Growth Rate and Morphology of Nb3Sn Layers in ITER-Type Bronze-Processed Wires Under Different Diffusion Annealing Regimes
The Nb3Sn-based bronze-processed multifilamentary composites have been fabricated at the Bochvar Institute of Inorganic Materials, Moscow, Russia, and studied by electron microscopy to determine the relationships between their structural parameters and annealing duration at different temperatures (575 °C, 650 °C, 750 °C). The structure of superconducting layers during their formation is characterized by thickness, average size of equiaxed grains, and by the fraction ratio of columnar and equiaxed grains. It was found that at high diffusion annealing temperatures (above 650 °C), the superconducting layers grow much faster, but the average size of equiaxed Nb3Sn grains even under a short exposure (10 h) is much larger than after a long low-temperature annealing. It is shown that to ensure the best current-carrying capacity of Nb3Sn-based wires in high magnetic fields, it is necessary to take into account different trends: on the one hand, the possibility of approaching the Nb3Sn phase stoichiometry and providing its maximum amount and on the other hand to avoid the undesirable growth of grains resulting in a lower pinning force.
Development of the  ${\rm Nb}_{3}{\rm Sn}$ Bronze Strand of TF Conductor Sample for Testing in SULTAN Facility
The results on research of the recent design Nb3Sn bronze strand with increased critical current capacity are presented. The strand has been designed and fabricated for use in full scale ITER TF conductor sample for testing in the SULTAN facility. The verification and qualification of strands have been done. The critical current measurements as a function of temperature in the range from 4.2 K to 15 K in magnetic fields up to 12 T have been performed. The results of testing of current sharing temperature Tcs of strand are discussed. The cable in conduit conductor was manufactured in accordance with ITER recommended scheme option 2. The cable design, thickness of wraps of subcable, void fraction and other characteristics of conductor for TF coil have been investigated to produce sample for testing in the SULTAN facility.
The anisotropy of Hc2 and its implications to grain‐boundary flux pinning in V3Si
We report that V3Si has an extremely large anisotropy in Hc2. This anisotropy is large enough to account for the observed strength of grain‐boundary pinning observed in polycrystalline V3Si.