Shigeo Nakayama

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.

Highly-strengthened alumina-copper alloy matrix (Nb,Ti)/sub 3/Sn conductor fabricated by using the tube process

In order to fabricate a large-bore, high-field magnet which achieves a low foil weight and volume, a high strength compound superconducting wire is required. The alumina-copper strengthened (Nb,Ti)/sub 3/Sn wire which contained 30 vol.% alumina-Cu alloy fabricated by using the tube process has been developed and tested for critical current density, mechanical properties, transverse compressive stress effects and related properties. As a result, it was found that the reinforced (Nb,Ti)/sub 3/Sn wire had high transverse compressive stress tolerance, for example only 3% decrease which was 1/3 of the Cu matrix wire in I/sub c//I/sub c0/ at 60 MPa and reversibility in I/sub c/ between 0 and 200 MPa. Using the newly developed reinforced-(Nb,Ti)/sub 3/Sn wire, it will be possible to fabricate a lightweight, large-bore, high-field and compact superconducting magnet in the near future.

A cryocooler-cooled 10 T superconducting magnet with 100 mm room temperature bore

A NbTi/Nb/sub 3/Sn superconducting magnet directly cooled by a 4 K cryocooler has been fabricated. It successfully attained a 10 T field at the center of a 100 mm room temperature bore. A 4 K Gifford-McMahon (GM) cryocooler, using Er/sub 3/Ni regenerator, cools the magnet without the use of liquid helium. Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ superconducting power leads were adopted to reduce heat input to the 4 K stage. The coil heat is removed through heat conducting copper cylinders. The coil winding is epoxy-impregnated without a bore tube to stabilize the magnet against quenching. Two diode shunt circuits are placed in the cryostat to protect the coils. A fast ramp of 10 T/20 min, was attained by reducing Nb/sub 3/Sn conductor hysteresis loss and by decreasing the contact resistance between the coil and the conduction cylinder.

A 10 T cryo-cooled superconducting magnet with 100 mm room temperature bore

Abstract A cryo-cooled NbTi/Nb 3 Sn superconducting magnet has been fabricated. It generated 10T field in the center of a 100 mm room temperature bore. A 4K GM refrigerator, using Er 3 Ni regenerator material, cooled the magnet without help of liquid helium. Heat generated in coils is removed through the heat conduction copper cylinder attached on the outer wall of each coil. Bi(2212) superconducting current leads are adopted to reduce heat leakage into the 4K stage. Two diodes shunt circuits were set into the cryostat to protect the coils. Fast ramp, 8T energization within 15 min, was attained by controlling the hysteresis loss for the Nb 3 Sn conductor.

Fabrication of superconductor for the DPC-TJ coil☆

Abstract A forced-cooled superconducting coil (DPC-TJ) was wound with a double walled cable-in-conduit referred to as preformed-armour type C ICC. In this paper, we describe the fabrication of the conductor for the DPC-TJ coil with the first conduit, which plays a role in sealing the supercritical helium from the vacuum. Because the DPC-TJ coil has a high average current density of 40 A mm−2 (12 T,4.2 K) in the winding area, an (NbTi)3Sn strand formed by the Nb tube method was selected, which has a very high critical current density in the non-Cu area. As a result of development work, a strand could be fabricated which met the following requirements: critical current density > 600 A mm−2 at 12 T and residual resistivity ratio (RRR) value > 50. A fabrication line for the cable-in-conduit conductors using the roll-forming method was also developed. Through fabrication of the conductor for the DPC-TJ coil, it was demonstrated that large and long conductors could be fabricated for future fusion reactors.