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Optics letters 44(7), 1650 - 1653 (2019). doi:10.1364/OL.44.001650, Intense, ultrashort, and high-repetition-rate X-ray pulses, combined with a femtosecond optical laser, allow pump-probe experiments with fast data acquisition and femtosecond time resolution. However, the relative timing of the X-ray pulses and the optical laser pulses can be controlled only to a level of the intrinsic error of the instrument which, without characterization, limits the time resolution of experiments. This limitation inevitably calls for a precise determination of the relative arrival time, which can be used after measurement for sorting and tagging the experimental data to a much finer resolution than it can be controlled to. The observed root-mean-square timing jitter between the X-ray and the optical laser at the SPB/SFX instrument at European XFEL was 308 fs. This first measurement of timing jitter at the European XFEL provides an important step in realizing ultrafast experiments at this novel X-ray source. A method for determining the change in the complex refractive index of samples is also presented., Published by OSA, Washington, DC

The linear accelerators employed to drive Free Electron Lasers (FELs), such as the X-ray Free Electron Laser (XFEL) currently being built in Hamburg, require sophisticated control systems. The Low Level Radio Frequency (LLRF) control system should stabilize the phase and amplitude of the electromagnetic field in accelerating modules with tolerances below 0.02 % for amplitude and 0.01 degree for phase to produce ultra-stable electron beam that meets the conditions required for Self-Amplified Spontaneous Emission (SASE). The LLRF control system of 32-cavity accelerating module of the XFEL accelerator requires acquisition of more than 100 analogue signals sampled with frequency around 100 MHz. Data processing in real-time loop should complete within a few hundreds of nanoseconds. Moreover, the LLRF control system should be reliable, upgradable and serviceable. The Advanced Telecommunications Computing Architecture (ATCA) standard, developed for telecommunication applications, can fulfil all of the above mentioned requirements. The paper presents the architecture of a prototype LLRF control system developed for the XFEL accelerator. The control system composed of ATCA carrier boards with Rear Transition Modules (RTM) is able to supervise 32 cavities. The crucial submodules, like DAQ, Vector Modulator or Timing Module, are designed according to AMC specification. The paper discusses results of the LLRF control system tests that were performed at the FLASH accelerator (DESY, Hamburg) during machine studies.

The measurements of superconducting cavity parameters before module assembly stage are very important, because they allow to evaluate critical properties (resonant frequency, quality factor of accelerating mods) of individual resonating cavities. Such measurements are performed in Vertical Test Stand facilities. One of such setups is Vertical Test Stand II (VTS II) at DESY. It is used for conditioning and characterization of cavities for FEL (Free Electron Laser) experiments (especially for FLASH and European XFEL). In the previous set-up cavities in VTS II were operated in Continuous Wave mode using analog control system. The core of the system was analog Phase Lock Loop used to lock phases of incident wave and transmitted wave. All measurements were done using external equipment such as oscilloscopes, spectrum network analyzers, etc. The main disadvantage of such system was lack of flexibility - each small modification required precise system tuning, no new functionality could be added and automation of measurements was hard to achieve. The paper presents new solution of the control system for VTS II based on digital hardware. It allows to overcome most of disadvantages of previous analog system. All measurements and control functions are integrated on a single (FPGA based) computation board, which is fully integrated with external control system. The usage of such system offers functionality such as long term data acquisition (due to Continuous Wave operation of the cavity), special modes of operation (like Self Excited Loop or Digital PLL - due to low bandwidth of measured resonator) and possibility of measurement process automation. Additionally developed user interfaces allow remote access to the system parameters and flexible configuration. The paper discusses each sub-system, presents measurement results and overall system performance evaluation together with some views for future functionality development.

The idea and realization of data presentation system is described in this paper. Data is received from the diagnostic system of the BAC detector. The presented system is a part of the DQMS (Data Quality Monitoring and Management). The system enables graphical presentation of the location of electronic blocks. It is possible to indicate the links between these blocks, and the actual state of the specified components. The aim to build this system was to assure the proper working of the BAC detector, and in the case of detecting abnormalities to find them out as soon as possible, detect the place of the error and the causes of the failure. The presented software helps to find the errors and is a sort of knowledge compendium about the BAC detector (its equipment, links structure, etc.). The engineering of the visualization system as well as functional tasks were described, and the discussion of the results was made. Some examples, showing the usage of the system, and the received results of its work were presented.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New hardware and software developments on the Backing Calorimeter (BAC) for the ZEUS detector are presented. The modernization of the detector was related to the recent luminosity upgrade of the HERA accelerator. The role and place of the BAC detector in the ZEUS experiment is described with special emphasis on the new BAC muon trigger and its diagnostic and monitoring system. This overview introduces a series of detailed articles following in this chapter of the SPIE proceedings.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The paper presents functional structure of database system of data measurement quality for BAC detector in ZEUS experiment. The system collects diagnostic and experimental data. Diagnostic data are: work parameters of the detector and electronics/photonics, tests of electronic/photonic blocks. These data are archived for certain period of time. The quality of current data collection process is estimated using these archived data. The result of such estimation is generated in a form of status map of the detector. Such maps, describing status of the hardware, are fundamental for elementary particle analysis by the calorimeter. The DAQ system, collecting data to the database, estimates data quality on-line during transmission and writing. This mechanism of fast on-line data quality management leads to early discoveries of detector work irregularities and faults.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The paper presents ideas and realization of hardware (photonics and electronics) and software diagnostic layers of TRIDAQ for BAC calorimeter of ZEUS experiment at HERA accelerator. The aim of diagnostic system (DS) is to provide high reliability of the BAC. The diagnostic system localizes, in the fastest possible way, place, time and cause of any breakdown inside the BAC. Functionalities of diagnostic system were discussed. Construction of distributed, diagnostic hardware layer was presented. The software layer of the system was designed using the object-oriented approach. Object oriented virtual classes were defined. These classes control electronics and photonics devices and sub-systems. Application examples were presented. The implementation results of DS for TRIDAQ were discussed.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.