Error Analysis of Directional Coupler for Lower Hybrid Wave Power Measurement

As one of the important parameters for lower hybrid wave (LHW) systems with 24 4.6 GHz/250 kW continuous-wave klystron amplifiers, the microwave power needs to be accurately acquired in real time for the experimental advanced superconducting tokamak (EAST) experiment. A new 4.6 GHz/250 kW directional coupler was developed for power measurements in an LHW system. The design principle and characteristic parameters of the coupler are discussed based on transmission line theory and the system requirements. The calculations and simulations indicate that the measurement error of the incident power is less than 5% when the isolation is greater than 25 dB. The directional coupler was also applied to the 4.6 GHz LHW system. The results show that the device can meet the requirements of LHW system operations. Comprehensive Research Facility for Fusion Technology(CRAFT)is being built. This work is beneficial to the design of power measurement system for LHW system.