A rotating bias magnetic field EMAT and applications to NDT of ITER divertor components

In this paper, an electromagnetic acoustic transducer (EMAT) method using rotating bias magnetic field was proposed for NDT of delamination defect in a thin multilayer tube of W-Cu monoblock in ITER divertor. To investigate its feasibility, a numerical simulation code was developed for EMAT signal simulation of tube configuration and uniform bias magnetic field. The EMAT signals of a typical EMAT transducer under bias magnetic field applied outside the tube were simulated for deboning defect of different size in the W-Cu interface of the mono-block. The reasonable sound speed and simple dependence of the signal amplitude on defect size demonstrated that the developed code is efficient and the proposed rotating bias field EMAT is feasible for inspecting delamination defect in thin multilayer tubes. In addition, an experiment was carried out to investigate the influence of the rotating speed on the EMAT signals. It is found that a normal rotation speed does not give significant influence on the EMAT signals, which further support the validity of the rotating bias field EMAT.