Interpretive and predictive transport analyses of KSTAR plasmas supporting disruption event characterization and forecasting*

KSTAR plasmas have reached high stability parameters (normalized beta β_N reaching 4.3) at relatively low plasma internal inductance l_i (β_N/l_i>6), including operation at high β_N > β_N^no-wall [1]. Transport analyses are conducted to best understand a disruption-free path toward the design target of β_N=5 while aiming to maximize the non-inductive current fraction f_NI. Interpretive analysis using the TRANSP code indicates that f_NI in existing KSTAR plasmas can reach up to 75%. It also shows that the bootstrap and total non-inductive current profiles can vary significantly with f_NI across the regimes. The predictive capability of the TRANSP code is used to examine the effects of the second NBI system installed on KSTAR for the 2018 run determining plasma parameters and profiles important for plasma stability. Values of the global energy confinement quality (H98y2) and the Greenwald density fraction are set to match past KSTAR performance for reliable extrapolation. These ‘predict-first’ analyses are used to design 2018 high-β experiments yielding solutions with β_N~4.5 at f_NI~100%. Ideal and resistive stability of MHD modes is evaluated using the DCON code.

[1] Y.S. Park, S.A. Sabbagh, et al., Phys. Plasmas 24 (2017) 012512.