Measurement of vertical stability metrics in KSTAR

The paper summarizes results of multi-year ITPA experiments regarding measurement of the vertical stabilization capability of KSTAR discharges, including most recent measurements at the highest achievable elongation ($\kappa \sim 2.0-2.1$). The measurements of the open-loop growth rate of VDE ($\gamma_z$) and the maximum controllable vertical displacement ($\Delta Z_{max}$) are done by the release-and-catch method. The dynamics of the vertical movement of the plasma is verified by both relevant magnetic reconstructions and non-magnetic diagnostics. The measurements of $\gamma_z$ and $\Delta Z_{max}$ were done for different plasma currents, $\beta_p$, internal inductances, elongations and different configurations of the vessel conductors that surround the plasma as the first wall. Effects of control design choice and diagnostics noise are discussed, and comparison with the axisymmetric plasma response model is given for partial accounting for the measured control capability.