Application of eddy current testing inspection to the first wall of fusion reactor with wavelet analysis

The eddy current testing (ECT) technique is introduced for the non-destructive evaluation of the first wall of a fusion reactor. With the aim of in-service inspection of the first wall, a method to evaluate cracks in the first wall is studied theoretically utilizing impedance signals and magnetic field data obtained from ECT. From the impedance signals, the depth of the cracks is determined using an impedance—depth calibrating curve. Since an impedance signal may be caused by some undesired factors as well as by a crack, an approach to extracting crack information from such a composite signal is developed using wavelet analysis. For reconstruction of the surface shape of the cracks, the magnetic field data are inverted into the distribution of the current vector potential T by solving an inverse problem and the wavelet coefficients of T are calculated to characterize the shape of the cracks. It is shown that the combination of ECT and wavelet analysis provides an efficient method of non-destructive evaluation of cracks in the first wall.