Design and development of 105GHz KFE compact gyrotron components for KSTAR ECH system

Korea Superconducting Tokamak Advanced Research (KSTAR) is planning to install an electron cyclotron (EC) system for a total of 6MW Radiofrequency (RF) output and is currently in progress. A total of 4 EC systems were installed in the 2022 KSTAR campaign, but only 2 EC systems are in operation. Both EC systems have a problem with the gyrotron and are currently being repaired. The 4 gyrotrons currently installed are 1MW, 105/140Ghz dual-frequency gyrotrons that can operate for up to 300 seconds. In the 2020 KSTAR campaign, an EC system called EC4 provided about 1450 shots to the tokamak. Of these, about 500 shots were used for start-up with a pulse length of less than 0.5 seconds. This is about 35% of the total shot. We conclude that it is inefficient to use a high-spec gyrotron for low power less than 500kW and short pulses. Therefore, we are developing a start-up gyrotron with an RF power of 500kW and a pulse length of less than 0.5 seconds. The design value was determined based on the specifications of the gyrotron, which are mainly required by KSTAR. We will explain the specifications of the Gyrotron for startups in this paper. In addition, we will present in detail the design of the core components of the gyrotron for startups, such as cavity, electron gun, window, mode converter, and collector.