Two-fluid model of RF condensation effects*

RF condensation is a nonlinear effect caused by the dependence of RF wave damping (either for EC or LH waves) on the local electron temperature perturbation. This effect has not yet been studied in an experimental setting. One possible challenge is that of ITG heat transport within the island, where high temperature perturbations could be limited by the onset of ITG instability at a critical temperature gradient. In ECH heated plasmas in W7X and ASDEX-U, it has been observed that, although ion temperatures may be clamped due to ITG instability, the electron temperature may be only indirectly affected through electron-ion coupling. In order to study the implications for RF condensation, we adapt the existing OCCAMI code to properly model these two-fluid effects for RF condensation. First, we show that this new two-fluid code reproduces the single-fluid results in the appropriate limits. Secondly, we demonstrate that in regimes of interest, electron-ion temperature coupling strongly influences the predicted RF condensation effect. Finally, we perform calculations for a wider range of experimental scenarios, including rotating islands and rotating islands with modulated power.