The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Stephen R. Duncan - One of the best experts on this subject based on the ideXlab platform.
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Symmetry Exploitation in Orbit Feedback Systems of Synchrotrons for Computational Efficiency
IEEE Transactions on Nuclear Science, 2021Co-Authors: Idris Kempf, Stephen R. Duncan, Paul J. Goulart, Guenther RehmAbstract:Structural symmetries in the storage ring of Synchrotrons are intentionally created during the design phase of the magnetic lattices, but they are rarely considered in the design of control algorithms that stabilize the beam of accelerated particles. The choice of control algorithm, however, is limited by the high actuation frequency and the large number of inputs and outputs. Standard control algorithms for Synchrotrons are based on a singular value decomposition (SVD) of the orbit response matrix. SVD controllers neither exploit the structural symmetries nor exhibit any speed advantages. By considering the periodicity and the reflection properties of the betatron function, we show that these structural symmetries are inherited by the orbit response matrix. We then show that the resulting block-circulant and centrosymmetric properties of the matrix can be used for different computationally efficient decompositions of the controller. We also address the case of broken symmetry caused by odd placements of individual magnets and monitors. Our efficient decomposition enables the use of more advanced control techniques for Synchrotrons, such as control algorithms that require real-time optimization. These advanced control techniques can in turn increase the stability of photon beams in synchrotron light sources.
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Optimal Control of Perturbed Static Systems for Synchrotron Electron Beam Stabilisation
IFAC-PapersOnLine, 2017Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:Abstract This paper considers the problem of designing an optimal controller for the linear static system associated with electron beam stabilisation systems in Synchrotrons. The relationship between the actuators and sensors used for electron beam control in Synchrotrons is modelled as a static response matrix which is typically ill-conditioned. Singular Value Decomposition (SVD) is commonly used to invert the response matrix and modes associated with small singular values are either discarded or filtered. In this paper, a robust control approach is used to determine the optimal static controller to the perturbed system. It is demonstrated how this approach compares to the use of Tikhonov regularisation for an inverse-based controller. A detailed example from the Diamond Light Source synchrotron is presented, applying both the inverse-based method and the robust control approach to stabilise electron beam motion.
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Discrete-time anti-windup compensation for synchrotron electron beam controllers with rate constrained actuators
Automatica, 2016Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:By accelerating electrons to relativistic speeds, Synchrotrons generate extremely intense and narrow beams of electromagnetic light that are used for academic research and commercial development across a range of scientific disciplines. In order to achieve optimum performance, the stability of the electron beam is a crucial parameter for Synchrotrons and is achieved by a beam stabilisation system that is used to control the location of the electron beam and minimise any instability of the electron beam caused by external disturbances. Slew rate limits are common nonlinearities encountered with the actuators in synchrotron feedback systems which can impose significant limitations on the robustness and the performance of the control system. This paper describes an Internal Model Control (IMC) based anti-windup synthesis using an algebraic Riccati equation for a discrete-time control system to compensate against the performance deterioration in the presence of rate constraints. An Integral Quadratic Constraint (IQC) framework is used to analyse the robust stability of the anti-windup augmented closed loop system in the presence of norm-bounded uncertainty. The anti-windup augmented controller is implemented at Diamond Light Source, the UK's national synchrotron facility and improvements in robustness and performance were achieved with respect to the use of no anti-windup compensation.
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Design of an electron beam stabilisation controller for a synchrotron
Control Engineering Practice, 2014Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:Abstract Synchrotrons are used to generate light for academic and industry research by accelerating electrons travelling in a circular path to relativistic speeds. In order to achieve optimum performance, electron beam stability is a crucial parameter for Synchrotrons. This paper describes the design of a beam stabilisation controller, using Internal Model Control. Basis functions are used to identify the controllable components of the system and it is demonstrated how by selecting dynamics for each spatial mode, enhanced performance is achieved. The robust stability of the controller in the presence of spatial uncertainties is developed within an Integral Quadratic Constraint framework using two methods of spatial decomposition: Singular Value decomposition and Fourier decomposition. The controller has been implemented at Diamond Light Source, the UK׳s national synchrotron science facility. Results from the controller implementation are presented and it is demonstrated how the controller design and robust stability analysis are used to tradeoff performance and robustness.
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Design of multi-array controllers for electron beam stabilisation on Synchrotrons
2013 American Control Conference, 2013Co-Authors: Stephen R. Duncan, William P. HeathAbstract:This paper considers the design of electron beam stabilisation control systems for Synchrotrons that simultaneously determine the inputs to multiple arrays of actuators for regulating variations in the electron beam position. An approach based on determining the interaction of the controllable subspaces is used. This enables the control problem to be decomposed into a series of single-input, single-output; multiple-input, single output and multiple-input, multiple-output problems. An Internal Model Control structure is used to design the controllers for each case and mid-ranging control is proposed for the case where the control directions align. Results from a simulation study using machine data from the Booster synchrotron of the UK's national synchrotron facility, Diamond Light Source are presented.
