Dipole Windings Research Articles

Early Optical Observations of GRB 150910A: Bright Jet Optical Afterglow and X-Ray Dipole Radiation from a Magnetar Central Engine

Abstract Gamma-ray burst (GRB) 150910A was detected by Swift/Burst Alert Telescope (BAT), and then rapidly observed by Swift/XRT, Swift/Ultraviolet-Optical Telescope, and ground-based telescopes. We report Lick Observatory spectroscopic and photometric observations of GRB 150910A, and we investigate the physical origins of both the optical and X-ray afterglows, incorporating data obtained with BAT and XRT. The light curves show that the jet-emission episode lasts ∼360 s with a sharp pulse from BAT to XRT (Episode I). In Episode II, the optical emission has a smooth onset bump followed by a normal decay (α R,2 ≈ −1.36), as predicted in the standard external shock model, while the X-ray emission exhibits a plateau (α X,1 ≈ −0.36) followed by a steep decay (α X,2 ≈ −2.12). The light curves show obvious chromatic behavior with an excess in the X-ray flux. Our results suggest that GRB 150910A is an unusual GRB driven by a newly born magnetar with its extremely energetic magnetic dipole (MD) wind in Episode II, which overwhelmingly dominates the observed early X-ray plateau. The radiative efficiency of the jet prompt emission is η γ ≈ 11%. The MD wind emission was detected in both the BAT and XRT bands, making it the brightest among the current sample of MD winds seen by XRT. We infer the initial spin period (P 0) and the surface polar cap magnetic field strength (B p ) of the magnetar as 1.02 × 1015 G ≤ B p ≤ 1.80 × 1015 G and 1 ms ≤ P 0 v ≤ 1.77 ms, and the radiative efficiency of the wind is η w ≥ 32%.

Mesoscale Analysis on the Asymmetric Rainband of Typhoon Matmo (2014) and the Related Weather Situations for the GE222 Aircraft Crash Case

Typhoon Matmo (2014) was formed over the Central Pacific Ocean on 18 July 2014, and later, it became moderate in intensity (32.7~50.9 m/s) with maximum wind speed of 38 m/s. After it landed the southeast coast of China, the typhoon circulation showed an asymmetric pattern in dipole wind field based upon the composite mean winds at 925 hPa in use of NCEP/NCAR reanalysis data and NOAA/ESRL atmospheric variables plotting approach. The wind dipole feature was due to the steep gradient of the geopotential height anomaly at the east flank of the typhoon circulation and the friction effect at its lowest levels over land from the synoptic scale point of view. The study focuses on investigating the characteristics of the line echo wave pattern (LEWP) embedded within the typhoon rainband through the multi-scale processes, and try to realize the possible causes of crash event from the meteorological point of view for TransAsia Airways GE222 occurrence at Makung Airport influenced by the LEWPs in use of mesonet surface analysis based on 1-minute interval data measured by Makung Airport weather station and dual-Doppler radar analysis composited from Makung and Chiku weather radar data. The preliminary results delineated that the wave-like echoes organized by deep convections featured a key factor on the development of short duration heavy rainfall, low visibility and significant turbulence from the mesoscale point of view. Conclusively speaking, the aircraft faced multiple and severe weather situations, including the intense crosswind, obvious downdraft and extremely low visibility. Therefore, the impact of deep convections inside LEWPs embedded within the typhoon rainband on aviation safety was remarkable, and this case is a good lesson for flight safety.

Superconducting Magnet Performance for the LCLS-II Project

The new LCLS-II Superconducting Linear Accelerator Cryomodules are under construction at Fermilab. Installed inside each Super Conducting Radio Frequency (SCRF) Cryomodule is a superconducting magnet package to focus and steer an electron beam. The iron-dominated magnet package has conductively cooled racetrack-type coils with both quadrupole and dipole windings. For ease of installation, the magnet is splittable in the vertical plane. To confirm magnet specifications, we performed a quality acceptance in a liquid helium bath for quench testing, and we performed high-precision magnetic field measurements. The magnetic and mechanical center alignment was investigated using the vibrating wire technique. Several prototypes and all production units have been tested. This paper summarizes the magnetic measurements and quench test results of all tested units, including comparison of performance and repeatability between different units.

