Search

At the free-electron lasers FLASH and European-XFEL bunch arrival times are monitored with a high-accuracy electro-optical based data acquisition system (BAM). Due to only a couple of picoseconds time measurement range of this system, large timing changes might cause the monitor to fail. To remove any ambiguity and for health status monitoring a high-speed direct-sampling FPGA mezzanine card (FMC) and an analogue RF front-end was added. The circuitry has lower precision than the electro-optical based BAM, but it can determine bunch arrival time with respect to a reference signal over a large time range, i.e. of the order of 1 ms. After restarts or larger energy changes during operation, the electron bunch arrival time may have been changed by tens or even hundreds of picoseconds, which causes that the BAM is out of its operation range and needs to be recalibrated. With the solution developed, the BAM gets the coarse bunch timing from the digitizer and adjusts its optical delay lines accordingly. This allows for finding the operation point fast and automatically. Performance data of the fast direct-sampling digitizer FMC and first measurement data from FLASH will be presented.

This document describes a new package to compute high performance simulations of a module of superconducting accelerating cavities from the LLRF controller perspective. The reason to make a dedicated C++/Python package is to simulate all the effects that arise during Continuous Wave (CW) operations at different timescales to speed-up the LLRF controller design. In particular the speed of the sampling rate of the ADCs used in a LLRF control system (some MHz) are $10^4$ - $10^5$ times faster than typical mechanical resonances and microphonics frequencies., Poster presented at LLRF Workshop 2017 (LLRF2017, arXiv:1803.07677)

29th Linear Accelerator Conference, LINAC18, Beijing, China, 17 Sep 2018 - 21 Sep 2018; JACoW 3 pp. (2018)., To investigate the feasibility of the continuous wave (cw) upgrade of the European XFEL (E-XFEL) DESY, on-going tests are performed on E-XFEL prototype and production cryomodules since 2011. For these studies, DESY's Cryo-Module Test Bench (CMTB) has been equipped with a 105 kW cw operating IOT in addition to the 10MW pulsed klystron, making CMTB a very flexible test stand, enabling both cw and pulse operation. For these tests, E-XFEL-like LLRF electronics is used to stabilize amplitude and phase of the voltage Vector Sum (VS) of all 8 cavities of the cryomodule under test. The cryomodule most often tested is the pre-series XM-3, unique since it is housing one fine grain niobium and seven large grain niobium cavities. In autumn 2017, additional spacers were installed on all 8 input couplers to increase the maximum reachable loaded quality factor Ql beyond 2·107. With higher Ql, up to 6·107 for 6 cavities and 2.7·107 for 2 cavities, we have investigated the VS stability and SRF-performance of this cryomodule under various conditions of cooling down rate and operation temperature 1.65K, 1.8K and 2K, at gradients up to ca. 18MV/m. The results of these tests are presented in this paper., Published by JACoW

The program of low charge mode of operation is under development at free electron laser FLASH aiming in single mode radiation pulses. A short pulse photoinjector laser has been installed at FLASH allowing production of ultrashort electron pluses with moderate compression factor of the beam formation system. Here we present pilot results of free electron laser FLASH operating at the wavelength of 13.1 nm and driven by 70 pC electron bunches. Relevant theoretical analysis has been performed showing good agreement with experimental results.

Extreme-ultraviolet to x-ray free-electron lasers (FELs) in operation for scientific applications are up to now single-user facilities. While most FELs generate around 100 photon pulses per second, FLASH at DESY can deliver almost two orders of magnitude more pulses in this time span due to its superconducting accelerator technology. This makes the facility a prime candidate to realize the next step in FELs—dividing the electron pulse trains into several FEL lines and delivering photon pulses to several users at the same time. Hence, FLASH has been extended with a second undulator line and self-amplified spontaneous emission (SASE) is demonstrated in both FELs simultaneously. FLASH can now deliverMHzpulse trains to two user experiments in parallel with individually selected photon beam characteristics. First results of the capabilities of this extension are shown with emphasis on independent variation of wavelength, repetition rate, and photon pulse length.

With the international interest focused on continuous wave (CW) operation for free-electron laser (FEL) superconducting accelerators, an R&D program is carried at the Deutsches Elektronen Synchrotron (DESY) in Germany to study the possible operation of the European Xray FEL cryomodules in CW or long pulse mode. This contribution presents the latest results obtained when driving XFEL series production cryomodules in CW mode, using the XFEL MicroTCA-based LLRF system. Considerations about the cryomodule dynamic heat load, piezo-based resonance control for a cavity loaded quality factor QL = 1.5e7, CW data acquisition and RF control performance at 11 and up to 16 MV/m using vector sum feedback will be presented.