Sandira Gayadeen - One of the best experts on this subject based on the ideXlab platform.
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Optimal Control of Perturbed Static Systems for Synchrotron Electron Beam Stabilisation
IFAC-PapersOnLine, 2017Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:Abstract This paper considers the problem of designing an optimal controller for the linear static system associated with electron beam stabilisation systems in Synchrotrons. The relationship between the actuators and sensors used for electron beam control in Synchrotrons is modelled as a static response matrix which is typically ill-conditioned. Singular Value Decomposition (SVD) is commonly used to invert the response matrix and modes associated with small singular values are either discarded or filtered. In this paper, a robust control approach is used to determine the optimal static controller to the perturbed system. It is demonstrated how this approach compares to the use of Tikhonov regularisation for an inverse-based controller. A detailed example from the Diamond Light Source synchrotron is presented, applying both the inverse-based method and the robust control approach to stabilise electron beam motion.
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Discrete-time anti-windup compensation for synchrotron electron beam controllers with rate constrained actuators
Automatica, 2016Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:By accelerating electrons to relativistic speeds, Synchrotrons generate extremely intense and narrow beams of electromagnetic light that are used for academic research and commercial development across a range of scientific disciplines. In order to achieve optimum performance, the stability of the electron beam is a crucial parameter for Synchrotrons and is achieved by a beam stabilisation system that is used to control the location of the electron beam and minimise any instability of the electron beam caused by external disturbances. Slew rate limits are common nonlinearities encountered with the actuators in synchrotron feedback systems which can impose significant limitations on the robustness and the performance of the control system. This paper describes an Internal Model Control (IMC) based anti-windup synthesis using an algebraic Riccati equation for a discrete-time control system to compensate against the performance deterioration in the presence of rate constraints. An Integral Quadratic Constraint (IQC) framework is used to analyse the robust stability of the anti-windup augmented closed loop system in the presence of norm-bounded uncertainty. The anti-windup augmented controller is implemented at Diamond Light Source, the UK's national synchrotron facility and improvements in robustness and performance were achieved with respect to the use of no anti-windup compensation.
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Synchrotron electron beam control
2014Co-Authors: Sandira GayadeenAbstract:This thesis develops techniques for the design and analysis of controllers to achieve sub-micron accuracy on the position of electron beams for the optimal performance of Synchrotrons. The techniques have been applied to Diamond Light Source, the UK's national synchrotron facility. Electron beam motion in Synchrotrons is considered as a large-scale, two-dimensional process and by using basis functions, controllable modes of the process are identified which are independent and allow the design to be approached in terms of a family of single-input, single-output transfer functions. This thesis develops techniques for the design and analysis of controllers to achieve sub-micron accuracy on the position of electron beams for the optimal performance of Synchrotrons. The techniques have been applied to Diamond Light Source, the UK's national synchrotron facility. Electron beam motion in Synchrotrons is considered as a large-scale, two-dimensional process and by using basis functions, controllable modes of the process are identified which are independent and allow the design to be approached in terms of a family of single-input, single-output transfer functions. In this thesis, loop shaping concepts for dynamical systems are applied to the two-dimensional frequency domain to meet closed loop specifications. Spatial uncertainties are modelled by complex Fourier matrices and the closed loop robust stability, in the presence of spatial uncertainties is analysed within an Integral Quadratic Constraint framework. Two extensions to the unconstrained, single-actuator array controller design are considered. The first being anti-windup augmentation to give satisfactory performance when rate limit constraints are imposed on the actuators and the second being a strategy to account for two arrays of actuators with different dynamics. The resulting control schemes offer both stability and performance guarantees within structures that are feasible for online computation in real time.
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Design of an electron beam stabilisation controller for a synchrotron
Control Engineering Practice, 2014Co-Authors: Sandira Gayadeen, Stephen R. DuncanAbstract:Abstract Synchrotrons are used to generate light for academic and industry research by accelerating electrons travelling in a circular path to relativistic speeds. In order to achieve optimum performance, electron beam stability is a crucial parameter for Synchrotrons. This paper describes the design of a beam stabilisation controller, using Internal Model Control. Basis functions are used to identify the controllable components of the system and it is demonstrated how by selecting dynamics for each spatial mode, enhanced performance is achieved. The robust stability of the controller in the presence of spatial uncertainties is developed within an Integral Quadratic Constraint framework using two methods of spatial decomposition: Singular Value decomposition and Fourier decomposition. The controller has been implemented at Diamond Light Source, the UK׳s national synchrotron science facility. Results from the controller implementation are presented and it is demonstrated how the controller design and robust stability analysis are used to tradeoff performance and robustness.
