Long Pulse High β_N Scenario in KSTAR

The high β_N scenario with a relatively high value of li ~ 1 is one of the promising candidates for the ITER steady-state scenario and future power reactors. Stationary high β_N ~ 3 operation has been extended to ~15 sec longer than multiple current relaxation time (> 5τ_R). No obvious sign of performance degradation has been observed at β_N = 2.8. However, the β_N oscillation often causes further evolution of the current profile at higher target β_N > 3, which eventually triggers resistive n = 2 MHD modes, resulting in substantial confinement degradation. The β_N oscillation are correlated largely with interaction between the fishbone-like n=1 modes and long ELM-free period. The confinement strongly depends on the presence of small amplitude of n = 2 MHD modes, while off-axis Electron Cyclotron (EC) heating and current drive (H/CD) helps to avoid the performance-limiting n = 2 modes. Predict-First approach with the IPS-FASTRAN integrated modeling will be presented to optimize high β_N scenarios with the planned KSTAR H/CD upgrade.