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Sample records for magnetic field probe

  1. Magnetic field concentrator for probing optical magnetic metamaterials.

    PubMed

    Antosiewicz, Tomasz J; Wróbel, Piotr; Szoplik, Tomasz

    2010-12-01

    Development of all dielectric and plasmonic metamaterials with a tunable optical frequency magnetic response creates a need for new inspection techniques. We propose a method of measuring magnetic responses of such metamaterials within a wide range of optical frequencies with a single probe. A tapered fiber probe with a radially corrugated metal coating concentrates azimuthally polarized light in the near-field into a subwavelength spot the longitudinal magnetic field component which is much stronger than the perpendicular electric one. The active probe may be used in a future scanning near-field magnetic microscope for studies of magnetic responses of subwavelength elementary cells of metamaterials.

  2. Behavior of a Single Langmuir Probe in a Magnetic Field.

    ERIC Educational Resources Information Center

    Pytlinski, J. T.; And Others

    1978-01-01

    Describes an experiment to demonstrate the influence of a magnetic field on the behavior of a single Langmuir probe. The experiment introduces the student to magnetically supported plasma and particle behavior in a magnetic field. (GA)

  3. Effect of magnetic field on Langmuir probe measurements

    NASA Astrophysics Data System (ADS)

    Bredin, Jerome; Grondein, Pascaline; Chabert, Pascal; Godyak, Valery; Aanesland, Ane

    2013-09-01

    In the context of PEGASES thruster where an ion-ion plasma is formed across a localized magnetic field, a study to understand how magnetic field affects the Langmuir probe measurements has been made. Several theoretical works have predict that the plasma anisotropy created by a magnetic field will influence Langmuir probe measurement as a function of the orientation of the probe tip. The study has been made in an electropositive plasma of argon for a uniform magnetic field to avoid effects of magnetic field gradient. The electron energy distribution functions (EEDF) measured with various magnetic field show that the measurements with the probe tip along the magnetic field are depleted in the low energy range compared to the one perpendicular to the magnetic field. Comparison of the results obtained with different magnetic field and different probe orientations allows for evaluation the effect of magnetic field on accuracy of EEDF measurement in plasma with magnetic field. These results confirm the theory on Langmuir probes in magnetized plasma that predict a depletion of low electron energy for measurements along the magnetic field lines.

  4. Magnetic probe array with high sensitivity for fluctuating field.

    PubMed

    Kanamaru, Yuki; Gota, Hiroshi; Fujimoto, Kayoko; Ikeyama, Taeko; Asai, Tomohiko; Takahashi, Tsutomu; Nogi, Yasuyuki

    2007-03-01

    A magnetic probe array is constructed to measure precisely the spatial structure of a small fluctuating field included in a strong confinement field that varies with time. To exclude the effect of the confinement field, the magnetic probes consisting of figure-eight-wound coils are prepared. The spatial structure of the fluctuating field is obtained from a Fourier analysis of the probe signal. It is found that the probe array is more sensitive to the fluctuating field with a high mode number than that with a low mode number. An experimental demonstration of the present method is attempted using a field-reversed configuration plasma, where the fluctuating field with 0.1% of the confinement field is successfully detected.

  5. Bunker probe: A plasma potential probe almost insensitive to its orientation with the magnetic field.

    PubMed

    Costea, S; Fonda, B; Kovačič, J; Gyergyek, T; Schneider, B S; Schrittwieser, R; Ionita, C

    2016-05-01

    Due to their ability to suppress a large part of the electron current and thus measuring directly the plasma potential, ion sensitive probes have begun to be widely tested and used in fusion devices. For these probes to work, almost perfect alignment with the total magnetic field is necessary. This condition cannot always be fulfilled due to the curvature of magnetic fields, complex magnetic structure, or magnetic field reconnection. In this perspective, we have developed a plasma potential probe (named Bunker probe) based on the principle of the ion sensitive probe but almost insensitive to its orientation with the total magnetic field. Therefore it can be used to measure the plasma potential inside fusion devices, especially in regions with complex magnetic field topology. Experimental results are presented and compared with Ball-Pen probe measurements taken under identical conditions. We have observed that the floating potential of the Bunker probe is indeed little affected by its orientation with the magnetic field for angles ranging from 90° to 30°, in contrast to the Ball-Pen probe whose floating potential decreases towards that of a Langmuir probe if not properly aligned with the magnetic field. PMID:27250426

  6. Bunker probe: A plasma potential probe almost insensitive to its orientation with the magnetic field.

    PubMed

    Costea, S; Fonda, B; Kovačič, J; Gyergyek, T; Schneider, B S; Schrittwieser, R; Ionita, C

    2016-05-01

    Due to their ability to suppress a large part of the electron current and thus measuring directly the plasma potential, ion sensitive probes have begun to be widely tested and used in fusion devices. For these probes to work, almost perfect alignment with the total magnetic field is necessary. This condition cannot always be fulfilled due to the curvature of magnetic fields, complex magnetic structure, or magnetic field reconnection. In this perspective, we have developed a plasma potential probe (named Bunker probe) based on the principle of the ion sensitive probe but almost insensitive to its orientation with the total magnetic field. Therefore it can be used to measure the plasma potential inside fusion devices, especially in regions with complex magnetic field topology. Experimental results are presented and compared with Ball-Pen probe measurements taken under identical conditions. We have observed that the floating potential of the Bunker probe is indeed little affected by its orientation with the magnetic field for angles ranging from 90° to 30°, in contrast to the Ball-Pen probe whose floating potential decreases towards that of a Langmuir probe if not properly aligned with the magnetic field.

  7. Field measuring probe for SSC (Superconducting Super Collider) magnets

    SciTech Connect

    Ganetis, G.; Herrera, J.; Hogue, R.; Skaritka, J.; Wanderer, P.; Willen, E.

    1987-03-01

    The field probe developed for measuring the field in SSC dipole magnets is an adaptation of the rotating tangential coil system in use at Brookhaven for several years. Also known as the MOLE, it is a self-contained room-temperature mechanism that is pulled through the aperture of the magnet with regular stops to measure the local field. Several minutes are required to measure the field at each point. The probe measures the multipole components of the field as well as the field angle relative to gravity. The sensitivity of the coil and electronics is such that the field up to the full 6.6 T excitation of the magnet as well as the field when warm with only 0.01 T excitation can be measured. Tethers are attached to both ends of the probe to carry electrical connections and to supply dry nitrogen to the air motors that rotate the tangential windings as well as the gravity sensor. A small computer is attached to the probe for control and for data collection, analysis and storage. Digital voltmeters are used to digitize the voltages from the rotating coil and several custom circuits control motor speeds in the probe. The overall diameter of the probe is approximately 2 cm and its length is 2.4 m; the field sensitive windings are 0.6 m in length.

  8. Performance of field measuring probes for SSC magnets

    SciTech Connect

    Thomas, R.; Ganetis, G.; Herrera, J.; Hogue, R.; Jain, A.; Louie, W.; Marone, A.; Wanderer, P.

    1993-12-31

    Several years of experience have been acquired on the operation of probes (``moles``) constructed for the measurement of the multipole components of the magnetic fields of SSC magnets. The field is measured by rotating coils contained in a 2.4-m long tube that is pulled through the aperture of the magnet by an external device-the transporter. In addition to the measuring coils, the tube contains motors for rotating the coil and a system for sensing local vertical using gravity sensors to provide an absolute reference for the field measurements. We describe the steps that must be taken in order to ensure accurate, repeatable measurements; the design changes that have been motivated by difficulties encountered (noise, vibration, variations in temperature); and other performance issues. The mechanical interface between the probe and the hewn tube of the magnet is also described.

  9. Ultralow Magnetic Fields and Gravity Probe B Gyroscope Readout

    NASA Astrophysics Data System (ADS)

    Mester, J. C.; Lockhart, J. M.; Muhlfelder, B.; Murray, D. O.; Taber, M. A.

    We describe the generation of an ultralow magnetic field of < 10-11Tesla in the flight dewar of the Gravity Probe B Relativity Mission. The field was achieved using expanded-superconducting-shield techniques and is maintained with the aid of a magnetic materials control program. A high performance magnetic shield system is required for the proper function of gyroscope readout. The readout system employs a dc SQUID to measure the London moment generated by the superconducting gyro rotor in order to resolve sub-milliarcsecond changes in the gyro spin direction. In addition to a low residual dc magnetic field, attenuation of external field variation is required to be 1012 at the gyro positions. We discuss the measurement of the dc magnetic field and ac attenuation factor and the performance of the readout system

  10. Analysis of magnetic field plasma interactions using microparticles as probes.

    PubMed

    Dropmann, Michael; Laufer, Rene; Herdrich, Georg; Matthews, Lorin S; Hyde, Truell W

    2015-08-01

    The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles. PMID:26382535

  11. Analysis of magnetic field plasma interactions using microparticles as probes.

    PubMed

    Dropmann, Michael; Laufer, Rene; Herdrich, Georg; Matthews, Lorin S; Hyde, Truell W

    2015-08-01

    The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles.

  12. Modified pulsar current analysis: probing magnetic field evolution

    NASA Astrophysics Data System (ADS)

    Igoshev, A. P.; Popov, S. B.

    2014-10-01

    We use a modified pulsar current analysis to study magnetic field decay in radio pulsars. In our approach, we analyse the flow not along the spin period axis as has been performed in previous studies, but study the flow along the direction of growing characteristic age, τ =P/(2dot{P}). We perform extensive tests of the method and find that in most of the cases it is able to uncover non-negligible magnetic field decay (more than a few tens of per cent during the studied range of ages) in normal radio pulsars for realistic initial properties of neutron stars. However, precise determination of the magnetic field decay time-scale is not possible at present. The estimated time-scale may differ by a factor of few for different sets of initial distributions of neutron star parameters. In addition, some combinations of initial distributions and/or selection effects can also mimic enhanced field decay. We apply our method to the observed sample of radio pulsars at distances <10 kpc in the range of characteristic ages 8 × 104 < τ < 106 yr where, according to our study, selection effects are minimized. By analysing pulsars in the Parkes Multibeam and Swinburne surveys, we find that, in this range, the field decays roughly by a factor of 2. With an exponential fit, this corresponds to the decay time-scale ˜4 × 105 yr. With larger statistics and better knowledge of the initial distribution of spin periods and magnetic field strength, this method can be a powerful tool to probe magnetic field decay in neutron stars.

  13. Magnetic field mapping using an image-intensifying fluorescent probe

    NASA Astrophysics Data System (ADS)

    Tou, T. Y.; Blackwell, B. D.; Sharp, L. E.

    1991-05-01

    A simple, cost-effective image-intensifying fluorescent probe designed for mapping the magnetic surfaces in the heliac sheila is described. It consists of a phosphor-coated metal plate which is enclosed in a grounded U-channel that provides electrostatic shielding. An adjustable accelerating voltage is applied to the metal plate to greatly increase the cathodoluminescence produced by the directed electron beam from an electron gun, and the visible electron-beam image is recorded by a CCD camera. The gain in the image brightness allows significant reduction of the electron-beam energy to minimize the deviation of the measured drift surfaces from the true magnetic surfaces, and to improve resolution for detailed studies of surfaces in the newer stellarator experiments. This technique is particularly suited to electron energies below the phosphor activation threshold, when external image intensifying systems are likely to be very inefficient. Up to 36 toroidal rotations have been observed, limited mainly by the effective cross sections of the fluorescent probe and the electron gun. Mapping at low magnetic field strengths allows detection of small fixed amplitude field errors. Measurements of the gain characteristics and resolution are presented, with an example of the electrically variable resolution achievable with this design. The effect of electron energy on drift surfaces of a heliac is demonstrated.

  14. Probing the Earth's core with magnetic field observations from Swarm

    NASA Astrophysics Data System (ADS)

    Finlay, Christopher; Olsen, Nils; Kotsiaros, Stavros; Gillet, Nicolas; Tøffner-Clausen, Lars

    2016-07-01

    By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core. Variations of this core-generated field thus provide a unique means of probing the dynamics taking place in the deepest reaches of the Earth. In this contribution we present a new high resolution model of the core-generated magnetic field, and its recent time changes, derived from a dataset that includes more two years of observations from the Swarm mission. Resulting inferences regarding the underlying core flow, its dynamics, and the nature of the geodynamo process will be discussed. The CHAOS-6 geomagnetic field model, covering the interval 1999-2016, is derived from magnetic data collected by the three Swarm missions, as well as the earlier CHAMP and Oersted satellites, and monthly means data collected from 160 ground observatories. Advantage is taken of the constellation aspect of the Swarm mission by ingesting both scalar and vector field differences along-track and across track between the lower pair of Swarm satellites. The internal part of the model consists of a spherical harmonic (SH) expansion, time-dependent for degrees 20 and below. The model coefficients are estimated using a regularized, iteratively reweighted, least squares scheme involving Huber weights. At Earth's surface, CHAOS-6 shows evidence for positive acceleration of the field intensity in 2015 over a broad area around longitude 90deg E that is also seen at ground observatories such as Novosibirsk. At the core surface, we are able to map the secular variation (linear trend in the magnetic field) up to SH degree 16. The radial field acceleration at the core surface in 2015 is found be largest at low latitudes under the India-South East Asia region and under the region of northern South America, as well as at high northern latitudes under Alaska and Siberia. Surprisingly, there is also evidence for some acceleration in the central Pacific region, for example

  15. Magnetic field probes for use in radio frequency plasma

    SciTech Connect

    Reilly, Michael P.; Miley, George H.; Lewis, William

    2009-05-15

    An impedance analyzer has been used in the characterization of a magnetic induction probe (B-dot probe) for use in plasma. The role of the impedance analyzer was to determine the frequency response of a B-dot probe up to 100 MHz. The probe was specifically designed to take measurements in rf plasma driven at 13.56 MHz. Probe sensitivity and calibration are considered based on the impedance values obtained when a B-dot probe is swept over a wide frequency range. Effects such as unbalanced loads based on transmission line inductances and termination impedance are shown to be limiting factors on the probes useful frequency range. The use of an impedance analyzer allows these effects to readily be characterized.

  16. Probe measurements of the three-dimensional magnetic field structure in a rotating magnetic field sustained field-reversed configuration

    SciTech Connect

    Velas, K. M.; Milroy, R. D.

    2014-01-15

    A translatable three-axis probe was constructed and installed on the translation, confinement, and sustainment upgrade (TCSU) experiment. With ninety windings, the probe can simultaneously measure B{sub r}, B{sub θ}, and B{sub z} at 30 radial positions, and can be placed at any desired axial position within the field reversed configuration (FRC) confinement chamber. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Measurements were made for odd-parity rotating magnetic field (RMF) antennas and even-parity RMF. The steady state data from applying a 10 kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Comparisons will be made to the 3D magnetic structure predicted by NIMROD simulations, with parameters adjusted to match that of the TCSU experiments. The probe provides sufficient data to utilize a Maxwell stress tensor approach to directly measure the torque applied to the FRC's electrons, which combined with a resistive torque model, yields an estimate of the average FRC resistivity.

  17. Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Hill, Carrie S.; Turchi, Peter J.; Burton, Rodney L.; Messer, Sarah; Lovberg, Ralph H.; Hallock, Ashley K.

    2013-01-01

    Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are often employed to perform field measurements in electric propulsion applications where there are time-varying fields. Magnetic field probes provide the means to measure these magnetic fields and can even be used to measure the plasma current density indirectly through the application of Ampere's law. Measurements of this type can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. Results of the development of a standard for B-dot probe measurements are presented, condensing the available literature on the subject into an accessible set of rules, guidelines, and techniques to standardize the performance and presentation of future measurements.

  18. NMR probing of quantum electron solids in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Rhone, Trevor David

    2015-03-01

    In the presence of a high magnetic field, a two dimensional electron system (2DES) is expected to manifest Wigner crystal phases. Over thirty years ago, the search for the Wigner solid led to the discovery of the fractional quantum Hall effect (FQHE). Since then, with the advent of GaAs quantum wells with increasingly high mobility, 2DESs in the quantum Hall regime have proved to be a hunting ground for exceedingly rich many-body physics. Incompressible liquid FQHE states were found to occur in the first Landau level at several fractional filling factors v with odd-denominator. The sequence of FQHE states is truncated by the formation of a Wigner crystal of electrons at very low filling factors, the transition being affected by disorder. In the second Landau level, composite fermions, the quasiparticles of the FQHE, can pair to yield a remarkable even-denominator FQHE state, whose properties are at the forefront of investigation. More recently, electron solid phases have been shown to emerge around integer quantum Hall states. In this talk, I will discuss a new tool, resistively detected NMR, which serves as a direct local probe of in-plane charge density modulations in the 2DES. In our recent work [1] we probe the local charge density landscape of Wigner solids in the vicinity of v = 2 and v<1/3 revealing quantum correlations. This unprecedented access to the microscopic behavior of these exotic solid phases opens up new venues in FQH studies. Furthermore, our NMR technique can probe in-plane charge density fluctuations due to disorder, allowing increased access to understanding roles of disorder in quantum Hall systems. In addition, our latest NMR measurements reveal evidence for charge inhomogeneity in the third Landau level which leads to the possibility of studying bubble and stripe phases in this regime. Future directions may find our NMR technique applied to other exotic phases such as quasiparticle solid phases, which have been proposed to emerge near the v

  19. Probing intergalactic magnetic fields with simulations of electromagnetic cascades

    NASA Astrophysics Data System (ADS)

    Alves Batista, Rafael; Saveliev, Andrey; Sigl, Günter; Vachaspati, Tanmay

    2016-10-01

    We determine the effect of intergalactic magnetic fields on the distribution of high-energy gamma rays by performing three-dimensional Monte Carlo simulations of the development of gamma-ray-induced electromagnetic cascades in the magnetized intergalactic medium. We employ the so-called "Large Sphere Observer" method to efficiently simulate blazar gamma ray halos. We study magnetic fields with a Batchelor spectrum and with maximal left- and right-handed helicities. We also consider the case of sources whose jets are tilted with respect to the line of sight. We verify the formation of extended gamma ray halos around the source direction, and observe spiral-like patterns if the magnetic field is helical. We apply the Q -statistics to the simulated halos to extract their spiral nature and also propose an alternative method, the S -statistics. Both methods provide a quantitative way to infer the helicity of the intervening magnetic fields from the morphology of individual blazar halos for magnetic field strengths B ≳10-15 G and magnetic coherence lengths Lc≳100 Mpc . We show that the S -statistics has a better performance than the Q -statistics when assessing magnetic helicity from the simulated halos.

  20. Probing Mars Crustal Magnetic Field and Ionosphere with the MGS Electron Reflectometer

    NASA Technical Reports Server (NTRS)

    Mitchell, D. L.; Lin, R. P.; Reme, H.; Cloutier, P. A.; Connerney, J. E. P.; Acuna, M. H.; Ness, N. F.

    2002-01-01

    MGS Electron Reflectometer data are used to probe the shape and variability of Mars ionosphere and to identify weak crustal magnetic fields within the Hellas basin. Additional information is contained in the original extended abstract.

  1. Magnification bias as a novel probe for primordial magnetic fields

    SciTech Connect

    Camera, S.; Fedeli, C.; Moscardini, L. E-mail: cosimo.fedeli@oabo.inaf.it

    2014-03-01

    In this paper we investigate magnetic fields generated in the early Universe. These fields are important candidates at explaining the origin of astrophysical magnetism observed in galaxies and galaxy clusters, whose genesis is still by and large unclear. Compared to the standard inflationary power spectrum, intermediate to small scales would experience further substantial matter clustering, were a cosmological magnetic field present prior to recombination. As a consequence, the bias and redshift distribution of galaxies would also be modified. Hitherto, primordial magnetic fields (PMFs) have been tested and constrained with a number of cosmological observables, e.g. the cosmic microwave background radiation, galaxy clustering and, more recently, weak gravitational lensing. Here, we explore the constraining potential of the density fluctuation bias induced by gravitational lensing magnification onto the galaxy-galaxy angular power spectrum. Such an effect is known as magnification bias. Compared to the usual galaxy clustering approach, magnification bias helps in lifting the pathological degeneracy present amongst power spectrum normalisation and galaxy bias. This is because magnification bias cross-correlates galaxy number density fluctuations of nearby objects with weak lensing distortions of high-redshift sources. Thus, it takes advantage of the gravitational deflection of light, which is insensitive to galaxy bias but powerful in constraining the density fluctuation amplitude. To scrutinise the potentiality of this method, we adopt a deep and wide-field spectroscopic galaxy survey. We show that magnification bias does contain important information on primordial magnetism, which will be useful in combination with galaxy clustering and shear. We find we shall be able to rule out at 95.4% CL amplitudes of PMFs larger than 5 × 10{sup −4} nG for values of the PMF power spectral index n{sub B} ∼ 0.

  2. Probing correlations of early magnetic fields using μ-distortion

    SciTech Connect

    Ganc, Jonathan; Sloth, Martin S. E-mail: sloth@cp3.dias.sdu.dk

    2014-08-01

    The damping of a non-uniform magnetic field between the redshifts of about 10{sup 4} and 10{sup 6} injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called μ-distortion. We can calculate the correlation (μ T) of this distortion with the temperature anisotropy T of the CMB to search for a correlation ( B{sup 2}ζ) between the magnetic field B and the curvature perturbation ζ; knowing the ( B{sup 2}ζ) correlation would help us distinguish between different models of magnetogenesis. Since the perturbations which produce the μ-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of ( B{sup 2}ζ), which is naturally parameterized by b{sub NL} (a parameter defined analogously to f{sub NL}). We find that a PIXIE-like CMB experiments has a signal to noise S/N≈ 1.0 × b{sub NL} ( B-tilde {sub μ}/10nG){sup 2}, where B-tilde {sub μ} is the magnetic field's strength on μ-distortion scales normalized to today's redshift; thus, a 10 nG field would be detectable with b{sub NL}=O(1). However, if the field is of inflationary origin, we generically expect it to be accompanied by a curvature bispectrum (ζ{sup 3}) induced by the magnetic field. For sufficiently small magnetic fields, the signal ( B{sup 2} ζ) will dominate, but for B-tilde {sub μ}∼> 1 nG, one would have to consider the specifics of the inflationary magnetogenesis model. We also discuss the potential post-magnetogenesis sources of a ( B{sup 2}ζ) correlation and explain why there will be no contribution from the evolution of the magnetic field in response to the curvature perturbation.

  3. Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Hill, Carrie S.

    2013-01-01

    Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are useful for performing measurements in electric space thrusters and various plasma accelerator applications where a time-varying magnetic field is present. Magnetic field probes have proven to be a mainstay in diagnosing plasma thrusters where changes occur rapidly with respect to time, providing the means to measure the magnetic fields produced by time-varying currents and even an indirect measure of the plasma current density through the application of Ampère's law. Examples of applications where this measurement technique has been employed include pulsed plasma thrusters and quasi-steady magnetoplasmadynamic thrusters. The Electric Propulsion Technical Committee (EPTC) of the American Institute of Aeronautics and Astronautics (AIAA) was asked to assemble a Committee on Standards (CoS) for Electric Propulsion Testing. The assembled CoS was tasked with developing Standards and Recommended Practices for various diagnostic techniques used in the evaluation of plasma thrusters. These include measurements that can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. This paper presents a summary of the standard, describing the preferred methods for fabrication, calibration, and usage of inductive magnetic field probes for use in diagnosing plasma thrusters. Inductive magnetic field probes (also called B-dot probes throughout this document) are commonly used in electric propulsion (EP) research and testing to measure unsteady magnetic fields produced by time-varying currents. The B-dot probe is relatively simple in construction, and requires minimal cost, making it a low-cost technique that is readily accessible to most researchers. While relatively simple, the design of a B-dot probe is not trivial and there are many opportunities for errors in

  4. First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

    SciTech Connect

    Rosenberg, M. J.; Li, C. K.; Fox, W.; Igumenshchev, I.; Seguin, F. H.; Town, R. P.; Frenje, J. A.; Stoeckl, C.; Glebov, V.; Petrasso, R. D.

    2015-04-08

    Novel experiments to study the strongly-driven collision of parallel magnetic fields in β~10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell (PIC) simulations predict a stronger flux compression and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.

  5. Nanoscale magnetic field mapping with a single spin scanning probe magnetometer

    SciTech Connect

    Rondin, L.; Tetienne, J.-P.; Spinicelli, P.; Roch, J.-F.; Jacques, V.; Dal Savio, C.; Karrai, K.; Dantelle, G.; Thiaville, A.; Rohart, S.

    2012-04-09

    We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.

  6. Modeling magnetic fields measured by surface probes embedded in a cylindrical flux conserver.

    PubMed

    Golingo, R P

    2007-03-01

    Calculating magnetic fields at the surface of a flux conserver, perfect conductor, for displaced plasma currents is useful for understanding modes of a Z-pinch. The magnetic fields measured at the flux conserver are a sum of the magnetic fields from the plasma current and the eddy currents which form in the walls to keep the flux constant. While the magnetic field at the wall from the plasma current alone is easily calculated using the Biot-Savart law, finding the eddy currents in the flux conserver which satisfy the boundary conditions can be a tedious process. A simple method of calculating the surface magnetic field for a given Z-pinch displacement off-axis is derived for a cylindrical flux conserver. This relationship does not require the explicit calculation of the eddy currents, saving time when analyzing surface magnetic probe measurements. Analytic expressions can be used to describe the surface magnetic field which increase the understanding of the magnetic probe measurements. PMID:17411182

  7. Design and Application of Hybrid Magnetic Field-Eddy Current Probe

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Wallace, Terryl; Newman, Andy; Leser, Paul; Simpson, John

    2013-01-01

    The incorporation of magnetic field sensors into eddy current probes can result in novel probe designs with unique performance characteristics. One such example is a recently developed electromagnetic probe consisting of a two-channel magnetoresistive sensor with an embedded single-strand eddy current inducer. Magnetic flux leakage maps of ferrous materials are generated from the DC sensor response while high-resolution eddy current imaging is simultaneously performed at frequencies up to 5 megahertz. In this work the design and optimization of this probe will be presented, along with an application toward analysis of sensory materials with embedded ferromagnetic shape-memory alloy (FSMA) particles. The sensory material is designed to produce a paramagnetic to ferromagnetic transition in the FSMA particles under strain. Mapping of the stray magnetic field and eddy current response of the sample with the hybrid probe can thereby image locations in the structure which have experienced an overstrain condition. Numerical modeling of the probe response is performed with good agreement with experimental results.

  8. Design and application of hybrid magnetic field-eddy current probe

    NASA Astrophysics Data System (ADS)

    Wincheski, Buzz; Wallace, Terryl; Newman, Andy; Leser, Paul; Simpson, John

    2014-02-01

    The incorporation of magnetic field sensors into eddy current probes can result in novel probe designs with unique performance characteristics. One such example is a recently developed electromagnetic probe consisting of a twochannel magnetoresistive sensor with an embedded single-strand eddy current inducer. Magnetic flux leakage maps of ferrous materials are generated from the DC sensor response while high-resolution eddy current imaging is simultaneously performed at frequencies up to 5 MHz. In this work the design and optimization of this probe will be presented, along with an application toward analysis of sensory materials with embedded ferromagnetic shape-memory alloy (FSMA) particles. The sensory material is designed to produce a paramagnetic to ferromagnetic transition in the FSMA particles under strain. Mapping of the stray magnetic field and eddy current response of the sample with the hybrid probe can thereby image locations in the structure which have experienced an overstrain condition. Numerical modeling of the probe response is performed with good agreement with experimental results.

  9. Rotational shear near the solar surface as a probe for subphotospheric magnetic fields

    NASA Astrophysics Data System (ADS)

    Kitchatinov, L. L.

    2016-05-01

    Helioseismology revealed an increase in the rotation rate with depth just beneath the solar surface. The relative magnitude of the radial shear is almost constant with latitude. This rotational state can be interpreted as a consequence of two conditions characteristic of the near-surface convection: the smallness of convective turnover time in comparison with the rotation period and absence of a horizontal preferred direction of convection anisotropy. The latter condition is violated in the presence of a magnetic field. This raises the question of whether the subphotospheric fields can be probed with measurements of near-surface rotational shear. The shear is shown to be weakly sensitive to magnetic fields but can serve as a probe for sufficiently strong fields of the order of one kilogauss. It is suggested that the radial differential rotation in extended convective envelopes of red giants is of the same origin as the near-surface rotational shear of the Sun.

  10. Continuous Magnetic Field Monitoring Using Rapid Re-Excitation of NMR Probe Sets.

    PubMed

    Dietrich, Benjamin E; Brunner, David O; Wilm, Bertram J; Barmet, Christoph; Pruessmann, Klaas P

    2016-06-01

    MRI relies on static and spatially varying dynamic magnetic fields of high accuracy. NMR field probes permit the direct observation of spatiotemporal field dynamics for diverse purposes such as data correction, field control, sequence validation, and hardware characterization. However, due to probe signal decay and dephasing existing field cameras are limited in terms of readout duration and the extent of k -space that can be covered. The present work aims to overcome these limitations by the transition to short-lived NMR probes and rapid re-excitation. The proposed approach uses probes with T 2 so short that thermal relaxation dominates signal decay even in the presence of strongest gradients. They are integrated with transmit, receive and sequencing electronics that permit high-rate re-excitation with optional probe alternation as well as complementary RF pulse recording. The system is demonstrated by monitoring of sample MRI sequences with long readouts and large gradient moments. It is compared with the conventional long-lived probe concept and characterized in terms of net sensitivity and sources of systematic error. Continuous k -space trajectory mapping is demonstrated and validated by trajectory-based image reconstruction.

  11. Spectral functions in a magnetic field as a probe of spin-charge separation

    NASA Astrophysics Data System (ADS)

    Rabello, Silvio; Si, Qimiao

    2001-03-01

    We show that the single-particle spectral functions in a magnetic field can be used to probe spin-charge separation[1]. For concreteness our discussion will be focused on the Luttinger liquid, but our idea is applicable to spin-charge separated metals in general. We will show two types of manifestations of spin-charge separation. For the energy dispersion away from the Fermi momentum, the magnetic field splits both the spinon peak and holon peak; here the spin-charge separation nature is reflected in the different magnitude of the two splittings. For the energy dispersion at the Fermi momentum, the magnetic field splits the zero-field peak into FOUR peaks. The effect of a magnetic field on the momentum dispersion, on the other hand, is very different. Either at or away from the Fermi energy, the magnetic field splits the zero-field peak into only two peaks; the magnitude of the splittings of the spinon and holon peaks is always the same. The contrast between the energy dispersion and momentum dispersion reflects the generic physics that the magnetic field causes as main effect the splitting of the spinon Fermi momentum. Finally, we will discuss the feasibility of studying this effect using angle-resolved photoemission and momentum-resolved tunneling[2]. [1] S. Rabello and Q. Si, cond-mat/0008065. [2]S. A. Grigera, S. Rabello et al, in preparation; A. Altland et al. Phys. Rev. Lett. 83, 1203 (1999).

  12. First experiments probing the collision of parallel magnetic fields using laser-produced plasmas

    DOE PAGES

    Rosenberg, M. J.; Li, C. K.; Fox, W.; Igumenshchev, I.; Seguin, F. H.; Town, R. P.; Frenje, J. A.; Stoeckl, C.; Glebov, V.; Petrasso, R. D.

    2015-04-08

    Novel experiments to study the strongly-driven collision of parallel magnetic fields in β~10, laser-produced plasmas have been conducted using monoenergetic proton radiography. These experiments were designed to probe the process of magnetic flux pileup, which has been identified in prior laser-plasma experiments as a key physical mechanism in the reconnection of anti-parallel magnetic fields when the reconnection inflow is dominated by strong plasma flows. In the present experiments using colliding plasmas carrying parallel magnetic fields, the magnetic flux is found to be conserved and slightly compressed in the collision region. Two-dimensional (2D) particle-in-cell (PIC) simulations predict a stronger flux compressionmore » and amplification of the magnetic field strength, and this discrepancy is attributed to the three-dimensional (3D) collision geometry. Future experiments may drive a stronger collision and further explore flux pileup in the context of the strongly-driven interaction of magnetic fields.« less

  13. Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy

    PubMed Central

    Li, Xiang; Lu, Wei; Song, Yiming; Wang, Yuxin; Chen, Aiying; Yan, Biao; Yoshimura, Satoru; Saito, Hitoshi

    2016-01-01

    Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10−20 A m2, respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution. PMID:26932357

  14. PROBING THE LARGE-SCALE TOPOLOGY OF THE HELIOSPHERIC MAGNETIC FIELD USING JOVIAN ELECTRONS

    SciTech Connect

    Owens, M. J.; Horbury, T. S.; Arge, C. N.

    2010-05-10

    Jupiter's magnetosphere acts as a point source of near-relativistic electrons within the heliosphere. In this study, three solar cycles of Jovian electron data in near-Earth space are examined. Jovian electron intensity is found to peak for an ideal Parker spiral connection, but with considerable spread about this point. Assuming the peak in Jovian electron counts indicates the best magnetic connection to Jupiter, we find a clear trend for fast and slow solar wind to be over- and under-wound with respect to the ideal Parker spiral, respectively. This is shown to be well explained in terms of solar wind stream interactions. Thus, modulation of Jovian electrons by corotating interaction regions (CIRs) may primarily be the result of changing magnetic connection, rather than CIRs acting as barriers to cross-field diffusion. By using Jovian electrons to remote sensing magnetic connectivity with Jupiter's magnetosphere, we suggest that they provide a means to validate solar wind models between 1 and 5 AU, even when suitable in situ solar wind observations are not available. Furthermore, using Jovian electron observations as probes of heliospheric magnetic topology could provide insight into heliospheric magnetic field braiding and turbulence, as well as any systematic under-winding of the heliospheric magnetic field relative to the Parker spiral from footpoint motion of the magnetic field.

  15. Theoretical Investigation of Dynamic Properties of Magnetic Molecule Systems as Probed by NMR and Pulsed Fields Experiments

    SciTech Connect

    Rousochatzakis, Ioannis

    2005-12-17

    The field of molecular magnetism[l-6] has become a subject of intense theoretical and experimental interest and has rapidly evolved during the last years. This inter-disciplinary field concerns magnetic systems at the molecular or "nanoscopic" level, whose realization has become feasible due to recent advances in the field of chemical synthesis. The present theoretical work provides a first step towards exploiting the possibilities that are offered by probing magnetic molecules using external magnetic fields with high sweep rates. These probes, apart for providing information specific to magnetic molecules, offer the possibility of conducting a detailed study of the relaxational behavior of interacting spin systems as a result of their coupling with a "heat bath" and in particular the excitations of the host lattice. Development of a broad theoretical framework for dealing with relaxational phenomena induced by dynamical magnetic fields is indeed a worthy goal.

  16. Three dimensional imaging of helicon wave fields via magnetic induction probes

    NASA Astrophysics Data System (ADS)

    Reilly, Michael P.

    The majority of data presented in this work is for a helicon plasma discharge driven at 13.56 MHz, 500 Watts input power, 900 Gauss applied magnetic field, 10 mTorr neutral Argon gas, and cylindrical plasma of 5 cm diameter approximately 50 cm long. High frequency magnetic induction probes were developed to measure helicon wave propagation using a new technique for frequency calibration through an impedance analyzer; up to 100 MHz. This work demonstrates magnetic field measurements in high frequency plasma are greatly simplified through this new frequency characterization method. Line-lengths and transmission-cable-types are readily identified as diagnostic limiting factors. The magnetic probe design enables the first 3-dimensional imaging of plasma waves through detailed radial and axial measurements. Strong agreement is obtained between the measured br, btheta, and bz radial profiles with the numerical solutions of helicon waves when a non-uniform radial density profile is considered. The axial helicon wavelength predicted by the non-uniform radial density theory also agrees with the measured wavelength when the full three dimensional wave is accurately analyzed. In some cases, the differences between the three dimensional wavelength and the numerically solved values are less than 35%. This is in contrast to the two dimensional wavelengths which can differ from the numerical values by greater than 100%. We show a complete visual representation of helicon waves through 3-d imaging which provides significantly more accurate analysis of the helicon wavelength. This work also observed a density peak downstream from the antenna/source through axial density measurements with a RF compensated Langmuir probe (calibrated against a 90 GHz microwave interferometer). Here, the downstream density peak is explained in terms of a global energy balance modeled by an axially decaying electron temperature peaked at the source; Te → 3 - 7 eV. This model does not require an

  17. Optical probe of spin-orbit fields in metallic magnetic structures

    NASA Astrophysics Data System (ADS)

    Montazeri, Mohammad; Upadhyaya, Pramey; Yu, Guoqiang; Wong, Kin L.; Lang, Murong; Fan, Yabin; Khalili Amiri, Pedram; Schwartz, Robert N.; Wang, Kang L.

    2015-03-01

    We report a novel self-consistent optical approach based on magneto-optical Kerr effect to directly and quantitatively probe the spin-orbit fields of magnetic devices with 1um diffraction limited spatial resolution. The optical probe is exemplified by investigating the spin-orbit fields in a magnetic stack of Ta(5 nm)/CoFeB(1.1 nm)/MgO(2.0 nm)/TaOx with enhanced perpendicular anisotropy. Both field-like and damping-like contributions were measured independently and their coefficients are quantified at 3 . 3 ×10-6 and - 2 . 0 ×10-6 Oe / A . cm-2 respectively. A detailed comparison with standard transport technique is presented in which a very good agreement were found. Our results establish the relevance of the optical methods for studying spin-orbit torque related physics. We acknowledge the support from the National Science Foundation (DMR-1411085) and the FAME Center, one of the six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  18. Rapid rise time pulsed magnetic field circuit for pump-probe field effect studies.

    PubMed

    Salaoru, T A; Woodward, Jonathan R

    2007-03-01

    Here we describe an electronic circuit capable of producing rapidly switched dc magnetic fields of up to 20 mT with a rise time of 10 ns and a pulse length variable from 50 ns to more than 10 micros, suitable for use in the study of magnetic field effects on radical pair (RP) reactions. This corresponds to switching the field on a time scale short relative to the lifetime of typical RPs and maintaining it well beyond their lifetimes. Previous experiments have involved discharging a capacitor through a low inductance coil for a limited time using a switching circuit. These suffer from decaying field strength over the duration of the pulse given primarily by the ratio of the pulse width to the RC constant of the circuit. We describe here a simple yet elegant solution that completely eliminates this difficulty by employing a feedback loop. This allows a constant field to be maintained over the entire length of the pulse. PMID:17411229

  19. Magnetic field and quadruple Langmuir probe measurements in the plume of the plasmoid thruster experiment

    NASA Astrophysics Data System (ADS)

    Koelfgen, Syri Jo

    The development of high specific impulse rocket engines is essential for fast and efficient space travel. The plasmoid thruster, a novel propulsion concept with the potential for producing a high specific impulse, was investigated in light of this need. This pulsed inductive rocket utilizes the Lorentz force to accelerate plasmoids and produce thrust. The Plasmoid Thruster Experiment (PTX) was designed to experimentally evaluate the thruster concept. PTX operates by producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. Measurements of the plasmoid magnetic fields, electron temperature (Te), electron number density (n e) and Mach number (M) were taken in the PTX plume with a B˙ probe array and a quadruple Langmuir probe. The measurements were used for calculating exit velocity and Isp. High-speed photographs were also obtained for capturing images of the plasmoids and estimating their velocity. The magnetic field data showed behavior characteristic of plasmoids, such as the occurrence of the maximum axial magnetic field on axis and magnetic field reversal. The quadruple Langmuir probe data revealed several factors that influence thruster operation, including propellant choice, supply pressure and propellant injection timing (tpuff). For Ar propellant at supply pressures of 14--34 psig and tpuff = 2200 mus, Te ranged from 2--7 eV, ne ranged from 1.5 x 1020 m-3 to 3.5 x 1020 m-3, and M ranged from 3.3--3.8 in PTX. For H2 propellant, T e ranged from 15--27 eV, ne ranged from 0.8 x 1020 m-3 to 1.5 x 1020 m-3, and M ranged from 1.4--2.6, for supply pressures of 9--38 psig and tpuff = 1200--2400 mus. Analysis of the plume measurements yielded high thruster exit velocities, indicating that the plasmoid thruster can produce a high Isp. Velocities of 24 km/s, 35 km/s and 46 km/s were calculated for supply pressures of 38 psig, 24 psig and 9 psig of H2 propellant, respectively. These exit velocities deliver Isp values of 2,400 s, 3,500 s and 4

  20. Magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Silva, Nicolas

    2012-09-01

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

  1. BLAZAR HALOS AS PROBE FOR EXTRAGALACTIC MAGNETIC FIELDS AND MAXIMAL ACCELERATION ENERGY

    SciTech Connect

    Dolag, K.; Kachelriess, M.; Ostapchenko, S.; Tomas, R.

    2009-09-20

    High-energy photons from blazars interact within tens of kpc with the extragalactic photon background, initiating electromagnetic pair cascades. The charged component of such cascades is deflected by extragalactic magnetic fields (EGMFs), leading to halos even around initially point-like sources. We calculate the intensity profile of the resulting secondary high-energy photons for different assumptions on the initial source spectrum and the strength of the EGMF, employing also fields found earlier in a constrained simulation of structure formation including magnetohydrodynamics processes. We find that the observation of halos around blazars like Mrk 180 probes an interesting range of EGMF strengths and acceleration models: in particular, blazar halos test if the photon energy spectrum at the source extends beyond {approx}100 TeV and how anisotropic this high-energy component is emitted.

  2. Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-Ray Background

    NASA Technical Reports Server (NTRS)

    Venters, T. M.; Pavlidou, V.

    2012-01-01

    The intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the extragalactic gamma-ray background, through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thus inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that the two extreme cases (zero IGMF and IGMF strong enough to completely isotropize cascade photons) would be separable by ten years of Fermi observations and reasonable model parameters for the gamma-ray background. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

  3. Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background

    NASA Technical Reports Server (NTRS)

    Venters, T. M.; Pavlidou, V.

    2013-01-01

    The intergalactic magnetic field (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

  4. Using the morphology and magnetic fields of tailed radio galaxies as environmental probes

    NASA Astrophysics Data System (ADS)

    Johnston-Hollitt, M.; Dehghan, S.; Pratley, L.

    2015-03-01

    Bent-tailed (BT) radio sources have long been known to trace over densities in the Universe up to z ~ 1 and there is increasing evidence this association persists out to redshifts of 2. The morphology of the jets in BT galaxies is primarily a function of the environment that they have resided in and so BTs provide invaluable clues as to their local conditions. Thus, not only can samples of BT galaxies be used as signposts of large-scale structure, but are also valuable for obtaining a statistical measurement of properties of the intra-cluster medium including the presence of cluster accretion shocks & winds, and as historical anemometers, preserving the dynamical history of their surroundings in their jets. We discuss the use of BTs to unveil large-scale structure and provide an example in which a BT was used to unlock the dynamical history of its host cluster. In addition to their use as density and dynamical indicators, BTs are useful probes of the magnetic field on their environment on scales which are inaccessible to other methods. Here we discuss a novel way in which a particular sub-class of BTs, the so-called `corkscrew' galaxies might further elucidate the coherence lengths of the magnetic fields in their vicinity. Given that BTs are estimated to make up a large population in next generation surveys we posit that the use of jets in this way could provide a unique source of environmental information for clusters and groups up to z = 2.

  5. OPEN CLUSTERS AS PROBES OF THE GALACTIC MAGNETIC FIELD. I. CLUSTER PROPERTIES

    SciTech Connect

    Hoq, Sadia; Clemens, D. P. E-mail: clemens@bu.edu

    2015-10-15

    Stars in open clusters are powerful probes of the intervening Galactic magnetic field via background starlight polarimetry because they provide constraints on the magnetic field distances. We use 2MASS photometric data for a sample of 31 clusters in the outer Galaxy for which near-IR polarimetric data were obtained to determine the cluster distances, ages, and reddenings via fitting theoretical isochrones to cluster color–magnitude diagrams. The fitting approach uses an objective χ{sup 2} minimization technique to derive the cluster properties and their uncertainties. We found the ages, distances, and reddenings for 24 of the clusters, and the distances and reddenings for 6 additional clusters that were either sparse or faint in the near-IR. The derived ranges of log(age), distance, and E(B−V) were 7.25–9.63, ∼670–6160 pc, and 0.02–1.46 mag, respectively. The distance uncertainties ranged from ∼8% to 20%. The derived parameters were compared to previous studies, and most cluster parameters agree within our uncertainties. To test the accuracy of the fitting technique, synthetic clusters with 50, 100, or 200 cluster members and a wide range of ages were fit. These tests recovered the input parameters within their uncertainties for more than 90% of the individual synthetic cluster parameters. These results indicate that the fitting technique likely provides reliable estimates of cluster properties. The distances derived will be used in an upcoming study of the Galactic magnetic field in the outer Galaxy.

  6. Probing the innermost regions of AGN jets and their magnetic fields: LBA

    NASA Astrophysics Data System (ADS)

    Anderson, James M.; Lobanov, Andrei; Perez Torres, Miguel Angel; Ros, Eduardo; Alberdi, Antxon; Taylor, Greg; Zensus, Anton; Cawthorne, Tim; Kovalev, Yuri; Krichbaum, Thomas P.; Savolainen, Tuomas; Gomez, Jose Luis; Bach, Uwe; Bernhart, Simone; Clausen-Brown, Eric; Eilek, Jean; Fromm, Christian

    2013-10-01

    RadioAstron provides the first true full-polarization capabilities for space-VLBI. As part of our RadioAstron key science project to study magnetic fields in AGNs, we propose that the LBA participates in two global VLBI imaging observations (10 to 20 hours of total observing time) at K-band from a list of possible imaging targets (including OJ~287, 3C~273, 3C~279, and 3C~454.3 for the LBA) and sessions in the timerange 2013 October through 2014 April currently under consideration by other global VLBI stations. These measurements will exploit the unprecedented high-angular resolution polarization capabilities of RadioAstron to probe the innermost regions of AGN jets and their magnetic fields. Our initial target sample contains bright, strongly polarized AGN jets for which we confidently expect to measure polarization and be able to perform Faraday rotation synthesis analysis that will allow us to construct 3D maps of the magnetic field structure and strength in the vicinity of the central black hole. Comparison with 3D relativistic-MHD and emission simulations will allow us to obtain a better understanding of the jet formation and high-energy emission mechanisms. Perigee imaging with RadioAstron requires support from a truly global VLBI array that can co-observe for the full RadioAstron track. As very sensitive stations are required at all times to locate and track fringes to the weak RadioAstron K-band system, the LBA, including DSS-43, the ATCA, and Parkes, is crucial for the far eastern latitude region of the global array.

  7. Thermonuclear Supernovae: Probing Magnetic Fields by Positrons and Late-time IR Line Profiles

    NASA Astrophysics Data System (ADS)

    Penney, R.; Hoeflich, P.

    2014-11-01

    We show the importance of γ and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 μm, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M Ch) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 109 G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a γ-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 μm can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M Ch mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central 56Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M Ch. Good time coverage is required to separate the effects of optical

  8. Thermonuclear supernovae: probing magnetic fields by positrons and late-time IR line profiles

    SciTech Connect

    Penney, R.; Hoeflich, P. E-mail: rpenney@g.clemson.edu

    2014-11-01

    We show the importance of γ and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 μm, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M {sub Ch}) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 10{sup 9} G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a γ-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 μm can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M {sub Ch} mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central {sup 56}Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M {sub Ch}. Good time coverage is required to

  9. Probing of field-induced structures and tunable rheological properties of surfactant capped magnetically polarizable nanofluids.

