Long Pulse Control Enhancements on KSTAR

N. Eidietis, J. Barr, M. Boyer, S.H. Hahn, D.A. Humphreys, Y.M. Jeon, D. Mueller, E. Schuster, M.L. Walker

KSTAR Conference

Muju, South Korea, February 21-23, 2018

Numerous control enhancements are under active development to enable the Korea Superconducting Tokamak Advanced Research (KSTAR) to meet its long-pulse and steady-state missions. A novel real-time feed-forward algorithm (rtFF) continuously updates feed-forward coil current waveforms during a discharge, avoiding compounded errors in FF and dramatically reducing the correction burden placed upon the feedback control system. Decoupled fast and slow vertical control prevents large DC currents in the interior vertical control (IVC) coil, avoiding vertical control saturation and undesirable heating of the coil. Both of these techniques were utilized to improve short-pulse ITER baseline discharge scenarios in 2017. Further enhancements of the rtFF algorithm to reduce control discontinuities between re-calculation cycles and adjust calculations dynamically based upon plasma shape are planned in 2018 and beyond. Strike point control, critical to maintaining acceptable divertor heating during planned high-performance long-pulse discharges, is planned for initial exercise in 2018. An integrated off-normal and fault response (ONFR) system has been implemented and experimentally tested that allow asynchronous handling of multiple simultaneous events, providing the supervision required to sustain long-pulse discharges under uncertain plasma conditions. Finally, current profile control algorithms are under development to provide reliable access to the conditions necessary to meet the KSTAR steady-state mission.