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Magnetics, IEEE Transactions on

Issue 1 • Date January 1981

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Displaying Results 1 - 25 of 288
  • [Front cover and table of contents]

    Publication Year: 1981 , Page(s): 0
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    Freely Available from IEEE
  • Editor's comments

    Publication Year: 1981 , Page(s): 15
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    Freely Available from IEEE
  • Chairman's comments

    Publication Year: 1981 , Page(s): 18
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    Freely Available from IEEE
  • One, two, three - Zero resistance! In defence applications

    Publication Year: 1981 , Page(s): 19 - 30
    Cited by:  Papers (1)
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    First Page of the Article
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  • Superconducting magnets for toroidal fusion reactors

    Publication Year: 1981 , Page(s): 31 - 37
    Cited by:  Papers (7)
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    Fusion reactors will soon be employing superconducting magnets to confine plasma in which deuterium and tritium (D-T) are fused to produce usable energy. At present there is one small confinement experiment with superconducting toroidal field (TF) coils: Tokamak 7 (T-7), in the USSR, which operates at 4 T. By 1983, six different 2.5 × 3.5-m D-shaped coils from six manufacturers in four countries will be assembled in a toroidal array in the Large Coil Test Facility (LCTF) at Oak Ridge National Laboratory (ORNL) for testing at fields up to 8 T. Soon afterwards ELMO Bumpy Torus (EBT-P) will begin operation at Oak Ridge with superconducting TF coils. At the same time there will be tokamaks with superconducting TF coils 2 to 3 m in diameter in the USSR and France. Toroidal field strength in these machines will range from 6-9 T. NbTi and Nb3Sn, bath cooling and forced flow, cryostable and metastable - various designs are being tried in this period when this new application of superconductivity is growing and maturing. View full abstract»

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  • Test of a model coil of "Tore Supra"

    Publication Year: 1981 , Page(s): 38 - 41
    Cited by:  Papers (1)
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    Inside the qualifying test programme, supporting the "Tore Supra" Tokamak design, a reduced scale model of coil was fabricated by an industrial firm and fully tested. This model coil is provided with the same features as those retained for the complete magnet and is built according to the same design; in particular the Nb-Ti mixed matrix monolithic conductor is cooled by a pressurized superfluid helium bath, supplied from a model of the envisaged complete cryogenic system. Three main objectives have been assigned to this test: operation of the cryogenic system, stability of the superconductor winding under high mechanical stresses, mainly shear, and simulation of coil quench conditions. For this purpose, the model coil (outside bore 0.8 m) is located inside a 4 T magnet, an hydraulic jack applies a 1 MN force along a coil diameter. Operation of the model coil has been found highly stable, under the conditions of applied field and forces, a coil transition can be induced by an electrical heater only when the superfluid bath temperature is close to Tλ. The 1.8 K cryogenic system provides a useful calorimetric measure of total losses induced inside the winding; its operation has been quite simple and reliable, permitting a sure extrapolation to a much larger size. View full abstract»

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  • Pulsed field loss characteristics of the Japanese test coil for the large coil task

    Publication Year: 1981 , Page(s): 42 - 45
    Cited by:  Papers (6)
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    This paper describes some results of an analytical calculation and the measurements of a pulsed field loss on the Japanese LCT conductor. The conductor, whose aspect ratio is around 2.5, is wound edge wise to reduce the pulsed field loss. The Japanese LCT coil, with the conductor thus designed, was evaluated to have a pulsed field loss of about 19W. This includes the loss of the helium vessel under the normal LCT test with a pulsed field of 0 to 0.14T. In addition, the loss measurement has been carried out up to 25 T/s. Measured results on the relation between the loss of a single strand and that of a whole strand pack well supports the validity of the loss analysis which includes a newly arranged set of analytical equations. View full abstract»

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  • Pulsed magnetic field losses of two 15000 A test superconductors designed for the swiss fusion research LCT coil

    Publication Year: 1981 , Page(s): 46 - 48
    Cited by:  Papers (1)
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    Pulsed magnetic field losses have been investigated on two different NbTi superconductors designed for direct cooling with supercritical He and for Itr= 15000 A. The loss measurements were performed with perpendicular and parallel pulsed field components. The influence of the dc field component on the pulsed field hysteresis losses was measured up to 7 Tesla. View full abstract»

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  • Further investigations of the upper critical field and the high field critical current density in Nb-Ti and its alloys

