• M.-E. Couprie, M. LABAT
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• B. Carre, D. Garzella, G. Lambert
  CEA/Saclay, Gif-sur-Yvette
• O.V. Chubar, A. Loulergue, L. Nahon
  SOLEIL, Gif-sur-Yvette
• M. Jablonka, F. Meot, A. Mosnier
  CEA/DSM/DAPNIA, Gif-sur-Yvette
• J.-R. Marques
  LULI, Palaiseaux
• P. Monot
  CEA/DSM, Gif-sur-Yvette
• J.-M. Ortega
  LURE, Orsay
• A. Rousse
  LOA, Palaiseau

ARC-EN-CIEL (Accelerator-Radiation for Enhanced Coherent Intense Extended Light), the French project of a fourth generation light source aims at providing the user community with coherent femtosecond light pulses covering from UV to soft X ray. It is based on a CW 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches with a high repetition rate. The FEL is based on in the injection of High Harmonics in Gases in a High Gain Harmonic Generation scheme, leading to a rather compact solution. The produced radiation extending down to 0.8 nm with the Non Linear Harmonic reproduces the good longitudinal and transverse coherence of the harmonics in gas. Optional beam loops are foreseen to increase the beam current or the energy. They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges and a FEL oscillator in the 10 nm range. An important synergy is expected between accelerator and laser communities. Indeed, electron plasma acceleration will be tested for possible future compact electron beam sources for Xray FEL. Fs hard X ray can also be produced by Thomson Scattering. An overview of the user scientific case will also be given.

• I.S. Ko
  PAL, Pohang, Kyungbuk

Pohang Accelerator Laboratory (PAL) has recently launched a new XFEL project based on SASE technology. This PAL-XFEL will utilize the existing 2.5 GeV injection linac to the storage ring by upgrading its energy up to 3.7 GeV initially and possibly up to 4.5 GeV later on. The wavelength covers up to 0.18 nm when the electron beam energy is 4.5 GeV. In-vacuum undulator will be used to generate FEL lasing. Overall design philosophy and some details will be presented.

• W. Decking
  DESY, Hamburg

X-ray Free-Electron Lasers facilities are planned or already under construction around the world. This talk covers the X-Ray Free-Electron Lasers LCLS (SLAC), European XFEL (DESY) and SCSS (Spring8). All aim for self-amplified spontaneous emission (SASE) FEL radiation of approximately 0.1 nm wavelengths. The required excellent electron beam qualities pose challenges to the accelerator physicists. Space charge forces, coherent synchrotron radiation and wakefields can deteriorate the beam quality. The accelerator physics and technological challenges behind each of the projects will be reviewed, covering the critical components low-emittance electron gun, bunch-compressors, accelerating structures and undulator systems.

• H. Ogasawara, D. Nordlund
  SLAC, Menlo Park, California
• A. Nilsson
  New Affiliation Request Pending, Menlo Park, California

The microscopic understanding of surface chemistry requires a detailed understanding of the dynamics of elementary processes at surfaces. The ultrashort electron pulse obtained in the linear accelerator to feed the FEL can be used for generation of coherent synchrotron radiation in the low energy THz regime. With the current parameters for LCLS this corresponds to radiation with energy corresponding to excitations of low-energy vibrational modes of molecules on surfaces or phonons in substrates. The coherent radiation can coherently manipulate atoms or molecules on surfaces. In this respect a chemical reaction can be initiated by coherent atomic motion along a specific reaction coordinate. Since the THz radiation is generated from the same source as the FEL radiation full-time synchronization for pump-probe experiments will be possible. The possibility to perform time-resolved X-ray Emission Spectroscopy (XES) and X-ray Photoelectron Spectroscopy (XPS) measurements as a probe of chemical dynamics is an exciting prospect. The combination of THz and soft x-ray spectroscopy could be a unique possibility for low repetition FEL facilities for ultrafast surface chemistry studies.

