Study of Current Distribution in ITER TFMC NbTi Busbar III

In the framework of the development of High Temperature Superconducting current leads (HTSCL), one demonstrator was tested at Forschungszentrum Karlsruhe (FZK) in 2004 together with a conventional current lead. Both were connected by a superconducting short circuit NbTi conductor, referred as busbar III (BBIII). Here the BBIII was used for current distribution measurements. In addition to a 64 Hall Probe (HP) system, two additional 4-HP heads from CEA were assembled at both ends of the BBIII. This system, already successfully used during the TFMC test phase II, was now adapted by FZK to the present BBIII set-up. Electrical tests were performed for conductor currents up to 80 kA without background magnetic field. In this paper, the analysis of the current distribution is presented using two methods: (1) The current barycenter excursion was investigated in various runs. A comparative study is presented between resistive and inductive hypotheses where the current is supposed to be uniformly distributed. In particular, we show that the two hypotheses lead to different results. (2) A global model of the current bundles distribution between four artificial subcables is investigated. More quantitative results show current imbalances between subcables to be either significant or weak, depending on whether the resistive or the inductive hypothesis is considered. A discussion on why the second solution is thought to be more likely is presented. In addition, a global comparison with results previously obtained during the TFMC tests will be shown