Satoru Murase

Critical current density of wire type Y-Ba-Cu oxide superconductor

We have fabricated wire type Y-Ba-Cu oxide superconductor by powder metallurgy technique. A large critical current density Jc of 7.25 × 102 A/cm2 at 77 K and 0 T and the resistive Tc transition of 89 K to 87 K were obtained for the wire type conductor heat treated without Cu sheath. However, the Jc(77 K) drastically decreased by a factor of 200, applying a magnetic field of 1 T. On the contrary, Jc(4.2 K) little changed; 1.63 × 102 A/cm2 at 1 T and 1.33 × 102 A/cm2 at 12 T. Based on the magnetic field dependence of Jc, we estimate upper critical field Bc2 (i.e. corresponding to Bc2 defined by Tc (offset)) and GL coherence length ζ.

AC loss measurement of 46 kA-13T Nb/sub 3/Sn conductor for ITER

AC losses of Nb/sub 3/Sn conductor samples with various void fractions for the ITER Central Solenoid Model Coil (CSMC) were measured by using calorimetric and magnetization techniques. The CSMC is designed to generate the magnetic field of 13 T at the operating current of 46 kA. The conductor consists of the multi-stage cable, having 1152 Nb/sub 3/Sn strands, and Incoloy 908 square jacket with circular hole. The strands are coated by chrome plating with 2 /spl mu/m layer. The last sub-cables are wrapped with Inconel tape, having high electric resistivity, to reduce the coupling current loss. The optimum void fraction for pulse coils is obtained from the relation between the coupling time constant and the void fraction. It is indicated that the sub-cable wrapping is very effective in limiting the coupling current between the sub-cables, as expected. The AC losses of the CS Insert were measured in various operating modes. From these obtained results, the validity of conductor design is demonstrated.

Microstructure and Superconducting Properties of Ag Sheathed (Bi, Pb)2Sr2Ca2Cu3Ox Tapes

For Ag sheathed Bi based (2223) phase tapes made by the powder-in-tube method, high critical current densities, Jc’s, of 66000 A/cm2 at 77K, 0T and 360000 A/cm2 at 4.2K, 0T were obtained based on the study of hardness or density in the oxide and the interface effect on Jc. Other important improvements were also achieved on the mechanical properties: Ag powders addition to oxides suppressed remarkably Jc degradation with bending after heat treatment; Ag-Al alloy sheath increased hardness, expecting high tensile strength.

Bulk and Wire Type Y–Ba–Cu Oxide Superconductor

We have fabricated the bulk Y–Ba–Cu oxide, various types of wire conductors and coils, and especially studied the critical current density Jc. Large Jcs were obtained at 77K and OT: 725A/cm2 for the non sheath wire, 560A/cm2 for the Ag sheathed wire. However, the Jc(77K) drastically decreased by a factor of hundred in a magnetic field lower than 1T while Jc(4.2K) little changed up to 12T. Based on the magnetic field dependence of Jc, for example, 2T of upper critical field Bc2(77K) and 47 to 80T of Bc2(4.2K) were obtained for the wire conductor.

FEM analysis of three directional strain states under applied tensile stress for various composite superconductors

Composite superconductors such as Cu/Nb/sub 3/Sn and Ag/Bi-oxides are subjected to thermally-induced residual strain by other component materials due to the around 1,000 K temperature difference between the reaction temperature and the cryogenic temperatures, and to applied tensile strain by the hoop stress of longitudinal (z) direction during the coil operation. To clarify especially the radial (r) and tangential (/spl theta/) strain behaviors including z-strain, we analyzed elastic-plastically multi-core model by computing of FEM for various composite conductors. As a result, applied tensile stress on the z-direction of the composite conductor gave monotonous decrease of thermally-induced rand /spl theta/-strains, which changed tensile to compressive strain. With increase in the z-strain effective strain showed the minimum value, not zero, at around z-strain-free state. Moreover it was found that all conductors are classified into three types by combination of component materials.

Effects of a high magnetic field on fracture toughness at 4.2 K for austenitic stainless steels

Abstract Structural stainless steels for cryogenic use in superconducting magnets for fusion reactors are used under high magnetic field and stress. The authors have performed fracture thoughness tests, using the unloading compliance method at 4.2 K on SUS304, 316LN and 304L stainless steels precracked at 77 K, in a varying magnetic field (0 and 8 T). Fracture toughness values ( J IC ) for 304 and 316 LN steels at 8 T decreased by 17 and 20%, respectively, as compared with the 0 T condition. On the other hand, J IC for 304L steel was 30% increased by applying a high magnetic field of 8 T. Details of martensite formation and austenite stability are considered in discussion.

Pb Introduction to the High-Tc Superconductor Bi-Sr-Ca-Cu-O

The effect of Pb substitution has been studied for the new high-Tc superconductor Bi-Sr-Ca-Cu-O. The zero resistivity temperature Tc(offset) was increased with increasing Pb content. A maximum Tc(offset) value of 85.5 K was obtained for the composition Bi0.5Pb0.5SrCaCu2Oy: an enhancement of 10 K compared with a non-Pb-additive sample. Further introduction of Pb caused a decrease in Tc, and finally an insulator phase transition occurred due to a second phase formation.

Thermal stability of oxide superconductor at various temperatures

Quench properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8//AgMg tape were experimentally investigated under a cryocooled condition in high magnetic fields. The critical current (I/sub c/), quench current (I/sub q/), and minimum quench energy (MQE) were measured at various initial temperatures of 4.2 K, 10 K, and 20 K and at magnetic fields of 7 T and 9 T. MQE was the minimum disturbance energy enough to make thermal quench and was evaluated from the input energy by a resistive heater. It was found that MQE exhibited the minimum value around 20 K. The temperature margin, difference between the initial temperature and the thermal runaway temperature, decreased monotonously with increase at the operating temperature. Since the temperature dependence of MQE did not agree with that of temperature margin, we focused on the internal energy calculated by integrating specific heat of the sample. The temperature dependence of the internal energy was in agreement with that of MQE qualitatively.

Development of 40 tesla class hybrid magnet system

The construction of a 40-T class hybrid magnet system is in progress at the National Research Institute for Metals, Japan. The present design concept for this system includes a 15-T superconducting magnet with a room-temperature clear bore of 400 mm and a 20-T polyhelix-type water-cooled resistive magnet with a clear bore of 50 mm, and a 25-T resistive magnet with a clear bore of 30 mm. The total maximum field to be reached is 40 T for the clear bore of 30 mm, and 35 T for the clear bore of 50 mm. Analytical results on the mechanical stress induced in the magnet system are presented. A new design of a Cu-housing conductor with vacancy is proposed for reducing the transverse compressive stress of the Nb/sub 3/Sn monolith. Cu-Al/sub 2/O/sub 3/ and Cu-Cr alloys are used as the conductor materials for the 25-T and 20-T water-cooled magnets, respectively. The final designs of the water-cooled magnets are also presented. >

Oxygen Deficiency and Cu Valence States of Superconducting Y-Ba-Cu Oxide

The oxygen deficiency, Cu valence states and superconducting properties were analized on Y0.4Ba0.6CuO3-x. The critical temperature and the normal-state resistivity varied depending on the change of CuIII/CuII ratio and/or the oxygen deficiency caused by the sintering atmospheres.