Formation and Dynamics of a Long-Lived Eddy Train in the South China Sea: A Modeling Study

AbstractA process-oriented numerical modeling study was conducted to investigate the formation and underlying forcing of an anticyclonic eddy train observed in the northern South China Sea. Observations showed that long-lived anticyclonic eddies formed an eddy train along an eastward separated jet across the northern South China Sea in summer. The eddy train plays a critical role in regulating ocean circulation in the region. Forced by the southwesterly monsoon and prevailing dipole wind stress curl in the summer, the northward coastal jet separates from the west boundary of the South China Sea basin and overshoots northeastward into the basin. The anticyclonic recirculation of the separated jet forms the first anticyclonic eddy in the eddy train. The jet meanders downstream with a strong negative shear vorticity that forms a second and a third anticyclonic eddy along the jet’s path. These three eddies form the eddy train. These eddies weaken gradually with depth from surface, but they can extend to approximately 500 m deep. The inherent stratification in the region regulates the three-dimensional scale of the anticyclonic eddies and constrains their intensity vertical extension by weakening the geostrophic balance within these eddies. Analyses of the vorticity balance indicate that the eddy train’s negative vorticity originates from the beta effect of northward western boundary current and from the subsequent downstream vorticity advection in the jet. The jet separation is a necessary condition for the formation of the eddy train, and the enhanced stratification, increased summer wind stress, and associated negative wind stress curl are favorable conditions for the formation of the anticyclonic eddies.

Summer Arctic dipole wind pattern affects the winter Siberian High

This study investigates the relationship between the summer [June–July–August (JJA)] Arctic dipole wind pattern and the following winter [December–January–February (DJF)] Siberian High. It is found that the summer Arctic dipole wind pattern is not confined only to the Arctic region; it spans the large domain north of 20°N. The negative phase of this wind pattern depicts an anomalous anticyclone over the Arctic Ocean and its marginal seas, except for the Barents-Kara seas where an anomalous cyclone is dominant. This wind pattern is significantly correlated with the strength of the Siberian High during the following winter and with the frequency of extreme cold events over East Asia during the winters of 1979–2014. The relationship of this wind pattern with the winter Siberian High has strengthened over the past decades, particularly since the late 1980s. The more robust relationship coincides with significant changes in the winter atmospheric circulation and frequent occurrences of the negative phase of this wind pattern, which dynamically contributes to low September sea ice extent. The present study's results suggest that autumn Arctic sea ice provides a link between this wind pattern and climate variability over East Asia during the following winter. Results of simulation experiments suggest that (1) autumn sea ice loss favors the occurrence of a stronger East Asian winter monsoon; (2) the summer Arctic dipole wind pattern modulates winter atmospheric responses to sea ice loss, and the negative phase of this wind pattern enhances the negative feedback of Arctic sea ice loss on winter atmospheric variability over Eurasia and North America. These simulation experiments also imply that complex and varying summer circulation patterns obscure linkages between sea ice loss and large-scale circulation responses over Eurasia. Isolation of the summer Arctic dipole wind pattern, however, provides a potential precursor for the seasonal prediction of winter surface air temperature in a populous region of the world.

Performance of Conduction Cooled Splittable Superconducting Magnet Package for Linear Accelerators

New linear superconducting accelerators need superconducting magnet packages installed inside SCRF cryomodules to focus and steer electron or proton beams. A superconducting magnet package was designed and built as a collaborative effort of FNAL and KEK. The magnet package includes one quadrupole and two dipole windings. It has a splittable in the vertical plane configuration and features for conduction cooling. The magnet was successfully tested at room temperature, in a liquid He bath, and in a conduction cooling experiment. This paper describes the design and test results, including magnet cooling, training, and magnetic measurements by rotational coils. The effects of superconductor and iron yoke magnetization, hysteresis, and fringe fields are discussed.

