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Magnetics, IEEE Transactions on

Issue 3 • Date May 1983

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Displaying Results 1 - 25 of 322
  • [Front cover and table of contents]

    Page(s): 0
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  • Editorial

    Page(s): 156 - 157
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    Freely Available from IEEE
  • Chairman's comments

    Page(s): 160
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  • Status and trends of S.C. magnet development in Europe

    Page(s): 167 - 178
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    Many applications of s.c. magnets have been proposed and considered during the last decade. They may be classified into three catagories: S.c. magnets as research tools in particle and solid state physics, in energy technology, and for various industrial applications. All these are still pursued in Europe but a considerable shift in effort to specific projects has occurred during the last decade. Some main projects are discussed: beam line magnets for new particle accelerators, high field magnets including hybrid magnets, s.c. magnets for fusion devices such as the Large Coil Project or Tore-Supra, and s.c. magnets for NMR devices or magnetic separation of weak magnetic materials. The main trend is towards very high fields and magnets with large field volume. Both are extremely challenging for improving the conductor and magnet performance with respect to stable and non-degrading operation under mechanical load conditions. Developments in the focus of present interest are improvement of the stress-strain behaviour of Nb3Sn conductors and operation of magnets with subcooled helium. In addition, engineering and computations to predict mechanical performance are getting more and more important. View full abstract»

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  • Superconducting magnet development in Japan

    Page(s): 179 - 188
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    The present state of R & D works on the superconducting magnet and its applications in Japan are presented. On electrical rotating machines, 30 MVA superconducting synchronous rotary condenser (Mitsubishi and Fuji) and 50 MVA generator are under construction. Two ways of ship propulsion by superconducting magnets are developing. A superconducting magnetically levitated and linear motor propelled train "MAGLEV" has developed by the Japan National Railways (JNR). A large scale test track of 7 Km was constructed in Kyushu and the test vehicle reached its target speed of 517 Km/hr. The first manned test running was made by three-vehicles train on new U-shaped guideway. The superconducting magnet development for fusion is the most active field in Japan. The Cluster Test program has beer demonstrated on a 10 T Nb3Sn coil and the first coil of Large Coil Task in IEA collaboration has been constructed and the domestic test was completed in JAERI. These works are for the development of toroidal coils of the next generation tokamak machine. R & D works on superconducting ohmic heating coil are in progress in JAERI and ETL. The latter group has constructed 3.8 MJ pulsed coil. A high ramp rate of changing field in pulsed magnet, 200 T/s, has been tested successfully, for burning tokamak device project in IPP, by joint work of Nihon University, ETL, Mitsubishi and IPP. High Energy Physics Laboratory (KEK) are conducting active works. The superconducting μ meson channel and π meson channel have been constructed and are operating successfully. KEK has also a project of big accelerator named "TRISTAN", which is similar to ISABELLE project of BNL. Superconducting synchrotron magnets are developed for this project. The development of superconducting three thin wall solenoid has been started. One of them, CDF, is progressing under USA-Japan collaboration. View full abstract»

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  • Status reports on ISABELLE magnets

    Page(s): 189 - 194
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    The design of the ISABELLE "Palmer" magnets is described. The performance of thirteen such magnets is reported. Average quench fields of 55 kG at 4.5°K have been obtained with essentially no training. The magnets can be shown to be limited only by the short sample characteristics of the cable. Required field quality was achieved in the last four magnets. View full abstract»

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  • Status of the energy saver

    Page(s): 195 - 197
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    The one-TeV proton synchrotron which has been under construction at Fermilab is nearly complete and is now entering the commissioning phase. The assembly and testing of the ring of more than 1000 superconducting magnets with its associated cryogenic, vacuum, power, R.F., controls and safety systems has gone extremely well. View full abstract»

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  • Dipole magnet development in Japan

    Page(s): 198 - 203
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    Recent development of superconducting accelerator dipole magnets in Japan is described. A series of NbTi/Cu dipoles in the region of 5 to 10 T is being developed at KEK. The maximum field will depend on the maximum proton energy of the TRISTAN ring from 300 to 600 GeV. On the other hand, development of a special Nb3Sn/Cu dipole magnet in the region of 10 T has been started for the future multi-TeV pp andbar{p}pcolliding beam accelerator. View full abstract»