    Publication Year: 1981 , Page(s): 49 - 52
    Cited by:  Papers (12)
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    The work described in this report was undertaken, within the context of the 12 Tesla program, to investigate the possibility of increasing the upper critical field, Hc2, of Nb-Ti through alloying additions. A preliminary report has previously been given by us. In the first part of this paper we report further measurements of Hc2in the Nb-Ti-Ta and Nb-Ti-Hf systems. Whilst we find only small enhacements of ∼0.3 Tesla in μoHc2(4.2K) compared to binary Nb-Ti, at 2K there is a wide composition range in the Nb-Ti-Ta system where μoHc2(2K) exceeds 15 Tesla, reaching a maximum of 15.5 Tesla. This represents an enhancements of 1.3 Tesla over unalloyed Nb-Ti. By comparison alloys in the Nb-Ti-Hf system show a maximum enhancement in μoHc2(2K) of only 0.3 Tesla. The reasons both for the enhancements in Hc2and for the differences in behavior systems shown by alloys containing Ta and Hf are briefly discussed. In part II we discuss common features in the behavior of the high field critical current density, Jc, of four commercial Nb-Ti composites and upon the basis of this behavior predict the enhancements in the high field Jcto be expected from using Nb-Ti-Ta and its alloys. View full abstract»

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  • The use of NbTiTa as a high field superconducting alloy

    Publication Year: 1981 , Page(s): 53 - 56
    Cited by:  Papers (8)  |  Patents (1)
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    NbTi-based alloys containing 8% and 25% tantalum have been studied for use at fields around 12 tesla and at temperatures between 2 K and 3 K. These materials have significantly higher current densities at reduced temperatures than other NbTi-based alloys. Using the results of these studies, a 10,000 A, nominal 12 tesla conductor has been designed and is presently being fabricated for use in a test coil for the Lawrence Livermore Laboratory HFTF. The alloy selected for that conductor is Nb-43% Ti-25% Ta. View full abstract»

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  • Stability analysis of NbTi-Ta- based high field conductor cooled by pool boiling below 4 K

    Publication Year: 1981 , Page(s): 57 - 60
    Cited by:  Papers (2)
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    Stability analysis has been performed for cabled NbTi-Ta-based superconductors intended for the high field (12 T) toroidal field coils for a large scale tokamak device such as ETF. Ternary NbTi-Ta was selected as the superconductor because of its superior critical current density at high field as compared to the binary alloy NbTi. The operating temperature was chosen to be 2.5 K or below to optimize the performance of the superconductor. A cabled conductor was selected to minimize the pulsed field losses. The conductor is cooled by pool boiling in a subcooled (∼ 2.5 K, 0.25 atm) bath, or in a superfluid helium (He-II) bath (∼ 1.8 K, 0.02 atm). The analysis was based on numerically simulating the evolution of a normal zone in the conductor. Appropriate superconductor properties and heat transfer characteristics were utilized in the simulation. In the case of subcooled bath, the low bath temperature reduces both the peak nucleate boiling flux (PNBF) and the minimum film boiling flux (MFBF). In the case of He II bath, the heat transfer characteristic is determined by the cooling channel size, bath pressure and the Kapitza resistance. Results indicated that in both cases of cooling the NbTi-Ta-based conductor can be designed to satisfy the commonly followed stability performance criterion for such large coils. In particular, He II cooling was found to offer significant enhancement in the stability performance of the conductor. The implications of the results are discussed. View full abstract»

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  • Superconducting properties of Ti-Nb-Hf alloys

    Publication Year: 1981 , Page(s): 61 - 64
    Cited by:  Papers (1)
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    To achieve improvements in superconducting properties of the Ti-Nb superconductor, effects of ternary additions of Hf have been extensively studied on 42 Ti-Nb-Hf alloys with compositions of 25 - 65at%Nb, 0- 15at%Hf and the balance Ti. Critical temperatures are found to depend upon Hf addition and aging temperature. In as-rolled Ti-40at%Nb-3at%Hf alloy the critical temperature is raised by about 0.3K over Ti- 40at%Nb alloy. Aging at 800°C can raise critical temperatures of high Hf alloys by 0.6 - 1.8K. The upper critical field at 4.2K of as-rolled Ti-40at%Nb-3at%Hf reaches 11.7 tesla, a value higher by 0.4 tesla than that of Ti-40at%Nb. High field critical current densities are also improved by the 3at%Hf addition. 2 step aging treatment is found effective in enhancing critical current densities of high Hf alloys. No degradation in fabricability is caused by a few at% Hf additions. View full abstract»

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  • Microstructure superconducting property relationships in a fermilab Nb-46.5w/o Ti filamentary superconducting composite

