• D. Garzella
  CEA/Saclay, Gif-sur-Yvette
• C. Bruni
  PhLAM/CERCLA, Villeneuve d'Ascq Cedex
• M.-E. Couprie
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• G. De Ninno, B. Diviacco, M. Marsi, M. Trovo
  ELETTRA, Basovizza, Trieste

The ELETTRA Storage Ring FEL succeded in operating in the Ultraviolet range, around 350 nm, with an etalon Fabry Perot inserted in the optical cavity. The high vacuum vessel, integrating a totally motorized control system for the principal degrees of freedom of the silica plate, allowed to obtain the laser oscillation, showing a reduction of the spectral linewidth by more than an order of magnitude. Temporal analysis by a double sweep streak camera showed also a broadening of the temporal pulse width. These major results are here exposed and compared with a numerical analysis and the Storage Ring FEL dynamics theory.

• M. Labat, M.-E. Couprie
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• M. Hosaka, M. Katoh, A. Mochihashi
  UVSOR, Okazaki
• Y. Takashima
  Nagoya University Graduate School of Engineering, Nagoya

Storage Ring Free-Electron Laser dynamics and behaviour can be explored versus the detuning, i.e. a small difference between the frequencies of revolution of the electron bunches, and of the optical pulse circulating into the optical cavity. In fact, it provides situations ranging from the maximum initial gain over losses conditions to threshold ones. Systematic measurements of the UVSOR2 detuning curves have been performed. A complete detuning curve gives the intensity of the FEL versus the detuning. On such a plot, one can distinguish five distinct zones: three corresponding to continuous modes of emission for the FEL, and two pulsed modes. Each zone can then be described with its width and period for the pulsed modes. Streak camera also provides a full characterisation of the FEL versus detuning: position of the centre of mass of the laser, bunch lengthening. The energy spread is deduced from the electron beam transverse sizes. The analysis of the FEL behaviour versus detuning is compared with simulations performed with LAS. The detuning behaviour is then illustrated under different cases (current, control of the pulsed zone, chromatic or achromatic electron-beam optics).

• S. Bielawski, C. Szwaj
  PhLAM/CERCLA, Villeneuve d'Ascq Cedex
• M.-E. Couprie, M. Labat, G. Lambert
  CEA/Saclay, Gif-sur-Yvette
• M. Hosaka, M. Katoh, A. Mochihashi
  UVSOR, Okazaki
• Y. Takashima
  Nagoya University Graduate School of Engineering, Nagoya

FEL oscillator operation is known to be strongly affected by instability issues. Recently, it has been demonstrated experimentally and theoretically that the "macropulse instabilities" which affects the laser pulse train enveloppe can be suppressed using feedback control techniques. From a detailed experimental and numerical study, we show here that "hidden" dynamical evolutions remain in controlled FELs. Though not visible in the evolution of the pulse enveloppe, this affects the internal pulse shape evolution, and thus the FEL spectrum and coherence properties. The experiments are performed on the UVSOR FEL. The modeling is made using the field master equation [1] based on the Dattoli/Elleaume approach. The shochastic nature of spontaneous emission is taken into account, and appears as an essential ingredient.

[1] S. Bielawski, C. Bruni, D. Garzella, G.-L. Orlandi and M.E. Couprie, Phys. Rev. Lett. to appear.

• E. Allaria, G. De Ninno
  ELETTRA, Basovizza, Trieste
• A. Antoniazzi, D. Fanelli
  Universita di Firenze, Florence
• F.T. Arecchi
  UNIFI, Sesto Fiorentino (FI)
• R. Meucci
  INOA, Firenze

We numerically investigate the effect of a delayed control method on the stabilization of the dynamics of the Elettra storage-ring free-electron laser in Trieste (Italy). Simulations give evidence of a significant reduction of the typical large oscillations of the laser intensity. Results are compared with numerical and experimental data obtained with a derivative feedback. The possibility of an experimental implementation of the proposed method is also discussed.

