DECAF Code Multi-device Investigation of Disruption Timing and Categorization Indicated by Abnormal Variations in the Plasma Vertical Position and Current

Plasma disruption in tokamaks is a multi-step process in which the loss of plasma vertical position control and the quenching of the plasma current are typically among the last events preceding plasma deconfinement. Deviation from a normal waveform of either of these two parameters has served in various forms as an indicator of the disruption onset in the past. The present non-uniformity of disruption time definitions across the tokamak community brings ambiguity in cross-comparisons of various predictor performances. Here, we present a systematic study of abnormal plasma current and vertical position waveforms and evaluate their capacity to serve as disruption onset indicators. The study is conducted with the DECAF code, on multi-year and device databases with a focus on KSTAR, MAST/-U and NSTX/-U tokamaks. The frequency of occurrence of different types of abnormal waveforms and the disruption categories that they define will be presented in the context of the operational spaces of each device. Interconnection of the abnormal waveforms will be discussed as well. Results obtained hereby might serve to define a reliable indicator of the disruption onset. *This research was supported by the U.S. Department of Energy under grants DE-SC0020415, DE-SC0018623 and DE-SC0021311.