Estimation of Mutual Inductance Caused by Misalignment of JT-60SA TF Coil

The JT-60 Super Advanced (JT-60SA) was built as part of a project aimed at the early realization of fusion energy. The JT-60SA is used to support and complement work for ITER and to develop young fusion scientists and engineers. The superconducting coil system of the JT-60SA includes the toroidal field (TF) coils, equilibrium field (EF) coils, and central solenoid (CS) modules. Each TF coil is monitored by the quench detection voltage (QDV) system, which compares voltages at adjacent TF coils using a bridge circuit. The EF coils do not produce a voltage in the TF coils because, ideally, the TF coils are orthogonal to the EF coils. However, when the EF coils are energized, the QDV in the TF coils sometimes exceeds the threshold, falsely detecting quenches, which leads to the discharge of a TF current. It is believed that a magnetic flux from the EF coils passing through the TF coils may occur due to coil misalignment during installation and inadequate clearance design. As a result, an induced voltage could be generated in the TF coils. To understand how other coils influence the TF QDV system and to ensure the stable operation of the JT-60SA, it is crucial to investigate the cause of the induced voltage in the TF coils. In this study, a coil misalignment model was developed using finite element analysis software. This model was used to calculate the mutual inductance between the TF and EF coils. Furthermore, a circuit simulation model of the TF QDV system was created to quantitatively analyze the induced voltage caused by the misalignment of superconducting coils.