Full-wave simulations of helicon wave coupling optimization and possible parasitic excitation of slow waves near the edge plasma

Helicon waves are thought to be promising since they can penetrate reactor-grade high-density core and drive off-axis current. In the frequency regime ~ 476 MHz, both slow electrostatic and fast electromagnetic helicon waves can coexist in the scrape-off layer (SOL). This work uses the Petra-M simulation code to perform 2D and 3D full-wave simulations of helicon and slow waves. We launch the helicon waves for 2D simulations by assuming an antenna with a finite wave number in radial and vertical directions in a realistic vacuum vessel boundary and discuss SOL power losses of the helicon waves. Slow mode excitation is examined using 3D full-wave Petra-M simulations, accounting for the 3D antenna geometry and SOL plasma. We use a realistic 8-module helicon antenna in Petra-M and limit the simulation domain near the antenna to examine slow and fast wave mode characteristics in detail. The 3D simulations confirm slow mode excitation and indicate that the slow-wave branch can be excited even for zero antenna misalignment angle (Φ). SOL power losses and antenna loading at various values of Φ and SOL density in a 3D simulation are also discussed.