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Sample records for equatorial magnetic helicity

  1. Equatorially coordinated lanthanide single ion magnets.

    PubMed

    Zhang, Peng; Zhang, Li; Wang, Chao; Xue, Shufang; Lin, Shuang-Yan; Tang, Jinkui

    2014-03-26

    The magnetic relaxation dynamics of low-coordinate Dy(III) and Er(III) complexes, namely three-coordinate ones with an equatorially coordinated triangle geometry and five-coordinate ones with a trigonal bipyramidal geometry, have been exploited for the first time. The three-coordinate Er-based complex is the first equatorially coordinated mononuclear Er-based single-molecule magnet (SMM) corroborating that simple models can effectively direct the design of target SMMs incorporating 4f-elements. PMID:24625001

  2. Conservation of magnetic helicity during plasma relaxation

    SciTech Connect

    Ji, H.; Prager, S.C.; Sarff, J.S.

    1994-07-01

    Decay of the total magnetic helicity during the sawtooth relaxation in the MST Reversed-Field Pinch is much larger than the MHD prediction. However, the helicity decay (3--4%) is smaller than the magnetic energy decay (7--9%), modestly supportive of the helicity conservation hypothesis in Taylor`s relaxation theory. Enhanced fluctuation-induced helicity transport during the relaxation is observed.

  3. Magnetic helicity in emerging solar active regions

    SciTech Connect

    Liu, Y.; Hoeksema, J. T.; Bobra, M.; Hayashi, K.; Sun, X.; Schuck, P. W.

    2014-04-10

    Using vector magnetic field data from the Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory, we study magnetic helicity injection into the corona in emerging active regions (ARs) and examine the hemispheric helicity rule. In every region studied, photospheric shearing motion contributes most of the helicity accumulated in the corona. In a sample of 28 emerging ARs, 17 follow the hemisphere rule (61% ± 18% at a 95% confidence interval). Magnetic helicity and twist in 25 ARs (89% ± 11%) have the same sign. The maximum magnetic twist, which depends on the size of an AR, is inferred in a sample of 23 emerging ARs with a bipolar magnetic field configuration.

  4. Magnetic Helicity in Solar Dynamo Simulations

    NASA Astrophysics Data System (ADS)

    Miesch, Mark; Augustson, Kyle C.; Zhang, Mei

    2015-08-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. Yet, despite its significance, magnetic helicity is often neglected in observational and theoretical studies of solar magnetism. This can be attributed to two factors; First, the calculation of the magnetic helicity is not unique; in general it depends on an electromagnetic guage through the magnetic vector potential. Second, unless it is explicitly calculated as part of the computational algorithm in numerical models, it is not always straightforward to obtain the magnetic vector potential. Here we consider gauge-invariant measures of the magnetic helicity and magnetic helicity flux and we describe how they can be computed from measurable quantities such as the magnetic field, the bulk plasma velocity, and the electrical current density. These measures can be applied to local Cartesian geometries as well as global spherical shells. Here we apply them to two global dynamo simulations, each exhibiting regular magnetic cycles. These include a convective MHD dynamo model and a 3-D Babcock-Leighton dynamo model. Both exhibit patterns of magnetic helicity evolution that reflect the global restructuring of the magnetic field over the

  5. Magnetic Helicity and the Solar Dynamo

    NASA Technical Reports Server (NTRS)

    Canfield, Richard C.

    1997-01-01

    The objective of this investigation is to open a new window into the solar dynamo, convection, and magnetic reconnection through measurement of the helicity density of magnetic fields in the photosphere and tracing of large-scale patterns of magnetic helicity in the corona.

  6. Magnetic Helicity in a Cyclic Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Miesch, Mark S.; Zhang, Mei; Augustson, Kyle C.

    2016-05-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. We investigate the role of magnetic helicity in a convective dynamo model that exhibits regular magnetic cycles. The cycle is marked by coherent bands of toroidal field that persist within the convection zone and that are antisymmetric about the equator. When these toriodal bands interact across the equator, it initiates a global restructuring of the magnetic topology that contributes to the reversal of the dipole moment. Thus, the polar field reversals are preceeded by a brief reversal of the subsurface magnetic helicity. There is some evidence that the Sun may exhibit a similar magnetic helicity reversal prior to its polar field reversals.

  7. The AGS synchrotron with four helical magnets

    SciTech Connect

    Tsoupas N.; Huang, H.; Roser, T.; MacKay, W.W.; Trbojevic, D.

    2012-05-20

    The idea of using two partial helical magnets was applied successfully to the AGS synchrotron to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. The placement of four helical magnets in the AGS ring provides many advantages over the present setup of the AGS which uses two partial helical magnets. First, the symmetric placement of the four helical magnets allows for a better control of the AGS optics with reduced values of the beta functions especially near beam injection, second, the vertical spin direction during beam injection and extraction is closer to vertical, and third, it provides for a larger 'spin tune gap', which allows the vertical and horizontal tunes to be placed, and prevent the horizontal and vertical intrinsic spin resonances of the AGS to occur during the acceleration cycle. Although the same spin gap can be obtained with a single or two partial helices, the required high field strength of a single helix makes its use impractical, and that of the double helix rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare these results with the present setup of the AGS that uses two partial helical magnets.

  8. The AGS with four helical magnets

    SciTech Connect

    Tsoupas, N.; Huang, H.; MacKay, W.W.; Roser, T.; Trbojevic, D.

    2010-02-25

    The idea of using multiple partial helical magnets was applied successfully to the AGS synchrotron, to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. This modification provides many advantages over the present setup of the AGS that uses two partial helical magnets. First, it provides a larger 'spin tune gap' for the placement of the vertical betatron tune of the AGS during acceleration, second, the vertical spin direction during the beam injection and extraction is closer to vertical, third, the symmetric placement of the snakes allows for a better control of the AGS optics, and for reduced values of the beta and eta functions, especially near injection, fourth, the optical properties of the helical magnets also favor the placement of the horizontal betatron tune in the 'spin tune gap', thus eliminating the horizontal spin resonances. In this paper we provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and we compare these results with the present setup of the AGS that uses two partial helical magnets.

  9. On the helicity of open magnetic fields

    SciTech Connect

    Prior, C.; Yeates, A. R.

    2014-06-01

    We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically open. It is demonstrated that, while the magnetic helicity is gauge-dependent, its value in any gauge may be physically interpreted as the average winding number among all pairs of field lines with respect to some orthonormal frame field. In fact, the choice of gauge is equivalent to the choice of reference field in the relative helicity, meaning that the magnetic helicity is no less physically meaningful. We prove that a particular gauge always measures the winding with respect to a fixed frame, and propose that this is normally the best choice. For periodic fields, this choice is equivalent to measuring relative helicity with respect to a potential reference field. However, for aperiodic fields, we show that the potential field can be twisted. We prove by construction that there always exists a possible untwisted reference field.

  10. Primordial magnetic helicity from stochastic electric currents

    NASA Astrophysics Data System (ADS)

    Calzetta, Esteban; Kandus, Alejandra

    2014-04-01

    We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, HM. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point scalar quantum electrodynamics Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle not null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case, the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of HM for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is D=1/2. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case, the fractal dimension is D=0. We finally estimate the intensity of fields induced at the horizon scale of reheating and evolve them until the decoupling of matter and radiation under the hypothesis of the inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation.

  11. Magnetic stripes and skyrmions with helicity reversals.

    PubMed

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-06-01

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion--a nano-sized bundle of noncoplanar spins--that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide-M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom--helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure. PMID:22615354

  12. A Helical Magnet Design for RHIC^*.

    NASA Astrophysics Data System (ADS)

    Willen, E.; Gupta, R.; Kelly, E.; Muratore, J.

    1997-05-01

    Helical dipole magnets are required in a project for the Relativistic Heavy Ion Collider (RHIC) to control and preserve the beam polarization in order to allow the collision of polarized proton beams. The project requires superconducting magnets with a 100 mm coil aperture and a 4 Tesla field in which the field rotates 360 degrees over a distance of 2.4 meters. A design restraint is that the magnets operate at relatively low current (less than 500 amperes) in order to minimize the heat load from the current leads. A magnet has been developed that uses a small diameter superconducting cable wound into helical grooves machined into a thick-walled aluminum cylinder. The design and test results of this prototype magnet will be described. ^*Work supported by the U.S. Department of Energy.

  13. 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.

  14. Novel Design of Superconducting Helical Dipole Magnet

    NASA Astrophysics Data System (ADS)

    Meinke, R.; Senti, M.; Stelzer, G.

    1997-05-01

    Superconducting helical dipole magnets with a nominal field of 4 Tesla are needed for the spin physics program at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The magnets are required to operate at a relatively low current of 400 A since many of these magnets have to be independently controlled. The Advanced Magnet Lab, Inc., in Palm Bay, FL has designed and built two prototype magnets using advanced computer controlled coil winding technology. The AML design is extremely cost effective since it avoids magnet specific tooling despite the required complex coil pattern and any precision machined inserts or spacers. It is the first time an accelerator magnet of this technology has reached a field above 4 Tesla. Results from the prototype testing at BNL are presented.

  15. Absolute magnetic helicity and the cylindrical magnetic field

    NASA Astrophysics Data System (ADS)

    Low, B. C.

    2011-05-01

    The different magnetic helicities conserved under conditions of perfect electrical conductivity are expressions of the fundamental property that every evolving fluid surface conserves its net magnetic flux. This basic hydromagnetic point unifies the well known Eulerian helicities with the Lagrangian helicity defined by the conserved fluxes frozen into a prescribed set of disjoint toroidal tubes of fluid flowing as a permanent partition of the entire fluid [B. C. Low, Astrophys. J. 649, 1064 (2006)]. This unifying theory is constructed from first principles, beginning with an analysis of the Eulerian and Lagrangian descriptions of fluids, separating the ideas of fluid and magnetic-flux tubes and removing the complication of the magnetic vector potential's free gauge from the concept of helicity. The analysis prepares for the construction of a conserved Eulerian helicity, without that gauge complication, to describe a 3D anchored flux in an upright cylindrical domain, this helicity called absolute to distinguish it from the well known relative helicity. In a version of the Chandrasekhar-Kendall representation, the evolving field at any instant is a unique superposition of a writhed, untwisted axial flux with a circulating flux of field lines all closed and unlinked within the cylindrical domain. The absolute helicity is then a flux-weighted sum of the writhe of that axial flux and its mutual linkage with the circulating flux. The absolute helicity is also conserved if the frozen-in field and its domain are continuously deformed by changing the separation between the rigid cylinder-ends with no change of cylinder radius. This hitherto intractable cylindrical construction closes a crucial conceptual gap for the fundamentals to be complete at last. The concluding discussion shows the impact of this development on our understanding of helicity, covering (i) the helicities of wholly contained and anchored fields; (ii) the Eulerian and Lagrangian descriptions of field

  16. THE MAGNETIC ENERGY-HELICITY DIAGRAM OF SOLAR ACTIVE REGIONS

    SciTech Connect

    Tziotziou, Kostas; Georgoulis, Manolis K.; Raouafi, Nour-Eddine

    2012-11-01

    Using a recently proposed nonlinear force-free method designed for single-vector magnetograms of solar active regions, we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 162 vector magnetograms corresponding to 42 different active regions. We find a statistically robust, monotonic correlation between the free magnetic energy and the relative magnetic helicity in the studied regions. This correlation implies that magnetic helicity, in addition to free magnetic energy, may be an essential ingredient for major solar eruptions. Eruptive active regions appear well segregated from non-eruptive ones in both free energy and relative helicity with major (at least M-class) flares occurring in active regions with free energy and relative helicity exceeding 4 Multiplication-Sign 10{sup 31} erg and 2 Multiplication-Sign 10{sup 42} Mx{sup 2}, respectively. The helicity threshold agrees well with estimates of the helicity contents of typical coronal mass ejections.

  17. Study of magnetic transient variations signature at equatorial region

    NASA Astrophysics Data System (ADS)

    Santos, J.; Trivedi, N.; Dutra, S.

    Transient variations in the H magnetic field component of magnetograms at high latitude are a common feature. They are associated with interaction process between solar wind and Earth's magnetic field. Abrupt changes in the solar wind interacting with Earth's magnetic field generate Alfvén and fast mode waves. The Alfvén wave doesn't propagate in the direction perpendicular to the geomagnetic field, so equatorial signatures are probably caused by fast mode waves. On the other hand, complex signatures observed at high latitudes represent a composition of Alfvén and fast mode waves. A second suggested propagation mechanism to low latitudes is the Earth-ionosphere wave-guide. In this work, geomagnetic data from the Brazilian magnetic stations at Belém/Tatuoca (BLM), Eusébio (EUS), Ji-Paraná (JIP), São luis (SLZ) and São Martinho da Serra (SMS) were used to look for equatorial signatures of magnetic transient events. We identified their morphological characteristics and time occurrence distribution. Satellite data (ACE and GOES) were used to see magnetosphere signatures and solar wind and interplanetary magnetic field conditions that increase the probability of occurrence for the equatorial events. Trivedi et al. (2002a) present evidence for corresponding signatures of TCV at Belém, São Luis, and Terezina and other stations under or nearby the equatorial electrojet. The conclusions of Trivedi et al. (2002a) are that equatorial signatures differ greatly from event to event; when the high-latitude transient events exhibited clear, strong, isolated signatures corresponding to TCVs, they generally detected isolated bipolar compressional signatures at geosynchronous orbit and transient impulses in equatorial ground magnetograms; when high-latitude events were quasiperiodic, weaker, spatially limited, or did not exhibit clear TCV signatures the equatorial signatures are difficult to identify; the equatorial signatures cannot be simply result from remote

  18. Faraday signature of magnetic helicity from reduced depolarization

    SciTech Connect

    Brandenburg, Axel; Stepanov, Rodion

    2014-05-10

    Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows for the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. Similar polarization peaks can tentatively also be identified for the bi-helical magnetic fields that are generated self-consistently by a dynamo from helically forced turbulence, even though the magnetic energy spectrum is then continuous. Finally, we discuss the possibility of detecting magnetic fields with helical and non-helical properties in external galaxies using the Square Kilometre Array.

  19. Magnetic design constraints of helical solenoids

    SciTech Connect

    Lopes, M. L.; Krave, S. T.; Tompkins, J. C.; Yonehara, K.; Flanagan, G.; Kahn, S. A.; Melconian, K.

    2015-01-30

    Helical solenoids have been proposed as an option for a Helical Cooling Channel for muons in a proposed Muon Collider. Helical solenoids can provide the required three main field components: solenoidal, helical dipole, and a helical gradient. In general terms, the last two are a function of many geometric parameters: coil aperture, coil radial and longitudinal dimensions, helix period and orbit radius. In this paper, we present design studies of a Helical Solenoid, addressing the geometric tunability limits and auxiliary correction system.

  20. Helicity of the Solar Magnetic Field

    NASA Astrophysics Data System (ADS)

    Tiwari, Sanjiv Kumar

    2009-11-01

    Magnetic helicity is a physical quantity that measures the degree of linkages and twistedness in the field lines. It is given by a volume integral over the scalar product of magnetic field B and its vector potential A. Direct computation of magnetic helicity in the solar atmosphere is not possible due to two reasons. First, we do not have the observations at different heights in the solar atmosphere to compute the volume integral. Second, the vector potential A is non-unique owing to gauge variance. Many researchers incorrectly inferred twist, a component of magnetic helicity, from the force-free parameter α. We clarified the physical meaning of α and its relation with the magnetic helicity. Also, a direct method is proposed for the computation of global α values of sunspots. An analytical bipole was generated to study the effect of polarimetric noise on the estimation of various magnetic parameters. We find that the effect of polarimetric noise, present in the recent vector magnetograms e.g., from Hinode (Solar Optical Telescope/Spectro- Polarimeter (SOT/SP)), on the magnetic parameters like α and magnetic energy, is negligible. We examined the fine structures of local current and α in the sunspots. Local α patches of opposite signs are present in the umbra of each sunspot. The amplitude of the spatial variation of local α in the umbra is typically of the order of the global α of the sunspot. We find that the local α and current are distributed as alternately positive and negative filaments in the penumbra. The amplitude of azimuthal variation of the local α in the penumbra is approximately an order of magnitude larger than that in the umbra. The contributions of the local positive and negative currents and α in the penumbra cancel each other giving almost no contribution for their global values for whole sunspot. We have introduced the concept of signed shear angle (SSA) for sunspots and establish its importance for non force

  1. Evolution of field line helicity during magnetic reconnection

    SciTech Connect

    Russell, A. J. B. Hornig, G.; Wilmot-Smith, A. L.; Yeates, A. R.

    2015-03-15

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  2. JOINT INVERSE CASCADE OF MAGNETIC ENERGY AND MAGNETIC HELICITY IN MHD TURBULENCE

    SciTech Connect

    Stepanov, R.; Frick, P.; Mizeva, I.

    2015-01-10

    We show that oppositely directed fluxes of energy and magnetic helicity coexist in the inertial range in fully developed magnetohydrodynamic (MHD) turbulence with small-scale sources of magnetic helicity. Using a helical shell model of MHD turbulence, we study the high Reynolds number MHD turbulence for helicity injection at a scale that is much smaller than the scale of energy injection. In a short range of scales larger than the forcing scale of magnetic helicity, a bottleneck-like effect appears, which results in a local reduction of the spectral slope. The slope changes in a domain with a high level of relative magnetic helicity, which determines that part of the magnetic energy is related to the helical modes at a given scale. If the relative helicity approaches unity, the spectral slope tends to –3/2. We show that this energy pileup is caused by an inverse cascade of magnetic energy associated with the magnetic helicity. This negative energy flux is the contribution of the pure magnetic-to-magnetic energy transfer, which vanishes in the non-helical limit. In the context of astrophysical dynamos, our results indicate that a large-scale dynamo can be affected by the magnetic helicity generated at small scales. The kinetic helicity, in particular, is not involved in the process at all. An interesting finding is that an inverse cascade of magnetic energy can be provided by a small-scale source of magnetic helicity fluctuations without a mean injection of magnetic helicity.

  3. CURRENT HELICITY OF ACTIVE REGIONS AS A TRACER OF LARGE-SCALE SOLAR MAGNETIC HELICITY

    SciTech Connect

    Zhang, H.; Gao, Y.; Xu, H.; Moss, D.; Kleeorin, N.; Rogachevskii, I.; Kuzanyan, K.; Sokoloff, D.

    2012-05-20

    We demonstrate that the current helicity observed in solar active regions traces the magnetic helicity of the large-scale dynamo generated field. We use an advanced two-dimensional mean-field dynamo model with dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic two-dimensional mean-field dynamo model with simple algebraic alpha-quenching only. Using these numerical models we obtained butterfly diagrams both for the small-scale current helicity and also for the large-scale magnetic helicity, and compared them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by -A {center_dot} B evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here B and A are, respectively, the dynamo generated mean magnetic field and its vector potential. A theoretical interpretation of these results is given.

  4. The magnetic helicity spectrum from solar vector magnetograms

    NASA Astrophysics Data System (ADS)

    Brandenburg, Axel; Zhang, Hongqi; Sokoloff, Dmitry

    2016-05-01

    The gauge-invariant (or relative) magnetic helicity is often measured to characterize the degree of magnetic complexity of active regions. However, magnetic helicity is expected to have different signs on different length scales that can be identified with the large- and small-scale fields used in dynamo theory. To address this, it is important to determine magnetic helicity spectra as functions of wavenumber. These spectra are defined such that the integral over all wavenumbers gives the usual magnetic helicity density in a particular patch of interest. Using vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory for active region NOAA 11515, which was on the southern hemisphere, we show that the magnetic helicity spectrum has positive sign on scales below 30 Mm, but negative sign on larger scales. This active region was rather complex and its magnetic helicity was within 26% of its theoretical maximum value. This is much more than that of NOAA 11158, which was also rather complex, but only within 5% of its theoretical maximum value. Since the contribution of larger length scales turned out to be important in the case of NOAA 11515, its total magnetic helicity is dominated by the negative values from large length scales, which explains the unusual sign for the southern hemisphere. Measuring magnetic helicity spectra with DKIST may become an important tool to learn about the workings of the underlying dynamo.

  5. 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.

  6. Helical dipole magnets for polarized protons in RHIC

    SciTech Connect

    Syphers, M.; Courant, E.; Fischer, W.

    1997-07-01

    Superconducting helical dipole magnets will be used in the Brookhaven Relativistic Heavy Ion Collider (RHIC) to maintain polarization of proton beams and to perform localized spin rotations at the two major experimental detector regions. Requirements for the helical dipole system are discussed, and magnet prototype work is reported.

  7. A Half Century of Magnetic Helicity in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Bieber, J. W.

    2015-12-01

    Using NASA's "OMNI" dataset, this work presents observations of the net magnetic helicity and the normalized helicity spectrum at 1 AU over the period 1965 - 2014. Past studies (1,2) reported that the helicity at large scales has a definite dominant sign organized with respect to the heliospheric current sheet, with negative helicities occurring north of the current sheet, and positive helicities south. The present study confirms this pattern and extends it by more than two solar cycles and past the most recent solar maximum. Particle scattering by turbulence with finite magnetic helicity is one of only two known particle transport mechanisms that are sensitive to particle charge sign and magnetic field polarity. Implications to cosmic ray transport will be discussed. References: (1) Bieber, Evenson, and Matthaeus, Geophys. Res. Lett. , Vol 14, p 864, 1987. (2) Smith and Bieber, Proc. 23rd Internat. Cosmic Ray Conf. (Calgary), Vol 3, p 493, 1993.

  8. Determining How Magnetic Helicity Injection Really Works

    SciTech Connect

    Paul M. Bellan

    2001-10-09

    OAK-B135 The goal of the Caltech program is to determine how helicity injection works by investigating the actual dynamics and topological evolution associated with magnetic relaxation. A new coaxial helicity injection source has been constructed and brought into operation. The key feature of this source is that it has maximum geometric simplicity. Besides being important for fusion research, this work also has astrophysical implications. Photos obtained using high-speed cameras show a clear sequence of events in the formation process. In particular, they show initial merging/reconnection processes, jet-like expansion, kinking, and separation of the plasma from the source. Various diagnostics have been developed, including laser induced fluorescence and soft x-ray detection using high speed diodes. Gas valves have been improved and a patent disclosure relating to puffed gas valves has been filed. Presentations on this work have been given in the form of invited talks at several university physics departments that were previously unfamiliar with laboratory plasma experiments.

  9. Small-Scale Magnetic Reconnection at Equatorial Coronal Hole Boundaries

    NASA Astrophysics Data System (ADS)

    Lamb, Derek; DeForest, C. E.

    2011-05-01

    Coronal holes have long been known to be the source of the fast solar wind at both high and low latitudes. The equatorial extensions of polar coronal holes have long been assumed to have substantial magnetic reconnection at their boundaries, because they rotate more rigidly than the underlying photosphere. However, evidence for this reconnection has been sparse until very recently. We present some evidence that reconnection due to the evolution of small-scale magnetic fields may be sufficient to drive coronal hole boundary evolution. We hypothesize that a bias in the direction of that reconnection is sufficient to give equatorial coronal holes their rigid rotation. We discuss the prospects for investigating this using FLUX, a reconnection-controlled coronal MHD simulation framework. This work was funded by the NASA SHP-GI program.

  10. SMART Observation of Magnetic Helicity in Solar Filaments

    NASA Astrophysics Data System (ADS)

    Hagino, M.; Kitai, R.; Shibata, K.

    2006-08-01

    We examined the magnetic helicity of solar filaments from their structure in the chromosphere and corona. The H-alpha telescope of the Solar Magnetic Activity Research Telescope (SMART) observed 239 intermediate filaments from 2005 July 1 to 2006 May 15. The intermediate filament usually locates between two active regions. Using these images, we identified the filament spine and its barbs, and determined the chromospheric filament helicity from the mean angle between each barbs and a spine. We found that 71% (78 of 110) of intermediate filaments in the northern hemisphere are negative helicity and 67% (87 of 129) of filaments in the southern hemisphere are positive, which agreed with the well-known hemispheric tendency of the magnetic helicity. Additionally, we studied the coronal helicity of intermediate filaments. The coronal filament helicity is defined as the crossing angle of threads formed a filament. The helicity pattern of coronal filaments obtained with EIT/SOHO 171A also shows the helicity hemispheric tendency. Namely, 65% (71 of 110) of coronal filaments in the northern hemisphere exhibit negative helicity and the 65% (84 of 129) of filaments in the southern hemisphere show negative helicity. These data were observed in the same day with the SMART H-alpha data. Moreover, we found 12 filament eruptions in our data. The 7 of 12 filaments show the clear opposite sign of the hemispheric tendency of the magnetic helicity. The helicity seems to be change during temporal evolution. This results suggest that filament instability may be driven by the opposite sign helicity injection from the foot point of the barb.

  11. Scale Dependence of Magnetic Helicity in the Solar Wind

    NASA Technical Reports Server (NTRS)

    Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L.

    2011-01-01

    We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k approximately equal to 2AU(sup -1) (or frequency nu approximately equal to 2 microHz) at distances below 2.8AU and at k approximately equal to 30AU(sup -1) (or nu approximately equal to 25 microHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10(sup 45) Mx(sup 2) cycle(sup -1) at large scales and to a three times lower value at smaller scales.

  12. SCALE DEPENDENCE OF MAGNETIC HELICITY IN THE SOLAR WIND

    SciTech Connect

    Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L. E-mail: kandu@iucaa.ernet.in E-mail: melvyn.l.goldstein@nasa.gov

    2011-06-10

    We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k {approx} 2 AU{sup -1} (or frequency {nu} {approx} 2 {mu}Hz) at distances below 2.8 AU and at k {approx} 30 AU{sup -1} (or {nu} {approx} 25 {mu}Hz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10{sup 45} Mx{sup 2} cycle{sup -1} at large scales and to a three times lower value at smaller scales.

  13. Decay of magnetic helicity producing polarized Alfven waves

    SciTech Connect

    Yoshida, Z.; Mahajan, S.M.

    1994-02-01

    When a super-Alfvenic electron beam propagates along an ambient magnetic field, the left-hand circularly polarized Alfven wave is Cherenkov-emitted (two stream instability). This instability results in a spontaneous conversion of the background plasma helicity to the wave helicity. The background helicity induces a frequency (energy) shift in the eigenmodes, which changes the critical velocity for Cherenkov emission, and it becomes possible for a sub-Alfvenic electron beam to excite a nonsingular Alfven mode.

  14. Near-equatorial magnetic field of the photosphere

    NASA Astrophysics Data System (ADS)

    Vernova, Elena; Tyasto, Marta; Baranov, Dmitrii

    2016-04-01

    The heliolatitude distribution of magnetic field groups of different strength was studied on the basis of the synoptic maps of NSO Kitt Peak (1976-2003). The analysis of the synoptic maps averaged over 3 solar cycles allowed to distinguish four typical groups of magnetic fields: B = 0 - 5 G; B = 5 - 15 G; B = 15 - 50 G and B > 50 G. It is shown that there exists a definite relation between the strength of the magnetic field and its latitudinal localization. The time-dependence is studied for different groups of magnetic fields. The fields of different polarity are considered separately for the North and the South solar hemispheres. A special attention is given to the weakest magnetic fields (B = 0 - 5 G) which are localized near the equator (latitudes ± 5°) and in the interval 40° - 60° in each of the hemispheres. For the near-equatorial region the weakest fields in the North and the South hemispheres change synchronously and are approximately in anti-phase with the Wolf numbers. On the contrary the stronger fields (B = 5 - 10 G and higher) change in the phase with the solar cycle. Thus the magnetic field strength of the 5 G value represents the threshold below which the time-course of the magnetic field is in anti-phase with the solar cycle, while above 5 G it changes in the phase with the solar cycle. It should be noted that in the near-equatorial region the fields of the same sign in the North and the South hemispheres change almost synchronously, while the relation between the fields of the opposite signs in one hemisphere is much less pronounced. This relation differs sharply from the case of strong magnetic fields in the sunspot zone where a strong correlation is observed for the magnetic fields of opposite sign within the same hemisphere. The obtained results allow to conclude that the weak magnetic fields of the near-equatorial region of the Sun are not just the "wings" of the magnetic field distribution of the sunspot zone, but represent a separate

  15. Josephson junction through a disordered topological insulator with helical magnetization

    NASA Astrophysics Data System (ADS)

    Zyuzin, Alexander; Alidoust, Mohammad; Loss, Daniel

    2016-06-01

    We study supercurrent and proximity vortices in a Josephson junction made of disordered surface states of a three-dimensional topological insulator with a proximity induced in-plane helical magnetization. In a regime where the rotation period of helical magnetization is larger than the junction width, we find supercurrent 0 -π crossovers as a function of junction thickness, magnetization strength, and parameters inherent to the helical modulation and surface states. The supercurrent reversals are associated with proximity induced vortices, nucleated along the junction width, where the number of vortices and their locations can be manipulated by means of the superconducting phase difference and the parameters mentioned above.

  16. Determining how magnetic helicity injection really works. Annual progress report

    SciTech Connect

    Bellan, P.M.

    1998-10-21

    Magnetic helicity injection is the essential process underlying both spheromak formation and helicity injection toroidal current drive in tokamaks (e.g., HIT and NSTX). The dynamical details of the helicity injection process are poorly understood because existing models avoid a dynamic description. In particular, Taylor relaxation, the main model motivating helicity injection efforts, is an argument that predicts the state to which a turbulent magnetic configuration relaxes after all dynamics are over. The goal of the Caltech experiment is to investigate the actual dynamics and topological evolution associated with relaxation and so determine how helicity injection really works. Although the global relaxation model (i.e., Taylor model) typically invokes axisymmetry, simple physical arguments (Cowling`s theorem) show that the detailed dynamics must involve topologically complex, non-axisymmetric processes. Progress for this project is given here.

  17. Nonlinear stability of magnetic islands in a rotating helical plasma

    SciTech Connect

    Nishimura, S.; Toda, S.; Narushima, Y.; Yagi, M.

    2012-12-15

    Coexistence of the forced magnetic reconnection by a resonant magnetic perturbation (RMP) and the curvature-driven tearing mode is investigated in a helical (stellarator) plasma rotated by helical trapped particle-induced neoclassical flows. A set of Rutherford-type equations of rotating magnetic islands and a poloidal flow evolution equation is revisited. Using the model, analytical expressions of criteria of spontaneous shrinkage (self-healing) of magnetic islands and sudden growth of locked magnetic islands (penetration of RMP) are obtained, where nonlinear saturation states of islands show bifurcation structures and hysteresis characteristics. Considering radial profile of poloidal flows across magnetic islands, it is found that the self-healing is driven by neoclassical viscosity even in the absence of micro-turbulence-induced anomalous viscosity. Effects of unfavorable curvature in stellarators are found to modify the critical values. The scalings of criteria are consistent with low-{beta} experiments in the large helical device.

  18. The Effects of Spatial Smoothing on Solar Magnetic Helicity and the Hemispheric Helicity Sign Rule

    NASA Astrophysics Data System (ADS)

    Koch Ocker, Stella; Petrie, Gordon

    2016-05-01

    The hemispheric sign rule for solar magnetic helicity, which states that negative/positive helicity occurs preferentially in the northern/southern hemisphere, provides clues to the causes of twisted, flaring magnetic fields. However, previous studies on the hemisphere rule may have been significantly affected by seeing from atmospheric turbulent motions. Using Hinode/SOT-SP data spanning from 2006 to 2012, we studied the effects of two important data processing steps that imitate the effects of atmospheric seeing: noise reduction by ignoring pixel values that are weaker than the estimated noise threshold, and Gaussian spatial smoothing. We applied these processing techniques to the helicity distribution maps for active regions NOAA 11158 and NOAA 11243, along with the average helicities of 36 active regions, in order to imitate and understand the effects of seeing from atmospheric turbulence. We found that rather than changing trends in the helicity distributions, Gaussian smoothing and noise reduction enhanced existing trends by pushing outliers towards the mean or removing them altogether. We also found that, when separated for weak and strong magnetic fields, the average helicities of the 36 active regions conformed to the hemisphere rule for weak field helicities and breached the rule for strong field helicities. In general, we found that data processing did not affect whether the hemisphere rule held for data taken from space-based instruments, and thus that seeing from atmospheric turbulence did not significantly affect previous studies' ground-based results on the hemisphere rule. This work was carried out through the National Solar Observatory Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation (NSF). The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the NSF.

  19. Resonant Landau-Zener transitions in a helical magnetic field

    NASA Astrophysics Data System (ADS)

    Wójcik, P.; Adamowski, J.; Wołoszyn, M.; Spisak, B. J.

    2015-06-01

    Spin-dependent electron transport has been studied in magnetic semiconductor waveguides (nanowires) in the helical magnetic field. We have shown that—apart from the well-known conductance dip located at the magnetic field equal to the helical-field amplitude Bh—the additional conductance dips (with zero conductance) appear at a magnetic field different from Bh. This effect occurring in the non-adiabatic regime is explained as resulting from the resonant Landau-Zener transitions between the spin-split subbands.

  20. Spectral Study of the Equatorial Electric and Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kelley, M. C.; Rothman, R.; Nicolls, M. J.

    2007-05-01

    We report on the spectral analysis of four years of daytime electric and magnetic field data obtained near the magnetic equator. The former were obtained using the JULIA radar system at the Jicamarca Radio Observatory using the so-called 150 km echo, which can be used reliably to determine the zonal electric field component during daytime. The magnetic field data were obtained using magnetometers located at Jicamarca and Piura in Peru. Due to the nighttime data gap, we can study variations with periods longer than two days and shorter than eight hours. Our goal for the longer periods is to study the variability of atmospheric drivers of the equatorial electrojet. This is straightforward for the electric field, but requires subtracting the ring current and other external effects from the magnetic field data. This is done by using the Gonzales/Anderson technique and employing the two magnetic field measurements. The electrojet strength decreased almost linearly over the four-year period as the solar cycle wound down. Spectral analysis reveals a clear semi-annual peak with maxima at the equinoxes and a secondary peak with a period of fourteen days. The latter seems to indicate that the lunar gravitational tide adds constructively to the semi-diurnal solar thermal tide. At higher frequencies the data must be parsed according to magnetic activity and solar wind conditions due to the importance of penetrating electric fields from the solar wind, and will be presented in this format.

  1. Magnetic helicity transport in the advective gauge family

    SciTech Connect

    Candelaresi, Simon; Brandenburg, Axel; Hubbard, Alexander; Mitra, Dhrubaditya

    2011-01-15

    Magnetic helicity fluxes are investigated in a family of gauges in which the contribution from ideal magnetohydrodynamics takes the form of a purely advective flux. Numerical simulations of magnetohydrodynamic turbulence in this advective gauge family exhibit instabilities triggered by the build-up of unphysical irrotational contributions to the magnetic vector potential. As a remedy, the vector potential is evolved in a numerically well behaved gauge, from which the advective vector potential is obtained by a gauge transformation. In the kinematic regime, the magnetic helicity density evolves similarly to a passive scalar when resistivity is small and turbulent mixing is mild, i.e., when the fluid Reynolds number is not too large. In the dynamical regime, resistive contributions to the magnetic helicity flux in the advective gauge are found to be significant owing to the development of small length scales in the irrotational part of the magnetic vector potential.

  2. MAGNETIC HELICITY AND ENERGY SPECTRA OF A SOLAR ACTIVE REGION

    SciTech Connect

    Zhang, Hongqi; Brandenburg, Axel; Sokoloff, D. D.

    2014-04-01

    We compute for the first time the magnetic helicity and energy spectra of the solar active region NOAA 11158 during 2011 February 11-15 at 20° southern heliographic latitude using observational photospheric vector magnetograms. We adopt the isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field. The sign of the magnetic helicity turns out to be predominantly positive at all wavenumbers. This sign is consistent with what is theoretically expected for the southern hemisphere. The magnetic helicity normalized to its theoretical maximum value, here referred to as relative helicity, is around 4% and strongest at intermediate wavenumbers of k ≈ 0.4 Mm{sup –1}, corresponding to a scale of 2π/k ≈ 16 Mm. The same sign and a similar value are also found for the relative current helicity evaluated in real space based on the vertical components of magnetic field and current density. The modulus of the magnetic helicity spectrum shows a k {sup –11/3} power law at large wavenumbers, which implies a k {sup –5/3} spectrum for the modulus of the current helicity. A k {sup –5/3} spectrum is also obtained for the magnetic energy. The energy spectra evaluated separately from the horizontal and vertical fields agree for wavenumbers below 3 Mm{sup –1}, corresponding to scales above 2 Mm. This gives some justification to our assumption of isotropy and places limits resulting from possible instrumental artifacts at small scales.

  3. Magnetic Helicity Reversals in a Cyclic Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Miesch, Mark S.; Zhang, Mei; Augustson, Kyle C.

    2016-06-01

    We investigate the role of magnetic helicity in promoting cyclic magnetic activity in a global, 3D, magnetohydrodynamic (MHD) simulation of a convective dynamo. This simulation is characterized by coherent bands of toroidal field that exist within the convection zone, with opposite polarities in the northern hemisphere (NH) and southern hemisphere (SH). Throughout most of the cycle, the magnetic helicity in these bands is negative in the NH and positive in the SH. However, during the declining phase of each cycle, this hemispheric rule reverses. We attribute this to a global restructuring of the magnetic topology that is induced by the interaction of the bands across the equator. This band interaction appears to be ultimately responsible for, or at least associated with, the decay and subsequent reversal of both the toroidal bands and the polar fields. We briefly discuss the implications of these results within the context of solar observations, which also show some potential evidence for toroidal band interactions and helicity reversals.

  4. Particle acceleration in helical magnetic fields in the corona

    NASA Astrophysics Data System (ADS)

    Gordovskyy, Mykola; Browning, Philippa; Bareford, Michael; Pinto, Rui; Kontar, Eduard; Bian, Nicolas

    2014-05-01

    Twisted magnetic fields should be ubiquitous in the solar corona. Emerging twisted ropes as well as complex photospheric motions provide continuous influx of the magnetic helicity. Twisted coronal fields, in turn, contain excess magnetic energy, which can be released, causing solar flares and other explosive phenomena. It has been shown recently, that reconnection in helical magnetic structures results in particle acceleration distributed within large volume, including the lower corona and chromosphere. Hence, the magnetic reconnection and particle acceleration scenario involving magnetic helicity can be a viable alternative to the standard flare model, where particles are accelerated in a small volume located in the upper corona. We discuss our recent results on the energy release and particle acceleration during magnetic reconnection in twisted coronal loops. Evolution of various helical structures is described in terms of resistive MHD, including heat conduction and radiation. We consider the effects of field topology and photospheric motions on the energy accumulation and release. In particular, we focus on scenarios with continuous helicity injection, leading to recurrent explosive events. Using the obtained MHD models, ion and electron acceleration is investigated, taking into account Coulomb collisions. We derive time-dependent energy spectra and spatial distribution for these species, and calculate resulting non-thermal radiation intensities. Based on the developed numerical models, we investigate observational implications of particle acceleration in helical magnetic structures. Thus, we compare temporal variations of thermal and non-thermal emission in different configurations. Furthermore, we consider spatial distributions of the thermal EUV and X-ray emission and non-thermal X-ray emission and compare them with observational data.

  5. Helical Dipole Magnets for Polarized Protons in RHIC

    NASA Astrophysics Data System (ADS)

    Syphers, M.; Courant, E.; Fischer, W.; Luccio, A.; Mariam, F.; Peggs, S.; Pilat, F.; Roser, T.; Tepikian, S.; Tsoupas, N.; Willen, E.; Katayama, T.; Hatanaka, K.; Kawaguchi, T.; Okamura, M.; Tominaka, T.; Wu, H.; Ptitsin, V.; Shatunov, Y.

    1997-05-01

    The Brookhaven Relativistic Heavy Ion Collider (RHIC) will be able to support experiments using polarized proton beams. Siberian Snakes are used to maintain polarization in this high energy superconducting collider. To make efficient use of available space while taking advantage of high field superconducting magnets, 4 Tesla helical dipole magnets will be used. These magnets generate a central dipole field in which the field direction rotates through 360^circ about the longitudinal axis over the length of the device. An arrangement of four such magnets can produce the desired change in the spin direction while keeping the proton orbit outside of the ``Snake'' unaltered. Similar magnet arrangements will be used to produce longitudinal polarization at the two major interaction points in RHIC. The basic requirements and layout of these magnets are described, as well as tolerances on field quality and integrated field strengths. First results of tests of prototype helical magnets will be discussed.

  6. Configuration of Jupiter's magnetic tail and equatorial current sheet

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Burlaga, L. F.

    1981-01-01

    Recent research reports by Behannon et al. (1981) and Connerney et al. (1981) are summarized. It is noted that the analysis made of the detailed neutral sheet crossings by the minimum variance method shows a consistent result with regard to the orientation of the neutral sheet in the magnetic tail as a two-dimensional surface rocking back and forth about the Jupiter sun-line as the rotation of the planet leads to a precession of the tilted dipole magnetic axis. The occurrence of neutral sheet crossings is found not to be consistent with any of the axially symmetric theoretical models proposed earlier on the basis of the 1974 Pioneer 10 observations. It is noted that a simple nonaxially symmetric model has been developed on the basis of the Voyager results which indicates the strong control upon orientation by the interaction of the solar wind with the Jovian magnetosphere. The model is described as simple because it improves the fit of theory to observation but uses fewer parameters. A quantitative model of the magnetodisc equatorial current sheet has been developed for the inner magnetosphere region which matches well the in-situ magnetic field observations.

  7. Electric Control of Spin Helicity in a Magnetic Ferroelectric

    SciTech Connect

    Yamasaki, Y.; Goto, T.; Sagayama, H.; Matsuura, M.; Hirota, K.; Arima, T.; Tokura, Y.

    2007-04-06

    Magnetic ferroelectrics or multiferroics, which are currently extensively explored, may provide a good arena to realize a novel magnetoelectric function. Here we demonstrate the genuine electric control of the spiral magnetic structure in one such magnetic ferroelectric, TbMnO{sub 3}. A spin-polarized neutron scattering experiment clearly shows that the spin helicity, clockwise or counterclockwise, is controlled by the direction of spontaneous polarization and hence by the polarity of the small electric field applied on cooling.

  8. Helical cosmological magnetic fields from extra-dimensions

    NASA Astrophysics Data System (ADS)

    Atmjeet, Kumar; Seshadri, T. R.; Subramanian, Kandaswamy

    2015-05-01

    We study the inflationary generation of helical cosmological magnetic fields in a higher-dimensional generalization of the electromagnetic theory. For this purpose, we also include a parity breaking piece to the electromagnetic action. The evolution of an extra-dimensional scale factor allows the breaking of conformal invariance of the effective electromagnetic action in 1 +3 dimensions required for such generation. Analytical solutions for the vector potential can be obtained in terms of Coulomb wave-functions for some special cases. We also present numerical solutions for the vector potential evolution in more general cases. In the presence of a higher-dimensional cosmological constant there exist solutions for the scale factors in which both normal and extra dimensional space either inflate or deflate simultaneously with the same rate. In such a scenario, with the number of extra dimensions D =4 , a scale invariant spectrum of helical magnetic field is obtained. The net helicity arises, as one helical mode comes to dominate over the other at the superhorizon scales. A magnetic field strength of the order of 10-9 G can be obtained for the inflationary scale H ≃1 0-3 Mpl . Weaker fields will be generated for lower scales of inflation. Magnetic fields generated in this model respects the bounds on magnetic fields by Planck and γ -ray observations (i.e., 10-16 G

  9. Injection of magnetic flux and helicity in the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Pariat, E.

    2006-09-01

    This thesis is related to the mechanisms of emergence into the solar atmosphere, of two quantities playing key roles in solar activity: magnetic flux and magnetic helicity. Helicity, which is a topological measure of twist and shear, is believed to be a conserved quantity for solar conditions, in the frame of magnetohydrodynamics (MHD). A crucial phase in the emergence process of these quantities, which are generated and amplified in the solar interior, are their injection through the solar photosphere, the transition region between the solar interior and atmosphere. The first part of my work provided new answers to questions unsolved by the classical scenario of emergence. I have analyzed multi-wavelength observations (FGE, TRACE, SoHO, THEMIS) of an emerging active region. I demonstrated that magnetic flux tubes emerge with a flat undulated shape and that small scale magnetic reconnection events, are necessary to this emergence process. Then, using a 3D MHD numerical simulation, I studied the mechanism of magnetic reconnection and in particular the natural formation of current layers where regions of strong variations of magnetic connectivity, called quasi-separatrix layers, are present. Finally, I demonstrated that the classical definition of helicity flux density is biased and proposed a more accurate definition. I applied my new definition to observations of active regions and showed that the photospheric injection pattern of magnetic helicity is unipolar and homogenous. This study allows to link the generation of helicity in the solar atmosphere, its injection and its distribution in the solar corona and its ejection in the interplanetary medium.

  10. Rashba Torque Driven Domain Wall Motion in Magnetic Helices

    NASA Astrophysics Data System (ADS)

    Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Yershov, Kostiantyn V.; Makarov, Denys; Gaididei, Yuri

    2016-03-01

    Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii–Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii–Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii–Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.

  11. Magnetic clouds, helicity conservation, and intrinsic scale flux ropes

    NASA Technical Reports Server (NTRS)

    Kumar, A.; Rust, D. M.

    1995-01-01

    An intrinsic-scale flux-rope model for interplanetary magnetic clouds, incorporating conservation of magnetic helicity, flux and mass is found to adequately explain clouds' average thermodynamic and magnetic properties. In spite their continuous expansion as they balloon into interplanetary space, magnetic clouds maintain high temperatures. This is shown to be due to magnetic energy dissipation. The temperature of an expanding cloud is shown to pass through a maximum above its starting temperature if the initial plasma beta in the cloud is less than 2/3. Excess magnetic pressure inside the cloud is not an important driver of the expansion as it is almost balanced by the tension in the helical field lines. It is conservation of magnetic helicity and flux that requires that clouds expand radially as they move away from the Sun. Comparison with published data shows good agreement between measured cloud properties and theory. Parameters determined from theoretical fits to the data, when extended back to the Sun, are consistent with the origin of interplanetary magnetic clouds in solar filament eruptions. A possible extension of the heating mechanism discussed here to heating of the solar corona is discussed.

  12. Rashba Torque Driven Domain Wall Motion in Magnetic Helices.

    PubMed

    Pylypovskyi, Oleksandr V; Sheka, Denis D; Kravchuk, Volodymyr P; Yershov, Kostiantyn V; Makarov, Denys; Gaididei, Yuri

    2016-01-01

    Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii-Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii-Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii-Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism. PMID:27008975

  13. Rashba Torque Driven Domain Wall Motion in Magnetic Helices

    PubMed Central

    Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Yershov, Kostiantyn V.; Makarov, Denys; Gaididei, Yuri

    2016-01-01

    Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii–Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii–Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii–Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism. PMID:27008975

  14. Fabrication of a magnetic helical mesostructured silica rod

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Zhang Qiao, Shi; Cheng, Lina; Yan, Zifeng; Qing Lu, Gao Max

    2008-10-01

    We report a one-step synthesis of magnetic helical mesostructured silica (MHMS) by self-assembly of an achiral surfactant, magnetic nanocrystals with stearic acid ligands and silicate. This core-shell structured material consists of an Fe3O4 superparamagnetic nanocrystal core and a highly ordered periodic helical mesoporous silica shell. We propose that the formation of the helical structure is induced by the interaction between the surfactant and dissociated stearic acid ligands. The MHMS obtained possesses superparamagnetism, uniform mesostructure, narrow pore size distribution, high surface area, and large pore volume. Furthermore, the drug release process is demonstrated using aspirin as a drug model and MHMS as a drug carrier in a sodium phosphate buffer solution.

  15. ALFVEN SIMPLE WAVES: EULER POTENTIALS AND MAGNETIC HELICITY

    SciTech Connect

    Webb, G. M.; Hu, Q.; Dasgupta, B.; Zank, G. P.; Roberts, D. A.

    2010-12-20

    The magnetic helicity characteristics of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulae. Two basic Alfven modes are identified: (1) the plane one-dimensional Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis with wave phase {psi} = k{sub 0}(z - {lambda}t), where k{sub 0} is the wave number and {lambda} is the group velocity of the wave and (2) the generalized Barnes simple Alfven wave in which the wave normal n moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (1) is analogous to the slab Alfven mode and the generalized Barnes solution (2) is analogous to the two-dimensional mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Alfvenic fluctuations and structures observed in the solar wind are discussed.

  16. Self-sustained annihilation of magnetic islands in helical plasmas

    SciTech Connect

    Itoh, Kimitaka; Itoh, Sanae-I.; Yagi, Masatoshi

    2005-07-15

    The evolution of the magnetic island which is induced by the resonant deformation by external currents in helical systems (such as the large helical device (LHD) [A. Iiyoshi, Phys. Plasmas 2, 2349 (1995)]) is analyzed. The defect of the bootstrap current, caused by the magnetic island, has a parity which reduces the size of the magnetic island, if the bootstrap current enhances the vacuum rotational transform. The width of magnetic island can be suppressed to the level of ion banana width if the pressure gradient exceeds a threshold value. This island annihilation is self-sustained. That is, the annihilation continues, for fixed beta value, until the external drive for island generation exceeds a threshold. The effects of the reversal of the direction of the bootstrap current and of the sign of radial electric field are also investigated. The possibility of the neoclassical tearing mode in the LHD-like plasma is discussed.

  17. Current-induced Orbital and Spin Magnetizations in Crystals with Helical Structure

    PubMed Central

    Yoda, Taiki; Yokoyama, Takehito; Murakami, Shuichi

    2015-01-01

    We theoretically show that in a crystal with a helical lattice structure, orbital and spin magnetizations along a helical axis are induced by an electric current along the helical axis. We propose a simple tight-binding model for calculations, and the results can be generalized to any helical crystals. The induced magnetizations are opposite for right-handed and left-handed helices. The current-induced spin magnetization along the helical axis comes from a radial spin texture on the Fermi surface. This is in sharp contrast to Rashba systems where the induced spin magnetization is perpendicular to the applied current. PMID:26156643

  18. Magnetic helicity injection in NOAA 11261 associated with flares

    NASA Astrophysics Data System (ADS)

    Xu, Haiqing; Zhang, Hongqi; Su, Jiangtao; Ruan, Guiping; liu, Jihong

    2013-07-01

    Magnetic helicity was found important in understanding solar activities such as flares and coronal mass ejections (CME). Berger and field (1984) derived an expression for helicity flux dHm/dt, that can be applied to an individual solar active region (AR) occupying an area S of the photosphere, (1) \\begin{linenomath}dHm/dt=-2\\ints[(\\mathbf{Ap}\\cdot \\mathbf{V})\\mathbf{B}-(\\mathbf{Ap} \\cdot \\mathbf{B})\\mathbf{V}] dS, \\eqno{(1)}\\end{linenomath} where Ap is the vector potential of potential field, and V is the plasma velocity at the surface S. The first term describes the effect of magnetic footpoint motions on the surface S. The second term describes the flux of helicity advected through the surface when already twisted and/or writhed flux ropes emerge. Chae (2001) proposed a method of self-consistently determining magnetic helicity injection rate, dH/dt, using a time series of longitudinal magnetograms only: (2) \\begin{linenomath}dH/dt=-\\int2(\\textbf{A}p\\cdot \\textbf{V}LCT)BndS, \\eqno{(2)}\\end{linenomath} where n is the normal component of magnetic field. Ap is the vector potential computed from Bn by Fourier transform method. V LCT is the horizontal component of velocity determined by the technique of local correlation tracking (LCT). This technique was applied by some scientists (e.g., Chae et al., 2001; Nindos and Zhang, 2002; Romano et al., 2003). Magnetic helicity injection was found to be strongly correlated with the occurrence of major flares (Moon et al. 2002a, 2002b; Park et al., 2008; Labonte et al., 2007; Maeshiro et al., 2009).

  19. Dependence of magnetization processes on vortex helicities in Permalloy nanorings

    NASA Astrophysics Data System (ADS)

    Lai, Mei-Feng; Liao, Chun-Neng; San, Zheng-Hong; Lee, Chung-Peng; Hsieh, Yi-Ping; Ho, Tung-Feng

    2008-04-01

    Two different magnetization reversal processes, which are caused by the helicities of the two small vortex domain walls in the two sides of the onion state, are found numerically to exist in thin film rings. When the two vortex domain walls are in the same helicity, the onion state will transform to flux closure state (vortex state) with increasing of the field, and then transform from the flux closure state (vortex state) to the reverse onion state with further increasing of the field. When the two vortex domain walls are in opposite helicities, however, with increasing of the field, the onion state will transform directly to the reverse onion state skipping the flux closure state (vortex state).

  20. Investigation of TEC variations over the magnetic equatorial and equatorial anomaly regions of the African sector

    NASA Astrophysics Data System (ADS)

    Oryema, B.; Jurua, E.; D'ujanga, F. M.; Ssebiyonga, N.

    2015-11-01

    This paper presents the annual, seasonal and diurnal variations in ionospheric TEC along the African equatorial region. The study also investigated the effects of a geomagnetic storm on ionospheric TEC values. Dual-frequency GPS derived TEC data obtained from four stations within the African equatorial region for the high solar activity year 2012 were used in this study. Annual variations showed TEC having two peaks in the equinoctial months, while minima values were observed in the summer and winter solstices. The diurnal pattern showed a pre-dawn minimum, a steady increase from about sunrise to an afternoon maximum and then a gradual fall after sunset to attain a minimum just before sunrise. Nighttime enhancements of TEC were observed mostly in the equinoctial months. There was comparably higher percentage TEC variability during nighttime than daytime and highest during equinoxes, moderate in winter and least during summer solstice. TEC was observed to exhibit a good correlation with geomagnetic storm indices.

  1. Roles of effective helical ripple rates in nonlinear stability of externally induced magnetic islands

    SciTech Connect

    Nishimura, Seiya

    2015-02-15

    Magnetic islands are externally produced by resonant magnetic perturbations (RMPs) in toroidal plasmas. Spontaneous annihilation of RMP-induced magnetic islands called self-healing has been observed in helical systems. A possible mechanism of the self-healing is shielding of RMP penetration by helical ripple-induced neoclassical flows, which give rise to neoclassical viscous torques. In this study, effective helical ripple rates in multi-helicity helical systems are revisited, and a multi-helicity effect on the self-healing is investigated, based on a theoretical model of rotating magnetic islands. It is confirmed that effective helical ripple rates are sensitive to magnetic axis positions. It is newly found that self-healing thresholds also strongly depend on magnetic axis positions, which is due to dependence of neoclassical viscous torques on effective helical ripple rates.

  2. Jet Rotation Driven by Magnetohydrodynamic Shocks in Helical Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Fendt, Christian

    2011-08-01

    In this paper, we present a detailed numerical investigation of the hypothesis that a rotation of astrophysical jets can be caused by magnetohydrodynamic (MHD) shocks in a helical magnetic field. Shock compression of the helical magnetic field results in a toroidal Lorentz force component that will accelerate the jet material in the toroidal direction. This process transforms magnetic angular momentum (magnetic stress) carried along the jet into kinetic angular momentum (rotation). The mechanism proposed here only works in a helical magnetic field configuration. We demonstrate the feasibility of this mechanism by axisymmetric MHD simulations in 1.5 and 2.5 dimensions using the PLUTO code. In our setup, the jet is injected into the ambient gas with zero kinetic angular momentum (no rotation). We apply different dynamical parameters for jet propagation such as the jet internal Alfvén Mach number and fast magnetosonic Mach number, the density contrast of the jet to the ambient medium, and the external sonic Mach number of the jet. The mechanism we suggest should work for a variety of jet applications, e.g., protostellar or extragalactic jets, and internal jet shocks (jet knots) or external shocks between the jet and the ambient gas (entrainment). For typical parameter values for protostellar jets, the numerically derived rotation feature looks consistent with the observations, i.e., rotational velocities of 0.1%-1% of the jet bulk velocity.

  3. JET ROTATION DRIVEN BY MAGNETOHYDRODYNAMIC SHOCKS IN HELICAL MAGNETIC FIELDS

    SciTech Connect

    Fendt, Christian

    2011-08-10

    In this paper, we present a detailed numerical investigation of the hypothesis that a rotation of astrophysical jets can be caused by magnetohydrodynamic (MHD) shocks in a helical magnetic field. Shock compression of the helical magnetic field results in a toroidal Lorentz force component that will accelerate the jet material in the toroidal direction. This process transforms magnetic angular momentum (magnetic stress) carried along the jet into kinetic angular momentum (rotation). The mechanism proposed here only works in a helical magnetic field configuration. We demonstrate the feasibility of this mechanism by axisymmetric MHD simulations in 1.5 and 2.5 dimensions using the PLUTO code. In our setup, the jet is injected into the ambient gas with zero kinetic angular momentum (no rotation). We apply different dynamical parameters for jet propagation such as the jet internal Alfven Mach number and fast magnetosonic Mach number, the density contrast of the jet to the ambient medium, and the external sonic Mach number of the jet. The mechanism we suggest should work for a variety of jet applications, e.g., protostellar or extragalactic jets, and internal jet shocks (jet knots) or external shocks between the jet and the ambient gas (entrainment). For typical parameter values for protostellar jets, the numerically derived rotation feature looks consistent with the observations, i.e., rotational velocities of 0.1%-1% of the jet bulk velocity.

  4. Properties of magnetic helicity flux in turbulent dynamos

    SciTech Connect

    Vishniac, Ethan T.; Shapovalov, Dmitry E-mail: dmsh@jhu.edu

    2014-01-10

    We study the flux of small-scale magnetic helicity in simulations of driven statistically homogeneous magnetohydrodynamic turbulence in a periodic box with an imposed large-scale shear. The simulations show that in the regime of strong dynamo action the eddy-scale magnetic helicity flux has only two significant terms: advective motion driven by the large-scale velocity field and the Vishniac-Cho (VC) flux which moves helicity across the magnetic field lines. The contribution of all the other terms is negligible. The VC flux is highly correlated with the large-scale electromotive force and is responsible for large-scale dynamo action, while the advective term is not. The VC flux is driven by the anisotropy of the turbulence. We derive analytical expressions for it in terms of the small-scale velocity or magnetic field. These expressions are used to predict the existence and strength of dynamo action for different turbulent anisotropies and tested against the results of the simulations.

  5. Goldstone mode in the conical phase of helical magnets

    NASA Astrophysics Data System (ADS)

    Sang, Yan; Belitz, D.; Kirkpatrick, T. R.

    2010-03-01

    We investigate theoretically the nature of the Goldstone mode in the conical phase of helical magnets such as MnSi. A Dzyaloshinsky-Moriya term in the action leads to helical order in the ground state, characterized by a pitch vector q [1]. The Goldstone mode in the helical phase, the helimagnon, is known to have an anisotropic dispersion relation of the form 2̂kz^2 + k^4/q^2, analogous to smectic or cholesteric liquid crystals [2]. In the presence of a homogeneous external magnetic field H the helix is superimposed by a homogeneous magnetization, which leads to a conical phase [3]. The Goldstone mode in the latter is found to be a modified helimagnon, with a dispersion relation of the structure 2̂φ0^2 + H^2 k^2. The additional term H^2 k^2 is a result of the magnetic field breaking the rotational symmetry. In addition, there are remnants of ferromagnetic magnons with masses H^2. [1] P. Bak and M.H. Jensen, J. Phys. C 13, L881 (1980). [2] D. Belitz, T.R. Kirkpatrick, and A. Rosch, Phys. Rev. B 73, 054431 (2006). [3] Y. Ishikawa, G. Shirane, J.A. Tarvin, and M. Kohgi, Phys. Rev. B 16, 4956 (1977).

  6. RF Integration into Helical Magnet for Muon 6-Dimensional Beam Cooling

    SciTech Connect

    Yonehara, K.; Kashikhin, V.; Lamm, M.; Lee, A.; Lopes, M.; Zlobin, A.; Johnson, R.P.; Kahn, S.; Neubauer, M.; /Muons Inc., Batavia

    2009-05-01

    The helical cooling channel is proposed to make a quick muon beam phase space cooling in a short channel length. The challenging part of the helical cooling channel magnet design is how to integrate the RF cavity into the compact helical cooling magnet. This report shows the possibility of the integration of the system.

