A Double Check Process for CCL Positional Plates in ITER TF Coil Integration

A current center line (CCL) was precisely controlled with markers called "CCL positional plates (CCLPPs)" during the ITER toroidal filed (TF) coil integration. CCLPPs with the same x and y coordinates (CCLPP pair) are attached on both sides of the TF coil Winding Pack (WP). The CCLPP insufficiently fixed has to be replaced with new one to ensure the accuracy of CCL. On the other hand, the replacement possibly leads to some issues, such as, dropping the CCLPP into the CC and damaging the WP. Thus, unnecessary replacement should be avoided. We have therefore implemented a double check process to confirm soundness of the CCLPPs. First, change of the distance of CCLPP pair ( increment WCCLPP) is evaluated (Check A). However, increment WCCLPP would be influenced by the WP deformation. Thus, the Check A possibly judges the fixing condition of the CCLPP as "unusual" even if it has no issue. This may lead to the unnecessary replacement of the CCLPP. To avoid the unnecessary replacement, the local displacement of each CCLPPs ( increment rCCLPP) is also evaluated (Check B). In this paper, we define the criteria for "unusual" increment WCCLPP and increment rCCLPP based and verify its validity for the TF coil integration by considering the measurement error and geometrical configuration of the CCLPPs. In the case of one Toshiba TF coil, the double check process confirmed that CCLPPs were insufficiently fixed, and they were successfully replaced to the new ones. Thus, it was demonstrated that the proposed criteria indicated the appropriate action to keep the CCLPP soundness. The method proposed in this paper would be powerful tool to inspect the soundness of the CCLPP which is important for the CCL control not only in the ITER TF coil, but also in the future fusion magnets.(c) 2023 The Japan Society of Plasma Science and Nuclear Fusion Research