Masayuki Ishizuka

Superconducting properties and microstructures of Bi-2223 AgCu alloy sheathed tapes doped with Ti, Zr or Hf

Abstract AgCu doped with Ti, Zr or Hf have been used as sheath material for Bi-2223 superconducting tapes prepared by the powder-in-tube technique. Critical current density, Jc, was obtained to be 9.2 × 104 A/cm2at 4.2 K, 14 T and 3.4 × 104 A/cm2 at 77 K, 0 T, which is 2–3 times larger than that of non-doped samples. A small amount of doping such as Ti, Zr or Hf of 0.03–0.1 at.% into Ag-10 at.% Cu alloy sheath enhanced growth of large plate-like grains, especially at interfaces between the AgCu alloy sheath and oxide core. Furthermore, Bi-2223 phase alignment was significantly improved. These microstructural modifications are believed to be responsible for the improved high-Jc property.

Influences of Cu composition and sintering condition in Bi-2223 tapes using AgCu alloy sheath doped with Ti, Zr or Hf

Abstract Bi-2223 AgCu alloy sheathed tapes doped with Ti, Zr or Hf were fabricated by a powder-in-tube technique using intermediate uniaxial presses and variations in total sintering times. Increasing Cu compositions in the AgCu alloy sheath doped with certain elements into the sheath, combined with appropriate total sintering times were found to lead good superconducting properties. Furthermore, the best total sintering time varied according to the amount of Cu in the AgCu alloy sheath and the existence of doping elements. A transport critical current density, J c , of 4.1 × 10 4 A/cm 2 at 4.2 K, 14 T and 2.2 × 10 4 A/cm 2 at 77 K, 0 T was achieved in Ag-10 at% Cu-0.1 at% Hf sheathed Bi-2223 tapes sintered for total 200 h.

Jc property and microstructure of Bi2223 tapes made using AgCu alloy sheaths doped with Ti, Zr or Hf

Abstract Bi-2223 superconducting tapes were prepared by the powder-in-tube technique using Ag-10 at%Cu alloy sheaths with and without a small amount of doping elements of Ti, Zr or Hf, and repetition of sintering and cold pressing. The doped samples showed a high critical current density, J c of 5–9 × 10 4 A/cm 2 , at 4.2 K and 14 T. Micrograph examinations on these samples revealed a modified Bi-2223 grain structure at the sheath/core interface and also a more dense and aligned microstructure. Furthermore, amorphous, small disc-like regions, less than 5 nm in thickness parallel to the (001) plane, were found to be incorporated in the Bi-2223 lattice only for the doped samples. Critical current properties measured by magnetization and resistive methods were described correlating with the microstructures and the magnetic plux pinning. These amorphous regions are likely to provide the effective flux pinning centers in the Bi-2223 superconductors.

Microstructure evolution in high-Tc Bi(Pb)-2223/Ag(Hf) tapes

Abstract The microstructures of high- T c Bi(Pb)-2223 tapes in Ag sheaths doped with Hf have been examined by high resolution transmission electron microscopy. Different microstructural features are found in samples with different annealing times. The J c values increase with annealing time, reach a maximum after 150 h at 827°C and then decrease. The low J c after a short annealing time is attributed to a poor connectivity of the grains and the presence of frequent stacking faults due to an incomplete formation of Bi(Pb)-2223. For longer annealing times a deterioration of the superconductor is observed which starts at grain boundaries and leads to the formation of amorphous phase between adjoining grains. The samples with the highest J c reveal a well-developed texture with large plate-like grains strongly linked together. Many defects like dislocations, small voids, small and large angle grain boundaries and, in particular, tilt-type subgrain boundaries are possible pinning centers of magnetic flux.

Critical current densities of AgCu-sheathed Bi-2212 multifilamentary round wires in long length

Abstract Ag–Cu alloy sheathed Bi-2212 round wires have been fabricated by the powder-in-tube method. Short samples show critical current ( I c ) values of more than 150 A at 4.2 K and 10 T, while I c for a small coil with total length of 10 m reduces to about 30% of the values obtained for short samples. In order to clarify the factors to deteriorate I c for coils, superconducting properties and the microstructures have been examined. The difference in transport I c between short samples and coils can be attributed not to the intrinsic properties of Bi-2212 grains but to the extrinsic limiting factors, such as voids that are formed by the released gases inside the wires with long length during heat treatment.

