POSTER SESSION 1PO6: Wires, Magnets, and Components

Monday, Feb. 21, 2:30 p.m. – 4:30 p.m., Hall D (GRB)

1PO6-1 Effect of Various Processing Variables on Grain Alignment at Bi-2212/Ag Interface

Mark O. Rikel*, Jodi L. Reeves, Nicole A. Scarbrough, David Zwicky, Eric E. Hellstrom, and David C. Larbalestier. Applied Superconductivity Center, University of Wisconsin, Madison, WI 53706, USA. *On leave from Lebedev Physics Institute, Russian Academy of Sciences, Moscow, 117924 Russia.

Presenting Author: M.O. Rikel

The effect of conductor geometry, maximum melt-processing temperature (Tm), Bi₂Sr₂CaCu₂O_x (Bi-2212) composition, and preannealing and intermediate rolling (PAIR) on grain alignment at the Bi2212/Ag interface was studied using scanning electron microscopy and X-ray diffraction. We confirmed that Bi-2212 grains with the ab-planes parallel to the Bi2212/Ag interface are the dominant microstructural feature in both wires and tapes. In round wires, we observed a pronounced axial texture and found that this texture is strongly dependent on Tm because of the development of outgrowths at higher Tm. In monocore tapes, we found that grain alignment depends on Bi2212 composition: the 0020 rocking curves were 25 ± 5% narrower for Bi2212 with Sr/Ca = 1.3 than for Sr/Ca = 2.75. PAIR conditions also affect grain alignment by changing the roughness of the interface and also the texture of the Ag sheath: changing the dominant texture component from (110) to (111) resulted in a 20 ± 5% better alignment. The results suggest that grain alignment in the vicinity of Bi2212/Ag interface is affected by the factors that modify the surface energy between BSCCO and Ag.

1PO6-2 Fabrication of Heavily Pb-doped Bi2212/Ag Composite Tapes

Keisuke Sugita, Keita Murakami, Jun-ichi Shimoyama, Kenji D. Otzschi and Kohji Kishio, Department of Superconductivity, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Presenting Author: K. Sugita

Although Bi2212 is one of the most promising high J_c superconductors, the drastic decrease of J_c under magnetic fields at higher temperature has been preventing its extensive applications. Recently, we have found that heavy Pb-doping dramatically improves J_c properties of the Bi2212 single crystal, and hence, development of Bi(Pb)2212 wires have been expected.

We have attempted to fabricate Bi(Pb)2212/Ag tapes with high J_c even at high temperatures in magnetic fields by two methods. One is the conventional melt-solidification under 1%O₂/Ar atmosphere and the other is a two-step synthesis, where amorphous Bi(Pb)2212 was prepared on Ag substrate by quenching from molten state in air, and then annealed in 1%O₂/Ar gas at the temperature just below the partial melting point for crystallization.

The melt-solidified tapes had a good alignment of large grains (~100m m) throughout the superconducting layer, but impurity phases grew large (~10m m). On the other hand, amorphous-to-crystallized tapes contained less amount of impurities with smaller size, but the Bi(Pb)2212 crystals became rather small (· 20m m) and morphology is yet to be optimized. So far, their J_c at 10K under 0T (9.8x10³A/cm² and 2.8x10³A/cm², respectively) are lower than Pb-free Bi2212/Ag tapes. Both tapes seems to have less-sophisticated grain coupling, and detailed differences between these tapes and strategy to fabricate better tapes will be presented.

1PO6-3 Strain-Tolerant Bi-2212 Cable-in-Conduit

Peter M. McIntyre 1, Nikoli Diaczenko 1, Timothy Elliott 1, Rainer Soika 1, Mustafa Yavuz 1, Leszek Motowidlo 2, and Gan Liang 3. 1 Department of Physics, Texas A&M University, College Station, TX 77843-4242. 2 IGC Advanced Superconductor; Waterbury, CT 06704. 3 Sam Houston State University, Huntsville, TX.

