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VAMAS interlaboratory comparisons of critical current vs. strain in Nb{sub 3}Sn

Description: A comparison is made of measurements of the effect of axial tensile strain on the critical current of multifilamentary Nb{sub 3}Sn superconductors by three different laboratories. Two of the laboratories used short sample testing apparatus wherein a straight section of conductor was cooled in a force-free state. One of the laboratories used a spring apparatus wherein a long sample was reacted in a coil shape and attached to a spring sample holder. The agreement between the results for the two laboratories that used the straight sample apparatus was quite good, within 15% for all three conductors at 15 T, except at very high strain for one conductor which had an upper critical field close to the measurement field. To make a comparison with the data obtained using the spring method, it was necessary to fit the data to the compressive prestrain determined using the straight-sample technique. With such a fit, the agreement was variable, between 15 and 25% depending on the conductor. Values of the prestrain and irreversible strain obtained from the straight sample data agreed within 0.06% and 0.05% respectively. Values of the maxi (strain-free) upper critical fields agreed within several tenths of a tesla.
Date: December 31, 1989
Creator: Ekin, J.W.
Partner: UNT Libraries Government Documents Department

Electromechanical properties of superconductors for DOE/OFE applications. Final report

Description: In many superconductor applications, especially large magnets, the superconductor is required to perform while under the influence of strong mechanical forces. These forces are commonly due to residual fabrication stress, differential thermal contraction of dissimilar materials, and electromagnetic forces generated within an energized magnet coil. Thorough knowledge of a superconductor`s electrical performance under the influence of these forces (electromechanical properties) is required for successful magnet engineering. This report presents results of research conducted during the period from august 1993 through March 1997 on the electromechanical properties of superconductors for DOE/OFE fusion applications.
Date: September 1, 1998
Creator: Ekin, J.W. & Bray, S.L.
Partner: UNT Libraries Government Documents Department

Transverse stress effect on the critical current of internal tin and bronze process Nb{sub 3}Sn superconductors

Description: The effect of transverse stress on the critical current density, J{sub c}, has been shown to be significant in bronze process Nb{sub 3}Sn, with the onset of significant degradation at about 50 Mpa. In an applied field of 10 T, the magnitude of the effect is about seven times larger for transverse stress than for axial tensile stress. In a subsequent study, similar results were observed in another bronze process Nb{sub 3}Sn conductor made by a different manufacturer. The mechanism accounting for the transverse stress effect and its large magnitude compared with the axial tensile effect is still the subject of speculation. In an attempt to better understand the nature of the effect, The authors have undertaken a series of experiments to determine whether the transverse stress effect depends on the grain morphology of the Nb{sub 3}Sn reaction layer in the superconductor. To do this, the authors have measured the effect in an internal tin conductor with excess tin, which yields a more equiaxed Nb{sub 3}Sn grain morphology than for bronze process Nb{sub 3}Sn, where the grains are more columnar. The results for the effect of transverse compression on the J{sub c} of a round bronze process Nb{sub 3}Sn wire are given. The data are probably applicable to a wide variety of Nb{sub 3}Sn conductors for magnet engineering.
Date: December 31, 1989
Creator: Ekin, J.W.; Bray, S.L.; Danielson, P.; Smathers, D.; Sabatini, R.L. & Suenaga, M.
Partner: UNT Libraries Government Documents Department

Electromechanical properties of superconductors for DOE fusion applications

Description: The electrical performance of many superconducting materials is strongly dependent on mechanical load. This report presents electromechanical data on a broad range of high-magnetic-field superconductors. The conductors that were studied fall into three general categories: Candidate conductors, experimental conductors, and reference conductors. Research on candidate conductors for fusion applications provides screening data for superconductor selection as well as engineering data for magnet design and performance analysis. The effect of axial tensile strain on critical-current density was measured for several Nb{sub 3}Sn candidate conductors including the US-DPC (United States Demonstration Poloidal Coil) cable strand and an ITER (International Thermonuclear Experimental Reactor) candidate conductor. Also, data are presented on promising experimental superconductors that have strong potential for fusion applications. Axial strain measurements were made on a V{sub 3}Ga tape conductor that has good performance at magnetic fields up to 20 T. Axial strain data are also presented for three experimental Nb{sub 3}Sn conductors that contain dispersion hardened copper reinforcement for increased tensile strength. Finally, electromechanical characteristics were measured for three different Nb{sub 3}Sn reference conductors from the first and second VAMAS (Versailles Project on Advanced Materials and Standards) international Nb{sub 3}Sn critical-current round robins. Published papers containing key results, including the first measurement of the transverse stress effect in Nb{sub 3}Sn, the effect of stress concentration at cable-strand crossovers, and electromechanical characteristics of Nb{sub 3}Al, are included throughout the report. Selected papers were indexed separately for inclusion in the Energy Science and Technology Database.
Date: January 1994
Creator: Ekin, J. W.; Bray, S. L.; Lutgen, C. L. & Bahn, W. L.
Partner: UNT Libraries Government Documents Department