Estimation of electrical parameters of large-scale superconducting coil system for fusion plasma experimental facility

The Large Helical Device (LHD) in the National Institute for Fusion Science (NIFS) has six sets of large scale superconducting coils and six dc power supplies to charge them. For the current controllers of these power supplies, high accuracy of current control, good response and robustness of system are required. In the design of the controller, it was pointed out that the correct inductance matrix of the coil system and some electrical parameters that describe metal structures such as a supporting shell are necessary. This paper introduces a method based on a frequency response of impedance to estimate these parameters. First, the measured inductances of the LHD superconducting coils, which are measured from coil terminals, are presented and discussed. Next, an estimation method for circuit parameters is described. Finally, an experimental result of coil excitation using these parameters is presented. The experimental result show that the coil current controller using the estimated model satisfies previous requirements and it is confirmed that this parameter estimation method is valid for the large scale coil system.