Yukinobu Murakami

Development of Nb/sub 3/Sn superconductors for a 1 GHz NMR magnet. Dependence of high-field characteristics on tin content in bronze matrix

To realize a 1 GHz NMR magnet, superconducting properties such as critical current density (J/sub c/) and n-value are fundamental for conductors. J/sub c/ improvements of 15% to 27% have been observed in the conductor with Cu-15wt.%Sn-0.3wt.%Ti matrix compared with J/sub c/ in a conductor with Cu-13.wt%Sn-0.3wt.%Ti matrix. In contrast to J/sub c/, differences in n-values between conductors have not appeared. In this study, systematic analysis for dependence of J/sub c/ and n-value in the high field region on Sn content over 13wt.% in bronze was examined based on the microstructures, i.e. the amount of reacted layer, grain size of Nb/sub 3/Sn, and upper critical field (H/sub c2/) supported with stoichiometric analyses.

Development of high Sn content bronze processed Nb/sub 3/Sn superconducting wire for high field magnets

Bronze processed Nb/sub 3/Sn superconducting wire with Cu-16wt%Sn-0.3wt%Ti (16%Sn bronze) matrix has been developed. For the development, two-step approach was taken. At the first step, two kinds of small size round wires, having a bronze to niobium ratio (bronze ratio) of 2.5 and 1.9, were prepared. Heat treatment was made on these wires at 650/spl deg/C or 700/spl deg/C and the effects of bronze ratio and heat treatment temperature on critical current density (J/sub c/) in magnetic field region from 18 to 25 T were examined. A sample with a bronze ratio of 2.5 and heated at 700/spl deg/C was found to show the highest J/sub c/ of all. In the second step, we manufactured commercial scale rectangular cross-sectioned wire using 16%Sn bronze. J/sub c/ n-value in high magnetic field region are estimated for this wire. As a result, the wire showed J/sub c/ and n-value of 115 A/mm/sub 2/ and 37, respectively, at 22 T, 2.1 K, demonstrating the possibility as a candidate superconducting wire for high field magnets such as over-920 MHz NMR magnet.

Bronze route conductors for 1 GHz NMR superconducting magnet

Bronze route Nb/sub 3/Sn conductors applied to 1 GHz nuclear magnetic resonance spectrometer have been manufactured. Cu-1Swt%Sn-0.3wt%Ti (15% Sn-bronze) Nb/sub 3/Sn conductors employed in inner coils have shown overall J/sub c/ over 100 A/mm/sup 2/ in 21 T at 1.8 K. Other conductors with a Ta-core as a reinforcement employed in outer coils have presented a 0.2% proof strength of 300 MPa at 4.2 K. It is also reported that J/sub c/ of 15%-bronze conductors is enhanced to match that of the tube-processed Nb/sub 3/Sn conductors in the middle magnetic field region of 12-16 T.

Development of Bi-2212 multifilamentary wire for NMR usage

Abstract Double-sheathed Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi-2212) multifilamentary wire has proven that overall critical current density and mechanical strength, which meet the requirement of the driven-mode operation of the superconducting magnet of 1 GHz-class nuclear magnetic resonance (NMR). For the persistent-current (PC) mode operation, superconducting joint techniques in both cases of oxide–oxide and oxide–NbTi have been developed. It has been clarified that superconducting currents over 300 and 100 A can be transported through the joints, respectively, at 4.2 K in 0 T.

Field and temperature dependences of critical current in direct-heated Nb-tube processed Nb/sub 3/Al wires

High-field performance of Nb-tube processed Nb/sub 3/Al conductors is improved and allows these conductors for use above 20 T, when continuous direct-heating is applied before final annealing in the fabrication process. In the present study we prepared 0.74 mm/spl phi/ Nb/sub 3/Al wires containing 121/spl times/121 7-core elementary Nb/Al-Mg composites by this modified method and measured their critical current, magnetization and susceptibility as a function of field and temperature. From these measurements, we have found that the volume pinning force, F/sub p/ of these wires simply follows the Kramers scaling law, i.e. F/sub p//spl prop/B/sub c2//sup 2.5/b/sup 0.5/(1-b)/sup 2/ w here b=B/B/sub c2/, for the entire range of temperature measured, 4.2/spl sim/16 K. Since A15 phase grains formed are very fine, the most probable pinning source seems to be grain boundaries which are dense compared to other possible sources such as interfaces between Nb-Al alloy phase and Nb/sub 3/Al filaments.

