Finite Element Model to Study the Deformations of Nb3_{3}Sn Wires for the Next European Dipole (NED)

The Next European Dipole (NED) activity is aimed at the development of a large-aperture, high-field superconducting magnet relying on high-performances Nb$_{3}$Sn conductors. Part of the NED program is devoted to the mechanical study of a new generation of Nb$_{3}$Sn wires and to predict and describe their behavior under the severe loading conditions of the cabling process. The deformation resulting from the cabling process was simulated through mechanical analyses by Finite Elements (FE). The ensuing results of FE analyses are presented, allowing the wire behavior under simple uni-axial loads to be described. They are compared to cross section micrographs of deformed wires

Cu-Ti Formation in Nb-Ti/Cu Superconducting Strand Monitored by in situ Techniques

In order to investigate the high temperature exposure effect on Nb-Ti/Cu superconducting strands, as might be encountered in joining by soldering and in cabling annealing, X-ray diffraction and resistometry measurements were performed in situ during heat treatment, and complemented by conventional metallography, mechanical tests and superconducting properties measurements. Changes of the Nb-Ti nanostructure at temperatures above 300 degrees C are manifested in the degradation of critical current in an applied external magnetic field, although degradation at self field was insignificant up to 400 degrees C for several minutes. Above 500 degrees C, the formation of various Cu-Ti intermetallic compounds, due to Ti diffusion from Nb-Ti into Cu, is detected by in situ XRD albeit not resolvable by SEM-EDS. There is a ductile to brittle transition near 600 degrees C, and liquid formation is observed below 900 degrees C. The formation of Cu-Ti causes a delayed reduction of the residual resistivity ratio (RRR) and adversely affects the deformation behaviour of the strands

Cu-Ti Formation in Nb-Ti/Cu Superconducting Strand Monitored by <em>In Situ</em> Techniques

In order to investigate the high temperature exposure effect on Nb Ti/Cu superconducting strands, as might be encountered in joining by soldering and in cabling annealing, X-ray diffraction and resistometry measurements were performed in situ during heat treatment, and complemented by conventional metallography, mechanical tests and superconducting properties measurements. Changes of the Nb Ti nanostructure at temperatures above 300°C are manifested in the degradation of critical current in an applied external magnetic field, although degradation at self field was insignificant up to 400°C for several minutes. Above 500°C, the formation of various Cu Ti intermetallic compounds, due to Ti diffusion from Nb Ti into Cu, is detected by in situ XRD albeit not resolvable by SEM-EDS. There is a ductile to brittle transition near 600°C, and liquid formation is observed below 900°C. The formation of Cu Ti causes a delayed reduction of the residual resistivity ratio (RRR) and adversely affects the deformation behaviour of the strands

World-Wide Benchmarking of ITER Nb3_{3}Sn Strand Test Facilities

The world-wide procurement of Nb$_{3}$Sn and NbTi for the ITER superconducting magnet systems will involve eight to ten strand suppliers from six Domestic Agencies (DAs) on three continents. To ensure accurate and consistent measurement of the physical and superconducting properties of the composite strand, a strand test facility benchmarking effort was initiated in August 2008. The objectives of this effort are to assess and improve the superconducting strand test and sample preparation technologies at each DA and supplier, in preparation for the more than ten thousand samples that will be tested during ITER procurement. The present benchmarking includes tests for critical current (I-c), n-index, hysteresis loss (Q(hys)), residual resistivity ratio (RRR), strand diameter, Cu fraction, twist pitch, twist direction, and metal plating thickness (Cr or Ni). Nineteen participants from six parties (China, EU, Japan, South Korea, Russia, and the United States) have participated in the benchmarking. This round, conducted with a bronze-route Nb$_{3}$Sn strand, involved samples prepared by a common laboratory (CERN) and sent out to the participants ({''}IO-prepared samples{''}) and also samples prepared by each individual participant ({''}self-prepared samples{''}). I-c samples prepared and measured by CERN were found to have an average I-c of 188.7 A and a standard deviation of 1.8 A (1.0\%), while those same set of samples measured by all the participating labs in round-robin fashion were found to have a standard deviation of 2.1 A. Self-prepared samples had an average I-c of 188.1 A, and showed a lab-to-lab standard deviation of 3.5 A. The results demonstrate significant progress in the world-wide capability to accurately and reproducibly measure Nb$_{3}$Sn critical current over the past decade. Future benchmarking efforts will include an annual cross-check of supplier and DA facilities, and also a round of internal tin Nb$_{3}$Sn samples to assess each contributor's sample-preparation techniques. A separate round of NbTi benchmarking is also envisioned