  7. Magnetic helicity and the relaxation of fossil fields

    NASA Astrophysics Data System (ADS)

    Broderick, Avery E.; Narayan, Ramesh

    2008-01-01

    In the absence of an active dynamo, purely poloidal magnetic field configurations are unstable to large-scale dynamical perturbations, and decay via reconnection on an Alfvénic time-scale. Nevertheless, a number of classes of dynamo-free stars do exhibit significant, long-lived, surface magnetic fields. Numerical simulations suggest that the large-scale poloidal field in these systems is stabilized by a toroidal component of the field in the stellar interior. Using the principle of conservation of total helicity, we develop a variational principle for computing the structure of the magnetic field inside a conducting sphere surrounded by an insulating vacuum. We show that, for a fixed total helicity, the minimum energy state corresponds to a force-free configuration. We find a simple class of axisymmetric solutions, parametrized by angular and radial quantum numbers. However, these solutions have a discontinuity in the toroidal magnetic field at the stellar surface which will exert a toroidal stress on the surface of the star. We then describe two other classes of solutions, the standard spheromak solutions and ones with fixed surface magnetic fields, the latter being relevant for neutron stars with rigid crusts. We discuss the implications of our results for the structure of neutron star magnetic fields, the decay of fields, and the origin of variability and outbursts in magnetars.

  8. New mode of operating a magnetized coaxial plasma gun for injecting magnetic helicity into a spheromak.

    PubMed

    Woodruff, S; Hill, D N; Stallard, B W; Bulmer, R; Cohen, B; Holcomb, C T; Hooper, E B; McLean, H S; Moller, J; Wood, R D

    2003-03-01

    By operating a magnetized coaxial plasma gun continuously with just sufficient current to enable plasma ejection, large gun-voltage spikes (approximately 1 kV) are produced, giving the highest sustained voltage approximately 500 V and highest sustained helicity injection rate observed in the Sustained Spheromak Physics Experiment. The spheromak magnetic field increases monotonically with time, exhibiting the lowest fluctuation levels observed during formation of any spheromak (B/B>/=2%). The results suggest an important mechanism for field generation by helicity injection, namely, the merging of helicity-carrying filaments. PMID:12689228

  9. Chiral charge erasure via thermal fluctuations of magnetic helicity

    NASA Astrophysics Data System (ADS)

    Long, Andrew J.; Sabancilar, Eray

    2016-05-01

    We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, λ gtrsim 1/(αμ5), the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential μ5 parametrizes the chiral asymmetry and α is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale λ, finding δScript H ~ λT and τ ~ αλ3T2 for a relativistic plasma at temperature T. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively for a time t ~ T3/(α5μ54) until it reaches an equilibrium value Script H ~ μ5T2/α, and the chiral asymmetry is partially erased. If the chiral asymmetry is small, μ5 < T/α, this avenue for chiral charge erasure is found to be slower than the chiral magnetic effect for which t ~ T/(α3μ52). This mechanism for chiral charge erasure can be important for the hypercharge sector of the Standard Model as well as extensions including U(1) gauge interactions, such as asymmetric dark matter models.

  10. Magnetic helicity as a constraint on coronal dissipation

    NASA Technical Reports Server (NTRS)

    Choudhuri, Arnab Rai

    1986-01-01

    The Taylor hypothesis has provided a model for the relaxed magnetic configurations of not only laboratory plasmas, but also of astrophysical plasmas. However, energy dissipation is possible only for systems which depart from a strict Taylor state, and hence a parameter describing that departure must be introduced, when the Taylor hypothesis is used to estimate the dissipation. An application of the Taylor hypothesis to the problem of coronal heating provides an insight into this difficult problem. When particular sorts of footpoint motions put energy and helicity in the corona, the conservation of helicity puts a constraint on how much of the energy can be dissipated. However, on considering a random distribution of footpoint motions, this constraint gets washed away, and the Taylor hypothesis is probably not going to play any significant role in the actual calculation of relevant physical quantities in the coronal heating problem.

  11. Chiral Magnetism in an Itinerant Helical Magnet, MnSi - An Extended 29Si NMR Study

    NASA Astrophysics Data System (ADS)

    Yasuoka, Hiroshi; Motoya, Kiyoichiro; Majumder, Mayukh; Witt, Sebastian; Krellner, Cornelius; Baenitz, Michael

    2016-07-01

    The microscopic magnetism in the helical, conical and ferromagnetically polarized phases in an itinerant helical magnet, MnSi, has been studied by an extended 29Si NMR at zero field and under external magnetic fields. The temperature dependence of the staggered moment, MQ(T), determined by the 29Si NMR frequency, ν(T), and the nuclear relaxation rate, 1/T1(T), at zero field is in general accord with the SCR theory for weak itinerant ferromagnetic metals and its extension to helical magnets. The external field dependence of resonance frequency, ν(H), follows a vector sum of the contributions from the atomic hyperfine and macroscopic fields with a field induced moment characteristic to itinerant magnets. A discontinuous jump of the resonance frequency at the critical field, Hc, between the conical and the polarized phases has also been found, which suggests a first order like change of the electronic states at Hc.

  12. Can slow roll inflation induce relevant helical magnetic fields?

    NASA Astrophysics Data System (ADS)

    Durrer, Ruth; Hollenstein, Lukas; Jain, Rajeev Kumar

    2011-03-01

    We study the generation of helical magnetic fields during single field inflation induced by an axial coupling of the electromagnetic field to the inflaton. During slow roll inflation, we find that such a coupling always leads to a blue spectrum with B2(k)proptok, as long as the theory is treated perturbatively. The magnetic energy density at the end of inflation is found to be typically too small to backreact on the background dynamics of the inflaton. We also show that a short deviation from slow roll does not result in strong modifications to the shape of the spectrum. We calculate the evolution of the correlation length and the field amplitude during the inverse cascade and viscous damping of the helical magnetic field in the radiation era after inflation. We conclude that except for low scale inflation with very strong coupling, the magnetic fields generated by such an axial coupling in single field slow roll inflation with perturbative coupling to the inflaton are too weak to provide the seeds for the observed fields in galaxies and clusters.

  13. A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere 1. Equatorial occurrence distributions

    SciTech Connect

    Anderson, B.J.; Erlandson, R.E.; Zanetti, L.J. )

    1992-03-01

    A study of AMPTE CCE magnetic field data covering the frequency range 0.1-4.0 Hz using all data obtained during the first complete local time precession of the satellite orbit major axis (7,500 hours of observations) has been made to evaluate the occurrence of transverse, narrowband Pc 1-2 emissions, identified as electromagnetic ion cyclotron (EMIC) waves, in the equatorial magnetosphere from L = 3.5 to L = 9 at all local times. A set of example events illustrates the pattern of Pc 1-2 occurrence: events occur primarily for L > 7, and a radial separation of several R{sub E} between low (<6) and high L(>6) pulsations is observed. Statistically, the highest concentration of events occurred near apogee in the afternoon. The L>6 and L,6 event populations appear to be radially separated in the morning but merge together in the afternoon. The authors construct a normalized occurrence distribution throughout the equatorial plane from L = 3.5 to L = 9 of Pc 1-2 with peak to peak amplitudes greater than 0.8 nT. The occurrence distribution exhibits a number of properties: for L > 7, Pc 1-2 occur at any given place in the early afternoon (1200-1500 MLT) with 10-20% probability and in the morning (0300-0900 MLT) with {approx} 3% probability; the L = 6-7 local time distribution reproduces results obtained previously from data at geostationary orbit; L < 5 events occur with a probability of {le}1% and a relatively uniform local time distribution. The predominance of L > 7 events implies that plasma sheet ion develop sufficient temperature anisotropy to generate EMIC waves on a routine basis in their drift from the nightside to the dayside and that plasma sheet ions on open drift paths rather than ring current ions on closed drift paths present the greatest source of equatorially generated EMIC waves.

  14. PERFORMANCE SUMMARY OF THE HELICAL MAGNETS FOR RHIC.

    SciTech Connect

    WILLEN,E.; ANERELLA,M.; ESCALLIER,J.; GANETIS,G.; GHOSH,A.; GUPTA,R.; HARRISON,M.; JAIN,A.; MACKAY,W.; MARONE,A.; MURATORE,J.; PLATE,S.; THOMAS,R.; WANDERER,P.; WU,K.C.; OKAMURA,M.

    2003-05-12

    A series of four Snake and eight Rotator superconducting helical magnet assemblies has been built and installed in RHIC to control the polarization of protons during acceleration and storage in that machine. Each of these assemblies consists of four 2.4 m long dipole magnets in each of which the field rotates through 360 degrees along the magnet's length. The magnets were made by winding one millimeter diameter superconducting 7-strand cable into slots milled into thick-walled aluminum tubes. The magnets produce 4 Tesla field at a current of 320 amperes and are quench-protected with 0.050 ohm resistors placed across the winding in each slot. A total of 48 of these 2.4 m magnets has been built, tested and installed. This paper summarizes their quench performance as well as their field uniformity, of which the integral field is the most critical. All magnets reached the required operating field level of 4 T, and the integral field of the magnets was generally about half of the maximum permissible level of 0.050 Tesla meters.

  15. Nonlinear decay of magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field

    NASA Technical Reports Server (NTRS)

    Stribling, Troy; Matthaeus, William H.; Ghosh, Sanjoy

    1994-01-01

    We show that the magnetic helicity associated with fluctuations in homogeneous incompressible magnetohydrodynamic (MHD) turbulence with a mean magnetic field decays in time because of nonlinear processes. Evidence is obtained numerically, by use of both dissipative and nondissipative spectral method simulations. The described effect stands in contrast to expectations based on studies of MHD turbulence without an applied mean field, in which magnetic helicity is transferred nonlinearly to long wavelengths and is preserved in time because of selective decay when dissipation is present. The process of nonlinear decay is described in terms of a generalized ideal helicity invariant and is characterized by the transient production of a mean induced electric field aligned with the applied magnetic field, an effect reminiscent of the alpha effect in dynamo theory. A simple phenomenological model for the decay process is proposed.

  16. Magnetic and luminescent binuclear double-stranded helicates.

    PubMed

    Cucos, Paula; Tuna, Floriana; Sorace, Lorenzo; Matei, Iulia; Maxim, Catalin; Shova, Sergiu; Gheorghe, Ruxandra; Caneschi, Andrea; Hillebrand, Mihaela; Andruh, Marius

    2014-07-21

    Three new binuclear helicates, [M2L2]·3DMF (M = Co(II), 1, Zn(II), 3) and [Cu2L2]·DMF·0.4H2O (2), have been assembled using the helicand H2L that results from the 2:1 condensation reaction between o-vanillin and 4,4'-diaminodiphenyl ether. The metal ions within the binuclear helicates are tetracoordinated with a distorted tetrahedral geometry. Direct current magnetic characterization and EPR spectroscopy of the Co(II) derivative point to an easy axis type anisotropy for both Co(II) centers, with a separation of at least 55 K between the two doublets. Dynamic susceptibility measurements evidence slow relaxation of the magnetization in an applied dc field. Since the distance between the cobalt ions is quite large (11.59 Å), this is attributed in a first instance to the intrinsic properties of each Co(II) center (single-ion magnet behavior). However, the temperature dependence of the relaxation rate and the absence of slow dynamics in the Zn(II)-doped sample suggest that neither the simple Orbach mechanism nor Raman or direct processes can account for the relaxation, and collective phenomena have to be invoked for the observed behavior. Finally, due to the rigidization of the two organic ligands upon coordination, the pure zinc derivative exhibits fluorescence emission in solution, which was analyzed in terms of fluorescence quantum yields and lifetimes. PMID:24998701

  17. Distribution of Helical Properties of Solar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kuzanyan, Kirill M.; Lamburt, Victor G.; Zhang, Hong-Qi; Bao, Shu-Dong

    2003-06-01

    We summarize studies of helical properties of solar magnetic fields such as current helicity and twist of magnetic fields in solar active regions (ARs), that are observational tracers of the alpha-effect in the solar convective zone (SCZ). Information on their spatial distribution is obtained by analysis of systematic magnetographic observations of active regions taken at Huairou Solar Observing Station of National Astronomical Observatories of Chinese Academy of Sciences. The main property is that the tracers of the alpha-effect are antisymmetric about the solar equator. Identifying longitudinal migration of active regions with their individual rotation rates and taking into account the internal differential rotation law within the SCZ known from helioseismology, we deduce the distribution of the effect over depth. We have found evidence that the alpha-effect changes its value and sign near the bottom of the SCZ, and this is in accord with the theoretical studies and numerical simulations. We discuss other regularities which can be revealed by further analysis such as possible dependence on longitude, time, and magnetic field strength, etc.

  18. Magnetic helicity signature produced by cross-field 2D turbulence

    SciTech Connect

    Markovskii, S. A.; Vasquez, Bernard J.

    2013-06-13

    Hybrid numerical simulations of freely decaying 2D turbulence are presented. The background magnetic field is perpendicular to the simulation plane, which eliminates linear kinetic Alfven waves from the system. The normalized magnetic helicity of the initial large-scale fluctuations is zero, while the normalized cross-helicity is not. As the turbulence evolves, it develops nonzero magnetic helicity at smaller scales, in the proton kinetic range. In the quasi-steady state of evolution, the magnetic helicity spectrum has a peak consistent with the solar wind observations.

  19. Vortex wall dynamics and pinning in helical magnets

    NASA Astrophysics Data System (ADS)

    Roostaei, Bahman

    2014-06-01

    Domain walls formed by one dimensional array of vortex lines have been recently predicted to exist in disordered helical magnets and multiferroics. These systems are on one hand analogues to the vortex line lattices in type-II superconductors while on the other hand they propagate in the magnetic medium as a domain boundary. Using a long wavelength approach supported by numerical optimization we lay out detailed theory for dynamics and structure of such topological fluctuations at zero temperature in presence of weak disorder. We show the interaction between vortex lines is weak. This is the direct consequence of the screening of the vorticity by helical background in the system. We explain how one can use this result to understand the elasticity of the wall with a vicinal surface approach. Also we show the internal degree of freedom of this array leads to the enhancement of its mobility. We present estimates for the interaction and mobility enhancements using the microscopic parameters of the system. Finally we determine the range of velocities/force densities in which the internal movement of the vortex wall can be effective in its dynamics.

  20. Particle energization through time-periodic helical magnetic fields.

    PubMed

    Mitra, Dhrubaditya; Brandenburg, Axel; Dasgupta, Brahmananda; Niklasson, Eyvind; Ram, Abhay

    2014-04-01

    We solve for the motion of charged particles in a helical time-periodic ABC (Arnold-Beltrami-Childress) magnetic field. The magnetic field lines of a stationary ABC field with coefficients A=B=C=1 are chaotic, and we show that the motion of a charged particle in such a field is also chaotic at late times with positive Lyapunov exponent. We further show that in time-periodic ABC fields, the kinetic energy of a charged particle can increase indefinitely with time. At late times the mean kinetic energy grows as a power law in time with an exponent that approaches unity. For an initial distribution of particles, whose kinetic energy is uniformly distributed within some interval, the probability density function of kinetic energy is, at late times, close to a Gaussian but with steeper tails. PMID:24827325

  1. Current induced vortex wall dynamics in helical magnetic systems

    NASA Astrophysics Data System (ADS)

    Roostaei, Bahman

    2015-03-01

    Nontrivial topology of interfaces separating phases with opposite chirality in helical magnetic metals result in new effects as they interact with spin polarized current. These interfaces or vortex walls consist of a one dimensional array of vortex lines. We predict that adiabatic transfer of angular momentum between vortex array and spin polarized current will result in topological Hall effect in multi-domain samples. Also we predict that the motion of the vortex array will result in a new damping mechanism for magnetic moments based on Lenz's law. We study the dynamics of these walls interacting with electric current and use fundamental electromagnetic laws to quantify those predictions. On the other hand discrete nature of vortex walls affects their pinning and results in low depinning current density. We predict the value of this current using collective pinning theory.

  2. Ion-temperature gradient modes affected by helical magnetic field of magnetic islands

    SciTech Connect

    Ishizawa, A.; Diamond, P. H.

    2010-07-15

    Ion temperature gradient mode (ITG) affected by static magnetic field of magnetic islands is investigated numerically by means of Landau fluid model. The ITG is localized around O-points of magnetic islands, and the localization in poloidal direction is similar to the poloidal localization of toroidal ITG. This is because the helical magnetic field of magnetic islands causes geometrical coupling, and thus Fourier modes that have the same helicity as the islands are coupled together. The strength of coupling is characterized by the square of island width, and it corresponds to the fact that the strength of mode coupling of toroidal ITG is characterized by the inverse aspect ratio of torus in reduced fluid models.

  3. Multiple Magnetic Storm Study of the High-Altitude Redistribution of Equatorial Plasma

    NASA Astrophysics Data System (ADS)

    Bust, G. S.; Crowley, G.; Curtis, N.; Anderson, D.

    2008-12-01

    During geomagnetic storms, particularly when prompt penetration electric fields (PPE) occur, the equatorial plasma can be lifted to very high altitudes and then diffuse along magnetic field lines to higher than normal latitudes. During these cases very high plasma density (total electron content (TEC) greater than 200 TECU) can be found at these higher latitudes. Shortly after the PPE lifts the equatorial plasma to higher altitudes, at least in the US sector, phenomena known as storm-enhanced density (SED) can occur. SEDs occur in the post-noon time frame and consist of a very high density bulge that seems to occur in the southern USA and Caribbean region, followed by a narrow plume of high density plasma that flows into the high-latitude throat near local noon, and across the polar cap. An outstanding research question is: Exactly how is the high density SED plasma, particularly in the bulge related to the PPE and lifting of the equatorial plasma? Ionospheric imaging of electron density and TEC seem to show a gap in density between the poleward extent of the equatorial plasma and the equatorial extent of the SED plasma. Further, there are magnetic storm events where SEDs do not form (November 2004 as a good example). This paper will investigate the relationship between the equatorial high altitude plasma distribution during magnetic storms, and the initiation and evolution of the SED feature. We will examine eight separate storms from 2003-2006 using the ionospheric data assimilation algorithm IDA4D. In particular we will focus on time periods when LEO satellite GPS TEC data is available from CHAMP, SACC, GRACE and the COSMIC constellation (2006 and beyond). These data sets directly measure the TEC above the satellites, and therefore are good tracers of the high altitude plasma distribution. IDA4D ingests these data sets and uses them to get an improved image of the plasma density for the topside ionosphere and plasmasphere. The resulting 4D images of high

  4. Dual-body magnetic helical robot for drilling and cargo delivery in human blood vessels

    NASA Astrophysics Data System (ADS)

    Lee, Wonseo; Jeon, Seungmun; Nam, Jaekwang; Jang, Gunhee

    2015-05-01

    We propose a novel dual-body magnetic helical robot (DMHR) manipulated by a magnetic navigation system. The proposed DMHR can generate helical motions to navigate in human blood vessels and to drill blood clots by an external rotating magnetic field. It can also generate release motions which are relative rotational motions between dual-bodies to release the carrying cargos to a target region by controlling the magnitude of an external magnetic field. Constraint equations were derived to selectively manipulate helical and release motions by controlling external magnetic fields. The DMHR was prototyped and various experiments were conducted to demonstrate its motions and verify its manipulation methods.

  5. Three-dimensional prominence-hosting magnetic configurations: Creating a helical magnetic flux rope

    SciTech Connect

    Xia, C.; Keppens, R.; Guo, Y.

    2014-01-10

    The magnetic configuration hosting prominences and their surrounding coronal structure is a key research topic in solar physics. Recent theoretical and observational studies strongly suggest that a helical magnetic flux rope is an essential ingredient to fulfill most of the theoretical and observational requirements for hosting prominences. To understand flux rope formation details and obtain magnetic configurations suitable for future prominence formation studies, we here report on three-dimensional isothermal magnetohydrodynamic simulations including finite gas pressure and gravity. Starting from a magnetohydrostatic corona with a linear force-free bipolar magnetic field, we follow its evolution when introducing vortex flows around the main polarities and converging flows toward the polarity inversion line near the bottom of the corona. The converging flows bring the feet of different loops together at the polarity inversion line, where magnetic reconnection and flux cancellation happen. Inflow and outflow signatures of the magnetic reconnection process are identified, and thereby the newly formed helical loops wind around preexisting ones so that a complete flux rope grows and ascends. When a macroscopic flux rope is formed, we switch off the driving flows and find that the system relaxes to a stable state containing a helical magnetic flux rope embedded in an overlying arcade structure. A major part of the formed flux rope is threaded by dipped field lines that can stably support prominence matter, while the total mass of the flux rope is in the order of 4-5× 10{sup 14} g.

  6. Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

    NASA Astrophysics Data System (ADS)

    Franke, Christine; von Dobeneck, Tilo; Drury, Martyn R.; Meeldijk, Johannes D.; Dekkers, Mark J.

    2007-12-01

    The magnetic microparticle and nanoparticle inventories of marine sediments from equatorial Atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution, origin, transport, and preservation. This information is used to establish source-to-sink relations and to constrain environmental magnetic proxy interpretations for this area. Magnetic extracts were prepared from sediments of three supralysoclinal open ocean gravity cores located at the Ceará Rise (GeoB 1523-1; 3°49.9'N/41°37.3'W), the Mid-Atlantic Ridge (GeoB 4313-2; 4°02.8'N/33°26.3'W), and the Sierra Leone Rise (GeoB 2910-1; 4°50.7'N/21°03.2'W). Sediments from two depths corresponding to marine isotope stages 4 and 5.5 were processed. This selection represents glacial and interglacial conditions of sedimentation for the western, central, and eastern equatorial Atlantic and avoids interferences from subsurface and anoxic processes. Crystallographic, elemental, morphological, and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy. On basis of these properties, nine particle classes could be defined: detrital magnetite, titanomagnetite (fragmental and euhedral), titanomagnetite-hemoilmentite intergrowths, silicates with magnetic inclusions, microcrystalline hematite, magnetite spherules, bacterial magnetite, goethite needles, and nanoparticle clusters. Each class can be associated with fluvial, eolian, subaeric, and submarine volcanic, biogenic, or chemogenic sources. Large-scale sedimentation patterns are delineated as well: detrital magnetite is typical of Amazon discharge, fragmental titanomagnetite is a submarine weathering product of mid-ocean ridge basalts, and titanomagnetite-hemoilmenite intergrowths are common magnetic particles in West African dust. This clear regionalization underlines

  7. Measuring the magnetic field of a trans-equatorial loop system using coronal seismology

    NASA Astrophysics Data System (ADS)

    Long, David; Perez-Suarez, David; Valori, Gherardo

    2016-05-01

    First observed by SOHO/EIT, "EIT waves" are strongly associated with the initial evolution of coronal mass ejections (CMEs) and after almost 20 years of investigation a consensus is being reached which interprets them as freely-propagating waves produced by the rapid expansion of a CME in the low corona. An "EIT wave" was observed on 6 July 2012 to erupt from active region AR11514 into a particularly structured corona that included multiple adjacent active regions as well as an adjacent trans-equatorial loop system anchored at the boundary of a nearby coronal hole. The eruption was well observed by SDO/AIA and CoMP, allowing the effects of the "EIT wave" on the trans-equatorial loop system to be studied in detail. In particular, it was possible to characterise the oscillation of the loop system using Doppler velocity measurements from CoMP. These Doppler measurements were used to estimate the magnetic field strength of the trans-equatorial loop system via coronal seismology. It was then possible to compare these inferred magnetic field values with extrapolated magnetic field values derived using a Potential Field Source Surface extrapolation as well as the direct measurements of magnetic field provided by CoMP. These results show that the magnetic field strength of loop systems in the solar corona may be estimated using loop seismology.

  8. Helical magnetorotational instability in magnetized Taylor-Couette flow

    SciTech Connect

    Liu Wei; Ji Hantao; Goodman, Jeremy; Herron, Isom

    2006-11-15

    Hollerbach and Ruediger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this 'helical' MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only), and that it might be relevant to cooler astrophysical disks, especially those around protostars, which may be quite resistive. We confirm previous results for marginal stability and calculate HMRI growth rates. We show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Large axial currents are required. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit, at least if viscosity is neglected. Also, Keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of a toroidal field lowers thresholds for instability even in finite cylinders.

  9. Increasing the magnetic helicity content of a plasma by pulsing a magnetized source.

    PubMed

    Woodruff, S; Stallard, B W; McLean, H S; Hooper, E B; Bulmer, R; Cohen, B I; Hill, D N; Holcomb, C T; Moller, J; Wood, R D

    2004-11-12

    By operating a magnetized coaxial gun in a pulsed mode it is possible to produce large voltage pulses of duration approximately 500 mus while reaching a few kV, giving a discrete input of helicity into a spheromak. In the sustained spheromak physics experiment (SSPX), it is observed that pulsing serves to nearly double the stored magnetic energy and double the temperature. We discuss these results by comparison with 3D MHD simulations of the same phenomenon. PMID:15600933

  10. Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930

    NASA Astrophysics Data System (ADS)

    Park, Sung-Hong; Chae, Jongchul; Jing, Ju; Tan, Changyi; Wang, Haimin

    2010-09-01

    To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 × 1043 Mx2 just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 × 1043 Mx2, in the corona over ~1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

  11. TIME EVOLUTION OF CORONAL MAGNETIC HELICITY IN THE FLARING ACTIVE REGION NOAA 10930

    SciTech Connect

    Park, Sung-Hong; Jing, Ju; Wang Haimin; Chae, Jongchul; Tan, Changyi

    2010-09-10

    To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 x 10{sup 43} Mx{sup 2} just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 x 10{sup 43} Mx{sup 2}, in the corona over {approx}1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

  12. Evolution of Magnetic Helicity and Energy Spectra of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Zhang, Hongqi; Brandenburg, Axel; Sokoloff, D. D.

    2016-03-01

    We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30-60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field.

  13. PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS

    SciTech Connect

    Park, Sung-hong; Wang Haimin; Chae, Jongchul

    2010-07-20

    The main objective of this study is to better understand how magnetic helicity injection in an active region (AR) is related to the occurrence and intensity of solar flares. We therefore investigate the magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr averaged helicity injection rate and unsigned magnetic flux are compared with the flare index and the flare-productive probability in the next 24 hr following a measurement. In addition, we study the variation of helicity over a span of several days around the times of the 19 flares above M5.0 which occurred in selected strong flare-productive ARs. The major findings of this study are as follows: (1) for a sub-sample of 91 large ARs with unsigned magnetic fluxes in the range from (3-5) x 10{sup 22} Mx, there is a difference in the magnetic helicity injection rate between flaring ARs and non-flaring ARs by a factor of 2; (2) the GOES C-flare-productive probability as a function of helicity injection displays a sharp boundary between flare-productive ARs and flare-quiet ones; (3) the history of helicity injection before all the 19 major flares displayed a common characteristic: a significant helicity accumulation of (3-45) x 10{sup 42} Mx{sup 2} during a phase of monotonically increasing helicity over 0.5-2 days. Our results support the notion that helicity injection is important in flares, but it is not effective to use it alone for the purpose of flare forecast. It is necessary to find a way to better characterize the time history of helicity injection as well as its spatial distribution inside ARs.

  14. Helicity from observational solar magnetic fields and the relationship with solar activities

    NASA Astrophysics Data System (ADS)

    Zhang, Hongqi

    The helicity is important to present the basic topological configuration of magnetic field trans-ferred form the solar subatmosphere into the interplanetary space. In this talk, the basic configuration of magnetic field and helicity in the solar atmosphere have been discussed in the following: 1) The Hinode high resolution vector magnetograms provide the important infor-mation on the fine features of current helicity density and the possible accumulated process of magnetic helicity in the solar atmosphere. 2) The relationship between the eruption of solar flare-CMEs and helicity transfer from the suntamosphere has be presented based on the analy-sis of photospheric vector magnetograms. 3) The statistical distribution of magnetic field (and helicity) in solar atmosphere and its reversals with solar cycles are presented by means of the observational (vector) magnetograms. As the magnetic fields in the solar surface provides the information on the formation of magnetic field in the solar convection zone, the statistical anal-ysis of the observational magnetic helicity is important for the confirmation of the alpha-effect of the solar dynamo.

  15. Dynamics of Laboratory Astrophysical Jets with Magnetized Helical Flows

    NASA Astrophysics Data System (ADS)

    von der Linden, Jens; You, Setthivoine

    2014-10-01

    A triple electrode planar plasma gun (MOCHI LabJet) designed to study the dynamics of magnetized helical flows in plasma jets provides boundary conditions and dimensionless numbers relevant to astrophysical jets. The goal is to observe the effect of current and flow profiles on the collimation and stability of jets to address the questions: why are jets collimated and long? How are jet irregularities related to plasma instabilities? The current and azimuthal flow profiles of the jets are tailored by biasing the electrodes at different potentials. High-speed camera images, high-resolution Ḃ probe measurements, and 3D vector tomography of plasma flows will map a stability space for varying current and flow profiles. An analytical stability space is derived with Newcomb's variational analysis applied to collimated magnetic flux tubes with skin and core currents. Two numerical stability spaces are also computed by integrating the Euler-Lagrange equation and applying a shooting method to the ideal MHD eigenvalue problem. The eigenvalue problem is generalized to include azimuthal flows and computed with a monotonicity condition for minimizing the required scanning of the complex eigenvalue space. This work was sponsored in part by the US DOE Grant DE-SC0010340.

  16. Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930

    NASA Astrophysics Data System (ADS)

    Park, Sung-Hong; Jing, J.; Wang, H.

    2010-05-01

    To study the three-dimensional (3D) magnetic field topology and its long-term (a few days) evolution associated with the X3.4 flare of 2006 December 13, we investigate the temporal evolution of the relative coronal magnetic helicity in NOAA active region (AR) 10930 during the time period of December 8, 21:20 UT through December 14, 5:00 UT. The coronal helicity is calculated based on the 3D nonlinear force-free (NLFF) magnetic fields reconstructed by the optimization method (Wheatland et al. 2000) as implemented by Wiegelmann (2004). As the boundary conditions for the force-free reconstruction, we use the preprocessed Hinode Spectropolarimeter (SP) vector magnetograms in which the net Lorentz force and the torque in the photosphere are minimized (see Wiegelmann et al. 2006 for the details). The major findings of this study are: (1) a negative (left-handed) helicity of -5×1043 Mx2 in the AR corona is estimated right before the X3.4 flare; (2) the major flare is preceded by a significantly and consistently large amount of negative helicity injection (-2×1043 Mx2) into the corona over 2 days; (3) the temporal variation of helicity is comparable to that of the rotational speed in the southern sunspot with positive polarity; (4) in general, the time profile of the coronal helicity is well-matched with that of the helicity accumulation by the time integration of the simplified helicity injection rate (Chae 2001) determined by using SOHO MDI magnetograms; (5) at the time period of the channel structure development (December 11, 4:00-8:00 UT) with newly emerging flux and just right before the C5.7 class flare, the time variation of the coronal helicity shows a rapid and huge increase of negative helicity, but that of the helicity accumulation by MDI magnetograms indicates a monotonous increase of negative helicity.

  17. 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.

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

    PubMed

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

    2013-09-01

    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. PMID:24089823

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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)], 10.1088/0029-5515/51/3/033001, 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.

  20. Helicity-vorticity turbulent pumping of magnetic fields in the solar dynamo

    NASA Astrophysics Data System (ADS)

    Pipin, V. V.

    2013-07-01

    The interaction of helical convective motions and differential rotation in the solar convection zone results in turbulent drift of a large-scale magnetic field. We discuss the pumping mechanism and its impact on the solar dynamo.

  1. On the resilience of helical magnetic fields to turbulent diffusion and the astrophysical implications

    NASA Astrophysics Data System (ADS)

    Blackman, Eric G.; Subramanian, Kandaswamy

    2013-02-01

    The extent to which large-scale magnetic fields are susceptible to turbulent diffusion is important for interpreting the need for in situ large-scale dynamos in astrophysics and for observationally inferring field strengths compared to kinetic energy. By solving coupled evolution equations for magnetic energy and magnetic helicity in a system initialized with isotropic turbulence and an arbitrarily helical large-scale field, we quantify the decay rate of the latter for a bounded or periodic system. The magnetic energy associated with the non-helical large-scale field decays at least as fast as the kinematically estimated turbulent diffusion rate, but the decay rate of the helical part depends on whether the ratio of its magnetic energy to the turbulent kinetic energy exceeds a critical value given by M1, c = (k1/k2)2, where k1 and k2 are the wavenumbers of the large and forcing scales. Turbulently diffusing helical fields to small scales while conserving magnetic helicity requires a rapid increase in total magnetic energy. As such, only when the helical field is subcritical can it so diffuse. When supercritical, it decays slowly, at a rate determined by microphysical dissipation even in the presence of macroscopic turbulence. In effect, turbulent diffusion of such a large-scale helical field produces small-scale helicity whose amplification abates further turbulent diffusion. Two curious implications are that (1) standard arguments supporting the need for in situ large-scale dynamos based on the otherwise rapid turbulent diffusion of large-scale fields require re-thinking since only the large-scale non-helical field is so diffused in a closed system. Boundary terms could however provide potential pathways for rapid change of the large-scale helical field. (2) Since M1, c ≪ 1 for k1 ≪ k2, the presence of long-lived ordered large-scale helical fields as in extragalactic jets do not guarantee that the magnetic field dominates the kinetic energy.

  2. Evolution of Magnetic Helicity During Eruptive Flares and Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Priest, E. R.; Longcope, D. W.; Janvier, M.

    2016-08-01

    During eruptive solar flares and coronal mass ejections, a non-potential magnetic arcade with much excess magnetic energy goes unstable and reconnects. It produces a twisted erupting flux rope and leaves behind a sheared arcade of hot coronal loops. We suggest that the twist of the erupting flux rope can be determined from conservation of magnetic flux and magnetic helicity and equipartition of magnetic helicity. It depends on the geometry of the initial pre-eruptive structure. Two cases are considered, in the first of which a flux rope is not present initially but is created during the eruption by the reconnection. In the second case, a flux rope is present under the arcade in the pre-eruptive state, and the effect of the eruption and reconnection is to add an amount of magnetic helicity that depends on the fluxes of the rope and arcade and the geometry.

  3. Riemannian geometry of twisted magnetic flux tubes in almost helical plasma flows

    SciTech Connect

    Garcia de Andrade, L.C.

    2006-02-15

    Riemannian geometry of curves applied recently by Ricca [Fluid Dyn. Res 36, 319 (2005)] in the case of inflectional disequilibrium of twisted magnetic flux tubes is used here to compute the magnetic helicity force-free field case. Here the application of Lorentz force-free to the magnetic flux tube in tokamaks allows one to obtain an equation that generalizes the cylindrical tokamak equation by a term that contains the curvature of the magnetic flux tube. Another example of the use of the magnetic flux tube is done by taking the electron magnetohydrodynamics (MHD) fluid model (EMHD) of plasma physics that allows one to compute the velocity of the fluid in helical and almost helical flows in terms of the Frenet torsion of thin magnetic flux tubes. The cases of straight and curved twisted tubes are examined. Second-order effects on the Frenet torsion arise on the poloidal component of the magnetic field, while curvature effects appear in the toroidal component. The magnetic fields are computed in terms of the penetration depth used in superconductors. The ratio between poloidal and toroidal components of the magnetic field depends on the torsion and curvature of the magnetic flux tube. It is shown that the rotation of the almost helical plasma flow contributes to the twist of the magnetic flux tube through the total Frenet torsion along the tube.

  4. Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field

    NASA Astrophysics Data System (ADS)

    Xu, Yangyang; Yang, Guang; Xia, Hongyan; Zou, Gang; Zhang, Qijin; Gao, Jiangang

    2014-09-01

    Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine.

  5. New method to determine proton trajectories in the equatorial plane of a dipole magnetic field.

    PubMed

    Ioanoviciu, Damaschin

    2015-01-01

    A parametric description of proton trajectories in the equatorial plane of Earth's dipole magnetic field has been derived. The exact expression of the angular coordinate contains an integral to be performed numerically. The radial coordinate results from the initial conditions by basic mathematical operations and by using trigonometric functions. With the approximate angular coordinate formula, applicable for a wide variety of cases of protons trapped in Earth's radiation belts, no numerical integration is needed. The results of exact and approximate expressions were compared for a specific case and small differences were found. PMID:25815248

  6. Abnormal fb Es enhancements in equatorial Es layers during magnetic storms of solar cycle 23

    NASA Astrophysics Data System (ADS)

    Resende, L. C. A.; Denardini, C. M.; Batista, I. S.

    2013-09-01

    We have analyzed the behavior of blanketing frequency of the Es layer (fb Es) occurring at an equatorial station covering the days before, during and subsequent to 24 intense and very intense magnetic storms (Dst≤-100 nT) that occurred during the solar cycle 23. The fb Es was measured by digital ionosonde over São Luís, Brazil (2.33° S, 44.2° W, dip: -4.5°). Our analysis shows that there are significant changes in the fb Es, mainly during the recovery phase of magnetic storms, characterized by occurrence of peaks that exceed the ambient background values. Also, these peaks are associated to other types of sporadic E layer than the Esq (a non-blanketing layer detected due the plasma irregularities in the equatorial electrojet), which in turn means competing mechanisms. The results are discussed in terms of the statistics of the abnormal enhancement taking into account the phase of the magnetic storm.

  7. Magnetic Helicity of the Global Field in Solar Cycles 23 and 24

    NASA Astrophysics Data System (ADS)

    Pipin, V. V.; Pevtsov, A. A.

    2014-07-01

    For the first time we reconstruct the magnetic helicity density of the global axisymmetric field of the Sun using the method proposed by Brandenburg et al. and Pipin et al. To determine the components of the vector potential, we apply a gauge which is typically employed in mean-field dynamo models. This allows for a direct comparison of the reconstructed helicity with the predictions from the mean-field dynamo models. We apply this method to two different data sets: the synoptic maps of the line-of-sight magnetic field from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) and vector magnetic field measurements from the Vector Spectromagnetograph (VSM) on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) system. Based on the analysis of the MDI/SOHO data, we find that in solar cycle 23 the global magnetic field had positive (negative) magnetic helicity in the northern (southern) hemisphere. This hemispheric sign asymmetry is opposite to the helicity of the solar active regions, but it is in agreement with the predictions of mean-field dynamo models. The data also suggest that the hemispheric helicity rule may have reversed its sign during the early and late phases of cycle 23. Furthermore, the data indicate an imbalance in magnetic helicity between the northern and southern hemispheres. This imbalance seems to correlate with the total level of activity in each hemisphere in cycle 23. The magnetic helicity for the rising phase of cycle 24 is derived from SOLIS/VSM data, and qualitatively its latitudinal pattern is similar to the pattern derived from SOHO/MDI data for cycle 23.

  8. Using Magnetic Helicity Diagnostics to Determine the Nature of Solar Active-Region Formation

    NASA Astrophysics Data System (ADS)

    Georgoulis, Manolis K.

    Employing a novel nonlinear force-free (NLFF) method that self-consistently infers instantaneous free magnetic-energy and relative magnetic-helicity budgets from single photospheric vector magnetograms, we recently constructed the magnetic energy-helicity (EH) diagram of solar active regions. The EH diagram implies dominant relative helicities of left-handed or right-handed chiralities for the great majority of active regions. The amplitude (budget) of these helicities scales monotonically with the free magnetic energy. This constructive, strongly preferential accumulation of a certain sense of magnetic helicity seems to disqualify recently proposed mechanisms relying on a largely random near-surface convection for the formation of the great majority of active regions. The existing qualitative formation mechanism for these regions remains the conventional Omega-loop emergence following a buoyant ascension from the bottom of the convection zone. However, exceptions to this rule include even eruptive active regions: NOAA AR 11283 is an obvious outlier to the EH diagram, involving significant free magnetic energy with a small relative magnetic helicity. Relying on a timeseries of vector magnetograms of this region, our methodology shows nearly canceling amounts of both senses of helicity and an overall course from a weakly left-handed to a weakly right-handed structure, in the course of which a major eruption occurs. For this and similarly behaving active regions the latest near-surface formation scenario might conceivably be employed successfully. Research partially supported by the EU Seventh Framework Programme under grant agreement No. PIRG07-GA-2010-268245 and by the European Union Social Fund (ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.

  9. Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers

    NASA Astrophysics Data System (ADS)

    Hwang, G.; Decanini, D.; Leroy, L.; Haghiri-Gosnet, A. M.

    2016-03-01

    Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels.

  10. Theory for nanoparticle retention time in the helical channel of quadrupole magnetic field-flow fractionation

    NASA Astrophysics Data System (ADS)

    Williams, P. Stephen; Carpino, Francesca; Zborowski, Maciej

    2009-05-01

    Quadrupole magnetic field-flow fractionation (QMgFFF) is a separation and characterization technique for magnetic nanoparticles such as those used for cell labeling and for targeted drug therapy. A helical separation channel is used to efficiently exploit the quadrupole magnetic field. The fluid and sample components therefore have angular and longitudinal components to their motion in the thin annular space occupied by the helical channel. The retention ratio is defined as the ratio of the times for non-retained and a retained material to pass through the channel. Equations are derived for the respective angular and longitudinal components to retention ratio.

  11. Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.

    2014-12-01

    In earlier works we introduced and tested a nonlinear force-free (NLFF) method designed to self-consistently calculate the coronal free magnetic energy and the relative magnetic helicity budgets of observed solar magnetic structures. In principle, the method requires only a single, photospheric or low-chromospheric, vector magnetogram of a quiet-Sun patch or an active region and performs calculations without three-dimensional magnetic and velocity-field information. In this work we strictly validate this method using three-dimensional coronal magnetic fields. Benchmarking employs both synthetic, three-dimensional magnetohydrodynamic simulations and nonlinear force-free field extrapolations of the active-region solar corona. Our time-efficient NLFF method provides budgets that differ from those of more demanding semi-analytical methods by a factor of approximately three, at most. This difference is expected to come from the physical concept and the construction of the method. Temporal correlations show more discrepancies that are, however, soundly improved for more complex, massive active regions, reaching correlation coefficients on the order of, or exceeding, 0.9. In conclusion, we argue that our NLFF method can be reliably used for a routine and fast calculation of the free magnetic energy and relative magnetic helicity budgets in targeted parts of the solar magnetized corona. As explained in this article and in previous works, this is an asset that can lead to valuable insight into the physics and triggering of solar eruptions.

  12. A theoretical model for the magnetic helicity of solar active regions

    NASA Astrophysics Data System (ADS)

    Chatterjee, Piyali; Choudhuri, Arnab Rai; Petrovay, Kristof; Nandy, Dibyendu

    Active regions on the solar surface are known to possess magnetic helicity, which is predominantly negative in the northern hemisphere and positive in the southern hemisphere. Choudhuri et al. [Choudhuri, A.R. On the connection between mean field dynamo theory and flux tubes. Solar Phys. 215, 31 55, 2003] proposed that the magnetic helicity arises due to the wrapping up of the poloidal field of the convection zone around rising flux tubes which form active regions. Choudhuri [Choudhuri, A.R., Chatterjee, P., Nandy, D. Helicity of solar active regions from a dynamo model. ApJ 615, L57 L60, 2004] used this idea to calculate magnetic helicity from their solar dynamo model. Apart from getting broad agreements with observational data, they also predict that the hemispheric helicity rule may be violated at the beginning of a solar cycle. Chatterjee et al. [Chatterjee, P., Choudhuri, A.R., Petrovay, K. Development of twist in an emerging magnetic flux tube by poloidal field accretion. A&A 449, 781 789, 2006] study the penetration of the wrapped poloidal field into the rising flux tube due to turbulent diffusion using a simple 1-d model. They find that the extent of penetration of the wrapped field will depend on how weak the magnetic field inside the rising flux tube becomes before its emergence. They conclude that more detailed observational data will throw light on the physical conditions of flux tubes just before their emergence to the photosphere.

  13. Interplanetary magnetic field variations and the electromagnetic state of the equatorial ionosphere

    NASA Technical Reports Server (NTRS)

    Patel, V. L.

    1978-01-01

    The Esq phenomena were selected in order to examine the effect of the interplanetary magnetic field (IMF) on the ionospheric plasma and to obtain insight into the interplanetary ionospheric coupling processes. January-March 1973 interplanetary magnetic field data of Explorer 43, Huancayo ionograms, and surface equatorial magnetograms were used. The IMF observations from Explorer 43 in the form of 15-sec averages were examined around the time of disappearance of the Esq. The IMF z-component was observed to change from a negative to a positive value before the disappearance of the Esq in four events where simultaneous data were available. The general explanation is that the induced electric field becomes westward from a previous eastward direction, coinciding with the IMF z-component reversal. Thus, just before the Esq disappears, the magnetosphere is subjected to the westward electric field. If this field is impressed to the low-latitude ionosphere, the resultant electric field in the equatorial ionosphere changes from eastward (westward) to westward (eastward) in the daytime (nighttime).

  14. Detrital and Authigenic Magnetic Micro- and Nanoparticles in Pelagic Sediments of the Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Franke, C.; von Dobeneck, T.; Dekkers, M.

    2004-12-01

    Magnetic paleofield and paleoenvironmental information of marine sediments is mostly carried by submicron magnetic particles from various sources. Most existing studies make plausible, but largely unconfirmed assumptions about the origin, mineralogy and grain size of the magnetic mineral assemblages of pelagic sediments. This study intends to provide a detailed characterization of magnetic micro- and nanoparticles in oxic to mildly suboxic sedimentary environments of the Equatorial Atlantic and compares three sites (Ceará Rise, Mid Atlantic Ridge (MAR), Sierra Leone Rise) along a W-E transect. This region offers magnetic particle sources such as continental dust, fluvial discharge and weathering of ocean ridge basalts. Remanence, hysteresis, low- and high-temperature rock magnetic investigations were performed on bulk sediments, magnetic extracts and heavy liquid separates and were combined with analytic scanning (SEM) and transmission (TEM) electron microscopy. Curie temperatures between 580 and 600° C indicate oxidized magnetite as the major low coercivity component in all samples. The Verwey transition ( ˜110 K) is weakly expressed in the samples from the Ceará Rise and the MAR and disappears at the Sierra Leone Rise. SEM studies on the magnetic extracts show that the quantitative main components are detrital titanomagnetite particles with increasing Ti-content throughout the transect towards the East. Magnetite particles with very low to zero Ti-content provide about one third of the detrital component. They often show shrinking cracks indicating external maghemitization. Further components are octahedral titanomagnetite crystals, silicates with (titano-) magnetite inclusions and spherules with low Ti-content. An important high coercive component, most likely goethite, is unsaturated at 2.5 T and missing in the magnetic extracts. It is manifested by a large discrepancy of the slopes in field cooling and the zero field cooling low-temperature curves, which

  15. Vacuum magnetic field mapping experiments for validated determination of the helical field coil location in stellarators

    SciTech Connect

    Peterson, J.; Hanson, J.; Hartwell, G.; Knowlton, S.

    2010-03-15

    Understanding the behavior of plasmas in magnetic confinement fusion devices typically requires accurate knowledge of the magnetic field structure. In stellarator-type confinement devices, the helical magnetic field is produced by currents in external coils and may be traced experimentally in the absence of plasma through the experimental technique of vacuum magnetic field mapping. Field mapping experiments, such as these, were performed on the recently constructed compact toroidal hybrid to verify the range of accessible magnetic configurations, compare the actual magnetic configuration with the design configuration, and identify any vacuum field errors that lead to perturbations of the vacuum magnetic flux surfaces. Furthermore, through the use of a new coil optimization routine, modifications are made to the simulation coil model such that better agreement exists between the experimental and simulation results. An outline of the optimization procedure is discussed in conjunction with the results of one such optimization process performed on the helical field coil.

  16. Search for CP violating signature of intergalactic magnetic helicity in the gamma-ray sky

    NASA Astrophysics Data System (ADS)

    Tashiro, Hiroyuki; Chen, Wenlei; Ferrer, Francesc; Vachaspati, Tanmay

    2014-11-01

    The existence of a cosmological magnetic field could be revealed by the effects of non-trivial helicity on large scales. We evaluate a CP (conjugation plus parity) odd statistic, Q, using gamma-ray data obtained from Fermi satellite observations at high galactic latitudes to search for such a signature. Observed values of Q are found to be non-zero; the probability of a similar signal in Monte Carlo simulations is ˜0.2 per cent. Contamination from the Milky Way does not seem to be responsible for the signal since it is present even for data at very high galactic latitudes. Assuming that the signal is indeed due to a helical cosmological magnetic field, our results indicate left-handed magnetic helicity and field strength ˜10-14 G on ˜10 Mpc scales.

  17. A theoretical model for the magnetic helicity of solar active regions

    NASA Astrophysics Data System (ADS)

    Choudhuri, A. R.; Chatterjee, P.; Petrovay, K.; Nandy, D.

    Active regions on the solar surface are known to possess magnetic helicity which is predominantly negative in the northern hemisphere and positive in the southern hemisphere Choudhuri 2003 Sol Phys 123 217 proposed that the magnetic helicity arises due to the wrapping up of the poloidal field of the convection zone around rising flux tubes which form active regions Choudhuri Chatterjee and Nandy 2004 ApJ 615 L57 used this idea to calculate magnetic helicity from their solar dynamo model and found broad agreements with observational data Chatterjee Choudhuri and Petrovay 2006 A A in press have studied the penetration of the wrapped poloidal field into the rising flux tube and concluded that more detailed observational data will throw light on the physical conditions of flux tubes just before their emergence to the photosphere

  18. Ionospheric effects of the March 13, 1989, magnetic storm at low and equatorial latitudes

    SciTech Connect

    Batista, I.S.; De Paula, E.R.; Abdu, M.A.; Trivedi, N.B. ); Greenspan, M.E. )

    1991-08-01

    The great geomagnetic storm of March 13, 1989 caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza indicated F region upward plasma drifts exceeding 200 m s{sup {minus}1} at 1,830 LT as compared to normal values of 40 m s{sup {minus}1} for this epoch. Large negative phases were observed in foF2 over Fortaleza and Cachoeira Paulista and in total electron content measured over Sao Jose dos Campos. The equatorial ionization anomaly was totally absent either because of its anomalous expansion to higher latitudes or because of inhibition of its development on the two nights following the storm. Many anomalous variations in F region peak density and height, occurring simultaneously with sharp variations on H component of magnetic field over Fortaleza and with auroral substorms, give strong evidence of penetration of magnetospheric electric fields to equatorial and low latitudes. Auroral type sporadic E and night E layers are observed after 1,830 LT over Cachoeira Paulista, the latter showing peak electron density of about 6 {times} 10{sup 4} el cm{sup {minus}3}, therefore comparable to the E layer peak density in the morning hours at that station. The Fortaleza ionograms show the presence of the F1 layer at night, a phenomenon that has never been observed over our two stations before. The role played by electric fields penetrating from high to low latitudes, particle precipitation, and composition changes in explaining the observations is discussed.

  19. Formation of giant molecular clouds and helical magnetic fields by the Parker instability

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari; Matsumoto, Ryoji

    1991-10-01

    It is suggested that the Orion molecular cloud complex formed through the Parker instability (the buoyancy of a magnetic field entrained in matter) and that the helical filament found by Uchida et al. (1991) in the L1641 in the Orion cloud complex is the result of spinning gas falling along the magnetic field and twisting it. The twisted magnetic field, unlike a purely planar field, suppresses the Parker instability on small scales, allowing the generation of finite clouds rather than general turbulence.

  20. Plasma transport in the equatorial ionosphere during the great magnetic storm of March 1989

    SciTech Connect

    Rasmussen, C.E. ); Greenspan, M.E. )

    1993-01-01

    We have modeled plasma transport in the low-latitude and equatorial ionosphere during the great magnetic storm of March 1989. Our goal was to provide a consistent explanation for the DMSP (Defense Meteorological Satellite Program) observations of dramatic decreases in ion density and rapid ion drifts in the low latitude ionosphere over South America during the storm. The modeling effort supports the hypothesis that abnormally large upward drifts lifted F region plasma above the satellite's altitude and created the density depletions observed by DMSP. Modeled O[sup +] densities at the satellite's altitude have a strong qualitative resemblance to DMSP observations. Both the model and the observations indicate a deep density through with extremely sharp boundaries surrounding the equator. The widths of both the modeled and the observed equatorial troughs increase with time. Vertical ion drifts predicted by the model also have been compared with DMSP measurements. Like the observed vertical drifts, the modeled drifts reversed sign near the trough boundaries. The modeled vertical drifts are of the same order and direction as the vertical component of E x B convection near the equator, but of opposite direction (downward) near the trough boundaries and outside of the trough. 12 refs., 8 figs., 1 tab.

  1. Magnetic Energy and Helicity in Two Emerging Active Regions in the Sun

    NASA Technical Reports Server (NTRS)

    Liu, Y.; Schuck, P. W.

    2012-01-01

    The magnetic energy and relative magnetic helicity in two emerging solar active regions, AR 11072 and AR 11158,are studied. They are computed by integrating over time the energy and relative helicity fluxes across the photosphere. The fluxes consist of two components: one from photospheric tangential flows that shear and braid field lines (shear term), the other from normal flows that advect magnetic flux into the corona (emergence term). For these active regions: (1) relative magnetic helicity in the active-region corona is mainly contributed by the shear term,(2) helicity fluxes from the emergence and the shear terms have the same sign, (3) magnetic energy in the corona (including both potential energy and free energy) is mainly contributed by the emergence term, and(4) energy fluxes from the emergence term and the shear term evolved consistently in phase during the entire flux emergence course.We also examine the apparent tangential velocity derived by tracking field-line footpoints using a simple tracking method. It is found that this velocity is more consistent with tangential plasma velocity than with the flux transport velocity, which agrees with the conclusion by Schuck.

  2. Free magnetic energy and relative magnetic helicity diagnostics for the quality of NLFF field extrapolations

    NASA Astrophysics Data System (ADS)

    Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos; Georgoulis, Manolis K.

    We calculate the instantaneous free magnetic energy and relative magnetic helicity of solar active regions using two independent approaches: a) a non-linear force-free (NLFF) method that requires only a single photospheric vector magnetogram, and b) well known semi-analytical formulas that require the full three-dimensional (3D) magnetic field structure. The 3D field is obtained either from MHD simulations, or from observed magnetograms via respective NLFF field extrapolations. We find qualitative agreement between the two methods and, quantitatively, a discrepancy not exceeding a factor of 4. The comparison of the two methods reveals, as a byproduct, two independent tests for the quality of a given force-free field extrapolation. We find that not all extrapolations manage to achieve the force-free condition in a valid, divergence-free, magnetic configuration. This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.

  3. Electrical manipulation of dynamic magnetic impurity and spin texture of helical Dirac fermions

    NASA Astrophysics Data System (ADS)

    Wang, Rui-Qiang; Zhong, Min; Zheng, Shi-Han; Yang, Mou; Wang, Guang-Hui

    2016-05-01

    We have theoretically investigated the spin inelastic scattering of helical electrons off a high-spin nanomagnet absorbed on a topological surface. The nanomagnet is treated as a dynamic quantum spin and driven by the spin transfer torque effect. We proposed a mechanism to electrically manipulate the spin texture of helical Dirac fermions rather than by an external magnetic field. By tuning the bias voltage and the direction of impurity magnetization, we present rich patterns of spin texture, from which important fingerprints exclusively associated with the spin helical feature are obtained. Furthermore, it is found that the nonmagnetic potential can create the resonance state in the spin density with different physics as the previously reported resonance of charge density.

  4. Rigidity evaluation of a superconducting helical coil for an LHD-type fusion magnet

    NASA Astrophysics Data System (ADS)

    Tamura, H.; Imagawa, S.; Takahata, K.; Mito, T.; Sagara, A.

    2010-06-01

    The large helical device (LHD) type fusion power reactor has many advantages in operations such as steady state and no active plasma current. The magnet system of the LHD-type fusion device consists of superconducting helical coils and superconducting poloidal coils. Since the helical coil is a complicated three-dimensional structure, designs of the coil and the supporting structure have to be performed carefully. Clarifying the mechanical behavior during coil excitation is very important for a design of the coil system. The mechanical behavior for components in the helical coil can be estimated using a simplified two dimensional axisymmetric model which has a mean radius of curvature of the actual helical coil. To evaluate the accuracy of this simplified model, stress distribution was calculated with three-dimensional finite element model and the result was compared with that of the simplified model. The stress distribution of a candidate design of LHD-type helical reactor was estimated by using the simplified model and the result showed that the stress / strain level were within the reasonable range for composed materials.

  5. Disorder effects on helical edge transport in graphene under a strong tilted magnetic field

    NASA Astrophysics Data System (ADS)

    Huang, Chunli; Cazalilla, Miguel A.

    2015-10-01

    In a recent experiment, Young et al. [Nature (London) 505, 528 (2014), 10.1038/nature12800] observed a metal to insulator transition as well as transport through helical edge states in monolayer graphene under a strong, tilted magnetic field. Under such conditions, the bulk is a magnetic insulator which can exhibit metallic conduction through helical edges. It was found that the two-terminal conductance of the helical channels deviates from the expected quantized value (=e2/h per edge, at zero temperature). Motivated by this observation, we study the effect of disorder on the conduction through the edge channels. We show that, unlike for helical edges of topological insulators in semiconducting quantum wells, a disorder Rashba spin-orbit coupling does not lead to backscattering, at least to leading order. Instead, we find that the lack of perfect antialignment of the electron spins in the helical channels to be the most likely cause for backscattering arising from scalar (i.e., spin-independent) impurities. The intrinsic spin-orbit coupling and other time-reversal symmetry-breaking and/or sublattice parity-breaking potentials also lead to (subleading) corrections to the channel conductance.

  6. HF wave propagation and induced ionospheric turbulence in the magnetic equatorial region

    NASA Astrophysics Data System (ADS)

    Eliasson, B.; Papadopoulos, K.

    2016-03-01

    The propagation and excitation of artificial ionospheric turbulence in the magnetic equatorial region by high-frequency electromagnetic (EM) waves injected into the overhead ionospheric layer is examined. EM waves with ordinary (O) mode polarization reach the critical layer only if their incidence angle is within the Spitze cone. Near the critical layer the wave electric field is linearly polarized and directed parallel to the magnetic field lines. For large enough amplitudes, the O mode becomes unstable to the four-wave oscillating two-stream instability and the three-wave parametric decay instability driving large-amplitude Langmuir and ion acoustic waves. The interaction between the induced Langmuir turbulence and electrons located within the 50-100 km wide transmitter heating cone at an altitude of 230 km can potentially accelerate the electrons along the magnetic field to several tens to a few hundreds of eV, far beyond the thresholds for optical emissions and ionization of the neutral gas. It could furthermore result in generation of shear Alfvén waves such as those recently observed in laboratory experiments at the University of California, Los Angeles Large Plasma Device.

  7. Characteristics of magnetic island formation due to resistive interchange instability in helical plasma

    SciTech Connect

    Ueda, R.; Matsumoto, Y.; Itagaki, M.; Oikawa, S.; Watanabe, K. Y.; Sato, M.

    2014-05-15

    Focusing attention on the magnetic island formation, we investigate the characteristics of the resistive interchange magnetohydrodynamics instabilities, which would limit a high beta operational regime in helical type fusion reactors. An introduction of a new index, i.e., the ratio of the magnetic fluctuation level to the radial displacement, enables us to make a systematic analysis on the magnetic island formation in the large helical device-like plasmas during the linear growth phase; (i) the interchange instability with the second largest growth rate makes the magnetic island larger than that with the largest growth rate when the amplitude of the radial displacement in both cases is almost the same as each other; (ii) applied to a typical tearing instability, the index is smaller than that for the interchange instability with the second largest growth rate.

  8. Optimization of Saturn paraboloid magnetospheric field model parameters using Cassini equatorial magnetic field data

    NASA Astrophysics Data System (ADS)

    Belenkaya, Elena S.; Kalegaev, Vladimir V.; Cowley, Stanley W. H.; Provan, Gabrielle; Blokhina, Marina S.; Barinov, Oleg G.; Kirillov, Alexander A.; Grigoryan, Maria S.