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  • Mo base superconducting materials prepared by multi-target reactive sputtering

    Page(s): 204 - 207
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    With an aim of developing new types of superconducting materials, Mo-N films and Mo/Si multi-layered films were fabricated by reactive and two-target sputtering methods, respectively. The superconducting properties such as Tc, Hc2and Jcwere examined. The crystal structure of Mo-N films changed from bcc to fcc with increasing N2gas flow rate during sputtering and a homogeneous fcc Mo2N superconductor was obtained. On the other hand, the superconducting characteristics of the Mo/Si multi-layered film with a layer spacing 32.3 Å were confirmed to be similar to those of amorphous Mo-Si alloys except the occurrence of anisotropic vortex pinning. View full abstract»

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  • Effect of rapid quenching and with Carbon and Nitrogen on the structure and superconducting properties of the Nb3Ge compound

    Page(s): 208 - 211
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    The effect of rapid quenching and alloying with carbon and nitrogen on the superconducting properties of the Nb3Ge compound has been studied. The quantitative phase X-ray analysis of the studied specimens depending on the content of alloying components has been carried out. The temperature at which the transition into the superconducting state occurs as well the parameters of the alloy lattices have been investigated. View full abstract»

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  • Quenches of formvar - coated NbTi/Cu caused by step input in power

    Page(s): 212 - 215
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    We have investigated the stability of the composite Nb48Ti/Cu coated with a formvar layer (30 μm thick). Starting from thermal equilibrium in the superfluid liquid He II range below the lambda temperature (T = Tλ), the composite temperature is found to rise first monotonically with time t, upon onset of energy dissipation. However, restricted stability is visible as a relative temperature maximum (Tmax) of the composite at the time tmax, followed by a relative minimum in T at tmin. These coated composite phenomena are similar to stability conditions of bare composites in the same "conductor-in-box " geometry employed. However at a specified power the times tmaxand tminare shifted in comparison to the bare composite. Diagnosis is based on power-time functions whose tangents are characterized by power law exponents (m) . The m-values found are re - presentative of strong, localized solid - coolant interaction, of a caloric condition, or of locally turbulent fluid motion. In the range covered by the present transients, stability is available by creation of entropy - rich buffer domains of fluid, below the superconducting transition temperature, between He II and the heated composite. The latter is quench - protected in an intermediate power range. View full abstract»

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  • An attempt to reduce training using filled epoxy as an impregnating material

    Page(s): 216 - 219
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    Selection of impregnating materials has been made in order to reduce training of superconducting magnets based on their mechanical and/or thermal properties. Race track shaped coils which are assumed to show marked training, are impregnated with several materials and energized. Epoxy resin filled with alumina powder is found to show superior behavior to those of wax or epoxy resin itself as an impregnating materials. View full abstract»

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  • Computer analysis of transient heat transfer from coated surfaces

    Page(s): 220 - 223
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    The transient thermal response of internally heated, coated surfaces in contact with liquid helium was investigated with a previously developed computer model. The coatings were found to affect the time required to initiate film boiling or to quench a superconductor in the substrate. The energy which can be absorbed without an unacceptably large temperature rise depends most strongly upon the coating thermal property group (kpCp)½and on the peak nucleate boiling heat flux. Dielectric materials for electrical insulation usually have low thermal property group values, but a new class of ceramic materials shows great promise for application with superconducting devices aselectrical insulations with good thermal properties. Coating materials with thermal property group values greater than that of OFHC copper at liquid helium temperatures provide the same thermal stability as a bare copper surface exposed to the helium bath. Possible applications of the new materials to potted windings are also discussed. View full abstract»

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  • Nb3Sn-composite conductors with Aluminum as electrical stabilizer and stainless steel as mechanical reinforcement