The drift compensation module uses an injected reference approach which is used to compensate for amplitude and phase drifts in thereceiver section induced by environmental changes. In the contribution we present the electrical and mechanical design flows for various frequencies and the two different modes of operation. During the design process we used several microwave modelling tools and the contribution summarizes the results. The evaluation results include long term measurements of one drift calibration module in a realistic environment. Special emphasis is put on the implementation of the mechanics of the module since it is tightly coupled to the final performance.

LLRF modules in the European XFEL are a set of devices that need a common interface for management and control. A generic software structure was designed on the top of Distributed Object Oriented Control System (DOOCS) framework to allow easy and flexible implementation of new applications, that provide direct access to such devices as the Drift Compensation Module (DCM), Local Oscillator & Generator Module (LOGM) and Power Supply Module (PSM). The current design's structure allows decoupling from DOOCS framework without introducing much performance overhead, also allowing the addition of safety redundancy mechanisms, which are not available in the framework itself. The design has proven to work with register-based protocol access (SNMP, DMA and PCIE readout), but does not restrict usage for just device access, as it can be used for LLRF data computation and any other action-on-demand features. This contribution presents the software architecture, its implementation and some experimental results acquired on devices already installed in the XFEL accelerator.

The RF Phase Reference Distribution system followed by the LLRF control system must assure precise stabilization of the RF field withinthe accelerating cavities of the European XFEL accelerator. The required amplitude and phase accuracy respectively dA/A

The optical synchronization group at DESY is operating and continuously enhancing their laser-based synchronization systems for various facilities which need femtosecond-stable timing. These include the free-electron lasers FLASH and the upcoming European XFEL as well as the electron diffraction machine REGAE(Relativistic Electron Gun for Atomic Exploration) and the future plasma acceleration test facilities (LAO LA and FLASHforward). One of the major upgrades under development is the migration of the entire electronic control hardware to the new MTCA.4 platform which w as introduced as the new standard for accelerator control in many facilities worldwide. In this paper we present the applied modules and the topology of the new systems. Main advantages are a compact design with higher performance, redundancy, and remote management.

For seeding of a free-electron laser, the spatial and temporal overlap of the seed laser pulse and the electron bunch in the modulator is critical. To establish the temporal overlap, the time difference between pulses from the seed laser and spontaneous undulator radiation is reduced to a few pico-seconds with a combination of a photomultiplier tube and a streak camera. Finally, for the precise overlap the impact of the seed laser pulses on the electron bunches is observed. In this contribution, we describe the current experimental setup, discuss the techniques applied to establish the temporal overlap and analyze its stability.

The superconducting continuous wave (CW) accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded to generate electron bunches with sub picosecond duration, charges of up to 1 nC at repetition rates of up to 500 kHz (CW). The electron pulses are compressed to their desired length using two magnetic chicanes. To measure the timing of the electron bunches with respect to ELBEs RF reference at the target position a Bunch Arrival-time Monitor (BAM) has been setup and commissioned. Improvements concerning the beamline pickup and readout electronics are discussed which leads to a higher temporal resolution. First measurement results carried out are presented.

This archive summarizes a working paper and conference proceedings related to laser wire scanner development for the Future Linear Collider (FLC) in the years 2001 to 2006. In particular the design, setup and data taking for the laser wire experiments at PETRA II and CT2 are described. The material is focused on the activities undertaken by Royal Holloway University of London (RHUL)., Comment: 61 pages

At today’s free-electron lasers, high-resolution electron bunch arrival time measurements become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultrashort laser pulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1 nC down to 20 pC with equally sub-10fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40 GHz has been developed. These pickups are installed at the free-electron laser FLASH and at the continuous wave electron accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes. The integration of these pickups into the arrival time monitor system is described.

Laser driven plasma accelerators are offering high gradient (∼10-100 GV/m), high quality (low emittance, short bunch length) electron beams, which can be suitable for future compact, bright and tunable light sources. In the framework of the Laboratory for Laser-and beam-drivenplasma Acceleration (LAOLA) collaboration at Deutsches Elektronen-Synchrotron (DESY) the external injection experiment for injecting electron bunches from a conventional RF accelerator into the linear plasma wave is in progress. External injection experiments at REGAE (Relativistic Elec-tron gun for Atomic Exploration) require sub-20fs precision synchronization of laser and electron beams in order to perform a beam scan into the plasma wave by varying the delay between electron beam and laser pulses. In this paper we present a novel optical to microwave synchronizationscheme, based on a balanced single output integrated Mach-Zehnder Modulator (MZM). The scheme offers a highly sensitive phase detector between a pulsed 800 nm Ti:Sa. laser and a 3 GHz microwave reference source. It is virtually independent of input laser power fluctuations and it offers femtosecond long-term precision. Together with the principal of operation of this setup, we will present promising preliminary experimental measurements of the new detector stability.