    2016-07-01

    The paraboloid model of Saturn's magnetosphere describes the magnetic field as being due to the sum of contributions from the internal field of the planet, the ring current, and the tail current, all contained by surface currents inside a magnetopause boundary which is taken to be a paraboloid of revolution about the planet-Sun line. The parameters of the model have previously been determined by comparison with data from a few passes through Saturn's magnetosphere in compressed and expanded states, depending on the prevailing dynamic pressure of the solar wind. Here we significantly expand such comparisons through examination of Cassini magnetic field data from 18 near-equatorial passes that span wide ranges of local time, focusing on modelling the co-latitudinal field component that defines the magnetic flux passing through the equatorial plane. For 12 of these passes, spanning pre-dawn, via noon, to post-midnight, the spacecraft crossed the magnetopause during the pass, thus allowing an estimate of the concurrent subsolar radial distance of the magnetopause R1 to be made, considered to be the primary parameter defining the scale size of the system. The best-fit model parameters from these passes are then employed to determine how the parameters vary with R1, using least-squares linear fits, thus providing predictive model parameters for any value of R1 within the range. We show that the fits obtained using the linear approximation parameters are of the same order as those for the individually selected parameters. We also show that the magnetic flux mapping to the tail lobes in these models is generally in good accord with observations of the location of the open-closed field line boundary in Saturn's ionosphere, and the related position of the auroral oval. We then investigate the field data on six passes through the nightside magnetosphere, for which the spacecraft did not cross the magnetopause, such that in this case we compare the observations with three

  9. Global-scale consequences of magnetic-helicity injection and condensation on the sun

    SciTech Connect

    Mackay, Duncan H.; DeVore, C. Richard; Antiochos, Spiro K.

    2014-04-01

    In the recent paper of Antiochos, a new concept for the injection of magnetic helicity into the solar corona by small-scale convective motions and its condensation onto polarity inversion lines (PILs) was developed. We investigate this concept through global simulations of the Sun's photospheric and coronal magnetic fields, and compare the results with the hemispheric pattern of solar filaments. Assuming that the vorticity of the cells is predominantly counterclockwise/clockwise in the northern/southern hemisphere, the convective motions inject negative/positive helicity into each hemisphere. The simulations show that: (1) on a north-south oriented PIL, both differential rotation and convective motions inject the same sign of helicity, which matches that required to reproduce the hemispheric pattern of filaments. (2) On a high-latitude east-west oriented polar crown or subpolar crown PIL, the vorticity of the cells has to be approximately 2-3 times greater than the local differential-rotation gradient in order to overcome the incorrect sign of helicity injection from differential rotation. (3) In the declining phase of the cycle, as a bipole interacts with the polar field, in some cases, helicity condensation can reverse the effect of differential rotation along the east-west lead arm but not in all cases. The results show that this newly developed concept of magnetic helicity injection and condensation, in conjunction with the mechanisms used in Yeates et al., is a viable explanation for the hemispheric pattern of filaments. Future observational studies should focus on examining the vorticity component within convective motions to determine both its magnitude and latitudinal variation relative to the differential-rotation gradient on the Sun.

  10. Global-Scale Consequences of Magnetic-Helicity Injection and Condensation on the Sun

    NASA Technical Reports Server (NTRS)

    Mackay, Duncan H.; DeVore, C. Richard; Antiochos, Spiro K.

    2013-01-01

    In the recent paper of Antiochos, a new concept for the injection of magnetic helicity into the solar corona by small-scale convective motions and its condensation onto polarity inversion lines (PILs) has been developed. We investigate this concept through global simulations of the Sun's photospheric and coronal magnetic fields and compare the results with the hemispheric pattern of solar filaments. Assuming that the vorticity of the cells is predominately counter-clockwise/clockwise in the northern/southern hemisphere, the convective motions inject negative/positive helicity into each hemisphere. The simulations show that: (i) On a north-south orientated PIL, both differential rotation and convective motions inject the same sign of helicity which matches that required to reproduce the hemispheric pattern of filaments. (ii) On a high latitude east-west orientated polar crown or sub-polar crown PIL, the vorticity of the cells has to be approximately 2-3 times greater than the local differential rotation gradient in order to overcome the incorrect sign of helicity injection from differential rotation. (iii) In the declining phase of the cycle, as a bipole interacts with the polar field, in some cases helicity condensation can reverse the effect of differential rotation along the East-West lead arm, but not in all cases. The results show that this newly developed concept of magnetic helicity injection and condensation is a viable method to explain the hemispheric pattern of filaments in conjunction with the mechanisms used in Yeates et al. (2008). Future observational studies should focus on determining the vorticity component within convective motions to determine, both its magnitude and latitudinal variation relative to the differential rotation gradient on the Sun.

  11. Formation of sheet plumes, current coils, and helical magnetic fields in a spherical magnetohydrodynamic dynamo

    NASA Astrophysics Data System (ADS)

    Miyagoshi, Takehiro; Kageyama, Akira; Sato, Tetsuya

    2011-07-01

    Aiming at understanding of magnetic field generation process in rapidly rotating stars and planets represented by the Earth, computer simulations of magnetohydrodynamic (MHD) dynamo were performed in a rotating spherical shell geometry. Thermal convection and dynamo process with Ekman number of the order of 10-7 were studied. New structures of convection motion, dynamo-generated electrical current, and magnetic field are found. The flow is organized as a set of thin, sheet-like plumes. The current is made of small-scale coil structure with magnetic flux tubes within each of the coil. These flux tubes are connected each other to form a large scale helical magnetic field structure.

  12. BNL alternating gradient synchrotron with four helical magnets to minimize the losses of the polarized proton beam

    NASA Astrophysics Data System (ADS)

    Tsoupas, N.; Huang, H.; MacKay, W. W.; Meot, F.; Roser, T.; Trbojevic, D.

    2013-04-01

    The principle of using multiple partial helical magnets to preserve the polarization of the proton beam during its acceleration was applied successfully to the alternating gradient synchrotron (AGS) which currently operates with two partial helical magnets. In this paper we further explore this idea by using four partial helical magnets placed symmetrically in the AGS ring. This provides many advantages over the present setup of the AGS, which uses two partial helical magnets. First, the symmetric placement of the four helical magnets and their relatively lower field of operation allows for better control of the AGS optics with reduced values of the beta functions especially near beam injection and allows both the vertical and horizontal tunes to be placed within the “spin tune gap,” therefore eliminating the horizontal and vertical intrinsic spin resonances of the AGS during the acceleration cycle. Second, it provides a wider spin tune gap. Third, the vertical spin direction during beam injection and extraction is closer to vertical. Although the spin tune gap, which is created with four partial helices, can also be created with a single or two partial helices, the high field strength of a single helical magnet which is required to generate such a spin tune gap makes the use of the single helical magnet impractical, and that of the two helical magnets rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare them with those from the present setup of the AGS that uses two partial helical magnets. Although in this paper we specifically discuss the effect of the four partial helices on the AGS, this method which can eliminate simultaneously the vertical and horizontal intrinsic spin resonances is a general method and can be applied to any medium energy synchrotron which operates in similar energy range like the AGS and provides the required space to accommodate the four

  13. Solvent triggered structural diversity of triple-stranded helicates: single molecular magnets.

    PubMed

    Li, Hongfeng; Chen, Peng; Sun, Wenbin; Zhang, Lei; Yan, Pengfei

    2016-02-21

    Multiple-stranded helicates are of interest in respect of their simplicity in geometry and significance in biology and materials. Bis-β-diketones have shown their advantage in terms of structure and geometry in the construction of multiple-stranded helicates, but further studies on their properties are limited due to their poor crystallization. In this study, solvents are found to play a decisive role in the crystallization of triple-stranded helicates. [Dy2(BTB)3(H2O)4] is used as a precursor to solvent-dependently crystallize three complexes [Dy2(BTB)3(CH3OH)4]·3CH3OH (1), [Dy2(BTB)3(DME)2] (2) and [Dy2(BTB)3(DOA)(H2O)2]·4.5DOA (3) (BTB = 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl), where the key structural motif of the triple-stranded helicate, [Dy2(BTB)3], is retained. Four methanol molecules are found to ligate to Dy(3+) ions in 1, while each Dy(3+) ion is chelated by one DME molecule in 2. Interestingly, it is observed that 1,4-dioxane as a bridge ligates to two adjacent Dy(3+) ions, giving rise to the formation of a 1D chain structure. Magnetic measurement shows that 1 and 2 display slow magnetic relaxation under zero dc field, while single molecular magnet behavior is obtained for 3 under an applied dc field of 2000 Oe. PMID:26781997

  14. eRMHD simulations of jets with helical magnetic fields

    NASA Astrophysics Data System (ADS)

    Roca-Sogorb, M.; Perucho, M.; Gómez, J. L.; Martí, J. M.; Antón, L.; Aloy, M. A.; Agudo, I.

    We present numerical magnetohydrodynamic and emission (eRMHD) simulations of relativistic jets in active galactic nuclei. We focus our study on the role played by the magnetic field in the dynamics of the jet, analyzing the balance of the main driving forces which determine the jet evolution. Overpressured jets with different magnetizations are considered in order to study their influence in the jet collimation, confinement and overall stability. Computation of the synchrotron emission from these models allows a direct comparison with actual sources. We find that the relative brightness of the knots associated with the recollimation shocks decreases with increasing magnetization, suggesting that overpressured jets presenting stationary components may have a relatively weak magnetization, with magnetic fields of the order of equipartition or below.

  15. Short-term magnetic field alignment variations of equatorial ionospheric irregularities

    SciTech Connect

    Johnson, A.L.

    1988-06-01

    The ionospheric irregularities that cause equatorial scintillation are elongated along the north-south magnetic field lines. During a 1981 field campaign at Ascension Island, 250-MHz receivers were spaced from 300 m to 1.6 km along the field lines, and the signals received from the Marisat satellite were cross correlated. Data collected during eight nights of fading showed a linear relationship between fading rate and cross correlation. The alignment of the antennas was adjusted to give a zero time lag between the widely spaced receivers with a measurement accuracy of 0.03 s. Since the average irregularity velocity was 125 m/s, this time accuracy translated to an angular measurement accuracy of 0.1 deg. During a 4-hour period of nightly fading, occasional differences in time of arrival were noted that corresponded to a tilt in the north-south alignment of + or - 1 deg. Data from several nights of fading were analyzed, and each night exhibited the same variance in the north-south irregularity alignment. It is postulated that the shift in the measured peak correlation may have been caused by patches of irregularities at different altitudes where the magnetic field lines have a slightly different direction. 13 references.

  16. Noiseless manipulation of helical edge state transport by a quantum magnet

    NASA Astrophysics Data System (ADS)

    Silvestrov, P. G.; Recher, P.; Brouwer, P. W.

    2016-05-01

    The current through a helical edge state of a quantum spin Hall insulator may be fully transmitted through a magnetically gapped region due to a combination of spin-transfer torque and spin pumping [Meng et al., Phys. Rev. B 90, 205403 (2014), 10.1103/PhysRevB.90.205403]. Using a scattering approach, we here argue that in such a system the current is effectively carried by electrons with energies below the magnet-induced gap and well below the Fermi energy. This has striking consequences, such as the absence of shot noise, an exponential suppression of thermal noise, and an obstruction of thermal transport. For two helical edges covered by the same quantum magnet, the device can act as a robust noiseless current splitter.

  17. One-way helical electromagnetic wave propagation supported by magnetized plasma

    NASA Astrophysics Data System (ADS)

    Yang, Biao; Lawrence, Mark; Gao, Wenlong; Guo, Qinghua; Zhang, Shuang

    2016-02-01

    In this paper we reveal the presence of photonic one-way helical surface states in a simple natural system- magnetized plasma. The application of an external magnetic field to a bulk plasma body not only breaks time-reversal-symmetry but also leads to separation of Equi-Frequency Contour surfaces (EFCs) to form topologically nontrivial gaps in k space. Interestingly, these EFCs support topologically protected surface states. We numerically investigate an interface between magnetized plasma, using a realistic model for parameter dispersion, and vacuum, to confirm the existence of one-way scatter-immune helical surface states. Unlike previous proposals for achieving photonic one-way propagation, our scheme does not require the use of artificial structures and should therefore be simple to implement experimentally.

  18. One-way helical electromagnetic wave propagation supported by magnetized plasma

    PubMed Central

    Yang, Biao; Lawrence, Mark; Gao, Wenlong; Guo, Qinghua; Zhang, Shuang

    2016-01-01

    In this paper we reveal the presence of photonic one-way helical surface states in a simple natural system- magnetized plasma. The application of an external magnetic field to a bulk plasma body not only breaks time-reversal-symmetry but also leads to separation of Equi-Frequency Contour surfaces (EFCs) to form topologically nontrivial gaps in k space. Interestingly, these EFCs support topologically protected surface states. We numerically investigate an interface between magnetized plasma, using a realistic model for parameter dispersion, and vacuum, to confirm the existence of one-way scatter-immune helical surface states. Unlike previous proposals for achieving photonic one-way propagation, our scheme does not require the use of artificial structures and should therefore be simple to implement experimentally. PMID:26883883

  19. Formation of Opposite-Sign Magnetic Helicity by an Erupting Filament in a Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Kurokawa, Hiroki

    2004-06-01

    It is unclear whether it is possible for magnetic helical fields of opposite signs to co-exist in a coronal mass ejection (CME). During filament eruption with high-cadence observations for the initial stage, evidence is found for the formation of right-handed helical fields in a rising dextral filament that is embedded in a CME with helical fields in a left-handed sense. The data include Mees multi-off-band Hα observations with 16s cadence and TRACE 1600Å observations of 2s cadence. The filament material is ejected outward and is associated with the expanding CME, suggesting that both of the opposite-sign helical fields are injected into interplanetary space. In this paper, we consider the key observational features, including the formation of a coil-like structure (due to barb reconnections) and the alignment of reconnected field lines with the primary axis of the filament. It is found that they are consistent with the predicted changes during filament eruption by the filament model of Martin and McAllister. However, our results do not reject the filament model of Rust and Kumar. Moreover, a model that reconciles both of them seems to be more convenient for understanding the complicated observations. Therefore, the formation of opposite-sign helicity in an eruptive flux rope should be common for such types of filament eruptions.

  20. Helical Magnetic Fields in the NGC 1333 IRAS 4A Protostellar Outflows

    NASA Astrophysics Data System (ADS)

    Ching, Tao-Chung; Lai, Shih-Ping; Zhang, Qizhou; Yang, Louis; Girart, Josep M.; Rao, Ramprasad

    2016-03-01

    We present Submillimeter Array polarization observations of the CO J = 3-2 line toward NGC 1333 IRAS 4A. The CO Stokes I maps at an angular resolution of ˜1″ reveal two bipolar outflows from the binary sources of NGC 1333 IRAS 4A. The kinematic features of the CO emission can be modeled by wind-driven outflows at ˜20° inclined from the plane of the sky. Close to the protostars the CO polarization, at an angular resolution of ˜2.″3, has a position angle approximately parallel to the magnetic field direction inferred from the dust polarizations. The CO polarization direction appears to vary smoothly from an hourglass field around the core to an arc-like morphology wrapping around the outflow, suggesting a helical structure of magnetic fields that inherits the poloidal fields at the launching point and consists of toroidal fields at a farther distance of outflow. The helical magnetic field is consistent with the theoretical expectations for launching and collimating outflows from a magnetized rotating disk. Considering that the CO polarized emission is mainly contributed from the low-velocity and low-resolution data, the helical magnetic field is likely a product of the wind-envelope interaction in the wind-driven outflows. The CO data reveal a PA of ˜30° deflection in the outflows. The variation in the CO polarization angle seems to correlate with the deflections. We speculate that the helical magnetic field contributes to ˜10° deflection of the outflows by means of Lorentz force.

  1. Flow Driven by an Archimedean Helical Permanent Magnetic Field. Part I: Flow Patterns and Their Transitions

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Wang, Xiaodong; Etay, Jacqueline; Na, Xianzhao; Zhang, Xinde; Fautrelle, Yves

    2016-04-01

    In this study, an Archimedean helical permanent magnetic field was constructed and its driving effects on liquid metal were examined. A magnetic stirrer was constructed using a series of arc-like magnets. The helical distribution of its magnetic field, which was confirmed via Gauss probe measurements and numerical simulations, can be considered a combination of rotating and traveling magnetic fields. The characteristics of the flow patterns, particularly the transitions between the meridian secondary flow (two vortices) and the global axial flow (one vortex), driven by this magnetic field were quantitatively measured using ultrasonic Doppler velocimetry. The transient and modulated flow behaviors will be presented in a companion article. The D/ H dimension ratio was used to characterize the transitions of these two flow patterns. The results demonstrated that the flow patterns depend on not only the intrinsic structure of the magnetic field, e.g., the helix lead angle, but also the performance parameters, e.g., the dimensional ratio of the liquid bulk. The notable opposing roles of these two flow patterns in the improvement of macrosegregations when imposing such magnetic fields near the solidifying front were qualitatively addressed.

  2. Characteristics of 3-component Magnetic Fields of Equatorial Pi 2s - MAGDAS/CPMN Observations in Daytime and Nighttime -

    NASA Astrophysics Data System (ADS)

    Hirayama, Y.; Yumoto, K.; Uozumi, T.; Yoshikawa, A.; Group, M.

    2008-12-01

    At the onset of magnetospheric substorms, impulsive hydromagnetic oscillations with periods of 40-150 sec, so called Pi 2 magnetic pulsations, occur globally in the magnetosphere. Pi 2 pulsations have been researched for a long time. However, equatorial Pi 2 pulsations have not been analyzed sufficiently and in the most of past studies only H-component of equatorial Pi 2 pulsations were examined. In our previous study, we analyzed H-component magnetic data obtained from MAGDAS/CPMN stations, AAB(G.long.=38.77), LKW(99.78), CEB(123.91), DAV(125.40), YAP(138.08), ANC(-77.15) and EUS(-38.43) which are located near the dip equator. We found that enhancement of H-component wave amplitude of Pi 2 pulsations are occurred near the daytime dip equator. Furthermore, by comparing the data obtained from CEB, DAV and YAP, we also found that as the observation site is nearer to the dip equator, the Pi 2 amplitudes tended to become larger. This amplitude enhancement of Pi 2 pulsations was seen not only in daytime but also in nighttime. We could explain the enhancement in daytime as effect of equatorial electrojet, but we had no idea to explain the enhancement in nighttime. In the present study, we analyze H, D and Z-component wave amplitudes of equatorial Pi 2 pulsations obtained from CEB, DAV and ANC stations for the period of January 1-31, March 1~31 and Jun 1~30 2005. The following new results are obtained; (1) Amplitude ratio of H-component of equatorial Pi 2s at DAV (Dip Lat =-0.65) to CEB (2.73) is found to be almost 1.5 in nighttime, while that in daytime to show the equatorial enhancement and a monthly dependence. (2) Amplitude ratio of D-component to H-component of equatorial Pi 2 are found to be almost 0.3, in particularly to enhance to 0.5 at near local sunrise and sunset time, while H-component equatorial Pi 2 amplitude decrease at sunrise and sunset time. (3) Amplitude ratio of Z-component to H-component of equatorial Pi 2 are found to be 0.3 at CEB and ANC, and 0

  3. Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers.

    PubMed

    Hwang, G; Decanini, D; Leroy, L; Haghiri-Gosnet, A M

    2016-03-01

    Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels. PMID:27036837

  4. Modulated helical metals at magnetic domain walls of pyrochlore iridium oxides

    NASA Astrophysics Data System (ADS)

    Yamaji, Youhei; Imada, Masatoshi

    2016-05-01

    Spontaneous symmetry breakings, metal-insulator transitions, and transport properties of magnetic-domain-wall states in pyrochlore iridium oxides are studied by employing a symmetry-adapted effective Hamiltonian with a slab perpendicular to the (111) direction of the pyrochlore structure. Emergent metallic domain wall, which has an unconventional topological nature with a controllable and mobile metallic layer, is shown to host Fermi surfaces with modulated helical spin textures resembling Rashba metals. The helical nature of the domain-wall Fermi surfaces is experimentally detectable by anomalous Hall conductivity, circular dichroism, and optical Hall conductivity under external magnetic fields. Possible applications of the domain-wall metals to spin-current generation and "half-metallic" conduction are also discussed.

  5. Cross and magnetic helicity in the outer heliosphere from Voyager 2 observations

    NASA Astrophysics Data System (ADS)

    Iovieno, M.; Gallana, L.; Fraternale, F.; Richardson, J. D.; Opher, M.; Tordella, D.

    2016-01-01

    Plasma velocity and magnetic field measurements from the Voyager 2 mission are used to study solar wind turbulence in the slow solar wind at two different heliocentric distances, 5 and 29 astronomical units, sufficiently far apart to provide information on the radial evolution of this turbulence. The magnetic helicity and the cross-helicity, which express the correlation between the plasma velocity and the magnetic field, are used to characterize the turbulence. Wave number spectra are computed by means of the Taylor hypothesis applied to time resolved single point Voyager 2 measurements. The overall picture we get is complex and difficult to interpret. A substantial decrease of the cross-helicity at smaller scales (over 1-3 hours of observation) with increasing heliocentric distance is observed. At 5 AU the only peak in the probability density of the normalized residual energy is negative, near -0.5. At 29 AU the probability density becomes doubly peaked, with a negative peak at -0.5 and a smaller peak at a positive values of about 0.7. A decrease of the cross-helicity for increasing heliocentric distance is observed, together with a reduction of the unbalance toward the magnetic energy of the energy of the fluctuations. For the smaller scales, we found that at 29 AU the normalized polarization is small and positive on average (about 0.1), it is instead zero at 5 AU. For the larger scales, the polarization is low and positive at 5 AU (average around 0.1) while it is negative (around - 0.15) at 29 AU.

  6. Response of Helical Luttinger Liquid in InAs/GaSb Edges to a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Li, Tingxin; Tong, Bingbing; Liu, Xiaoxue; Han, Zhongdong; Zhang, Chi; Sullivan, Gerard; Du, Rui-Rui

    Electron-electron interactions have been shown to play an important role in InAs/GaSb quantum spin Hall (QSH) edge states, leading to power-law behaviors of the helical edge conductance as a function of temperature and bias voltage (Li et al., Phys. Rev. Lett. 115 136804). A variety of inelastic and/or multiparticle backscattering processes could occur in helical edges when taking electron-electron interactions into account. On the other hand, in the presence of an external magnetic field, single-particle elastic backscattering is also allowed in QSH edge due to the breaking of time-reversal symmetry (TRS). It would be interesting to pursue experimental investigations for the combined effect of electron-electron interactions and TRS breaking on QSH edge transport. We report work in progress for low temperature conductance measurements of the helical edge in InAs/GaSb under perpendicular or in-plane magnetic fields. We found that the magnetic field responses are generally correlated with the interaction strength in the edge states. The work at Peking University were supported by NBRPC Grants (No. 2012CB921301 and No. 2014CB920901), and by Collaborative Innovation Center of Quantum Matter.

  7. A statistical study of Pc 1-2 magnetic pulsations in the equatorial magnetosphere. I - Equatorial occurrence distributions. II - Wave properties

    NASA Technical Reports Server (NTRS)

    Anderson, B. J.; Erlandson, R. E.; Zanetti, L. J.

    1992-01-01

    AMPTE CCE magnetic field data from a period spanning a complete local time revolution of the satellite orbit major axis are used to examine the occurrence distribution of transverse narrowband Pc 1-2 emissions in the equatorial magnetosphere from L = 3.5 to L = 9 at all local times. Three examples are presented to illustrate the properties of events occurring at dawn, noon, and dusk. The early afternoon outer magnetosphere is found to be the dominant site for electromagnetic ion cyclotron wave occurrence. Pc 1-2 exhibited a radial structure with a gap between high- and low-L events. The example intervals indicate that a significant local time variation of wave properties may exist. Distributions are presented of narrowband Pc 1-2 frequency, ellipticity, normalized frequency and spectral power vs local time, L, and magnetic latitude, using the data base of more than 9000 events obtained from AMPTE CCE magnetometer data. Events occurring in the region 0300-0900 MLT, L greater than 7 are distinctly different from the remainder of Pc 1-2. The unique features of this population are linear polarization at all latitudes and high normalized frequency, 0.4 to 0.5 on average.

  8. Magnetic field components in a sinusoidally varying helical wiggler

    SciTech Connect

    Caspi, S.

    1994-07-27

    One may be interested in a pure multipole magnetic field (i.e., proportional to sin(n{theta}) or cos(n{theta}) whose strength varies purely as a Fourier sinusoidal series of the longitudinal coordinate z (say proportional to cos{sub L}/{sup (2m-1){pi}z}), where L denotes the half-period of the wiggler and m=1,2,3{hor_ellipsis}). Associated with such a z variation, there necessarily will be presented a z component of magnetic field which in the source-free region, in fact, will give rise to both normal and skew transverse fields associated with the functions A{sub n}(z) and {Angstrom}{sub n}(z) as expressed in Reference{sup bc}. In this note the field components and expression for the scalar potential both inside and outside a thin pure winding surface are included with additional contributions from a possible high permeable shield. It is also shown that for a pure dipole case of n=1 and pure axial variation of m=1 the transverse field can be derived from a simple two dimensional field.

  9. Final Techical Report - "Determining How Magnetic Helicity Injection Really Works"

    SciTech Connect

    Paul M. Bellan

    2005-02-15

    This research program involved direct observation of the complicated plasma dynamics underlying spheromak formation. Spheromaks are self-organizing magnetically dominated plasma configurations which potentially offer a simple, low-cost means for confining the plasma in a controlled thermonuclear fusion reactor. The spheromak source used in these studies was a coaxial co-planar magnetized plasma gun which was specifically designed to have the simplest relevant geometry. The simplicity of the geometry facilitated understanding of the basic physics and minimized confusion that would otherwise have resulted from complexities due to the experimental geometry. The coaxial plasma gun was mounted on one end of a large vacuum tank that had excellent optical access so the spheromak formation process could be tracked in detail using ultra-high speed cameras. The main accomplishments of this research program were (1) obtaining experimental data characterizing the detailed physics underlying spheromak formation and the development of new theoretical models motivated by these observations, (2) determining the relationship between spheromak physics and astrophysical jets, (3) developing a new high-speed camera diagnostic for the SSPX spheromak at the Lawrence Livermore National Lab, and (4) training graduate students and postdoctoral fellows.

  10. Helical order in one-dimensional magnetic atom chains and possible emergence of Majorana bound states

    NASA Astrophysics Data System (ADS)

    Kim, Younghyun; Cheng, Meng; Bauer, Bela; Lutchyn, Roman M.; Das Sarma, S.

    2014-08-01

    We theoretically obtain the phase diagram of localized magnetic impurity spins arranged in a one-dimensional chain on top of a one- or two-dimensional electron gas. The interactions between the spins are mediated by the Ruderman-Kittel-Kasuya-Yosida mechanism through the electron gas. Recent work predicts that such a system may intrinsically support topological superconductivity without spin-orbit coupling when a helical spin-density wave is spontaneously formed in the spins, and superconductivity is induced in the electron gas. We analyze, using both analytical and numerical techniques, the conditions under which such a helical spin state is stable in a realistic situation in the presence of disorder. We show that (i) it appears only when the spins are coupled to a (quasi-) one-dimensional electron gas, and (ii) it becomes unstable towards the formation of (anti)ferromagnetic domains if the disorder in the impurity spin positions δR becomes comparable with the Fermi wavelength. We also examine the stability of the helical state against Gaussian potential disorder in the electronic system using a diagrammatic approach. Our results suggest that in order to stabilize the helical spin state and thus the emergent topological superconductivity under realistic experimental conditions, a sufficiently strong Rashba spin-orbit coupling, giving rise to Dzyaloshinskii-Moriya interactions, is required.

  11. Generation of uniform magnetic field using a spheroidal helical coil structure

    NASA Astrophysics Data System (ADS)

    Öztürk, Yavuz; Aktaş, Bekir

    2016-01-01

    Uniformity of magnetic fields are of great importance especially in magnetic resonance studies, namely in magnetic resonance spectroscopy applications (NMR, FMR, ESR, EPR etc.) and magnetic resonance imaging applications (MRI, FMRI). Field uniformity is also required in some other applications such as eddy current probes, magnetometers, magnetic traps, particle counters etc. Here we proposed a coil winding regime, which follows the surface of a spheroid (an ellipsoid of rotation); in light of previous theoretical studies suggesting perfect uniformity for a constant ampere per turn in the axial direction thereof. We demonstrated our theoretical results from finite element calculations suggesting 0.15% of field uniformity for the proposed structure, which we called a Spheroidal Helical Coil.

  12. Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3

    NASA Astrophysics Data System (ADS)

    Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.

    2015-10-01

    Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R 3 m ) comprising triangular motifs of Fe3 + coupled by strong antiferromagnetic interactions (| ΘC W|>900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below TN = 163 K, with the helical axis in the hexagonal a b plane and a modulation length to ˜86 Å. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 Å along the hexagonal c axis but is limited to ˜70 Å in the a b plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T =TN/40 , indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3 . Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below TN. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3 + ions (S =5 /2 ), μ ˜4.2 μB , is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3 -x )GaxPO4O3 , and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) μB. We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.

  13. Helicity, anisotropies, and their competition in a multiferroic magnet: Insight from the phase diagram

    NASA Astrophysics Data System (ADS)

    Gvozdikova, M. V.; Ziman, T.; Zhitomirsky, M. E.

    2016-07-01

    Motivated by the complex phase diagram of MnWO4, we investigate the competition between anisotropy, magnetic field, and helicity for the anisotropic next-nearest-neighbor Heisenberg model. Apart from two competing exchanges, which favor a spiral magnetic structure, the model features the biaxial single-ion anisotropy. The model is treated in the real-space mean-field approximation and the phase diagram containing various incommensurate and commensurate states is obtained for different field orientations. We discuss the similarities and differences of the theoretical phase diagram and the experimental diagram of MnWO4.

  14. Direct Detection of the Helical Magnetic Field Geometry from 3D Reconstruction of Prominence Knot Trajectories

    NASA Astrophysics Data System (ADS)

    Zapiór, Maciej; Martínez-Gómez, David

    2016-02-01

    Based on the data collected by the Vacuum Tower Telescope located in the Teide Observatory in the Canary Islands, we analyzed the three-dimensional (3D) motion of so-called knots in a solar prominence of 2014 June 9. Trajectories of seven knots were reconstructed, giving information of the 3D geometry of the magnetic field. Helical motion was detected. From the equipartition principle, we estimated the lower limit of the magnetic field in the prominence to ≈1-3 G and from the Ampère’s law the lower limit of the electric current to ≈1.2 × 109 A.

  15. Relationships between Fluid Vorticity, Kinetic Helicity, and Magnetic Field on Small-scales (Quiet-Network) on the Sun

    NASA Astrophysics Data System (ADS)

    Sangeetha, C. R.; Rajaguru, S. P.

    2016-06-01

    We derive horizontal fluid motions on the solar surface over large areas covering the quiet-Sun magnetic network from local correlation tracking of convective granules imaged in continuum intensity and Doppler velocity by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. From these we calculate the horizontal divergence, the vertical component of vorticity, and the kinetic helicity of fluid motions. We study the correlations between fluid divergence and vorticity, and between vorticity (kinetic helicity) and the magnetic field. We find that the vorticity (kinetic helicity) around small-scale fields exhibits a hemispherical pattern (in sign) similar to that followed by the magnetic helicity of large-scale active regions (containing sunspots). We identify this pattern to be a result of the Coriolis force acting on supergranular-scale flows (both the outflows and inflows), consistent with earlier studies using local helioseismology. Furthermore, we show that the magnetic fields cause transfer of vorticity from supergranular inflow regions to outflow regions, and that they tend to suppress the vortical motions around them when magnetic flux densities exceed about 300 G (from HMI). We also show that such an action of the magnetic fields leads to marked changes in the correlations between fluid divergence and vorticity. These results are speculated to be of importance to local dynamo action (if present) and to the dynamical evolution of magnetic helicity at the small-scale.

  16. Evolution of the magnetic helicity flux during the formation and eruption of flux ropes

    SciTech Connect

    Romano, P.; Zuccarello, F. P.; Guglielmino, S. L.; Zuccarello, F.

    2014-10-20

    We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We found a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.

  17. Helicity-vorticity turbulent pumping of magnetic fields in the solar convection zone

    NASA Astrophysics Data System (ADS)

    Pipin, V. V.

    2013-02-01

    We study the effect of turbulent drift of a large-scale magnetic field that results from the interaction of helical convective motions and differential rotation in the solar convection zone. The principal direction of the drift corresponds to the direction of the large-scale vorticity vector. Thus, the effect produces a latitudinal transport of the large-scale magnetic field in the convective zone wherever the angular velocity has a strong radial gradient. The direction of the drift depends on the sign of helicity and it is defined by the Parker-Yoshimura rule. The analytic calculations are done within the framework of mean-field magnetohydrodynamics using the minimal \\tau-approximation. We estimate the magnitude of the drift velocity and find that it can be several m/s near the base of the solar convection zone. The implications of this effect for the solar dynamo are illustrated on the basis of an axisymmetric mean-field dynamo model with a subsurface shear layer. We find that the helicity--vorticity pumping effect can have an influence on the features of the sunspot time--latitude diagram, producing a fast drift of the sunspot activity maximum at the rise phase of the cycle and a slow drift at the decay phase of the cycle.

  18. Anomalous scaling of the magnetic field in the helical Kazantsev-Kraichnan model.

    PubMed

    Jurčišinová, E; Jurčišin, M

    2015-06-01

    The field-theoretic renormalization group and the operator product expansion are used to investigate the influence of spatial parity violation of the conductive turbulent environment on the anomalous scaling behavior of correlation functions of a weak magnetic field in the framework of the Kazantsev-Kraichnan rapid change model. Two-loop expressions for the critical dimensions of the leading composite operators, which drive the anomalous scaling of the two-point single-time correlation functions of the magnetic field in the presence of large-scale anisotropy, are found to be functions of the helicity parameter. It is shown that the presence of helicity in the system leads to a significantly stronger manifestation of anomalous scaling than in the nonhelical case. At the same time, it is also shown that helicity does not destroy the standard hierarchy of the anisotropic anomalous exponents in the framework of which the leading contribution to anomalous scaling is given by the isotropic shell. PMID:26172794

  19. Sign-Singularity of the Reduced Magnetic Helicity in the Solar Wind Plasma

    SciTech Connect

    Carbone, V.; Perri, S.; Yordanova, E.; Khotyaintsev, Y.; Andre, M.; Veltri, P.; Bruno, R.

    2010-05-07

    We investigate the scaling laws of a signed measure derived from the reduced magnetic helicity which has been determined from Cluster data in the solar wind. This quantifies the handedness of the magnetic field; namely, it can be related to the polarization of the magnetic field fluctuations (right or left hand). The measure results to be sign-singular; that is, we do not observe any scale-dependent effect at the ion- and at electron-cyclotron frequencies. Cancellations between right- and left-hand polarizations go on in the dispersive or dissipative range, beyond the electron-cyclotron frequency. This means that the mechanism responsible for the generation of the dispersive or dissipative range is rather insensitive to the polarization of the magnetic field fluctuations.

  20. Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity

    SciTech Connect

    Charbonneau, James; Zhitnitsky, Ariel E-mail: arz@phas.ubc.ca

    2010-08-01

    The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation.

  1. Magnetic helicity conservation and inverse energy cascade in electron magnetohydrodynamic wave packets.

    PubMed

    Cho, Jungyeon

    2011-05-13

    Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence. PMID:21668138

  2. Sign-singularity of the reduced magnetic helicity in the solar wind plasma.

    PubMed

    Carbone, V; Perri, S; Yordanova, E; Veltri, P; Bruno, R; Khotyaintsev, Y; André, M

    2010-05-01

    We investigate the scaling laws of a signed measure derived from the reduced magnetic helicity which has been determined from Cluster data in the solar wind. This quantifies the handedness of the magnetic field; namely, it can be related to the polarization of the magnetic field fluctuations (right or left hand). The measure results to be sign-singular; that is, we do not observe any scale-dependent effect at the ion- and at electron-cyclotron frequencies. Cancellations between right- and left-hand polarizations go on in the dispersive or dissipative range, beyond the electron-cyclotron frequency. This means that the mechanism responsible for the generation of the dispersive or dissipative range is rather insensitive to the polarization of the magnetic field fluctuations. PMID:20482162

  3. Magnetic Helicity Conservation and Inverse Energy Cascade in Electron Magnetohydrodynamic Wave Packets

    SciTech Connect

    Cho, Jungyeon

    2011-05-13

    Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.

  4. Ion heating during magnetic relaxation in the helicity injected torus-II experiment

    SciTech Connect

    O'Neill, R.G.; Redd, A.J.; Hamp, W.T.; Smith, R.J.; Jarboe, T.R.

    2005-12-15

    Ion doppler spectroscopy (IDS) is applied to the helicity injected torus (HIT-II) spherical torus to measure impurity ion temperature and flows. [A. J. Redd et al., Phys. Plasmas 9, 2006 (2002)] The IDS instrument employs a 16-channel photomultiplier and can track temperature and velocity continuously through a discharge. Data for the coaxial helicity injection (CHI), transformer, and combined current drive configurations are presented. Ion temperatures for transformer-driven discharges are typically equal to or somewhat lower than electron temperatures measured by Thomson scattering. Internal reconnection events in transformer-driven discharges cause rapid ion heating. The CHI discharges exhibit anomalously high ion temperatures >250 eV, which are an order of magnitude higher than Thomson measurements, indicating ion heating through magnetic relaxation. The CHI discharges that exhibit current and poloidal flux buildup after bubble burst show sustained ion heating during current drive.

  5. Lanthanide-Directed Fabrication of Four Tetranuclear Quadruple Stranded Helicates Showing Magnetic Refrigeration and Slow Magnetic Relaxation.

    PubMed

    Mondal, Amit Kumar; Jena, Himanshu Sekhar; Malviya, Amita; Konar, Sanjit

    2016-06-01

    A rare class of four tetranuclear lanthanide based quadruple stranded helicates namely, [Ln4L4(OH)2](OAc)2·xH2O (Ln = Gd(III)(1), Dy(III)(2) and x = 4, 5 respectively), [Er4L4(OH)2](NO3)2·9H2O (3), and [Dy4L4(NO3)](NO3)2·2CH3OH·H2O (4) were synthesized by employing succinohydrazone derived bis-tridentate ligand (H2L) and characterized. Structures of 1-3 are similar to each other except the nature of counterions and number of lattice water molecules. In 4, a distorted nitrate ion was arranged in a hexagonal manner holding four dysprosium centers in a slightly twisted manner. Because of the symmetrical nature of each complex, the C4 axis crosses the center of helicate resulting a pseudo-D4 coordination environment. Each ligand coordinates to lanthanide centers in helical manner forming mixture of left (Λ) and right (Δ) handed discrete units. Complex 1 exhibits antiferromagnetic exchange interaction between nearby Gd(III) centers and shows magnetic refrigeration (-ΔSm = 24.4 J kg(-1) K(-1) for ΔH = 7 T at 3 K). AC magnetic susceptibility measurements of 2 and 4 demonstrate slow relaxation behavior, with Ueff (effective energy barrier) of 20.5 and 4.6 K, respectively. As per our knowledge, complexes 1, 2, and 4 represent the first examples of aesthetically pleasing quadruple stranded helicates showing potential magnetocaloric effect and single-molecule-magnet-like behavior. PMID:27196362

  6. Helical states with ordered magnetic topology in the Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Bonfiglio, D.; Cappello, S.; Gobbin, M.; Spizzo, G.

    2008-11-01

    The reversed field pinch (RFP) configuration for magnetic confinement has shown to develop helical configurations characterized by good magnetic surfaces both in experiments and visco-resistive 3D MHD numerical computations [1]. In the RFX-mod experiment, quasi-single helicity (QSH) states with ordered magnetic topology have been found to develop both spontaneously during high current discharges [2] and in a stimulated way through the periodic oscillation of the toroidal flux (so-called OPCD technique) [3]. In both cases, the expulsion of the separatrix of the dominant mode has proved to be the key for significant chaos healing [4], as expected by theory [5]. In this work, we present results of visco-resistive 3D MHD numerical modeling aiming at clarifying the mechanism and the conditions for separatrix expulsion and chaos healing in spontaneous and stimulated cases. The effect is investigated by reconstruction of the magnetic topology through field line tracing algorithms and by study of test particle dynamics. [1] S. Cappello, Plasma Phys. Control. Fusion 46, B313 (2004) & references therein. [2] M. Valisa et al., invited oral, EPS Conf. on Plasma Physics (2008). [3] D. Terranova et al., Phys. Rev. Lett. 99, 095001 (2007). [4] R. Lorenzini et al., Phys. Rev. Lett. 101, 025005 (2008). [5] D. F. Escande, R. Paccagnella et al., Phys. Rev. Lett. 85, 3169 (2000).

  7. INTERPRETING ERUPTIVE BEHAVIOR IN NOAA AR 11158 VIA THE REGION'S MAGNETIC ENERGY AND RELATIVE-HELICITY BUDGETS

    SciTech Connect

    Tziotziou, Kostas; Georgoulis, Manolis K.; Liu Yang

    2013-08-01

    In previous works, we introduced a nonlinear force-free method that self-consistently calculates the instantaneous budgets of free magnetic energy and relative magnetic helicity in solar active regions (ARs). Calculation is expedient and practical, using only a single vector magnetogram per computation. We apply this method to a time series of 600 high-cadence vector magnetograms of the eruptive NOAA AR 11158 acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory over a five-day observing interval. Besides testing our method extensively, we use it to interpret the dynamical evolution in the AR, including eruptions. We find that the AR builds large budgets of both free magnetic energy and relative magnetic helicity, sufficient to power many more eruptions than the ones it gave within the interval of interest. For each of these major eruptions, we find eruption-related decreases and subsequent free-energy and helicity budgets that are consistent with the observed eruption (flare and coronal mass ejection (CME)) sizes. In addition, we find that (1) evolution in the AR is consistent with the recently proposed (free) energy-(relative) helicity diagram of solar ARs, (2) eruption-related decreases occur before the flare and the projected CME-launch times, suggesting that CME progenitors precede flares, and (3) self terms of free energy and relative helicity most likely originate from respective mutual terms, following a progressive mutual-to-self conversion pattern that most likely stems from magnetic reconnection. This results in the non-ideal formation of increasingly helical pre-eruption structures and instigates further research on the triggering of solar eruptions with magnetic helicity firmly placed in the eruption cadre.

  8. Engineered materials for all-optical helicity-dependent magnetic switching.

    PubMed

    Mangin, S; Gottwald, M; Lambert, C-H; Steil, D; Uhlíř, V; Pang, L; Hehn, M; Alebrand, S; Cinchetti, M; Malinowski, G; Fainman, Y; Aeschlimann, M; Fullerton, E E

    2014-03-01

    The possibility of manipulating magnetic systems without applied magnetic fields have attracted growing attention over the past fifteen years. The low-power manipulation of the magnetization, preferably at ultrashort timescales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization in engineered magnetic materials. We demonstrate that all-optical helicity-dependent switching (AO-HDS) can be observed not only in selected rare earth-transition metal (RE-TM) alloy films but also in a much broader variety of materials, including RE-TM alloys, multilayers and heterostructures. We further show that RE-free Co-Ir-based synthetic ferrimagnetic heterostructures designed to mimic the magnetic properties of RE-TM alloys also exhibit AO-HDS. These results challenge present theories of AO-HDS and provide a pathway to engineering materials for future applications based on all-optical control of magnetic order. PMID:24531398

  9. Electrically controlled spin-transistor operation in a helical magnetic field

    NASA Astrophysics Data System (ADS)

    Wójcik, P.; Adamowski, J.

    2016-03-01

    A proposal of an electrically controlled spin transistor in a helical magnetic field is presented. In the proposed device, the transistor action is driven by the Landau-Zener transitions that lead to a backscattering of spin polarized electrons and switching the transistor into the high-resistance state (off state). The on/off state of the transistor can be controlled by the all-electric means using Rashba spin-orbit coupling that can be tuned by the voltages applied to the side electrodes.

  10. Helical equilibrium

    SciTech Connect

    Yoshikawa, S.

    1981-08-01

    A straight, helical plasma equilibrium equation is solved numerically for a plasma with a helical magnetic axis. As is expected, by a suitable choice of the plasma boundary, the vacuum configuration is made line ..integral.. dl/B stable. As the plasma pressure increases, the line ..integral.. dl/B criterion will improve (again as expected). There is apparently no limit on the plasma ..beta.. from the equilibrium consideration. Thus helical-axis stellarator ..beta.. will presumably be limited by MHD stability ..beta.., and not by equilibrium ..beta...

  11. Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

    DOE PAGESBeta

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2015-12-28

    For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current—this is the chiral magnetic effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity toward the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electricmore » and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. In conclusion, we devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.« less

  12. Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

    SciTech Connect

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2015-12-28

    For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current—this is the chiral magnetic effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity toward the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electric and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. In conclusion, we devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.

  13. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 April-30 June 1995

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1995-06-30

    The equatorial and high latitudes data set included magnetically quiet periods and magnetically disturbed periods. It was found that extremely high altitude plumes developed on the magnetic equator in early phases of 7 magnetic storms. Comparisons were made between 6300 A depletions and phase fluctuations in a cooperative study. The spatial correlation between optical depletions and phase scintillation worked well but in some case the phase fluctuations were only of moderate level.

  14. Magnetic field-induced helical mode and topological transitions in a topological insulator nanoribbon.

    PubMed

    Jauregui, Luis A; Pettes, Michael T; Rokhinson, Leonid P; Shi, Li; Chen, Yong P

    2016-04-01

    The spin-helical Dirac fermion topological surface states in a topological insulator nanowire or nanoribbon promise novel topological devices and exotic physics such as Majorana fermions. Here, we report local and non-local transport measurements in Bi2Te3 topological insulator nanoribbons that exhibit quasi-ballistic transport over ∼2 μm. The conductance versus axial magnetic flux Φ exhibits Aharonov-Bohm oscillations with maxima occurring alternately at half-integer or integer flux quanta (Φ0 = h/e, where h is Planck's constant and e is the electron charge) depending periodically on the gate-tuned Fermi wavevector (kF) with period 2π/C (where C is the nanoribbon circumference). The conductance versus gate voltage also exhibits kF-periodic oscillations, anti-correlated between Φ = 0 and Φ0/2. These oscillations enable us to probe the Bi2Te3 band structure, and are consistent with the circumferentially quantized topological surface states forming a series of one-dimensional subbands, which undergo periodic magnetic field-induced topological transitions with the disappearance/appearance of the gapless Dirac point with a one-dimensional spin helical mode. PMID:26780658

  15. Magnetic field-induced helical mode and topological transitions in a topological insulator nanoribbon

    NASA Astrophysics Data System (ADS)

    Jauregui, Luis A.; Pettes, Michael T.; Rokhinson, Leonid P.; Shi, Li; Chen, Yong P.

    2016-04-01

    The spin-helical Dirac fermion topological surface states in a topological insulator nanowire or nanoribbon promise novel topological devices and exotic physics such as Majorana fermions. Here, we report local and non-local transport measurements in Bi2Te3 topological insulator nanoribbons that exhibit quasi-ballistic transport over ∼2 μm. The conductance versus axial magnetic flux Φ exhibits Aharonov–Bohm oscillations with maxima occurring alternately at half-integer or integer flux quanta (Φ0 = h/e, where h is Planck's constant and e is the electron charge) depending periodically on the gate-tuned Fermi wavevector (kF) with period 2π/C (where C is the nanoribbon circumference). The conductance versus gate voltage also exhibits kF-periodic oscillations, anti-correlated between Φ = 0 and Φ0/2. These oscillations enable us to probe the Bi2Te3 band structure, and are consistent with the circumferentially quantized topological surface states forming a series of one-dimensional subbands, which undergo periodic magnetic field-induced topological transitions with the disappearance/appearance of the gapless Dirac point with a one-dimensional spin helical mode.

  16. Magnetic crystals and helical liquids in alkaline-earth fermionic gases.

    PubMed

    Barbarino, Simone; Taddia, Luca; Rossini, Davide; Mazza, Leonardo; Fazio, Rosario

    2015-01-01

    The joint action of a magnetic field and of interactions is crucial for the appearance of exotic quantum phenomena, such as the quantum Hall effect. Owing to their rich nuclear structure, equivalent to an additional synthetic dimension, one-dimensional alkaline-earth(-like) fermionic gases with synthetic gauge potential and atomic contact repulsion may display similar related properties. Here we show the existence and the features of a hierarchy of fractional insulating and conducting states by means of analytical and numerical methods. We demonstrate that the gapped states are characterized by density and magnetic order emerging solely for gases with effective nuclear spin larger than 1/2, whereas the gapless phases can support helical modes. We finally argue that these states are related to an unconventional fractional quantum Hall effect in the thin-torus limit and that their properties can be studied in state-of-the-art laboratories. PMID:26350624

  17. Magnetic crystals and helical liquids in alkaline-earth fermionic gases

    PubMed Central

    Barbarino, Simone; Taddia, Luca; Rossini, Davide; Mazza, Leonardo; Fazio, Rosario

    2015-01-01

    The joint action of a magnetic field and of interactions is crucial for the appearance of exotic quantum phenomena, such as the quantum Hall effect. Owing to their rich nuclear structure, equivalent to an additional synthetic dimension, one-dimensional alkaline-earth(-like) fermionic gases with synthetic gauge potential and atomic contact repulsion may display similar related properties. Here we show the existence and the features of a hierarchy of fractional insulating and conducting states by means of analytical and numerical methods. We demonstrate that the gapped states are characterized by density and magnetic order emerging solely for gases with effective nuclear spin larger than 1/2, whereas the gapless phases can support helical modes. We finally argue that these states are related to an unconventional fractional quantum Hall effect in the thin-torus limit and that their properties can be studied in state-of-the-art laboratories. PMID:26350624

  18. Helical plasma striations in liners in the presence of an external axial magnetic field

    NASA Astrophysics Data System (ADS)

    Atoyan, L.; Hammer, D. A.; Kusse, B. R.; Byvank, T.; Cahill, A. D.; Greenly, J. B.; Pikuz, S. A.; Shelkovenko, T. A.

    2016-02-01

    Awe et al. found on the 20 MA Z machine [Acta Phys. Pol. A 115, 956 (2009)] that applying an externally generated axial magnetic field to an imploding liner leads to a helical pattern in the liner when viewed with soft x-ray radiography ([Phys. Rev. Lett. 111, 235005 (2013)] and [Phys. Plasmas 21, 056303 (2014)]). Here, we show that this phenomenon is also observed in extreme ultraviolet self-emission images of 10 mm long cylindrical metal liners having varying diameters and varying wall thicknesses on a 1 MA, 100-200 ns pulsed power generator. The magnetic field in these experiments is created using either twisted return current wires positioned close to the liner, generating a time-varying Bz, or a Helmholtz coil, generating a steady-state Bz.

  19. Magnetic reconnection in a comparison of topology and helicities in two and three dimensional resistive magnetohydrodynamic simulations

    SciTech Connect

    Čemeljić, M. Huang, R.-Y.

    2014-03-15

    Through a direct comparison between numerical simulations in two and three dimensions, we investigate topological effects in reconnection. A simple estimate on increase in reconnection rate in three dimensions by a factor of √(2), when compared with a two-dimensional case, is confirmed in our simulations. We also show that both the reconnection rate and the fraction of magnetic energy in the simulations depend linearly on the height of the reconnection region. The degree of structural complexity of a magnetic field and the underlying flow is measured by current helicity and cross-helicity. We compare results in simulations with different computational box heights.

  20. Numerical Simulation of Magnetic Flux Compression in Helical-Cone Magnetoexplosive Generators

    NASA Astrophysics Data System (ADS)

    Deryugin, Yu. N.; Korolev, P. V.; Kargin, V. I.; Pikar, A. S.; Popkov, N. F.; Ryaslov, E. A.

    2004-11-01

    We present the results of calculations of the physical processes of magnetic flux compression in a magnetocumulative generator with a large diameter spiral. The generator considered is a modification of the one developed for the multimegajoule energy source and intended for the PIRIT-EMG stationary electrophysical facility, pumping a pulsed energy of 80 MJ. The development of the magnetocumulative generator required calculating its output parameters and optimizing the generator dimensions, choosing the form and calculating the shape and thickness, insulation type and electric strength of the spiral wire. The authors developed a program package to simulate the helical-cone generator operation and numerically investigate the physical processes occurring at magnetic flux compression. To calculate the liner scatter dynamics, Eulerian equations were solved for counter-running sliding detonation waves. The system of equations is integrated using a finite-difference method for 2-D stationary grids adapting to the peculiarities of the flow. The liner collision with spiral coils as well as the destruction of the insulation is considered in 2-D through a model of nonviscous gas without heat conductivity. The magnetic flux compression is calculated using the analytical solutions of dynamic tasks and a 1-D non-linear diffusion of the magnetic field in conductors. Moreover, using a sufficiently simple algorithm, we managed to account for the basic losses of the magnetic flux related to diffusion, cuts-off at section and wire joints, and the losses related to spiral and liner misalignment.

  1. Magnetic material in mean-field dynamos driven by small scale helical flows

    NASA Astrophysics Data System (ADS)

    Giesecke, A.; Stefani, F.; Gerbeth, G.

    2014-07-01

    We perform kinematic simulations of dynamo action driven by a helical small scale flow of a conducting fluid in order to deduce mean-field properties of the combined induction action of small scale eddies. We examine two different flow patterns in the style of the G O Roberts flow but with a mean vertical component and with internal fixtures that are modelled by regions with vanishing flow. These fixtures represent either rods that lie in the center of individual eddies, or internal dividing walls that provide a separation of the eddies from each other. The fixtures can be made of magnetic material with a relative permeability larger than one which can alter the dynamo behavior. The investigations are motivated by the widely unknown induction effects of the forced helical flow that is used in the core of liquid sodium cooled fast reactors, and from the key role of soft iron impellers in the von-Kármán-sodium dynamo. For both examined flow configurations the consideration of magnetic material within the fluid flow causes a reduction of the critical magnetic Reynolds number of up to 25%. The development of the growth-rate in the limit of the largest achievable permeabilities suggests no further significant reduction for even larger values of the permeability. In order to study the dynamo behavior of systems that consist of tens of thousands of helical cells we resort to the mean-field dynamo theory (Krause and Rädler 1980 Mean-field Magnetohydrodynamics and Dynamo Theory (Oxford: Pergamon)) in which the action of the small scale flow is parameterized in terms of an α- and β-effect. We compute the relevant elements of the α- and the β-tensor using the so called testfield method. We find a reasonable agreement between the fully resolved models and the corresponding mean-field models for wall or rod materials in the considered range 1\\leqslant {{\\mu }_{r}}\\leqslant 20. Our results may be used for the development of global large scale models with recirculation

  2. Evidence for helical kink instability in the Venus magnetic flux ropes

    NASA Technical Reports Server (NTRS)

    Elphic, R. C.; Russell, C. T.

    1983-01-01

    Empirical models of the magnetic field structure of flux ropes found in the Venus ionosphere are seen as suggesting that the ropes are unstable to long-wavelength (more than 100 km) helical-kink perturbations. The onset of such an instability can explain the apparent volume distribution of flux ropes with altitude, as well as their orientation as a function of altitude. In the subsolar region, the fraction of volume occupied by flux ropes increases from approximately 20 percent at high altitudes to more than 50 percent at low altitudes; this is a greater increase than would be expected if ropes convect downward as simple straight horizontal cylinders. The helical kink instability raises the fractional volume occupied by ropes by turning the originally straight, horizontal flux tubes into corkscrew-shaped structures as they convect to lower altitudes. It is noted that this instability also explains why high altitude ropes tend to be horizontal and low altitude ropes appear to have almost any orientation.

  3. Helical Magnetic Self-Organization in the RFX-mod and MST devices

    NASA Astrophysics Data System (ADS)

    Franz, P.; Piovesan, P.; Spolaore, M.; Cappello, S.; Puiatti, M. E.; Chapman, B. E.; Sarff, J. S.; den Hartog, D. J.; Goetz, J. A.; McGarry, M. B.; Parke, E.; Reusch, J. A.; Stephens, H. D.; Yang, Y. M.

    2010-11-01

    Self-organization of the reversed field pinch with large helical structure (QSH regimes) is predominant as plasma current is increased. In RFX-mod, the persistence and strength of the QSH state increases markedly above 1 MA. An internal transport barrier appears, and plasma thermalization within the helical magnetic surfaces reflects improved confinement. The QSH regime is also obtained in MST plasmas, which operates with plasma current up to nearly 0.6 MA. We report here a statistical analysis of the tearing mode behavior in MST (e.g., amplitudes and QSH persistency) that reveals a trend with plasma current similar to that observed in RFX-Mod. This trend supports an expectation for universal behavior that depends on parameters such as the Lundquist number that vary with the plasma current. Analysis of the common database from the two devices should help reveal key physics for QSH onset and dynamics. Planned Thomson scattering measurements and transport analysis on MST will be important to compare with the confinement behavior established for RFX-Mod. Work supported by USDoE.

  4. Status of UCLA Helical Permanent-Magnet Inverse Free Electron Laser

    SciTech Connect

    Knyazik, A.; Tikhoplav, R.; Frederico, J. T.; Affolter, M.; Rosenzweig, J. B.

    2009-01-22

    A helical undulator, utilizing permanent-magnet of cylindrically symmetric (Halbach) geometry is being developed at UCLA's Neptune Facility. The initial prototype is a short 10 cm, 7 periods long helical undulator, designed to test the electron-photon coupling by observing the micro-bunching is currently being constructed. The Neptune IFEL facility utilizes a 15 MeV Photoinjector-generated electron beam of 0.5 nC interacting with CO{sub 2} of peak energy up to 100 J, estimated to have acceleration of 100 MeV/m. An Open Iris-Loaded Waveguide Structure (OILS) scheme which conserves laser mode size and wave fronts throughout the undulator, is utilized to avoid Gouy phase shift caused by focusing of the drive laser. Undulator design was tested by computer simulations Radia and Genesis 1.3. Coherent Transition Radiation and Coherent Cherenkov Radiation will be used for micro-bunching diagnostic. Currently permanent dipoles and their aluminum holders have been built, and the project is in its final state of assembly and undulator testing.

  5. Status of UCLA Helical Permanent-Magnet Inverse Free Electron Laser

    NASA Astrophysics Data System (ADS)

    Knyazik, A.; Tikhoplav, R.; Frederico, J. T.; Affolter, M.; Rosenzweig, J. B.

    2009-01-01

    A helical undulator, utilizing permanent-magnet of cylindrically symmetric (Halbach) geometry is being developed at UCLA's Neptune Facility. The initial prototype is a short 10 cm, 7 periods long helical undulator, designed to test the electron-photon coupling by observing the micro-bunching is currently being constructed. The Neptune IFEL facility utilizes a 15 MeV Photoinjector-generated electron beam of 0.5 nC interacting with CO2 of peak energy up to 100 J, estimated to have acceleration of 100 MeV/m. An Open Iris-Loaded Waveguide Structure (OILS) scheme which conserves laser mode size and wave fronts throughout the undulator, is utilized to avoid Gouy phase shift caused by focusing of the drive laser. Undulator design was tested by computer simulations Radia and Genesis 1.3. Coherent Transition Radiation and Coherent Cherenkov Radiation will be used for micro-bunching diagnostic. Currently permanent dipoles and their aluminum holders have been built, and the project is in its final state of assembly and undulator testing.

  6. Magnetic Reconnection and Ion Flows During Point-Source DC Helicity Injection on the Pegasus Toroidal Experiment

    NASA Astrophysics Data System (ADS)

    Burke, M. G.; Bongard, M. W.; Fonck, R. J.; Schlossberg, D. J.; Winz, G. R.

    2012-10-01

    A passive ion temperature polychromator has been deployed on Pegasus to study power balance and non-thermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 Czerny-Turner polychromator whose output is recorded by an intensified high-speed camera. During helicity injection, stochastic magnetic fields keep Te low and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (Ti 1.2 keV, Te 0.1 keV) using spectral lines from CIII, NIII, and BIV. This rapid ion heating is seen to coincide with internal MHD activity. The ion temperature closely follows the injection bias voltage, indicating that power from the guns is strongly coupled to the ions through this MHD activity. Bi-directional toroidal ion flows of ˜60 km/s have been observed on the BIV line during helicity injection when looking near the front of the injectors. The flow is on the order of the Alfv'en velocity, as predicted by Sweet-Parker reconnection, and is indicative of magnetic reconnection occurring near the injectors. When looking away from the helicity injectors, the bi-directional flow appears to be replaced by strong toroidal rotation, suggesting that ion acceleration during helicity injection is asymmetric and 3D in nature.

