DESY, Hamburg
The capability of the free-electron laser (FEL) user facility FLASH at DESY was expanded by several upgrades during the shutdown in 2009/2010. A key extension is the installation of a third-harmonic (3.9 GHz) RF system for the linearization of the longitudinal phase space in front of the bunch compressors. In order to control the bunch compression and make full use of the third-harmonic RF system, a new diagnostic section for the measurements of sliced bunch parameters directly in front of the undulators was designed and commissioned. In this paper, we describe the beam imaging systems and their optical performance. The achievable resolution of both time and energy is shown and compared to the design values. First measurements of the linearized longitudinal phase space with high resolution are presented.
Uni HH, Hamburg
DESY, Hamburg
The Free Electron Laser FLASH has been upgraded during winter 2009/10. Amongst other components, a third harmonic module operating at 3.9 GHz (ACC39) has been installed. Together with the energy chirp induced by off-crest operation, it allows for a linearisation of the longitudinal phase space, leading to a uniform compression of the electron bunch with final bunch lengths of 150 μm rms. In contrast to the old non-linear compression scheme, peak current and bunch length are extremely sensitive to the phases of ACC39 and ACC1 and have to be monitored continuously. The foreseen bunch length is within the resolution of electro-optic spectral decoding methods. An ytterbium fibre laser system in combination with a 175 μm thick GaP crystal is used to achieve a good match between the electric field phase velocity and the laser pulse group velocity in the electro-optic crystal. This ensures a large modulation of the polarisation of the chirped laser pulse in the EO crystal. The information on the electron bunch length carried by the laser pulse is decoded in a spectrometer and read out with an InGaAs line scan camera.
Mesa+, Enschede
ELETTRA, Basovizza
UT-MESA+ OS, Enschede
FERMI@Elettra is a free electron laser user facility currently under construction at Sincrotrone Trieste S.C.p.A. Its goals are to produce high-brightness, ultra-short pulses with wavelengths ranging from 100 - 20 nm (FEL1) and 40 - 4 nm (FEL2) and deliver these pulses to a wide range of user experiments. Currently, FERMI uses the HGHG technique to improve both the stability and the longitudinal and spectral coherence of the output of the laser. Direct seeding of FEL1 using a High Harmonic (HH) source is also foreseen and allows a direct comparison between the two seeding methods. For an HH source, we will use neutral atoms in a hollow waveguide in combination with coherent control of the drive laser pulse to provide wavelength tuning as well as selective enhancement of the harmonic orders. For direct seeding of FEL 2 we propose HH generation from ions in a modulated plasma waveguide. The ions allow generation of shorter wavelengths, while the modulated plasma waveguide provides a long interaction length as well as quasi-phase matching for boosting the output energy of the source. In this paper, we will present the HH source for FEL1 as well as a concept for HH seeding of FEL2.
Uni HH, Hamburg
DESY, Hamburg
Since 2004, the free-electron laser FLASH at DESY has operated in the Self-Amplified Stimulated Emission mode (SASE), delivering gigawatt pulses with wavelengths between 6.5 nm and 40 nm in the femtosecond domain. In 2009, DESY installed an additional radiofrequency module for controlling the phase space of the electron bunches that gives the possibility to generate bunches with high peak currents (~kA), but ten times larger pulse durations (~250 fs) compared to the previous configuration. The relaxed timing requirements of the new configuration make it possible to externally seed FLASH with high-order harmonics of an optical laser below 40nm generated in a gas target (sFLASH). Because in this case amplification is triggered within the seed pulse length instead of starting from shot-noise as in the SASE process, spikes in the temporal/spectral pulse profiles should be absent and the temporal jitter should be eliminated. In this contribution the present status of the sFLASH photon diagnostics including first commissioning will be discussed.