• R. Tatchyn
  SLAC, Menlo Park, California

The temporal resolution of pump-flash interactions in the ultrashort (fs-as) regime is limited by the characteristic time constants of the excited states in the detector material. If the relaxation time constant is appreciably longer that the time interval between the pump and probe signals the response of the detector material to the probe represents a temporal convolution of the pump and probe responses, setting a lower limit on the resolution to which the interval between the two pulses can be measured. In most of the solid state ultrafast detection schemes that are being considered for the ultra-short pulse x-ray sources under current development at SLAC and elsewhere the characteristic time constants are related to the bound states of the atoms comprising the material or to the relaxation times of phase transitions or charge carrier populations of the lattice, setting a probable lower limit on the attainable resolution on the order of ~0.1 ps. In this paper we consider a novel detection principle predicated on the excitation of specially prepared unbound states in an ionized plasma and estimate its potential for extending the lower limit of resolution into the as regime.

• W.B. Colson, R. Vigil, T. Voughs
  NPS, Monterey, California

Funding: JTO, ONR, NAVSEA

Twenty-eight years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are listed and discussed.

• O. Williams, A. Doyuran, R.J. England, C. Joshi, J. Lim, J.B. Rosenzweig, S. Tochitsky, G. Travish
  UCLA, Los Angeles, California

An Inverse Compton Scattering (ICS) experiment investigating the polarized harmonic production in the nonlinear regime has begun which will utilize the existing terawatt CO2 laser system and 15 MeV photoinjector in the Neptune Laboratory at UCLA. A major motivation for a source of high brightness polarized x-rays is the production of polarized positrons for use in future linear collider experiments. Analytical calculations have been performed to predict the angular and frequency spectrums for various polarizations and different scattering angles. Currently, the experiment is running and we report the set-up and initial results. The advantages and limitations of using a high laser vector potential, ao, in an ICS-based polarized positron source are expected to be revealed with further measurement of the harmonic spectrum and angular characteristics.

• T. Tanaka
  RIKEN Spring-8, Hyogo
• T. Bizen, D. Iwaki, X. Marechal, T. Seike, R. Tsuru
  JASRI/SPring-8, Hyogo
• T. Hara, H. Kitamura
  RIKEN Spring-8 Harima, Hyogo

In-vacuum undulators are now widely used in lots of SR facilities to provide highly-brilliant hard x-rays not only in large-scale facilities such as SPring-8, ESRF and APS, but also in medium-scale facilities with an electron energy up to 3 GeV. In addition, the SCSS (SPring-8 Compact SASE Source) project is going to adopt the in-vacuum undulator not only for reducing the electron energy to achieve angstrom X-ray FEL but also for commissioning and alignment of components in the undulator line that takes advantage of variable vacuum gap (physical aperture for the electron beam). In this talk, overview of technologies required for development of the in-vacuum undulator will be presented together with practical examples. In addition, ongoing R&Ds at SPring-8 (cryogenic undulator, in-situ field measurement system) will be described in brief.

• J. Pflueger
  DESY, Hamburg

The undulator systems for the European XFEL project will produce 0.1nm radiation. Their length will exceed 200m. they will be segmented into 40-50 segments. There will be very demanding requirements on the performance of the undulator segments. The concept for building these systems will be explained in detail. This includes drive systems, magnet structures, control systems, phase shifter and othe components in the intersections as well. An important role plays the photon diagnostic station which is foreseen for each SASE FEL beam line. It can be used for steering the beam through the undulator line, for precision gap tuning of individual undulator segments and for precise phase matching of neighbouring devices. An important role plays the interaction with the undulator control system.

• B.W. Adams
  ANL, Argonne, Illinois

Funding: U.S. Department of Energy, Office of Basic Energy Sciences under contract W-31-109-ENG-38

A way is proposed to obtain intense infrared/visible light from an electron bunch in an x-ray free-electron laser in femtosecond synchronism with the x-rays themselves. It combines the recently proposed technique of emittance slicing in a free-electron laser with transition undulator radiation (TUR). The part of the electron bunch that is left unspoiled in the emittance slicing process is the source of both coherent x-rays and of coherent TUR at near-infrared wavelengths. An extension of the concept also exploits the fact that the electrons that participate in the free-electron lasing process lose a significant part of their energy.