    PubMed

    Felicia, Leona J; Philip, John

    2013-01-01

    Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths. PMID:23210900

  10. Probing of field-induced structures and tunable rheological properties of surfactant capped magnetically polarizable nanofluids.

    PubMed

    Felicia, Leona J; Philip, John

    2013-01-01

    Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths.

  11. 2D profile of poloidal magnetic field diagnosed by a laser-driven ion-beam trace probe (LITP)

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoyi; Xiao, Chijie; Chen, Yihang; Xu, Tianchao; Lin, Chen; Wang, Long; Xu, Min; Yu, Yi

    2016-11-01

    Based on large energy spread of laser-driven ion beam (LIB), a new method, the Laser-driven Ion-beam Trace Probe (LITP), was suggested recently to diagnose the poloidal magnetic field (Bp) and radial electric field (Er) in toroidal devices. Based on another property of LIB, a wide angular distribution, here we suggested that LITP could be extended to get 2D Bp profile or 1D profile of both poloidal and radial magnetic fields at the same time. In this paper, we show the basic principle, some preliminary simulation results, and experimental preparation to test the basic principle of LITP.

  12. Spectropolarimetry of Giant stars: Probing the influence of magnetic field on evolved stars Spectropolarimetry of Giant stars: Probing the influence of magnetic field on evolved stars

    NASA Astrophysics Data System (ADS)

    da Costa, Jefferson; Castro, Matthieu; Petit, Pascal; do Nascimento, José-Dias, Jr.

    2015-08-01

    It is know that lithium is element easily destroyed in stellar interior, the existence of lithium rich stars means a great challenge in stellar evolution. In this context our observations ravels the serendipitous discovery of an unusually high lithium abundance star. This is a K0III HD 150050, which has strong deepening on lithium line (6707.8 Å) this means lithium abundance of 2.81 0.2 dex, therefore this star belong a rare group called super Li-Rich stars. A possible source of the non-standard episodes required to produce Li-rich stars were identified in magneto-thermohaline mixing accounted by models of extra-mixing induced by magnetic buoyancy. However to better understand this is necessary more observational data. In last three decades several studies has showed that late type red giant stars presents a remarkable modifications in these outer atmosphere layers when they become late type star in HR diagram. These changes are founded through X-ray, Ultraviolet, and Chromospheric activity analyses, and then we can establish the called “Dividing lines”. We made spectropalarimetric observations with ESPaDOnS@CFHT to achieve two main objectives: analyze the influence of magnetic field in the Li-rich giant stars, and understand how works the magnetic field in late type giants and supergiants across the “dividing line”.

  13. Analysis of magnetic probe signals including effect of cylindrical conducting wall for field-reversed configuration experiment

    SciTech Connect

    Ikeyama, Taeko; Hiroi, Masanori; Nemoto, Yuuichi; Nogi, Yasuyuki

    2008-06-15

    A confinement field is disturbed by magnetohydrodynamic (MHD) motions of a field-reversed configuration (FRC) plasma in a cylindrical conductor. The effect of the conductor should be included to obtain a spatial structure of the disturbed field with a good precision. For this purpose, a toroidal current in the plasma and an eddy current on a conducting wall are replaced by magnetic dipole and image magnetic dipole moments, respectively. Typical spatial structures of the disturbed field are calculated by using the dipole moments for such MHD motions as radial shift, internal tilt, external tilt, and n=2 mode deformation. Then, analytic formulas for estimating the shift distance, tilt angle, and deformation rate of the MHD motions from magnetic probe signals are derived. It is estimated from the calculations by using the dipole moments that the analytic formulas include an approximately 40% error. Two kinds of experiment are carried out to investigate the reliability of the calculations. First, a magnetic field produced by a circular current is measured in an aluminum pipe to confirm the replacement of the eddy current with the image magnetic dipole moments. The measured fields coincide well with the calculated values including the image magnetic dipole moments. Second, magnetic probe signals measured from the FRC plasma are substituted into the analytic formulas to obtain shift distance and deformation rate. The experimental results are compared to the MHD motions measured by using a radiation from the plasma. If the error included in the analytic formulas and the difference between the magnetic and optical structures in the plasma are considered, the results of the radiation measurement support well those of the magnetic analysis.

  14. Fast Radio Bursts as Probes of Magnetic Fields in the Intergalactic Medium

    NASA Astrophysics Data System (ADS)

    Akahori, Takuya; Ryu, Dongsu; Gaensler, B. M.

    2016-06-01

    We examine the proposal that the dispersion measures (DMs) and Faraday rotation measures (RMs) of extragalactic linearly polarized fast radio bursts (FRBs) can be used to probe the intergalactic magnetic field (IGMF) in filaments of galaxies. The DM through the cosmic web is dominated by contributions from the warm-hot intergalactic medium (WHIM) in filaments and from the gas in voids. On the other hand, RM is induced mostly by the hot medium in galaxy clusters, and only a fraction of it is produced in the WHIM. We show that if one excludes FRBs whose sightlines pass through galaxy clusters, the line of sight (LOS) strength of the IGMF in filaments, {B}| | , is approximately C(< 1+z> /{f}{DM})({RM}/{DM}), where C is a known constant. Here, the redshift of the FRB is not required to be known; f DM is the fraction of total DM due to the WHIM, while < 1+z> is the redshift of interevening gas weighted by the WHIM gas density, both of which can be evaluated for a given cosmology model solely from the DM of an FRB. Using data on structure formation simulations and a model IGMF, we show that C(< 1+z> /{f}{DM})({RM}/{DM}) closely reproduces the density-weighted LOS strength of the IGMF in filaments of the large-scale structure.

  15. Fisher analysis on wide-band polarimetry for probing the intergalactic magnetic field

    NASA Astrophysics Data System (ADS)

    Ideguchi, Shinsuke; Takahashi, Keitaro; Akahori, Takuya; Kumazaki, Kohei; Ryu, Dongsu

    2014-02-01

    We investigate the capability of current radio telescopes for probing Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) in the large-scale structure of the universe, which is expected to be of order O (1) rad m-2. We consider polarization observations of a compact radio source such as quasars behind a diffuse source such as the Galaxy, and calculate Stokes parameters Q and U assuming a simple model of the Faraday dispersion functions with Gaussian shape. Then, we perform the Fisher analysis to estimate the expected errors in the model parameters from QU-fitting of polarization intensity, accounting for the sensitivities and frequency bands of Australian Square Kilometer Array Pathfinder, Low Frequency Array, and the Giant Meterwave Radio Telescope. Finally, we examine the conditions on the source intensities which are required to detect the IGMF. Our analysis indicates that the QU-fitting is promising for forthcoming wideband polarimetry to explore RM due to the IGMF in filaments of galaxies.

  16. High-Resolution B Dot Probe for Measuring 3D Magnetic Fields in the MOCHI Labjet Experiment

    NASA Astrophysics Data System (ADS)

    Azuara Rosales, Manuel; von der Linden, Jens; You, Setthivoine

    2014-10-01

    The MOCHI Labjet experiment will use a triple electrode planar plasma gun to explore canonical helicity transport in laboratory astrophysical jets. Canonical helicity transport suggests that destabilizing magnetic energy can be converted into stabilizing shear flows at two-fluid spatial scales li ~c/wpi . A high-resolution . B probe array, capable of measuring magnetic field dynamics at length and time scales important to canonical helicity transport is being built. The probe array consists of three tridents, made of 5 . 13 mm OD and 4 . 32 mm ID stainless steel tubes of 102 cm length, enclosing a total of 1215 commercial inductor chips with a three axis spatial resolution of 11 mm. The average value for the effective NA of each inductor chip is 1 . 21 .10-4 m2. The probe array lays in a plane perpendicular to the jet, and is axially translatable. This work is supported by US DOE Grant DE-SC0010340.

  17. Optically Detected Scanned Probe Magnetic Resonance Imaging

    NASA Astrophysics Data System (ADS)

    Wolfe, Christopher; Bhallamudi, Vidya; Wang, Hailong; Du, Chunhui; Manuilov, Sergei; Adur, Rohan; Yang, Fengyuan; Hammel, P. Chris

    2014-03-01

    Magnetic resonance is a powerful tool for studying magnetic properties and dynamics of spin systems. Scanned magnetic probes can induce spatially localized resonance due to the strong magnetic field and gradient near the magnetic tip., Nitrogen vacancy centers (NV) in diamond provide a sensitive means of measuring magnetic fields at the nanoscale. We report preliminary results towards using the high sensitivity of NV detection with a scanned magnetic probe to study local magnetic phenomena. This work is supported by the Center for Emergent Materials at The Ohio State University, a NSF Materials Research Science and Engineering Center (DMR-0820414).

  18. Magnetic field dependence of spatial frequency encoding NMR as probed on an oligosaccharide.

    PubMed

    Pitoux, D; Hu, Z; Plainchont, B; Merlet, D; Farjon, J; Bonnaffé, D; Giraud, N

    2015-10-01

    The magnetic field dependence of spatial frequency encoding NMR techniques is addressed through a detailed analysis of (1)H NMR spectra acquired under spatial frequency encoding on an oligomeric saccharide sample. In particular, the influence of the strength of the static magnetic field on spectral and spatial resolutions that are key features of this method is investigated. For this purpose, we report the acquisition of correlation experiments implementing broadband homodecoupling or J-edited spin evolutions, and we discuss the resolution enhancements that are provided by these techniques at two different magnetic fields. We show that performing these experiments at higher field improves the performance of high resolution NMR techniques based on a spatial frequency encoding. The significant resolution enhancements observed on the correlation spectra acquired at very high field make them valuable analytical tools that are suitable for the assignment of (1)H chemical shifts and scalar couplings in molecules with highly crowded spectrum such as carbohydrates.

  19. A new probe of the magnetic field power spectrum in cosmic web filaments

    NASA Astrophysics Data System (ADS)

    Hales, Christopher A.; Greiner, Maksim; Ensslin, Torsten A.

    2015-08-01

    Establishing the properties of magnetic fields on scales larger than galaxy clusters is critical for resolving the unknown origin and evolution of galactic and cluster magnetism. More generally, observations of magnetic fields on cosmic scales are needed for assessing the impacts of magnetism on cosmology, particle physics, and structure formation over the full history of the Universe. However, firm observational evidence for magnetic fields in large scale structure remains elusive. In an effort to address this problem, we have developed a novel statistical method to infer the magnetic field power spectrum in cosmic web filaments using observation of the two-point correlation of Faraday rotation measures from a dense grid of extragalactic radio sources. Here we describe our approach, which embeds and extends the pioneering work of Kolatt (1998) within the context of Information Field Theory (a statistical theory for Bayesian inference on spatially distributed signals; Enfllin et al., 2009). We describe prospects for observation, for example with forthcoming data from the ultra-deep JVLA CHILES Con Pol survey and future surveys with the SKA.

  20. Probing the Role of Magnetic Fields in Star Formation with BLAST-Pol

    NASA Astrophysics Data System (ADS)

    Fissel, Laura M.; BLAST-Pol Collaboration

    2012-01-01

    Polarimetry is a powerful tool for studying the importance of magnetic fields in the star formation process. However, at present there are very few submm/mm polarimetry observations of large scale fields within molecular clouds. BLAST-Pol, the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry, maps linearly polarized dust emission at 250, 350 and 500 microns; it has the unique combination of sensitivity to large scale magnetic fields, and arcminute resolution necessary to trace fields into prestellar cores and dense filaments. In this presentation I will give a brief overview of the instrument, its performance during the first BLAST-Pol science flight completed in January 2011, and plans for future flights. I will also show preliminary maps from the first science flight and explain how these maps will be used to study the relationship between large and small scale magnetic fields in molecular clouds, the degree of order in the field, and the relationship between the magnetic field structure and the morphology of filaments and cores within the clouds. The BLAST-Pol collaboration gratefully acknowledges the support of NASA, NSF Office of Polar Programs, the CSA (Canada), the STFC (UK), NSERC (Canada), and the Leverhulme Trust (UK).

  1. Current-modulating magnetic force microscope probe

    SciTech Connect

    Wang, Frank Z.; Helian, Na; Clegg, Warwick W; Windmill, James F. C.; Jenkins, David

    2001-06-01

    A new current-modulating probe for the magnetic force microscope (MFM) is proposed in this article. The magnetic field, which will be used to interact with a magnetic specimen{close_quote}s stray field, is induced on the sharp tip of the conical magnetic core surrounded by a microfabricated single turn conductive coil. The reciprocity principle is used to obtain the force acting on the probe due to the specimen{close_quote}s stray field when scanned over a magnetic specimen. The magnetic field intensity is adjustable by control of the applied current. Images of specimens have been modeled using this probe. The suitability to different specimens is seen to be the biggest advantage of this scheme over the conventional probe designs. {copyright} 2001 American Institute of Physics.

  2. Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas

    NASA Astrophysics Data System (ADS)

    Stevenson, B. A.; Knowlton, S. F.; Hartwell, G. J.; Hanson, J. D.; Maurer, D. A.

    2014-09-01

    A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.

  3. Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas

    SciTech Connect

    Stevenson, B. A.; Knowlton, S. F.; Hartwell, G. J. Hanson, J. D.; Maurer, D. A.

    2014-09-15

    A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.

  4. Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas.

    PubMed

    Stevenson, B A; Knowlton, S F; Hartwell, G J; Hanson, J D; Maurer, D A

    2014-09-01

    A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.

  5. Magnetic domains in multiferroic YMn$2O5 probed by Spherical Neutron Polarimetry under electric field

    NASA Astrophysics Data System (ADS)

    Vecchini, Carlo; Chapon, Laurent; Radaelli, Paolo; Daoud-Aladine, Aziz; Brown, Jane; Chatterji, Tapan; Park, Soonyong; Cheong, Sang-Wook

    2008-03-01

    Precise determination of the magnetic structures in multiferroics RMn2O5 (R: Y, Ho, Bi) have been obtained by single crystal neutron diffraction. The analysis shows the presence of zig-zag antiferromagnetic chains in the ab-plane. An additional weak magnetic component parallel to the c-axis was detected which is modulated in phase quadrature with the a-b components. The nature and population of the coexisting antiferromagnetic domains in YMn2O5 have been determined by Spherical Neutron Polarimetry under an external electric field. We have proved that reversing the electrical polarity results in the inversion of the population of two types of antiferromagnetic domains, with opposite in-plane spin components. This analysis strongly supports theories in which the coupling of the magnetic configuration to the ferroelectric polarisation is due to magnetic exchange striction and likely not related to the small cycloidal modulation in the bc-plane.

  6. A challenge for probing the statistics of interstellar magnetic fields: beyond the Planck resolution with Herschel

    NASA Astrophysics Data System (ADS)

    Bracco, Andrea; André, Philippe; Boulanger, Francois

    2015-08-01

    The recent Planck results in polarization at sub-mm wavelengths allow us to gain insight into the Galactic magnetic field topology, revealing its statistical correlation with matter, from the diffuse interstellar medium (ISM), to molecular clouds (MCs) (Planck intermediate results. XXXII, XXXIII, XXXV). This correlation has a lot to tell us about the dynamics of the turbulent ISM, stressing the importance of considering magnetic fields in the formation of structures, some of which eventually undergo gravitational collapse producing new star-forming cores.Investigating the early phases of star formation has been a fundamental scope of the Herschel Gould Belt survey collaboration (http://gouldbelt-herschel.cea.fr), which, in the last years, has thoroughly characterized, at a resolution of few tens of arcseconds, the statistics of MCs, such as their filamentary structure, kinematics and column density.Although at lower angular resolution, the Planck maps of dust emission at 353GHz, in intensity and polarization, show that all MCs are complex environments, where we observe a non-trivial correlation between the magnetic field and their density structure. This result opens new perspectives on their formation and evolution, which we have started to explore.In this talk, I will present first results of a comparative analysis of the Herschel-Planck data, where we combine the high resolution Herschel maps of some MCs of the Gould Belt with the Planck polarization data, which sample the structure of the field weighted by the density.In particular, I will discuss the large-scale envelopes of the selected MCs, and, given the correlation between magnetic field and matter, I will show how to make use of the high resolution information of the density structure provided by Herschel to investigate the statistics of interstellar magnetic fields in the Planck data.

  7. Terahertz probes of magnetic field induced spin reorientation in YFeO{sub 3} single crystal

    SciTech Connect

    Lin, Xian; Jiang, Junjie; Ma, Guohong; Jin, Zuanming; Wang, Dongyang; Tian, Zhen; Han, Jiaguang; Cheng, Zhenxiang

    2015-03-02

    Using the terahertz time-domain spectroscopy, we demonstrate the spin reorientation of a canted antiferromagnetic YFeO{sub 3} single crystal, by evaluating the temperature and magnetic field dependence of resonant frequency and amplitude for the quasi-ferromagnetic (FM) and quasi-antiferromagnetic modes (AFM), a deeper insight into the dynamics of spin reorientation in rare-earth orthoferrites is established. Due to the absence of 4f-electrons in Y ion, the spin reorientation of Fe sublattices can only be induced by the applied magnetic field, rather than temperature. In agreement with the theoretical predication, the frequency of FM mode decreases with magnetic field. In addition, an obvious step of spin reorientation phase transition occurs with a relatively large applied magnetic field of 4 T. By comparison with the family members of RFeO{sub 3} (R = Y{sup 3+} or rare-earth ions), our results suggest that the chosen of R would tailor the dynamical rotation properties of Fe ions, leading to the designable spin switching in the orthoferrite antiferromagnetic systems.

  8. Probing the Interior Dynamics of Jupiter and Saturn with Gravity and Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Cao, H.; Stevenson, D. J.

    2015-12-01

    The inner working of solar system gas giant planets remain elusive after decades of exploration. One lasting debate concerns the nature of east-west zonal flows observed on the cloud level of these planets with amplitude on the order of 100 m/s: an observational fact is yet to be established about whether these flows are shallow atmospheric dynamics or surface expression of deep interior dynamics. There is a good chance that such an observational fact can be established within the next few years, given the upcoming gravity and magnetic field measurements to be carried out by the Juno mission and the Cassini Grand Finale. In this presentation, I will first describe a critical assessment of the applicability of the thermal wind equation (TWE) in calculating the gravity field associated with deep zonal flows. The TWE, which is a local diagnostic relation, captures the local density variations associated with the zonal flows while neglects the global shape change and density variations with non-local origins. Our analysis shows that the global corrections to the high degree gravity moments are small (less than a few tens of percent). Our analysis also shows that the applicability of the TWE in calculating the gravity moments does depend crucially on retaining the non-sphericity of the background density and gravity. Only when the background non-sphericity of the planet is taken into account in the calculation, the thermal wind equation (TWE) makes accurate enough prediction for the high-degree gravity moments associated with deep zonal flows (with errors less than a few tens of percent). I will then turn to the magnetic signals associated with deep zonal flows. Using mean field dynamo theory (MFDT), we show that detectable magnetic signals are expected: in the spatial domain, poloidal magnetic fields spatially correlated with deep zonal flows are expected; in the temporal domain, periodic oscillations of the poloidal magnetic field are expected. The period of the

  9. The Auroral Spatial Structures Probe: magnetic and electric field measurements during an active aurora at fine spatial and temporal scales

    NASA Astrophysics Data System (ADS)

    Martineau, R. J.; Pratt, J.; Swenson, C.

    2015-12-01

    The Auroral Spatial Structures Probe was a rocket campaign that launched from Poker Flat on January 28, 2015 at 10:41:01 UTC to make multi-point vector observations of the magnetic and electric fields during an active aurora. With 6 instrumented payloads deployed from the rocket in addition to the main payload, each payload making simultaneous measurements of the magnetic and electric fields, the goals of this mission are to resolve the temporal-spatial ambiguity concerning the structures of the electric and magnetic fields during an active auroral event. The vector nature of these measurements requires an accurate knowledge of attitude throughout the flight. Each payload was equipped with gyroscopes to obtain a post-processed attitude solution after the flight. While the main payload's inertial sensors functioned well, the spin axis gyroscope on the subpayloads saturated due to a design flaw. To obtain the attitude and render the vector measurements useful, a least-squares based approach to estimate the attitude history of the payloads was devised using the magnetic and electric field measurements. Once the attitude solution was applied the temporal structures seen in the magnetic and electric fields while flying through the auroral arc are strongly correlated between payloads. We present the new attitude history estimation approach and discuss its strengths and weaknesses compared to traditional attitude methods. We also present preliminary findings from the magnetic and electric field instruments.The Auroral Spatial Structures Probe was a rocket campaign that launched from Poker Flat on January 28, 2015 at 10:41:01 UTC to make multi-point vector observations of the magnetic and electric fields during an active aurora. With 6 instrumented payloads deployed from the rocket in addition to the main payload, each payload making simultaneous measurements of the magnetic and electric fields, the goals of this mission are to resolve the temporal-spatial ambiguity

  10. Probing the magnetic field structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

    NASA Astrophysics Data System (ADS)

    Gold, Roman; McKinney, Jonathan; Johnson, Michael; Doeleman, Sheperd; Event Horizon Telescope Collaboration

    2016-03-01

    Accreting black holes (BHs) are at the core of relativistic astrophysics as messengers of the strong-field regime of General Relativity and prime targets of several observational campaigns, including imaging the black hole shadow in SagA* and M87 with the Event Horizon Telescope. I will present results from general-relativistic, polarized radiatiative transfer models for the inner accretion flow in Sgr A*. The models use time dependent, global GRMHD simulations of hot accretion flows including standard-and-normal-evolution (SANE) and magnetically arrested disks (MAD). I present comparisons of these synthetic data sets to the most recent observations with the Event Horizon Telescope and show how the data distinguishes the models and probes the magnetic field structure.

  11. SQUID readout and ultra-low magnetic fields for Gravity Probe-B (GP-B)

    NASA Technical Reports Server (NTRS)

    Lockhart, James M.

    1986-01-01

    The superconducting readout system to be used for resolving 0.001 arcsec changes in the gyroscope spin direction in the Relativity Gyroscope (GP-B) experiment is described. This system couples the London magnetic moment flux of the spinning gyro to a low noise superconducting quantum interference device (SQUID) detector. Resolution limits and noise performance of the detection system are discussed, and improvements obtained and expected with advanced SQUIDs are presented. Also described is the novel use of superconducting magnetic shielding techniques to obtain a 250 dB attenuation of the earth's magnetic field at the location of the gyroscopes. In this approach, expanded superconducting foil shields are coupled with fixed cylindrical superconducting shields and special geometric considerations to obtain the extremely high attenuation factor required. With these shielding techniques, it appears that the 0.5-Gauss earth field (which appears to the gyroscopes as an ac field at the satellite roll rate) can be reduced to the 10 to the -13th G level required by the experiment. Recent results concerning improvements in the performance of the superconducting foil techniques obtained with the use of a new computer-controlled cooling system are presented.

  12. Erratum: He I 10830 Å Line Polarimetry: A New Tool to Probe the Filament Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Lin, Haosheng; Penn, Matt J.; Kuhn, Jeffrey R.

    2001-10-01

    In the paper ``He I 10830 Å Line Polarimetry: A New Tool to Probe the Filament Magnetic Fields'' by Haosheng Lin, Matt J. Penn, and Jeffrey R. Kuhn (ApJ, 493, 978 [1998]), several mathematical and typographical errors escaped the authors' attention. These are mostly errors in the scaling factor of the expressions, however, and they did not affect the results of the paper. 1. There was an error in the scaling factor in the right-hand side of equation (4). The correct expression for equation (4) should be ES(r,ω,t)=-e(ω/c)2 (e-i(ωt-k˙r))/r × r×x(ω) . This error propagated into the paper and affected several equations derived later on. First, the correct expression for equation (33) (and eq. [A24]) should be N(ω)~((ω0)/2m)(e/c)21)/ (ω0-ω)+iΓ/2) Accordingly, the correction expressions for equations (34), (35), and (36) are NN*=1/4((ω0)/m)2(e/c)4 1/(ω0-ω)2+(Γ/2)2), Re(iNN*)=1/4((ω0)/m)2 ((e/c)4Γ/2)/[(ω0-ω)2+ (Γ/2)2]2, Im(iNN*)=1/4((ω0)/m)2 (e/c)4(ω0-ω)/[(ω0- ω)2+(Γ/2)2]2 Similarly, this correction should be applied to the coefficient of equations (A25), (A26), and (A37). That is, the factor (eω0/2m)2 in equations (A25), (A25), and (A37) should be replaced by (1/4)(ω0/m)2(e/c)4. Finally, the correct expressions for the Doppler-broadened profiles h(a,v), k(a,v), and f(a,v) in equations (39), (40), and (41) should be h(a,v)=3/8(sqrt(π)e2)/mc 1/(▵ωD) a/πΣ-∞∞ (e-y^2dy)((v-y)2+a2) = 3/8(sqrt(π)e2)/mc 1/(▵ωD) H(a,v), k(a,v)=3/4(sqrt(π)e2)/mc 1/(▵ω2D) (a2)/πΣ-∞∞ (e-y^2dy)([(v-y)2+a2]2), f(a,v)=3/4(sqrt(π)e2)/mc 1/(▵ω2D) πΣ-∞∞ ((v-y)e-y^2dy)([(v-y)2+a2]2. 2. The h2 factor in equations (17), (22), and (23) should be removed. 3. The sentence after equation (7) should read ``The oscillator solution can be written as X(ω)=e-1(ω/c)-2NEI.''

  13. Interaction of solar wind with Mercury and its magnetic field. [as observed by Mariner 10 space probe

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Lepping, R. P.; Whang, Y. C.

    1976-01-01

    A brief review is presented of magnetic field and solar wind electron observations by Mariner 10 spacecraft. The intrinsic magnetic field of the planet Mercury and the implications of such a field for the planetary interior are also discussed.

  14. Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Chiang, H. C.; Christensen, P. R.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falceta-Gonçalves, D.; Falgarone, E.; Ferrière, K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Guillet, V.; Harrison, D. L.; Helou, G.; Hennebelle, P.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Holmes, W. A.; Hornstrup, A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Netterfield, C. B.; Noviello, F.; Novikov, D.; Novikov, I.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Soler, J. D.; Stolyarov, V.; Sudiwala, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Ysard, N.; Yvon, D.; Zonca, A.

    2016-02-01

    Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10' FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH≈ 1021 to1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

  15. Triaxial Probe Magnetic Data Analysis

    NASA Technical Reports Server (NTRS)

    Shultz, Kimberly; Whittlesey, Albert; Narvaez, Pablo

    2007-01-01

    The Triaxial Magnetic Moment Analysis software uses measured magnetic field test data to compute dipole and quadrupole moment information from a hardware element. It is used to support JPL projects needing magnetic control and an understanding of the spacecraft-generated magnetic fields. Evaluation of the magnetic moment of an object consists of three steps: acquisition, conditioning, and analysis. This version of existing software was extensively rewritten for easier data acquisition, data analysis, and report presentation, including immediate feedback to the test operator during data acquisition. While prior JPL computer codes provided the same data content, this program has a better graphic display including original data overlaid with reconstructed results to show goodness of fit accuracy and better appearance of the report graphic page. Data are acquired using three magnetometers and two rotations of the device under test. A clean acquisition user interface presents required numeric data and graphic summaries, and the analysis module yields the best fit (least squares) for the magnetic dipole and/or quadrupole moment of a device. The acquisition module allows the user to record multiple data sets, selecting the best data to analyze, and is repeated three times for each of the z-axial and y-axial rotations. In this update, the y-axial rotation starting position has been changed to an option, allowing either the x- or z-axis to point towards the magnetometer. The code has been rewritten to use three simultaneous axes of magnetic data (three probes), now using two "rotations" of the device under test rather than the previous three rotations, thus reducing handling activities on the device under test. The present version of the software gathers data in one-degree increments, which permits much better accuracy of the fit ted data than the coarser data acquisition of the prior software. The data-conditioning module provides a clean data set for the analysis module

  16. An appraisal of the influence of a weak magnetic field to the estimation of plasma density by a cylindrical Langmuir probe

    SciTech Connect

    Kudrna, P.; Chudacek, O.; Sicha, M.; Tichy, M.

    1995-12-31

    During the course of the study of the cylindrical magnetron discharge at the Greifswald University we used the cylindrical Langmuir probe for estimation of radial dependences of the plasma density and of the electron energy distribution function. Since the probe had to be operated in a magnetoplasma we attempted to assess experimentally the influence of the applied magnetic field on the plasma density determined by a cylindrical probe. The theoretical assessment of the effect of the magnetic field on the charged particle collection by a Langmuir probe has been treated by Rubinstein and Laframboise in assuming the cylindrical probe operating in a {open_quotes}large Debye length{close_quotes} (i.e. {lambda}{sub D}>>a{sub g}, {lambda}{sub D}=({epsilon}{sub 0}kT{sub e}/q{sub 0}{sup 2}n{sub e}){sup 1/2} is the Debye length, a{sub g}=({pi}m{sub e,i}kT{sub e,i}/2){sup 1/2}/(q{sub 0}B) is the electron/ion mean gyroradius, all the symbols have their usual meanings) collisionless plasma. The theory calculated a.o. the electron currents to a cylindrical Langmuir probe at the space potential with the result that this current is minimally influenced by the magnetic field when the axis of the cylindrical probe is positioned perpendicular to the magnetic field lines. This particular result is suitable for the assessment of the error introduced by the magnetic field to the plasma density estimation since the electron density can be estimated from the electron probe current at the space potential. The dependence of this error on the Debye length {lambda}{sub D} remains, however, unknown and has not been to our knowledge fully resolved even in newer works.

  17. Probing the magnetic field of the nearby galaxy pair Arp 269

    NASA Astrophysics Data System (ADS)

    Nikiel-Wroczyński, B.; Jamrozy, M.; Soida, M.; Urbanik, M.; Knapik, J.

    2016-06-01

    We present a multiwavelength radio study of the nearby galaxy pair Arp 269 (NGC 4490/85). High sensitivity to extended structures gained by using the merged interferometric and single-dish maps allowed us to reveal a previously undiscovered extension of the radio continuum emission. Its direction is significantly different from that of the neutral gas tail, suggesting that different physical processes might be involved in their creation. The population of radio-emitting electrons is generally young, signifying an ongoing, vigorous star formation - this claim is supported by strong magnetic fields (over 20 μG), similar to the ones found in much larger spiral galaxies. From the study of the spectral energy distribution, we conclude that the electron population in the intergalactic bridge between member galaxies originates from the disc areas, and therefore its age (approximately 3.7-16.9 Myr, depending on the model used) reflects the time-scale of the interaction. We have also discovered an angularly near compact steep source - which is a member of a different galaxy pair - at a redshift of approximately 0.125.

  18. Note: Fiber optic transport probe for Hall measurements under light and magnetic field at low temperatures: Case study of a two dimensional electron gas

    SciTech Connect

    Bhadauria, P. P. S.; Gupta, Anurag; Kumar, Pramod; Dogra, Anjana; Budhani, R. C.

    2015-05-15

    A fiber optic based probe is designed and developed for electrical transport measurements in presence of quasi-monochromatic (360–800 nm) light, varying temperature (T = 1.8–300 K), and magnetic field (B = 0–7 T). The probe is tested for the resistivity and Hall measurements performed on a LaAlO{sub 3}–SrTiO{sub 3} heterointerface system with a conducting two dimensional electron gas.

  19. Elasticity of Lyotropic Chromonic Liquid Crystals Probed by Director Reorientation in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Zhou, Shuang; Nastishin, Yu. A.; Omelchenko, M. M.; Tortora, L.; Nazarenko, V. G.; Boiko, O. P.; Ostapenko, T.; Hu, T.; Almasan, C. C.; Sprunt, S. N.; Gleeson, J. T.; Lavrentovich, O. D.

    2012-07-01

    Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twist K2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher than K2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not found in conventional thermotropic and lyotropic liquid crystals formed by covalently bound units of a fixed length.

  20. Enhanced magnetic field probe array for improved excluded flux calculations on the C-2U advanced beam-driven field-reversed configuration plasma experiment

    NASA Astrophysics Data System (ADS)

    Roche, T.; Thompson, M. C.; Mendoza, R.; Allfrey, I.; Garate, E.; Romero, J.; Douglass, J.

    2016-11-01

    External flux conserving coils were installed onto the exterior of the C-2U [M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)] confinement vessel to increase the flux confinement time of the system. The 0.5 in. stainless steel vessel wall has a skin time of ˜5 ms. The addition of the external copper coils effectively increases this time to ˜7 ms. This led to better-confined/longer-lived field-reversed configuration (FRC) plasmas. The fringing fields generated by the external coils have the side effect of rendering external field measurements invalid. Such measurements were key to the previous method of excluded flux calculation [M. C. Thompson et al., Rev. Sci. Instrum. 83, 10D709 (2012)]. A new array of B-dot probes and Rogowski coils were installed to better determine the amount of flux leaked out of the system and ultimately provide a more robust measurement of plasma parameters related to pressure balance including the excluded flux radius. The B-dot probes are surface mountable chip inductors with inductance of 33 μH capable of measuring the DC magnetic field and transient field, due to resistive current decay in the wall/coils, when coupled with active integrators. The Rogowski coils measure the total change in current in each external coil (150 A/2 ms). Currents were also actively driven in the external coils. This renders the assumption of total flux conservation invalid which further complicates the analysis process. The ultimate solution to these issues and the record breaking resultant FRC lifetimes will be presented.

  1. Negative Differential Velocity in Artificial Crystals Probed by High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Patanè, A.

    , for x > 0.2%, which we have attributed to the emergence of defect states with deep (~ 0.3 eV) energy levels. Electron trapping onto these states was not observed at low x (x = 0.2%). In this ultra-dilute alloy regime and at low electric fields (F < 1 kV/cm) the electrical conductivity retains the characteristic features of transport through extended states, albeit with relatively low mobility (µ ~ 0.1 m2/Vs at RT) due to scattering of electrons by N-atoms. We have focused our research on this ultra-dilute regime and exploited the admixing of the localized single N-impurity level with the extended conduction band states of GaAs to realize an unusual type of negative differential velocity (NDV) effect: at large F (> 1 kV/cm), electrons gain sufficient energy to approach the energy of the resonant N-level, where they become spatially localized.7-10 This Resonant Electron Localization in Electric Field, to which we give the acronym RELIEF, leads to NDV and strongly non-linear current-voltage characteristics. We envisage that the RELIEF-effect could be observed in other III-N-V alloys, such as InP1-xNx and InAs1-xNx. In these compounds the nature of the resonant interaction between the N-level and the conduction band states of the host-crystal is still relatively unexplored. However, it is clear that the different energy positions of the N-level relative to the conduction band minimum of different materials could offer new degrees of freedom in the design of the electronic band structure and electron dynamics. The RELIEF-effect may open up prospects for future applications in fast electronics. We have shown that the maximum response frequency, fmax, of a RELIEF-diode can be tuned by the applied electric field in the THz frequency range.7 This is of potential technological significance for the development of detectors/sources in the 0.6-1 THz region, which is not currently attainable using conventional Transferred Electron Devices and Quantum Cascade Lasers. Our recent

  2. A novel magnetic field probing technique for determining state of health of sealed lead-acid batteries

    NASA Astrophysics Data System (ADS)

    Khare, Neeta; Singh, Pritpal; Vassiliou, John K.

    2012-11-01

    State of Health (SOH) is a critical index for a Sealed Lead-Acid (SLA) battery diagnostic which provides the information about battery replacement and aging effects. SOH is a complex function of chemical parameters of a battery such as stratification in electrolyte, electrode structure (sulfation and hard sulfation) in addition to electrical parameters of a battery. This paper describes a method of online determination of stratification, electrode structure, electrode polarization and current profile within the battery under the influence of a magnetic field. An AC magnetic field is used as a noninvasive tool during battery cycles. An induced emf in a secondary coil (SCV) is used as a measure of change in the magnetic field. The H+ proton density varies with change in sulfuric acid (electrolyte) concentration during battery cycles. The magnetic flux lines are affected by the density of H+ protons whose magnetic dipole moments try to align along the magnetic flux lines. The stratification is seen by a 12% decrease in magnetic flux linking from the top to the bottom of the electrolyte in a battery. Additional experimental results demonstrate the variation in magnetic flux linking which correlates with current profile across the electrode and electrode structure.

  3. Probing the effective nuclear-spin magnetic field in a single quantum dot via full counting statistics

    SciTech Connect

    Xue, Hai-Bin; Nie, Yi-Hang; Chen, Jingzhe; Ren, Wei

    2015-03-15

    We study theoretically the full counting statistics of electron transport through a quantum dot weakly coupled to two ferromagnetic leads, in which an effective nuclear-spin magnetic field originating from the configuration of nuclear spins is considered. We demonstrate that the quantum coherence between the two singly-occupied eigenstates and the spin polarization of two ferromagnetic leads play an important role in the formation of super-Poissonian noise. In particular, the orientation and magnitude of the effective field have a significant influence on the variations of the values of high-order cumulants, and the variations of the skewness and kurtosis values are more sensitive to the orientation and magnitude of the effective field than the shot noise. Thus, the high-order cumulants of transport current can be used to qualitatively extract information on the orientation and magnitude of the effective nuclear-spin magnetic field in a single quantum dot. - Highlights: • The effective nuclear-spin magnetic field gives rise to the off-diagonal elements of the reduced density matrix of single QD. • The off-diagonal elements of reduced density matrix of the QD have a significant impact on the high-order current cumulants. • The high-order current cumulants are sensitive to the orientation and magnitude of the effective nuclear-spin magnetic field. • The FCS can be used to detect the orientation and magnitude of the effective nuclear-spin magnetic field in a single QD.

  4. Role of incoherent pumping field on absorption-dispersion properties of probe pulse in a graphene nanostructure under external magnetic field

    NASA Astrophysics Data System (ADS)

    Asadpour, Seyyed Hossein; Hamedi, H. R.; Soleimani, H. Rahimpour

    2015-07-01

    The optical properties of weak probe light based on quantum coherence and interference in Landau-quantized graphene nanostructure driven by two coherent fields and incoherent pumping field is investigated. The linear dynamical properties of the graphene by means of density matrix method and perturbation theory are discussed. It is found that under certain condition and for appropriate choosing the parameters of the medium, the absorption, dispersion, group index of the weak probe light can be controlled. Moreover, it is shown that by means of incoherent pumping field the superluminal light propagation in the system is accompanied by amplification to make sure that the probe field is amplified as it passes through the system. Moreover, it is observed that the probe amplification can be obtained in the presence or absence of population inversion by properly choosing of system's parameters. We hope that these results may have useful in the future quantum communicational system and networks.

  5. Study of interaction of proflavin with triethylamine in homogeneous and micellar media: Photoinduced electron transfer probed by magnetic field effect

    NASA Astrophysics Data System (ADS)

    Chakraborty, Brotati; Basu, Samita

    2009-08-01

    Interaction of triethylamine (TEA) with cationic proflavin (PF +) in homogeneous and micellar media is studied using absorption spectroscopy, steady-state as well as time-resolved fluorescence spectroscopy and laser flash photolysis in conjunction with an external magnetic field. The two prime phenomena that have been highlighted in this study are photoinduced electron transfer (PET) and ground-state complex formation. This study shows that it is the medium which determines the reaction pathways to be followed. Magnetic field effect (MFE) helps to elucidate the reaction mechanism involved and this work also highlights the distance dependence factor associated with MFE.

  6. PHYSICAL BASIS OF QUANTUM ELECTRONICS: Inversion-free amplification of a probe field in a medium consisting of two-level degenerate atoms in the presence of a magnetic field

    NASA Astrophysics Data System (ADS)

    Konopleva, N. P.; Tumaikin, Anatolii M.

    1999-08-01

    The propagation of a probe field in a medium consisting of two-level atoms, degenerate in relation to the Jg = 1/2 → Je = 1/2 transition, is examined. The atoms are pumped by a circularly polarised resonant field in the presence of a static magnetic field. It is shown that under these conditions one of the normal waves may be amplified in the absence of inversion in the medium. In strong optical and magnetic fields, inversion-free amplification is possible for a pump with a finite spectral width, which may be much greater than the natural width of the excited level.

  7. Optical sensor of magnetic fields

    DOEpatents

    Butler, M.A.; Martin, S.J.

    1986-03-25

    An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

  8. Probing fine magnetic particles with neutron scattering

    SciTech Connect

    Pynn, R.

    1991-12-31

    Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

  9. Probing fine magnetic particles with neutron scattering

    SciTech Connect

    Pynn, R.

    1991-01-01

    Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

  10. Van Allen Probes observations of magnetic field dipolarization and its associated O+ flux variations in the inner magnetosphere at L < 6.6

    NASA Astrophysics Data System (ADS)

    Nosé, M.; Keika, K.; Kletzing, C. A.; Spence, H. E.; Smith, C. W.; MacDowall, R. J.; Reeves, G. D.; Larsen, B. A.; Mitchell, D. G.

    2016-08-01

    We investigate the magnetic field dipolarization in the inner magnetosphere and its associated ion flux variations, using the magnetic field and energetic ion flux data acquired by the Van Allen Probes. From a study of 74 events that appeared at L = 4.5-6.6 between 1 October 2012 and 31 October 2013, we reveal the following characteristics of the dipolarization in the inner magnetosphere: (1) its time scale is approximately 5 min; (2) it is accompanied by strong magnetic fluctuations that have a dominant frequency close to the O+ gyrofrequency; (3) ion fluxes at 20-50 keV are simultaneously enhanced with larger magnitudes for O+ than for H+; (4) after a few minutes of the dipolarization, the flux enhancement at 0.1-5 keV appears with a clear energy-dispersion signature only for O+; and (5) the energy-dispersed O+ flux enhancement appears in directions parallel or antiparallel to the magnetic field. From these characteristics, we discuss possible mechanisms that can provide selective acceleration to O+ ions at >20 keV. We conclude that O+ ions at L = 5.4-6.6 undergo nonadiabatic local acceleration caused by oscillating electric field associated with the magnetic fluctuations and/or adiabatic convective transport from the plasma sheet to the inner magnetosphere by the impulsive electric field. At L = 4.5-5.4, however, only the former acceleration is plausible. We also conclude that the field-aligned energy-dispersed O+ ions at 0.1-5 keV originate from the ionosphere and are extracted nearly simultaneously to the onset of the dipolarization.

  11. OH MASER SOURCES IN W49N: PROBING MAGNETIC FIELD AND DIFFERENTIAL ANISOTROPIC SCATTERING WITH ZEEMAN PAIRS USING THE VERY LONG BASELINE ARRAY

    SciTech Connect

    Deshpande, Avinash A.; Goss, W. M.; Mendoza-Torres, J. E. E-mail: mgoss@aoc.nrao.edu

    2013-09-20

    Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ∼20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ∼10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s{sup –1}. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

  12. Magnetic Probing of Core Geodynamics

    NASA Technical Reports Server (NTRS)

    Voorhies, Coerte V.

    2004-01-01

    To better understand geomagnetic theory and observation, we can use spatial magnetic spectra for the main field and secular variation to test core dynamical hypotheses against seismology. The hypotheses lead to theoretical spectra which are fitted to observational spectra. Each fit yields an estimate of the radius of Earth's core and uncertainty. If this agrees with the seismologic value, then the hypothesis passes the test. A new way to obtain theoretical spectra extends the hydromagnetic scale analysis of Benton to scale-variant field and flow. For narrow scale flow and a dynamically weak field by the top of Earth's core, this yields a generalized Stevenson-McLeod spectrum for the core-source field, and a secular variation spectrum modulated by a cubic polynomial in spherical harmonic degree n. The former passes the tests. The latter passes many tests, but does not describe rapid dipole decline and quadrupole rebound; some tests suggest it is a bit hard, or rich in narrow scale range. In a core geodynamo, motion of the fluid conductor does work against the Lorentz force. This converts kinetic into magnetic energy which, in turn, is lost to heat via Ohmic dissipation. In the analysis at length-scale 1/k, if one presumes kinetic energy is converted in either eddy-overturning or magnetic free-decay time-scales, then Kolmogorov or other spectra in conflict with observational spectra can result. Instead, the rate work is done roughly balances the dissipation rate, which is consistent with small-scale flow. The conversion time-scale depends on dynamical constraints. These are summarized by the magnetogeostrophic vertical vorticity balance by the top of the core, which includes anisotropic effects of rotation, the magnetic field, and the core-mantle boundary. The resulting theoretical spectra for the core-source field and its SV are far more compatible with observation. The conversion time-scale of order 120 years is pseudo-scale-invariant. Magnetic spectra of other

  13. Magnetic Probing of Core Geodynamics

    NASA Technical Reports Server (NTRS)

    Voorhies, Coerte V.

    2004-01-01

    To better understand geomagnetic theory and observation, we can use spatial magnetic spectra for the main field and secular variation to test core dynmcal hypotheses against seismology. The hypotheses lead to theoretical spectra which are fitted to observational spectra. Each fit yields an estimate of the radius of Earth's core and uncertainty. If this agrees with the seismologic value, then the hypothes pass the test. A new way to obtain theoretical spectra extends the hydromagnetic scale analysis of Benton to scale-variant field and flow. For narrow scale flow and a dynamically weak field by the top of Earth's core, this yields a generalized Stevenson-McLeod spectrum for the core-source field, and a secular variation spectrum modulated by a cubic polynomial in spherical harmonic degree n. The former passes the tests. The latter passes many tests, but does not describe rapid dipole decline and quadrupole rebound; some tests suggest it is a bit hard, or rich in narrow scale change. In a core geodynamo, motion of the fluid conductor does work against the Lorentz force. This converts kinetic into magnetic energy which, in turn, is lost to heat via Ohmic dissipation. In the analysis at lentgh-scale l/k, if one presumes kinetic energy is converted in either eddy- overturning or magnetic free-decay time-scales, then Kolmogorov or other spectra in conflict with observational spectra can result. Instead, the rate work is done roughly balances the dissipation rate, which is consistent with small scale flow. The conversion time-scale depends on dynamical constraints. These are summarized by the magneto-geostrophic vertical vorticity balance by the top of the core, which includes anisotropic effects of rotation, the magnetic field, and the core- mantle boundary. The resulting theoretical spectra for the core-source field and its SV are far more compatible with observation. The conversion time-scale of order l20 years is pseudo-scale-invarient. Magnetic spectra of other

  14. Magnetic Probing of Core Geodynamics

    NASA Astrophysics Data System (ADS)

    Voorhies, C. V.

