KSTAR program for closing gaps to fusion energy

Since the initial long-pulse H-mode operation in 2012, the H-mode has been sustained longer and the operational regime of plasma parameters has been significantly extended in KSTAR tokamak. The progress in long-pulse operation is mainly due both to the increased NBI heating power of PNBI ~ 3.5 MW and the advance in the shaping control which is not trivial with slow superconducting coils. In 2013 campaign, the duration of H-mode phase has been extended up to 25 sec with 0.5 MA of plasma current and 3 MW of PNBI and, in the coming campaign as main operational goal, it is expected to be extended up to more than 30 sec using 5 MW of PNBI. In addition, in 2014 campaign, the long-pulse operation will be in accordance with ITER requirement, i.e., in ITER similar shape, low safety factor (q
₉₅
~3) and normalized beta (~2.0) with real-time control of density and power. ELM suppression is discovered in wide range of coil configuration and the suppression window in the safety factor q
₉₅
has extended from 6.5 to 3.9 depending on the configuration, i.e., q
₉₅
~6.5 for n=1, q
₉₅
~5.0 for the mixed n=1 & n=2, and q
₉₅
~4.0 for n=2 indicating the strong impact of resonant component on ELM suppression. In addition to the suppression, strong mitigation of ELM, i.e., order of magnitude increase of ELM frequency (fELM), has been also demonstrated in wide range of non-resonant field configuration. Significant progress has been on the investigation of the underlying mechanism on RMP suppression using measurements of pedestal fluctuations and modeling of plasma response especially for n=1 case where field penetration is global and full response modeling is required including the sielding effect of toroidal rotation. Since the initial 2 segment measurements in 2012, detailed evaluation of error field (EF) has been performed by 4 segment compass scan by measuring maximum current in middle internal coils for each quadrant. In agreement with the previous measurements, the measured level of intrinsic error field is at order of 10-5 at the magnetic axis, which is an order of magnitude lower than other tokamaks. Not only for the 3D RMP experiments, both low level of error field and versatile in-vessel 3D coils provide ideal platform to investigate momentum transport and MHD stability without complicated influence of residual error field. Strong focus is on the extended identification of detailed pattern of n=1 error field utilizing the full poloidal sets of internal coils and its impact on the operational boundary is investigated especially for q
₉₅
range below three where effect of error field is critical due to the locked mode and MHD activities. Including above topics, the presentation will address the recent results on rotation & transport physics, newly installed diagnostics, MHD activities and the future plan.