• F. Curbis, F. Curbis
  Universita degli Studi di Trieste, Trieste
• G. De Ninno
  ELETTRA, Basovizza, Trieste

Coherent harmonic generation can be obtained by means of frequency up-conversion of a high-power external laser focused into the first undulator of an optical klystron. The standard configuration is based on a single-pass device, where the seed laser is synchronized with an electron beam entering the first undulator of the optical klystron after being accelerated using a linear accelerator. As an alternative, the optical klystron may be installed on a storage ring, where it is normally used as interaction region for an oscillator free-electron laser. In this case, removing the optical cavity and using an external seed, one obtains a configuration which is similar to the standard one but also presents some peculiar characteristics. In this paper we investigate the possibility of harmonic generation using the Elettra storage-ring optical klystron. We explore different experimental set-ups varying the beam energy, the seed characteristics and the strength of the optical-klystron dispersive section. We also study the performance sensitivity to fluctuations of some beam parameters and the coherent/incoherent signal ratio for different harmonics. Numerical simulations are performed using different 3-D numerical codes.

• G. De Ninno, B. Diviacco, M. Trovo
  ELETTRA, Basovizza, Trieste
• A. Antoniazzi, D. Fanelli
  Universita di Firenze, Florence
• R. Meucci
  INOA, Firenze

The possibility of establishing and maintaining a stable operation mode of a storage-ring free electron laser finally resides in a deep understanding of the strongly coupled laser-electron dynamics. Such a dynamics may be affected by electron-beam instabilities whose origin can be traced back either to electromagnetic wake fields or to "external" perturbations (e.g. line-induced modulations, mechanical vibrations, etc.). This is the case of the Elettra storage-ring free-electron laser which is significantly affected by a 50-Hz perturbation of the electron beam density. We have developed a simple theoretical model which has been proved to be able to provide insight into the evolution of the laser intensity. In this framework, we have also proposed the possibility of utilizing a derivative closed-loop feedback to create or enlarge the region of stable signal. A feedback of this type has been implemented on the Elettra storage-ring free-electron laser. The obtained results, which fully confirm our predictions, are discussed in this paper.

• K. Hayakawa, Y. Hayakawa, K. Nakao, K. Nogami, T. Sakai, I. Sato, T. Tanaka
  LEBRA, Funabashi

Funding: "Academic Frontier" Project for Private Universities: matching fund subsidy from MEXT (Ministry of Educatin, Culture, Sports, Science and Technology), 2000-2004

In general, maximum gain and maximum power of a free-electron laser (FEL) oscillator are not simultaneously satisfied at an identical length of the optical resonator. Use of a short bunch electron beam, therefore, can cause a large fluctuation of gain and saturated power of the FEL due to only a small change in the resonator length. If the length of the resonator can be adjusted at the middle in the macropulse duration of the electron beam, both maximizing conditions will be satisfied simultaneously, which will result in a large FEL output power compared with a normal operation. Since it is difficult to change the length of the resonator during the macro pulse, modulation of the bunch interval has been attempted for the LEBRA FEL system by modulating the phase of the accelerating rf of the electron linac, which has an equivalent effect to change of the resonator length. The modulation of the rf phase has resulted in intensification of the output energy per macro pulse by approximately twice compared with that in normal operation, which is consistent with numerical simulation.

• M. Hosaka, M. Katoh, A. Mochihashi
  UVSOR, Okazaki
• S. Bielawski, C. Szwaj
  PhLAM/CERCLA, Villeneuve d'Ascq Cedex
• M.-E. Couprie
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• Y. Takashima
  Nagoya University Graduate School of Engineering, Nagoya

On the UVSOR-II storage ring upgraded in 2003, improved performance of the electron beam allowed a high power FEL lasing in the deep UV region: an out-coupled power of the FEL reached to 0.3 W in the wavelength around 250 nm. User application of the FEL is in progress now. This spring, we installed a new RF cavity whose accelerating voltage is three times higher than that of previous one. The commissioning was successfully carried out and the voltage reached the designed value. The bunch length of the electron beam becomes shorter and thus further improved performance of the FEL is expected. In the presentation, latest performance of the UVSOR-FEL will be reported. Meanwhile we are going to perform an experiment on higher harmonic generation using an external short pulse laser (Ti:Sa). The laser system will be soon installed and the experimental setup will be reported in the presentation.

• H. Yamada
  SLLS, Shiga

Funding: JSP

The photon storage ring (PhSR) is based on an exact circular synchrotron. Yamada and his colleague have successfully produced two synchrotrons [1,2]. Both have 0.156 m small electron orbit radius. One is the 20 MeV version for PhSR, and the other is the 6 MeV version for brilliant hard X-ray production. The brilliance of this machine is comparable to the large conventional SR source. These tabletop synchrotrons are realized by the special beam injection scheme using resonance in betatron motion. This scheme provides nearly 100% beam injection efficiency leading to 3 A accumulated beam current as 100 mA peak current is injected from 6 or 20 MeV microtron. The beam lifetime is an order of 10 ms, and we perform the injection at 400 Hz. Interesting feature is the 10μsecond order fast radiation damping that appears due to the residual gas [3]. We think that the radiation from electrons caused by the residual gas enhances the stochastic radiation damping. This technology is useful for the low energy synchrotron.

