Speaker
Description
We present a dual-frequency gyrotron for the electron cyclotron heating and current drive (ECH/ECCD) system to achieve steady-state tokamak plasma operation for future K-DEMO. We will use this dual-frequency gyrotron to study the transmission lines and a launching system, including nonlinear harmonic signals generated from the gyrotron, which interrupt the RF beam steering. The gyrotron operates in TE7,2 and TE9,3 modes at 142 and 208 GHz, respectively. The electron gun is designed as a diode-type and operates at a cathode voltage of 40 kV and a current of 7 A. The simulated output power is about 60~100 kW, and the output beam has a duration of about 20 us, which should be enough for studying purity of the output modes and the nonlinear harmonic signals. We designed the gyrotron with in-house code (UGDT) [2], and compared it with the commercial code (CST) [3]. We designed the cavity generating two modes under two different conditions of the electron beams with the same size of the cavity. To operate the TE7,2 and TE9,3 modes in a single size of the cavity, electron beam radii of 2.4 mm, and 2.2 mm are required, respectively. We re-use the existing electron gun optimized for the previously operated 95 GHz gyrotron. Therefore, the electron beam was not optimized for the two operating modes, which led to limits in the dual gyrotron efficiency. The size of the interaction cavity was also chosen delicately so that two modes are generated with similar power. The simulated output power is 100 kW for 208 GHz, and 60 kW for 142 GHz according to the in-house UGDT code. The mode converter can convert the higher-order mode to gaussian mode with 95% of power coupling.
We finished fabricating the gyrotron components and planning to operate the gyrotron. This gyrotron will be used for several applications, including analysis of the nonlinear harmonic signals of the gyrotron, transmission line mode purity study, and the remote detection of plasma breakdown.
ACKNOWLEDGMENTS
This work was supported by National R&D Program through the National Research Foundation of Korea(NRF) grant funded by the Korea government (MIST), (No. 2021M1A7A4091139).
References
[1] S. G. Kim, et al., Journal of Infrared, Millimeter, and Terahertz Waves 37, 209-229 (2016)
[2] A. Sawant, et al., J. Korean Phys. Soc.73,1750–1759 (2018)
[3] Computer Simulation Technology, CST Studio Suite, [Online]. Available: https://www.cst.com/
