Speaker
Description
We report the neoclassical tearing mode (NTM) stabilization experimental results by injection of the electron cyclotron (EC) beam in KSTAR, and its analysis by calculating tearing stability index Δ′. In KSTAR #31747 experiment, the neoclassical tearing mode (NTM) is intentionally induced, and the KSTAR plasma control system (PCS) injects EC beam to stabilize the NTM. Here the EC is injected based on the minimum seeking control for the island growth rate [1,2,3], but unfortunately the EC deposition didn’t change enough. Consequently, the amplitude of the NTM instability significantly decreased towards the end of the experiment, followed by the recovery of plasma performance. To assess the NTM stabilization experiment from a stability perspective, we employed the STRIDE code [4], which can compute the Δ′ with toroidal geometry with a high speed. Utilizing the reconstructed equilibrium with magnetic diagnostics, we calculated the Δ′ for this experiment. As a result, we observed that the Δ′ is differed as the plasma’s state and the timing of EC injection. The result implies that calculation of Δ′ can be valuable in assessing the NTM stability, and that when we analyse the stability of NTM in experiment, careful consideration is needed.
