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Applied Superconductivity, IEEE Transactions on

Issue 1  Part 2 • Date March 2001

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Displaying Results 1 - 25 of 298
  • Conference Author Index

    Page(s): 2638 - 2655
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    Freely Available from IEEE
  • Design considerations for force-balanced coil applied to SMES

    Page(s): 1920 - 1923
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    Strong electromagnetic force caused by high magnetic field and large coil current is a serious problem in superconducting magnetic energy storage (SMES) systems. In facing this problem, we propose the concept of force-balanced coil (FBC) which is a helical-winding toroidal coil and can reduce the centering force of toroidal field coil (TFC). The helical-winding of the FBC is modulated in order to reduce the torsional force. This paper describes the cost-related parameters of the FBC in terms of the dimension of the coil, the ampere-meters of superconductors and the surface area of the coil compared with the TFC and the solenoid. Moreover, we discuss the structure requirements by the virial theorem and improve the concept of FBC in terms of the further optimization of SMES through the structural analysis View full abstract»

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  • Superconductivity, an enabling technology for 21st century power systems?

    Page(s): 1447 - 1453
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    Several technologies based on superconductivity are moving to practical use on electric power systems. The next decade will see operational prototypes of superconducting cables, transformers, SMES, and motors installed on electric utilities in sizes that are appropriate for power distribution applications. Will these installations lead to a change in the power system of the future? Will that power system (or parts of it) look different from what we see today? Two independent and very different issues will determine the answers to these questions. The first is the future demand for electric power, both locally and worldwide. The second is the progress in superconducting materials and the subsequent development of the applications mentioned above. Several very different scenarios have been proposed for the growth and evolution of electric power in the 21st century. These scenarios will be described briefly and their implication for superconductivity will be discussed. Finally, the author predicts the likely penetration of superconducting technologies into electric power systems View full abstract»

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  • Analysis of the behaviour of superconducting windings with short-circuited turns

    Page(s): 1454 - 1457
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    Though it is widely known that short-circuited turns can considerably spoil the performance of superconducting windings, this problem (to our knowledge) was not properly discussed in the literature. We performed an analysis of the consequences of the presence of shorted turns inside superconducting windings. The main conclusions are as follows: such windings can undergo premature quenches during their charging, therefore the acceptable charging rates should be very low; such windings can also quench during their planned discharge; and a considerable amount of the stored magnetic energy cannot be effectively evacuated out of a short-circuited winding in the case of its quench View full abstract»

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  • Analysis of wire motion in a superconducting magnet by Monte Carlo method

    Page(s): 1470 - 1473
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    The wire motion in a superconducting magnet has been analyzed by means of Monte Carlo and finite element method (FEM). A sufficient analysis about the instability originated from wire motion has not been made because the wire motion is not clarified in the irregular area in the coil. The study of the wire motion has been made in the irregular area such as “step up” or “cross over” position where a wire steps up at the flanges or crosses over the wires of the lower layer. Using FEM, the stress in the coil was calculated and the boundary conditions of the irregular area were determined. In the area using Monte Carlo method, the wire motion was analyzed. It was clarified that in the irregular area the wire motion is easily generated. The frictional heating of the magnet is discussed in connection to the mechanical behavior of a coil View full abstract»

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  • A diagnosis method for properties of superconducting magnet using fast current discharge

    Page(s): 2595 - 2598
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    The authors studied a diagnosis method to investigate the properties of superconducting magnets throughout their life. The magnet current, initially held constant, is damped with a short time constant. One can evaluate the properties of the magnet using the normal voltage, which may appear during the damping phase. A bridge circuit, which can adjust both amplitude and phase with over five orders of accuracy, was developed to measure unbalance voltages. Experiments were carried out using a small solenoidal NbTi magnet. By adjusting bridge parameters and numerically processing the voltage waveform, the authors measured the normal transition voltage with the S/N ratio of over 10-4 in the damping phase. The applicability of the diagnosis method was studied in both numerical simulations and experiments View full abstract»

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  • Quench performance of Fermilab model magnets for the LHC inner triplet quadrupoles

    Page(s): 1633 - 1636
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    As part of the US LHC program to develop high gradient superconducting quadrupoles for the LHC interaction regions, a series of 2 meter long model magnets has been built and tested at Fermilab. This R&D program was used to refine the mechanical and magnetic design, optimize fabrication and assembly tooling and ensure adequate quench performance. The final design, fabrication, and assembly procedures developed in this program have produced magnets which meet the LHC requirements of operating at 215 T/m with excellent magnetic field harmonics. This paper summarizes the test results of the last five model magnets, including quench tests over several thermal cycles, and excitation current ramp rate and temperature dependence studies View full abstract»

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  • Overcurrent experiments on HTS tape and cable conductor