  7. Physics of forced magnetic reconnection in coaxial helicity injection experiments in National Spherical Torus Experiment

    SciTech Connect

    Ebrahimi, F.; Bhattacharjee, A.; Raman, R.; Hooper, E. B.; Sovinec, C. R.

    2014-05-15

    We numerically examine the physics of fast flux closure in transient coaxial helicity injection (CHI) experiments in National Spherical Torus Experiment (NSTX). By performing resistive Magnetohydrodynamics (MHD) simulations with poloidal injector coil currents held constant in time, we find that closed flux surfaces are formed through forced magnetic reconnection. Through a local Sweet-Parker type reconnection with an elongated current sheet in the injector region, closed flux surfaces expand in the NSTX global domain. Simulations demonstrate outflows approaching poloidally Alfvénic flows and reconnection times consistent with the Sweet-Parker model. Critical requirements for magnetic reconnection and flux closure are studied in detail. These primary effects, which are magnetic diffusivity, injector flux, injector flux footprint width, and rate of injector voltage reduction, are simulated for transient CHI experiments. The relevant time scales for effective reconnection are τ{sub V}<τ{sub rec}≈τ{sub A}√(S)(1+Pm){sup 1/4}<τ{sub R}, where τ{sub V} is the time for the injector voltage reduction, τ{sub A} is the poloidal Alfvén transit time, τ{sub R} is the global resistive diffusion time, and Pm and S are Prandtl and Lundquist numbers.

  8. Simulation of RF Cavity Dark Current in Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Unlisted

    2010-09-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  9. The dynamics of Wolf numbers based on nonlinear dynamos with magnetic helicity: comparisons with observations

    NASA Astrophysics Data System (ADS)

    Kleeorin, Y.; Safiullin, N.; Kleeorin, N.; Porshnev, S.; Rogachevskii, I.; Sokoloff, D.

    2016-08-01

    We investigate the dynamics of solar activity using a nonlinear one-dimensional dynamo model and a phenomenological equation for the evolution of Wolf numbers. This system of equations is solved numerically. We take into account the algebraic and dynamic nonlinearities of the alpha effect. The dynamic nonlinearity is related to the evolution of a small-scale magnetic helicity, and it leads to a complicated behaviour of solar activity. The evolution equation for the Wolf number is based on a mechanism of formation of magnetic spots as a result of the negative effective magnetic pressure instability (NEMPI). This phenomenon was predicted 25 yr ago and has been investigated intensively in recent years through direct numerical simulations and mean-field simulations. The evolution equation for the Wolf number includes the production and decay of sunspots. Comparison between the results of numerical simulations and observational data of Wolf numbers shows a 70 per cent correlation over all intervals of observation (about 270 yr). We determine the dependence of the maximum value of the Wolf number versus the period of the cycle and the asymmetry of the solar cycles versus the amplitude of the cycle. These dependences are in good agreement with observations.

  10. Simulation of RF Cavity Dark Current In Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Fermilab

    2012-05-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  11. POSSIBLE EVIDENCE OF ALFVEN-CYCLOTRON WAVES IN THE ANGLE DISTRIBUTION OF MAGNETIC HELICITY OF SOLAR WIND TURBULENCE

    SciTech Connect

    He Jiansen; Tu Chuanyi; Yao Shuo; Tian Hui; Marsch, Eckart

    2011-04-20

    The fluctuating magnetic helicity is considered an important parameter in diagnosing the characteristic modes of solar wind turbulence. Among them is the Alfven-cyclotron wave, which is probably responsible for the solar wind plasma heating, but has not yet been identified from the magnetic helicity of solar wind turbulence. Here, we present the possible signatures of Alfven-cyclotron waves in the distribution of magnetic helicity as a function of {theta}{sub VB}, which is the angle between the solar wind velocity and local mean magnetic field. We use magnetic field data from the STEREO spacecraft to calculate the {theta}{sub VB} distribution of the normalized reduced fluctuating magnetic helicity {sigma}{sub m}. We find a dominant negative {sigma}{sub m} for 1 s < p < 4 s (p is time period) and for {theta}{sub VB} < 30 deg. in the solar wind outward magnetic sector, and a dominant positive {sigma}{sub m} for 0.4 s < p < 4 s and for {theta}{sub VB}>150 deg. in the solar wind inward magnetic sector. These features of {sigma}{sub m} appearing around the Doppler-shifted ion-cyclotron frequencies may be consistent with the existence of Alfven-cyclotron waves among the outward propagating fluctuations. Moreover, right-handed polarized waves at larger propagation angles, which might be kinetic Alfven waves or whistler waves, have also been identified on the basis of the {sigma}{sub m} features in the angular range 40 deg. < {theta}{sub VB} < 140 deg. Our findings suggest that Alfven-cyclotron waves (together with other wave modes) play a prominent role in turbulence cascading and plasma heating of the solar wind.

  12. Synthesis, structure, and electrochemistry and magnetic properties of a novel 1D homochiral MnIII(5-Brsalen) coordination polymer with left-handed helical character

    NASA Astrophysics Data System (ADS)

    Dong, Dapeng; Yu, Naisen; Zhao, Haiyan; Liu, Dedi; Liu, Jia; Li, Zhenghua; Liu, Dongping

    2016-01-01

    A novel homochiral manganese (III) Mn(5-Brsalen) coordination polymer with left-handed helical character by spontaneous resolution on crystallization by using Mn(5-Brsalen) and 4,4-bipyridine, [MnIII(5-Brsalen)(4,4-bipy)]·ClO4·CH3OH (1) (4,4-bipy = 4,4-bipyridine) has been synthesized and structurally characterized by X-ray single-crystal diffraction, elemental analysis and infrared spectroscopy. In compound 1, each manganese(III) anion is six-coordinate octahedral being bonded to four atoms of 5-Brsalen ligand in an equatorial plane and two nitrogen atoms from a 4,4-bipyridine ligand in axial positions. The structure of compound 1 can be described a supramolecular 2D-like structure which was formed by the intermolecular π-stacking interactions between the neighboring chains of the aromatic rings of 4,4-bipyridine and 5-Brsalen molecules. UV-vis absorption spectrum, electrochemistry and magnetic properties of the compound 1 have also been studied.

  13. Engineered materials for all-optical helicity-dependent magnetic switching

    NASA Astrophysics Data System (ADS)

    Fullerton, Eric

    2014-03-01

    The possibilities of manipulating magnetization without applied magnetic fields have attracted growing attention over the last fifteen years. The low-power manipulation of magnetization, preferably at ultra-short time scales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization of engineered materials and devices using 100 fs optical pulses. We demonstrate that all optical - helicity dependent switching (AO-HDS) can be observed not only in selected rare-earth transition-metal (RE-TM) alloy films but also in a much broader variety of materials, including alloys, multilayers, heterostructures and RE-free Co-Ir-based synthetic ferrimagnets. The discovery of AO-HDS in RE-free TM-based synthetic ferrimagnets can enable breakthroughs for numerous applications since it exploits materials that are currently used in magnetic data storage, memories and logic technologies. In addition, this materials study of AO-HDS offers valuable insight into the underlying mechanisms involved. Indeed the common denominator of the diverse structures showing AO-HDS in this study is that two ferromagnetic sub-lattices exhibit magnetization compensation (and therefore angular momentum compensation) at temperatures near or above room temperature. We are highlighting that compensation plays a major role and that this compensation can be established at the atomic level as in alloys but also over a larger nanometers scale as in the multilayers or in heterostructures. We will also discuss the potential to extend AO-HDS to new classes of magnetic materials. This work was done in collaboration with S. Mangin, M. Gottwald, C-H. Lambert, D. Steil, V. Uhlíř, L. Pang, M. Hehn, S. Alebrand, M. Cinchetti, G. Malinowski, Y. Fainman, and M. Aeschlimann. Supported by the ANR-10-BLANC-1005 ``Friends,'' a grant from the Advanced Storage Technology Consortium, Partner University Fund

  14. The influence of differential rotation on the equatorial component of the sun's magnetic dipole field

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.

    1981-01-01

    This paper examines the effect that solar differential rotation would have on a hypothetical large-scale equatorial dipole field. The evolving large-scale field pattern is expressed as a series of non-axisymmetric moments. As time increases, power is transferred to progressively higher order moments. In the 27d rotating coordinate system, each moment undergoes a small retrograde drift which remains nearly uniform until that mode begins to fade. The synodic rotation periods of the first few moments are comparable to the observed 28.5d period of the sun's large-scale field near sunspot maximum. Differential rotation may be the source of this 28.5d period, but the eruption of new flux is necessary to keep the pattern going.

  15. Two new Dy3 triangles with trinuclear circular helicates and their single-molecule magnet behavior.

    PubMed

    Lin, Shuang-Yan; Zhao, Lang; Guo, Yun-Nan; Zhang, Peng; Guo, Yang; Tang, Jinkui

    2012-10-15

    Self-assembly of polydentate Schiff base 2,6-diformyl-4-methylphenol di(benzoy1hydrazone) (H(3)L), with dysprosium thiocyanate and sodium azide, affords two novel trinuclear triangular circular helicate dysprosium(III) complexes, [Dy(3)(μ(3)-OCH(3))(2)(HL)(3)(SCN)]·4CH(3)OH·2CH(3)CN·2H(2)O (1) or [Dy(3)(μ(3)-N(3))(μ(3)-OH)(H(2)L)(3)(SCN)(3)](SCN)·3CH(3)OH·H(2)O (2), depending on the presence or absence of base. Single-crystal X-ray analyses show that two μ(3)-methoxy oxygens cap the Dy(3) triangle in complex 1 and that one μ(3)-OH and one μ(3)-N(3)(-) cap the Dy(3) triangle of complex 2, representing the first example of a μ(3)-N(3)(-)-capped lanthanide complex reported to date. Ac susceptibility measurements reveal that multiple relaxation processes and the onset of slow magnetization relaxation occur for complex 1 and 2, respectively. Theoretical calculations are required to elucidate the underlying mechanism; however, the different magnetic anisotropy of the respective structures, which is dictated by the coordination environment of Dy(III) ions and structural parameters of the triangles, is mostly responsible for the distinctive relaxation dynamics observed. PMID:22510150

  16. Magnetic moments in a helical edge can make weak correlations seem strong

    NASA Astrophysics Data System (ADS)

    Väyrynen, Jukka I.; Geissler, Florian; Glazman, Leonid I.

    2016-06-01

    We study the effect of localized magnetic moments on the conductance of a helical edge. Interaction with a local moment is an effective backscattering mechanism for the edge electrons. We evaluate the resulting differential conductance as a function of temperature T and applied bias V for any value of V /T . Backscattering off magnetic moments, combined with the weak repulsion between the edge electrons, results in a power-law temperature and voltage dependence of the conductance; the corresponding small positive exponent is indicative of insulating behavior. Local moments may naturally appear due to charge disorder in a narrow-gap semiconductor. Our results provide an alternative interpretation of the recent experiment by Li et al. [Phys. Rev. Lett. 115, 136804 (2015)], 10.1103/PhysRevLett.115.136804 where a power-law suppression of the conductance was attributed to strong electron repulsion within the edge, with the value of Luttinger-liquid parameter K fine tuned close to 1 /4 .

  17. Phase diagram of the itinerant helical magnet MnSi at high pressures and strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Stishov, Sergei

    We performed a series of resistivity, heat capacity and ultrasound speed measurements of a MnSi single crystal at high pressures and strong magnetic fields [1-3]. Two notable features of the phase transition in MnSi that disappear on pressure increasin are a sharp peak marking the first order phase transition and a shallow maximum, situated slightly above the critical temperature and pointing to the domain of prominent helical fluctuations. The longitudinal and transverse ultrasound speeds and attenuation were measured in a MnSi single crystal in the temperature range of 2-40 K and magnetic fields to 7 Tesla. The magnetic phase transition in MnSi in zero magnetic field is signified by a quasi-discontinuity in the c11 elastic constant, which almost vanishes at the skyrmion - paramagnetic transition at high magnetic fields. The powerful fluctuations at the minima of c11 make the mentioned crossing point of the minima and the phase transition lines similar to a critical end point, where a second order phase transition meets a first order one.

  18. THEOS-2 Orbit Design: Formation Flying in Equatorial Orbit and Damage Prevention Technique for the South Atlantic Magnetic Anomaly (SAMA)

    NASA Astrophysics Data System (ADS)

    Pimnoo, Ammarin

    2016-07-01

    Geo-Informatics and Space Technology Development Agency (GISTDA) has initiative THEOS-2 project after the THEOS-1 has been operated for more than 7 years which is over the lifetime already. THEOS-2 project requires not only the development of earth observation satellite(s), but also the development of the area-based decision making solution platform comprising of data, application systems, data processing and production system, IT infrastructure improvement and capacity building through development of satellites, engineering model, and infrastructures capable of supporting research in related fields. The developing satellites in THEOS-2 project are THAICHOTE-2 and THAICHOTE-3. This paper focuses the orbit design of THAICHOTE-2 & 3. It discusses the satellite orbit design for the second and third EOS of Thailand. In this paper, both THAICHOTE will be simulated in an equatorial orbit as a formation flying which will be compared the productive to THAICHOTE-1 (THEOS-1). We also consider a serious issue in equatorial orbit design, namely the issue of the geomagnetic field in the area of the eastern coast of South America, called the South Atlantic Magnetic Anomaly (SAMA). The high-energy particles of SAMA comprise a radiation environment which can travel through THAICHOTE-2 & 3 material and deposit kinetic energy. This process causes atomic displacement or leaves a stream of charged atoms in the incident particles' wake. It can cause damage to the satellite including reduction of power generated by solar arrays, failure of sensitive electronics, increased background noise in sensors, and exposure of the satellite devices to radiation. This paper demonstrates the loss of ionizing radiation damage and presents a technique to prevent damage from high-energy particles in the SAMA.

  19. Domain size criterion for the observation of all-optical helicity-dependent switching in magnetic thin films

    NASA Astrophysics Data System (ADS)

    El Hadri, Mohammed Salah; Hehn, Michel; Pirro, Philipp; Lambert, Charles-Henri; Malinowski, Grégory; Fullerton, Eric E.; Mangin, Stéphane

    2016-08-01

    To understand the necessary condition for the observation of all-optical helicity-dependent switching (AO-HDS) of magnetization in thin films, we investigated ferromagnetic Co/Pt and Co/Ni multilayers as well as ferrimagnetic TbCo alloys as a function of magnetic layer compositions and thicknesses. We show that both ferro- and ferrimagnets with high saturation magnetization show AO-HDS if their magnetic thickness is strongly reduced below a material-dependent threshold thickness. By taking into account the demagnetizing energy and the domain wall energy, we are able to define a criterion to predict whether AO-HDS or thermal demagnetization (TD) will be observed. This criterion for the observation of AO-HDS is that the equilibrium size of magnetic domains forming during the cooling process should be larger than the laser spot size. From these results we anticipate that more magnetic materials are expected to show AO-HDS. However, the effect of the optical pulses' helicity is hidden by the formation of small magnetic domains during the cooling process.

  20. Observation of slow magnetic relaxation in triple-stranded lanthanide helicates.

    PubMed

    Lin, Shuang-Yan; Xu, Gong-Feng; Zhao, Lang; Guo, Yun-Nan; Guo, Yang; Tang, Jinkui

    2011-08-28

    Two dinuclear triple-stranded helicates [Ln(2)L(3)](3+) (Ln = Dy and Tb) obtained via self-assembly from the ligand HL (2,6-diformyl-4-methylphenol di(benzoylhydrazone)) and lanthanide perchlorate have been synthesized and characterized. The crystal structural analysis demonstrates that three ligand strands wrap around a pseudo-threefold axis defined by the two metal ions, leading to a 'meso'-relation between the right- (Δ) and left-hand (Λ) configurations of [Ln(2)L(3)](3+) in the crystal. Each Ln(III) ion is coordinated by nine donor atoms in a distorted tricapped trigonal-prismatic arrangement. Alternating current (ac) susceptibility measurements of [Dy(2)L(3)](3+) reveal a frequency-dependent out-of-phase signal under a 700 Oe dc field, indicating the onset of the slow relaxation of magnetization with a roughly estimated activation energy of ∼5 K and τ(0) of 10(-7) s. PMID:21743912

  1. Possible signature of Alfvén wave dissipation in the localized magnetic funnels of the equatorial solar corona

    NASA Astrophysics Data System (ADS)

    Dwivedi, Bhola N.; Srivastava, Abhishek Kumar; Mohan, Anita

    2014-12-01

    We analyse the Hinode/EIS 2″-spectroscopic scan data containing the spectral line formed at typical inner coronal temperature. The strong Fe XII 195.120 Å line shows the existence of funnel-like expanding flux-tubes which exhibit the signature of blue-/red-shifted plasma motions in the off-limb equatorial corona. These coronal funnels expand in the form of open magnetic field channels up to inner coronal heights. They are most likely the parts of large-scale and closed magnetic fields (loops) which exist at higher heights in the diffused equatorial corona. We also find the signature of decreasing line-widths with altitude in observed coronal funnels (e.g., funnel 1), which is the lower part of a curved loop system. This provides the most likely signature of Alfvén wave dissipation in lower part of this loop system. We also examine the blue-shifted and diffused coronal loop boundary and interfaced region (funnel 3) which shows increasing Fe XII 195.120 Å line-width along it. Therefore, it exhibits the most likely signature of Alfvén wave growth in this region which is slightly curved and rising higher in the corona. Density measurements in these funnels show that it falls off with height, but more rapidly in the second funnel. We conjecture the almost constant line-width trend as a most likely signature of Alfvén wave dissipation in this density-stratified second coronal funnel, which is also the lower part of a large-scale closed loop system. Both dissipative and growing Alfvén waves can change the non-thermal component and thus the full width at half-maximum of the Fe XII 195.120 Å line. We find the clues of Alfvén wave dissipation along the expanding field lines of the coronal funnel (lower parts of the loop system) imparting its energy to the outflowing plasma and thereby contributing to the formation of the nascent solar wind in the inner corona.

  2. Control of the Helicity Content of a Gun-Generated Spheromak by Incorporating a Conducting Shell into a Magnetized Coaxial Plasma Gun

    NASA Astrophysics Data System (ADS)

    Matsumoto, Tadafumi; Sekiguchi, Jun'ichi; Asai, Tomohiko

    In the formation of magnetized plasmoid by a magnetized coaxial plasma gun (MCPG), the magnetic helicity content of the generated plasmoid is one of the critical parameters. Typically, the bias coil to generate a poloidal flux is mounted either on the outer electrode or inside the inner electrode. However, most of the flux generated in the conventional method spreads even radially outside of the formation region. Thus, only a fraction of the total magnetic flux is actually exploited for helicity generation in the plasmoid. In the proposed system, the plasma gun incorporates a copper shell mounted on the outer electrode. By changing the rise time of the discharge bias coil current and the geometrical structure of the shell, the magnetic field structure and its time evolution can be controlled. The effect of the copper shell has been numerically simulated for the actual gun structure, and experimentally confirmed. This may increase the magnetic helicity content results, through increased poloidal magnetic field.

  3. Towards developing an analytical procedure of defining the equatorial electrojet for correcting satellite magnetic anomaly data

    NASA Technical Reports Server (NTRS)

    Ravat, Dhananjay; Hinze, William J.

    1991-01-01

    Analysis of the total magnetic intensity MAGSAT data has identified and characterized the variability of ionospheric current effects as reflected in the geomagnetic field as a function of longitude, elevation, and time (daily as well as monthly variations). This analysis verifies previous observations in POGO data and provides important boundary conditions for theoretical studies of ionospheric currents. Furthermore, the observations have led to a procedure to remove these temporal perturbations from lithospheric MAGSAT magnetic anomaly data based on 'along-the-dip-latitude' averages from dawn and dusk data sets grouped according to longitudes, time (months), and elevation. Using this method, high-resolution lithospheric magnetic anomaly maps have been prepared of the earth over a plus or minus 50 deg latitude band. These maps have proven useful in the study of the structures, nature, and processes of the lithosphere.

  4. Rotation of the Large-Scale Solar Magnetic Fields in the Equatorial Region

    NASA Astrophysics Data System (ADS)

    Latushko, S.

    1996-07-01

    A study is made of the rotation of large-scale magnetic fields using the synoptic maps from the Kitt Peak National Observatory for the time interval 1976 1985. The auto-correlation method and the mass-centers method of magnetic structures was applied to infer mean differential rotation profiles and rotation profiles separately for each magnetic field polarity. It has been found that in both hemispheres the leading polarity rotates faster than the following polarity at all latitudes by about 0.04° day-1. The maximum rotation rate of the leading polarity is reached at about 6° latitude. In the mean profile for both polarities, this brings about two angular velocity maxima at 6° latitudes in both hemispheres. Such a profile appears as to have a ‘dimple’ on the equator.

  5. Evidence for Helical Magnetic fields in Kiloparsec-Scale AGN Jets and the Action of a Cosmic Battery

    NASA Technical Reports Server (NTRS)

    Gabuzda, D. C.; Christodoulou, D. M.; Contopulos, I.; Kazanas, D.

    2012-01-01

    A search for transverse kiloparsec-scale gradients in Faraday rotation-measure (RM) maps of extragalactic radio sources in the literature has yielded 6 AGNs displaying continuous, monotonic RM gradients across their jets, oriented roughly orthogonal to the local jet direction. The most natural interpretation of such transverse RM gradients is that they are caused by the systematic change in the line-of-sight components of helical magnetic fields associated with these jets. All the identified transverse RM gradients increase in the counterclockwise (CCW) direction on the sky relative to the centers of these AGNs. Taken together with the results of Contopoulos et al. who found evidence for a predominance of clockwise (CW) transverse RM gradients across parsec-scale (VLBI) jets, this provides new evidence for preferred orientations of RM gradients due to helical jet magnetic fields, with a reversal from CW in the inner jets to CCW farther from the centers of activity. This can be explained by the "Poynting-Robertson cosmic-battery" mechanism, which can generate helical magnetic fields with a. characteristic "twist," which are expelled with the jet outflows. If the Poynting-Robertson battery mechanism is not operating, an alternative mechanism must be identified, which is able to explain the 'predominance of CW /CCW RM gradients on parsec/kiloparsec scales.

  6. Three-dimensional inversion of marine magnetic anomalies on the equatorial Atlantic Ridge (St. Paul Fracture Zone): Delayed magnetization in a magmatically starved spreading center?

    NASA Astrophysics Data System (ADS)

    Sichler, Bertrand; HéKinian, Roger

    2002-12-01

    The St. Paul Fracture Zone (FZ) in the equatorial Atlantic is interrupted by three intratransform ridge (ITR) spreading centers. A detailed magnetic survey, corrected for the diurnal variations using a moored magnetic station, six submersible dives, and three bottom-towed video camera tracks provide data on the most eastern ITR (0°37'N, 25°27'W). Visual observations and submersible sampling displayed a high ultramafic/volcanic ratio, supporting the assumption that the ITR is in a magmatically starved state. Volcanics were mainly found on the rift valley floor from 4700 to 4000 m and as a thin cap (<160 m) on the top of the eastern rift crest (2700 m). Most of the rift walls consist essentially of serpentinized peridotites and gabbros. The magnetic data show a well-defined ridge centered anomaly. A generalized inversion method was applied to the field data to calculate the crustal equivalent magnetization, assuming that the seafloor is broken down into elementary cells of 1 × 1 × 0.5 km3 which fit the topography. The average of absolute value of equivalent magnetization is 2.7 A m-1. The width of the central normal polarity (Brunhes epoch) is wider (at least 34 km) than that indicated by the NUVEL-1 kinematic model (24.5 km). This 40% excess is believed to be significant and is thought to be the result of prolonged chemical remanent magnetization acquired during the serpentinization of peridotites. In a magmatically starved accretion segment, we suggest that peridotites could continue to acquire magnetization as long as tectonic activities facilitate the circulation of seawater in the upper mantle.

  7. Analysis of the Variation of Energetic Electron Flux with Respect to Longitude and Distance Normal to the Magnetic Equatorial Plane for Galileo Energetic Particle Detector Data

    NASA Technical Reports Server (NTRS)

    Swimm, Randall; Garrett, Henry B.; Jun, Insoo; Evans, Robin W.

    2004-01-01

    In this study we examine ten-minute omni-directional averages of energetic electron data measured by the Galileo spacecraft Energetic Particle Detector (EPD). Count rates from electron channels B1, DC2, and DC3 are evaluated using a power law model to yield estimates of the differential electron fluxes from 1 MeV to 11 MeV at distances between 8 and 51 Jupiter radii. Whereas the orbit of the Galileo spacecraft remained close to the rotational equatorial plane of Jupiter, the approximately 11 degree tilt of the magnetic axis of Jupiter relative to its rotational axis allowed the EPD instrument to sample high energy electrons at limited distances normal to the magnetic equatorial plane. We present a Fourier analysis of the semi-diurnal variation of electron fluxes with longitude.

  8. New-generation empirical magnetic field models: Increasing resolution of equatorial and Birkeland currents and transition from modeling to nowcasting

    NASA Astrophysics Data System (ADS)

    Stephens, G. K.; Sitnov, M. I.; Redmon, R. J.

    2015-12-01

    Classical empirical geomagnetic field models were built using rigid electric current modules whose amplitude and size were determined by predefined functions of solar wind and global parameters, which limited their ability to reconstruct the global morphology of the magnetosphere and its dynamic evolution during geomagnetic storms. The TS07D model mitigated these limitations by replacing the equatorial current modules with basis-function expansions and by introducing a dynamical binning approach based on nearest neighbors. Here we further progress this avenue. Firstly, the number of basis functions is increased and new data from Van Allen Probes and THEMIS missions is added, allowing the model to resolve the spatial structure and evolution of the innermost eastward and banana currents. Then, an enhanced Birkeland current module that more accurately reconstructs the realistic morphology, including the Harang discontinuity and IMF By dependence, is discussed. Lastly, the performance of various nowcasting versions of the model with different sets of the binning parameters is examined for the first time using their direct validation by in-situ geomagnetic field observations, leading to an optimum nowcasting version of the model. Furthermore, the plasma pressure is reconstructed assuming force balance with the empirical magnetic field, and the role of pressure-driven currents is examined.

  9. EFFECTS OF NON-ISOTROPIC SCATTERING, MAGNETIC HELICITY, AND ADIABATIC FOCUSING ON DIFFUSIVE TRANSPORT OF SOLAR ENERGETIC PARTICLES

    SciTech Connect

    Litvinenko, Yuri E.

    2012-06-10

    Transport of solar energetic particles in interplanetary space is analyzed. A new systematic derivation of the diffusion approximation is given, which incorporates the effects of non-isotropic scattering, magnetic helicity, and adiabatic focusing in a non-uniform large-scale magnetic field. The derivation is based on a system of stochastic differential equations, equivalent to the Fokker-Planck equation, and the new method is a generalization of the Smoluchowski approximation in the theory of the Brownian motion. Simple, physically transparent expressions for the transport coefficients are derived. Different results of earlier treatments of the problem are related to the assumptions regarding the evolving particle distribution.

  10. An equatorial solar wind model with angular momentum conservation and nonradial magnetic fields and flow velocities at an inner boundary

    NASA Astrophysics Data System (ADS)

    Tasnim, S.; Cairns, Iver H.

    2016-06-01

    An analytic, self-consistent, theoretical model for the solar wind is developed that generalizes previous models to include all of the following: conservation of angular momentum, frozen-in magnetic fields, both radial (r) and azimuthal (ϕ) components of the magnetic field (Br and Bϕ) and velocity (vr and vϕ) from the inner boundary rs to 1 AU, and the detailed tracing back of observations at 1 AU to the inner boundary and all intervening (r,ϕ). The new model applies near the solar equatorial plane, assumes constant radial wind speed at each heliolongitude, and enforces corotation at the inner boundary. It is shown that the new theoretical model can be reduced to the previous models in the appropriate limits. We apply the model to two solar rotations of Wind spacecraft data, one near solar minimum (1-27 August 2010) and one near solar maximum (1-27 July 2002). The model analytically predicts the Alfvénic critical radius ra from the radial Alfvénic Mach number observed at 1 AU. Typically, the values are less than 15 solar radii, in agreement with some recent observations, and vary with longitude. Values of vϕ(r,ϕ) are predicted from the model, being always in the sense of corotation but varying in magnitude with r and ϕ. Reasonable and self-consistent results are found for Br(r,ϕ), Bϕ(r,ϕ), vϕ(r,ϕ), and n(r,ϕ) from rs to 1 AU. Both the azimuthal and radial magnetic fields at rs vary with time by more than an order of magnitude and usually |Br(rs,ϕs)|≥|Bϕ(rs,ϕs)|. Typically, though not always, magnetic contributions to the total angular momentum are small. Interestingly, however, the azimuthal flow velocities observed at 1 AU are not always in the corotation direction and usually have much larger magnitudes than predicted by the model. Conservation of angular momentum alone cannot explain these azimuthal velocities and the standard interpretation involving stream-stream interactions and dynamical behavior seems reasonable. Issues regarding the

  11. WAVELET ANALYSIS AS A TOOL TO LOCALIZE MAGNETIC AND CROSS-HELICITY EVENTS IN THE SOLAR WIND

    SciTech Connect

    Telloni, D.; Bruno, R.; D'Amicis, R.; Pietropaolo, E.; Carbone, V.

    2012-05-20

    In this paper, we adopt the use of the wavelet transform as a new tool to investigate the time behavior at different scales of reduced magnetic helicity, cross-helicity, and residual energy in space plasmas. The main goal is a better characterization of the fluctuations in which interplanetary flux ropes are embedded. This kind of information is still missing in the present literature, and our tool can represent the basis for a new treatment of in situ measurements of this kind of event. There is a debate about the origins of small-scale flux ropes. It has been suggested that they are formed through magnetic reconnection in the solar wind, such as across the heliospheric current sheet. On the other hand, it has also been suggested that they are formed in the corona, similar to magnetic clouds. Thus, it looks like that there are two populations, one originating in the solar wind via magnetic reconnection across the current sheet in the inner heliosphere and the other originating in the corona. Small-scale flux ropes might be the remnants of the streamer belt blobs formed from disconnection; however, a one-to-one observation of a blob and a small-scale flux rope in the solar wind has yet to be found. Within this panorama of possibilities, this new technique appears to be very promising in investigating the origins of these objects advected by the solar wind.

  12. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 April-30 June 1996

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1996-06-30

    Analysis of equatorial observations of GPS from stations on the magnetic equator and in the anomaly region allow the authors to begin to study the morphology of height of plumes and the occurrence pattern of thin layers of irregularities during years of low solar flux. Very high altitude plumes have been observed during magnetic storms in the data sets analyzed for 1993-1996. At high latitudes, a storm expands the irregularity oval moving the irregularity regions-producing scintillation and phase fluctuations to lower latitudes and to polar latitudes.

  13. Magnetic Helicity Spectrum of Solar Wind Fluctuations as a Function of the Angle with Respect to the Local Mean Magnetic Field

    NASA Astrophysics Data System (ADS)

    Podesta, J. J.; Gary, S. P.

    2011-06-01

    Magnetic field data acquired by the Ulysses spacecraft in high-speed streams over the poles of the Sun are used to investigate the normalized magnetic helicity spectrum σ m as a function of the angle θ between the local mean magnetic field and the flow direction of the solar wind. This spectrum provides important information about the constituent modes at the transition to kinetic scales that occurs near the spectral break separating the inertial range from the dissipation range. The energetically dominant signal at scales near the thermal proton gyroradius k bottomρ i ~ 1 often covers a wide band of propagation angles centered about the perpendicular direction, θ ~= 90° ± 30°. This signal is consistent with a spectrum of obliquely propagating kinetic Alfvén waves with k bottom Gt k par in which there is more energy in waves propagating away from the Sun and along the direction of the local mean magnetic field than toward the Sun. Moreover, this signal is principally responsible for the reduced magnetic helicity spectrum measured using Fourier transform techniques. The observations also reveal a subdominant population of nearly parallel propagating electromagnetic waves near the proton inertial scale k par c/ωpi ~ 1 that often exhibit high magnetic helicity |σ m | ~= 1. These waves are believed to be caused by proton pressure anisotropy instabilities that regulate distribution functions in the collisionless solar wind. Because of the existence of a drift of alpha particles with respect to the protons, the proton temperature anisotropy instability that operates when T pbottom/T ppar > 1 preferentially generates outward propagating ion-cyclotron waves and the fire-hose instability that operates when T pbottom/T ppar < 1 preferentially generates inward propagating whistler waves. These kinetic processes provide a natural explanation for the magnetic field observations.

  14. MAGNETIC HELICITY SPECTRUM OF SOLAR WIND FLUCTUATIONS AS A FUNCTION OF THE ANGLE WITH RESPECT TO THE LOCAL MEAN MAGNETIC FIELD

    SciTech Connect

    Podesta, J. J.; Gary, S. P.

    2011-06-10

    Magnetic field data acquired by the Ulysses spacecraft in high-speed streams over the poles of the Sun are used to investigate the normalized magnetic helicity spectrum {sigma}{sub m} as a function of the angle {theta} between the local mean magnetic field and the flow direction of the solar wind. This spectrum provides important information about the constituent modes at the transition to kinetic scales that occurs near the spectral break separating the inertial range from the dissipation range. The energetically dominant signal at scales near the thermal proton gyroradius k{sub perpendicular{rho}i} {approx} 1 often covers a wide band of propagation angles centered about the perpendicular direction, {theta} {approx_equal} 90{sup 0} {+-} 30{sup 0}. This signal is consistent with a spectrum of obliquely propagating kinetic Alfven waves with k{sub perpendicular} >> k{sub ||} in which there is more energy in waves propagating away from the Sun and along the direction of the local mean magnetic field than toward the Sun. Moreover, this signal is principally responsible for the reduced magnetic helicity spectrum measured using Fourier transform techniques. The observations also reveal a subdominant population of nearly parallel propagating electromagnetic waves near the proton inertial scale k{sub ||} c/{omega}{sub pi} {approx} 1 that often exhibit high magnetic helicity |{sigma}{sub m}| {approx_equal} 1. These waves are believed to be caused by proton pressure anisotropy instabilities that regulate distribution functions in the collisionless solar wind. Because of the existence of a drift of alpha particles with respect to the protons, the proton temperature anisotropy instability that operates when T{sub pperpendicular}/T{sub p||} > 1 preferentially generates outward propagating ion-cyclotron waves and the fire-hose instability that operates when T{sub pperpendicular}/T{sub p||} < 1 preferentially generates inward propagating whistler waves. These kinetic processes

  15. Effects of magnetic-storm phases on F-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 April-30 June 1990

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1990-06-30

    In progress is a major study of the effect of the ring current on the sub-auroral and equatorial generation of patches of irregularities. In addition studies are on-going for determining the dynamics of electric field penetration in latitude with the start of a major geomagnetic storm. For the first time simultaneous observations of irregularities at high and equatorial latitudes will be utilized. The studies use scintillation and spread F data as well as optical observations for data from 1971-1989. Two basic concepts are being studied. With the statistics of morphology of F-layer irregularities now in hand, it is possible to forecast in broad terms what to expect at equatorial, auroral and polar latitudes during various levels of solar flux. With the beginning of an understanding of the effect of the various phases of magnetic storms on generating irregularities as noted from the solar wind, ring current, convection, auroral index, and magnetic index parameters, it is possible to roughly forecast levels of F-layer irregularity intensity. With these in hand, the utility of space, time, and frequency diversity can be evaluated. Diversity could be used if forecasting in real time was possible.

  16. FIRST SYNOPTIC MAPS OF PHOTOSPHERIC VECTOR MAGNETIC FIELD FROM SOLIS/VSM: NON-RADIAL MAGNETIC FIELDS AND HEMISPHERIC PATTERN OF HELICITY

    SciTech Connect

    Gosain, S.; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov, S. A.

    2013-07-20

    We use daily full-disk vector magnetograms from Vector Spectromagnetograph on Synoptic Optical Long-term Investigations of the Sun system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of the observed radial field with the radial field estimate from line-of-sight magnetograms. Furthermore, we employ these maps to study the hemispheric pattern of current helicity density, H{sub c} , during the rising phase of solar cycle 24. The longitudinal average over the 23 consecutive solar rotations shows a clear signature of the hemispheric helicity rule, i.e., H{sub c} is predominantly negative in the north and positive in the south. Although our data include the early phase of cycle 24, there appears to be no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of the cycle as predicted by some dynamo models. Furthermore, we compute the hemispheric pattern in active region latitudes (-30 Degree-Sign {<=} {theta} {<=} 30 Degree-Sign ) separately for weak (100 G < |B{sub r} | < 500 G) and strong (|B{sub r} | > 1000 G) radial magnetic fields. We find that while the current helicity of strong fields follows the well-known hemispheric rule (i.e., {theta} {center_dot} H{sub c} < 0), H{sub c} of weak fields exhibits an inverse hemispheric behavior (i.e., {theta} {center_dot} H{sub c} > 0), albeit with large statistical scatter. We discuss two plausible scenarios to explain the opposite hemispheric trend of helicity in weak and strong field regions.

  17. Effects of magnetic storm phases on F-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 July-30 September 1993

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1993-09-30

    Although the general pattern of equatorial F-layer irregularities as a function of latitude, longitude, and geophysical conditions is in hand, the day to day variations are still difficult to evaluate. The forcing functions for day to day variations appear to be neutral winds and electric field conditions. The data indicate that at times in the irregularity season', irregularities are produced day after day. However nights of irregularities are at other times followed by one or more nights with an absence of irregularities. For the equatorial region, using scintillation data at 136 MHz, the authors have correlated the occurrence of irregularities at several stations along a relatively narrow range of longitudes at various latitudes in the Pacific sector. The sites used are in the Philippines, Taiwan, and Korea. The correlation of daily occurrence was poor. For example at magnetically quiet times there are irregularities noted at a station such as Osan, Korea (dip latitude 30 deg) with little irregularity activity at Manila (dip latitude 5 deg ), relatively close in longitude. For latitudes somewhat higher that the anomaly region, the problem arises of separating polewards effects of the equatorial plumes and the equatorwards motion of irregularity development originating in the auroral region during severe magnetic storms. A possibility exists for the generation of another class of F-layer irregularities at mid-latitudes with a body of data from Japan, Port Moresby, Osan, and Palehua, Hawaii. This is suggestive that at least in the Pacific region there is a low latitude generation of irregularities distinct from equatorial or auroral mechanisms.

  18. Controllable synthesis of helical, straight, hollow and nitrogen-doped carbon nanofibers and their magnetic properties

    SciTech Connect

    Li, Xun; Xu, Zheng

    2012-12-15

    Graphical abstract: The helical, straight and hollow carbon nanofibers can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. Display Omitted Highlights: ► CNFs were synthesized via pyrolysis of acetylene on copper NPs. ► The helical, straight, hollow and N-doped CNFs can be selectively synthesized. ► The growth mechanism of different types of CNFs was proposed. -- Abstract: Carbon nanofibers (CNFs) with various morphologies were synthesized by catalytic pyrolysis of acetylene on copper nanoparticles which were generated from the in situ decomposition of copper acetylacetonate. The morphology of the pristine and acid-washed CNFs was investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. Helical, straight and hollow CNFs can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. The growth mechanism for these three types of CNFs was proposed.

  19. Modification of tokamak edge plasma turbulence and transport by biasing and resonant helical magnetic field.

    PubMed

    Lafouti, Mansoureh; Ghoranneviss, Mahmood; Meshkani, Sakineh; Salar Elahi, Ahmad

    2013-05-01

    In this paper, both Resonant Helical magnetic Field (RHF) and limiter biasing have been applied to the tokamak. We have investigated their effects on the turbulence and transport of the particles at the edge of the plasma. The biased limiter voltage has been fixed at 200 V and RHF has L = 2 and L = 3. Also, the effects of the time order of the application of RHF and biasing to the tokamak have been explored. The experiment has been performed under three conditions. At first, the biasing and RHF were applied at t = 15 ms and at t = 20 ms. In the next step, RHF and biasing were applied at t = 15 ms and t = 20 ms, respectively. Finally, both of them were turned on at t = 15 ms until the end of the shot. For this purpose, the ion saturation current (I(sat)) and the floating potential (V(f)) have been measured by the Langmuir probe at r/a = 0.9. Moreover, the power spectra of I(sat) and floating potential gradient (∇V(f)), the coherency, the phase between them, and the particle diffusion coefficient have been calculated. The density fluctuations of the particles have been measured by the Rake probe and they have been analyzed with the Probability Distribution Function (PDF) technique. Also the particle diffusion coefficient has been determined by the Fick's law. The results show that, when RHF and biasing were applied at the same time to the plasma (during flatness region of plasma current), the radial particle density gradient, the radial particle flux, and the particle diffusion coefficient decrease about 50%, 60%, and 55%, respectively, compared to the other conditions. For more precision, the average values of the particle flux and the particle density gradient were calculated in the work. When the time is less than 15 ms, the average values of the particle flux and the particle density gradient are identical under all conditions, but in the other time interval they change. They reduce with the simultaneous application of biasing and RHF. The same results obtain

  20. Helical Tomotherapy Planning for Lung Cancer Based on Ventilation Magnetic Resonance Imaging

    SciTech Connect

    Cai Jing; McLawhorn, Robert; Altes, Tallisa A.; Lange, Eduard de; Read, Paul W.; Larner, James M.; Benedict, Stanley H.; Sheng Ke

    2011-01-01

    To investigate the feasibility of lung ventilation-based treatment planning, computed tomography and hyperpolarized (HP) helium-3 (He-3) magnetic resonance imaging (MRI) ventilation images of 6 subjects were coregistered for intensity-modulated radiation therapy planning in Tomotherapy. Highly-functional lungs (HFL) and less-functional lungs (LFL) were contoured based on their ventilation image intensities, and a cylindrical planning-target-volume was simulated at locations adjacent to both HFL and LFL. Annals of an anatomy-based plan (Plan 1) and a ventilation-based plan (Plan 2) were generated. The following dosimetric parameters were determined and compared between the 2 plans: percentage of total/HFL volume receiving {>=}20 Gy, 15 Gy, 10 Gy, and 5 Gy (TLV{sub 20}, HFLV{sub 20}, TLV{sub 15}, HFLV{sub 15}, TLV{sub 10}, HFLV{sub 10}, TLV{sub 5}, HFLV{sub 5}), mean total/HFL dose (MTLD/HFLD), maximum doses to all organs at risk (OARs), and target dose conformality. Compared with Plan 1, Plan 2 reduced mean HFLD (mean reduction, 0.8 Gy), MTLD (mean reduction, 0.6 Gy), HFLV{sub 20} (mean reduction, 1.9%), TLV{sub 20} (mean reduction, 1.5%), TLV{sub 15} (mean reduction, 1.7%), and TLV{sub 10} (mean reduction, 2.1%). P-values of the above comparisons are less than 0.05 using the Wilcoxon signed rank test. For HFLV{sub 15}, HFLV{sub 10}, TLV{sub 5}, and HTLV{sub 5}, Plan 2 resulted in lower values than plan 1 but the differences are not significant (P-value range, 0.063-0.219). Plan 2 did not significantly change maximum doses to OARs (P-value range, 0.063-0.563) and target conformality (P = 1.000). HP He-3 MRI of patients with lung disease shows a highly heterogeneous ventilation capacity that can be utilized for functional treatment planning. Moderate but statistically significant improvements in sparing functional lungs were achieved using helical tomotherapy plans.

  1. Equatorial Guinea.

    PubMed

    1984-06-01

    Attention in this discussion of Equatorial Guinea is directed to the following: the people, history, geography, government, political conditions, the economy, foreign relations, and relations between the US and Equatorial Guinea. The population was estimated at 304,000 in 1983 and the annual growth rate was estimated in the range of 1.7-2.5. The infant mortality rate is 142.9/1000 with a life expectancy of 44.4 years for males and 47.6 years for females. The majority of the Equatoguinean people are of Bantu origin. The largest tribe, the Fang, is indigenous to the mainland, although many now also live on Bioko Island. Portuguese explorers found the island of Bioko in 1471, and the Portuguese retained control until 1778, when the island, adjacent islets, and the commercial rights to the mainland between the Niger and Ogooue Rivers were ceded to Spain. Spain lacked the wealth and the interest to develop an extensive economic infrastructure in Equatorial Guinea during the 1st half of this century, but the Spanish did help Equatorial Guinea achieve 1 of the highest literacy rates in Africa. They also founded a good network of health care facilities. In March 1968, under pressure from Guinean nationalists, Spain announced that it would grant independence to Equatorial Guinea as rapidly as possible. A referendum was held on August 11, 1968, and 63% of the electorate voted in favor of the constitution, which provided for a government with a general assembly and presidentially appointed judges in the Supreme Court. After the coup in August 1979, power was placed in the hands of a Supreme Military Council. A new constitution came into effect after a popular vote in August 1982, abolishing the Supreme Military Council. Under the terms of the constitution, the president was given extensive powers. By the end of 1983, a 60-member Chamber of Representatives of the people had been formed. The government, which is credited with restoring greater personal freedom, is regarded

  2. Goddard Space Flight Center specification for Helical-Scan 8-millimeter (mm) magnetic digital data tape cartridge

    NASA Technical Reports Server (NTRS)

    Perry, Jimmy L.

    1992-01-01

    The same kind of standard and controls are established that are currently in use for the procurement of new analog, digital, and IBM/IBM compatible 3480 tape cartridges, and 1 in wide channel video magnetic tapes. The Magnetic Tape Certification Facility (MTCF) maintains a Qualified Products List (QPL) for the procurement of new magnetic media and uses the following specifications for the QPL and Acceptance Tests: (1) NASA TM-79724 is used for the QPL and Acceptance Testing of new analog magnetic tapes; (2) NASA TM-80599 is used for the QPL and Acceptance Testing of new digital magnetic tapes; (3) NASA TM-100702 is used for the QPL and Acceptance Testing of new IBM/IBM compatible 3840 magnetic tape cartridges; and (4) NASA TM-100712 is used for the QPL and Acceptance Testing of new 1 in wide channel video magnetic tapes. This document will be used for the QPL and Acceptance Testing of new Helical Scan 8 mm digital data tape cartridges.

  3. Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly

    NASA Astrophysics Data System (ADS)

    Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.

    2014-06-01

    Ionospheric scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.

  4. Equatorial sporadic E-layer abnormal density enhancement during the recovery phase of the December 2006 magnetic storm: A case study

    NASA Astrophysics Data System (ADS)

    Resende, L. C. A.; Denardini, C. M.

    2012-04-01

    Sporadic layers appear in the equatorial region ( E sq) between 90 and 130 km mainly due to irregularities in the electrojet equatorial (EEJ) current. In the present work, we have analyzed the behavior of the frequency parameters associated with these sporadic layers, covering the days before, during, and subsequent to, the intense magnetic storm that occurred on December 14, 2006. The parameters used in our analyses are the top frequency ( f t E s) and blanketing frequency ( f b E s) of the E s layer as measured over São Luís, Brazil (2.33°S, 44.2°W, dip: -4.5°) by digital ionosonde. A tentative association between these parameters and X-ray data measured by sensors on board the GOES satellite was carried out. Also, we investigated the effects on the dynamics of the equatorial electrojet using magnetometer data related to the presence of these E s layers. Our analyses show that there are notable changes in the f b E s, which are characterized by the occurrence of peaks that exceed the ambient background values.

  5. Helical plasma thruster

    NASA Astrophysics Data System (ADS)

    Beklemishev, A. D.

    2015-10-01

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR® rocket engine.

  6. Helical plasma thruster

    SciTech Connect

    Beklemishev, A. D.

    2015-10-15

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR{sup ®} rocket engine.

  7. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 October-31 December 1993

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1993-12-31

    During this quarter there was the start of an extensive review of the literature on middle latitude irregularities. In earlier reports the authors have noted the levels of irregularities at latitudes above the equatorial anomaly region (within 15 degrees of the magnetic equator) thru their analysis of a few examples of raw data from Osan, Korea. They then began to reduce and analyze data from Puerto Rico and Hawaii using 136 MHz scintillation data taken during both high and low solar flux years. At the levels that can be noted (peak to peak excursions of 15-20 dB) there is considerable activity.

  8. Impact of magnetic topology on radial electric field profile in the scrape-off layer of the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Suzuki, Y.; Ida, K.; Kamiya, K.; Yoshinuma, M.; Tsuchiya, H.; Kobayashi, M.; Kawamura, G.; Ohdachi, S.; Sakakibara, S.; Watanabe, K. Y.; Hudson, S.; Feng, Y.; Yamada, I.; Yasuhara, R.; Tanaka, K.; Akiyama, T.; Morisaki, T.; The LHD Experiment Group

    2016-09-01

    The radial electric field in the plasma edge is studied in the Large Helical Device (LHD) experiments. When magnetic field lines become stochastic or open at the plasma edge and connected to the vessel, electrons are lost faster than ions along these field lines. Then, a positive electric field appears in the plasma edge. The radial electric field profile can be used to detect the effective plasma boundary. Magnetic topology is an important issue in stellarator and tokamak research because the 3D boundary has the important role of controlling MHD edge stability with respect to ELMs, and plasma detachment. Since the stochastic magnetic field layer can be controlled in the LHD by changing the preset vacuum magnetic axis, this device is a good platform to study the properties of the radial electric field that appear with the different stochastic layer width. Two magnetic configurations with different widths of the stochastic layer as simulated in vacuum are studied for low-β discharges. It has been found that a positive electric field appeared outside of the last closed flux surface. In fact the positions of the positive electric field are found in the boundary between of the stochastic layer and the scrape-off layer. To understand where is the boundary of the stochastic layer and the scrape-off layer, the magnetic field lines are analyzed statistically. The variance of the magnetic field lines in the stochastic layer is increased outwards for both configurations. However, the skewness, which means the asymmetry of the distribution of the magnetic field line, increases for only one configuration. If the skewness is large, the connection length becomes effectively short. Since that is consistent with the experimental observation, the radial electric field can be considered as an index of the magnetic topology.

  9. Nonlinear theory of a free electron laser with a helical wiggler and an axial guide magnetic field

    NASA Astrophysics Data System (ADS)

    Ginzburg, N. S.; Peskov, N. Yu.

    2013-09-01

    A 1D nonlinear theory of a free electron laser (FEL) with a helical wiggler and an axial guide magnetic field is developed based on averaged equations of the electron motion. By averaging we separated two different cases of the e-beam/rf-wave interaction. The first one corresponds to the traditional wiggler synchronism (resonance) of rf wave with the electrons moving along stationary helical trajectories. The second one corresponds to combination resonances distinguishing by excitation of oscillation of the electrons near the stationary helical trajectory. Comparative analysis of the FEL operation in different regimes has been studied under the traditional wiggler synchronism condition. It was shown that FELs operated far from cyclotron resonance (including a reversed guide field orientation) possess low sensitivity to the initial velocity spread in the driving beam resulting in high electron efficiency. In contrast, under the weak guide field (the gyrofrequency is less than the bounce frequency) of a conventional orientation, the FEL efficiency is restricted by a significant increase in the transverse velocity of the electrons during the interaction with the rf wave that results in violation of the synchronism conditions and is accompanied by electron current losses. An additional mechanism of FEL efficiency enhancement under the conventional guide field orientation in the conditions when the gyrofrequency is higher than the bounce frequency, based on the dependence of the effective mass of the oscillating electrons on their energy, was demonstrated. Results of the theoretical analysis are compared with the results of experimental studies of FEL oscillators. The specific features of energy extraction from the electron beam under condition of an abnormal Doppler effect in the case of the combination resonance are described. This regime is beneficial to increase radiation frequency keeping wiggler period and electron energies.

  10. Nighttime VHF scintillations at 23 deg N magnetic latitude and their association with equatorial F region irregularities

    SciTech Connect

    Dabas, R.S.; Reddy, B.M.

    1986-06-01

    Based on ETS-II geostationary satellite (130 deg E) 136-MHz radio beacon amplitudes, a study of postsunset VHF scintillations observed during the January-February 1980 solar maximum period confirms that they are essentially controlled by the generation of equatorial F region irregularities. This latitude is substantially beyond the 84.4 deg E geographic meridian equatorial anomaly daytime crest. Good agreement between the observed scintillation occurrence pattern and characteristics, and previous results reported up to 21 deg N (Somayajulu et al., 1984), is found, and the occurrence of 23 deg N scintillations is found to be conditional to their prior occurrence at lower latitudes. It is also shown that, at least during high solar activity, the equator irregularities extend to altitudes in excess of 1300 km in the Indian sector, and consequently, cause scintillations in a much wider latitudinal belt. 36 references.

  11. Site-Selective Determination of Magnetic Helices in BaTiCoFe{sub 10}O{sub 19} by Resonant Magnetic Scattering

    SciTech Connect

    Okube, Maki; Kaneko, Yuhei; Ohsawa, Seiji; Sasaki, Satoshi; Toyoda, Takeshi; Mori, Takeharu

    2010-06-23

    Synchrotron radiation intensity measurements were made for single crystals of ferrimagnetic BaTiCoFe{sub 10}O{sub 19} at the BL-6C(3A) beamline of the Photon Factory. The resonant x-ray magnetic scattering (RXMS) method at the Fe K edge makes it possible to determine the magnetic crystal structure, having the magnetic helices for Fe ions in tetrahedral 4f{sub 1}, bipyramidal 2b, and octahedral 2a, 4f{sub 2} and 12k sites. Based on the information on x-ray magnetic circular dichroism (XMCD) and a resonant magnetic scattering factor f''{sub m} ( = 0.23) estimated from BaFe{sub 12}O{sub 19} at E = 7128.2 eV, the magnetic structures have been determined from an asymmetrical ratio {Delta}R (Y{sup +}-Y{sup -})/(Y{sup +}+Y{sup -}), where Y{sup +} and Y{sup -} are scattering intensities for left- and right-circular polarizations, respectively. Spin orientations were estimated in the least-squares procedure to minimize a residual factor of {Sigma}({Delta}R{sub obs}-{Delta}R{sub calc}){sup 2}. The canting angles estimated in this study are 180 deg., 19 deg., 118 deg., 180 deg. and 65 deg. for the magnetic moments of Fe ions in 4f{sub 1}, 2b, 2a, 4f{sub 2} and 12k sites, respectively.

  12. A novel approach to calculate inductance and analyze magnetic flux density of helical toroidal coil applicable to Superconducting Magnetic Energy Storage systems (SMES)

    NASA Astrophysics Data System (ADS)

    Alizadeh Pahlavani, M. R.; Shoulaie, A.

    2010-04-01

    In this paper, formulas are proposed for the self and mutual inductance calculations of the helical toroidal coil (HTC) by the direct and indirect methods at superconductivity conditions. The direct method is based on the Neumann’s equation and the indirect approach is based on the toroidal and the poloidal components of the magnetic flux density. Numerical calculations show that the direct method is more accurate than the indirect approach at the expense of its longer computational time. Implementation of some engineering assumptions in the indirect method is shown to reduce the computational time without loss of accuracy. Comparison between the experimental measurements and simulated results for inductance, using the direct and the indirect methods indicates that the proposed formulas have high reliability. It is also shown that the self inductance and the mutual inductance could be calculated in the same way, provided that the radius of curvature is >0.4 of the minor radius, and that the definition of the geometric mean radius in the superconductivity conditions is used. Plotting contours for the magnetic flux density and the inductance show that the inductance formulas of helical toroidal coil could be used as the basis for coil optimal design. Optimization target functions such as maximization of the ratio of stored magnetic energy with respect to the volume of the toroid or the conductor’s mass, the elimination or the balance of stress in some coordinate directions, and the attenuation of leakage flux could be considered. The finite element (FE) approach is employed to present an algorithm to study the three-dimensional leakage flux distribution pattern of the coil and to draw the magnetic flux density lines of the HTC. The presented algorithm, due to its simplicity in analysis and ease of implementation of the non-symmetrical and three-dimensional objects, is advantageous to the commercial software such as ANSYS, MAXWELL, and FLUX. Finally, using the

  13. Excitation of stable Alfven eigenmodes by application of alternating magnetic field perturbations in the Compact Helical System

    SciTech Connect

    Ito, T.; Toi, K.; Isobe, M.; Nagaoka, K.; Takeuchi, M.; Akiyama, T.; Matsuoka, K.; Minami, T.; Nishimura, S.; Okamura, S.; Shimizu, A.; Suzuki, C.; Yoshimura, Y.; Takahashi, C.; Matsunaga, G.

    2009-09-15

    Stable toroidicity-induced Alfven eigenmodes (TAEs) with low toroidal mode number (n=1 and n=2) were excited by application of alternating magnetic field perturbations generated with a set of electrodes inserted into the edge region of neutral beam injection heated plasmas on the Compact Helical System [K. Nishimura, K. Matsuoka, M. Fujiwara et al., Fusion Technol. 17, 86 (1990)]. The gap locations of TAEs excited by the electrodes are in the plasma peripheral region of {rho}>0.7 ({rho} is the normalized minor radius) where energetic ion drive is negligibly small, while some AEs are excited by energetic ions in the plasma core region of {rho}<0.4. The damping rate of these stable TAEs derived from plasma responses to applied perturbations is fairly large, that is, {approx}9% to {approx}12% of the angular eigenfrequency. This large damping rate is thought to be dominantly caused by continuum damping and radiative damping.

  14. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, Allan; Boozer, Allen H.

    1987-01-01

    A helical axis stellarator using only noninterlocking planar, non-circular coils, generates magnetic fields having a magnetic well and large rotational transform with resultant large equilibrium beta.

  15. Radio wave scintillations at equatorial regions

    NASA Technical Reports Server (NTRS)

    Poularikas, A. D.

    1972-01-01

    Radio waves, passing through the atmosphere, experience amplitude and phase fluctuations know as scintillations. A characterization of equatorial scintillation, which has resulted from studies of data recorded primarily in South America and equatorial Africa, is presented. Equatorial scintillation phenomena are complex because they appear to vary with time of day (pre-and postmidnight), season (equinoxes), and magnetic activity. A wider and more systematic geographical coverage is needed for both scientific and engineering purposes; therefore, it is recommended that more observations should be made at earth stations (at low-geomagnetic latitudes) to record equatorial scintillation phenomena.

  16. Overview of transport and MHD stability study: focusing on the impact of magnetic field topology in the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Ida, K.; Nagaoka, K.; Inagaki, S.; Kasahara, H.; Evans, T.; Yoshinuma, M.; Kamiya, K.; Ohdach, S.; Osakabe, M.; Kobayashi, M.; Sudo, S.; Itoh, K.; Akiyama, T.; Emoto, M.; Dinklage, A.; Du, X.; Fujii, K.; Goto, M.; Goto, T.; Hasuo, M.; Hidalgo, C.; Ichiguchi, K.; Ishizawa, A.; Jakubowski, M.; Kawamura, G.; Kato, D.; Morita, S.; Mukai, K.; Murakami, I.; Murakami, S.; Narushima, Y.; Nunami, M.; Ohno, N.; Pablant, N.; Sakakibara, S.; Seki, T.; Shimozuma, T.; Shoji, M.; Tanaka, K.; Tokuzawa, T.; Todo, Y.; Wang, H.; Yokoyama, M.; Yamada, H.; Takeiri, Y.; Mutoh, T.; Imagawa, S.; Mito, T.; Nagayama, Y.; Watanabe, K. Y.; Ashikawa, N.; Chikaraishi, H.; Ejiri, A.; Furukawa, M.; Fujita, T.; Hamaguchi, S.; Igami, H.; Isobe, M.; Masuzaki, S.; Morisaki, T.; Motojima, G.; Nagasaki, K.; Nakano, H.; Oya, Y.; Suzuki, C.; Suzuki, Y.; Sakamoto, R.; Sakamoto, M.; Sanpei, A.; Takahashi, H.; Tsuchiya, H.; Tokitani, M.; Ueda, Y.; Yoshimura, Y.; Yamamoto, S.; Nishimura, K.; Sugama, H.; Yamamoto, T.; Idei, H.; Isayama, A.; Kitajima, S.; Masamune, S.; Shinohara, K.; Bawankar, P. S.; Bernard, E.; von Berkel, M.; Funaba, H.; Huang, X. L.; T., Ii; Ido, T.; Ikeda, K.; Kamio, S.; Kumazawa, R.; Kobayashi, T.; Moon, C.; Muto, S.; Miyazawa, J.; Ming, T.; Nakamura, Y.; Nishimura, S.; Ogawa, K.; Ozaki, T.; Oishi, T.; Ohno, M.; Pandya, S.; Shimizu, A.; Seki, R.; Sano, R.; Saito, K.; Sakaue, H.; Takemura, Y.; Tsumori, K.; Tamura, N.; Tanaka, H.; Toi, K.; Wieland, B.; Yamada, I.; Yasuhara, R.; Zhang, H.; Kaneko, O.; Komori, A.; Collaborators

    2015-10-01

    The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0) ˜ Te(0) ˜ 6 keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1 × 1019 m-3 and with high electron and ion temperatures (Ti(0) ˜ Te(0) ˜ 2 keV), resulting in 3.36 GJ of input energy, is achieved.

