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Eidietis, N.W.,Choi, W.,Hahn, S.H.,Humphreys, D.A.,Sammuli, B.S.,Walker, M.L. International Atomic Energy Agency 2018 Nuclear fusion Vol.58 No.5
<P>A finite-state off-normal and fault response (ONFR) system is presented that provides the supervisory logic for comprehensive disruption avoidance and machine protection in tokamaks. Robust event handling is critical for ITER and future large tokamaks, where plasma parameters will necessarily approach stability limits and many systems will operate near their engineering limits. Events can be classified as off-normal plasmas events, e.g. neoclassical tearing modes or vertical displacements events, or faults, e.g. coil power supply failures. The ONFR system presented provides four critical features of a robust event handling system: sequential responses to cascading events, event recovery, simultaneous handling of multiple events and actuator prioritization. The finite-state logic is implemented in Matlab<SUP>®</SUP>/Stateflow<SUP>®</SUP> to allow rapid development and testing in an easily understood graphical format before automated export to the real-time plasma control system code. Experimental demonstrations of the ONFR algorithm on the DIII-D and KSTAR tokamaks are presented. In the most complex demonstration, the ONFR algorithm asynchronously applies ‘catch and subdue’ electron cyclotron current drive (ECCD) injection scheme to suppress a virulent 2/1 neoclassical tearing mode, subsequently shuts down ECCD for machine protection when the plasma becomes over-dense, and enables rotating 3D field entrainment of the ensuing locked mode to allow a safe rampdown, all in the same discharge without user intervention. When multiple ONFR states are active simultaneously and requesting the same actuator (e.g. neutral beam injection or gyrotrons), actuator prioritization is accomplished by sorting the pre-assigned priority values of each active ONFR state and giving complete control of the actuator to the state with highest priority. This early experience makes evident that additional research is required to develop an improved actuator sharing protocol, as well as a methodology to minimize the number and topological complexity of states as the finite-state ONFR system is scaled to a large, highly constrained device like ITER.</P>
Achievements and lessons learned from the operation of KSTAR plasma control system upgrade
Hahn, Sang-hee,Penaflor, B.G.,Milne, P.G.,Bak, J.G.,Eidietis, N.W.,Han, H.,Hong, J.S.,Jeon, Y.M.,Johnson, R.D.,Kim, H.-S.,Kim, HeungSu,Kim, Y.J.,Kwon, G.I.,Lee, W.R.,Woo, M.H.,Sammuli, B.S.,Walker, M. Elsevier 2018 Fusion engineering and design Vol.130 No.-
<P><B>Abstract</B></P> <P>Results on the integration and the operation of the KSTAR plasma control system (PCS) upgrade are given. Real-time hardware, new realtime-capable operating system, and a brand-new data acquisition are assembled in order to extend the performance and compatibility with modern computer systems. The first full commissioning and eventual routine use performed in 2016 so that the system can now acquire more than 400 channels for more than 100 seconds of data with 5 kHz sampling. The performance test results are summarized, featuring In/Out streaming echo tests and the synchronization verifications. Examples of general performance improvements are demonstrated, and additional features added to the software are also described.</P>
Implementation of the forced landing scheme under off-normal events in KSTAR
Woo, M.H.,Hahn, S.H.,Jeon, Y.M.,Kim, J.,Han, H.,Bak, J.G.,Oh, Y.K.,Eidietis, N.W.,Johnson, R.D.,Walker, M.L. Elsevier 2018 Fusion engineering and design Vol.128 No.-
<P><B>Abstract</B></P> <P>Disruption avoidance is one of the most critical issues in KSTAR due to its high current, temperature and long operation characteristics of the superconducting tokamak. To minimize possible damages to the machine, we imposed a real time handling algorithm of off-normal events, named “forced landing” to ramp down the plasma with well-controlled plasma current and position. Two different plasma control schemes are implemented for different purposes and situations. Both schemes have been successfully demonstrated with careful classifications of actions on the machine in real experiments and they show routine performance with effective reduction of impacts on the machine. Such “machine-protection” schemes enable more aggressive operations such as mega-ampere or high beta experiment, resulting in an expansion of the KSTAR operation regime due to reduced less concerns regarding mechanical safety issues.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A real time handling algorithm of off-normal events, named “forced landing” scheme is developed. </LI> <LI> Off-normal events are categorized for “forced landing”. </LI> <LI> Two different plasma control for “forced landing” is presented. </LI> <LI> Validation and experimental result in KSTAR is represented. </LI> </UL> </P>
Controls on KSTAR Superconducting Poloidal Field (PF) Magnets
Hahn, Sang-Hee,Kim, K.H.,Choi, J.H.,Ahn, H.S.,Lee, D.K.,Park, K.R.,Eidietis, N.W.,Leuer, J.A.,Walker, M.L.,Yang, H.L.,Kim, W.C.,Oh, Y.K. The Korean Society of Superconductivity and Cryoge 2008 한국초전도저온공학회논문지 Vol.10 No.4
As a part of the plasma control system (PCS) for the first plasma campaign of KSTAR, seven sets of fast feedback control loop for the superconducting poloidal field magnet power supply (PF MPS) have been implemented. A special real-time digital communication interface has been developed for the simultaneous exchanges of the current/voltage data from the 7 sets of 12-thyristor power supplies in a 200 microsecond control cycle. Preliminary power supply tests have been performed before actual cooldown of the device. A $29mH/50m{\Omega}$ solenoid dummy has been fabricated for a series of single power supply tests. Connectivity and response speed of the plasma control system have been verified. By changing hardware cabling, this load was also used to estimate mutual inductance coupling effects of two geometrically adjacent solenoid coils on each power supply. After the cooldown was complete, each pair of the up/down symmetric PF coils has been serially connected and tested as part of the device commissioning process. Bipolar operation and longer pulse attempts have been investigated. The responses of the coils and power supplies corresponding to the plasma magnetic controls in plasma discharges are also analyzed for the future upgrades.
Progress and plan of KSTAR plasma control system upgrade
Hahn, S.h.,Kim, Y.J.,Penaflor, B.G.,Bak, J.G.,Han, H.,Hong, J.S.,Jeon, Y.M.,Jeong, J.H.,Joung, M.,Juhn, J.W.,Kim, J.S.,Kim, H.S.,Lee, W.R.,Woo, M.H.,Eidietis, N.W.,Ferron, J.R.,Humphreys, D.A.,Hyatt, North-Holland ; Elsevier Science Ltd 2016 Fusion engineering and design Vol.112 No.-
The plasma control system (PCS) has been one of essential systems in annual KSTAR plasma campaigns: starting from a single-process version in 2008, extensive upgrades are done through the previous 7 years in order to achieve major goals of KSTAR performance enhancement. Major implementations are explained in this paper. In consequences of successive upgrades, the present KSTAR PCS is able to achieve ~48s of 500kA plasma pulses with full real-time shaping controls and real-time NB power controls. It has become a huge system capable of dealing with 8 separate categories of algorithms, 26 actuators directly controllable during the shot, and real-time data communication units consisting of +180 analog channels and +600 digital input/outputs through the reflective memory (RFM) network. The next upgrade of the KSTAR PCS is planned in 2015 before the campaign. An overview of the upgrade layout will be given for this paper. The real-time system box is planned to use the CERN MRG-Realtime OS, an ITER-compatible standard operating system. New hardware is developed for faster real-time streaming system for future installations of actuators/diagnostics.