    Publication Year: 1981 , Page(s): 65 - 68
    Cited by:  Papers (2)
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    A transmission electron microscopy study has been performed on a production Fermilab Energy Saver composite from an intermediate stage in the manufacturing process. Studies of the dynamics of sub-band growth and α-Ti precipitation show that sub-band growth is quite rapid and occurs to a significant extent before α-Ti precipitation starts. Following analysis at intermediate size, the behavior of heat-treated samples was compared to that of samples drawn to final size without heat-treatment. Heat-treated samples were found to have smaller final sub-band diameters, in spite of the initial increase caused by heat-treatment and their critical current densities were also greater. The microstructural evidence points to the crucial role played by α-Ti precipitation in developing high Jcvalues in this Nb46.5w/oTi alloy. View full abstract»

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  • Lap joint resistance and intrinsic critical current measurements on a NbTi superconducting wire

    Publication Year: 1981 , Page(s): 69 - 72
    Cited by:  Papers (3)
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    The lap joint resistance between two Cu:Nb-Ti wires (rectangular cross section, 0.53 × 0.68 mm) was measured at 4 K as a function of current, magnetic field and joint area (0.5 to 7 mm2). A simple model, using the magnetoresistance and current dependence, allowed the Joint interface resistance and the current transfer resistance to be separated. The critical current of the wire was also measured adjacent to the Joint. These critical current data were compared with data taken on the control sample (no lap joint). From these comparisons operational checks were deduced for an intrinsic measurement of the critical current adjacent to a joint. The operational checks were on the reversibility of the V-I curves and on their current ramp-rate dependence. When these operational checks were applied to the critical current data of all the joints tested, the results agreed to ±2%. View full abstract»

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  • Development of critical current measurement standards

    Publication Year: 1981 , Page(s): 73 - 76
    Cited by:  Papers (2)
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    This paper deals with the development of criteria for critical current measurements. The two tasks investigated were: (1) the determination of critical current of short samples as a function of transition criterion, and (2) analysis of current transfer from sample holder to sample. Critical currents were measured using the equivalent resistivity criterion with sensitivities ranging from 10-7Ω-cm to 10-12Ω-cm and using the electric field criterion with sensitivities of 1 mV/cm to 100 nV/cm. Current transfer measurements were performed on monolithic conductors with critical currents greater than 1,000 amps. The results of the program are that no single measurement standard and no single test holder are suitable for all types of critical current measurements, and that sample holders must be designed with sufficiently large copper current contacts in order to minimize current transfer effects. View full abstract»

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  • Quench properties of high current superconductors

    Publication Year: 1981 , Page(s): 77 - 80
    Cited by:  Papers (3)
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    A technique has been developed which allows the simultaneous determination of most of the important parameters of a high current superconductor. The critical current, propagation velocity, normal state resistivity, magnetoresistance, and enthalpy are determined as a function of current and applied field. The measurements are made on non-inductive samples which simulate conditions in full scale magnets. For wide, braided conductors the propagation velocity was found to vary approximately quadratically with current in the 2 to 5 kA region. A number of conductors have been tested including some Nb3Sn braids which have critical currents in excess of 10 kA at 5 T, 4.2K. View full abstract»

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  • Static and dynamic properties of short, narrow, variable-thickness microbridges

    Publication Year: 1981 , Page(s): 81 - 84
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    The electrical properties, including the Josephson-effect response to microwave radiation, have been studied for extremely small, high-resistance microbridges of Pb-In alloy and unalloyed In, with dimensions ranging from 300Å to 2000Å. The IcR product of In and Pb-In microbridges decreases smoothly as the bridge cross section is reduced, approaching the Ginzburg-Landau limit of 0.64 mV/K for the smallest bridges. The voltage range of microwave response and the temperature range of hysteresis-free operation both increase (improve) as the bridge is made narrower, in agreement with Joule heating theory. For example, an 8 ohm Pb0.9In0.1bridge with all dimensions ≤500 Å has a maximum step voltage of V_{\max } = 1.5 mV and a nonhysteretic temperature range of \Delta T_{no hyst} = 1.2 K. Bridges of unalloyed In can show still better response due to a longer coherence length, and nonhysteretic operation over the full temperature range below Tcis possible. View full abstract»

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  • Josephson effects in Nb3Sn microbridges

    Publication Year: 1981 , Page(s): 85 - 87
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    We have studied Josephson effects in long narrow Nb3Sn microbridges at temperatures up to 17 K. These microbridges are formed by photolithographic techniques and subsequently subjected to controlled electrical discharges to modify the intrinsic Tcof the bridge region. The bridges exhibit 10 GHz micro wave steps in their I-V characteristics whose amplitudes are in excellent agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics (with and without microwaves) can be fit assuming an effective temperature approximately 15 K above the bath temperature. We have also investigated in detail structures in the I-V characteristics in the absence of microwaves. We show experimentally that phase-slip centers are induced at weak superconducting positions along the bridge when the S-N boundary of an expanding hot spot reaches within a thermal healing distance. The critical current of the phase-slip center thus formed exhibits a temperature dependence (1-T/Tc)1/2instead of the usual mean field result (1-T/Tc)3/2. View full abstract»