[1] Hironari Yamada, Nucl.Instrum.Methods in Phys. Res. B199、2003, p.509 [2] D. Hasegawa et al., AIP Conference Proc. 716 ed. by Hironari Yamada, (2004) p.166 [3] Hironari Yamada, Advances in Colloid and Interface Sci. 71-72 (1997) p. 371

• H. Ogawa, N. Sei, K.W. Watanabe, K. Y. Yamada, M.Y. Yasumoto
  AIST, Tsukuba, Ibaraki

Funding: This study was financially supported by the Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology, based on the screening and counseling by the Atomic Energy Commission, Japan.

At AIST, we have been making an effort to obtain FELs with an ultra-wide wavelength range from the vacuum ultraviolet (VUV) to the infrared (IR) on a compact storage ring NIJI-IV. Recently, performance of the NIJI-IV FEL was improved at the deep UV (DUV) around 200 nm and it became possible to make real-time observation of chemical reactions on the transition metal surfaces using the photoelectron emission microscopy (PEEM) combined with the DUV FELs. To observe dynamic behavior of the chemical reactions in detail, the FEL-PEEM system is being improved by optimizing experimental conditions. The performance of the system and the experimental results will be presented.

• N. Sei, H. Ogawa, K.W. Watanabe, K. Y. Yamada, M.Y. Yasumoto
  AIST, Tsukuba, Ibaraki

Funding: This work was supported by the Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Free electron lasers (FELs) are being developed in a broad wavelength region from the VUV to the IR with the compact storage ring NIJI-IV at AIST. In the DUV and VUV regions, the FEL is used as an intense light source for real-time surface observation with the photoelectron emission microscopy. To extend the application field of the NIJI-IV FEL, for example to the structural analysis of proteins, experiments to obtain FEL oscillations at the wavelength below 195 nm are going on. In addition, a 3.6-m optical klystron, ETLOK-III, for developing infrared FELs has been installed in the north straight section of the NIJI-IV. Fundamental and higher harmonic spontaneous emissions from the ETLOK-III were observed in the visible and near-infrared regions. It was expected that the FEL gain for the 3rd harmonics exceed 5%. In the presentation, we will report the recent results of the VUV and IR FEL experiments.

• G. De Ninno, E. Allaria, F. Curbis, M.B. Danailov, B. Diviacco, M. Marsi, M. Trovo
  ELETTRA, Basovizza, Trieste
• M. Coreno
  CNR - IMIP, Trieste
• S. Günster, D. Ristau
  Laser Zentrum Hannover, Hannover

Thanks to an intensive technological effort in the framework of the EEC Contract HPRI CT-2001-50025 (EUFELE), the European FEL at ELETTRA was able to break the previous record for the shortest wavelength of an FEL oscillator. Novel solutions were adopted for multilayer mirrors to allow FEL operation in the wavelength region between 160 and 190 nm, which is one of the main targets of the project. The characteristics of the FEL pulses measured at 176 nm (spectral profiles, high intensity, meV bandpass, MHz repetition rate) make it a competitive light source for spectroscopy, in particular for fluorescence studies in the VUV spectral range. Proof of principle experiments have been performed on different types of silica glasses, yielding information on the mechanisms of light absorption in this material.

• 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.

• P.P. Crooker, R.L. Armstead, J. Blau, O.E. Bowlin, W.B. Colson, R. Vigil, T. Voughs, B.W. Williams
  NPS, Monterey, California

Funding: JTO, ONR, NAVSEA

The short-Rayleigh length FEL configuration leaves the optical resonator near the cold-cavity stability limit. Studies show that the electron beam interaction stabilizes the optical modes and establishes limits to the vibrations of mirrors and the electron beam. Several types of vibrations are considered.

