Proximity Control and Robust VDE Protection on DIII-D and KSTAR

ITER will require exceptionally low disruptivity while pushing performance limits. This will require a comprehensive strategy, including continuous regulation of the proximity to stability and control limits (Proximity Control). DIII-D has been developing a real-time Proximity Control architecture which modifies control targets and actuator constraints based on stability metrics. Robust Vertical Displacement Event (VDE) avoidance has been demonstrated using real-time adjustment in shaping to regulate the VDE growth-rate at 800 rad/s for >3s, intervening only beyond thresholds in acceptable growth-rates. H-L back-transition protection has been demonstrated with real-time modification of minimum input power based on radiated power, and a machine learning predictor for the likelihood of H-/L-mode. Limited controllability of edge gradients in J|| in the ITER Baseline Scenario using adjustments in plasma triangularity and squareness has been demonstrated, providing a potential tool for tearing mode avoidance.

Experiments on KSTAR have diagnosed the limits of its vertical control using machine-scalable metrics, including measured VDE growth rates and the max Z-excursion that the vertical control system can withstand (dZ_max), while reaching a new max > 2.2 sustained for more than 3s.