Improved Plasma Vertical Position Control on TCV Using Model-Based Optimized Controller Synthesis

Pesamosca, F.; Felici, F.; Coda, S.; Galperti, C.

doi:10.1080/15361055.2022.2043511

Cited by 11 publications

(9 citation statements)

References 56 publications

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“…Within the modeled DIII-D design space, δ has a relatively small direct effect on the modeled vertical growth rates, optimistically suggesting that vertical control of a NT reactor with a proper coil set should be relatively simple, despite the inherently higher levels of instability that characterize the NT design space. Further developments of vertical position control algorithms, as recently demonstrated on TCV in NT configurations [15], would also benefit NT reactor operation. To fully assess the vertical stability properties for an NT reactor, additional work is needed to validate flexible MHD codes like AVSTAB [14] with experimental data and realistic vessel wall configurations including up-down asymmetry.…”

Section: Discussionmentioning

confidence: 99%

“…NT plasmas are subject to relatively degraded vertical stability compared to their PT counterparts, limiting operation at high elongations (κ) that would otherwise be expected to lead to desirable improvements in volume and energy confinement time (τ e ∼ κ 0.7 ) [12][13][14][15][16]. Extensive modeling with the magneto-hydrodynamic (MHD) instability code AVSTAB (Axisymmetric Vertical STABility) has demonstrated that high poloidal beta (β p ) provides more instability drive in NT due to larger Shafranov shifts and increased inner flux surface elongation [14].…”

Section: Introductionmentioning

confidence: 99%

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Vertical control of DIII-D discharges with strong negative triangularity

Nelson

Hyatt

Wehner

et al. 2023

Plasma Phys. Control. Fusion

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Through predictive modeling validated by a series of experiments on DIII-D, the vertical stability of low β diverted plasmas with strong negative triangularity (δ~-0.6) is assessed. As a result of their unique magnetic geometry, negative triangularity (NT) plasmas feature larger Shafranov shifts and more elongated inner flux surfaces than positive triangularity counterparts, typically leading to enhanced vertical instability growth rates. However, coupling with the non-conformal vessel DIII-D wall reduces these growth rates to controllable values, providing a path forward for stabilizing strongly NT plasma with a diverted geometry. These discharges are used to validate GSdesign (part of the TokSys code suite) stability calculations in strong NT plasmas on DIII-D, with errors of no more than ~20% observed between modeled and experimentally measured growth rates. Additions of diagnostic noise and power supply tuning to the TokSys model are needed to accurately capture the time dependence of DIII-D NT discharges, assisting with the design of control schemes specific to the DIII-D poloidal field coils. Finally, implications of these results on a future NT reactor are briefly described.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vertical control of DIII-D discharges with strong negative triangularity

Nelson

Hyatt

Wehner

et al. 2023

Plasma Phys. Control. Fusion

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“…feedback control using a set of external magnetic coils to stabilize the vertical position. In the area of shape, current, and position control, a range of control strategies have been applied, including classic proportional integral derivative (PID), linear-quadratic regulator (LQR) [1,2], H-infinity [3], and model predictive control (MPC) techniques [4]. Feed-forward or PID methods are regularly used to control core parameters such as the line-averaged density and plasma pressure using heating systems and gas puff actuators [5].…”

Section: Introductionmentioning

confidence: 99%

Time-dependent SOLPS-ITER simulations of the tokamak plasma boundary for model predictive control using SINDy ^*

et al. 2023

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Time-dependent SOLPS-ITER simulations have been used to identify reduced models with the Sparse Identification of Nonlinear Dynamics (SINDy) method and develop model-predictive control of the boundary plasma state using main ion gas puff actuation. A series of gas actuation sequences are input into SOLPS-ITER to produce a dynamic response in upstream and divertor plasma quantities. The SINDy method is applied to identify reduced linear and nonlinear models for the electron density at the outboard midplane $\nesepm$ and the electron temperature at the outer divertor $\tesepa$. Note that $\tesepa$ is not necessarily the peak value of $T_e$ along the divertor. The identified reduced models are interpretable by construction (i.e., not black box), and have the form of coupled ordinary differential equations (ODEs). Despite significant noise in $\tesepa$, the reduced models can be used to predict the response over a range of actuation levels to a maximum deviation of 0.5$\%$ in $\nesepm$ and 5 - 10$\%$ in $\tesepa$ for the cases considered. Model retraining using time history data triggered by a preset error threshold is also demonstrated. A Model Predictive Control (MPC) strategy for nonlinear models is developed and used to perform feedback control of a SOLPS-ITER simulation to produce a setpoint trajectory in $\nesepm$ using the Integrated Plasma Simulator (IPS) framework. The developed techniques are general and can be applied to time-dependent data from other boundary simulations or experimental data. Ongoing work is extending the approach to model identification and control for divertor detachment, which will present transient nonlinear behavior from impurity seeding, including realistic latency and synthetic diagnostic signals derived from the full SOLPS-ITER output.

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“…In the SST1, the RZIP model is applied to the vertical position control, and the control system is evaluated for the effects of various disturbances [9]. In the TCV, a structured H-infinity design extending classical H-infinity to fixed-structure control systems was applied to obtain an optimized controller using all available coils for position control [10]. Recently, KSTAR developed improved fast vertical position control, which uses relative flux for the Z-position estimate and the loop voltage difference from a pair of up-down symmetric loops; it provided a sensitive and less noisy vertical estimate, and the control loop for the inner coil was decoupled from the slow motion controlled by the superconducting coils using a highpass filter in the control software [11].…”

Section: Introductionmentioning

confidence: 99%

Using LQR controller for vertical position control on EAST

Rui,

Wang,

Song

et al. 2024

Nucl. Fusion

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Vertical position control is essential for stabilizing plasma with elongated configurations. Currently, a PD controller with fixed parameters is used for the vertical position control of EAST plasma. However, the response of the plasma in the vertical position changes with changes in plasma configuration, which can result in different control parameter requirements. It is essential to develop a model-based fast-tuning control algorithm for ensuring stability in the vertical position under different configurations. In this study, a model-based vertical position controller tuning method based on a linear quadratic regulator algorithm (LQR) is proposed. Compared with contemporary PD controllers, the proposed model-based LQR controller can enable adjusting controller parameters based on the response of the system, achieving stable control under different vertical position responses. In the EAST experiment, the model-based LQR controller achieved stable control under a shot with a continuously increasing growth rate and reached a maximum controllable vertical displacement growth rate of 968 s-1. The robustness of the system was also demonstrated in a free drift experiment. The new vertical displacement control method can be adapted to different system states and plasma configurations and improve the controllability and safety of future devices.

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Improved Plasma Vertical Position Control on TCV Using Model-Based Optimized Controller Synthesis

Cited by 11 publications

References 56 publications

Vertical control of DIII-D discharges with strong negative triangularity

Vertical control of DIII-D discharges with strong negative triangularity

Time-dependent SOLPS-ITER simulations of the tokamak plasma boundary for model predictive control using SINDy ^*

Using LQR controller for vertical position control on EAST

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Improved Plasma Vertical Position Control on TCV Using Model-Based Optimized Controller Synthesis

Cited by 11 publications

References 56 publications

Vertical control of DIII-D discharges with strong negative triangularity

Vertical control of DIII-D discharges with strong negative triangularity

Time-dependent SOLPS-ITER simulations of the tokamak plasma boundary for model predictive control using SINDy *

Using LQR controller for vertical position control on EAST

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Resources

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Time-dependent SOLPS-ITER simulations of the tokamak plasma boundary for model predictive control using SINDy ^*