Design of variable fundamental power coupler

This paper aims to design a new 650 MHz variable fundamental power coupler. The external quality factor Q_e ranges from 1.5% × 10⁵ to 2% × 10⁶ to meet the requirements of different current modes of the Beam Test Facility of PAPS (Platform of Advanced Photon Source Technology R and D). This is the first time to develop a variable continuous wave type power coupler in China. In this paper, the RF transmission and field distribution of the coupler are calculated by HFSS three-dimensional electromagnetic software. The external quality factor at different antenna penetration depth is simulated by CST microwave studio. The penetration depth adjusting experiment is carried out by integrating with a 650 MHz 2-cell superconducting cavity. The simulated and measured results of Q_e agree well with each other. (authors)