Uni HH, Hamburg
DESY, Hamburg
PSI, Villigen
DELTA, Dortmund
The free-electron laser facility FLASH at DESY (Hamburg) was upgraded during a five month shutdown in winter 2009. Part of this upgrade was the installation of a direct seeding experiment in the XUV spectral range. Beside all components for transport and diagnostics of the photon beam in and out of the accelerator environment, a new 10m long variable gap undulator was installed upstream of the existing FLASH undulator system. The seed pulses are generated within a noble gas jet by focusing 40 fs long Ti:Sa laser pulses into it resulting a comb of higher harmonics. In the first phase of the experiment the 21st harmonic of the 800nm drive laser will be used to seed the FEL process. The commissioning of the experiment has started in April and the first results are expected after the FLASH commissioning period mid of summer 2010. The experimental setup and the commissioning procedures as well as first result will be presented.
PSI, Villigen
DESY, Hamburg
Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub picosecond) electron bunches. A prototype of a compact EO bunch length monitor system for the future SwissFEL facility was designed and built at PSI. Its core components are an optical setup including the electro optically active crystal and an Ytterbium fiber laser system which emits broadband pulses at 1050nm. The new monitoring system is described in detail and first experimental results from the SLS injector are presented.
Fermilab, Batavia
It is recognized that beam manipulations such as a flat beam transformation followed by an emittance exchange (EEX) could support a high gain free-electron laser (FEL) push for shorter wavelengths. An ongoing program on demonstrating the exchange of transverse horizontal and longitudinal emittances at the Fermilab A0 photoinjector (A0PI) has benefited recently from the upgrade of several of the key diagnostics stations. The use of an array of 50-micron wide slits to sample the phase spaces to measure divergences of less than 100 microradians resulted in 20 times smaller images with positions distributed over several mm. Improvements in the screen resolution term and reduction of the system depth-of-focus impact by using YAG:Ce single crystals normal to the beam direction will be described. On the longitudinal side, the requirements to measure small energy spreads (<10 keV) in the spectrometer and bunch lengths less than 500 fs dictated specifications. Upgrades to the Hamamatsu C5680 streak camera and the addition of the Martin-Puplett interferometer addressed the short bunch lengths. An example of the EEX tables will be presented.
NPS, Monterey, California
Niowave, Inc., Lansing, Michigan
Boeing Company, Seattle, Washington State
Stanford University, Stanford, California
The Naval Postgraduate School Beam Physics Laboratory, Niowave, Inc., and The Boeing Company have completed construction of a superconducting 500 MHz quarter-wave gun and photocathode drive laser system. This prototype gun went from conception to initial operation in just under one calendar year. Such rapid progress is due in part to the decision to develop the gun as a prototype, deliberately omitting some features, such as tuners and cathode loadlocks, desired for a linac beam source. This will enable validation of the basic concept for the gun, including high-charge bunch dynamics, as rapidly as possible, with lessons learned applied to the next generation gun. This paper presents results from initial testing of the gun, technical challenges of the prototype design, and improvements that would enhance capabilities in future versions of this novel design.
ELETTRA, Basovizza
The optics design of the first bunch compressor area in the FERMI@elettra linac is presented. Several constraints on the Twiss parameters are set by the preservation of beam quality in the first magnetic compressor, the optimization of diagnostics performance, the collimation process and the beam matching to the downstream lattice. A compact multi-purpose arrangement of magnetic and diagnostic elements is presented that, in principle, satisfies several different needs over a total length of 14m.
DESY, Hamburg
Uni HH, Hamburg
At FLASH, UV and soft X-Ray pulses with durations in the order of 10 fs are generated. To fully exploit the opportunities provided by these short laser pulses, an optical synchronization system provides the possibility to synchronize external lasers and stabilize the electron bunch arrival time with 10 fs precision. A seeded free-electron-laser (FEL) section, called sFLASH, is installed upstream of the existing SASE undulators. After higher-harmonic-generation, the femtosecond seed laser pulse needs to be temporarily and spatially overlapped with the electron bunch. Furthermore, for time-resolved pump-probe experiments, using an experimental laser and the FEL pulse, either of sFLASH or of the ordinary SASE process, the synchronization between pump and probe laser pulses is crucial. While the best performance for synchronizing these lasers within 10 fs will be achieved by using an optical cross-correlator, in this paper we present a precursor that relies on an RF-based locking mechanism. The setup includes a coarse and a fine phase measurement between the laser pulses of the reference and the synchronized system after their conversion to an RF signal.
