NIMROD simulations of high beta MAST-U shots in support of Disruption Event Characterization and Forecasting (DECAF)

As the fusion community prepares for the next generation of high-performance tokamaks, disruption prediction and avoidance remains of paramount importance. The Disruption Event Characterization and Forecasting (DECAF) code [1] automates the identification of the chain of events leading to a disruption and provides appropriate forecasting of such events, allowing appropriate plasma control systems to be activated to prevent (or mitigate) plasma disruptions. In support of DECAF, recent NIMROD simulations have been performed for MAST-U. These simulations, which agree with experiment, show that the safety factor dipping below one leads to the creation of magnetic islands extending between the two q=1 surfaces, which results in a redistribution of angular momentum in the plasma. Results are shown both for the case of a conducting wall and a resistive wall - utilizing a recently updated resistive wall formulation in NIMROD. Future simulations will further investigate the causes of mode growth and loss of high beta in MAST-U plasmas. The interplay of rotation, rotation shear, plasma shaping, safety factor q and its shear on plasma stability and mode dynamics will be examined. [1] S. A. Sabbagh, et al., “Disruption event characterization and forecasting in tokamaks”, Phys. Plasmas 30, 032506 (2023).