    Page(s): 224 - 227
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    Three-component conductors composed of a preheat-treated Nb3Sn flat cable, aluminium, and stainless steel were soldered together in a straight alignment and then wound in a single-layer coil with a diameter of 90 mm. The performance of the composite conductor was determined mainly by the position of the steel, because the steel shifts the neutral plane considerably due to its high modulus of elasticity and can generate high compressive forces on the Nb3Sn with a consequent reduction of critical current density. The aluminum stabilizer developed its full stabilizing performance only in close contact with the superconductor, because resistive layers between them cause partial resistivity in the superconductor. View full abstract»

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  • Oxygen-free Copper at 4 K: Resistance and magnetoresistance

    Page(s): 228 - 231
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    Oxygen-free copper is the most common material used for stabilizing practical superconductors. This type of copper may show residual resistance ratios (RRR) that vary from 50 to 700 in the full soft condition. Knowledge of the exact RRR value is often essential for optimum system design. We have investigated the effect of stress, temper, and reanneal on the RRR and magnetoresistance of several hundred samples of oxygen-free copper from many sources. In this paper we describe the program and present a sampling of the results obtained to date. View full abstract»

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  • Origination and oscillations of normal zone in superconductors

    Page(s): 236 - 239
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    Dynamics of normal (N) zone regions (resistive domains) in uniform and nonuniform superconductors has been investigated both theoretically and experimentally. An analytical theory has been proposed to describe the resistive domains (RD) dynamics in nonuniform superconductors with the alternating current. The origination and localization of RD have been considered. The self-exited relaxation oscillations of the voltage were observed experimentally. The oscillations are due to the self-exited ones of the RD length when the inductance of the circuit is large enough. The superconducting sample in our experiment was made from the multifilament Nb-40%Ti cable, the characteristic values of the oscillations frequency f and the inductance L were of the order of 1 Hz and 20 μH respectively. The theory proposed is in a good agreement with the experiment. View full abstract»

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  • Normal zone stationary distribution in superconducting composites with contact resistance

    Page(s): 232 - 235
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    Heat and electrical contact resistances exist in composite superconductors between the normal metal and the superconductor in most cases. Frequently by some reasons these resistances are high enough. It is shown in this paper that in composite superconductors with noticeable contact resistance the existence of the resistive regions of finite size is possible. Such regions (resistive domains) are stable in the regime of fixed current and the temperature and the current density are non-uniform in the cross-section of the composite superconductor in the vicinity of the resistive domain. We find the I-V characteristic of a sample with a resistive domain and the minimum domain existence current ir. It is shown that the current iris much less than the minimum normal zone propagation current ip. We investigate the process of the resistive domain formation due to the heat pulse. Note that the resistive domains are unstable in the regime of fixed current in uniform composite superconductors without the contact resistance and are stable in non-uniform ones. The existence of the stable resistive domains largely regulates the process of the superconductivity destruction and the following recovery of the superconductivity in the presence of the transport current. Moreover the resistive domains existence is responsible for some hysteresis phenomena accompanying the superconductivity destruction and recovery. Some previous results were published in the short note. View full abstract»

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  • Current-carrying capacity of composite superconductors

    Page(s): 240 - 243
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    The maximum transport current Imof the composite superconductors is investigated both theoretically and experimentally. It is shown that the high values of the transport current observed in these materials is due to the non-linear part of the current-voltage characteristic in the range of low electric fields (E lsim 10^{-6}Vcm-1). The conductors of rather different structure with Nb-Ti superconducting filaments were tested in a wide range of the external parameters. It is shown that in the external magnetic fieldsB_{a} gsim 1 Tthe ratio Im/Ic(where Icis the critical current) is the universal function of the single dimensionless parameter which depends on the sample properties and the external conditions. The theory and experiment are in a good agreement. View full abstract»

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  • The effect of field orientation on current transfer in multifilamentary superconductors

    Page(s): 244 - 247
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    Experimental data and discussion are presented on the current distribution along the length of a superconducting wire when subjected to multiple parallel and perpendicular magnetic fields. The experimental data were taken on a rectangular pancake coil with the applied magnetic field in the plane of the coil. These data indicate that significant current transfer occurs in the first and last perpendicular magnetic field sections and little transfer occurs between these two sections. The implication for superconducting magnet design will also be discussed. View full abstract»

