Identification of a magnetohydrodynamic trigger for plasma explosions in magnetic fusion beyond existing paradigms.

In magnetic-fusion devices, magnetohydrodynamic (MHD) disturbances such as edge-localized modes (ELMs) have interesting similarities to explosive dynamical events observed in space. Various models for the mechanisms triggering such disturbances have been proposed. However, current studies have focused on developing methods for controlling such effects based on empirical scaling. Although unanswered questions remain regarding ITER, diverse viewpoints beyond the current paradigm can provide a deeper understanding, even for widely accepted answers. Herein, we define the triggering time of an ELM using precise diagnostics to eliminate the uncertainty that can accompany the determination of causal relationships. This has enabled us to identify a precursor MHD with tearing parity (poloidal/toroidal mode numbers m/n = 4/1) as the cause of an ELM; it leads to the development of a macroscopic ELM when the magnetic perturbation exceeds a threshold of ~ 10 Gauss within [Formula: see text]100 [Formula: see text]s, providing a consistent representation of this phenomenon that extends from the precursor to the collapse. The explosive growth timescale from the triggering time is consistent with a hyper-resistive model of magnetic braiding and stochasticity. This approach to solving the triggering problem provides valuable scientific insights into diverse magnetized-plasma-explosion physics.