    2004-05-01

    To better understand geomagnetic theory and observation, we can use spatial magnetic spectra for the main field and secular variation to test core dynamical hypotheses against seismology. The hypotheses lead to theoretical spectra which are fitted to observational spectra. Each fit yields an estimate of the radius of Earth's core and uncertainty. If this agrees with the seismologic value, then the hypotheses pass the test. A new way to obtain theoretical spectra extends the hydromagnetic scale analysis of Benton [1992; GAFD] to scale-variant field and flow [Voorhies, 2004; JGR-SE, in press]. For narrow scale flow and a dynamically weak field by the top of Earth's core, this yields a generalized Stevenson-McLeod spectrum for the core-source field [Voorhies, Sabaka and Purucker, 2002; JGR-P], and a secular variation spectrum modulated by a cubic polynomial in spherical harmonic degree n. The former passes the tests. The latter passes many tests, but does not describe rapid dipole decline and quadrupole rebound; some tests suggest it is a bit hard, or rich in narrow scale change. In a core geodynamo, motion of the fluid conductor does work against the Lorentz force. This converts kinetic into magnetic energy which, in turn, is lost to heat via Ohmic dissipation. In the analysis at length-scale 1/k, if one presumes kinetic energy is converted in either eddy-overturning or magnetic free-decay time-scales, then Kolmogorov or other spectra in conflict with observational spectra can result. Instead, the rate work is done roughly balances the dissipation rate, which is consistent with small scale flow. The conversion time-scale depends on dynamical constraints. These are summarized by the magneto-geostrophic vertical vorticity balance by the top of the core, which includes anisotropic effects of rotation, the magnetic field, and the core-mantle boundary. The resulting theoretical spectra for the core-source field and its SV are far more compatible with observation. The

  15. Dichotomy between the Hole and Electron Behavior in Multiband Superconductor FeSe Probed by Ultrahigh Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Watson, M. D.; Yamashita, T.; Kasahara, S.; Knafo, W.; Nardone, M.; Béard, J.; Hardy, F.; McCollam, A.; Narayanan, A.; Blake, S. F.; Wolf, T.; Haghighirad, A. A.; Meingast, C.; Schofield, A. J.; v. Löhneysen, H.; Matsuda, Y.; Coldea, A. I.; Shibauchi, T.

    2015-07-01

    Magnetoresistivity ρx x and Hall resistivity ρx y in ultrahigh magnetic fields up to 88 T are measured down to 0.15 K to clarify the multiband electronic structure in high-quality single crystals of superconducting FeSe. At low temperatures and high fields we observe quantum oscillations in both resistivity and the Hall effect, confirming the multiband Fermi surface with small volumes. We propose a novel approach to identify from magnetotransport measurements the sign of the charge carriers corresponding to a particular cyclotron orbit in a compensated metal. The observed significant differences in the relative amplitudes of the quantum oscillations between the ρx x and ρx y components, together with the positive sign of the high-field ρx y, reveal that the largest pocket should correspond to the hole band. The low-field magnetotransport data in the normal state suggest that, in addition to one hole and one almost compensated electron band, the orthorhombic phase of FeSe exhibits an additional tiny electron pocket with a high mobility.

  16. Dichotomy between the Hole and Electron Behavior in Multiband Superconductor FeSe Probed by Ultrahigh Magnetic Fields.

    PubMed

    Watson, M D; Yamashita, T; Kasahara, S; Knafo, W; Nardone, M; Béard, J; Hardy, F; McCollam, A; Narayanan, A; Blake, S F; Wolf, T; Haghighirad, A A; Meingast, C; Schofield, A J; Löhneysen, H v; Matsuda, Y; Coldea, A I; Shibauchi, T

    2015-07-10

    Magnetoresistivity ρ(xx) and Hall resistivity ρ(xy) in ultrahigh magnetic fields up to 88 T are measured down to 0.15 K to clarify the multiband electronic structure in high-quality single crystals of superconducting FeSe. At low temperatures and high fields we observe quantum oscillations in both resistivity and the Hall effect, confirming the multiband Fermi surface with small volumes. We propose a novel approach to identify from magnetotransport measurements the sign of the charge carriers corresponding to a particular cyclotron orbit in a compensated metal. The observed significant differences in the relative amplitudes of the quantum oscillations between the ρ(xx) and ρ(xy) components, together with the positive sign of the high-field ρ(xy), reveal that the largest pocket should correspond to the hole band. The low-field magnetotransport data in the normal state suggest that, in addition to one hole and one almost compensated electron band, the orthorhombic phase of FeSe exhibits an additional tiny electron pocket with a high mobility.

  17. Dichotomy between the Hole and Electron Behavior in Multiband Superconductor FeSe Probed by Ultrahigh Magnetic Fields.

    PubMed

    Watson, M D; Yamashita, T; Kasahara, S; Knafo, W; Nardone, M; Béard, J; Hardy, F; McCollam, A; Narayanan, A; Blake, S F; Wolf, T; Haghighirad, A A; Meingast, C; Schofield, A J; Löhneysen, H v; Matsuda, Y; Coldea, A I; Shibauchi, T

    2015-07-10

    Magnetoresistivity ρ(xx) and Hall resistivity ρ(xy) in ultrahigh magnetic fields up to 88 T are measured down to 0.15 K to clarify the multiband electronic structure in high-quality single crystals of superconducting FeSe. At low temperatures and high fields we observe quantum oscillations in both resistivity and the Hall effect, confirming the multiband Fermi surface with small volumes. We propose a novel approach to identify from magnetotransport measurements the sign of the charge carriers corresponding to a particular cyclotron orbit in a compensated metal. The observed significant differences in the relative amplitudes of the quantum oscillations between the ρ(xx) and ρ(xy) components, together with the positive sign of the high-field ρ(xy), reveal that the largest pocket should correspond to the hole band. The low-field magnetotransport data in the normal state suggest that, in addition to one hole and one almost compensated electron band, the orthorhombic phase of FeSe exhibits an additional tiny electron pocket with a high mobility. PMID:26207500

  18. Using variable-frequency asymmetries to probe the magnetic field dependence of radial transport in a Malmberg-Penning trap

    NASA Astrophysics Data System (ADS)

    Eggleston, D. L.

    2009-03-01

    A new experimental technique is used to study the dependence of asymmetry-induced radial particle flux Γ on axial magnetic field B in a modified Malmberg-Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity vr = Eθ/B and in the zeroth order azimuthal drift velocity vθ = Er/B. To separate these, we employ the hypothesis that the latter always enters the physics in the combination ω-lωR, where ωR = vθ/r is the column rotation frequency and ω and l are the asymmetry frequency and azimuthal mode number, respectively. Points where ω-lωR = 0 are then selected from a Γ vs r vs ω data set, thus insuring that any function of this combination is constant. When the selected flux Γsel is plotted versus the density gradient, a roughly linear dependence is observed, showing that this selected flux is diffusive. This linear dependence is roughly independent of the bias of the center wire in our trap φcw. Since in our experiment ωR is proportional to φcw, this latter point shows that our technique has successfully removed any dependence on ωR and its derivatives, thus confirming our hypothesis. The slope of a least-squares fitted line through the Γsel vs density gradient data then gives the diffusion coefficient D0 under the condition ω-lωR = 0. Varying the magnetic field, we find D0 is proportional to B-1.33±0.05, a scaling that does not match any theory we know. These findings are then used to constrain the form of the empirical flux equation. It may be possible to extend this technique to give the functional dependence of the flux on ω-lωR.

  19. Contributions of the electronic spin and orbital current to the CoCl{sub 4}{sup 2-} magnetic field probed in polarised neutron diffraction experiments

    SciTech Connect

    Cassam-Chenaie, Patrick; Jayatilaka, Dylan

    2012-08-14

    Polarised neutron diffraction experiments conducted at 4.2 K on Cs{sub 3}CoCl{sub 5} crystals have been analysed by using a four-dimensional model Hilbert space made of ab initio n-electron wave functions of the CoCl{sub 4}{sup 2-} molecular ion. Two spin-orbit mixing coefficients and several configuration interaction coefficients have been optimized by fitting calculated magnetic structure factors to experimental ones, to obtain the best ensemble density operator that is representable in the model space. A goodness of fit, {chi}{sup 2}, less then 1 has been obtained for the first time for the two experimental data sets available. In the present article, the optimized density operators are used to calculate the magnetic field densities that are the genuine observables probed in neutron diffraction experiments. Density maps of such observables are presented for the first time and numerical details are provided. The respective contributions of spin density and orbital current to the magnetic field density are analyzed.

  20. Facility Measures Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Honess, Shawn B.; Narvaez, Pablo; Mcauley, James M.

    1991-01-01

    Partly automated facility measures and computes steady near magnetic field produced by object. Designed to determine magnetic fields of equipment to be installed on spacecraft including sensitive magnetometers, with view toward application of compensating fields to reduce interfernece with spacecraft-magnetometer readings. Because of its convenient operating features and sensitivity of its measurements, facility serves as prototype for similar facilities devoted to magnetic characterization of medical equipment, magnets for high-energy particle accelerators, and magnetic materials.

  1. MTRAP: The Magnetic Transition Region Probe

    NASA Technical Reports Server (NTRS)

    Davis, J. M.; West, E. A.; Moore, R. L.; Gary, G. A.; Kobayashi, K.; Oberright, J. F.; Evans, D. C.; Wood, H. J.; Saba, J. L. R.; Alexander, D.

    2005-01-01

    The Magnetic Transition Region Probe is a space telescope designed to measure the magnetic field at several heights and temperatures in the solar atmosphere, providing observations spanning the chromospheric region where the field is expected to become force free. The primary goal is to provide an early warning system (hours to days) for solar energetic particle events that pose a serious hazard to astronauts in deep space and to understand the source regions of these particles. The required magnetic field data consist of simultaneous circular and linear polarization measurements in several spectral lines over the wavelength range from 150 to 855 nm. Because the observations are photon limited an optical telescope with a large (>18sq m) collecting area is required. To keep the heat dissipation problem manageable we have chosen to implement MTRAP with six separate Gregorian telescopes, each with approx. 3 sq m collecting area, that are brought to a common focus. The large field of view (5 x 5 arcmin(sup 2)) and angular resolution (0.025 arcsec pixels) require large detector arrays and, because of the requirements on signal to noise (10(exp 3)), pixels with large full well depths to reduce the readout time and improve the temporal resolution. The optical and engineering considerations that have gone into the development of a concept that meets MTRAP's requirements are described.

  2. Magnetic field mapper

    NASA Technical Reports Server (NTRS)

    Masters, R. M.; Stenger, F. J.

    1969-01-01

    Magnetic field mapper locates imperfections in cadmium sulphide solar cells by detecting and displaying the variations of the normal component of the magnetic field resulting from current density variations. It can also inspect for nonuniformities in other electrically conductive materials.

  3. Broad-band magnetic induction probe calibration using a frequency-corrected reference probe.

    PubMed

    Hill, Carrie

    2013-10-01

    Finite impedances of magnetic induction probes attenuate and shift the field fluctuations measured by the probe so that they differ from the measured signal at the digitizer. These effects vary with frequency. Traditionally, impedance effects have been accounted for in the calibration process by sweeping the frequency of the magnetic field source through a range of frequencies. Situations arise where the conventional calibration method is not feasible due to probe geometry or hardware constraints. A new calibration technique is presented in this paper which calibrates the probe in situ at a single frequency and uses impedance measurements of the probe assembly across the desired frequency range to account for broad-band effects. The in situ calibration technique requires a reference probe with a known proportionality constant NA and known impedances. Impedance effects are corrected in the probe signal using broad-band impedance measurements included in a transfer function in frequency space. The in situ calibration technique is shown to be complicated by capacitive coupling between the probes and the high voltage source coil. Circuit modeling demonstrates that this coupling introduces negligible attenuation and a small phase-delay so that the relative phase-delay between the reference and target probe signals can be corrected by shifting the signals in time. In summary, this calibration method extends traditional single-frequency calibration techniques to broad-band applications, accounting for important non-ideal effects to improve the accuracy of the magnetic field measurement.

  4. Molecules as magnetic probes of starspots

    NASA Astrophysics Data System (ADS)

    Afram, N.; Berdyugina, S. V.

    2015-04-01

    Context. Stellar dynamo processes can be explored by measuring the magnetic field. This is usually obtained using the atomic and molecular Zeeman effect in spectral lines. While the atomic Zeeman effect can only access warmer regions, the use of molecular lines is of advantage for studying cool objects. The molecules MgH, TiO, CaH, and FeH are suited to probe stellar magnetic fields, each one for a different range of spectral types, by considering the signal that is obtained from modeling various spectral types. Aims: We have analyzed the usefulness of different molecules (MgH, TiO, CaH, and FeH) as diagnostic tools for studying stellar magnetism on active G-K-M dwarfs. We investigate the temperature range in which the selected molecules can serve as indicators for magnetic fields on highly active cool stars and present synthetic Stokes profiles for the modeled spectral type. Methods: We modeled a star with a spot size of 10% of the stellar disk and a spot comprising either only longitudinal or only transverse magnetic fields and estimated the strengths of the polarization Stokes V and Q signals for the molecules MgH, TiO, CaH, and FeH. We combined various photosphere and spot models according to realistic scenarios. Results: In G dwarfs, the molecules MgH and FeH show overall the strongest Stokes V and Q signals from the starspot, whereas FeH has a stronger Stokes V signal in all G dwarfs with a spot temperature of 3800 K. In K dwarfs, CaH signals are generally stronger, and the TiO signature is most prominent in M dwarfs. Conclusions: Modeling synthetic polarization signals from starspots for a range of G-K-M dwarfs leads to differences in the prominence of various molecular signatures in different wavelength regions, which helps to efficiently select targets and exposure times for observations.

  5. DC-based magnetic field controller

    DOEpatents

    Kotter, D.K.; Rankin, R.A.; Morgan, J.P.

    1994-05-31

    A magnetic field controller is described for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a Hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage. 1 fig.

  6. DC-based magnetic field controller

    DOEpatents

    Kotter, Dale K.; Rankin, Richard A.; Morgan, John P,.

    1994-01-01

    A magnetic field controller for laboratory devices and in particular to dc operated magnetic field controllers for mass spectrometers, comprising a dc power supply in combination with improvements to a hall probe subsystem, display subsystem, preamplifier, field control subsystem, and an output stage.

  7. Magnetic field structure evolution in rotating magnetic field plasmas

    SciTech Connect

    Petrov, Yuri; Yang Xiaokang; Huang, T.-S.

    2008-07-15

    A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80 cm long/40 cm diameter cylindrical chamber, in which a plasma current I{sub p}{approx_equal}2 kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial I{sub z} current. With a relatively small current (I{sub m} {<=} 600 A) in the middle coil, the plasma current is boosted up to 5 kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.

  8. An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?

    NASA Astrophysics Data System (ADS)

    Bonnoli, G.; Tavecchio, F.; Ghisellini, G.; Sbarrato, T.

    2015-07-01

    High-energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray versus radio flux ratio. We assembled the multiwavelength spectral energy distribution of the resulting nine sources, profiting of publicly available archival observations performed by Swift, GALEX, and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected very high energy flux, finding that in the majority of cases it is within the reach of present generation of Cherenkov arrays or of the forthcoming Cherenkov Telescope Array.

  9. Selective electric and magnetic sensitivity of aperture probes.

    PubMed

    Singh, Dilip K; Ahn, Jae Sung; Koo, Sukmo; Kang, Taehee; Kim, Joonyeon; Lee, Sukho; Park, Namkyoo; Kim, Dai-Sik

    2015-08-10

    We report the effect of geometrical factors governing the polarization profiles of near-field scanning optical microscope (NSOM) probes. The most important physical parameter controlling the selective electric or magnetic field sensitivity is found to be the width of the metal rim surrounding aperture. Probes with metal rim width w < λ/2 selectively senses the optical electric field, while those with w > λ/2 selectively senses the optical magnetic field. Intensity variation of optical Hertz standing wave formed upon reflection at oblique incidence shows a phase difference of π/2 between electric and magnetic probes: an analogue of the classical Wiener's experiment. Our work paves way towards electromagnetic engineering of nanostructures. PMID:26367935

  10. The magnetic-distortion probe: Velocimetry in conducting fluids

    NASA Astrophysics Data System (ADS)

    Miralles, Sophie; Verhille, Gautier; Plihon, Nicolas; Pinton, Jean-François

    2011-09-01

    A new type of velocimeter, capable of local velocity measurements in conducting fluids, is introduced. The principle of the "magnetic-distortion probe" is based on the measurement of the induced magnetic field by the flow of a conducting fluid in the vicinity of a localized magnetic field. The new velocimeter has no moving parts, and can be enclosed in a sealed cap, easing the implementation in harsh environments, such as liquid metals. The proposed method allows one to probe both the continuous part and fluctuations of the velocity, the temporal and spatial resolution being linked to the actual geometric configuration of the probe. A prototype probe has been tested in a gallinstan pipe flow and in a fully turbulent flow of liquid gallium generated by the counter rotation of two coaxial impellers in a cylinder. The signals have been compared to a reference potential probe and show very good agreement both for time-averaged velocities and turbulent fluctuations. The prototype is shown to detect motion from a few cm s-1 to a few m s-1. Moreover, the use of the magnetic-distortion probe with large-scale applied magnetic field is discussed.

  11. Spin-lattice coupling in uranium dioxide probed by magnetostriction measurements at high magnetic fields (P08358-E001-PF)

    SciTech Connect

    Gofryk, K.; Jaime, M.

    2014-12-01

    Our preliminary magnetostriction measurements have already shown a strong interplay of lattice dynamic and magnetism in both antiferromagnetic and paramagnetic states, and give unambiguous evidence of strong spin- phonon coupling in uranium dioxide. Further studies are planned to address the puzzling behavior of UO2 in magnetic and paramagnetic states and details of the spin-phonon coupling.

  12. Magnetic fields during galaxy mergers

    NASA Astrophysics Data System (ADS)

    Rodenbeck, Kai; Schleicher, Dominik R. G.

    2016-09-01

    Galaxy mergers are expected to play a central role for the evolution of galaxies and may have a strong effect on their magnetic fields. We present the first grid-based 3D magnetohydrodynamical simulations investigating the evolution of magnetic fields during merger events. For this purpose, we employed a simplified model considering the merger event of magnetized gaseous disks in the absence of stellar feedback and without a stellar or dark matter component. We show that our model naturally leads to the production of two peaks in the evolution of the average magnetic field strength within 5 kpc, within 25 kpc, and on scales in between 5 and 25 kpc. The latter is consistent with the peak in the magnetic field strength previously reported in a merger sequence of observed galaxies. We show that the peak on the galactic scale and in the outer regions is most likely due to geometrical effects, as the core of one galaxy enters the outskirts of the other one. In addition, the magnetic field within the central ~5 kpc is physically enhanced, which reflects the enhancement in density that is due to efficient angular momentum transport. We conclude that high-resolution observations of the central regions will be particularly relevant for probing the evolution of magnetic field structures during merger events.

  13. Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet

    SciTech Connect

    Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

    2014-06-15

    We present the designs of probes for making critical current density (J{sub c}) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ∼0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J{sub c} measurements, made by uniformly ramping the current up to a maximum current (I{sub max}) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b{sup ′}), and the maximum safe temperature for the critical-current leads (T{sub max}). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI{sub max}/A=[1.46D{sup −0.18}L{sup 0.4}(T{sub max}−300){sup 0.25D{sup −{sup 0{sup .{sup 0{sup 9}}}}}}+750(b{sup ′}/I{sub max})D{sup 10{sup −{sup 3I{sub m}{sub a}{sub x}−2.87b{sup ′}}}}]× 10{sup 6}A m{sup −1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm{sup 2} is obtained when I{sub max} = 1000 A, T{sub max} = 400 K, D = 0.2, b{sup ′} = 0.3 l h{sup −1} and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h{sup −1}. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I{sub max } ≈ (1.35 × 10

  14. Photospheric magnetic fields

    NASA Technical Reports Server (NTRS)

    Howard, R.

    1972-01-01

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

  15. Probing the magnetic topologies of magnetic clouds by means of solar energetic particles

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Reames, D. V.

    1991-01-01

    Solar energetic particles (SEPs) have been used as probes of magnetic cloud topologies. The rapid access of SEPs to the interiors of many clouds indicates that the cloud field lines extend back to the sun and hence are not plasmoids. The small modulation of galactic cosmic rays associated with clouds also suggests that the magnetic fields of clouds are not closed.

  16. High-Resolution and Frequency, Printed Miniature Magnetic Probes

    NASA Astrophysics Data System (ADS)

    Prager, James; Ziemba, Timothy; Miller, Kenneth; Picard, Julian

    2013-10-01

    Eagle Harbor Technologies, Inc. (EHT) is developing a technique to significantly reduce the cost and development time of producing magnetic field diagnostics. EHT is designing probes that can be printed on flexible PCBs thereby allowing for extremely small coils to be produced while essentially eliminating the time to wind the coils. The coil size can be extremely small when coupled with the EHT Hybrid Integrator, which is capable of high bandwidth measurements over short and long pulse durations. This integrator is currently being commercialized with the support of a DOE SBIR. Additionally, the flexible PCBs allow probes to be attached to complex surface and/or probes that have a complex 3D structure to be designed and fabricated. During the Phase I, EHT will design and construct magnetic field probes on flexible PCBs, which will be tested at the University of Washington's HIT-SI experiment and in EHT's material science plasma reactor. Funding provided by DOE SBIR/STTR Program.

  17. Probing magnetic and electric optical responses of silicon nanoparticles

    SciTech Connect

    Permyakov, Dmitry; Sinev, Ivan; Markovich, Dmitry; Samusev, Anton; Belov, Pavel; Ginzburg, Pavel; Valuckas, Vytautas; Kuznetsov, Arseniy I.; Luk'yanchuk, Boris S.; Miroshnichenko, Andrey E.; Neshev, Dragomir N.; Kivshar, Yuri S.

    2015-04-27

    We study experimentally both magnetic and electric optically induced resonances of silicon nanoparticles by combining polarization-resolved dark-field spectroscopy and near-field scanning optical microscopy measurements. We reveal that the scattering spectra exhibit strong sensitivity of electric dipole response to the probing beam polarization and attribute the characteristic asymmetry of measured near-field patterns to the excitation of a magnetic dipole mode. The proposed experimental approach can serve as a powerful tool for the study of photonic nanostructures possessing both electric and magnetic optical responses.

  18. Magnetic-field-dependent assembly of silica-coated magnetite nanoclusters probed by Ultra-Small-Angle X-ray Scattering (USAXS)

    NASA Astrophysics Data System (ADS)

    Malik, Vikash; Suthar, Kamleshkumar J.; Mancini, Derrick C.; Ilavsky, Jan

    2014-03-01

    Colloidal suspension of the silica coated magnetic nanoclusters (MNCs) was used to study the magnetic field mediated assembly of magnetic nanoparticles. The spatial arrangement of these MNCs in colloidal suspension was studied using the ultra-small-angle X-ray scattering (USAXS) technique with magnetic field applied in directions orthogonal and parallel to the scattering vector. In situ magnetic field analysis of the USAXS scattering measurement showed anisotropic behavior that can be attributed to the formation of colloidal crystals. During magnetization, the clustered magnetic core induces a large dipole moment, and the thickness of the silica shell helps keep distance between the neighboring particles. The assembly of these hybrid nanostructured particles was found to be dependent on the strength and orientation of this external magnetic field. The dipolar chains formed of MNCs arranged themselves into colloidal crystals formed by two-dimensional magnetic sheets. The structure factor calculations suggested that the lattice parameters of these colloidal crystals can be tuned by changing the strength of the external magnetic field. These experiments shed light on the stimuli-responsive assembly of magnetic colloidal nanoparticles that leads to the creation of tunable photonic crystals.

  19. Magnetic microwire probes for the magnetic rod interfacial stress rheometer.

    PubMed

    Tajuelo, J; Pastor, J M; Martínez-Pedrero, F; Vázquez, M; Ortega, F; Rubio, R G; Rubio, M A

    2015-02-01

    The magnetic needle interfacial shear rheometer is a valuable tool for the study of the mechanical properties of thin fluid films or monolayers. However, it is difficult to differentiate the interfacial and subphase contributions to the drag on the needle. In principle, the problem can be addressed by decreasing the needle diameter, which decreases the bulk contribution while the interfacial contribution remains essentially the same. Here we show the results obtained when using a new type of needle, that of magnetic microwires with diameter approximately 10 times thinner than for commercial needles. We show that the lower inertia of the microwires calls for a new calibration procedure. We propose such a new calibration procedure based on the flow field solution around the needle introduced in refs 1 and 2. By measuring thin silicone oil films with well-controlled interfacial viscosities as well as eicosanol (C20) and pentadecanoic acid (PDA, C15) Langmuir monolayers, we show that the new calibration method works well for standard needles as well as for the microwire probes. Moreover, we show that the analysis of the force terms contributing to the force on the needle helps to ascertain whether the measurements obtained are reliable for given surface shear viscosity values. We also show that the microwire probes have at least a 10-fold-lower resolution limit, allowing one to measure interfacial viscosities as low as 10(-7) N·m/s. PMID:25495270

  20. Magnetic microwire probes for the magnetic rod interfacial stress rheometer.

    PubMed

    Tajuelo, J; Pastor, J M; Martínez-Pedrero, F; Vázquez, M; Ortega, F; Rubio, R G; Rubio, M A

    2015-02-01

    The magnetic needle interfacial shear rheometer is a valuable tool for the study of the mechanical properties of thin fluid films or monolayers. However, it is difficult to differentiate the interfacial and subphase contributions to the drag on the needle. In principle, the problem can be addressed by decreasing the needle diameter, which decreases the bulk contribution while the interfacial contribution remains essentially the same. Here we show the results obtained when using a new type of needle, that of magnetic microwires with diameter approximately 10 times thinner than for commercial needles. We show that the lower inertia of the microwires calls for a new calibration procedure. We propose such a new calibration procedure based on the flow field solution around the needle introduced in refs 1 and 2. By measuring thin silicone oil films with well-controlled interfacial viscosities as well as eicosanol (C20) and pentadecanoic acid (PDA, C15) Langmuir monolayers, we show that the new calibration method works well for standard needles as well as for the microwire probes. Moreover, we show that the analysis of the force terms contributing to the force on the needle helps to ascertain whether the measurements obtained are reliable for given surface shear viscosity values. We also show that the microwire probes have at least a 10-fold-lower resolution limit, allowing one to measure interfacial viscosities as low as 10(-7) N·m/s.

  1. Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography.

    PubMed

    Albisetti, E; Petti, D; Pancaldi, M; Madami, M; Tacchi, S; Curtis, J; King, W P; Papp, A; Csaba, G; Porod, W; Vavassori, P; Riedo, E; Bertacco, R

    2016-06-01

    The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method.

  2. Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography

    NASA Astrophysics Data System (ADS)

    Albisetti, E.; Petti, D.; Pancaldi, M.; Madami, M.; Tacchi, S.; Curtis, J.; King, W. P.; Papp, A.; Csaba, G.; Porod, W.; Vavassori, P.; Riedo, E.; Bertacco, R.

    2016-06-01

    The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method.

  3. Probing Gravitational Sensitivity in Biological Systems Using Magnetic Body Forces

    NASA Astrophysics Data System (ADS)

    Valles, James; Guevorkian, Karine; Wurzel, Samuel; Mihalusova, Mariana

    2003-03-01

    We have commissioned a superconducting solenoid based apparatus designed to exert strong magnetic body forces on biological specimens and other organic materials in ambient environmental conditions for extended periods. In its room temperature bore, it can produce a maximum magnetic field-field gradient product of 16 T^2-cm-1 which is sufficient to levitate frog embryos Xenopus Laevis[1]. We will discuss how we are applying these magnetic body forces to probe the known influences of gravitational forces on frog embryos and the swimming behavior of Paramecium Caudatum. In the process, we will describe a novel method for measuring the diamagnetic susceptibilities of specimens such as paramecia.

  4. Specialized probes with nanowhisker structures for high resolution magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Zhukov, M. V.; Belousov, K. I.; Mozharov, A. M.; Mukhin, I. S.; Golubok, A. O.

    2015-11-01

    Creation and study of specialized nanowhisker probes with magnetic coating are performed for high-precision imaging of various objects by means of atomic force and magnetic force microscopy. Thin layers of Ni and Co are deposited on the surface of nanowhisker structures to perform visualization of magnetic fields on the sample surface, in particular, structure of pits on a hard disk drive (HDD). It is revealed that probes with nanowhisker structures covered with magnetic coating due to their high aspect ratio demonstrate a higher spatial resolution and contrast of magnetic fields visualization in comparison with standard magnetic probes.

  5. Morphology and orientational behavior of silica-coated spindle-type hematite particles in a magnetic field probed by small-angle X-ray scattering.

    PubMed

    Reufer, Mathias; Dietsch, Hervé; Gasser, Urs; Hirt, Ann; Menzel, Andreas; Schurtenberger, Peter

    2010-04-15

    Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core-shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles.

  6. Internal magnetic probe for use in high temperature FRCs

    NASA Astrophysics Data System (ADS)

    Wang, Xiaomei; Slough, John; Miller, Ken

    1998-11-01

    In the TCS and STX experiments a Rotating Magnetic Field is used to drive the FRC current. An internal magnetic probe has been built to measure both Bθ and Bz along the plasma radius. The probe has 24 multi-turn coils which are made of 0.0015" dia copper wire. The coils are enclosed in a 0.08 cm ID, 0.20 cm OD, 24 cm long berillum oxide (BeO) tube chosen for its high thermal conductivity, high melting point and low contamination potential. Measurements made on high temperature FRCs will be presented. (www.aa.washington.edu/AERP/RPPL) Supported by USDOE.

  7. Comparison of magnetic probe calibration at nano and millitesla magnitudes

    NASA Astrophysics Data System (ADS)

    Pahl, Ryan A.; Rovey, Joshua L.; Pommerenke, David J.

    2014-01-01

    Magnetic field probes are invaluable diagnostics for pulsed inductive plasma devices where field magnitudes on the order of tenths of tesla or larger are common. Typical methods of providing a broadband calibration of dot{{B}} probes involve either a Helmholtz coil driven by a function generator or a network analyzer. Both calibration methods typically produce field magnitudes of tens of microtesla or less, at least three and as many as six orders of magnitude lower than their intended use. This calibration factor is then assumed constant regardless of magnetic field magnitude and the effects of experimental setup are ignored. This work quantifies the variation in calibration factor observed when calibrating magnetic field probes in low field magnitudes. Calibration of two dot{{B}} probe designs as functions of frequency and field magnitude are presented. The first dot{{B}} probe design is the most commonly used design and is constructed from two hand-wound inductors in a differential configuration. The second probe uses surface mounted inductors in a differential configuration with balanced shielding to further reduce common mode noise. Calibration factors are determined experimentally using an 80.4 mm radius Helmholtz coil in two separate configurations over a frequency range of 100-1000 kHz. A conventional low magnitude calibration using a vector network analyzer produced a field magnitude of 158 nT and yielded calibration factors of 15 663 ± 1.7% and 4920 ± 0.6% {T}/{V {s}} at 457 kHz for the surface mounted and hand-wound probes, respectively. A relevant magnitude calibration using a pulsed-power setup with field magnitudes of 8.7-354 mT yielded calibration factors of 14 615 ± 0.3% and 4507 ± 0.4% {T}/{V {s}} at 457 kHz for the surface mounted inductor and hand-wound probe, respectively. Low-magnitude calibration resulted in a larger calibration factor, with an average difference of 9.7% for the surface mounted probe and 12.0% for the hand-wound probe. The

  8. Mach Probe Wakes are Important in Weakly Magnetized, Collisional Plasmas

    NASA Astrophysics Data System (ADS)

    Gosselin, Jordan James; Thakur, Saikat; Sears, Stephanie; McKee, John; Scime, Earl; Tynan, George

    2015-11-01

    Mach probes are often used as the diagnostic for flow in the scrape off layer (SOL) of tokamaks and in linear devices because of their low cost and ease of construction. However, proper interpretation of the Mach number has been debated, and interpretation methods use different calibration factors for different plasma parameters. The Controlled Shear Decorrelation eXperiment (CSDX) operates in an intermediate magnetization regime. To validate theories in this regime, measurements of the parallel ion velocity were made with Mach probes and laser induced fluorescence (LIF) at magnetic fields from 400 to 1600 gauss. We find that Mach probe measurements indicate higher velocities than LIF at fields above 400 gauss. Reduced downstream plasma density due to probe shadowing is a strong candidate for the cause of the discrepancy. An advective-diffusive model for the geometric shadowing and downstream plasma density is presented. When the model for the density drop is included, the Mach probe results agree with the LIF data. This result should be included by groups using Mach probes to measure parallel velocities in plasmas where the ion-neutral mean free path is shorter than the probe shadow length, Lps = a2Cs /Dperp in linear devices, the SOL, or divertor region of tokamaks. This material is based upon work supported by the U.S. Department of Energy, Office of Science, under Awards Number DE-FG02-07ER54912.

  9. A modified Katsumata probe--Ion sensitive probe for measurement in non-magnetized plasmas.

    PubMed

    Čada, M; Hubička, Z; Adámek, P; Olejníček, J; Kment, Š; Adámek, J; Stöckel, J

    2015-07-01

    A modified Katsumata probe has been developed for measurement of ion velocity distribution function (IVDF) in technological non-magnetized plasmas. A simple construction of the modified Katsumata probe consists of adding a pair of permanent Sm-Co magnets in front of Katsumata probe. A comparative study regarding IVDF measurement in a high power impulse magnetron sputtering system operating in pure argon atmosphere by means of developed modified Katsumata probe and commercially available gridded retarding field analyzer (RFA) has been carried out. A time-resolved measurement of IVDF for two different pressures whilst other plasma conditions have been kept unchanged has revealed that the main advantage of the modified Katsumata probe compared to the RFA consists in significantly smaller angular aperture of entrance orifice of modified Katsumata probe being approximately 15° in comparison with a commercial RFA having angular aperture more than 160°. It leads in much better velocity resolution in measured IVDF since the transversal part of velocity vector is much more suppressed compared to RFA. Furthermore, the modified Katsumata probe less suffers from collisions of ions in the space charge sheath in front or inside of the probe compared to the RFA.

  10. Matched dipole probe for precise electron density measurements in magnetized and non-magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Rafalskyi, Dmytro; Aanesland, Ane

    2015-09-01

    We present a plasma diagnostics method based on impedance measurements of a short matched dipole placed in the plasma. This allows measuring the local electron density in the range from 1012-1015 m-3 with a magnetic field of at least 0-50 mT. The magnetic field strength is not directly influencing the data analysis and requires only that the dipole probe is oriented perpendicularly to the magnetic field. As a result, the magnetic field can be non-homogeneous or even non-defined within the probe length without any effect on the final tolerance of the measurements. The method can be applied to plasmas of relatively small dimensions (< 10 cm) and doesn't require any special boundary conditions. The high sensitivity of the impedance measurements is achieved by using a miniature matching system installed close to the probe tip, which also allows to suppress sheath resonance effects. We experimentally show here that the tolerance of the electron density measurements reaches values lower than 1%, both with and without the magnetic field. The method is successfully validated by both analytical modeling and experimental comparison with Langmuir probes. The validation experiments are conducted in a low pressure (1 mTorr) Ar discharge sustained in a 10 cm size plasma chamber with and without a transversal magnetic field of about 20 mT. This work was supported by a Marie Curie International Incoming Fellowships within FP7 (NEPTUNE PIIF-GA-2012-326054).

  11. Manipulating Cells with Static Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Valles, J. M.; Guevorkian, K.

    2005-07-01

    We review our investigations of the use of static magnetic fields, B, for manipulating cells and cellular processes. We describe how B fields modify the cell division pattern of frog embryos and consequently can be used to probe the pattern determinants. We also observe that magnetic fields modify the swimming behavior of Paramecium Caudatum. We describe these modifications and their potential application to investigations of their swimming behavior.

  12. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi

    The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.

  13. Magnetic field dosimeter development

    SciTech Connect

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

    1980-09-01

    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.

  14. Solar Wind Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Smith, E. J.

    1995-01-01

    The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

  15. Coronal Magnetic Field

    NASA Astrophysics Data System (ADS)

    Lin, Haosheng

    2007-05-01

    Centuries after the birth of modern solar astronomy, the Sun's corona still keeps many of its secrets: How is it heated to a million-degree temperature? How does it harbor the cool and dense prominence gas amid the tenuous and hot atmosphere? How does it drive the energetic events that eject particles into interplanetary space with speed exceeding 1% of the speed of light? We have greatly improved our knowledge of the solar corona with decades of space X-ray and EUV coronal observations, and many theories and models were put forward to address these problems. In our current understanding, magnetic fields are undoubtedly the most important fields in the corona, shaping its structure and driving its dynamics. It is clear that the resolution of these important questions all hinge on a better understanding of the organization, evolution, and interaction of the coronal magnetic field. However, as the direct measurement of coronal magnetic field is a very challenging observational problem, most of our theories and models were not experimentally verified. Nevertheless, we have finally overcome the experimental difficulties and can now directly measure the coronal magnetic field with great accuracy. This new capability can now be used to study the static magnetic structure of the corona, and offers hope that we will, in the near future, be able to directly observe the evolution of the coronal magnetic field of energetic solar events. More importantly, it finally allows us to conduct vigorous observational tests of our theories and models. In this lecture, I will review current research activities related to the observation, interpretation, and modeling of the coronal magnetic field, and discuss how they can help us resolve some of the long standing mysteries of the solar corona.

  16. Magnetic Field Solver

    NASA Technical Reports Server (NTRS)

    Ilin, Andrew V.

    2006-01-01

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

  17. Magnetic Probe Construction using Thick-film Technology

    SciTech Connect

    Takahashi, H.; Sakakibara, S.; Kubota, Y.; and Yamada, H.

    2001-02-02

    Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultra-high vacuum and high-temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 degrees C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low-frequency coils have a measured coupling area of 296-323 cm squared and a frequency response of about 300 kHz. High-frequency coils have a design coupling area of 12-15 cm squared.

  18. Magnetic fields at uranus.

    PubMed

    Ness, N F; Acuña, M H; Behannon, K W; Burlaga, L F; Connerney, J E; Lepping, R P; Neubauer, F M

    1986-07-01

    The magnetic field experiment on the Voyager 2 spacecraft revealed a strong planetary magnetic field of Uranus and an associated magnetosphere and fully developed bipolar masnetic tail. The detached bow shock wave in the solar wind supersonic flow was observed upstream at 23.7 Uranus radii (1 R(U) = 25,600 km) and the magnetopause boundary at 18.0 R(U), near the planet-sun line. A miaximum magnetic field of 413 nanotesla was observed at 4.19 R(U ), just before closest approach. Initial analyses reveal that the planetary magnetic field is well represented by that of a dipole offset from the center of the planet by 0.3 R(U). The angle between Uranus' angular momentum vector and the dipole moment vector has the surprisingly large value of 60 degrees. Thus, in an astrophysical context, the field of Uranus may be described as that of an oblique rotator. The dipole moment of 0.23 gauss R(3)(U), combined with the large spatial offset, leads to minimum and maximum magnetic fields on the surface of the planet of approximately 0.1 and 1.1 gauss, respectively. The rotation period of the magnetic field and hence that of the interior of the planet is estimated to be 17.29+/- 0.10 hours; the magnetotail rotates about the planet-sun line with the same period. Thelarge offset and tilt lead to auroral zones far from the planetary rotation axis poles. The rings and the moons are embedded deep within the magnetosphere, and, because of the large dipole tilt, they will have a profound and diurnally varying influence as absorbers of the trapped radiation belt particles.

  19. Electrically silent magnetic fields.

    PubMed Central

    Roth, B J; Wikswo, J P

    1986-01-01

    There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

  20. Mapping the magnetic field vector in a fountain clock

    SciTech Connect

    Gertsvolf, Marina; Marmet, Louis

    2011-12-15

    We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.

  1. ARTEMIS Low Altitude Magnetic Field Measurements

    NASA Astrophysics Data System (ADS)

    Glassmeier, Karl-Heinz; Constantinescu, Dragos; Auster, Hans-Ulrich

    2016-10-01

    Since 2011, two spacecraft of the five THEMIS mission spacecraft are in orbit around the Moon. These two ARTEMIS probes provide for very interesting observations of plasma physical properties of the lunar environment. In particular, the very low periselene of the ARTEMIS probes allows for the detection of crustal magnetic features of our terrestrial companion. Repeated low passes over the same region are used to confirm the crustal origin of the measured magnetic field variations. Using a model for the decay of the magnetic field intensity and measurements at several altitudes, we estimate the magnetic moment and the depth of the equivalent dipole. Some of these magnetic anomalies are strong enough to produce upstream waves due to the interaction with the solar wind with the anomaly driven mini-magnetospheres.

  2. Magnetic Fields in Galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 μG) and in central starburst regions (50-100 μG). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 μG strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field α -Ω dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos

  3. Orienting Paramecium with intense static magnetic fields

    NASA Astrophysics Data System (ADS)

    Valles, James M., Jr.; Guevorkian, Karine; Quindel, Carl

    2004-03-01

    Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic fields, 2.5 T < B < 8 T were applied to immobilized (non-swimming) Paramecium Caudatum that were suspended in a density matched medium. The organisms align with their long axis parallel to the applied magnetic field. Their intrinsic diamagnetic anisotropy is 3x10-11 in cgs units. We will discuss the implications of these results for employing magnetic fields to probe the behavior of swimming Paramecium. [1] J. M. Valles, Jr. et al., Expt. Cell Res.274, 112-118 (2002).

  4. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  5. Magnetic field emission gun with zirconiated emitter.

    PubMed

    Troyon, M

    1989-03-01

    A magnetic-field-superimposed field emission gun with low aberrations and equipped with a zirconiated tungsten emitter has been developed for applications where very stable high probe currents are required. It has been tested on a conventional electron microscope at 10 kV and on an electron beam testing system at 1 kV. Probe current i = 250 nA in a probe size d = 0.4 micron is obtained at 10 kV; at 1 kV the resolution is 0.1 micron with i = 5 nA, and 0.4 micron with i = 30 nA. For these probe currents, the spatial broadening effect due to electron-electron interactions in the beam is the preponderant factor limiting the probe size.

  6. Magnetic Probe to Study Plasma Jets for Magneto-Inertial Fusion

    SciTech Connect

    Martens, Daniel; Hsu, Scott C.

    2012-08-16

    A probe has been constructed to measure the magnetic field of a plasma jet generated by a pulsed plasma rail-gun. The probe consists of two sets of three orthogonally-oriented commercial chip inductors to measure the three-dimensional magnetic field vector at two separate positions in order to give information about the magnetic field evolution within the jet. The strength and evolution of the magnetic field is one of many factors important in evaluating the use of supersonic plasma jets for forming imploding spherical plasma liners as a standoff driver for magneto-inertial fusion.

  7. Application of the hall-probe technique for magnetization measurements of superconductors

    NASA Astrophysics Data System (ADS)

    Koziol, Z.; Franse, J. J. M.

    1994-03-01

    A commercial Hall probe (supplied by Lake Shore Cryotronics, Inc.) is used as a sensor of the magnetic field at the surface of a magnetized sample. With the Linear Research resistance bridge LR-400, an excellent stability, linearity of response on field and an extremely small temperature dependence of the background signal is obtained, which is essential for this kind of applications of a Hall probe. At certain conditions, a resolution in field measurements of about 10 mG is reached. Examples of magnetization measurements as a function of temperature, magnetic field and time, performed on high-T(sub c) and heavy-fermion superconductors, are discussed.

  8. High Magnetic field generation for laser-plasma experiments

    SciTech Connect

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

    2006-05-01

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

  9. Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)

    NASA Technical Reports Server (NTRS)

    Koelfgen, Syri J.; Eskridge, Richard; Lee, Michael H.; Martin, Adam; Hawk, Clark W.; Fimognan, Peter

    2004-01-01

    The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. A plasmoid is a plasma with an imbedded closed magnetic field structure. The shape and magnetic field structure of the translating plasmoids have been measured with of an array of magnetic field probes. Six sets of two B-dot probes were constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes are wound on a square G10 form, and have an average (calibrated) NA of 9.37 x l0(exp -5) square meters, where N is the number of turns and A is the cross-sectional area. The probes were calibrated with a Helmholtz coil, driven by a high-voltage pulser to measure NA, and by a signal generator to determine the probe's frequency response. The plasmoid electron number density n(sub e) electron temperature T(sub e), and velocity ratio v/c(sub m), (where v is the bulk plasma flow velocity and c(sub m), is the ion thermal speed) have also been measured with a quadruple Langmuir probe. The Langmuir probe tips are 10 mm long, 20-mil diameter stainless steel wire, housed in a 6-inch long 4-bore aluminum rod. Measurements on PTX with argon and hydrogen from the magnetic field probes and quadruple Langmuir probe will be presented in this paper.

  10. Magnetic probing of the solar interior

    NASA Technical Reports Server (NTRS)

    Benton, E. R.; Estes, R. H.

    1985-01-01

    The magnetic field patterns in the region beneath the solar photosphere is determined. An approximate method for downward extrapolation of line of sight magnetic field measurements taken at the solar photosphere was developed. It utilizes the mean field theory of electromagnetism in a form thought to be appropriate for the solar convection zone. A way to test that theory is proposed. The straightforward application of the lowest order theory with the complete model fit to these data does not indicate the existence of any reasonable depth at which flux conservation is achieved.

  11. The fast reciprocating magnetic probe system on the J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Li, Fuming; Chen, Zhipeng; Zhuang, Ge; Liu, Hai; Zhu, Lizhi

    2016-11-01

    The fast reciprocating magnetic probe (FRMP) system is newly developed on the Joint Texas Experimental Tokamak (J-TEXT) to measure the local magnetic fluctuations at the plasma edge. The magnetic probe array in the FRMP consists of four 2-dimensional magnetic probes arranged at different radial locations to detect local poloidal and radial magnetic fields. These probes are protected by a graphite and boron nitride casing to improve the frequency response of each probe; they are mounted on the head of a movable rod, which is oriented along radial direction at the top of the torus. In the experiments, multiple core diagnostics show that the insertion of the FRMP has little impact on the equilibrium of the plasma. Local magnetic fluctuations inside the last closed flux surface are successfully measured by the FRMP.

  12. Magnetization dynamics using ultrashort magnetic field pulses

    NASA Astrophysics Data System (ADS)

    Tudosa, Ioan

    Very short and well shaped magnetic field pulses can be generated using ultra-relativistic electron bunches at Stanford Linear Accelerator. These fields of several Tesla with duration of several picoseconds are used to study the response of magnetic materials to a very short excitation. Precession of a magnetic moment by 90 degrees in a field of 1 Tesla takes about 10 picoseconds, so we explore the range of fast switching of the magnetization by precession. Our experiments are in a region of magnetic excitation that is not yet accessible by other methods. The current table top experiments can generate fields longer than 100 ps and with strength of 0.1 Tesla only. Two types of magnetic were used, magnetic recording media and model magnetic thin films. Information about the magnetization dynamics is extracted from the magnetic patterns generated by the magnetic field. The shape and size of these patterns are influenced by the dissipation of angular momentum involved in the switching process. The high-density recording media, both in-plane and perpendicular type, shows a pattern which indicates a high spin momentum dissipation. The perpendicular magnetic recording media was exposed to multiple magnetic field pulses. We observed an extended transition region between switched and non-switched areas indicating a stochastic switching behavior that cannot be explained by thermal fluctuations. The model films consist of very thin crystalline Fe films on GaAs. Even with these model films we see an enhanced dissipation compared to ferromagnetic resonance studies. The magnetic patterns show that damping increases with time and it is not a constant as usually assumed in the equation describing the magnetization dynamics. The simulation using the theory of spin-wave scattering explains only half of the observed damping. An important feature of this theory is that the spin dissipation is time dependent and depends on the large angle between the magnetization and the magnetic

  13. Probing latitudinal variations of the solar magnetic field in cycles 21-23 by Parker's Two-Layer Dynamo Model with meridional circulation

    NASA Astrophysics Data System (ADS)

    Popova, E.; Zharkova, V.; Zharkov, S.

