Fusion Science and Technology / Volume 61 / Number 4 / May 2012 / Pages 314-320
With increases in the heating and driving power in EAST, the present SiC-C plasma-facing components (PFCs) will be replaced by W coatings on actively cooled Cu heat sinks in the lower-heat-flux zone (first wall), prepared by vacuum plasma spraying, and by ITER-like W-Cu monoblocks in the higher-heat-flux zone (divertor). These components are provided with thousands of joints that should be assessed to demonstrate their integrity. An ultrasonic method named pulse echo using high-frequency probes and normal incidence of the ultrasonic beam to the joint interface has been developed. For the W-coating PFC, although the existence of porous structure, shrinkage cracks, and delamination in W coating can adversely affect the sensibility of detecting interface defects, the ultrasonic technique is able to detect, locate, and size them in certain conditions; for the W-Cu monoblocks, the ultrasonic technique is also able to detect, locate, and size defects in the W-oxygen-free high conductivity (OFHC) Cu interface, but further detecting and analysis should be carried out for the OFHC Cu-CuCrZr interface based on the preliminary work.