Optimization of the Sextupole Magnets With Trim Coils for the Collector Ring of the FAIR Project

The collector ring (CR) is a part of the challenging international project facility for antiproton and ion research started in Darmstadt, Germany. The ion optics of the CR includes sextupole magnets with embedded dipole correction coils. To fulfill the requirements of the field quality in the magnet aperture, it is necessary to find an optimal pole tip shape as well as an optimal configuration of the coil system. We used a specially developed optimization procedure for designing the magnet cross section. This procedure consists of two steps. The first one is based on a representation of the pole border line by a superposition of hyperbolic functions corresponding to different Fourier components of the magnetic field expansion. The optimization procedure based on the Newton–Raphson descend algorithm minimizes amplitudes of the undesired field harmonics. At the second step of the magnet design procedure, the parameters of the dipole winding are optimized to provide the required field characteristics in the magnet aperture.

Design of a <formula formulatype="inline"><tex Notation="TeX">$\hbox{MgB}_{2}$</tex></formula> Beam Transport Channel for a Strong-Focusing Cyclotron

A superconducting strong-focusing cyclotron is being developed for high current applications. Alternating-gradient focusing is provided by ~ 6 T/m superconducting beam transport channels which lie in the sectors along the arced beam trajectory of each orbit of the cyclotron. The ~ 1 T sector dipoles, corrector dipoles, and Panofsky type quadrupoles utilize MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductor operating around 15-20 K. The operating temperature provides a valuable margin for a cost-effective cryogenic design, and large thermal stability in the event of occasional heat loads from intercepted beam or other sources. The main dipole windings are designed with sufficiently large curvature so that they can be fabricated using react-and-wind procedure; the quadrupole windings require small-radius end bends and so must be fabricated using wind-and-react procedure. Initial magnetic modeling on the end field region is presented.

Oscillating supertubes and neutral rotating black hole microstates

The construction of neutral black hole microstates is an important problem, with implications for the information paradox. In this paper we conjecture a construction of non-supersymmetric supergravity solutions describing D-brane configurations which carry mass and angular momentum, but no other conserved charges. We first study a classical string solution which locally carries dipole winding and momentum charges in two compact directions, but globally carries no net winding or momentum charge. We investigate its backreaction in the D1-D5 duality frame, where this object becomes a supertube which locally carries oscillating dipole D1-D5 and NS1-NS5 charges, and again carries no net charge. In the limit of an infinite straight supertube, we find an exact supergravity solution describing this object. We conjecture that a similar construction may be carried out based on a class of two-charge non-supersymmetric D1-D5 solutions. These results are a step towards demonstrating how neutral black hole microstates may be constructed in string theory.

Winter Weather Patterns over Northern Eurasia and Arctic Sea Ice Loss

Abstract Using NCEP–NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) winter daily (1 December–28 February) data for the period 1979–2012, this paper reveals the leading pattern of winter daily 850-hPa wind variability over northern Eurasia from a dynamic perspective. The results show that the leading pattern accounts for 18% of the total anomalous kinetic energy and consists of two subpatterns: the dipole and the tripole wind patterns. The dipole wind pattern does not exhibit any apparent trend. The tripole wind pattern, however, has displayed significant trends since the late 1980s. The negative phase of the tripole wind pattern corresponds to an anomalous anticyclone over northern Eurasia during winter, as well as two anomalous cyclones occurring over southern Europe and in the mid- to high latitudes of East Asia. These anomalous cyclones in turn lead to enhanced winter precipitation in these two regions, as well as negative surface temperature anomalies over the mid- to high latitudes of Asia. The intensity of the tripole wind pattern and the frequency of its extreme negative phase are significantly correlated with autumn Arctic sea ice anomalies. Simulation experiments further demonstrate that the winter atmospheric response to Arctic sea ice decrease is dynamically consistent with the observed trend in the tripole wind pattern over the past 24 winters, which is one of the causes of the observed declining winter surface air temperature trend over Central and East Asia. The results of this study also imply that East Asia may experience more frequent and/or intense winter extreme weather events in association with the loss of Arctic sea ice.

A dipole wind curl pattern induced by Taiwan Island and its effect on upper stratification in the northeastern South China Sea

Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean responses to orographically induced dipole wind stress curl (WSC). Results indicate that mixed-layer depth (MLD) and its relationship with thermocline depth varied under different local wind forcings. Average MLD along the transects from the 2004 to 2007 cruises were 18.5, 30.7, 39.2 and 24.5 m, respectively. The MLD along the transects deepened remarkably and resulted in thermocline ventilation in 2005 and 2006, whereas ventilation did not occur in 2004 and 2007. Estimates indicate that frictional wind speed was the major factor in MLD variations. To a large degree, the combined effects of frictional wind speed and Ekman pumping are responsible for the spatial pattern of MLD during the cruises.

