Development status of the HVPS and control system for KSTAR ECH system upgrade

Abstract

The Korea Superconducting Tokamak Advanced Research (KSTAR) is planned to be installed with an electron cyclotron (EC) system to achieve a 6 MW radiofrequency (RF) output by 2024, and this installation is currently in progress. At present, five gyrotrons are installed for the EC system of the KSTAR. Among these, four EC systems are installed with 105/140 GHz dual-frequency gyrotrons, each generating 950 kW of RF power at 140 GHz and 800 kW of RF power at 105 GHz. Moreover, an EC system additionally installed in 2022 is a 170 GHz single-frequency gyrotron, and it generates 1 MW of RF power. The high-voltage power supply (HVPS) and the EC integrated control system (ECICS) were developed in 2019 to obtain a more stable and efficient EC system. Several useful functions were added to the newly developed ECICS for efficient EC system operation. Real-time control operations and shot retrigger are now possible with the application of this integrated control system. In addition, a function to automatically save and recall shot information was added and is essential for reducing operator errors. The new HVPS was designed in the pulse step modulation (PSM) topology, and a crowbar system was applied as a double protection device to protect the gyrotron. Instead of the heavy and bulky oil-cooling type high-voltage switch, a light and low-maintenance natural air-cooling type commercial switch was applied. The newly developed HVPS and ECICS were applied in the 2020 and 2021 KSTAR campaigns. Unfortunately, serious problems such as noise and timing issues were discovered during the two-year KSTAR campaign. Therefore, the second upgrade of the HVPS and ECICS was conducted in 2022 to realize a more stable and accurate EC system. The core part of the ECICS was developed anew, and the structure of the control system was significantly upgraded. In addition, the control method of the HVPS PSM module was newly developed. Moreover, the communication method between the ECICS and the controller of the HVPS was upgraded. In this paper, the upgraded HVPS and ECICS are explained in detail, and a discussion on the experimental results of the upgraded system for the next KSTAR campaign is also presented.