Modeling Enhanced Impurity Sputtering due to RF Sheaths in front of ICRH actuators

RF sheaths exhibit potential drops an order of magnitude larger than classical thermal sheaths, causing an enhancement of the impurity flux sputtered by the accelerated ions impacting on the Plasma-Facing components. In particular, minimizing the material emission in front of ICRH actuators is a pivotal task for future reactor operations. In this study, we used a one-dimensional fluid model of the RF sheath coupled to the BCA sputtering code F-TRIDYN to parametrically investigate the dependence of particle impurity fluxes emitted by the RF antenna as a function of the plasma and magnetic field conditions. The model provides the energy-angle distributions of both the impacting ions and the emitted impurities. We highlight the frequency dependence of the energy of the impacting ions, sputtering yield, and distributions of emitted particles as a function of the RF period. On average, the sputtered impurity flux was found to have a parabolic relation with the RF wave frequency (plateauing at the extremes), and an inversely proportional relation to the magnetic field angle.