Analysis of current and voltage distribution in the first Japanese qualification sample of an ITER TF conductor

Koizumi, Norikiyo; Matsui, Kunihiro; Okuno, Kiyoshi

Japan Atomic Energy Institute (JAEA), as Japanese Domestic Agency, has responsibility to procure 25% Toroidal Field (TF) coil conductor for ITER. The proto conductor was successfully developed and qualification test of these conductors were performed in the SULTAN test facility in Switzerland. Since the conductor length is only 2.5 m, the current distribution in the conductor is affected by joint. Because the joint is subjected to back ground magnetic field distributed from 2 T to 7 T, joint resistance is not uniform along the cable axis due to electromagnetic resistance of copper in the joint. This causes non-uniform current distribution in the conductor and voltage on surface of jacket is not a constant along circumference direction. It is therefore made difficult to correctly evaluate conductor critical current performance. Thus, the authors developed a simulation model to calculate current distribution in the conductor using a lumped circuit model and voltage distribution on the jacket using a 2-dimensinal steady state potential model. In addition, effect of electromagnetic resistance in the joint is carefully considered by using a model taking account of shape of current path. These simulation results show that the current sharing temperature estimated from the measured voltage is a few hundred milli-Kelvin lower than the one when the current distribution is uniform. In addition, it is figured out that the electromagnetic resistance in the joint originates relatively large non-uniform current distribution. This can be reduced by inserting high resistive thin layer in the joint to decrease the effect of the electromagnetic resistance.