    2013-11-01

    Principle component analysis (PCA) of the solar background magnetic field (SBMF) measured from Wilcox Solar Observatory (WSO) magnetograms revealed the following principal components (PCs) in latitudes: two main symmetric components, which are the same for all cycles 21-23, and three pairs of asymmetric components, which are unique for each cycle. These SBMF variations are assumed to be those of poloidal magnetic field travelling slightly off-phase from pole to pole while crossing the equator. They are assumed to be caused by a joint action of dipole and quadruple magnetic sources in the Sun. In the current paper, we make the first attempt to interpret these latitudinal variations in the surface magnetic field with Parker's two-layer dynamo model. The latitudinal distributions of such waves are simulated for cycles 21-23 by the modified Parker's dynamo model taking into account both α and ω effects operating simultaneously in the two (upper and lower) layers of the solar convective zone (SCZ) and having opposite directions of meridional circulation. The simulations are carried out for both dipole and quadruple magnetic sources with the dynamo parameters specifically selected to provide the curves fitting closely the PCs derived from SBMF variations in cycles 21-23. The simulations are optimised for matching the positions of maximums in latitude, the number of equator crossings and the phase difference between the two dynamo waves operating in the two layers. The dominant pair of PCs present in each cycle is found to be fully asymmetric with respect to the magnetic poles and produced by a magnetic dipole. This pair is found to account for the two main dynamo waves operating between the two magnetic poles. There are also three further pairs of waves unique to each cycle and associated with multiple magnetic sources in the Sun. For the odd cycle 21 the simulated poloidal field fits the observed PCs, only if they are produced by magnetic sources with a quadruple

  14. Crustal Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; Ravat, D.; Frawley, James J.

    1999-01-01

    Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

  15. Electrostatic probe disruption of drift waves in magnetized microdischarges

    SciTech Connect

    Ito, T.; Cappelli, M. A.

    2009-05-25

    Ultrahigh speed images of ExB discharges are collected during electrostatic probing of magnetized microdischarges. Two azimuthally separated floating micro-Langmuir probes inserted into an axisymmetric microscale magnetically confined plasma are used to characterize azimuthal drift waves. The images reveal features associated with probe intrusion, showing how the electrostatic probes may disrupt the otherwise coherent azimuthal waves. The resulting wave dispersion calculated from the probe signals is consistent with the disruptions seen in the images. These images demonstrate how probe measurements of fluctuations and turbulence, even when probe dimensions are much smaller than characteristic discharge scales, must be interpreted with caution.

  16. Probing and manipulating magnetization at the nanoscale

    NASA Astrophysics Data System (ADS)

    Samarth, Nitin

    2012-02-01

    Combining semiconductors with magnetism in hetero- and nano-structured geometries provides a powerful means of exploring the interplay between spin-dependent transport and nanoscale magnetism. We describe two recent studies in this context. First, we use spin-dependent transport in ferromagnetic semiconductor thin films to provide a new window into nanoscale magnetism [1]: here, we exploit the large anomalous Hall effect in a ferromagnetic semiconductor as a nanoscale probe of the reversible elastic behavior of magnetic domain walls and gain insight into regimes of domain wall behavior inaccessible to more conventional optical techniques. Next, we describe novel ways to create self-assembled hybrid semiconductor/ferromagnet core-shell nanowires [2] and show how magnetoresistance measurements in single nanowires, coupled with micromagnetic simulations, can provide detailed insights into the magnetization reversal process in nanoscale ferromagnets [3]. The work described here was carried out in collaboration with Andrew Balk, Jing Liang, Nicholas Dellas, Mark Nowakowski, David Rench, Mark Wilson, Roman Engel-Herbert, Suzanne Mohney, Peter Schiffer and David Awschalom. This work is supported by ONR, NSF and the NSF-MRSEC program.[4pt] [1] A. L. Balk et al., Phys. Rev.Lett. 107, 077205 (2011).[0pt] [2] N. J. Dellas et al., Appl. Phys. Lett. 97, 072505 (2010).[0pt] [3] J. Liang et al., in preparation.

  17. Probes for High Field Solid-state NMR of Lossy Biological Samples

    PubMed Central

    Grant, Christopher V.; Wu, Chin H.; Opella, Stanley J.

    2010-01-01

    In solid-state NMR exphydrated samples biopolymers are susceptible to radio-frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed. PMID:20435493

  18. Associated electron and proton transfer between Acridine and Triethylamine in AOT reverse micelles probed by laser flash photolysis with magnetic field

    NASA Astrophysics Data System (ADS)

    Sarangi, Manas Kumar; Basu, Samita

    2011-04-01

    Laser flash photolysis with magnetic field (MF ˜0.08 T) has been used to study interaction between Acridine (Acr) and Triethylamine (TEA) in reverse micelles with w0 = 2.5-40. Dynamic protonation equilibrium exists between 3Acr and 3AcrH +. The intermediates indicate excited-state proton transfer (PT) between 3AcrH + and TEA. However, application of MF highlights the formation of geminate radical ion pairs (RIPs) with triplet spin-correlation, a signature of latent photoinduced electron transfer between 3AcrH + and TEA co-exists with PT. Magnetic field effect (MFE) is prominent for smaller w0 showing importance of optimum separation between RIP to maximize MFE, whereas PT remains unaltered.

  19. UNDERSTANDING THE GEOMETRY OF ASTROPHYSICAL MAGNETIC FIELDS

    SciTech Connect

    Broderick, Avery E.; Blandford, Roger D.

    2010-08-01

    Faraday rotation measurements have provided an invaluable technique for probing 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/1 rad m{sup -2}){sup 1/4}(B/1 G){sup 1/2} MHz, the character of Faraday rotation changes, entering what we term the 'super-adiabatic regime' in which the rotation measure (RM) is proportional to the integrated absolute value of the line-of-sight component of the field. As a consequence, comparing RMs at high frequencies with those in this new regime provides direct information about the geometry of the magnetic field along the line of sight. Furthermore, the frequency defining the transition to this new regime, {nu}{sub SA}, depends directly upon the local electron density and magnetic field strength where the magnetic field is perpendicular to the line of sight, allowing the unambiguous distinction between Faraday rotation within and in front of the emission region. Typical values of {nu}{sub SA} range from 10 kHz (below the ionospheric cutoff, but above the heliospheric cutoff) to 10 GHz, depending upon the details of the Faraday rotating environment. In particular, for resolved active galactic nuclei, including the black holes at the center of the Milky Way (Sgr A*) and M81, {nu}{sub SA} ranges from roughly 10 MHz to 10 GHz, and thus can be probed via existing and up-coming ground-based radio observatories.

  20. Micromachined near-field probe arrays

    NASA Astrophysics Data System (ADS)

    Srinivasan, Pradeep; Beyette, Fred R., Jr.; Papautsky, Ian

    2003-01-01

    In this paper, we describe the fabrication of cantilevered arrays of tapered near-field probes with pyramidal, sub-micrometer tips that are micromachined from glass substrates. High density data storage and page-oriented retrieval are the potential applications of the described microdevice. Heating and pulling or chemical etching of optic fibers are the common approaches to sub-wavelength aperture fabrication necessary to probe the near-field. Arrays have been previously formed by chemical etching of or film deposition on an opaque substrate and were later coupled to optical fibers for use as near-field probes though; alignment of optical fibers with the apertures for guiding the light to the detector in the far-field is not trivial. Probe arrays described in this work were initially fabricated by dicing a 175-μm thick borosilicate glass substrate using a 250-μm thick resinoid blade and were subsequently tapered and sharpened in a two-step chemical etch process performed at room temperature. The tips were then metallized using a 100nm thick coating of aluminum. Arrays of upto eight 1cm to 2.5 cm long probes with center-to-center spacing of 450 μm and tip sizes of approximately 200 nm were fabricated. Roughness on the vertical sidewall was characterized and the dependence of optical loss coefficients of the light guiding bulk on etch duration was investigated.

  1. Shimming of a Magnet for Calibration of NMR Probes for the Muon g-2 Experiment

    NASA Astrophysics Data System (ADS)

    Bielajew, Rachel

    2013-10-01

    The Muon g-2 Experiment at Fermilab aims to measure the anomalous magnetic moment aμ ≡ (g-2)/2 of the muon to the precision of 0.14 parts per million. This experimental value of aμ can then be compared to the similarly precise theoretical predictions of the Standard Model in order to test the completeness of the model. The value of aμ is extracted from muons precessing in a magnetic field. The magnetic field will be measured with a set of 400 Nuclear Magnetic Resonance (NMR) probes, which have the ability to measure the field to a precision of tens of parts per billion. Before the Muon g-2 Experiment can take place, new NMR probes must be designed, built, and tested using a 1.45 Tesla test magnet at the University of Washington Center for Experimental Nuclear Physics and Astrophysics (CENPA). In order to achieve a significant signal from NMR probes, the magnetic field in which the probes are immersed must be extremely uniform. The existing magnet at CENPA has an approximately linear gradient in magnetic field of about 1 Gauss per centimeter in the smoothest direction. A pair of adjacent square Helmholtz coils was designed and built to create a linear gradient in order to cancel the existing gradient. The length of the NMR signals improved with the implementation of the coils. The results of the addition of the coils to the magnet on the signals from the NMR probes will be presented.

  2. Low field magnetic resonance imaging

    DOEpatents

    Pines, Alexander; Sakellariou, Dimitrios; Meriles, Carlos A.; Trabesinger, Andreas H.

    2010-07-13

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

  3. Magnetic Field Topology in Jets

    NASA Technical Reports Server (NTRS)

    Gardiner, T. A.; Frank, A.

    2000-01-01

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

  4. THE GALACTIC MAGNETIC FIELD

    SciTech Connect

    Jansson, Ronnie; Farrar, Glennys R.

    2012-12-10

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

  5. The Martian magnetic field

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1979-01-01

    The paper presents an overview of the Martian magnetic field measurements and the criticisms made of them. The measurements of the Mars 2, 3, and 5 spacecraft were interpreted by Dolginov et al. (1976, 1978) to be consistent with an intrinsic planetary magnetic moment of 2.5 times 10 to the 22nd power gauss cu cm, basing this result on the apparent size of the obstacle responsible for deflecting the solar wind and an apparent encounter of the spacecraft with the planetary field. It is shown that if the dependence of the Martian magnetic moment on the rotation rate was linear, the estimate of the moment would be far larger than reported by Dolginov et al. An upper limit of 250 km is calculated for the dynamo radius using the similarity law, compared with 500 km obtained by Dolginov et al. It is concluded that the possible strength of a Martian dynamo is below expectations, and it is likely that the Mars dynamo is not presently operative.

  6. Design of a dual sensor probe array for internal field measurement in Versatile Experiment Spherical Torusa)

    NASA Astrophysics Data System (ADS)

    Jeong-hun, Yang; Chung, Kyoung-Jae; An, YoungHwa; Jung, Bong Ki; Jo, Jong Gab; Hwang, Y. S.

    2012-10-01

    A dual sensor probe array is designed and constructed for internal magnetic field measurement at Versatile Experiment Spherical Torus (VEST) at the Seoul National University. Simultaneous use of Hall sensors and chip inductors allows cross-calibration among the measurements and compensation for each other's weaknesses while their small sizes are expected to cause only mild plasma perturbations. Calibration of the dual sensor probe array, using a Helmholtz coil, shows good sensitivity for the magnetic field measurement of the VEST. Prior to Ohmic start-up, the magnetic field structure inside the vacuum chamber is measured by using the calibrated probe array. The dual sensor probe array is expected to be useful in analyzing the temporal magnetic field structure change during the magnetic reconnection and in reconstruction of the current profile during the discharge of the VEST device.

  7. Design of a dual sensor probe array for internal field measurement in Versatile Experiment Spherical Torus.

    PubMed

    Jeong-hun, Yang; Chung, Kyoung-Jae; An, YoungHwa; Jung, Bong Ki; Jo, Jong Gab; Hwang, Y S

    2012-10-01

    A dual sensor probe array is designed and constructed for internal magnetic field measurement at Versatile Experiment Spherical Torus (VEST) at the Seoul National University. Simultaneous use of Hall sensors and chip inductors allows cross-calibration among the measurements and compensation for each other's weaknesses while their small sizes are expected to cause only mild plasma perturbations. Calibration of the dual sensor probe array, using a Helmholtz coil, shows good sensitivity for the magnetic field measurement of the VEST. Prior to Ohmic start-up, the magnetic field structure inside the vacuum chamber is measured by using the calibrated probe array. The dual sensor probe array is expected to be useful in analyzing the temporal magnetic field structure change during the magnetic reconnection and in reconstruction of the current profile during the discharge of the VEST device.

  8. Magnetic field switchable dry adhesives.

    PubMed

    Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

    2015-02-01

    A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.

  9. Electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

    1982-01-01

    A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

  10. Antenna Near-Field Probe Station Scanner

    NASA Technical Reports Server (NTRS)

    Zaman, Afroz J. (Inventor); Lee, Richard Q. (Inventor); Darby, William G. (Inventor); Barr, Philip J. (Inventor); Lambert, Kevin M (Inventor); Miranda, Felix A. (Inventor)

    2011-01-01

    A miniaturized antenna system is characterized non-destructively through the use of a scanner that measures its near-field radiated power performance. When taking measurements, the scanner can be moved linearly along the x, y and z axis, as well as rotationally relative to the antenna. The data obtained from the characterization are processed to determine the far-field properties of the system and to optimize the system. Each antenna is excited using a probe station system while a scanning probe scans the space above the antenna to measure the near field signals. Upon completion of the scan, the near-field patterns are transformed into far-field patterns. Along with taking data, this system also allows for extensive graphing and analysis of both the near-field and far-field data. The details of the probe station as well as the procedures for setting up a test, conducting a test, and analyzing the resulting data are also described.

  11. Fast superconducting magnetic field switch

    SciTech Connect

    Goren, Y.; Mahale, N.K.

    1995-12-31

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

  12. Scanning Hall probe microscopy of a diluted magnetic semiconductor

    SciTech Connect

    Kweon, Seongsoo; Samarth, Nitin; Lozanne, Alex de

    2009-05-01

    We have measured the micromagnetic properties of a diluted magnetic semiconductor as a function of temperature and applied field with a scanning Hall probe microscope built in our laboratory. The design philosophy for this microscope and some details are described. The samples analyzed in this work are Ga{sub 0.94}Mn{sub 0.06}As films grown by molecular beam epitaxy. We find that the magnetic domains are 2-4 mum wide and fairly stable with temperature. Magnetic clusters are observed above T{sub C}, which we ascribe to MnAs defects too small and sparse to be detected by a superconducting quantum interference device magnetometer.

  13. Polar Magnetic Field Experiment

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1999-01-01

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

  14. Photonic Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Wyntjes, Geert

    2002-02-01

    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.

  15. Magnetic Fields: Visible and Permanent.

    ERIC Educational Resources Information Center

    Winkeljohn, Dorothy R.; Earl, Robert D.

    1983-01-01

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

  16. Spin Polarized Electron Probes and Magnetic Nanostructures

    SciTech Connect

    D.L. Mills

    2003-10-15

    OAK B188 This report summarizes progress to date in our theoretical research program, for the period from July 1, 2002 to November 1, 2003. In addition, our research priorities for the coming year are set forth. The reporting period has been a most exciting and significant one. For the past several years, one of our principal thrust areas has been development of the theory of spin dynamics in magnetic nanostructures with emphasis on the use of spin polarized electrons as probes of short wavelength spin dynamics in such entities. Our program stimulated the first experiment which detected large wave vector spin waves in ultrathin films in 1999 through spin polarized electron loss spectroscopy (SPEELS); the publication which announced this discovery was a joint publication between a group in Halle (Germany) with our theory effort. The continued collaboration has led to the design and implementation of the new SPEELS spectrometer and we now have in hand the first detailed measurements of spin wave dispersion in an ultrathin film. A second such spectrometer is now operational in the laboratory of Prof. H. Hopster, at UC Irvine. We are thus entering a most exciting new era in the spectroscopy of spin excitations in magnetic nanostructures. During the reporting period, we have completed very important new analyses which predict key aspects of the spectra which will be uncovered by these new instruments, and the calculations continue to be developed and to expand our understanding. In addition, we have initiated a new series of theoretical studies directed toward spin dynamics of single magnetic adatoms on metal surfaces, with STM based studies of this area n mind. In the near future, these studies will continue, and we will expand our effort into new areas of spin dynamics in magnetic nanostructures.

  17. Magnetic field therapy: a review.

    PubMed

    Markov, Marko S

    2007-01-01

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

  18. Seismic probes of solar interior magnetic structure.

    PubMed

    Hanasoge, Shravan; Birch, Aaron; Gizon, Laurent; Tromp, Jeroen

    2012-09-01

    Sun spots are prominent manifestations of solar magnetoconvection, and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wave speeds and flow-advection-related Doppler shifts. Here, we employ partial-differential-equation-constrained optimization to determine the appropriate parametrization of the structural properties of the magnetic interior. Seven different wave speeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity, and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfvén waves, each of which propagates at a different wave speed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun. PMID:23005276

  19. Seismic probes of solar interior magnetic structure.

    PubMed

    Hanasoge, Shravan; Birch, Aaron; Gizon, Laurent; Tromp, Jeroen

    2012-09-01

    Sun spots are prominent manifestations of solar magnetoconvection, and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wave speeds and flow-advection-related Doppler shifts. Here, we employ partial-differential-equation-constrained optimization to determine the appropriate parametrization of the structural properties of the magnetic interior. Seven different wave speeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity, and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfvén waves, each of which propagates at a different wave speed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun.

  20. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Yehuda; Mahale, Narayan K.

    1996-01-01

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

  1. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Y.; Mahale, N.K.

    1996-08-06

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

  2. Magnetic field modification of optical magnetic dipoles.

    PubMed

    Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

    2015-03-11

    Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

  3. Magnetic field modification of optical magnetic dipoles.

    PubMed

    Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

    2015-03-11

    Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate.

  4. Cyclical magnetic field flow fractionation

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  5. Using Jupiter's gravitational field to probe the Jovian convective dynamo.

    PubMed

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-03-23

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.

  6. Using Jupiter's gravitational field to probe the Jovian convective dynamo.

    PubMed

    Kong, Dali; Zhang, Keke; Schubert, Gerald

    2016-01-01

    Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472

  7. Exposure guidelines for magnetic fields

    SciTech Connect

    Miller, G.

    1987-12-01

    The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

  8. [Magnetic fields and fish behavior].

    PubMed

    Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

    2013-01-01

    In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior.

  9. [Magnetic fields and fish behavior].

    PubMed

    Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

    2013-01-01

    In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

  10. [Magnetic fields and fish behavior].

    PubMed

    2013-01-01

    In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

  11. Magnetic fields in the cosmos

    NASA Astrophysics Data System (ADS)

    Parker, E. N.

    1983-08-01

    Descriptive models for the dynamo processes that generate magnetic fields around celestial objects are reviewed. Magnetic fields are produced, along with an electric current, when a conductor is moved perpendicularly through a magnetic field, so long as the resulting current is fed back into the conductor to amplify the current and field. In MHD theory, the lines of force of the magnetic field travel with the conducting fluid. A weak current or field must be present initially to generate the field. Planets have molten cores and stars have ionized gases to act as the conductors, and all space has sufficient gas with free electrons. The rotations of the planets, stars, and galaxy enhance the magnetic fields. Convective patterns have been characterized in the earth's molten core because of anomalies observed in the magnetic field at the surface. It has been shown that the faster a planet rotates, the more powerful its magnetic field is. However, fluid motions will produce fields only if the fluid motion is helical. The exact mechanism in stars could be primordial magnetism trapped during formation. However, in galaxies, the Biermann battery effect, wherein free electrons move along the surfaces of stars, could create enough of a field for the amplification process to proceed.

  12. Magnetic-field-dosimetry system

    SciTech Connect

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

    1981-01-21

    A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

  13. USING COORDINATED OBSERVATIONS IN POLARIZED WHITE LIGHT AND FARADAY ROTATION TO PROBE THE SPATIAL POSITION AND MAGNETIC FIELD OF AN INTERPLANETARY SHEATH

    SciTech Connect

    Xiong, Ming; Feng, Xueshang; Liu, Ying D.; Davies, Jackie A.; Harrison, Richard A.; Owens, Mathew J.; Davis, Chris J.

    2013-11-01

    Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons and therefore depend on both viewing geometry and electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component B{sub ∥} and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modeling of an Earth-directed shock and synthesize the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depends on scattering angle, WL radiance I decreases with heliocentric distance r roughly according to the expression I∝r {sup –3}. The sheath region downstream of the Earth-directed shock is well viewed from the L4 and L5 Lagrangian points, demonstrating the benefits of these points in terms of space weather forecasting. The spatial position of the main scattering site r{sub sheath} and the mass of plasma at that position M{sub sheath} can be inferred from the polarization of the shock-associated enhancement in WL radiance. From the FR measurements, the local B{sub ∥sheath} at r{sub sheath} can then be estimated. Simultaneous observations in polarized WL and FR can not only be used to detect CMEs, but also to diagnose their plasma and magnetic field properties.

  14. Suppression of probe background signals via B1 field inhomogeneity

    SciTech Connect

    Feng, Jian; Reimer, Jeffrey

    2011-01-27

    A new approach combining a long pulse with the DEPTH sequence (Cory and Ritchey, Journal of Magnetic Resonance, 1988) greatly improves the efficiency for suppressing probe background signals arising from spinning modules. By applying a long initial excitation pulse in the DEPTH sequence, instead of a {pi}/2 pulse, the inhomogeneous B{sub 1} fields outside the coil can dephase the background coherence in the nutation frame. The initial long pulse and the following two consecutive EXORCYCLE {pi} pulses function complementarily and prove most effective in removing background signals from both strong and weak B{sub 1} fields. Experimentally, the length of the long pulse can be optimized around odd multiples of the {pi}/2 pulse, depending on the individual probe design, to preserve signals inside the coil while minimizing those from probe hardware. This method extends the applicability of the DEPTH sequence to probes with small differences in B{sub 1} field strength between the inside and outside of the coil, and can readily combine with well-developed double resonance experiments for quantitative measurement. In general, spin systems with weak internal interactions are required to attain efficient and uniform excitation for powder samples, and the principles to determine the applicability are discussed qualitatively in terms of the relative strength of spin interactions, r.f. power and spinning rate.

  15. Mars Observer magnetic fields investigation

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.; Connerney, J. E. P.; Wasilewski, P.; Lin, R. P.; Anderson, K. A.; Carlson, C. W.; Mcfadden, J.; Curtis, D. W.; Reme, H.; Cros, A.

    1992-01-01

    The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

  16. Magnetic Field of Mars

    NASA Astrophysics Data System (ADS)

    Cain, J. C.; Ferguson, B.; Mozzoni, D.; Hood, L.

    2000-07-01

    bodies combined with later absolute dating of Martian geologic units could lead to a quantitative constraint on the thermal history of the planet, i.e. the time when convective dynamo generation ceased in the core. Determination of directions of magnetization of anomaly sources as a function of age combined with the expectation that the Martian dynamo field was roughly aligned with the rotation axis would lead to a means of investigating polar wandering for Mars. Preliminary analysis of two magnetic anomalies in the northern polar region has yielded paleomagnetic pole positions near 50 N, 135 W, about 30 degrees north of Olympus Mons. This location is roughly consistent with the orientation of the planet expected theoretically prior to the formation of the Tharsis region. In the future, more accurate observations of the vector field at the lowest possible altitudes would significantly improve our understanding of Martian thermal history, polar wandering, and upper crustal evolution. Mapping potential resources (e.g., iron-rich source bodies) for future practical use would also be a side benefit. Additional information is contained in the original abstract.

  17. Consistency relation for cosmic magnetic fields

    NASA Astrophysics Data System (ADS)

    Jain, Rajeev Kumar; Sloth, Martin S.

    2012-12-01

    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.

  18. Vestibular stimulation by magnetic fields

    PubMed Central

    Ward, Bryan K.; Roberts, Dale C.; Della Santina, Charles C.; Carey, John P.; Zee, David S.

    2015-01-01

    Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging (MRI) studies, these reports have become more common. It was recently learned that humans, mice and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662

  19. Magnetic fields around evolved stars

    NASA Astrophysics Data System (ADS)

    Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

    2014-04-01

    A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

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

    PubMed Central

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

    2013-01-01

    While magnetic resonance imaging of static magnetic fields generated by external probes has been previously demonstrated, there is an unmet need to image time-varying magnetic fields, such as those generated by transcranial magnetic stimulators or radiofrequency hyperthermia probes. A method to image such time-varying magnetic fields is introduced in this work. This article presents the theory behind the method and provides proof of concept by imaging time-varying magnetic fields generated by a figure-eight coil inside simple phantoms over a range of frequencies and intensities, using a 7T small animal MRI scanner. The method is able to reconstruct the three-dimensional components of the oscillating magnetic field vector. PMID:23355446

  1. Evidence for the Reversal of Magnetic Field Polarity in Coronal Streamers

    NASA Technical Reports Server (NTRS)

    Woo, Richard

    1996-01-01

    Faraday rotation observations are unique amongst radio occultation measurements in that they respond to magnetic field in addition to electron density, making it possible to probe the coronal magnetic field.

  2. Origin of cosmic magnetic fields.

    PubMed

    Campanelli, Leonardo

    2013-08-01

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

  3. The Capacitive Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Zyatkov, D. O.; Yurchenko, A. V.; Balashov, V. B.; Yurchenko, V. I.

    2016-01-01

    The results of a study of sensitive element magnetic field sensor are represented in this paper. The sensor is based on the change of the capacitance with an active dielectric (ferrofluid) due to the magnitude of magnetic field. To prepare the ferrofluid magnetic particles are used, which have a followingdispersion equal to 50 < Ø < 56, 45 < Ø < 50, 40 < Ø < 45 and Ø < 40micron of nanocrystalline alloy of brand 5BDSR. The dependence of the sensitivity of the capacitive element from the ferrofluid with different dispersion of magnetic particles is considered. The threshold of sensitivity and sensitivity of a measuring cell with ferrofluid by a magnetic field was determined. The experimental graphs of capacitance change of the magnitude of magnetic field are presented.

  4. Measurements of magnetic field alignment

    SciTech Connect

    Kuchnir, M.; Schmidt, E.E.

    1987-11-06

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

  5. Solar energetic particles as probes of the structures of magnetic clouds

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Reames, D. V.

    1990-01-01

    Two possible closed magnetic topologies are considered for clouds: an elongated bottle with field lines rooted at both ends in the sun and a magnetic bubble or plasmoid consisting of closed field lines. Solar energetic particles (SEPs) are used as probes of the cloud topologies. The rapid access of SEPs to clouds in many events indicates that the cloud field lines extend back to the sun.

  6. Solar Polarimetry - from Turbulent Magnetic Fields to Sunspots

    NASA Astrophysics Data System (ADS)

    Kleint, Lucia

    2016-07-01

    Polarimetric measurements are essential to investigate the solar magnetic field. Scattering polarization and the Hanle effect allow us to probe the turbulent magnetic field and the still open questions of its strength and variability. Directed magnetic fields can be detected via the Zeeman effect. To derive their orientation and strength, so-called inversion codes are used, which iteratively modify a model atmosphere and calculate the resulting polarization profiles that are then compared to the observations. While photospheric polarimetry is well-established, chromospheric polarimetry is still in its infancy, especially because it requires a treatment in non-LTE, making it a complex non-linear problem. But some of the most important open questions concern the strength and geometry of the chromospheric magnetic field. In this talk, I will review different polarimetric analysis techniques and recent advances in magnetic field measurements going from the small scales of turbulent magnetic fields to changes of magnetic fields in an active region during flares.

  7. Structure of magnetic field lines

    NASA Astrophysics Data System (ADS)

    Golmankhaneh, Ali Khalili; Golmankhaneh, Alireza Khalili; Jazayeri, Seyed Masud; Baleanu, Dumitru

    2012-02-01

    In this paper the Hamiltonian structure of magnetic lines is studied in many ways. First it is used vector analysis for defining the Poisson bracket and Casimir variable for this system. Second it is derived Pfaffian equations for magnetic field lines. Third, Lie derivative and derivative of Poisson bracket is used to show structure of this system. Finally, it is shown Nambu structure of the magnetic field lines.

  8. The MAVEN Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2015-12-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.

  9. The MAVEN Magnetic Field Investigation

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2014-01-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

  10. Cosmic Magnetic Fields - An Overview

    NASA Astrophysics Data System (ADS)

    Wielebinski, Richard; Beck, Rainer

    Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

  11. The Magnetic Field in Tapia's Globule 2

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Carretti, Ettore; Bhat, Ramesh; Robishaw, Timothy; Crutcher, Richard; Vaillancourt, John

    2014-04-01

    We propose to measure the magnetic field in the Southern Coalsack using the Zeeman effect in OH at 1665 and 1667 MHz. This is motivated by (1) the measurement of a large magnetic field (B~90 uG) in the Coalsack region from optical and near infrared polarimetry and (2) a very low magnetic field (B~1 uG) measured ~30' from the cloud edge using pulsar Faraday rotation measurements. While the derived field strength in the cloud is significantly larger than usually seen in the interstellar medium, the existence of an X-ray emitting envelope around the cloud that contains significant amounts of O VI ions puts the magnetic pressure at approximate equipartition with the thermal pressure of such gas. A chain of observational results indicate that the Coalsack might be a unique, nearby example of externally triggered star formation. This chain starts with the passage of the Upper Centaurus-Lupus super bubble over the cloud, eventually causing triggered star formation. Probing the high magnetic field strength and providing accurate constraints for the interpretation of the observations of the cloud is therefore of great importance for testing this hypothesis.

  12. Reionization constraints on primordial magnetic fields

    NASA Astrophysics Data System (ADS)

    Pandey, Kanhaiya L.; Choudhury, T. Roy; Sethi, Shiv K.; Ferrara, Andrea

    2015-08-01

    We study the impact of the extra density fluctuations induced by primordial magnetic fields on the reionization history in the redshift range: 6 < z < 10. We perform a comprehensive Markov chain Monte Carlo (MCMC) physical analysis allowing the variation of parameters related to primordial magnetic fields (strength, B0, and power-spectrum index n_{B}), reionization and Λ cold dark matter cosmological model. We find that magnetic field strengths in the range: B0 ≃ 0.05-0.3 nG (for nearly scale-free power spectra) can significantly alter the reionization history in the above redshift range and can relieve the tension between the Wilkinson Microwave Anisotropy Probe and quasar absorption spectra data. Our analysis puts upper limits on the magnetic field strength B0 < 0.358, 0.120 and 0.059 nG (95 per cent c.l.) for n_{B} = -2.95, -2.9 and -2.85, respectively. These represent the strongest magnetic field constraints among those available from other cosmological observables.

  13. Laboratory Measurements of Astrophysical Magnetic Fields

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  14. Magnetic field synthesis for microwave magnetics

    NASA Astrophysics Data System (ADS)

    Morgenthaler, F. R.

    1982-04-01

    The Microwave and Quantum Magnetics Group of the M.I.T. Department of Electrical Engineering and Computer Science undertook a two-year research program directed at developing synthesis procedures that allow magnetostatic and/or magnetoelastic modes to be specially tailored for microwave signal processing applications that include magnetically tunable filters and limiters as well as delay lines that are either linearly dispersive or nondispersive over prescribed bandwidths. Special emphasis was given to devices employing thin films of yttrium iron garnet (YIG) that are blessed with spatially nonuniform dc magnetic fields.

  15. Application of a portable nuclear magnetic resonance surface probe to porous media.

    PubMed

    Marko, Andriy; Wolter, Bernd; Arnold, Walter

    2007-03-01

    A portable nuclear magnetic resonance (NMR) surface probe was used to determine the time-dependent self-diffusion coefficient D(t) of water molecules in two fluid-filled porous media. The measuring equipment and the inhomogeneous magnetic fields in the sensitive volume of the probe are described. It is discussed how to evaluate D(t) using a surface probe from the primary and stimulated echoes generated in three-pulse experiments. Furthermore, the evaluation of D(t) allows one to determine the geometrical structure of porous materials.

  16. Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)

    NASA Technical Reports Server (NTRS)

    Koelfgen, Syri J.; Eskridge, Richard; Fimognari, Peter; Hawk, Clark W.; Lee, Mike; Martin, Adam

    2004-01-01

    The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and subsequently ejecting them at high velocity. An overview of PTX is described in a companion paper. The shape and magnetic field structure of the translating plasmoids will be measured with of an array of inductive magnetic field probes. Six sets of two B-dot probes (for a total of twelve probes) have been constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes were calibrated with a Helmholtz coil, driven alternately by a high-voltage pulser or a signal generator. The probes are wound on a G-10 form, and have an average (calibrated) NA of 9.37 x 10(exp -5) square meters, where N is the number of turns and A is cross-sectional area. The frequency response of the probes was measured over the range from 1 kHz to 10 MHZ. The electron number density n(sub e), electron temperature T(sub e) and velocity v will be determined from measurements taken with a quadruple Langmuir probe, situated in the exhaust chamber. Three of the four probes on the quadruple probe sample the current-voltage characteristic, and from this yield measurements of T(sub e) and n(sub e). The fourth probe provides a measurement of plasma flow velocity. A 6-inch long alumina rod, hollowed with four holes to house the probe wires, is being used to construct the quadruple probe. A variety of propellants will be used, including hydrogen, nitrogen and argon. From the measurements of the plasmoid mass, density, temperature, and velocity, the basic propulsion characteristics of PTX will be evaluated.

  17. Estimation of fluctuating magnetic fields by an atomic magnetometer

    SciTech Connect

    Petersen, Vivi; Moelmer, Klaus

    2006-10-15

    We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

  18. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    DOEpatents

    Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.

    1978-01-01

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

  19. PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS

    SciTech Connect

    Yamamoto, Tetsuya T.; Kusano, K.

    2012-06-20

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

  20. Resonant magnetic fields from inflation

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

    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 Script 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.

  1. The magnetic field of Neptune

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

    1992-01-01

    A model is given of the planetary magnetic field of Neptune based on a spherical harmonic analysis of the observations obtained by the Voyager 2. Generalized inverse techniques are used to partially solve a severely underdetermined inverse problem, and the resulting model is nonunique since the observations are limited in spatial distribution. Dipole, quadrupole, and octupole coefficients are estimated independently of other terms, and the parameters are shown to be well constrained by the measurement data. The large-scale features of the magnetic field including dipole tilt, offset, and harmonic content are found to characterize a magnetic field that is similar to that of Uranus. The traits of Neptune's magnetic field are theorized to relate to the 'ice' interior of the planet, and the dynamo-field generation reflects this poorly conducting planet.

  2. Preflare magnetic and velocity fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

    1986-01-01

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

  3. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

  4. Magnetic Field of Strange Dwarfs

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. S.

    2016-03-01

    The generation of a magnetic field in a strange quark star owing to differential rotation of the superfluid and superconducting quark core relative to the normal electron-nuclear crust of the star is examined. The maximum possible magnetic field on the surface is estimated for various models of strange dwarfs. Depending on the configuration parameters, i.e., the mass M and radius R of the star, a range of 103-105 G is found. These values of the magnetic field may be an additional condition for identification of strange dwarfs among the extensive class of observed white dwarfs.

  5. Magnetoconvection in sheared magnetic fields

    SciTech Connect

    Bian, N. H.; Garcia, O. E.

    2008-10-15

    The development of magnetoconvection in a sheared magnetic field is investigated. The equilibrium magnetic field B{sub 0} is horizontal and its orientation varies linearly along the vertical axis. Preliminary consideration of the transition from the inertial to the viscous regime of the gravitational resistive interchange instability, reveals that the latter is characterized by the existence of viscoresistive boundary layers of vertical width which scales as Q{sup -1/6}, where Q is the Chandrasekhar number. The situation is analogous to the one encountered in magnetically confined laboratory plasmas, where convective flows are constrained by the magnetic shear to develop in boundary layers located around resonant magnetic surfaces in order to fulfill the 'interchange condition'k{center_dot}B{sub 0}=0, where k is the wave vector of the magnetic perturbation. It follows that when the effect of thermal diffusion is taken into account in the process, convection can only occur above a certain critical value of the Rayleigh number which scales as Q{sup 2/3} for large Q. At the onset, the convection pattern is a superposition of identically thin convective rolls everywhere aligned with the local magnetic field lines and which therefore adopt the magnetic field geometry, a situation also reminiscent of the penumbra of sunspots. Using this degeneracy, equations describing the weakly nonlinear state are obtained and discussed. A reduced magnetohydrodynamic description of magnetoconvection is introduced. Since it is valid for arbitrary magnetic field configurations, it allows a simple extension to the case where there exists an inclination between the direction of gravity and the plane spanned by the equilibrium magnetic field. These reduced magnetohydrodynamic equations are proposed as a powerful tool for further investigations of magnetoconvection in more complex field line geometries.

  6. Bioluminescence under static magnetic fields

    NASA Astrophysics Data System (ADS)

    Iwasaka, M.; Ueno, S.

    1998-06-01

    In the present study, the effect of magnetic fields on the emission of light by a living system was studied. The fireflies Hotaria parvula and Luciola cruciata were used as the bioluminescence systems. The firefly light organ was fixed at the edge of an optical fiber. The emitted light was introduced into a single-channel photon-counting system using an optical fiber. We measured both the spectrum of a constant light emission and, the time course of bioluminescence pulses. Two horizontal-type superconducting magnets, which produced 8 and 14 T magnetic fields at their center, were used as the magnetic-field generators. We also carried out an in vitro study of bioluminescence. The enzymatic activity of luciferase was measured under a 14 T magnetic field. We measured emission spectra of bioluminescence over the interval 500-600 nm at 25 °C in a stable emission state. It was observed that the peak wavelength around 550 nm shifted to 560 nm under a 14 T magnetic field. However, the effects of magnetic fields were not significant. Also, we measured the time course of emissions at 550 nm in a transient emission state. The rate in the light intensity under a 14 T magnetic field increased compared to the control. There is a possibility that the change in the emission intensities under a magnetic field is related to a change in the biochemical systems of the firefly, such as the enzymatic process of luciferase and the excited singlet state with subsequent light emission.

  7. Magnetic field structure of Mercury

    NASA Astrophysics Data System (ADS)

    Hiremath, K. M.

    2012-04-01

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

  8. High magnetic fields in the USA

    NASA Astrophysics Data System (ADS)

    Campbell, Laurence J.; Parkin, Don E.; Crow, Jack E.; Schneider-Muntau, Hans J.; Sullivan, Neil S.

    During the past thirty years research using high magnetic fields has technically evolved in the manner, but not the magnitude, of the so-called big science areas of particle physics, plasma physics, neutron scattering, synchrotron light scattering, and astronomy. Starting from the laboratories of individual researchers it moved to a few larger universities, then to centralized national facilities with research and maintenance staffs, and, finally, to joint international ventures to build unique facilities, as illustrated by the subject of this conference. To better understand the nature of this type of research and its societal justification it is helpful to compare it, in general terms, with the aforementioned big-science fields. High magnetic field research differs from particle physics, plasma physics, and astronomy in three respects: (1) it is generic research that cuts across a wide range of scientific disciplines in physics, chemistry, biology, medicine, and engineering; (2) it studies materials and processes that are relevant for a variety of technological applications and it gives insight into biological processes; (3) it has produced, at least, comparably significant results with incomparably smaller resources. Unlike neutron and synchrotron light scattering, which probe matter, high magnetic fields change the thermodynamic state of matter. This change of state is fundamental and independent of other state variables, such as pressure and temperature. After the magnetic field is applied, various techniques are then used to study the new state.

  9. Field quality measurements of a 2-Tesla transmission line magnet

    SciTech Connect

    Velev, G.V.; Foster, W.; Kashikhin, V.; Mazur, P.; Oleck, A.; Piekarz, H.; Schlabach, P.; Sylvester, C.; Wake, M.; /KEK, Tsukuba

    2005-09-01

    A prototype 2-Tesla superconducting transmission line magnet for future hadron colliders was designed, built and tested at Fermilab. The 1.5 m long, combined-function gradient-dipole magnet has a vertical pole aperture of 20 mm. To measure the magnetic field quality in such a small magnet aperture, a specialized rotating coil of 15.2 mm diameter, 0.69 m long was fabricated. Using this probe, a program of magnetic field quality measurements was successfully performed. Results of the measurements are presented and discussed.

  10. A versatile rotary-stage high frequency probe station for studying magnetic films and devices

    NASA Astrophysics Data System (ADS)

    He, Shikun; Meng, Zhaoliang; Huang, Lisen; Yap, Lee Koon; Zhou, Tiejun; Panagopoulos, Christos

    2016-07-01

    We present a rotary-stage microwave probe station suitable for magnetic films and spintronic devices. Two stages, one for field rotation from parallel to perpendicular to the sample plane (out-of-plane) and the other intended for field rotation within the sample plane (in-plane) have been designed. The sample probes and micro-positioners are rotated simultaneously with the stages, which allows the field orientation to cover θ from 0∘ to 90∘ and φ from 0∘ to 360∘. θ and φ being the angle between the direction of current flow and field in a out-of-plane and an in-plane rotation, respectively. The operation frequency is up to 40 GHz and the magnetic field up to 1 T. The sample holder vision system and probe assembly are compactly designed for the probes to land on a wafer with diameter up to 3 cm. Using homemade multi-pin probes and commercially available high frequency probes, several applications including 4-probe DC measurements, the determination of domain wall velocity, and spin transfer torque ferromagnetic resonance are demonstrated.

  11. A versatile rotary-stage high frequency probe station for studying magnetic films and devices.

    PubMed

    He, Shikun; Meng, Zhaoliang; Huang, Lisen; Yap, Lee Koon; Zhou, Tiejun; Panagopoulos, Christos

    2016-07-01

    We present a rotary-stage microwave probe station suitable for magnetic films and spintronic devices. Two stages, one for field rotation from parallel to perpendicular to the sample plane (out-of-plane) and the other intended for field rotation within the sample plane (in-plane) have been designed. The sample probes and micro-positioners are rotated simultaneously with the stages, which allows the field orientation to cover θ from 0(∘) to 90(∘) and φ from 0(∘) to 360(∘). θ and φ being the angle between the direction of current flow and field in a out-of-plane and an in-plane rotation, respectively. The operation frequency is up to 40 GHz and the magnetic field up to 1 T. The sample holder vision system and probe assembly are compactly designed for the probes to land on a wafer with diameter up to 3 cm. Using homemade multi-pin probes and commercially available high frequency probes, several applications including 4-probe DC measurements, the determination of domain wall velocity, and spin transfer torque ferromagnetic resonance are demonstrated. PMID:27475578

  12. Measuring Earth's Magnetic Field Simply.

    ERIC Educational Resources Information Center

    Stewart, Gay B.

    2000-01-01

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

  13. Observation of low magnetic field density peaks in helicon plasma

    SciTech Connect

    Barada, Kshitish K.; Chattopadhyay, P. K.; Ghosh, J.; Kumar, Sunil; Saxena, Y. C.

    2013-04-15

    Single density peak has been commonly observed in low magnetic field (<100 G) helicon discharges. In this paper, we report the observations of multiple density peaks in low magnetic field (<100 G) helicon discharges produced in the linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. Experiments are carried out using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 G to 100 G. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a magnetic field value of {approx}25 G. Another peak of smaller magnitude in density has been observed near 50 G. Measurement of amplitude and phase of the axial component of the wave using magnetic probes for two magnetic field values corresponding to the observed density peaks indicated the existence of radial modes. Measured parallel wave number together with the estimated perpendicular wave number suggests oblique mode propagation of helicon waves along the resonance cone boundary for these magnetic field values. Further, the observations of larger floating potential fluctuations measured with Langmuir probes at those magnetic field values indicate that near resonance cone boundary; these electrostatic fluctuations take energy from helicon wave and dump power to the plasma causing density peaks.

  14. Effect of Ge substitution for Si on the magnetic hyperfine field in LaMn2Si2 compound measured by perturbed angular correlation spectroscopy with 140Ce as probe nuclei

    NASA Astrophysics Data System (ADS)

    Bosch-Santos, B.; Carbonari, A. W.; Cabrera-Pasca, G. A.; Costa, M. S.; Saxena, R. N.

    2013-05-01

    The effect of substitution of Ge for Si in LaMn2Si2 compound on the magnetic hyperfine field (Bhf) has been investigated by perturbed γ -γ angular correlation (PAC) spectroscopy using 140La(140Ce) as probe nuclei. This compound exhibits antiferromagnetism followed by a ferromagnetic ordering when temperature decreases. The behavior of the ferromagnetic transition when Ge gradually replaces Si, with concentrations of 20%, 40%, 80%, and 100% is discussed. PAC measurements were carried out in the temperature range from 15 K to 325 K. Results for LaMn2Si2 compound showed that the dependence of Bhf with temperature follows the expected behavior for the host magnetization and could be fitted by a Brillouin function for JMn = 5/2. However, the temperature dependence of Bhf for compounds when Si is gradually replaced by Ge showed a deviation from such a behavior, which gradually increases up to a strong deviation observed for LaMn2Ge2. This striking behavior was ascribed to the hybridization of d band of the host and f band of the Ce impurities, which is stronger when the unit cell volume increase as Si ions are substituted by Ge atoms.

  15. Pattern Formation in a Complex Plasma in High Magnetic Fields

    SciTech Connect

    Schwabe, M.; Konopka, U.; Bandyopadhyay, P.; Morfill, G. E.

    2011-05-27

    Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments.

  16. Implementation of Akiyama probe in low temperature magnetic force microscope

    NASA Astrophysics Data System (ADS)

    Sass, Paul; Wu, Weida

    Exotic phenomena often call for high sensitivity scanning probe microscopic techniques working at extremely low temperatures. Specifically, it is of great fundamental interest to detect the weak magnetic signals in a range of interesting systems such as, quantum anomalous Hall, skyrmion, heavy-fermion, and multiferroic systems. To this end, we are developing low temperature magnetic force microscope (MFM) using a self-sensing cantilever called Akiyama-probe (A-probe). The main advantage of this specific probe is its extremely low power-dissipation compared to other self-sensing (e.g. piezoresistive) cantilevers for low temperature application. We will present progress of the implementation of A-probe and preliminary results under various conditions. This work is supported by DOE BES under Award DE-SC0008147.

  17. Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere

    PubMed Central

    Zhang, T. L.; Baumjohann, W.; Russell, C. T.; Luhmann, J. G.; Xiao, S. D.

    2016-01-01

    The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234

  18. Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere

    NASA Astrophysics Data System (ADS)

    Zhang, Tielong; Baumjohann, Wolfgang; Russell, Christopher; Luhmann, Janet

    2016-04-01

    The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.