• K.S.B. Li, A. Adelmann, A. Anghel, R.J. Bakker, M. Boge, A.E. Candel, M. Dehler, R. Ganter, C. Gough, G. Ingold, S.C. Leemann, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, V. Schlott, A. Streun, A. Wrulich
  PSI, Villigen

The Paul Scherrer Institute (PSI) in Switzerland currently develops a Low-Emittance electron-Gun (LEG) based on field-emitter technology [1]. The target is a normalized transverse emittance of 5 10(-8) m rad or less. Such a source is particularly interesting for FELs that target wavelengths below 0.3 nm since it permits a reduction of the required beam-energy and hence, a reduction of the construction- and operational costs of X-ray FELs. That is, for the case that this initial low emittance can be maintained throughout the accelerator. Here we present a concept for a 0.1 nm X-FEL based on LEG, which can be located close to the Swiss Light Source (SLS). Special attention goes to the maintenance of the emittance during the process of acceleration and bunch-compression, in particular in the regimes where either space-charge forces or coherent-synchrotron radiation are of importance.

[1] R. Ganter et al, Proceedings of the 2004 FEL Conference, Trieste, Italy, p. 602 (2004)

• M.B. Danailov
  ELETTRA, Basovizza, Trieste
• F.O. Ilday, F.X. Kaertner
  MIT, Cambridge, Massachusetts

Laser systems will undoubtedly be one of the key factors determining the performance of VUV and X-ray FELs. In particular, harmonic generation scheme based FELs require at least three mutually synchronized solid-state laser systems: photoinjector laser, seeding laser, end station lasers. In addition, a laser heater is also included in recent FEL designs. It is therefore very important to consider the possibility of integrating these systems to a maximum possible degree. In this paper we consider a promising approach to the integration of the above specified laser systems for the FERMI@ Elettra FEL, based on the distribution of a fiber laser generated seed signal at 1550 nm. This signal, after further amplification and frequency doubling, is used as a seed for Ti:Sapphire amplifiers at the different locations. The paper presents a general layout of the system, the main pulse parameters (i.e. pulse energy and duration) needed in different parts of the system and discusses possible technical solutions

• L. Palumbo
  Rome University La Sapienza, Roma
• D. Alesini, M. Bellaveglia, S. Bertolucci, M.E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, D. Filippetto, V. Fusco, A. Gallo, A. Ghigo, S. Guiducci, M.  Migliorati, A. Mostacci, L. Pellegrino, M.A. Preger, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario
  INFN/LNF, Frascati (Roma)
• F. Alessandria, A. Bacci
  INFN/LASA, Segrate (MI)
• F. Broggi, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, M. Mauri, V. Petrillo, M. Rome, L. Serafini
  INFN-Milano, Milano
• L. Catani, E. Chiadroni, A. Cianchi, C. Schaerf
  INFN-Roma II, Roma
• F. Ciocci, G. Dattoli, A. Doria, F. Flora, G.P. Gallerano, L. Giannessi, E. Giovenale, G. Messina, P.L. Ottaviani, G. Parisi, L. Picardi, M. Quattromini, A. Renieri, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• P. Emma
  SLAC, Menlo Park, California
• M. Mattioli
  Universita di Roma I La Sapienza, Roma
• P. Musumeci
  INFN-Roma, Roma
• S. Reiche, J.B. Rosenzweig
  UCLA, Los Angeles, California

The first phase of the SPARX project, now funded by MIUR (Research Department of Italian Government), is an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. This project is the natural extension of the activities under development within the ongoing SPARC collaboration. The aim is the generation of electron beams characterized by an ultra-high peak brightness with a linear accelerator based on the upgrade of the existing Frascati 800 MeV LINAC and to drive a single pass FEL experiment in the range of 3-5 nm, both in SASE and SEEDED FEL configurations, exploiting the use of superconducting and exotic undulator sections. In this paper we discuss the present status of the collaboration.

• 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).

• H.-S. Kang, J. Choi, T.-Y. Lee
  PAL, Pohang, Kyungbuk

Funding: The Ministry of Science and Technology, Korea

PAL-XFEL has been designed to generate 0.3-nm SASE radiation with 3.7-GeV electron beam and 4-mm gap in-vacuum undulator. The requirement of energy spread in undulator is tighter than LCLS and EU-FEL. Laser beam heating to reduce the micro-bunching instability inevitably induces an increase of energy spread during the bunching process in bunch compressor. Two factors are contradictory, which should be compromised. Transverse higher modes have comparatively large growth rates which results in poor transverse coherency. Growth rates of transverse modes are calculated with different beam conditions.

• E.-S. Kim
  PAL, Pohang, Kyungbuk

We have quantitatively investigated effects of wakefields that are important for the controlling of short bunch length and small emittnace in X-ray FEL. We present the effects of coherent synchrotron radiation, linac geometrical wake in S-band and X-band linacs, space charge wake, resistive wall wake and roughness wake on the emittance and energy spread in the PAL-XFEL. The analytical results on the effects of the wakefields are also compared with the numerical simulation ones.