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Anti-windup compensation for electron beam stabilisation control systems on Synchrotrons with rate constrained actuators
2013 European Control Conference (ECC), 2013Co-Authors: Sandira Gayadeen, Stephen DuncanAbstract:In modern synchrotron machines, electrons travelling at relativistic speeds in a closed circular path are bent by strong electromagnetic fields, which cause the electrons to lose energy in the form of synchrotron radiation. In order to achieve optimum performance, electron beam stability is a crucial parameter for modern Synchrotrons. In particular, sub-micron stability is now a common requirement for the vertical position of the beam and to achieve the required performance, beam stabilisation feedback systems are used. A common nonlinearity encountered with the actuators in synchrotron feedback systems are the slew rate limits that are included in the circuits that apply power to the magnets in order to limit voltage changes. The large dimensions of synchrotron feedback systems and fast sample rates mean that robust Model Predictive Control (MPC) is not feasible. Therefore, for this application, anti-windup techniques for rate constrained nonlinearities are appropriate. The approach in this paper is anti-windup synthesis based on Internal Model Control (IMC) where it is demonstrated how IMC anti-windup synthesis for static constraints can be extended to rate constraints to improve constrained performance and guarantee stability. An Integral Quadratic Constraint (IQC) framework is used to analyse the robust stability of the system in the presence of both rate constraints and an infinity norm bounded uncertainty. Robust stability tests results and simulation of the anti-windup performance using machine data of the implementation of the control design on the Storage Ring of the UK's national synchrotron facility, Diamond Light Source are presented.
Zwi Barnea - One of the best experts on this subject based on the ideXlab platform.
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X-ray absorption fine structure for single crystals.
Journal of Applied Crystallography, 2009Co-Authors: Christopher T. Chantler, Chanh Q. Tran, Zwi BarneaAbstract:X-ray absorption fine structure measurements are a prime tool at Synchrotrons around the world, accounting for over 30% of all synchrotron research. They are incisive tools for elucidating local structure, ionization state and coordination geometry. However, in general, it has not been possible to apply them to perfect or near-perfect crystals, and their dominant application is to micro-samples, powders, metals and solutions. The reasons for this are given, and an experimental technique to yield high-precision data for good crystals is developed. This widens the applicability of the technique dramatically, and permits standards and calibration samples to be used and transferred for new types of measurement. It is shown that this is particularly appropriate for discrete measurements of absorption, X-ray absorption fine structure and X-ray absorption near-edge spectroscopy, and in cases of strong oscillations.
Christopher T. Chantler - One of the best experts on this subject based on the ideXlab platform.
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X-ray absorption fine structure for single crystals.
Journal of Applied Crystallography, 2009Co-Authors: Christopher T. Chantler, Chanh Q. Tran, Zwi BarneaAbstract:X-ray absorption fine structure measurements are a prime tool at Synchrotrons around the world, accounting for over 30% of all synchrotron research. They are incisive tools for elucidating local structure, ionization state and coordination geometry. However, in general, it has not been possible to apply them to perfect or near-perfect crystals, and their dominant application is to micro-samples, powders, metals and solutions. The reasons for this are given, and an experimental technique to yield high-precision data for good crystals is developed. This widens the applicability of the technique dramatically, and permits standards and calibration samples to be used and transferred for new types of measurement. It is shown that this is particularly appropriate for discrete measurements of absorption, X-ray absorption fine structure and X-ray absorption near-edge spectroscopy, and in cases of strong oscillations.
Stephen Duncan - One of the best experts on this subject based on the ideXlab platform.
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Anti-windup compensation for electron beam stabilisation control systems on Synchrotrons with rate constrained actuators
2013 European Control Conference (ECC), 2013Co-Authors: Sandira Gayadeen, Stephen DuncanAbstract:In modern synchrotron machines, electrons travelling at relativistic speeds in a closed circular path are bent by strong electromagnetic fields, which cause the electrons to lose energy in the form of synchrotron radiation. In order to achieve optimum performance, electron beam stability is a crucial parameter for modern Synchrotrons. In particular, sub-micron stability is now a common requirement for the vertical position of the beam and to achieve the required performance, beam stabilisation feedback systems are used. A common nonlinearity encountered with the actuators in synchrotron feedback systems are the slew rate limits that are included in the circuits that apply power to the magnets in order to limit voltage changes. The large dimensions of synchrotron feedback systems and fast sample rates mean that robust Model Predictive Control (MPC) is not feasible. Therefore, for this application, anti-windup techniques for rate constrained nonlinearities are appropriate. The approach in this paper is anti-windup synthesis based on Internal Model Control (IMC) where it is demonstrated how IMC anti-windup synthesis for static constraints can be extended to rate constraints to improve constrained performance and guarantee stability. An Integral Quadratic Constraint (IQC) framework is used to analyse the robust stability of the system in the presence of both rate constraints and an infinity norm bounded uncertainty. Robust stability tests results and simulation of the anti-windup performance using machine data of the implementation of the control design on the Storage Ring of the UK's national synchrotron facility, Diamond Light Source are presented.