Full wave simulation of RF waves in cold plasma with the stabilized open-source finite element tool ERMES

When RF waves are applied in tokamaks with metal walls, sheath rectification effects associated with the fields induced in the scrape-off layer (SOL) may lead to enhanced plasma-wall interactions (i.e. heat-loads in the limiters, RF-induced impurity sources) which can endanger the integrity of the machine and limit the RF power. Currently, some numerical tools are being used to simulate the RF antenna near fields in the presence of magnetized plasmas, but they have their limitations. Some neglect completely the interaction of the RF waves with the low-density plasma close to the antenna. Others take into account these interactions, but generate numerical spurious oscillations around the Lower Hybrid Resonance (LHR). Simplifications to reach convergence had also been tried (e.g. neglect gyrotropy, increase electron density to avoid the LHR), but the fields obtained with these simplifications can be very different to the real ones and this difference can affect the accuracy of derived magnitudes which use these fields as an input (e.g. sheath rectification effects). In this work we try to overcome all the limitations mentioned above by customizing the open-source finite element code ERMES. This code implements a finite element formulation which allows to simulate the near fields of the RF antenna in a continuous gyrotropic non-homogeneous media without limits in the minimum value of the plasma density and provides stable solutions even in the presence of the LHR. Benchmarking of this approach is underway and comparison against measurements, semi-analytical approaches and other codes will be presented.