Progress of KSTAR high $\beta $N operation by optimizing fast-ion confinement

Over the past several years, KSTAR has successfully performed the high beta steady-state experiments with beam heating at relatively low Greenwald fraction regime. This study reports the recent results on KSTAR high $\beta $N experiment results aiming long-pulse $\beta $N \textasciitilde 3. Owing to relatively long fast-ion slowing time characteristics, optimizing fast-ion confinement was the key reaching high beta operation at KSTAR. Based on database on fast-ion related MHD mode control experiments, it is found that the plasma performance degradation is often accompanied by Alfv\'{e}nic activities and tearing modes. Numerical investigation with TRANSP / NOVA / Kick-model performed, so that the impact of the mode on plasma performance is analyzed. The q profile of the highest $\beta $N is evaluated, and the future prospects are shown with near-term heating upgrade.