| Paper | Title | Other Keywords | Page | ||
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| MOO1A02 | High Resolution Transverse Profile Measurement | electron, synchrotron, emittance, photon | 1 | ||
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In many cases the performance of a particle accelerator is in large part defined by the transverse emittance of the beams. In most cases, like colliders and light sources (Synchrotrons or Free Electron Lasers), the quality of the final product, i.e. luminosity and brilliance, is directly linked to this parameter. For this reason many techniques and devices have been developed over the years for monitoring the transverse distribution of particles along accelerator chains or over machine cycles. Moreover modern designs of accelerators allow smaller size and/or higher current beams. New, more demanding, emittance measurement techniques have to be introduced and existing ones expanded. This presentation will review the different methods and the different instruments developed so far.
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| MOO2A01 | Physics And Diagnostics Of Laser-Plasma Accelerators | electron, focusing, target, radio-frequency | 11 | ||
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The recent and continuing development of powerful laser systems, which can now deliver light pulses containing a few Joules of energy in pulse durations of a few tens of femto seconds, has permitted the emergence of new approaches for generating energetic particle beams. By focusing these laser pulses onto matter, extremely large electric fields can be generated, reaching the TV/m level. Such fields are 10,000 times greater than those produced in the radio-frequency cavities of conventional accelerators. As a result, the distance over which particles extracted from the target can be accelerated GeV energy range is reduced to distances on the order of millimetres. A few years ago, several experiments have shown that laser-plasma accelerators can produce electron beam with maxwellian-like distribution [1], in 2004 high-quality electron beams, with quasi-mono energetic energy distributions at the 100 MeV level [2] and recently in the GeV range using a capillary discharge [3]. These experiments were performed by focusing a single ultra short and ultra intense laser pulse into an under dense plasma. More recently we produced a high quality electron beam using two counter-propagating
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| MOO2A02 | Electron Beam Diagnostics for the European X-Ray Free-Electron Laser | diagnostics, electron, emittance, linac | 17 | ||
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At the European XFEL, dedicated diagnostic sections are located in the injector, downstream of the bunch compressors, in the beam distribution area and undulator systems. Very challenging is the measurement and control of the compression process based on magnetic chicanes in combination with off-crest acceleration in both fundamental and 3rd-harmonic structures. Non-linear effects, e.g. CSR or LSC, which also depend on the compression process may degrade the slice emittance or energy spread. Moreover, a beam energy jitter transforms into a time jitter in the magnetic chicanes, and the beam arrival time is of crucial importance for other synchronised laser systems, e.g. for diagnostics, seeding or pump-probe experiments. The overlap of the electron and photon beams in the up to 250m-long undulators is relevant for the lasing process. BPMs with high single-bunch resolution are being developed for orbit monitoring and beam based alignment procedures. The general layout of the electron beam diagnostics for the European XFEL is presented. The development status of various diagnostic components is discussed, and, where appropriate, experimental results obtained at FLASH* are presented.
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* Many special diagnostic tools and prototypes are being developed and tested at the Free-Electron LASer in Hamburg FLASH. |
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| TUPB11 | A laserwire beam profile measuring device for the RAL Front End Test Stand | ion, diagnostics, electron, emittance | 81 | ||
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The Front End Test Stand at the Rutherford Appleton Laboratory (RAL) is being developed to demonstrate a chopped H- beam of 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-powered proton accelerators. As such, it requires a suite of diagnostic instruments to provide detailed measurements of the ion beam. Due to the high beam brightness and a desire to be able to have online instrumentation, a series of non-intrusive and non-destructive diagnostics based on laser-detachment are being developed. The progress that has been made towards construction of a laserwire instrument that can measure the beam profile at an arbitrary angle are described. In particular, the principle behind the instrument, the simulation and design of it and the vacuum vessel in which it will be mounted are given. In addition, the reconstruction software that will be used to reconstruct the 2D transverse beam density distribution from the profiles of the beam is described.
