Study and analysis of high-power coupler failure due to asymmetric electric field distribution

Microwave vacuum electronics play a vital role in numerous applications, and high-power couplers are a critical component. However, coupler failure is a common problem in high-energy accelerators, especially in situations involving high continuous wave (CW) power operation, leading to costly downtime and reduced performance. This paper focuses on addressing the issue of coupler failure in high-power scenarios by studying the specific case of the Circular Electron-Positron Collider (CEPC) 650 MHz high-efficiency klystron, designed for a power of 800 kW and tested up to 700 kW. The failure was attributed to the cracking of the coupler ceramics due to asymmetric electric field distribution, a previously unnoticed issue. Consequently, this study describes the coupler testing process, analyzes the problem, and proposes corresponding solutions to achieve symmetrical electric field distribution and reduce thermal stress. After evaluating three approaches, we recommend the T-bar coupler with water cooling and forced air cooling as the most viable option. This research is significant for the future development of high-power couplers, as it offers references for overcoming technical challenges and optimizing structural designs. As a result, other high-power coupler designers may find inspiration in the suggested solutions as they strive for increased dependability and performance. •Ceramic breakage of the coupler is a common failure in microwave vacuum electronic devices.•The asymmetric electric field distribution causing high-power coupler failure is rarely discussed.•The introducing of T-bar transition and optimizing the structure can effectively suppress the issue of asymmetric field distribution.•Addressing the asymmetric field distribution problem is significant for improving coupler performance.