Kenneth R. Marken

Development of round multifilament Bi-2212/Ag wires for high field magnet applications

Bi-2212/Ag conductor is one of the most promising materials for expanding superconducting magnet applications to higher fields and/or temperatures than present LTS systems. From the view point of practical application, Bi-2212 round wires have significant advantages over more typical HTS tape conductors, such as no anisotropy, ease of handling and simpler coil winding, allowing considerable flexibility in the magnet design. Development efforts at OST have been aimed at enhancing transport properties in long length round wires for high field magnet applications. Recently, significant improvements in the J/sub E/ and J/sub c/ performance have been achieved by optimizing the starting powders, the filament size and fill factor, the deformation processes, and the melt-solidification parameters. The highest J/sub E/ of 266 A/mm/sup 2/ and J/sub c/ of 950 A/mm/sup 2/ at 4.2 K, 45 T with n-value of 17 was obtained in 0.81 mm wire. In this paper progress on the development of Bi-2212 round wires will be reported.

BSCCO-2212 conductor development at Oxford Superconducting Technology

Three types of BSCCO-2212 conductor are in development at Oxford Superconducting Technology (OST). Prototype size batches of multifilament tape continue to be manufactured for use in a 5 T high field insert magnet demonstration in collaboration with the National High Magnetic Field Lab. Progress will be reported in improving uniformity of microstructure and transport properties in these tapes. Development of multifilament wire has been renewed in response to interest from the high energy physics community. Issues of interest in these wires include the effects on J/sub c/ from filament size and distribution, as well as chemical composition and impurity content in the ceramic. Progress in J/sub c/ and J/sub E/ at 4.2 K in these wires will be discussed. Optimization of dip-coated 2212 tape for MRI magnet applications is also underway, as part of a Superconductivity Partnership Initiative. Various cost and performance tradeoffs will be considered, including the silver/ceramic ratio, the thickness of the ceramic, and the choice of batch or continuous heat treatment. The status of these optimization efforts will be reported.

Development of 3 T class Bi-2212 insert coils for high field NMR

Based on a successful 1 T Class PIT insert coil, the authors are now pursuing a 3 T Class insert coil. This paper describes the design and the latest conductor and coil test results, as well as supporting experiments. The final product is envisioned to contain 3 concentric sections, requiring over one kilometer of conductor. This will be tested in a 20 T large bore resistive magnet at the NHMFL. Experimental work focuses on the use of conductor with a silver-alloy matrix in the outer sections, that are subject to the largest stresses when operated in a background field. Results from heat treatment optimization for wound coils, mechanical test of conductors and coil design studies are reported.

High Field Insert Coils From Bi-2212/Ag Round Wires

Bi-2212/Ag round wire is a promising and practical material for extending high field superconducting magnets beyond the limits of Nb3Sn. Efforts to develop superconducting magnets in the 25 to 30 T range include fabrication and test of practical size insert coils using this wire. Recent studies have focused on improvements in wire performance, wire insulation, and coil fabrication for wind-and-react coils. Continued improvements in the engineering critical current density (JE) and the critical current density (Jc) performance have been achieved by optimizing the starting precursor composition, and the heat treatments. The highest Je of 1580 A/mm2 at 4.2 K, 0 T and 420 A/mm2 at 4.2 K, 31 T were obtained in 0.81 mm wire. In particular, significant progress on braided insulation has been made for enabling a robust procedure for wind-and-react Bi-2212 solenoid coils. Performance of three of these coils has been measured in background fields up to 19 T, showing good prospects for high field magnet application of this conductor.