• E.-S. Kim, Y.J. Han, J.Y. Huang, S.J. Park
  PAL, Pohang, Kyungbuk

Longitudinal space charge wake is an important source that can generate microbunching instability at accelerator systems for X-ray free-electron laser. We present investigation to minimize gain of energy modulation due to the longitudinal space charge wakes that are caused at RF photocathode gun, two bunch compressors and linac at the PAL-XFEL, which include optimization of parameters for two bunch compressors and consideration of a laser heater. These studies are performd by using integral equation and numerical simulation methods. Design studies of a system for the laser heater are presented. We also show simulation results on effects of interaction between electron beam and laser.

• T.-Y. Lee, J. Choi, H.-S. Kang
  PAL, Pohang, Kyungbuk

PAL-XFEL is the newly announced SASE FEL project that is going to achieve 0.3 nm wavelength radiation with 3.7 GeV electron beam. To overcome the relatively low energy of 3.7 GeV, short period and small gap in-vacuum undulator will be adopted. Wake field effects of this in-vacuum undulator on the SASE process is studied in this paper.

• B.W.J. McNeil, G.R.M. Robb
  Strathclyde University, Glasgow
• C. Gerth
  DESY, Hamburg
• J.K. Jones, M.W. Poole, N. Thompson
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

An XUV Free-Electron Laser operating in the photon energy range 10-100eV is a key component of the proposed 4th Generation Light Source (4GLS) at Daresbury Laboratory in the UK. The current design proposal is an amplifier FEL seeded by a Higher Harmonic Generation (HHG) source. In this paper we present and discuss the considerations that led to the current design. We also present 3D simulation results that illustrate the potential radiation output characteristics.

• A.E. Charman, J.S. Wurtele
  UCB, Berkeley, California
• G. Penn
  LBNL, Berkeley, California

Funding: Division of High energy Phyiscs, DOE; and DARPA, DOD

Within the framework of a Hilbert space formalism, we derive a maximum-power variational principle (MPVP) applicable to classical spontaneous radiation from prescribed current sources. The principe appears similar to, but actually is distinct from, other well-known variational principles associated with Hamilton's principle of stationary action or Rumsey's methods involving "reaction." The techniques have been developed for and applied to the case of undulator radiation from relativistic electron beams, specifically to X-ray generation using an harmonic cascade. Such processes are currently evaluated using extensive calculations or simulation codes which can be slow to evaluate and difficult to set up. The variational principle emerged as a natural step in a simple analytic algorithm to predict the output of a harmonic generation beamline in the low-gain regime based on trial functions for the output radiation. Full three-dimensional effects are included, and it may be generalized to include further effects such as asymmetric beams and misalignments. This method has been implemented and compared with simulation results using the FEL code GENESIS, both for single stages of harmonic generation and for the LUX project.

• K.L.F. Bane, P. Emma, Z. Huang, H.-D. Nuhn, G.V. Stupakov
  SLAC, Menlo Park, California
• W.M. Fawley
  LBNL, Berkeley, California
• S. Reiche
  UCLA, Los Angeles, California

Funding: Work supported in part by the Office of Science,U.S. Dept. of Energy under Contracts DE-AC02-76F00515 and DE-AC03-76SF0098.

Energy loss due to wakefields within a long undulator, if not compensated by an appropriate tapering of the magnetic field strength, can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive component is the most critical and depends upon the chamber wall material (e.g. Cu) and its radius. Of recent interest [1] is the so-called "AC" component of the resistive wake which can lead to strong variations on very short timescales (e.g. ~20 fs). To study the expected performance of the LCLS in the presence of these wakefields, we have made an extensive series of start-to-end SASE simulations with tracking codes PARMELA and ELEGANT, and time-dependent FEL simulation codes GENESIS1.3 and GINGER. We discuss the impact of the wakefield losses upon output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation of the time-dependent wake losses obtained with an undulator field taper. We compare these results to those predicted analytically [2].

[1] K.Bane and G. Stupakov, SLAC PUB-10707 (2004). [2] Z. Huang and G. Stupakov, Phys. Rev. ST Accel. Beams 8, 040702 (2005).