  17. Specific features of the motion of neutrons in a medium with a helical magnetic structure

    SciTech Connect

    Fraerman, A. A. Udalov, O. G.

    2007-02-15

    The specific features of the motion of neutrons in a noncoplanar magnetic field are considered by an example of the magnetization distribution in the form of a conical helix. The reflection coefficients of neutrons from holmium crystals are calculated. It is shown that, for a noncoplanar distribution of a magnetic field in a crystal, the reflection coefficient of neutrons with spin flip exhibits an additional feature.

  18. A COMPARATIVE STUDY OF RIBO-, DEOXYRIBO-, AND HYBRID OLIGONUCLEOTIDE HELICES BY NUCLEAR MAGNETIC RESONANCE

    SciTech Connect

    Pardi, Arthur; Martin, Francis H.; Tinoco, Jr., Ignacio

    1980-11-01

    The nonexchangeable base protons and the hydrogen- bonding NH-N imino protons were used to study the conformations and the helix-coil transitions in the following oligonucleotides: (I) dCT{sub 5}G + dCA{sub 5}G, (II) rCU{sub 5}G + rCA{sub 5}G, (III) dCT{sub 5}G + rCA{sub 5}G, (IV) rCU{sub 5}G + dCA{sub 5}G. The first three mixtures all form stable double-helical structures at 5{degrees}C, whereas IV forms a triple strand with a ratio of 2:1 rCU{sub 5}G:dCA{sub 5}G. The chemical shifts of the imino protons in the double strands indicate that I, II, and III have different conformations in solution. For example, the hydrogen-bonded proton of one of the C-G base pairs is more shielded (a 0.4-ppm upfield shift) in helix I than in helix II or III. This implies a significant change in helical parameters, such as the winding angle, the distance between base pairs, or overlap of the bases. The coupling constants of the H1’ sugar protons show that helix I has 90% 2’-endo sugar conformation, whereas helix III has greater than 85% 3’-endo conformation for the observed sugar rings. The sugar pucker data are consistent with helix I having B-family geometry; III has A-family geometry. The chemical shifts of the nonexchangeable base protons in system I were followed with increasing temperature. The midpoints for the transitions, T{sub m}’s, for all the base protons were 28-30 {degrees}C; this indicates an all-or-none transition.

  19. Combined effects of a magnetic field and a helical force on the onset of a rotating Rayleigh-Bénard convection with free-free boundaries

    NASA Astrophysics Data System (ADS)

    Chabi Orou, Jean Bio; Pomalégni, Gisèle

    2015-11-01

    We investigate the combined effects of rotation , magnetic field and helical force on the onset of stationary and oscillatory convection in a horizontal electrically conducting fluid layer heated from below with free-free boundary conditions. For this investigation the linear stability analysis studied by Chandrasekhar (1961) is used. We obtain the condition for the formation of a single large scale structure. In (Pomalégni et al., 2014) it was shown the existence of a critical value Scr of the intensity of the helical force for which the apparition of two cells at marginal stability for the oscillatory convection is obtained. Then, we have shown here how the increasing of parameter Ta influences this critical value of the helical force intensity.

  20. Physical interpretation of the angle-dependent magnetic helicity spectrum in the solar wind: The nature of turbulent fluctuations near the proton gyroradius scale

    SciTech Connect

    Klein, Kristopher G.; Howes, Gregory G.; TenBarge, Jason M.; Podesta, John J.

    2014-04-20

    Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.

  1. Design and development of high-temperature superconducting magnet system with joint-winding for the helical fusion reactor

    NASA Astrophysics Data System (ADS)

    Yanagi, N.; Ito, S.; Terazaki, Y.; Seino, Y.; Hamaguchi, S.; Tamura, H.; Miyazawa, J.; Mito, T.; Hashizume, H.; Sagara, A.

    2015-05-01

    An innovative winding method is developed by connecting high-temperature superconducting (HTS) conductors to enable efficient construction of a magnet system for the helical fusion reactor FFHR-d1. A large-current capacity HTS conductor, referred to as STARS, is being developed by the incorporation of several innovative ideas, such as the simple stacking of state-of-the-art yttrium barium copper oxide tapes embedded in a copper jacket, surrounded by electrical insulation inside a conductor, and an outer stainless-steel jacket cooled by helium gas. A prototype conductor sample was fabricated and reached a current of 100 kA at a bias magnetic field of 5.3 T with the temperature at 20 K. At 4.2 K, the maximum current reached was 120 kA, and a current of 100 kA was successfully sustained for 1 h. A low-resistance bridge-type mechanical lap joint was developed and a joint resistance of 2 nΩ was experimentally confirmed for the conductor sample.

  2. The storm-time equatorial electrojet

    NASA Technical Reports Server (NTRS)

    Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

    1977-01-01

    A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed, and the large field depression at the flight time must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

  3. The storm-time equatorial electrojet

    NASA Technical Reports Server (NTRS)

    Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

    1976-01-01

    A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed and the large field depression, at the flight time, must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

  4. Field evolution of the magnetic phase transition in the helical magnet MnSi inferred from ultrasound studies

    NASA Astrophysics Data System (ADS)

    Petrova, A. E.; Stishov, S. M.

    2015-06-01

    The longitudinal and transverse ultrasound speeds and attenuation were measured in a MnSi single crystal in the temperature range of 2-40 K and magnetic fields up to 7 Tesla. The magnetic phase diagram of MnSi in applied magnetic field appears to depend on the experimental setups, which is related to a difference in demagnetization factors arising due to the disk shape of the sample. The magnetic phase transition in MnSi in zero magnetic field is signified by a quasidiscontinuity in the c11 elastic constant, which varies significantly with magnetic field. It is notable that the region where the c11 discontinuity almost vanishes closely corresponds to the extent of skyrmion phase along the magnetic to paramagnetic transition. This implies that the c11 elastic constant is almost continuous through the transition from the skyrmion to paramagnetic phases. A recovery of the discontinuity of c11 and enhanced sound absorption occur at the crossing of the phase transition line and the line of minima in c11. The powerful fluctuations at the minima of c11 make the mentioned crossing point similar to a critical end point, where a second order phase transition meets a first order one.

  5. Detachment stabilization with n/m=1/1 resonant magnetic perturbation field applied to the stochastic magnetic boundary of the Large Helical Device

    SciTech Connect

    Kobayashi, M.; Masuzaki, S.; Yamada, I.; Tamura, N.; Sato, K.; Goto, M.; Narushima, Y.; Akiyama, T.; Miyazawa, J.; Shoji, M.; Morita, S.; Peterson, B. J.; Funaba, H.; Ohyabu, N.; Narihara, K.; Morisaki, T.; Yamada, H.; Komori, A.; Feng, Y.; Reiter, D.

    2010-05-15

    It is found that the remnant island structure created by n/m=1/1 resonant magnetic perturbation field in the stochastic magnetic boundary of the Large Helical Device (LHD) [A. Komori et al., Nucl. Fusion 49, 104015 (2009)] has a stabilizing effect on formation of radiating plasma, realizing stably sustained divertor detachment operation with the core plasma being unaffected. The data from the several diagnostics, (profiles of electron temperature and density, radiation and temporal evolution of divertor particle flux) indicate selective cooling around X-point of the island and thus peaked radiation there, which is stabilized outside of the last closed flux surface throughout the detachment phase. The vacuum ultraviolet spectroscopy measurements of high Z impurity (iron) emission shows significant decrease during the detachment, indicating core plasma decontamination. The results from the three-dimensional (3D) edge transport code, edge Monte Carlo 3D (EMC3) [Y. Feng et al., Contrib. Plasma Phys. 44, 57 (2004)]-EIRENE [D. Reiter et al., Fusion Sci. Technol. 47, 172 (2005)] show similar tendency in the radiation pattern. The island size and its radial location are varied to investigate the magnetic topology effects on the detachment control. The divertor particle flux and neutral pressure exhibit intermittent oscillation as well as modification of recycling pattern during the detachment, which are found to reflect the island structure.

  6. TEST OF THE HEMISPHERIC RULE OF MAGNETIC HELICITY IN THE SUN USING THE HELIOSEISMIC AND MAGNETIC IMAGER (HMI) DATA

    SciTech Connect

    Liu, Y.; Hoeksema, J. T.; Sun, X.

    2014-03-01

    Magnetic twist in solar active regions (ARs) has been found to have a hemispheric preference in sign (hemisphere rule): negative in the northern hemisphere and positive in the southern. The preference reported in previous studies ranges greatly, from ∼ 58% to 82%. In this study, we examine this hemispheric preference using vector magnetic field data taken by Helioseismic and Magnetic Imager and find that 75% ± 7% of 151 ARs studied obey the hemisphere rule, well within the preference range in previous studies. If the sample is divided into two groups—ARs having magnetic twist and writhe of the same sign and having opposite signs—the strength of the hemispheric preference differs substantially: 64% ± 11% for the former group and 87% ± 8% for the latter. This difference becomes even more significant in a sub-sample of 82 ARs having a simple bipole magnetic configuration: 56% ± 16% for the ARs having the same signs of twist and writhe, and 93% with lower and upper confidence bounds of 80% and 98% for the ARs having the opposite signs. The error reported here is a 95% confidence interval. This may suggest that, prior to emergence of magnetic tubes, either the sign of twist does not have a hemispheric preference or the twist is relatively weak.

  7. Helical modulation of the electrostatic plasma potential due to edge magnetic islands induced by resonant magnetic perturbation fields at TEXTOR

    SciTech Connect

    Ciaccio, G. Spizzo, G.; Schmitz, O. Frerichs, H.; Abdullaev, S. S.; Evans, T. E.; White, R. B.

    2015-10-15

    The electrostatic response of the edge plasma to a magnetic island induced by resonant magnetic perturbations to the plasma edge of the circular limiter tokamak TEXTOR is analyzed. Measurements of plasma potential are interpreted by simulations with the Hamiltonian guiding center code ORBIT. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward from the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code ORBIT, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.

  8. Helicity patterns on the Sun

    NASA Astrophysics Data System (ADS)

    Pevtsov, A.

    Solar magnetic fields exhibit hemispheric preference for negative (pos- itive) helicity in northern (southern) hemisphere. The hemispheric he- licity rule, however, is not very strong, - the patterns of opposite sign helicity were observed on different spatial scales in each hemisphere. For instance, many individual sunspots exhibit patches of opposite he- licity inside the single polarity field. There are also helicity patterns on scales larger than the size of typical active region. Such patterns were observed in distribution of active regions with abnormal (for a give hemisphere) helicity, in large-scale photospheric magnetic fields and coronal flux systems. We will review the observations of large-scale pat- terns of helicity in solar atmosphere and their possible relationship with (sub-)photospheric processes. The emphasis will be on large-scale pho- tospheric magnetic field and solar corona.

  9. The transport of relative canonical helicity

    SciTech Connect

    You, S.

    2012-09-15

    The evolution of relative canonical helicity is examined in the two-fluid magnetohydrodynamic formalism. Canonical helicity is defined here as the helicity of the plasma species' canonical momentum. The species' canonical helicity are coupled together and can be converted from one into the other while the total gauge-invariant relative canonical helicity remains globally invariant. The conversion is driven by enthalpy differences at a surface common to ion and electron canonical flux tubes. The model provides an explanation for why the threshold for bifurcation in counter-helicity merging depends on the size parameter. The size parameter determines whether magnetic helicity annihilation channels enthalpy into the magnetic flux tube or into the vorticity flow tube components of the canonical flux tube. The transport of relative canonical helicity constrains the interaction between plasma flows and magnetic fields, and provides a more general framework for driving flows and currents from enthalpy or inductive boundary conditions.

  10. An improved neoclassical drift-magnetohydrodynamical fluid model of helical magnetic island equilibria in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Richard

    2016-05-01

    The effect of the perturbed ion polarization current on the stability of neoclassical tearing modes in tokamak plasmas is calculated using an improved, neoclassical, four-field, drift-magnetohydrodynamical model. The calculation involves the self-consistent determination of the pressure and scalar electric potential profiles in the vicinity of the associated magnetic island chain, which allows the chain's propagation velocity to be fixed. Two regimes are considered. First, a regime in which neoclassical ion poloidal flow damping is not strong enough to enhance the magnitude of the polarization current (relative to that found in slab geometry). Second, a regime in which neoclassical ion poloidal flow damping is strong enough to significantly enhance the magnitude of the polarization current. In both regimes, two types of solution are considered. First, a freely rotating solution (i.e., an island chain that is not interacting with a static, resonant, magnetic perturbation). Second, a locked solution (i.e., an island chain that has been brought to rest in the laboratory frame via interaction with a static, resonant, magnetic perturbation). In all cases, the polarization current is found to be either always stabilizing or stabilizing provided that ηi≡d ln Ti/d ln ne does not exceed some threshold value. In certain ranges of ηi, the polarization current is found to have a stabilizing effect on a freely rotating island, but a destabilizing effect on a corresponding locked island.

  11. Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F

    NASA Astrophysics Data System (ADS)

    Hickey, Dustin A.; Martinis, Carlos R.; Rodrigues, Fabiano S.; Varney, Roger H.; Milla, Marco A.; Nicolls, Michael J.; Strømme, Anja; Arratia, Juan F.

    2015-12-01

    In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10-500 km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50-200 km scale sizes using the all-sky imager, at 3 m scale sizes using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.

  12. Forced magnetic reconnection and field penetration of an externally applied rotating helical magnetic field in the TEXTOR tokamak.

    PubMed

    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

    2006-08-25

    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. PMID:17026312

  13. Conductance of a helical edge liquid coupled to a magnetic impurity.

    SciTech Connect

    Tanaka, Y.; Furusaki, A.; Matveev, K. A.

    2011-06-01

    Transport in an ideal two-dimensional quantum spin Hall device is dominated by the counterpropagating edge states of electrons with opposite spins, giving the universal value of the conductance, 2e{sup 2}/h. We study the effect on the conductance of a magnetic impurity, which can backscatter an electron from one edge state to the other. In the case of isotropic Kondo exchange we find that the correction to the electrical conductance caused by such an impurity vanishes in the dc limit, while the thermal conductance does acquire a finite correction due to the spin-flip backscattering.

  14. foF2 long-term trend linked to Earth's magnetic field secular variation at a station under the northern crest of the equatorial ionization anomaly

    NASA Astrophysics Data System (ADS)

    Pham Thi Thu, Hong; Amory-Mazaudier, Christine; Le Huy, Minh; Elias, Ana G.

    2016-01-01

    Long-term trend of the critical frequency of the F2 ionospheric region, foF2, at Phu Thuy station (21.03°N, 105.96°E), Vietnam, located under the northern crest of the equatorial ionization anomaly, EIA, is studied. Annual mean data are analyzed at 04 LT and 12 LT for the period 1962-2002 using monthly median values and monthly mean values during magnetically quiet days (am < 20). In both cases we obtain similar trends at 4 LT and 12 LT, which we interpret as an absence of geomagnetic activity effect over trends. The positive trends obtained are not consistent with the negative values expected from greenhouse gases effect at this layer of the upper atmosphere. The increasing trend observed at 12 LT is qualitatively in agreement with the expected effect of the secular displacement of the dip equator over the EIA latitudinal profile. At 04 LT, when the EIA is absent, the positive trend is in qualitative agreement with the secular variation of the Earth's magnetic field inclination, I, and the consequent increase of the sin(I)cos(I) factor at the corresponding location.

  15. Electric and thermoelectric transport in graphene and helical metal in finite magnetic fields

    NASA Astrophysics Data System (ADS)

    Chao, Sung-Po; Aji, Vivek

    2011-10-01

    We study the electrical and thermoelectric transport properties of the surface state of a topological insulator and graphene in the presence of randomly distributed impurities. For finite impurity strength, the dependence of the transport coefficients as a function of the gate voltage, magnetic field, and impurity potential are obtained numerically. In the limit of zero impurities (clean limit), analytic results for the peak values of the magneto-oscillations in thermopower are derived. Analogous with the conventional two-dimensional electron gas, the peak values are universal in the clean limit. Unlike graphene, in topological insulators the coupling of the electron spin to its momentum leads to a dependence of the transport coefficients on the gyromagnetic ratio (g). We compare our results with data on graphene and identify unique signatures expected in topological insulators due to the magnetoelectric coupling.

  16. Single-molecule magnet behavior in an octanuclear dysprosium(iii) aggregate inherited from helical triangular Dy3 SMM-building blocks.

    PubMed

    Zhang, Li; Zhang, Peng; Zhao, Lang; Wu, Jianfeng; Guo, Mei; Tang, Jinkui

    2016-06-28

    An unprecedented octanuclear dysprosium(iii) cluster with the formula [Dy8L6(μ3-OH)4(μ2-CH3O)2(CH3OH)6(H2O)2]·6H2O·10CH3OH·2CH3CN () based on a nonlinearly tritopic aroylhydrazone ligand H3L has been isolated, realizing the successful linking of pairwise interesting triangular Dy3 SMMs. It is noteworthy that two enantiomers (Λ and Δ configurations) individually behaving as a coordination-induced chirality presented in the Dy3 helicate are connected in the meso Dy8 cluster. Remarkably, alternating-current magnetic susceptibility measurements revealed that the Dy8 cluster shows typical SMM behavior inherited from its Dy3 helical precursor. It is one of the rare polynuclear Lnn SMMs (n > 7) under zero dc field. PMID:27231152

  17. Effects of magnetic-storm phases on F-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 Oct-31 Dec 91

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1991-12-31

    Several periods of interest in the low sunspot years of 1985 and 1986 have been identified when data were available from Kiruna, Sweden and from Goose Bay, Labrador as well as from equatorial sites. A contouring program was developed to handle the Transit data and in fact have received data from several sample periods of very low magnetic activity over a period of several days. Just begun is this study of determining the pattern of F-layer irregularities during years of low solar flux. The evaluation of data sets has included new analysis (for Manila, for example) as well as evaluating older data, much of it at this date unused for scientific purposes. While F-region irregularities are frequently spoken of occuring in the auroral region, the behavior of the irregularities as a function of sunspot number is significantly different from the behavior of the auroral region. Auroral data, primarily of the E layer green line, show no significant changes as a function of sunspot number in the latitude of the occurrence of this phenomenon; F-region irregularities show a great movement towards the polar region with a low sunspot number. In order to predict the occurrence and level of the effects on trans-ionospheric propagation, the relationship to sunspot number must be ascertained. We feel the comparison of high latitude data from Sweden and Canada will allow us to state that a polar movement of the region during low sunspot years is a global phenomenon.

  18. Substorm currents in the equatorial magnetotail

    SciTech Connect

    Iijima, T.; Watanabe, M.; Potemra, T.A.; Zanetti, L.J.; Kan, J.R.; Akasofu, S.I.

    1993-10-01

    The authors have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed from these variations, and systems of field-aligned currents were deduced. During the growth phase to the maximum phase of the taillike reconfiguration of the near-Earth magnetic field, a positive divergence (away from the equatorial plane) of the westward equatorial current occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the premidnight to early morning MLT sector. This flow direction pattern is the same as that of the region 2 field-aligned current system. The authors have also determined the presence of a radial current that flows toward the earth in the late evening to premidnight sector and flows away from the Earth in the midnight to morning sector. The intensity of the radial currents increases before the expansion phase. Consequently, the patterns of field-aligned currents associated with various substorm phases are the superposition of currents driven by multiple sources with different temporal variations. They have identified at least three different but related sources of field-aligned currents during the growth and expansion phases. These sources are related to the divergence of the westward flowing equatorial current and to distributions of pressure and magnetic field gradients that evolve in the magnetotail. When combined, these complicated systems support the basic region 1 to region 2 field-aligned current flow pattern. 22 refs., 12 figs., 1 tab.

  19. Effects of magnetic-storm phases on F-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 Jan-31 Mar 92

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1992-03-31

    Determining the morphology of F layer irregularities as a function of longitude in the equatorial region is vital for understanding the physics of the development of these irregularities. We aim to lay the observational basis which then can be used to test theoretical models. Theoretical models have been developed, notably the papers by R.T. Tsunoda (Rev. Geophys. 26, 719, 1988) and by T. Maruyama and N. Matuura (J. Geophys. Res. 89, 10903, 1984). The question is whether the models are consistent with the morphology as we see it. According to our criteria, the data used should be confined to observations taken near the magnetic equator during quiet magnetic periods and at times within a few hours after sunset. Anomaly region data should be omitted for studying the generation mechanism. The questions to be answered by proposed mechanisms are: (1) why do the equinox months have high levels of occurrence over all longitudes; (2) why are there relatively high levels of occurrence in the Central Pacific Sector in the July-August period and in the 0-75 deg West Sector in the November-December period; and (3) why are there very low levels of occurrence in November and December in the Central Pacific Sector and in July and August in the 0-75 deg West Sector. Satellite in-situ data, scintillation and spread F observations will be reviewed. The limitation of each data set will be outlined particularly as relevant to the bias produced by the existence of thin versus extended layers of irregularities. A cartoon as to the occurrence pattern, as we see it, as a function of longitude will be shown.

  20. Equatorial longitude and local time variations of topside magnetic field-aligned ion drifts at solar minimum

    NASA Astrophysics Data System (ADS)

    Burrell, A. G.; Heelis, R. A.; Stoneback, R. A.

    2012-04-01

    In the topside ionosphere, the high mobility of the plasma along the magnetic field allows field-aligned ion drifts to occur readily as a result of field-aligned gravitational forces, collisional forces, or pressure gradients. Therefore, variations in the field-aligned ion drifts can be used to explore the influence of thermospheric, electrodynamic, and chemical processes on the ionosphere. Longitude and local time variations in the field-aligned ion drifts near the magnetic equator are presented using observations from the Coupled Ion Neutral Dynamics Investigation on board the Communications/Navigation Outage Forecast System satellite. These observations were obtained during the period of extremely low solar activity present in 2008 and 2009, allowing the seasonal, local time, and longitudinal variations to reveal the relative importance of the processes responsible for topside field-aligned plasma drifts during solar minimum. This investigation found that the low-altitude winds and tides, the net ionization or loss, and the meridional E×B drift were all influential in creating longitudinal and local time variations in the field-aligned drift, though the strength of the influence seen by each driver was found to vary with season, local time, and longitude.

  1. Helical logic

    NASA Astrophysics Data System (ADS)

    Merkle, Ralph C.; Drexler, K. Eric

    1996-12-01

    Helical logic is a theoretical proposal for a future computing technology using the presence or absence of individual electrons (or holes) to encode 1s and 0s. The electrons are constrained to move along helical paths, driven by a rotating electric field in which the entire circuit is immersed. The electric field remains roughly orthogonal to the major axis of the helix and confines each charge carrier to a fraction of a turn of a single helical loop, moving it like water in an Archimedean screw. Each loop could in principle hold an independent carrier, permitting high information density. One computationally universal logic operation involves two helices, one of which splits into two `descendant' helices. At the point of divergence, differences in the electrostatic potential resulting from the presence or absence of a carrier in the adjacent helix controls the direction taken by a carrier in the splitting helix. The reverse of this sequence can be used to merge two initially distinct helical paths into a single outgoing helical path without forcing a dissipative transition. Because these operations are both logically and thermodynamically reversible, energy dissipation can be reduced to extremely low levels. This is the first proposal known to the authors that combines thermodynamic reversibility with the use of single charge carriers. It is important to note that this proposal permits a single electron to switch another single electron, and does not require that many electrons be used to switch one electron. The energy dissipated per logic operation can very likely be reduced to less than 0957-4484/7/4/004/img5 at a temperature of 1 K and a speed of 10 GHz, though further analysis is required to confirm this. Irreversible operations, when required, can be easily implemented and should have a dissipation approaching the fundamental limit of 0957-4484/7/4/004/img6.

  2. Evidence of internal rotation and a helical magnetic field in the jet of the quasar NRAO 150

    NASA Astrophysics Data System (ADS)

    Molina, Sol N.; Agudo, Iván; Gómez, José L.; Krichbaum, Thomas P.; Martí-Vidal, Iván; Roy, Alan L.

    2014-06-01

    The source NRAO 150 is a very prominent millimeter to radio emitting quasar at redshift z = 1.52 for which previous millimeter VLBI observations revealed a fast counterclockwise rotation of the innermost regions of the jet. Here we present new polarimetric multi-epoch VLBI-imaging observations of NRAO 150 performed at 8, 15, 22, 43, and 86 GHz with the Very Long Baseline Array (VLBA), and the Global Millimeter VLBI Array (GMVA) between 2006 and 2010. All new and previous observational evidence - i.e., spectral index maps, multi-epoch image cross-correlation, and low level of linear polarization degree in optically thin regions - are consistent with an interpretation of the source behavior where the jet is seen at an extremely small angle to the line of sight, and the high frequency emitting regions in NRAO 150 rotate at high speeds on the plane of the sky with respect to a reference point that does not need to be related to any particularly prominent jet feature. The observed polarization angle distribution at 22, 43, and 86 GHz during observing epochs with high polarization degree suggests that we have detected the toroidal component of the magnetic field threading the innermost jet plasma regions. This is also consistent with the lower degree of polarization detected at progressively poorer angular resolutions, where the integrated polarization intensity produced by the toroidal field is explained by polarization cancellation inside the observing beam. All this evidence is fully consistent with a kinematic scenario where the main kinematic and polarization properties of the 43 GHz emitting structure of NRAO 150 are explained by the internal rotation of such emission regions around the jet axis when the jet is seen almost face on. A simplified model developed to fit helical trajectories to the observed kinematics of the 43 GHz features fully supports this hypothesis. This explains the kinematics of the innermost regions of the jet in NRAO 150 in terms of internal

  3. Effects of magnetic storm phases on F-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 Apr-30 Jun 92

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1992-06-30

    The review of equatorial data relative to F-layer irregularities continued during this period with an emphasis in this quarter on the results of a long series of optical measurements. The study uses the largest optical data base yet obtained of equatorial airglow depletions to describe such observational features of irregularity plume onset and development under different seasonal and geomagnetic conditions. They are most interested in the data showing the extreme altitudes/latitudes reached by such effects.

  4. A mechanism for the dynamo terms to sustain closed-flux current, including helicity balance, by driving current which crosses the magnetic field

    SciTech Connect

    Jarboe, T. R.; Nelson, B. A.; Sutherland, D. A.

    2015-07-15

    An analysis of imposed dynamo current drive (IDCD) [T.R. Jarboe et al., Nucl. Fusion 52 083017 (2012)] reveals: (a) current drive on closed flux surfaces seems possible without relaxation, reconnection, or other flux-surface-breaking large events; (b) the scale size of the key physics may be smaller than is often computationally resolved; (c) helicity can be sustained across closed flux; and (d) IDCD current drive is parallel to the current which crosses the magnetic field to produce the current driving force. In addition to agreeing with spheromak data, IDCD agrees with selected tokamak data.

  5. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 January-31 March 1993

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1993-03-31

    Equatorial ionospheric irregularities in the F layer have been the subject of intensive experimental and theoretical investigations during recent years. The class of irregularities which continues to receive much attention is characterized by large scale plasma depletions, generally referred to as ionospheric plumes and bubbles. The F-region nightglow emissions arising from recombination processes can be used to observe the dynamics of transequatorial ionospheric plasma bubbles and smaller scale plasma irregularities. In a collaborative project between the Center for Space Physics of Boston University and the Brazilian Institute for Space Research (INPE), an all-sky imaging system was operated at Cachoeira Paulista (22.7 deg S, 45.0 deg W, dip latitude 15.8 deg S), between March 1987 and October 1991. In addition to the imager, photometer and VHF polarimeter observations were conducted at Cachoeira Paulista with ionospheric soundings carried out at C. Paulista and Fortaleza, the latter at 3.9 deg S. 38.4 deg W, dip latitude 3.7 deg S. A VHF electronic polarimeter is in operation at C. Paulista. This long series of 01 630.0 nm imaging observations has permitted determination that when there are extended plumes, the altitudes affected over the magnetic equator often exceed 1500 km and probably exceed 2500 km at times, the maximum projection that can be seen from Cachoeira Paulista. This holds true even during years of low solar flux. For this longitude, the observed seasonal variation of the airglow depletions shows a maximum from October through March and a very low occurrence of airglow depletions from April through September.

  6. Quasi-single helicity state by a small positive pulse of toroidal magnetic field in TPE-RX reversed field pinch experiment

    SciTech Connect

    Hirano, Y.; Koguchi, H.; Yambe, K.; Sakakita, H.; Kiyama, S.

    2006-12-15

    By applying a small positive pulse ({delta}B{sub ta}) in toroidal magnetic field, the quasi-single helicity (QSH) state can be obtained with a controllable and reproducible manner in a reversed-field pinch (RFP) experiment on the large RFP machine, TPE-RX [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. The QSH state in RFP is one of the states where the improved confinement can be observed, and is important for development toward the pure single helicity (SH) state. In the SH state, the dynamo-action for sustaining the RFP configuration will be driven by a single helical mode and its harmonics, and the anomalous plasma loss can be avoided which is caused by the multi-helicity dynamo action in ordinary RFPs. In the operating condition presented here, the reversal of toroidal magnetic field (B{sub ta}) is maintained at a shallow value ({approx}-1 mT) for a certain period ({approx}20 ms) after the setting up of the RFP configuration and then the positive {delta}B{sub ta} ((less-or-similar sign)5 mT magnitude and {approx}2 ms width) is applied to the B{sub ta}, which is usually negative during the sustaining phase of RFP. Just after applying the pulse, the m/n=1/6 mode (m and n being the poloidal and toroidal Fourier mode numbers, respectively) grows dominantly and the configuration goes into QSH state. This QSH state can be sustained for a long period (up to {approx}45 ms) almost until the end of discharge by applying a delayed reversal of B{sub ta} with appropriate timing and magnitude. The setting up of the QSH states shows a reproducibility of almost 100% with the same timing corresponding to the applied positive pulse. This observation can confirm the interpretation in the former report [Y. Hirano et al., Phys. Plasmas 12, 112501 (2005)], in which it is claimed that the QSH state is obtained when a small positive pulse in toroidal magnetic field spontaneously appears.

  7. Electron acceleration based on a laser pulse propagating through a plasma in the simultaneous presence of a helical wiggler and an obliquely applied external magnetic field

    NASA Astrophysics Data System (ADS)

    Gashti, M. A.; Jafari, S.

    2016-06-01

    Electron acceleration based on a laser pulse propagating through plasma channel has been studied in the simultaneous presence of a helical magnetic wiggler and an obliquely applied external magnetic field. A numerical study of electron energy and electron trajectory has been made using the fourth-order Runge-kutta method. Numerical results indicate that electron energy increases with decreasing θ -angle of the obliquely external magnetic field. Besides, it increases with increasing the amplitude of the obliquely magnetic field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of the wiggler field Ωw . Therefore, employing a magnetic wiggler field is very beneficial for electron acceleration in short distances. Further new results reveal that in the absence of the wiggler field (Ωw=0) , the electron energy increases with increasing the laser intensity, whereas in the presence of the wiggler field (Ωwneq0) , the electron energy increases with decreasing the laser intensity. As a result, employing a wiggler magnetic field in the laser-based electron accelerators can be worthwhile in the design of table top accelerators and it can enhance the electron energy at lower laser intensities.

  8. Helically linked mirror arrangement

    SciTech Connect

    Ranjan, P.

    1986-08-01

    A scheme is described for helical linking of mirror sections, which endeavors to combine the better features of toroidal and mirror devices by eliminating the longitudinal loss of mirror machines, having moderately high average ..beta.. and steady state operation. This scheme is aimed at a device, with closed magnetic surfaces having rotational transform for equilibrium, one or more axisymmetric straight sections for reduced radial loss, a simple geometrical axis for the links and an overall positive magnetic well depth for stability. We start by describing several other attempts at linking of mirror sections, made both in the past and the present. Then a description of our helically linked mirror scheme is given. This example has three identical straight sections connected by three sections having helical geometric axes. A theoretical analysis of the magnetic field and single-particle orbits in them leads to the conclusion that most of the passing particles would be confined in the device and they would have orbits independent of pitch angle under certain conditions. Numerical results are presented, which agree well with the theoretical results as far as passing particle orbits are concerned.

  9. Instability of wave modes in a two-stream free-electron laser with a helical wiggler and an axial magnetic field

    SciTech Connect

    Mohsenpour, Taghi; Mehrabi, Narges

    2013-08-15

    The dispersion relation of a two-stream free-electron laser (TSFEL) with a one-dimensional helical wiggler and an axial magnetic field is studied. Also, all relativistic effects on the space-charge wave and radiation are considered. This dispersion relation is solved numerically to find the unstable interaction among the all wave modes. Numerical calculations show that the growth rate is considerably enhanced in comparison with single-stream FEL. The effect of the velocity difference of the two electron beams on the two-stream instability and the FEL resonance is investigated. The maximum growth rate of FEL resonance is investigated numerically as a function of the axial magnetic field.

  10. Three-dimensional analysis of the effect of the ergodic magnetic field line structure on particle fueling in the large helical device

    NASA Astrophysics Data System (ADS)

    Shoji, M.; Yamazaki, K.; Komori, A.; Yamada, H.; Miyazawa, J.; LHD Experimental Group

    2003-03-01

    The particle fueling via the ergodic magnetic field line structure formed around the core plasma is investigated by using a CCD camera with an H α interference filter and a fully three-dimensional neutral particle transport simulation. The measurements of the plasma density profile and the calculations of the radial profile of the particle fueling rate in additional gas fueling experiments show inward plasma transport from around the last closed magnetic surface (LCMS) into the core plasma. The analyses of the particle fueling rate in various plasma density cases prove that the dependence of the particle fueling inside of the LCMS on the line averaged plasma density agrees with that of the measured increments of the plasma content due to the gas fueling, which indicates that particle fueling just inside of the LCMS can effectively contribute to the core plasma density by the effect of the inward plasma transport in large helical device plasmas.

  11. Swarm Equatorial Electric Field Inversion Chain

    NASA Astrophysics Data System (ADS)

    Alken, Patrick; Maus, Stefan; Vigneron, Pierre; Sirol, Olivier; Hulot, Gauthier

    2014-05-01

    The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere, in order to recover the EEF. We will present preliminary estimates of the EEF using the first Swarm geomagnetic field measurements, and compare them with independently measured electric fields from the JULIA ground-based radar in Peru.

  12. Flexible helical-axis stellarator

    DOEpatents

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  13. Helical filaments

    NASA Astrophysics Data System (ADS)

    Barbieri, Nicholas; Hosseinimakarem, Zahra; Lim, Khan; Durand, Magali; Baudelet, Matthieu; Johnson, Eric; Richardson, Martin

    2014-06-01

    The shaping of laser-induced filamenting plasma channels into helical structures by guiding the process with a non-diffracting beam is demonstrated. This was achieved using a Bessel beam superposition to control the phase of an ultrafast laser beam possessing intensities sufficient to induce Kerr effect driven non-linear self-focusing. Several experimental methods were used to characterize the resulting beams and confirm the observed structures are laser air filaments.

  14. Thermally activated helicity reversals of skyrmions

    NASA Astrophysics Data System (ADS)

    Yu, X. Z.; Shibata, K.; Koshibae, W.; Tokunaga, Y.; Kaneko, Y.; Nagai, T.; Kimoto, K.; Taguchi, Y.; Nagaosa, N.; Tokura, Y.

    2016-04-01

    Magnetic bubbles with winding number S =1 are topologically equivalent to skyrmions. Here we report the discovery of helicity (in-plane magnetization-swirling direction) reversal of skyrmions, while keeping their hexagonal lattice form, at above room temperature in a thin hexaferrite magnet. We have observed that the frequency of helicity reversals dramatically increases with temperature in a thermally activated manner, revealing that the generation energy of a kink-soliton pair for switching helicity on a skyrmion rapidly decreases towards the magnetic transition temperature.

  15. Helical axis stellarator equilibrium model

    SciTech Connect

    Koniges, A.E.; Johnson, J.L.

    1985-02-01

    An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

  16. A SOLAR TORNADO OBSERVED BY AIA/SDO: ROTATIONAL FLOW AND EVOLUTION OF MAGNETIC HELICITY IN A PROMINENCE AND CAVITY

    SciTech Connect

    Li, Xing; Morgan, Huw; Leonard, Drew; Jeska, Lauren

    2012-06-20

    During 2011 September 24, as observed by the Atmospheric Imaging Assembly instrument of the Solar Dynamic Observatory and ground-based H{alpha} telescopes, a prominence and associated cavity appeared above the southwest limb. On 2011 September 25 8:00 UT, material flows upward from the prominence core along a narrow loop-like structure, accompanied by a rise ({>=}50,000 km) of the prominence core and the loop. As the loop fades by 10:00, small blobs and streaks of varying brightness rotate around the top part of the prominence and cavity, mimicking a cyclone. The most intense and coherent rotation lasts for over three hours, with emission in both hot ({approx}1 MK) and cold (hydrogen and helium) lines. We suggest that the cyclonic appearance and overall evolution of the structure can be interpreted in terms of the expansion of helical structures into the cavity, and the movement of plasma along helical structures which appears as a rotation when viewed along the helix axis. The coordinated movement of material between prominence and cavity suggests that they are structurally linked. Complexity is great due to the combined effect of these actions and the line-of-sight integration through the structure which contains tangled fields.

  17. Planetary dynamos driven by helical waves - II

    NASA Astrophysics Data System (ADS)

    Davidson, P. A.; Ranjan, A.

    2015-09-01

    In most numerical simulations of the Earth's core the dynamo resides outside the tangent cylinder and may be crudely classified as being of the α2 type. In this region the flow comprises a sea of thin columnar vortices aligned with the rotation axis, taking the form of alternating cyclones and anticyclones. The dynamo is thought to be driven by these columnar vortices within which the flow is observed to be highly helical, helicity being a crucial ingredient of planetary dynamos. As noted in Davidson, one of the mysteries of this dynamo cartoon is the origin of the helicity, which is observed to be positive in the south and negative in the north. While Ekman pumping at the mantle can induce helicity in some of the overly viscous numerical simulations, it is extremely unlikely to be a significant source within planets. In this paper we return to the suggestion of Davidson that the helicity observed in the less viscous simulations owes its existence to helical wave packets, launched in and around the equatorial plane where the buoyancy flux is observed to be strong. Here we show that such wave packets act as a potent source of planetary helicity, constituting a simple, robust mechanism that yields the correct sign for h north and south of the equator. Since such a mechanism does not rely on the presence of a mantle, it can operate within both the Earth and the gas giants. Moreover, our numerical simulations show that helical wave packets dispersing from the equator produce a random sea of thin, columnar cyclone/anticyclone pairs, very like those observed in the more strongly forced dynamo simulations. We examine the local dynamics of helical wave packets dispersing from the equatorial regions, as well as the overall nature of an α2-dynamo driven by such wave packets. Our local analysis predicts the mean emf induced by helical waves, an analysis that rests on a number of simple approximations which are consistent with our numerical experiments, while our global

  18. Helical flux ropes in solar prominences

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    The present numerical method for the computation of force-free, cancelling magnetic structures shows that flux cancellation at the neutral line in a sheared magnetic arcade generates helical field lines that can support a prominence's plasma. With increasing flux cancellation, the axis of the helical fields moves to greater heights; this is suggestive of a prominence eruption. Two alternative scenarios are proposed for the formation of polar crown prominences which yield the correct axial magnetic field sign. Both models are noted to retain the formation of helical flux tubes through flux cancellation as their key feature.

  19. Selective control for helical microswimmers

    NASA Astrophysics Data System (ADS)

    Katsamba, Panayiota; Lauga, Eric

    2015-11-01

    One of the greatest aspirations for artificial microswimmers is their application in non-invasive medicine. For any practical use, adequate mechanisms enabling control of multiple artificial swimmers is of paramount importance. Here we propose a multi-helical, freely-jointed motor as a novel selective control mechanism. We show that the nonlinear step-out behavior of a magnetized helix driven by a rotating magnetic field can be exploited, when used in conjunction with other helices, to obtain a velocity profile that is non-negligible only within a chosen interval of operating frequencies. Specifically, the force balance between the competing opposite-handed helices is tuned to give no net motion at low frequencies while in the middle frequency range, the swimming velocity increases monotonically with the driving frequency if two opposite helices are used, thereby allowing speed adjustment by varying the driving frequency. We illustrate this idea in detail on a two-helix system, and demonstrate how to generalize to N helices, both numerically and theoretically. We finish by explaining how to solve the inverse problem and design an artificial swimmer with an arbitrarily-complex velocity vs. frequency relationship.

  20. Equatorial MST radars: Further consideration

    NASA Technical Reports Server (NTRS)

    Lagos, P.

    1983-01-01

    The results presented give additional support to the need of equatorial MST radars in order to obtain more information on the nature of equatorial waves in the MST region. Radar deduced winds such as obtained at Jicamarca for periods of months indicate that with these data the full range of equatorial waves, with time scales of seconds to years, can be studied.

  1. Magnetic turbulence and pressure gradient feedback effect of the 1/2 mode soft-hard magnetohydrodynamic limit in large helical device

    SciTech Connect

    Varela, J.; Watanabe, K. Y.; Ohdachi, S.; Narushima, Y.

    2014-09-15

    The aim of this study was to analyze the feedback process between the magnetic turbulence and the pressure gradients in Large Helical Device (LHD) inward-shifted configurations as well as its role in the transition between the soft-hard magnetohydrodynamic (MHD) regimes for instabilities driven by the mode 1/2 in the middle plasma. In the present paper, we summarize the results of two simulations with different Lundquist numbers, S=2.5×10{sup 5} and 10{sup 6}, assuming a plasma in the slow reconnection regime. The results for the high Lundquist number simulation show that the magnetic turbulence and the pressure gradient in the middle plasma region of LHD are below the critical value to drive the transition to the hard MHD regime, therefore only relaxations in the soft MHD limit are triggered (1/2 sawtooth-like events) [Phys. Plasmas 19, 082512 (2012)]. In the case of the simulation with low Lundquist number, the system reaches the hard MHD limit and a plasma collapse is observed.

  2. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 September-31 December 1992

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1992-01-01

    The review of equatorial data relative to F-layer irregularities continued during this period with an emphasis in this quarter on determining the effects of localized effects on the generation of F-region irregularities. The study compares initially for one month TEC and scintillation data for Manila, the Philippines, Palehau, Hawaii, Tepei, Taiwan, and Osan, Korea all in the Pacific Sector. We are working on airglow depletion data taken in Brazil over a span of years which include years of both high and low solar flux.

  3. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 July-30 September 1992

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1992-09-30

    The review of equatorial data relative to F-layer irregularities continued during this period with an emphasis in this quarter on determining the effects of localized effects on the generation of F-region irregularities. The study compares initially for one month TEC and scintillation data for Manila, the Philippines, Palehua, Hawaii Tepei, Taiwan, and Osan, Korea all in the Pacific Sector. For some periods in 1980 and 1981, all the data are available. The initial study will be the data set for July 1980.

  4. Studies of Solar Helicity Using Vector Magnetograms

    NASA Technical Reports Server (NTRS)

    Hagyard, Mona J.; Pevstov, Alexei A.

    1999-01-01

    observations of photospheric magnetic fields made with vector magnetographs have been used recently to study solar helicity. In this paper we indicate what can and cannot be derived from vector magnetograms, and point out some potential problems in these data that could affect the calculations of 'helicity'. Among these problems are magnetic saturation, Faraday rotation, low spectral resolution, and the method of resolving the ambiguity in the azimuth.

  5. On the Hemispheric Rule of Magnetic Helicity in the Sun: Test with the Active Regions in Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Liu, Y.

    2015-12-01

    Magnetic twist in solar active regions (ARs) has been found to have a hemispheric preference in sign (hemisphere rule): negative in the northern hemisphere and positive in the southern. The preference reported in previous studies ranges greatly, from ~ 58% to 82%. In this study, we examine this hemispheric preference with ARs in Solar Cycle 24 using vector magnetic field data taken by Helioseismic and Magnetic Imager (HMI) and find that 75% ± 7% of 151 ARs studied obey the hemisphere rule, well within the preference range in previous studies. If the sample is divided into two groups: ARs having magnetic twist and writhe of the same sign (group-same) and having opposite signs (group-opposite), the strength of the hemispheric preference differs substantially: 64% ± 11% for group-same and 87% ± 8% for group-opposite. This difference becomes even more significant in a sub-sample of 82 ARs having a simple bipole magnetic configuration: 56% ± 16% for the ARs in group-same, and 93% with lower and upper confidence bounds of 80% and 98% for the ARs in group-opposite. This may suggest that, prior to emergence of magnetic tubes, either the sign of twist does not have a hemispheric preference or the twist is relatively weak. Emerging ARs show an even greater difference between the two groups. In a sample of 116 emerging ARs, it is found that 84% of ARs in group-opposite follows the hemispheric rule, whereas only 34% of ARs in group-same follows the rule. A sample without emerging ARs (120 ARs) shows 88% in group-opposite and 71% of ARs in group-opposite that obey the rule. This suggests that surface dynamics plays a role in building-up magnetic twist in ARs after they emerge.

  6. Swarm equatorial electric field chain: First results

    NASA Astrophysics Data System (ADS)

    Alken, P.; Maus, S.; Chulliat, A.; Vigneron, P.; Sirol, O.; Hulot, G.

    2015-02-01

    The eastward equatorial electric field (EEF) in the E region ionosphere drives many important phenomena at low latitudes. We developed a method of estimating the EEF from magnetometer measurements of near-polar orbiting satellites as they cross the magnetic equator, by recovering a clean signal of the equatorial electrojet current and modeling the observed current to determine the electric field present during the satellite pass. This algorithm is now implemented as an official Level-2 Swarm product. Here we present first results of EEF estimates from nearly a year of Swarm data. We find excellent agreement with independent measurements from the ground-based coherent scatter radar at Jicamarca, Peru, as well as horizontal field measurements from the West African Magnetometer Network magnetic observatory chain. We also calculate longitudinal gradients of EEF measurements made by the A and C lower satellite pair and find gradients up to about 0.05 mV/m/deg with significant longitudinal variability.

  7. Helicity Generation by Heat Pulses

    NASA Astrophysics Data System (ADS)

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

    1996-11-01

    In a large laboratory plasma (ne ~= 10^12 cm-3, k Te ~= 2 eV, B0 ~= 30 G, 1 m ⊥ B_0, 2.5 m allel B_0), the electrons are heated locally by a short intense current pulse (100 A, 0.2 μs) using a magnetic loop antenna or a biased electrode. The heat transport along the field establishes a flux tube with strong radial and weak axial temperature gradients. The time scale of temperature relaxation (Δ t ~= 50 μs) is much longer than that of the transient whistler wave pulse excited by the initial current pulse (Δ t < 2 μs). The temperature gradients drive linked field-aligned and diamagnetic currents which, due to their linkage, exhibit helicity and form a flux rope with J × B ~= 0.(R. L. Stenzel and J. M. Urrutia, Phys. Rev. Lett. 76), 1469 (1996). Alternatively, the helicity generation can be understood by the twisting of magnetic field lines which, in the parameter regime of electron MHD, are frozen into the electron fluid. The electron heating at one end of the flux tube causes a nonuniform diamagnetic rotation, hence the helicity. The heat transport by helical convection and conduction is investigated. The slowly time-varying magnetic field may excite Alfvénic perturbations.

  8. On the response of the equatorial and low latitude ionospheric regions in the Indian sector to the large magnetic disturbance of 29 October 2003

    NASA Astrophysics Data System (ADS)

    Manju, G.; Pant, T. Kumar; Ravindran, S.; Sridharan, R.

    2009-06-01

    The present paper investigates the response of the equatorial and low latitude ionosphere over the Indian longitudes to the events on 29 October 2003 using ionosonde data at Trivandrum (8.5° N (0.5° N geomagnetic), 77° E) and SHAR (13.7° N (5.7° N geomagnetic), 80.2° E), ground-based magnetometer data from Trivandrum and Total Electron Content (TEC) derived from GPS data at the locations of Ahmedabad (23° N (15° N geomagnetic), 72° E), Jodhpur (26.3° N (18.3° N geomagnetic), 73° E) and Delhi (28° N (20° N geomagnetic), 77° E). Following the storm sudden commencement, the TEC at all the three stations showed an overall enhancement in association with episodes of inter-planetary electric field penetration. Interestingly, real ionospheric height profiles derived using the ionosonde data at both Trivandrum and SHAR showed significant short-term excursions and recoveries. In the post noon sector, these features are more pronounced over SHAR, an off equatorial station, than those over Trivandrum indicating the increased effects of neutral winds.

  9. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.

    2015-06-01

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.

  10. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    SciTech Connect

    Andreev, Pavel A.

    2015-06-15

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.

  11. Study of equatorial scintillations

    NASA Technical Reports Server (NTRS)

    Pomalaza, J.; Woodman, R.; Tisnado, G.; Nakasone, E.

    1972-01-01

    Observations of the amplitude scintillations produced by the F-region in equatorial areas are presented. The equipment used for conducting the observations is described. The use of transmissions from the ATS-1, ATS-3, and ATS-5 for obtaining data is described. The two principal subjects discussed are: (1) correlation between satellite and incoherent radar observations of scintillations and (2) simultaneous observations of scintillations at 136 MHz and 1550 MHz.

  12. Generalized helicity and Beltrami fields

    SciTech Connect

    Buniy, Roman V.; Kephart, Thomas W.

    2014-05-15

    We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.

  13. Helicity in dynamical processes in the atmosphere

    NASA Astrophysics Data System (ADS)

    Kurgansky, Michael; Maksimenkov, Leonid; Khapaev, Alexey; Chkhetiani, Otto

    2016-04-01

    In modern geophysical fluid dynamics and dynamic meteorology, a notable interest is observed to the notion of helicity ("kinetic helicity" to be distinguished from "magnetic helicity" widely used in magnetohydrodynamics, astrophysics and Solar physics), which is defined by the scalar product of 3D vectors of velocity and vorticity. In this contribution, we bring together different, both known in the literature and novel formulations of the helicity balance equation, by also taking into account the effects of air compressibility and Earth rotation. Equations and relationships are presented that are valid under different approximations customarily made in the dynamic meteorology, e.g. Boussinesq approximation, quasi-static approximation, quasi-geostrophic approximation. An emphasis is placed on the helicity budget analysis in large-scale atmospheric motions. An explicit expression is presented for the rate of helicity injection from the free atmosphere into a non-linear Ekman boundary layer. This injection is shown to be exactly balanced by the helicity viscous destruction within the boundary layer. It is conjectured that this helicity injection may characterize the intensity of atmospheric circulation in extratropical latitudes of both terrestrial hemispheres. Examples are provided based on re-analyses data. Vertical distribution of helicity and superhelicity in different Ekman boundary layers is also discussed.

  14. The influence of helical background fields on current helicity and electromotive force of magnetoconvection

    NASA Astrophysics Data System (ADS)

    Rüdiger, G.; Küker, M.

    2016-07-01

    Motivated by the empirical finding that the known hemispheric rules for the current helicity at the solar surface are not strict, we demonstrate the excitation of small-scale current helicity by the influence of large-scale helical magnetic background fields on nonrotating magnetoconvection. This is shown within a quasilinear analytic theory of driven turbulence and by nonlinear simulations of magnetoconvection that the resulting small-scale current helicity has the same sign as the large-scale current helicity, while the ratio of both pseudoscalars is of the order of the magnetic Reynolds number of the convection. The same models do not provide finite values of the small-scale kinetic helicity. On the other hand, a turbulence-induced electromotive force is produced including the diamagnetic pumping term, as well as the eddy diffusivity but, however, no α effect. It has thus been argued that the relations for the simultaneous existence of small-scale current helicity and α effect do not hold for the model of nonrotating magnetoconvection under consideration. Calculations for various values of the magnetic Prandtl number demonstrate that, for the considered diffusivities, the current helicity increases for growing magnetic Reynolds number, which is not true for the velocity of the diamagnetic pumping, which is in agreement with the results of the quasilinear analytical approximation.

  15. Evolution of helicities in dynamo problems

    NASA Astrophysics Data System (ADS)

    Reshetnyak, M. Yu.

    2015-07-01

    The properties of wavelet spectra of kinetic and magnetic energies, as well as of helicities, are considered by the example of a three-dimensional dynamo model in a rapidly rotating a plane layer and heated from below. It is shown that the transition from the kinematic mode to the full dynamo mode is accompanied by a decrease in the magnetic energy of the system. The hydrodynamic helicity changes its sign by height and has the same sign for all scales. The current and magnetic helicities also have the dipole form of symmetry in the physical space; however, their sign at small and large scales is different—the so-called effect of separation in scales. The cross-helicity has no separation in scales, but it can change the sign with time so that its averaged value is small.

  16. Helicity Injected Torus Program Overview

    NASA Astrophysics Data System (ADS)

    Redd, A. J.; Jarboe, T. R.; Aboulhosn, R. Z.; Akcay, C.; Hamp, W. T.; Marklin, G.; Nelson, B. A.; O'Neill, R. G.; Raman, R.; Sieck, P. E.; Smith, R. J.; Sutphin, G. L.; Wrobel, J. S.; Mueller, D.; Roquemore, L.

    2006-10-01

    The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT--SI) spheromak experiment [Sieck, Nucl. Fusion v.46, p.254 (2006)] addresses critical issues for spheromaks, including current drive, high-beta operation, confinement quality and efficient steady-state operation. HIT--SI has a ``bow-tie'' shaped axisymmetric confinement region (major radius R=0.33 m, axial extent of 0.57 m) and two half-torus helicity injectors, one mounted on each end of the flux conserver. HIT--SI has produced spheromaks with up to 30 kA of toroidal current, using less than 4 MW of applied power, demonstrating that Steady Inductive Helicity Injection can generate and sustain discharges with modest power requirements. Fast camera images of HIT--SI discharges indicate a toroidally rotating n=1 structure, driven by the helicity injectors. The direction of the toroidal current is determined by the direction of rotation of the driven n=1. Measured surface and internal magnetic fields in HIT--SI discharges are consistent with that of the true 3D Taylor state, including the injectors. Recent HIT--SI physics studies, diagnostic improvements and machine upgrades will also be summarized.

  17. Effects of magnetic storm phases on f-layer irregularities from auroral to equatorial latitudes. Quarterly report, 1 October-31 December 1994

    SciTech Connect

    Aarons, J.; Mendillo, M.

    1994-12-31

    During the past twenty years the understanding of Equatorial Scintillation Storms (ES S) has reached a considerable maturity. The average occurrence pattern and underlying physics are quite well understood. Many of the processes which create the day to day variability and which are crucial to the development of forecasting techniques are well understood. Yet there remains a persistent, illusive quality in predicting degradation of signals propagating through the ionosphere because no one has created a synthesis of this understanding. The purpose of this joint study is to outline a three year program which brings together the capabilities of the three major ONR groups in the Northeast for a cooperative venture to predict ESS on time scales of 3-6 hours.

  18. Crystal structure and magnetic properties of a helical ribbon polymer based on dimeric manganese(II) subunits

    NASA Astrophysics Data System (ADS)

    Zhang, Ling-Yun; Zeng, Ming-Hua; Sun, Xian-Zhong; Shi, Zhan; Feng, Shou-Hua; Chen, Xiao-Ming

    2004-07-01

    One mixed-ligand complex of [Mn 2(mpa) 2(2,2'-bpy) 2] n ( 1) (mpa= m-phthalate and 2,2'-bpy=2,2'-bipyridine) has been synthesized and structurally established by single-crystal X-ray diffraction. It consists of one-dimensional ribbons featuring carboxylate-bridged dinuclear units. The one-dimensional ribbons are assembled into three-dimensional networks by π-π stacking interactions. It was stable in air up to ca. 245 °C. The magnetic measurements suggest that the polymer gives weak antiferromagnetic behavior.

  19. Equatorial oceanography. [review of research

    NASA Technical Reports Server (NTRS)

    Cane, M. A.; Sarachik, E. S.

    1983-01-01

    United States progress in equatorial oceanography is reviewed, focusing on the low frequency response of upper equatorial oceans to forcing by the wind. Variations of thermocline depth, midocean currents, and boundary currents are discussed. The factors which determine sea surface temperature (SST) variability in equatorial oceans are reviewed, and the status of understanding of the most spectacular manifestation of SST variability, the El Nino-Southern Oscillation phenomenon, is discussed. The problem of observing surface winds, regarded as a fundamental factor limiting understanding of the equatorial oceans, is addressed. Finally, an attempt is made to identify those current trends which are expected to bear fruit in the near and distant future.

  20. Helical channel design and technology for cooling of muon beams

    SciTech Connect

    Yonehara, K; Derbenev, Y.S.; Johnson, R.P.; /MUONS Inc., Batavia

    2010-08-01

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  1. Helical Channel Design and Technology for Cooling of Muon Beams

    NASA Astrophysics Data System (ADS)

    Yonehara, K.; Derbenev, Y. S.; Johnson, R. P.

    2010-11-01

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  2. Helical Channel Design and Technology for Cooling of Muon Beams

    SciTech Connect

    Yonehara, K.; Derbenev, Y. S.; Johnson, R. P.

    2010-11-04

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  3. Topside sounder observations of equatorial bubbles

    NASA Technical Reports Server (NTRS)

    Dyson, P. L.; Benson, R. F.

    1978-01-01

    Large scale regions of depleted equatorial ionospheric plasma, called equatorial bubbles, are investigated using topside sounder data. The sounder's unique remote measuring capability enables the magnetic field-aligned nature of the bubbles to be investigated. A search of all available Alouette 2 and ISIS 1 ionograms during nighttime perigee passes near the magnetic equator has revealed a variety of echo signatures associated with bubbles. In addition to a sudden drop in electron density, these signatures usually include in situ spread F and ducted traces. The ducted traces have been used to determine the electron density distribution and to infer changes in ion composition along the magnetic field line within the duct associated with the bubble. In some cases it can be determined that the bubble is asymmetric with respect to the magnetic equator. Even though such features require 3 dimensional models for their explanation, the great field-aligned extent of the bubbles (relative to their cross section) suggests that current theories, which ignore variations along the magnetic field, are still applicable.

  4. AMISR-14: Observations of equatorial spread F

    NASA Astrophysics Data System (ADS)

    Rodrigues, F. S.; Nicolls, M. J.; Milla, M. A.; Smith, J. M.; Varney, R. H.; Strømme, A.; Martinis, C.; Arratia, J. F.

    2015-07-01

    A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F(ESF) irregularities made with the system. Colocation with the 50 MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to "image" scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of F region scattering structures as they evolve and drift across the radar beams.

  5. An experimental superconducting helical undulator

    SciTech Connect

    Caspi, S.; Taylor, C.

    1995-12-31

    Improvements in the technology of superconducting magnets for high energy physics and recent advancements in SC materials with the artificial pinning centers (APC){sup 2}, have made a bifilar helical SC device an attractive candidate for a single-pass free electron laser (FEL){sup 3}. Initial studies have suggested that a 6.5 mm inner diameter helical device, with a 27 mm period, can generate a central field of 2-2.5 Tesla. Additional studies have also suggested that with a stored energy of 300 J/m, such a device can be made self-protecting in the event of a quench. However, since the most critical area associated with high current density SC magnets is connected with quenching and training, a short experimental device will have to be built and tested. In this paper we discuss technical issues relevant to the construction of such a device, including a conceptual design, fields, and forces.

