Yuji Aoki

Critical current variation of Rutherford cable of Bi-2212 in high magnetic fields with transverse stress

Abstract 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 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 with transverse stress. The results show that the cable can withstand stresses up to 60 MPa with a strain of about 0.3% for the face loading orientation and 100 MPa for the edge loading orientation.

A High-Tc Superconducting Rutherford Cable Using Bi-2212 Oxide Superconducting Round Wire

We developed a new robust Rutherford cable using Bi-2212 high temperature superconducting (HTS) wire, which consisted of 427 superconducting filaments and which had a critical current density (Jc) value of 2.400D7;1 05A/cm2 at 4.2K in self-field. For applications requiring a Rutherford cable with a core such as NiCr, we found that a plasma sprayed ZrO2 film was most effective in preventing “poisoning” elements present in the core from diffusing into and poisoning the HTS wire. Rutherford cable made with this wire and a thin NiCr, core protected by ZrO2 film barrier layer was able to carry an Ic value of 3,570A. The Ic degradation in Bi-2212 AgMgSb sheathed wire was only 10%. Finally, we demonstrated the successful fabrication of an 80m-long Rutherford cable.

Superconducting Properties of (Bi,Pb)2Sr2Ca2Cu3Ox Multifilament Wires and Fabrication of a Coil

We successfully fabricated the 200m-class (Bi,Pb)2Sr2Ca2Cu3Ox Ag sheathed wires with Jc value of 12,000A/cm2 at 77K and 0T. The Ag sheathed wires had very good reproducibility and the distribution of Jc value was reduced to be ±7% by reduction of sausaging. We fabricated a coil with 50mm in inner diameter, 160mm in outer diameter and 108mm in height using a react & wind technique. The coil was evaluated using a GM-type refrigerator and carried Ic value of 33A and generated Bmax of 2.3T at 20K.

Development of large current capacity Bi-2212 monolithic conductors

Abstract We developed rectangular-shaped Bi-2212 conductors. At 4.2 K and 30 T, the 37- and 349-filament conductors exhibited J C values of 151 and 125 kA/cm 2 , respectively. Moreover, we measured the distribution of I C for a 25 m-class 349-filament conductor. The end-to-end I C value was 66 A at 63 K, self-field, and the variation in I C was about ±10%. We also fabricated a test coil with 50 m-class, 349-filament conductor. The test coil carried 510 A (using a criterion of 10 −13 Ωxa0m) and generated B 0 =0.95 T at 4.2 K without backup field, resulting in a current density in the test coil of 150 A/mm 2 . The coil performance was almost 80% that of a short sample with a magnetic field applied perpendicular to the tape surface.

Effects of Microstructural Improvement on the Superconducting Properties of Bi2Sr2CaCu2Ox Multilayer Tapes

The reduction of Ca and Cu concentration from 2212 composition was effective to improve the Jc value of the multilayer tapes. The amount of (11) phase was reduced and superconducting phase was increased by this reduction. High Jc value of 150kA/cm2 was obtained at 20K in self field. The Jc-B characteristics at 20K suggested that the reduction of Ca and Cu concentration introduced pinning centers. The coil fabricated by a react & wind technique using 100m class superconducting tapes carried 65A at 12K and generated 1.62T.