• G. Dattoli, A. Renieri
  ENEA C.R. Frascati, Frascati (Roma)

The existing soft and hard X-Ray FEL Projects are discussed, along with the underlying design and technological strategies. We consider two main categories: large facilities, which will involve the joint efforts of big laboratories and will take benefit from the heritage of high energy Physics facilities and smaller devices, which are aimed at exploiting high quality accelerators with modest e-beam energy to reach shorter wavelengths with alternative schemes. We will discuss advantages and drawbacks of the different conceptions and make an outlook to the future developments, with particular attention to combinations of different solutions like exotic undulators, seeding and so on, aimed not only at improving X-ray beam qualities but also at reducing device complexity and cost.

• A.A. Shcherbakov, V.P. Androsov, E.V. Bulyak, A. Dovbnya, I.V. Drebot, P. Gladkikh, V.A. Grevtsev, Yu.N. Grigor'ev, A. Gvozd, V.A. Ivashchenko, I.M. Karnaukhov, V.P. Kozin, V. Lapshin, V.P. Lyashchenko, V. Markov, N.I. Mocheshnikov, V.B. Molodkin, A. Mytsykov, I.M. Necklyudov, F.A. Peev, A.V. Rezaev, A. Shpak, V.L. Skirda, V. Skomorokhov, Y.N. Telegin, V.I. Trotsenko, A.Y. Zelinsky, O.D. Zvonarjova, N. kovalyova
  NSC/KIPT, Kharkov
• A. Agafonov, A.N. Lebedev
  LPI, Moscow
• J.I.M. Botman
  TUE, Eindhoven
• R. Tatchyn
  SLAC, Menlo Park, California

The sources of the X-rays based on Compton scattering of intense Nd:YAG laser beam on electron beam circulating in a storage ring with beam energy 43 - 225 MeV is under construction in NSC KIPT. In the paper the progress in development and construction of Kharkov X-ray generator NESTOR is presented. The current status of the main facility system design and development are described. New scheme and main parameters of injection system are presented. The facility is going to be in operation in the middle of 2007 and generated X-rays flux is expected to be of about 10(13) phot/s.

• S.-H. Park, Y. Cha, Y.U. Jeong, B.C. Lee, K. Lee
  KAERI, Daejon
• S.V. Miginsky
  BINP SB RAS, Novosibirsk

The KAERI SC RF linac with one 352 MHz cryomodule is routinely operating at 10 MeV. The maximum accelerating gradient achieved so far is about 7.7 MV/m and is expected to increase up to 9 MV/m, if thermal loss and/or vibration instability is sufficiently suppressed. As a next step, we plan to generate Compton X-rays using external lasers at the straight section, just after the SC linac. This beamline will be relocated to downstream next to undulator beamline for a FEL, when the recirculating beamline is built. In this presentation, we estimate the parameters of Compton X-rays at a given system and suggest the new scheme to increase the flux, or to generate fs X-ray pulses using electron beams with a few tens ps pulse duration, using an intense ultra-short laser. We discussed a coherent condition for Relativistic Nonlinear Thomson Scattered (RNTS) radiation (or Nonlinear Compton Scattered radiation).

• V. Petrillo, C. Maroli
  Universita' degli Studi di Milano, MILANO
• A. Bacci, L. Serafini
  INFN-Milano, Milano
• M. Ferrario
  INFN/LNF, Frascati (Roma)

Funding: Università degli Studi di MIlano-INFN Via Celoria,16 MIlano (Italy)

Collective effects in the radiation emission process via Thomson back-scattering of an intense optical laser pulse by high brightness electron beams are analyzed. The micro-bunching of the electron beam on the scale of the emitted radiation wavelength and the consequent free-electron-laser instability may enhance significantly the total number of emitted photons. Scalings of the radiation properties, both in the collective and in the incoherent spontaneous regime, versus laser and electron beam parameters are discussed. Transverse effects due to radiation diffraction, finite emittance of the beam, and transverse distribution of the laser energy are studied.

