ICRF Mode Conversion Studies with Phase Contrast Imaging and Comparisons with Full-Wave Simulations

Waves in the ion cyclotron range of frequencies (ICRF) are widely used to heat toka‐mak plasmas. In a multi‐ion‐species plasma, the FW converts to ion cyclotron waves (ICW) and ion Bernstein waves (IBW) around the ion‐ion hybrid resonance (mode conversion). The mode converted wave is of interest as an actuator to optimise plasma performance through flow drive and current drive. Numerical simulations are essential to describe these processes accurately, and it is important that these simulation codes be validated. On Alcator C‐Mod, direct measurements of the mode converted waves have been performed using Phase Contrast Imaging (PCI), which measures the line‐integrated electron density fluctuations. The results were compared to full‐wave simulations AORSA and TORIC. AORSA is coupled to a Fokker‐Planck code CQL3D for self‐consistent simulation of the wave electric field and the minority distribution function. The simulation results are compared to PCI measurements using synthetic diagnostic. The experiments were performed in D‐H and D‐3He plasmas over a wide range of ion species concentrations. The simulations agreed well with the measurements in the strong absorption regime. However, the measured fluctuation intensity was smaller by 1–2 orders of magnitudes in the weakly abosorbing regime, and a realistic description of the plasma edge including dissipation and antenna geometry may be required in these cases.