Current separation and upwelling over the southeast shelf of Vietnam in the South China Sea

The high‐resolution, unstructured grid Finite‐Volume Community Ocean Model (FVCOM) was used to examine the physical mechanisms that cause current separation and upwelling over the southeast shelf of Vietnam in the South China Sea (SCS). Process‐oriented experiments suggest that the southwesterly monsoon wind is a key physical mechanism for upwelling in that area but not a prerequisite to cause current separation. With no wind forcing, current separation in summer can occur as a result of the encounter of a southward along‐shelf coastal current from the north and northeastward buoyancy‐driven and stratified tidal‐rectified currents from the southwest. The southward current can be traced upstream to the Hong River in the Gulf of Tonkin. This current is dominated by semigeostrophic dynamics and is mostly confined to the narrow shelf along the northern Vietnamese coast. The northeastward currents are generated by tidal rectification and are intensified by the Mekong River discharge and southwesterly monsoon wind forcing. The dynamics controlling this current are fully nonlinear, with significant contributions from advection and vertical turbulent mixing. Upwelling in the current separation zone can be produced by a spatially uniform constant wind field and can be explained using simple wind‐induced Ekman transport theory. This finding differs from previous theory in which the regional dipole wind stress curl is claimed as a key mechanism for current separation and upwelling in this coastal region. Our SCS FVCOM, driven by the wind stress, river discharge, and tides, is capable of reproducing the location and tongue‐like offshore distribution of temperature as those seen in satellite‐derived sea surface temperature imagery.

Self‐limiting feedback between baroclinic waves and a NAO‐like sheared zonal flow

The eddy‐mean flow interaction associated with the North Atlantic Oscillation (NAO) is examined by using the baroclinic wave life cycle experiments. When a sheared zonal flow perturbation akin to the NAO‐related dipole wind anomaly is added to the basic state, momentum fluxes due to baroclinic waves tend to reinforce the initial zonal flow dipole in the upper troposphere both for the anticyclonic and cyclonic shears. The eddy feedback is stronger for the anticyclonic shear because the node of the dipole flow is asymmetric about the basic jet, suggesting that the positive NAO is more favored by the eddy feedback. For the zonal wind anomaly with extremely large amplitude, the baroclinic wave breaking cannot efficiently intensify the zonal flow dipole, indicating a self‐limitation in the positive eddy feedback to the NAO‐like zonal flow anomaly.

An Evaluation of the Helical Winding Method Applied to the Next European Dipole Project

The Next European Dipole (NED) Collaboration is working to develop the technology of high field, dipole magnets for a future luminosity upgrade of the LHC at CERN. The challenge is to design and build a short prototype, large aperture (88 mm), dipole magnet to operate at 15 T using conductors. While the baseline design uses a cosine- winding configuration, a key part of the NED program has been the evaluation of other winding configurations. This paper reports on an evaluation of the helical dipole winding method and its applicability to the high field, large aperture magnets required for NED. The paper describes the development of magnetic models using the OPERA3D code. These models have been used to assess the field homogeneity, peak field performance, forces and conductor efficiency of the helical winding. The parameters developed from this analysis are compared with cosine- models. A conceptual winding geometry is presented and evaluated.