• R. Kuroda
  AIST, Tsukuba, Ibaraki
• H. Hayano, J.U. Urakawa
  KEK, Ibaraki
• K. Hidume, M. Kawaguchi, S. Minamiguchi, R. Moriyama, T. Saito, K. Sakaue, M. Washio
  RISE, Tokyo
• S. Kashiwagi
  ISIR, Osaka

Funding: This research was partially supported by a High Tech Research Project of MECSST 707, a Grant-in-Aid for Scientific Research (B) 16340079, a Grant-in-Aid for Young Scientists (B) 16760049.

A compact soft X-ray source is required in various research fields such as material and biological science. The laser undulator based on Compton backward scattering has been developed as a compact soft X-ray source for the biological observation at Waseda University. It is performed in a water window region (250eV - 500 eV) using the interaction between 1047 nm Nd:YLF laser (10ps FWHM) and about 5 MeV high quality electron beam (10ps FWHM) generated from rf gun system. The range of X-ray energy in the water window region has K-shell absorption edges of Oxygen, Carbon and Nitrogen, which mainly constitute of living body. Since the absorption coefficient of water is much smaller than the protein's coefficient in this range, a dehydration of the specimens is not necessary. To generate the soft X-ray pulse stably, the electron beam diagnostics have been developed such as the emittance measurement using double slit scan technique, the bunch length measurement using two frequency analysis technique. In this conference, we will report results of beam beamdiagnostics experiments, soft X-ray generation and our future plan.

• A.H. Lumpkin, W. Berg, N. Sereno, B.X. Yang, C. Yao
  ANL, Argonne, Illinois
• D.W. Rule
  NSWC, West Bethesda, Maryland

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

The challenge of providing nonintercepting beam diagnostics that address transverse parameters such as beam size and divergence in a linear transport line has been met. We have successfully used near-field imaging of optical diffraction radiation (ODR) from a 7-GeV electron beam passing near a single edge of a conducting screen to obtain beam size for the first time [1]. In this case appreciable visible wavelength ODR is emitted for impact parameters of 1 to 2 mm, values that are close to gamma times the reduced observation wavelength. We have now upgraded our imaging system to include an intensified camera; selectable bandpass filters, neutral density filters, and polarizers; a steering mirror; and an optical lens setup that provides either near-field or far-field imaging. The ODR has been obtained in both the single-edge mode and aperture mode with a single pulse of 3.3 nC. Beam-size resolution in the 20-50 micron regime is projected while beam position resolution to 10 microns with a smaller beam and higher optical magnification should be feasible with near-field imaging. Applications to high-energy accelerators that drive x-ray FELs or energy recovering linacs for light sources should be possible.

[1] A.H. Lumpkin et al., "First Near-Field Imaging of Optical Diffraction Radiation Generated by a 7-GeV Electron Beam,” submitted to Phys. Rev. Lett., May 4, 2005.

• A. Winter, H. Schlarb
  DESY, Hamburg
• dc. Cheever, J. Chen, F.O. Ilday, F.X. Kaertner, J. Kim, D. Wang, T. Zwart
  MIT, Middleton, Massachusetts
• P. Schmuser
  Uni HH, Hamburg

X-ray pulses with a pulse duration of down to 30 fs FWHM or even sub-fs are desired for various experiments planned at next generation free electron lasers, such as the European XFEL. A synchronization of the probe system in the experimental area to the x-ray pulses with stability on the order of the pulse width is highly desirable for these experiments. This requirement translates to distributing an ultra-stable timing signal to various subsystems of the machine and the experimental area to provide synchronization at the fs level over distances of up to several kilometers. A few years ago, a timing and synchronization system providing stability to the fs level was unthinkable. Recent advances in the field of ultra-short pulse lasers have made optical synchronization systems with such a precision feasible. This talk will focus on an optical approach using a train of ultra-short pulses distributed through optical fiber links. The timing information is contained in the precise repetition rate. First results of such a system operating in an accelerator environment will be reported.