at Fermilab. Magnetic field properties were studied in term of transfer function variation and multipole components. The results were satisfactory. Observation of periodicity of remanent field along the axis is also reported

1992-03-24

240

Electron scattering from the octupole band in 238U  

International Nuclear Information System (INIS)

A simple model for nuclear surface vibrations in permanently deformed nuclei does well in reproducing electron scattering cross sections of rotational levels built on a K/sup ?/= 0- intrinsic octupole vibration in 238U

1978-03-06

 
 
 
 
241

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

242

Whistler Propagation in Nonuniform Magnetic Fields  

Science.gov (United States)

The propagation of whistler waves when the magnetic field presents gradients comparable or smaller to the plane wavelength has been studied. Such a magnetic field occurs when a Helmholtz coil is immersed in a uniform background magnetic field, leading to magnetic null regions and islands as well as closed field lines. Whistler wavepackets have been launched in three distinct regions of this magnetic configuration and detailed maps of their propagation been obtained in situ. The packets are observed to be trapped on closed field lines where they propagate as Gendrin modes. In contrast, when the packets are launched against the null regions,they are observed to propagate around the nulls. Hence, the oblique nature of whistlers is very evident as they travel in non-uniform field regions. (Work supported by DOE/NSF.)

Urrutia, J. M.; Stenzel, R. L.

2011-12-01

243

Beginning stages of local magnetic field formation  

International Nuclear Information System (INIS)

On the basis of the investigation of the initial stages of local magnetic field formation the conclusion was reached that the appearance of a new photospheric magnetic flux - which plays an important role in the background magnetic field development - is highly influenced both by the convectional elements of different modes and by its interrelation with old magnetic fields. It seems to be very difficult to explain the observed regularities by terms of the magnetic flux tube emergence only, the practically simultaneous development of active regions belonging to different solar hemispheres and even to different activity cycles in one relatively narrow ''unipolar sector'' of the background field. The same is true as regards the different role and speed of negative and positive polarity fields in new field formations. The importance of velocity measurements for the solution of observed phenomena is stressed. (author)

1981-01-01

244

Magnetic field decay in model SSC dipoles  

Energy Technology Data Exchange (ETDEWEB)

We have observed that some of our model SSC dipoles have long time constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 tesla for one to three hours and changes in the magnetic field were observed. One explanation for the observed field decay is time dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep for the observed field decay is discussed. 10 refs., 5 figs., 2 tabs.

Gilbert, W.S.; Althaus, R.F.; Barale, P.J.; Benjegerdes, R.W.; Green, M.A.; Green, M.I.; Scanlan, R.M.

1988-08-01

245

Structure of magnetic field in Tokamaks  

International Nuclear Information System (INIS)

Magnetic surfaces, necessary to plasma confinement, can be extinguished by resonant helical perturbations with small intensities due to plasma oscillations or external helical currents. The mapping of magnetic field is obtained intergrating numerically the differential equation of its lines. Criteria which evaluate the chaotic distribution of lines between resonant magnetic islands are presented. (M.C.K.)

1990-01-01

246

Mean magnetic field generation in sheared rotators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Blackman, Eric G.

1999-01-01

247

Magnetic field in Perseus spiral arm  

International Nuclear Information System (INIS)

The rotation measures data for extragalactic radio sources are used to estimate the value and direction of large-scale galactic magnetic field in the Perseus spiral arm. The field of a value of |B| ? 3.2 ?G lies in the galactic plane. It is directed along ? 280 deg in the opposite direction compared to the magnetic field in the local Orion arm. A variance of the field is of the other of ?B/B ? 1.4

1988-01-01

248

Field induced superconductivity in magnetically modulated films  

International Nuclear Information System (INIS)

The transport properties of Al superconducting thin films covering arrays of Co/Pt pinning centers of two different sizes are measured and compared. Detailed magnetization characterization of the dots allow us to gain control over the average magnetization of the dots through the application of an external magnetic field. By increasing the magnetization of the dots a gradually increasing shift of the superconducting phase boundary is observed. This shift is explained in terms of vortex-antivortex pair generation. It is shown that the resulting field-induced-superconductivity is strongly dependent on the size of the magnetic dots

2008-04-01

249

Hybrid stars in a strong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

We study the effects of high magnetic fields on the particle population and equation of state of hybrid stars using an extended hadronic and quark SU(3) non-linear realization of the sigma model. In this model the degrees of freedom change naturally from hadrons to quarks as the density and/or temperature increases. The effects of high magnetic fields and anomalous magnetic moment are visible in the macroscopic properties of the star, such as mass, adiabatic index, moment of inertia, and cooling curves. Moreover, at the same time that the magnetic fields become high enough to modify those properties, they make the star anisotropic. (orig.)

Dexheimer, V. [UFSC, Florianopolis (Brazil); Gettysburg College, Gettysburg, PA (United States); Negreiros, R. [Johann Wolfgang Goethe University, FIAS, Frankfurt (Germany); UFF, Instituto de Fisica, Niteroi (Brazil); Schramm, S. [Johann Wolfgang Goethe University, FIAS, Frankfurt (Germany)

2012-12-15

250

Diffusion of magnetic field via turbulent reconnection  

Science.gov (United States)

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar.

Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon

2010-05-01

251

Programming the control of magnetic field measurements  

International Nuclear Information System (INIS)

This paper gives a short review concerning the new NMR probe measurement control system. Then it presents the new program 'CYCLOCHAMP' attached to the magnetic field measurement which also allows to cycle the magnetic field inside the cyclotrons and to equilibrate it among the SSC sectors. (authors)

1998-01-01

252

Field configurations in Helical magnetic wigglers  

Energy Technology Data Exchange (ETDEWEB)

We consider the field configuration produced in a system of two intercalcated concentric coils of radius {ital a} and pitch {Lambda} carrying currents in opposite directions (magnetic wigglers). The magnetic field and vector potential inside are obtained exactly at the coils axis and in a multipole-type expansion off the axis. The effect of finite coils is also considered.

Calvo, M. (Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020A, Venezuela (VE)); Rendon, O. (Departamento de Fisica, Universidad Simon Bolivar, Apartado Postal 80659, Caracas 1080-A, (Venezuela))

1990-01-01

253

METALLIC GLASSES CAST IN MAGNETIC FIELD  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fe-Cr-B metallic glass ribbons were prepared in a magnetic field applied during the melt stage or when the ribbon part had already solidified. The Curie temperature of the alloy was modified by adding Cr to separate the effect of the field on solidification from the influence of magnetic annealing.

Potocky?, L.; Kisdi-koszo?, E?; Lovas, A.; Poga?ny, L.; Kre?n, E.; Kova?c, J.; Nova?k, L.; Kolla?r, P.

1988-01-01

254

Lattice Planar QED in external magnetic field  

CERN Document Server

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

Cea, Paolo; Giudice, Pietro; Papa, Alessandro

2011-01-01

255

Magnetic Field Line Stickiness in Tokamaks  

CERN Document Server

We present simulated figures of the diverted magnetic field lines of the tokamak ITER, obtained by numerically integrating a Hamiltonian model with electrical currents in five wire loops and control coils. We show evidences of a sticky island embedded in the chaotic region near the divertor plates, which traps magnetic field lines for many toroidal turns increasing their connection lengths to these plates.

Martins, Caroline G L; Caldas, I L

2013-01-01

256

Two-axis magnetic field sensor  

Science.gov (United States)

A ferromagnetic thin-film based magnetic field sensor with first and second sensitive direction sensing structures each having a nonmagnetic intermediate layer with two major surfaces on opposite sides thereof having a magnetization reference layer on one and an anisotropic ferromagnetic material sensing layer on the other having a length in a selected length direction and a smaller width perpendicular thereto and parallel to the relatively fixed magnetization direction. The relatively fixed magnetization direction of said magnetization reference layer in each is oriented in substantially parallel to the substrate but substantially perpendicular to that of the other. An annealing process is used to form the desired magnetization directions.

Jander, Albrecht (Inventor); Nordman, Catherine A. (Inventor); Qian, Zhenghong (Inventor); Smith, Carl H. (Inventor)

2006-01-01

257

The generation of cosmic magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

Most of the magnetic fields of cosmic objects are generated and maintained by dynamo action of the motions of electrically conducting fluids. A brief survey on observational facts concerning cosmic magnetic fields is given. Some basic principles of magnetofluiddynamics are explained. On this basis essential features of the dynamo theory of cosmic objects are developed, first on the kinematic level and later taking into account the full interaction between magnetic field and motion. Particular attention is paid on mean-field electrodynamics and mean-field magnetofluiddynamics and their application to mean-field dynamo models for objects showing irregular or turbulent motions and magnetic fields. A few explanations are given on dynamos in the Earth and the planets, in the Sun and stellar objects and in galaxies. (orig.)

Raedler, K.H. [Astrophysikalisches Inst. Potsdam (Germany)

2000-07-01

258

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

259

Fields from a relativistic magnetic explosion  

CERN Multimedia

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

Gourgouliatos, K N

2008-01-01

260

Sonoluminescence Coupling to an Applied Magnetic Field  

CERN Document Server

We investigate several means of coupling between a sonoluminescing bubble and an applied magnetic field. Recent experiments show a strong quadratic dependence between the forcing pressures required for stable sonoluminescence and magnetic field amplitude. However, all coupling mechanisms calculated here are at most one percent perturbations. The most likely explanation is a sensitive hydrodynamic effect linked to a relatively small but characteristically inhomogeneous magnetically induced pressure on the bubble wall. We suggest experiments to test this effect.

Di Donna, B A; Young, J B

1997-01-01

 
 
 
 
261

Local magnetic fields and muon states in some magnetic oxides  

International Nuclear Information System (INIS)

The local magnetic field Bsub(?) at the interstitial ?+ site is investigated in the magnetic oxides ?-Fe2O3, Cr2O3, Fe3O4 and the rare earth orthoferrites R FeO3 (R=Eu, Dy, Ho, Er, Y). The temperature dependence of (Bsub(?)) in zero applied field and the dependence of Bsub(?) on an external field applied along certain crystallographic directions have been measured. The determined precession frequencies ?=?Bsub(?) are plotted as a function of temperature. (Auth.)

1979-01-01

262

Exposure guidelines for steady magnetic fields  

International Nuclear Information System (INIS)

The powerful magnetic fields produced by many DOE energy-research experiments, including the Mirror Fusion Test Facility-B (MFTF-B) experiment at LLNL, necessitate the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers show that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. Further research is needed, however, to develop definitive exposure standards. An overview of the results of past research into the bioeffects of magnetic fields is presented, hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants are discussed, and the LLNL steady magnetic-field exposure guidelines are presented

1986-06-01

263

Structure of magnetic fields in intracluster cavities  

CERN Document Server

Observations of clusters of galaxies show ubiquitous presence of X-ray cavities, presumably blown by the AGN jets. We consider magnetic field structures of these cavities. Stability requires that they contain both toroidal and poloidal magnetic fields, while realistic configurations should have vanishing magnetic field on the boundary. For axisymmetric configurations embedded in unmagnetized plasma, the continuity of poloidal and toroidal magnetic field components on the surface of the bubble then requires solving the elliptical Grad-Shafranov equation with both Dirichlet and Neumann boundary conditions. This leads to a double eigenvalue problem, relating the pressure gradients and the toroidal magnetic field to the radius of the bubble. We have found fully analytical stable solutions. This result is confirmed by numerical simulation. We present synthetic X-ray images and synchrotron emission profiles and evaluate the rotation measure for radiation traversing the bubble.

Gourgouliatos, Konstantinos Nektarios; Lyutikov, Maxim

2010-01-01

264

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

2004-07-01

265

Polarized neutron diffraction in high magnetic fields  

International Nuclear Information System (INIS)

The use of magnetic fields in the general area of neutron scattering is briefly surveyed, and some specific areas of research are identified which would benefit by the availability of higher fields. Since most of the past work combining neutron scattering and high magnetic fields has involved the polarized neutron technique, a description of this technique is presented along with a discussion of experimental errors produced by the magnetic field. The current status of polarized-beam research in four areas is reviewed: induced form factors in transition metals, mixed-valence systems, Kondo systems and complicated paramagnets

1978-09-21

266

Warm inflation in presence of magnetic fields  

CERN Multimedia

We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales, which rises the possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger proper time method.

Piccinelli, Gabriella; Ayala, Alejandro; Mizher, Ana Julia

2013-01-01

267

Warm inflation in presence of magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales which rises de possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger's proper time method.

Piccinelli, Gabriella [Centro Tecnológico, FES Aragón, Universidad Nacional Autónoma de México, Avenida Rancho Seco S/N, Bosques de Aragón, Nezahualcóyotl, Estado de México 57130 (Mexico); Sánchez, Ángel [Department of Physics, University of Texas at El Paso, El Paso, Texas 79968 (United States); Ayala, Alejandro; Mizher, Ana Julia [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510 (Mexico)

2013-07-23

268

Ohm's law for mean magnetic fields  

International Nuclear Information System (INIS)

Spatially complicated magnetic fields are frequently treated as the sum of a large, slowly varying, mean field and a small, rapidly varying, field. The primary effect of the small field is to modify the Ohm's law of the mean field. A set of plausible assumptions leads to a form of the mean field Ohm's law which is fundamentally different from the conventional alpha effect of dynamo theory

1984-01-01

269

Hypernuclear matter in strong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10{sup 14}–10{sup 15} G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta–Bodmer–Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B?10{sup 17} G, in particular the matter properties become anisotropic. Moreover, for the central fields B?10{sup 18} G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value B{sub cr}?10{sup 19} G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value B{sub cr}.

Sinha, Monika [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany); Indian Institute of Technology Rajasthan, Old Residency Road, Ratanada, Jodhpur 342011 (India); Mukhopadhyay, Banibrata [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Sedrakian, Armen, E-mail: sedrakian@th.physik.uni-frankfurt.de [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany)

2013-01-17

270

Population Synthesis of Pulsars Magnetic Field Effects  

CERN Multimedia

New results based on methods of population synthesis, concerning magnetic field effects on the evolution of pulsars are reported. The present study confirms that models with timescales for the magnetic field decay longer than the pulsar lifetime are in better agreement with data. These new simulations indicate that the diagram log($P\\dot P$) - log($t_s$) alone cannot be used to test field decay models. The dispersion of the values of the initial period and magnetic field can explain the observed behaviour of the data points in such a diagram. The simulations also indicate that the statistical properties of anomalous X-ray pulsars and soft-gamma repeaters (magnetar candidates) are compatible with those derived for objects born in the high side tail of the magnetic field distribution. The predicted birth rate of neutron stars having field strengths in excess of 10$^{14}$ G is one object born each 750 yr.

Regimbau, T

2001-01-01

271

On the magnetic fields in voids  

CERN Document Server

We study the possible magnetization of cosmic voids by void galaxies. Recently, observations revealed isolated starforming galaxies within the voids. Furthermore, a major fraction of a voids volume is expected to be filled with magnetic fields of a minimum strength of about $10^{-15}$ G on Mpc scales. We estimate the transport of magnetic energy by cosmic rays (CR) from the void galaxies into the voids. We assume that CRs and winds are able to leave small isolated void galaxies shortly after they assembled, and then propagate within the voids. For a typical void, we estimate the magnetic field strength and volume filling factor depending on its void galaxy population and possible contributions of strong active galactic nuclei (AGN) which border the voids. We argue that the lower limit on the void magnetic field can be recovered, if a small fraction of the magnetic energy contained in the void galaxies or void bordering AGNs is distributed within the voids.

