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The ITER Correction Coil (CC) was wound with cable-in-conduit conductors (CICC) in a square 316 L stainless steel jacket into multiple pancakes embedded into the coil case. These coils relied on the CICC, the supercritical cooling circuit of which contained helium inlets and outlets. The oblong weld used to connect the nozzle to the stainless steel conductor is a critical process and required full penetration through the thickness of the nozzle. The special welding clamp contained a cooling block was designed to control the total deformation of the nozzle and the temperature of the superconducting strands. The data concerning the temperature gathering of the superconducting strand shows that the maximum temperature was lower than the allowed temperature, and thus did not degrade the superconducting strand. Based on the metallographic examination, some defects in the weld were found and corrected to meet the requisite requirements following the backing clean-up process. Volumetric X-Ray examination revealed no defects after the clean-up process, and fatigue and leak tests proved the reliability of nozzle weld as well as its welding and processing.

For the insulation materials of the superconducting magnet, the mechanical and electrical properties should be guaranteed under stresses of cryogenic temperature and intense radiation. In this study, two types of epoxy resins were prepared, which consist of diglycidyl ether of bisphenol-F (DGEBF) and triglycidyl-p-aminophenol (TGPAP) as matrixes respectively, and diethyl toluene diamine (DETD), isopropylidenebisphenol bis[(2-glycidyloxy-3-n-butoxy)-1-propylether] (IPBE) and boron-free glass fibre were used as curing, toughing and reinforcing agents for each resin. The direct-current (dc) electric breakdown strength and flashover voltage, dielectric properties and space charge characteristics of both epoxy composites were investigated. According to the results, DGEBF composite shown a higher dielectric strength, lower permittivity and dielectric loss at cryogenic temperature and smaller shallow trap density, which makes it more potential to be used for the cryogenic insulation.

The ITER Correction Coils (CCs) consist of three sets of six coils, Bottom (BCC), Side (SCC) and Top Correction Coils (TCC), respectively. The CCs rely on 10 kA NbTi cable-in-conduit conductor. Each CC winding pack is enclosed inside a 20 mm thick 316LN stainless steel case, providing structural reinforcement against the electromagnetic loads arising in the winding pack. The material of coil cases shall feature ready weldability both by laser and conventional techniques, high strength and toughness at 4 K. Material production involves not only hot rolled plates of different thicknesses, but also heavy gauge extrusions. An adapted steelmaking route including Electroslag Remelting (ESR) combined with a hot transformation step involving redundant multidirectional forging of the slabs and of the billets was adopted. This route allowed the stringent material specification to be fulfilled and permitted to achieve cleanliness, fineness of the structure and homogeneity on the final products. An extensive follow-up of the steel manufacturing through systematic non-destructive and destructive examinations was carried out in order to ascertain the soundness and the homogeneity of the final products. The progresses accomplished throughout the steel manufacturing are highlighted. The properties achieved on the final products that were enabled by the selected manufacturing route are discussed.

Cyanate ester/epoxy resin was used as a cryogenic-grade polymer matrix and glass fiber reinforced polymer (GFRP) composite was manufactured. The processing properties of matrix resin in terms of the isothermal viscosity at 45 °C were investigated. The specimens were exposed with gamma irradiation of 1 MGy, 5 MGy and 10 MGy, respectively. The effect of gamma irradiation on thermal properties and structure of cyanate ester/epoxy matrix was investigated. The interlaminar shear strength (ILSS) of the composites before and after irradiation were investigated at room temperature, 77 K and 4.2 K. Results showed that cyanate ester/epoxy system had a low viscosity and a long pot life at 45 °C. The glass transition temperature of the matrix resin decreased with the increasing irradiation dose. Moreover, the ILSS of GFRP composite slightly increases after irradiation and toughening mechanism was also discussed.

Laser welding of modified 316LN steel with a thickness of 20 mm was conducted using a YLS-20000 fiber laser. The microstructure of the weld joint was characterized and tensile and fracture toughness tests were carried out. The microstructure evolution of the fracture specimens was studied systematically to elucidate the fracture mechanism. The weld was composed of the single austenite phase and was characterized by cellular and columnar grains, and the grain size became coarser with a weak orientation. The Rm values of the laser welded joints were almost equal to that of the base metal both at RT and 4.2 K, and the fracture surfaces were featured by ductile fracture with quantities of dimples and microvoids. The fracture toughness of the weldments decreased to ˜84% of that of the parent metal at 4.2 K. Enhancement of the fracture toughness was attributed predominantly to the presence of twins and to the fine grain size, and the reduction was caused by the partially stress-induced phase transformation of the austenite to martensite. The synergistic effects of these factors result in a favorable improvement in the fracture toughness of the weldment.

316LN stainless steel is selected as a material for toroidal-field (TF) conductor jacket of International Thermonuclear Experimental Reactor (ITER). In order to evaluate the true mechanical performance of the jacket material at 4.2 K and its suitability as the ITER TF conductor jacket, the mechanical properties of the full-size TF conductor jacket tube and sub-size specimens at 4.2 K and 300 K were investigated according to ASTM standards. The measured yield strength and elongation at 4.2 K for sub-size specimens and full-size tubes are more than 950 MPa and 20%, respectively. In addition, the fractographies of all fractured specimens were observed using scanning electron microscope (SEM). These results suggest that the TF conductor jacket can satisfy ITER requirements and the result of the full-size tube at 4.2 K is more representative and important for practical applications.

Glass fiber reinforced epoxy-based composites were developed as insulating materials for fusion superconducting magnets. The processing properties of various epoxy matrices were investigated in terms of the isothermal viscosity at 45 °C. The interlaminar shear strength (ILSS) at 77 K and the thermal expansion coefficient (CTE) of the composites were assessed before and after gamma irradiation at ambient temperature up to 10 MGy. It is found that the TGPAP-based systems showed lower initial viscosities, longer working life and higher radiation resistance compared to the DGEBF-based systems with the same modifier. Furthermore, there was no significant effect of the irradiation dose on the CTE of the composites.

The ITER feeders are the components that connect the ITER magnet systems located inside the main cryostat to the cryogenics, power-supply and control system interfaces outside the cryostat. The feeder busbars rely on the Cable-In-Conduit Conductor (CICC) design concept as all the conductors for the ITER magnet systems. There are two types of busbars for the feeder systems. One is the Main Busbar (MB) for the TF, CS and PF feeders, and the other is the Corrector Busbar (CB) for the CC feeders. The busbar cable is wound from multiple stage sub-cables made with Cu and superconducting strands. The superconducting material is NbTi for the busbar strands of all feeder systems. All Feeder conductors are provided by China. The R&D programs are needed to acquire knowledge on the behavior of such conductors. Since the conductors are new, some full size copper dummy conductors have been produced for the testing of the cabling parameters, definition of automatic TIG welding of seamless jacket section, elaboration of cable insertion and compaction. Then, two short qualification conductor samples (MB and CB) are prepared in ASIPP, and NbTi advanced strands are produced by Western Superconductor Technology (WST). The details of manufacturing procedures for Feeder conductor samples will be described in this paper. (C) 2013 Elsevier B.V. All rights reserved.

This paper focuses on mechanical tests on the ITER correction coils (CC) and Feeder jacket 316L stainless steel material. During manufacture, the conductor will be compacted and spooled after cable insertion. Therefore, sample jackets were prepared under compaction in order to simulate the status of conductor during manufacturing. Yield strength (0.2% offset), ultimate tensile strength, Young's modulus and elongation at failure shall be reported. The mechanical properties of materials were measured at 300 K and low temperature (