Disruptivity and Density Limits in MAST and other Tokamaks*

The Disruption Event Characterization and Forecasting (DECAF) code was written to automate analysis of tokamak data for disruptivity characterization of existing databases and related testing of specific physics analyses for disruption forecasting, such as density limits. DECAF analysis has been performed on the MAST, KSTAR, NSTX, NSTX-U, and TCV devices. DECAF is equipped to produce event probability plots of events leading to the disruption identified by DECAF physics models, such as MHD modes, no-wall beta limits, or the current quench itself. It was found that low q₉₅ was especially disruptive for MAST, as was density above the Greenwald limit. Recently a local island power balance limit theory, developed to explain the observed density limit in tokamaks, has been implemented in DECAF and tested on a set of NSTX discharges with long periods of rising density, eventual onset of low frequency n = 1 MHD activity, and disruption. Both the local island and global Greenwald limit criteria were found to rise towards, or surpass theoretical limits associated with the termination of the discharges. Both criteria are being evaluated for their utility as disruption predictors for the MAST-U device.