  6. New Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence

    NASA Astrophysics Data System (ADS)

    Banerjee, Supratik; Galtier, Sebastien

    2016-04-01

    Hall magnetohydrodynamics is a mono-fluid plasma model appropriate for probing Final{some of the} physical processes (other than pure kinetic effects) at length scales smaller than the scales of standard MHD. In sub-ionic space plasma turbulence (e.g. the solar wind) this fluid model has been proved to be useful. Three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses three inviscid invariants which are the total energy, the magnetic helicity and the generalized helicity. In this presentation, we would like to discuss new exact relations for helicities (magnetic helicities and generalized helicities) which are derived for homogeneous stationary (not necessarily isotropic) Hall MHD turbulence (and also for its inertialess electron MHD limit) in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e. the scalar product of two different increments and are written simply as ηM = di < δ ( {b} × {j}) \\cdot δ {b} >, with ηM the average magnetic helicity flux rate, {b} the magnetic field, {j} the current and ± ηG = < δ ( {v} × {Ω} ) \\cdot δ {Ω} > , with ηM the average generalized helicity flux rate, {v} the fluid velocity and {Ω} = {b} + dI {ω} being the generalized helicity where ω is simply the fluid vorticity ( = nabla × {v}). It provides, therefore, a direct measurement of the dissipation rates for the corresponding helicities even in case of an anisotropic plasma turbulence. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations while the magnetic helicity cascade is linked to the right polarized fluctuations. The newly derived relations also show that like energy, a non-zero helicity flux can only be associated to a departure of Beltrami flow state. {Reference} S. Banerjee & S. Galtier, {Chiral Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence} (submitted).

  7. Enhanced helical swimming in Boger fluids

    NASA Astrophysics Data System (ADS)

    Godinez, Francisco; Mendez-Rojano, Rodrigo; Zenit, Roberto; Lauga, Eric

    2014-11-01

    We conduct experiments with force-free magnetically-driven helical swimmers in Newtonian and viscoelastic (Boger) fluids. In order assess the effect of viscoelasticity on the swimming performance, we conduct experiments for swimmers with different helical tail geometries. We use helices with the same wave length and total length but vary the angle of the helix. As previously reported by the computational study of Spagniole and collaborators, we found that the swimming performance can either increase, decrease or remain unchanged, depending on the geometry of the tail. With the right geometry, the enhancement can be up to a factor of two.

  8. Helicity oscillations of Dirac and Majorana neutrinos

    NASA Astrophysics Data System (ADS)

    Dobrynina, Alexandra; Kartavtsev, Alexander; Raffelt, Georg

    2016-06-01

    The helicity of a Dirac neutrino with mass m evolves under the influence of a B field because it has a magnetic dipole moment proportional to m . Moreover, it was recently shown that a polarized or anisotropic medium engenders the same effect for both Dirac and Majorana neutrinos. Because a B field polarizes a background medium, it instigates helicity oscillations even for Majorana neutrinos unless the medium is symmetric between matter and antimatter. Motivated by these observations, we review the impact of a B field and of an anisotropic or polarized medium on helicity oscillations for Dirac and Majorana neutrinos from the common perspective of in-medium dispersion.

  9. HELICITY CONSERVATION IN NONLINEAR MEAN-FIELD SOLAR DYNAMO

    SciTech Connect

    Pipin, V. V.; Sokoloff, D. D.; Zhang, H.; Kuzanyan, K. M.

    2013-05-01

    It is believed that magnetic helicity conservation is an important constraint on large-scale astrophysical dynamos. In this paper, we study a mean-field solar dynamo model that employs two different formulations of the magnetic helicity conservation. In the first approach, the evolution of the averaged small-scale magnetic helicity is largely determined by the local induction effects due to the large-scale magnetic field, turbulent motions, and the turbulent diffusive loss of helicity. In this case, the dynamo model shows that the typical strength of the large-scale magnetic field generated by the dynamo is much smaller than the equipartition value for the magnetic Reynolds number 10{sup 6}. This is the so-called catastrophic quenching (CQ) phenomenon. In the literature, this is considered to be typical for various kinds of solar dynamo models, including the distributed-type and the Babcock-Leighton-type dynamos. The problem can be resolved by the second formulation, which is derived from the integral conservation of the total magnetic helicity. In this case, the dynamo model shows that magnetic helicity propagates with the dynamo wave from the bottom of the convection zone to the surface. This prevents CQ because of the local balance between the large-scale and small-scale magnetic helicities. Thus, the solar dynamo can operate in a wide range of magnetic Reynolds numbers up to 10{sup 6}.

  10. REPRODUCTION OF THE OBSERVED TWO-COMPONENT MAGNETIC HELICITY IN SOLAR WIND TURBULENCE BY A SUPERPOSITION OF PARALLEL AND OBLIQUE ALFVEN WAVES

    SciTech Connect

    He Jiansen; Tu Chuanyi; Marsch, Eckart; Yao Shuo

    2012-04-10

    The angular distribution of the normalized reduced magnetic helicity density ({sigma} r{sub m}) in solar wind turbulence reveals two components of distinct polarity in different angle ranges. This kind of two-component {sigma}{sup r}{sub m} may indicate the possible wave modes and power spectral densities (PSDs) of the turbulent fluctuations. Here we model the measured angular distribution of {sigma}{sup r}{sub m} by assuming a PSD distribution for Alfven fluctuations in wavevector space, and then fit the model results to the observations by adjusting the pattern of the PSD distribution. It is found that the two-component form of the PSD, which has a major and minor component close to k and k{sub ||}, respectively, seems to be responsible for the observed two-component {sigma}{sup r}{sub m}. On the other hand, both an isotropic PSD and a PSD with only a single component bending toward k fail to reproduce the observations. Moreover, it is shown that the effect of gradual balance between outward and inward wave-energy fluxes with decreasing spatial scale needs to be considered in order to reproduce the observed diminishing of |{sigma}{sup r}{sub m}| at shorter scales. Therefore, we suggest that the observed two-component {sigma}{sup r}{sub m} in the solar wind turbulence may be due to a superposition of Alfven waves with quasi-perpendicular (major part) and quasi-parallel (minor part) propagation. The waves seem to become gradually balanced toward shorter scales.

  11. Equatorial MU Radar project

    NASA Astrophysics Data System (ADS)

    Yamamoto, Mamoru; Hashiguchi, H.; Tsuda, Toshitaka; Yamamoto, Masayuki

    Research Institute for Sustainable Humanosphere, Kyoto University (RISH) has been studying the atmosphere by using radars. The first big facility was the MU (Middle and Upper atmosphere) radar installed in Shiga, Japan in 1984. This is one of the most powerful and multi-functional radar, and is successful of revealing importance of atmospheric waves for the dynamical vertical coupling processes. The next big radar was the Equatorial Atmosphere Radar (EAR) installed at Kototabang, West Sumatra, Indonesia in 2001. The EAR was operated under close collaboration with LAPAN (Indonesia National Institute for Aeronautics and Space), and conducted the long-term continuous observations of the equatorial atmosphere/ionosphere for more than 10 years. The MU radar and the EAR are both utilized for inter-university and international collaborative research program for long time. National Institute for Polar Research (NIPR) joined EISCAT Scientific Association together with Nagoya University, and developed the PANSY radar at Syowa base in Antarctica as a joint project with University of Tokyo. These are the efforts of radar study of the atmosphere/ionosphere in the polar region. Now we can find that Japan holds a global network of big atmospheric/ionospheric radars. The EAR has the limitation of lower sensitivity compared with the other big radars shown above. RISH now proposes a plan of Equatorial MU Radar (EMU) that is to establish the MU-radar class radar next to the EAR. The EMU will have an active phased array antenna with the 163m diameter and 1055 cross-element Yagis. Total output power of the EMU will be more than 500kW. The EMU can detect turbulent echoes from the mesosphere (60-80km). In the ionosphere incoherent-scatter observations of plasma density, drift, and temperature would be possible. Multi-channel receivers will realize radar-imaging observations. The EMU is one of the key facilities in the project "Study of coupling processes in the solar-terrestrial system

  12. Theory of helical electron beams in gyrotrons

    SciTech Connect

    Kuftin, A.N.; Lygin, V.K.; Manuilov, V.N.; Raisky, B.V.; Solujanova, E.A.; Tsimring, S.E.

    1993-04-01

    Helical electron beams (HEB) with disturbed axial symmetry of currents density and HEB with locking electrons in magnetic trap are described. The theory of magnetron injection gun (MIG) in space-charge limited current is developed. Systems on permanent magnets forming HEB are considered. 30 refs., 12 figs., 5 tabs.

  13. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, A.; Boozer, A.H.

    1984-03-06

    The present invention generates stellarator fields having favorable properties (magnetic well and large rotational transform) by a simple coil system consisting only of unlinked planar non-circular coils. At large rotational transform toroidal effects on magnetic well and rotational transform are small and can be ignored. We do so herein, specializing in straight helical systems.

  14. Bioinspired helical microswimmers based on vascular plants.

    PubMed

    Gao, Wei; Feng, Xiaomiao; Pei, Allen; Kane, Christopher R; Tam, Ryan; Hennessy, Camille; Wang, Joseph

    2014-01-01

    Plant-based bioinspired magnetically propelled helical microswimmers are described. The helical microstructures are derived from spiral water-conducting vessels of different plants, harnessing the intrinsic biological structures of nature. Geometric variables of the spiral vessels, such as the helix diameter and pitch, can be controlled by mechanical stretching for the precise fabrication and consistent performance of helical microswimmers. Xylem vessels of a wide variety of different plants have been evaluated for the consistency and reproducibility of their helical parameters. Sequential deposition of thin Ti and Ni layers directly on the spiral vessels, followed by dicing, leads to an extremely simple and cost-efficient mass-production of functional helical microswimmers. The resulting plant-based magnetic microswimmers display efficient propulsion, with a speed of over 250 μm/s, as well as powerful locomotion in biological media such as human serum. The influence of actuation frequencies on the swimming velocity is investigated. Such use of plant vessels results in significant savings in the processing costs and provides an extremely simple, cost-effective fabrication route for the large-scale production of helical magnetic swimmers. PMID:24283342

  15. Lightning over Equatorial Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These two images were taken 9 seconds apart as the STS-97 Space Shuttle flew over equatorial Africa east of Lake Volta on December 11, 2000. The top of the large thunderstorm, roughly 20 km across, is illuminated by a full moon and frequent bursts of lightning. Because the Space Shuttle travels at about 7 km/sec, the astronaut perspectives on this storm system becomes more oblique over the 9-second interval between photographs. The images were taken with a Nikon 35 mm camera equipped with a 400 mm lens and high-speed (800 ISO) color negative film. Images are STS097-351-9 and STS097-351-12, provided and archived by the Earth Science and Image Analysis Laboratory, Johnson Space Center. Additional images taken by astronauts can be viewed at NASA-JSC's Gateway to Astronaut Photography of Earth at http://eol.jsc.nasa.gov/

  16. Equatorially trapped plasma populations

    NASA Technical Reports Server (NTRS)

    Olsen, R. C.

    1981-01-01

    The SCATHA observations of the equatorially trapped plasmas are presented in order to emphasize the importance of making measurements at the equator. The UCSD plasma detector and the GSFC electric field experiment are described, as are the pertinent characteristics of the magnetometer and mass spectrometers. The electron distribution reveals a width of 20 deg to 60 deg, narrowing with increasing energy. The 20- to 100-eV ion fluxes typically exhibit temperatures in the 20to 50-eV range and densities of 1-10 per cu cm. The electron population typically ranges from 50 to 500 eV, with temperatures of 100-200 eV and densities also in the 1-10 per cu cm range. Field-aligned populations of lower energy are occasionally found in both ions and electrons at the same location.

  17. Sunrise enhancement of equatorial vertical plasma drift

    NASA Astrophysics Data System (ADS)

    Liu, Libo; Zhang, Ruilong; Le, Huijun

    2016-04-01

    Sunrise enhancement in vertical plasma drift over equatorial regions is not discernible in the statistical picture compared with the significant enhancement during dusk hours. In this report, it is the first time to investigate the occurrence of the dawn enhancement in the equatorial ionospheric vertical plasma drift from ROCSAT-1 observations during geomagnetic quiet times. The dawn enhancements occur most frequently in June solstice and least frequently in December solstice. The statistical survey shows that the occurrence depends on the magnetic declination. The enhancement has the strongest amplitude in regions near 320° longitude and peaks during June solstice. The dawn enhancement reaches its peak after the sunrise in conjugated E regions. Furthermore, it is found that the dawn enhancement is closely related to the difference between the sunrise times in the conjugated E regions (sunrise time lag). The dawn enhancement occurs easily in regions with a large sunrise time lag. Moreover, we will report the effects of the sunrise enhancement of vertical plasma drift on the equatorial ionosphere as indicated from the observations and model simulations. We thanks National Central University of Taiwan providing the ROCSAT-1 data. The Ap and F107 indices are obtained from the National Geophysical Data Center (http://spidr.ngdc.noaa.gov/spidr/). This research is supported by National Natural Science Foundation of China (41231065), the Chinese Academy of Sciences project (KZZD-EW-01-3), National Key Basic Research Program of China (2012CB825604) and National Natural Science Foundation of China (41321003).

  18. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-01-01

    The helicity condensation model has been proposed by Antiochos (2013) to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the system. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of, for example, a bipolar active region. The calculations demonstrate that, contrary to common belief, coronal loops having opposite helicity do not reconnect, whereas loops having the same sense of helicity do reconnect. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  19. Two-fluid and finite Larmor radius effects on helicity evolution in a plasma pinch

    NASA Astrophysics Data System (ADS)

    Sauppe, J. P.; Sovinec, C. R.

    2016-03-01

    The evolution of magnetic energy, helicity, and hybrid helicity during nonlinear relaxation of a driven-damped plasma pinch is compared in visco-resistive magnetohydrodynamics and two-fluid models with and without the ion gyroviscous stress tensor. Magnetic energy and helicity are supplied via a boundary electric field which initially balances the resistive dissipation, and the plasma undergoes multiple relaxation events during the nonlinear evolution. The magnetic helicity is well conserved relative to the magnetic energy over each event, which is short compared with the global resistive diffusion time. The magnetic energy decreases by roughly 1.5% of its initial value over a relaxation event, while the magnetic helicity changes by at most 0.2% of the initial value. The hybrid helicity is dominated by magnetic helicity in low-β pinch conditions and is also well conserved. Differences of less than 1% between magnetic helicity and hybrid helicity are observed with two-fluid modeling and result from cross helicity evolution. The cross helicity is found to change appreciably due to the first-order finite Larmor radius effects which have not been included in contemporary relaxation theories. The plasma current evolves towards the flat parallel current state predicted by Taylor relaxation theory but does not achieve it. Plasma flow develops significant structure for two-fluid models, and the flow perpendicular to the magnetic field is much more substantial than the flow along it.

  20. The equatorial electrojet satellite and surface comparison

    NASA Technical Reports Server (NTRS)

    Cain, J. C. (Editor); Sweeney, R. E. (Editor)

    1972-01-01

    The OGO 4 and 6 (POGO) magnetic field results for the equatorial electrojet indicate that while the present models are approximately correct, the possibility of a westward component must be incorporated. The scatter diagrams of POGO amplitudes and surface data show a correlation. The ratios between the amplitudes estimated from surface data and those at 400 km altitude are as follows: India 5 to 8, East Africa (Addis Ababa) 4, Central Africa 3, West Africa (Nigeria) 3, South America (Huancayo) 5, and Philippines 5. The variation in the ratio is due to the conductivity structure of the earth in various zones.

  1. An equatorial coronal hole at solar minimum

    NASA Technical Reports Server (NTRS)

    Bromage, B. J. I.; DelZanna, G.; DeForest, C.; Thompson, B.; Clegg, J. R.

    1997-01-01

    The large transequatorial coronal hole that was observed in the solar corona at the end of August 1996 is presented. It consists of a north polar coronal hole called the 'elephant's trunk or tusk'. The observations of this coronal hole were carried out with the coronal diagnostic spectrometer onboard the Solar and Heliospheric Observatory (SOHO). The magnetic field associated with the equatorial coronal hole is strongly connected to that of the active region at its base, resulting in the two features rotating at almost the same rate.

  2. Specification of the Occurrence of Equatorial Ionospheric Scintillations During the Main Phase of the Early Magnetic Storms Within Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Basu, S.; Groves, K. M.; Roddy, P. A.; MacKenzie, E.

    2010-12-01

    Two moderate magnetic storms with their Dst minima on the order of -75nt were observed during the rising phase of solar cycle 24 in 2010. Earlier these authors had shown with a statistical study for solar cycle 23 that during large magnetic storms with Dst < -100nT and dDst/dt >50nt/hour, scintillations and plasma bubbles occur over a specific longitude sector for which the evening period corresponds to the time interval of the main phase of storms (S. Basu et al., Radio Science, 2010, in press). This was attributed to the penetration of the high latitude electric field to the magnetic equator which enhanced the rise in the F-region at dusk thereby generating the instability that give rise to plasma bubbles. This result overrides the climatological pattern of quiet-time variation of scintillation with longitude and season that shows an equinoctial maximum at all longitudes, a maximum in the December solstice over the African/American sector and a maximum in the June solstice over the Pacific sector. The scintillations observed for the magnetic storms during solar cycle 24 did not require a large rate of change of the Dst index leading to the implication that smaller electric field perturbations were sufficient to destabilize the ionosphere which has been cooled and contracted by the unusually long and quiet current sunspot phase. We will present two storms, one of which perturbs the SCINDA sites in the African/American sector and the other one which perturbs the Pacific sector sites, both at dusk. The outstanding addition to our study in this case is the availability of the perigee orbits of the in-situ C/NOFS data allowing the tracking of the plasma bubbles in space in the development of these storms.

  3. Tokamak Startup Using Point-Source dc Helicity Injection

    SciTech Connect

    Battaglia, D. J.; Bongard, M. W.; Fonck, R. J.; Redd, A. J.; Sontag, A. C.

    2009-06-05

    Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation.

  4. Tokamak startup using point-source dc helicity injection.

    PubMed

    Battaglia, D J; Bongard, M W; Fonck, R J; Redd, A J; Sontag, A C

    2009-06-01

    Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation. PMID:19658871

  5. Helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    Ideal fluid flow conserves a special quantity known as helicity, in addition to energy, momentum and angular momentum. Helicity can be understood as a measure of the knottedness of vortex lines of the flow, providing an important geometric tool to study diverse physical systems such as turbulent fluids and plasmas. Since superfluids flow without resistance just like ideal (Euler) fluids, a natural question arises: Is there an extra conserved quantity akin to helicity in superfluids? We address the question of a ''superfluid helicity'' theoretically and examine its consequences in numerical simulations.

  6. Low-altitude equatorial ions: A new look with SAMPEX

    NASA Astrophysics Data System (ADS)

    Greenspan, M. E.; Mason, G. M.; Mazur, J. E.

    1999-09-01

    We have used the Low-Energy Ion Composition Analyzer (LICA) instrument on the low altitude, polar orbiting SAMPEX spacecraft to survey energetic ions near the magnetic equator from late 1992 through 1998; that is, through the declining phase of Solar Cycle 22, solar minimum, and into the rise of Solar Cycle 23. This survey gives us a unique opportunity to examine both the long-term variation in the low-altitude equatorial ion population and short-term enhancements that occur during magnetic storms. During the survey period, 40 storms with minimum Dst<=100nT occurred: the majority were accompanied by increases in the equatorial ion flux. Although LICA detects ions with energies far above the bulk of the ring current ion population, the times of the maximum equatorial fluxes clustered around the time of minimum Dst, i.e., the time of maximum ring current energy content. The storm associated flux maxima were unevenly distributed in geographic longitude, with the maximum flux enhancements occurring at longitudes just west of the South Atlantic Anomaly. Except for an increase in 1994, the quiet time monthly average equatorial flux declined steadily from 1992 until early 1998; then it began to rise again. The monthly average equatorial ion fluxes had a very significant correlation with the Ap index during this period (R=0.54), indicating that geomagnetic activity dominated the long-term variation. During the survey, we also discovered enhancements in the equatorial ion flux that occurred shortly after the onsets of three recent, large solar energetic particle events. These enhancements began well before the commencements of the associated geomagnetic storms. The major ion species present were H, He, C, and O, therefore ruling out an ionospheric source. These ions could not have penetrated directly from interplanetary space to the magnetic equator, and we do not understand the mechanism that produces the SEP-associated enhancements.

  7. Distortions in protein helices.

    PubMed

    Geetha, V

    1996-08-01

    alpha-helices are the most common secondary structures in observed proteins. However, they are not always found in ideal helical conformation and they often exhibit structural distortions. Quantification of these irregularities become essential in understanding the packing of helices and therefore, their role in the functional characteristics of the protein. The backbone torsions phi, psi are of limited utility in this endeavor, because distorted helices often maintain the backbone geometry. The local compensatory effects are responsible for the preservation of the entire hydrogen bond network of the helical stretch. Earlier descriptions of helical linearity and curvature rest mostly on approximation, thus motivating the search for a better method for understanding and quantifying helical irregularities. We developed a method which involves the rotation and superposition of identical repeating units of the protein by the quaternion method. The set of parameters derived from the rotation-superposition algorithm helps in identifying the bends and kinks which are not necessarily induced by unusual amino acids like proline. The quantification of irregularities of observed helices might lead to a better understanding of their packing interactions. PMID:8842770

  8. A Helical Stairway Project

    ERIC Educational Resources Information Center

    Farmer, Tom

    2008-01-01

    We answer a geometric question that was raised by the carpenter in charge of erecting helical stairs in a 10-story hospital. The explanation involves the equations of lines, planes, and helices in three-dimensional space. A brief version of the question is this: If A and B are points on a cylinder and the line segment AB is projected radially onto…

  9. Emerging double helical nanostructures

    NASA Astrophysics Data System (ADS)

    Zhao, Meng-Qiang; Zhang, Qiang; Tian, Gui-Li; Wei, Fei

    2014-07-01

    As one of the most important and land-mark structures found in nature, a double helix consists of two congruent single helices with the same axis or a translation along the axis. This double helical structure renders the deoxyribonucleic acid (DNA) the crucial biomolecule in evolution and metabolism. DNA-like double helical nanostructures are probably the most fantastic yet ubiquitous geometry at the nanoscale level, which are expected to exhibit exceptional and even rather different properties due to the unique organization of the two single helices and their synergistic effect. The organization of nanomaterials into double helical structures is an emerging hot topic for nanomaterials science due to their promising exceptional unique properties and applications. This review focuses on the state-of-the-art research progress for the fabrication of double-helical nanostructures based on `bottom-up' and `top-down' strategies. The relevant nanoscale, mesoscale, and macroscopic scale fabrication methods, as well as the properties of the double helical nanostructures are included. Critical perspectives are devoted to the synthesis principles and potential applications in this emerging research area. A multidisciplinary approach from the scope of nanoscience, physics, chemistry, materials, engineering, and other application areas is still required to the well-controlled and large-scale synthesis, mechanism, property, and application exploration of double helical nanostructures.

  10. Helicity and singular structures in fluid dynamics

    PubMed Central

    Moffatt, H. Keith

    2014-01-01

    Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described. PMID:24520175

  11. Callisto's Equatorial Region

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This mosaic covers part of the equatorial region of Jupiter's moon, Callisto. The mosaic combines six separate image frames obtained by the solid state imaging (CCD) system on NASA's Galileo spacecraft during its ninth orbit around Jupiter. North is to the top of the picture. The mosaic shows several new features and characteristics of the surface revealed by Galileo. These include deposits that may represent landslides in the southern and southwestern floors of many craters. Two such deposits are seen in a 12 kilometer (7.3 mile) crater in the west-central part of the image, and in a 23 kilometer (14 mile) crater just north of the center of the image. Also notable are several sinuous valleys emanating from the southern rims of 10 to 15 kilometer (6.2 to 9.3 mile) irregular craters in the west-central part of the image. The pervasive local smoothing of Callisto's surface is well represented in the plains between the craters in the southeastern part of the image. Possible oblique impacts are suggested by the elongated craters in the northeastern and southeastern parts of the image.

    The mosaic, centered at 7.4 degrees south latitude and 6.6 degrees west longitude, covers an area of approximately 315 by 215 kilometers (192 by 131 miles). The sun illuminates the scene from the west (left). The smallest features that can be seen are about 300 meters (993 feet) across. The images were obtained on June 25, 1997, when the spacecraft was at a range of 15,200 kilometers (8,207 miles) from Callisto.

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.

    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  12. Modelling of magnetic satellite intensity in the neutron diffraction of an incommensurate helical structure: NiBr 2 and Ni 0.91Fe 0.09Br 2

    NASA Astrophysics Data System (ADS)

    Day, P.; Moore, M. W.; Wilkinson, C.; Ziebeck, K. R. A.

    1985-05-01

    We describe the application of a neutron multidetector diffractometer (D16, I.L.L.) to the study of the incommensurate helical magnetic structure of pure and Fe 2+-doped single crystals of NiBr 2. Use of the multidetector permits detailed mapping of satellite intensity around 003 M arising from three magnetic domains, from which the magnitude and direction of the helix propagation vector τ are deduced. τ moves from [110] (0.0138(5) Å -1) in NiBr 2 to [100] (0.0151(5) Å -1) in Ni 0.91 Fe 0.09Br 2. The measured intensity profiles in (2θ, ω, v space are fitted to model profiles constructed by superimposing profiles measured at 003 M in the collinear phase at 28 K on a ring with radius τ, and optimizing the weighting of intensity around the ring.

  13. The equatorial electrojet current modelling from SWARM satellite data

    NASA Astrophysics Data System (ADS)

    Benaissa, Mahfoud

    2016-07-01

    Equatorial ElectroJet (EEJ) is an intense eastward electric current circulating in the ionospheric magnetic equator band between 100 and 130 km of altitude in E region. These currents vary by day, by season, by solar activity, and also with the main magnetic field of internal origin. The irregularity of the ionosphere has a major impact on the performance of communication systems and navigation (GPS), industry.... Then it becomes necessary study the characteristics of EEJ. In this paper, we present a study of the equatorial electrojet (EEJ) phenomenon along one year (2014) period. In addition, the satellite data used in this study are obtained with SWARM satellite scalar magnetometer data respecting magnetically quiet days with KP < 2. In this paper, we process to separate and extract the electrojet intensity signal from other recorded signal-sources interfering with the main signal and reduce considerably the signal to noise ratio during the SWARM measurements. This pre-processing step allows removing all external contributions in regard to EEJ intensity value. Key words: Ionosphere (Equatorial ionosphere; Electric fields and currents; Equatorial electrojet (EEJ)); SWARM.

  14. Filament Channel Formation by Helicity Condensation

    NASA Astrophysics Data System (ADS)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C.

    2013-12-01

    A major unexplained feature of the solar atmosphere is the accumulation of magnetic shear, in the form of filament channels, at photospheric polarity inversion lines (PILs). In addition to free energy, this shear also represents magnetic helicity, which is conserved under reconnection. Consequently, the observations raise the question: Why is helicity observed to be concentrated along PILs? Preliminary results of 3D MHD simulations using the Adaptively Refined MHD Solver (ARMS) are presented that support the magnetic-helicity condensation model of filament-channel formation (Antiochos 2013). In this work, we address the problem of filament-channel formation by considering supergranular twisting of a quasi-potential flux system, bounded by a PIL and containing a coronal hole (CH). The magnetic helicity injected by small-scale photospheric motions is shown to inverse-cascade up to the largest allowable scales that define the closed flux system: the PIL and the CH boundary. This, in effect, produces field lines that are both sheared and smooth and, in agreement with Antiochos (2013), are sheared in opposite senses at the PIL and the CH. We present a detailed analysis of our simulation results and discuss their implications for observations.

  15. Exabyte helical scan devices at Fermilab

    SciTech Connect

    Constanta-Fanourakis, P.; Kaczar, K.; Oleynik, G.; Petravick, D.; Votava, M.; White, V.; Hockney, G.; Bracker, S.; de Miranda, J.M.

    1989-05-01

    Exabyte 8mm helical scan storage devices are in use at Fermilab in a number of applications. These devices have the functionality of magnetic tape, but use media which is much more economical and much more dense than conventional 9 track tape. 6 refs., 3 figs.

  16. Limits to solar cycle predictability: Cross-equatorial flux plumes

    NASA Astrophysics Data System (ADS)

    Cameron, R. H.; Dasi-Espuig, M.; Jiang, J.; Işık, E.; Schmitt, D.; Schüssler, M.

    2013-09-01

    Context. Within the Babcock-Leighton framework for the solar dynamo, the strength of a cycle is expected to depend on the strength of the dipole moment or net hemispheric flux during the preceding minimum, which depends on how much flux was present in each hemisphere at the start of the previous cycle and how much net magnetic flux was transported across the equator during the cycle. Some of this transport is associated with the random walk of magnetic flux tubes subject to granular and supergranular buffeting, some of it is due to the advection caused by systematic cross-equatorial flows such as those associated with the inflows into active regions, and some crosses the equator during the emergence process. Aims: We aim to determine how much of the cross-equatorial transport is due to small-scale disorganized motions (treated as diffusion) compared with other processes such as emergence flux across the equator. Methods: We measure the cross-equatorial flux transport using Kitt Peak synoptic magnetograms, estimating both the total and diffusive fluxes. Results: Occasionally a large sunspot group, with a large tilt angle emerges crossing the equator, with flux from the two polarities in opposite hemispheres. The largest of these events carry a substantial amount of flux across the equator (compared to the magnetic flux near the poles). We call such events cross-equatorial flux plumes. There are very few such large events during a cycle, which introduces an uncertainty into the determination of the amount of magnetic flux transported across the equator in any particular cycle. As the amount of flux which crosses the equator determines the amount of net flux in each hemisphere, it follows that the cross-equatorial plumes introduce an uncertainty in the prediction of the net flux in each hemisphere. This leads to an uncertainty in predictions of the strength of the following cycle.

  17. Solar flares controlled by helicity conservation

    NASA Technical Reports Server (NTRS)

    Gliner, Erast B.; Osherovich, Vladimir A.

    1995-01-01

    The energy release in a class of solar flares is studied on the assumption that during burst events in highly conducting plasma the magnetic helicity of plasma is approximately conserved. The available energy release under a solar flare controlled by the helicity conservation is shown to be defined by the magnetic structure of the associated prominence. The approach throws light on some solar flare enigmas: the role of the associated prominence. The approach throws light on some solar flare enigmas: the role of the associated prominences; the discontinuation of the reconnection of magnetic lines long before the complete reconnection of participated fields occurs; the existence of quiet prominences which, in spite of their usual optical appearance, do not initiate any flare events; the small energy release under a solar flare in comparison with the stockpile of magnetic energy in surrounding fields. The predicted scale of the energy release is in a fair agreement with observations.

  18. Chiral transport of neutrinos in supernovae: Neutrino-induced fluid helicity and helical plasma instability

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naoki

    2016-03-01

    Chirality of neutrinos modifies the conventional kinetic theory and hydrodynamics, leading to unusual chiral transport related to quantum anomalies in field theory. We argue that these corrections have new phenomenological consequences for hot and dense neutrino gases, especially in core-collapse supernovae. We find that the neutrino density can be converted to the fluid helicity through the chiral vortical effect. This fluid helicity effectively acts as a chiral chemical potential for electrons via the momentum exchange with neutrinos and induces a "helical plasma instability" that generates a strong helical magnetic field. This provides a new mechanism for converting the gravitational energy released by the core collapse to the electromagnetic energy and potentially explains the origin of magnetars. The other possible applications of the neutrino chiral transport theory are also discussed.

  19. Two-impurity helical Majorana problem

    NASA Astrophysics Data System (ADS)

    Eriksson, Erik; Zazunov, Alex; Sodano, Pasquale; Egger, Reinhold

    2015-02-01

    We predict experimentally accessible signatures for helical Majorana fermions in a topological superconductor by coupling to two quantum dots in the local moment regime (corresponding to spin-1 /2 impurities). Taking into account Ruderman-Kittel-Kasuya-Yosida interactions mediated by bulk and edge modes, where the latter cause a long-range antiferromagnetic Ising coupling, we formulate and solve the low-energy theory for this two-impurity helical Majorana problem. In particular, we show that the long-time spin dynamics after a magnetic field quench displays weakly damped oscillations with universal quality factor.

  20. Evolution of Ion Clouds in the Equatorial Ionosphere

    NASA Astrophysics Data System (ADS)

    Petrochuk, Yevgeny; Blaunstein, Nathan; Mishin, Evgeny; Pedersen, Todd; Caton, Ron; Viggiano, Al; Schuman, Nick

    2015-11-01

    We report on the results of 2- and 3-dimentional numerical investigations of the evolution of samarium ion clouds injected in the equatorial ionosphere, alike the recent MOSC experiments. The ambient conditions are described by a standard model of the quiet-time equatorial ionosphere from 90 to 350 km. The altitudinal distribution of the transport processes and ambient electric and magnetic fields is taken into account. The fast process of stratification of ion clouds and breaking into small plasmoids occur only during the late stage of the cloud evolution. The role of the background plasma and its depletion zones formed due to the short-circuiting currents is not as evident as in mid latitudes. It is also revealed that the altitudinal dependence of the diffusion and drift plays a minor role in the cloud evolution at the equator. Likewise, the cloud remains stable with respect to the Raleigh-Taylor and gradient-drift instabilities. These two features are defined by the equatorial near-horizontal magnetic field which leads to a strongly-elongated ellipsoid-like plasma cloud. The critical dip angle separating the stable (equatorial) and unstable (mid-latitude) cloud regimes will be defined in future simulation studies, as well as the dependence on the ambient electric field and neutral wind. 2Space Vehicles Directorate, Air Force Research Laboratory

  1. Muon Beam Helical Cooling Channel Design

    SciTech Connect

    Johnson, Rolland; Ankenbrandt, Charles; Flanagan, G; Kazakevich, G M; Marhauser, Frank; Neubauer, Michael; Roberts, T; Yoshikawa, C; Derbenev, Yaroslav; Morozov, Vasiliy; Kashikhin, V S; Lopes, Mattlock; Tollestrup, A; Yonehara, Katsuya; Zloblin, A

    2013-06-01

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet.

  2. Equatorial zonal circulations: Historical perspectives

    NASA Astrophysics Data System (ADS)

    Hastenrath, Stefan

    2007-04-01

    The changing perceptions on zonal circulations in the equatorial belt are traced for (a) stratospheric wind regimes, and (b) vertical-zonal circulation cells in the troposphere. (a) Observations from the Krakatoa eruption 1883 and Berson's 1908 expedition to East Africa, along with later soundings over Batavia (Jakarta) led to the notion of "Krakatoa easterlies" around 30 km (10 mb) and "Berson westerlies" around 20 km (50 mb). Prompted by contrary observations since the late 1950s, this dogma was replaced by the notion of easterlies alternating with westerlies in the equatorial stratosphere at a rhythm of about 26 months. (b) Stimulated by Bjerknes' postulate of a "Walker circulation" along the Pacific Equator, a multitude of such cells have been hypothesized at other longitudes, in part from zonal contrasts of temperature and cloudiness. Essential for the diagnosis of equatorial zonal circulation cells is the continuity following the flow between the centers of ascending and subsiding motion. Evaluation of the recent NCEP-NCAR and ECMWF Reanalysis upper-air datasets reveals equatorial zonal circulation cells over the Pacific all year round, over the Atlantic only in boreal winter, and over the Indian Ocean only in autumn, all being seasons and oceanic longitudes with strong zonal flow in the lower troposphere.

  3. Higher-order harmonic effect of a three-dimensional helical wiggler on the Larmor rotation of the equilibrium electrons in a free-electron laser with a positive or a reversed guide magnetic field

    SciTech Connect

    Zhang, Shi-Chang

    2013-10-15

    Analytical formulas of the Larmor rotation are derived in detail for the equilibrium electrons motion in a free-electron laser with combination of a three-dimensional (3-D) helical wiggler and a positive or a reversed guide magnetic field. Generally, the Larmor radius in the configuration of a reversed guide field is much smaller than that in a positive guide field. At non-resonance, a helical orbit governed by the zero-order component of a 3-D wiggler field could hold; meanwhile, the higher-harmonic effect definitely influences those electrons with off-axis guiding centers and induces the electron-beam spreads. At resonance, the Larmor radius in the configuration of a positive guide field has a singularity with a limit tending to infinite, which causes all the electrons to hit the waveguide wall before the exit of the wiggler. Although Larmor-radius singularity does not exist in the configuration of a reversed guide field, at anti-resonance, the first-order harmonic of a 3-D wiggler field induces a transverse displacement which rapidly grows in proportion to a square of time, and leads part of the electron beam to hit the waveguide wall before reaching the wiggler exit, which depends on the specific parameters of the individual electrons. The analytical conclusions derived in the present paper are examined by the nonlinear simulations and the experimental observation. Disagreement with the previous literatures is discussed in detail.

  4. S-duality and helicity amplitudes

    NASA Astrophysics Data System (ADS)

    Colwell, Kitran; Terning, John

    2016-03-01

    We examine interacting Abelian theories at low energies and show that holomorphically normalized photon helicity amplitudes transform into dual amplitudes under SL(2, {Z} ) as modular forms with weights that depend on the number of positive and negative helicity photons and on the number of internal photon lines. Moreover, canonically normalized helicity amplitudes transform by a phase, so that even though the amplitudes are not duality invariant, their squares are duality invariant. We explicitly verify the duality transformation at one loop by comparing the amplitudes in the case of an electron and the dyon that is its SL(2, {Z} ) image, and extend the invariance of squared amplitudes order by order in perturbation theory. We demonstrate that S-duality is a property of all low-energy effective Abelian theories with electric and/or magnetic charges and see how the duality generically breaks down at high energies.

  5. Biot-Savart helicity versus physical helicity: A topological description of ideal flows

    NASA Astrophysics Data System (ADS)

    Sahihi, Taliya; Eshraghi, Homayoon

    2014-08-01

    For an isentropic (thus compressible) flow, fluid trajectories are considered as orbits of a family of one parameter, smooth, orientation-preserving, and nonsingular diffeomorphisms on a compact and smooth-boundary domain in the Euclidian 3-space which necessarily preserve a finite measure, later interpreted as the fluid mass. Under such diffeomorphisms the Biot-Savart helicity of the pushforward of a divergence-free and tangent to the boundary vector field is proved to be conserved and since these circumstances present an isentropic flow, the conservation of the "Biot-Savart helicity" is established for such flows. On the other hand, the well known helicity conservation in ideal flows which here we call it "physical helicity" is found to be an independent constant with respect to the Biot-Savart helicity. The difference between these two helicities reflects some topological features of the domain as well as the velocity and vorticity fields which is discussed and is shown for simply connected domains the two helicities coincide. The energy variation of the vorticity field is shown to be formally the same as for the incompressible flow obtained before. For fluid domains consisting of several disjoint solid tori, at each time, the harmonic knot subspace of smooth vector fields on the fluid domain is found to have two independent base sets with a special type of orthogonality between these two bases by which a topological description of the vortex and velocity fields depending on the helicity difference is achieved since this difference is shown to depend only on the harmonic knot parts of velocity, vorticity, and its Biot-Savart vector field. For an ideal magnetohydrodynamics (MHD) flow three independent constant helicities are reviewed while the helicity of magnetic potential is generalized for non-simply connected domains by inserting a special harmonic knot field in the dynamics of the magnetic potential. It is proved that the harmonic knot part of the vorticity

  6. Field of a helical Siberian Snake

    SciTech Connect

    Luccio, A.

    1995-02-01

    To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such a prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.

  7. Phase space variations of near equatorially mirroring ring current ions

    NASA Technical Reports Server (NTRS)

    Williams, D. J.

    1981-01-01

    Observations of near equatorially mirroring ring current ions before and after a magnetic storm are presented in the form of phase space densities with respect to the first adiabatic invariant. Particle densities were obtained from the medium energy particles instrument covering the energy range 24-2081 keV on ISEE 1 at L values between 3 and 8 earth radii and ratios of the magnetic field at the satellite position to the magnetic field at the magnetic equator less than 1.2. Analysis of the phase space densities through the magnetosphere reveals a well-defined high magnetic moment peak in the prestorm near-equatorial ring current ion phase space density distribution, with the magnetic storm resulting from an enhancement of phase space densities at magnetic moment values below the peak and phase space densities remaining constant above the peak. Results are found to be in good agreement with those obtained by Explorer 45 six years previously, indicating that the observed phase space density variations are characteristic of energetic ion behavior during magnetic storms.

  8. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-05-01

    The helicity condensation model has been proposed by Antiochos to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences are observed to form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the corona. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of a bipolar active region, for example. The calculations demonstrate that, contrary to common belief, opposite helicity twists do not lead to significant reconnection in such a coronal system, whereas twists with the same sense of helicity do produce substantial reconnection. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  9. Adding helicity to inflationary magnetogenesis

    SciTech Connect

    Caprini, Chiara; Sorbo, Lorenzo E-mail: sorbo@physics.umass.edu

    2014-10-01

    The most studied mechanism of inflationary magnetogenesis relies on the time-dependence of the coefficient of the gauge kinetic term F{sub μν} F{sup μν}. Unfortunately, only extremely finely tuned versions of the model can consistently generate the cosmological magnetic fields required by observations. We propose a generalization of this model, where also the pseudoscalar invariant F{sub μν}  F-tilde {sup μν} is multiplied by a time dependent function. The new parity violating term allows more freedom in tuning the amplitude of the field at the end of inflation. Moreover, it leads to a helical magnetic field that is amplified at large scales by magnetohydrodynamical processes during the radiation dominated epoch. As a consequence, our model can satisfy the observational lower bounds on fields in the intergalactic medium, while providing a seed for the galactic dynamo, if inflation occurs at an energy scale ranging from 10{sup 5} to 10{sup 10} GeV. Such energy scale is well below that suggested by the recent BICEP2 result, if the latter is due to primordial tensor modes. However, the gauge field is a source of tensors during inflation and generates a spectrum of gravitational waves that can give a sizable tensor to scalar ratio r=O(0.2) even if inflation occurs at low energies. This system therefore evades the Lyth bound. For smaller values of r, lower values of the inflationary energy scale are required. The model predicts fully helical cosmological magnetic fields and a chiral spectrum of primordial gravitational waves.

  10. Occurrence of equatorial spread F during intense geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Ray, S.; Roy, B.; Das, A.

    2015-07-01

    Equatorial spread F (ESF) has been observed in response to the prompt penetration of magnetospheric electric field to equatorial latitudes during intense (minimum Dst ≤ -100 nT; Bz ≤ -10 nT for at least 3 h) magnetic storms using global ion density plots of Defense Meteorological Satellite Program (DMSP) over nearly one solar cycle (1996-2005). Geostationary amplitude scintillation observations from Calcutta at VHF and L band for 1996-2005 and GPS amplitude scintillation measurements during 2004-2005 from the Indian Satellite Based Augmentation System Geostationary and GPS Navigation Outlay (GPS Aided GEO Augmented Navigation) network of stations all over India have been used to corroborate the DMSP observations. Subsequent to the time of southward interplanetary magnetic field Bz crossing -10 nT for an intense storm, it has been observed that within 4 h, ESF is generated at a longitude where the local time is dusk.

  11. CONVECTIVE BURSTS AND THE COUPLING OF SATURN'S EQUATORIAL STORMS AND INTERIOR ROTATION

    SciTech Connect

    Heimpel, Moritz; Aurnou, Jonathan M. E-mail: aurnou@ucla.edu

    2012-02-10

    Temporal variations of Saturn's equatorial jet and magnetic field hint at rich dynamics coupling the atmosphere and the deep interior. However, it has been assumed that rotation of the interior dynamo must be steady over tens of years of modern observations. Here we use a numerical convection model and scaling estimates to show how equatorial convective bursts can transfer angular momentum to the deeper interior. The numerical model allows angular momentum transfer between a fluid outer spherical shell and a rigid inner sphere. Convection drives a prograde equatorial jet exhibiting quasiperiodic bursts that fill the equatorial volume outside the tangent cylinder. For each burst strong changes in the equatorial surface velocity are associated with retrograde torque on the inner sphere. Our results suggest that Saturn's Great White Spot, a giant storm that was observed to fill the equatorial region in 1990, could mobilize a volume of fluid carrying roughly 15% of Saturn's moment of inertia. Conservation of angular momentum then implies that a 20% change in the equatorial jet angular velocity could change the average interior rotation rate by about 0.1%-roughly an order of magnitude less than the apparent rotation rate changes associated with Saturn's kilometric radio (SKR) signal. However, if the SKR signal originates outside the liquid metal core in a 'planetary tachocline' that separates the layer of fast zonal flow from the magnetically controlled and slowly convecting deep interior, then convective bursts can provide a possible mechanism for the observed {approx}1% SKR changes.

  12. The alpha dynamo parameter and measurability of helicities in magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Matthaeus, W. H.; Goldstein, M. L.; Lantz, S. R.

    1986-01-01

    Alpha, an important parameter in dynamo theory, is shown to be proportional to either the kinetic, current, magnetic, or velocity helicities of the fluctuating magnetic field and fluctuating velocity field. The particular helicity to which alpha is proportional depends on the assumptions used in deriving the first-order smoothed equations that describe the alpha effect. In two cases, viz., when alpha is proportional to either the magnetic helicity or velocity helicity, alpha can be determined experimentally from two-point measurements of the fluctuating fields in incompressible, homogeneous turbulence with arbitrary rotational symmetry. For the other two possibilities, alpha can be determined if the turbulence is isotropic.

  13. Dynamics of helical states in MST

    NASA Astrophysics Data System (ADS)

    Munaretto, Stefano; Auriemma, F.; Brower, D.; Chapman, B. E.; den Hartog, D. J.; Ding, W. X.; Duff, J.; Franz, P.; Goetz, J. A.; Holly, D.; Lin, L.; McCollam, K. J.; McGarry, M.; Morton, L.; Nornberg, M. D.; Parke, E.; Sarff, J. S.

    2014-10-01

    The thermal and the magnetic dynamics of quasi-single-helicity (QSH) plasmas evolve independently during the formation and sustainment of the core helical structure. At higher plasma current (and Lundquist number) MST plasmas transition from an axisymmetric multi-helicity state to a QSH state characterized by a strong core helical mode and reduced secondary mode amplitudes. Plasmas in the QSH state tend to wall-lock, often in an orientation that is unfavorable for optimized measurements of the 3D structure using MST's advanced diagnostics. Recently a technique to control the locking position through an applied resonant magnetic perturbation has been developed. Using this technique it is possible to adjust the 3D phase more optimally for specific diagnostics, to study the dynamics of the QSH structure and thermal features. The multi-chord FIR interferometer shows the presence of a density structure for the duration of the QSH state. Measurements of the time evolution of the electron temperature profile using the Thomson Scattering diagnostic reveal that the transition to QSH allows the presence of a 3D thermal structure, but this structure is intermittent. Understanding the mechanism(s) driving these dynamics is the goal of this work. Work supported by the US DOE and NSF.

  14. Longitudinal variation of sudden commencement of geomagnetic storm at equatorial stations

    SciTech Connect

    Rastogi, R.G.

    1993-09-01

    The author reports the observation of a correlation between the strength of storm sudden commencements in the equatorial electrojet region with the equatorial electrojet current itself, as a function of daytime, latitude, and longitude. The author argues that electric fields generated at the magnetopause by interaction with solar wind plasma transmits to the polar region along field lines, and there converts to magnetic waves which rapidly propogate to equatorial regions in the conducting plasma between the ionosphere and the earth. The strength of the arrival fields is dependent upon the ionospheric conductivity at the particular location in question.

  15. Spheromak Power and Helicity Balance

    SciTech Connect

    Thomassen, K.I.

    2000-05-18

    This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to a Taylor state, {mu}{sub o}J = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential difference between the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. When these volumes have different values of {lambda} (ratio of {mu}{sub o}B{sup -2}j {center_dot} B in each region) in the open line volume V{sub 1} and the closed spheromak volume V{sub 2} the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss is the {lambda}-ratio of these regions, in the limit V{sub 1} << V{sub 2}. This result follows immediately from helicity balance in that limit. Here we give an accounting of all the gun power, and do not assume a small edge (open line) region.

  16. Helical screw viscometer

    DOEpatents

    Aubert, J.H.; Chapman, R.N.; Kraynik, A.M.

    1983-06-30

    A helical screw viscometer for the measurement of the viscosity of Newtonian and non-Newtonian fluids comprising an elongated cylindrical container closed by end caps defining a circular cylindrical cavity within the container, a cylindrical rotor member having a helical screw or ribbon flight carried by the outer periphery thereof rotatably carried within the cavity whereby the fluid to be measured is confined in the cavity filling the space between the rotor and the container wall. The rotor member is supported by axle members journaled in the end caps, one axle extending through one end cap and connectable to a drive source. A pair of longitudinally spaced ports are provided through the wall of the container in communication with the cavity and a differential pressure meter is connected between the ports for measuring the pressure drop caused by the rotation of the helical screw rotor acting on the confined fluid for computing viscosity.

  17. The origin of the helicity hemispheric sign rule reversals in the mean-field solar-type dynamo

    NASA Astrophysics Data System (ADS)

    Pipin, V. V.; Zhang, H.; Sokoloff, D. D.; Kuzanyan, K. M.; Gao, Y.

    2013-11-01

    Observations of proxies of the magnetic helicity in the Sun over the past two solar cycles revealed reversals of the helicity hemispheric sign rule (negative in the North and positive in the South hemispheres). We apply the mean-field solar dynamo model to study the reversals of the magnetic helicity sign for the dynamo operating in the bulk of the solar convection zone. The evolution of the magnetic helicity is governed by the conservation law. We found that the reversal of the sign of the small-scale magnetic helicity follows the dynamo wave propagating inside the convection zone. Therefore, the spatial patterns of the magnetic helicity reversals reflect the processes which contribute to generation and evolution of the large-scale magnetic fields. At the surface, the patterns of the helicity sign reversals are determined by the magnetic helicity boundary conditions at the top of the convection zone. We demonstrate the impact of fluctuations in the dynamo parameters and variability in dynamo cycle amplitude on the reversals of the magnetic helicity sign rule. The obtained results suggest that the magnetic helicity of the large-scale axisymmetric field can be treated as an additional observational tracer for the solar dynamo and it probably can be used for the solar activity forecast as well.

  18. Observations of ULF wave related equatorial electrojet and density fluctuations

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Zesta, E.; Biouele, C. M.; Moldwin, M. B.; Boudouridis, A.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.; Hartinger, M.

    2013-10-01

    We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.

  19. HF Doppler radar observations of equatorial plasma drifts and spread-F

    NASA Astrophysics Data System (ADS)

    Jayachandran, B.; Namboothiri, S. P.; Balan, N.; Rao, P. B.; Sastri, J. H.

    Vertical plasma drift measurements have been made by an HF Doppler radar at the equatorial station of Trivandrum. For magnetically quiet conditions, Doppler observations are presented dealing with (1) the postsunset vertical plasma drifts and their seasonal dependence, (2) the prereversal enhancement in the vertical plasma drift and the occurrence of equatorial spread-F, and (3) the vector plasma drift measurements for a sample equinoctial day.

  20. Trend of photospheric helicity flux in active regions generating halo CMEs

    NASA Astrophysics Data System (ADS)

    Smyrli, Aimilia; Zuccarello, Francesco; Zuccarello, Francesca; Romano, Paolo; Guglielmino, Salvatore Luigi; Spadaro, Daniele; Hood, Alan; Mackay, Duncan

    Coronal Mass Ejections (CMEs) are very energetic events initiated in the solar atmosphere, re-sulting in the expulsion of magnetized plasma clouds that propagate into interplanetary space. It has been proposed that CMEs can play an important role in shedding magnetic helicity, avoiding its endless accumulation in the corona. We therefore investigated the behavior of magnetic helicity accumulation in sites where the initiation of CMEs occurred, in order to de-termine whether and how changes in magnetic helicity accumulation are temporally correlated with CME occurrence. After identifying the active regions (AR) where the CMEs were ini-tiated by means of a double cross-check based on the flaring-eruptive activity and the use of SOHO/EIT difference images, we used MDI magnetograms to calculate magnetic flux evolu-tion, magnetic helicity injection rate and magnetic helicity injection in 10 active regions that gave rise to 12 halo CMEs observed during the period February 2000 -June 2003. No unique behavior in magnetic helicity injection accompanying halo CME occurrence is found. In fact, in some cases there is an abrupt change in helicity injection timely correlated with the CME event, while in some others no significant variation is recorded. However, our analysis show that the most significant changes in magnetic flux and magnetic helicity injection are associated with impulsive CMEs rather than gradual CMEs. Moreover, the most significant changes in mag-netic helicity are observed when X-class flares or eruptive filaments occur, while the occurrence of flares of class C or M seems not to affect significantly the magnetic helicity accumulation.

  1. CURRENT AND KINETIC HELICITY OF LONG-LIVED ACTIVITY COMPLEXES

    SciTech Connect

    Komm, Rudolf; Gosain, Sanjay

    2015-01-01

    We study long-lived activity complexes and their current helicity at the solar surface and their kinetic helicity below the surface. The current helicity has been determined from synoptic vector magnetograms from the NSO/SOLIS facility, and the kinetic helicity of subsurface flows has been determined with ring-diagram analysis applied to full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values (78%; 78%, respectively, with a 95% confidence level of 31%) in the southern hemisphere and negative ones (80%; 93%, respectively, with a 95% confidence level of 22% and 14%, respectively) in the northern hemisphere. The locations with the dominant sign of kinetic helicity derived from Global Oscillation Network Group (GONG) and SDO/HMI data are more organized than those of the secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. This is the case for both hemispheres even for the northern one where it is not as obvious visually due to the large amount of magnetic activity present as compared to the southern hemisphere. The current helicity shows a similar behavior. The dominant sign of current helicity is the same as that of kinetic helicity for the majority of the activity complexes (83% with a 95% confidence level of 15%). During the 24 Carrington rotations analyzed here, there is at least one longitude in each hemisphere where activity complexes occur repeatedly throughout the epoch. These ''active'' longitudes are identifiable as locations of strong current and kinetic helicity of the same sign.

  2. The quantum Hall effect helicity

    SciTech Connect

    Shrivastava, Keshav N.

    2015-04-16

    The quantum Hall effect in semiconductor heterostructures is explained by two signs in the angular momentum j=l±s and g=(2j+1)/(2l+1) along with the Landau factor (n+1/2). These modifications in the existing theories explain all of the fractional charges. The helicity which is the sign of the product of the linear momentum with the spin p.s plays an important role for the understanding of the data at high magnetic fields. In particular it is found that particles with positive sign in the spin move in one direction and those with negative sign move in another direction which explains the up and down stream motion of the particles.

  3. Helical Muon Beam Cooling Channel Engineering Design

    SciTech Connect

    Kashikhin, V.S.; Lopes, M.L.; Romanov, G.V.; Tartaglia, M.A.; Yonehara, K.; Yu, M.; Zlobin, A.V.; Flanagan, G.; Johnson, R.P.; Kazakevich, G.M.; Marhauser, F.; /MUONS Inc., Batavia

    2012-05-01

    The Helical Cooling Channel (HCC), a novel technique for six-dimensional (6D) ionization cooling of muon beams, has shown considerable promise based on analytic and simulation studies. However, the implementation of this revolutionary method of muon cooling requires new techniques for the integration of hydrogen-pressurized, high-power RF cavities into the low-temperature superconducting magnets of the HCC. We present the progress toward a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb{sub 3}Sn based HCC test section. We include discussions on the pressure and thermal barriers needed within the cryostat to maintain operation of the magnet at 4.2 K while operating the RF and energy absorber at a higher temperature. Additionally, we include progress on the Nb{sub 3}Sn helical solenoid design.

  4. Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)

    NASA Astrophysics Data System (ADS)

    Veenadhari, B.; Alex, S.

    2006-11-01

    veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earth’s space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earth’s magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

  5. Modelling of magnetic satellite intensity in the neutron diffraction of an incommensurate helical structure: NiBr 2 and Ni 0.9Fe 0.1Br 2

    NASA Astrophysics Data System (ADS)

    Day, P.; Moore, M. W.; Wilkinson, C.; Ziebeck, K. R. A.

    1986-02-01

    We describe the application of a neutron multidetector diffractometer (D16, ILL) to study the incommensurate helical magnetic structure of pure and Fe 2+ -doped single crystals of NiBr 2. Detailed mapping of satellite intensity around (0, 0, 3/2) yields the magnitude and direction of the helix propagation vector τ. τ moves from [110] in NiBr 2 to [100] in Ni 09Fe 0.1Br 2 with only a 5% increase in magnitude. The incommensurate-commensurate transition temperature is unchanged. The measured intensity profiles in (2ϑ, ω, v) space are fitted to model profiles constructed by superimposing profiles measured in the collinear phase at 28 K on a ring with radius τ, and optimizing the weighting of intensity around the ring. Based on the models optimized for these two crystals data from single detector instruments has been analysed for a range of Ni 1-xFe xBr 2 crystals and the magnetic phase diagram derived.

  6. Interplay Between the Equatorial Geophysical Processes

    NASA Astrophysics Data System (ADS)

    Sridharan, R.

    2006-11-01

    r_sridharanspl@yahoo.com With the sun as the main driving force, the Equatorial Ionosphere- thermosphere system supports a variety of Geophysical phenomena, essentially controlled by the neutral dynamical and electro dynamical processes that are peculiar to this region. All the neutral atmospheric parameters and the ionospheric parameters show a large variability like the diurnal, seasonal semi annual, annual, solar activity and those that are geomagnetic activity dependent. In addition, there is interplay between the ionized and the neutral atmospheric constituents. They manifest themselves as the Equatorial Electrojet (EEJ), Equatorial Ionization Anomaly (EIA), Equatorial Spread F (ESF), Equatorial Temperature and Wind Anomaly (ETWA). Recent studies have revealed that these phenomena, though apparently might show up as independent ones, are in reality interlinked. The interplay between these equatorial processes forms the theme for the present talk.

  7. Magnetic island formation in tokamaks

    SciTech Connect

    Yoshikawa, S.

    1989-04-01

    The size of a magnetic island created by a perturbing helical field in a tokamak is estimated. A helical equilibrium of a current- carrying plasma is found in a helical coordinate and the helically flowing current in the cylinder that borders the plasma is calculated. From that solution, it is concluded that the helical perturbation of /approximately/10/sup /minus/4/ of the total plasma current is sufficient to cause an island width of approximately 5% of the plasma radius. 6 refs.

  8. Aerosol Transport Over Equatorial Africa

    NASA Technical Reports Server (NTRS)

    Gatebe, C. K.; Tyson, P. D.; Annegarn, H. J.; Kinyua, A. M.; Piketh, S.; King, M.; Helas, G.

    1999-01-01

    Long-range and inter-hemispheric transport of atmospheric aerosols over equatorial Africa has received little attention so far. Most aerosol studies in the region have focussed on emissions from rain forest and savanna (both natural and biomass burning) and were carried out in the framework of programs such as DECAFE (Dynamique et Chimie Atmospherique en Foret Equatoriale) and FOS (Fires of Savanna). Considering the importance of this topic, aerosols samples were measured in different seasons at 4420 meters on Mt Kenya and on the equator. The study is based on continuous aerosol sampling on a two stage (fine and coarse) streaker sampler and elemental analysis by Particle Induced X-ray Emission. Continuous samples were collected for two seasons coinciding with late austral winter and early austral spring of 1997 and austral summer of 1998. Source area identification is by trajectory analysis and sources types by statistical techniques. Major meridional transports of material are observed with fine-fraction silicon (31 to 68 %) in aeolian dust and anthropogenic sulfur (9 to 18 %) being the major constituents of the total aerosol loading for the two seasons. Marine aerosol chlorine (4 to 6 %), potassium (3 to 5 %) and iron (1 to 2 %) make up the important components of the total material transport over Kenya. Minimum sulfur fluxes are associated with recirculation of sulfur-free air over equatorial Africa, while maximum sulfur concentrations are observed following passage over the industrial heartland of South Africa or transport over the Zambian/Congo Copperbelt. Chlorine is advected from the ocean and is accompanied by aeolian dust recirculating back to land from mid-oceanic regions. Biomass burning products are transported from the horn of Africa. Mineral dust from the Sahara is transported towards the Far East and then transported back within equatorial easterlies to Mt Kenya. This was observed during austral summer and coincided with the dying phase of 1997/98 El

  9. The Writhe of Helical Structures in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Toeroek, T.; Berger, M. A.; Kliem, B.

