CQL3D-Hybrid-FOW modeling of the temporal dynamics of NSTX NBI+HHFW discharges

R W Harvey,D Liu,G Taylor,P T Bonoli,Yu V Petrov,W W Heidbrink

doi:10.1063/1.4864551

Abstract

The CQL3D Fokker-Planck code[1] has been upgraded to include physics of finite-orbit-width (FOW) guiding-center orbits[2,3], as compared with the previous zero-orbit-width (ZOW) model, and a recent first-order orbit calculation[2]. The Fast Ion Diagnostic FIDA[4,5] signal resulting from neutral beam (NBI) and high harmonic fast wave (HHFW) RF power injected into the NSTX spherical tokamak can now be modeled quite accurately, using ion distributions from the CQL3D-Hybrid-FOW code, a rapidly executing variant that includes FOW+gyro-orbit losses to the plasma edge, FOW effects on NBI injection and HHFW diffusion, but does not include neoclassical radial diffusion. Accurate simulation of prompt fast ion (FI) losses is a key feature of the marked modeling improvement relative to previous ZOW results. By comparing NBI-only and NBI+HHFW shots, independent confirmation of the usual 35% edge loss of HHFW in NSTX is obtained. Further, HHFW prompt losses from the plasma core are shown to be 3X as large (>25%) as the NBI-only case. The modulated NBI and time-dependent background plasma variations and charge exchange losses of fast ions are accounted for, and the temporal neutron variation is in approximate agreement with NSTX observations.

Highlights

Most of the CQL3D applications to date have been in the zero-orbit-width (ZOW) approximation[1], neglecting most effects of radial drift on the transiting and trapped tokamak orbits
The first step, referred to as CQL3D-HYBRID-FOW, has greatly improved agreement with FOW effects measured by the experimental NSTX FIDA diagnostic, yet the required execution time is only increased by 30% for the NBI-only case, and by 75% for NBI+high harmonic fast wave (HHFW) compared to CQL3D-ZOW
NBI FIDA signals are normalized to the same peak value, and this normalization is used with the NBI+HHFW

Summary

Introduction

Most of the CQL3D applications to date have been in the zero-orbit-width (ZOW) approximation[1], neglecting most effects of radial drift on the transiting and trapped tokamak orbits. The FOW effects are included in a “hybrid” mode[3], to be explained more fully below; the results have shown much more accurate simulation of radial orbit shift effects and prompt losses in NSTX FIDA experiments.

Results

Conclusion