  19. Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere

    NASA Astrophysics Data System (ADS)

    Zhang, T. L.; Baumjohann, W.; Russell, C. T.; Luhmann, J. G.; Xiao, S. D.

    2016-03-01

    The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.

  20. Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere.

    PubMed

    Zhang, T L; Baumjohann, W; Russell, C T; Luhmann, J G; Xiao, S D

    2016-01-01

    The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234

  1. Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere.

    PubMed

    Zhang, T L; Baumjohann, W; Russell, C T; Luhmann, J G; Xiao, S D

    2016-03-24

    The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.

  2. Nuclear magnetic resonance force microscopy at high magnetic field and low temperature

    NASA Astrophysics Data System (ADS)

    Marohn, John A.; Harrell, Lee H.; Thurber, Kent; Fainchtein, Raul; Smith, Doran D.

    2000-03-01

    We will report detection of nuclear magnetic resonance at 6.5 Tesla from a micron-scale sample by magnetic resonance force microscopy (MRFM) at low-temperature. We will detail a ``bare bones" one-inch diameter probe (including a novel ``string and spring" fiber positioning element, a tuned and matched RF coil, and a heating element) suitable for simple variable-temperature magnetic-resonance force microscopy studies. The compact probe design succeeded in minimizing both deleterious thermal drifts in the positions of probe components and pickup of environmental vibrations. In studying Nd-doped calcium fluoride at a magnetic field higher than has previously been employed in an MRFM experiment, we found that even sample-on-cantilever experiments can be complicated by the cantilever's resonance frequency changing with magnetic field.

  3. Detecting magnetic ordering with atomic size electron probes

    DOE PAGES

    Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Cantoni, Claudia; Lupini, Andrew R.

    2016-05-27

    While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setupmore » presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.« less

  4. Dynamos and cosmic magnetic fields.

    NASA Astrophysics Data System (ADS)

    Kulsrud, R.; Cowley, S. C.; Gruzinov, A. V.; Sudan, R. N.

    1997-04-01

    This paper discusses the origin of the galactic magnetic field. The theory of the mean field dynamo in the interstellar medium is reviewed and shown to be flawed because it ignores the strong amplification of small-scale magnetic fields. An alternative origin is offered. It is proposed that the galactic fields are created in the protogalaxy by protogalactic turbulence. It is shown that they are first created from zero by the turbulence through the Biermann battery mechanism. The resulting weak seed fields are then amplified by the dynamo action of the protogalactic turbulence up to a field strength adequate for a primordial field origin of the galactic magnetic field. It is suggested that the amplification of the small-scale fields, that are a problem for the interstellar origin, are suppressed in the protogalaxy by collisionless processes that act on scales smaller than the mean free path. Since the relative size of the mean free path is quite large in the protogalaxy, the dynamo would generate only large-scale fields. After compression this field could become the galactic field. It is possible that no further amplification of it need occur in the interstellar medium.

  5. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    2015-12-01

    Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 \\upmu G) and in central starburst regions (50-100 \\upmu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 \\upmu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with

  6. Magnetic fields in ring galaxies

    NASA Astrophysics Data System (ADS)

    Moss, D.; Mikhailov, E.; Silchenko, O.; Sokoloff, D.; Horellou, C.; Beck, R.

    2016-07-01

    Context. Many galaxies contain magnetic fields supported by galactic dynamo action. The investigation of these magnetic fields can be helpful for understanding galactic evolution; however, nothing definitive is known about magnetic fields in ring galaxies. Aims: Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. Methods: We use tested methods for modelling α-Ω galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Results: Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513, where the ring counter-rotates with respect to the disc. Strong shear in the region between the disc and the ring is associated with unusually strong dynamo drivers in such counter-rotators. The effect of the strong drivers is found to be unexpectedly moderate. With counter-rotation in the disc, a generic model shows that a steady mixed parity magnetic configuration that is unknown for classical spiral galaxies, may be excited, although we do not specifically model NGC 4513. Conclusions: We deduce that ring galaxies constitute a morphological class of galaxies in which identification of large-scale magnetic fields from observations of polarized radio emission, as well as dynamo modelling, may be possible. Such studies have the potential to throw additional light on the physical nature of rings, their lifetimes, and evolution.

  7. Magnetic fields in spiral galaxies

    SciTech Connect

    Beck, R. )

    1990-02-01

    Radio polarization observations have revealed large-scale magnetic fields in spiral galaxies. The average total field strength most probably increases with the rate of star formation. The uniform field generally follows the orientation of the optical spiral arms, but is often strongest {ital outside} the arms. Long magnetic-field filaments are seen, sometimes up to a 30 kpc length. The field seems to be anchored in large gas clouds and is inflated out of the disk; e.g., by a galactic wind. The field in radio halos around galaxies is highly uniform in limited regions, resembling the structure of the solar corona. The detection of Faraday rotation in spiral galaxies excludes the existence of large amounts of antimatter. The distribution of Faraday rotation in the disks shows two different large-scale structures of the interstellar field: Axisymmetric-spiral and bisymmetric-spiral, which are interpreted as two modes of the galactic dynamo driven by differential rotation.

  8. Magnetic fields in quiescent prominences

    NASA Technical Reports Server (NTRS)

    Van Ballegooijen, A. A.; Martens, P. C. H.

    1990-01-01

    The origin of the axial fields in high-latitude quiescent prominences is considered. The fact that almost all quiescent prominences obey the same hemisphere-dependent rule strongly suggests that the solar differential rotation plays an important role in producing the axial fields. However, the observations are inconsistent with the hypothesis that the axial fields are produced by differential rotation acting on an existing coronal magnetic field. Several possible explanations for this discrepancy are considered. The possibility that the sign of the axial field depends on the topology of the magnetic field in which the prominence is embedded is examined, as is the possibility that the neutral line is tilted with respect to the east-west direction, so that differential rotation causes the neutral line also to rotate with time. The possibility that the axial fields of quiescent prominences have their origin below the solar surface is also considered.

  9. Magnetic fields and coronal heating

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  10. MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.

    SciTech Connect

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

    2004-10-03

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

  11. Vortex telegraph noise in high magnetic fields

    SciTech Connect

    Shung, E.; Rosenbaum, T.F.; Coppersmith, S.N.; Crabtree, G.W.; Kwok, W.

    1997-11-01

    We cool untwinned single crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} with columnar defects down to liquid-He temperatures and study the development of pinning in the strongly interacting Bose glass with local Hall-probe magnetometry. We are able to resolve discrete fluctuations in the local vortex density resulting from reconfigurations of the vortex assembly between metastable states nearby in energy. By varying the applied magnetic field, and therefore the mean vortex density, we gain microscopic information about vortex-vortex interactions. {copyright} {ital 1997} {ital The American Physical Society}

  12. Modeling Earth's magnetic field variation

    NASA Astrophysics Data System (ADS)

    Wardinski, I.

    2012-12-01

    Observations of the Earth's magnetic field taken at the Earth's surface and at satellite altitude have been combined to construct models of the geomagnetic field and its variation. Lesur et al. (2010) developed a kinematic reconstruction of core field changes that satisfied the frozen-flux constraint. By constraining the field evolution to be entirely due to advection of the magnetic field at the core surface it maintained the spatial complexity of the field morphology imposed by a satellite field model backward in time [Wardinski & Lesur,2012]. In this study we attempt a kinematic construction of future variation in Earth's magnetic field variation. Our approach, first seeks to identify typical time scales of the magnetic field and core surface flows present in decadal and millennial field and flow models. Therefore, the individual spherical harmonic coefficients are treated by methods of time series analysis. The second step employs stochastic modelling of the temporal variability of such spherical harmonic coefficients that represent the field and core surface flow. Difficulties arise due to the non-stationary behavior of the field and core surface flow. However, the broad behavior may consist of some homogeneity, which could be captured by a generalized stochastic model that calls for the d'th difference of the time series to be stationary (ARIMA-Model), or by detrending the coefficient time series. By computing stochastic models, we obtain two sets of field-forecasts, the first set is obtained from stochastic models of the Gauss coefficients. Here, first results suggest that secular variation on time scales shorter than 5 years behaves rather randomly and cannot be described sufficiently well by stochastic models. The second set is derived from forward modeling the secular variation using the diffusion-less induction equation (kinematic construction). This approach has not provide consistent results.

  13. Dynamical Field Line Connectivity in Magnetic Turbulence

    NASA Astrophysics Data System (ADS)

    Ruffolo, D. J.; Matthaeus, W. H.

    2014-12-01

    Point-to-point magnetic connectivity has a stochastic character whenever magnetic fluctuations cause a field line random walk, with observable manifestations such as dropouts of solar energetic particles and upstream events at Earth's bow shock. This can also change due to dynamical activity. Comparing the instantaneous magnetic connectivity to the same point at two different times, we provide a nonperturbative analytic theory for the ensemble average perpendicular displacement of the magnetic field line, given the power spectrum of magnetic fluctuations. For simplicity, the theory is developed in the context of transverse turbulence, and is numerically evaluated for two specific models: reduced magnetohydrodynanmics (RMHD), a quasi-two dimensional model of anisotropic turbulence that is applicable to low-beta plasmas, and two-dimensional (2D) plus slab turbulence, which is a good parameterization for solar wind turbulence. We take into account the dynamical decorrelation of magnetic fluctuations due to wave propagation, nonlinear distortion, random sweeping, and convection by a bulk wind flow relative to the observer. The mean squared time-differenced displacement increases with time and with parallel distance, becoming twice the field line random walk displacement at long distances and/or times, corresponding to a pair of uncorrelated random walks. These results are relevant to a variety of astrophysical processes, such as electron transport and heating patterns in coronal loops and the solar transition region, changing magnetic connection to particle sources near the Sun or at a planetary bow shock, and thickening of coronal hole boundaries. Partially supported by the Thailand Research Fund, the US NSF (AGS-1063439 and SHINE AGS-1156094), NASA (Heliophysics Theory NNX11AJ44G), and by the Solar Probe Plus Project through the ISIS Theory team.

  14. Exploring dense and cold QCD in magnetic fields

    NASA Astrophysics Data System (ADS)

    Ferrer, E. J.; de la Incera, V.

    2016-08-01

    Strong magnetic fields are commonly generated in off-central relativistic heavy-ion collisions in the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Lab and in the Large Hadron Collider at CERN and have been used to probe the topological configurations of the QCD vacua. A strong magnetic field can affect the character and location of the QCD critical point, influence the QCD phases, and lead to anomalous transport of charge. To take advantage of the magnetic field as a probe of QCD at higher baryon densities, we are going to need experiments capable to scan the lower energy region. In this context, the nuclotron-based ion collider facility (NICA) at JINR offers a unique opportunity to explore such a region and complement alternative programs at RHIC and other facilities. In this paper we discuss some relevant problems of the interplay between QCD and magnetic fields and the important role the experiments at NICA can play in tackling them.

  15. Internal magnetic field measurement on C-2 field-reversed configuration plasmas.

    PubMed

    Gota, H; Thompson, M C; Knapp, K; Van Drie, A D; Deng, B H; Mendoza, R; Guo, H Y; Tuszewski, M

    2012-10-01

    A long-lived field-reversed configuration (FRC) plasma has been produced in the C-2 device by dynamically colliding and merging two oppositely directed, highly supersonic compact toroids (CTs). The reversed-field structure of the translated CTs and final merged-FRC state have been directly verified by probing the internal magnetic field structure using a multi-channel magnetic probe array near the midplane of the C-2 confinement chamber. Each of the two translated CTs exhibits significant toroidal fields (B(t)) with opposite helicity, and a relatively large B(t) remains inside the separatrix after merging.

  16. Calculating ultra-low-frequency wave power of the compressional magnetic field vs. L and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES

    NASA Astrophysics Data System (ADS)

    Sarris, Theodore E.; Li, Xinlin

    2016-06-01

    Ultra-low-frequency (ULF) pulsations are critical in radial diffusion processes of energetic particles, and the power spectral density (PSD) of these fluctuations is an integral part of the radial diffusion coefficients and of assimilative models of the radiation belts. Using simultaneous measurements from two Geostationary Operational Environmental Satellites (GOES) geosynchronous satellites, three satellites of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation and the two Van Allen probes during a 10-day period of intense geomagnetic activity and ULF pulsations of October 2012, we calculate the PSDs of ULF pulsations at different L shells. By following the time history of measurements at different L it is shown that, during this time, ULF wave power is not enhanced uniformly throughout the magnetosphere but instead is mostly enhanced in the outer L shells, close to the magnetopause, and to a lesser extent in the inner magnetosphere, closer to the plasmapause. Furthermore, by using phase differences between two GOES geosynchronous satellite pairs, we estimate the daily-averaged distribution of power at different azimuthal wave numbers. These results can have significant implications in better defining the effect of radial diffusion in the phase space density of energetic particles for different wave numbers or L shell distributions of ULF power.

  17. Indoor localization using magnetic fields

    NASA Astrophysics Data System (ADS)

    Pathapati Subbu, Kalyan Sasidhar

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

  18. Magnetic field of the Earth

    NASA Astrophysics Data System (ADS)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  19. Galactic and Intergalactic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Klein, U.; Fletcher, A.

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible. In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later chapters address the role of magnetic fields in the evolution of the interstellar medium, galaxies and galaxy clusters. The book is intended for advanced undergraduate and postgraduate students in astronomy and physics and will serve as an entry point for those starting their first research projects in the field.

  20. Satellite to study earth's magnetic field

    NASA Technical Reports Server (NTRS)

    1979-01-01

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

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

    PubMed

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ∼  10(-16) Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

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

    NASA Astrophysics Data System (ADS)

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ˜  10-16 Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

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

    PubMed

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ∼  10(-16) Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields. PMID:27243368

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

    NASA Astrophysics Data System (ADS)

    Subramanian, Kandaswamy

    2016-07-01

    The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak  ∼  10‑16 Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

  5. Mars Crustal Magnetic Field Remnants

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The radial magnetic field measured is color coded on a global perspective view that shows measurements derived from spacecraft tracks below 200 km overlain on a monochrome shaded relief map of the topography.

    This image shows especially strong Martian magnetic fields in the southern highlands near the Terra Cimmeria and Terra Sirenum regions, centered around 180 degrees longitude from the equator to the pole. It is where magnetic stripes possibly resulting from crustal movement are most prominent. The bands are oriented approximately east - west and are about 100 miles wide and 600 miles long, although the longest band stretches more than 1200 miles.

    The false blue and red colors represent invisible magnetic fields in the Martian crust that point in opposite directions. The magnetic fields appear to be organized in bands, with adjacent bands pointing in opposite directions, giving these stripes a striking similarity to patterns seen in the Earth's crust at the mid-oceanic ridges.

    These data were compiled by the MGS Magnetometer Team led by Mario Acuna at the Goddard Space Flight Center in Greenbelt, MD.

  6. Probing of multiple magnetic responses in magnetic inductors using atomic force microscopy

    PubMed Central

    Park, Seongjae; Seo, Hosung; Seol, Daehee; Yoon, Young-Hwan; Kim, Mi Yang; Kim, Yunseok

    2016-01-01

    Even though nanoscale analysis of magnetic properties is of significant interest, probing methods are relatively less developed compared to the significance of the technique, which has multiple potential applications. Here, we demonstrate an approach for probing various magnetic properties associated with eddy current, coil current and magnetic domains in magnetic inductors using multidimensional magnetic force microscopy (MMFM). The MMFM images provide combined magnetic responses from the three different origins, however, each contribution to the MMFM response can be differentiated through analysis based on the bias dependence of the response. In particular, the bias dependent MMFM images show locally different eddy current behavior with values dependent on the type of materials that comprise the MI. This approach for probing magnetic responses can be further extended to the analysis of local physical features. PMID:26852801

  7. Helical Magnetic Fields from Sphaleron Decay and Baryogenesis

    SciTech Connect

    Copi, Craig J.; Ferrer, Francesc; Vachaspati, Tanmay; Achucarro, Ana

    2008-10-24

    Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

  8. Helical Magnetic Fields from Sphaleron Decay and Baryogenesis

    NASA Astrophysics Data System (ADS)

    Copi, Craig J.; Ferrer, Francesc; Vachaspati, Tanmay; Achúcarro, Ana

    2008-10-01

    Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

  9. Analysis of the Distribution of Magnetic Fluid inside Tumors by a Giant Magnetoresistance Probe

    PubMed Central

    Gooneratne, Chinthaka P.; Kurnicki, Adam; Yamada, Sotoshi; Mukhopadhyay, Subhas C.; Kosel, Jürgen

    2013-01-01

    Magnetic fluid hyperthermia (MFH) therapy uses the magnetic component of electromagnetic fields in the radiofrequency spectrum to couple energy to magnetic nanoparticles inside tumors. In MFH therapy, magnetic fluid is injected into tumors and an alternating current (AC) magnetic flux is applied to heat the magnetic fluid- filled tumor. If the temperature can be maintained at the therapeutic threshold of 42°C for 30 minutes or more, the tumor cells can be destroyed. Analyzing the distribution of the magnetic fluid injected into tumors prior to the heating step in MFH therapy is an essential criterion for homogenous heating of tumors, since a decision can then be taken on the strength and localization of the applied external AC magnetic flux density needed to destroy the tumor without affecting healthy cells. This paper proposes a methodology for analyzing the distribution of magnetic fluid in a tumor by a specifically designed giant magnetoresistance (GMR) probe prior to MFH heat treatment. Experimental results analyzing the distribution of magnetic fluid suggest that different magnetic fluid weight densities could be estimated inside a single tumor by the GMR probe. PMID:24312280

  10. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  11. Correlation analysis of magnetic field and density fluctuations in SSX

    NASA Astrophysics Data System (ADS)

    Parks, Holden; Rock, Ariel; Schaffner, David; Brown, Michael; SSX Team

    2015-11-01

    The cross correlation and cross spectrum of magnetic field and density fluctuations of plasmas created by the Swarthmore Spheromak Experiment (SSX) MHD wind tunnel are examined. The SSX MHD wind tunnel produces dynamic magnetized plasma plumes with typical values B ~ 0 . 2 T, n >=1021 m-3, and Ti >= 20 eV. Magnetic field fluctuations of these plasmas are measured with a Ḃ probe and local density fluctuations are measured with a double Langmuir probe inserted radially within 1 mm of the Ḃ probe. The axial distance of both probes from the plasma source is varied to examine plasmas of different ``turbulent ages.'' Linearized MHD theory admits three types of waves - slow, fast, and Alfvén - each with different correlation values between magnetic field and density. By taking the Fourier transforms of B (t) and n (t) time series data, the cross spectrum B~* (f) ñ (f) is calculated, and the correlation between magnetic field and density can be determined as a function of frequency. Preliminary results of SSX data analysis indicate a pressure balanced structure present at 100 kHz, likely in the form of a flux tube, as well as predominately positive correlations in the frequency range 100 kHz to 10 MHz. Work supported by DOE OFES and NSF CMSO.

  12. Analytical Methods for Characterizing Magnetic Resonance Probes

    PubMed Central

    Manus, Lisa M.; Strauch, Renee C.; Hung, Andy H.; Eckermann, Amanda L.; Meade, Thomas J.

    2012-01-01

    SUMMARY The efficiency of Gd(III) contrast agents in magnetic resonance image enhancement is governed by a set of tunable structural parameters. Understanding and measuring these parameters requires specific analytical techniques. This Feature describes strategies to optimize each of the critical Gd(III) relaxation parameters for molecular imaging applications and the methods employed for their evaluation. PMID:22624599

  13. Tracing ultrafast dynamics of strong fields at plasma-vacuum interfaces with longitudinal proton probing

    SciTech Connect

    Abicht, F.; Braenzel, J.; Koschitzki, Ch.; Schnürer, M.; Priebe, G.; Andreev, A. A.; Nickles, P. V.; Sandner, W.

    2014-07-21

    If regions of localized strong fields at plasma-vacuum interfaces are probed longitudinally with laser accelerated proton beams their velocity distribution changes sensitively and very fast. Its measured variations provide indirectly a higher temporal resolution as deduced from deflection geometries which rely on the explicit temporal resolution of the proton beam at the position of the object to probe. With help of reasonable models and comparative measurements changes of proton velocity can trace the field dynamics even at femtosecond time scale. In longitudinal probing, the very low longitudinal emittance together with a broad band kinetic energy distribution of laser accelerated protons is the essential prerequisite of the method. With a combination of energy and one-dimensional spatial resolution, we resolve fast field changes down to 100 fs. The used pump probe setup extends previous schemes and allows discriminating simultaneously between electric and magnetic fields in their temporal evolution.

  14. Crystal field and magnetic properties

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

  15. Transverse Magnetic Field Propellant Isolator

    NASA Technical Reports Server (NTRS)

    Foster, John E.

    2000-01-01

    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.

  16. A magnetically driven reciprocating probe for tokamak scrape-off layer measurements.

    PubMed

    Gunn, J P; Pascal, J-Y

    2011-12-01

    A new in situ reciprocating probe system has been developed to provide scrape-off layer measurements in the Tore Supra tokamak. The probe motion is provided by the rotation of an energized coil in the tokamak magnetic field. Simple analytic approximations to the exact numerical model were used to identify the important parameters that govern the dynamics of the system, and optimize the coil geometry, the electrical circuit, and the stiffness of the retaining spring. The linear speed of the probe is directly proportional to the current induced by the coil's rotation; its integral gives the coil position, providing a means to implement real-time feedback control of the probe motion. Two probes were recently mounted on a movable outboard antenna protection limiter in Tore Supra and provided automatic measurements during the 2011 experimental campaign.

  17. Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities.

    PubMed

    Demidov, V I; Koepke, M E; Raitses, Y

    2010-10-01

    By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time.

  18. Magnetically insulated baffled probe for real-time monitoring of equilibrium and fluctuating values of space potentials, electron and ion temperatures, and densities

    SciTech Connect

    Demidov, V. I.; Koepke, M. E.; Raitses, Y.

    2010-10-15

    By restricting the electron-collection area of a cold Langmuir probe compared to the ion-collection area, the probe floating potential can become equal to the space potential, and thus conveniently monitored, rather than to a value shifted from the space potential by an electron-temperature-dependent offset, i.e., the case with an equal-collection-area probe. This design goal is achieved by combining an ambient magnetic field in the plasma with baffles, or shields, on the probe, resulting in species-selective magnetic insulation of the probe collection area. This permits the elimination of electron current to the probe by further adjustment of magnetic insulation which results in an ion-temperature-dependent offset when the probe is electrically floating. Subtracting the floating potential of two magnetically insulated baffled probes, each with a different degree of magnetic insulation, enables the electron or ion temperature to be measured in real time.

  19. Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination

    PubMed Central

    Jaafar, Miriam; Iglesias-Freire, Oscar; Serrano-Ramón, Luis; Ibarra, Manuel Ricardo; de Teresa, Jose Maria

    2011-01-01

    Summary The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM) and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample. PMID:22003461

  20. Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales

    NASA Astrophysics Data System (ADS)

    Pizzini, Stefania; Vogel, Jan; Bonfim, Marlio; Fontaine, Alain

    Many synchrotron radiation techniques have been developed in the last 15 years for studying the magnetic properties of thin-film materials. The most attractive properties of synchrotron radiation are its energy tunability and its time structure. The first property allows measurements in resonant conditions at an absorption edge of each of the magnetic elements constituting the probed sample, and the latter allows time-resolved measurements on subnanosecond timescales. In this review, we introduce some of the synchrotron-based techniques used for magnetic investigations. We then describe in detail X-ray magnetic circular dichroism (XMCD) and how time-resolved XMCD studies can be carried out in the pump-probe mode. Finally, we illustrate some applications to magnetization reversal dynamics in spin valves and tunnel junctions, using fast magnetic field pulses applied along the easy magnetization axis of the samples. Thanks to the element-selectivity of X-ray absorption spectroscopy, the magnetization dynamics of the soft (Permalloy) and the hard (cobalt) layers can be studied independently. In the case of spin valves, this allowed us to show that two magnetic layers that are strongly coupled in a static regime can become uncoupled on nanosecond timescales.Present address: Universidade Federal do Paraná, Centro Politécnico CP 19011, Curitiba - PR CEP 81531-990, Brazil

  1. Separation of magnetic field lines

    SciTech Connect

    Boozer, Allen H.

    2012-11-15

    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.

  2. Advances in Langmuir probe diagnostics of the plasma potential and electron-energy distribution function in magnetized plasma

    NASA Astrophysics Data System (ADS)

    Popov, Tsv K.; Dimitrova, M.; Ivanova, P.; Kovačič, J.; Gyergyek, T.; Dejarnac, R.; Stöckel, J.; Pedrosa, M. A.; López-Bruna, D.; Hidalgo, C.

    2016-06-01

    Advanced Langmuir probe techniques for evaluating the plasma potential and electron-energy distribution function (EEDF) in magnetized plasma are reviewed. It is shown that when the magnetic field applied is very weak and the electrons reach the probe without collisions in the probe sheath the second-derivative Druyvesteyn formula can be used for EEDF evaluation. At low values of the magnetic field, an extended second-derivative Druyvesteyn formula yields reliable results, while at higher values of the magnetic field, the first-derivative probe technique is applicable for precise evaluation of the plasma potential and the EEDF. There is an interval of intermediate values of the magnetic field when both techniques—the extended second-derivative and the first-derivative one—can be used. Experimental results from probe measurements in different ranges of magnetic field are reviewed and discussed: low-pressure argon gas discharges in the presence of a magnetic field in the range from 0.01 to 0.08 T, probe measurements in circular hydrogen plasmas for high-temperature fusion (magnetic fields from 0.45 T to 1.3 T) in small ISTTOK and CASTOR tokamaks, D-shape COMPASS tokamak plasmas, as well as in the TJ-II stellarator. In the vicinity of the last closed flux surface (LCFS) in tokamaks and in the TJ-II stellarator, the EEDF obtained is found to be bi-Maxwellian, while close to the tokamak chamber wall it is Maxwellian. The mechanism of the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is discussed. Comparison of the results from probe measurements with those obtained from calculations using the ASTRA and EIRENE codes shows that the main reason for the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is the ionization of the neutral atoms.

  3. Practical method using superposition of individual magnetic fields for initial arrangement of undulator magnets

    SciTech Connect

    Tsuchiya, K.; Shioya, T.

    2015-04-15

    We have developed a practical method for determining an excellent initial arrangement of magnetic arrays for a pure-magnet Halbach-type undulator. In this method, the longitudinal magnetic field distribution of each magnet is measured using a moving Hall probe system along the beam axis with a high positional resolution. The initial arrangement of magnetic arrays is optimized and selected by analyzing the superposition of all distribution data in order to achieve adequate spectral quality for the undulator. We applied this method to two elliptically polarizing undulators (EPUs), called U#16-2 and U#02-2, at the Photon Factory storage ring (PF ring) in the High Energy Accelerator Research Organization (KEK). The measured field distribution of the undulator was demonstrated to be excellent for the initial arrangement of the magnet array, and this method saved a great deal of effort in adjusting the magnetic fields of EPUs.

  4. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  5. Probing Gravitational Sensitivity in Biological Systems Using Magnetic Body Forces

    NASA Technical Reports Server (NTRS)

    Guevorkian, Karine; Wurzel, Sam; Mihalusova, Mariana; Valles, Jim

    2003-01-01

    At Brown University, we are developing the use of magnetic body forces as a means to simulate variable gravity body forces on biological systems. This tool promises new means to probe gravi-sensing and the gravi-response of biological systems. It also has the potential as a technique for screening future systems for space flight experiments.

  6. Magnetic fields in the sun

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1974-01-01

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

  7. A high-field superferric NMR magnet.

    PubMed

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

    1993-01-01

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

  8. Magnetic field of the Earth

    NASA Astrophysics Data System (ADS)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  9. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1991-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  10. In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect

    SciTech Connect

    Fang, Jiancheng; Wang, Tao Quan, Wei; Yuan, Heng; Li, Yang; Zhang, Hong; Zou, Sheng

    2014-06-15

    A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz{sup 1/2}, which was mainly dominated by the noise of the magnetic shield.

  11. In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect.

    PubMed

    Fang, Jiancheng; Wang, Tao; Quan, Wei; Yuan, Heng; Zhang, Hong; Li, Yang; Zou, Sheng

    2014-06-01

    A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz(1/2), which was mainly dominated by the noise of the magnetic shield.

  12. Sensor probes and phantoms for advanced transcranial magnetic stimulation system developments

    NASA Astrophysics Data System (ADS)

    Meng, Qinglei; Patel, Prashil; Trivedi, Sudhir; Du, Xiaoming; Hong, Elliot; Choa, Fow-Sen

    2015-05-01

    Transcranial magnetic stimulation (TMS) has become one of the most widely used noninvasive method for brain tissue stimulation and has been used as a treatment tool for various neurological and psychiatric disorders including migraine, stroke, Parkinson's disease, dystonia, tinnitus and depression. In the process of developing advanced TMS deep brain stimulation tools, we need first to develop field measurement devices like sensory probes and brain phantoms, which can be used to calibrate the TMS systems. Currently there are commercially available DC magnetic or electric filed measurement sensors, but there is no instrument to measure transient fields. In our study, we used a commercial figure-8 shaped TMS coil to generate transient magnetic field and followed induced field and current. The coil was driven by power amplified signal from a pulse generator with tunable pulse rate, amplitude, and duration. In order to obtain a 3D plot of induced vector electric field, many types of probes were designed to detect single component of electric-field vectors along x, y and z axis in the space around TMS coil. We found that resistor probes has an optimized signal-to-noise ratio (SNR) near 3k ohm but it signal output is too weak compared with other techniques. We also found that inductor probes can have very high output for Curl E measurement, but it is not the E-field distribution we are interested in. Probes with electrical wire wrapped around iron coil can directly measure induced E-field with high sensitivity, which matched computer simulation results.

  13. X-Ray Detected Magnetic Resonance: A Unique Probe of the Precession Dynamics of Orbital Magnetization Components

    PubMed Central

    Goulon, Jośe; Rogalev, Andrei; Goujon, Gérard; Wilhelm, Fabrice; Ben Youssef, Jamal; Gros, Claude; Barbe, Jean-Michel; Guilard, Roger

    2011-01-01

    X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence. PMID:22272105

  14. Probing magnetic microstructures with quasi-ballistic Hall crosses

    NASA Astrophysics Data System (ADS)

    Fasbender, S.; Schluck, J.; Cerchez, M.; Heinzel, T.; Sievers, S.; Pierz, K.; Schumacher, H. W.

    2016-03-01

    Hall sensing is performed on a localized magnetic field pattern using a quasi-ballistic Hall cross device. The Hall resistance shows a pronounced peak as a function of the magnetic field amplitude which is absent in the magnetization hysteresis loop. This non-monotonic response exemplifies qualitatively the failure of conventional Hall sensing. It is demonstrated how, by using a numerical simulation based on the Landauer-Büttiker model, the amplitude of the magnetic field profile can be determined from such measurements.

  15. Local magnetism in palladium bionanomaterials probed by muon spectroscopy.

    PubMed

    Creamer, Neil J; Mikheenko, Iryna P; Johnson, Clive; Cottrell, Stephen P; Macaskie, Lynne E

    2011-05-01

    Palladium bionanomaterial was manufactured using the sulfate-reducing bacterium, Desulfovibrio desulfuricansm, to reduce soluble Pd(II) ions to cell-bound Pd(0) in the presence of hydrogen. The biomaterial was examined using a Superconducting Quantum Interference Device (SQUID) to measure bulk magnetisation and by Muon Spin Rotation Spectroscopy (µSR) which is uniquely able to probe the local magnetic environment inside the sample. Results showed behaviour attributable to interaction of muons both with palladium electrons and the nuclei of hydrogen trapped in the particles during manufacture. Electronic magnetism, also suggested by SQUID, is not characteristic of bulk palladium and is consistent with the presence of nanoparticles previously seen in electron micrographs. We show the first use of μSR as a tool to probe the internal magnetic environment of a biologically-derived nanocatalyst material.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  17. Three axis vector magnet set-up for cryogenic scanning probe microscopy.

    PubMed

    Galvis, J A; Herrera, E; Guillamón, I; Azpeitia, J; Luccas, R F; Munuera, C; Cuenca, M; Higuera, J A; Díaz, N; Pazos, M; García-Hernandez, M; Buendía, A; Vieira, S; Suderow, H

    2015-01-01

    We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor β-Bi2Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert.

  18. Three axis vector magnet set-up for cryogenic scanning probe microscopy

    SciTech Connect

    Galvis, J. A.; Herrera, E.; Buendía, A.; Guillamón, I.; Vieira, S.; Suderow, H.; Azpeitia, J.; Luccas, R. F.; Munuera, C.; García-Hernandez, M.; and others

    2015-01-15

    We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor β-Bi{sub 2}Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert.

  19. Three axis vector magnet set-up for cryogenic scanning probe microscopy.

    PubMed

    Galvis, J A; Herrera, E; Guillamón, I; Azpeitia, J; Luccas, R F; Munuera, C; Cuenca, M; Higuera, J A; Díaz, N; Pazos, M; García-Hernandez, M; Buendía, A; Vieira, S; Suderow, H

    2015-01-01

    We describe a three axis vector magnet system for cryogenic scanning probe microscopy measurements. We discuss the magnet support system and the power supply, consisting of a compact three way 100 A current source. We obtain tilted magnetic fields in all directions with maximum value of 5T along z-axis and of 1.2T for XY-plane magnetic fields. We describe a scanning tunneling microscopy-spectroscopy (STM-STS) set-up, operating in a dilution refrigerator, which includes a new high voltage ultralow noise piezodrive electronics and discuss the noise level due to vibrations. STM images and STS maps show atomic resolution and the tilted vortex lattice at 150 mK in the superconductor β-Bi2Pd. We observe a strongly elongated hexagonal lattice, which corresponds to the projection of the tilted hexagonal vortex lattice on the surface. We also discuss Magnetic Force Microscopy images in a variable temperature insert. PMID:25638089

  20. Magnetic field of a combined plasma trap

    NASA Astrophysics Data System (ADS)

    Kotenko, V. G.; Moiseenko, V. E.; Ågren, O.

    2012-06-01

    This paper presents numerical simulations performed on the structure of a magnetic field created by the magnetic system of a combined plasma trap. The magnetic system includes the stellarator-type magnetic system and one of the mirror-type. For the stellarator type magnetic system the numeric model contains a magnetic system of an l=2 torsatron with the coils of an additional toroidal magnetic field. The mirror-type magnetic system element is considered as being single current-carrying turn enveloping the region of existence of closed magnetic surfaces of the torsatron. The calculations indicate the existence of a vast area of the values of the additional magnetic field magnitude and magnetic field of the single turn where, in principle, the implementation of the closed magnetic surface configuration is quite feasible.

  1. Quark stars in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Chu, Peng-Cheng; Chen, Lie-Wen; Wang, Xin

    2014-09-01

    Within the confined isospin- and density-dependent mass model, we study the properties of strange quark matter (SQM) and quark stars (QSs) in 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 results indicate that including the magnetic fields with radial (transverse) orientation can significantly decrease (increase) the maximum mass of QSs, demonstrating the importance of the magnetic field orientation inside the magnetized compact stars.

  2. Matched dipole probe for magnetized low electron density laboratory plasma diagnostics

    SciTech Connect

    Rafalskyi, Dmytro; Aanesland, Ane

    2015-07-15

    In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (10{sup 12}–10{sup 15 }m{sup −3}), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10 cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B ∼ 170 G) and unmagnetized (B = 0) low density (7 × 10{sup 12 }m{sup −3}–7 × 10{sup 13 }m{sup −3}) low pressure (1 mTorr) 10 cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7 × 10{sup 12 }m{sup −3}–7 × 10{sup 13 }m{sup −3} show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2 × 10{sup 13 }m{sup −3}. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling.

  3. Matched dipole probe for magnetized low electron density laboratory plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Rafalskyi, Dmytro; Aanesland, Ane

    2015-07-01

    In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (1012-1015 m-3), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10 cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B ˜ 170 G) and unmagnetized (B = 0) low density (7 × 1012 m-3-7 × 1013 m-3) low pressure (1 mTorr) 10 cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7 × 1012 m-3-7 × 1013 m-3 show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2 × 1013 m-3. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling.

  4. Dynamic nuclear polarization at high magnetic fields

    PubMed Central

    Maly, Thorsten; Debelouchina, Galia T.; Bajaj, Vikram S.; Hu, Kan-Nian; Joo, Chan-Gyu; Mak–Jurkauskas, Melody L.; Sirigiri, Jagadishwar R.; van der Wel, Patrick C. A.; Herzfeld, Judith; Temkin, Richard J.; Griffin, Robert G.

    2009-01-01

    Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (μw) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (γe/γl), being ∼660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (≥5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms—the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in μw and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments. PMID:18266416

  5. Field errors in superconducting magnets

    SciTech Connect

    Barton, M. Q.

    1982-01-01

    The mission of this workshop is a discussion of the techniques for tracking particles through arbitrary accelerator field configurations to look for dynamical effects that are suggested by various theoretical models but are not amenable to detailed analysis. A major motivation for this type of study is that many of our accelerator projects are based on the use of superconducting magnets which have field imperfections that are larger and of a more complex nature than those of conventional magnets. Questions such as resonances, uncorrectable closed orbit effects, coupling between planes, and diffusion mechanisms all assume new importance. Since, simultaneously, we are trying to do sophisticated beam manipulations such as stacking, high current accelerator, long life storage, and low loss extraction, we clearly need efficient and accurate tracking programs to proceed with confidence.

  6. QED in inhomogeneous magnetic fields

    SciTech Connect

    Fry, M.P.

    1996-11-01

    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 {bold B}({bold r})={bold (}0,0,{ital B}({bold r}){bold )}, where {ital B}({bold r}){ge}0 or {ital B}({bold r}){le}0 and {bold r} is a point in the {ital xy} plane. Bounds are also obtained for the induced spin for (2+1)-dimensional QED in the presence of {bold B}({bold 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 {bold B}({bold r}) on R{sup 3}. {copyright} {ital 1996 The American Physical Society.}

  7. Probing magnetization dynamics in individual magnetite nanocrystals using magnetoresistive scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Hevroni, Amir; Tsukerman, Boris; Markovich, Gil

    2015-12-01

    The magnetization dynamics of individual magnetite nanocrystals was probed by variable-temperature magnetoresistive scanning tunneling microscopy, in which a magnetoresistive junction is formed between the substrate and the magnetic particle under study. By tuning the temperature close to the magnetization blocking of a superparamagnetic particle, the slow magnetization switching of the particle caused fluctuations in the tunnel current passing through the particle, which appeared as telegraph noise in current vs time measurements. Analysis of the current fluctuations yielded estimates for the low local magnetic field sensed by the particle, its magnetic anisotropy energy, and the low limit for the spin-polarization degree of the nanocrystals, which for some particles appeared to be as high as 90%.

  8. Spin noise explores local magnetic fields in a semiconductor

    PubMed Central

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  9. Thermomagnetism with external and internal magnetic field quantities

    NASA Astrophysics Data System (ADS)

    Egolf, Peter W.; Gama, Sergio; Vuarnoz, Didier

    2015-07-01

    In magnetism literature, usually the applied or external field H0 is taken to present the results of an investigation. But for certain purposes, it is advantageous to work with the internal magnetic field H that occurs inside a magnetic body. It is well-known that the susceptibility of the material and the demagnetization effect, given by the geometry of a body, link the two usually different fields under consideration. If a probe is a long needle with the external magnetic field and the magnetization in the probe parallel to the axis of the slender body, the two fields are identical. But when building thermomagnetic machines, other demands may require also other shapes (porous materials, particle beds, wavy structures, etc.) of the magnetized material and then a correct distinction of these fields becomes important and in some cases also laborious if one of them must be theoretically determined from the other. This article shows how—from a theoretical point of view—the most important physical properties of thermomagnetism/magnetocalorics, namely, the adiabatic entropy change, the effective specific heat capacity, and the adiabatic temperature change must be transformed. Furthermore, this theory reveals the invariants of magnetocalorics, which are combinations of these three most important properties.

  10. Wall scanning probe for high-field side plasma measurements on Alcator C-Mod.

    PubMed

    Smick, Noah; LaBombard, Brian

    2009-02-01

    A new, high-field side scanning probe has been added to Alcator C-Mod's complement of edge diagnostics. The wall scanning probe is designed to provide all the benefits of a linear plunge, multielectrode scanning probe while working from the confined space of the inner tokamak wall. The drive mechanism is an embedded coil which produces a torque with the ambient toroidal magnetic field when energized, thus allowing the probe to plunge to different preprogramed depths at different times during a plasma discharge. The probe tip is designed for easy replacement and is presently configured to operate as a modified, high heat-flux "Gundestrup-type" probe with four tungsten electrodes. The probe has demonstrated the ability to obtain cross-field profiles for electron temperature, density, floating potential, and plasma flow information (parallel and perpendicular to B) up to a depth of a few millimiters inside the last-closed flux surface in standard C-Mod discharges. The tungsten-tipped probe has proved very robust and shows little or no damage though it routinely handles surface heat fluxes on the order of 100 MW/m(2) at peak insertion.

  11. Relaxation of magnetic systems after sudden magnetic field changes

    NASA Astrophysics Data System (ADS)

    Zvyagin, A. A.

    2015-09-01

    In magnetic systems where the projection of the total spin moment of the system parallel to an external magnetic field is not conserved, a sudden change in the field produces oscillations in the magnetization. The amplitude and frequency of these oscillations depend nonlinearly on the change in the field. Landau-Lifshitz relaxation in the magnetic system leads to a nonlinear dependence of the amplitude and frequency of the oscillations on the relaxation parameter, as well as to a dependence of the damping rate on the energy parameters of the magnet and on the amplitude of the jump in the external magnetic field.

  12. Deformation of Water by a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Chen, Zijun; Dahlberg, E. Dan

    2011-03-01

    After the discovery that superconducting magnets could levitate diamagnetic objects,1,2 researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields,3-5 which was given the name "The Moses Effect."5 Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary were produced by superconducting magnets.

  13. Triaxial fiber optic magnetic field sensor for MRI applications

    NASA Astrophysics Data System (ADS)

    Filograno, Massimo L.; Pisco, Marco; Catalano, Angelo; Forte, Ernesto; Aiello, Marco; Soricelli, Andrea; Davino, Daniele; Visone, Ciro; Cutolo, Antonello; Cusano, Andrea

    2016-05-01

    In this paper, we report a fiber-optic triaxial magnetic field sensor, based on Fiber Bragg Gratings (FBGs) integrated with giant magnetostrictive material, the Terfenol-D. The realized sensor has been designed and engineered for Magnetic Resonance Imaging (MRI) applications. A full magneto-optical characterization of the triaxial sensing probe has been carried out, providing the complex relationship among the FBGs wavelength shift and the applied magnetostatic field vector. Finally, the developed fiber optic sensors have been arranged in a sensor network composed of 20 triaxial sensors for mapping the magnetic field distribution in a MRI-room at a diagnostic center in Naples (SDN), equipped with Positron emission tomography/magnetic resonance (PET/MR) instrumentation. Experimental results reveal that the proposed sensor network can be efficiently used in MRI centers for performing quality assurance tests, paving the way for novel integrated tools to measure the magnetic dose accumulated day by day by MRI operators.

  14. Magnetic holes in the solar wind. [(interplanetary magnetic fields)

    NASA Technical Reports Server (NTRS)

    Turner, J. M.; Burlaga, L. F.; Ness, N. F.; Lemaire, J. F.

    1976-01-01

    An analysis is presented of high resolution interplanetary magnetic field measurements from the magnetometer on Explorer 43 which showed that low magnetic field intensities in the solar wind at 1 AU occur as distinct depressions or 'holes'. These magnetic holes are new kinetic-scale phenomena, having a characteristic dimension on the order of 20,000 km. They occurred at a rate of 1.5/day in the 18-day time span (March 18 to April 6, 1971) that was analyzed. Most of the magnetic holes are characterized by both a depression in the absolute value of the magnetic field, and a change in the magnetic field direction; some of these are possibly the result of magnetic merging. However, in other cases the magnetic field direction does not change; such holes are not due to magnetic merging, but might be a diamagnetic effect due to localized plasma inhomogeneities.

  15. Design, construction, and calibration of a three-axis, high-frequency magnetic probe (B-dot probe) as a diagnostic for exploding plasmas

    SciTech Connect

    Everson, E. T.; Pribyl, P.; Constantin, C. G.; Zylstra, A.; Schaeffer, D.; Kugland, N. L.; Niemann, C.

    2009-11-15

    A three-axis, 2.5 mm overall diameter differential magnetic probe (also known as B-dot probe) is discussed in detail from its design and construction to its calibration and use as diagnostic of fast transient effects in exploding plasmas. A design and construction method is presented as a means to reduce stray pickup, eliminate electrostatic pickup, reduce physical size, and increase magnetic signals while maintaining a high bandwidth. The probe's frequency response is measured in detail from 10 kHz to 50 MHz using the presented calibration method and compared to theory. The effect of the probe's self-induction as a first order correction in frequency, O({omega}), on experimental signals and magnetic field calculations is discussed. The probe's viability as a diagnostic is demonstrated by measuring the magnetic field compression and diamagnetism of a sub-Alfvenic ({approx}500 km/s,M{sub A}{approx}0.36) flow created from the explosion of a high-density energetic laser plasma through a cooler, low-density, magnetized ambient plasma.

  16. Survey of the frequency dependent latitudinal distribution of the fast magnetosonic wave mode from Van Allen Probes Electric and Magnetic Field Instrument and Integrated Science waveform receiver plasma wave analysis

    NASA Astrophysics Data System (ADS)

    Boardsen, Scott A.; Hospodarsky, George B.; Kletzing, Craig A.; Engebretson, Mark J.; Pfaff, Robert F.; Wygant, John R.; Kurth, William S.; Averkamp, Terrance F.; Bounds, Scott R.; Green, Jim L.; De Pascuale, Sebastian

    2016-04-01

    We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (fcP) has a distinct funnel-shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra-ordinary (whistler) mode at wave normal angles (θk) near 90°. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with θk randomly chosen between 87 and 90°, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to θk of 60°, suggesting that another approach is necessary to estimate the true distribution of θk. We find that the histograms of the synthetically derived ellipticities and θk are consistent with the observations of ellipticities and θk derived using polarization analysis. We make estimates of the median equatorial θk by comparing observed and model ray tracing frequency-dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial θk distribution around noon and 4 RE, with the median of ~4 to 7° from 90° at f/fcP = 2 and dropping to ~0.5° from 90° at f/fcP = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.

  17. Comparing Magnetic Fields on Earth and Mars

    NASA Video Gallery

    This animation compares the magnetic fields on Earth and Mars. The Earth has a large-scale planetary magnetic field that can protect it from space weather and other hazards. Mars, on the other hand...

  18. Field quality aspects of CBA superconducting magnets

    SciTech Connect

    Kahn, S.; Engelmann, R.; Fernow, R.; Greene, A.F.; Herrera, J.; Kirk, H.; Skaritka, J.; Wanderer, P.; Willen, E.

    1983-01-01

    A series of superconducting dipole magnets for the BNL Colliding Beam Accelerator which were manufactured to have the proper field quality characteristics has been tested. This report presents the analysis of the field harmonics of these magnets.

