• T. Hara, H. Tanaka, K. Togawa
  RIKEN/SPring-8, Hyogo

The commissioning of the XFEL/SPring-8 facility is scheduled in the spring of 2011. Since the accelerator of XFEL/SPring-8 uses a thermionic gun with an 1 A initial beam current, the total bunch compression ratio reaches about 3000, which is one order higher than a photocathode system. For nonlinearity compensation in the bunch compression, two correction cavities are installed, which are operated at the same frequency as the linac and not at its higher-harmonic. A large compression ratio, particularly at the velocity bunching, results in larger projected parameters of the electron bunch compared to its slice values. The transverse optics of the accelerator is designed for the projected parameters using newly introduced linear formulation of the beam envelope including acceleration effects. The beam optics of the main linac and undulator sections are based on a FODO-like lattice and additional quadrupole magnets are installed at each chicane for dispersion correction. In this presentation, the XFEL/SPring-8 accelerator layout and its expected beam parameters are shown to achieve the 0.1 nm X-ray FEL.

• E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

With the present undulator (planar, period 2.73 cm, peak field 0.486 T) the minimum wavelength of 4.5 nm at FLASH is determined by the maximum electron beam energy of approximately 1.2 GeV. On the other hand, many perspective user applications require shorter wavelength radiation and circular polarization. In this paper we perform analysis of a helical afterburner for generation of short wavelength, helically polarized radiation. We consider two options, operation of the afterburner at the second (frequency doubler), and the fourth (frequency quadrupler) harmonics. Since even harmonic of the SASE FEL radiation are suppressed, there is no linearly polarized background radiation from the main undulator. Our simulations show that relatively high level of the radiation power can be achieved in the afterburner, about 60 MW in the frequency doubler, and about 5 MW in the frequency quadrupler.

• E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

This report deals with the analysis of the parameter space of the European XFEL. An impact of two potential changes is analyzed: consequences of the operation with low-emittance beams, and decrease of the driving energy of the accelerator from 17.5 to 14 GeV.

• E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

Wavelength range of high scientific interest refers to K- and L- absorption edges of magnetic elements which spans from 2.5 nm to 1.4 nm (500 - 900 eV). This wavelength range can be partially covered by SASE3 at the European XFEL, from 1.6 nm and down when operating at the nominal energy of 17.5 GeV. Operation at the reduced energy would allow to cover complete wavelength range of interest. Currently SASE3 is a planar device producing linearly polarized radiation. On the other hand, it is important to have circular polarization for experiments with magnetic samples. Solution of the problem of polarization is installation of an afterburner generating circularly polarized radiation. This can be helical afterburner or crossed-planar afterburner operating at the fundamental or double frequency. Here we present the results for a helical afterburner operating at the double frequency.

• R. Brinkmann, E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

With bright electron beams the full length of gap-tunable X-ray FEL undulators can be efficiently used to generate multiple x-ray beams with different independent wavelengths for simultaneous multi-user operation. We propose a betatron switcher and show that one only needs to install a compact fast kicker in front of an undulator without any modifications of the undulator itself. Different groups of bunches get different angular kicks, and for every group a kick is compensated statically (by corrections coils or moving quadrupoles) in a part of the undulator, tuned to the wavelength designated to the given group. As a generalization of the method of the betatron switcher, we briefly describe a scheme for pump-probe experiments.

• C. Behrens, C. Gerth
  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.

• L.-G. Wißmann, J. Breunlin
  Uni HH, Hamburg
• B. Schmidt, B. Steffen
  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.

• J. Breunlin, L.-G. Wißmann
  Uni HH, Hamburg
• B. Schmidt, B. Steffen
  DESY, Hamburg

The free electron laser in Hamburg (FLASH) underwent major modifications during a 6 months shutdown like the installation of a 3rd harmonic module, a seeding experiment (sFLASH) and a 7th accelerating module. Also instrumentation has been improved. A new compact electro-optic (EO) bunch length monitor has been installed downstream the first bunch compressor. At this position, the bunches are expected to have a length of about 1 ps, well suited for the resolution of an EO bunch length monitor with spectral decoding of the time (EO-SD). The setup uses a commercial ytterbium fiber laser, a compact optics inside the beam pipe designed at PSI (Switzerland) and a spectrometer with fast InGaAs line scan camera. These components, together with RF synchronisation unit and readout electronics, will be installed in the accelerator tunnel. Reliability, robustness and high uptime are key features as the EO monitor is meant to serve as permanent beam diagnostics. Here we report on the commissioning of the components and first experiments with the complete system.