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| TUPB20 | Large Horizontal Aperture BPM and Precision Bunch Arrival Pickup | pick-up, electron, simulation, vacuum | 108 | ||
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The large horizontal aperture chicane BPM and the precision bunch arrival monitor at FLASH will be important tools to stabilize the arrival-time of the beam at the end of the linac. The pickups for these monitors will be paired with front-ends that sample the zero-crossing of the beam transient through the use of electro-optical modulators and sub-picosecond-long laser pulses delivered by the master-laser oscillator. The design of pickups for this front-end requires the consideration of the beam transient shape as well as the amplitude. Simulations and oscilloscope traces from pickups that use or will use the EOM based phase measurement and the expected limitations and benefits of each pickup are presented. In particular, the design for a 5 um resolution BPM with a 10 cm horizontal aperture is demonstrated in terms of its capability to measure the beam energy and its sensitivity to the shape and orientation of the beam.
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| TUPB29 | Experimental Optimization of the Cathode Laser Temporal Profile | cathode, emittance, simulation, electron | 135 | ||
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Producing a flat-top temporal intensity profile of the cathode laser pulse is a key issue for the XFEL photo injector. The photo injector test facility at DESY in Zeuthen (PITZ) serves as a test bench for FEL photo injectors. The PITZ cathode laser contains a pulse shaper to produce flat-top temporal pulse profiles. Based on birefringent filters the pulse shaper includes four degrees of freedom to achieve a pulse profile with parameters closer to the required XFEL photo injector specifications (20 ps FWHM, 2 ps rise/fall time). A procedure for experimental temporal laser profile optimization is presented in this paper. The laser profile is measured using a streak camera. The four parameters - pulse length (FWHM), rise and fall time as well as modulation of the flat-top which are obtained from a flat-top fit of the measured profile - are used in the profile evaluation. Utilizing results of beam dynamics simulations for various cathode laser profiles a single value of the goal function – the expected emittance growth due to measured imperfections of the profile - can be obtained. The procedure of the goal function minimization has been implemented and tested at PITZ.
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| TUPC02 | Photo Injector Cathode Laser Beam Intensity and Pointing Position Diagnostics at PITZ | cathode, diagnostics, monitoring, electron | 147 | ||
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A photo cathode laser with unique parameters is used at the Photo Injector Test facility at DESY in Zeuthen, PITZ. It is cabable of producing laser pulse trains consisting of up to 800 pulses with a repetition rate of 1 MHz where each laser pulse has a flat-top temporal profile. The knowledge of the laser stability is very important for the emittance measurements procedure. Therefore, a system for monitoring the laser beam intensity and pointing position stability was created at PITZ. It is capable of measuring the laser spot position and pulse intensity for each of the laser pulses in the train using a quadrant diode and a photomultiplier tube, respectively. Taking into account the laser beam spot transverse intensity distribution measured by a CCD camera allows to study the position of the laser spot on the photo cathode with a resolution of 8.3 um. Laser intensity measurements can be done for a wide dynamical range of intensities due to the tunable photo multiplier tube gain. The first experiments with the new system show very small laser spot position jitter on the cathode surface of about 20 um and laser intensity fluctuations of about 14 %.
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| TUPC11 | The Beam Diagnostics System for the FERMI@elettra Photoinjector | diagnostics, emittance, linac, gun | 171 | ||
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The quality of the photoinjector high brightness electron beam plays a crucial role for the performance of the seeded FERMI@elettra FEL. Optimization of the gun is possible with an extensive characterization of the 5 MeV electron beam longitudinal and transverse phase space. The photoinjector diagnostics system includes interceptive instrumentation as YAG:Ce screens for transverse position and profile measurements and Faraday cups for the absolute beam charge measurements; a Cherenkov radiator coupled to a streak camera provides an accurate reconstruction of the longitudinal profile and a pepper pot is foreseen for the transverse emittance measurement. Information on beam transverse position and charge is obtained non-disruptively with respectively stripline BPMs and a current transformer. A dispersive beamline is also foreseen for the beam energy, energy spread and longitudinal phase space measurements. The diagnostics system performances and design principles are presented.
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| TUPC25 | Design and Calibration of an Emittance Monitor for the PSI XFEL Project | emittance, electron, acceleration, gun | 198 | ||
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Paul Scherrer Institute (PSI) intends to realize a compact X-ray Free Electron Laser (XFEL) by developing a high brightness, high current electron source. Field emitter arrays (FEA) in combination with high gradient acceleration promise a substantial reduction of transverse emittances by up to one order of magnitude compared to existing electron sources for XFELs. A flexible, high resolution emittance monitor based on the "pepperpot measurement techique" has been designed for this "low emittance gun" project at PSI. The realization and the calibration procedure of the monitor will be described in this presentation.
