Design of mid-plane passive active multijunction antenna for 5-GHz KSTAR LHCD system

The major upgrade of KSTAR LHCD system to 4 MW is planned in 2021. 4-MW RF power will be provided by 8 × 0.5 MW klystrons. Highly oversized circular waveguide transmitting TE01° mode will be adopted for the low loss transmission line longer than 50 m. The design of the 4-MW mid-plane Passive Active Multijunction launcher has been performed. Considering parallel refractive index N|| for the efficient current drive and the maximum power density at the launcher mouth, the launcher is composed of 256 active waveguides whose dimension is 58 mm x 7 mm and 18 mm of spatial period for N||0 = 2.5. Multijunction with Emax < 3.5 kV/cm and high power waveguide components have been designed using HFSS code. The antenna properties were evaluated using ALOHA. Prototype PAM launcher with 32 active waveguides is under development for 0.5-MW pulsed operation.