To develop an economical process that can produce an improved superconducting material for high and intermediate field magnets to be used in future accelerators, it is necessary to increase the stability of the strands and cables, particularly in the lower field regions. However, this must be done without lowering the the critical current carrying capability (Jc) in the high field region. One way of doing this is to employ a tubular internal-tin Nb3Sn material, which already has many small subelements, and surround it with a matrix that has good electrical and thermal conductivity. Unfortunately, at the present time, such materials have relatively low current carrying capability. Therefore, this project seeks to improve the critical current carrying capability of this tubular internal-tin Nb3Sn material. The new material system will have low cost, good ductility, and many small subelements surrounded by a matrix with high electrical and thermal conductivity. Phase I will: (1) optimize the proportions of NbTa or Nb, copper and tin in the subelement, then optimize the design of the restack and the heat treatments to determine the best baseline properties; (2) introduce titanium into arrays of both NbTa and Nb tubes; (3) add wraps of Ta around the NbTa tube subelement to allow it to react more with the tin without serious matrix contamination; and (4) if ductility problems are encountered in the third step, a double restack will be attempted to achieve a structure that is a compromise between a single barrier and a multi barrier design. The materials will be tested for current carrying capability, losses, RRR, and stability by field-sweep measurements.
Commercial Applications and Other Benefits as described by the awardee: In addition to being used for HEP accelerator applications, the product should have application in open area MRI where the patient is more accessible to the surgeon (MRI is the largest commercial application of low temperature superconductors), and in small magnets for high field laboratory applications and NMR