Superconducting Double Dipole High Field Magnet

Recent progress in Nb3Sn superconductor technology provides the base for increasing magnet field in accelerator magnets up to 15-16 T. The work on such magnets based on both block-type and shell-type coils are in progress at Fermilab, LBNL and elsewhere. One of the novel approaches to the design of this magnet is to split the magnet winding into two separate dipole windings powered in series or separately. Each winding generates a homogeneous magnetic field in the magnet aperture. The paper presents conceptual magnetic and mechanical designs of 15 T double dipole magnets and discusses several scenarios of magnet powering. The inner dipole winding is based on the 2-layer Nb3Sn coils previously developed and tested at Fermilab. The outer dipole winding is made of sub-sized Nb3Sn cable and has about two times higher current density. Both windings have the shell-type configuration. For the different powering scenarios the results of calculation of the field quality, coil magnetization effects, and the stress analysis are presented

Induced axial oscillations in superconducting dipole windings

When superconducting accelerator magnets wound from a multi-stranded conductor are energized, a periodic variation appears in the magnetic field along the axis. This oscillation is present in all components of the field and has a period that is equal to the transposition pitch of the superconducting cable. Such axial variations have been observed even in windings which are not carrying any transport current. A magnetic field was applied to a portion of a dipole winding using a second magnet. Axial oscillations were induced along the total length of the windings including the portion not in the applied field. The amplitude of these oscillations varied with the amount of inert winding inside the energizing magnet and with the angle of the applied field. These field variations could be completely eliminated in the external portion of the coil by heating a small section of the winding above the transition temperature. >

Persistent currents in LHC magnets

The field errors due to persistent currents in LHC (Large Hadron Collider) dipoles, quadrupoles, and correction windings are discussed. The errors due to variations in the magnetization are shown to be significant. The author discusses the influence of magnetic cycling, the contribution of the different parts of the dipole winding, and simple scaling with coil radius and field. The partial cancellation of the sextupole and decapole in the different winding regions indicates that an effort should be made to study other coil geometries. The calculations made show the importance of using magnet poles with the same magnetization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sextupole Correction Coils for SSC Model Dipoles

Local correction of the sextupole error field is proposed for the dipoles of the SSC. This requirement is imposed on the design by the high field quality required both during injection at low fields and during colliding beam operation at high fields. Error fields in the main dipole windings due to superconductor magnetization and conductor misplacements add unwanted sextupole and decapole magnetic field terms. To correct the sextupole error field we have constructed sextupole coils made of a single layer of superconducting wire and have mounted them with high precision on the stainless steel bore tube. These correction coils have been operated with 1 meter long SSC model dipoles in both the self-powered and externally-powered modes. The sextupole field in the bore has been reduced by as much as a factor of 50. The level of correction depends strongly on the angular alignment of the correction coil with respect to the sextupole error field it is to correct. Results of tests, performance of the correction coils and alignment requirements for the system are presented.

Maximum Field Capability of Energy Saver Superconducting Magnets

At an energy of 1 TeV the superconducting cable in the Energy Saver dipole magnets will be operating at ca. 96% of its nominal short sample limit; the corresponding number in the quadrupole magnets will be 81%. All magnets for the Saver are individually tested for maximum current capability under two modes of operation; some 900 dipoles and 275 quadrupoles have now been measured. The dipole winding is composed of four individually wound coils which in general come from four different reels of cable. As part of the magnet fabrication quality control a short piece of cable from both ends of each reel has its critical current measured at 5T and 4.3K. In this paper the authors describe and present the statistical results of the maximum field tests (including quench and cycle) on Saver dipole and quadrupole magnets and explore the correlation of these tests with cable critical current.

A Low Power Magnetic Channel with Dipole Compensation

A magnetic channel capable of guiding deflected 60 MeV protons through the fringing field of an AVF cyclotron without perturbing inner orbits, has been tested in a 0.394 scale model. The full scale channel will be composed of a 1010 steel cylindrical shell 3.00 in. O. D., 1.18 in. I.D., and 10 in. long with an external dipole winding extending to 5.92 in. O.D. A cosinoidal distribution of current density is approximated by dividing the winding into 16 sections, with centers about 22.5° apart, and by making N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sub> o = N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> cos θ, where N is the number of turns in a section and θ is the altitude angle of the center of a section. Scaling the model measurements to full size, the power is 14 kW with 3/8 in. square O.D. and 1/8 in. round I.D. water-cooled copper conductors at 330 A, and the field at the midpoint inside the channel is reduced from 7000 to 90 G, with a 20 G/in. gradient across the channel opening on the median plane. As close as 5 in. from the outside edge of the coil, the first harmonic introduced is 1.1 G. Without dipole current, the field in the channel is 1560 G with a 16.2 G first harmonic, at the same distance.