Uni HH, Hamburg
DESY, Hamburg
The optical synchronization system of the free-electron laser in Hamburg (FLASH) is based on the stabilized pulse-train distribution of a passively mode-locked laser. This master laser oscillator is based on erbium-doped fiber technology and is built in a σ-configuration, enabling passive mode-locking through nonlinear polarization evolution. Recently, a commercial laser system has been installed in addition to the existing laser. Besides maintenance-free operation, this SESAM-based laser shows an even lower timing jitter, enabling a tighter synchronization to the accelerator's RF reference. In this paper we report on the commissioning, the characterization and the long-term stabilty of the new laser system, as well as on the performance of the laser with the existing pulse-train distribution scheme and optical front-ends of the synchronization system in comparison to the old one.
ELETTRA, Basovizza
DEEI, Trieste
The cavity Beam Position Monitor (BPM) is a fundamental beam diagnostic instrument for a seeded FEL, like FERMI@Elettra. It allows the measurements of the electron beam trajectory in a non-destructive way and with sub-micron resolution. The high resolution cavity BPM relies on the excitation of the dipole mode that is originated when the bunch passes off axis in the cavity. In this paper we present the prototype of cavity BPM developed for the FERMI@Elettra facility. The RF parameters of the cavities have been determined by means of Ansoft HFSS; while using the CST Particle Studio the level of the output signals from the cavities have been also estimated. Furthermore, the design of the RF frontend for the acquisition and conditioning of the signals from the BPM cavities is presented as well. The prototype has been succesfully installed in the FERMI Linac during the last commissioning phase and preliminary results with the electron beam are also presented.
SLAC, Menlo Park, California
This talk is about the experience gained in commissioning the X-Ray diagnostics at the LCLS over the past year. Though the designs of the diagnostics are based largely on technology from synchrotron light sources, the high intensity and high brightness of LCLS X-Ray beam are well outside of the range of parameters for synchrotron light sources, so the diagnostics must perform in essentially new territory. It turned out that some capabilities of the diagnostics were not utilized because the FEL beam was so strong right from the beginning. On the other hand, in some cases the diagnostics were used to perform novel measurements that were not envisioned in the original design. The talk will cover each of the diagnostics systems, how it performed, and what it told us about the FEL beam.
ELETTRA, Basovizza
The advent of FEL sources has brought new possibilities for experimentalists performing measurements that are challenging in terms of time resolution, flux, coherence, and so on. One of the most important points, however, is the capability of characterizing the FEL photon beam so to determine the different parameters of each pulse hitting the system under investigation. For this reason it is mandatory to realize diagnostics sections along FEL user facilities recording beam pulse-resolved features such as the absolute intensity, the energy spectrum, the beam position, the time arrival, and the wavefront. For other parameters like the coherence and the pulse length, on the other side, a direct and online detection is not possible. At FERMI@Elettra, the Italian FEL facility, a dedicated diagnostic section called PADReS (Photon Analysis Delivery and Reduction System) will be installed after the undulatory' exit, and it will serve as a source of pulse-resolved informations for end-users. In this talk the instruments that are part of typical FEL diagnostic sections will be described using PADReS as a real example to see the roles of the different diagnostic tools.
SINAP, Shanghai
Abstract: The Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is designed and most equipment of accelerator is performed and operating. In this paper, we present the instrumentations on the proof-of principle experiment of FEL physics study. We discuss diagnostic techniques for testing photo cathode RF gun and magnetic bunch compressors, and undulator sections including a modulator undulator. The multiple alignment-laser station is used for pop-in equipments alignment in the undulators. We also investigated the observed e-beam size using OTR and YAG in the cameras using the near-field focus. Network camera and network techniques are used on monitor components. It will be described in this report also.
* SDUV-FEL is at SINAP in Shanghai.