Residual Strains in ITER Conductors by Neutron Diffraction

Abstract

Measurements of internal strains in the superconducting constituent (Nb3Sn phase in Nb3Sn strand) in two cable-in-conduit conductors (CICC) for International Thermonuclear Experimental Reactor were performed using an engineering materials diffractometer TAKUMI of J-PARC. From strain measurements in a CICC for the toroidal field magnet after a performance test of cyclic current, in 100 mm long cut bars, a peak broadening and a large relaxation on residual strain were observed in Nb3Sn phase at a portion received a high magnetic field (high field zone). Internal strain measurements were also conducted in a CICC for the central solenoidal magnets after the similar performance test, in the full-size shape as used in the performance test (3.6 m long) and in 100 mm long cut bars. Three main results were obtained. (1) Residual strain difference before and after the cutting to 100 mm long bar was about 0.1%, (2) a large relaxation on residual thermal strain was observed at the high field zone, and (3) the large relaxation on residual thermal strain at the high field zone was found mainly in a cross sectional side where the Lorentz force coming in.