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| WEO1A01 | Sub-ps Timing and Synchronization Systems for Longitudinal Electron Bunch Profile Measurements | electron, radiation, undulator, diagnostics | 204 | ||
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Precise timing and synchronization systems have become an increasingly important topic for next generation light sources. Particularly free electron lasers can emit X-ray pulses with pulse durations down to the few-tens of femtoseconds level. In order to utilize this potential temporal resolution for pump-probe experiments, a precise synchronization of the experimental laser to the X-ray pulse and stabilization of the electron beam arrival time at the undulators are mandatory. This requires a timing and synchronization system which can supply ultra-stable phase references over long distances, thus enabling the temporal stabilization of the electron beam to a sub-100 fs level. Furthermore, a precise timing and synchronization system renders possible extremely accurate measurements of the longitudinal electron bunch profile. This talk will give an overview of the status of existing sub-ps timing and synchronization systems and of systems currently under construction.
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| WEO2A02 | Single Shot Longitudinal Bunch Profile Measurements by Temporally Resolved Electro-Optical Detection | electron, resonance, diagnostics, linac | 221 | ||
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For the high-gain operation of a SASE FEL, extremly short electron bunches are essential to generate sufficiently high peak currents. At the superconducting linac of FLASH at DESY, we have installed an electro-optic experiment to probe the time structure of the electric field of single sub 200fs e-bunches. In this technique, the field-induced birefringence in an electro-optic crystal is encoded on a chirped ps laser pulse. The longitudinal electric field profile of the electron bunch is then obtained from the encoded optical pulse by a single-shot cross correlation with a 30 fs laser pulse using a second-harmonic crystal (temporal decoding). In the temporal decoding measurements an electro-optic signal of 180 fs FWHM was observed, and is close to the limit due to the material properties of the particular electro-optic crystal used. The measured electro-optical signals are compared to bunch shapes simultaneously measured with a transversly deflecting cavity.
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| WEO2A03 | Advanced Measurements at the SPARC Photoinjector | emittance, simulation, electron, space-charge | 224 | ||
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The objective of the first stage of the SPARC commissioning was the optimization of the RF-gun setting that best matches the design working point and a detailed study of the emittance compensation process providing the optimal value of emittance at the end of the linac. For this purpose an innovative beam diagnostic, the emittance-meter, consisting of a movable emittance measurement system, was conceived and built. More than a simple improvement over conventional, though non-trivial, beam diagnostic tools this device defines a new strategy for the characterization of new high performance photo-injectors. The emittance meter allows to measure at different location along the beamline the evolution of important beam parameters both in longitudinal and in the transverse phase space such as beam sizes, energy spread and rms transverse emittances in a region where the space-charge effect dominate the electron dynamics. The quality and the amount of the data allowed a clear reconstruction of the phase space evolution. We report also the first experimental observation of the double emittance minima effect on which is based the optimized matching with the SPARC linac
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| WEPB03 | Femtosecond Yb-Doped Fiber Laser System at 1 um of Wavelength with 100-nm Bandwidth and Variable Pulse Structure for Accelerator Diagnostics | electron, radiation, diagnostics, polarization | 235 | ||
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Laser-based diagnostic systems play an increasingly important role in accelerator diagnostics in, for instance, measurements of the electron bunch length. To date, the laser system of choice for electro-optic experiments has been the Ti:Sa laser. These offer nJ pulse energies at fixed repetition rate between 50-100 MHz, which is not well suited to the bunch structure of facilities such as FLASH (several hundred pulses with 1 MHz spacing at 1-5 Hz repetition rate).The limited robustness, stability and operability of Ti:Sa systems make them less than an ideal candidate for a continuously running measurement system requiring minimal maintenance. Fiber lasers represent a promising alternative, since gating and subsequent amplification is simple and of low cost, hence a pulse pattern corresponding exactly to the linac bunch pattern can be generated. Furthermore, these lasers offer superior robustness at a fraction of the cost of a Ti:Sa laser and have been shown to work without maintenance for several months and longer. Here, we present an ytterbium-doped fiber laser system with 80 nm bandwidth and multi-nJ pulse energy with adjustable bunch pattern for use in electro-optic experiments.
