Time-dependent integrated modeling of high power helicon experiments on DIII-D

Helicon current drive is a potential solution for driving off-axis current for advanced scenarios in reactor conditions. Dedicated DIII-D experiments have recently been conducted to assess power coupling, absorption, and current drive for a MW-level helicon system. Time-dependent modeling was performed with TRANSP in order to aid experimental interpretation and also validate physics models for future experimental design and physics studies. Within TRANSP, the helicon power deposition and current drive is calculated via the GENRAY ray tracing code, while temperature fluctuations are predicted with the TGLF turbulent transport model. In helicon modulation experiments, cross spectral analysis techniques are used to compare ECE measurements of temperature perturbations to predictions from the simulations. Reference discharges with modulated ECH (for which well-validated forward models exist) are used as a reliable benchmark for the helicon cases. A synthetic MSE diagnostic within TRANSP is used to predict the detectable signature of helicon current drive. Lastly, injected helicon power scans are performed in TRANSP in order to constrain estimates of the fractional power lost in the edge region via parasitic mechanisms.