Speaker
Taesik Seong
(Department of Physics)
Description
The KSTAR LHCD system is using a 5-GHz, 0.5-MW c. w. klystron and oversized rectangular waveguides. The WR187 output waveguide of the klystron transmits the RF power to the LH launcher via 80-m of transmission line composed of WR284 oversized rectangular waveguide. The overall transmission loss was about 34% including 26% of Ohmic loss. In order to transfer RF power effectively from a klystron to the launcher, low loss transmission-lines should be used. The resistive loss of the transmission line can be extremely reduced by adopting oversized circular waveguide. The Ohmic loss of TE01 circular mode decreased as the radius of the waveguide increases. In this case, mode converters are required to connect the rectangular output waveguide of klystron to the circular waveguides. Two types of mode converters were designed. One is the side wall type mode converter that converts the TE10 rectangular mode to TE01 circular mode. The other is the serpentine type mode converter which converts the TE11 circular mode to TE01 circular mode. TE11 circular mode can be easily excited by simple adiabatic transform of rectangular to circular waveguide. Mock-ups of two types of mode converters are under construction. In this paper, it will be presented that the comparison of the HFSS design and the measurement of the two types of mode converters. The transmission efficiency from TE10 rectangular to TE01 circular mode of side wall coupling and serpentine mode converters are -0.04 dB and -0.046 dB, respectively, according to the HFSS calculation. This mode converter design can be applied to the KSTAR LHCD system which is planned to be upgraded to 4-MW system with low loss transmission-line in 2020.
* This research was supported by National R&D Program through NRF of Korea funded by MSIP (NRF-2014M1A7A1A02029891), BK21+ program and Korean ITER project.
Co-authors
Jeehyun Kim
(National Fusion Research Institute (NFRI), Daejeon, South Korea)
Moohyun Cho
(Department of Physics, POSTECH, Pohang, Gyeongbuk, South Korea)
Taesik Seong
(Department of Physics, POSTECH, Pohang, Gyeongbuk, South Korea)
Won Namkung
(Pohang Accelerator Laboratory (PAL), Pohang, Gyeongbuk, South Korea)
