178 research outputs found

    Thermal Conductivity of Industrial Nb3Sn Wires Fabricated by Various Techniques

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    We have developed a new experimental setup specifically designed for measuring thermal conductivity on technical superconductors in the range of temperatures from 3 to 330 K in magnetic fields up to 21 T. Three Nb3Sn wires, produced by the powder in tube technique, the bronze route and the internal tin restacked rod process, respectively, have been investigated. We show that, due to the complexity of the architecture of these wires, direct measurement of thermal conductivity is required for a correct estimation of thermal stability in superconducting magnets.Comment: Accepted for publication in IEEE ASC 2012 Special Issu

    High-field thermal transport properties of REBCO coated conductors

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    The use of REBCO coated conductors is envisaged for many applications, extending from power cables to high-field magnets. Whatever the case, thermal properties of REBCO tapes play a key role for the stability of superconducting devices. In this work, we present the first study on the longitudinal thermal conductivity (Îș\kappa) of REBCO coated conductors in magnetic fields up to 19 T applied both parallelly and perpendicularly to the thermal-current direction. Copper-stabilized tapes from six industrial manufacturers have been investigated. We show that zero-field Îș\kappa of coated conductors can be calculated with an accuracy of ±15\pm 15% from the residual resistivity ratio of the stabilizer and the Cu/non-Cu ratio. Measurements performed at high fields have allowed us to evaluate the consistency of the procedures generally used for estimating in-field Îș\kappa in the framework of the Wiedemann-Franz law from an electrical characterization of the materials. In-field data are intended to provide primary ingredients for the thermal stability analysis of high-temperature superconductor-based magnets.Comment: Accepted for publication in Superconductor Science and Technolog

    Thermal conductivity and stability of commercial MgB2_2 conductors

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    This paper presents a study of the thermal transport properties of MgB2_2 tapes differing in architecture, stabilization and constituent materials. The temperature and field dependence of thermal conductivity, Îș(T,B)\kappa(T,B), was investigated both along the conductor and in the direction perpendicular to the tape. These data provide fundamental input parameters to describe the 3D heat diffusion process in a winding. Thermal transport properties - even in field - are typically deduced using semi-empirical formulas based on the residual resistivity ratio of the stabilizer measured in absence of magnetic field. The accuracy of these procedures was evaluated comparing the calculated Îș\kappa values with the measured ones. Based on the experimental thermal conduction properties Îș(T,B)\kappa(T,B) and critical current surface JC(T,B)J_C(T,B) we determined the dependence of minimum quench energy and normal zone propagation velocity on the operating parameters of the conductor. The correlation between thermal properties and tape layout allowed us to provide information on how to optimize the thermal stability of MgB2_2 conductors.Comment: Accepted for publication in Superconductor Science and Technolog

    Formation and upper critical fields of the two distinct A15 phases in the subelements of Powder-In-Tube Nb3Sn wires

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    It is well known that the A15 layer in the subelements of a Powder-In-Tube (PIT) Nb3Sn wire exhibits two different grain morphologies: a region with fine grains (~200 nm in size) representing about 60% of the total A15 area and one with large grains (1-2 {\mu}m in size). By means of high field specific heat and magnetization measurements we have shown that these two A15 phases correspond to two distinctly different Tc distributions, the large grains region exhibiting a higher Tc and a lower Bc2, the fine grains region a lower Tc and a higher Bc2. We report here the values of the superconducting parameters (Tc, Bc2) of the two A15 phases, as determined from an original model to fit the experimental Tc distribution. After a prolonged reaction treatment (625{\deg}C/320h), an increase of the fine grain region was observed at the expenses of the large grain region, the Bc2(0K) value of the former being raised from 28.8 to 31.7 T. These changes explain the marked increase of Jc to 2'700 A/cm2 at 4.2K/12T, the highest value measured so far in PIT wires

    An equation for the quench propagation velocity valid for high field magnet use of REBCO coated conductors

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    Based on a study of the thermophysical properties, we derived a practical formula for the normal zone propagation velocity appropriate for REBa2_2Cu3_3O7−x_{7-x} coated conductors in high magnetic fields. An analytical expression to evaluate the current sharing temperature as a function of the operating conditions is also proposed. The presented study has allowed us to account for experimental results not fully understood in the framework of the models widely used in the literature. In particular, we provided a fundamental understanding of the experimental evidence that the normal zone propagation velocity in REBa2_2Cu3_3O7−x_{7-x} coated conductors can be mainly determined by the operating current, regardless of the applied field and temperature

    Electro-mechanical properties of REBCO coated conductors from various industrial manufacturers at 77 K, self-field and 4.2 K, 19 T

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    Rare-earth-barium-copper-oxide (REBCO) tapes are now available from several industrial manufacturers and are very promising conductors in high field applications. Due to diverging materials and deposition processes, these manufacturers' tapes can be expected to differ in their electro-mechanical and mechanical properties. For magnets designers, these are together with the conductors' in-field critical current performance of the highest importance in choosing a suitable conductor. In this work, the strain and stress dependence of the current carrying capabilities as well as the stress and strain correlation are investigated for commercial coated conductors from Bruker HTS, Fujikura, SuNAM, SuperOx and SuperPower at 77 K, self-field and 4.2 K, 19 T

    Transverse Thermal Conductivity of REBCO Coated Conductors

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    REBCO coated conductors (CCs) have the potential to widen considerably the application areas of superconductivity. Quench protection of REBCO-based devices represents one of the major obstacles to this expansion. Thermal conductivity data are mandatory ingredients for quench simulation studies. In particular, the transverse thermal conductivity (ÎșT\kappa_T) of the CC plays a key role in case of quenches in superconducting magnets. In the present work, we report ÎșT\kappa_T of thermally stabilized REBCO CCs produced by different manufacturers. We have measured ÎșT\kappa_T on single CCs rather than on stacks of soldered tapes, this excludes spurious contributions in the measurements. We have found that the presence of the stabilizer at the tape edges in Cu-electroplated CCs increases the overall ÎșT\kappa_T. In the absence of this effect, the overall thermal resistance is dominated by the substrate.Comment: ASC Charlotte 2014, IEEE Transactions on Applied Superconductivity Vol. 25 Issue 3 JUNE 201

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    Modeling of the interaction of rigid wheels with dry granular media

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    We analyze the capabilities of various recently developed techniques, namely Resistive Force Theory (RFT) and continuum plasticity implemented with the Material Point Method (MPM), in capturing dynamics of wheel--dry granular media interactions. We compare results to more conventionally accepted methods of modeling wheel locomotion. While RFT is an empirical force model for arbitrarily-shaped bodies moving through granular media, MPM-based continuum modeling allows the simulation of full granular flow and stress fields. RFT allows for rapid evaluation of interaction forces on arbitrary shaped intruders based on a local surface stress formulation depending on depth, orientation, and movement of surface elements. We perform forced-slip experiments for three different wheel types and three different granular materials, and results are compared with RFT, continuum modeling, and a traditional terramechanics semi-empirical method. Results show that for the range of inputs considered, RFT can be reliably used to predict rigid wheel granular media interactions with accuracy exceeding that of traditional terramechanics methodology in several circumstances. Results also indicate that plasticity-based continuum modeling provides an accurate tool for wheel-soil interaction while providing more information to study the physical processes giving rise to resistive stresses in granular media
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