Presenting Author: R. Soika

The strain sensitivity of Bi-2212 remains a major obstacle for its use in high-field magnet applications. We have designed and fabricated a Bi-2212 cable-in-conduit with improved mechanical properties. Six strands of Bi-2212 are cabled around a hollow Inconel X 750 tube and then sheathed in an Inconel X 750 armor tube that is drawn onto this assembly. When this cable assembly is compressively loaded, the thin-wall inner tube protects the superconductor by virtue of its soft effective modulus whereas the outer armor carries nearly all the mechanical load. We will review the design and present test results of the cable.

1PO6-4 Development of Laminated Bi-2212 Powder-In-Tube Conductors

Dah-Wei Yuan, Concurrent Technologies Corporation, Johnstown, PA 15904, and Thomas L. Francavilla, Code 6340, Naval Research Laboratory, Washington, DC 20375

Presenting Author: D.-W. Yuan

Bi-2212 superconducting wires and tapes are good candidates for high magnetic field (>20 Tesla) applications, where the use of conventional metallic superconductors is inappropriate. In this study, a modified powder-in-tube approach to make silver-sheathed multifilamentary tapes is reported. The conductor consists of laminated Bi-2212 monocore tapes and is rolled using a turkshead. The resultant fully-treated multifilamentary tapes exhibit satisfactory integrity without any structural defects. The cryogenic properties of the conductors are found to depend on the filament dimension and uniformity. For short conductors, optimum critical current density (J_c) at 4.2 K is determined to be 90 000 A/cm² in a 7-filament tape (5T and B perpendicular to tape surface) where the average filament thickness is about 16 mm. The enhancement of J_c is attributed to the high Bi-2212 grain alignment along the Ag/oxide interfaces and uniform dimensions within the laminate conductors.

1PO6-5 Stability for Ag Sheathed Bi₂Sr₂CaCu₂O₈ Tape Coils under Strong Electromagnetic Force State

S. Awaji 1, K. Watanabe 1, M. Motokawa 1, T. Wakuda 2, and M. Okada 2. 1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan, CREST, Japan Science and Technology Corporation, Japan. 2 Hitachi Research Laboratory, Hitach, Ltd.,Hitachi 319-1292, Japan.

Presenting Author: S. Awaji

We made a test magnet with large bore by using Ag sheathed Bi₂Sr₂CaCu₂O₈ tape for investigation of the mechanical and transport properties under strong electromagnetic force state. The Bi₂Sr₂CaCu₂O₈ tape used in this study is reinforced by using AgMg alloy for sheath materials. This test magnet consists of five double pancake coils which are reinforced by a cowinding technique with Hastelloy tapes. Outer and inner diameter of the coils are 234 mm and 280 mm, respectively. Strain gauges are mounted at inner, middle and outer part of each coil in order to measure strain directly. The experiment was performed in immersing liquid He and the back-up field of 10 T generated by a large bore superconducting magnet SM1 in High Field Laboratory for Superconducting Materials, IMR, Tohoku University.

Although the critical current value was about 200 A, the operation currents up to 256 A could be flew stably. However, when the operation current reached to 275 A, the total voltage increased rapidly. The strain values at the operation current of 275 A was about 0.25% for a coil reinforced by one Hastelloy tape but 0.1% for that reinforced by three Hastelloy tape. These values are consistent with calculated values. It is found that the voltage increase occurred first at the one Hastelloy tape reinforced coil and propagated to the other coils. The stability of superconductivity for this test coil will be discussed.

1PO6-6 Critical Current Variation of Rutherford Cable of Bi-2212 in High Magnetic Fields with Transverse Stress

Daniel R. Dietderich 1, Takayo Hasegawa 2, Yuji Aoki 2, and Ronald M. Scanlan 1. 1 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 2 Showa Electric Wire & Cable Co. Ltd., Kawasaki, Japan.