Beck, Alexander M; Lesch, Harald; Remus, Rhea-Silvia; Stasyszyn, Federico A

2012-01-01

272

Nuclear matter in strong magnetic fields  

CERN Document Server

Strongly magnetized nuclear matter within the context of Quantum Hadrodynamics (Walecka-model) and its extensions is investigated in this article. The magnetic field is coupled to the charge and dipole moment of the baryons by including the appropriate terms in the Lagrangian density. The saturation density of magnetized, symmetric nuclear matter was calculated for magnetic fields of the order of 10^17 gauss. For the calculated range of saturation densities the binding energy, symmetry energy coefficient and compressibility of nuclear matter were also calculated. It is found that with an increasing magnetic field the saturation density also increases, while the system becomes less bound. Furthermore, the depopulation of proton Landau levels leaves a distinct oscillatory imprint on both the symmetry energy coefficient and the compressibility. The calculations were also performed for increased values of the baryon magnetic dipole moment. By increasing the dipole moment strength the saturation density is found t...

Diener, J P W

2013-01-01

273

Field-free line formation in a magnetic field  

International Nuclear Information System (INIS)

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

2010-01-08

274

External-field-free magnetic biosensor  

Science.gov (United States)

In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 ?l magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping

2014-03-01

275

Microscopic study of octupole-deformations in even-even 226-230Th isotopes  

International Nuclear Information System (INIS)

Study of octupole correlations in the actinides has attracted interest because of the predictions that octupole deformation would be present in the Z ? 88 and N ?134 region. These predictions have been explored through a series of experimental studies, which have centred on energy spectra and transition properties. In the present work, the octupole-octupole interaction is incorporated to the pairing plus quadrupole-quadrupole model. The microscopic Cranked Hartree Bogoliubov framework (CHB) is employed with pairing plus quadrupole-quadrupole plus octupole-octupole interaction to study the non-axial nature of 226-230Th.

2013-12-01

276

Emittance measurement in a magnetic field  

International Nuclear Information System (INIS)

Emittance can be measured by intercepting an electron beam on a range thick plate and then observing the expansion of beamlets transmitted through small holes. The hole size is selected to minimize space charge effects. In the presence of a magnetic field the beamlets have a spiral trajectory and the usual field free formulation must be modified. To interpret emittance in the presence of a magnetic field an envelope equation is derived in the appropriate rotating frame. 1 ref

1991-05-06

277

Temporal Chiral Spiral in Strong Magnetic Fields  

CERN Document Server

Vacuum properties of quantum chromodynamics in strong magnetic and finite electric fields are investigated. We show that when a uniform electric field is instantaneously applied in the parallel direction to a strong magnetic field, it induces temporal oscillation of the chiral and pion condensates. This is a temporal analog to the chiral spiral. The oscillation originates with the propagation of the collective mode, which is protected by the axial anomaly and thus nondissipative.

Hayata, Tomoya; Yamamoto, Arata

2013-01-01

278

Polarization Evolution in Strong Magnetic Fields  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Extremely strong magnetic fields change the vacuum index of refraction. Although this polarization dependent effect is small for typical neutron stars, it is large enough to decouple the polarization states of photons traveling within the field. The photon states evolve adiabatically and follow the changing magnetic field direction. The combination of a rotating magnetosphere and a frequency dependent state decoupling predicts polarization phase lags between different wave b...

Heyl, Jeremy S.; Shaviv, Nir J.

1999-01-01

279

Collisionless reconnection: magnetic field line interaction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic field lines are quantum objects carrying one quantum ?0 = 2?h/e of magnetic flux and have finite radius ?m. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attra...

Treumann, R. A.; Baumjohann, W.; Gonzalez, W. D.

2012-01-01

280

The first magnetic fields in the universe  

CERN Multimedia

We show that the first structures that form in the universe should spontaneously generate magnetic fields. No primordial seed field is required for this "first dynamo". Although the first dynamo starts with kinetic plasma instabilities, we argue that an adequate magnetohydrodynamic description might be possible via a simple trick. This should allow a numerical study of the effect of the first magnetic fields on the first baryonic objects.

Gruzinov, Andrei

2009-01-01

 
 
 
 
281

Magnetic field errors in bumpy torus configurations  

International Nuclear Information System (INIS)

The effects of magnetic field errors in a bumpy torus confinement devices are studied. The analysis relies on large-aspect-ratio and near-axis approximations, but includes toroidal effects and allows for any shape of the magnetic field bumps. The main features of the present results agree with those of previous numerical studies. However, the analysis of field line trajectories can be made surprisingly explicit and reveals some features which have not been anticipated

1984-01-01

282

Magnetic field evolution in neutron stars  

CERN Document Server

Neutron stars contain persistent, ordered magnetic fields that are the strongest known in the Universe. However, their magnetic fluxes are similar to those in magnetic A and B stars and white dwarfs, suggesting that flux conservation during gravitational collapse may play an important role in establishing the field, although it might also be modified substantially by early convection, differential rotation, and magnetic instabilities. The equilibrium field configuration, established within hours (at most) of the formation of the star, is likely to be roughly axisymmetric, involving both poloidal and toroidal components. The stable stratification of the neutron star matter (due to its radial composition gradient) probably plays a crucial role in holding this magnetic structure inside the star. The field can evolve on long time scales by processes that overcome the stable stratification, such as weak interactions changing the relative abundances and ambipolar diffusion of charged particles with respect to neutr...

Reisenegger, Andreas

2007-01-01

283

Bihelical Magnetic Relaxation and Large Scale Magnetic Field Growth  

CERN Document Server

A unified, three-scale system of equations accommodating nonlinear velocity driven helical dynamos, as well as time-dependent relaxation of magnetically dominated unihelical or bihelical systems is derived and solved herein. When opposite magnetic helicities of equal magnitude are injected on the intermediate and small scales, the large scale magnetic helicity grows kinematically (independent of the magnetic Reynolds number) to equal that on the intermediate scale. For both free and driven relaxation large scale fields are rapidly produced. Subsequently, a dissipation-limited dynamo, driven by growth of small scale kinetic helicity, further amplifies the large scale field. The results are important for astrophysical coronae fed with bihelical structures by dynamos in their host rotators. The large scale for the rotator corresponds to the intermediate scale for the corona. That bihelical magnetic relaxation can produce global scale fields may help to explain the formation of astrophysical coronal holes and mag...

Blackman, E G

2004-01-01

284

Strongly interacting matter in magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

Provides a first coherent and introductory account of this new topic. Edited and Authored by leading researchers in the field. Suitable as both self-study text and advanced course material for graduate courses, thematic schools and seminars. The physics of strongly interacting matter in an external magnetic field is presently emerging as a topic of great cross-disciplinary interest for particle, nuclear, astro- and condensed matter physicists. It is known that strong magnetic fields are created in heavy ion collisions, an insight that has made it possible to study a variety of surprising and intriguing phenomena that emerge from the interplay of quantum anomalies, the topology of non-Abelian gauge fields, and the magnetic field. In particular, the non-trivial topological configurations of the gluon field induce a non-dissipative electric current in the presence of a magnetic field. These phenomena have led to an extended formulation of relativistic hydrodynamics, called chiral magnetohydrodynamics. Hitherto unexpected applications in condensed matter physics include graphene and topological insulators. Other fields of application include astrophysics, where strong magnetic fields exist in magnetars and pulsars. Last but not least, an important new theoretical tool that will be revisited and which made much of the progress surveyed in this book possible is the holographic principle - the correspondence between quantum field theory and gravity in extra dimensions. Edited and authored by the pioneers and leading experts in this newly emerging field, this book offers a valuable resource for a broad community of physicists and graduate students.

Kharzeev, Dmitri [State Univ. of New York, Stony Brook, NY (United States). Dept. of Physics; Landsteiner, Karl [Universidad Autonoma de Madrid (Spain). Inst. de Fisica Teorica UAM/CSIC; Schmitt, Andreas [Technische Univ., Vienna (Austria). 1. Inst. fuer Theoretische Physik; Yee, Ho-Ung (eds.) [Illinois Univ., Chicago, IL (United States). Dept. of Physics

2013-08-01

285

Tuning permanent magnets with adjustable field clamps  

International Nuclear Information System (INIS)

The effective length of a permanent-magnet assembly can be varied by adjusting the geometrical parameters of a field clamp. This paper presents measurements on a representative dipole and quadrupole as the field clamp is withdrawn axially or radially. The detailed behavior depends upon the magnet multipolarity and geometry. As a rule-of-thumb, a 3-mm-thick iron plate placed at one end plane of the magnet will shorten the length by one-third of the magnet bore radius

1987-03-16

286

Equilibrium of non-neutral plasmas in a Malmberg-Penning trap with a weakly tilted magnetic field  

International Nuclear Information System (INIS)

The effect of small asymmetric magnetic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint, known in the theory of tandem mirrors as the condition of current closure, is derived for non-neutral plasmas. Together with Poisson's equation, this constraint provides a set of equations for determining self-consistent asymmetric equilibria of non-neutral plasmas in Malmberg-Penning traps. As an example of this approach, the non-neutral plasma equilibrium in the presence of a weak magnetic tilt is analyzed. Analytical and semianalytical solutions for the electric potential variations inside the trap are found in a paraxial limit for various radial density profiles of the plasma, including the case of global thermal equilibrium. The numerical procedure aimed to obtain self-consistent plasma equilibria for a magnetic field with a large asymmetry is also discussed. The newly developed method can be straightforwardly applied to determine plasma equilibria under the effect of the magnetic perturbations of higher multipolarity (such as, quadrupole or octupole fields).

2008-07-01

287

Spintronic Oscillator Based on Magnetic Field Feedback  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a circuit design of a spintronic oscillator based on magnetic tunnel junction. In this design, a dc current is passed through a magnetic tunnel junction which is connected to a feed-back wire below it. Any fluctuation in the magnetization direction of the free layer of MTJ, drives a fluctuating current through the feed-back wire, which exerts a magnetic field on the free layer. This in turn can amplify the magnetization fluctuations of the free layer. If the dc cu...

Dixit, D.; Konishi, K.; Tomy, C. V.; Suzuki, Y.; Tulapurkar, A. A.

2013-01-01

288

Evolution of the interplanetary magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple open'' configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic bottles,'' still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-01-01

289

Evolution of the interplanetary magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Remote observations of magnetic field topologies in the solar corona and in situ observations of the solar wind and interplanetary magnetic field (IMF) in interplanetary space are used to examine the temporal evolution of the spatial distribution of open and closed field regions emanating from the Sun. The simple ``open`` configuration of inward and outward pointing sectors in the IMF is periodically disrupted by magnetically distinct coronal mass ejections (CMEs) which erupt from previously closed magnetic field regions in the corona into interplanetary space. At 1 AU, CMEs contain counterstreaming halo electrons which indicate their distinct magnetic topologies. This topology is generally thought to be: plasmoids that are completely disconnected from the Sun; magnetic ``bottles,`` still tied to the corona at both ends; or flux ropes which are only partially disconnected. Fully disconnected plasmoids would have no long term effect on the amount of open flux; however, both in situ observations of details of the halo electron distributions and remote coronagraph observations of radial fields following CMEs indicate that CMEs generally do retain at least partial attached to the Sun. Both the magnetic-bottle and flux rope geometries require some mitigating process to close off previously open fields in order to avoid a flux catastrophe. In addition, the average amount of magnetic flux observed in interplanetary space varies over the solar cycle, also indicating that there must be ways in which new flux is opened and previously open flux is closed off. The most likely scenario for closing off open magnetic fields is for reconnection to occurs above helmet streamers, where oppositely directed field regions are juxtaposed in the corona. These events would serve to return closed field arches to the Sun and release open, U-shaped structures into the solar wind.

McComas, D.J.

1993-05-01

290

Pulsed field magnets at the United States National High Magnetic Field Laboratory  

Energy Technology Data Exchange (ETDEWEB)

The pulsed field facility of the National High Magnetic Field Laboratory (NHMFL) consists of four components. Now available are (1) explosive driven flux compression, (2) capacitor-driven magnets, and (3) a 20 T superconducting magnet. The fourth component, a 60 T quasi-continuous magnet, has been designed and is scheduled for installation in early 1995. All magnets have He-4 cryostats giving temperatures from room temperature (RT) to 2.2--1.5 K. Dilution refrigerators for the superconducting 20 T magnet and the 50 T pulsed magnet will be installed by early 1994. A wide range of experiments has been completed within the past year.

Campbell, L.J.; Parkin, D.M. [Los Alamos National Lab., NM (United States); Crow, J.E.; Schneider-Muntau, H.J. [Florida State Univ., Tallahassee, FL (United States). NHMFL; Sullivan, N.S. [Univ. of Florida, Gainesville, FL (United States). Dept. of Physics

1993-11-01

291

Magnetic field considerations in fusion power plant environs  

International Nuclear Information System (INIS)

A summary of magnetic field production mechanisms and effects is given. Discussions are included on the following areas: (1) stray magnetic and electric fields from tokamaks, (2) methods for reducing magnetic fields, (3) economics of magnetic field reductions, (4) forces on magnetizable objects near magnetic confinement fusion reactors, (5) electric field transients in tokamaks, (6) attenuation and decay of electromagnetic fields, and (7) magnetic field transients from tokamak malfunctions

1976-01-01

292

Magnetic field considerations in fusion power plant environs  

Energy Technology Data Exchange (ETDEWEB)

A summary of magnetic field production mechanisms and effects is given. Discussions are included on the following areas: (1) stray magnetic and electric fields from tokamaks, (2) methods for reducing magnetic fields, (3) economics of magnetic field reductions, (4) forces on magnetizable objects near magnetic confinement fusion reactors, (5) electric field transients in tokamaks, (6) attenuation and decay of electromagnetic fields, and (7) magnetic field transients from tokamak malfunctions.

Liemohn, H.B.; Lessor, D.L.; Duane, B.H.

1976-09-01

293

Surface magnetic field effects in local helioseismology  

CERN Multimedia

Using helioseismic holography strong evidence is presented that the phase (or equivalent travel-time) of helioseismic signatures in Dopplergrams within sunspots depend upon the line-of-sight angle in the plane containing the magnetic field and vertical directions. This is shown for the velocity signal in the penumbrae of two sunspots at 3, 4 and 5 mHz. Phase-sensitive holography demonstrates that they are significantly affected in a strong, moderately inclined magnetic field. This research indicates that the effects of the surface magnetic field are potentially very significant for local helioseismic analysis of active regions.

Schunker, H; Cally, P S; 10.1002/asna.200610732

2010-01-01

294

Behavior of neutrinos in stochastic magnetic fields  

International Nuclear Information System (INIS)

If massive neutrinos possess magnetic moments, they can undergo spin flip in a magnetic field. The magnetic fields needed for a meaningful measurement of neutrino moments could be very high and may occur in astronomical objects such as some supernovae or active galactic nuclei: they are typically chaotic ones. The general theory of the passage of neutrinos through such fields is developed. A simple model which becomes solvable in the high energy limit is also developed. Both helicities occur with equal probability, independently of the initial distribution. Observational consequences are discussed. (author)

1997-01-01

295

Chern band insulators in a magnetic field.  

