Theory Highlights for December 2020

Theory Weekly Highlights for December 2020

December 18, 2020

The Stability, Transport, Equilibrium, and Pedestal (STEP) workflow, implemented in the OMFIT integrated-modeling framework, has been validated against a DIII-D negative-central-shear (NCS) plasma, an advanced-tokamak scenario that improves MHD stability by maintaining a safety factor greater than two throughout the plasma. By coupling the Current, HEating, and Fueling (CHEF) module for sources, ONETWO for current evolution, EFIT for equilibrium calculation, and TGYRO (TGLF + NEO with EPED neural networks) for core transport, STEP was able to accurately recreate the equilibrium and kinetic profiles seen in experiment. While previously validated against standard H-modes, STEP required several upgrades to reproduce this more-exotic scenario. A current source driven by toroidal-field ramp was added to CHEF, allowing STEP to incorporate this significant source of off-axis current used in the experiment. In addition, an ad-hoc fast-ion diffusion model was added to FREYA neutral-beam code heating and current-drive calculations. Initial simulations with DCON and GATO in STEP have been carried out for this plasma, looking at the ideal magnetohydrodynamic stability of the scenario. Future work will seek to vary the neutral-beam power in STEP to calculate the observed ideal stability limit in NCS plasmas, with the goal of creating a theory-based predictive stability tool that can be used in the design of future tokamak experiments and reactors.

These highlights are reports of research work in progress and are accordingly subject to change or modification