Progress in

The high field critical current density (Jc) and engineering current density (JE) in multifilament Bi-2212 round wires continue to improve, suggesting this material may well enable the next generation of high field magnets. The critical current in round wires shows no anisotropy with respect to applied field. Recent efforts have focused on characterizing the anisotropy in low aspect ratio rectangular wires; these results show that isotropic 2212 wire should be possible with rectangular cross sections if the aspect ratio is kept below 1.6. A braided insulation is now available for these conductors, enabling a robust procedure for wind-and-react coils. Ic and generated field have been measured in a series of such coils of increasing dimensions. Performance of two of these coils has been measured in background fields up to 19 T, showing good prospects for high field magnet application of this conductor

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Ceramic-silver composite conductors have been fabricated in lengths greater than 200 meters using both powder-in-tube and dip-coated methods. Progress has been made in conductor uniformity through control of process steps including powder packing, tape coating, deformation, and heat treatment. Critical current density (J/sub c/) in lengths up to 100 meters has been evaluated by measuring end to end current in coils, both pancake wound and solenoid wound. These coils were made using a wind-and-react technique. J/sub c/ values greater than 10/sup 5/ A/cm/sup 2/ have been attained over 17 m lengths of conductor in these coils in self field at 4.2 K. The magnetic field dependence of 4.2 K J/sub c/ in fields its high as 17 T will be reported for these coils. Microstructural factors affecting J/sub c/ are discussed.

-2212 Wires for High Magnetic Field Applications

Efforts to increase critical current density (Jc) and engineering current density (JE) in round multifilament Bi‐2212/Ag wires have included studies of the effect of precursor composition. Variations in the cation ratios in the precursor have a number of effects on conductor processing and properties, including the melt temperature, the relative sharpness of the melting event, the crystallization behavior including secondary phase formation and growth, and the peak Jc and JE attainable. Multifilamentary wires and dip coated tapes made from four precursors with different cation ratios were studied using an experimental matrix of heat treatments that systematically varied melt temperature, cooling rate, annealing temperature, and annealing time. Average Jc and JE were determined for all samples. In addition two different levels of Ag additions were given to two of the cation ratios, and subjected to the same heat treatment matrix. The results showed a strong dependence of microstructure and Jc on cation rat...

Progress in BSCCO-2212/silver composite tape conductors

Engineering considerations for the production of small HT/sub c/ coils for commercial high current applications have been evaluated. Part of this study involved investigations of the conditions under which coils are wound, heat treated and potted in order to reproduce, in lengths exceeding 50 m, the critical current density (J/sub c/) which can be attained in short samples of a few cm in length. Individual pancake coils were evaluated by testing their 4.2 K superconducting current capacity in the presence of an applied magnetic field up to 10 T. The performance of each coil was compared to the J/sub c/ capacity predicted from short sample J/sub c/ testing on samples of a few cm length. Coils were then stacked to form prototype magnets and the field generated by the magnet was measured using a Hall probe.<<ETX>>

Studies of Precursor Composition Effect on Jc in Bi‐2212/Ag Wires and Tapes

The development of a 25 T superconducting magnet is usually envisioned with the use of an HTS insert coil. Previously, we reported the successful development of a 3 T coil in a 19 T background field based on BSCCO 2212 conductor. Here we report on the progress toward a larger 5 T insert with 38 mm free bore. The design is introduced, which calls for 2 stacks of double pancakes and an outer layer wound section, all electrically in series. Reacted conductor is used with insulated steel tapes as reinforcement. Results in terms of field dependence of the critical currents and stress tolerance are presented for both bare conductors and double pancakes. The latter are tested in a 19 T, 0.17 m cold bore, magnet assembly.

Fabrication of high T/sub c/ coils from BSCCO 2212 powder in tube and dip coated tape

Issues for controlling the critical current density (J/sub c/) in long tapes and wires include homogeneity of the starting powders, optimization of the ceramic size and shape, uniformity of the deformation or coating processes, and control of the heat treatment parameters. This range of issues is discussed for both multilayer dip-coated and multifilamentary powder-in-tube composites. In particular, J/sub c/ is shown to depend strongly on ceramic size and shape. Continuing efforts to correlate J/sub c/ with processing issues are presented. Progress toward applications in high field coils is described.