Thermal Stability of Butt Joint for CS Conductor in JT-60SA

Thermal stability for a butt joint of a central solenoid (CS) is experimentally and numerically estimated. The butt joint is fabricated using a strand bundle for the CS conductor, and the quench current of the butt joint is measured by changing the temperature of supercritical helium (SHe). The results show that even if the SHe flow slows to 50% of the rated flow, the temperature margin of the joint is 4 K, the butt joint is sufficiently stable. We also calculate the thermal stability of the butt joint by changing certain operating conditions. According to the simulation data, when connection resistance becomes high, from 2 to 5 nΩ, there is little change in the temperature margin. The experimental and numerical results suggest that the butt joint does not quench and can be operated with stability.