KSTAR Grounding System and the Operation Result of the Ground Current Detection System

An appropriate grounding system must be established to safely operate the superconducting tokamak machine and reduce electrical noise, because the device generates high eddy current and electromagnetic force in surrounding structures during the operation. A plasma experiment device for fusion energy, Korea Superconducting TOKAMAK Advanced Research (KSTAR), has three different ground meshes; KSTAR building grounding for Tokamak devices, Electron Cyclotron Current Drive (ECCD) building grounding for diagnostics, and Neutral Beam Injection (NBI) grounding. Several diagnostics and Tokamak components (thermal shield, toroidal field magnet structures, cryostats, vacuum pump ducts, and deck) are connected in the KSTAR building grounding. To measure the level of ground current during plasma operation, four ground current detection system (GCDS) has been operated since 2018, divided into ex-vessel components (thermal shield, magnet structures), vacuum system, Vacuum Vessel (VV) & cryostat structure, and Poloidal Field (PF) Magnet Power Supply (MPS). The flow of ground current for each system closely corresponds with the current profile of the PF magnet. The peak ground current was observed in three groups; initial magnetization, PF magnet current swing, and demagnetization. The maximum instantaneous peak current was measured at the vacuum system and the VV & cryostat structure circuit after blip in which drives PF magnet current for plasma start-up, and was more than 100 A and 150 A, respectively. This paper will describe the operation results of KSTAR grounding system and the operation results of GCDS.