Development of welding and processing technologies of helium inlet for ITER Correction Coil

Abstract

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.