Enhancement of detachment control with simplified real-time modelling on the KSTAR tokamak

Detachment control based on ion saturation current I-sat measurements from Langmuir probes (LPs) is implemented in the KSTAR tokamak and shown to be capable of following dynamic and constant target trajectories with good accuracy, in H-mode, by moderating the flow rate of nitrogen or deuterium. I-sat controllers normalize I-sat in order to form attachment fraction (A(frac)) as their control parameter. The KS TAR implementation of A(frac) control differs from previous work in that it continuously calculates a model for attached I sa r and uses that as the denominator in A(frac), whereas prior implementations either record peak I-sat at rollover as they pass it or take estimated I-sat,I-rollover as a manual input prior to the shot. The KSTAR controller therefore does not need to keep track of rollover status and keep separate targets for pre- and post-rollover states, and it can automatically adapt to changes in scenario at any time. It is also less vulnerable to noise as it will not lock in an outlier as a rollover point.