Practical Solutions to the Non-Minimum Phase and Vibration Problems Under the Disturbance Rejection Paradigm

This dissertation tackles two kinds of control problems under the disturbance rejection paradigm (DRP): 1) the general problem of non-minimum phase (NMP) systems, such as systems with right half plane (RHP) zeros and those with time delay 2) the specific problem of vibration, a prevailing problem facing practicing engineers in the real world of industrial control. It is shown that the DRP brings to the table a refreshingly novel way of thinking in tackling the persistently challenging problems in control. In particular, the problem of NMP has confounded researchers for decades in trying to find a satisfactory solution that is both rigorous and practical. The active disturbance rejection control (ADRC), originated from DRP, provides a potential solution. Even more intriguingly, the DRP provides a new framework to tackle the ubiquitous problem of vibration, whether it is found in the resonant modes in industrial motion control with compliant load, which is almost always the case, or in the microphonics of superconducting radio frequency (SRF) cavities in high energy particle accelerators. That is, whether the vibration is caused by the environment or by the characteristics of process dynamics, DRP provides a single framework under which the problem is better understood and resolved. New solutions are tested and validated in both simulations and experiments, demonstrating the superiority of the new design over the previous ones. For systems with time delay, the stability characteristic of the proposed solution is analyze

Practical Solutions to the Non-Minimum Phase and Vibration Problems Under the Disturbance Rejection Paradigm

This dissertation tackles two kinds of control problems under the disturbance rejection paradigm (DRP): 1) the general problem of non-minimum phase (NMP) systems, such as systems with right half plane (RHP) zeros and those with time delay 2) the specific problem of vibration, a prevailing problem facing practicing engineers in the real world of industrial control. It is shown that the DRP brings to the table a refreshingly novel way of thinking in tackling the persistently challenging problems in control. In particular, the problem of NMP has confounded researchers for decades in trying to find a satisfactory solution that is both rigorous and practical. The active disturbance rejection control (ADRC), originated from DRP, provides a potential solution. Even more intriguingly, the DRP provides a new framework to tackle the ubiquitous problem of vibration, whether it is found in the resonant modes in industrial motion control with compliant load, which is almost always the case, or in the microphonics of superconducting radio frequency (SRF) cavities in high energy particle accelerators. That is, whether the vibration is caused by the environment or by the characteristics of process dynamics, DRP provides a single framework under which the problem is better understood and resolved. New solutions are tested and validated in both simulations and experiments, demonstrating the superiority of the new design over the previous ones. For systems with time delay, the stability characteristic of the proposed solution is analyze

Design and Development of a Digital Radio Frequency Control System for Linear Accelerators

The new control system for Radio Frequency (RF) structures at Legnaro National Laboratories (LNL) is presented in this document. LNL is one of the four national laboratories of the National Institute for Nucler Physics (INFN) and it is devoted to basic research in nuclear physics and nuclear-astrophysics, together with applications of nuclear technologies. The subject of this Ph.D. thesis is indeed the development of a fully digital RF feedback system, focusing on the validation of the RF controller, its programming and its integration in the particle accelerator control system. The RF controller interacts directly with the cavities and it works in a real-time closed loop. It is a set of analog and digital electronics which provides phase, amplitude and frequency corrections to stabilize the RF field in presence of disturbances and vibrations due to other subsystems of the accelerator. The control algorithm is implemented via a programmable device as an FPGA. This increases dramatically the flexibility and the programmability of the controller. The digital board of the RF controller can work in a wide range of the RF spectrum. It is a versatile tool, easy to adapt to 40/80/160/352 MHz resonators, thus spanning all types of cavities of the final SPES configuration. At LNL, it may be used to control RF cavities like bunchers to pulse the beam, superconducting cavities to accelerate the beam and RF quadrupoles (RFQ) to both accelerate and focus the beam. Most of them work in superconducting condition, while the other ones in normal condition. The controlling and the monitoring of the RF controller is done by the particle accelerator control system based on EPICS (Experimental Physics and Industrial Control System). It is a widely adopted software framework for control systems. EPICS is a set of tools, libraries and applications developed collaboratively and used worldwide to create distributed soft real-time control systems for scientific instruments such as particle accelerators. Beam transport was carried out with the 8 cavities working in superconducting mode with the new instruments. The controller kept locked the cavities for few days. In this time the controller has proven to be more stable and reliable than the precedent system. The first chapter of the document introduces the SPES and ALPI facility and the RF subsystem to a certain level of details: RF acceleration concepts and Low Level RF (LLRF) control for an optimum energy gain of the particle beam. In order to better understand the issues faced during the design of the control system it is useful to derive mathematical models of the RF cavities. This is the subject of the second chapter. In the third chapter the disturbance sources of the accelerating field are listed, besides clarifying the stability requirements, the frequency tuning of the cavities and their driving modes. Furthermore, the choice of the frequency sampling is outlined. The fourth chapter introduces the controller in detail. The boards functionalities are highlighted, the fundamental elements of the boards are described as well as the communication between components and boards. The fifth, sixth and seventh chapters describe the main contribution of this Ph.D. thesis. The firmware development for the Field Programmable Field Array, that is the heart of the RF controller, is covered in chapter five, emphasizing the module for the communication with the accelerator control system and the module that implements the control algorithms. The sixth chapter gives an overview of the EPICS framework, focusing on the driver support, the integration of the RF controller with the EPICS based control system is further expanded while in the last section the RF cavity tuning is explained. The seventh chapter is split in two sections. The first section lists the tests performed in order to qualify the boards of the RF controller. The second section analyzes some key parameters acquired during a successful beam test in real working conditions, where the performance of the new controller has been evaluated. Finally, a concluding chapter summarizes the results obtained so far and outlines improvements and future upgrades that can implement new functionalities in the Radio Frequency control system

