Impact of Cabling Pattern, Magnet Field Profile and Joint Properties on Short Sample Qualification Tests of ITER Conductors

Abstract

The voltage signals measured in short sample qualification tests for the ITER conductors often show a linear relationship with the current starting from zero. This behavior is most likely caused by non-uniform current distribution in the joints. To counteract this, two samples have been equipped with extra sets of six voltage tap pairs, connected with regular spacing, as a star configuration around the conductor. The linear relationship still showed up in the average of the extra voltage signals, and were sometimes even seen to be inverse. In some occasions, it was negative for all individual signals. A fair judgment of the approval criterion requires a proper understanding of this behavior. This paper describes the analyses with the aid of the numerical model 'JackPot'. It demonstrates that the described observation is the result of the chosen cabling pattern in combination with the position of the voltage taps. The model also shows that this problem cannot be solved by changing the positions of the voltage taps, but that completely filling the joints with solder can greatly improve the situation.