    Page(s): 1781 - 1784
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    Overcurrents in the power grid can have a magnitude of up to 20 times or higher than the rated current. This may cause problems and permanent damage to electrical equipment in the grid. High temperature superconducting (HTS) tapes are known to be sensitive to currents much larger than their critical current. In this light, it is important to investigate the response of HTS tapes and cable conductors to overcurrents several times the critical current. A number of experiments have been performed on HTS tapes and cable conductors, with currents up to 20 times the critical current. During overcurrent experiments, the voltage, and the temperature were measured as functions of time in order to investigate the dynamic behavior of the HTS tape and cable conductor. After each experiment, damage to the superconductors was assessed by measuring the critical current. Preliminary results show that within seconds an HTS tape (critical current=17 A) heats above room temperature with an overcurrent larger than 140 A. Similar overcurrent experiments showed that a HTS cable conductor could sustain damage with overcurrents exceeding 10 times the critical current of the cable conductor View full abstract»

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  • Quench performance and mechanical behavior of 1 m model magnet for the LHC low-beta quadrupoles at KEK

    Page(s): 1637 - 1640
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    High gradient 70 mm aperture superconducting low-beta quadrupole magnets have been developed at KEK as part of the collaboration between CERN and KEK for the Large Hadron Collider (LHC). After development of two 1 m model magnets, the third model magnet with the new coil design was built and excitation tests were completed. The third model successfully reached the design field gradient of 240 T/m and showed training memory after full thermal cycles. Other quench tests were performed and it was verified that the third model exhibited reliable quench performance and sufficient safety margin during operation View full abstract»

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  • Development of 9.5 T NbTi cryogen-free magnet

    Page(s): 2619 - 2622
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    A 9.5 T cryogen-free superconducting NbTi magnet system has been designed, constructed and tested at Cryomagnetics, Inc. The system has a horizontal Φ32 mm clear room temperature bore through the high field region. The cryostat has a compact 432 mm outside diameter by 305 mm length. The magnet system, featured high-Tc BSCCO current leads and NbTi superconducting persistent switch, and was cooled directly by a new generation pulse tube refrigerator. Tests show that the magnet generates a magnetic field up to 9.5 T with 0.1% homogeneity over a 10 mm diameter volume. The cool-down time from room temperature to operating temperature is approximately 14 hours. The magnet was charged from zero to 9.5 T In less than 10 minutes. After intentional quench at 9.2 T. the system recovered in temperature in less than 3 hours. In this paper, the design, analysis and the system test results are reported View full abstract»

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  • Mechanical design and analysis of 2-in-1 shell-type Nb3Sn dipole models for VLHC

    Page(s): 2288 - 2291
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    Fermilab has begun investigating Nb3Sn twin aperture dipole magnet designs as a next step towards the realization of high field magnets for a Very Large Hadron Collider (VLHC). The magnet design is based on two-layer shell-type Nb3Sn coils with 43.5 mm aperture. Two different mechanical designs were investigated, one with “cold” iron yoke and the other with “warm” iron yoke. The former has a vertically split three-piece iron yoke with a cut parallel to a flux line to reduce the transverse magnetic flux. The two outer halves are locked in place by aluminum clamps. Both the clamps and the stainless skin provide the required pre-stress to the coils. The “warm” iron yoke design consists of thick freestanding stainless steel collars with wide keys and an insert separating the two coil blocks. The paper presents both the mechanical design and analysis for the two designs View full abstract»

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  • The ATLAS magnet test facility at CERN

    Page(s): 1713 - 1716
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    The ATLAS magnet system consists of a barrel toroid (BT), two end-cap toroids (ECT) and a central solenoid (CS). The BT with overall dimensions of 20 m diameter by 26 m length is made of 8 coils placed in their individual cryostats and symmetrically assembled around the central axis. The ATLAS magnet test facility is being completed at CERN and will host in the next years to come pairs of BT coils at the same time as well as the ECT and the CS systems already fully assembled. Two model coils will be tested in the years 2000-2001, the B00 model coil and the B0 model coil, a 9 m short version of the BT coil built to verify the functionality and the construction concepts of the BT View full abstract»

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  • FCL location selection in large scale power system

    Page(s): 2489 - 2494
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    Maximum short circuit current of a modern power system is becoming so large that the current should be reduced to make more efficient use of power system transmission capability. The fault current limiter (FCL) is a promising solution of this problem and it can be categorized into two types: constant impedance type FCL and current limiting type FCL. Current limiting type FCL such as rectifier type superconducting FCL (RSFCL) has variable equivalent impedance depending on the limit of the current through FCL and power system impedances. In this paper, a method is proposed to incorporate RSFCL into short circuit current analysis, which is needed to evaluate the effectiveness of FCL installed in a large scale power system. Also, an efficient method to find FCL locations suitable for reduction of short circuit currents of more than one fault location is developed. The efficiency and effectiveness of these methods are shown by numerical examples View full abstract»