Science.gov (United States)

The effect of a magnetic field on a two-dimensional Chern band insulator is discussed. It is shown that, unlike the trivial insulator, an anomalous Hall insulator with Chern number C becomes a metal when a magnetic field is applied at constant particle density, for any C > 0. For a time-reversal invariant topological insulator with a spin Chern resolved number, C? = ?C? = C, the magnetic field induces a spin polarized spin Hall insulator. We consider also the effect of a superlattice potential and extend previous results for the quantization of the Hall conductance of filled Hofstadter bands to this problem. PMID:24627894

Araújo, Miguel A N; Castro, Eduardo V

2014-02-19

296

XUV harmonic enhancement by magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

We examine three ways to enhance harmonic output of an XUV planar free-electron laser (FEL) operating in the Compton regime. The first method is to increase the rms static magnetic field, making it as large as possible. The second is by adding effective magnetic fields at the harmonics, thereby increasing the coupling to the harmonics. The third is by phase programming; i.e. programming the magnetic field to introduce jumps in the phase of the electrons as they move through phase space.

Elliott, C.J.; Schmitt, M.J.

1986-09-01

297

Magnetic field generation in shock waves  

Energy Technology Data Exchange (ETDEWEB)

The equation which governs the changes in the magnetic field as function of time is given. The first two terms on the right hand side are the convection and diffusion term. The third term represents the source term for magnetic field generation in a plasma due to non-parallel temperature and density gradients. Such gradients develop when a supersonic plasma jet interacts with a background plasma. For large Mach numbers the axial shock compression ratio of the density approaches a limiting value of four while the temperature ratio can increase far above four. Perpendicular to this axial temperature gradient the radial density gradient of the jet is dictated by ion motion. Due to their large thermal velocity, a radial electron temperature gradient relaxes faster than the radial density gradient. This cross product of the dominant gradients, radial density gradient of the jet and shock created axial temperature gradient causes magnetic field generation in azimuthal direction as experimentally observed. Recent numerical simulations, guided by experimental data, provide useful insights and verification of the field generating mechanism. This mechanism for magnetic field generation can occur in a field free region where B = 0, in contrast to the dynamo mechanism which requires an initial seed magnetic field. It may be assumed that this mechanism of magnetic field generation is also of importance under astrophysical conditions.

Schwirzke, F.; Carter, J.P. [Naval Postgraduate School, Monterey, CA (United States). Physics Dept.

1994-12-31

298

The theory of the Galactic magnetic field  

Science.gov (United States)

The paper discusses the role of the magnetic field in determining the large scale structure and dynamics of the interstellar medium. It then discusses the origin and maintenance of the Galactic field. The two major competing theories are that the field is primordial and connected to an intergalactic field or that the field is removed from and regenerated within the Galaxy. Finally, cosmic ray acceleration and confinement in the interstellar medium are discussed.

Zweibel, Ellen G.

1987-01-01

299

Some Structural Properties of Solar Magnetic Fields  

Science.gov (United States)

We discuss some results of the study of spatial characteristics of solar magnetic fields. The analysis is based on the magnetic field data obtained with a new spectromagnetograph installed on the IZMIRAN Tower Telescope (Fe I 6302.5 Å) (Kozhevatov et al., 2002), the data of the MSFC solar vector magnetograph (Fe I 5250.2 Å) and the data of longitudinal magnetic 96 m daily maps of SOHO/MDI magnetograph (Ni I 6768 Å) downloaded through Internet. Our study was directed in some different ways: the fractal properties of sunspots; fractal properties of space distribution of the magnetic fields along great distances comparable with the size of active regions or active complexes; fractal properties of active and quiet regions as global entities. To do it we used some different methods, particularly, the well known method using the relation between the area and the perimeter of magnetic field lines (see (Feder, 1988; Meunier, 1999; Nesme-Ribes at al., 1996; Balke et al., 1993)) and technique developed by Higuchi (1988), who applied it to the investigation of long time series. Note also that magnetic structure in terms of the fractal models was developed earlier in (Zelenyi & Milovanov, 1991; Milovanov & Zelenyi, 1993; Mogilevskii, 1994; Mogilevskii, 2001; Abramenko et al., 2002; Abramenko, 2005; Salakhudinova & Golovko, 2005). The main results are: 1. Fractal analysis of sunspot magnetic field indicated the existence of three families of self-similar contour lines roughly belonging to the umbra, penumbra and the ambient photosphere correspondingly. The greatest fractal dimension corresponds to the regions of weakest fields (ambient photosphere), the least one corresponds to the intermediate region (penumbra). 2. More detailed analysis shows that the fractal coefficient has a maximum (about 1.50) near the umbra--penumbra interface. 3. The global fractal numbers of space distribution of magnetic field on solar surface is closely connected with the mean absolute values of the longitudinal magnetic field for this surface. The fractal numbers diminish with the rising of mean magnetic field (from values about 2.0 for the relatively quiet region to 1- 1.2 for very active regions). 4. The dependences of fractal numbers of the space distribution of longitudinal and transversal fields versus mean longitudinal field are similar by their character but the fractal values for transversal field are higher than the corresponding factor values for longitudinal field by factor about 1.5. This means that the distribution of transversal field along the space is more chaotic than the distribution of longitudinal field.

Ioshpa, B.; Mogilevskii, E.; Obridko, V.

2007-05-01

300

Intergalactic Magnetic Fields from Quasar Outflows  

CERN Document Server

Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model the expansion of the remnant quasar bubbles and calculate their distribution as a function of size and magnetic field strength at different redshifts. We generically find that by a redshift z=3, about 5-20% of the IGM volume is filled by magnetic fields with an energy density >10% of the mean thermal energy density of a photo-ionized IGM (at T=10^4 K). As massive galaxies and X-ray clusters condense out of the magnetized IGM, the adiabatic compression of the magnetic field could result in the field strength observed in these systems without a need for further dynamo amplification. The intergalactic magnetic field could also provide a nonthermal contribution to the pressure of the photo-ionized gas that may account for the claimed discrepancy between the simulated and observed Doppler width distributions of the Ly-al...

Furlanetto, S; Furlanetto, Steven; Loeb, Abraham

2001-01-01

 
 
 
 
301

Discovery of a magnetic field on Vega  

CERN Multimedia

We report the detection of a magnetic field on Vega through spectropolarimetric observations. We acquired 257 Stokes V high signal-to-noise and high-resolution echelle spectra during four consecutive nights with NARVAL spectropolarimeter at the 2-m Telescope Bernard Lyot of Observatoire du Pic du Midi (France). A circularly polarized signal in line profiles is detected after gathering the contribution of about 1200 spectral lines for each spectrum and summing up the signal over the 257 spectra. Interpreting this polarization as a Zeeman signature leads to a value of $-0.6 \\pm 0.3$ G for the disk-averaged line-of-sight component of the surface magnetic field. This is the first time a magnetic field is unambiguously detected in an A-type star which is not an Ap chemically peculiar star. Moreover, the Vega longitudinal magnetic field is smaller by about two orders of magnitude than the longitudinal magnetic field (taken at its maximum phase) of the most weakly magnetic Ap stars. Magnetic fields similar to the Ve...

Lignières, F; Böhm, T; Aurière, M

2009-01-01

302

The CMS Magnetic Field Map Performance  

CERN Document Server

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field ...

Klyukhin, VI; Sarycheva, L I; Klyukhin, V I; Ball, A; Gaddi, A; Amapane, N; Gerwig, H; Andreev, V; Cure, B; Mulders, M; Loveless, R; Karimaki, V; Popescu, S; Herve, A

2010-01-01

303

Directed Plasma Flow across Magnetic Field  

Science.gov (United States)

The Hall effect plays a significant role in the penetration of plasma flows across magnetic field. For example, its effect may become dominant in the solar wind penetration into the magnetosphere, in the magnetic field advection in wire array z-pinch precursors, or in the arcing of magnetically insulated transmission lines. An experiment performed at the Nevada Terawatt Facility explored the penetration of plasma with large Hall parameter (˜10) across ambient magnetic field. The plasma was produced by ablation with the short pulse high intensity laser Leopard (0.35 ps, 10^17W/cm^2) and the magnetic field with the pulsed power generator Zebra (50 T). The expanding plasma assumed a jet configuration and propagated beyond a distance consistent with a diamagnetic bubble model. Without magnetic field, the plasma expansion was close to hemispherical. The ability to produce the plasma and the magnetic field with distinct generators allows a controlled, quasi-continuous variation of the Hall parameter and other plasma parameters making the experiments useful for benchmarking numerical simulations.

Presura, R.; Stepanenko, Y.; Neff, S.; Sotnikov, V. I.

2008-04-01

304

Design of heliac vacuum magnetic fields  

International Nuclear Information System (INIS)

The design of vacuum magnetic fields for helical axis stellarators (HELIACS) is investigated. The aim is to produce realistic configurations possessing magnetic wells (for stability), favourable transform with low shear (to avoid resonant rational surfaces), and small variation of Q=?dl/B (to minimize parallel currents). An asymmetric toroidal domain whose boundary is assumed to be an outer magnetic surface is created by helically winding a poloidal cross-section about a circle. The magnetic scalar potential inside the domain is computed numerically and field-line integrations are performed in order to evaluate the field properties. The magnetic field is generated by skin currents flowing along the equipotential contours on the boundary. These currents are then discretized into a modular coil system, whose resulting magnetic field is compared with that of the corresponding continuum. Skin current configurations having a shallow well and favourable beta limitations and Q-variation are presented. Discretization of the skin current usually results in a magnetic field which preserves the transform and Q-variation, but with less favourable well properties. (author)

1985-01-01

305

Magnetic field measurements on ISABELLE storage ring magnets  

International Nuclear Information System (INIS)

In 1978 the magnetic field shapes of six ISABELLE prototype dipole magnets were measured in detail. All the harmonic terms that are forbidden by symmetry in dipole magnets are found to have values that are zero to within the allowed tolerances. This result indicates that the random errors in conductor placement are within tolerances and that the assembly techniques are satisfactory in this regard. However, the first allowed error term in a dipole magnet, the sextupole term, is much too large, and varies greatly from magnet to magnet resulting in field errors at the edge of the desired good field region that are 10"-"3 of the central field value, whereas the tolerable field errors are of the order of 10"-"4 of the central field value. This large sextupole term has been traced to assembly errors which yield a coil assembly which instead of being circular in cross section is racetrack shaped, with the vertical axis being 10 to 20 thousandths of an inch greater than the horizontal axis. This problem will be corrected in the future production series

1979-03-14

306

The magnetic field structure of Rotamak discharges  

International Nuclear Information System (INIS)

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

1983-01-01

307

Magnetic fields of HgMn stars  

DEFF Research Database (Denmark)

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims. We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system ARAur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. Methods. We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. Results. Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars aswell as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars.

Hubrig, S.; Gonzalez, J. F.

2012-01-01

308

Gutzwiller wave function under magnetic field  

CERN Multimedia

Magnetization process of the Gutzwiller wave function is studied accurately by a variational Monte Carlo method. We apply it to the one-dimensional (1D) and 2D Hubbard models (HM), and to the 1D periodic Anderson model (PAM) without orbital degeneracy. For the HM, magnetization varies discontinuously to the full moment, as the magnetic field increases. For the PAM, the paramagnetic state is unstable against ferromagnetism, although the energy reduction thereof is small.

Yokoyma, H; Yokoyma, Hisatoshi; Tokizaki, Shinya

1996-01-01

309

Relativistic magnetic gyroscope wheel in electromagnetic fields  

International Nuclear Information System (INIS)

Consideration is given to the precession of a relativistic magnetic gyroscope wheel (GW) which when rotating moves forward in electromagnetic field. It is guessed that orientation of its own mechanical moment (spin) and that of the gyroscope wheel's magnetic moment coincides. Elegant formulation of the classical spin equations and of the criterion of magnetic GW free motion is presented. General solutions of the equations of spin precession are derived

1993-11-01

310

Magnetic monopoles in field theory and cosmology.  

Science.gov (United States)

The existence of magnetic monopoles is predicted by many theories of particle physics beyond the standard model. However, in spite of extensive searches, there is no experimental or observational sign of them. I review the role of magnetic monopoles in quantum field theory and discuss their implications for particle physics and cosmology. I also highlight their differences and similarities with monopoles found in frustrated magnetic systems. PMID:23166376

Rajantie, Arttu

2012-12-28

311

Juno and Jupiter's Magnetic Field (Invited)  

Science.gov (United States)

The Juno spacecraft, launched in August 2011, will reach Jupiter in early July 2016, where it will enter a polar orbit, with an 11 day period and a perijove altitude of approximately 5000 km. The baseline mission will last for one year during which Juno will complete 32 orbits, evenly spaced in longitude. The baseline mission presents an unparalleled opportunity for investigating Jupiter's magnetic field. In many ways Jupiter is a better planet for studying dynamo-generated magnetic fields than the Earth: there are no crustal fields, of course, which otherwise mask the dynamo-generated field at high degree; and an orbiting spacecraft can get proportionately much closer to the dynamo region. Assuming Jupiter's dynamo extends to 0.8 Rj, Juno at closet approach is only 0.3 Rc above the dynamo, while Earth orbiting magnetic field missions sample the field at least 1 Rc above the dynamo (where Rc is the respective outer core or dynamo region radius). Juno's MAG Investigation delivers magnetic measurements with exceptional vector accuracy (100 ppm) via two FGM sensors, each co-located with a dedicated pair of non-magnetic star cameras for attitude determination at the sensor. We expect to image Jupiter's dynamo with unsurpassed resolution. Accordingly, we anticipate that the Juno magnetic field investigation may place important constraints on Jupiter's interior structure, and hence on the formation and evolution of Jupiter.

Bloxham, J.; Connerney, J. E.; Jorgensen, J. L.

2013-12-01

312

Magnetic fields in laser heated plasmas  

International Nuclear Information System (INIS)

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

1984-10-05

313

Hubbard ladders in a magnetic field  

CERN Document Server

The behavior of a two leg Hubbard ladder in the presence of a magnetic field is studied by means of Abelian bosonization. We predict the appearance of a new (doping dependent) plateau in the magnetization curve of a doped 2-leg spin ladder in a wide range of couplings. We also discuss the extension to N-leg Hubbard ladders.

Cabra, D C; Pujol, P; Simon, P

2000-01-01

314

Bloch electrons in electric and magnetic fields  

CERN Document Server

We investigate Bloch electrons in two dimensions subject to constant electric and magnetic fields. The model that results from our pursuit is governed by a finite difference equation with a quasienergy spectrum that interpolates between a butterfly-like structure and a Stark ladder structure. These findings ensued from the use of electric and magnetic translation operators.

Kunold, A; Kunold, Alejandro; Torres, Manuel

1999-01-01

315

Toroidal Plasma Containment with Rotating Magnetic Field.  

Science.gov (United States)

Experimental investigations were conducted on a toroidal plasma with alternating pinch- and theta-pinch magnetic fields as well as with a theta-pinch and with a screw pinch. For the alternating pinch, the resultant magnetic vector is rotating, so that the...

D. E. Brown H. G. Loos

1966-01-01

316

Understanding the Geometry of Astrophysical Magnetic Fields  

CERN Multimedia

Faraday rotation measurements have provided an invaluable technique with which to measure the properties of astrophysical magnetized plasmas. Unfortunately, typical observations provide information only about the density-weighted average of the magnetic field component parallel to the line of sight. As a result, the magnetic field geometry along the line of sight, and in many cases even the location of the rotating material, is poorly constrained. Frequently, interpretations of Faraday rotation observations are dependent upon underlying models of the magnetic field being probed (e.g., uniform, turbulent, equipartition). However, we show that at sufficiently low frequencies, specifically below roughly 13 (RM/rad m^-2)^(1/4) (B/G)^(1/2) MHz, the character of Faraday rotation changes, entering what we term the ``super-adiabatic regime'' in which the rotation measure is proportional to the integrated absolute value of the line-of-sight component of the field. As a consequence, comparing rotation measures at high ...

