Taking the relay of the Large Hadron Collider (LHC) at CERN, ITER has become the largest project in applied superconductivity. In addition to its technical complexity, ITER is also a management challenge as it relies on an unprecedented collaboration of 7 partners, representing more than half of the world population, who provide 90% of the components as in-kind contributions. The ITER magnet system has a stored energy of 51 GJ and involves 6 of the ITER partners. The coils are wound from Cable-In-Conduit Conductors (CICCs) made up of superconducting and copper strands assembled into a fully transposed, rope-type cable, inserted into a conduit of butt-welded austenitic steel tubes. The conductors for the Toroidal Field (TF) and Central Solenoid (CS) coils require about 500 tons of Nb 3 Sn strands while the Poloidal Field (PF) and Correction Coil (CC) and busbar conductors need around 250 tons of Nb-Ti strands. The required amount of Nb 3 Sn strands far exceeds pre-existing industrial capacity and has called for a significant worldwide production scale up. The TF conductors are the first ITER components to be mass produced and are more than 50% complete. During its life time, the CS coil will have to sustain several tens of thousands of electromagnetic (EM) cycles to high current and field conditions, way beyond anything a large Nb 3 Sn coil has ever experienced. Following a comprehensive R&D program, a technical solution has been found for the CS conductor, which ensures stable performance versus EM and thermal cycling. Productions of PF, CC and busbar conductors are also underway. After an introduction to the ITER project and magnet system, we describe the ITER conductor procurements and the Quality Assurance/Quality Control programs that have been implemented to ensure production uniformity across numerous suppliers. Then, we provide examples of technical challenges that have been encountered and we present a status of ITER conductor production worldwide.

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The differences in thermal contraction of the composite materials in a cable in conduit conductor (CICC) for the International Thermonuclear Experimental Reactor (ITER), in combination with electromagnetic charging, cause axial, transverse contact and bending strains in the Nb 3 Sn filaments. These local loads cause distributed strain alterations, reducing the superconducting transport properties. The sensitivity of ITER strands to different strain loads is experimentally explored with dedicated probes. The starting point of the characterization is measurement of the critical current under axial compressive and tensile strain, determining the strain sensitivity and the irreversibility limit corresponding to the initiation of cracks in the Nb 3 Sn filaments for axial strain. The influence of spatial periodic bending and contact load is evaluated by using a wavelength of 5 mm. The strand axial tensile stress-strain characteristic is measured for comparison of the axial stiffness of the strands. Cyclic loading is applied for transverse loads following the evolution of the critical current, n-value and deformation. This involves a component representing a permanent (plastic) change and as well as a factor revealing reversible (elastic) behavior as a function of the applied load.The experimental results enable discrimination in performance reduction per specific load type and per strand type, which is in general different for each manufacturer involved. Metallographic filament fracture studies are compared to electromagnetic and mechanical load test results. A detailed multifilament strand model is applied to analyze the quantitative impact of strain sensitivity, intrastrand resistances and filament crack density on the performance reduction of strands and full-size ITER CICCs. Although a full-size conductor test is used for qualification of a strand manufacturer, the results presented here are part of the ITER strand verification program. In this paper, we present an overview of the results and comparisons.

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We analyzed the ITER TFEU5 cable-in-conduit conductor (CICC) after the full SULTAN conductor qualification test in order to explore whether Lorentz force induced strand movement inside the CICC produces any fracture of the brittle Nb 3 Sn filaments. Metallographic image analysis was used to quantify the change in void fraction of each sub-cable (petal); strands move in the direction of the Lorentz force, increasing the void space on the low force side of the CICC and producing a densification on the high force side. Adjacent strand counting shows that local increases in void space result in lower local strand-strand support. Extensive metallographic sampling unambiguously confirms that Nb 3 Sn filament fracture occurred in the TFEU5 CICC, but the filament fracture was highly localized to strand sections with high local curvature (likely produced during cabling, where strands are pivoted around each other). More than 95% of the straighter strand sections were free of filament cracks, while less than 60% of the bent strand sections were crack free. The high concentration of filament fractures on the tensile side of the strand-strand pivot points indicates that these pivot points are responsible for the vast majority of filament fracture. Much lower crack densities were observed in CICC sections extracted from a lower, gradient-field region of the SULTAN-tested cable. We conclude that localized filament fracture is induced by high Lorentz forces during SULTAN testing of this prototype toroidal field CICC and that the strand sections with the most damage are located at the petal corners of the high field zone.