Analysis of Final Loss Events due to Vertically Unstable Runaway Electron Beams in DIII-D

Runaway electrons (REs) in tokamak fusion plasmas pose a significant challenge. A non-collisional technique called the 'benign termination strategy' shows promise for RE beam termination with minimal first-wall heating. This work analyzes RE vertical displacement event (VDE) experimental data from DIII-D tokamak benign termination experiments and simulation with the TokSys code suite. This research aims to investigate correlations between experimental parameters related to equilibrium evolution and parameters associated with final loss events and MHD instabilities, which can provide valuable insights on accessing and optimizing the benign termination strategy . Equilibrium evolution analysis examines plasma stability in plasma current (IP)/ plasma minor radius (a-minor) and edge safety factor (qa)/internal inductance (li) spaces to gain insight on what influences the final loss events. Derivative metrics are applied to assess the speed of VDEs and its effect on access to the final loss event. Comparisons are made between experimental EFITs and simulated TOKSYS-derived EFITs. Analysis of bursts and final loss events includes the hard x-ray (HXR) loss duration, correlation with burst duration and time into current quench. This research enhances understanding of the crucial plasma compression phase and which details are most crucial for accessing the final MHD loss event, improving confidence in the benign termination strategy for RE beams.