A multi-tokamak comparative study of methods for detecting and predicting disruptivity of vertical displacement events

Vertical displacement events (VDEs) in tokamaks involve large displacements of the plasma magnetic axis from the vessel plane of symmetry, often leading to disruptions. These events are particularly dangerous for their potential to cause damage to plasma-facing components, as well as large forces on the vessel due to halo currents generated during the disruption that run through the plasma and vessel. Detection and control of these events and mitigation or avoidance of a potential disruption is crucial, and is often achieved through either real-time equilibrium reconstructions or real-time comparisons of magnetic probe measurements. For example, external flux loops typically located above and below the midplane of the tokamak are employed to monitor the displacement and velocity of the plasma magnetic axis. Using the DECAF code, we compare these two detection approaches in terms of their reliability and accuracy in predicting disruptions of the plasma. Further, we present results of a comparative study between VDEs on KSTAR and NSTX indicating critical metrics and thresholds for predicting these events and their propensity to result in disruption.