LHC Beam Stability and Feedback Control - Orbit and Energy -

This report presents the stability and control of the Large Hadron Collider's (LHC) two beam orbits and their particle momenta using beam-based feedback systems. The LHC, presently being built at CERN, will store, accelerate and provide particle collisions with a maximum particle momentum of 7TeV/c and a nominal luminosity of L = 10^34 cm^â2s^â1. The presence of two beams, with both high intensity as well as high particle energies, requires excellent control of particle losses inside a superconducting environment, which will be provided by the LHC Cleaning and Machine Protection System. The performance and function of this and other systems depends critically on the stability of the beam and may eventually limit the LHC performance. Environmental and accelerator-inherent sources as well as failure of magnets and their power converters may perturb and reduce beam stability and may consequently lead to an increase of particle loss inside the cryogenic mass. In order to counteract these disturbances, control of the key beam parameters â orbit, tune, energy, coupling and chromaticity â will be an integral part of LHC operation. Since manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that requires automatic feedback control systems for safe and reliable machine operation. The aim of this report is to help and contribute towards these efforts

LHC Beam Stability and Feedback Control - Orbit and Energy -

This report presents the stability and control of the Large Hadron Collider's (LHC) two beam orbits and their particle momenta using beam-based feedback systems. The LHC, presently being built at CERN, will store, accelerate and provide particle collisions with a maximum particle momentum of 7TeV/c and a nominal luminosity of L = 10^34 cm^â2s^â1. The presence of two beams, with both high intensity as well as high particle energies, requires excellent control of particle losses inside a superconducting environment, which will be provided by the LHC Cleaning and Machine Protection System. The performance and function of this and other systems depends critically on the stability of the beam and may eventually limit the LHC performance. Environmental and accelerator-inherent sources as well as failure of magnets and their power converters may perturb and reduce beam stability and may consequently lead to an increase of particle loss inside the cryogenic mass. In order to counteract these disturbances, control of the key beam parameters â orbit, tune, energy, coupling and chromaticity â will be an integral part of LHC operation. Since manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that requires automatic feedback control systems for safe and reliable machine operation. The aim of this report is to help and contribute towards these efforts

Development and commissioning of a digital rf control system for the S-DALINAC and migration of the accelerator control system to an EPICS-based system

The high resolution scattering experiments conducted at the superconducting Darmstadt electron linear accelerator S-DALINAC call for a small energy spread of (ΔE/E) ≈ 1×10⁻⁴ of the beam. This requires stabilization of amplitude and phase of the electric field inside the accelerating cavities to (ΔA/A)ᵣₘₛ = 8×10⁻⁵ and (Δφ)ᵣₘₛ = 0.7°. The design and the commissioning of a new digital rf control system is the subject of this thesis. At the S-DALINAC two types of cavities are in use. The normal-conducting chopper and buncher cavities only need corrections for slow temperature drifts and can be controlled by a generator-driven resonator control algorithm. The superconducting accelerating cavities have a very high quality factor and thus are very susceptible to vibrations. Therefore they are operated in a self-excited loop. The rf control system is based on in-house developed hardware that converts the rf signal down to the baseband, digitizes it and feeds it into an FPGA. Inside this FPGA, a soft digital signal processor executes the control algorithm. The resulting correction is modulated onto the rf signal again and sent back to the cavity. All accelerator components are remote-controlled from a central room via an accelerator control system. Since complex and re-programmable devices are not supported well by the existing in-house developed control system, the design and implementation of a new accelerator control system is also subject of this thesis. Further important aspects are expandability, usability and maintainability of the system. Therefore the new accelerator control system uses the EPICS framework as a basis since it already provides much of the basic functionality like graphical user interfaces and flexible control servers that can be customized rapidly. This allowed the implementation of more advanced functionality like extensive read-out and diagnostics for the rf control system. The read out data can be visualized with a software oscilloscope and a spectrum analyzer software. Additionally the system provides on-line rms errors that can be used to optimize the control parameters very precisely and to monitor the performance of the controllers. Measurements show that the performance of the rf control system has been improved by one order of magnitude compared to the analog system, yielding a phase stability of (Δφ)ᵣₘₛ = 0.8° and an amplitude stability of (ΔA/A)ᵣₘₛ = 7×10⁻⁵ and thus meeting the specification. The described rf control system has been commissioned and successfully used for beam operation for two years. During this time the system has proven to be significantly more stable and reliable than the old analog system

Particle Physics Reference Library

This third open access volume of the handbook series deals with accelerator physics, design, technology and operations, as well as with beam optics, dynamics and diagnostics. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open acces