Enhancement of detachment control with simplified real-time modelling on the KSTAR tokamak
D. Eldon, H. Anand, J-G Bak, J.L. Barr, S.H. Hahn, Junhyung Jeong, H-S Kim, H H Lee, A.W. Leonard, B. Sammuli, Giwook Shin, Huiqian Wang
Abstract
Abstract 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 KSTAR implementation of A frac control differs from previous work in that it continuously calculates a model for attached I sat 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi>s</mml:mi> <mml:mi>a</mml:mi> <mml:mi>t</mml:mi> <mml:mo>,</mml:mo> <mml:mi>r</mml:mi> <mml:mi>o</mml:mi> <mml:mi>l</mml:mi> <mml:mi>l</mml:mi> <mml:mi>o</mml:mi> <mml:mi>v</mml:mi> <mml:mi>e</mml:mi> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> 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.