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Applied Superconductivity, IEEE Transactions on

Issue 2 • Date Jun 2002

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Displaying Results 1 - 11 of 11
  • Simulations of microwave characteristics of high-temperature superconducting microstrip lines by using an empirical two-fluid model

    Page(s): 1776 - 1783
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (361 KB) |  | HTML iconHTML  

    A numerical analysis of the microwave propagation characteristics of a high-temperature superconducting microstrip transmission line is presented. It is based on the transmission line theory and empirical two-fluid model which appropriately incorporates the quasiparticle scattering and residual loss of the superconductor. First, the calculated attenuation constant and phase velocity are compared with those predicted by the conventional two-fluid model for a YBa2Cu3O7-δ microstrip line with a linear substrate, lanthanum aluminate, LaAlO3. Next, we have specifically investigated the effects of nonlinear substrate such as strontium titanate, SrTiO3, on the attenuation constant and phase velocity. The tunable feature of such a microwave device owing to the nonlinear dielectric ferroelectric is illustrated and discussed. View full abstract»

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  • Compact superconducting dual-log spiral resonator with high Q-factor and low power dependence

    Page(s): 1813 - 1817
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    A new dual-log spiral geometry is proposed for microstrip resonators, offering substantial advantages in performance and size reduction at subgigahertz frequencies when realized in superconducting materials. The spiral is logarithmic in line spacing and width such that the width of the spiral line increases smoothly with the increase of the current density, reaching its maximum where the current density is maximum (in its center for λ/2 resonators). Preliminary results of such a logarithmic ten-turn (2 × 5 turns) spiral, realized with double-sided YBCO thin film, showed a Q.-factor seven times higher than that of a single ten-turn uniform spiral made of YBCO thin film and 64 times higher than a copper counterpart. The insertion loss of the YBCO dual log-spiral has a high degree of independence of the input power in comparison with a uniform Archimedian spiral, increasing by only 2.5% for a 30-dBm increase of the input power, compared with nearly 31% for the uniform spiral. A simple approximate method, developed for prediction of the resonant frequency of the new resonators, shows a good agreement with the test results. View full abstract»

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  • Design of superconducting MRI surface coil by using method of moment

    Page(s): 1823 - 1827
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    A method of moment with an enhanced model to design high-temperature superconductor (HTS) RF surface coils for magnetic resonant image (MRI) is presented. The resonant frequency and quality factor (Q) of HTS RF spiral coils are simulated using this method. The agreements of resonant frequencies and Qs between the simulation and measurement are excellent with differences less than 1 % and 3 %, respectively. The 0.2-μ m-thick YBaCuO (YBCO) thin films are deposited onto single side of 0.508-mm-thick LaAlO3 (LAO) and sapphire substrate and patterned into a spiral shape. To accurately analyze the resonant frequency and Q of a coil, an enhanced two-fluid model is employed. HTS RF coils with diameter of 65 mm for 0.2 T and 1.5 T MRI systems are designed and fabricated with the measured Q of 19 K and 23 K, respectively. In addition, the shift of resonant frequency due to the mutual coupling between two HTS spiral coils is predicted by this method, which is important for design of HTS coil arrays in an MRI system. View full abstract»

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  • Thermomechanical properties of the coil of the superconducting magnets for the Large Hadron Collider

    Page(s): 1804 - 1812
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    The correct definition and measurement of the thermomechanical properties of the superconducting cable used in high-field magnets is crucial to study and model the behavior of the magnet coil from assembly to the operational conditions. In this paper, the authors analyze the superconducting coil of the main dipoles for the Large Hadron Collider. They describe an experimental setup for measuring the elastic modulus at room and at liquid nitrogen temperature and for evaluating the thermal contraction coefficient. The coils exhibit strong nonlinear stress-strain behavior characterized by hysteresis phenomena, which decreases from warm to cold temperature, and a thermal contraction coefficient, which depends on the stress applied to the cable during cooldown. View full abstract»

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  • Noise properties of HTS Josephson mixers at 345 GHz and operating temperatures at 20 K

    Page(s): 1828 - 1831
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    The authors report on the mixing properties of high-temperature superconductor bicrystal Josephson junctions at 345 GHz and high-operating temperatures. A variable backshort and E-plane tuner enabled the control of impedance matching between the junction and the RF environment. The local oscillator frequency and intermediate frequency were 345 and 1.4 GHz, respectively. The double-side band (DSB) mixer noise temperature and the conversion efficiency were determined using the hot/cold method. The authors observed that the noise temperature was strongly dependent on the matching conditions. The lowest noise temperatures were observed for tuner positions supporting the formation of a subharmonic step which appeared between the zeroth and first Shapiro step. At T = 20 K they obtained a lowest DSB mixer noise temperature of 1003 K and a conversion efficiency of -1.2 dB. They have investigated the dependence of the noise temperature on the operating temperature in detail. The impact of resonances on the device performance will be discussed. View full abstract»

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  • A novel energy efficient SFCL with a silver-free contact switchgear for application in electricity and transportation

