Application of calorimetry to the assessment of the performance of ITER Nb3Sn TF conductor samples in SULTAN tests

In the frame of the International Thermonuclear Experimental Reactor (ITER), several short full-size Nb3Sn samples of candidate toroidal field (TF) conductors were tested in 2007 at the SULTAN facility, PSI Villigen, Switzerland, in conditions relevant to the ITER TF (background magnetic field of 10.78 T and transport current of 68 kA). The performance of a SULTAN sample is determined by the current sharing temperature T-CS. This can be obtained in principle from voltage measurements along the conductor sample, but the procedure is not free of issues and ambiguities. Here a complementary approach, based on the calorimetric assessment of the Joule heating due to current sharing, is critically discussed. Suitable algorithms are defined and the respective error bars are estimated, also based on numerical thermal-hydraulic modeling. The calorimetric approach is then applied to assess the performance of the samples tested in 2007 and compared with the results of the standard (electrical) approach.