• J. Wu, Z. Huang
  SLAC, Menlo Park, California

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515

LINAC Coherent Light Source (LCLS) will be the world's first hard x-ray FEL based on self-amplified spontaneous emission (SASE). As one of the options to improve the temporal coherence of the SASE FELs, in this paper, we study the High-Gain Harmonic Generation (HGHG) scheme. With a High-order Harmonic-Generation (HHG) laser at 30 - 50 nm as the seed, and the LCLS nominal beam quality, our study shows that it is feasible to use a two-stage HGHG to reach a radiation wavelength of about 1 nm. We also discuss the possibilities of generating sub-nanometer coherent radiation using this method.

• H. Delsim-Hashemi, O. Grimm, J. Rossbach, H. Schlarb, B. Schmidt, P. Schmuser
  DESY, Hamburg
• A.F.G. van der Meer
  FOM Rijnhuizen, Nieuwegein

Funding: DESY

FEL facilities are pushing to achieve higher peak currents mainly by means of compressing bunches longitudinally. This process defines a machine parameter that has to be fine-tuned empirically. Among the operational types of diagnostic tools for longitudinal phase-space are those based on IR spectroscopy. The most commonly used IR spectrometers at the FEL facilities are operating in the scanning mode and are not fast enough to be applicable for monitoring bunch compression. On the other hand, any non-scanning spectrometer may suffer from the low intensity that is available from coherent IR radiation in short time intervals in different wavelengths. The proposed "Single Shot Spectrometer" is based on using gratings as dispersive elements. Pioneering tests with a transmission grating have shown the feasibility of the concept. In a second step, a version with "Reflective Blazed Grating" will be tested and should allow getting the maximum available signal for the whole spectrum and improved resolution. Parallel to the study of optical parts, an array of pyroelectric detectors with integrated multi-channel readout is under development.

• Y. Kim, K. Floettmann, S. Schreiber
  DESY, Hamburg
• D. Son
  CHEP, Daegu

Funding: for the TTF2 VUV-FEL Team

By the help of nonlinearity in the longitudinal phase space, the VUV-FEL at the TESLA Test Facility phase 2 (TTF2) is under operating in the femtosecond (fs) FEL mode which generates coherent and ultra-bright SASE source with photon pulse duration time of around 20 fs (FWHM) and wavelength of around 32 nm. For the fs FEL mode operation, bunch length of electron beams should be compressed by two bunch compressors to have a leading spike in the longitudinal beam density distribution or peak current. The required peak current at the spike is higher than about 1.0 kA, and the spike length is shorter than around 200 fs (FWHM). In this paper, we describe our commissioning experiences to optimize two TTF2 bunch compressors for the fs FEL mode operation.

• K. Lee, Y. Cha, Y.U. Jeong, B.C. Lee, S.-H. Park
  KAERI, Daejon

In contrast to some recent experimental results, which state that the Nonlinear Thomson Scattered (NTS) radiation is incoherent, a coherent condition under which the scattered radiation of an incident laser pulse by a bunch of electrons can be coherently superposed has been investigated. The Coherent Relativistic Nonlinear Thomson Scattered (C-RNTS) radiation makes it possible utilizing the ultra-short pulse nature of NTS radiation with a bunch of electrons, such as plasma or electron beams. A numerical simulation shows that a 25 attosecond X-ray pulse can be generated by irradiating an ultra-intense laser pulse of 4x10(19) W/cm2 on an ultra-thin solid target of 50 nm thickness, which is commercially available. The coherent condition can be easily extended to an electron beam from accelerators. Different from the solid target, much narrower electron beam is required for the generation of an attosecond pulse. Instead, this condition could be applied for the generation of intense Compton scattered X-rays with a modulated electron beam.

• T. Watanabe, D.F.L. Liu, J.B. Murphy, J. Rose, T.V. Shaftan, Y. Shen, T. Tsang, X.J. Wang, L.-H. Yu
  BNL, Upton, Long Island, New York
• L. Giannessi, S. Spampinati
  ENEA C.R. Frascati, Frascati (Roma)
• P. Musumeci
  Universita di Roma I La Sapienza, Roma
• S. Reiche
  UCLA, Los Angeles, California

Funding: Work suppoted by the Brookhaven National Lab and Office of Naval Research

The SDL facility at BNL[1] is an excellent platform to explore some of the recent ideas related to superradiance in a seeded single pass FEL. At the SDL facility there is an operating FEL with a Ti:Sapphire seed laser and a high brightness e-beam with an energy up to 250 MeV. Seeding may be realized with pulses shorter than the e-beam bunch length to induce the superradiant regime. A status report concerning this experiment will be presented.

