Development of (Nb,Ti)3Sn forced flow cooled superconducting coils

A superconducting magnet for nuclear fusion has to be high in coil rigidity, voltage resistance and stability and low in alternating current loss. Attention has recently been given to forced flow cooled superconducting material as a conductor material to meet these severe requirements. In the present study, bundle-type forced flow cooled superconducting (Nb,Ti)3Sn material is developed for application to superconducting magnets for nuclear fusion. Small forced flow cooled superconducting coils are produced and their performance is investigated. The tests cover their high-temperature stability, rapid excitation performance, and alternating current loss. Results show that the samples, very high in high-temperature stability, can resist thermal disturbance four times as large as compared to conventional NbTi cable material. Under a 10 T magnetic field, they can perform rapid repeating pulsed excitation at 13kA/s (0.85T/s) up to the rated current. The superconducting cables suffer an alternating current loss of 3.3 kW/m3 under the conditions of 50Hz and 100A excitation, indicating that the cables match three-layer NbTi/Cu/CuNi material. (N.K.)