    2010-01-01

    Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope topology, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low-lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed.

  10. Influence of the E region dynamo on equatorial spread F

    NASA Technical Reports Server (NTRS)

    Hanson, W. B.; Sanatani, S.; Patterson, T. N. L.

    1983-01-01

    The integrated E region Pedersen conductivity can be an important parameter in determining whether the bottomside of the equatorial F layer will be stable against the Rayleigh-Taylor gravitational instability. The F layer is observed to become unstable when it rises to great heights after sunset. One effect of this height rise is to decrease the stabilizing influence of ion-neutral collisions at F region heights. It is shown here that the same eastward electric field that raises the F layer also decreases the Pedersen conductivity of the E region, which further destabilizes convective overturning. Because the conductivity of magnetic tubes that penetrate the main F layer is large compared to the E layer contribution, these effects are important only for the bottomside of the equatorial F layer.

  11. The dawn enhancement of the equatorial ionospheric vertical plasma drift

    NASA Astrophysics Data System (ADS)

    Zhang, Ruilong; Liu, Libo; Chen, Yiding; Le, Huijun

    2015-12-01

    Previous studies have reported that a dawn enhancement does not present in the statistical picture of the equatorial ionospheric vertical plasma drift, while it clearly shows in case measurements. In this statistical study, it is the first time to investigate the occurrence of the dawn enhancement in the equatorial ionospheric vertical plasma drift from ROCSAT-1 observations during geomagnetic quiet times. The dawn enhancements occur most frequently in June solstice and least frequently in December solstice. The statistical survey shows that the occurrence depends on the magnetic declination. The enhancement has the strongest amplitude in regions near 320° longitude and peaks during June solstice. The dawn enhancement reaches its peak after the sunrise in conjugated E regions. Furthermore, it is found that the dawn enhancement is closely related to the difference between the sunrise times in the conjugated E regions (sunrise time lag). The dawn enhancement occurs easily in regions with a large sunrise time lag.

  12. Conceptual Design for Superconducting Planar Helical Undulator

    NASA Astrophysics Data System (ADS)

    Sasaki, Shigemi

    2004-05-01

    A preliminary consideration was made on a short-period superconducting planar helical undulator (SCHU) for circularly polarized radiation. The SCHU consists of coils and iron poles/yokes. There is no magnetic structure in the horizontal plane of the electron orbit. The SCHU would provide the large horizontal aperture needed to allow injection into the storage ring. The expected field strength is at least 30% larger than that by an APPLE-type permanent-magnet device with the same gap and the same period.

  13. Helicon wave excitation with helical antennas

    SciTech Connect

    Light, M.; Chen, F.F.

    1995-04-01

    Components of the wave magnetic field in a helicon discharge have been measured with a single-turn, coaxial magnetic probe. Left- and right-handed helical antennas, as well as plane-polarized antennas, were used; and the results were compared with the field patterns computed for a nonuniform plasma. The results show that the right-hand circularly polarized mode is preferentially excited with all antennas, even those designed to excite the left-hand mode. For right-hand excitation, the radial amplitude profiles are in excellent agreement with computations. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  14. Central Equatorial Pacific Experiment (CEPEX)

    SciTech Connect

    Not Available

    1993-01-01

    The Earth's climate has varied significantly in the past, yet climate records reveal that in the tropics, sea surface temperatures seem to have been remarkably stable, varying by less than a few degrees Celsius over geologic time. Today, the large warm pool of the western Pacific shows similar characteristics. Its surface temperature always exceeds 27[degree]C, but never 31[degree]C. Heightened interest in this observation has been stimulated by questions of global climate change and the exploration of stabilizing climate feedback processes. Efforts to understand the observed weak sensitivity of tropical sea surface temperatures to climate forcing has led to a number of competing ideas about the nature of this apparent thermostat. Although there remains disagreement on the processes that regulate tropical sea surface temperature, most agree that further progress in resolving these differences requires comprehensive field observations of three-dimensional water vapor concentrations, solar and infrared radiative fluxes, surface fluxes of heat and water vapor, and cloud microphysical properties. This document describes the Central Equatorial Pacific Experiment (CEPEX) plan to collect such observations over the central equatorial Pacific Ocean during March of 1993.

  15. Effects of the equatorial ionosphere on L-band Earth-space transmissions

    NASA Technical Reports Server (NTRS)

    Smith, Ernest K.; Flock, Warren L.

    1993-01-01

    Ionosphere scintillation can effect satellite telecommunication up to Ku-band. Nighttime scintillation can be attributed to large-scale inhomogeneity in the F-region of the ionosphere predominantly between heights of 200 and 600 km. Daytime scintillation has been attributed to sporadic E. It can be thought of as occurring in three belts: equatorial, high-latitude, and mid-latitude, in order of severity. Equatorial scintillation occurs between magnetic latitudes +/- 25 degrees, peaking near +/- 10 degrees. It commonly starts abruptly near 2000 local time and dies out shortly after midnight. There is a strong solar cycle dependence and a seasonal preference for the equinoxes, particularly the vernal one. Equatorial scintillation occurs more frequently on magnetically quiet than on magnetically disturbed days in most longitudes. At the peak of the sunspot cycle scintillation depths as great as 20 dB were observed at L-band.

  16. A dynamo explanation for Mercury's anomalous magnetic field

    NASA Astrophysics Data System (ADS)

    Cao, Hao; Aurnou, Jonathan M.; Wicht, Johannes; Dietrich, Wieland; Soderlund, Krista M.; Russell, Christopher T.

    2014-06-01

    Recent MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) measurements have shown that Mercury's magnetic field is axial-dominant, yet strongly asymmetric with respect to the equator: the field strength in the Northern Hemisphere is approximately 3 times stronger than that in the Southern Hemisphere. Here we show that convective dynamo models driven by volumetric buoyancy with north-south symmetric thermal boundaries are capable of generating quasi-steady north-south asymmetric magnetic fields similar to Mercury's. This symmetry breaking is promoted and stabilized when the core-mantle boundary heat flux is higher at the equator than at high latitudes. The equatorially asymmetric magnetic field generation in our dynamo models corresponds to equatorially asymmetric kinetic helicity, which results from mutual excitation of two different modes of columnar convection. Our dynamo model can be tested by future assessment of Mercury's magnetic field from MESSENGER and BepiColombo as well as through investigations on Mercury's lower mantle temperature heterogeneity and buoyancy forcing in Mercury's core.

  17. Understanding the Longitudinal Variability of Equatorial Electrodynamics using integrated Ground- and Space-based Observations

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Moldwin, M.; Zesta, E.

    2015-12-01

    The currently funded African Meridian B-Field Education and Research (AMBER) magnetometer array comprises more than thirteen magnetometers stationed globally in the vicinity of geomagnetic equator. One of the main objectives of AMBER network is to understand the longitudinal variability of equatorial electrodynamics as function of local time, magnetic activity, and season. While providing complete meridian observation in the region and filling the largest land-based gap in global magnetometer coverage, the AMBER array addresses two fundamental areas of space physics: first, the processes governing electrodynamics of the equatorial ionosphere as a function of latitude (or L-shell), local time, longitude, magnetic activity, and season, and second, ULF pulsation strength at low/mid-latitude regions and its connection with equatorial electrojet and density fluctuation. The global AMBER network can also be used to augment observations from space-based instruments, such us the triplet SWARM mission and the upcoming ICON missions. Thus, in coordination with space-based and other ground-based observations, the AMBER magnetometer network provides a great opportunity to understand the electrodynamics that governs equatorial ionosphere motions. In this paper we present the longitudinal variability of the equatorial electrodynamics using the combination of instruments onboard SWARM and C/NOFS satellites and ground-based AMBER network. Both ground- and pace-based observations show stronger dayside and evening sector equatorial electrodynamics in the American and Asian sectors compared to the African sector. On the other hand, the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This raises the question if the evening sector equatorial electrodynamics (vertical drift), which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the

  18. Hindered Energy Cascade in Highly Helical Isotropic Turbulence

    NASA Astrophysics Data System (ADS)

    Stepanov, Rodion; Golbraikh, Ephim; Frick, Peter; Shestakov, Alexander

    2015-12-01

    The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.

  19. Hindered Energy Cascade in Highly Helical Isotropic Turbulence.

    PubMed

    Stepanov, Rodion; Golbraikh, Ephim; Frick, Peter; Shestakov, Alexander

    2015-12-01

    The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum. PMID:26684120

  20. Multifunctionality in bimetallic Ln(III)[W(V)(CN)8]3- (Ln = Gd, Nd) coordination helices: optical activity, luminescence, and magnetic coupling.

    PubMed

    Chorazy, Szymon; Nakabayashi, Koji; Arczynski, Mirosław; Pełka, Robert; Ohkoshi, Shin-ichi; Sieklucka, Barbara

    2014-06-01

    Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)-iPr-Pybox (2,6-bis[4-isopropyl-2-oxazolin-2-yl]pyridine) and (SRSR/RSRS)-Ind-Pybox (2,6-bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine), have been combined with lanthanide ions (Gd(3+), Nd(3+)) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN(-)-bridged coordination chains: {[Ln(III)(SS/RR-iPr-Pybox)(dmf)4]3[W(V)(CN)8]3}n ⋅dmf⋅4 H2O (Ln = Gd, 1-SS and 1-RR; Ln = Nd, 2-SS and 2-RR) and {[Ln(III)(SRSR/RSRS-Ind-Pybox)(dmf)4][W(V)(CN)8]}n⋅5 MeCN⋅4 MeOH (Ln = Gd, 3-SRSR and 3-RSRS; Ln = Nd, 4-SRSR and 4-RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200-450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the Gd(III)-W(V) chains show dominant ligand-based red phosphorescence, with λmax ≈660 nm for 1-(SS/RR) and 680 nm for 3-(SRSR/RSRS). The Nd(III)-W(V) chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra-f (4)F3/2 → (4)I9/2,11/2,13/2 transitions of the Nd(III) centers. This emission is realized through efficient ligand-to-metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W(V)(CN)8](3-) moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd(III) (SGd = 7/2) and W(V) (SW = 1/2) centers with J1-(SS) = -0.96(1) cm(-1), J1-(RR) =-0.95(1) cm(-1), J3-(SRSR) = -0.91(1) cm(-1), and J3-(RSRS) =-0.94(1) cm(-1). 2-(SS/RR) and 4-(SRSR/RSRS) display ferromagnetic coupling within their Nd(III)-NC-W(V) linkages. PMID:24740567

  1. Studies on equatorial shock formation during plasmaspheric refilling

    NASA Technical Reports Server (NTRS)

    Singh, N.

    1994-01-01

    Investigations based on small-scale simulations of microprocesses occurring when a magnetic flux tube refills with a cold plasma are summarized. Results of these investigations are reported in the following attached papers: (1) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: The Role of Ion Beam-Driven Instabilities'; and (2) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: Effects of Magnetically Trapped Hot Plasma'. Other papers included are: 'Interaction of Field-Aligned Cold Plasma Flows with an Equatorially-Trapped Hot Plasma: Electrostatic Shock Formation'; and 'Comparison of Hydrodynamic and Semikinetic Treatments for a Plasma Flow along Closed Field Lines'. A proposal for further research is included.

  2. Equatorial potassium currents in lenses.

    PubMed

    Wind, B E; Walsh, S; Patterson, J W

    1988-02-01

    Earlier work with the vibrating probe demonstrated the existence of outward potassium currents at the equator and inward sodium currents at the optical poles of the lens. By adding microelectrodes to the system, it is possible to relate steady currents (J) to the potential difference (PD) measured with a microelectrode. By injecting an outward current (I), it is possible to determine resistances and also the PD at which the steady outward potassium current becomes zero (PDJ = 0). At this PD the concentration gradient for potassium efflux and the electrical gradient for potassium influx are balanced so that there is no net flow of potassium across the membranes associated with the production of J. The PDJ = 0 for 18 rat lenses was 86 mV and that for 12 frogs lenses was -95 mV. This agrees with the potassium equilibrium potential and provides strong evidence to support the view that the outward equatorial current, J, is a potassium current. With the injection of outward current, I, the PD becomes more negative, the outward equatorial current, J, decreases, and the inward current at the optical poles increases. This suggests that there are separate electrical loops for K+ and Na+ that are partially linked by the Na, K-pump. Using Ohm's law, it is possible to calculate the input resistance (R = delta PD/I), the resistance related to the production of J (RJ = delta PD/delta J), and the effect of the combined resistances (delta J/I). The driving force for J can be estimated (PDJ = 0-PD). The relationships among currents, voltages and resistance can be used to determine the characteristics of the membranes that are associated with the outward potassium current observed at the equator. The effects of graded deformation of the lens were determined. The effects were reversible. The sites of inward and outward currents were not altered. Following deformation, the equatorial current, J, increased, and the PD became less negative. The PDJ = 0 remains the same so the ratio of K

  3. Equatorial noise emissions with quasiperiodic modulation of wave intensity

    NASA Astrophysics Data System (ADS)

    Němec, F.; Santolík, O.; Hrbáčková, Z.; Pickett, J. S.; Cornilleau-Wehrlin, N.

    2015-04-01

    Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio-Temporal Analysis of Field Fluctuations and Wide-Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5% of events. We perform a systematic analysis of these EN events with QP modulation of the wave intensity. Such events occur usually in the noon-to-dawn magnetic local time sector. Their occurrence seems to be related to the increased geomagnetic activity, and it is associated with the time intervals of enhanced solar wind flow speeds. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN wave intensity and magnitudes on the order of a few tenths of nanotesla were identified in about 46% of events. We suggest that these compressional magnetic field pulsations might be responsible for the observed QP modulation of EN wave intensity, in analogy to formerly reported VLF whistler mode QP events.

  4. Broadband optical isolator based on helical metamaterials.

    PubMed

    Cao, Hu; Yang, ZhenYu; Zhao, Ming; Wu, Lin; Zhang, Peng

    2015-05-01

    Based on helical metamaterials, a new broadband optical isolator with a triple-helix structure is proposed in this paper. The right-handed circularly polarized light can transmit through the isolator with its polarization unchanged. The reverse propagating light, which is caused by the reflection of the latter optical devices, is converted into left-handed circularly polarized light that is suppressed by the proposed isolator because of absorption. Our design has some unprecedented advantages such as broad frequency ranges and a compact structure; moreover, neither polarizers nor adscititious magnetic fields are required. Properties of the isolator are investigated using the finite-difference time-domain method, and this phenomenon is studied by the mechanism of helical antenna theory. PMID:26366900

  5. Helical relativistic electron beam Vlasov equilibria

    NASA Astrophysics Data System (ADS)

    Lai, H. M.

    1980-08-01

    Three existing helical relativistic electron beam models are discussed and compared. Both Yoshikawa's and Lawson's models are shown to be derivable from appropriate Vlasov equilibria. A new helical Vlasov equilibrium with energy spread is presented and studied. Unlike Auer's axial current model in which the allowance of an energy spread limits the total current in the relativistic beam case, the present model, with the addition of an azimuthal current, permits solutions with arbitrarily large current. On the other hand, like the model studied by Kan and Lai, the present model leads to nonhollowed-out beam solutions in which, the larger the beam current, the more force-free is the magnetic field configuration.

  6. Coherent electron transport in a helical nanotube

    NASA Astrophysics Data System (ADS)

    Liang, Guo-Hua; Wang, Yong-Long; Du, Long; Jiang, Hua; Kang, Guang-Zhen; Zong, Hong-Shi

    2016-09-01

    The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.

  7. Conservation of writhe helicity under anti-parallel reconnection

    PubMed Central

    Laing, Christian E.; Ricca, Renzo L.; Sumners, De Witt L.

    2015-01-01

    Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts. PMID:25820408

  8. Macroscopic ordering of helical pores for arraying guest molecules noncentrosymmetrically

    PubMed Central

    Li, Chunji; Cho, Joonil; Yamada, Kuniyo; Hashizume, Daisuke; Araoka, Fumito; Takezoe, Hideo; Aida, Takuzo; Ishida, Yasuhiro

    2015-01-01

    Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightforward is the macroscopic orientation of helices. Here as a versatile scaffold to rationally construct this hardly accessible structure, we report a polymer framework with helical pores that unidirectionally orient over a large area (∼10 cm2). The framework, prepared by crosslinking a supramolecular liquid crystal preorganized in a magnetic field, is chemically robust, functionalized with carboxyl groups and capable of incorporating various basic or cationic guest molecules. When a nonlinear optical chromophore is incorporated in the framework, the resultant complex displays a markedly efficient nonlinear optical output, owing to the coherence of signals ensured by the macroscopically oriented helical structure. PMID:26416086

  9. Macroscopic ordering of helical pores for arraying guest molecules noncentrosymmetrically

    NASA Astrophysics Data System (ADS)

    Li, Chunji; Cho, Joonil; Yamada, Kuniyo; Hashizume, Daisuke; Araoka, Fumito; Takezoe, Hideo; Aida, Takuzo; Ishida, Yasuhiro

    2015-09-01

    Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightforward is the macroscopic orientation of helices. Here as a versatile scaffold to rationally construct this hardly accessible structure, we report a polymer framework with helical pores that unidirectionally orient over a large area (~10 cm2). The framework, prepared by crosslinking a supramolecular liquid crystal preorganized in a magnetic field, is chemically robust, functionalized with carboxyl groups and capable of incorporating various basic or cationic guest molecules. When a nonlinear optical chromophore is incorporated in the framework, the resultant complex displays a markedly efficient nonlinear optical output, owing to the coherence of signals ensured by the macroscopically oriented helical structure.

  10. Conservation of writhe helicity under anti-parallel reconnection.

    PubMed

    Laing, Christian E; Ricca, Renzo L; Sumners, De Witt L

    2015-01-01

    Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts. PMID:25820408

  11. Hydrodynamic interactions between rotating helices.

    PubMed

    Kim, MunJu; Powers, Thomas R

    2004-06-01

    Escherichia coli bacteria use rotating helical flagella to swim. At this scale, viscous effects dominate inertia, and there are significant hydrodynamic interactions between nearby helices. These interactions cause the flagella to bundle during the "runs" of bacterial chemotaxis. Here we use slender-body theory to solve for the flow fields generated by rigid helices rotated by stationary motors. We determine how the hydrodynamic forces and torques depend on phase and phase difference, show that rigid helices driven at constant torque do not synchronize, and solve for the flows. We also use symmetry arguments based on kinematic reversibility to show that for two rigid helices rotating with zero phase difference, there is no time-averaged attractive or repulsive force between the helices. PMID:15244620

  12. Analysis of scrape-off layer in toroidal helical systems

    NASA Astrophysics Data System (ADS)

    Nagasaki, Kazunobu; Itoh, Kimitaka; Itoh, Sanae-I.; Fukuyama, Atsushi

    1990-03-01

    Magnetic field structure of the scrape-off layer region in toroidal helical systems is analyzed by using toroidal harmonic functions. The connection length of the field line to the wall is calculated for various configurations. It is found that L has a logarythmic dependence on the distance from the outermost magnetic surface or from the residual magnetic islands. The effect of the axisymmetric fields on the stress structure is also discussed.

  13. Reversed field pinch current drive with oscillating helical fields

    SciTech Connect

    Farengo, Ricardo; Clemente, Roberto Antonio

    2006-04-15

    The use of oscillating helical magnetic fields to produce and sustain the toroidal and poloidal currents in a reversed field pinch (RFP) is investigated. A simple physical model that assumes fixed ions, massless electrons, and uniform density and resistivity is employed. Thermal effects are neglected in Ohm's law and helical coordinates are introduced to reduce the number of coupled nonlinear equations that must be advanced in time. The results show that it is possible to produce RFP-like magnetic field profiles with pinch parameters close to the experimental values. The efficiencies obtained for moderate resistivity, and the observed scaling, indicate that this could be a very attractive method for high temperature plasmas.

  14. Longitudinal differences of ionospheric vertical density distribution and equatorial electrodynamics

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Zesta, E.; Moldwin, M. B.; Damtie, B.; Mebrahtu, A.; Valladares, C. E.; Pfaff, R. F.

    2012-07-01

    Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian ˜37°E and 290°E, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation, such as

  15. Longitudinal Differences of Ionospheric Vertical Density Distribution and Equatorial Electrodynamics

    NASA Technical Reports Server (NTRS)

    Yizengaw, E.; Zesta, E.; Moldwin, M. B.; Damtie, B.; Mebrahtu, A.; Valledares, C.E.; Pfaff, R. F.

    2012-01-01

    Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian approx. 37 deg and 290 deg E, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation

  16. Conservation of helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    2015-03-01

    Helicity arises as a special conserved quantity in ideal fluids, in addition to energy, momentum and angular momentum. As a measure of the knottedness of vortex lines, Helicity provides an important tool for studying a wide variety of physical systems such as plasmas and turbulent fluids. Superfluids flow without resistance just like ideal (Euler) fluids, making it natural to ask whether their knottedness is similarly preserved. We address the conservation of helicity in superfluids theoretically and examine its consequences in numerical simulations.

  17. UVCS/SOHO Observations of Equatorial and Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Kohl, J. L.; Miralles, M. P.; Cranmer, S. R.; Suleiman, R. M.

    2000-05-01

    A large equatorial coronal hole was observed above the west limb with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO from November 1999 to March 2000. Observations in H I Lyα and O VI 103.2, 103.7 nm provided spectroscopic diagnostics of proton and O5+ velocity distributions and outflow velocities. These properties will be compared to those of the large polar coronal holes observed near solar minimum. The equatorial coronal hole corresponded to a high-speed solar wind stream at 1 AU, but there were significant differences between the interplanetary properties of this stream and the steady high-speed wind seen over the poles at solar minimum. The several obvious differences between the two structures in the extended corona may be associated with the different densities and magnetic field configurations and flux tube expansion factors. Preliminary results from a detailed empirical model of the equatorial coronal hole will be presented. This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  18. Helical muon beam cooling channel engineering design

    SciTech Connect

    Johnson, Rolland

    2015-08-07

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb3Sn based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb3Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb3Sn solenoid as originally planned. Instead, a complementary project was approved by the DOE

  19. Controlling skyrmion helicity via engineered Dzyaloshinskii-Moriya interactions.

    PubMed

    Díaz, Sebastián A; Troncoso, Roberto E

    2016-10-26

    Single magnetic skyrmion dynamics in chiral magnets with a spatially inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) is considered. Based on the relation between DMI coupling and skyrmion helicity, it is argued that the latter must be included as an extra degree of freedom in the dynamics of skyrmions. An effective description of the skyrmion dynamics for an arbitrary inhomogeneous DMI coupling is obtained through the collective coordinates method. The resulting generalized Thiele equation is a dynamical system for the center of mass position and helicity of the skyrmion. It is found that the dissipative tensor and hence the Hall angle become helicity dependent. The skyrmion position and helicity dynamics are fully characterized by our model in two particular examples of engineered DMI coupling: half-planes with opposite-sign DMI and linearly varying DMI. In light of the experiment of Shibata et al (2013 Nat. Nanotechnol. 8 723) on the magnitude and sign of the DMI, our results constitute the first step toward a more complete understanding of the skyrmion helicity as a new degree of freedom that could be harnessed in future high-density magnetic storage and logic devices. PMID:27588612

  20. Automatically identification of Equatorial Spread-F occurrence on ionograms

    NASA Astrophysics Data System (ADS)

    Fagundes, P. R.; Pillat, V. G.; Guimarães, L. N. F.

    2015-12-01

    F-region large-scale irregularities, also called plasma bubbles, are one of the most interesting equatorial ionospheric phenomena. These irregularities are generated in the equatorial region and afterwards extend to lower latitudes. They are one of the important topics of investigation in equatorial ionosphere electrodynamics and, therefore, are subject to intense theoretical and experimental research. The ionosonde is the most used scientific equipment to study the ionosphere and the F-region. With advancement of digital ionosonde, it is now possible to carry out an ionospheric sounding with a cadence of 5 minutes or even with 1-minute cadence. To analyse a large amount of ionograms, more sophisticated tools are needed. Thus, development of algorithms to identify and analyse different aspects of ionograms has become very important to space science researchers. Multiple echoes recorded on ionograms are the signature of these irregularities in the ionograms, usually called Spread-F. Spread-F is classified into three types: range, frequency, and mixed. Thus, automatic identification of Spread-F is important in ionospheric studies, because studies usually involve the analysis and interpretation of large numbers of ionograms. The main objective of this paper is to present a new computational tool, based on fuzzy relation, designed to automatically identify the occurrence of Spread-F in ionograms. The test was conducted in ionograms recorded in the Brazilian sector (São José dos Campos (23.2° S, 45.9° W, dip latitude 17.6° S - low latitude) and Palmas (10.2° S, 48.2° W, dip latitude 5.5° S - near the magnetic equatorial)). The automatic identification of Spread-F occurrence was compared with those obtained manually and good agreement was found.

  1. Automatically identification of Equatorial Spread-F occurrence on ionograms

    NASA Astrophysics Data System (ADS)

    Pillat, Valdir Gil; Fagundes, Paulo Roberto; Guimarães, Lamartine Nogueira Frutuoso

    2015-12-01

    F-region large-scale irregularities, also called plasma bubbles, are one of the most interesting equatorial ionospheric phenomena. These irregularities are generated in the equatorial region and afterwards extend to lower latitudes. They are one of the important topics of investigation in equatorial ionosphere electrodynamics and, therefore, are subject to intense theoretical and experimental research. The ionosonde is the most used scientific equipment to study the ionosphere and the F-region. With advancement of digital ionosonde, it is now possible to carry out an ionospheric sounding with a cadence of 5 min or even with 1-minute cadence. To analyse a large amount of ionograms, more sophisticated tools are needed. Thus, development of algorithms to identify and analyse different aspects of ionograms has become very important to space science researchers. Multiple echoes recorded on ionograms are the signature of these irregularities in the ionograms, usually called Spread-F. Spread-F is classified into three types: range, frequency, and mixed. Thus, automatic identification of Spread-F is important in ionospheric studies, because studies usually involve the analysis and interpretation of large numbers of ionograms. The main objective of this paper is to present a new computational tool, based on fuzzy relation, designed to automatically identify the occurrence of Spread-F in ionograms. The test was conducted in ionograms recorded in the Brazilian sector (São José dos Campos (23.2°S, 45.9°W, dip latitude 17.6°S-low latitude) and Palmas (10.2°S, 48.2°W, dip latitude 5.5°S-near the magnetic equatorial)). The automatic identification of Spread-F occurrence was compared with those obtained manually and good agreement was found.

  2. EQUATORIAL SUPERROTATION ON TIDALLY LOCKED EXOPLANETS

    SciTech Connect

    Showman, Adam P.; Polvani, Lorenzo M.

    2011-09-01

    The increasing richness of exoplanet observations has motivated a variety of three-dimensional (3D) atmospheric circulation models of these planets. Under strongly irradiated conditions, models of tidally locked, short-period planets (both hot Jupiters and terrestrial planets) tend to exhibit a circulation dominated by a fast eastward, or 'superrotating', jet stream at the equator. When the radiative and advection timescales are comparable, this phenomenon can cause the hottest regions to be displaced eastward from the substellar point by tens of degrees longitude. Such an offset has been subsequently observed on HD 189733b, supporting the possibility of equatorial jets on short-period exoplanets. Despite its relevance, however, the dynamical mechanisms responsible for generating the equatorial superrotation in such models have not been identified. Here, we show that the equatorial jet results from the interaction of the mean flow with standing Rossby waves induced by the day-night thermal forcing. The strong longitudinal variations in radiative heating-namely intense dayside heating and nightside cooling-trigger the formation of standing, planetary-scale equatorial Rossby and Kelvin waves. The Rossby waves develop phase tilts that pump eastward momentum from high latitudes to the equator, thereby inducing equatorial superrotation. We present an analytic theory demonstrating this mechanism and explore its properties in a hierarchy of one-layer (shallow-water) calculations and fully 3D models. The wave-mean-flow interaction produces an equatorial jet whose latitudinal width is comparable to that of the Rossby waves, namely the equatorial Rossby deformation radius modified by radiative and frictional effects. For conditions typical of synchronously rotating hot Jupiters, this length is comparable to a planetary radius, explaining the broad scale of the equatorial jet obtained in most hot-Jupiter models. Our theory illuminates the dependence of the equatorial jet

  3. Detection of in-depth helical spin structures by planar Hall effect

    SciTech Connect

    Basaran, Ali C. Guénon, S.; Schuller, Ivan K.; Morales, R.

    2015-06-22

    We developed a method to determine the magnetic helicity and to study reversal mechanisms in exchange biased nanostructures using Planar Hall Effect (PHE). As a test case, we use an in-depth helical spin configuration that occurs during magnetization reversal in exchange coupled Ni/FeF{sub 2} heterostructures. We show the way to induce and determine the sign of the helicity from PHE measurements on a lithographically patterned cross. The helicity sign can be controlled by the angle between the externally applied magnetic field and a well-defined unidirectional anisotropy axis. Furthermore, the PHE signal reveals complex reversal features due to small deviations of the local unidirectional anisotropy axes from the crystallographic easy axis. The simulations using an incomplete domain wall model are in excellent agreement with the experimental data. These studies show that helical spin formations in nanomagnetic systems can be studied using laboratory-based magnetotransport.

  4. New Evidence for Equatorially Trapped Thermal Plasma During Early Post-Storm Recovery

    NASA Technical Reports Server (NTRS)

    Gallagher, D. L.; Green, J. L.

    2005-01-01

    Almost 20 years ago Olsen et al. [1987] reported Dynamics Explorer 1 Retarding Ion Mass Spectrometer observations of equatorially trapped, cold ions in the vicinity of the plasmapause. In that study the trapped population corresponded to a local minimum in density at the magnetic equator. During that time period observations were uncovered of a local maximum in plasma density at the equator. Until IMAGE there has been no good opportunity to experimentally revisit this topic, however until now no direct evidence of a relevant equatorial process has been recognized near the plasmapause during early recovery conditions. It appears that evidence has now been found in both the Extreme Ultraviolet Imager and Radio Plasma Imager observations. The observations, conditions, and properties of what appears to be an equatorially trapped and enhanced density near the magnetic equator will be presented and discussed.

  5. Vertical cloud structure of Jupiter's equatorial plumes

    NASA Technical Reports Server (NTRS)

    Stoker, C. R.; Hord, C.

    1985-01-01

    Multiple-scattering radiative transfer calculations were used to deduce the vertical cloud structure (VCS) of Jupiter's equatorial region. The VCS model of the equatorial plumes is obtained through an analysis of Voyager images of the 6190-A methane band and the 6000-A continuum, and ground-based 8900-A methane band images. The VCS of the equatorial plumes is found to be consistent with the hypothesis that the plumes are caused by upwelling at the ammonia condensation level produced by buoyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the plumes.

  6. Helical tomotherapy quality assurance.

    PubMed

    Balog, John; Soisson, Emilie

    2008-01-01

    Helical tomotherapy uses a dynamic delivery in which the gantry, treatment couch, and multileaf collimator leaves are all in motion during treatment. This results in highly conformal radiotherapy, but the complexity of the delivery is partially hidden from the end-user because of the extensive integration and automation of the tomotherapy control systems. This presents a challenge to the medical physicist who is expected to be both a system user and an expert, capable of verifying relevant aspects of treatment delivery. A related issue is that a clinical tomotherapy planning system arrives at a customer's site already commissioned by the manufacturer, not by the clinical physicist. The clinical physicist and the manufacturer's representative verify the commissioning at the customer site before acceptance. Theoretically, treatment could begin immediately after acceptance. However, the clinical physicist is responsible for the safe and proper use of the machine. In addition, the therapists and radiation oncologists need to understand the important machine characteristics before treatment can proceed. Typically, treatment begins about 2 weeks after acceptance. This report presents an overview of the tomotherapy system. Helical tomotherapy has unique dosimetry characteristics, and some of those features are emphasized. The integrated treatment planning, delivery, and patient-plan quality assurance process is described. A quality assurance protocol is proposed, with an emphasis on what a clinical medical physicist could and should check. Additionally, aspects of a tomotherapy quality assurance program that could be checked automatically and remotely because of its inherent imaging system and integrated database are discussed. PMID:18406907

  7. Helical Tomotherapy Quality Assurance

    SciTech Connect

    Balog, John Soisson, Emilie

    2008-05-01

    Helical tomotherapy uses a dynamic delivery in which the gantry, treatment couch, and multileaf collimator leaves are all in motion during treatment. This results in highly conformal radiotherapy, but the complexity of the delivery is partially hidden from the end-user because of the extensive integration and automation of the tomotherapy control systems. This presents a challenge to the medical physicist who is expected to be both a system user and an expert, capable of verifying relevant aspects of treatment delivery. A related issue is that a clinical tomotherapy planning system arrives at a customer's site already commissioned by the manufacturer, not by the clinical physicist. The clinical physicist and the manufacturer's representative verify the commissioning at the customer site before acceptance. Theoretically, treatment could begin immediately after acceptance. However, the clinical physicist is responsible for the safe and proper use of the machine. In addition, the therapists and radiation oncologists need to understand the important machine characteristics before treatment can proceed. Typically, treatment begins about 2 weeks after acceptance. This report presents an overview of the tomotherapy system. Helical tomotherapy has unique dosimetry characteristics, and some of those features are emphasized. The integrated treatment planning, delivery, and patient-plan quality assurance process is described. A quality assurance protocol is proposed, with an emphasis on what a clinical medical physicist could and should check. Additionally, aspects of a tomotherapy quality assurance program that could be checked automatically and remotely because of its inherent imaging system and integrated database are discussed.

  8. Note on the helicity decomposition of spin and orbital optical currents

    NASA Astrophysics Data System (ADS)

    Aiello, Andrea; Berry, M. V.

    2015-06-01

    In the helicity representation, the Poynting vector (current) for a monochromatic optical field, when calculated using either the electric or the magnetic field, separates into right-handed and left-handed contributions, with no cross-helicity contributions. Cross-helicity terms do appear in the orbital and spin contributions to the current. But when the electric and magnetic formulas are averaged (‘electric-magnetic democracy’), these terms cancel, restoring the separation into right-handed and left-handed currents for orbital and spin separately.

  9. Wave Properties of Equatorial Magnetosonic Waves as Observed by Cluster

    NASA Astrophysics Data System (ADS)

    Balikhin, M. A.; Walker, S. N.; Shprits, Y.

    2014-12-01

    A survey of the Cluster STAFF data set shows a number of periods in which Equatorial Magnetosonic Waves display a discrete spectrum. In some of these instances, the frequency of emissions varies in the same fashion as the background magnetic field, indicating that the wars are observed within their source region. This paper analyses the propagation characteristics of these emissions and investigates the appropriateness of the quasi-linear assumption of a gaussian spectrum used in the numerical modelling of their role in the electron dynamics within the radiation belts based in the Chirikov resonance overlap criterion.

  10. Quasi-periodic modulation of equatorial noise intensity

    NASA Astrophysics Data System (ADS)

    Nemec, Frantisek; Santolik, Ondrej; Hrbackova, Zuzana; Pickett, Jolene S.; Cornilleau-Wehrlin, Nicole

    2015-04-01

    Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed routinely in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field. Although their harmonic structure, which is characteristic of the proton cyclotron frequency in the source region has been known for a couple of decades, they were generally believed to be continuous in time. The analysis of more than 2000 EN events observed by the STAFF-SA and WBD instruments on board the Cluster spacecraft reveals that this is not always the case, with about 5% of events exhibiting a clear quasi-periodic (QP) modulation of the wave intensity. We perform a systematic analysis of these events, and we discuss possible mechanisms of the QP intensity modulation. It is shown that the events occur usually in the noon-to-dawn magnetic local time sector, and their occurrence seems to be related to the periods of increased geomagnetic activity. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN were identified in about half of the events. These ULF pulsations might modulate the EN wave intensity, similarly as they modulate the intensity of formerly reported VLF whistler-mode QP events.

  11. The night when the auroral and equatorial ionospheres converged

    NASA Astrophysics Data System (ADS)

    Martinis, C.; Baumgardner, J.; Mendillo, M.; Wroten, J.; Coster, A.; Paxton, L.

    2015-09-01

    An all-sky imaging system at the McDonald Observatory (30.67°N, 104.02°W, 40° magnetic latitude) showed dramatic ionospheric effects during a moderate geomagnetic storm on 1 June 2013. The auroral zone expanded, leading to the observation of a stable auroral red (SAR) arc. Airglow depletions associated with equatorial spread F (ESF) were also seen for the first time at such high magnetic latitude. Total electron content measurements from a Global Positioning System (GPS) receiver exhibited ionospheric irregularities typically associated with ESF. We explore why this moderate geomagnetic disturbance leads to such dramatic ionospheric perturbations at midlatitudes. A corotating interaction region-like driver and a highly contracted plasmasphere caused the SAR arc to occur at L shell ~ 2.3. For ESF at L ~ 2.1, timing of the storm intensification, alignment of the sunset terminator with the central magnetic meridian, and sudden variations in the westward auroral electrojet all combined to trigger equatorial irregularities that reached altitudes of ~ 7000 km. The SAR arc and ESF signatures at the ionospheric foot points of inner magnetosphere L shells (L ~ 2) represent a dramatic convergence of pole to equator/equator to pole coupling at midlatitudes.

  12. Magnetic Field Structure in the Madison Dynamo Experiment

    NASA Astrophysics Data System (ADS)

    Rasmus, A. M.; Clark, M.; Kaplan, E. J.; Nornberg, M. D.; Rahbarnia, K.; Taylor, N. Z.; Forest, C. B.

    2011-10-01

    The Madison Dynamo Experiment(MDE) is expected to spontaneously self-generate a magnetic field in a two vortex flow geometry driven by counter rotating impellers in a 1 m diameter sphere filled with liquid sodium. Prevoiusly an equatorial baffle was installed and has been demonstrated to reduce the largest scale turbulent-eddies. An additonal set of six rotatable baffles have been installed to optimize the helicity of the flow, lowering the critical magnetic Reynolds number. This poster will focus on the spatial structure of the magnetic field associated with the dynamo eigenmodes and the turbulent fluctuations. Singular value decomposition (SVD) and cross correlation analysis between the surface harmonics and internal probes will be used to determine the internal structure associated with each spherical harmonic. Spherical harmonic decomposition is of limited utility when analysing the equatorial array of internal probes as there is a limited angular spread (only one theta value and two phi values), whereas cross correlation and SVD allow the use of time domain data to infer internal modes excited via three-wave couplings. This work is supported by the NSF/DOE partnership in plasma physics.

  13. Spheromak Power and Helicity Balance

    SciTech Connect

    Thomassen, K.I.

    2000-05-18

    This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to an axisymmetric Taylor state, {mu}{sub o}j = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential difference between the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. These volumes have different values of {lambda} in each region (open line volume V{sub 1} and closed spheromak volume V{sub 2}) and we want to calculate the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss in steady state.

  14. Chaotic coordinates for the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Hudson, S. R.; Suzuki, Y.

    2014-10-01

    The theory of quadratic-flux-minimizing (QFM) surfaces is reviewed, and numerical techniques that allow high-order QFM surfaces to be efficiently constructed for experimentally relevant, non-integrable magnetic fields are described. As a practical example, the chaotic edge of the magnetic field in the Large Helical Device (LHD) is examined. A precise technique for finding the boundary surface is implemented, the hierarchy of partial barriers associated with the near-critical cantori is constructed, and a coordinate system, which we call chaotic coordinates, that is based on a selection of QFM surfaces is constructed that simplifies the description of the magnetic field, so that flux surfaces become "straight" and islands become "square."

  15. Cool and hot flux ropes, their helicity

    NASA Astrophysics Data System (ADS)

    Nindos, Alexander

    2016-07-01

    We will review recent indirect and direct evidence for the existence of magnetic flux ropes in the solar atmosphere. Magnetic flux ropes may appear as S-shaped or reverse S-shaped (sigmoidal) structures in regions that are likely to erupt, and may also show in nonlinear force-free field extrapolations that use data from photospheric vector magnetograms as boundary condition. The availability of high sensitivity data recorded with unprecedented spatial and temporal resolution in hot EUV wavelengths by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has revealed the existence of coherent structures identified as hot flux ropes. In this presentation, we will review the properties of both cool and hot flux ropes with an emphasis on the frequency of their occurrence in large flares and on their magnetic helicity content.

  16. Equilibrium Reconstruction on the Large Helical Device

    SciTech Connect

    Samuel A. Lazerson, D. Gates, D. Monticello, H. Neilson, N. Pomphrey, A. Reiman S. Sakakibara, and Y. Suzuki

    2012-07-27

    Equilibrium reconstruction is commonly applied to axisymmetric toroidal devices. Recent advances in computational power and equilibrium codes have allowed for reconstructions of three-dimensional fields in stellarators and heliotrons. We present the first reconstructions of finite beta discharges in the Large Helical Device (LHD). The plasma boundary and magnetic axis are constrained by the pressure profile from Thomson scattering. This results in a calculation of plasma beta without a-priori assumptions of the equipartition of energy between species. Saddle loop arrays place additional constraints on the equilibrium. These reconstruction utilize STELLOPT, which calls VMEC. The VMEC equilibrium code assumes good nested flux surfaces. Reconstructed magnetic fields are fed into the PIES code which relaxes this constraint allowing for the examination of the effect of islands and stochastic regions on the magnetic measurements.

  17. DYNAMO EFFICIENCY WITH SHEAR IN HELICAL TURBULENCE

    SciTech Connect

    Leprovost, Nicolas; Kim, Eun-jin

    2009-05-10

    To elucidate the influence of shear flow on the generation of magnetic fields through the modification of turbulence property, we consider the case where a large-scale magnetic field is parallel to a large-scale shear flow without direct interaction between the two in the kinematic limit where the magnetic field does not backreact on the velocity. By nonperturbatively incorporating the effect of shear in a helically forced turbulence, we show that turbulence intensity and turbulent transport coefficients (turbulent viscosity, {alpha} and {beta} effect) are enhanced by a weak shear, while strongly suppressed for strong shear. In particular, {beta} is shown to be much more strongly suppressed than {alpha} effect. We discuss its important implications for dynamo efficiency, i.e., on the scaling of the dynamo number with differential rotation.

  18. Chaotic coordinates for the Large Helical Device

    SciTech Connect

    Hudson, S. R.; Suzuki, Y.

    2014-10-15

    The theory of quadratic-flux-minimizing (QFM) surfaces is reviewed, and numerical techniques that allow high-order QFM surfaces to be efficiently constructed for experimentally relevant, non-integrable magnetic fields are described. As a practical example, the chaotic edge of the magnetic field in the Large Helical Device (LHD) is examined. A precise technique for finding the boundary surface is implemented, the hierarchy of partial barriers associated with the near-critical cantori is constructed, and a coordinate system, which we call chaotic coordinates, that is based on a selection of QFM surfaces is constructed that simplifies the description of the magnetic field, so that flux surfaces become “straight” and islands become “square.”.

  19. Bifurcated helical core equilibrium states in tokamaks

    NASA Astrophysics Data System (ADS)

    Cooper, W. A.; Chapman, I. T.; Schmitz, O.; Turnbull, A. D.; Tobias, B. J.; Lazarus, E. A.; Turco, F.; Lanctot, M. J.; Evans, T. E.; Graves, J. P.; Brunetti, D.; Pfefferlé, D.; Reimerdes, H.; Sauter, O.; Halpern, F. D.; Tran, T. M.; Coda, S.; Duval, B. P.; Labit, B.; Pochelon, A.; Turnyanskiy, M. R.; Lao, L.; Luce, T. C.; Buttery, R.; Ferron, J. R.; Hollmann, E. M.; Petty, C. C.; van Zeeland, M.; Fenstermacher, M. E.; Hanson, J. M.; Lütjens, H.

    2013-07-01

    Tokamaks with weak to moderate reversed central shear in which the minimum inverse rotational transform (safety factor) qmin is in the neighbourhood of unity can trigger bifurcated magnetohydrodynamic equilibrium states, one of which is similar to a saturated ideal internal kink mode. Peaked prescribed pressure profiles reproduce the ‘snake’ structures observed in many tokamaks which has led to a novel explanation of the snake as a bifurcated equilibrium state. Snake equilibrium structures are computed in simulations of the tokamak à configuration variable (TCV), DIII-D and mega amp spherical torus (MAST) tokamaks. The internal helical deformations only weakly modulate the plasma-vacuum interface which is more sensitive to ripple and resonant magnetic perturbations. On the other hand, the external perturbations do not alter the helical core deformation in a significant manner. The confinement of fast particles in MAST simulations deteriorate with the amplitude of the helical core distortion. These three-dimensional bifurcated solutions constitute a paradigm shift that motivates the applications of tools developed for stellarator research in tokamak physics investigations.

  20. Design principles for Bernal spirals and helices with tunable pitch

    NASA Astrophysics Data System (ADS)

    Fejer, Szilard N.; Chakrabarti, Dwaipayan; Kusumaatmaja, Halim; Wales, David J.

    2014-07-01

    Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment.Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00324a

  1. Vertical shear in the Jovian equatorial zone.

    NASA Technical Reports Server (NTRS)

    Layton, R. G.

    1971-01-01

    Jupiter photographs taken in two different wavelength regions (blue and red) are studied for clues to differing Jovian atmosphere motions. The relative motions of features visible on these photographs may be interpreted as a vertical shear at visible cloud level. The value obtained implies that the north equatorial zone must be about 0.35 deg K warmer than the adjacent equatorial zone. Deeper in the atmosphere the reverse must hold.

  2. EQUATORIAL ZONAL JETS AND JUPITER's GRAVITY

    SciTech Connect

    Kong, D.; Liao, X.; Zhang, K.; Schubert, G.

    2014-08-20

    The depth of penetration of Jupiter's zonal winds into the planet's interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet's high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds.

  3. The Advanced Helical Generator

    SciTech Connect

    Reisman, D B; Javedani, J B; Ellsworth, G F; Kuklo, R M; Goerz, D A; White, A D; Tallerico, L J; Gidding, D A; Murphy, M J; Chase, J B

    2009-10-26

    A high explosive pulsed power (HEPP) generator called the Advanced Helical Generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 Mega-Amperes of current and 11 Mega-Joules of energy to a quasi-static 80 nH inductive load. A current gain of 154 times was obtained with a peak exponential rise time of 20 {micro}s. We will describe in detail the design and testing of the AHG.

  4. ASYMMETRY OF HELICITY INJECTION FLUX IN EMERGING ACTIVE REGIONS

    SciTech Connect

    Tian Lirong; Alexander, David

    2009-04-20

    Observational and modeling results indicate that typically the leading magnetic field of bipolar active regions (ARs) is often spatially more compact, while more dispersed and fragmented in following polarity. In this paper, we address the origin of this morphological asymmetry, which is not well understood. Although it may be assumed that, in an emerging {omega}-shaped flux tube, those portions of the flux tube in which the magnetic field has a higher twist may maintain its coherence more readily, this has not been tested observationally. To assess this possibility, it is important to characterize the nature of the fragmentation and asymmetry in solar ARs and this provides the motivation for this paper. We separately calculate the distribution of the helicity flux injected in the leading and following polarities of 15 emerging bipolar ARs, using the Michelson Doppler Image 96 minute line-of-sight magnetograms and a local correlation tracking technique. We find from this statistical study that the leading (compact) polarity injects several times more helicity flux than the following (fragmented) one (typically 3-10 times). This result suggests that the leading polarity of the {omega}-shaped flux tube possesses a much larger amount of twist than the following field prior to emergence. We argue that the helicity asymmetry between the leading and following magnetic field for the ARs studied here results in the observed magnetic field asymmetry of the two polarities due to an imbalance in the magnetic tension of the emerging flux tube. We suggest that the observed imbalance in the helicity distribution results from a difference in the speed of emergence between the leading and following legs of an inclined {omega}-shaped flux tube. In addition, there is also the effect of magnetic flux imbalance between the two polarities with the fragmented following polarity displaying spatial fluctuation in both the magnitude and sign of helicity measured.

  5. Peri-equatorial paleolatitudes for Jurassic radiolarian cherts of Greece

    USGS Publications Warehouse

    Aiello, I.W.; Hagstrum, J.T.; Principi, G.

    2008-01-01

    Radiolarian-rich sediments dominated pelagic deposition over large portions of the Tethys Ocean during middle to late Jurassic time as shown by extensive bedded chert sequences found in both continental margin and ophiolite units of the Mediterranean region. Which paleoceanographic mechanisms and paleotectonic setting favored radiolarian deposition during the Jurassic, and the nature of a Tethys-wide change from biosiliceous to biocalcareous (mainly nannofossil) deposition at the beginning of Cretaceous time, have remained open questions. Previous paleomagnetic analyses of Jurassic red radiolarian cherts in the Italian Apennines indicate that radiolarian deposition occurred at low peri-equatorial latitudes, similar to modern day deposition of radiolarian-rich sediments within equatorial zones of high biologic productivity. To test this result for other sectors of the Mediterranean region, we undertook paleomagnetic study of Mesozoic (mostly middle to upper Jurassic) red radiolarian cherts within the Aegean region on the Peloponnesus and in continental Greece. Sampled units are from the Sub-Pelagonian Zone on the Argolis Peninsula, the Pindos-Olonos Zone on the Koroni Peninsula, near Karpenissi in central Greece, and the Ionian Zone in the Varathi area of northwestern Greece. Thermal demagnetization of samples from all sections removed low-temperature viscous and moderate-temperature overprint magnetizations that fail the available fold tests. At Argolis and Koroni, however, the cherts carry a third high-temperature magnetization that generally exhibits a polarity stratigraphy and passes the available fold tests. We interpret the high-temperature component to be the primary magnetization acquired during chert deposition and early diagenesis. At Kandhia and Koliaky (Argolis), the primary declinations and previous results indicate clockwise vertical-axis rotations of ??? 40?? relative to "stable" Europe. Due to ambiguities in hemispheric origin (N or S) and thus

  6. Primary Cardiac Lymphoma: Helical CT Findings and Radiopathologic Correlation

    SciTech Connect

    Marco de Lucas, Enrique Pagola, Miguel Angel; Fernandez, Fidel; Lastra, Pedro; Delgado, M. Luisa Ruiz; Sadaba, Pablo; Pinto, Jesus; Ballesteros, Ma Angeles; Ortiz, Antonio

    2004-03-15

    Primary tumors of the heart are extremely rare.Clinical manifestations are nondiagnostic and the patients are often misdiagnosed. Magnetic resonance imaging and echocardiography are standard in this diagnostic workup. We report a case of a man with acromegaly, dysphagia, chest pain and weight loss. An invasive cardiac mass was diagnosed by helical-CT. Autopsy demonstrated a B-cell aggressive lymphoma.

  7. Template electrosynthesis of tailored-made helical nanoswimmers.

    PubMed

    Li, Jinxing; Sattayasamitsathit, Sirilak; Dong, Renfeng; Gao, Wei; Tam, Ryan; Feng, Xiaomiao; Ai, Stephen; Wang, Joseph

    2014-08-21

    We demonstrate a template electrosynthesis for large-scale low-cost preparation of remarkably small magnetically driven tailored-made helical nanoswimmers that display efficient propulsion behavior and hold considerable promise for future miniature devices in the human body. PMID:24126904

  8. Jupiter's Great Red Spot and South Equatorial Belt

    NASA Technical Reports Server (NTRS)

    1979-01-01

    This Voyager 2 picture shows the Great Red Spot and the south equatorial belt extending into the equatorial region. At right is an interchange of material between the south equatorial belt and the equatorial zone. The clouds in the equatorial zone are more diffuse and do not display the structures seen in other locations. Considerable structure is evident within the Great Red Spot. The Voyagers are managed for NASA's Office of Space Science by Jet Propulsion Laboratory.

  9. Latitudinal comparisons of equatorial Pacific zooplankton

    NASA Astrophysics Data System (ADS)

    Roman, M. R.; Dam, H. G.; Le Borgne, R.; Zhang, X.

    Zooplankton biomass and rates of ingestion, egestion and production in the equatorial Pacific Ocean along 140°W and 180° exhibit maximum values in the High-Nutrient Low-Chlorophyll (HNLC) zone associated with equatorial upwelling (5°S-5°N) as compared to the more oligotrophic regions to the north and south. Zooplankton biomass and rates are not usually highest on the equator, but increase "downstream" of the upwelling center as the zooplankton populations exhibit a delayed response to enhanced phytoplankton production. The vertical distribution of zooplankton biomass in the equatorial HNLC area tends to be concentrated in surface waters and is more uniform with depth in oligotrophic regions to the north and south of the equatorial upwelling zone. In general, the amount of mesozooplankton (>200 μm) carbon biomass is approximately 25% of estimated phytoplankton biomass and 30% of bacterial biomass in the HNLC area of the equatorial Pacific Ocean. Zooplankton grazing on phytoplankton is low in the equatorial Pacific Ocean, generally <5% of the total chlorophyll-a standing stock grazed per day. Based on estimates of metabolic demand, it is apparent that zooplankton in the equatorial Pacific Ocean are omnivores, consuming primarily microzooplankton and detritus. Estimated zooplankton growth rates in the warm waters of the HNLC equatorial Pacific Ocean are high, ranging from 0.58 d -1 for 64-200 μm zooplankton to 0.08 d -1 for 1000-2000 μm zooplankton. Thus, the numerical and functional response of equatorial zooplankton to increases in phytoplankton production are more rapid than normally occurs in sub-tropical and temperate waters. Potential zooplankton fecal pellet production, estimated from metabolic demand, is approximately 1.6 times the estimated gravitational carbon flux at 150 m in the zone of equatorial upwelling (5°S-5°N) and 1.1 times the export flux in the more oligotrophic regions to the north and south. The active flux of carbon by diel migrant

  10. Dynamics of equatorial irregularity patch formation, motion, and decay

    SciTech Connect

    Aarons, J.; Mullen, J.P.; Whitney, H.E.; MacKenzie, E.M.

    1980-01-01

    Using scintillation observations from a series of equatorial propagation paths as well as backscatter and airglow data, the development, motion, and decay of equatorial irregularity patches have been studied. Assembling the results of earlier studies in the field with our observations, we find the following: the patch has limited east-west dimensions with a minimum of 100 km. Several patches may be melded together to reach an extent of 1500 km. Its magnetic north-south dimensions are often greater than 2000 km; the most intense irregularities (as evidenced by the Jicamarca radar at the dip equator) are from 225 to 450 km in altitude, although irregularities are found as high as 1000 km. The patch initially has a westward expansion following the solar terminator, then, maintaining its integrity, moves eastward. Evidence over a limited series of experiments suggests that premidnight patches are formed within 1 1/2 hours after ionospheric sunset in the absence of special magnetic conditions. From Ascension Island (approx.16 /sup 0/S dip latitude) the individual patches can be clearly distinguished. The decay of patches in the midnight time period was studied, pointing to a rapid decrease in scintillation intensity in this time period.

  11. Use of Helical Fields to Allow a Long Pulse Reversed Field Pinch

    SciTech Connect

    A. Boozer and N. Pomphrey

    2008-11-20

    The maintenance of the magnetic configuration of a Reversed Field Pinch (RFP) is an unsolved problem. Even a toroidal loop voltage does not suffice to maintain the magnetic configuration in axisymmetry but could if the plasma had helical shaping. The theoretical tools for plasma optimization using helical shaping have advanced, so an RFP could be relatively easily designed for optimal performance with a spatially constant toroidal loop voltage. A demonstration that interesting solutions exist is given.

  12. Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas

    SciTech Connect

    Predebon, I.; Xanthopoulos, P.

    2015-05-15

    Turbulence induced by the ion temperature gradient (ITG) is investigated in the helical and axisymmetric plasma states of a reversed field pinch device by means of gyrokinetic calculations. The two magnetic configurations are systematically compared, both linearly and nonlinearly, in order to evaluate the impact of the geometry on the instability and its ensuing transport, as well as on the production of zonal flows. Despite its enhanced confinement, the high-current helical state demonstrates a lower ITG stability threshold compared to the axisymmetric state, and ITG turbulence is expected to become an important contributor to the total heat transport.

  13. Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas

    NASA Astrophysics Data System (ADS)

    Predebon, I.; Xanthopoulos, P.

    2015-05-01

    Turbulence induced by the ion temperature gradient (ITG) is investigated in the helical and axisymmetric plasma states of a reversed field pinch device by means of gyrokinetic calculations. The two magnetic configurations are systematically compared, both linearly and nonlinearly, in order to evaluate the impact of the geometry on the instability and its ensuing transport, as well as on the production of zonal flows. Despite its enhanced confinement, the high-current helical state demonstrates a lower ITG stability threshold compared to the axisymmetric state, and ITG turbulence is expected to become an important contributor to the total heat transport.

  14. Using ionospheric scintillation observations for studying the morphology of equatorial ionospheric bubbles

    NASA Astrophysics Data System (ADS)

    Dandekar, B. S.; Groves, K. M.

    2004-06-01

    For a study of the equatorial ionosphere, ionospheric scintillation data at VHF and L-band frequencies have been routinely collected by ground-based receivers at Ancon, Peru, Antofagasta, Chile, and Ascension Island, UK, since May 1994. The receivers routinely monitor VHF transmissions from two geosynchronous satellites located at 100°W longitude and 23°W longitude, and L-band signals from satellites located at 75°W longitude and 15°W longitude. This combination provides a network of seven usable, reasonably separated links for monitoring ionospheric equatorial bubble activity in the South American longitude sector. A data set of seven years covering the period from 1995 to 2001 was studied to determine the temporal, diurnal, and seasonal behavior of equatorial bubbles. The results of our statistical study are presented here. In general the equatorial ionospheric bubble activity shows a strong systematic and primary dependence in temporal, diurnal, and seasonal variation, and a secondary weak dependence on geomagnetic and solar flux activity. At present, the dependence on solar and magnetic activity is not usable for near-time and short-term prediction of the equatorial bubble activity. Equatorial bubbles usually start 1 hour after sunset, the activity peaks before local midnight, and vanishes by early morning. The activity peaks in the months of November and January-February and is practically absent (weak) from May to August. On a daily basis on the average one sees 1 to 3 bubbles. The duration of bubbles is about 70 min, and the time spacing between the bubbles is 1 to 2 hours. The bubble activity in general follows the phase of solar cycle activity. The observed systematic behavior of the equatorial bubbles allows for a now cast and short-term forecast of the bubble activity in the South American sector.

  15. Twist Helicity in Classical Vortices

    NASA Astrophysics Data System (ADS)

    Scheeler, Martin W.; Kedia, Hridesh; Kleckner, Dustin; Irvine, William T. M.

    2015-11-01

    Recent experimental work has demonstrated that a partial measure of fluid Helicity (the sum of linking and writhing of vortex tubes) is conserved even as those vortices undergo topology changing reconnections. Measuring the total Helicity, however, requires additional information about how the vortex lines are locally twisted inside the vortex core. To bridge this gap, we have developed a novel technique for experimentally measuring twist Helicity. Using this method, we are able to measure the production and eventual decay of twist for a variety of vortex evolutions. Remarkably, we observe twist dynamics capable of conserving total Helicity even in the presence of rapidly changing writhe. This work was supported by the NSF MRSEC shared facilities at the University of Chicago (DMR-0820054) and an NSF CAREER award (DMR-1351506). W.T.M.I. further acknowledges support from the A.P. Sloan Foundation and the Packard Foundation.

  16. Helicity multiplexed broadband metasurface holograms

    PubMed Central

    Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Yue Bun Pun, Edwin; Zhang, Shuang; Chen, Xianzhong

    2015-01-01

    Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices. PMID:26354497

  17. Helicity multiplexed broadband metasurface holograms.

    PubMed

    Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Pun, Edwin Yue Bun; Zhang, Shuang; Chen, Xianzhong

    2015-01-01

    Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices. PMID:26354497

  18. Microinstability Studies for the Large Helical Device

    SciTech Connect

    G. Rewoldt; L.-P. Ku; W.M. Tang; H. Sugama; N. Nakajima; K.Y. Watanabe; S. Murakami; H. Yamada; W.A. Cooper

    2002-01-28

    Fully kinetic assessments of the stability properties of toroidal drift modes have been obtained for cases for the Large Helical Device (LHD). This calculation employs the comprehensive linear microinstability code FULL, as recently extended for nonaxisymmetric systems. The code retains the important effects in the linearized gyrokinetic equation, using the lowest-order ''ballooning representation'' for high toroidal mode number instabilities in the electrostatic limit. These effects include trapped particles, FLR, transit and bounce and magnetic drift frequency resonances, etc., for any number of plasma species. Results for toroidal drift waves destabilized by trapped electrons and ion temperature gradients are presented, using numerically-calculated three-dimensional MHD equilibria. These are reconstructed from experimental measurements. Quasilinear fluxes of particles and energy for each species are also calculated. Pairs of LHD discharges with different magnetic axis positions and with and without pellet injection are compared.