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  • A low loss NbTi multifilamentary composite conductor for A.C. use

    Page(s): 248 - 251
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    Investigations of a.c. losses and stability of a mixed-matrix NbTi multifilamentary conductor are presented. Fine filament size of 1.0 μm and a tight twist of 5.5 times the wire diameter 0.2 mm result in a time constant of the eddy current of 0.024 msec at 1.0 T. If this conductor is used in superconducting armature windings of rotating machines or in a.c. magnets, generating a maximum field of 1.0 T, economical benefits are expected at operation frequencies below 20 Hz. View full abstract»

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  • Selffield losses and selffield stability of superconducting wires with low conductivity matrix material

    Page(s): 252 - 255
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    The influence of the normal material in a superconducting wire on the selffield losses has been investigated. The results show that the contribution of the normal material is considerable in the case of a highly conductive material like Cu. Measurements on wires with CuNi-material show no significant contribution of the normal material to the losses. In the latter case, however, special attention should be paid to stability. Measurements show that the obtainable maximum current under a.c. conditions obeys the adiabatic stability criterion rather well. The dependence of the maximum current amplitude on the critical current density and the diameter of the wire has been obtained. Wires with Al cores inside the NbTi filaments for better stabilization have also been investigated regarding maximum current and selffield losses. View full abstract»

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  • Reduction of A.C. losses by decrease of the surface barrier

    Page(s): 256 - 260
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    We report on an extensive computational investigation of the effect of the surface barrier on hysteresis losses. These model calculations reveal that the losses can be substantially diminished by lowering the height of the surface barrier. The calculations were carried out for planar (ribbon) and for cylindrical (wire) geometry with the applied magnetic field directed along the surface(s) of the sample and swept between (i) 0 and Hmax. (half-wave cycle) and (ii) ±Hmax(full-wave cycle). We examined the behavior for amplitudes below and above that required for full penetration of the flux disturbance to the center of the specimen. We have explored the phenomena for two extremal types of bulk pinning, namely the Bean-London (Jc= α1) and the Kim-Anderson (Jc= α0/B) approximations. We have, for simplicity, assumed that the barrier height is field independent and either symmetric (opposing flux entry and exit equally) or asymmetric (opposing flux entry only). View full abstract»

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  • Extending an internally cooled superconducting magnet to higher fields

    Page(s): 261 - 263
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    An internally cooled superconducting (ICS) magnet was built and tested earlier at Oak Ridge National Laboratory (ORNL), and its stability margin as a function of operating fields was measured at an ambient helium temperature of 4.2 K. In the experiment reported here, we retested this magnet with lower bulk helium temperatures. The stability margins of the magnet as a function of temperature were measured. The results demonstrate clearly the flexibility offered by an ICS magnet: The stability margin can be improved substantially or the field output can be extended without sacrificing the stability margin simply by feeding the magnet with lower temperature helium. The analysis made in a previous paper on extended field operation of an ICS magnet is thus confirmed. View full abstract»

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  • Conductor design for superfluid Helium II

    Page(s): 264 - 267
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    This paper derives some design formulas and charts for a high-field (12 Tesla) application using Nb43Ti25Ta alloy superconductor. This material is selected because of its large critical current (Jc= 71,000 A/cm2) at 12 Tesla and 1.8K. Its ductility is beneficial to manufacturing processes and accommodating of the operating condition under stress. A coil packing factor of 70% and an insulation void fraction of 35% are assumed. These are nominal values which, after analysis, leave adequate turn-to-turn space for insulation bearing area, Helium II volume, and voltage standoff. The stabilizer is oxygen-free, high-purity copper in the full-hard condition, ρ = 7.17 × 10-8ohm.cm, wherein the magnetoresistivity at 12 Tesla accounts for 69% of the total. Basing a trial conductor on these assumptions will produce a design very close to optimum. Further refinement would be an iterative process whereby one checks the design against all constraints using the fundamental engineering formulas and makes parametric adjustments as necessary. View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology