Analysis on the access condition to hybrid scenario in KSTAR

 After the successful operation of hybrid scenarios with a stationary performance of β_N ≤ 3.0 and H₈₉ ≤ 2.4 with the limited heating power P_aux < 4.5MW [1], several experiments have been attempted to identify the robust access condition to the high-performance hybrid scenarios. In the 2020 campaign, it was found that the discharges with relatively high D_α baseline level and line averaged density could achieve the high performance after a performance bifurcation while other conditions were similar. The major cause is found to be the excitation of the edge localized coherent mode with mode number of n=6 and following broad-band fluctuations growing in the inter-ELM crashes. They enhance the transport in the edge region, which widens the pedestal and reduces its gradient, leading to the higher pedestal pressure [2]. Dedicated experiments to scan D₂ fueling at the divertor region (using PVD) reveal that the increase of the D_α baseline level and edge density not only extied the edge localized coherent mode and broad-band fluctuations but also reproduce the high performance.