Experimental study of the vertical stability of high decay index plasmas in the DIII-D tokamak

Lister, J.B.; Lazarus, E. A.; Kellman, A.G.; Moret, J.-M.; Ferron, J. R.; Helton, F.J.; Lao, L. L.; Leuer, J.A.; Strait, E.J.; Taylor, T.S.; Turnbull, A. D.

doi:10.1088/0029-5515/30/11/011

Cited by 58 publications

(27 citation statements)

References 8 publications

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“…Linearized models of the vertical instability were used during early JET operation, based on equivalent point currents to represent the stabilizing property of the vacuum vessel [2]. This was extended, for application to DIII-D, to an eigenmode approximation of the vessel description, retaining the first up-down asymmetric eigenmode of the vessel currents and exploring the controllability with a proportional-derivative (PD) feedback controller, both theoretically and experimentally [3,4]. These approaches considered the plasma to be a filament.…”

Section: Modellingmentioning

confidence: 99%

Improving tokamak vertical position control in the presence of power supply voltage saturation

Favez

Lister

Müllhaupt

et al. 2005

Plasma Phys. Control. Fusion

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The control of the current, position and shape of an elongated cross-section tokamak plasma is complicated by the so-called instability of the current vertical position. Linearized models all share the feature of a single unstable eigenmode, attributable to this vertical instability of the plasma equilibrium movement, and a large number of stable or marginally stable eigenmodes, attributable to zero or positive resistance in all other model circuit equations. Due to the size and therefore cost of the ITER tokamak, there will naturally be smaller margins in the poloidal field coil power supplies, implying that the feedback control will experience actuator saturation during large transients due to a variety of plasma disturbances. Current saturation is relatively benign, due to the integrating nature of the tokamak, resulting in a reasonable time horizon for strategically handling the approach to saturation which leads to the loss of one degree of freedom in the feedback control for each saturated coil. On the other hand, voltage saturation is produced by the feedback controller itself, with no intrinsic delay. This paper presents a feedback controller design approach which explicitly takes saturation of the power supply voltage into account when producing the power supply demand signals. We consider the vertically stabilizing part of the ITER controller (fast controller) with one power supply and therefore a single saturated input. We consider an existing ITER controller and enlarge its region of attraction to the full null controllable region by adding a continuous nonlinearity into the control. In a system with a single unstable eigenmode and a single stable eigenmode we have already provided a proof of the asymptotical stability of the closed loop system, and we have examined the performance of this new continuous nonlinear controller. We have subsequently extended this analysis to a system with a single eigenmode and multiple stable eigenmodes. The method requires state feedback control, and therefore a reconstruction of the states is indispensable. We discuss the feasibility of extracting these states from the available diagnostic information as well as other implementation details. As a complement to our ITER simulations

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Section: Modellingmentioning

confidence: 99%

Improving tokamak vertical position control in the presence of power supply voltage saturation

Favez

Lister

Müllhaupt

et al. 2005

Plasma Phys. Control. Fusion

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“…A detailed description of the development of a PD controller based on a reduced order model showing the correlations between some plasma parameters and the choice of the controller parameters was presented in [6]. A PD controller was also used on DIII-D [7] to obtain a stable closed-loop system so that the plasma parameters could be identified. Experiments on the JET-Tokamak [8] used a PD controller whose gains were varied to measure the stability range and identify the settings that maximized the state space region over which stability could be guaranteed for a given growth rate .…”

Section: A Review Of Earlier Workmentioning

confidence: 99%

A discrete adaptive near-time optimum control for the plasma vertical position in a Tokamak

Kouvaritakis

2001

IEEE Trans. Contr. Syst. Technol.

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A novel nonlinear controller for the plasma vertical position in a Tokamak, based on a discrete-time adaptive near time optimum control algorithm (DANTOC) is designed to stabilize the system and to maximize the state-space region over which stability can be guaranteed. The controller is also robust to the edge localized modes (ELMs) and the 600 Hz noise from the thyristor power supplies that are the primary source of disturbances and measurement noise. The controller is tested in simulation for the JET Tokamak and the results confirm its efficacy in controlling the vertical position for different plasma configurations. The controller is also tested experimentally on a real Tokamak, COMPASS-D, and the results demonstrate the improvement with respect to a simple linear P + D controller in the presence of disturbances and measurement noise. The emphasis of the present paper is on the development of the design methodology.

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“…Off-normal events originate in the plasma and can eventually lead to a disruption over varying time intervals, e.g. neoclassical tearing modes (NTM) [5], locked modes (LM) [6], density limits [7], or vertical displacement events (VDE) [8]. Fault events originate in the plant hardware surrounding the plasma, and may be minor and recoverable (e.g.…”

Section: Introductionmentioning

confidence: 99%

Implementing a finite-state off-normal and fault response system for disruption avoidance in tokamaks

et al. 2018

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Abstract. 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 R /Stateflow R 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.

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Experimental study of the vertical stability of high decay index plasmas in the DIII-D tokamak

Cited by 58 publications

References 8 publications

Improving tokamak vertical position control in the presence of power supply voltage saturation

Improving tokamak vertical position control in the presence of power supply voltage saturation

A discrete adaptive near-time optimum control for the plasma vertical position in a Tokamak

Implementing a finite-state off-normal and fault response system for disruption avoidance in tokamaks

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