• A.H. Lumpkin, M.D. Church, H.T. Edwards, S. Nagaitsev, M. Wendt
  Fermilab, Batavia

A superconducting (SC) RF Test Accelerator at the New Muon Lab (NML) is currently under construction at Fermilab. Its design goals include the replication of the pulse train proscribed for the International Linear Collider (ILC) and operations with the prototypic beam of the base RF unit. At 3 nC per micropulse and with 3000 micropulses per macropulse at a 5-Hz rate and at 750 MeV, a 40-kW beam would be generated. An RF photoelectric gun based on the PITZ-Zeuthen design will generate the beam which has a lower emittance of about 1-2 pi mm mrad when run at 1 nC or less per micropulse based on tests at Zeuthen. This beam quality is sufficient, when properly bunch compressed, to provide the driving beam for an extreme ultraviolet (EUV) and soft x-ray (SXR) self-amplified spontaneous emission (SASE) free-electron laser (FEL) or seeded FEL. Estimates for the gain length and output power have been calculated for wavelengths from 80 to 12 nm (at 1.5 GeV) using the simple scaling formula of M. Xie. This wavelength regime with 200-fs bunch lengths would complement the hard x-ray SASE FEL project at SLAC in the USA.

• J. Wu, Y.T. Ding, P. Emma, Z. Huang, H. Loos, M. Messerschmidt
  SLAC, Menlo Park, California
• E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

For a SASE-FEL, the FEL pulse energy fluctuates from shot to shot, because the lasing process starts up from shot noise. When operating in the exponential growth regime, the radiation exhibits the properties of completely chaotic polarized light. Hence, the probability distribution of the FEL pulse energy follows a gamma distribution. Based on the measurement of such a distribution function, one can calculate the average number of ‘degrees of freedom’ or ‘modes’ in the radiation pulse. Thus, one can measure the FEL pulse temporal duration. In this paper, we report experimental results at LCLS. Measurements are conducted for both nominal charge (250 pC) and low charge (20 pC) cases. For both cases, results are obtained for different undulator lengths and various electron peak current settings.

• Y.T. Ding, Z. Huang
  SLAC, Menlo Park, California
• S.A. Ocko
  MIT, Cambridge, Massachusetts

The Linac Coherent Light Source has achieved stable operation at x-ray wavelengths of 20-1.2 Angstrom with peak brightness many orders of magnitude beyond conventional synchrotron sources. Understanding transverse coherence properties of such a SASE source is of great practical importance for user experiments. Based on a fast Monte Carlo algorithm, we present numerical analysis of the LCLS coherence properties for the simulated radiation fields at different wavelengths and bunch charges.

• H.-S. Kang, S.H. Nam
  PAL, Pohang, Kyungbuk

Pohang Accelerator Laboratory (PAL) is proposing an X-ray free-electron laser facility that is designed to generate 0.1-nm wavelength coherent X-ray by using self-amplified spontaneous emission mechanism. A 10-GeV electron linear accelerator is required to generate high brightness electron beam with 0.2 nC charge, normalized emittance of 0.5 um-rad, and peak current of over 2.66 kA in order to reduce the required length of undulator for saturation below 60 meters. The radiation that is coherent and a few tens of femto-second long will cover the hard X-ray (0.1 ~ 1 nm) and the soft X-ray in the ranges of 2~ 5 nm. Advanced X-ray free-electron laser concepts are also being considered in the design: the self-seeded operation for narrow band spectrum as well as the attosecond X-ray pulse generation using the energy modulation of electron beam by optical laser beam. The baseline design of femtosecond X-ray generation for PAL-XFEL as well as challenges toward attosecond X-ray pulse generation will be presented.

• S. Reiche, B. Pedrini
  PSI, Villigen

The proposed SwissFEL project is an X-ray Free-Electron Laser, which operates down to a wavelength of 1 Ångstrom. In comparison to other XFELs (LCLS, SCSS and European XFEL) SwissFEL has the lowest beam energy of 5.8 GeV. Therefore a short period in vacuum undulator (15 mm) and a low beam emittance is required for maximum overlap between the electron beam and the fundamental FEL mode and a sufficient degree of transverse coherence at the saturation point. We present the numerical analysis of the radiation field properties along the undulator with an emphasis on the degree of coherence at saturation and undulator exit.

• J.P.M. Beijers, S. Brandenburg, K. Eikema, R. Hoekstra, S. Hoekstra, K. Jungmann, T. Schlathoelter, R.G. Timmermans, L. Willmann
  KVI, Groningen
• F. Bijkerk
  FOM, Utrecht
• O.J. Luiten
  TUE, Eindhoven
• B. Noheda, T.T. Palstra, P. Rudolf, P.H.M. van Loosdrecht
  RUG, Groningen

We outline our plans to construct a soft X-ray FEL facility at KVI, University of Groningen, The Netherlands. This new facility will be based on a 2.6 GeV normal-conducting electron linac followed by an undulator and will produce X-ray laser light with wavelengths downto 0.5 nm. The electron linac will be driven by a RF photo-injector and X-band acceleration structures based on CLIC developments with an acceleration gradient of 100 MeV/m. Various techniques will be implemented to also establish longitudinal coherence. The entire length of the FEL will be on the order of 100 meters. The facility is meant as a international user facility with a strong contribution of local AMO, material science and biochemistry groups. The design and construction will be a collaborative effort with contributions from different (inter)national research groups.