Development of hollow cooling monolithic conductor for ITER TF coil

Results of verification tests for the TMC (Test Module Coil)-FF hollow cooling monolithic conductor are presented. With various strands to test the optimal bronze ratio, the critical current of full-scale samples was measured at 13 T and 4.2 K. The maximum critical current density is 404 A/mm², which is smaller than the requirement of over 500 A/mm² at 12 T. There is no degradation of the critical current of a full size conductor compared with the same sample before cabling. AC losses of the conductor were measured in parallel and perpendicular fields. The results of the time constant measurements are larger than the calculated values in each direction. The stability margin of the full size conductor is 40 mJ/cc-metal at the nominal point, assuming long length disturbance. This result is estimated from experimental results for a reduced size conductor and from thermal analysis. The heat generation of the joint between Nb₃Sn and Nb-Ti is much smaller than that of nuclear heating