In spite of the maturity of Nb3Sn internal tin wires designing and production routes there are still significant R&D needed for attaining of the challenging set of requirements specific for high field dipole magnets. The development of layouts and processing of Nb3Sn internal tin strands with non copper critical current density exceeding 2450 A/mm2 altogether with reasonably low hysteresis losses are carried out in the Bochvar Institute (RF).
Experimental study on the limitations of the different approaches to the diffusion barrier design has been carried out. Two types of strands containing one common barrier and numerous barriers surrounding each of the subelements have been produced. The model wires 1.0 to 0.36 mm in diameter have been subjected to reaction heat treatment and the microstructure of Nb3Sn layers was investigated. The superconducting characteristics of the strands designed and produced were investigated.
The influence of the design features of developed superconductors and the heat treatment regimes on the current-carrying capacity and relative residual resistance ratio (RRR) has been studied. The relationship between temperature and duration of reaction and the characteristics of the superconducting Nb3Sn layer in the manufactured superconductors are discussed.
As the result of the carried out research the optimal regimes of the reaction for each layout of the obtained superconductors have been developed.