Description
Ion Cyclotron Resonance Heating (ICRH) is a key auxiliary system for present-day tokamaks and a crucial actuator for ITER baseline scenarios. Beyond plasma heating, ICRH contributes to scenario flexibility, impurity control, and fast-ion physics. However, its efficiency depends on a delicate interplay among wave coupling, single-pass absorption, plasma mixture control, impurity production and fast-ion confinement. Optimizing ICRH performance under reactor-relevant conditions is therefore essential for steady-state fusion plasmas.
In this context, the WEST tokamak, operating in a fully metallic environment, provides a unique experimental platform to investigate ICRH optimization in conditions relevant to future devices. This work presents a systematic experimental study of optimizing the fundamental H-minority ICRH power deposition in deuterium plasmas, exploring the parameter space by scanning the radial position of the IC resonance, and the minority ion concentration, while keeping global plasma parameters and antenna coupling conditions constant [1].
By monitoring the main plasma performance indicators, it is demonstrated that the ICRH efficiency is maximized when the IC resonance is shifted by ~7 cm from the center to the HFS. A strong degradation is observed when the resonance is shifted further inward (>20 cm on the HFS), while the efficiency is approximately halved when located >5 cm on the LFS. Reflectometry-based turbulence characterization does not show a clear dependence on the resonance position, suggesting that the IC impact on the confinement properties mainly relies on the wave absorption rather than the fine micro-scale stability physics. The resonance position is also constrained by infrared thermography and calorimetry analysis on the fast-ion ripple-induced losses, which are found to be minimal when the resonant layer is located beyond 10 cm on the HFS, requiring a compromise between loss mitigation and optimal absorption, as previously determined through particle-tracking modelling efforts [2].
Overall, this study demonstrates that an optimized control of the IC resonant layer position combined with an appropriate control of the minority concentration, can simultaneously maximize ICRH efficiency, improve fast-ion confinement and reduce detrimental wall loads in WEST.
[1] S. Mazzi et al., in preparation for Nucl. Fusion (2026)
[2] H. Corvoysier et al., Submitted to Nucl. Fusion (2026)