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Session Chairpersons: L.R. Motowidlo, IGC Advanced Superconductors, Waterbury, CT; J. Schwartz, National High Magnetic Field Laboratory, Tallahassee, FL
8:30 am INVITED
Bi-2212/Ag HTSC MAGNETS FOR HIGH FIELD GENERATION: H. Kitaguchi, H. Kumakura, K. Togano, T. Kiyoshi, K. Inoue, National Research Institute for Metals, 1-2-1 Sengen Tsukuba 305, Japan; M. Okada, K. Tanaka, Hitachi Ltd., 7-1-1 Ohmika, Hitachi 319-12, Japan; J. Sato, Hitachi Cable Ltd., 3550 Kidamari, Tsuchiura 300, Japan
Two kinds of compact superconducting magnet have been fabricated with Bi-2212/Ag multifilamentary tapes. These magnets are stacked double pancake type and made by a wind and react process. One of them has the dimensions of 55 mm in height, 49 mm in outer diameter, and 12.5 mm in clear bore. The magnet was inserted in a 21-T-class superconducting magnet system and tested in various field at 4.2 K. In zero bias field, the magnet carries 400 A (criterion: 10-13 Wm) and generates 2.5 T. In the bias field of 21.1 T, the magnet successfully generates 1.76 T with the current of 281 A, i.e., the total field reaches 22.8 T which is the highest field ever achieved with a superconducting magnet. Transport current properties in bias fields for the other magnet with the outer diameter over 90 mm are also reported.
8:50 am INVITED
EFFECTS OF MECHANCIAL STRAIN ON Bi2Sr2CaCu2Ox/AgX COMPOSITE CONDUCTORS: J. Schwartz, B.C. Amm, H. Garmestani, Y. Hascicek, D.K. Hilton, National High Magnetic Field Laboratory, Tallahassee, FL 32310
The development of powder-in-tube Bi2Sr2Can-1)CunOx technology has progressed such that high critical current density (Jc) conductors are produced by many researchers. An important issue that remains, however, is the effects of mechanical strain. While it is evident that large strains induce irreversible damage, applications may be limited by fatigue at low strain values due to crack propagation. Here we report upon the effects of cyclic fatigue on Jc of Ag and Ag-alloy clad Bi2Sr2CaCu2Ox as measured by electrical transport and magnetic hysteresis. Measurements of the constituent and composite mechanical properties and bulk Bi2Sr2CaCu2Ox fracture toughness are also reported. As Jc may be limited by microcracks before straining, studies of crack propagation and mechanical strain effects may also provide insight into the fundamental limits to transport Jc. Results are interpreted within this framework as well.
9:10 am INVITED
PROPERTIES AND PROCESSING OF MULTIFILAMENTARY PIT FORMED USING THE CTFF PROCESS: M.D. Sumption*, S.X. Dou**, N.V. Vo**, and E.W. Collings*; *MSE, The Ohio State University, Columbus, OH, USA; **CSEM, The University of Wollongong, NSW, Australia
Multifilamentary Bi2212 strands with up to 37 filaments have been formed using Continuous-Tube-Forming-Filling (CTFF). The CTFF process is used for the initial monocore, which is then restacked via a conventional PIT process, and these strands are then rolled into tapes. A sterling Ag outer shell is used, but the matrix region used pure Ag. Self field Jc at 4.2 K is 9.16 kA/cm2. The resulting filaments are aspected, with dimensions 7.5 x 370 mm. A vibrating sample magnetometer has been used to measure M-H loops (losses). Losses were measured, and it was possible to separate out; (i) critical state losses, (ii) eddy current losses, (iii) logarithmic type creep influences on the losses, and (iv) exponential type creep influences on the losses.
9:30 am INVITED
Bi2Sr2Ca1Cu2Ox MULTIFILAMENT WIRES AND TAPES FOR MAGNET APPLICATIONS UP TO 20 K: L.R. Motowidlo, G. Galinski, G.M. Ozeryansky, F. Krahula, R.S. Sokolowski, IGC Advanced Superconductors, Waterbury, CT 06704
Long lengths of Ag-alloy sheathed Bi2Sr2Ca1Cu2Ox (2212) multifilament wires and tapes have been fabricated and heat treated. Sample lengths of one to two meters are cut after melt processing and wound into standard holders used to test NbTi for MRI. The performance characteristics of the 2212 conductors, that is the critical current density, the overall critical current density, and the n-values of a number of samples as a function of the applied magnetic field (0-9 Tesla) at 4.2 K will be reported. Work supported by IGC Advanced Superconductors.
IMPROVEMENTS IN Bi2Sr2CaCu2Ox CONDUCTOR VIA DOPANTS: J. Schwartz*, A. Bhargava**, B. Boutemy*, and W. Wei*; *National High Magnetic Field Laboratory, 1800 E. Dirac Dr., Tallahassee, FL 32310; **University of Queensland, Brisbane, Qld 3072, Australia
An important characteristic of high temperature superconducting materials is the ability to carry large Jc at high magnetic field. As a result, the NHMFL anticipates using HTS conductor for the highest field region of the 1 GHz NMR magnet system. Two obstacles to high field Jc over long lengths are poor flux pinning and carbon-induced bubbling and tunneling. Here we report progress on these two challenges via fine-scale additives to the starting powder. To address the flux pinning issue, we are investigating nano-scale MgO additions. By growing the 2212 grains around the MgO particles, pinning centers are directly incorporated in the superconducting grains. To prevent bubbling and tunneling from CO2 gas that forms during melt processing we are investigating Ba-O additions. By trapping the carbon in BaCO3, CO2 formation is prevented. We report magnetic and electrical measurements of Jc, extensive microscopy, and x-ray diffraction of tapes formed with these approaches.
10:10 am INVITED
CRITICAL CURRENT DENSITY, HYSTERESIS LOSSES AND STRUCTURE ALONG HTSC WIRES: P.V. Bratukhin, I.A. Rudnev, Moscow State Engineering Physics Institute (Technical University), Kashirskoe sh. 31, 115409, Moscow, Russia
Critical current density hysteresis and losses were measured along Bi-HTSC/Ag wire. X-ray diffraciton analysis of the same samples allowed to observe structure features connected with critical current distribution along wire length.
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