A wideband hybrid combiner design for ITER ion cyclotron radio frequency source

Abstract

The high-power radio frequency source for ion cyclotron heating and current drive of ITER tokamak consists of two identical 1.5 MW amplifier chains. These two chains will be combined using a wideband hybrid combiner with adequate coupling flatness, phase balance, return loss, and isolation response to generate 2.5 MW radio frequency (RF) power in the frequency range of 36 to 60 MHz. As part of the in-house development program at ITER-India, a wideband hybrid combiner with coupling flatness and return loss/isolation better than 0.4 and −25 dB, respectively, has been simulated. A detailed analysis for matched load performance of the hybrid combiner for the output power level of 3 MW as well as mismatched load performance for load power of 2.5 MW with voltage standing wave ratio 2.0 and 3.0 MW with voltage standing wave ratio 1.5 has been performed. Based on the simulation, a prototype model was in-house fabricated, and the simulated results have been validated experimentally in splitter and combiner mode. To evaluate performance as a combiner, two solid-state power amplifiers were combined through the prototype combiner for input power levels up to 2.5 kW on matched and mismatched load conditions. In the power splitter experiment, the RF power level up to 1.5 MW from a single amplifier chain was split through the prototype combiner to be dumped in the high power loads in the frequency range of 36 to 60 MHz.