    Page(s): 1770 - 1775
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    A novel concept of a switchgear based on the combination of an AC superconducting fault current limiter (SFCL) and silver-free electrical contacts is proposed. In the combined system SFCL+switchgear, it is possible to employ cheaper materials for electrical contacts. The SFCL device includes inductive coupling of high-Tc superconducting active elements, in the form of layered flat rings of a Bi1.8Pb0.3Sr1.9Ca2Cu3Ox compound, prepared by a solid-state reaction technique. Experimental results obtained by testing a prototype SFCL in short circuit regime at AC 50 Hz under quasistationary conditions are presented. The use of the superconducting rings enables a wide range variation of the dissipated power. Copper/diamond composites, prepared by explosive synthesis, are employed as contact materials for the switchgear. The addition of particles (<1 μm) leads to improved mechanical characteristics and increased stability of the composite materials. The combination of switchgear with silver-free electrical contacts and SFCL allows a short circuit regime to withstand the switchgear and provides increased system reliability. View full abstract»

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  • A model for calculating magnetic forces between monolithic YBa2Cu3O7-δ superconductors

    Page(s): 1818 - 1822
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    One of the fundamental barriers to the use of electromagnetic launchers is the high power required to reach launch speed in a reasonable distance. It has been proposed that large external power supplies can be avoided by using superconducting persistent currents in the barrel of the launcher to store energy. With this application in mind, the use of melt-textured YBCO for these persistent current magnets was studied. Presented in this paper is the development of a model for calculating the current distribution and magnetic force for two YBCO rings, each with a trapped field such that an attractive force is developed between them. Two different methods were used to calculate current as a function of time. The first is a differential equation for the time dependence of the current distribution, which is solved using the four-step vector Runge-Kutta method. The second method limits the local current density to its critical value. The integral equation for force at each time step is solved using the finite sum method. Results from the model were compared to quasistatic experiments and found to agree to within 10%. The model was then used to predict behavior of a melt-textured YBCO launcher at speeds up to 10 000 m/s. The results show that energy transfer is almost independent of speed for a properly designed launcher, and heating due to flux flow is minimal. View full abstract»

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  • AC losses in superconducting solenoids

    Page(s): 1790 - 1794
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (257 KB) |  | HTML iconHTML  

    This paper presents an analytical model to determine AC losses in monolayer and multilayer superconducting solenoids. The case of a transformer with several coils is also presented. This model is based on an infinite cylindrical geometry and the Bean model. Under this assumption, the electromagnetic variables distributions are determined and then instantaneous losses are simply calculated. For a monolayer coil the mean losses are given too. Then, analytical results are compared to numerical results performed with previous development in Flux3D (finite elements software). Finally, a comparison with measurements on a two-layer coil is presented. View full abstract»

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  • Temperature and magnetic field dependence of the critical current density for a mass-produced Nb3Al multifilamentary strand fabricated by a jelly-roll method [for ITER]

    Page(s): 1799 - 1803
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    JAERI has been developing jelly-roll processed multifilamentary Nb3Al-Cu strands for the toroidal field (TF) coils of fusion tokamak machines since 1986, in cooperation with Sumitomo Electric Industries. One ton of mass-produced strands were successfully manufactured for the 13 T-46 kA Nb3 Al insert which will be tested in the ITER Central Solenoid model coil. The critical current of the Nb3Al strand developed for the ITER project was measured in temperatures from 4.2 to 15 K and in applied magnetic fields up to 16 T. An empirical equation for the critical current density Was obtained by using these data and the pinning force scaling method. The obtained equation is useful in evaluating the performance of the full-size conductor and in establishing the optimum design criteria for the conductor in fusion machines. In this work, we did not take into account the influence of mechanical strain on the strand. IC measurement of the strands under mechanical strain will be carried out and an expression for JC with the strain will be completed in the next phase. View full abstract»

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  • Method for estimating future markets for high-temperature superconducting power devices

    Page(s): 1784 - 1789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    This paper describes a spreadsheet model for estimating the impact of high-temperature superconducting (HTS) power devices on the national electric grid. The distribution of losses in the national grid is carefully traced and those losses that HTS can eliminate are identified. The energy savings achievable by the many sizes of HTS generators, transformers, cables, and motors are then computed and totaled using a spreadsheet analysis. The economic savings are very sensitive to the price (and Je) of HTS wire, and to the cost of cooling the devices to operating temperature. A market penetration model is used to estimate how fast HTS devices become commercially,successful. The emphasis of the paper is the analytic tool, not the numerical results of one specific case. This entire model is explicitly designed to allow others to enter their own estimated parameters and arrive at their own conclusions. View full abstract»

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  • Measurement of the coherence length of sputtered Nb0.62Ti0.38N thin films

    Page(s): 1795 - 1798
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    Superconducting and normal state properties of the useful film material NbxTi1-xN have been characterized. In particular, the coherence length of reactively sputtered Nb0.62Ti0.38N thin films is determined to be 2.4±0.3 nm. The results are inferred from fitting the de Gennes-Werthamer theory to experimental measurements of the proximity-induced depression of the transition temperature in Nb-Nb0.62Ti0.38N-Nb structures. The coherence length, as defined by this theory, can be used to infer the zero-temperature Ginzburg-Landau coherence length, ξGL (0), of 3.8 nm for the Nb0.62Ti0.38N synthesized in this study. The shorter coherence length and lower resistivity of these films, when compared to NbN, indicates that they are an appealing choice for electrodes in rapid single flux quantum circuits. View full abstract»

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

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