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| WEPB07 | Time Domain Diagnostics for the ISAC-II Superconducting Heavy Ion Linac | linac, ion, electron, emittance | 247 | ||
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The medium beta section of the ISAC-II superconducting linac has 20 bulk niobium quarter wave resonators and adds up to 20 MV of energy to the 1.5Mev/u and A/q<=6 ion beam injected from the ISAC-I accelerators. The commissioning of this new linac started April 2006 and the first radioactive beam was delivered to an experiment in January 2007. A standard array of ISAC diagnostics were added to the ISAC-II section to commission and tune the transport beamline and linac optics. In addition two new devices were developed: an ion implanted silicon detector measuring beam particles scattered from a gold foil and time of flight (TOF) monitors based on micro-channel plates. These are used both to tune the LINAC and to characterize the accelerated beams in the longitudinal phase space. The TOF monitors have the time resolution below 100ps, energy resolution of 0.1% and dynamic range spanning 6 orders of magnitude. Data acquisition and analysis is highly automatic and integrated into the EPICS based ISAC control system. Design of the monitors and first measurements will be presented.
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| WEPB08 | Noise and drift characterization of critical components for the laser based synchronization system at FLASH | extraction, free-electron-laser, optics, radiation | 250 | ||
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At FLASH, a new synchronization system based on distributing streams of short laser pulses through optical fibers will be installed and commissioned in 2007. At several end stations, a low drift- and low noise conversion of the optical signal into RF signals is needed. In this paper, we present the influence of photodiodes on the phase stability of the optical pulse streams and investigate the drift performance of the photo-detection scheme for the extraction of the RF signal.
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| WEPB15 | A Sub-50 Femtosecond bunch arrival time monitor system for FLASH | pick-up, electron, feedback, polarization | 262 | ||
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A bunch arrival time monitor system using the future laser based synchronization system at FLASH has been developed. The signal of a beam pick-up with several GHz bandwidth is sampled by a sub-ps laser pulse using a broadband electro-optical modulator. Bunch arrival time deviations are converted into amplitude modulations of the sampling laser pulses which are then detected by a photo-detector. A resolution of 30 fs could be reached, with the capability towards sub-10 fs level. In this paper we describe the design of the optical system and we present recent results.
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| WEPB16 | First prototype of an optical cross-correlation based fiber-link stabilization for the FLASH synchronization system | polarization, feedback, free-electron-laser, electron | 265 | ||
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A drift free synchronization distribution system with femtosecond accuracy is of great interest for free-electron-lasers such as FLASH or the European XFEL. Stability at that level can be reached by distributing laser pulses from a mode-locked erbium-doped fiber laser master oscillator over actively optical-length stabilized fiber-links. In this paper we present a prototype of a fiber-link stabilization system based on balanced optical cross-correlation. The optical cross-correlation offers drift-free timing jitter detection. With this approach we were able to reduce the timing jitter added by a 400 m long fiber-link installed in a noisy accelerator environment to below 10 fs (rms) over 12 hours.
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| WEPC01 | Beam Based Measurements of RF Phase and Amplitude Stability at FLASH | gun, acceleration, electron, feedback | 307 | ||
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Beam based techniques to determine the phase and amplitude stability of the photo-cathode laser, the RF gun and superconducting acceleration modules become key tools for the understanding and quality control for FEL operation critical acceleration sub-system. The measurements are used to identify the sources of instabilities, to determine response functions and to optimize RF feedback parameters and algorithm. In this paper, an overview on the measurement techniques and their limitation is given, together with some important results on the currently achieved RF and laser stability.
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| WEPC02 | Developments at Elettra of the Electronics for the Bunch-Arrival Monitor | controls, pick-up, monitoring, coupling | 310 | ||
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Within the framework of the EUROFEL project, a task has been started in 2006 for a joint development of a Bunch Arrival Monitor (BAM), based on the original idea from DESY. ELETTRA is responsible for the development of the VME-controlled clock-delay board of the BAM system. A variable clock-delay circuit (a phase shifter) is required to adjust the acquisition sampling point of the pick-up-modulated optical pulses of the master-laser oscillator. Since the optical pulses have a repetition rate of 40.625MHz (54MHz in the future) and the acquisition sampling frequency is double of this value, the clock-delay module operates in the 80-120MHz frequency range. The clock timing jitter of the acquisition system greatly affects the measurements of the system: the output timing jitter from the clock-delay board should be less than 0.5ps-rms. Therefore, due to the very strict additive timing-jitter requirements, three phase shifter versions were designed, built and phase-noise evaluated. Low-pass-filter implementation achieved 563fs (at 283fs source jitter) of total-system timing jitter, integrated IQ multiplier 365fs (at 188fs of source) and passive IQ modulator 265fs (at 208fs of source).
