High-Power Fast-Response Ferrite Tuner for ICRF Impedance Matching in EAST

Ion cyclotron resonance frequency (ICRF) heating is one of the traditional auxiliary heating methods adopted in the Experimental Advanced Superconducting Tokamak (EAST). The radio-frequency (rf) source consisting of eight transmitters has been fabricated since 2012 and has a working frequency of 24 to 70 MHz. It has a maximum total power of ~12 MW. However, the power injection into plasma has been restricted by the variable antenna load, which is sensitive to the scrape-off-layer boundary condition and the gradient distribution of plasma density. Triple liquid stub tuners, which have been employed for ICRF impedance matching, cannot cope with such rapid variations because of the low response speed. In previous research, a 300-kW ferrite tuner (FT) was developed and tested, but it was not good enough to meet the requirements of real-time impedance matching. Research on a high-power fast-response FT with maximum power of 1.5 MW was carried out to achieve real-time tuning to trace the load variations of the antenna. The design parameters of the FT were determined according to the experimental data of the antenna load in EAST. The ferrite material, rf circuit, and magnet system of the FT were discussed to satisfy the design goals. The test results showed good performance of response time, differential phase shift, and insertion loss, which was extremely significant for the high-power, real-time operation of an impedance matching network based on FTs.