In order to improve the efficiency of lower hybrid current drive (LHCD) system on HL-3 tokamak,new functions such as power real-time control and phase real-time feedback are needed in the new microwave exciter. The DDS and frequency mixing scheme are used in the microwave exciter to attain low phase noise, high frequency stability and high spurious rejection ratio of the microwave output signal in a certain frequency band.The phase real-time feedback control with response time less than 50 μs is realized by using digital-analog phase shifter + FPGA. Real-time power control with response time less than 50 μs is achieved using a digital-analog attenuator + FPGA. Based on the above design ideas, the design of microwave excitation source for LHCD system on HL-3 tokamak is completed.

LHCD, Microwave exciter, Power control, Phase feedback control