Laboratory scale solenoids with multifilamentary Nb3Sn superconductors

By the bronze technique Nb3Sn multifilamentary conductors with different numbers and densities of filaments and partly with an integrated CuTa stabilization were fabricated. For currents exceeding 1000 A at 10 T we have manufactured fully transposed and calibrated flat cables with different numbers of strands and different ratios of superconducting to CuTa stabilizing strands. From long lengths (km) of these cables we have fabricated solenoids with manifold graded windings using the wind-and-react-technique and a final vacuum impregnation after reaction. Two different variants of this technique will be described. Magnetic flux densities up to 15 T at 4.2 K in a free bore of 40 mm diameter have been reached in a 7 T NbTi background field. The solenoids attained the short sample current within some percent requiring only short training on initial excitation but no training after heating to room temperature. High excitation speeds were obtained without degradation of the quench current.