Fusion Science and Technology / Volume 61 / Number 3 / April 2012 / Pages 216-226
High radio frequency (rf) power amplifiers were designed as a part of research and development of an ion cyclotron range of frequency (ICRF) system that aimed at long-pulse operation at the megawatt level in a frequency range of 25 to 70 MHz. A study on the high-power amplifiers for ICRF heating in Experimental Advanced Superconducting Tokamak (EAST) is presented. To realize the design with a compact structure, a double coaxial cavity was employed as the output circuit of the final power amplifier (FPA) for tuning and matching, and the strip line was adopted for the input impedance matching circuit of the drive power amplifier (DPA). A double-stub tuner matching network with a variable-length U-link was used to obtain the impedance matching between the DPA and the FPA. To ensure the stable operation of the amplifiers, a grounded-grid configuration was chosen, and precautions were taken to suppress all parasitic oscillations of the anode output circuit. The rf power amplifiers performed successfully in stable operation at the megawatt level at each integer frequency from 25 to 70 MHz during the tests, and a rf power of 1.5 MW was achieved in a matching dummy load. The test results show a good agreement with the calculated values. The amplifiers operated reliably in long-pulse mode in EAST, and the total rf power of [approximately]1.8 MW was injected into plasmas in EAST ICRF heating experiments in the 2010 autumn campaign.