ICRH simulations for the Wendelstein 7-X stellarator

We present the current status of ion-cyclotron-resonance heating (ICRH) simulations for Wendelstein 7-X (W7-X), a large, superconducting, optimized stellarator in Greifswald, Germany. More experimental experience with the ICRH antenna at W7-X, in dipole and monopole configuration, has been gained in the experimental campaign conducted from autumn 2024 to spring 2025. Several tools are available for explaining the experimental findings and for planning new experiments. They range from simple cold plasma models, targeting basic ICRH physics aspects, such as the locations of resonances and cutoffs in the plasma, to more advanced full-wave modeling. The reduced models are valuable for quickly comparing different magnetic configurations of W7-X and for checking the sensibleness of more advanced simulations, for which we use the SCENIC suite of codes [1]. SCENIC iteratively couples LEMan [2], an eigenvalue code solving Maxwell’s equations, and VENUS-LEVIS [3], a Monte-Carlo code assessing the wave-particle energy transfer and modeling the build-up of a fast-ion distribution function. Especially, the capabilities of the ICRH system to generate fast ions are of interest, because a future stellarator fusion reactor needs to adequately confine such fast ions. We give an overview of the tools that are currently available and highlight some of the results that have been obtained with SCENIC. We focus on minority heating of H ions in a 4 He background plasma, which is an important ICRH scenario considered in W7-X. Different magnetic configurations and plasmas with varying minority concentration are compared regarding the locations of resonances and mode-conversion layers which impact e.g. fast-ion generation properties. We also explore schemes with varying antenna frequencies, which shift the resonance location toroidally in the 3D magnetic field of W7-X. Additionally, ICRH can also be operated together with neutral-beam injection (NBI), making use of synergetic effects when both heating systems are used simultaneously, and allowing higher fast-ion energies to be reached [4].