New Inspection Method of Soldering Region at Room Temperature for ITER TF Termination

For inter-double-pancake joints of ITER TF it is required to achieve sufficiently low joint resistance ( $R_{J}$ ), as 3 nΩ, to reduce Joule heating during operation with a background field of 2 T and nominal current of 68 kA. If $R_{J}$ value is measured directly, a large cryostat is required to cool down the TF coil with huge mass and size during $R_{J}$ measurement at 4 K. As alternative, authors have developed new inspection methods to obtain $R_{J}$ value. The contributions to $R_{J}$ can be divided mainly into contact resistance between the copper sole and cable ( $R_{c}$ ) and resistance of soldered region between copper soles ( $R_{sol}$ ). For the measurement of the former, the authors developed the inspection method in a past study. In this paper, the authors focus on the development of a measurement method for the latter. If there is a defect in the soldered region, a current distribution in the copper sole varies from the case of no defect, resulting in a change in the voltage profile along the copper sole. Thus, the voltage profile along the copper sole is measured at room temperature by supplying 20 A to the termination. To confirm the sensitivity to existence of a defect in soldered region, the measurements were performed for good (no-defect) and bad (defect) joints. An example of good joint was a joint sample the R J value of which was sufficiently low, while bad joint was simulated by artificially isolating a part of the soldered region. From the results of the measurements, a significant difference was observed between good and bad joint samples. Thus, it can be concluded that the developed method is practically effective for inspection of soldering quality between copper soles.