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.
Testing of RF 100 m TF Qualification Conductor in the SULTAN Test Facility
A conductor for ITER toroidal field (TF) coils is the cable-in-conduit conductor (CICC) type, which is made of Nb3Sn superconducting strands encased in a stainless steel tubular jacket. A 120-m-long prototype has been designed in accordance with ITER requirements and manufactured prior to production of 26 full-sized CICC lengths that are the contribution of Russia to the ITER TF magnet system. Ten meters of the prototype have been used to produce a sample for testing in the SULTAN facility in order to qualify the strand/cable/jacket combination. A test aimed at qualifying the conductor performance based on Tcs measurements in representative condition regarding the transport current and magnetic field has been carried out. At the same time, the test was used to compare the conductor behavior after different heat treatment cycles. Each of two legs has been reacted in accordance with one of the specified heat treatment cycles for the ITER TF conductor. Test results are presented and discussed. Based on the test results, the eligibility of the conductor for the ITER TF magnet system has been assessed.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.