High-Power MHz to 100s of GHz Circuits and Systems for Nuclear Fusion Reactors With Examples From SST-1 and ITER

Nuclear fusion on earth is a highly complex and challenging multidisciplinary field that aims to solve the global energy puzzle by providing infinite energy with zero carbon emissions. Achieving controlled thermonuclear fusion requires high-power RF and microwave circuits and systems covering a broad frequency range from MHz to sub-THz to reach critical plasma temperature and current density parameters. These systems differ from conventional RF systems and are massive (length/weight: kms/tonnes), deliver high CW power, and must operate in harsh environments such as ultra-high vacuum (UHV), high thermal and radiation stresses, and plasma disruption forces. This paper discusses the essential requirements and importance of various radio frequencies in fusion reactors, such as ion cyclotron, electron cyclotron, and hybrid resonances. It overviews high-power CW (100 s kW to MWs) amplifiers/sources, circuits, and complete systems incorporating antenna arrays and covering MHz to 100 s of GHz with examples of the SST-1 and ITER tokamaks from a microwave engineering perspective. The paper also highlights material selection, design, fabrication, and implementation challenges and techniques for high-power amplifiers and systems. The subsystems incorporate large coaxial, rectangular, and circular corrugated waveguide lines and components with fluid cooling, gas pressurization and UHV compatibility. They launch TEM, TE10, and HE11 modes to rapidly fluctuating plasma loads through various antenna modules with real-time matching, positioning, and beam steering capabilities. The paper concludes by discussing the RF system requirements, status, schedule, and key technical challenges of ITER, the world's largest and most ambitious nuclear fusion-based reactor project.