  19. Measurements of Solar Vector Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J. (Editor)

    1985-01-01

    Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

  20. Internal Magnetic Field Measurements in STX Generated FRCs

    NASA Astrophysics Data System (ADS)

    Andreason, Samuel; Miller, Ken; Slough, John

    1999-11-01

    The internal magnetic field probes installed in the STX experiment at the Redmond Plasma Physics laboratory are designed to provide a one dimensional internal magnetic field profile of a 25 eV 10^19 m-3 FRC. The probe consists of 24 1cm × 1mm 8 turn coils interconnected like a chain to provide information on the RMF field components. This probe can be swept through the vacuum chamber to provide field information for different points throughout the FRC. The coils themselves are made with one mil magnet wire (half mil insulation). Structural and thermal support for the field coils is provided by a 53 mil ID × 78 mil OD berylium oxide tube capped with a boron nitride tip. Berylium oxide is an insulator with good thermal diffusivity/ablation properties. Calculations and test results indicate minimal perturbations to the plasma caused by the probe. Information on the construction methods employed as well as physical and external electrical design will be presented along with representative experimental results. This work is funded by the USDOE. www.aa.washington.edu/AERP/RPPL

  1. The rectangular array of magnetic probes on J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Chen, Zhipeng; Li, Fuming; Zhuang, Ge; Jian, Xiang; Zhu, Lizhi

    2016-11-01

    The rectangular array of magnetic probes system was newly designed and installed in the torus on J-TEXT tokamak to measure the local magnetic fields outside the last closed flux surface at a single toroidal angle. In the implementation, the experimental results agree well with the theoretical results based on the Spool model and three-dimensional numerical finite element model when the vertical field was applied. Furthermore, the measurements were successfully used as the input of EFIT code to conduct the plasma equilibrium reconstruction. The calculated Faraday rotation angle using the EFIT output is in agreement with the measured one from the three-wave polarimeter-interferometer system.

  2. Forced Magnetic Reconnection and Field Penetration of an Externally Applied Rotating Helical Magnetic Field in the TEXTOR Tokamak

    NASA Astrophysics Data System (ADS)

    Kikuchi, Y.; de Bock, M. F. M.; Finken, K. H.; Jakubowski, M.; Jaspers, R.; Koslowski, H. R.; Kraemer-Flecken, A.; Lehnen, M.; Liang, Y.; Matsunaga, G.; Reiser, D.; Wolf, R. C.; Zimmermann, O.

    2006-08-01

    The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization.

  3. Superposition of DC magnetic fields by cascading multiple magnets in magnetic loops

    NASA Astrophysics Data System (ADS)

    Sun, Fei; He, Sailing

    2015-09-01

    A novel method that can effectively collect the DC magnetic field produced by multiple separated magnets is proposed. With the proposed idea of a magnetic loop, the DC magnetic field produced by these separated magnets can be effectively superimposed together. The separated magnets can be cascaded in series or in parallel. A novel nested magnetic loop is also proposed to achieve a higher DC magnetic field in the common air region without increasing the DC magnetic field in each magnetic loop. The magnetic loop can be made by a magnetic hose, which is designed by transformation optics and can be realized by the combination of super-conductors and ferromagnetic materials.

  4. Rotating copper plasmoid in external magnetic field

    SciTech Connect

    Pandey, Pramod K.; Thareja, Raj K.

    2013-02-15

    Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

  5. Note: 3D printed spheroid for uniform magnetic field generation

    NASA Astrophysics Data System (ADS)

    Öztürk, Y.; Aktaş, B.

    2016-10-01

    This article is focused on a novel and practical production method for a uniform magnetic field generator. The method involves building of a surface coil template using a desktop 3D printer and winding of a conducting wire onto the structure using surface grooves as a guide. Groove pattern was based on the parametric spheroidal helical coil formula. The coil was driven by a current source and the magnetic field inside was measured using a Hall probe placed into the holes on the printed structure. The measurements are found to be in good agreement with our finite element analysis results and indicate a fairly uniform field inside.

  6. Field induced anisotropic cooperativity in a magnetic colloidal glass

    NASA Astrophysics Data System (ADS)

    Wandersman, E.; Chushkin, Y.; Dubois, E.; Dupuis, V.; Robert, A.; Perzynski, R.

    The translational dynamics in a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. Structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

  7. Magnetic field perturbartions in closed-field-line systems with zero toroidal magnetic field

    SciTech Connect

    Mauel, M; Ryutov, D; Kesner, J

    2003-12-02

    In some plasma confinement systems (e.g., field-reversed configurations and levitated dipoles) the confinement is provided by a closed-field-line poloidal magnetic field. We consider the influence of the magnetic field perturbations on the structure of the magnetic field in such systems and find that the effect of perturbations is quite different from that in the systems with a substantial toroidal field. In particular, even infinitesimal perturbations can, in principle, lead to large radial excursions of the field lines in FRCs and levitated dipoles. Under such circumstances, particle drifts and particle collisions may give rise to significant neoclassical transport. Introduction of a weak regular toroidal magnetic field reduces radial excursions of the field lines and neoclassical transport.

  8. Novel rotating field probe for inspection of tubes

    SciTech Connect

    Xin, J.; Tarkleson, E.; Lei, N.; Udpa, L.; Udpa, S. S.

    2012-05-17

    Inspection of steam generator tubes in nuclear power plants is extremely critical for safe operation of the power plant. In the nuclear industry, steam generator tube inspection using eddy current techniques has evolved over the years from a single bobbin coil, to rotating probe coil (RPC) and array probe, in an attempt to improve the speed and reliability of inspection. The RPC probe offers the accurate spatial resolution but involves complex mechanical rotation. This paper presents a novel design of eddy current probes based on rotating fields produced by three identical coils excited by a balanced three-phase supply. The sensor thereby achieves rotating probe functionality by electronic means and eliminates the need for mechanical rotation. The field generated by the probe is largely radial that result in induced currents that flow circularly around the radial axis and rotating around the tube at a synchronous speed effectively producing induced eddy currents that are multidirectional. The probe will consequently be sensitive to cracks of all orientations in the tube wall. The finite element model (FEM) results of the rotating fields and induced currents are presented. A prototype probe is being built to validate simulation results.

  9. Circularly polarized Magnetic Field of Whistler Wave during Fast Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Zhai, Xiang; Wongwaitayakornkul, Pakorn; Bellan, Paul; Bellan Group Team

    2014-10-01

    Obliquely propagating whistler waves are expected to have circularly polarized magnetic components and to be associated with fast magnetic reconnection. In the Caltech plasma jet experiment, a current-carrying collimated jet is created from the merging of eight plasma-filled flux ropes. Fast magnetic reconnection occurs during the merging process. When the current- carrying jet undergoes fast kink instability, a lateral Rayleigh-Taylor instability occurs on the jet surface and induces another fast magnetic reconnection event. A capacitive coupling probe placed near the jet has measured fast electric field fluctuations at 15MHz which is in the whistler regime for this plasma. A 3D fast Bdot probe with good electrostatic rejection has been specifically designed to measure the 3D magnetic components of the whistler wave. Preliminary results have revealed a 3D 15 MHz magnetic fluctuation. Work is underway to increase the sensitivity of the induction probe and also to reduce electrostatic pickup. With the improved probe, the polarization property of the magnetic component of the whistler wave is expected to be resolved if it exists.

  10. The influence of magnetic field on electron beam generated plasmas

    NASA Astrophysics Data System (ADS)

    Petrov, G. M.; Boris, D. R.; Lock, E. H.; Petrova, Tz B.; Fernsler, R. F.; Walton, S. G.

    2015-06-01

    Magnetically confined argon plasma in a long cylindrical tube driven by an electron beam is studied experimentally and theoretically. Langmuir probes are used to measure the electron energy distribution function, electron density and temperature in plasmas generated by 2 keV, 10 mA electron beams in a 25 mTorr argon background for magnetic field strengths of up to 200 Gauss. The experimental results agree with simulations done using a spatially averaged Boltzmann model adapted to treat an electron beam generated plasma immersed in a constant magnetic field. The confining effect of the magnetic field is studied theoretically using fluid and kinetic approaches. The fluid approach leads to two regimes of operation: weakly and strongly magnetized. The former is similar to the magnetic field-free case, while in the latter the ambipolar diffusion coefficient and electron density depend quadratically on the magnetic field strength. Finally, a more rigorous kinetic treatment, which accounts for the impact of the magnetic field over the whole distribution of electrons, is used for accurate description of the plasma.

  11. Bats respond to very weak magnetic fields.

    PubMed

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

    2015-01-01

    How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.

  12. High RF Magnetic Field Near-Field Microwave Microscope

    NASA Astrophysics Data System (ADS)

    Tai, Tamin; Mircea, Dragos I.; Anlage, Steven M.

    2010-03-01

    Near-field microwave microscopes have been developed to quantitatively image RF and microwave properties of a variety of materials on deep sub-wavelength scales [1]. Microscopes that develop high-RF magnetic fields on short length scales are useful for examining the fundamental electrodynamic properties of superconductors [2]. We are creating a new class of near-field microwave microscopes that develop RF fields on the scale of 1 Tesla on sub-micron length scales. These microscopes will be employed to investigate defects that limit the RF properties of bulk Nb materials used in accelerator cavities, and the nonlinear Meissner effect in novel superconductors. Work funded by the US Department of Energy. [1] S. M. Anlage, V. V. Talanov, A. R. Schwartz, ``Principles of Near-Field Microwave Microscopy,'' in Scanning Probe Microscopy: Electrical and Electromechanical Phenomena at the Nanoscale, Volume 1, edited by S. V. Kalinin and A. Gruverman (Springer-Verlag, New York, 2007), pp. 215-253. [2] D. I. Mircea, H. Xu, S. M. Anlage, ``Phase-sensitive Harmonic Measurements of Microwave Nonlinearities in Cuprate Thin Films,'' Phys. Rev. B 80, 144505 (2009).

  13. Interplanetary magnetic field data book

    NASA Technical Reports Server (NTRS)

    King, J. H.

    1975-01-01

    An interplanetary magnetic field (IMF) data set is presented that is uniform with respect to inclusion of cislunar IMF data only, and which has as complete time coverage as presently possible over a full solar cycle. Macroscale phenomena in the interplanetary medium (sector structure, heliolatitude variations, solar cycle variations, etc.) and other phenomena (e.g., ground level cosmic-ray events) for which knowledge of the IMF with hourly resolution is necessary, are discussed. Listings and plots of cislunar hourly averaged IMP parameters over the period November 27, 1963, to May 17, 1974, are presented along with discussion of the mutual consistency of the IMF data used herein. The magnetic tape from which the plots and listings were generated, which is available from the National Space Science Data Center (NSSDC), is also discussed.

  14. Interaction between two magnetic dipoles in a uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Ku, J. G.; Liu, X. Y.; Chen, H. H.; Deng, R. D.; Yan, Q. X.

    2016-02-01

    A new formula for the interaction force between two magnetic dipoles in a uniform magnetic field is derived taking their mutual magnetic interaction into consideration and used to simulate their relative motion. Results show that when the angle β between the direction of external magnetic field and the centerline of two magnetic dipoles is 0 ° or 90 °, magnetic dipoles approach each other or move away from each other in a straight line, respectively. And the time required for them to contact each other from the initial position is related to the specific susceptibility and the diameter of magnetic particles, medium viscosity and magnetic field strength. When β is between 0 ° and 90 °, magnetic dipole pair performs approximate elliptical motion, and the motion trajectory is affected by the specific susceptibility, diameter and medium viscosity but not magnetic field strength. However, time required for magnetic dipoles to complete the same motion trajectory is shorter when adopting stronger magnetic field. Moreover, the subsequent motion trajectory of magnetic dipoles is ascertained once the initial position is set in a predetermined motion trajectory. Additionally, magnetic potential energy of magnetic dipole pairs is transformed into kinetic energy and friction energy during the motion.

  15. Parametric Harmonic Generation as a Probe of Unconstrained Spin Magnetization Precession in the Shallow Barrier Limit.

    PubMed

    Capua, Amir; Rettner, Charles; Parkin, Stuart S P

    2016-01-29

    We study the parametric excitation of high orders of magnetization precession in ultrathin films having perpendicular magnetic anisotropy. We observe that for a given driving field amplitude the harmonic generation can be increased by lowering the barrier with the application of an in-plane magnetic field in the manner of the Smit-Beljers effect. In this effect, the magnetic stiffness is reduced not by lowering the magnitude of the magnetic field upon which the spins precess, but rather by effectively releasing the field's "anchoring" point. This results in a shallow energy barrier where the electrons' spin is locally unconstrained. While the observation is unveiled in the form of nonlinear high harmonic generation, we believe that the physics whereby the barrier is suppressed by an external magnetic field may apply to other phenomena associated with ultrathin films. In these cases, such unconstrained motion may serve as a sensitive probe of the torques associated with proximate spin currents. Moreover, our approach may be used as a model system for the study of phase transitions in the field of nonlinear dynamics.

  16. Parametric Harmonic Generation as a Probe of Unconstrained Spin Magnetization Precession in the Shallow Barrier Limit.

    PubMed

    Capua, Amir; Rettner, Charles; Parkin, Stuart S P

    2016-01-29

    We study the parametric excitation of high orders of magnetization precession in ultrathin films having perpendicular magnetic anisotropy. We observe that for a given driving field amplitude the harmonic generation can be increased by lowering the barrier with the application of an in-plane magnetic field in the manner of the Smit-Beljers effect. In this effect, the magnetic stiffness is reduced not by lowering the magnitude of the magnetic field upon which the spins precess, but rather by effectively releasing the field's "anchoring" point. This results in a shallow energy barrier where the electrons' spin is locally unconstrained. While the observation is unveiled in the form of nonlinear high harmonic generation, we believe that the physics whereby the barrier is suppressed by an external magnetic field may apply to other phenomena associated with ultrathin films. In these cases, such unconstrained motion may serve as a sensitive probe of the torques associated with proximate spin currents. Moreover, our approach may be used as a model system for the study of phase transitions in the field of nonlinear dynamics. PMID:26871356

  17. A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy.

    PubMed

    Yamaguchi, Akinobu; Saito, Hiromasa; Shimizu, Masayoshi; Miyajima, Hideki; Matsumoto, Satoru; Nakamura, Yoshiharu; Hirohata, Atsufumi

    2008-08-01

    We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm(2)Co(17) permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 mum, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement. PMID:19044353

  18. A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy.

    PubMed

    Yamaguchi, Akinobu; Saito, Hiromasa; Shimizu, Masayoshi; Miyajima, Hideki; Matsumoto, Satoru; Nakamura, Yoshiharu; Hirohata, Atsufumi

    2008-08-01

    We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm(2)Co(17) permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 mum, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement.

  19. Saturn's Magnetic Field and Magnetosphere.

    PubMed

    Smith, E J; Davis, L; Jones, D E; Coleman, P J; Colburn, D S; Dyal, P; Sonett, C P

    1980-01-25

    The Pioneer Saturn vector helium magnetometer has detected a bow shock and magnetopause at Saturn and has provided an accurate characterization of the planetary field. The equatorial surface field is 0.20 gauss, a factor of 3 to 5 times smaller than anticipated on the basis of attempted scalings from Earth and Jupiter. The tilt angle between the magnetic dipole axis and Saturn's rotation axis is < 1 degrees , a surprisingly small value. Spherical harmonic analysis of the measurements shows that the ratio of quadrupole to dipole moments is < 10 percent, indicating that the field is more uniform than those of the Earth or Jupiter and consistent with Saturn having a relatively small core. The field in the outer magnetosphere shows systematic departures from the dipole field, principally a compression of the field near noon and an equatorial orientation associated with a current sheet near dawn. A hydromagnetic wake resulting from the interaction of Titan with the rotating magnetosphere appears to have been observed.

  20. Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor

    NASA Astrophysics Data System (ADS)

    Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanuelidu, Eve; Ni, Ni; Bleszynski Jayich, Ania

    The nitrogen vacancy (NV) defect in diamond has emerged as a promising candidate for high resolution magnetic imaging based on its atomic size and quantum-limited sensing capabilities afforded by long spin coherence times. Although the NV center has been successfully implemented as a nanoscale scanning magnetic probe at room temperature, it has remained an outstanding challenge to extend this capability to cryogenic temperatures, where many solid-state systems exhibit non-trivial magnetic order. In this talk, we present NV magnetic imaging at T = 6 K, first benchmarking the technique with a magnetic hard disk sample, then utilizing the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with Tc = 30 K. In addition, we discuss other candidate solid-state systems that can benefit from the high spatial resolution and field sensitivity of the scanning NV magnetometer.

  1. The somatosensory evoked magnetic fields.

    PubMed

    Kakigi, R; Hoshiyama, M; Shimojo, M; Naka, D; Yamasaki, H; Watanabe, S; Xiang, J; Maeda, K; Lam, K; Itomi, K; Nakamura, A

    2000-08-01

    Averaged magnetoencephalography (MEG) following somatosensory stimulation, somatosensory evoked magnetic field(s) (SEF), in humans are reviewed. The equivalent current dipole(s) (ECD) of the primary and the following middle-latency components of SEF following electrical stimulation within 80-100 ms are estimated in area 3b of the primary somatosensory cortex (SI), the posterior bank of the central sulcus, in the hemisphere contralateral to the stimulated site. Their sites are generally compatible with the homunculus which was reported by Penfield using direct cortical stimulation during surgery. SEF to passive finger movement is generated in area 3a or 2 of SI, unlike with electrical stimulation. Long-latency components with peaks of approximately 80-120 ms are recorded in the bilateral hemispheres and their ECD are estimated in the secondary somatosensory cortex (SII) in the bilateral hemispheres. We also summarized (1) the gating effects on SEF by interference tactile stimulation or movement applied to the stimulus site, (2) clinical applications of SEF in the fields of neurosurgery and neurology and (3) cortical plasticity (reorganization) of the SI. SEF specific to painful stimulation is also recorded following painful stimulation by CO(2) laser beam. Pain-specific components are recorded over 150 ms after the stimulus and their ECD are estimated in the bilateral SII and the limbic system. We introduced a newly-developed multi (12)-channel gradiometer system with the smallest and highest quality superconducting quantum interference device (micro-SQUID) available to non-invasively detect the magnetic fields of a human peripheral nerve. Clear nerve action fields (NAFs) were consistently recorded from all subjects.

  2. Batch-fabrication of cantilevered magnets on attonewton-sensitivity mechanical oscillators for scanned-probe nanoscale magnetic resonance imaging.

    PubMed

    Hickman, Steven A; Moore, Eric W; Lee, SangGap; Longenecker, Jonilyn G; Wright, Sarah J; Harrell, Lee E; Marohn, John A

    2010-12-28

    We have batch-fabricated cantilevers with ∼100 nm diameter nickel nanorod tips and force sensitivities of a few attonewtons at 4.2 K. The magnetic nanorods were engineered to overhang the leading edge of the cantilever, and consequently the cantilevers experience what we believe is the lowest surface noise ever achieved in a scanned probe experiment. Cantilever magnetometry indicated that the tips were well magnetized, with a ≤ 20 nm dead layer; the composition of the dead layer was studied by electron microscopy and electron energy loss spectroscopy. In what we believe is the first demonstration of scanned probe detection of electron-spin resonance from a batch-fabricated tip, the cantilevers were used to observe electron-spin resonance from nitroxide spin labels in a film via force-gradient-induced shifts in cantilever resonance frequency. The magnetic field dependence of the magnetic resonance signal suggests a nonuniform tip magnetization at an applied field near 0.6 T.

  3. Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization

    DOEpatents

    Doughty, Frank C.; Spencer, John E.

    2000-12-19

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

  4. Imaging of electric and magnetic fields near plasmonic nanowires

    NASA Astrophysics Data System (ADS)

    Kabakova, I. V.; de Hoogh, A.; van der Wel, R. E. C.; Wulf, M.; Le Feber, B.; Kuipers, L.

    2016-03-01

    Near-field imaging is a powerful tool to investigate the complex structure of light at the nanoscale. Recent advances in near-field imaging have indicated the possibility for the complete reconstruction of both electric and magnetic components of the evanescent field. Here we study the electro-magnetic field structure of surface plasmon polariton waves propagating along subwavelength gold nanowires by performing phase- and polarization-resolved near-field microscopy in collection mode. By applying the optical reciprocity theorem, we describe the signal collected by the probe as an overlap integral of the nanowire’s evanescent field and the probe’s response function. As a result, we find that the probe’s sensitivity to the magnetic field is approximately equal to its sensitivity to the electric field. Through rigorous modeling of the nanowire mode as well as the aperture probe response function, we obtain a good agreement between experimentally measured signals and a numerical model. Our findings provide a better understanding of aperture-based near-field imaging of the nanoscopic plasmonic and photonic structures and are helpful for the interpretation of future near-field experiments.

  5. Imaging of electric and magnetic fields near plasmonic nanowires

    PubMed Central

    Kabakova, I. V.; de Hoogh, A.; van der Wel, R. E. C.; Wulf , M.; le Feber, B.; Kuipers, L.

    2016-01-01

    Near-field imaging is a powerful tool to investigate the complex structure of light at the nanoscale. Recent advances in near-field imaging have indicated the possibility for the complete reconstruction of both electric and magnetic components of the evanescent field. Here we study the electro-magnetic field structure of surface plasmon polariton waves propagating along subwavelength gold nanowires by performing phase- and polarization-resolved near-field microscopy in collection mode. By applying the optical reciprocity theorem, we describe the signal collected by the probe as an overlap integral of the nanowire’s evanescent field and the probe’s response function. As a result, we find that the probe’s sensitivity to the magnetic field is approximately equal to its sensitivity to the electric field. Through rigorous modeling of the nanowire mode as well as the aperture probe response function, we obtain a good agreement between experimentally measured signals and a numerical model. Our findings provide a better understanding of aperture-based near-field imaging of the nanoscopic plasmonic and photonic structures and are helpful for the interpretation of future near-field experiments. PMID:26947124

  6. Double transition in PrOs 4Sb 12 probed by local magnetization measurements using Hall probe array

    NASA Astrophysics Data System (ADS)

    Kasahara, Shigeru; Hirata, Kazuto; Tamegai, Tsuyoshi; Sugawara, Hitoshi; Kikuchi, Daisuke; Sato, Hideyuki

    2007-09-01

    Double superconducting transition in PrOs4Sb12 has been studied carefully by local magnetization measurements using Hall probe array. Local magnetization curves for each element of the Hall probe reveal that there exists a significant difference in the transition temperature at each point; two phases which give different Tc are stabilized in the crystal. The characteristics of superconducting double transition in PrOs4Sb12 are discussed based on the local magnetization measurements at multi-points.

  7. A dipole probe for electric field measurements in the LVPD

    NASA Astrophysics Data System (ADS)

    Srivastava, P. K.; Awasthi, L. M.; Ravi, G.; Kumar, Sunil; Mattoo, S. K.

    2016-01-01

    This paper describes the design, construction, and calibration of an electric dipole probe and demonstrates its capability by presenting results on the measurement of electric field excited by a ring electrode in the Large Volume Plasma Device (LVPD). It measures the electric field in vacuum and plasma conditions in a frequency range lying between 1-10 \\text{MHz} . The results show that it measures electric field ≥slant 2 mV cm-1 for frequency ≤slant 10 \\text{MHz} . The developed dipole probe works on the principle of amplitude modulation. The probe signal is transmitted through a carrier of 418 MHz, a much higher frequency than the available sources of noise present in the surrounding environment. The amplitude modulation concept of signal transmission is used to make the measurement; it is qualitatively better and less corrupted as it is not affected by the errors introduced by ac pickups. The probe is capable of measuring a variety of electric fields, namely (1) space charge field, (2) time varying field, (3) inductive field and (4) a mixed field containing both space charge and inductive fields. This makes it a useful tool for measuring electric fields in laboratory plasma devices.

  8. Characterization of Residual Stresses in Ferrous Components by Magnetic Anisotropy Measurements Using a Hall Effect Sensor Array Probe

    NASA Astrophysics Data System (ADS)

    Lo, C. C. H.

    2011-06-01

    A new surface sensor probe comprising an angular array of Hall effect sensors has been developed for characterization of residual stresses in ferrous materials by means of stress-induced magnetic anisotropy measurements. The sensor probe applies a radially spreading ac magnetic field to a test sample, and detects stray fields in different directions simultaneously to determine the principal stress axes. In situ measurements were conducted on a annealed steel plate under four-point bending stresses to evaluate the probe performance. The ratio of stray field signals measured along and perpendicular to the stress axis varies linearly with the surface stress, indicating the possibility of characterizing residual stresses in ferrous components using the sensor array probe.

  9. Quenching of flames by magnetic fields (abstract)

    NASA Astrophysics Data System (ADS)

    Ueno, S.

    1988-11-01

    The effects of magnetic fields on combustion of alcohol with the aid of platinum catalysis have been studied to simulate in part the oxidation of organic matter in the living body, and it has been found that the combustion reactions are influenced by magnetic fields. It has also been observed that candle flames are pressed down by magnetic fields of higher intensities when flames are exposed to gradient magnetic fields in a range 20-200 T/m under 0.5-1.4 T. Apart from the combustion experiments, flows of carbon dioxide, oxygen, nitrogen, and argon gases were exposed to magnetic fields up to 2.2 T and 300 T/m. The flows of these gases were blocked or disturbed by the magnetic fields. The purpose of the present study is to clarify the mechanisms for the phenomena observed in the experiments of magnetic effects on combustion and gas flow. An electromagnet with a pair of columnar magnetic poles of which inner sidepieces were hollowed out was used. The magnetic fields of 1.5 T at the brim gave a gradient of 50-100 T/m in the direction perpendicular to the pole axis when the distance of the airgap was in a range 5-10 mm. A candle was burned in the hollowed space between magnetic poles, and candle flames were exposed to magnetic fields. The flames were quenched in a few seconds after the onset of field exposures. Oxygen gas as a paramagnetic molecule can be attracted to the magnetic fields of higher intensities. However, under the intensities of magnetic fields concerned, oxygen gases are not concentrated but are aligned so as to make a ``wall of oxygen'' or an ``air curtain.'' The air curtain, which is also called the ``magnetic curtain,'' blocks air flow into and out of the hollowed space. The interception of oxygen by magnetic curtain quenches flames. The magnetic curtain also presses back flames and other gases.

  10. Effects of Horizontal Magnetic Fields on Acoustic Travel Times

    NASA Astrophysics Data System (ADS)

    Jain, Rekha

    2007-02-01

    Local helioseismology techniques seek to probe the subsurface magnetic fields and flows by observing waves that emerge at the solar surface after passing through these inhomogeneities. Active regions on the surface of the Sun are distinguished by their strong magnetic fields, and techniques such as time-distance helioseismology can provide a useful diagnostic for probing these structures. Above the active regions, the fields fan out to create a horizontal magnetic canopy. We investigate the effect of a uniform horizontal magnetic field on the travel time of acoustic waves by considering vertical velocity in a simple plane-parallel adiabatically stratified polytrope. It is shown that such fields can lower the upper turning point of p-modes and hence influence their travel time. It is found that acoustic waves reflected from magnetically active regions have travel times up to a minute less than for waves similarly reflected in quiet regions. It is also found that sound speeds are increased below the active regions. These findings are consistent with time-distance measurements.

  11. Magnetic fields from the electroweak phase transition

    SciTech Connect

    Tornkvist, O.

    1998-02-01

    I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.

  12. Chiral plasmons without magnetic field

    PubMed Central

    Song, Justin C. W.; Rudner, Mark S.

    2016-01-01

    Plasmons, the collective oscillations of interacting electrons, possess emergent properties that dramatically alter the optical response of metals. We predict the existence of a new class of plasmons—chiral Berry plasmons (CBPs)—for a wide range of 2D metallic systems including gapped Dirac materials. As we show, in these materials the interplay between Berry curvature and electron–electron interactions yields chiral plasmonic modes at zero magnetic field. The CBP modes are confined to system boundaries, even in the absence of topological edge states, with chirality manifested in split energy dispersions for oppositely directed plasmon waves. We unveil a rich CBP phenomenology and propose setups for realizing them, including in anomalous Hall metals and optically pumped 2D Dirac materials. Realization of CBPs will offer a powerful paradigm for magnetic field-free, subwavelength optical nonreciprocity, in the mid-IR to terahertz range, with tunable splittings as large as tens of THz, as well as sensitive all-optical diagnostics of topological bands. PMID:27071090

  13. Chiral plasmons without magnetic field.

    PubMed

    Song, Justin C W; Rudner, Mark S

    2016-04-26

    Plasmons, the collective oscillations of interacting electrons, possess emergent properties that dramatically alter the optical response of metals. We predict the existence of a new class of plasmons-chiral Berry plasmons (CBPs)-for a wide range of 2D metallic systems including gapped Dirac materials. As we show, in these materials the interplay between Berry curvature and electron-electron interactions yields chiral plasmonic modes at zero magnetic field. The CBP modes are confined to system boundaries, even in the absence of topological edge states, with chirality manifested in split energy dispersions for oppositely directed plasmon waves. We unveil a rich CBP phenomenology and propose setups for realizing them, including in anomalous Hall metals and optically pumped 2D Dirac materials. Realization of CBPs will offer a powerful paradigm for magnetic field-free, subwavelength optical nonreciprocity, in the mid-IR to terahertz range, with tunable splittings as large as tens of THz, as well as sensitive all-optical diagnostics of topological bands. PMID:27071090

  14. Magnetic field effects on microwave absorbing materials

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

  15. Magnetic field waves at Uranus

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  16. Probing Magnetic Materials Using Synchrotron Radiation and Phase Retarding Optics

    NASA Astrophysics Data System (ADS)

    Lang, Jonathan

    2007-03-01

    Synchrotron radiation has become an essential tool in the study of magnetic materials. The utility of x-ray measurements arises from the fact that the resonant and polarization properties observed near core-level resonances probe the valence-electron spin and orbital properties in an element specific manner. Critical to enabling such studies, however, has been the ability to easily manipulate the polarization of the x-ray beam. Circularly polarized x-rays pay a particularly important role, due to their coupling to the net ferromagnetic moment in a material. This talk will focus on how phase retarding optical elements can be used to tailor the focus on how phase retarding optical elements can be used to tailor the x-ray beam polarization in order to enable various types of magnetic measurements. Examples of magnetic spectroscopy, scattering, and imaging measurements employing such optics will be presented.

  17. Magnetic field observations in Comet Halley's coma

    NASA Astrophysics Data System (ADS)

    Riedler, W.; Schwingenschuh, K.; Yeroshenko, Ye. G.; Styashkin, V. A.; Russell, C. T.

    1986-05-01

    During the encounter with Comet Halley, the magnetometer (MISCHA) aboard the Vega 1 spacecraft observed an increased level of magnetic field turbulence, resulting from an upstream bow wave. Both Vega spacecraft measured a peak field strength of 70-80 nT and observed draping of magnetic field lines around the cometary obstacle. An unexpected rotation of the magnetic field vector was observed, which may reflect either penetration of magnetic field lines into a diffuse layer related to the contact surface separating the solar-wind and cometary plasma, or the persistence of pre-existing interplanetary field structures.

  18. Magnetic Trapping of Bacteria at Low Magnetic Fields.

    PubMed

    Wang, Z M; Wu, R G; Wang, Z P; Ramanujan, R V

    2016-01-01

    A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells. PMID:27254771

  19. Magnetic Trapping of Bacteria at Low Magnetic Fields

    PubMed Central

    Wang, Z. M.; Wu, R. G.; Wang, Z. P.; Ramanujan, R. V.

    2016-01-01

    A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells. PMID:27254771

  20. Magnetic Trapping of Bacteria at Low Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Wang, Z. M.; Wu, R. G.; Wang, Z. P.; Ramanujan, R. V.

    2016-06-01

    A suspension of non-magnetic entities in a ferrofluid is referred to as an inverse ferrofluid. Current research to trap non-magnetic entities in an inverse ferrofluid focuses on using large permanent magnets to generate high magnetic field gradients, which seriously limits Lab-on-a-Chip applications. On the other hand, in this work, trapping of non-magnetic entities, e.g., bacteria in a uniform external magnetic field was studied with a novel chip design. An inverse ferrofluid flows in a channel and a non-magnetic island is placed in the middle of this channel. The magnetic field was distorted by this island due to the magnetic susceptibility difference between this island and the surrounding ferrofluid, resulting in magnetic forces applied on the non-magnetic entities. Both the ferromagnetic particles and the non-magnetic entities, e.g., bacteria were attracted towards the island, and subsequently accumulate in different regions. The alignment of the ferrimagnetic particles and optical transparency of the ferrofluid was greatly enhanced by the bacteria at low applied magnetic fields. This work is applicable to lab-on-a-chip based detection and trapping of non-magnetic entities bacteria and cells.

  1. The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons

    DOE PAGES

    Yu, J.; Li, L. Y.; Cao, J. B.; Reeves, Geoffrey D.; Baker, D. N.; Spence, H.

    2016-07-22

    Using the Van Allen Probe in situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2 nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (Bz-IMF < –2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (magnetic local time (MLT) ~ 06:00–18:00, and L > 4), the pitch angles of relativistic electrons are mainly pancakemore » distributions with a flux peak around 90° (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However, in the nighttime decreased magnetic field region (MLT ~ 18:00–06:00, and L ≥ 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45° and 135° (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. The dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. As a result, these variations are consistent with the drift shell splitting and/or magnetopause shadowing effect.« less

  2. The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons

    NASA Astrophysics Data System (ADS)

    Yu, J.; Li, L. Y.; Cao, J. B.; Reeves, G. D.; Baker, D. N.; Spence, H.

    2016-07-01

    Using the Van Allen Probe in situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2 nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (Bz-IMF < -2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (magnetic local time (MLT) ~ 06:00-18:00, and L > 4), the pitch angles of relativistic electrons are mainly pancake distributions with a flux peak around 90° (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However, in the nighttime decreased magnetic field region (MLT ~ 18:00-06:00, and L ≥ 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45° and 135° (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. The dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. These variations are consistent with the drift shell splitting and/or magnetopause shadowing effect.

  3. Exploring Magnetic Fields with a Compass

    ERIC Educational Resources Information Center

    Lunk, Brandon; Beichner, Robert

    2011-01-01

    A compass is an excellent classroom tool for the exploration of magnetic fields. Any student can tell you that a compass is used to determine which direction is north, but when paired with some basic trigonometry, the compass can be used to actually measure the strength of the magnetic field due to a nearby magnet or current-carrying wire. In this…

  4. Deformation of Water by a Magnetic Field

    ERIC Educational Resources Information Center

    Chen, Zijun; Dahlberg, E. Dan

    2011-01-01

    After the discovery that superconducting magnets could levitate diamagnetic objects, researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields, which was given the name "The Moses Effect." Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary…

  5. Magnetic field effect on charged Brownian swimmers

    NASA Astrophysics Data System (ADS)

    Sandoval, M.; Velasco, R. M.; Jiménez-Aquino, J. I.

    2016-01-01

    We calculate the effective diffusion of a spherical self-propelled charged particle swimming at low Reynolds number, and subject to a time-dependent magnetic field and thermal agitation. We find that the presence of an external magnetic field may reduce or enhance (depending on the type of swimming and magnetic field applied) the swimmer's effective diffusion, hence we get another possible strategy to control its displacement. For swimmers performing reciprocal motion, and under an oscillating time-dependent magnetic field, mechanical resonance appears when the swimmer and magnetic frequencies coincide, thus enhancing the particle's effective diffusion. Our analytical results are compared with Brownian Dynamics simulations and we obtain excellent agreement.

  6. Frustrated magnets in high magnetic fields-selected examples.

    PubMed

    Wosnitza, J; Zvyagin, S A; Zherlitsyn, S

    2016-07-01

    An indispensable parameter to study strongly correlated electron systems is the magnetic field. Application of high magnetic fields allows the investigation, modification and control of different states of matter. Specifically for magnetic materials experimental tools applied in such fields are essential for understanding their fundamental properties. Here, we focus on selected high-field studies of frustrated magnetic materials that have been shown to host a broad range of fascinating new and exotic phases. We will give brief insights into the influence of geometrical frustration on the critical behavior of triangular-lattice antiferromagnets, the accurate determination of exchange constants in the high-field saturated state by use of electron spin resonance measurements, and the coupling of magnetic degrees of freedom to the lattice evidenced by ultrasound experiments. The latter technique as well allowed new, partially metastable phases in strong magnetic fields to be revealed. PMID:27310818

  7. Analysis of magnetic field levels at KSC

    NASA Technical Reports Server (NTRS)

    Christodoulou, Christos G.

    1994-01-01

    The scope of this work is to evaluate the magnetic field levels of distribution systems and other equipment at Kennedy Space Center (KSC). Magnetic fields levels in several operational areas and various facilities are investigated. Three dimensional mappings and contour are provided along with the measured data. Furthermore, the portion of magnetic fields generated by the 60 Hz fundamental frequency and the portion generated by harmonics are examined. Finally, possible mitigation techniques for attenuating fields from electric panels are discussed.

  8. Cytoplasmic motions, rheology, and structure probed by a novel magnetic particle method

    PubMed Central

    1985-01-01

    The motions of magnetic particles contained within organelles of living cells were followed by measuring magnetic fields generated by the particles. The alignment of particles was sensed magnetometrically and was manipulated by external fields, allowing non-invasive detection of particle motion as well as examination of cytoplasmic viscoelasticity. Motility and rheology data are presented for pulmonary macrophages isolated from lungs of hamsters 1 d after the animals had breathed airborne gamma-Fe2O3 particles. The magnetic directions of particles within phagosomes and secondary lysosomes were aligned, and the weak magnetic field produced by the particles was recorded. For dead cells, this remanent field was constant, but for viable macrophages, the remanent field decreased rapidly so that only 42% of its initial magnitude remained 5 min after alignment. A twisting field was applied perpendicular to the direction of alignment and the rate at which particles reoriented to this new direction was followed. The same twisting was repeated for particles suspended in a series of viscosity standards. Based on this approach, the low-shear apparent intracellular viscosity was estimated to be 1.2-2.7 X 10(3) Pa.s (1.2-2.7 X 10(4) poise). Time-lapse video microscopy confirmed the alignment of ingested particles upon magnetization and showed persistent cellular motility during randomization of alignment. Cytochalasin D and low temperature both reduced cytoplasmic activity and remanent-field decay, but affected rheology differently. Magnetic particles were observed in association with the microtubule organizing center by immunofluorescence microscopy; magnetization did not affect microtubule distribution. However, both vimentin intermediate filaments and f-actin reorganized after magnetization. These data demonstrate that magnetometry of isolated phagocytic cells can probe organelle movements, rheology, and physical properties of the cytoskeleton in living cells. PMID:4040136

  9. Mapping magnetism with atomic resolution using aberrated electron probes

    NASA Astrophysics Data System (ADS)

    Idrobo, Juan; Rusz, Ján; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Lupini, Andrew R.

    2015-03-01

    In this talk, we report a direct experimental real-space mapping of magnetic circular dichroism with atomic resolution in aberration-corrected scanning transmission electron microscopy (STEM). Using an aberrated electron probe with customized phase distribution, we reveal with electron energy-loss (EEL) spectroscopy the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The aberrated probes allow the collection of EEL spectra using the transmitted beam, which results in a magnetic circular dichroic signal with intrinsically larger signal-to-noise ratios than those obtained via nanodiffraction techniques (where most of the transmitted electrons are discarded). The novel experimental setup presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution. This research was supported by DOE SUFD MSED, by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the US DOE, and by the Swedish Research Council and Swedish National Infrastructure for Computing (NSC center)

  10. A multichannel magnetic probe system for analysing magnetic fluctuations in helical axis plasmas

    SciTech Connect

    Haskey, S. R.; Blackwell, B. D.; Seiwald, B.; Hole, M. J.; Pretty, D. G.; Howard, J.; Wach, J.

    2013-09-15

    The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

  11. Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus

    NASA Astrophysics Data System (ADS)

    Yang, J.; Lee, J. W.; Jung, B. K.; Chung, K. J.; Hwang, Y. S.

    2014-11-01

    An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

  12. Abnormal Magnetic Field Effects on Electrogenerated Chemiluminescence

    NASA Astrophysics Data System (ADS)

    Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin

    2015-03-01

    We report abnormal magnetic field effects on electrogenerated chemiluminescence (MFEECL) based on triplet emission from the Ru(bpy)3Cl2-TPrA electrochemical system: the appearance of MFEECL after magnetic field ceases. In early studies the normal MFEECL have been observed from electrochemical systems during the application of magnetic field. Here, the abnormal MFEECL suggest that the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes may become magnetized in magnetic field and experience a long magnetic relaxation after removing magnetic field. Our analysis indicates that the magnetic relaxation can gradually increase the density of charge-transfer complexes within reaction region due to decayed magnetic interactions, leading to a positive component in the abnormal MFEECL. On the other hand, the magnetic relaxation facilitates an inverse conversion from triplets to singlets within charge-transfer complexes. The inverse triplet --> singlet conversion reduces the density of triplet light-emitting states through charge-transfer complexes and gives rise to a negative component in the abnormal MFEECL. The combination of positive and negative components can essentially lead to a non-monotonic profile in the abnormal MFEECL after ceasing magnetic field. Nevertheless, our experimental studies may reveal un-usual magnetic behaviors with long magnetic relaxation from the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes in solution at room temperature.

  13. Mapping the magnetic hyperfine field in GdCo5

    NASA Astrophysics Data System (ADS)

    Krylov, V. I.; Bosch-Santos, B.; Cabrera-Pasca, G. A.; Delyagin, N. N.; Carbonari, A. W.

    2016-05-01

    The magnetic hyperfine field (Bhf) in ferrimagnetic GdCo5 compound has been investigated as a function of temperature by Mössbauer effect (ME) spectroscopy and perturbed angular correlation (PAC) spectroscopy using 119Sn and 111Cd probe nuclei, respectively. Results show that the non-magnetic probe atoms 119Sn and 111Cd substitute all three non-equivalent positions in GdCo5: Gd, CoI, and CoII. For 119Sn and 111Cd probes at Gd sites, the saturation magnetic hyperfine fields are very different with values of Bhf1 = 57.0(1) T and Bhf1= 20.7(1) T, respectively. For 119Sn and 111Cd atoms localized at CoI and CoII sites the magnetic hyperfine fields are practically identical and, in saturation, reach the values of Bhf2 = 11.6(1) T and Bhf2 = 11.1(2) T, and Bhf3 = 14.8(1) T and Bhf3 = 14.4(2) T, respectively.

  14. Magnetic field distribution inside the aperture of a steerer magnet prototype

    NASA Astrophysics Data System (ADS)

    Chiriţă, Ionel; Dan, Daniel; Tănase, Nicolae

    2015-11-01

    The High Energy Storage Ring (HESR), an important part of the Facility for Antiproton and Ion Research (FAIR) international project [1], which will be set up in Darmstadt in the next years, contains, among other magnets, several corrector magnets used for vertical and horizontal beam deviation. A prototype of a 2mrad vertical steerer magnet was designed by National Institute for R&D in Electrical Engineering (ICPE-CA) Romania in close cooperation with Forschungszentrum Jülich Germany [2] and then manufactured and tested by ICPE-CA [3], Romanian Institute for Electrical Engineering—Advanced Research. Magnetic field measurements using a 3D Hall probe were performed. Measured data and their analysis are presented. The system used for Hall probe positioning and data acquisition is also described.

  15. Application peculiarities of magnetic materials for protection from magnetic fields

    NASA Astrophysics Data System (ADS)

    Wai, P.; Dmitrenko, V.; Grabchikov, S.; Vlasik, K.; Novikov, A.; Petrenko, D.; Trukhanov, V.; Ulin, S.; Uteshev, Z.; Chernysheva, V.; Shustov, A.

    2016-02-01

    In different materials for magnetic shields, the maximum permeability is achieved for different values of the magnetic field. This determines the choice of material. So for protection from magnetic fields strength of 10 - 150 A/m it is advisable to apply the amorphous ribbon 84KXCP. For stronger fields (more than 400 A/m) it is recommended to use MFS based on Ni20Fe80. Use of these materials allows creating an effective shield working in a wide range of magnetic field strengths.

  16. Bipolar pulse field for magnetic refrigeration

    DOEpatents

    Lubell, M.S.

    1994-10-25

    A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies. 2 figs.

  17. Bipolar pulse field for magnetic refrigeration

    DOEpatents

    Lubell, Martin S.

    1994-01-01

    A magnetic refrigeration apparatus includes first and second steady state magnets, each having a field of substantially equal strength and opposite polarity, first and second bodies made of magnetocaloric material disposed respectively in the influence of the fields of the first and second steady state magnets, and a pulsed magnet, concentric with the first and second steady state magnets, and having a field which cycles between the fields of the first and second steady state magnets, thereby cyclically magnetizing and demagnetizing and thus heating and cooling the first and second bodies. Heat exchange apparatus of suitable design can be used to expose a working fluid to the first and second bodies of magnetocaloric material. A controller is provided to synchronize the flow of working fluid with the changing states of magnetization of the first and second bodies.

  18. The magnetic fields of forming solar-like stars

    NASA Astrophysics Data System (ADS)

    Gregory, S. G.; Jardine, M.; Gray, C. G.; Donati, J.-F.

    2010-12-01

    Magnetic fields play a crucial role at all stages of the formation of low-mass stars and planetary systems. In the final stages, in particular, they control the kinematics of in-falling gas from circumstellar discs, and the launching and collimation of spectacular outflows. The magnetic coupling with the disc is thought to influence the rotational evolution of the star, while magnetized stellar winds control the braking of more evolved stars and may influence the migration of planets. Magnetic reconnection events trigger energetic flares which irradiate circumstellar discs with high energy particles that influence the disc chemistry and set the initial conditions for planet formation. However, it is only in the past few years that the current generation of optical spectropolarimeters has allowed the magnetic fields of forming solar-like stars to be probed in unprecedented detail. In order to do justice to the recent extensive observational programs new theoretical models are being developed that incorporate magnetic fields with an observed degree of complexity. In this review we draw together disparate results from the classical electromagnetism, molecular physics/chemistry and the geophysics literature, and demonstrate how they can be adapted to construct models of the large scale magnetospheres of stars and planets. We conclude by examining how the incorporation of multipolar magnetic fields into new theoretical models will drive future progress in the field through the elucidation of several observational conundrums.

  19. Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations

    SciTech Connect

    Heinrich, Jonathon R.; Cooke, David L.

    2013-09-15

    Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (ω{sub pe}<ω{sub ce}). A large drift velocity (Mach 4.5 with respect to the ion acoustic speed) between the plasma and probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

  20. Probing neutrino magnetic moments at the Spallation Neutron Source facility

    NASA Astrophysics Data System (ADS)

    Kosmas, T. S.; Miranda, O. G.; Papoulias, D. K.; Tórtola, M.; Valle, J. W. F.

