UKAEA-CCFE-CP(23)20

TOKAMAK DISRUPTION EVENT CHARACTERIZATION AND FORECASTING RESEARCH AND EXPANSION TO REAL-TIME APPLICATION

Disruption prediction and avoidance is critical for ITER and reactor-scale tokamaks to maintain steady plasma operation and to avoid damage to device components. The present status and results from the disruption event characterization and forecasting (DECAF) research effort are shown. The DECAF paradigm is primarily physics-based and provides quantitative disruption prediction for disruption avoidance. DECAF automatically determines the relation of events leading to disruption and quantifies their appearance to characterize the most probable and deleterious event chains, and to forecast their onset. Automated analysis of rotating MHD modes now allows the identification of disruption event chains for several devices including coupling, bifurcation, locking, and potential triggering by other MHD activity. DECAF can now provide an early disruption forecast (on transport timescales) allowing the potential for disruption avoidance through profile control. Disruption prediction research using DECAF also allows quantifiable figures of merit (i.e. the plasma disruptivity) to provide an objective assessment of the relative performance of different models. There is an extensive physics research effort supporting DECAF model development. First, analysis of high performance KSTAR experiments using TRANSP shows non-inductive current fraction has reached 75%. Resistive stability including ’ calculation by the Resistive DCON code is evaluated for these plasmas. “Predict-first” TRANSP analysis was performed showing that with the newly-installed 2nd NBI system (assuming usual energy confinement quality and Greenwald density fraction), 100% non-inductive plasmas scenarios are found in the range N = 3.5–5.0. Second, new analysis of MAST plasmas has uncovered global MHD events at high N identified as resistive wall modes (RWMs). A stability analysis of MAST plasmas shows a significant ballooning shape of the three-dimensional RWM eigenfunction that compares well to fast camera images. Real-time DECAF analysis is now being constructed for KSTAR. Four of five real-time (r/t) computers and diagnostic interfaces have been installed to measure and decompose rotating MHD activity, measure the r/t toroidal plasma velocity profile, r/t plasma electron temperature profile, and provide r/t two-dimensional measurement of electron temperature fluctuations at a given toroidal position. A fifth system to provide r/t measurement of the internal magnetic field pitch angle profile using the motional Stark effect is under design for installation in the coming year.

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28th IAEA Fusion Energy Conference, Nice, France, 10-15th May 2021