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Item type:Publication, Access status: with files , Towards a fault detection infrastructure for the European XFEL(2024); This thesis aims to analyze techniques for improving the fault detection capabilities of large cyber-physical systems. The Low-Level Radio Frequency (LLRF) control system of the European X-ray Free Electron Laser (XFEL) is the main target system. In Part I, the thesis describes the contributions toward the usage of anomaly detection for detecting faults. In Part II, the thesis describes the flow that, starting from an existing hardware digital design, automatically derives runtime monitors, i.e., hardware property checkers that ensure that the system operates correctly.Publicationtype: Doctoral Thesis102 365 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A carrier-suppressing interferometer for ultra-low-noise amplitude- and phase-detection(2023); This thesis introduces the application of the Carrier-Suppression Interferometer (CSI) method for precision phase-noise measurements at attosecond resolution in the field of particle accelerator control systems. Starting from the thorough investigation of crucial system components and their phase noise contribution, the CSI setup reported here outperforms conventional noise detection methods for accelerator controls by more than two orders of magnitude. Furthermore, setup resolution limits and calibration methods are discussed.Publicationtype: Doctoral Thesis216 139 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Identification and control of the laser-based synchronization system for the European X-ray Free Electron Laser(2018); The European X-ray Free-Electron Laser is currently under construction at theDeutsches ElektronenSynchrotron in Hamburg, Germany. This linear accelerator, with a length of 3.4 km,will generate extremely intense and short X-ray laser light pulses with a duration in the femtosecondrange and wavelengths down to 0.05 nm. These laser pulses provide physicists with alight source to take a closer look into small structures on atomic scale.Those precise measurements require timing with an error margin in the femto-second rangefor most subsystems within the facility. Usually, this timing signal is distributed electricallyvia coaxial cables. With the new requirements in timing, this kind of distribution is no longersuitable and a new laser-based synchronization system is used. This system generates a laserpulse train via a master laser oscillator and distributes this via optical fiber to multiple endstationsin the facility.The effective length of the optical path inside the fiber is actively stabilizedby a link stabilizing unit.This thesis analyzes this new system from a control point of view. It is shown that the masterlaser oscillator can be modeled by an integrator, with the H2 norm as the performance criteriaand two filters corresponding to the noise and disturbances of the master laser oscillator itselfas well as the electrical oscillator of the facility. Those influences, as well as the dynamic behaviorof the master laser oscillator, are identified for a laboratory setup. With these models inhand, different controllers are designed and experimentally evaluated. A sufficient controllerperformance can be achieved by a PI controller. However, using a feedback controller witha model-based optimization increase this performance, but these require a high order of thecontroller, which is currently not implementable given the installed hardware.The second part of thiswork analyses the link stabilizing units. This is achievedwith an attachedoptical fiber and a timing measurement by an optical cross correlator. If a short optical fiber isconnected the system can be approximated by a third order system with a time delay of a fewsample. Amodel is identified and used for controller design. It can be shown that a performanceincrease by factor of 4.5 can be achieved if an LQG controller, including a model of the timedelay, is used instead of the previously used PI controller. Moreover, different approaches forlong optical fibers and the operation in the non-linear region of the sensor are shown. Thesecould not be tested in an experiment.The work closes with an analysis of the overall system and gives suggestions of how to increasethe performance of the individual components and of the whole laser-based synchronizationsystem including the attached devices. It will be shown that the optimal performance can beachieved if all systems are connected to the laser-based synchronization system and if the dynamicbehavior of the link stabilizing unit and end-station is equal for all subsystems.Publicationtype: Doctoral Thesis309 407 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Laser-to-RF phase detection with femtosecond precision for remote reference phase stabilization in particle acceleratorsThe invention of a femtosecond stable Laser-to-RF phase detector allows to measure with femtosecond precision the relative phase between a phase stable optical reference and an RF signal. Thereby one can stabilize RF reference signals in modern FELs on a femtosecond scale. A pulsed optical synchronization system is used to deliver the required optical reference signals. The L2RF phase detector is based on an integrated Mach-Zehnder modulator (MZM) in which the phase error between both signals is encoded in an amplitude modulation of the optical pulse train. Different configurations for different operation scenarios have been evaluated. A full mathematical representation has been derived. The impact of multiple error sources has been investigated. Error sources of the measurement setup have been identified and eliminated. The femtosecond performance has been verified with two different prototypes. The achieved stability of 3.6fs over 12h is currently unmatched.Publicationtype: Doctoral Thesis607 1164