    2015-07-01

    Majorana neutrino electromagnetic properties are studied through neutral current coherent neutrino-nucleus scattering. We focus on the potential of the recently planned COHERENT experiment at the Spallation Neutron Source to probe muon-neutrino magnetic moments. The resulting sensitivities are determined on the basis of a χ2 analysis employing realistic nuclear structure calculations in the context of the quasiparticle random phase approximation. We find that they can improve existing limits by half an order of magnitude. In addition, we show that these facilities allow for standard model precision tests in the low energy regime, with a competitive determination of the weak mixing angle. Finally, they also offer the capability to probe other electromagnetic neutrino properties, such as the neutrino charge radius. We illustrate our results for various choices of experimental setup and target material.

  1. Probing electric fields within organic transistors by nonlinear optics

    NASA Astrophysics Data System (ADS)

    Miranda, Paulo B.; Motti, Silvia G.; Gomes, Douglas J. C.

    2015-03-01

    Organic field-effect transistors (OFETs) are important building blocks in many organic devices, but further improvements in their performance will require a detailed knowledge of their operation mechanism. Thus mapping the electric fields in OFETs, both in the active organic layer and inside the gate dielectric, will allow a direct comparison with theoretical OFET models and guide advances in device engineering. The nonlinear optical processes of sum-frequency generation (SFG) and second-harmonic generation (SHG) may be used to probe electric fields in OFETs. With a proper choice of pump wavelength, SHG can selectively probe the field component along the OFET channel, inside the organic semiconductor. In contrast, SFG may probe the field within any organic material by selecting a specific molecular vibration and monitoring the field-enhanced SFG signal. Here we investigate OFETs fabricated with a polythiophene derivative (P3HT) on silicon substrates and with the insulating polymer PMMA for the dielectric layer. Both the strength and sign of the electric field in PMMA can be determined, yielding a direct probe of charge accumulation along the OFET channel. An extension of this technique to map the spatial distribution of accumulated charge along the channel will also be discussed. Work funded by FAPESP and CNPq (Brazil).

  2. A field-sweep/field-lock system for superconducting magnets--Application to high-field EPR.

    PubMed

    Maly, Thorsten; Bryant, Jeff; Ruben, David; Griffin, Robert G

    2006-12-01

    We describe a field-lock/field-sweep system for the use in superconducting magnets. The system is based on a commercially available field mapping unit and a custom designed broad-band 1H NMR probe. The NMR signal of a small water sample is used in a feedback loop to set and control the magnetic field to high accuracy. The current instrumental configuration allows field sweeps of +/-0.4 T and a resolution of up to 10(-5) T (0.1 G) and the performance of the system is demonstrated in a high-field electron paramagnetic resonance (EPR) application. The system should also be of utility in other experiments requiring precise and reproducible sweeps of the magnetic field such as DNP, ENDOR or PELDOR.

  3. A Field-Sweep/Field-Lock System for Superconducting Magnets-Application to High-Field EPR

    PubMed Central

    Maly, Thorsten; Bryant, Jeff; Ruben, David; Griffin, Robert G.

    2007-01-01

    We describe a field-lock/field-sweep system for the use in superconducting magnets. The system is based on a commercially available field mapping unit and a custom designed broad-band 1H-NMR probe. The NMR signal of a small water sample is used in a feedback loop to set and control the magnetic field to high accuracy. The current instrumental configuration allows field sweeps of ± 0.4 T and a resolution of up to 10-5 T (0.1 G) and the performance of the system is demonstrated in a high-field electron paramagnetic resonance (EPR) application. The system should also be of utility in other experiments requiring precise and reproducible sweeps of the magnetic field such as DNP, ENDOR or PELDOR. PMID:17027306

  4. A novel magnetic fluid based magnetic field F-P current sensor

    NASA Astrophysics Data System (ADS)

    Xia, Ji; Wang, Qi; Jiang, Shuyu; Luo, Hong

    2015-08-01

    A novel current measuring method based on the magnetic controllable refractive index characteristic of magnetic fluid and fiber optic Fabry-Perot (F-P) interferometer is proposed and demonstrated. A current sensing probe composed of fiber optic F-P interferometer filled with magnetic fluid (MF) is analyzed theoretically and numerically. Based on the theoretical analysis and numerical simulation results, the structure of the fiber optic F-P current sensor is designed and fabricated experimentally. The relationship of the magnetic fluid at various magnetic field is measured experimentally and the numerical model of relationship between the refractive index of magnetic fluid and the characteristics of F-P current sensor is built up. The sensor has the advantages of simple structure, low cost, and high magnetic field measurement sensitivity. A high magnetic field measurement sensitivity of 0.034 nm/Gs is achieved with the magnetic field varied from 0 to 391.5Gs, and the experiment results are consistent with the theoretical analysis and numerical simulation.

  5. Magnetic field waves at Uranus

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The proposed research efforts funded by the UDAP grant to the BRI involve the study of magnetic field waves associated with the Uranian bow shock. This is a collaborative venture bringing together investigators at the BRI, Southwest Research Institute (SwRI), and Goddard Space Flight Center (GSFC). In addition, other collaborations have been formed with investigators granted UDAP funds for similar studies and with investigators affiliated with other Voyager experiments. These investigations and the corresponding collaborations are included in the report. The proposed effort as originally conceived included an examination of waves downstream from the shock within the magnetosheath. However, the observations of unexpected complexity and diversity within the upstream region have necessitated that we confine our efforts to those observations recorded upstream of the bow shock on the inbound and outbound legs of the encounter by the Voyager 2 spacecraft.

  6. Magnetic nanoparticles as both imaging probes and therapeutic agents.

    PubMed

    Lacroix, Lise-Marie; Ho, Don; Sun, Shouheng

    2010-01-01

    Magnetic nanoparticles (MNPs) have been explored extensively as contrast agents for magnetic resonance imaging (MRI) or as heating agents for magnetic fluid hyperthermia (MFH) [1]. To achieve optimum operation conditions in MRI and MFH, these NPs should have well-controlled magnetic properties and biological functionalities. Although numerous efforts have been dedicated to the investigations on MNPs for biomedical applications [2-5], the NP optimizations for early diagnostics and efficient therapeutics are still far from reached. Recent efforts in NP syntheses have led to some promising MNP systems for sensitive MRI and efficient MFH applications. This review summarizes these advances in the synthesis of monodisperse MNPs as both contrast probes in MRI and as therapeutic agents via MFH. It will first introduce the nanomagnetism and elucidate the critical parameters to optimize the superparamagnetic NPs for MRI and ferromagnetic NPs for MFH. It will further outline the new chemistry developed for making monodisperse MNPs with controlled magnetic properties. The review will finally highlight the NP functionalization with biocompatible molecules and biological targeting agents for tumor diagnosis and therapy. PMID:20388109

  7. Direct probing of band-structure Berry phase in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Granada, M.; Lucot, D.; Giraud, R.; Lemaître, A.; Ulysse, C.; Waintal, X.; Faini, G.

    2015-06-01

    We report on experimental evidence of the Berry phase accumulated by the charge-carrier wave function in single-domain nanowires made from a (Ga, Mn)(As, P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should thus be considered a band-structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga, Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.

  8. Connecting Photospheric Magnetic Fields and Transition Temperature Plasma Emission

    NASA Astrophysics Data System (ADS)

    Schmit, Donald

    2016-05-01

    The connectivity of quiet sun magnetic fields is not well understood. One observational obstacle to probe this question has been the sparse spectral observations spanning the transition temperatures (3×104 K< T < 1×105K) between the chromosphere and corona. The Si IV lines observed by IRIS provide a rich dataset to address the structure of the cool quiet sun. We use over 900 deep exposures from IRIS to map the correlation between transition-temperature emission structures and magnetic field concentrations. Ultimately, our aim is to discern the topology and energetic equilibrium of the magnetic structures that span the quiet sun. We use both a potential field model and a snapshot of the Bifrost 3D MHD simulation to interpret our emission data. In a broad sense, we find there is a clear correlation between magnetic fields and strong Si IV emission. However, more pointed statistics suggest that the relationship is quite complex. We do not find evidence for cool loops longer than 3 Mm in length, but we see ubiquitous, smooth emission nearly everywhere in the quiet sun. Emission voids on scales larger than 8 Mm cannot be well explained by their proximity to magnetic fields. This evidence suggests that weak-field transition-temperature loops contribute significantly to quiet sun transition-temperature emission measure, and evolutionary effects likely play a role in structuring the magnetic atmosphere.

  9. A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments

    SciTech Connect

    Smith, Doran D.; Alexson, Dimitri A.; Garbini, Joseph L.

    2013-09-15

    The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 μm diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

  10. A 4 K cryogenic probe for use in magnetic resonance force microscopy experiments

    NASA Astrophysics Data System (ADS)

    Smith, Doran D.; Alexson, Dimitri A.; Garbini, Joseph L.

    2013-09-01

    The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 μm diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

  11. Design and calibration of high-frequency magnetic probes for the SUNIST spherical tokamak.

    PubMed

    Liu, Yangqing; Tan, Yi; Pan, Ou; Ke, Rui; Wang, Wenhao; Gao, Zhe

    2014-11-01

    A new high-frequency magnetic diagnostic system is designed, installed, and calibrated in the Sino-United Spherical Tokamak (SUNIST) to investigate Alfvén waves (AWs). The system consists of a fixed toroidal array and a movable radial array of high-frequency magnetic probes (HFMPs) with 21 and 60 probes, respectively. Based on the method of vacuum enameled wire wound on ceramic bobbins, the fixed toroidal array is located as near as possible to the plasma and carefully shielded to reduce the attenuation of high-frequency magnetic field. Meanwhile, by using the technology of commercial chip inductors mounted on printed circuit boards, the movable radial array is inserted into a thin quartz tube that allows positioning along radial direction. A Helmholtz coil is utilized to calibrate the effective areas as well as the frequency response of each HFMP. The calibration results are consistent with the calculated results of an equivalent probe-and-cable circuit model. High-frequency magnetic signals related to AW are detected with these HFMPs. These HFMPs are expected to play a key role in analyzing Alfvén eigenmodes excited by AW antenna in the SUNIST.

  12. Design and calibration of high-frequency magnetic probes for the SUNIST spherical tokamak.

    PubMed

    Liu, Yangqing; Tan, Yi; Pan, Ou; Ke, Rui; Wang, Wenhao; Gao, Zhe

    2014-11-01

    A new high-frequency magnetic diagnostic system is designed, installed, and calibrated in the Sino-United Spherical Tokamak (SUNIST) to investigate Alfvén waves (AWs). The system consists of a fixed toroidal array and a movable radial array of high-frequency magnetic probes (HFMPs) with 21 and 60 probes, respectively. Based on the method of vacuum enameled wire wound on ceramic bobbins, the fixed toroidal array is located as near as possible to the plasma and carefully shielded to reduce the attenuation of high-frequency magnetic field. Meanwhile, by using the technology of commercial chip inductors mounted on printed circuit boards, the movable radial array is inserted into a thin quartz tube that allows positioning along radial direction. A Helmholtz coil is utilized to calibrate the effective areas as well as the frequency response of each HFMP. The calibration results are consistent with the calculated results of an equivalent probe-and-cable circuit model. High-frequency magnetic signals related to AW are detected with these HFMPs. These HFMPs are expected to play a key role in analyzing Alfvén eigenmodes excited by AW antenna in the SUNIST. PMID:25430367

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

    NASA Astrophysics Data System (ADS)

    Ida, Tetsuya; Watasaki, Masahiro; Kimura, Yosuke; Miki, Motohiro; Izumi, Mitsuru

    2010-06-01

    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.

  14. Representation of magnetic fields in space

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1975-01-01

    Several methods by which a magnetic field in space can be represented are reviewed with particular attention to problems of the observed geomagnetic field. Time dependence is assumed to be negligible, and five main classes of representation are described by vector potential, scalar potential, orthogonal vectors, Euler potentials, and expanded magnetic field.

  15. Behaviour of ferrocholesterics under external magnetic fields

    NASA Astrophysics Data System (ADS)

    Petrescu, Emil; Motoc, Cornelia

    2001-08-01

    The influence of an external magnetic field on the orientational behaviour of a ferrocholesteric with a positive magnetic anisotropy is investigated. Both the phenomena arising when the field was switched on or switched off are considered. It is found that the field needed for a ferrocholesteric-ferronematic transition BFC↑ is higher when compared to that obtained for the pure cholesteric ( BC↑). A similar result was obtained when estimating the critical field for the homeotropic ferronematic-ferrocholesteric (focal conic) transition, occurring when the magnetic field was decreased or switched off. We found that BFC↓> BC↓. These results are explained when considering that the magnetic moments of the magnetic powder are not oriented parallel to the liquid crystal molecular directors, therefore hindering their orientation under a magnetic field.

  16. Static uniform magnetic fields and amoebae

    SciTech Connect

    Berk, S.G.; Srikanth, S.; Mahajan, S.M.; Ventrice, C.A.

    1997-03-01

    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.

  17. Ordered arrays of near-field optical probes

    NASA Astrophysics Data System (ADS)

    Sojic, Neso; Chovin, Arnaud; Garrigue, Patrick; Manek-Honninger, Inka; Servant, Laurent

    2005-06-01

    Ordered arrays of nanometer-sized optical probes with electrochemiluminescent properties were developed on the distal face of imaging fiber bundles. The fabrication steps are adapted from SNOM probes and nanoelectrodes methodologies and allow to produce high-density arrays of opto-electrochemical probes which retain the initial architecture of the bundle. Apertureless probe arrays and also nanoaperture arrays have thus been prepared. The angular distribution of the far-field intensity transmitted through such nanostructured arrays depends both on their respective architectures and on the characteristic dimensions of the nanoprobes. The subwavelength aperture arrays show a diffracting behavior which is a function of the optical aperture size. The far-field analysis demonstrates their potential application as a parallel near-field optical array in both apertureless and aperture configurations. In addition, each optical nanoaperture is surrounded by a ring-shaped gold nanoelectrode. The electrochemical response of the array is sigmoidal in shape indicating that the nanoelectrodes forming the array are diffusively independent. In other words, each nanoelectrode of the array probes electrochemically a different micro-environment. We show also that the nanoaperture array can be used as an electrochemiluminescent nanosensor array for NADH. Eventually, the arrays keep the imaging properties at both nanometer and micrometer scales. Indeed, each nanoprobe can explore optically a near-field region, whereas the global array allows imaging simultaneously a large micrometric area. This optical array format plays therefore a bridging role by interrelating optical and electrochemiluminescent information obtained concomitantly at the nanometer and micrometer scales.

  18. Can we probe the conductivity of the lithosphere and upper mantle using satellite tidal magnetic signals?

    NASA Astrophysics Data System (ADS)

    Schnepf, N. R.; Kuvshinov, A.; Sabaka, T.

    2015-05-01

    A few studies convincingly demonstrated that the magnetic fields induced by the lunar semidiurnal (M2) ocean flow can be identified in satellite observations. This result encourages using M2 satellite magnetic data to constrain subsurface electrical conductivity in oceanic regions. Traditional satellite-based induction studies using signals of magnetospheric origin are mostly sensitive to conducting structures because of the inductive coupling between primary and induced sources. In contrast, galvanic coupling from the oceanic tidal signal allows for studying less conductive, shallower structures. We perform global 3-D electromagnetic numerical simulations to investigate the sensitivity of M2 signals to conductivity distributions at different depths. The results of our sensitivity analysis suggest it will be promising to use M2 oceanic signals detected at satellite altitude for probing lithospheric and upper mantle conductivity. Our simulations also suggest that M2 seafloor electric and magnetic field data may provide complementary details to better constrain lithospheric conductivity.

  19. Long-pulse magnetic field facility at Zaragoza

    NASA Astrophysics Data System (ADS)

    Algarabel, P. A.; del Moral, A.; Martín, C.; Serrate, D.; Tokarz, W.

    2006-11-01

    The long-pulse magnetic field facility of the Laboratorio de Magnetismo - Instituto de Ciencia de Materiales de Aragón (Universidad de Zaragoza-CSIC) produces magnetic fields up to 31, with a pulse duration of 2.2s. Experimental set-ups for measurements of magnetization, magnetostriction and magnetoresistance are available. The temperature can be controlled between 1.4 and 335 K, being the inner bore of the He cryostat of 22.5 mm. Magnetization is measured using the mutual induction technique, the magnetostriction is determined with the strain-gage and the capacitive cantilever methods, and the magnetoresistance is measured by means of the aclock-in technique in the 4-probes geometry. An overview of the facility will be presented and the presently available experimental techniques will be discussed.

  20. Swarm: ESA's Magnetic Field Mission

    NASA Astrophysics Data System (ADS)

    Drinkwater, M. R.; Haagmans, R.; Floberghagen, R.; Plank, G.; Menard, Y.

    2011-12-01

    Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2012. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently approaching the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products to the Swarm user community. The setup of Swarm ground segment and the contents of the data products will be addressed. More information on the Swarm mission can be found at the mission web site (see URL below).

  1. Swarm: ESA's Magnetic Field Mission

    NASA Astrophysics Data System (ADS)

    Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

    2013-12-01

    Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

  2. Swarm: ESA's Magnetic Field Mission

    NASA Astrophysics Data System (ADS)

    Plank, Gernot; Haagmans, Roger; Floberghagen, Rune; Menard, Yvon

    2013-04-01

    Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in 2013. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of 3 identical satellites. The Mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. More information on Swarm can be found at www.esa.int/esaLP/LPswarm.html.

  3. Swarm: ESA's Magnetic Field Mission

    NASA Astrophysics Data System (ADS)

    Plank, G.; Floberghagen, R.; Menard, Y.; Haagmans, R.

    2012-12-01

    Swarm is the fifth Earth Explorer mission in ESA's Living Planet Programme, and is scheduled for launch in fall 2012. The objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution using a constellation of three identical satellites. The mission shall deliver data that allow access to new insights into the Earth system by improved scientific understanding of the Earth's interior and near-Earth electromagnetic environment. After launch and triple satellite release at an initial altitude of about 490 km, a pair of the satellites will fly side-by-side with slowly decaying altitude, while the third satellite will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission science goals are to provide a unique view into Earth's core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the final stage of the development phase, will be addressed. A consortium of European scientific institutes is developing a distributed processing system to produce geophysical (Level 2) data products for the Swarm user community. The setup of the Swarm ground segment and the contents of the data products will be addressed. In case the Swarm satellites are already in orbit, a summary of the on-going mission operations activities will be given.

  4. Nonlinear energy dissipation of magnetic nanoparticles in oscillating magnetic fields

    NASA Astrophysics Data System (ADS)

    Soto-Aquino, D.; Rinaldi, C.

    2015-11-01

    The heating of magnetic nanoparticle suspensions subjected to alternating magnetic fields enables a variety of emerging applications such as magnetic fluid hyperthermia and triggered drug release. Rosensweig (2002) [25] obtained a model for the heat dissipation rate of a collection of non-interacting particles. However, the assumptions made in this analysis make it rigorously valid only in the limit of small applied magnetic field amplitude and frequency (i.e., values of the Langevin parameter that are much less than unity and frequencies below the inverse relaxation time). In this contribution we approach the problem from an alternative point of view by solving the phenomenological magnetization relaxation equation exactly for the case of arbitrary magnetic field amplitude and frequency and by solving a more accurate magnetization relaxation equation numerically. We also use rotational Brownian dynamics simulations of non-interacting magnetic nanoparticles subjected to an alternating magnetic field to estimate the rate of energy dissipation and compare the results of the phenomenological theories to the particle-scale simulations. The results are summarized in terms of a normalized energy dissipation rate and show that Rosensweig's expression provides an upper bound on the energy dissipation rate achieved at high field frequency and amplitude. Estimates of the predicted dependence of energy dissipation rate, quantified as specific absorption rate (SAR), on magnetic field amplitude and frequency, and particle core and hydrodynamic diameter, are also given.

  5. Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane

    NASA Technical Reports Server (NTRS)

    Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

    2001-01-01

    A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

  6. Minimizing magnetic fields for precision experiments

    SciTech Connect

    Altarev, I.; Fierlinger, P.; Lins, T.; Marino, M. G.; Nießen, B.; Petzoldt, G.; Reisner, M.; Stuiber, S. Sturm, M.; Taggart Singh, J.; Taubenheim, B.; Rohrer, H. K.; Schläpfer, U.

    2015-06-21

    An increasing number of measurements in fundamental and applied physics rely on magnetically shielded environments with sub nano-Tesla residual magnetic fields. State of the art magnetically shielded rooms (MSRs) consist of up to seven layers of high permeability materials in combination with highly conductive shields. Proper magnetic equilibration is crucial to obtain such low magnetic fields with small gradients in any MSR. Here, we report on a scheme to magnetically equilibrate MSRs with a 10 times reduced duration of the magnetic equilibration sequence and a significantly lower magnetic field with improved homogeneity. For the search of the neutron's electric dipole moment, our finding corresponds to a 40% improvement of the statistical reach of the measurement. However, this versatile procedure can improve the performance of any MSR for any application.

  7. Magnetically filtered Faraday probe for measuring the ion current density profile of a Hall thruster

    SciTech Connect

    Rovey, Joshua L.; Walker, Mitchell L.R.; Gallimore, Alec D.; Peterson, Peter Y.

    2006-01-15

    The ability of a magnetically filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operating over the range of 300-500 V and 5-10 mg/s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of 4.4x10{sup -4} Pa Xe (3.3x10{sup -6} Torr Xe) to 1.1x10{sup -3} Pa Xe (8.4x10{sup -6} Torr Xe) in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operating condition. The differences between the current density profiles obtained by each probe are attributed to the ion filtering systems employed. Analysis of the results shows that the MFFP, operating at a +5 A solenoid current, provides the best agreement with flight-test data and across operating pressures.

  8. Operating a magnetic nozzle helicon thruster with strong magnetic field

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazunori; Komuro, Atsushi; Ando, Akira

    2016-03-01

    A pulsed axial magnetic field up to ˜2.8 kG is applied to a 26-mm-inner-diameter helicon plasma thruster immersed in a vacuum chamber, and the thrust is measured using a pendulum target. The pendulum is located 30-cm-downstream of the thruster, and the thruster rf power and argon flow rate are fixed at 1 kW and 70 sccm (which gives a chamber pressure of 0.7 mTorr). The imparted thrust increases as the applied magnetic field is increased and saturates at a maximum value of ˜9.5 mN for magnetic field above ˜2 kG. At the maximum magnetic field, it is demonstrated that the normalized plasma density, and the ion flow energy in the magnetic nozzle, agree within ˜50% and of 10%, respectively, with a one-dimensional model that ignores radial losses from the nozzle. This magnetic nozzle model is combined with a simple global model of the thruster source that incorporates an artificially controlled factor α, to account for radial plasma losses to the walls, where α = 0 and 1 correspond to zero losses and no magnetic field, respectively. Comparison between the experiments and the model implies that the radial losses in the thruster source are experimentally reduced by the applied magnetic field to about 10% of that obtained from the no magnetic field model.

  9. Free oscillations of magnetic fluid in strong magnetic field

    NASA Astrophysics Data System (ADS)

    Polunin, V. M.; Ryapolov, P. A.; Platonov, V. B.; Kuz'ko, A. E.

    2016-05-01

    The paper presents the esults of measuring the elastic parameters of an oscillatory system (coefficient of pondermotive elasticity, damping factor, and oscillation frequency) whose viscous inertial element is represented by a magnetic fluid confined in a tube by magnetic levitation in a strong magnetic field. The role of elasticity is played by the pondermotive force acting on thin layers at the upper and lower ends of the fluid column. It is shown that, by measuring the elastic oscillation frequencies of the magnetic fluid column, it is possible to develop a fundamentally new absolute method for determining the saturation magnetization of a magnetic colloid.

  10. Magnetic vector field tag and seal

    DOEpatents

    Johnston, Roger G.; Garcia, Anthony R.

    2004-08-31

    One or more magnets are placed in a container (preferably on objects inside the container) and the magnetic field strength and vector direction are measured with a magnetometer from at least one location near the container to provide the container with a magnetic vector field tag and seal. The location(s) of the magnetometer relative to the container are also noted. If the position of any magnet inside the container changes, then the measured vector fields at the these locations also change, indicating that the tag has been removed, the seal has broken, and therefore that the container and objects inside may have been tampered with. A hollow wheel with magnets inside may also provide a similar magnetic vector field tag and seal. As the wheel turns, the magnets tumble randomly inside, removing the tag and breaking the seal.

  11. Numerical analysis of magnetic field in superconducting magnetic energy storage

    SciTech Connect

    Kanamaru, Y. ); Amemiya, Y. )

    1991-09-01

    This paper reports that the superconducting magnetic energy storage (SMES) is more useful than the other systems of electric energy storage because of larger stored energy and higher efficiency. The other systems are the battery, the flywheel, the pumped-storage power station. Some models of solenoid type SMES are designed in U.S.A. and Japan. But a high magnetic field happens by the large scale SMES in the living environment, and makes the erroneous operations of the computer display, the pacemaker of the heart and the electronic equipments. We study some fit designs of magnetic shielding of the solenoidal type SMES for reduction of the magnetic field in living environment. When some superconducting shielding coils are over the main storage coil, magnetic field reduces remarkably than the case of non shielding coil. The calculated results of the magnetic field are obtained y the finite element method.

  12. Magnetic field measurements in tokamak plasmas

    SciTech Connect

    Feldman, U.; Seely, J.F.; Sheeley,Jr., N.R.; Suckewer, S.; Title, A.M.

    1984-11-01

    The measurement of the poloidal magnetic field in a tokamak plasma from the Zeeman splitting and polarization of the magnetic dipole radiation from heavy ions is discussed. When viewed from a direction perpendicular to the toroidal field, the effect of the poloidal field on the circularly polarized radiation is detectable using a photoelectric polarimeter. The Zeeman splittings for a number of magnetic dipole transitions with wavelengths in the range 2300--9300 A are presented. An imaging polarimeter is proposed that can measure the poloidal magnetic field with space and time resolution.

  13. Ferroelectric Cathodes in Transverse Magnetic Fields

    SciTech Connect

    Alexander Dunaevsky; Yevgeny Raitses; Nathaniel J. Fisch

    2002-07-29

    Experimental investigations of a planar ferroelectric cathode in a transverse magnetic field up to 3 kGs are presented. It is shown that the transverse magnetic field affects differently the operation of ferroelectric plasma cathodes in ''bright'' and ''dark'' modes in vacuum. In the ''bright'' mode, when the surface plasma is formed, the application of the transverse magnetic field leads to an increase of the surface plasma density. In the ''dark'' mode, the magnetic field inhibits the development of electron avalanches along the surface, as it does similarly in other kinds of surface discharges in the pre-breakdown mode.

  14. Flow Transitions in a Rotating Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    1996-01-01

    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.

  15. Magnetic field spectrum at cosmological recombination revisited

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  16. Bats Respond to Very Weak Magnetic Fields

    PubMed Central

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

    2015-01-01

    How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944

  17. Structure of magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Kotarba, Hanna; Lesch, H.; Dolag, K.; Naab, T.; Johansson, P. H.; Stasyszyn, F. A.

    2009-04-01

    We present a set of global, self-consistent N-body/SPH simulations of the dynamic evolution of galactic discs with gas and including magnetic fields. We have implemented a description to follow the ideal induction equation in the SPH part of the code Vine. Results from a direct implementation of the field equations are compared to a representation by Euler potentials, which pose a ∇ ċ B-free description, a constraint not fulfilled for the direct implementation. All simulations are compared to an implementation of magnetic fields in the code Gadget. Starting with a homogeneous field we find a tight connection of the magnetic field structure to the density pattern of the galaxy in our simulations, with the magnetic field lines being aligned with the developing spiral pattern of the gas. Our simulations clearly show the importance of non-axisymmetry of the dynamic pattern for the evolution of the magnetic field.

  18. Rydberg EIT in High Magnetic Field

    NASA Astrophysics Data System (ADS)

    Ma, Lu; Anderson, David; Miller, Stephanie; Raithel, Georg

    2016-05-01

    We present progress towards an all-optical approach for measurements of strong magnetic fields using electromagnetically induced transparency (EIT) with Rydberg atoms in an atomic vapor. Rydberg EIT spectroscopy is a promising technique for the development of atom-based, calibration- and drift-free technology for high magnetic field sensing. In this effort, Rydberg EIT is employed to spectroscopically investigate the response of Rydberg atoms exposed to strong magnetic fields, in which Rydberg atoms are in the strong-field regime. In our setup, two neodymium block magnets are used to generate fields of about 0.8 Tesla, which strongly perturb the atoms. Information on the field strength and direction is obtained by a comparison of experimental spectra with calculated spectral maps. Investigations of magnetic-field inhomogeneities and other decoherence sources will be discussed.

  19. Probing of field-induced structures and their dynamics in ferrofluids using oscillatory rheology.

    PubMed

    Felicia, Leona J; Philip, John

    2014-10-21

    We probe field-induced structures and their dynamics in ferrofluids using oscillatory rheology. The magnetic field dependence of the relaxation time and crossover modulus showed two distinct regions, indicating the different microstructures in those regions. The observed relaxation at various magnetic field strengths indicates that side chains are attached to the pinned single-sphere-width chains between the rheometer plates. Our results suggest that the ferrofluid under a magnetic field exhibits a soft solidlike behavior whose relaxation is governed by the imposed strain rate and the magnetic field. Using the scaling factors obtained from the frequency and modulus at the crossover point in the oscillatory rheological measurements, the constant strain-rate frequency sweep data is superimposed onto a single master curve. The frequency scaling factor increases with the strain rate as a power law with an exponent close to unity, whereas the amplitude scaling factor is almost strain-rate-independent at high magnetic field strengths. These findings are useful for a better understanding of field-induced ordering of nanoparticles in fluids and their optimization for practical applications.

  20. Probing of field-induced structures and their dynamics in ferrofluids using oscillatory rheology.

    PubMed

    Felicia, Leona J; Philip, John

    2014-10-21

    We probe field-induced structures and their dynamics in ferrofluids using oscillatory rheology. The magnetic field dependence of the relaxation time and crossover modulus showed two distinct regions, indicating the different microstructures in those regions. The observed relaxation at various magnetic field strengths indicates that side chains are attached to the pinned single-sphere-width chains between the rheometer plates. Our results suggest that the ferrofluid under a magnetic field exhibits a soft solidlike behavior whose relaxation is governed by the imposed strain rate and the magnetic field. Using the scaling factors obtained from the frequency and modulus at the crossover point in the oscillatory rheological measurements, the constant strain-rate frequency sweep data is superimposed onto a single master curve. The frequency scaling factor increases with the strain rate as a power law with an exponent close to unity, whereas the amplitude scaling factor is almost strain-rate-independent at high magnetic field strengths. These findings are useful for a better understanding of field-induced ordering of nanoparticles in fluids and their optimization for practical applications. PMID:25268053

  1. Probing arrays of circular magnetic microdots by ferromagnetic resonance.

    SciTech Connect

    Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V.

    2008-06-01

    X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

  2. Reducing Field Distortion in Magnetic Resonance Imaging

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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

  3. Magnetic field evolution in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Drzazga, R. T.; Chyży, K. T.; Jurusik, W.; Wiórkiewicz, K.

    2011-09-01

    Aims: Violent gravitational interactions can change the morphologies of galaxies and, by means of merging, transform them into elliptical galaxies. We aim to investigate how they affect the evolution of galactic magnetic fields. Methods: We selected 16 systems of interacting galaxies with available VLA archive radio data at 4.86 and 1.4 GHz and compared their radio emission and estimated magnetic field strengths with their star-forming activity, far-infrared emission, and the stage of tidal interaction. Results: The estimated mean of total magnetic field strength for our sample of interacting galaxies is 14 ± 5 μG, which is larger than for the non-interacting objects. The field regularity (of 0.27 ± 0.09) is lower than in typical spirals and indicates enhanced production of random magnetic fields in the interacting objects. We find a general evolution of magnetic fields: for weak interactions the strength of magnetic field is almost constant (10-15 μG) as interaction advances, then it increases up to 2× , peaks at the nuclear coalescence (25 μG), and decreases again, down to 5-6 μG, for the post-merger remnants. The main production of magnetic fields in colliding galaxies thus terminates somewhere close to the nuclear coalescence, after which magnetic field diffuses. The magnetic field strength for whole galaxies is weakly affected by the star formation rate (SFR), while the dependence is higher for galactic centres. We show that the morphological distortions visible in the radio total and polarized emission do not depend statistically on the global or local SFRs, while they do increase (especially in the polarization) with the advance of interaction. The constructed radio-far-infrared relations for interacting and non-interacting galaxies display a similar balance between the generation of cosmic rays, magnetic fields, and the production of the thermal energy and dust radiation. Conclusions: The regular magnetic fields are much more sensitive to

  4. Multi-echo imaging in highly inhomogeneous magnetic fields.

    PubMed

    Casanova, F; Perlo, J; Blümich, B; Kremer, K

    2004-01-01

    A new pulsed field gradient multi-echo imaging technique to encode position in the phase of every echo generated by a CPMG sequence in the presence of a strongly inhomogeneous static magnetic field is presented. It was applied to improve the sensitivity in an imaging experiment by adding the echo train acquired during the CPMG sequence and to spatially resolve relaxation times of inhomogeneous specimens using single-sided probes. The sequence was implemented in a new bar-magnet MOUSE equipped with a gradient coil system to apply a pulsed magnetic field with a constant gradient along one spatial coordinate. An important reduction by a factor larger than two orders of magnitude in the acquisition time was obtained compared to the previously published single-point imaging technique. PMID:14675822

  5. The AGN origin of cluster magnetic fields

    NASA Astrophysics Data System (ADS)

    Xu, Hao

    The origin of magnetic fields in galaxy clusters is one of the most fascinating but challenging problems in astrophysics. In this dissertation, the possibility of an Active Galactic Nucleus (AGN) origin of cluster magnetic fields is studied through state of the art simulations of magnetic field evolution in large scale structure formation using a newly developed cosmological Adaptive Mesh Refinement (AMR) Magnetohydrodynamics (MHD) code -- EnzoMHD. After presenting a complete but concise description and verification of the code, we discuss the creation of magnetic fields through the Biermann Battery effect during first star formation and galaxy cluster formation. We find that magnetic fields are produced as predicted by theory in both cases. For the first star formation, we obtain a lower limit of (~ 10 -9 G) for magnetic fields when the first generation stars form. On the other hand, we find that the magnetic energy is amplified 4 orders of magnitude within ~ 10 Gyr during cluster formation. We then study magnetic field injection from AGN into the Intra- Cluster Medium (ICM) and their impact on the ICM. We reproduce the X-ray cavities as well as weak shocks seen in observations in the simulation, and further confirm the idea that AGN outburst must contain lots of magnetic energy (up to 10 61 ergs) and the magnetic fields play an important part in the formation of jet/lobe system. We present high resolution simulations of cluster formation with magnetic fields injected from high redshift AGN. We find that these local magnetic fields are spread quickly throughout the whole cluster by cluster mergers. The ICM is in a turbulent state with a Kolmogorov-like power spectrum. Magnetic fields are amplified to and maintained at the observational level of a few mG by bulk flows at large scale and the ICM turbulence at small scale. The total magnetic energy increases about 25 times to ~ 1.2 × 10^61 ergs at the present time. We conclude that magnetic fields from AGN at high

  6. Feasibility of an intra-cardiac magnetic probe

    NASA Astrophysics Data System (ADS)

    Robbes, D.; Dolabdjian, C.; Monfort, Y.; Ciureanu, P.

    2002-08-01

    Recent progress on room temperature mini-magnetometers have led us to think that rf driven magneto-inductive (MI) probes could be used inside the cardiac cavities. This would improve the spatial resolution of heart magnetic imaging and would help us to better understand the cardiac magnetic sources. Using MI elements ( Ø 40 μm, 8 mm long), we show that a Mohri sensor, where the MI element acts as parametric feedback impedance of a Colpitts oscillator, can be modified in order to locate the active element at the termination of a 2 m long 50 Ω coaxial line. The MI element is a wire driven by an ac current with the frequency in the 100 MHz range and the amplitude in the mA range. Transfer coefficients as high as 10 000 V/T are easy to obtain, for a source resistance of 10-15 k Ω. The white noise levels falls in the pT/√Hz range. An MI probe can be attached to a small coaxial line in the same way as for in situ electrical mapping experiments. We believe that this approach could be very useful to SQUID magneto-cardiography, because it could help improving the modelling of current distributions inside the human heart.

  7. Design and validation of the ball-pen probe for measurements in a low-temperature magnetized plasma

    SciTech Connect

    Bousselin, G.; Cavalier, J.; Pautex, J. F.; Heuraux, S.; Lemoine, N.; Bonhomme, G.

    2013-01-15

    Ball-pen probes have been used in fusion devices for direct measurements of the plasma potential. Their application in low-temperature magnetized plasma devices is still subject to studies. In this context, a ball-pen probe has been recently implemented on the linear plasma device Mirabelle. Produced by a thermionic discharge, the plasma is characterized by a low electron temperature and a low density. Plasma confinement is provided by an axial magnetic field that goes up to 100 mT. The principle of the ball-pen probe is to adjust the saturation current ratio to 1 by reducing the electron current contribution. In that case, the floating potential of the probe is close to the plasma potential. A thorough study of the ball-pen probe operation is performed for different designs of the probe over a large set of plasma conditions. Comparisons between ball-pen, Langmuir, and emissive probes are conducted in the same plasma conditions. The ball-pen probe is successfully measuring the plasma potential in these specific plasma conditions only if an adapted electronics and an adapted probe size to the plasma characteristic lengths ({lambda}{sub D}, {rho}{sub ce}) are used.

  8. Design and validation of the ball-pen probe for measurements in a low-temperature magnetized plasma.

    PubMed

    Bousselin, G; Cavalier, J; Pautex, J F; Heuraux, S; Lemoine, N; Bonhomme, G

    2013-01-01

    Ball-pen probes have been used in fusion devices for direct measurements of the plasma potential. Their application in low-temperature magnetized plasma devices is still subject to studies. In this context, a ball-pen probe has been recently implemented on the linear plasma device Mirabelle. Produced by a thermionic discharge, the plasma is characterized by a low electron temperature and a low density. Plasma confinement is provided by an axial magnetic field that goes up to 100 mT. The principle of the ball-pen probe is to adjust the saturation current ratio to 1 by reducing the electron current contribution. In that case, the floating potential of the probe is close to the plasma potential. A thorough study of the ball-pen probe operation is performed for different designs of the probe over a large set of plasma conditions. Comparisons between ball-pen, Langmuir, and emissive probes are conducted in the same plasma conditions. The ball-pen probe is successfully measuring the plasma potential in these specific plasma conditions only if an adapted electronics and an adapted probe size to the plasma characteristic lengths (λ(D), ρ(ce)) are used.

  9. Characterization of internal interfaces by atom probe field ion microscopy

    SciTech Connect

    Miller, M.K.; Jayaram, R.

    1992-12-31

    The near atomic spatial resolution of the atom probe field ion microscope permits the elemental characterization of internal interfaces, grain boundaries and surfaces to be performed in a wide variety of materials. Information such as the orientation relationship between grains, topology of the interface, and the coherency of small precipitates with the surrounding matrix may be obtained from field ion microscopy. Details of the solute segregation may be obtained at the plane of the interface and as a function of distance from the interface for all elements simultaneously from atom probe compositional analysis. Capabilities and limitations of the atom probe technique in characterization of internal interfaces is illustrated with examples of grain boundaries and interphase interfaces in a wide range of materials including intermetallics, model alloys, and commercial steels.

  10. Characterization of internal interfaces by atom probe field ion microscopy

    SciTech Connect

    Miller, M.K.; Jayaram, R.

    1992-01-01

    The near atomic spatial resolution of the atom probe field ion microscope permits the elemental characterization of internal interfaces, grain boundaries and surfaces to be performed in a wide variety of materials. Information such as the orientation relationship between grains, topology of the interface, and the coherency of small precipitates with the surrounding matrix may be obtained from field ion microscopy. Details of the solute segregation may be obtained at the plane of the interface and as a function of distance from the interface for all elements simultaneously from atom probe compositional analysis. Capabilities and limitations of the atom probe technique in characterization of internal interfaces is illustrated with examples of grain boundaries and interphase interfaces in a wide range of materials including intermetallics, model alloys, and commercial steels.

  11. Probing the quality of Ni filled nanoporous alumina templates by magnetic techniques.

    PubMed

    Sousa, C T; Leitão, D C; Proença, M P; Apolinário, A; Azevedo, A M; Sobolev, N A; Bunyaev, S A; Pogorelov, Yu G; Ventura, J; Araújo, J P; Kakazei, G N

    2012-09-01

    Pulsed electrodeposition prepared porous alumina templates with Ni nanowires pore filling ranged from 1 to 100%, depending on the alumina barrier-layer thickness, were probed by continuous wave ferromagnetic resonance at room temperature. For completely filled samples, a single resonance peak was observed in the whole range of angles between the applied magnetic field and normal to the sample plane. Its position was described by Kittel formula that takes into account shape anisotropy of individual Ni wires and dipolar interactions between them. For the samples with lower pore filling the effective anisotropy field decreased and the resonance linewidth in the perpendicular configuration increased. Also a quite intense second peak was observed at lower fields for these samples. These changes are associated with reduction of pore filling percentage that can lead to decrease of dipolar interactions between nanowires and to appearance of magnetic inhomogeneities inside wires. PMID:23035501

  12. MDI Synoptic Charts of Magnetic Field: Interpolation of Polar Fields

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Hoeksema, J. T.; Zhao, X.; Larson, R. M.

    2007-05-01

    In this poster, we compare various methods for interpolation of polar field for the MDI synoptic charts of magnetic field. By examining the coronal and heliospheric magnetic field computed from the synoptic charts based on a Potential Field Source Surface model (PFSS), and by comparing the heliospheric current sheets and footpoints of open fields with the observations, we conclude that the coronal and heliospheric fields calculated from the synoptic charts are sensitive to the polar field interpolation, and a time-dependent interpolation method using the observed polar fields is the best among the seven methods investigated.

  13. Magnetic field measurements for study of fast electron transport in magnetized HED plasma

    NASA Astrophysics Data System (ADS)

    Sawada, Hiroshi; Griffin, Brandon; Presura, Radu; Haque, Showera; Sentoku, Yasuhiko

    2014-10-01

    Interaction of megagauss magnetic fields with high energy density (HED) plasma is of great interest in the field of magnetized plasma. The field changes fundamental properties of the HED plasma such as thermal and magnetic diffusion. A coupled capability utilizing the 1.0 MA Zebra pulsed power generator and the 50 TW Leopard laser at Nevada Terawatt Facility enables to create such a condition for studies of magnetized plasma properties. We have conducted an experiment to measure magnetic fields generated by a 1.0 MA, 100 ns Zebra pulsed current in stainless steel coils. Using a 532 nm continuous laser from a single longitudinal mode laser system, the temporal change in the magnetic field was measured with the Faraday rotation in F2 glass. The probe laser passing through the 1.5 mm in radius and 1.75 mm thick glass placed in the vicinity of the inductive coils was split with a Glan-Taylor prism to measure vertical and horizontal polarization components with photodiodes. We will present the analysis of the experimental result and a design of a coupled experiment for study of fast electron transport in the magnetized plasma.

  14. Magnetic Field Investigations During ROSETTA's Steins Flyby

    NASA Astrophysics Data System (ADS)

    Glassmeier, K.; Auster, H.; Richter, I.; Motschmann, U.; RPC/ROMAP Teams

    2009-05-01

    During the recent Steins flyby of the ROSETTA spacecraft magnetic field measurements have been made with both, the RPC orbiter magnetometer and the ROMAP lander magnetometer. These combined magnetic field measurements allow a detailed examination of any magnetic signatures caused either directly by the asteroid or indirectly by Steins different modes of interaction with the solar wind. Comparing our measurements with simulation results show that Steins does not possess a significant remanent magnetization. The magnetization is estimated at less than 1 mAm2/kg. This is significantly different from results at Braille and Gaspra.

  15. Near-Field Photothermal Heating with a Plasmonic Nanofocusing Probe

    NASA Astrophysics Data System (ADS)

    Chen, Xiang; Dong, Biqing; Balogun, Oluwaseyi

    2016-03-01

    Noble metal nanostructures support plasmon resonances—collective oscillation of charge carriers at optical frequencies—and serve as effective tools to create bright light sources at the nanoscale. These sources are useful in broad application areas including, super-resolution imaging and spectroscopy, nanolithography, and near-field optomechanical transducers. The feasibility of these applications relies on efficient conversion of free-space propagating light to plasmons. Recently, we demonstrated a hybrid nanofocusing scheme for efficient coupling of light to plasmons at the apex of a scanning probe. In the approach, free-space light is coupled to propagating surface plasmon polaritons (SPPs) on the tapered shaft of the scanning probe. The SPPs propagate adiabatically towards the probe tip where they are coupled to localized plasmons (LSPs). The nanofocusing scheme was explored in a near-field scanning optical microscope for super-resolution imaging, near-field transduction of nanomechanical vibrations, and local detection of ultrasound. Owing to the strong concentration of light at the probe, significant heating of the tip and a sample positioned in the optical near-field is expected. This paper investigates the local heating produced by the plasmonic nanofocusing probe under steady-state conditions using the tip-enhanced Raman scattering approach. In addition, a finite element model is explored to study the coupling of free propagating light to LSPs, and to estimate the temperature rise expected in a halfspace heated by absorption of the LSPs. This study has implications for exploring the plasmonic nanofocusing probe in heat-assisted nanofabrication and fundamental studies of nanoscale heat transport in materials.

  16. The Evolution of the Earth's Magnetic Field.

    ERIC Educational Resources Information Center

    Bloxham, Jeremy; Gubbins, David

    1989-01-01

    Describes the change of earth's magnetic field at the boundary between the outer core and the mantle. Measurement techniques used during the last 300 years are considered. Discusses the theories and research for explaining the field change. (YP)

  17. The Physics of Attraction and Repulsion: Magnetism and Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Nakotte, Heinz

    2001-11-01

    The development of new materials with improved magnetic properties completely changed the modern world in the past decades. Recent progress is predominantly due to a better understanding of magnetism that has gone far beyond compass needles rotating in a magnetic field and bar magnets attracting or repelling each other. New magnetic materials are used to build smaller and smaller read/write heads and hard disks with increased storage capacity, developments that are responsible the revolution in the computer industry. Another example is the field of magnetic levitation that became feasible for commercial applications with the discovery of new superconducting materials, and a prototype train is under development in Japan. In medicine, the development of magnetic resonance imaging (MRI) provides an alternative to other (destructive) radiation techniques.

  18. In Situ Magnetic Field Measurement using the Hanle Effect

    NASA Astrophysics Data System (ADS)

    Jackson, Jarom; Durfee, Dallin

    2016-05-01

    We have developed a simple method of in situ magnetic field mapping near zero points in magnetic fields. It is ideal for measuring trapping parameters such the field gradient and curvature, and should be applicable in most experiments with a magneto-optical trap (MOT) or similar setup. This method works by probing atomic transitions in a vacuum, and is based on the Hanle effect, which alters the polarization of spontaneous emission in the presence of a magnetic field. Unlike most techniques based on the Hanle effect, however, we look only at intensity. Instead of measuring polarization we use the change in directional radiation patterns caused by a magnetic field. Using one of the cooling beams for our MOT, along with a linear polarizer, a narrow slit, and an inexpensive webcam, we measure the three dimensional position of a magnetic field zero point within our vacuum to within +/-1 mm and the gradient through the zero point to an accuracy of 4%. This work was supported by NSF Grant Number PHY-1205736.