Presenting Author: D.R. Dietderich

For numerous high-energy physics applications superconducting cables are subjected to large stresses and high magnetic fields during service. It is essential to know how these cables perform in these operating conditions. Transverse loading experiments on wire has shown that a significant drop in critical current occurs for stresses greater than 50 MPa. However, many applications require that the Bi-2212 conductor withstand stresses greater than 100 MPa without permanent degradation. Therefore, a study of epoxy impregnated cables, identical to those used in accelerator magnet applications, has been performed. This work presents the first results of Rutherford cables of Bi-2212 in traverse field with transverse stress.

*This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.

1PO6-7 Is either liquid phase transformation or 2223 phase decomposition during finally processing of Bi-2223/Ag PIT tapes?

R. Zeng, X.K. Fu, P. Yao, H.K. Liu, S.X. Dou, Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia

Presenting Author: R. Zeng

In order to detailed determine that is either 2223 phase decomposition or residual liquid transformation during finally processing of Bi-2223/Ag PIT tapes, the two steps procedure and quenching technique at different temperature has been used to divide these two parts. It was found that the comparatively stable temperature is about between 823° C~832° C during finally cooling process. At higher than this stable temperature region, 2223 phase equilibrium with more liquid and other secondary phase. Below the stable temperature range, liquid phase transform major into 2212 and at lower than 810° C, 2223 phase decompose into 3221 phase. These indicate that the residual liquid phase almost transform into 2212 phase and other secondary phase at low temperature if did not used slow cooling or other heat-treatment procedure (for example the multi-steps procedure) and 2223 would decompose into 3221 and other secondary phase at lower than 810° C. It is indicated that the residual "frozen liquid strips" becomes the crucial barrier of current transport, and it illustrates a micro current limited mechanism.

1PO6-8 Correlations among Electromagnetic Parameters of (Bi,Pb)₂Sr₂Ca₂Cu₃O_x/Ag Multifilamentary Tapes

L.A. Schwartzkopf 1, J. Jiang 2, X.Y. Cai 2, D. Apodaca 2, and D.C. Larbalestier 2. 1 Dept. of Physics and Astronomy, Minnesota State U., Mankato, MN 56001. 2 Applied Superconductivity Center, U. of Wisconsin, Madison, WI 53706.

Presenting Author: L.A. Schwartzkopf

We have performed an extensive electromagnetic characterization of thirteen fully-processed (Bi,Pb)₂Sr₂Ca₂Cu₃O_x/Ag multifilamentary tapes. We have obtained extended voltage-current characteristics of the tapes, from which we have extracted the field-dependent J_c(H), the characteristic field obtained from the relation J_c ~ exp(-H/Hp), and the irreversibility field H*. All measurements were made at 77K and with the applied field H perpendicular to the tape surface. Correlations found among the parameters J_c(self-field), J_c(0.1T), Hp and H* will be presented.

1PO6-9 Local magnetooptic measurements of field penetration and T_c values in Multifilamentary BSCCO-2223 tapes

Lev A. Dorosinskii 1, Huseyin Bocuk 1, Ugur Topal 1, Cengiz Birlikseven 1, Anatolii Polyanskii 2, and Matthew Feldmann 2. 1 National Metrology Institute, P.K.21, 41470 Gebze-Kocaeli, Turkey. 2 Applied Superconductivity Center University of Wisconsin, 1500 Engineering Dr., Madison WI 53706 USA.

Presenting Author: H. Bocuk

Multifilamentary BSCCO-2223 tapes were studied using the magnetooptic imaging technique. The silver coating layer was polished off, so that single superconductor filaments could be observed, and magnetooptic images of field penetration were observed together with metallographic pictures of the filaments in the tape. An improvement, achieved compared to the earlier studies, was a possibility to measure locally the magnitude of dc or ac filed in the sample. Thus the superconducting transition was registered locally in various regions of the filaments using magnetooptic measurements of the local ac susceptibility. A slight scatter of the critical temperature T_c was observed and the values of T_c were found to correlate with the magnetooptic images of field penetration into the filaments. Such measurements can be useful for understanding the factors limiting the critical current density and for improving the quality of tapes.