DECAF Cross-device characterization of tokamak disruptions indicated by abnormalities in plasma vertical position and current
Abnormal (deviating from target) variations in the plasma current Ip and vertical position Z constitute common cross-shot/device elements of a disruption, a phenomenon that is to be avoided (or ultimately mitigated) in future reactor-relevant tokamaks. Those abnormalities constitute important instances within disruptive chain of events (e.g. spikes, quenches and vertical displacements) and the order and appearance (or not) of those events in chains depend on a particular device operational space promoting various physics phenomena, preprogrammed shot exit scenario and more. Here, occurrence of disruptions, explored via detection of a Ip quench, and exploration of disruptive event chains, constituted by Ip and Z abnormalities, is reported for in total full 7 years of operation of 3 devices (KSTAR, MAST-U and NSTX-U) using the DECAF code. It is shown that the disruption occurrence depends not only on details of the plasma state, but also on (device-dependent) technical elements of the shot exit scenario. A year-to-year change in main disruption triggers and a reduction of the disruptivity rate, bound with device and operation upgrades, are reported. Particular trigger instances of disruptive event chains (and the full chains, when applicable) are shown to occupy different parts of the operation space diagrams, in accordance with prior expectation, though details of the distributions are not directly cross-device transferable. Plasma elongation is identified as an important factor influencing details of the disruptive event chains and its role will be further explored.