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A 500-kW continuous-wave (CW) high-power 3-dB divider is designed for the 4.6-GHz lower hybrid current drive system in the Experimental and Advanced Superconducting Tokamak (EAST). A multistepped structure is used to increase the power capacity, and a water cooling structure is introduced to reduce the thermal deformation and gas breakdown, which keeps the maximum steady-state temperature of the divider below 60 °C under full-power (500 kW) operation. The result of the simulations of the electric field shows that the power capacity of the multi-stepped structure is more than twice compared with the traditional design. Moreover, the divider shows excellent performance in the low-power test, with low return loss (-35 dB) and similar division ratio (S21 = -3.004 dB and S31 = -3.035 dB) at 4.6 GHz. Both the division ratio test and the full reflection test were carried out successfully under 250-kW CW, which suggests that the development of the 3-dB divider satisfies the design requirements.

To satisfy various requirements of different physics experiments, a new power modulation method of the lower hybrid wave (LHW) has been developed in Experimental Advanced Superconducting Tokamak (EAST), including the development of a control source combining software and hardware. Such modulation system is realized by the main positive-intrinsic-negative diode switch located at the oscillator. The LHW modulation system has been installed and tested, demonstrating that the modulation parameters can be controlled flexibly. The maximal modulation frequency is about 10 kHz, which is limited by the hardware circuit speed. The system has been successfully used to study the influence of LHW on the performances of plasma. Under the modulation of LHW, strong mitigation of edge-localized modes (ELMs) has been observed, and ELM pace-making technique has been demonstrated. Further experimental studies with the modulation system will be continued in EAST.