Current distribution measurement on the ITER-type-NbTi Bus Bar III.

The Bus Bar III (BBIII), fabricated within the Toroidal Field Model Coil Task of the International Thermonuclear Experimental Reactor ITER), was tested at the Forschungszentrum Karlsruhe, Germany, in the spring of 2004. The BBIII consists of an approximately 7 m long NbTi ual-channel conductor with a thick square stainless steel jacket, ooled by forced flow supercritical He. It was energized with currents up to 80 kA and operates in its self magnetic field (up to ∼0.8 T). The BBIII was instrumented with Hall-probe heads and arrays, voltage ings and longitudinal voltage taps for electro-magnetic measurements, in order to get experimental data to be used for the validation of a ecently developed hybrid thermal-hydraulic electro-magnetic code THELMA), as well as for the assessment of the possibility of performing a reliable reconstruction of the current distribution in the conductor cross section under controlled conditions. In the ests, current ramps at different rates were applied to characterize the conductor time constants, while two different resistive heaters one upstream of the BBIII inlet, another one directly on the BBIII acket) were separately operated in order to approach current sharing in the conductor and to observe the related current re-distribution. In this paper, a summary of the collected experimental results is resented, with particular emphasis on those aspects more relevant for the forthcoming THELMA analysis.