Electron Beam Welding of the HTS Current Lead for the ITER Feeder

The high-temperature superconducting (HTS) current lead is one of the core components of the International Thermonuclear Experimental Reactor (ITER) magnet feeder system. Due to high-quality requirements, electron beam welding (EBW) was chosen to weld the room temperature terminal, the finned heat exchanger, and the HTS segment. The short mock-up was created to assess the performance of the welded joints. The analysis of macroscopic morphology and microstructure indicates that the welded joint of the short mock-up appeared to be free of visible defects. The tensile strength of the welded samples ranges from 185 to 208 MPa, which is higher than the design requirement of 150 MPa. The side bending test also shows no open discontinuity of the samples. Additionally, the thermal shock test was carried out. The dye penetrant test and the ultrasonic test after thermal shock shows that there are no obvious defects inside or on the surface of the weld seam. Furthermore, the leakage rate of the welded sample measured in the helium tightness leak test was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.2\times 10^{-10}$ </tex-math></inline-formula>Pa<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>m3/s, indicating no cracks detected in the joints in the joints. The same parameters were also used for the welding of the long mock-up equipped with fins. The maximum temperature during the welding process does not go over the prescribed limit. The actual HTS current lead was welded, and its performance was evaluated, based on the welding experiments of mock-ups. The welding quality of the HTS current lead was confirmed by all test results.