Quench analysis of multisection superconducting magnet

The numerical quench simulation code includes the effect of the filament coupling loss. We apply this simulation code to two multisection high field magnets. In this paper we describe the modified quench simulation code which includes the effect of filament coupling loss and make comparisons between the experimental and analytical results.<<ETX>>

VAMAS critical current round robin test on a 2212 BSCCO Ag-sheathed tape

Aiming at the establishment of a reliable critical current, I/sub c/, a measurement method for oxide superconductors, a round robin test (RRT) has been implemented in Japan in the framework of VAMAS (Versailles Project on Advanced Materials and Standards), using a 2212 BSCCO Ag-sheathed tape conductor. In this RRT each participant received two pre-instrumented and pre-measured specimens and one freestanding specimen. Measurements were made at 4.2 K and magnetic fields ranging from 0 to 10 T. One of the pre-instrumented specimens was also routed among participants as a RRT specimen. Together with the RRT specimen, a superconductor I-V simulator was circulated to intercompare the I-V measurement set-ups used at participant labs. Measurements on pre-instrumented specimens have shown that I/sub c/ of Ag-sheathed tapes is sensitive to the heat cycle, which may be attributed to the deformation of the oxide superconductor by swelling and/or to the formation of cracks inside the oxide layer.<<ETX>>

Development of Nb 3 Sn Superconducting Wires for High-field Magnets

Synopsis: Research and development activities and some recent results related to Nb3Sn superconducting wires produced by Kobe Steel, Ltd. and Japan Superconductor Technology Inc. (JASTEC) are introduced. An outline of the activities is described from a historical point of view. Improvements in the characteristics (i.e., critical current density (Jc), n-value and mechanical properties) of bronze-processed Nb3Sn wires are reviewed. Finally, the status of development for the Ta-Sn powder-in-tube (TS-PIT) process newly proposed by Tachikawa is described.

Influence of Wire Parameters on Critical Current Versus Strain Characteristics of Bronze Processed

In order to develop bronze processed Nb₃Sn wire for the ITER CS coil operating under higher compressive strain, the influence of various parameters of wires such as filament diameter, barrier materials, barrier thickness, heat treatment pattern and Ti addition on critical current (I_c) versus intrinsic strain ε_ν(-1.0% <; ε_ν <; +0.1%) characteristics was investigated. The change of these parameters brought significant changes to superconducting properties such as I_c and n-value. In spite of different wire parameters, the strain dependency of normalized I_c was almost the same, except that a Ti addition affects the upper critical field B_c2. This result suggests that assuming the same Ti-addition level, Nb₃Sn wire with higher performance at a certain ε_ν would exhibit higher performance at any ε_ν in the compressive regime. Based on the result, bronze processed Nb₃Sn wires with non-Cu critical current density more than 1100 A/mm² at 12 T, 4.2 K, zero applied strain have been successfully developed for the CS coil.

{\hbox {Nb}}_{3}{\hbox {Sn}}

A direct measurement has been carried out of the upper critical magnetic field (B/sub c2/) of bronze-processed Nb/sub 3/Sn wires with and without the addition of various third-elements to the Cu-Sn matrix using a hybrid-magnet at the Tsukuba Magnet Laboratory at fields up to 30 T. The B/sub c2/ of pure Nb/sub 3/Sn rose with increasing heat treatment temperature up to 880/spl deg/C (B/sub c2/=24.7 T at 4.2 K), above which point it decreased rapidly. Its value was independent of the Sn content in the bronze. In the Ti addition samples, the optimum value of B/sub c2/ (=26 T at 4.2 K) depended on both Ti content and heat treatment temperature. When Sb was added, B/sub c2/ showed a sharp fall below a heat treatment of 700/spl deg/C due to the replacement at the Sn site by a Sb atom.