The continuous wave electron accelerator ELBE is upgraded to generate short and highly charged electron bunches (~200fs duration, up to 1 nC) . In the last years a prototype of an optical synchronization system using a mode locked fiber laser has been build up at ELBE which is now in commissioning phase. The stabilized pulse train can be used for new methods of electron bunch diagnostics like bunch arrival time measurements with the potential of femtosecond resolution. At ELBE a bunch arrival time monitor (BAM) has been designed and tested at the accelerator. The contribution will show the design of the BAM and first measurement results at the ELBE accelerator.

The linear accelerator REGAE (Relativistic Electron Gun for Atomic Exploration) at DESY delivers electron bunches with a few femtosecond duration for time-resolved experiments of material structure in pump-probe configuration. To achieve the desired 10 fs resolution, the Low Level RF controls for the normal conducting S-band cavities must provide field stability of 0.01% in amplitude and of 0.01deg in phase. To achieve these demanding stability a recently developed LLRF controller based on the Micro-Telecommunications Computing Architecture (MTCA.4) have been installed and commission. In this paper, we report on measurement performance of the LLRF system, the achieved stability and current limitations.

Optical reference distributions have become an indispensable asset for femtosecond precision synchronization of free-electron lasers. At FLASH and for the future European XFEL, laser pulses are distributed over large distances in round-trip time stabilized fibers to all critical facility sub-systems. Novel Laser-to-RF phase detectors will be used to provide ultra phase stable and long-term drift free microwave signals for the accelerator RF controls. In this paper, we present the recent progress on the design of a fully integrated and engineered version of the L2RF phase detector, together with first experimental results demonstrating so-far unrivaled performance.

The continuous wave electron accelerator ELBE is upgraded to generate short and highly charged electron bunches (~200fs duration, up to 1 nC) with an energy of up to 40 MeV. In the last years a prototype of an optical synchronization system using a mode locked fiber laser has been build up which is now in commissioning phase. The stabilized pulse train can be used for new methods of electron bunch diagnostics like bunch arrival time measurement with the resolution down to a few femtoseconds. At ELBE a bunch arrival time monitor (BAM) has been designed and tested at the accelerator. The contribution will show the concept of the femtosecond synchronization system, the design of the BAM and first measurement results.

At free-electron lasers, today's pump-probe experiments and seeding schemes make high demands on the electron bunch timing stability with an arrival time jitter reduction down to the femtosecond level. At FLASH and the upcoming European XFEL, the bunch train structures with their high bunch repetition rates allow for an accurate intra-train stabilisation. To realise longitudinal beam-based feedbacks a reliable and precise arrival time detection over a broad range of bunch charges, which can even change from 1 nC down to 20 pC within a bunch train, is essential. Benefitting from the experience at FLASH, the current bunch arrival time monitors (BAMs), based on detection of RF signals from broad-band pick-ups by use of electro-optic modulators, are further developed to cope with the increased requirements. In this paper, we present the new BAM prototype, including an adapted electro-optical front-end and the latest development of the read-out electronics based on the MTCA.4 platform.

FLASH is a high-gain free-electron laser (FEL) in thesoft x-ray range. This paper discusses the generation ofvery short FEL pulses in the Self-Amplified SpontaneousEmission (SASE) - mode without an external seeding signal.In the optimal case a SASE-FEL can be operated inthe so-called single-spike mode. At FLASH a new photoinjectorlaser has been commissioned, which allows thegeneration of shorter bunches with low bunch charge directlyat the photo-cathode. This shorter injector laser reducesthe required bunch compression for short pulses andthus allows a stable SASE performance with shorter pulses.First SASE performance using the new injector laser hasbeen demonstrated and electron bunch and FEL radiationproperties have been measured. These measurements arepresented and next steps towards single spike operation arediscussed.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern free electron lasers. A continuous experimental optimization of the L-band photo injector for such FEL facilities like FLASH and the European XFEL has been performed for a wide range of electron bunch charges – from 20 pC to 2 nC – yielding very small emittance values for all charge levels. Experience and results of the experimental optimization will be presented in comparison with beam dynamics simulations. The influence of various parameters onto the photo injector performance will be discussed.

