Disruption Event Characterization and Forecasting (DECAF) analysis of tokamak plasma evolution and resultant disruptive and benign MHD for disruption avoidance*

The operational space set by MHD instabilities in tokamak plasmas limit the achievable plasma pressure, current and rotation, with the onset of MHD activity being strongly dependent on the profile characteristics at different radii, most notably close to rational surfaces and in large pressure gradient regions. Along with plasma performance limitations, the occurrence of certain non-linearly saturated, benign MHD modes can lead the plasma towards the stable domain of the operational space thus avoiding disruptions. Examples of both disruptive and non-disruptive modes include long-lived modes and the associated sawtooth instability, and the excitation of EHOs present in QH mode operation. In the present study, disruption event characterization and forecasting (DECAF) [1] analysis is used to examine the potential triggers and resulting effects of both disruption-inducing and benign MHD modes using the full databases of multiple tokamaks. Discrimination between the disruptive and non-disruptive behavior of the modes is examined including the evolution of the key plasma parameters defining stability thresholds, where comparisons with analytical theory are done. Results are presented through DECAF event chain and proximity analysis in the context of familiar plasma modes and operational scenarios.

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