Progress on an ion cyclotron range of frequency system for DEMO

An Ion Cyclotron Range of Frequency (ICRF) system can provide power for a number of tasks, experimentally verified on present machines: heating and current drive, first wall conditioning, plasma startup, removing central impurities, controlling sawteeth and current ramp down assist. The system has a high plug-to-power efficiency and most of the components external to the machine are sturdy, with industrial steady state capability. Traditional ICRF antenna systems are often characterized by a high operating voltage and high power density. Low power density and low voltage however provides a bonus in terms of reliability. Therefore, travelling wave type antennas have been proposed (Ragona and Messiaen, 2016). They can be integrated in the blanket and use only a limited number of feeders. The effect on the tritium breeding ratio of such an antenna incorporated in the blanket, including the feeders, is small. The k_// spectrum is peaked and the dominant k_// value can be optimized for coupling and bulk absorption, while avoiding the generation of coaxial modes in the edge. The coupling can be further enhanced with gas puffing near the antenna. Assuming the ITER-2010-low density profile, 50 MW can be coupled with a voltage on the antenna components of about 15 kV.