First application of minimum island width growth rate seeking feedback controller for neoclassical tearing mode stabilization

• Minimum seeking algorithm for the island width growth rate is applied to the neoclassical tearing mode control experiment in KSTAR. • Observed instability is identified as a 2/1 NTM with mode analyses, and its amplitude is diminished gradually. • The integrated modelling figured out that the 2/1 NTM is stabilized by the effect of the injected EC beam. • The stabilization of NTM is validated in KSTAR experiment and further experiments are planned. We report the neoclassical tearing mode (NTM) stabilization experimental results by injection of the electron cyclotron (EC) beam in KSTAR, along with its analysis using integrated modelling. We utilized a minimum seeking feedback control algorithm combined with real-time estimate of the island width growth rate. In this KSTAR experiment, deleterious instability is intentionally induced and stabilized by 700 kW of EC injection, with the launching angle determined by the minimum seeking controller. Mode analyses identified nature of the instability, with measured amplitude of approximately 15 G, as a 2/1 NTM. As a result, the island width decreased substantially towards the end of the experiment, followed by the recovery of plasma performance. To analyze how the NTM is stabilized, we performed integrated modelling with TRIASSIC using the experimental plasma pressure and computed plasma current contributed from Ohmic, neoclassical, and EC driven effects. By calculating various mechanisms acting on the island width growth with a simplified modified Rutherford equation, we observed that the 2/1 NTM is stabilized by EC injection.