Fullwave simulation of EBW mode conversion using non-local operator in finite element method*

The dielectric response to the RF fields in hot plasma is non-local, and the Maxwell wave problem becomes an integro-differential equation. A standard approach to construct a differential form based on the small k⊥ρ expansion is typically limited to small k⊥ρ. We recently proposed an alternative approach to construct a dielectric operator based on the rational approximation of the plasma dielectric tensor. The new approach yields an operator acting on dielectric current, which includes all-order finite Larmor radius effects without explicitly containing higher order derivatives of field variables. Therefore, it is more suited for describing the propagation of electron Bernstein waves (EBW). In this work, this new approach is applied for simulating various EBW mode conversion and propagation problems using 1D configuration. In the low field side O-X B conversion based on the NSTX-U device, we demonstrated that the predicted mode-conversion efficiency agrees with analytical calculations. 100% conservation of wave energy carried by the Poynting flux to electron thermal motion ("sloshing") is found. Using the high field side X-mode injection scenario based on the ST-40 parameters, it was demonstrated that the simulation model can capture the damping of X-mode and the conversion to EBW at the upper hybrid resonance (UHR) layer consistently. Extension to 2D geometry and potential application to assess the mode-conversion physics when the density fluctuation exists near UHR will be discussed.