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 Investigation of the Effect of Niobium Artificial Doping with Titanium on Nb3Sn Superconductors Properties
The effect on titanium doping of Nb filaments, and thus on the properties of bronze processed multifilamentary Nb3Sn wires and wires with internal tin sources with copper volume fraction up to 65 % has been analysed. Either titanium rods or rods of the Nb-50Ti alloy, inserted in the axial area of each filament, were used as a source of titanium. The influence of doping on the quantity, composition, structure and superconducting properties of intermetallic compound Nb3Sn after heat treatments at 570–750°C with duration up to 350 h was investigated by means of electrical measurements, optical metallography and methods of microanalysis and X-ray analysis. It was shown that the non-copper critical current density of the doped wires attained 600 and 270 A/mm2 in 12.5 and 16 T respectively for bronze processed wires and 800 and 300 A/mm2 for wires with internal tin source. Upper critical field calculated in accordance with Kramer’s extrapolation was equal to 29–32 T.