Current Center Line Measurement of the ITER TF Coil

Toroidal field (TF) coils are superconductive magnets, which create a magnetic field to confine plasma in a vacuum vessel. In order to confirm a TF coil's functionality, the magnetic field created by the TF coil needs to be evaluated, and therefore, accurate measurement of current center line (CCL) for winding pack (WP) within the TF coil is necessary. However, accurate determination of CCL by direct measurement is difficult for WP due to its complicated structure and manufacturing steps. To overcome these complications, a method to determine CCL positions by composition of magnetic field measurements and geometrical measurements was developed. Accurate determination of conductor position within double pancake (DP) was realized by magnetic field measurements, while a need to solve a complicated inverse problem of Biot-Savart law was eliminated by the geometrical measurements of stacked DP positions. With this developed composition method, CCL positions of WP can be determined with 0.58-mm accuracy. This method has been applied on WP of ITER TF coil #13, which is manufactured in Japan, and CCL positions of WP #13 have been determined. When the results were compared to nominal values, maximum difference of 1.49 mm was observed.