Ripple loss parametrization during ICRH in the WEST tokamak

Abstract The Ion Cyclotron Resonance Heating (ICRH) system is one of the primary additional heating methods in the WEST tokamak, playing a significant role in achieving high-performance plasmas. The European Transport Simulator provides valuable insights into the dynamics of fast ions resulting from ICRH, helping optimize plasma discharges and potentially enabling favorable conditions for the L–H transition. One key challenge for ICRH in WEST concerns magnetic ripple, generated by the discrete arrangement of the toroidal coils, which causes fast particles to deviate from their standard orbits and can lead to their loss if their perpendicular velocity is too high. Ripple losses due to ICRH have been measured to account for a non-negligible fraction of the injected ICRH power in certain conditions. To model these losses, 3D orbit-following Monte Carlo codes are typically used, but a faster and more practical approach is proposed by truncating the Ion Cyclotron Resonance Frequency (ICRF)-accelerated ion distribution functions based on an imposed loss energy threshold. This paper compares this simplified method with experimental data, demonstrating its validity in the WEST operational range and estimating the total ICRF power deposition while accounting for ripple losses. The relationship between various particle energy components related to the truncated ion distribution functions and induced lost power is discussed and scaling laws for the ripple losses linking electron temperature, plasma density, ICRH power and minority ion concentration are proposed.