[1] A. Doyuran et al., PRSTAB, Vol. 7, 050701 (2004).

• T.  Kamps, V. Duerr, K. Goldammer, D. Kraemer, P. Kuske, J. Kuszynski, D. Lipka, F. Marhauser, T. Quast, R. Richter
  BESSY GmbH, Berlin
• P. Evtushenko
  Jefferson Lab, Newport News, Virginia
• U. Lehnert, P. Michel, J. Teichert
  FZR, Dresden
• I. Will
  MBI, Berlin

Funding: Funded by the Bundesministerium für Bildung und Forschung, the State of Berlin and the Zukunftsfonds Berlin

A superconducting rf photo electron injector (SRF gun) is currently under construction by a collaboration between BESSY, DESY, FZR and MBI. The project aims at the design and setup of an CW SRF gun including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings ranging from low-charge (77pC), low-emittance (1 pi mm mrad) mode to high-charge (2.5nC) operation of the gun. For these operation modes beam dynamics simulations are resulting in boundary conditions for the beam instrumentation. Proven and mature technology is projected wherever possible, for example for current and beam position monitoring. The layout of the beam profile and emittance measurement systems is described. For the bunch length, which varies between 5 and 50 ps, two schemes using Electro-optical sampling and Cherenkov radiation are detailed. The beam energy and energy spread is measured with an especially designed 180 degree spectrometer.

• J. Teichert, A. Arnold, H. Buettig, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang
  FZR, Dresden
• T.  Kamps, D. Lipka, F. Marhauser
  BESSY GmbH, Berlin
• W.-D. Lehmann
  IfE, Dresden
• J. Stephan
  IKST, Drsden
• V. Volkov
  BINP SB RAS, Novosibirsk
• I. Will
  MBI, Berlin

A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of the beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application (BESSY-FEL, 4GLS). In 2005, a substantial progress has been made. The two 3.5-cell niobium cavities for the gun have been delivered from the company ACCEL. The main parts for gun cryostat like vacuum vessel, cryogenic and magnetic shields are ready. Test benches for the cathode cooling system and the cavity tuner are being assembled. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed (see T. Kamps et al., this conference). After delivering the gun cavities, their rf properties are being measured at room temperature and the warm tuning is being carried out. The set-up for this treatment and measurement as well as the results will be presented.

• M. Huening, A. Bolzmann, H. Schlarb
  DESY, Hamburg
• J.C. Frisch, D.J. McCormick, M.C. Ross, T.J. Smith
  SLAC, Menlo Park, California
• J. Rossbach
  Uni HH, Hamburg

The design of the VUV-FEL at DESY demands bunch lengths in the order of 50 fs and below.For the diagnostic of such very short bunches a transverse deflecting RF structure (LOLA) has been installed which streaks the beam according to the longitudinal distribution. Tests in the VUV-FEL yielded a rich substructure of the bunches. The most pronounced peak in the has a rms length of approximately 50 fs during FEL operation and below 20 fs FWHM at maximum compression. Depending on the transverse focusing a resolution between 10^-50 fs was achieved.

• M. Roehrs, A. Bolzmann, M. Huening, H. Schlarb
  DESY, Hamburg
• K. Honkavaara
  Uni HH, Hamburg

Among the very critical parameters for the operation of the VUV-FEL at DESY are the slice-emmittance and beam optics matching of the current peak in the electron bunch. Conventional tools for measuring the beam size are sensitive to the projected properties of the bunch only and hence suffer from mixing of different parts of the bunch. A combination of streaking with a transverse deflecting rf structure (LOLA) and a quadrupole scan allowed to measure the spike separate from the rest of the bunch. Indeed significant differences in terms of emmittance and optical functions have been found.

• Y. Kim, K. Floettmann, S. Schreiber
  DESY, Hamburg

Funding: for the TTF2 VUV-FEL Team

Generally, due to the space chare force, projected transverse emittance is increased at the region between gun and booster linac. However the emittance can be continuously damped in the booster linac by the so-called Ferrario's matching principle. Even though our longitudinal laser profile is not flat top shape during TTF2 commissioning, we could get a good emittance after booster linac (ACC1). For 1.0 nC and 90% beam intensity, our normalized projected transverse rms emittance was about 1.1 mm.mrad, and it was about 1.8 mm.mrad for 100% beam intensity. In this paper, we will compare our measured results with simulation ones, and we will show our first experimental demonstration of Ferrario's matching principle with Gaussian longitudinal laser beam profile.

