Effects of antenna misalignment and density turbulence on helicon and slow wave propagation in DIII-D

This study explores the behavior of helicon and slow wave propagation in the DIII-D tokamak using the Petra-M full-wave simulation code. At a frequency of 0.48 GHz in DIII-D, both slow and fast helicon waves can coexist in the scrape-off layer (SOL). It is crucial to minimize slow wave excitation since they can be easily damped in the SOL. To understand the excitation and propagation of slow waves, we conduct numerical surveys by scanning the angle between the magnetic flux and antenna surfaces, the antenna misalignment angle in the toroidal direction, and the plasma density in front of the antenna (n_ant). We also address the effects of turbulence near the last closed flux surface (LCFS) on the propagation of helicon and slow waves. We generate drift-wave turbulence with the XGC simulation code and plan to implement it in Petra-M. These small-scale spatial density fluctuations can affect both long-wavelength helicon and short-wavelength slow waves. Since the slow mode can reach the LCFS at a lower n_ant, turbulence is likely to impact slow wave propagation and absorption.