Curvature-induced singularities and stability analysis of curved perfectly matched layers for ICRF antenna–plasma coupling

In electromagnetic modeling of ion cyclotron range of frequencies (ICRF) antennas, curved coupling models provide a more realistic representation of the antenna and edge-plasma geometry, improving the accuracy of wave-coupling and loading predictions. However, limited radial space near the plasma boundary constrains the implementation of curved perfectly matched layers (PMLs), and field singularities may arise under such confined conditions. To investigate this issue, an idealized curved-domain model was formulated to analyze how curvature and the stretching function influence PML behavior. An analytical expression for the fast-wave reflection coefficient was derived and compared with finite-element simulations, which verified the analytical trends and revealed localized field enhancements associated with curvature and steep stretching. Building on these results, two-dimensional antenna–plasma coupling models incorporating J-TEXT–relevant parameters were used to evaluate PML performance under realistic spatial constraints. Planar models were also analyzed for reference. The 2D simulations show that stable absorption and smooth field distributions are maintained when the radial PML thickness lies within 0.12–0.13 m and the poloidal and toroidal PML spans satisfy θ PMLp > 0.3 rad and θ PMLt > 0.12 rad, with less than 2% variation in coupled power. These results provide practical reference values for configuring curved PMLs in fusion-relevant electromagnetic simulations.