Broderick, Avery E

2009-01-01

317

Magnetic Field dragging in accretion discs  

CERN Multimedia

Accretion discs are composed of ionized gas in motion around a central object. Sometimes, the disc is the source of powerful bipolar jets along its rotation axis. Theoretical models invoke the existence of a bipolar magnetic field crossing the disc and require two conditions to produce powerful jets: field lines need to be bent enough at the disc surface and the magnetic field needs to be close to equipartition. The work of Petrucci et al (2008) on the variability of X-ray binaries supposes that transitions between pure accretion phases and accretion-ejection phases are due to some variations of the disc magnetization. This rises the problem of the magnetic field dragging in accretion discs. We revisit the method developed by Lubow et al (1994) by including momentum and mass conservation equations in a time-dependent 1D MHD code.

de Guiran, Remi

2011-01-01

318

Reverse magnetic field pinch type thermonuclear device  

International Nuclear Information System (INIS)

Purpose: To improve the accuracy for the position control of plasmas, thereby increasing the plasma confinement time. Constitution: Vertical magnetic field coils, quadrad pole magnetic field coils and position detectors are disposed on opposite sides of a vacuum container respectively. Then, when the plasmas are deviated horizontally from the center, the position is detected by the position detectors disposed horizontally opposing to each other and the current in the vertical magnetic field coils is controlled to situate the plasma to the center. In the case where the plasmas are deviated vertically, the current of the quadrad magnetic fields coil are controlled by the position detectors disposed opposing vertically to each other, to position the plasmas to the center. Accordingly, the plasmas have a minimum potential with respect to the vertical movement, the plasmas are stabilized and the position control for the plasmas can be performed accurately, whereby plasma forming time is extended and the energy confinement time can be increased. (Yoshihara, H.)

1982-07-26

319

Revisiting holographic superconductor with Magnetic Fields  

CERN Document Server

We study the effect of the bulk magnetic field (charge) on scalar condensation using an analytical approach of matching. An AdS-magnetized black hole solution has been used as a probe solution of normal phase of a strongly coupled condensed matter system on boundary. In the zero temperature limit of the black hole and infinite temperature, we show that there exists a critical magnetic field and so, the Meissner's effect presented. We compare this analytical result with our previous variational approach. By studying the different between heat capacities of the normal and superconducting phases near the critical point, we show that this thermodynamic quantity becomes divergent as the Rutgers formula predicted. Mathematical pole of Rutgers formula gives us a maximum for magnetic field which at this value, the system backs to the normal phase. In zero temperature we investigate exact series solutions of the field equations using an appropriate boundary conditions set. We show that conformal dimension is fixed by ...

Momeni, Davood

2014-01-01

320

The Polar BEAR magnetic field experiment  

Science.gov (United States)

The objectives and the instrumentation of the Polar BEAR magnetic field experiment are described along with the preliminary results from simultaneous measurements of Birkeland currents and UV auroral emissions. The experiment consists of an integrated sensor head, analog electronics, and digital electronics. The sensor head is a single unit containing sensor windings for each of the three orthogonal axes, oriented parrallel to the spacecraft coordinates; to minimize interference from spacecraft-generated magnetic fields, the sensor unit is located at the end of the +y solar panel. The digital electronics package is essentially identical to that flown on HILAT. A signal processor digitizes the analog outputs of the three orthogonal axes of the flux-gate magnetometer to a 13-bit resolution, yielding a magnetic field range of + or - 63,000 nT and a resolution of 15.2 nT. The full-resolution magnetic field values are recovered by data processing techniques on the ground.

Bythrow, Peter F.; Potemra, Thomas A.; Zanetti, Lawrence J.; Mobley, Frederick F.; Scheer, Leonard

1987-09-01

 
 
 
 
321

ATLAS Barrel Toroid magnet reached nominal field  

CERN Document Server

 On 9 November the barrel toroid magnet reached its nominal field of 4 teslas, with an electrical current of 21 000 amperes (21 kA) passing through the eight superconducting coils as shown on this graph

2006-01-01

322

A Topology for the Penumbral Magnetic Fields  

CERN Multimedia

We describe a scenario for the topology of the magnetic field in penumbrae that accounts for recent observations showing upflows, downflows, and reverse magnetic polarities. According to our conjecture, short narrow magnetic loops fill the penumbral photosphere. Flows along these arched field lines are responsible for both the Evershed effect and the convective transport. This scenario seems to be qualitatively consistent with most existing observations, including the dark cores in penumbral filaments reported by Scharmer et al. Each bright filament with dark core would be a system of two paired convective rolls with the dark core tracing the common lane where the plasma sinks down. The magnetic loops would have a hot footpoint in one of the bright filament and a cold footpoint in the dark core. The scenario fits in most of our theoretical prejudices (siphon flows along field lines, presence of overturning convection, drag of field lines by downdrafts, etc). If the conjecture turns out to be correct, the mild...

Almeida, J Sanchez

2009-01-01

323

External magnetic field configurations for EXTRAP  

International Nuclear Information System (INIS)

The strongly inhomogeneous magnetic field for stabilization of a pinch in an Extrap configuration can be created in various ways. Some possibilities both for the linear case and for the toroidal case are discussed. (author)

1982-01-01

324

About the global magnetic fields of stars  

CERN Document Server

We present a review of observations of the stellar longitudinal (effective) magnetic field ($B_e$) and its properties. This paper also discusses contemporary views on the origin, evolution and structure of $B_e$.

Bychkov, V D; Madej, J

2013-01-01

325

Stellar effective magnetic fields. II. (Bychkov+, 2009)  

Science.gov (United States)

Averaged longitudinal magnetic fields and other da listed. For each star we present HD number, spectral type, , rms standard error of , chi2 for one degree of freedom, method of Be determination, reference number and comments. (2 data files).

Bychkov, V. D.; Bychkova, L. V.; Madej, J.

2011-11-01

326

Edge Magnetic Field Effect on Electron Radiation.  

Science.gov (United States)

The first quantum corrections to ultrarelativistic particle radiation in the ''short'' magnets with arbitrary non-homogeneity field have been found in the paper. A principle possibility to define the beam spin characteristics over circular polarization va...

V. L. Mikhalev R. A. Rzaev

1980-01-01

327

Magnetic field effect on selective photoionization.  

Science.gov (United States)

The magnetic field effects on selective photoionization of the atoms of Lanthanides have been examined in a point of view of the enhancement of the efficiency of selective photoionization. The Zeeman shifts and the hyperfine structures have been calculate...

J. M. Lee B. D. Yoo Y. J. Lee H. K. Cha A. S. Choe

1993-01-01

328

Orientation effects in pulsed magnetic field treatment  

International Nuclear Information System (INIS)

This paper presents the orientation effects on residual stress release by pulsed magnetic field treatment. Specimens are produced by tungsten inert gas (TIG) welding and the initial residual stresses in them are measured by the hole-drilling method. With different orientations these specimens are treated in the same magnetic field and the residual stresses are measured for the second time. By comparing the stress values before and after treatment it is obvious that magnetic field treatment effects are related to orientations. Based on a referred ferromagnetics formula, a supposition is proposed and a further survey of the magnetostriction constant is carried out. All experimental results support the proposed model and a prescription is given for pulsed magnetic field treatments

2005-05-25

329

Fractal structure of the interplanetary magnetic field  

International Nuclear Information System (INIS)

Under some conditions, time series of the interplanetary magnetic field strength and components have the properties of fractal curves. Magnetic field measurements made near 8.5 AU by Voyager 2 from June 5 to August 24, 1981 were self-similar over time scales from approximately 20 sec to approximately 3 x 100,000 sec, and the fractal dimension of the time series of the strength and components of the magnetic field was D = 5/3, corresponding to a power spectrum P(f) approximately f sup -5/3. Since the Kolmogorov spectrum for homogeneous, isotropic, stationary turbulence is also f sup -5/3, the Voyager 2 measurements are consistent with the observation of an inertial range of turbulence extending over approximately four decades in frequency. Interaction regions probably contributed most of the power in this interval. As an example, one interaction region is discussed in which the magnetic field had a fractal dimension D = 5/3

1985-01-01

330

Discontinuities in the magnetic field near Enceladus  

Science.gov (United States)

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

Simon, Sven; Saur, Joachim; Treeck, Shari C.; Kriegel, Hendrik; Dougherty, Michele K.

2014-05-01

331

High magnetic field ?SR instrument scientific case  

International Nuclear Information System (INIS)

In order to gain more insight into the specific behavior of materials, it is often necessary to perform measurements as a function of different external parameters. Despite its high sensitivity to internal fields, this simple observation also applies for the ?SR technique. The most common parameter which can be tuned during an experiment is the sample temperature. By using a range of cryostats, temperatures between 0.02 and 900 K can be covered at the PSI ?SR Facility. On the other hand, and by using high-energy muons, pressures as high as 10'000 bars can nowadays be reached during ?SR experiments. As will be demonstrated in the following Sections, the magnetic field is an additional external parameter playing a fundamental role when studying the ground state properties of materials in condensed matter physics and chemistry. However, the availability of high magnetic fields for ?SR experiments is still rather limited. Hence, if on one hand the high value of the gyromagnetic ratio of the muon provides the high magnetic sensitivity of the method, on the other hand it can lead to very high muon-spin precession frequencies when performing measurements in applied fields (the muon-spin precession frequency in a field of 1 Tesla s 135.5 MHz). Consequently, the use of ultra-fast detectors and electronics is mandatory when measuring in magnetic fields exceeding 1 Tesla. If such fields are very intense when compared to the Earth magnetic field -4 Tesla), the energy associated with them is still modest in view of the thermal energy. Hence, the Zeeman energy splitting of a free electron in a magnetic field of 1 Tesla corresponds to a thermal energy as low as 0.67 Kelvin. It is worth mentioning that nowadays magnetic fields of the order of 10 to 15 Tesla are quite common in condensed matter laboratories and have opened up vast new exciting experimental possibilities. (author)

2005-01-01

332

Critical-point behaviour of axially deformed nuclei in the octupole degree of freedom  

Energy Technology Data Exchange (ETDEWEB)

The evolution of the octupole excitation is investigated along the Th isotope chain. The isotope {sup 226}Th results to be close to the critical point (square-well potential in the octupole amplitude {beta}{sub 3}). (orig.)

Bizzeti, P.G.; Bizzeti-Sona, A.M. [Dipartimento di Fisica, Universita di Firenze and INFN, Sezione di Firenze, via G. Sansone 1, 50019, Sesto Fiorentino (Italy)

2004-04-01

333

Split-Field Magnet facility upgraded  

CERN Multimedia

The Split Field Magnet (SFM) was the largest spectrometer for particles from beam-beam collisions in the ISR. It could determine particle momenta in a large solid angle, but was designed mainly for the analysis of forward travelling particles.As the magnet was working on the ISR circulating beams, its magnetic field had to be such as to restore the correct proton orbit.The SFM, therefore, produced zero field at the crossing point and fields of opposite signs upstream and downstream of it and was completed by 2 large and 2 small compensator magnets. The gradient effects were corrected by magnetic channels equipped with movable flaps. The useful magnetic field volume was 28 m3, the induction in the median plane 1.14 T, the gap heigth 1.1 m, the length 10.5 m, the weight about 1000 ton. Concerning the detectors, the SFM was the first massive application of multiwire proportional chambers (about 70000 wires) which filled the main and the large compensator magnets. In 1976 an improved programme was started with tw...

1977-01-01

334

Magnetic Field Effect on the Stability of Flow Induced by a Rotating Magnetic Field  

Science.gov (United States)

A linear stability analysis has been performed for the flow induced by a rotating magnetic field in a cylindrical column filled with electrically conducting fluid. The first transition is time- independent and results in the generation of Taylor vortices. The critical value of the magnetic Taylor number has been examined as a function of the strength of the transverse rotating magnetic field, the strength of an axial static magnetic field, and thermal buoyancy. Increasing the transverse field increases the critical magnetic Taylor number and decreases the aspect ratio of the Taylor vortices at the onset of instability. An increase in the axial magnetic field also increases the critical magnetic Taylor number but increases the aspect ratio of the Taylor vortices. Thermal buoyancy is found to have only a negligible effect on the onset of instability.

Mazuruk, K.; Volz, M. P.; Gillies, D. C.

1999-01-01

335

Magnetic field dissipation in converging flows  

International Nuclear Information System (INIS)

Converging flows (e.g., gas accreting on to compact objects) are often ionized and magnetized. As the gas in these systems compresses towards smaller radii, flux conservation acts to intensify the magnetic field B, which can attain superequipartition values. (Throughout this paper, equipartition is meant to imply a comparison between the energy density in the field and that of the particles only, not including turbulence.) Since such a field probably cannot remain anchored in the gas, it is often assumed that the field intensity in excess of equipartition (i.e., B_e_q) is dissipated as heat, and that B therefore saturates at its B_e_q value -the so-called 'equipartition assumption'. In this paper we make an attempt at developing a model for magnetic field dissipation based on resistive magnetic tearing, in order to provide a more realistic means of determining the evolution of B in cases where the contribution to the spectrum from magnetic bremsstrahlung is important. We find that the violation of equipartition can vary in degree from large to small radii, and in either direction. Thus the spectrum predicted on the basis of the equipartition assumption is not always an adequate representation of the actual state of the system. However, several major shortcomings remain in our formulation. For example, our approach in this paper is to consider the turbulence as being initiated primarily by hydrodynamic processes. Arguing that the magnetic field is frozen into the highly ionized plasma, we therefore adopt a magnetic field spatial distribution that mirrors that of the gas. This may be valid Only when the field is subequipartition, for otherwise the turbulent cascade may be influenced primarily by magnetic dissipation, rather than the hydrodynamics

2000-01-01

336

Chromospheric trapping oscillations in horizontal magnetic field  

International Nuclear Information System (INIS)

The propagation of adiabatic MHD-waves in conductive isothermal atmosphere in the presence of a horizontal magnetic field and gravity is considered. It is shown that the oscillations may be trapped in the middle layer of three-layer atmosphere with the temperatures T_1>T_2>T_3 for a discrete frequences. In the presence of a horizontal magnetic field the solar chromospheric trapped waves have the periods in the range of 250-2730 s

1985-09-01

337

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 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 ar...

2009-01-01

338

LARGE SCALE MAGNETIC FIELD MEASUREMENTS AND MAPPING  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper illustrates the most recent techniques in the field of large-scale magnetic measurements. The main problems related to field mapping are discussed. The development of microelectronics during the last few years has created a revolution in magnetic measurement systems. Modular hardware and software as well as widely used industrial standards have influenced the architecture of measurement systems. The use of embedded microprocessors in the equipment and the application of modern algor...

Henrichsen, K.

