High harmonic fast waves (HHFW) are a versatile heating and current drive tool for scenario development. Extensive modeling scans were performed to find optimal parameters for different uses of HHFW in National Spherical Tokamak Experiment (NSTX-U). Scans of plasma density, temperature, magnetic field, and antenna phasing were performed both with and without neutral beam injection. For speed of calculation, the ray-tracing code GENRAY coupled to the quasilinear Fokker–Planck code CQL3D was used. CQL3D allows for a more accurate description of the fast ion population, as well as for quasilinear effects such as HHFW-induced modifications of the distribution function. Best current drive results are obtained at elevated electron temperatures and with the lowest kφ phasing. Adding neutral beams however typically strongly reduces the HHFW current drive efficiency at the low density cases due to HHFW absorption on beam ions. Results of this parametric study will feed into scenario development and predict-first whole-shot modeling of NSTX-U discharges.
This paper explores the use of high harmonic fast waves (HHFW) for heating and current drive in the National Spherical Tokamak Experiment (NSTX-U). The researchers performed extensive modeling to find optimal parameters for different HHFW applications, considering factors like plasma density, temperature, and magnetic field. They also studied the effects of adding neutral beam injection. The results will help with scenario development and whole-shot modeling for NSTX-U discharges.