Effective Low Magnetic Field J_c(B) Scaling of ITER Nb₃Sn Strands by Magnetization and Critical Current Measurements

Abstract

For the International Thermonuclear Experimental Reactor magnets, a significant fraction of the Nb 3 Sn conductors will be operating at a low field (B < 4 T), such as the outer turns of the central solenoid modules and toroidal field winding packs, while so far, the I c (B,T, Ɛ) parameterization has been derived from measurements carried out at higher fields (B ≥ 7 T). It may not be accurate enough to adopt this parameterization for the extrapolation of the conductors' operating performance in terms of critical current (I c ) and current sharing (T cs ). The critical current characteristic can be effectively extended to the lower field region by means of a relation between the magnetization and critical current. The parameterization of the derived critical current scaling law J c (B) is processed for the field range of the magnetization measurement (0 < B ≤ 9 T) and the critical current measurements (7 ≤ B < 12 T) in order to cover the full range up to 12 T.