Within the ELBE upgrade towards a Center for High Power Radiation Sources (HSQ), a mono energetic positron, a liquid lead photo neutron source and two new THz sources have been installed at the superconducting electron linac at ELBE. A variety of established as well as newly developed electron beam diagnostics were installed and tested. In this paper we want to present first results achieved with the currently existing prototype beam arrival time and bunch compression monitors (BAM, BCM) as well as one versatile EOS set-up.

Within the ELBE upgrade towards a Center for High Power Radiation Sources (HSQ), a mono energetic positron, a liquid lead photo neutron source and two new THz sources have been installed at the superconducting electron linac at ELBE. A variety of established as well as newly developed electron beam diagnostics were installed and tested. In this paper we want to present first results achieved with the currently existing prototype beam arrival time and bunch compression monitors (BAM, BCM) as well as one versatile EOS set-up. Based on these future developements and upgrades are discussed.

Due to its large scale, the European X-ray Free ElectronLaser accelerator (XFEL) requires a high level of automationfor commissioning and operation. Each of the800 superconducting RF cavities simultaneously runningduring normal operation can occasionally quench, potentiallytripping the cryogenic system and resulting into machinedown-time. A fast and reliable quench detection systemis then a necessity to rapidly detect individual cavityquenches and take immediate action, thus avoiding interruptionof machine operation. In this paper, the mechanismsimplemented in the low level RF system (LLRF) toprevent quenches and the algorithms developed to detectaccidental cavity quenches are explained. In particular, thedifferent types of cavity quenches and the techniques developedto identify them are shown. Experimental results acquiredduring the testing of XFEL cryomodules prototypesat DESY are presented, demonstrating the performance andefficiency of this machine operation and cavity protectiontool.

In order to measure the arrival time of the electron bunches in low (20 pC) and high (1 nC) charge operation mode, new high bandwidth pickups were developed as a part of the Bunch Arrival-time Monitors (BAMs) for FLASH at DESY *. The pickup signal is transported via radiation resistant coaxial cables to the electro-optic modulator (EOM) **. Due to the high losses of the 40 GHz RF front-end the signal in the RF path is attenuated well below the optimal operation voltage of the EOM. To improve the overall performance, the signal strength of the induced pickup signal needs to be increased and at the same time the losses in the RF front-end significantly reduced. In this paper, the analysis towards improving the induced pickup signal strength is presented. Simulations are performed with the CST STUDIO SUITE package and the results are compared with the state of the art high bandwidth pickups.

mopb017 - ISBN 978-3-95450-122-9; International audience; The production of the 103 superconducting accelerating modules for the European XFEL is an international effort.

The superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf is currently upgraded to enable continuous wave operation with bunch charges of up to 1 nC and durations down to 200 fs (RMS). The new beamline will drive a THz source and an X-ray source based on Thomson scattering. In collaboration with DESY, Hamburg, an optical synchronization system based on a mode locked master laser is currently being set up to ensure timing stability on the few 10 fs level. It allows high temporal resolution pump-probe experiments and new electron beam diagnostics like bunch arrival-time monitors. The synchronization system is assembled in a dedicated laboratory to ensure stable environmental conditions. In this paper the concept of the optical synchronization system is presented and first experience on the link stabilization system, its installation and commissioning is reported.

At the srf based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime and with pC bunch charge and repetition rates of 13 MHz is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and the generation of broad band and narrow bandwidth coherent THz pulses. In this paper we outline ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.

The superconducting radiofrequency (SRF) electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded with an SRF Gun and a femtosecond (fs) electron beamline to enable continuous wave operation with bunch charges of up to 1 nC and bunch durations down to 100 fs (RMS). The new femtosecond electron beamline will be used to drive two coherent THz sources and one X-ray source based on Thomson scattering. The two different THz sources, one narrow bandwidth undulator source and one broad bandwidth coherent transition/diffraction source, are guided into a dedicated THz Laboratory where they can be combined with various fs-laser systems. For the planned THz pump laser probe experiments, synchronization of the external pump-probe lasers on the fs- level is essential. Our approach is based on an optical synchronization system, adapted from a similar system installed at FLASH [*]. That system will be installed in collaboration between DESY and HZDR. In this contribution we will discuss the layout of the synchronization scheme and first ideas for measurements of the arrival time jitter of the THz pulses to evaluate the achieved degree of timing stability.