A Study on the Temperature Dependence of the Ginzburg-Landau Parameter, Thermodynamic and Upper Critical Field of Nb3Sn Strands

We report detailed magnetization measurement results for two internal-tin Nb₃Sn strands. The paramagnetic background of a Mitsubishi strand is about 4 times larger than that of a KAT strand below the transition temperature, which can be understood as combined effects of Pauli and Langevin paramagnetism. From magnetic relaxation measurement for the KAT strand, a possibility of surface barrier effect is discussed. After subtracting the paramagnetic background, reversible magnetization data are analysed using the Hao-Clem model and the Ginzburg-Landau parameters (kappa), the thermodynamic and the upper critical fields (B_c,B_c2) at various temperatures are obtained. The temperature dependences of kappa, B_c and B_c2 are compared with the recent theoretical calculation results for Nb₃Sn and also with widely used empirical formulas.