High li Steady State Scenario on KSTAR

The high li scenario on KSTAR has achieved β_N≈3, G=β_NH₈₉/q₉₅²≈0.3, V_loop≈0 at q₉₅=5, close to the performance required for the ITER steady-state mission. This high li scenario relies on a very peaked current profile with q_min≈1 for the improved confinement and stability. The large positive magnetic shear from the peaked current profile leads to enhanced confinement and results in a high no-wall β_N limit. The high β_N condition can be achieved even without the need for wall stabilization. A long Ohmic or L-mode phase was used to allow current to penetrate to the axis, followed by injecting on-axis NB (4.3 MW) and EC (1.1 MW) power at the highest li≈1.5. A new robust high li recipe has been developed under the given superconducting coil environment of slow PF coil response to maintain shape control during the rapid β_N ramp-up. High li≈1 discharges often develop small amplitude of n=2 MHD modes, resulting in the degradation of electron energy confinement. Good beam ion confinement was obtained with the estimated anomalous beam ion diffusion D_b~0 both with and without the n=2 modes. The theory-based FASTRAN modeling with TGLF and EPED reproduces the experimental profiles reasonably well. Extrapolation to ITER will be discussed.