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| WEPC11 | FERMI@elettra Timing System: Design and Recent Synchronization Achievements | linac, klystron, diagnostics, radio-frequency | 334 | ||
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FERMI@elettra is the fourth generation light source under construction at Sincrotrone Trieste. Being a seeded-FEL source, the requirements for the timing system are very tight as the final goal is a stable seeding process with sub-picosecond electron bunches and seeding laser pulses. Based on demonstrated results achieved in the main laboratories worldwide active in the field, like DESY, LBNL and MIT, an hybrid timing system scheme has been proposed which is currently under development. Both "pulsed" and "continuous wave (CW)" optical timing systems are being deployed, the choice being based on the differences among the different timing system clients; a Low Level Radio Frequency processor is a "quasi-CW" client whereas the lasers and some "longitudinal" diagnostics are "time discrete" clients. In this paper the FERMI@elettra timing system and the recent advances are presented. A pulsed optical clock has been locked to an ultra stable reference; its output pulses distributed over stabilized fiber optic links. As a benchmark client, a femto-second laser oscillator has been synchronized to the optical clock testing different possible schemes.
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| WEPC13 | Jitter Reduced Pump-Probe Experiments | electron, diagnostics, target, photon | 337 | ||
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For two-colour pump-probe experiments carried out at the free electron laser FLASH@DESY, the FEL laser pulses in the XUV have to be synchronized with femtosecond precision to optical laser pulses (Ti:Sapphire). An electro-optical sampling diagnostic measures the arrival time jitter of the infrared pump-probe laser pulse in respect to the electron bunch of the FEL. Here, the electron arrival time is encoded spatially into the laser pulse profile and readout by an intensified camera. In this paper we report about the improvement of the temporal resolution of pump-probe experiments on gaseous and solid targets using the arrival time data acquired by the described EO-diagnostic.
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| WEPC22 | Synchronization of a 3GHz Repetition Rate Harmonically Mode-Locked Fiber Laser for Optical Timing Applications | feedback, polarization, controls, linac | 358 | ||
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We have successfully stabilized a 3GHz Harmonically Mode-Locked fiber ring laser by a PLL feedback control of the cavity length to reduce the pulses RMS timing jitter. The laser cavity is composed of all PM fibers and components to eliminate polarization instabilities and to reduce the vibration sensitivity. The laser stability in terms of timing jitter was around 9ps in the range 10Hz-10MHz. Using a PLL scheme we synchronized the laser repetition rate to an ultra stable RF generator. The noise characteristics of the laser output were measured by observing the SSB noise spectra of the 1st harmonic, from 10Hz to the Nyquist frequency (1.5GHz). We have obtained a global reduction of fiber laser timing jitter value down to less than 100fs in the range 10Hz-10MHz; a complete overlapping between the laser and the RF generator spectral profiles in the loop bandwidth has been observed. An extended investigation has been performed to estimate the phase noise spectra and timing jitter up to 1.5GHz. By doing so, the contribution of the laser supermodes to the phase noise has been taken into account as well, to quantify the true value of the total RMS timing jitter of the optical pulses.
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| WEPC28 | Timing and Synchronization at the LCLS | electron, klystron, linac, controls | 373 | ||
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Timing and synchronization in the LCLS is a three tier process: At level 1 an event generator broadcasts timing fiducials to event receivers over a fiber network. Hardware and software triggers are created in the event receiver according to the digital pattern broadcast at 360 Hz by the event generator. Beam synchronous data acquisition driven by these triggers allows time-stamped acquisition of all diagnostic devices simultaneously on every pulse. Timing fiducials are phase synchronized to the low level RF reference system with 10 ps precision. Level 2 synchronization ensures that individual klystrons powering gun and accelerating sections remain within a few tenths of a degree S-band to the phase reference distribution scheme. The gun laser system is also phase locked to this reference to within 0.5 ps. Level 3 provides synchronization at the 10 fs level between the electron beam and pump-probe laser systems in the end station experiments. This will be achieved with electro-optic sampling of the electron bunch and by synchronizing the laser systems over a stabilized fiber distribution system. A fiber stabilization scheme is currently under test at Lawrence Berkeley Laboratory.
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