Electric Potential Profile with Distributed Degradation in the Terminal Joint for ITER TF Coil System

Abstract

ITER toroidal field coils are electrically connected to 68-kA main busbars (terminal joints). We propose the measurement of the electric potential distribution in a terminal joint using electrical probes (e-probe method) to inspect the contact resistance in the joint. In this study, we experimented with a mockup of a terminal joint. The test current was 20 A, and the electric potential was measured using the e-probe method at room temperature and 77 K. Nine different degradation patterns were prepared by distributing polyimide films in the joint interface. Next, we performed finite element analysis to investigate the detailed relationship between the electric potential distribution and contact resistance at 300 K and 77 K. In the numerical analysis, the same degradation patterns and test current as in the experiment were assumed. The analysis results agree with the experimental results. Different degradation patterns exhibit different electric potential profiles with 10-µV-scale differences. The analysis results also indicate that the e-probe method works when the contact resistance in the degraded area is larger than 1.0 × 10 −5 Ωmm 2 at 77 K and 300 K. c