Studies on the silver-coated patch with spot welding for the ITER Thermal Shield

Abstract ITER Thermal Shield (TS) reduces radiation heat loads from vacuum vessel and cryostat to superconducting magnet structure. One of the key process among the fabrication of TS is the silver electroplating to reduce the emissivity. Requirement on emissivity of TS surface after silver coating is below 0.05 at the room temperature. In practice, inevitable non-coated areas exist due to the intrinsic geometry of TS. These local defects can be repaired by attaching thin silver coated patch with spot welding. This paper treats structural characteristics on the spot welding of silver coated plates. Strength of spot welding is measured by tensile shear test. Distances between spot welding are verified by finite element analysis considering temperature deviation between TS surface and patch. Finally, thermal stress analysis for the several applications to TS main components are presented.