  19. Magnetic isotope and magnetic field effects on the DNA synthesis

    PubMed Central

    Buchachenko, Anatoly L.; Orlov, Alexei P.; Kuznetsov, Dmitry A.; Breslavskaya, Natalia N.

    2013-01-01

    Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases β with isotopic ions 24Mg2+, 25Mg2+ and 26Mg2+ in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases β carrying 24Mg2+ and 26Mg2+ ions with spinless, non-magnetic nuclei 24Mg and 26Mg. However, 25Mg2+ ions with magnetic nucleus 25Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases β with 24Mg2+ and 26Mg2+ ions. Such an isotopic dependence directly indicates that in the DNA synthesis magnetic mass-independent isotope effect functions. Similar effect is exhibited by polymerases β with Zn2+ ions carrying magnetic 67Zn and non-magnetic 64Zn nuclei, respectively. A new, ion–radical mechanism of the DNA synthesis is suggested to explain these effects. Magnetic field dependence of the magnesium-catalysed DNA synthesis is in a perfect agreement with the proposed ion–radical mechanism. It is pointed out that the magnetic isotope and magnetic field effects may be used for medicinal purposes (trans-cranial magnetic treatment of cognitive deceases, cell proliferation, control of the cancer cells, etc). PMID:23851636

  20. Beyond Solar-B: MTRAP, the Magnetic Transition Region Probe

    NASA Technical Reports Server (NTRS)

    Davis, John M.; Moore, Ronald L.; Hathaway, David H.

    2003-01-01

    The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of the solar atmosphere and heliosphere, were the focus of a science definition workshop, 'High-Resolution Solar Magnetography from Space: Beyond Solar-B,' held in Huntsville Alabama in April 2001. Forty internationally prominent scientists active in solar research involving fine-scale solar magnetism participated in this Workshop and reached consensus that the key science objective to be pursued beyond Solar-B is a physical understanding of the fine-scale magnetic structure and activity in the magnetic transition region, defined as the region between the photosphere and corona where neither the plasma nor the magnetic field strongly dominates the other. The observational objective requires high cadence (less than 10s) vector magnetic field maps, and spatially resolved spectra from the IR, visible, vacuum UV, to the EUV at high resolution (less than 50km) over a large FOV (approximately 140,000 km). A polarimetric resolution of one part in ten thousand is required to measure transverse magnetic fields of less than 30G. The latest SEC Roadmap includes a mission identified as MTRAP to meet these requirements. Enabling technology development requirements include large, lightweight, reflecting optics, large format sensors (16K x 16K pixels) with high QE at 150 nm, and extendable spacecraft structures. The Science Organizing Committee of the Beyond Solar-B Workshop recommends that: (1) Science and Technology Definition Teams should be established in FY04 to finalize the science requirements and to define technology development efforts needed to ensure the practicality of MTRAP

  1. RESOLVED MAGNETIC FIELD MAPPING OF A MOLECULAR CLOUD USING GPIPS

    SciTech Connect

    Marchwinski, Robert C.; Pavel, Michael D.; Clemens, Dan P. E-mail: pavelmi@bu.edu

    2012-08-20

    We present the first resolved map of plane-of-sky magnetic field strength for a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 Multiplication-Sign 10 pc at a distance of 1.88 kpc, masses 16,000 M{sub Sun }, and exhibits no star formation. Near-infrared background starlight polarizations were obtained for the Galactic Plane Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir instrument. The cloud area of 0.78 deg{sup 2} contains 2684 significant starlight polarizations for Two Micron All Sky Survey matched stars brighter than 12.5 mag in the H band. Polarizations are generally aligned with the cloud's major axis, showing an average position angle dispersion of 15 {+-} 2 Degree-Sign and polarization of 1.8 {+-} 0.6%. The polarizations were combined with Galactic Ring Survey {sup 13}CO spectroscopy and the Chandrasekhar-Fermi method to estimate plane-of-sky magnetic field strengths, with an angular resolution of 100 arcsec. The average plane-of-sky magnetic field strength across the cloud is 5.40 {+-} 0.04 {mu}G. The magnetic field strength map exhibits seven enhancements or 'magnetic cores'. These cores show an average magnetic field strength of 8.3 {+-} 0.9 {mu}G, radius of 1.2 {+-} 0.2 pc, intercore spacing of 5.7 {+-} 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their magnetic fields continue to suppress star formation. The magnetic field strength shows a power-law dependence on gas volume density, with slope 0.75 {+-} 0.02 for n{sub H{sub 2}} {>=}10 cm{sup -3}. This power-law index is identical to those in studies at higher densities, but disagrees with predictions for the densities probed here.

  2. The CASSIOPE/e-POP Magnetic Field Instrument (MGF)

    NASA Astrophysics Data System (ADS)

    Wallis, D. D.; Miles, D. M.; Narod, B. B.; Bennest, J. R.; Murphy, K. R.; Mann, I. R.; Yau, A. W.

    2015-06-01

    Field-aligned currents couple energy between the Earth's magnetosphere and ionosphere and are responsible for driving both micro and macro motions of plasma and neutral atoms in both regimes. These currents are believed to be a contributing energy source for ion acceleration in the polar ionosphere and may be detected via measurements of magnetic gradients along the track of a polar orbiting spacecraft, usually the north-south gradients of the east-west field component. The detection of such gradients does not require observatory class measurements of the geomagnetic field. The Magnetic Field instrument (MGF) measures the local magnetic field onboard the Enhanced Polar Outflow Probe (e-POP) satellite by using two ring-core fluxgate sensors to characterize and remove the stray spacecraft field. The fluxgate sensors have their heritage in the MAGSAT design, are double wound for reduced mass and cross-field dependence, and are mounted on a modest 0.9 m carbon-fiber boom. The MGF samples the magnetic field 160 times per sec (˜50 meters) to a resolution of 0.0625 nT and outputs data at 1952 bytes per second including temperature measurements. Its power consumption is 2.2 watts, and its noise level is 7 pT per root Hz at 1 Hz.

  3. Two-axis magnetic field sensor

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    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.

  4. A scanning Hall probe microscope for high resolution magnetic imaging down to 300 mK

    NASA Astrophysics Data System (ADS)

    Khotkevych, V. V.; Milošević, M. V.; Bending, S. J.

    2008-12-01

    We present the design, construction, and performance of a low-temperature scanning Hall probe microscope with submicron lateral resolution and a large scanning range. The detachable microscope head is mounted on the cold flange of a commercial H3e-refrigerator (Oxford Instruments, Heliox VT-50) and operates between room temperature and 300 mK. It is fitted with a three-axis slip-stick nanopositioner that enables precise in situ adjustment of the probe location within a 6×6×7 mm3 space. The local magnetic induction at the sample surface is mapped with an easily changeable microfabricated Hall probe [typically GsAs/AlGaAs or AlGaAs/InGaAs/GaAs Hall sensors with integrated scanning tunnel microscopy (STM) tunneling tips] and can achieve minimum detectable fields ⩾10 mG/Hz1/2. The Hall probe is brought into very close proximity to the sample surface by sensing and controlling tunnel currents at the integrated STM tip. The instrument is capable of simultaneous tunneling and Hall signal acquisition in surface-tracking mode. We illustrate the potential of the system with images of superconducting vortices at the surface of a Nb thin film down to 372 mK, and also of labyrinth magnetic-domain patterns of an yttrium iron garnet film captured at room temperature.

  5. Coronal magnetic fields produced by photospheric shear

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Yang, W.-H.

    1987-01-01

    The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

  6. Single-layer high field dipole magnets

    SciTech Connect

    Vadim V. Kashikhin and Alexander V. Zlobin

    2001-07-30

    Fermilab is developing high field dipole magnets for post-LHC hadron colliders. Several designs with a nominal field of 10-12 T, coil bore size of 40-50 mm based on both shell-type and block-type coil geometry are currently under consideration. This paper presents a new approach to magnet design, based on simple and robust single-layer coils optimized for the maximum field, good field quality and minimum number of turns.

  7. Probe Station and Near-Field Scanner for Testing Antennas

    NASA Technical Reports Server (NTRS)

    Zaman, Afroz; Lee, Richard Q.; Darby, William G.; Barr, Philip J.; Miranda, Felix A.; Lambert, Kevin

    2006-01-01

    A facility that includes a probe station and a scanning open-ended waveguide probe for measuring near electromagnetic fields has been added to Glenn Research Center's suite of antenna-testing facilities, at a small fraction of the cost of the other facilities. This facility is designed specifically for nondestructive characterization of the radiation patterns of miniaturized microwave antennas fabricated on semiconductor and dielectric wafer substrates, including active antennas that are difficult to test in traditional antenna-testing ranges because of fragility, smallness, or severity of DC-bias or test-fixture requirements. By virtue of the simple fact that a greater fraction of radiated power can be captured in a near-field measurement than in a conventional far-field measurement, this near-field facility is convenient for testing miniaturized antennas with low gains.

  8. The magnetic field of ζ Ori A

    NASA Astrophysics Data System (ADS)

    Blazère, A.; Neiner, C.; Bouret, J.-C.; Tkachenko, A.

    2015-01-01

    Magnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation (Wade et al. 2013) and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of ζ Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in ζ Ori A. We identify that it belongs to ζ Ori Aa and characterize it.

  9. Magnetic fields in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Viganò, D.; Pons, J. A.; Miralles, J. A.; Rea, N.

    2015-05-01

    Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

  10. The measurement of geodesic acoustic mode magnetic field oscillations in J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Lan, T.; Wu, J.; Shen, H. G.; Deng, T. J.; Liu, A. D.; Xie, J. L.; Li, H.; Liu, W. D.; Yu, C. X.; Sun, Y.; Liu, H.; Chen, Z. P.; Zhuang, G.

    2014-10-01

    Geodesic acoustic mode (GAM) magnetic field oscillations have been investigated using three-dimension magnetic probe and Langmuir probe arrays in the edge of J-TEXT tokamak. The probe arrays are placed on the two top windows of tokamak, separated toroidally. Inside the LCFS, GAM shows apparent oscillations in floating potential. In contrast, GAM magnetic field oscillations are not significant in raw magnetic fields signals. Using toroidal correlation technique, the GAM magnetic field oscillations are distinguished from ambient magnetic field. The amplitudes of three dimension GAM magnetic field fluctuations, as well as the dependence with local plasma parameters such as safety factor and plasma beta, are coincident with theoretical predictions. And its toroidal symmetry mode structure, i.e. n = 0, is identified. Furthermore, the GAM current sheet, in which GAM oscillates, is firstly verified with magnetic probes arrays in different radial positions, which may help us to understand the radial structure of GAM. Supported by NNSFC (Nos. 10990210, 10990211, 10335060, 10905057 and 11375188), CPSF (No. 20080440104), YIF (No. WK2030040019) and KIPCAS (No. kjcx-yw-n28).

  11. Disruption of coronal magnetic field arcades

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran; Linker, Jon A.

    1994-01-01

    The ideal and resistive properties of isolated large-scale coronal magnetic arcades are studied using axisymmetric solutions of the time-dependent magnetohydrodynamic (MHD) equations in spherical geometry. We examine how flares and coronal mass ejections may be initiated by sudden disruptions of the magnetic field. The evolution of coronal arcades in response to applied shearing photospheric flows indicates that disruptive behavior can occur beyond a critical shear. The disruption can be traced to ideal MHD magnetic nonequilibrium. The magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity in the magnetic field. In the presence of plasma resistivity, the resulting current sheet is the site of rapid reconnection, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid. We relate these results to previous studies of force-free fields and to the properties of the open-field configuration. We show that the field lines in an arcade are forced open when the magnetic energy approaches (but is still below) the open-field energy, creating a partially open field in which most of the field lines extend away from the solar surface. Preliminary application of this model to helmet streamers indicates that it is relevant to the initiation of coronal mass ejections.

  12. Fluctuating magnetic field induced resonant activation

    SciTech Connect

    Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

    2014-12-14

    In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (τ) increases under the fixed field strength then the mean first passage time rapidly grows at low τ and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers’ turn over phenomenon may occur in the presence of a fluctuating magnetic field.

  13. Magnetic resonance imaging: effects of magnetic field strength

    SciTech Connect

    Crooks, L.E.; Arakawa, M.; Hoenninger, J.; McCarten, B.; Watts, J.; Kaufman, L.

    1984-04-01

    Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. For any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields.

  14. Interplanetary stream magnetism: Kinematic effects. [solar magnetic fields and wind

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.; Barouch, E.

    1974-01-01

    The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

  15. Gravity field information from Gravity Probe-B

    NASA Technical Reports Server (NTRS)

    Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.

    1989-01-01

    The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.

  16. Probing the electromagnetic field distribution within a metallic nanodisk.

    PubMed

    Meneses-Rodríguez, David; Ferreiro-Vila, Elías; Prieto, Patricia; Anguita, José; González, María U; García-Martín, José M; Cebollada, Alfonso; García-Martín, Antonio; Armelles, Gaspar

    2011-12-01

    A Co nanolayer is used as a local probe to evaluate the vertical inhomogeneous distribution of the electromagnetic (EM) field within a resonant metallic nanodisk. Taking advantage of the direct relation between the magneto-optical activity and the electromagnetic field intensity in the Co layer, it is shown that the nonuniform EM distribution within the nanodisk under plasmon resonant conditions has maximum values close to the upper and lower flat faces, and a minimum value in the middle.

  17. Magnetohydrodynamic mode identification from magnetic probe signals via a matched filter method

    NASA Astrophysics Data System (ADS)

    Edgell, Dana H.; Kim, Jin-Soo; Bogatu, Ioan N.; Humphreys, David A.; Turnbull, Alan D.

    2002-04-01

    A matched filter analysis has been developed to identify the amplitude and phase of magnetohydrodynamic modes in DIII-D tokamak plasmas using magnetic probe signals (δBp). As opposed to conventional Fourier spatial analysis of toroidally spaced probes, this analysis includes data from both toroidally and poloidally spaced magnetic probe arrays. Using additional probes both improves the statistics of the analysis and more importantly incorporates poloidal information into the mode analysis. The matched filter is a numeric filter that matches signals from the magnetic probes with numerically predicted signals for the mode. The numerical predictions are developed using EFIT equilibrium reconstruction data as input to the stability code GATO and the vacuum field code VACUUM. Changes is the plasma equilibrium that occur on the same time scale as the mode are taken into account by modeling simple matched filter vectors corresponding to changes in total plasma current, plus vertical and horizontal plasma shifts. The matched filter method works well when there is good understanding of a mode and good modeling of its structure. Matched filter analysis results for a fast growing ideal kink mode, where equilibrium change effects are minimal, show the effectiveness of this method. A slow growing resistive-wall mode (RWM) is also analyzed using the matched filter method. The method gives good results for identifying the amplitude and phase of the RWM but the simple equilibrium vectors are insufficient for complete elimination of equilibrium changes on this time scale. An analysis of the computational requirements of the scheme indicates that real-time application of the matched filter for RWM identification will be possible.

  18. Magnetic Fields at the Center of Coils

    ERIC Educational Resources Information Center

    Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

    2014-01-01

    In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…

  19. Modeling the evolution of galactic magnetic fields

    SciTech Connect

    Yar-Mukhamedov, D.

    2015-04-15

    An analytic model for evolution of galactic magnetic fields in hierarchical galaxy formation frameworks is introduced. Its major innovative components include explicit and detailed treatment of the physics of merger events, mass gains and losses, gravitational energy sources and delays associated with formation of large-scale magnetic fields. This paper describes the model, its implementation, and core results obtained by its means.

  20. Couette flow in ferrofluids with magnetic field

    NASA Astrophysics Data System (ADS)

    Singh, Jitender; Bajaj, Renu

    2005-06-01

    Instability of a viscous, incompressible ferrofluid flow in an annular space between two coaxially rotating cylinders in the presence of axial magnetic field has been investigated numerically. The magnetic field perturbations in fluid in the gap between the cylinders have been taken into consideration and these have been observed to stabilize the Couette flow.

  1. Unsteady wandering magnetic field lines, turbulence and laboratory flux ropes

    NASA Astrophysics Data System (ADS)

    Intrator, T.; Sears, J.; Weber, T.; Liu, D.; Pulliam, D.; Lazarian, A.

    2011-12-01

    We describe earth bound laboratory experiment investigations of patchy, unsteady, bursty, patchy magnetic field structures that are unifying features of magnetic reconnection and turbulence in helio, space and astro physics. Macroscopic field lines occupy cross sectional areas, fill up three dimensional (3D) volumes as flux tubes. They contain mass with Newtonian dynamics that follow magneto-hydro-dynamic (MHD) equations of motion. Flux rope geometry can be ubiquitous in laminar reconnection sheet geometries that are themselves unstable to formation of secondary "islands" that in 3D are really flux ropes. Flux ropes are ubiquitous structures on the sun and the rest of the heliosphere. Understanding the dynamics of flux ropes and their mutual interactions offers the key to many important astrophysical phenomena, including magnetic reconnection and turbulence. We describe laboratory investigations on RSX, where 3D interaction of flux ropes can be studied in great detail. We use experimental probes inside the the flux ropes to measure the magnetic and electric fields, current density, density, temperatures, pressure, and electrostatic and vector plasma potentials. Macroscopic magnetic field lines, unsteady wandering characteristics, and dynamic objects with structure down to the dissipation scale length can be traced from data sets in a 3D volume. Computational approaches are finally able to tackle simple 3D systems and we sketch some intriguing simulation results that are consistent with 3D extensions of typical 2D cartoons for magnetic reconnection and turbulence.

  2. Permanent magnet edge-field quadrupole

    DOEpatents

    Tatchyn, R.O.

    1997-01-21

    Planar permanent magnet edge-field quadrupoles for use in particle accelerating machines and in insertion devices designed to generate spontaneous or coherent radiation from moving charged particles are disclosed. The invention comprises four magnetized rectangular pieces of permanent magnet material with substantially similar dimensions arranged into two planar arrays situated to generate a field with a substantially dominant quadrupole component in regions close to the device axis. 10 figs.

  3. Permanent magnet edge-field quadrupole

    DOEpatents

    Tatchyn, Roman O.

    1997-01-01

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

  4. Levitation of a magnet by an alternating magnetic field

    NASA Astrophysics Data System (ADS)

    Gough, W.; Hunt, M. O.; Summerskill, W. S. H.

    2013-01-01

    An experiment is described in which a small strong cylindrical magnet is levitated by a vertical non-uniform alternating magnetic field. Surprisingly, no superimposed constant field is necessary, but the levitation can be explained when the vertical motion of the magnet is taken into account. The theoretical mean levitation force is (0.26 ± 0.06) N, which is in good agreement with the levitated weight of (0.239 ± 0.001) N. This experiment is suitable for an undergraduate laboratory, particularly as a final year project. Students have found it interesting, and it sharpens up knowledge of basic magnetism.

  5. Magnetic diode for measurement of magnetic-field strength

    SciTech Connect

    Fedotov, S.I.; Zalkind, V.M.

    1988-02-01

    The accuracy of fabrication and assembly of the elements of the magnetic systems of thermonuclear installations of the stellarator type is checked by study of the topography of the confining magnetic field and is determined by the space resolution and accuracy of the measuring apparatus. A magnetometer with a galvanomagnetic sensor is described that is used to adjust the magnetic system of the Uragan-3 stellarator. The magnetometer measure magnetic-field induction in the range of 6 x 10/sup -7/-10/sup -2/ T with high space resolution.

  6. Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor

    NASA Astrophysics Data System (ADS)

    Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C.

    2016-08-01

    High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen-vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz-1/2 field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.

  7. Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor

    NASA Astrophysics Data System (ADS)

    Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C.

    2016-08-01

    High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen–vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz–1/2 field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.

  8. Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor.

    PubMed

    Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C

    2016-08-01

    High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen-vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz(-1/2) field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.

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

    NASA Astrophysics Data System (ADS)

    Blackman, Eric G.

    2015-05-01

    Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. Here I discuss how magnetic helicity has come to help us understand the saturation of and sustenance of large scale dynamos, the need for either local or global helicity fluxes to avoid dynamo quenching, and the associated observational consequences. I also discuss how magnetic helicity acts as a hindrance to turbulent diffusion of large scale fields, and thus a helper for fossil remnant large scale field origin models in some contexts. I briefly discuss the connection between large scale fields and accretion disk theory as well. The goal here is to provide a conceptual primer to help the reader efficiently penetrate the literature.

  10. Probing Magnetic Susceptibility Anisotropy of Large-Diameter Armchair Carbon Nanotubes via Magnetic Linear Dichroism Spectroscopy

    NASA Astrophysics Data System (ADS)

    Haroz, Erik; Kono, Junichiro; Searles, Thomas; Tu, Xiaomin; Zheng, Ming; Fagan, Jeffrey; McGill, Stephen; Smirnov, Dmitry

    2012-02-01

    We studied magnetic susceptibility anisotropy, via magnetic linear dichroism spectroscopy, of aqueous suspensions of single-walled carbon nanotubes in high magnetic fields up to 22T using a unique magnet system (Split-Florida Helix magnet). Specifically, we measured magnetic susceptibility anisotropies, δχ, of several armchair species ranging from (5,5)-(13,13) at room temperature over an excitation wavelength range of 400-900 nm. For large diameter armchairs such as (12,12) and (13,13), we have observed some of the strongest alignment in a static magnetic field due to their large diameters. Results will be discussed in comparison with detailed calculations involving the Aharonov-Bohm effect.

  11. Tracing magnetic field orientation in starless cores

    NASA Astrophysics Data System (ADS)

    Maheswar, G.; Ramaprakash, A. N.; Lee, C. W.; Dib, S.

    It is now well understood that stars are formed in the interiors of dense, gravitationally bound molecular cloud cores that are both magnetized and turbulent. But the relative role played by the magnetic field and the turbulence in cloud formation and evolution and in the subsequent star formation is a matter of debate. In a magnetically dominated scenario, the magnetic field geometry of the cores is expected to be inherited unchanged from their low-density envelope, even for an hour glass geometry of the field, unless the action of turbulence disturbs it. We carried out polarimetry of stars projected on starless molecular clouds, LDN 183 and LDN 1544, in R-filter. The comparison of these fields with those in the interiors of the cloud cores inferred from the sub-mm polarization shows that both magnetic field and turbulence are important in the cloud formation and evolution of star formation.

  12. Processing of polymers in high magnetic fields

    SciTech Connect

    Douglas, E.P.; Smith, M.E.; Benicewicz, B.C.; Earls, J.D.; Priester, R.D. Jr.

    1996-05-01

    Many organic molecules and polymers have an anisotropic diamagnetic susceptibility, and thus can be aligned in high magnetic fields. The presence of liquid crystallinity allows cooperative motions of the individual molecules, and thus the magnetic energy becomes greater than the thermal energy at experimentally obtainable field strengths. This work has determined the effect of magnetic field alignment on the thermal expansion and mechanical properties of liquid crystalline thermosets in the laboratory. Further advances in magnet design are needed to make magnetic field alignment a commercially viable approach to polymer processing. The liquid crystal thermoset chosen for this study is the diglycidyl ether of dihydroxy-{alpha}-methylstilbene cured with the diamine sulfamilamide. This thermoset has been cured at field strengths up to 18 Tesla.

  13. Magnetic susceptibility of an organosilicon based magnetic fluid in electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Dikanskii, Yu. I.; Gladkikh, D. V.; Kunikin, S. A.; Radionov, A. V.

    2015-02-01

    We have studied peculiarities of the behavior of magnetic susceptibility χ' of an organosilicon based magnetic fluid under the action of an electric field and a combination of electric and magnetic fields. It is established that an external electric field affects the temperature dependence of χ'. The obtained results are related to structural changes in the system—the appearance of a labyrinth structure in the electric field and transformation of this structure under the additional action of a magnetic field.

  14. Chaotic magnetic fields: Particle motion and energization

    SciTech Connect

    Dasgupta, Brahmananda; Ram, Abhay K.; Li, Gang; Li, Xiaocan

    2014-02-11

    Magnetic field line equations correspond to a Hamiltonian dynamical system, so the features of a Hamiltonian systems can easily be adopted for discussing some essential features of magnetic field lines. The integrability of the magnetic field line equations are discussed by various authors and it can be shown that these equations are, in general, not integrable. We demonstrate several examples of realistic chaotic magnetic fields, produced by asymmetric current configurations. Particular examples of chaotic force-free field and non force-free fields are shown. We have studied, for the first time, the motion of a charged particle in chaotic magnetic fields. It is found that the motion of a charged particle in a chaotic magnetic field is not necessarily chaotic. We also showed that charged particles moving in a time-dependent chaotic magnetic field are energized. Such energization processes could play a dominant role in particle energization in several astrophysical environments including solar corona, solar flares and cosmic ray propagation in space.

  15. How do galaxies get their magnetic fields?

    NASA Astrophysics Data System (ADS)

    Beck, Alexander M.

    2016-06-01

    The origin of magnetic fields in high-redshift and present-day galaxies is a long-standing problem. In this talk, we present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova (SN) explosions during the assembly of a protogalaxy self-consistently provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions.Our model explains the origin of strong magnetic fields of μG amplitude within the first starforming protogalactic structures shortly after the first stars have formed.We present cosmological simulations with the GADGET code of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the evolving magnetic field.Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr. Subsequently, the magnetic field strength increases exponentially on timescales of a few ten million years within the innermost regions of the halo.Furthermore, turbulent diffusion, shocks and gas motions transport the magnetic field towards the halo outskirts. At redshift z=0, the entire galactic structures are magnetized and the field amplitude is of the order of a few microG in the center of the halo and nG at the virial radius. Additionally, we analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m^2. Towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m^2. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread leading to a widespread distribution of large intrinsic RMs. Our model for the evolution of galactic magnetic fields solves the joint problem of magnetic field seeding and subsequent amplification and distribution. The

  16. Magnetic field amplification in young galaxies

    NASA Astrophysics Data System (ADS)

    Schober, J.; Schleicher, D. R. G.; Klessen, R. S.

    2013-12-01

    The Universe at present is highly magnetized, with fields of a few 10-5 G and coherence lengths greater than 10 kpc in typical galaxies like the Milky Way. We propose that the magnetic field was already amplified to these values during the formation and the early evolution of galaxies. Turbulence in young galaxies is driven by accretion, as well as by supernova (SN) explosions of the first generation of stars. The small-scale dynamo can convert the turbulent kinetic energy into magnetic energy and amplify very weak primordial seed fields on short timescales. Amplification takes place in two phases: in the kinematic phase the magnetic field grows exponentially, with the largest growth rate on the smallest nonresistive scale. In the following nonlinear phase the magnetic energy is shifted toward larger scales until the dynamo saturates on the turbulent forcing scale. To describe the amplification of the magnetic field quantitatively, we modeled the microphysics in the interstellar medium (ISM) of young galaxies and determined the growth rate of the small-scale dynamo. We estimated the resulting saturation field strengths and dynamo timescales for two turbulent forcing mechanisms: accretion-driven turbulence and SN-driven turbulence. We compare them to the field strength that is reached when only stellar magnetic fields are distributed by SN explosions. We find that the small-scale dynamo is much more efficient in magnetizing the ISM of young galaxies. In the case of accretion-driven turbulence, a magnetic field strength on the order of 10-6 G is reached after a time of 24-270 Myr, while in SN-driven turbulence the dynamo saturates at field strengths of typically 10-5 G after only 4-15 Myr. This is considerably shorter than the Hubble time. Our work can help for understanding why present-day galaxies are highly magnetized.

  17. Measuring exposed magnetic fields of welders in working time.

    PubMed

    Yamaguchi-Sekino, Sachiko; Ojima, Jun; Sekino, Masaki; Hojo, Minoru; Saito, Hiroyuki; Okuno, Tsutomu

    2011-01-01

    The assessment of the occupational electromagnetic field exposure of welders is of great importance, especially in shielded-arc welding, which uses relatively high electric currents of up to several hundred amperes. In the present study, we measured the magnetic field exposure level of welders in the course of working. A 3-axis Hall magnetometer was attached to a subject's wrist in order to place the sensor probe at the closest position to the magnetic source (a cable from the current source). Data was acquired every 5 s from the beginning of the work time. The maximum exposed field was 0.35-3.35 mT (Mean ± SD: 1.55 ± 0.93 mT, N=17) and the average value per day was 0.04-0.12 mT (Mean ± SD: 0.07 ± 0.02 mT, N=17). We also conducted a finite element method-based analysis of human hand tissue for the electromagnetic field dosimetry. In addition, the magnetic field associated with grinders, an air hammer, and a drill using electromagnetic anchorage were measured; however, the magnetic fields were much lower than those generated in the welding process. These results agreed well with the results of the electromagnetic field dosimetry (1.49 mT at the wrist position), and the calculated eddy current (4.28 mA/m(2)) was much lower than the well-known guideline thresholds for electrical nerve or muscular stimulation.

  18. Exoplanet Magnetic Fields and Their Detectability

    NASA Astrophysics Data System (ADS)

    Stanley, S.; Tian, B. Y.; Vilim, R.

    2014-12-01

    The investigation of planetary magnetic fields in our solar system provides a wealth of information on planetary interior structure and dynamics. Satellite magnetic data demonstrates that planetary dynamos can produce a range of magnetic field morphologies and intensities. Numerical dynamo simulations are working towards determining relationships between planetary properties and the resulting magnetic field characteristics. However, with only a handful of planetary dynamos in our solar system, it is challenging to determine specific dependence of magnetic field properties on planetary characteristics. Extrasolar planets therefore provide a unique opportunity by significantly increasing the number of planets for study as well as offering a much larger range of planetary properties to investigate. Although detection of exoplanet magnetic fields is challenging at present, the increasing sophistication of observational tools available to astronomers implies these extrasolar planetary magnetic fields may eventually be detectable. This presentation will discuss potential observational trends for magnetic field strength and morphology for exoplanets based on numerical simulations and interior structure modeling. We will focus on the influence of planetary age, environment, composition and structure.

  19. Bashful ballerina unveiled: Multipole analysis of the coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Virtanen, I.; Mursula, K.

    2012-12-01

    Heliospheric current sheet (HCS) is the continuum of the coronal magnetic equator, dividing the heliospheric magnetic field (HMF) into two sectors (polarities). Because of its wavy structure, the HCS is often called the ballerina skirt. Several studies have proven that the HCS is southward shifted during about three years in the solar declining phase. This persistent phenomenon, called the bashful ballerina, has been verified by geomagnetic indices since 1930s, by OMNI data base since 1960s, by the WSO PFSS model since mid-1970s and by the Ulysses probe measurements during the fast latitude scans in 1994-1995 and 2007. We study here the Wilcox Solar Observatory measurements of the photospheric magnetic field and the PFSS extrapolation of the coronal magnetic field. We show that the quadrupole moment of the photospheric magnetic field, which is important for the HCS asymmetry (bashful ballerina), mainly arises from the difference between northern and southern polar field strengths. According to the WSO data the minimum time quadrupole is mainly due to the difference between the highest northern and southern latitude bins. Related studies imply that the southward shift of the HCS is related to the delayed development of southern coronal holes. We also discuss the suggested connection of the HCS asymmetry to sunspot hemispheric asymmetry.

  20. Interferometric methods for mapping static electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Pozzi, Giulio; Beleggia, Marco; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

    2014-02-01

    The mapping of static electric and magnetic fields using electron probes with a resolution and sensitivity that are sufficient to reveal nanoscale features in materials requires the use of phase-sensitive methods such as the shadow technique, coherent Foucault imaging and the Transport of Intensity Equation. Among these approaches, image-plane off-axis electron holography in the transmission electron microscope has acquired a prominent role thanks to its quantitative capabilities and broad range of applicability. After a brief overview of the main ideas and methods behind field mapping, we focus on theoretical models that form the basis of the quantitative interpretation of electron holographic data. We review the application of electron holography to a variety of samples (including electric fields associated with p-n junctions in semiconductors, quantized magnetic flux in superconductors and magnetization topographies in nanoparticles and other magnetic materials) and electron-optical geometries (including multiple biprism, amplitude and mixed-type set-ups). We conclude by highlighting the emerging perspectives of (i) three-dimensional field mapping using electron holographic tomography and (ii) the model-independent determination of the locations and magnitudes of field sources (electric charges and magnetic dipoles) directly from electron holographic data.

  1. Toxoplasma gondii DNA detection with a magnetic molecular beacon probe

    NASA Astrophysics Data System (ADS)

    Xu, Shichao; Yao, Cuicui; Wei, Shuoming; Zhang, Jimei; Dai, Zhao; Zheng, Guo; Sun, Bo; Han, Qing; Hu, Fei; Zhou, Hongming

    2008-12-01

    Toxoplasma Gondii infection is widespread in humans worldwide and reported infection rates range from 3%-70%, depending on the populations or geographic areas, and it has been recognized as a potential food safety hazard in our daily life. A magnetic molecular beacon probe (mMBP), based on theory of fluorescence resonance energy transfer (FRET), was currently reported to detect Toxoplasma Gondii DNA. Nano-sized Fe3O4 were primarily prepared by coprecipitation method in aqueous phase with NaOH as precipitator, and was used as magnetic core. The qualified coreshell magnetic quantum dots (mQDs), i.e. CdTe(symbol)Fe3O4, were then achieved by layer-by-layer method when mol ratio of Fe3O4/CdTe is 1/3, pH at 6.0, 30 °C, and reactant solution was refluxed for 30 min, the size of mQDs were determined to be 12-15 nm via transmission electron microscopy (TEM). Over 70% overlap between emission spectrum of mQDs and absorbance spectrum of BHQ-2 was observed, this result suggests the synthesized mQDs and BHQ-2 can be utilized as energy donor and energy acceptor, respectively. The sensing probe was fabricated and a stem-loop Toxoplasma Gondii DNA oligonucleotide was labeled with mQDs at the 5' end and BHQ-2 at 3' end, respectively. Target Toxoplasma gondii DNA was detected under conditions of 37 °C, hybridization for 2h, at pH8.0 in Tris-HCl buffer. About 30% recovery of fluorescence intensity was observed via fluorescence spectrum (FS) after the Toxoplasma gondii DNA was added, which suggested that the Toxoplasma Gondii DNA was successfully detected. Specificity investigation of the mMBP indicated that relative low recovery of fluorescence intensity was obtained when the target DNA with one-base pair mismatch was added, this result indicated the high specificity of the sensing probe. Our research simultaneously indicated that mMBP can be conveniently separated from the unhybridized stem-loop DNA and target DNA, which will be meaningful in DNA sensing and purification process.

  2. Physics in Very Strong Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Lai, Dong

    2015-10-01

    This paper provides an introduction to a number of astrophysics problems related to strong magnetic fields. The first part deals with issues related to atoms, condensed matter and high-energy processes in very strong magnetic fields, and how these issues influence various aspects of neutron star astrophysics. The second part deals with classical astrophysical effects of magnetic fields: Even relatively "weak" fields can play a strong role in various astrophysical problems, ranging from stars, accretion disks and outflows, to the formation and merger of compact objects.

  3. Assessing the Structure of Isotropic and Anisotropic Turbulent Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Fatuzzo, Marco; Holden, Lisa; Grayson, Lindsay; Wallace, Kirk

    2016-10-01

    Turbulent magnetic fields permeate our universe, impacting a wide range of astronomical phenomena across all cosmic scales. A clear example is the magnetic field that threads the interstellar medium (ISM), which impacts the motion of cosmic rays through that medium. Understanding the structure of magnetic turbulence within the ISM and how it relates to the physical quantities that characterize it can thus inform our analysis of particle transport within these regions. Toward that end, we probe the structure of magentic turbulence through the use of Lyapunov exponents for a suite of isotropic and nonisotropic Alfvénic turbulence profiles. Our results provide a means of calculating a “turbulence lengthscale” that can then be connected to how cosmic rays propagate through magentically turbulent environments, and we perform such an analysis for molecular cloud environments.

  4. The Protogalactic Origin for Cosmic Magnetic Fields

    NASA Astrophysics Data System (ADS)

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

    1997-05-01

    It is demonstrated that strong magnetic fields are produced from a zero initial magnetic field during the pregalactic era, when the galaxy is first forming. Their development proceeds in three phases. In the first phase, weak magnetic fields are created by the Biermann battery mechanism. During the second phase, results from a numerical simulation make it appear likely that homogenous isotropic Kolmogorov turbulence develops that is associated with gravitational structure formation of galaxies. Assuming that this turbulence is real, then these weak magnetic fields will be amplified to strong magnetic fields by this Kolmogorov turbulence. During this second phase, the magnetic fields reach saturation with the turbulent power, but they are coherent only on the scale of the smallest eddy. During the third phase, which follows this saturation, it is expected that the magnetic field strength will increase to equipartition with the turbulent energy and that the coherence length of the magnetic fields will increase to the scale of the largest turbulent eddy, comparable to the scale of the entire galaxy. The resulting magnetic field represents a galactic magnetic field of primordial origin. No further dynamo action after the galaxy forms is necessary to explain the origin of magnetic fields. However, the magnetic field will certainly be altered by dynamo action once the galaxy and the galactic disk have formed. It is first shown by direct numerical simulations that thermoelectric currents associated with the Biermann battery build the field up from zero to 10-21 G in the regions about to collapse into galaxies, by z ~ 3. For weak fields, in the absence of dissipation, the cyclotron frequency -&b.omega;cyc = eB/mH c and &b.omega;/(1 + χ), where &b.nabla;Xv is the vorticity and χ is the degree of ionization, satisfy the same equations, and initial conditions &b.omega;cyc = &b.omega; = 0, so that, globally, -&b.omega;cyc(r, t) = &b.omega;(r, t)/(1 + χ). The vorticity grows

  5. The Measurement of Magnetic Fields

    ERIC Educational Resources Information Center

    Berridge, H. J. J.

    1973-01-01

    Discusses five experimental methods used by senior high school students to provide an accurate calibration curve of magnet current against the magnetic flux density produced by an electromagnet. Compares the relative merits of the five methods, both as measurements and from an educational viewpoint. (JR)

  6. Magnetic Field Measurements near Mars.

    PubMed

    Smith, E J; Davis, L; Coleman, P J; Jones, D E

    1965-09-10

    During the encounter between Mariner IV and Mars on 14-15 July, no magnetic effect that could be definitely associated with the planet was evident in the magnetometer data. This observation implies that the Martian magnetic dipole moment is, at most, 3 x 10(-4) times that of the earth.

  7. Neptunium Monochalcogenides: Magnetic Hyperfine Fields

    NASA Astrophysics Data System (ADS)

    Troć, R.

    This document is part of subvolume B6bβ`Actinide Monochalcogenides' of Volume 27 `Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III `Condensed Matter'. The volume presents magnetic and related properties of monochalcogenides based on actinides and their solid solutions.

  8. Magnetic fields in noninvasive brain stimulation.

    PubMed

    Vidal-Dourado, Marcos; Conforto, Adriana Bastos; Caboclo, Luis Otávio Sales Ferreira; Scaff, Milberto; Guilhoto, Laura Maria de Figueiredo Ferreira; Yacubian, Elza Márcia Targas

    2014-04-01

    The idea that magnetic fields could be used therapeutically arose 2000 years ago. These therapeutic possibilities were expanded after the discovery of electromagnetic induction by the Englishman Michael Faraday and the American Joseph Henry. In 1896, Arsène d'Arsonval reported his experience with noninvasive brain magnetic stimulation to the scientific French community. In the second half of the 20th century, changing magnetic fields emerged as a noninvasive tool to study the nervous system and to modulate neural function. In 1985, Barker, Jalinous, and Freeston presented transcranial magnetic stimulation, a relatively focal and painless technique. Transcranial magnetic stimulation has been proposed as a clinical neurophysiology tool and as a potential adjuvant treatment for psychiatric and neurologic conditions. This article aims to contextualize the progress of use of magnetic fields in the history of neuroscience and medical sciences, until 1985. PMID:23787954

  9. Magnetic fields in noninvasive brain stimulation.

    PubMed

    Vidal-Dourado, Marcos; Conforto, Adriana Bastos; Caboclo, Luis Otávio Sales Ferreira; Scaff, Milberto; Guilhoto, Laura Maria de Figueiredo Ferreira; Yacubian, Elza Márcia Targas

    2014-04-01

    The idea that magnetic fields could be used therapeutically arose 2000 years ago. These therapeutic possibilities were expanded after the discovery of electromagnetic induction by the Englishman Michael Faraday and the American Joseph Henry. In 1896, Arsène d'Arsonval reported his experience with noninvasive brain magnetic stimulation to the scientific French community. In the second half of the 20th century, changing magnetic fields emerged as a noninvasive tool to study the nervous system and to modulate neural function. In 1985, Barker, Jalinous, and Freeston presented transcranial magnetic stimulation, a relatively focal and painless technique. Transcranial magnetic stimulation has been proposed as a clinical neurophysiology tool and as a potential adjuvant treatment for psychiatric and neurologic conditions. This article aims to contextualize the progress of use of magnetic fields in the history of neuroscience and medical sciences, until 1985.

  10. External-field-free magnetic biosensor

    SciTech Connect

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

    2014-03-24

    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 μl 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.

  11. Decay of Resonaces in Strong Magnetic Field

    NASA Astrophysics Data System (ADS)

    Filip, Peter

    2015-08-01

    We suggest that decay properties (branching ratios) of hadronic resonances may become modified in strong external magnetic field. The behavior of K±*, K0* vector mesons as well as Λ* (1520) and Ξ0* baryonic states is considered in static fields 1013-1015 T. In particular, n = 0 Landau level energy increase of charged particles in the external magnetic field, and the interaction of hadron magnetic moments with the field is taken into account. We suggest that enhanced yield of dileptons and photons from ρ0(770) mesons may occur if strong decay channel ρ0 → π+π- is significantly suppressed. CP - violating π+π- decays of pseudoscalar ηc and η(547) mesons in the magnetic field are discussed, and superpositions of quarkonium states ηc,b and χc,b(nP) with Ψ(nS), ϒ(nS) mesons in the external field are considered.

  12. Simultaneous poloidal measurements using new magnetically driven reciprocating probes in COMPASS

    NASA Astrophysics Data System (ADS)

    Dejarnac, R.; Gunn, J. P.; Dimitrova, M.; Hron, M.; Panek, R.; Pascal, J.-Y.; Saragosti-Chausy, C.; Tamain, P.; the COMPASS team

    2016-03-01

    Particles and heat transport in the scrape-off layer (SOL) of tokamaks is not yet fully understood. COMPASS is a small-size tokamakp where the edge plasma is well diagnosed in view of studying the competition between the parallel and the cross-field transport in the SOL. In order to better characterize SOL dynamics, in particular the poloidal asymmetry of the main parameters' radial profiles, two new in-situ magnetically driven reciprocating manipulators have been recently installed in COMPASS. These manipulators, the so-called pecker probes, are two additional poloidal measurement points to the existing two (vertical and horizontal) reciprocating manipulators. The pecker probes are located at the low field side of COMPASS at ±47.5o with respect to the outer mid-plane and are equipped with identical tunnel probe heads, providing simultaneous measurements of the ion saturation current density Jsat, the electron temperature Te and the parallel Mach number M// with high temporal resolution. In this paper, a detailed description of the pecker probe system in COMPASS is described and first measurements are presented.

  13. Compact low field magnetic resonance imaging magnet: Design and optimization

    NASA Astrophysics Data System (ADS)

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

    2000-03-01

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

  14. Ohm's law for mean magnetic fields

    SciTech Connect

    Boozer, A.H.

    1984-11-01

    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.

  15. ICPP: Scale size of of magnetic turbulence as probed with 30 MeV runaway electrons

    NASA Astrophysics Data System (ADS)

    Jaspers, Roger

    2000-10-01

    This paper reviews results concerning generation, confinement and transport of runaway electrons in the energy range 20-30 MeV in the TEXTOR tokamak. For future fusion reactors, it is of major importance to know the processes of runaway generation and runaway loss after disruptions, because of the potential damage to first wall components. Second, since the runaway electrons are effectively collisionless, their confinement is determined by the magnetic field turbulence. In this way the runaway transport provides a unique opportunity to probe turbulence in the core of a thermonuclear plasma. Runaway electrons above 20 MeV emit synchrotron radiation in the (near) infrared, which can easily be detected by thermographic cameras. This technique is developed and exploited at the TEXTOR-94 tokamak and has resulted in some spectacular results. These include: the experimental evidence of the secondary (`knock-on') runaway generation; the discovery of the runaway snake; the observation of disruption generated runaways; the probing of magnetic turbulence in the core of the plasma in Ohmic and additionally heated plasmas. The paper reviews these results with special emphasis on the subject of probing magnetic turbulence in the core of the plasma. Measurements in the TEXTOR-94 tokamak show that after switching on Neutral Beam Injection, the runaway population decays. The decay only starts with a significant delay, which decreases with increasing NBI heating power. This delay provides direct evidence of the energy dependence of runaway confinement, which is expected if magnetic modes govern the loss of runaway electrons. These observations allow to estimate the mode width δ of the magnetic perturbations:δ smaller than 0.5 cm in Ohmic discharges, increasing to δ=3D 4.4 cm for 0.6 MW NBI power.

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  17. An Extraordinary Magnetic Field Map of Mars

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Acuna, M. H.; Ness, N. F.; Mitchell, D. L.; Lin, R. P.

    2004-01-01

    The Mars Global Surveyor spacecraft has completed two Mars years in nearly circular polar orbit at a nominal altitude of 400 km. The Mars crust is at least an order of magnitude more intensely magnetized than that of the Earth [1], and intriguing in both its global distribution and geometric properties [2,3]. Measurements of the vector magnetic field have been used to map the magnetic field of crustal origin to high accuracy [4]. We present here a new map of the magnetic field with an order of magnitude increased sensitivity to crustal magnetization. The map is assembled from > 2 full years of MGS night-side observations, and uses along-track filtering to greatly reduce noise due to external field variations.

  18. Vector Magnetic Field in Emerging Flux Regions

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Pariat, E.

    A crucial phase in magnetic flux emergence is the rise of magnetic flux tubes through the solar photosphere, which represents a severe transition between the very different environments of the solar interior and corona. Multi-wavelength observations with Flare Genesis, TRACE, SoHO, and more recently with the vector magnetographs at THEMIS and Hida (DST) led to the following conclusions. The fragmented magnetic field in the emergence region - with dipped field lines or bald patches - is directly related with Ellerman bombs, arch filament systems, and overlying coronal loops. Measurements of vector magnetic fields have given evidence that undulating "serpentine" fields are present while magnetic flux tubes cross the photosphere. See the sketch below, and for more detail see Pariat et al. (2004, 2007); Watanabe et al. (2008):

  19. Magnetic field homogeneity perturbations in finite Halbach dipole magnets.

    PubMed

    Turek, Krzysztof; Liszkowski, Piotr

    2014-01-01

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

  20. Ohm's law for mean magnetic fields

    SciTech Connect

    Boozer, A.H.

    1986-05-01

    The magnetic fields associated with plasmas frequently exhibit small amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions it is shown that the effect of MHD fluctuations on a force-free plasma can be represented by one parameter in Ohm's law, which is effectively the coefficient of electric current viscosity.