Magnetic field and temperature dependence of critical current density in Hf-doped Bi-2223/Ag–Cu alloy sheathed tapes

Abstract Bi-2223/Ag–Cu alloy sheathed tapes have been fabricated by the powder-in-tube technique using Ag–10 at.% Cu alloy sheath doped with Ti or Hf of less than 0.1 at.%. Critical current density ( J c ) was measured as a function of temperature between 30 and 90 K in the magnetic field up to 3 T. The flux-pinning force density ( F p = J c × B ) was also calculated. Normalized pinning force ( f = F p / F p max ) vs. normalized field ( b = B / B s ) curves for the Hf-doped samples were compared with those of non-doped Bi-2223/pure Ag and Bi-2223/Ag–Cu tapes. High J c values of 9.5×10 4 A/cm 2 at 30 K, 0 T and 4.5×10 4 A/cm 2 at 30 K, 3 T were obtained for the Hf-doped samples. The Hf-doping caused no substantial change in superconducting critical temperature ( T c ). The Hf-doping seems to be effective to enhance Bi-2223 crystallization and to improve grain alignment as well as electrical connection between Bi-2223 grains. The n value of Hf-doped sample reached about 13 at 30 K, 1 T, which is lower than 23 of non-doped Bi-2223/pure Ag.

Development of a 10 T Cryocooled Superconducting Magnet with a Room Temperature Bore of 360 mm for a 29 T Hybrid Magnet

We have manufactured and tested a cryocooled superconducting magnet designed for 10 T with a room temperature bore of 360 mm for a hybrid magnet designed for 29 T. The cryocooled superconducting magnet generated so far a magnetic field of 9.5 T. Furthermore, in combination with a water‐cooled resistive magnet it generated a magnetic field of 27.5 T. As we succeeded in the magnetic levitation test of InSb using this hybrid magnet, we confirmed the usefulness of the newly developed magnet system for a novel process development of diamagnetic materials in the minute gravity environment.

Chapter 132 – Cryogen-free superconducting magnet fabricated by a react-and-wind method employing Nb3Sn wires with CuNbTi reinforcement

Publisher Summary This chapter describes a cryogen-free superconducting magnet wound with pre-reacted CuNbTi/Nb3Sn wires. A newly developed high temperature heat-treatment furnace combined with the wide bore cryogen-free superconducting magnet is introduced for an in-field process application. Practical multifilamentary Nb3Sn wires with CuNbTi reinforcement (CuNbTi/Nb3Sn) exhibit the splendid mechanical tolerance of 340 MPa proof stress. The performance test for the CuNbTi/Nb3Sn coil is carried out, and the coil generated 2.2 T at 180 A as the individual test. In the combination test in a background field of 5.6 T, the react and wind processed CuNbTi/Nb3Sn coil generated 7.5 T in a 220 mm room temperature bore. The wide bore cryogen-free superconducting magnet wound with highly strengthened CuNbTi/Nb3Sn wires is now being used for a high field heat-treatment equipment at 7 T. This wide bore furnace provides special heat-treatment conditions of high temperature 1500oC in fields up to 7.0 T in a 40 mm sample bore. A react-and-wind method to fabricate a wide bore cryogen-free superconducting magnet is intended employing pre-reacted high-strength Nb3Sn wires reinforced with CuNbTi composite.

Microstructures and Pinning Forces of Ag-Cu Alloy Sheathed Tapes

We measured high-resolution transmission electron microscope images (HRTEM) for the Hf-doped Ag-Cu sheathed (Bi,Pb)2Sr2Ca2Cu3Oy (Bi-2223) tape and Ba-doped Bi-2223 bulk sample. The HRTEM images of the crystal a-c plane indicate that the several atoms in the SrO layers have different brightness. This suggests the possibility that Hf or Ba atoms are substituted for Sr atoms. The influence of the microstructures on the critical current was studied by the magnetic measurement. The result indicates the improvement of the magnetic Jc for the doped samples, suggesting that a small amount of the doping acts as the effective pinning centers of the fluxes in the both samples. The Hf or Ba doping effect is discussed based on the relation between the volume pinning force and the microstructures.

Superconducting Properties of Bi-2212 Multifilamentary Round Wires With Double Layered Core Filaments

Multifilamentary Ag-sheathed Bi-2212 round-shaped wires with double layered core-filaments and AgCu alloy sheathed Bi-2212 round wires were fabricated by the powder in tube technique. Composites consisting of Ag outer sheath and the filaments with number of 7, 37 and 61 and a composite of AgCu alloy outer sheath having 37 and 61 filaments were drawn into wires of 1mm in diameter. The wires were heat treated by a conventional partial-melting process. High oxide core ratio of ∼50% to wire-cross-sectional area could realize high overall critical current densities (Jc) of 280A/mm2 at 4.2K, 10T in Ag sheathed wires with 61-filaments and Jc of 310A/mm2 in AgCu alloy sheathed wires with 37-filaments.