1984-01-01

339

Adaptable controller of magnetic field homogeneity  

International Nuclear Information System (INIS)

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

1981-01-01

340

An evaluation of Tsyganenko magnetic field model  

International Nuclear Information System (INIS)

A long-standing goal of magnetospheric physics has been to produce a model of the Earth's magnetic field that can accurately predict the field vector at all locations within the magnetosphere for all dipole tilt angles and for various solar wind or magnetic activity conditions. A number of models make such predictions, but some only for limited spatial regions, some only for zero tilt angle, and some only for arbitrary conditions. No models depend explicitly on solar wind conditions. A data set of more than 22,000 vector averages of the magnetosphere magnetic field over 0.5 RE regions is used to evaluate Tsyganenko's 1982 and 1987 magnetospheric magnetic field models. The magnetic field predicted by the model in various regions is compared to observations to find systematic discrepancies which future models might address. While agreement is generally good, discrepancies are noted which include: (1) a lack of adequate field line stretching in the tail and ring current regions; (2) an inability to predict weak enough fields in the polar cusps; and (3) a deficiency of Kp as a predictor of the field configuration

1991-02-01

 
 
 
 
341

Laminated magnet field coil sheath  

Energy Technology Data Exchange (ETDEWEB)

a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

Skaritka, John R. (Coram, NY)

1987-12-01

342

Fast ignition studies and magnetic field generation  

International Nuclear Information System (INIS)

Experiments, theory and simulation have been carried out to describe intense, relativistic short pulse laser interaction with dense plasmas. Magnetic fields of up to 0.7 GGauss have been measured through polarization measurements of high order laser harmonics. Simulation and analytic theory show that these fields are associated with photon momentum deposition. The same mechanism can cause weaker fields in the speckle of long pulse laser in underdense plasmas, leading to termination of SBS. Other magnetic fields in gas-filled hohlraums lead to steep temperature gradients in regions where linear transport fails. A Vlasov-Fokker-Planck code has been developed to study these effects more accurately. (author)

2005-01-01

343

Electric and magnetic fields and ecology  

International Nuclear Information System (INIS)

Much of the paper explains electric and magnetic fields and how power transfer takes place in overhead transmission lines. Calculations of electric fields at ground level are shown, and how man may be affected by such fields is discussed. The article draws on some of the many reviews of data on the biological and health effects of electric and magnetic fields and discusses the role of the National Radiological Protection Board's Advisory Group on Non-Ionizing Radiation. The findings of US and Swedish groups who studied the effects of overhead lines on farm animals and crops are mentioned

1999-01-01

344

Untwisting magnetic fields in the solar corona  

Science.gov (United States)

The solar corona is the tenuous atmosphere of the Sun characterized by a temperature of the order of million degrees Kelvin, an ambient magnetic field of 10 to 15 Gauss and a very high magnetic Reynolds number because of which it qualifies as a near-ideal magnetofluid system. It is well known that for such a system, the magnetic flux across every fluid surface remains effectively constant to a good approximation. Under this so called ``frozen-in'' condition then, it is possible to partition this magnetofluid into contiguous magnetic subvolumes each entrapping its own subsystem of magnetic flux. Thin magnetic flux tubes are an elementary example of such magnetic subvolumes evolving in time with no exchange of fluid among them. The internal twists and interweaving of these flux tubes, collectively referred as the magnetic topology, remains conserved under the frozen-in condition. Because of the dynamical evolution of the magnetofluid, two such subvolumes can come into direct contact with each other by expelling a third interstitial subvolume. In this process, the magnetic field may become discontinuous across the surface of contact by forming a current sheet there. Because of the small spatial scales generated by steepening of magnetic field gradient, the otherwise negligible resistivity becomes dominant and allows for reconnection of field lines which converts magnetic energy into heat. This phenomenon of spontaneous current sheet formation and its subsequent resistive decay is believed to be a possible mechanism for heating the solar corona to its million degree Kelvin temperature. In this work the dynamics of spontaneous current sheet formation is explored through numerical simulations and the results are presented.

Bhattacharyya, Ramit; Smolarkiewicz, Piotr; Chye Low, Boon

2012-07-01

345

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

346

Helical Fields Possessing Mean Magnetic Wells  

International Nuclear Information System (INIS)

Recently Furth and Rosenbluth pointed out that a particular magnetic field having helical symmetry could provide a mean magnetic well, that is provide regions in which ?d?/B decreases away from a magnetic axis (or equivalently a region in which V'' is negative). In this paper we examine helical fields in general and the circumstances in which they may exhibit the negative V'' property. This investigation is made possible by the use of the stream function formalism which provides a simple picture of the field geometry, The existence of negative V'' is related to the topology of the magnetic surfaces which in turn is connected with the positions of the stationary points of the stream function ?. Detailed calculations are given of the shape of the flux surfaces and of the shape of the magnetic well (the variation of ?d?/B across it) for several examples of helical fields. These include the Furth-Rosenbluth configuration and a new configuration which provides a mean magnetic well without the necessity for a central conductor. A survey is also made of the magnetic well properties of these two classes of helical field in terms of two simple criteria: (1) the ratio Q of the field strength on the axis and on the separatrix (which provides an estimate of the overall well depth); and (2) the value of V'' on the magnetic axis (which provides a measure of the ''curvature'' of the well). This latter quantity is calculated analytically by using a general expression for the value of V'' on an arbitrary magnetic axis; It is pointed out that Q alone does not provide a realistic indication of the well shape. (author)

1966-04-01

347

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping.  

Science.gov (United States)

Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200 ps, which is ten times faster than the natural damping time constant. PMID:12152072

Gerrits, Th; Van Den Berg, H A M; Hohlfeld, J; Bär, L; Rasing, Th

2002-08-01

348

Magnetic Fields in Stellar Astrophysics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This is a white paper submitted to the Stars and Stellar Evolution (SSE) Science Frontier Panel (SFP) of the NRC's 2010 Astronomy and Astrophysics Decadal Survey. The white paper is endorsed by the NSF Physics Frontier Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas (CMSO).

Uzdensky, Dmitri; Forest, Cary; Ji, Hantao; Townsend, Richard; Yamada, Masaaki

2009-01-01

349

Collective properties of octupole-deformed atomic nuclei  

International Nuclear Information System (INIS)

Collective properties of even-even nuclei in the radium region are studied theoretically. Energy of the lowest collective states and reduced probabilities B(E2) and B(E3) of electromagnetic transitions between these states are mainly analysed. The excited states are treated as large-amplitude quadrupole and octupole vibrations coupled with each other. A large anharmonicity of the spectrum and a large value B(E3) of the transition from the first octupole excited state to the ground state are obtained, for octupole-deformed nuclei. A strong dependence of the results on the shape of the potential energy of a nucleus, treated as a function of its deformation, is stressed. (author)

1991-01-01

350

Superconductivity in Strong Magnetic Field (Greater Than Upper Critical Field)  

International Nuclear Information System (INIS)

The National High Magnetic Field Laboratory, funded by the National Science Foundation and other US federal Agencies, has in recent years built a wide range of magnetic fields, DC 25 to 35 Tesla, short pulse 50 - 60 Tesla, and quasi-continuous 60 Tesla. Future plans are to push the frontiers to 45 Tesla DC and 70 to 100 Tesla pulse. This user facility, is open for national and international users, and creates an excellent tool for materials research (metals, semiconductors, superconductors, biological systems ..., etc). Here we present results of a systematic study of the upper critical field of a novel superconducting material which is considered a promising candidate for the search for superconductivity beyond Hc2 as proposed by several new theories. These theories predict that superconductors with low carrier density can reenter the superconducting phase beyond the conventional upper critical field Hc2. This negates the conventional thinking that superconductivity and magnetic fields are antagonistic

1998-08-22

351

Instantons and Sphalerons in a Magnetic Field  

Energy Technology Data Exchange (ETDEWEB)

I study the properties of the Euclidean Dirac equation for a light fermion in the presence of both a constant abelian magnetic field and an SU(2) instanton. In particular, I analyze the zero modes analytically in various limits, in order to compare with recent lattice QCD results, and study the implications for the electric dipole moment of the instanton induced by the magnetic field. I also present a holographic computation of the sphaleron rate of a strongly coupled plasma in a the presence of a constant magnetic flux and discuss its physical implications on heavy ion collisions.

Ba?ar, Gökçe [Department of Physics, Stony Brook University, Stony Brook, New York 11794 (United States); Dunne, Gerald V. [Departmentof Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Kharzeev, Dmitri E. [Department of Physics, Stony Brook University, Stony Brook, New York 11794 (United States); Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2013-05-02

352

Torsion, neutrinos, and intergalactic magnetic field  

Energy Technology Data Exchange (ETDEWEB)

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

Massa, C. [Reggio Emilia, (Italy)

2001-03-01

353

Control of chaotic magnetic fields in tokamaks  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English 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 w [...] orks carried out at the Universidade de São Paulo and Universidade Federal do Paraná on theoretical and experimental aspects of generation and control of chaotic magnetic field lines in tokamaks.

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

354

Heavy nuclei in a superstrong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

The production of positrons by the Coulomb field of heavy nuclei in a superstrong magnetic field is considered. It is shown that in fields B>B/sub 0/ = m/sup 2/c/sup 3/e/sup -1/h/sup -1/G (B/B/sub 0/>Z/sup 3/..cap alpha../sup 2/) Z positrons with polarization along the vector B are produced in the field of a nucleus with charge Z>Z/sub c/r (Z/sub c/r is the critical charge of the nucleus) as well as a vacuum electron shell having a small magnetic moment. The vacuum charge distribution in superheavy nuclei (Z..cap alpha..>>1) located in a superstrong magnetic field Z/sup 3/..cap alpha../sup 2/>>B/B/sub 0/>>1 is found.

Ternov, I.M.; Khalilov, V.R.

1981-12-01

355

Bootstrapping the Coronal Magnetic Field with STEREO  

Science.gov (United States)

The 3D coronal magnetic field obtained from stereoscopically triangulated loops has been compared with standard photospheric magnetogram extrapolations. We found a large misalignment of 20-40 deg, depending on the complexity of an AR (Sandman et al. 2009; DeRosa et al. 2009). These studies prove that the magnetic field in the photosphere is not force-free and fundamentally cannot reproduce the coronal magnetic field. Bootstrapping with coronal loop 3D geometries are required to improve modeling of the coronal field. Such coronal field bootstrapping methods are currently developed using stereoscopically triangulated loops from STEREO/EUVI and preliminary results show already a significantly reduced misalignment of 10-20 deg.

Aschwanden, Markus J.

2010-05-01

356

Critical Magnetic Field Determination of Superconducting Materials  

Energy Technology Data Exchange (ETDEWEB)

Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.

Canabal, A.; Tajima, T.; /Los Alamos; Dolgashev, V.A.; Tantawi, S.G.; /SLAC; Yamamoto, T.; /Tsukuba, Natl. Res. Lab. Metrol.

2011-11-04

357

Suppressing drift chamber diffusion without magnetic field  

Science.gov (United States)

The spatial resolution in drift chamber detectors for ionizing radiation is limited by diffusion of the primary electrons. A strong magnetic field along the drift direction is often applied (Fancher et al., Nucl. Instr. and Meth. A 161 (1979) 383) because it suppresses the transverse diffusion, improving the resolution but at considerable increase in cost and complexity. Here we show that transverse track diffusion can be strongly suppressed without any magnetic field. This is achieved by using a gas additive which reversibly captures primary ionization electrons, forming negative ions. The ions drift with thermal energies even at very high drift fields and low pressures ( E/P=28.5 V/ cm torr), and the diffusion decreases with increasing drift field. Upon arrival at the avalanche region of the chamber the negative ions are efficiently stripped and ordinary avalanche gain is obtained. Using this technique, r.m.s. transverse diffusion less than 200 ?m has been achieved over a 15 cm drift path at 40 torr with zero magnetic field. The method can provide high spatial resolution in detectors with long drift distances and zero magnetic field. Negative ion drift chambers would be particularly useful at low pressures and in situations such as space-based or underground experiments where detector size scaleability is important and cost, space, or power constraints preclude the use of a magnetic field.

Martoff, C. J.; Snowden-Ifft, D. P.; Ohnuki, T.; Spooner, N.; Lehner, M.

2000-02-01

358

Near equipment magnetic field verification and scaling  

Science.gov (United States)

Magnetic field measurements are essential to the success of many scientific space missions. Outside of the Earth's magnetic field the biggest potential source of magnetic field contamination of these measurements is emitted by the spacecraft. Spacecraft magnetic cleanliness is enforced through the application of strict ground verification requirements for spacecraft equipment and instruments. Due to increasingly strict AC magnetic field requirements, many spacecraft units cannot be verified on the ground using existing techniques. These measurements must instead be taken close to the equipment under test (EUT) and then extrapolated. A traditional dipole power law of -3 (with a field fall-off proportional to r-3) cannot be applied at these close distances without risk of underestimating the field emitted by the EUT, but we demonstrate that a power law of -2 is too conservative. We propose a compromise that uses a power law of -2 up to a distance equal to 3 times the unit size, beyond which a dipole power law can be applied. When extrapolating from a distance of 0.20 to 1.00 m from the centre of a 0.20 m wide EUT, we demonstrate that this method avoids an underprediction of the field, and is at least twice as accurate as performing the extrapolation with a fixed power law of -2.

Pudney, M. A.; Carr, C. M.; Schwartz, S. J.; Howarth, S. I.

2013-07-01

359

Magnetic Field Generation by Relativistic Shear Flows  

Science.gov (United States)

We report PIC simulation results of magnetic field generation by relativistic shear flows. We find that the shear flow boundary layer in initially non-magnetic shear flows is unstable to the growth of oblique 2-stream and Weibel instabilities near the boundary layer. Such instabilities generate current sheets and loops which eventually form nonlinear ordered structures resembling magnetic flux tubes with alternating polarity, orthogonal to the shear flow direction. Peak magnetic fields can reach almost equipartition values. The size and amplitude of such magnetic structures reach a steady state when the free energy input of the shear flow is balanced by turbulence dissipation. Nonthermal particles are efficiently accelerated, likely by the drift-kink instability, into a power-law energy distribution. These results have important implications for many astrophysical settings, including multi-component blazar jets and gamma-ray bursts. This work was supported by NSF AST0909167 and NASA Fermi grants.

Liang, Edison; Boettcher, Markus; Smith, Ian

2011-11-01

360

Heavy nuclei in a superstrong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

The production of positrons by the Coulomb field of heavy nuclei located in a superstrong magnetic field is considered. It is shown that in fields with a magnetic induction B>BBsub(0)=mmsub(e)sup(2)csup(3)esup(-1)h/2..pi..sup(-1) Gs (I/B/sub 0/>Z/sup 2/..cap alpha../sup 2/, B/sub 0/ is the critical field strength) and fields of nuclei with cbarges Z>Zsub(cr) su(cr) is the critical nuclear charge) Z positrons are produced polarized along the B vector and a vacuum electron shell is formed which possesses a small magnetic moment. The distrihution of the vacuum charge in ultraheavy nuclei (Z..cap alpha..>>1) located in a superstrong magnetic field with Z/sup 3/..cap alpha../sup 2/ >> B/B/sub 0/ >> 1 is found on the basis of a modified relativistic equation of the Thomas-Fermi type. In superstrong fields B>>B/sub 0/ a critical charge of nucleus is considerably smaller than in the absence of the field. Therefore nuclei having a relatively small charge Z(Z<fields.

