Radio Frequency Power Combining With Reactance Steering Network for Fusion Plasma Heating

This article presents the design and implementation of an amplitude modulated radio-frequency (RF) power combiner system using a reactance steering network for driving variable impedance Inductively Coupled Plasma (ICP) heating coils in fusion reactors. The variation in the impedance of ICP coils depends greatly on factors such as the plasma electron density, pressure or temperature of the plasma. The matching network is used to reduce the range of variation in the ICP impedance, while the reactance steering network functions to make the branch impedances almost completely resistive. A prototype is designed, with two equivalent resonant Class-E power amplifiers, connected in parallel through a dedicated reactance steering network to a matching network, which in turn is connected to a load that emulates the impedance characteristics of an ICP coil. The frequency of system operation is set as 10 MHz, capable of driving the ICP load with 225 W of power at a peak efficiency of 75.6% in continuous operation mode. The simulation and experimental results, collected for a range of load points, both highlight the effectiveness of the combined reactance steering network and matching network structure when powering variable impedance ICP coils using impedance sensitive resonant power amplifiers, operating with ZVS.