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  • Transient response of superconducting Pb microbridges irradiated by picosecond laser pulses and its potential applications

    Publication Year: 1981 , Page(s): 88 - 91
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    We have observed voltage pulses having half-widths of less than 500ps generated by constant-current-biased superconducting Pb variable thickness microbridges driven normal by short (3-5ps) light pulses. This represents a first step in the effort to generate even shorter pulses, which according to our analysis of the Rothwarf-Taylor equations should be possible. The ultimate width should be equal to the phonon pair-breaking time, which for materials such as Nb can be as short as a few picoseconds. In addition to monitoring the voltage pulses directly, we have used a novel adoption of the optical autocorrelation technique having a time resolution limited only by the laser pulse width. It is pointed out that even shorter voltage pulses, and therefore greater potential for device applications, can be achieved by direct injection of quasiparticles. View full abstract»

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  • Microwave power spectra of variable thickness sub-micron bridges

    Publication Year: 1981 , Page(s): 92 - 94
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    The frequency variation of the radiated power and linewidth of variable thickness bridges from 2 to 18 GHz is reported. A new, simple technique for fabricating these bridges using electron beam lithography is described. The measured power is found to be in unexpectedly good agreement with that calculated using the resistively shunted junction model. The linewidth data are in striking disagreement with existing theories. View full abstract»

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  • Coherent arrays of thin-film Josephson microbridges

    Publication Year: 1981 , Page(s): 95 - 98
    Cited by:  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    We have investigated two different methods of coupling between the Josephson oscillations in arrays of superconducting microbridges made of Sn and In in order to establish a single free-running coherent state. We report on experiments involving a broadband inductive coupling between pairs of microbridges, each pair constituting a dc-SQUID; and a narrow hand coupling between microbridges via resonant structures in transmission lines consisting of microstrip or slot lines. We discuss the properties of these two ways of long range coupling of Josephson weak links and evaluate their potential for high-frequency applications. View full abstract»

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  • Microwave wideband tunable oscillators using coherent arrays of Josephson junctions

    Publication Year: 1981 , Page(s): 99 - 102
    Cited by:  Papers (5)  |  Patents (2)
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    Coherent microwave radiation from arrays containing up to 100 indium microbridges has been directly detected. As expected the power scales as N2and the linewidth as 1/N for an array containing N junctions. Design criteria and fabrication methods for these arrays are discussed. View full abstract»

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  • New wave phenomena in series Josephson junctions

    Publication Year: 1981 , Page(s): 103 - 106
    Cited by:  Papers (4)
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    The use of electromagnetic waves to obtain coherence between widely spaced Josephson tunnel junctions is explored. A pair of coupled non-linear differential equations is developed for the case of junctions used as series elements in a microstrip transmission line. We use analysis to demonstrate the existence of oscillatory traveling waves, solitary waves, and standing waves on such a transmission line. We report simulations that demonstrate these waves, and an observation of standing waves in a real series array. It appears that substantial power at frequencies above 100 GHz may be obtained from these series arrays. View full abstract»

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  • Microstrip coupling techniques applied to thin-film Josephson junctions at microwave frequencies

    Publication Year: 1981 , Page(s): 107 - 110
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    Three different schemes for coupling to low impedance Josephson devices have been investigated. They all employ superconducting thin-film microstrip circuit techniques. The schemes are: (i) a quarterwave stepped impedance transformer, (ii) a microstrip resonator, (iii) an adjustable impedance transformer in inverted microstrip. Using single microbridges to probe the performance we found that the most primising scheme in terms of coupling efficiency and useful bandwidth was the adjustable inverted microstrip transformer. View full abstract»

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  • Mutual phase locking in multijunction Josephson arrays

    Publication Year: 1981 , Page(s): 111 - 114
    Cited by:  Papers (4)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Mutual phase locking of Josephson oscillations in a two-junction cell and multijunction arrays is analysed. The locking is due to ac currents of Josephson frequency ω, which flow through some special coupling circuit. For the most important case of almost identical junctions, the locking frequency range is shown to be proportional to the imaginary part of the complex conductivity Y(ω) of the coupling circuit. The power and linewidth of coherent oscillations, as well as the coherence stability with respect to the junction intrinsic noise and parameter spread, have been calculated. The maximum locking range and, hence, the maximum parameter tolerances are shown to take place in the closed-loop-type (ring) structures with long-range junction interactions. 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