Ternov, I.M.; Khalilov, V.R. (Moskovskij Gosudarstvennyj Univ. (USSR))

1981-12-01

 
 
 
 
361

Magnetic field measurements in white dwarfs. Magnetic field, rotation and spectrum of 40 Eri B  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper describes results of magnetic field measurements of white dwarfs carried out on the 6-m telescope for the last years. A magnetic field of about Be ~ 28 kG has been discovered in the degenerate star WD 1953-011. A rotational period of WD 0009+501, 1.83 hours, has been discovered, the average magnetic field of the star is = -42.3 +/- 5.4 kG and its semi-amplitude of the rotational variability is 32.0 +/- 6.8 kG. The variable magnetic field of the bright norma...

Fabrika, S. N.; Valyavin, G. G.; Burlakova, T. E.; Barsukova, E. A.; Monin, D. N.

2000-01-01

362

Neutrino oscillations in strong magnetic fields  

International Nuclear Information System (INIS)

Neutrino conversion processes between two neutrino species and the corresponding oscillations induced by strong magnetic fields are considered. The value of the critical strength of magnetic field Bcr as a function of characteristics of neutrinos in vacuum (?m2?, mixing angle ?), effective particle density of matter neff, neutrino (transition) magnetic moment ?-tilde and energy E is introduced. It is shown that the neutrino conversion and oscillations effects induced by magnetic fields B ? Bcr are important and may result in the depletion of the initial type of ?'s in the bunch. A possible increase of these effects in the case when neutrinos pass through a sudden decrease of density of matter (''cross-boundary effect'') and applications to neutrinos from neutron stars and supernova are discussed. (author). 25 refs

1994-01-01

363

Poloidal magnetic fields in superconducting neutron stars  

Science.gov (United States)

We develop the formalism for computing the magnetic field within an axisymmetric neutron star with a strong type II superconductor core surrounded by a normal conductor. The formalism takes full account of the constraints imposed by hydrostatic equilibrium with a barotropic equation of state. A characteristic of this problem is that the currents and fields need to be determined simultaneously and self-consistently. Within the core, the strong type II limit B ? H allows us to compute the shapes of individual field lines. We specialize to purely poloidal magnetic fields that are perpendicular to the equator, and develop the `most dipolar case' in which field lines are vertical at the outer radius of the core, which leads to a magnetic field at the stellar surface that is as close to a dipole as possible. We demonstrate that although field lines from the core may only penetrate a short distance into the normal shell, boundary conditions at the inner radius of the normal shell control the field strength on the surface. Remarkably, we find that for a Newtonian N = 1 polytrope, the surface dipole field strength is Bsurf ? Hb?b/3, where Hb is the magnetic field strength at the outer boundary of the type II core and ?bR is the thickness of the normal shell. For reasonable models, Hb ? 1014 G and ?b ? 0.1 so the surface field strength is Bsurf ? 3 × 1012 G, comparable to the field strengths of many radio pulsars. In general, Hb and ?b are both determined by the equation of state of nuclear matter and by the mass of the neutron star, but Bsurf ˜ 1012 G is probably a robust result for the `most dipolar' case. We speculate on how the wide range of neutron star surface fields might arise in situations with less restrictions on the internal field configuration. We show that quadrupolar distortions are ˜-10-9(Hb/1014 G)2 and arise primarily in the normal shell for B ? Hb.

Henriksson, K. T.; Wasserman, I.

2013-06-01

364

Magnetic-field-induced changes in magnetic shape memory alloys  

International Nuclear Information System (INIS)

First-principles calculations have been used to investigate the physical properties of magnetic shape memory alloys. We find that the martensitic instability of the high-temperature cubic phase in X2YZ (X=Fe, Co, Ni, Pd; Y=Mn, Fe, Co; Z=Al, Ga, Ge, In, Sn) is strongly influenced by the anomalous change of the electronic density of states during the martensitic transformation. The tetragonal martensitic phase is stabilized by a largely reduced density of Ni-3d states near the Fermi level in the minority-spin channel. The magnetic nature of the materials allows for manipulation of the material properties by external magnetic fields. The calculations show that sufficiently large fields can suppress the martensitic transformation in the magnetic shape memory alloy Ni2MnIn

2008-05-25

365

The Magnetic Field in the Convection Zone  

CERN Multimedia

One of the key questions in solar physics that remains to be answered concerns the strength and the distribution of the magnetic fields at the base of the convection zone. The flux tube dynamics requires that toroidal fields of strength as large as 100 kilogauss be present at the base of the convection zone. The kinetic-magnetic equipartition argument leads to smaller field strengths. For possible detection of these relatively small (compared to pressure effects) fields by helioseismic methods it is important to know the range of the field strengths and their distribution. We estimate a range for the toroidal magnetic field strengths at the base of the convection zone using dynamo simulations in a spherical shell. These simulations involve the distribution of rotation provided by helioseismic inversions of the GONG and MDI data. Combining the simulations with the observed line-of-sight surface poloidal field we extract the spatial pattern and magnitude of the mean toroidal magnetic field at the base of the co...

Bigazzi, A; Bigazzi, Alberto; Ruzmaikin, Alexander A.

2002-01-01

366

Ultracold plasma expansion in a magnetic field.  

Science.gov (United States)

We measure the expansion of an ultracold plasma across the field lines of a uniform magnetic field. We image the ion distribution by extracting the ions with a high-voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (ambipolar diffusion model with anisotropic diffusion in two different directions. PMID:18643512

Zhang, X L; Fletcher, R S; Rolston, S L; Guzdar, P N; Swisdak, M

2008-06-13

367

Tuning Permanent Magnets with Adjustable Field Clamps.  

Science.gov (United States)

The effective length of a permanent-magnet assembly can be varied by adjusting the geometrical parameters of a field clamp. This paper presents measurements on a representative dipole and quadrupole as the field clamp is withdrawn axially or radially. The...

R. I. Schermer

1987-01-01

368

Source of the earth's magnetic field  

International Nuclear Information System (INIS)

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

1979-01-01

369

Quantum processes in strong magnetic fields  

Science.gov (United States)

Quantum-mechanical processes that occur in a piece of matter embedded in a magnetic field with a strength of the order of 10 to the 13th power G are described which either are entirely due to the presence of the field or become modified because of it. The conversion of rotational energy into electromagnetic energy in pulsars is analyzed as a mechanism for producing such a field, and it is shown that a strong magnetic field is not sufficient for quantum effects to play a significant role; in addition, the density must be adjusted to be as low as possible. The pressure and energy density of a free electron gas in a uniform magnetic field are evaluated, neutron beta-decay in the presence of a strong field is examined, and the effect of such a field on neutrino reactions is discussed. The thermal history of a neutron star is studied, and it is concluded that a strong magnetic field helps to increase the cooling rate of the star by producing new channels through which neutrinos can carry away energy.

Canuto, V.

1975-01-01

370

Neutrino dispersion in external magnetic fields  

CERN Multimedia

We calculate the neutrino self-energy operator Sigma (p) in the presence of a magnetic field B. In particular, we consider the weak-field limit e B << m_\\ell^2, where m_\\ell is the charged-lepton mass corresponding to the neutrino flavor \

Kuznetsov, A V; Raffelt, G G; Vassilevskaya, L A

2006-01-01

371

Magnetic Fields in the Early Universe  

Energy Technology Data Exchange (ETDEWEB)

Magnetic fields are present everywhere: Earth, other planets, stars, galaxies, galaxy clusters and probably all over the Universe. They extend over kiloparsecs and more, with constant amplitude and direction, and they have tangled components as well. When and how were they created, can we understand the mechanisms, do they influence particle physics, how stable are these fields?

Rubinstein, Hector (Stockholm University)

2004-01-14

372

Passive magnetic shielding in static gradient fields  

Directory of Open Access Journals (Sweden)

Full Text Available The effect of passive magnetic shielding on dc magnetic field gradients imposed by both external and internal sources is studied for two idealized shield models: concentric spherical and infinitely-long cylindrical shells of linear material. It is found that higher-order multipoles of an externally applied magnetic field are always shielded progressively better for either geometry by a factor related to the order of the multipole. In regard to the design of internal coil systems, we determine reaction factors for the general multipole field and provide examples of how one can take advantage of the coupling of the coils to the innermost shell to optimize the uniformity of the field. Furthermore, we provide formulae relevant to active magnetic compensation systems which attempt to stabilize the interior fields by sensing and cancelling the exterior fields close to the outermost shell. Overall this work provides a comprehensive framework that is useful for the analysis and optimization of dc magnetic shields, serving as a theoretical and conceptual design guide as well as a starting point and benchmark for finite-element analysis.

C. P. Bidinosti

2014-04-01

373

Joint Probability Distribution Function for the Electric Microfield and its Ion-Octupole Inhomogeneity Tensor  

International Nuclear Information System (INIS)

From experiments, see e.g. [W. Wiese, D. Kelleher, and D. Paquette, Phys. Rev. A 6, 1132 (1972); V. Helbig and K. Nich, J. Phys. B 14, 3573 (1981).; J. Halenka, Z. Phys. D 16, 1 (1990); . Djurovic, D. Nikolic, I. Savic, S. Sorge, and A.V. Demura, Phys. Rev. E 71, 036407 (2005)], results that the hydrogen lines formed in plasma with Ne ? 1016 cm-3 are asymmetrical. The inhomogeneity of ionic micro field and the higher order corrections (quadratic and next ones) in perturbation theory are the reason for such asymmetry. So far, the ion-emitter quadrupole interaction and the quadratic Stark effect have been included in calculations. The recent work shows that a significant discrepancy between calculations and measurements occurs in the wings of H-beta line in plasmas with cm-3. It should be stressed here that e.g. for the energy operator the correction raised by the quadratic Stark effect is proportional to (where is the emitter-perturber distance) similarly as the correction caused by the emitter-perturber octupole interaction and the quadratic correction from emitter-perturber quadrupole interaction. Thus, it is obvious that a model of the profile calculation is consistent one if all the aforementioned corrections are simultaneously included. Such calculations are planned in the future paper. A statistics of the octupole inhomogeneity tensor in a plasma is necessarily needed in the first step of such calculations. For the first time the distribution functions of the octupole inhomogeneity have been calculated in this paper using the Mayer-Mayer cluster expansion method similarly as for the quadrupole function in the paper [J. Halenka, Z. Phys. D 16, 1 (1990)]. The quantity is the reduced scale of the micro field strength, where is the Holtsmark normal field and is the mean distance defined by the relationship, that is approximately equal to the mean ion-ion distance; whereas is the screening parameter, where is the electronic Debye radius. (author)

2005-09-06

374

Diamond as a magnetic field calibration probe  

International Nuclear Information System (INIS)

An optical method is proposed for the calibration of pulsed magnetic fields using photoluminescence from synthetic diamond. Generally, the pulsed magnetic field profile is reconstructed by measuring the pick-up voltage in a small coil with an effective area that needs to be known accurately. A useful method to calibrate this area is presented using the 1.4040 eV optical transition at the 1.4 eV Ni-related centre in diamond. The field value is calculated from the Zeeman splitting of the optical lines using the g-factor previously characterized by electron spin resonance. Numerous advantages of the method presented are discussed

2004-04-07

375

Diamond as a magnetic field calibration probe  

Energy Technology Data Exchange (ETDEWEB)

An optical method is proposed for the calibration of pulsed magnetic fields using photoluminescence from synthetic diamond. Generally, the pulsed magnetic field profile is reconstructed by measuring the pick-up voltage in a small coil with an effective area that needs to be known accurately. A useful method to calibrate this area is presented using the 1.4040 eV optical transition at the 1.4 eV Ni-related centre in diamond. The field value is calculated from the Zeeman splitting of the optical lines using the g-factor previously characterized by electron spin resonance. Numerous advantages of the method presented are discussed.

Maes, J [Laboratorium voor Vaste-Stoffysica en Magnetisme, K U Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Iakoubovskii, K [Laboratorium voor Halfgeleiderfysica, K U Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Hayne, M [Laboratorium voor Vaste-Stoffysica en Magnetisme, K U Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Stesmans, A [Laboratorium voor Halfgeleiderfysica, K U Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Moshchalkov, V V [Laboratorium voor Vaste-Stoffysica en Magnetisme, K U Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)

2004-04-07

376

Heavy fermions in high magnetic fields  

International Nuclear Information System (INIS)

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The National High Magnetic Field Laboratory (NHMFL) has established major new facilities at LANL. This project sought to explore some exciting new problems in condensed matter physics that could be studied using these facilities. We studied the behavior of heavy-fermion compounds in high-magnetic fields. The unusual properties of these materials are governed by small energy scales arising from strong many-body correlations, demonstrating that the fields that can be achieved in the NHMFL can be used to probe these correlations

1996-01-01

377

Nuclear collision in strong magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model coupled with the Lorentz force equation, we studied nucleus-nucleus collision in strong magnetic field. We find that neutrons and protons can be separated from a nucleus by strong magnetic field and neutron-rich high density nuclear matter and low density proton collectivity matter can be formed during nucleus-nucleus collision. The electric field produced by proton collectivity can accelerate proton and charged meson up to very high energies. Besides the studies of isospin physics such as symmetry energy, these results may help us to understand the acceleration mechanisms of high energy charged particles in the cosmic rays.

Yong Gaochan, E-mail: yonggaochan@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

2011-06-13

378

Nuclear collision in strong magnetic field  

Science.gov (United States)

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model coupled with the Lorentz force equation, we studied nucleus-nucleus collision in strong magnetic field. We find that neutrons and protons can be separated from a nucleus by strong magnetic field and neutron-rich high density nuclear matter and low density proton collectivity matter can be formed during nucleus-nucleus collision. The electric field produced by proton collectivity can accelerate proton and charged meson up to very high energies. Besides the studies of isospin physics such as symmetry energy, these results may help us to understand the acceleration mechanisms of high energy charged particles in the cosmic rays.

Yong, Gao-Chan

2011-06-01

379

Polarization Evolution in Strong Magnetic Fields  

CERN Document Server

Extremely strong magnetic fields change the vacuum index of refraction. Although this polarization dependent effect is small for typical neutron stars, it is large enough to decouple the polarization states of photons traveling within the field. The photon states evolve adiabatically and follow the changing magnetic field direction. The combination of a rotating magnetosphere and a frequency dependent state decoupling predicts polarization phase lags between different wave bands, if the emission process takes place well within the light cylinder. This QED effect may allow observations to distinguish between different pulsar emission mechanisms and to reconstruct the structure of the magnetosphere.

Heyl, J S; Heyl, Jeremy S.; Shaviv, Nir J.

1999-01-01

380

Magnetic charges in local field theory  

Energy Technology Data Exchange (ETDEWEB)

Novel lagrangians are discussed in which (non-abelian) electric and magnetic gauge fields appear on a par. To ensure that these lagrangians describe the correct number of degrees of freedom, tensor gauge fields are included with corresponding gauge symmetries. Non-abelian gauge symmetries that involve both the electric and the magnetic gauge fields can then be realized at the level of a single gauge invariant Lagrangian, without the need of performing duality transformations prior to introducing the gauge couplings. The approach adopted, which was initially developed for gaugings of maximal supergravity, is particularly suited for the study of flux compactifications.

Wit, Bernard de [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, Postbus 80.195, NL-3508 TD Utrecht (Netherlands); Samtleben, Henning [II. Institut fuer Theoretische Physik der Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); Trigiante, Mario [Dept. of Physics, Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino (Italy)

2005-09-01

 
 
 
 
381

Magnetic charges in local field theory  

Energy Technology Data Exchange (ETDEWEB)

Novel Lagrangians are discussed in which (non-abelian) electric and magnetic gauge fields appear on a par. To ensure that these Lagrangians describe the correct number of degrees of freedom, tensor gauge fields are included with corresponding gauge symmetries. Non-abelian gauge symmetries that involve both the electric and the magnetic gauge fields can then be realized at the level of a single gauge invariant Lagrangian, without the need of performing duality transformations prior to introducing the gauge couplings. The approach adopted, which was initially developed for gaugings of maximal supergravity, is particularly suited for the study of flux compactifications. (orig.)

Wit, B. de [Utrecht Univ. (Netherlands). Inst. for Theoretical Physics and Spinoza Inst.; Samtleben, H. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Trigiante, M. [Politecnico di Torino (Italy). Dept. of Physics

2005-08-01

382

Discovery of magnetic fields in hot subdwarfs  

CERN Multimedia

We present initial results of a project to measure mean longitudinal magnetic fields in a group of sdB/OB/O stars. The project was inspired by the discovery of three super-metal-rich sdOB stars, each having metals (e.g. Ti, V) enhanced by factors of 10^3 to 10^5. Similar behaviour is observed in chemically peculiar A stars, where strong magnetic fields are responsible for the enrichment. With this in mind, we obtained circularly polarised spectra of two of the super-metal-rich sdOBs, two "normal" sdBs and two sdOs using FORS1 on the ESO/VLT. By examining circular polarisation in the hydrogen Balmer lines and in helium lines, we have detected magnetic fields with strengths of 1-2 kG in most of our targets. This suggests that such fields are relatively common in hot subdwarfs.

O'Toole, S J; Friedrich, S; Heber, U

2004-01-01

383

Measuring vector magnetic fields in solar prominences  

Science.gov (United States)

We present spectropolarimetric observations in the He I 1083.0 nm multiplet of a quiescent, hedgerow solar prominence. The data were taken with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife; Canary Islands; Spain). The observed He I circular and linear polarization signals are dominated by the Zeeman effect and by atomic level polarization and the Hanle effect, respectively. These observables are sensitive to the strength and orientation of the magnetic field vector at each spatial point of the field of view. We determine the magnetic field vector of the prominence by applying the HAZEL inversion code to the observed Stokes profiles. We briefly discuss the retrieved magnetic field vector configuration.

Orozco Suárez, D.; Asensio Ramos, A.; Trujillo Bueno, J.

2013-05-01

384

Magnetic field measurements of the DESY II magnets  

International Nuclear Information System (INIS)

A new method has been developed for the precise magnetic field measurements in ac magnets. The technique has been applied to the DESY II dipoles and quadrupoles. Movable coils of various lengths are used, and voltage induced by the ac excitatition is compensated by reference coil. A fast ADC triggered at different levels of magnet current converts the output of a low drift analogue integrator. Measurement and data handling are microprocessor controlled. The data are sent to the computer centre for analysis and storage. From there the results and a graphic display are sent back to a local interactive terminal for qualitative online checking

1985-10-01

385

Magnetic field measurements of the DESY II magnets  

International Nuclear Information System (INIS)

A new method has been developed for the precise magnetic field measurements in ac magnets. The technique has been applied to the DESY II dipoles and quadrupoles. Movable coils of various lengths are used, and voltage induced by the ac excitation is compensated by reference coil. A fast ADC triggered at different levels of magnet current converts the output of a low drift analogue integrator. Measurement and data handling are microprocessor controlled. The data are sent to the computer center for analysis and storage. From there the results and a graphic display are sent back to a local interactive terminal for qualitative online checking

1985-05-13

386

Whistler Modes with Wave Magnetic Fields Exceeding the Ambient Field  

International Nuclear Information System (INIS)

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background

2006-03-10

387

Whistler Modes with Wave Magnetic Fields Exceeding the Ambient Field  

Science.gov (United States)

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background.

Stenzel, R. L.; Urrutia, J. M.; Strohmaier, K. D.

2006-03-01

388

Electric/magnetic field sensor  

Science.gov (United States)

A UNLV novel electric/magnetic dot sensor includes a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conductor seamlessly secured to a second conductor within a second sheath; and the first sheath and the second sheath positioned adjacent each other. The UNLV novel sensor can be made by removing outer layers in a segment of coaxial cable, leaving a continuous link of essentially uncovered conductor between two coaxial cable legs.

Schill, Jr., Robert A. (Henderson, NV); Popek, Marc (Las Vegas, NV) [Las Vegas, NV

2009-01-27

389

Field Models in Electricity and Magnetism  

CERN Document Server

Covering the development of field computation in the past forty years, Field Models in Electricity and Magnetism intends to be a concise, comprehensive and up-to-date introduction to field models in electricity and magnetism, ranging from basic theory to numerical applications. The approach assumed throughout the whole book is to solve field problems directly from partial differential equations in terms of vector quantities. Theoretical issues are illustrated by practical examples. In particular, a single example is solved by different methods so that, by comparison of results, limitations and advantages of the various methods are made clear. The subjects of the synthesis of fields and of the optimal design of devices, which are growing in research and so far have not been adequately covered in textbooks, are developed in addition to more classical subjects of analysis. Topics covered include: vector fields: electrostatics, magnetostatics, steady conduction; analytical methods for solving boundary-value probl...

Barba, Paolo Di; Wiak, S

2008-01-01

390

Probing magnetic fields with GALFACTS  

CERN Document Server

GALFACTS is a large-area spectro-polarimetric survey on the Arecibo Radio telescope. It uses the seven-beam focal plane feed array receiver system (ALFA) to carry out an imaging survey project of the 12,700 square degrees of sky visible from Arecibo at 1.4 GHz with 8192 spectral channels over a bandwidth of 300 MHz sampled at 1 millisecond. The aggregate data rate is 875 MB/s. GALFACTS observations will create full-Stokes image cubes at an angular resolution of 3.5' with a band-averaged sensitivity of 90 $\\mu$Jy, allowing sensitive imaging of polarized radiation and Faraday Rotation Measure from both diffuse emission and extragalactic sources. GALFACTS is a scientific pathfinder to the SKA in the area of cosmic magnetism. Key to magnetism science with the SKA is the technique of RM synthesis. The technique of RM synthesis is introduced and we discuss practical aspects of RM synthesis including efficient computational techniques and detection thresholds in the resulting Faraday spectrum. We illustrate the use ...

George, Samuel J; Andrecut, Mircea; Taylor, A Russ

2011-01-01

391

Homogeneous magnetic field in a cylindrical shell  

International Nuclear Information System (INIS)

A highly homogeneous magnetic field complying with different criteria of homogeneity was generated using four coils. The design parameters that minimised the RMS deviation of the field intensity from a constant value throughout the region of interest, were determined numerically. Electrons' trajectories from points along the source to a plane target, were calculated to evaluate the effect of the residual inhomogeneity of the optimal field. A four-coil system accurately implementing optimal design parameters, was built and successfully tested. (author)

1984-01-01

392

Homogeneous magnetic field in a cylindrical shell  

Energy Technology Data Exchange (ETDEWEB)

A highly homogeneous magnetic field complying with different criteria of homogeneity was generated using four coils. The design parameters that minimised the RMS deviation of the field intensity from a constant value throughout the region of interest, were determined numerically. Electrons trajectories from points along the source to a plane target, were calculated to evaluate the effect of the residual inhomogeneity of the optimal field. A four-coil system accurately implementing optimal design parameters, was built and successfully tested.

Friedman, M.; Avida, R.; Brandstadter, J. (Israel Atomic Energy Commission, Beersheba); Erez, G.

1984-03-01

393

Magnetic field properties in a birdcage coil  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Radiofrequency magnetic fields used in MRI experiments have to satisfy specific properties. First, they need to be as homogeneous as possible to excite uniformly the nuclei. Secondly, as the nuclei, these fields need to have a precession movement at Larmor frequency. In this paper we present a numerical study of these properties in the case of the birdcage coil. We derive analytic expression of the RF field through an equivalent circuit model. Properties are validated through numerical simula...

Boissoles, Patrice; Caloz, Gabriel

2006-01-01

394

Generation of magnetic fields in planets  

International Nuclear Information System (INIS)

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

1986-01-01

395

The Magnetic Field Inside the Sun  

Science.gov (United States)

Duvall, Harvey and Pomerantz (1986) reported the existence of a "structural asymmetry" inside the Sun. The authors show here that this asymmetry is not a consequence of the Sun's rotation. They attribute the asymmetry, rather, to a toroidal magnetic field inside the Sun. Consistency requires a field of about one megagauss located in the lower part of the convection zone. Accounting for such a field would wreak havoc on our understanding of the solar dynamo and convection.

Dziembowski, W.; Goode, P. R.

396

Mean square charge radii of radium isotopes and octupole deformation in the /sup 220-228/Ra region  

Energy Technology Data Exchange (ETDEWEB)

The first investigation of isotope shifts in both the atomic and ionic resonance lines of radium has been carried out using the technique of on-line collinear fast-beam laser spectroscopy at the ISOLDE facility at CERN. The measurements cover 19 isotopes in the mass range 208 less than or equal to A less than or equal to 232 with half-lives between 23 ms and 1600 y. The differences in the nuclear mean square charge radii delta(r/sup 2/) have been evaluated and - together with earlier published spins and moments from the hyperfine structure - related to nuclear deformation. In particular the inversion of the odd-even staggering effect for the isotopes /sup 221/Ra, /sup 223/Ra and /sup 225/Ra can be interpreted by the presence of octupole instability and adds weight to the concept of near-stable octupole deformation in the odd-A isotopes which already explained their spins and magnetic moments.

Ahmad, S.A.; Klempt, W.; Ulm, G.; Neugart, R.; Otten, E.W.; Wendt, K.; Reinhard, P.G.

1988-06-20

397

Trapped field recovery of bulk superconductor magnets by static field magnetization  

International Nuclear Information System (INIS)

A series of initial trapped fields after ZFC or FC magnetization are used to simulate the attenuated trapped field. It is possible and easy to recover the lost trapped field and regain the best trapped field performance as before. In the re-magnetization process, the initial magnetic flux inside the bulk magnets will help to recover the trapped field. The optimum recovery field is recommended to be 2.5 times the saturation field of the bulk at LN2 temperature. Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa2Cu3Oy (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

2011-11-01

398

The measurement of magnetic field interference of adjacent to quadrupole magnets of J-PARC RCS  

International Nuclear Information System (INIS)

The magnet of J-PARC Rapid Cycle Synchrotron (RCS) consists of magnets with a large aperture. Therefore influence of magnetic field interference between adjacent magnets must be measured. This is important in order to reduce beam loss. This paper reports the measurement of magnetic field interference between steering or sextupole magnets and quadrupole magnets. (author)

2006-08-01

399

Magnetic Field Measurement with Ground State Alignment  

CERN Multimedia

Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields ($1{\\rm G}\\gtrsim B\\gtrsim 10^{-15}$G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already de...

Yan, Huirong

2013-01-01

400

Magnetic field of a solar flare stream  

International Nuclear Information System (INIS)

The structure of the flare stream is considered. Three models of the stream proposed earlier have been analyzed. The stream in the Hundhausen model consists of a shock wave, a region of compressed solar wind, a region of flare plasma, a region of plasma enriched with helium ions. The modernized Hundhausen model has been supplemented with an inverse shock wave propagating upward the flow. In the Ivanov model the region between the shock wave and the front of the flare stream is divided into the region of compressed solar wind and into that of a compressed magnetic field. The theoretical models have been compared with experimental data. It has been concluded that the flare flux is characterized in accordance with theory and experiment by an increased interplanetary magnetic field. The magnetic field lines of force are closed which agrees with the Hundhausen model. The regular constituent of the magnetic field vertical component in the flare stream is determined by the magnetic field on the Sun in the region of flare

1977-02-01

 
 
 
 
401

Magnetic Fields and Massive Star Formation  

CERN Document Server

Massive stars ($M > 8$ \\msun) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 $\\mu$m obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of $\\lsim$ 0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within $40^\\circ$ of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the ...

Zhang, Qizhou; Girart, Josep M; Hauyu,; Liu,; Tang, Ya-Wen; Koch, Patrick M; Li, Zhi-Yun; Keto, Eric; Ho, Paul T P; Rao, Ramprasad; Lai, Shih-Ping; Ching, Tao-Chung; Frau, Pau; Chen, How-Huan; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain; Csengeri, Timea; Juarez, Carmen

2014-01-01

402

Study on gradient magnetic fields of cascading magnets for oxygen enrichment  

International Nuclear Information System (INIS)

Based on the interception effect on oxygen molecules by a gradient magnetic field, a new device for oxygen enrichment is reported. The device, which is called a multi-channel cascading magnets array frame in the paper, is structured by cascading magnets and several air flow channels among the magnets. The distributions of magnetic fields in the magnetic field spaces of the air flow channels and the gradient fields at the boundary of the magnetic field spaces are simulated. Compared with the previous device formed by two magnets, the cascading structure increases both the magnetic flux density in magnetic field spaces and the magnetic field gradient at the boundary of magnetic field spaces. Also, the multi-channel cascading magnets array frame can increase the number of air flow channels and gas flux. This result offers a promising prospect for oxygen enrichment from air by the interception effect of a gradient magnetic field.

2009-09-21

403

Mechanism of magnetic field effect in cryptochrome  

CERN Multimedia

Creatures as varied as mammals, fish, insects, reptiles, and migratory birds have an intriguing `sixth' sense that allows them to distinguish north from south by using the Earth's intrinsic magnetic field. Yet despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically sensitive radical pair reactions occurring in the retina, the light-sensitive part of the eyes. A photoreceptor, cryptochrome, has been suggested to endow birds with magnetoreceptive abilities as the protein has been shown to exhibit the biophysical properties required for an animal magnetoreceptor to operate properly. Here, we propose a concrete light-driven reaction cycle in cryptochrome that lets a magnetic field influence the signaling state of the photoreceptor. The reaction cycle ties together transient absorption and electron-spin-resonance observations with known facts on avian magnetoreception. Our analysis establishes the feasibility of cryptochrome to act as a g...

Solov'yov, Ilia A

2011-01-01

404

Magnetic field measurements on the VEC  

International Nuclear Information System (INIS)

Magnetic field measurements carried out in two phases on the Variable Energy Cyclotron (VEC) at Calcutta are described. In phase I, first harmonic contents of the VEC magnet are computed by plotting the difference signal produced by two matched search coils connected in opposite polarity. The integrated difference signal after attenuation is plotted on X-ray recorder. The plots are analysed for the amplitude and phase of the first harmonic. By adjusting the position of the ion source, the first harmonic is maintained at approximately 5 gauss. In phase II, detailed measurements on the magnetic field due to the main, trim and valley coils in the geometrical median plane of the magnet are made. Details of the procedure are given. Processing data was done on BESM-6 computer. The accuracies achieved are discussed. (A.K.)

1978-12-31

405

Use of magnetic field aids oil search  

Energy Technology Data Exchange (ETDEWEB)

Efficient oil and gas exploration requires the measurement of the earth's magnetic field with the ability to determine and remove with high accuracy that part of the signal caused by changes in the magnetic basement, and measurement of rock drill cuttings when possible, only to add confidence that the magnetic mineral body is authigenic in origin (created in place), and not detrital. This paper reports that results show that anomalous areas developed from aeromagnetic data and drill holes shown to have anomalous authigenic altered drill cuttings are both 80-85% probable of oil and natural gas discovery, and similarly those areas not anomalous in either are 10-15% probable of oil and gas discovery. The method involves the gathering of low terrain clearance high resolution data of the earth's magnetic field using the cesium vapor magnetometer or equivalent.

1992-05-04

406

Evolution of primordial magnetic fields in mean-field approximation  

Science.gov (United States)

We study the evolution of phase-transition-generated cosmic magnetic fields coupled to the primeval cosmic plasma in the turbulent and viscous free-streaming regimes. The evolution laws for the magnetic energy density and the correlation length, both in the helical and the non-helical cases, are found by solving the autoinduction and Navier-Stokes equations in the 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 the radiation- and the matter-dominated era. The three possible viscous free-streaming phases are characterized by a drag term in the Navier-Stokes equation which depends on the free-streaming properties of neutrinos, photons, or hydrogen atoms, respectively. In the case of non-helical magnetic fields, the magnetic intensity and the magnetic correlation length evolve asymptotically with the temperature, , as and . Here, , , and are, respectively, the temperature, the number of magnetic domains per horizon length, and the bulk velocity at the onset of the particular regime. The coefficients , , , , , and , depend on the index of the assumed initial power-law magnetic spectrum, , and on the particular regime, with the order-one constants and depending also on the cutoff adopted for the initial magnetic spectrum. In the helical case, the quasi-conservation of the magnetic helicity implies, apart from logarithmic corrections and a factor proportional to the initial fractional helicity, power-like evolution laws equal to those in the non-helical case, but with equal to zero.

Campanelli, Leonardo

2014-01-01

407

Braneworld isotropization and magnetic fields  

International Nuclear Information System (INIS)

We consider a magnetic Bianchi I braneworld, embedded in between two Schwarzschild–AdS spacetimes, boosted equal amounts in opposite directions and compare them to the analogous solution in four-dimensional general relativity. The efficient dissipation of anisotropy on the brane is explicitly demonstrated, a process we dub braneworld isotropization. From the bulk point of view, we attribute this to anisotropic energy being carried into the bulk by hot gravitons leaving the brane. From the brane point of view this can be interpreted in terms of the production of particles in the dual CFT. We explain how this result enables us to gain a better understanding of the behaviour of anisotropic branes already studied in the literature. We also show how there is evidence of particles being over-produced, and comment on how this may ultimately provide a possible observational signature of braneworlds

2008-04-01

408

Photon Redshift in a Magnetic field  

CERN Document Server

Previous results from the authors concerning the arising a tiny photon anomalous paramagnetic moment are also interpreted as a red-shift in analogy to the gravitational known effect. It is due to the photon interaction with the magnetized virtual electron-positron background which withdraw transverse momentum from photons and is polarization-dependent. If the photon frequency red-shift implies a change in time, a clock would go faster for increasing magnetic field intensity.

Rojas, H Pérez

2010-01-01

409

Magnetic Linear Birefringence Measurements Using Pulsed Fields  

CERN Multimedia

In this paper we present the accomplishment of the further step towards the vacuum magnetic birefringence measurement based on pulsed fields. After describing our BMV experiment, we report the calibration of our apparatus with nitrogen gas and we discuss the precision of our measurement giving a detailed error budget. Our best present vacuum sensitivity is 2.1x 10^-19 T^-2 per 5 ms magnetic pulse. We finally discuss the perspectives to reach our final goal.

Berceau, Paul; Battesti, Remy; Rizzo, Carlo

2011-01-01

410

Fringe fields of current dominated multipole magnets  

Energy Technology Data Exchange (ETDEWEB)

We determine analytic functions that describe the fringe field region of Lambertson, or cosine-wound, magnets. In particular, we are interested in determining the aberrations, up to fifth order, of a beam transiting our large-bore current-dominated quadrupoles. We determine the scalar potential from the vector potential calculated first for a single current loop and then for a 2N symmetric current loop multipole magnet. 2 refs., 1 fig.

Wadlinger, E.A.

1988-01-01

411

Charged vector particles in the magnetic field  

Energy Technology Data Exchange (ETDEWEB)

Properties of the exact solutions of Proca equations in the magnetic field with an arbitrary value of phenomenological parameter k characterizing the magnetic moment of a particle are studied. The spin operator is constructed, for the case k=1 corresponding to the Weinberg-Salam model. The solutions can be classified according to the eigenvalues of this operator. Green functions of the Weinberg-Salam charged vector boson in the unitary gauge is found.

Obukhov, I.A.; Peres-Fernandes, V.K.; Ternov, I.M.; Khalilov, V.R. (Moskovskij Gosudarstvennyj Univ. (USSR))

1983-01-01

412

MAGNETIC FIELDS FROM QCD PHASE TRANSITIONS  

Energy Technology Data Exchange (ETDEWEB)

We study the evolution of QCD phase transition-generated magnetic fields (MFs) in freely decaying MHD turbulence of the expanding universe. We consider an MF generation model that starts from basic non-perturbative QCD theory and predicts stochastic MFs with an amplitude of the order of 0.02 {mu}G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: a 'weakly helical' turbulence regime, when magnetic helicity increases during decay, and 'fully helical' turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective MF being 0.007 nG. We demonstrate that the considered model of magnetogenesis can provide the seed MF for galaxies and clusters.

Tevzadze, Alexander G. [Faculty of Exact and Natural Sciences, Javakhishvili Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi 0128 (Georgia); Kisslinger, Leonard; Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Brandenburg, Axel, E-mail: aleko@tevza.org [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

2012-11-01

413

SSC collider dipole magnets field angle data  

International Nuclear Information System (INIS)

In the fabrication of both 40 and 50 mm collider dipole superconducting magnets, surveys of the direction of the magnetic field along their length have been taken. This data besides being used for certifying compliance with the specifications for the finished magnet, yields interesting information on the straightness and rigidity of the coil placement between some stages in their manufacture and testing. A discussion on the measuring equipment and procedures is given. All of the 40 mm magnets that were built or cryostat at Fermilab have at least one of these surveys, and a summary of the data on them is presented. Most of the 50 mm magnets built and cold tested at Fermilab have been surveyed before and after insertion in the cryostat and before and after being cold tested. A summary of this data is also presented

1992-07-20

414

Vector magnetic fields of Solar Granulation  

CERN Multimedia

Observations of quiet Sun from the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft would reveal the magnetic characters of the solar photosphere. By making use of the deep mode observations of three quiet regions, we have statistically studied the vector magnetic fields of solar granulation. More than 2000 normal granules are manually selected to form a sample. It is recognized that some granules are even darker than the mean photosphere in intensity, and there is a linear correlation between intensity and Doppler velocity in granules. The distributions of longitudinal and transverse apparent magnetic flux densities, Doppler velocity and continuum intensity of granules are obtained, and their unsigned magnetic flux measured. Two approaches are carried out in this study. First we obtained the magnetic properties of granulation by averaging the measurements for all the sampling granules. Secondly, we reconstructed an average granular cell based on a sub-sample, and obtained the...

Jin, Chunlan; Zhao, Meng

2008-01-01

415

Octupole correction system for the accelerating-storage complex  

International Nuclear Information System (INIS)

The betatron frequency spread and difference coupling resonance caused by cubic nonlinearity of the accelerating-storage complex (ASC) dipoles and quadrupoles are considered. Requirements for the nonlinearity correction system are formulated. The effect of the 4-th order resonances caused by the correcting octupoles is estimated

1984-01-01

416

Octupole collectivity in 98,100,102Mo  

International Nuclear Information System (INIS)

Excited states in 98,100,102Mo have been studied via the 30Si+168Er-induced fission reaction at a beam energy of 142 MeV. Prompt ? rays were detected with the EUROBALL III multidetector array. The level schemes are extended with more than 20 new transitions and interpreted in the framework of a soft-octupole vibration model

2007-01-01

417

On the asymptotic selection rules for octupole operators  

Energy Technology Data Exchange (ETDEWEB)

The selection rules and the values of the matrix elements of the octupole operators r'{sup 3}Y{sub 3{mu}} in the cylindrical basis vertical strokeNN{sub z}{Lambda}> are tabulated. Their applicability to 'normal-' and 'superdeformed' nuclei is discussed. (orig.).

Piepenbring, R. (Inst. des Sciences Nucleaires, 38 - Grenoble (France))

1992-05-04

418

Diffusive processes in a stochastic magnetic field  

International Nuclear Information System (INIS)

The statistical representation of a fluctuating (stochastic) magnetic field configuration is studied in detail. The Eulerian correlation functions of the magnetic field are determined, taking into account all geometrical constraints: these objects form a nondiagonal matrix. The Lagrangian correlations, within the reasonable Corrsin approximation, are reduced to a single scalar function, determined by an integral equation. The mean square perpendicular deviation of a geometrical point moving along a perturbed field line is determined by a nonlinear second-order differential equation. The separation of neighboring field lines in a stochastic magnetic field is studied. We find exponentiation lengths of both signs describing, in particular, a decay (on the average) of any initial anisotropy. The vanishing sum of these exponentiation lengths ensures the existence of an invariant which was overlooked in previous works. Next, the separation of a particle's trajectory from the magnetic field line to which it was initially attached is studied by a similar method. Here too an initial phase of exponential separation appears. Assuming the existence of a final diffusive phase, anomalous diffusion coefficients are found for both weakly and strongly collisional limits. The latter is identical to the well known Rechester-Rosenbluth coefficient, which is obtained here by a more quantitative (though not entirely deductive) treatment than in earlier works

1995-05-01

419

Magnetic Field Seeding by Galactic Winds  

CERN Document Server

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure formation shocks and galactic outflows. In this work we investigate how efficiently galactic winds can provide an intense and widespread "seed" magnetisation. This may be used to explain the magnetic fields observed today in clusters of galaxies and in the intergalactic medium (IGM). We use semi-analytic simulations of magnetised galactic winds coupled to high resolution N-body simulations of structure formation to estimate lower and upper limits for the fraction of the IGM which can be magnetised up to a specified level. We find that galactic winds are able to seed a substantial fraction of the cosmic volume with magnetic fields. Most regions affected by winds have magnetic fields in the range -12 < Log B < -8 G, while higher seed fields can be obtained only rarely and in close proximity to wind-blowing galaxies. These seed fields are suffic...

Bertone, S; Ensslin, T A; Bertone, Serena; Vogt, Corina; Ensslin, Torsten

2006-01-01

420

Near-field aperture-probe as a magnetic dipole source and optical magnetic field detector  

CERN Document Server

Scanning near-field field optical microscopy (SNOM) is a technique, which allows sub-wavelength optical imaging of photonic structures. While the electric field components of light can be routinely obtained, imaging of the magnetic components has only recently become of interest. This is so due to the development of artificial materials, which enhance and exploit the typically weak magnetic light-matter interactions to offer extraordinary optical properties. Consequently, both sources and detectors of the magnetic field of light are now required. In this paper, assisted by finite-difference time-domain simulations, we suggest that the circular aperture at the apex of a metal coated hollow-pyramid SNOM probe can be approximated by a lateral magnetic dipole source. This validates its use as a detector for the lateral magnetic near-field, as illustrated here for a plasmonic nanobar sample. Verification for a dielectric sample is currently in progress. We experimentally demonstrate the equivalence of the reciproc...

Denkova, Denitza; Silhanek, Alejandro V; Van Dorpe, Pol; Moshchalkov, Victor V

2014-01-01

 
 
 
 
421

High-field superconducting accelerator magnets  

International Nuclear Information System (INIS)

The next generation of accelerators for high-energy physics will require high-field, small-bore dipole magnets: in the region of 10 T and 40-mm diam. For such magnets, there is a great incentive to attain high overall current density through increasing the current density within the superconductor and minimizing the copper stabilizer. Both Nb-Ti operating at 1.8 K and Nb_3sn at 4.2 are candidate superconductors. Two programs in the US and one in Japan are directed toward the development of such magnets. The program at LBL is described below

1982-05-14

422

The CMS Magnetic Field Map Performance  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured insi...

2010-01-01

423

Validation of SWMF magnetic field and plasma  

Science.gov (United States)

The Space Weather Modeling Framework (SWMF), using the coupled BATSRUS model, the Rice Convection Model, and an ionosphere electrodynamics solver, is used to simulate 10 space weather events. The simulations are completed in near real time using a limited amount of computational resources. Satellite-specific magnetic field, plasma energy-density spectra, and integrated particle density and temperature are compared against in situ measurements to validate the coupled system. Results are examined both qualitatively and quantitatively to assess model performance. The results show that the system is adept at reproducing large-scale magnetic field variations and predicts plasma temperature and density at values near to the measured mean. Smaller-scale features, such as dipolarizations of the magnetic field at geosynchronous locations, are not reproduced well. Lack of cold particle sources in the inner magnetosphere causes the particle results to suffer. This work is part of a larger effort to thoroughly validate the SWMF.

Welling, D. T.; Ridley, A. J.

2010-03-01

424

Consistency relation for cosmic magnetic fields  

DEFF Research Database (Denmark)

If cosmic magnetic fields are indeed produced during inflation, they are likely to be correlated with the scalar metric perturbations that are responsible for the cosmic microwave background anisotropies and large scale structure. Within an archetypical model of inflationary magnetogenesis, we show that there exists a new simple consistency relation for the non-Gaussian cross correlation function of the scalar metric perturbation with two powers of the magnetic field in the squeezed limit where the momentum of the metric perturbation vanishes. We emphasize that such a consistency relation turns out to be extremely useful to test some recent calculations in the literature. Apart from primordial non-Gaussianity induced by the curvature perturbations, such a cross correlation might provide a new observational probe of inflation and can in principle reveal the primordial nature of cosmic magnetic fields. DOI: 10.1103/PhysRevD.86.123528

Jain, R. K.; Sloth, M. S.

2012-01-01

425

Field flattening in superconducting beam transport magnets  

International Nuclear Information System (INIS)

Dipoles in which the beam traverses the midplane well away from tie magnet axis may benefit from flattening of the vertical field on the midplane. A procedure is described for doing so, making use of Chebyshev polynomials. In the case of the large aperture ''DX'' magnets located immediately on each side of the six intersection regions of the Relativistic Heavy Ion Powder (RHIC), a comparison is made of the field of coils optimized in this way and of coils optimized in the more common way by minimizing the leading coefficients of the Fourier expansion about the magnet axis. The comparison is of the integrated Fourier coefficients of the field expanded locally along the beam trajectory

1994-10-16

426

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

427

Intrinsic Bispectra of Cosmic Magnetic Fields  

CERN Document Server

Forthcoming datasets from the Planck experiment and others are in a position to probe the CMB non-Gaussianity with higher accuracy than has yet been possible and potentially open a new window into the physics of the very early universe. However, a signal need not necessarily be inflationary in origin, and possible contaminants should be examined in detail. One such is provided by early universe magnetic fields, which can be produced by a variety of models including during an inflationary phase, at phase transitions, or seeded by cosmic defects. Should such fields have been extent in the early universe they provide a natural source of CMB non-Gaussianity. Knowledge of the CMB angular bispectrum requires the complete Fourier-space (or "intrinsic") bispectrum. In this paper I consider in detail the intrinsic bispectra of an early-universe magnetic field for a range of power-law and non-power law magnetic power spectra.

Brown, Iain A

2010-01-01

428

Manifestations of the Galactic Center Magnetic Field  

CERN Document Server

Several independent lines of evidence reveal that a relatively strong and highly ordered magnetic field is present throughout the Galaxy's central molecular zone (CMZ). The field