Modeling enhanced impurity sputtering due to rf sheaths in front of ICRH actuators

One of the main concerns over using the Ion Cyclotron Resonance Heating (ICRH) is the enhanced impurity sputtering phenomenon due to the emergence of RF sheaths near the Faraday Screen of the ICRH antenna. Here we present a semi-analytical fluid plasma model able to capture the enhanced sputtering yield from the Faraday Screen and the Plasma- Facing Components of an Ion Cyclotron Resonance Heating antenna in a fusion machine. The model is a one-dimensional phase-resolved model of a rectified radio frequency sheath in a magnetic field at an angle with respect to the material surface, solving for the momentum transport of both the ions and the impurities. The sputtering model of the impurities coming off from the wall is based on lookup tables obtained from the plasma-material interaction code Fractal-Tridyn. This study analyzes a range of magnetic angles and wave frequencies to parametrically investigate their effect on the energy-angle distributions of the impacting ions and sputtered impurities. Finally, an estimate of the impurity fluxes and of the gross-erosion rate is provided for ITER-relevant conditions