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  • Fault current tests of a 5-m HTS cable

    Page(s): 1785 - 1788
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    The first industrial demonstration of a three-phase, HTS power transmission cable at the Southwire manufacturing complex is in progress. One crucial issue during operation of the 30-m HTS cables is whether they can survive the fault current (which can be over an order of magnitude higher than the operating current) in the event of a short circuit fault and how HTS cables and the cryogenic system would respond. Simulated fault-current tests were performed at ORNL on a 5-m cable. This single-phase cable was constructed in the same way as the 30-m cables and is also rated for 1250 A at 7.2 kV AC line-to-ground voltage. Tests were performed with fault-current pulses of up to 15 kA (for 0.5 s) with pulse lengths of up to 5 s (at 6.8 kA). Although a large voltage drop was produced across the HTS cable during the fault-current pulse, no significant changes in the coolant temperature, pressure, or joint resistance were observed. The cable survived all 15 simulated fault-current shots without any degradation in its V-I characteristics View full abstract»

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  • Development of react and wind common coil dipoles for VLHC

    Page(s): 2172 - 2175
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    Common coil magnets are a promising option for post LAC hadron colliders. Fermilab, in collaboration with LBNL, is involved in an R&D program to develop 11 T, 30-40 mm aperture, common coil dipoles. The use of Nb3Sn wound after reaction is chosen in order to address cost reduction that is a key issue for future hadron colliders. The common coil design concept allows a large bending radius at the coil ends and is well suited to the react-and-wind technique with brittle superconductors. The horizontal component of the magnetic forces in a common coil is larger than the radial component in a shell type layout, imposing demanding requirements on the mechanical structure. Both a 2-layer and a single layer design have been studied. The development of the program is presented focusing on the mechanical designs and assembly techniques. R&D activities and plans are also presented View full abstract»

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  • Persistent current effects in BSCCO common coil dipoles

    Page(s): 2156 - 2159
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    A series of one-meter long racetrack-shaped windings has been fabricated from BSCCO tape conductors obtained from four manufacturers. Two coils were built from each conductor type and tested in the “common coil” dipole configuration in liquid helium. The effect of the remnant magnetization currents determined by measuring the residual dipole sextupole fields after cycling the magnets to progressively higher currents. Two coil sets have been measured and the results are compared to those obtained from a Nb3Sn ribbon magnet of the same geometry View full abstract»

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  • Study on designing high current density rotor windings of superconducting generator and relation of the stabilities in static and rotating conditions

    Page(s): 1458 - 1461
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    It is critically important to realize high current density superconducting rotor windings to make the superconducting generator economically competitive to a conventional one. High current density rotor windings inevitably suffer from instability problems. Therefore, the rotor windings should be designed for the quench currents to surely exceed the maximum operational currents in the rotating condition. In the next step of the Super-GM project, the current density required is 30% higher than that of the rotor winding developed in the former Super-GM project. To test the stability of the rotor windings, usually quench tests are conducted in a static and pool-cooled condition for the simplicity of the test but presently the relation between the stabilities in the static and rotating conditions is not clear. In the paper, we study what information can be obtained and how the stability in the rotating condition can be estimated from the static test. Based on this study, we investigate a method to design quench currents of high current density rotor windings to exceed a required value and discuss what level for the quench current to exceed in the static condition to satisfy the requirement in the rotating condition View full abstract»

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  • Structural design and analysis of a compact sweeper magnet for nuclear physics

    Page(s): 1721 - 1724
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    A superconducting dipole, designed for use as a sweeper magnet in nuclear physics experiments, is being constructed by the NHMFL for operation at the NSCL. The magnet operates at a peak field of 3.8 T in a 140 mm gap. A multi-particle beam enters the magnet from the upstream side. The neutrons continue straight through to a neutron detector. The charged particles are swept 40 degrees on a one-meter radius into a mass spectrometer. To allow space for the exit of the downstream neutron beam, the magnet iron and coil structure are built in a modified “C” configuration. There are two coils of “D” shape, one above and one below the beam. This configuration keeps the magnet compact and removes the need for a negative curvature side. The peak field in the winding is 6.5 T. The net force on the curved leg of a single “D” is 1.6 MN. Design of the structure to contain these forces in a superconducting magnet of such a geometry is presented along with details of stability and quench analysis, field profiles, etc View full abstract»

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  • Analysis of current after normal transition in a cable-in-conduit conductor

    Page(s): 2575 - 2578
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    When some strands carry a large current as a result of current imbalance, they may initially become normal and the current is transferred to other superconducting strands. A one-dimensional simulation code for stability and quench of a cable-in-conduit conductor is improved to study this phenomenon using an infinitely long distributed circuit model, in which the current can easily be calculated. The results show the normal zone propagation plays a significant role in the current decay. Also, they are indicated that the conductor is more stable for higher conductance but the stability of the conductor seems more important to prevent instability due to the current imbalance View full abstract»

