Disruption event chain analysis of high-radiation and high-density triggered disruptions in a multi-machine tokamak database using DECAF

The tokamak density limit represents an upper threshold on a critical plasma parameter that must be optimized to maximize fusion energy output without disruption. Many theoretical and empirical models seek to predict density limit disruptions, but none have proven universally reliable across plasma configurations. The common thread through disruptive events associated with density limit disruptions (e.g. local cooling, increased radiation or transport, H-L back transition) is loss of energy balance. We hypothesize that elevated density triggers disruptions through multiple distinct physical mechanisms, each exhibiting characteristic event chains initiated by local or global energy balance loss. Using the DECAF (Disruption Event Characterization and Forecasting) code [1], we examine entire tokamak databases to construct physics event chains in disruptive shots characterized by high density and radiation from NSTX, MAST-U, and KSTAR. This multi-machine analysis reveals diverse event sequences leading to disruption when triggered by elevated density and radiation, demonstrating the need for a multi-physics prediction model. Results identify the most common event sequences leading to disruption and their variations across different tokamak configurations. These event chains establish the foundation for developing improved physics-based disruption prediction models through this novel event chain methodology while enhancing our fundamental understanding of the underlying physical mechanisms.

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