  19. Theoretical study of the ionospheric plasma cave in the equatorial ionization anomaly region

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Tsung; Lin, C. H.; Chen, C. H.; Liu, J. Y.; Huba, J. D.; Chang, L. C.; Liu, H.-L.; Lin, J. T.; Rajesh, P. K.

    2014-12-01

    This paper investigates the physical mechanism of an unusual equatorial electron density structure, plasma cave, located underneath the equatorial ionization anomaly by using theoretical simulations. The simulation results provide important new understanding of the dynamics of the equatorial ionosphere. It has been suggested previously that unusual E>⇀×B>⇀ drifts might be responsible for the observed plasma cave structure, but model simulations in this paper suggest that the more likely cause is latitudinal meridional neutral wind variations. The neutral winds are featured by two divergent wind regions at off-equator latitudes and a convergent wind region around the magnetic equator, resulting in plasma divergences and convergence, respectively, to form the plasma caves structure. The tidal-decomposition analysis further suggests that the cave related meridional neutral winds and the intensity of plasma cave are highly associated with the migrating terdiurnal tidal component of the neutral winds.

  20. Investigation of height gradient in vertical plasma drift at equatorial ionosphere using multifrequency HF Doppler radar

    NASA Astrophysics Data System (ADS)

    Prabhakaran Nayar, S. R.; Sreehari, C. V.

    2004-12-01

    A multifrequency HF Doppler radar installed at the magnetic equatorial station Trivandrum provides an opportunity to study the height gradient in vertical plasma drift at the bottomside of equatorial F region during evening time. The multifrequency radar gives near-simultaneous observation of vertical plasma drift at three close by F region heights above the sounding station. The height gradient of the vertical drift shows a negative value during the prereversal enhancement (PRE) period and turns to positive value after the prereversal enhancement. The average height gradient in vertical plasma drift remains negative around PRE and its magnitude decreases with altitude, below F peak. This could be a clear-cut manifestation of the curl-free nature of the low-latitude electric field, and it could also indicate a partial signature of the postsunset velocity vortex at the equatorial F region. The magnitude of the mean height gradient around PRE exhibits a seasonal variation.

  1. Employing helicity amplitudes for resummation

    NASA Astrophysics Data System (ADS)

    Moult, Ian; Stewart, Iain W.; Tackmann, Frank J.; Waalewijn, Wouter J.

    2016-05-01

    Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in 4- and d -dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard matching coefficients, for p p →H +0 , 1, 2 jets, p p →W /Z /γ +0 , 1, 2 jets, and p p →2 , 3 jets. These operator bases are completely crossing symmetric, so the results can easily be applied to processes with e+e- and e-p collisions.

  2. Convection in deformed bodies: The effect of equatorial ellipticity on convective behavior

    NASA Astrophysics Data System (ADS)

    Evonuk, M.

    2015-11-01

    Tidal interactions between bodies such as hot jupiter planets and their host stars are likely to result in non-spherical geometries. These elliptical instabilities may have interesting effects on interior fluid convective patterns, which in turn could influence the nature of the magnetic dynamo within these planets. Simulations of thermal convection in the 2D rotating equatorial plane are conducted to determine to first order the effect of equatorial eccentricity on convection for varying density contrasts with differing convective vigor and rotation rates. This survey is conducted in two dimensions in order to simulate a broad range of eccentricities and to maximize the parameter space explored. The location of the three regimes documented in previous work (Evonuk and Samuel, 2012), dipolar flow, transitional flow, and differential flow, are found to be offset by the introduction of equatorial eccentricity to the system. The introduction of equatorial eccentricity changes the fluid behavior such that bodies with high amounts of deformation are likely to have weaker differential flows shifting their behavior towards transitional and dipolar flow structures. A scaling law based on the convective Rossby number, density contrast, and the eccentricity of the equatorial plane can therefore provide a way to estimate which regime a given body lies in.

  3. Response of the equatorial ionosphere to the geomagnetic DP 2 current system

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Magoun, M.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O. K.; Bamba, Z.; Paula, E. R.

    2016-07-01

    The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground-based multiinstrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP 2 current system. The quasiperiodic DP 2 current system, which fluctuates coherently with fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high-latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

  4. Seismo-ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements

    NASA Astrophysics Data System (ADS)

    Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Pulinets, S.

    2014-10-01

    We report the processes and results of statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a period of 6 years (2005-2010), in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which represent relative equatorial electron density increase, were performed for each region. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low-latitude region can accompany observable precursory and concurrent EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling is consistent with our observation, and the possibility of earthquake prediction using the EIA intensity variation is discussed.

  5. All-Optical Helicity Dependent Spin Switching in a Many-Spin System

    NASA Astrophysics Data System (ADS)

    Latta, Tanner; Zhang, G. P.

    All-optical helicity dependent magnetic switching (AOS) is achieved through using an ultrafast laser pulse to manipulate and switch the spin of an electron from one direction to another. This process happens in a short amount of femtoseconds after the laser pulse is introduced. All-optical helicity dependent magnetic switching (AOS) does not fall to the assistance of any external magnetic field. Linearly polarized light, as well as right and left circularly polarized light are used to manipulate the spin of the electrons. Ferrimagnetic, rather than ferromagnetic, materials are more suitable to create conditions in which AOS are viable due to the orientation of the spins within this material. In the following study we show and conclude that AOS is possible with the use of left and right circularly polarized laser pulses. All-optical helicity dependent magnetic switching has many applications in magnetic recording technology or magnetic memory devices. DE-FG02-06ER46304.

  6. Self-assembly of magnetite nanocubes into helical superstructures.

    PubMed

    Singh, Gurvinder; Chan, Henry; Baskin, Artem; Gelman, Elijah; Repnin, Nikita; Král, Petr; Klajn, Rafal

    2014-09-01

    Organizing inorganic nanocrystals into complex architectures is challenging and typically relies on preexisting templates, such as properly folded DNA or polypeptide chains. We found that under carefully controlled conditions, cubic nanocrystals of magnetite self-assemble into arrays of helical superstructures in a template-free manner with >99% yield. Computer simulations revealed that the formation of helices is determined by the interplay of van der Waals and magnetic dipole-dipole interactions, Zeeman coupling, and entropic forces and can be attributed to spontaneous formation of chiral nanocube clusters. Neighboring helices within their densely packed ensembles tended to adopt the same handedness in order to maximize packing, thus revealing a novel mechanism of symmetry breaking and chirality amplification. PMID:25061133

  7. 3D Modeling of Equatorial Plasma Bubbles

    NASA Astrophysics Data System (ADS)

    Huba, Joseph; Joyce, Glenn; Krall, Jonathan

    2011-10-01

    Post-sunset ionospheric irregularities in the equatorial F region were first observed by Booker and Wells (1938) using ionosondes. This phenomenon has become known as equatorial spread F (ESF). During ESF the equatorial ionosphere becomes unstable because of a Rayleigh-Taylor-like instability: large scale (10s km) electron density ``bubbles'' can develop and rise to high altitudes (1000 km or greater at times). Understanding and modeling ESF is important because of its impact on space weather: it causes radio wave scintillation that degrades communication and navigation systems. In fact, it is the focus of of the Air Force Communications/Navigation Outage Forecast Satellite (C/NOFS) mission. We will describe 3D simulation results from the NRL ionosphere models SAMI3 and SAMI3/ESF of this phenomenon. In particular, we will examine the causes of the day-to-day ariability of ESF which is an unresolved problem at this time. Post-sunset ionospheric irregularities in the equatorial F region were first observed by Booker and Wells (1938) using ionosondes. This phenomenon has become known as equatorial spread F (ESF). During ESF the equatorial ionosphere becomes unstable because of a Rayleigh-Taylor-like instability: large scale (10s km) electron density ``bubbles'' can develop and rise to high altitudes (1000 km or greater at times). Understanding and modeling ESF is important because of its impact on space weather: it causes radio wave scintillation that degrades communication and navigation systems. In fact, it is the focus of of the Air Force Communications/Navigation Outage Forecast Satellite (C/NOFS) mission. We will describe 3D simulation results from the NRL ionosphere models SAMI3 and SAMI3/ESF of this phenomenon. In particular, we will examine the causes of the day-to-day ariability of ESF which is an unresolved problem at this time. Research supported by ONR.

  8. Interaction of field-aligned cold plasma flows with an equatorially-trapped hot plasma - Electrostatic shock formation

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra

    1993-01-01

    Effects of equatorially trapped hot plasma on the highly supersonic cold-plasma flow occurring during early stage plasmaspheric refilling are studied by means of numerical simulations. It is shown that the equatorially trapped hot ions set up a potential barrier for the cold ion beams and facilitate formation of electrostatic shocks by reflecting them from the equatorial region. Simulations with and without the hot plasma show different flow properties; the formation of electrostatic shocks occur only in the former case. The simulation with the hot plasma also reveals that the magnetic trapping in conjunction with the evolution of the electrostatic potential barrier produces ion velocity distribution functions consisting of a cold core and a hot ring in the perpendicular velocity. Such a distribution function provides a source of free energy for equatorial waves. The corresponding electron population is warm and field-aligned.

  9. Yoshizawa's cross-helicity effect and its quenching

    NASA Astrophysics Data System (ADS)

    Brandenburg, A.; Rädler, K.-H.

    2013-02-01

    A central quantity in mean-field magnetohydrodynamics is the mean electromotive force EMF, which in general depends on the mean magnetic field. It may however have a part independent of the mean magnetic field. Here we study an example of a rotating conducting body of turbulent fluid with non-zero cross-helicity, in which a contribution to the EMF proportional to the angular velocity occurs (Yoshizawa 1990). If the forcing is helical, it also leads to an alpha effect, and large-scale magnetic fields can be generated. For not too rapid rotation, the field configuration is such that Yoshizawa's contribution to the EMF is considerably reduced compared to the case without alpha effect. In that case, large-scale flows are also found to be generated.

  10. Equatorial waves in the stratosphere of Uranus

    NASA Technical Reports Server (NTRS)

    Hinson, David P.; Magalhaes, Julio A.

    1991-01-01

    Analyses of radio occultation data from Voyager 2 have led to the discovery and characterization of an equatorial wave in the Uranus stratosphere. The observed quasi-periodic vertical atmospheric density variations are in close agreement with theoretical predictions for a wave that propagates vertically through the observed background structure of the stratosphere. Quantitative comparisons between measurements obtained at immersion and at emersion yielded constraints on the meridional and zonal structure of the wave; the fact that the two sets of measurements are correlated suggests a wave of planetary scale. Two equatorial wave models are proposed for the wave.

  11. Simulations of the equatorial thermosphere anomaly: Geomagnetic activity modulation

    NASA Astrophysics Data System (ADS)

    Lei, Jiuhou; Wang, Wenbin; Thayer, Jeffrey P.; Luan, Xiaoli; Dou, Xiankang; Burns, Alan G.; Solomon, Stanley C.

    2014-08-01

    The modulation of geomagnetic activity on the equatorial thermosphere anomaly (ETA) in thermospheric temperature under the high solar activity condition is investigated using the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations. The model simulations during the geomagnetically disturbed interval, when the north-south component of the interplanetary magnetic field (Bz) oscillates between southward and northward directions, are analyzed and also compared with those under the quiet time condition. Our results show that ionospheric electron densities increase greatly in the equatorial ionization anomaly (EIA) crest region and decrease around the magnetic equator during the storm time, resulting from the enhanced eastward electric fields. The impact of both the direct heat deposition at high latitudes and the modulation of the storm time enhanced EIA crests on the ETA are subsequently studied. The increased plasma densities over the EIA crest region enhance the field-aligned ion drag that accelerates the poleward meridional winds and consequently their associated adiabatic cooling effect. This process alone produces a deeper temperature trough over the magnetic equator as a result of the enhanced divergence of meridional winds. Moreover, the enhanced plasma-neutral collisional heating at higher latitudes associated with the ionospheric positive storm effect causes a weak increase of the ETA crests. On the other hand, strong changes of the neutral temperature are mainly confined to higher latitudes. Nevertheless, the changes of the ETA purely due to the increased plasma density are overwhelmed by those associated with the storm time heat deposition, which is the major cause of an overall elevated temperature in both the ETA crests and trough during the geomagnetically active period. Associated with the enhanced neutral temperature at high latitudes due to the heat deposition, the ETA crest-trough differences become larger under the minor

  12. TURBULENT CROSS-HELICITY IN THE MEAN-FIELD SOLAR DYNAMO PROBLEM

    SciTech Connect

    Pipin, V. V.; Kuzanyan, K. M.; Zhang, H.; Kosovichev, A. G.

    2011-12-20

    We study the dynamical and statistical properties of turbulent cross-helicity (correlation of the aligned fluctuating velocity and magnetic field components). We derive an equation governing generation and evolution of the turbulent cross-helicity and discuss its meaning for the dynamo. Using the symmetry properties of the problem we suggest a general expression for the turbulent cross-helicity. Effects of the density stratification, large-scale magnetic fields, differential rotation, and turbulent convection are taken into account. We investigate the relative contribution of these effects to the cross-helicity evolution for two kinds of dynamo models of the solar cycle: a distributed mean-field model and a flux-transport dynamo model. We show that the contribution from the density stratification follows the evolution of the radial magnetic field, while large-scale electric currents produce a more complicated pattern of the cross-helicity of comparable magnitude. The pattern of the cross-helicity evolution strongly depends on details of the dynamo mechanism. Thus, we anticipate that direct observations of the cross-helicity on the Sun may serve for the diagnostic purpose of the solar dynamo process.

  13. Studies on equatorial shock formation during plasmaspheric refilling

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra

    1993-01-01

    During the grant period starting August 1, 1992, our major effort has been on examining the presence of equatorially trapped hot plasma on plasmaspheric refilling. We performed one-dimensional PIC simulations of cold plasmas expanding into a hot plasma, consisting of hot anisotropic ions and warm isotropic electrons, trapped in a region of minimum magnetic field. Simulations showed that the electric potential barrier built up by the anisotropy of the hot ion population facilitates in the formation of electrostatic shocks when the cold ion beams begin to come into contact with the hot plasma. The shock formation occurs even when the cold ion beams are highly supersonic with respect to the ion-acoustic speed. This finding is interesting because equatorial shock formation during the early stage of plasmaspheric refilling has been debated over about two decades. In the past ion-ion instability has been invoked as the main mechanism for the coupling between the cold ion beams approaching the equator from the conjugate ionspheres. This coupling occurs when the beams are sufficiently slow; the beam velocity being less than three times the ion-acoustic speed. In the presence of hot plasma, the beams slow down by the potential barrier. The slowing down and the reflection process lead to the formation of the electrostatic shock even for highly supersonic ion beams. The mixing of hot and cold plasma was also studied.

  14. Equatorial Noise Emissions and Their Quasi-Periodic Modulation

    NASA Astrophysics Data System (ADS)

    Nemec, F.; Santolik, O.; Hrbackova, Z.; Pickett, J. S.; Cornilleau-Wehrlin, N.; Parrot, M.; Hayosh, M.

    2015-12-01

    Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic structure related to the ion cyclotron frequency in the source region. We analyze more than 2000 EN events observed by the wave instruments on board the Cluster spacecraft, and we find that about 5% of EN events are not continuous in time, but exhibit a quasi-periodic (QP) modulation of the wave intensity. Typical modulation periods are on the order of minutes. The events predominantly occur in the noon-to-dawn local time sector, and their occurrence is related to the periods of increased geomagnetic activity and higher solar wind speeds. We suggest that the QP modulation of EN events may be due to compressional ULF pulsations, which periodically modulate the wave growth in the source region. These compressional ULF pulsations were identified in about half of the events. Finally, we demonstrate that EN emissions with QP modulation of the wave intensity can propagate down to altitudes as low as 700 km.

  15. Flux amplification in Helicity Injected Torus (HIT-II) coaxial helicity injection discharges

    SciTech Connect

    Redd, A. J.; Jarboe, T. R.; Hamp, W. T.; Nelson, B. A.; O'Neill, R. G.; Smith, R. J.

    2008-02-15

    Recent coaxial helicity injection (CHI) studies using the Helicity Injected Torus device [Redd et al., Phys. Plasmas 9, 2006 (2002)] have produced discharges with measured toroidal plasma currents up to 350 kA and direct evidence of both poloidal flux amplification and toroidal current buildup, resulting from a steady process on millisecond time scales. Internal magnetic probes directly measure the poloidal flux amplification, and also measure a strong paramagnetism. Equilibrium reconstructions of these flux amplification discharges, using only surface magnetics, match the internal probes and multipoint Thomson scattering, and show current-profile relaxation during toroidal current ramp up. The criteria for producing flux amplification include both a sufficiently thin electrode-driven edge region and a large magnetic shear in the CHI injector region, which allows injector reconnection activity to overcome resistive decay and build up a closed plasma core. If the interelectrode distance d is small, then both criteria can be easily met. If d is comparable to the device minor radius, then the injector must be overdriven to produce significant flux amplification. The physics basis for generating CHI discharges with the theoretically maximum toroidal current is now understood, and this basis can be used to guide CHI experiments in any axisymmetric device.

  16. Expanding Non-solenoidal Startup with Local Helicity Injection to Increased Toroidal Field and Helicity Injection Rate

    NASA Astrophysics Data System (ADS)

    Perry, J. M.; Barr, J. L.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Lewicki, B. T.; Reusch, J. A.; Schlossberg, D. J.; Winz, G. R.

    2015-11-01

    Local helicity injection (LHI) is a non-solenoidal startup technique under development on the Pegasus ST. Plasma currents up to 0.18 MA have been initiated by LHI in conjunction with poloidal field induction. A 0-D power balance model has been developed to predict plasma current evolution by balancing helicity input against resistive dissipation. The model is being validated against a set of experimental measurements and magnetic reconstructions with radically varied plasma geometric evolutions. Outstanding physics issues with LHI startup are the scalings of confinement and MHD activity with helicity injection rate and toroidal field strength, as well as injector behavior at high field. Preliminary results from the newly-installed Thomson scattering system suggest core temperatures of a few hundred eV during LHI startup. Measurements are being expanded to multiple spatial points for ongoing confinement studies. A set of larger-area injectors is being installed in the lower divertor region, where increased toroidal field will provide a helicity injection rate over 3 times that of outboard injectors. In this regime helicity injection will be the dominant current drive. Experiments with divertor injectors will permit experimental differentiation of several possible confinement models, and demonstrate the feasibility of LHI startup at high field. Work supported by US DOE grant DE-FG02-96ER54375.

  17. Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet

    NASA Astrophysics Data System (ADS)

    Simon-Miller, A. A.; Rogers, J. H.; Gierasch, P. J.; Choi, D.; Allison, M. D.; Adamoli, G.; Mettig, H.-J.

    2012-03-01

    Jupiter's south equatorial winds and clouds are consistent with a high frequency, gravity-inertia, wave. A second, westward-moving, Rossby wave was also identified. Asymmetry with the north equatorial clouds are likely due to the Great Red Spot.

  18. Directions of equatorial noise propagation determined using Cluster and DEMETER spacecraft

    NASA Astrophysics Data System (ADS)

    Nemec, Frantisek; Hrbackova, Zuzana; Santolik, Ondrej; Pickett, Jolene S.; Parrot, Michel; Cornilleau-Wehrlin, Nicole

    2013-04-01

    Equatorial noise emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed within a few degrees of the geomagnetic equator at radial distances from about 2 to 6 Re. High resolution data reveal that the emissions are formed by a system of spectral lines, being generated by instabilities of proton distribution functions at harmonics of the proton cyclotron frequency in the source region. The waves propagate in the fast magnetosonic mode nearly perpendicularly to the ambient magnetic field, i.e. the corresponding magnetic field fluctuations are almost linearly polarized along the ambient magnetic field and the corresponding electric field fluctuations are elliptically polarized in the equatorial plane, with the major polarization axis having the same direction as wave and Poynting vectors. We conduct a systematic analysis of azimuthal propagation of equatorial noise. Combined WBD and STAFF-SA measurements performed on the Cluster spacecraft are used to determine not only the azimuthal angle of the wave vector direction, but also to estimate the corresponding beaming angle. It is found that the beaming angle is generally rather large, i.e. the detected waves come from a significant range of directions, and a traditionally used approximation of a single plane wave fails. The obtained results are complemented by a raytracing analysis in order to get a comprehensive picture of equatorial noise propagation in the inner magnetosphere. Finally, high resolution multi-component measurements performed by the low-altitude DEMETER spacecraft are used to demonstrate that equatorial noise emissions can reach altitudes as low as 660 km, and that the observed propagation properties are in agreement with the overall propagation picture.

  19. Spin susceptibility function of helical metal and RKKY interacton

    NASA Astrophysics Data System (ADS)

    Liu, Chunxiao; Roy, Bitan; Sau, Jay; CMTC; JQI Team

    Topological insulator is a peculiar material, which is insulating in the bulk, while conducting on the surface due to the topology in momentum space . Here, we study the surface of 3D topological insulator, which is also called helical metal. The Hamiltonian of the surface electrons is H = k × σ , which has spin-momentum locking and Dirac dispersion. The property that we are interested in is the spin susceptibility function of the helical metal. It describes how the system respond to the external magnetic field in the linear response regime. However, because the dispersion of helical metal is linear in momentum k, the spin susceptibility is easily divergent in terms of UV momentum cutoff. The talk we will present is focusing on how we renormalize the spin susceptibility function in the particular renormalization scheme we choose. In the second part of the talk, we will make use of the renormalized spin susceptibility to show how external magnetic impurities on the surface would interact with each other, with the interaction mediated by electrons of helical metal. This interaction is also called RKKY interaction. Treating impurities as classical spins, we show the pattern of ground state with numerical simulations. grants by NSF.

  20. Position and Trajectrories of helical microswimmers inside circular channels

    NASA Astrophysics Data System (ADS)

    Caldag, Hakan; Yesilyurt, Serhat

    2015-11-01

    This work reports the position and orientation of helical mm-sized microswimmers in circular channels obtained by image processing of recorded images. Microswimmers are biologically inspired structures with huge potential for medical practices such as delivery of potent drugs into tissues. In order to understand the hydrodynamic effects of confinement on the velocity and stability of trajectories of swimmers, we developed helical microswimmers with a magnetic head and a rigid helical tail, similar to those of E. coli bacteria. The experiments are recorded using a digital camera, which is placed above the experimental setup that consists of three Helmholtz pairs, generating a rotating magnetic field. A channel containing the microswimmer is placed along the axis of the innermost coil. Image processing tools based on contrast-enhancement are used to obtain the centroid of the head of the swimmer and orientation of the whole swimmer in the channel. Swimmers that move in the direction of the head, i.e. pushed kinematically by the tail, has helical trajectories, which are more unstable in the presence of Poiesuille flow inside the channel; and the swimmers that are pulled by the tail, have trajectories that stabilize at the centerline of the channel.

  1. Equatorial scintillations: advances since ISEA-6

    NASA Astrophysics Data System (ADS)

    Basu, Sunanda; Basu, Santimay

    1985-10-01

    Since the last equatorial aeronomy meeting in 1980, our understanding of the morphology of equatorial scintillations has advanced greatly due to more intensive observations at the equatorial anomaly locations in the different longitude zones. The unmistakable effect of the sunspot cycle in controlling irregularity belt width and electron concentration responsible for strong scintillation in the GHz range has been demonstrated. The fact that night-time F-region dynamics is an important factor in controlling the magnitude of scintillations has been recognized by interpreting scintillation observations in the light of realistic models of total electron content at various longitudes. A hypothesis based on the alignment of the solar terminator with the geomagnetic flux tubes as an indicator of enhanced scintillation occurrence and another based on the influence of a transequatorial thermospheric neutral wind have been postulated to describe the observed longitudinal variation. A distinct class of equatorial irregularities known as the bottomside sinusoidal (BSS) type has been identified. Unlike equatorial bubbles, these irregularities occur in very large patches, sometimes in excess of several thousand kilometers in the E-W direction and are associated with frequency spread on ionograms. Scintillations caused by such irregularities exist only in the VHF band, exhibit Fresnel oscillations in intensity spectra and are found to give rise to extremely long durations (~ several hours) of uninterrupted scintillations. These irregularities maximize during solstices, so that in the VHF range, scintillation morphology at an equatorial station is determined by considering occurrence characteristics of both bubble type and BSS type irregularities. The temporal structure of scintillations in relation to the in situ measurements of irregularity spatial structure within equatorial bubbles has been critically examined. A two-component irregularity spectrum with a shallow slope ( p1

  2. Equatorial deep jets in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Brandt, P.; Greatbatch, R. J.; Didwischus, S.-H.; Claus, M.; Hormann, V.; Funk, A.; Dengler, M.

    2012-04-01

    Vertically alternating deep zonal jets of short vertical wavelength were discovered in the equatorial oceans more than 35 years ago. These jets that are observed to be coherent across the equatorial basins are characterized by vertically alternating eastward and westward currents lying within 1° of the equator, with amplitudes of 0.1-0.2 ms-1 and vertical wavelengths between 300 and 700 m. In the Atlantic, equatorial deep jets oscillate with a period of about 4.5 years, while their energy propagates upward. The 4.5 year signal can be seen in sea surface temperature as well as atmospheric data (e.g. surface wind and rainfall) indicating the significance of the deep jets for climate. Here we analyse velocity data from more than 7 years of moored observations at the equator, 23°W as well as shipboard hydrographic and current observations along the 23°W repeat section. Our focus is on intermediate depth levels (300-700 m), where the deep jets are superimposed on a mean flow composed of the westward flowing Equatorial Intermediate Current centred on the equator and the eastward Southern and Northern Intermediate Countercurrents located at 2°S and 2°N, respectively. The large zonal oxygen gradient from the well ventilated western boundary toward low-oxygen values near the eastern boundary makes the meridional oxygen distribution in the central equatorial Atlantic sensitive to zonal flow variations in time and latitude. We compare the observed meridional structures of the mean and anomalous oxygen and zonal velocity distributions as well as their temporal evolution with results of an advection-diffusion model driven by a prescribed velocity field, restoring to high oxygen values at the western boundary, and otherwise constant oxygen consumption. The prescribed velocity field is composed of a high order baroclinic vertical normal mode aimed at representing the 4.5-year cycle and a mean velocity field resembling the observed mean zonal current structure. Similarities

  3. The Longitudinal Variation of Equatorial Electrodynamics Observations

    NASA Astrophysics Data System (ADS)

    Yizengaw, E.; Zesta, E.; Moldwin, M.; Valladares, C. E.; Damtie, B.; Mebrahtu, A.; Biouele, C. M.; Yumoto, K.; Pfaff, R. F.; Heelis, R. A.

    2010-12-01

    The uneven distribution of ground-based instruments due to the large ocean coverage in the equatorial regions hinders our ability to obtain a global understanding of the dynamics and structure of the equatorial ionosphere. In Africa, which has been mostly devoid of ground-based instruments, the ionospheric density structure has been traditionally estimated by model interpolation over vast geographic areas. Recent ground- and space-based observations have shown that geomagnetic storms can have dramatic longitudinal differences in equatorial ionospheric electrodynamics, such as enhanced generation of F-region plasma irregularities, and super fountain effect at low latitudes. For example, satellite observations have shown very unique equatorial ionospheric density structures in the African region. The African region is the longitude sector where the occurrence of large scale bubble activity (zonal width, depletion level, and spacing) peaks. No other region in the globe shows similar characteristics. One of the possible driving mechanisms that govern the equatorial electrodynamics is the vertical ExB drift, which strongly affects the structure and dynamics of the ionosphere in the low/mid-latitude region. According to the observations performed at different longitudes, using recently deployed limited ground-based instruments, the vertical ExB drift has significant longitudinal differences. This paper presents initial results of vertical ExB drifts observed at three different longitudes: East African, West African, and West American sectors. The drift is estimated using a pairs of ground-based magnetometers technique. In the African sector stations from the AMBER, INTERMAGNET, and MAGDAS, and in the American sector SAMBA and LISN magnetometer arrays have been used for this study. Finally, the comparison between the magnetometer estimated ExB drift and the vertical drift observations (VEFI and IVM) on board C/NOFS satellites have also been performed, showing promising

  4. Wave Forcing of Saturn's Equatorial Oscillation

    NASA Technical Reports Server (NTRS)

    Flasar, F. M.; Schlinder, P. J.; Guerlet, S.; Fouchet, T.

    2011-01-01

    Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn.

  5. Rational design of helical architectures

    PubMed Central

    Chakrabarti, Dwaipayan; Fejer, Szilard N.; Wales, David J.

    2009-01-01

    Nature has mastered the art of creating complex structures through self-assembly of simpler building blocks. Adapting such a bottom-up view provides a potential route to the fabrication of novel materials. However, this approach suffers from the lack of a sufficiently detailed understanding of the noncovalent forces that hold the self-assembled structures together. Here we demonstrate that nature can indeed guide us, as we explore routes to helicity with achiral building blocks driven by the interplay between two competing length scales for the interactions, as in DNA. By characterizing global minima for clusters, we illustrate several realizations of helical architecture, the simplest one involving ellipsoids of revolution as building blocks. In particular, we show that axially symmetric soft discoids can self-assemble into helical columnar arrangements. Understanding the molecular origin of such spatial organisation has important implications for the rational design of materials with useful optoelectronic applications.

  6. Airborne studies of equatorial F layer ionospheric irregularities

    SciTech Connect

    Weber, E.J.; Buchau, J.; Moore, J.G.

    1980-09-01

    Radio wave and optical experiments were conducted onboard a U.S. Air Force research aircraft in March 1977 and March 1978 at low magnetic latitudes to investigate the effects of F region electron density amplitude. Scintillation measurements were used to monitor the development and motion of F region 6300-A O I airglow depletions, spread F, and scintillation producing irregularities that are all associated with low-density bubbles in the postsunset equatorial ionosphere. The 6300-A airglow depletions are the bottomside signature of low plasma density within the bubbles. Examples of multiple airglow depletions and their relation to variations in the F layer virtual height (h'F) and to the occurrence of amplitude scintillations on 250-MHz satellite signals are described. Estimates of the average bottomside electron density, from simultaneous ionosonde measurements and 6300-A airglow intensities, show electron density decreases of approx.66% within the bubbles. These decreases are approximately the same for bubbles observed at the magnetic equator and near Ascension Island (18 /sup 0/S magnetic latitude). The measurements at Ascension Island show that airglow depletions extend away from the magnetic equator into the southern 6300-A intertropical arc. Variations in the maximum poleward extent of airglow depletions and of associated ionospheric irregularities that give rise to amplitude scintillations were observed. These latitudinal variations are interpreted, using field line mapping considerations, as variations in the maximum altitude of plasma bubbles over the magnetic equator. A north-south flight confirms that the overall pattern of airglow depletions and associated ionospheric irregularities extends continuously across the magnetic equator to +-15/sup 0/ magnetic latitude.

  7. Brownian motion of helical flagella.

    PubMed

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique. PMID:16997210

  8. OPE for all helicity amplitudes

    NASA Astrophysics Data System (ADS)

    Basso, Benjamin; Caetano, João; Córdova, Lucía; Sever, Amit; Vieira, Pedro

    2015-08-01

    We extend the Operator Product Expansion (OPE) for scattering amplitudes in planar SYM to account for all possible helicities of the external states. This is done by constructing a simple map between helicity configurations and so-called charged pentagon transitions. These OPE building blocks are generalizations of the bosonic pentagons entering MHV amplitudes and they can be bootstrapped at finite coupling from the integrable dynamics of the color flux tube. A byproduct of our map is a simple realization of parity in the super Wilson loop picture.

  9. Scale analysis of equatorial plasma irregularities derived from Swarm constellation

    NASA Astrophysics Data System (ADS)

    Xiong, Chao; Stolle, Claudia; Lühr, Hermann; Park, Jaeheung; Fejer, Bela G.; Kervalishvili, Guram N.

    2016-07-01

    In this study, we investigated the scale sizes of equatorial plasma irregularities (EPIs) using measurements from the Swarm satellites during its early mission and final constellation phases. We found that with longitudinal separation between Swarm satellites larger than 0.4°, no significant correlation was found any more. This result suggests that EPI structures include plasma density scale sizes less than 44 km in the zonal direction. During the Swarm earlier mission phase, clearly better EPI correlations are obtained in the northern hemisphere, implying more fragmented irregularities in the southern hemisphere where the ambient magnetic field is low. The previously reported inverted-C shell structure of EPIs is generally confirmed by the Swarm observations in the northern hemisphere, but with various tilt angles. From the Swarm spacecrafts with zonal separations of about 150 km, we conclude that larger zonal scale sizes of irregularities exist during the early evening hours (around 1900 LT).

  10. Solar Wind Associated with Near Equatorial Coronal Hole

    NASA Astrophysics Data System (ADS)

    Hegde, M.; Hiremath, K. M.; Doddamani, Vijayakumar H.; Gurumath, Shashanka R.

    2015-09-01

    Present study probes temporal changes in the area and radiative flux of near equatorial coronal hole associated with solar wind parameters such as wind speed, density, magnetic field and temperature. Using high temporal resolution data from SDO/AIA for the two wavelengths 193 Å and 211 Å, area and radiative flux of coronal holes are extracted and are examined for the association with high speed solar wind parameters. We find a strong association between different parameters of coronal hole and solar wind. For both the wavelength bands, we also compute coronal hole radiative energy near the earth and it is found to be of similar order as that of solar wind energy. However, for the wavelength 193 Å, owing to almost similar magnitudes of energy emitted by coronal hole and energy due to solar wind, it is conjectured that solar wind might have originated around the same height where 193 Å line is formed in the corona.

  11. Resilience of helical fields to turbulent diffusion - II. Direct numerical simulations

    NASA Astrophysics Data System (ADS)

    Bhat, Pallavi; Blackman, Eric G.; Subramanian, Kandaswamy

    2014-03-01

    Blackman and Subramanian (Paper I) found that sufficiently strong large-scale helical magnetic fields are resilient to turbulent diffusion, decaying on resistively slow rather than turbulently fast time-scales. This bolsters fossil field origins for magnetic fields in some astrophysical objects. Here, we study direct numerical simulations (DNS) of decaying large-scale helical magnetic fields in the presence of non-helical turbulence for two cases: (1) the initial helical field is large enough to decay resistively but transitions to fast decay; (2) the case of Paper I, wherein the transition energy for the initial helical field to decay fast directly is sought. Simulations and two-scale modelling (based on Paper 1) reveal the transition energy, Ec1 to be independent of the turbulent forcing scale, within a small range of RM. For case (2), the two-scale theory predicts a large-scale helical transition energy of Ec2 = (k1/kf)2Meq, where k1 and kf are the large-scale and small turbulent forcing scale, respectively, and Meq is the equipartition magnetic energy. The DNS agree qualitatively with this prediction but the RM, currently achievable, is too small to satisfy a condition 3/RM ≪ (k1/kf)2, necessary to robustly reveal the transition, Ec2. That two-scale theory and DNS agree wherever they can be compared suggests that Ec2 of Paper I should be identifiable at higher RM in DNS.

  12. Progress in Nonsolenoidal Plasma Startup Using Point-Source Helicity Injection in the Pegasus ST

    NASA Astrophysics Data System (ADS)

    Fonck, R. J.; Barr, J. L.; Bongard, M. W.; Burke, M. G.; Hinson, E. T.; Redd, A. J.; Schlossberg, D. J.; Thome, K. E.

    2010-11-01

    Compact, high-current plasma guns are employed as DC helicity injectors on the Pegasus ST. This startup technique has produced Ip˜0.17 MA to date, consistent with helicity balance and Taylor relaxation constraints. Once a tokamak-like plasma is formed, passive electrodes can act as helicity injectors for further growth. This may provide additional control of the edge current density, the Taylor relaxation limit, and provide a higher helicity input rate. Ion heating to Ti˜0.5 keV is observed in the strongly-reconnecting, helicity-driven phase. Efficient handoff from helicity to inductive drive requires the buildup of core current density. Following helicity formation, OH-driven plasmas are MHD-quiescent and sustained above 0.20 MA, apparently due to increased core magnetic shear. Outstanding issues for prediction to larger fusion experiments include: structure of the edge current density; impedance of the injected current channel; impurity behavior; and the behavior of the confinement and helicity dissipation rate as Ip and Te increase.

  13. Gyrokinetic investigation of ITG turbulence in helical RFPs

    NASA Astrophysics Data System (ADS)

    Predebon, I.; Xanthopoulos, P.; Terranova, D.

    2014-10-01

    Micro-instabilities in reversed field pinch (RFP) plasmas have been investigated in the last years from several viewpoints and with various numerical tools. So far, axisymmetry of the magnetic equilibrium has always been postulated. Nevertheless, experimental evidence suggests that the physical conditions mostly favoring the onset of electrostatic/electromagnetic turbulence, e.g., the occurrence of large pressure gradients, emerge when magnetic surfaces become helical, during the single helicity states. In this work, we investigate ion-temperature-gradient driven turbulence focusing on the 3D feature, with the aim to describe its distinct properties compared to the axisymmetric geometry. For this study, we will apply the 3D nonlinear gyrokinetic code GENE to RFP equilibria generated by the VMEC code.

  14. Model NbTi Helical Solenoid Fabrication and Test Results

    SciTech Connect

    Andreev, N.; Barzi, E.; Chlachidze, G.; Evbota, D.; Kashikhin, V.S.; Kashikhin, V.V.; Lamm, M.J.; Makarov, A.; Novitski, I.; Orris, D.F.; Tartaglia, M.A.; /Fermilab

    2011-09-01

    A program to develop model magnets for a helical cooling channel is under way at Fermilab. In the first steps of a planned sequence of magnets, two four-coil helical solenoid models with 300 mm aperture have been fabricated and tested. These two models, HSM01 and HSM02, used insulated NbTi Rutherford cable wound onto stainless steel rings with spliceless transitions between coils. Strip heaters were included for quench protection of each coil, and the coils were epoxy-impregnated after winding inside the support structures. Based on the results of the first model the second model was made using a cable with optimized cross-section, improved winding and epoxy-impregnation procedures, enhanced ground insulation, and included heat exchange tubing for a test of conduction cooling. We report on the results and lessons learned from fabrication and tests of these two models.

  15. Resistive magnetohydrodynamic simulations of helicity-injected startup plasmas in National Spherical Torus eXperiment

    SciTech Connect

    Hooper, E. B.; Sovinec, C. R.; Raman, R.; Ebrahimi, F.; Menard, J. E.

    2013-09-15

    The generation of helicity-injected startup plasmas in National Spherical Torus eXperiment (NSTX), including flux surface closure, is studied using resistive-magnetohydrodynamic simulations with plasma flows, currents, ohmic heating and anisotropic thermal conduction. An injection-voltage pulse shape is used that separates the injection and closure phases allowing elucidation of the physics. The formation of an X-point near the helicity-injection gap is triggered as the injector voltage drops to zero. Near the forming X-point, magnetic pressure due to toroidal field entrained in the E × B plasma flow from the helicity-injection gap drops, allowing resistive magnetic reconnection even though the total injected current is almost constant. Where appropriate, the simulations are compared with Transient Coaxial Helicity Injection experiments in the NSTX spherical tokamak, which have demonstrated the formation of a promising candidate for non-inductive startup plasmas [Raman et al., Phys. Rev. Lett. 90, 075005 (2003)].

  16. Note: Helical nanobelt force sensors

    SciTech Connect

    Hwang, G.; Hashimoto, H.

    2012-12-15

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 Multiplication-Sign 10{sup -10} Pa{sup -1}), low stiffness (0.03125 N/m), large-displacement capability ({approx}10 {mu}m), and good fatigue resistance, they are well suited to function as stand-alone, compact ({approx}20 {mu}m without the plug-in support), light ({approx}5 g including the plug-in support), versatile and large range ({approx}{mu}N) and high resolution ({approx}nN) force sensors.

  17. Note: Helical nanobelt force sensors

    NASA Astrophysics Data System (ADS)

    Hwang, G.; Hashimoto, H.

    2012-12-01

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10-10 Pa-1), low stiffness (0.03125 N/m), large-displacement capability (˜10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (˜20 μm without the plug-in support), light (˜5 g including the plug-in support), versatile and large range (˜μN) and high resolution (˜nN) force sensors.

  18. Note: helical nanobelt force sensors.

    PubMed

    Hwang, G; Hashimoto, H

    2012-12-01

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10(-10) Pa(-1)), low stiffness (0.03125 N/m), large-displacement capability (~10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (~20 μm without the plug-in support), light (~5 g including the plug-in support), versatile and large range (~μN) and high resolution (~nN) force sensors. PMID:23278031

  19. The persistence of equatorial spread F - an analysis on seasonal, solar activity and geomagnetic activity aspects

    NASA Astrophysics Data System (ADS)

    Sreeja, V.; Devasia, C. V.; Ravindran, Sudha; Sridharan, R.

    2009-02-01

    The persistence (duration) of Equatorial Spread F (ESF), which has significant impact on communication systems, is addressed. Its behavior during different seasons and geomagnetic activity levels under the solar maximum (2001) and minimum (2006) conditions, is reported using the data from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip 0.5° N) in India. The study reveals that the persistence of the irregularities can be estimated to a reasonable extent by knowing the post sunset F region vertical drift velocity (Vz) and the magnetic activity index Kp. Any sort of advance information on the possible persistence of the ionospheric irregularities responsible for ESF is important for understanding the scintillation morphology, and the results which form the first step in this direction are presented and discussed.

  20. Full-wave simulations on ultrashort-pulse reflectometry for helical plasmas

    SciTech Connect

    Hojo, H.; Fukuchi, A.; Itakura, A.; Mase, A.

    2004-10-01

    The full-wave simulations on ultrashort-pulse reflectometry for helical plasmas are studied based on the FDTD method in two dimensions. The propagation of an ultrashort-pulse electromagnetic wave is computed in helical plasmas modeled for the Large Helical Device magnetic field configuration. The density-profile reconstruction is performed by the Abel inversion method with the time delay data for the reflected waves from plasma, and it is shown that the reconstructed density profile coincides well with the original profile.

  1. EVOLUTION OF SPINNING AND BRAIDING HELICITY FLUXES IN SOLAR ACTIVE REGION NOAA 10930

    SciTech Connect

    Ravindra, B.; Yoshimura, Keiji; Dasso, Sergio E-mail: yosimura@solar.physics.montana.edu

    2011-12-10

    Multiplication-Sign 10{sup 43} Mx{sup 2}. The observed reversal in the sign of spinning and braiding helicity fluxes could be the signature of the emergence of a twisted flux tube, which acquires the writhe of an opposite sign. The magnetic cloud associated with the ejected mass has carried about -7 Multiplication-Sign 10{sup 41} Mx{sup 2} of helicity. A time integration of helicity flux of about 1.2 hr integrated backward in time of the observation of the coronal mass ejection is sufficient for this event.

  2. Atmosphere dynamics in the equatorial meteor zone

    NASA Technical Reports Server (NTRS)

    Kascheev, B. L.

    1987-01-01

    The study of the atmospheric circulation of the Earth from its surface to the altitudes of 100 to 110 km is essential for establishing atmospheric motion regularities with a view toward perfecting weather forecasting. The main results of the Soviet equatorial meteor expedition (SEME) are presented. A continuous cycle of measurements was carried out. Considerable interdiurnal variation of the zonal component was observed. Importantly, in the meridional component, the prevalence of a two day component was established in the equatorial meteor zone for the first time. The pronounced westward motion of the atmosphere over the equator is noted. The SEME data analysis has shown that the meteor zone is characterized by flashes of intensity of the internal gravity waves and turbulence at highest instability moments of atmosphere due to tidal motion.

  3. Metallic ions in the equatorial ionosphere

    NASA Technical Reports Server (NTRS)

    Aikin, A. C.; Goldberg, R. A.

    1972-01-01

    Four positive ion composition measurements of the equatorial E region made at Thumba, India, are presented. During the day, the major ions between 90 and 125 km are NO(+) and O2(+). A metallic ion layer centered at 92 km is observed, and found to contain Mg(+), Fe(+), Ca(+), K(+), Al(+), and Na(+) ions. The layer is explained in terms of a similarly shaped latitude distribution of neutral atoms which are photoionized and charge-exchanged with NO(+) and O2(+). Three body reactions form molecular metallic ions which are rapidly lost by dissociative ion-electron recombination. Nighttime observations show downward drifting of the metallic ion layer caused by equatorial dynamo effects. These ions react and form neutral metals which exchange charges with NO(+) and O2(+) to produce an observed depletion of those ions within the metallic ion region.

  4. Mechanical analysis and test results of 4-coil superconducting helical solenoid model

    SciTech Connect

    Yu, M.; Andreev, N.; Chlachidze, G.; Johnson, R.P.; Kashikhin, V.S.; Kashikhin, V.V.; Lamm, M.J.; Lopes, M.L.; Makarov, A.; Tartaglia, M.; Yonehara, K.; /Fermilab

    2010-01-01

    Novel configurations of helical superconducting magnets for muon beam 6D phase space cooling channels and demonstration experiments are being designed at Fermilab. Operating as needed for the beam cooling in a cryogenic environment, the helical solenoid generates longitudinal and transverse magnetic fields; meanwhile, large Lorentz forces are produced, so rigid coil support structures need to be designed. A short model of a helical solenoid (HS), consisting of four coils and supporting structures, was designed, built and tested at Fermilab. The magnetic and mechanical designs were analyzed using TOSCA and ANSYS. The supporting structures were fabricated and assembled using SSC NbTi cable. Strain gauges were utilized to monitor the deformation of the structures due to both thermal contraction and Lorentz forces. The superconducting coils were trained during the test. The model should prove the design concept, fabrication technology, and the magnet system performance.

  5. Large-scale convective instability in an electroconducting medium with small-scale helicity

    SciTech Connect

    Kopp, M. I.; Tur, A. V.; Yanovsky, V. V.

    2015-04-15

    A large-scale instability occurring in a stratified conducting medium with small-scale helicity of the velocity field and magnetic fields is detected using an asymptotic many-scale method. Such a helicity is sustained by small external sources for small Reynolds numbers. Two regimes of instability with zero and nonzero frequencies are detected. The criteria for the occurrence of large-scale instability in such a medium are formulated.

  6. A new index to monitor temporal and long-term variations of the equatorial electrojet by MAGDAS/CPMN real-time data: EE-Index

    NASA Astrophysics Data System (ADS)

    Uozumi, T.; Yumoto, K.; Kitamura, K.; Abe, S.; Kakinami, Y.; Shinohara, M.; Yoshikawa, A.; Kawano, H.; Ueno, T.; Tokunaga, T.; McNamara, D.; Ishituka, J. K.; Dutra, S. L. G.; Damtie, B.; Doumbia, V.; Obrou, O.; Rabiu, A. B.; Adimula, I. A.; Othman, M.; Fairos, M.; Otadoy, R. E. S.; Magdas Group

    2008-07-01

    A new index, EE-index (EDst, EU, and EL), is proposed to monitor temporal and long-term variations of the equatorial electrojet by using the MAGDAS/CPMN real-time data. The mean value of the H component magnetic variations observed at the nightside (LT = 18-06) MAGDAS/CPMN stations along the magnetic equatorial region is found to show variations similar to those of Dst; we defined this quantity as EDst. The EDst can be used as a proxy of Dst for the real-time and long-term geospace monitoring. By subtracting EDst from the H component data of each equatorial station, it is possible to extract the Equatorial Electrojet and Counter Electrojet components, which are defined as EU and EL, respectively.

  7. The wobbling-to-swimming transition of rotated helices

    NASA Astrophysics Data System (ADS)

    Man, Yi; Lauga, Eric

    2013-07-01

    A growing body of work aims at designing and testing micron-scale synthetic swimmers. One method, inspired by the locomotion of flagellated bacteria, consists of applying a rotating magnetic field to a rigid, helically shaped, propeller attached to a magnetic head. When the resulting device, termed an artificial bacteria flagellum, is aligned perpendicularly to the applied field, the helix rotates and the swimmer moves forward. Experimental investigation of artificial bacteria flagella shows that at low frequency of the applied field, the axis of the helix does not align perpendicularly to the field but wobbles around the helix, with an angle decreasing as the inverse of the field frequency. Using numerical computations and asymptotic analysis, we provide a theoretical explanation for this wobbling behavior. We numerically demonstrate the wobbling-to-swimming transition as a function of the helix geometry and the dimensionless Mason number which quantifies the ratio of viscous to magnetic torques. We then employ an asymptotic expansion for near-straight helices to derive an analytical estimate for the wobbling angle allowing to rationalize our computations and past experimental results. These results can help guide future design of artificial helical swimmers.

  8. Helicity and the ALPHA-EFFECT:DYNAMO Theory and Observations

    NASA Astrophysics Data System (ADS)

    Kuzanyan, Kirill M.

    The best available tracers of the alpha-effect in the solar convection zone are current helicity and twist of the photospheric magnetic fields obtained by vector magnetographic observations. Here we present results of systematic studies of the current helicity and twist of averaged over a series of solar active regions. The data analysis enables us to reveal latitudinal dependence of the effect which is antisymmetric over the solar equator. Consideration of individual rotation rates of active regions versus the solar internal differential rotation law indicates that the radial structure of the alpha-effect is likely sign-changing. These properties are in agreement with theoretical estimates and numerical simulations of flows in the solar convection zone and model assumptions of dynamo theory. The fine structure of observational signatures of the alpha-effect indicates that the magnetic field generation mainly occurs near the bottom of the convection zone. We revealed some cyclic evolution of current helicity over the solar cycle that is in accord with dynamo models under certain parameter range. Thus knowledge on the spatially-temporal structure of signatures of the alpha-effect leads to further improvement of dynamo theory in description of the mechanism of generation of solar magnetic fields.

  9. Equatorial scintillations: advances since ISEA-6

    SciTech Connect

    Not Available

    1985-01-01

    Our understanding of the morphology of equatorial scintillations has advanced due to more intensive observations at the equatorial anomaly locations in the different longitude zones. The unmistakable effect of the sunspot cycle in controlling irregularity belt width and electron concentration responsible for strong scintillation in the controlling the magnitude of scintillations has been recognized by interpreting scintillation observations inthe light of realistic models of total electron content at various longitudes. A hypothesis based on the alignment of the solar terminator with the geomagnetic flux tubes as an indicator of enhanced scintillation occurrence and another based on the influence of a transequatorial thermospheric neutral wind have been postulated to describe the observed longitudinal variation. A distinct class of equatorial irregularities known as the bottomside sinusoidal (BSS) type was identified. These irregularities occur in very large patches, sometimes in excess of several thousand kilometers in the E-W direction and are associated with frequency spread on ionograms. Scintillations caused by such irregularities exist only in the VHF band, exhibit Fresnel oscillations in intensity spectra and are found to give rise to extremely long durations (approx. several hours) of uninterrrupted scintillations.

  10. Investigation of electron beam transport in a helical undulator

    SciTech Connect

    Jeong, Y.U.; Lee, B.C.; Kim, S.K.

    1995-12-31

    Lossless transport of electrons through the undulator is essential for CW operation of the FELs driven by recirculating electrostatic accelerators. We calculate the transport ratio of an electron beam in a helical undulator by using a 3-D simulation code and compare the results with the experimental results. The energy and the current of the electron beam are 400 keV and 2 A, respectively. The 3-D distribution of the magnetic field of a practical permanent-magnet helical undulator is measured and is used in the calculations. The major parameters of the undutlator are : period = 32 mm, number of periods = 20, number of periods in adiabatic region = 3.5, magnetic field strength = 1.3 kG. The transport ratio is very sensitive to the injection condition of the electron beam such as the emittance, the diameter, the divergence, etc.. The injection motion is varied in the experiments by changing the e-gun voltage or the field strength of the focusing magnet located at the entrance of the undulator. It is confirmed experimentally and with simulations that most of the beam loss occurs at the adiabatic region of the undulator regardless of the length of the adiabatic region The effect of axial guiding magnetic field on the beam finish is investigated. According to the simulations, the increase of the strength of axial magnetic field from 0 to 1 kG results in the increase of the transport ratio from 15 % to 95%.

  11. Westward equatorial electrojet during daytime hours. [relation to geomagnetic horizontal field depression

    NASA Technical Reports Server (NTRS)

    Rastogi, R. G.

    1974-01-01

    The phenomenon of the depression of the geomagnetic horizontal field during the daytime hours of magnetically quiet days at equatorial stations is described. These events are generally seen around 0700 and 1600 LT, being more frequent during the evening than the morning hours. The evening events are more frequent during periods of low solar activity and in the longitude region of weak equatorial electrojet currents. The latitudinal extent of the phenomenon is limited to the normal equatorial electrojet region, and on some occasions the phenomenon is not seen at both stations, separated by only a few hours in longitude. During such an event, the latitudinal profile of the geomagnetic vertical field across the equator is reversed, the ionospheric drift near the equator is reversed toward the east, the q type of sporadic E layer is completely absent, and the height of the peak ionization in the F2 region is decreased. It is suggested that these effects are caused by a narrow band of current flowing westward in the E region of the ionosphere and within the latitude region of the normal equatorial electrojet, due to the reversal of the east-west electrostatic field at low latitudes.

  12. HF Radar for Long-Range Monitoring of Ionospheric Irregularities in the Equatorial Region

    NASA Astrophysics Data System (ADS)

    Pedersen, T. R.; Parris, R. T.; Dao, E. V.

    2014-12-01

    Ionospheric instabilities associated with plasma bubbles in the equatorial region are one of the major space weather impacts, creating scintillation that affects satellite communications and navigation as well as spread-F and propagation effects on lower frequency systems. Coherent scatter radars can be used to detect the presence of irregularities at a scale size corresponding to half the wavelength of the radar when the raypaths are perpendicular to the magnetic field. A number of vertical incidence radars operating in the VHF range near the magnetic equator use this effect to map out vertical irregularity structure in bubbles, while at high latitudes in both the northern and more recently southern hemisphere, HF radars in the SuperDARN network have successfully used refraction along near-horizontal paths to reach perpendicularity with the near-vertical magnetic field and map out ionospheric convection and irregularity structure over fields of view thousands of km across. In the equatorial region, perpendicularity can be obtained anywhere within a near-vertical plane even without refraction, although refraction can be used to achieve long ranges after one or more reflections from the earth's surface and bottomside ionosphere. This potentially provides a means of detecting and monitoring equatorial plasma bubbles over the oceans from long ranges using a small number of ground-based sites. We discuss the possible echoes that could be detected by such a system, the likely propagation modes and characteristics, and means of obtaining and utilizing elevation angle information to correctly locate distant plasma bubbles.

  13. A study of the equatorial signatures of long period transient events (600 - 7200 s)

    NASA Astrophysics Data System (ADS)

    Santos, J.; Dutra, S.; Trivedi, N.; Vieira, L.; Echer, E.; Schuch, N.

    Transient variations in the H magnetic field component of magnetograms at high latitude are a common feature. They are associated with energy transference from solar wind to the magnetosphere. Abrupt changes in the solar wind generate Alfvén and fast mode waves through the magnetosphere. The Alfvén wave doesn't propagate in the direction perpendicular to the geomagnetic field, so equatorial signatures are probably caused by fast mode waves. On the other hand, complicated signatures observed at high latitudes represent a composition of Alfvén and fast mode waves. A second suggested propagation mechanism to low latitudes is the Earth-ionosphere wave-guide. In this work, geomagnetic data from the Brazilian magnetic stations at Belém (BLM), Eusébio (EUS), Ji-Paraná (JIP), São luis (SLZ) and São Martinho da Serra (SMS), all located near the geomagnetic equator, are used to look for equatorial signatures of transient events with periods of 600 - 7200s. This period range includes two special types of transient variations named Traveling convection vortices (TCV) and DP2 fluctuations. We try to identify their morphological characteristics and compare with the high latitude phenomena's characteristics. Satellite data (WIND, ACE and GOES) are used to see magnetosphere signatures and solar wind and interplanetary magnetic field (IMF) conditions during the events. The main objective is try to find the contribution of each propagation mechanism of these transient events arriving at the equatorial latitudes.

  14. Helical rays in two-dimensional resonant wave conversion

    SciTech Connect

    Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

    2004-09-14

    The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.

  15. Helical rays in two-dimensional resonant wave conversion

    SciTech Connect

    Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.

    2004-12-08

    The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.

  16. Spatial and Temporal Variations of Solar Quiet Daily Sq Variation and Equatorial Electrojet Over Africa: Results From International Heliophysical Year

    NASA Astrophysics Data System (ADS)

    Rabiu, A.; Yumoto, K.; Bello, O.

    2010-12-01

    Space Environment Research Centre of Kyushu University, Japan, installed 13 units of Magnetic Data Acquisition Systems MAGDAS over Africa during the International Heliophysical Year IHY. Magnetic records from 10 stations along the African 96o Magnetic Meridian (Geographical 30o - 40o East) were examined for Solar quiet daily Sq variation in the three geomagnetic field components H, D and Z. Spatial variations of Sq in the geomagnetic components were examined. Signatures of equatorial electrojet and worldwide Sq were identified and studied in detail. H field experienced more variation within the equatorial electrojet zone. Diurnal and seasonal variations of the geomagnetic variations in the three components were discussed. Levels of inter-relationships between the Sq and its variability in the three components were statistically derived and interpreted in line with the mechanisms responsible for the variations of the geomagnetic field. Data from 2 magnetic observatories within equatorial electrojet EEJ strip and 2 stations outside the EEJ strip were employed to evaluate and study the signatures of the Equatorial electrojet over the African sector. The transient variations of the EEJ at two almost parallel axes using Lagos-Ilorin and Nairobi-Addis pairs were examined. The EEJ appear stronger in East than West Africa. The magnitudes and patterns of variation of EEJ strength along the two axes were examined for any simultaneity or otherwise of responses to ionospheric processes. The flow gradient of EEJ along the African sector was estimated and its diurnal variation studied.

  17. Majorana states in helical Shiba chains and ladders

    NASA Astrophysics Data System (ADS)

    Ojanen, Teemu; Poyhonen, Kim; Westsrom, Alex; Rontynen, Joel; Nanotheory Team

    2014-03-01

    Motivated by recent proposals to realize Majorana bound states in chains and arrays of magnetic atoms deposited on top of a superconductor, we study the topological properties of various chain structures, ladders and two-dimensional arrangements exhibiting magnetic helices. We show that magnetic domain walls where the chirality of a magnetic helix is inverted support two protected Majorana states giving rise to a tunneling conductance peak twice the height of a single Majorana state. Multiple overlapping Majorana states are protected by chiral symmetry which is present in systems exhibiting planar magnetic textures. Thus the topological properties of coupled chains exhibit nontrivial behaviour as a function of the number of chains beyond the even-odd dichotomy expected from Z2 classification. In addition, it is possible that a ladder of two or more coupled chains exhibit Majorana edge states even when decoupled chains are trivial. The authors acknowledge the Academy of Finland for support.

  18. Predictive supracolloidal helices from patchy particles

    NASA Astrophysics Data System (ADS)

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-11-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths.

  19. Predictive supracolloidal helices from patchy particles

    PubMed Central

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-01-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths. PMID:25387544

  20. Quasi-single helicity spectra in the Madison Symmetric Torus

    NASA Astrophysics Data System (ADS)

    Marrelli, L.; Martin, P.; Spizzo, G.; Franz, P.; Chapman, B. E.; Craig, D.; Sarff, J. S.; Biewer, T. M.; Prager, S. C.; Reardon, J. C.

    2002-07-01

    Evidence of a self-organized collapse towards a narrow spectrum of magnetic instabilities in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] reversed field pinch device is presented. In this collapsed state, dubbed quasi-single helicity (QSH), the spectrum of magnetic modes condenses spontaneously to one dominant mode more completely than ever before observed. The amplitudes of all but the largest of the m=1 modes decrease in QSH states. New results about thermal features of QSH spectra and the identification of global control parameters for their onset are also discussed.