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  • A mechanism causing an additional AC loss in a large CICC coil

    Page(s): 1860 - 1863
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    A large superconducting coil wound with cable-in-conduit (CIC) conductor caused an additional AC loss which cannot be estimated from short conductor sample test results. It was confirmed that the additional AC loss was generated by long current loops in the CIC conductor. Magnetic field decays of the loops with various long time constants were observed through Hall probes. We propose a mechanism forming the long loops. The CIC conductor is composed of several staged sub-cables. If one strand on the surface of a sub-cable contacts with the other strand on the surface of the adjacent sub-cable, the two strands must encounter each other again at LCM (least common multiplier) distance of all staged cable pitches and thereby result in forming a pair of a long loop. We traced each strand in the CIC according to a method that the sub-cables at all sub-stages rotate around a center of inertia. The long time constants were calculated and their results can explain the data measured in a large SMES coil. The proposed mechanism is effective for estimating the additional AC loss in the coil View full abstract»

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  • Improvement and evaluation of bearing stiffness in high Tc superconducting magnetic bearing

    Page(s): 1677 - 1680
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    This paper describes a new method of dynamics of passive type superconducting magnetic bearings (SMBs). In order to clarify the method, a simple experimental setup was constructed that consists of a superconductor attached to a mechanical x-stage and a permanent magnet attached to a z-stage. In the experiments, the stages were forced to move in the x and z directions to improve bearing stiffness and repulsive forces. Moreover, a simple theoretical model to explain the results is applied to the experimental setup. As a result, it is found that the improved method for SMBs is effective experimentally and theoretically View full abstract»

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  • Comparison of solenoidal and pancake model windings for a superconducting transformer

    Page(s): 1478 - 1481
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    We prepared 2 model windings from multifilamentary Bi-2223/Ag tape for a small experimental transformer and studied their electromagnetic behavior. The first winding was a solenoid consisting from 4 helically wound layers, the second one consisted of 3 double pancake coils. The outer dimensions of both types of windings were identical. We calculated the magnetic field in the space occupied by the winding and in its vicinity neglecting the magnetic properties of the tape. To study the influence of winding magnetization on the magnetic field distribution we measured the field in the vicinity of the coil and compared it with the calculated one. The relation between the electric field and the transport current in the turns of the windings was measured using several potential taps. By comparing these results with those obtained on short samples we find a way to estimate the critical current of a tape in the inhomogeneous magnetic field. AC loss of the coils was also measured and compared. Recommendations for improvements of the coil performance are presented View full abstract»

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  • Experimental study on on-line grasp of operating condition of longitudinal power system by use of SMES

    Page(s): 1924 - 1927
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    SMES (superconducting magnetic energy storage) system has excellent ability as not only an energy storage system but also a power system stabilizer, a load fluctuation compensator and so on. A new application of SMES in a power system has been proposed, that is, for on-line grasp of power system operating conditions. This paper shows the possibility and validity of the proposed application of SMES by use of a small SMES system and power system simulator of rotating machine type. The experimental system is a longitudinal four machine power system. It was confirmed the SMES can give a small power swing of known pattern without affecting operating conditions of the power system. On-line data of response due to the small power disturbance of SMES were analyzed to obtain natural frequencies and eigenvectors of the power system operated. The power system operating condition was estimated by these data. This application can be easily used with a SMES of small size View full abstract»

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  • Nonlinear current-voltage characteristics of HTS conductor and its application to the operation of SFCL

    Page(s): 1940 - 1943
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    A proper description of the nonlinear voltage-current relation of the superconductor is necessary for accurate analysis of the superconducting fault current limiters (SFCL). Discrepancies between the experimental results and the prediction of Bean's critical state model were observed. Using a recently found unified nonlinear response function of type-II superconductors, the authors derive the current-voltage characteristic of metal-sheathed HTS conductor and compare it with experiments. Its relation to the operation of SFCL is also discussed View full abstract»

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  • AC loss properties of a 1 MVA single-phase HTS power transformer

    Page(s): 1482 - 1485
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    We designed and built a single-phase 1 MVA-22/6.9 kV HTS transformer with the multi-layered cylindrical windings composed of Bi2223 parallel conductors. In advance of the design, the AC loss induced in the windings was estimated on the basis of the observed results in a strand. A subcooled liquid nitrogen cryogenic system with the corresponding cooling capacity was developed and attached to the transformer. The actual AC loss was measured by an electrical method. It was a great part of the total heat load and dominated the temperature rise of subcooled liquid nitrogen. We discussed the validity of the present estimation procedure of the AC loss in the windings as compared with the observed results View full abstract»

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Aims & Scope

IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Meet Our Editors

Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde