Synopsis:Recently the investigations on the local stress/strains and related properties in the engineered superconducting composites have been extensively carried out by using the pulsed neutron facilities, J-PARC TAKUMI. Firstly the key concepts are described in order to understand their mechanical-electromagnetic properties after the performance of TAKUMI is briefly introduced. Unique and important results have been obtained by the present diffraction studies. Highlights of the present review are the three dimensional description of strains in Nb 3 Sn filaments, the determination of force free strains at RT and 77 K for BSCCO and YBCO tapes, and of T o for the BSCCO tape and Nb 3 Sn wires, which is the initiation temperature of thermally induced residual strains. Typically the local axial strain exerted on Nb 3 Sn filaments has been firstly measured along the TF coil used for ITER project in the world.

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Synopsis:The Japan Atomic Energy Agency (JAEA) and National Institute for Material Science (NIMS) have been collaborating in the development of high-performance (i.e., more than 16 T and 80 kA) Nb 3 Al cable-in-conduit (CIC) conductor prepared using the rapid-heating, quenching and transformation (RHQT) process, and aiming for the application of this conductor to a demonstration plant. The technical issue relating to application of the RHQT Nb 3 Al strands to a fusion magnet is stabilization against perturbation. NIMS has developed a technique to attach a copper stabilizer using electroplating, and a sub-scale CIC conductor is developed using this conductor. JAEA performed a stability test of the developed CIC conductor to demonstrate the efficiency of this copper stabilization technique. The initial perturbation was applied via inductive heating, whose energy was calibrated using a calorimetric method. The measured stability margin is sufficiently high compared to that of a similar NbTi CIC conductor previously tested by the authors. In addition, a heat transfer coefficient to define the so-called limiting current is estimated to be about 1 kW/m 2 K, a sufficiently high value that is almost the same as that of a CIC conductor consisting of normal Cu stabilized strands. From these experimental results, it can be concluded that the copper stabilizer works efficiently from the viewpoint of stability, thus offering a solution to the remaining technical issues relating to the RHQT CIC conductor. On this basis, we can say that the RHQT Nb 3 Al CIC conductor is the most promising candidate for application to a magnet in the demonstration plant.

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