First Disruption Avoidance by Real-time Disruption Event Characterization and Forecasting on KSTAR and Related Physics Research*

Disruption avoidance simultaneously addressing multiple off-normal events has been a decades long-sought capability for large, long-pulse auxiliary-heated tokamaks and a critical need for ITER and reactor-scale tokamaks. Physics-based disruption event characterization and forecasting (DECAF**) research [1] determines the relation of physical events leading to disruption, producing event onset forecasts with high accuracy (100% accuracy in dedicated experiments exhibiting MHD-induced disruptions) and sufficiently early warning (~ 1 second on KSTAR). Recent experiments produced the first real-time demonstration of disruption avoidance using multiple DECAF “Events” to control actuators using “Event feedback” in KSTAR. These Events now examine various physical phenomena including plasma current anomalies, vertical instability, MHD mode-locking, and impurity radiative collapses. To produce an earlier VDE disruption warning in real-time, a VDE forecaster Event (VDE-f) was created based on a vertical force balance model including the applied equilibrium field, 2-D plasma current, and eddy currents [2] and was connected to plasma shape and current profile (ECCD) actuators that produced disruption avoidance. The target plasmas produced high transient normalized beta up to 3.9 (record levels for KSTAR with the new tungsten divertor). Disruption avoidance was demonstrated in both upper / lower single null configurations with separatrix strike points on the carbon / tungsten divertor, respectively. The LTM-f Event actuates an n = 1 rotating field prepared to avoid mode locking. Other new DECAF Events were studied using the tokamak databases and each have warning levels that correlate with plasma disruptions including a generalized capability to diagnose electron temperature collapses (TEC) that provide early disruption prediction (~ 0.7s). *Supported by U.S. DOE grants DE-SC0020415, DE-SC0021311, and DE-SC0018623. **U.S. and international patents pending.

[1] S.A. Sabbagh, et al., Phys. Plasmas 30 (2023) 032506; https://doi.org/10.1063/5.0133825

[2] M.T. Tobin, et al., Plasma Phys. Control. Fusion 66 (2024) 105020