• S. Schreiber
  DESY, Hamburg

The VUV-FEL is a free electron laser user facility being commissioned at DESY in Hamburg. In the current configuration, the linac accelerates an electron beam up to 800 MeV. The injector is a crucial part of the linac, since it has to generate and maintain a high brightness electron beam required for SASE operation. The injector includes a laser driven RF gun, a booster section, a bunch compressor, and diagnostic sections. The good performance of the injector was crucial for the first lasing of the VUV-FEL at a wavelength of 32 nm in January 2005. We report on the present layout of the injector, the properties of the electron beam and on upgrade plans scheduled in the near future.

• B. Steffen, S. Casalbuoni, E.-A. Knabbe, B. Schmidt
  DESY, Hamburg
• P. Schmuser, A. Winter
  Uni HH, Hamburg

For the operation of a SASE FEL, the longitudinal bunch profile is one of the most critical parameters. At the superconducting linac of the VUV-FEL at DESY, we have installed an electro optic spectral decoding (EOSD) experiment to probe the time structure of the electric field of the bunches to better than 200 fs rms. The field induced birefringence of a ZnTe crystal is detected by a 30 femtosecond laser pulse (TiSa) and the time structure is measured by encoding it on the spectrum of the chirped TiSa pulse. First results on jitter measurements and for the bunch length as function of the linac parameters are presented.

• J.R. Roensch, J. Rossbach
  Uni HH, Hamburg
• K. Abrahamyan, G. Asova, J.W. Baehr, G. Dimitrov, H.-J. Grabosch, J.H. Han, S. Khodyachykh, M. Krasilnikov, S. Liu, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan
  DESY Zeuthen, Zeuthen
• M.V. Hartrott, D. Lipka
  BESSY GmbH, Berlin

Funding: This work has partly been supported by the European Community, contract numbers RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Association, contract number VH-FZ-005.

The main goal of the Photo Injector Test facility at DESY Zeuthen (PITZ) is to test and to optimize photo injectors for Free-Electron Lasers (FELs). The demands on such a photo injector are small transverse emittances, short bunches and a high bunch charge. A FEL is driven by an accelerator which consists of a rf gun followed by an acceleration section and a magnetic bunch compressor. For the effective bunch compression detailed studies of the longitudinal phase space have to be performed. The correlation between the positions of the particles in the bunch and their longitudinal momenta has to be understood and the non-linearities of the longitudinal phase space have to be analysed. A special apparatus for longitudinal phase space tomography at 5 MeV using a dipole, a Cherenkov radiator, an optical transmission line and a streak camera was developed. Results of longitudinal phase space measurements are presented and compared with simulations.

• V. Miltchev
  DESY Zeuthen, Zeuthen

Funding: This work has partly been supported by the European Community, contract numbers RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Assciation, contract number VH-FZ-005

The high electron beam quality needed for SASE FEL processes requires considerable effort in characterisation and improvement of the electron source. The Photo Injector Test Facility at Zeuthen (PITZ) was built to study the production of minimum transverse emittance electron beams for Free Electron Lasers. In this work we present a study on the detailed reconstruction of the transverse phase space density distribution of electron beams at various operating conditions at PITZ. Transverse emittance values containing only a certain fraction of all particles in the distribution (core emittance) will be estimated for different operating conditions and the results will be compared with simulations.

• V. Miltchev, J.W. Baehr, H.-J. Grabosch, J.H. Han, M. Krasilnikov, A. Oppelt, B. Petrosyan, L. Staykov, F. Stephan
  DESY Zeuthen, Zeuthen
• M.V. Hartrott
  BESSY GmbH, Berlin

Funding: This work has partly been supported by the European Community, contract numbers RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Assciation, contract number VH-FZ-005

The thermal emittance determines the lower emittance limit and its measurement is of high importance to understand the ultimate injector performance. In this contribution we present results of thermal emittance measurements under rf operation conditions for various Cs2Te cathodes and different accelerating gradients. Measurements of thermal emittance scaling with the cathode laser spot size are presented and analysed. The significance of the Schottky effect in the emittance formation process is discussed.

• A. Oppelt, K. Abrahamyan, G. Asova, J.W. Baehr, G. Dimitrov, U. Gensch, H.-J. Grabosch, J.H. Han, S. Khodyachykh, G. Klemz, M. Krasilnikov, S. Liu, V. Miltchev, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan
  DESY Zeuthen, Zeuthen
• W. Ackermann, W.F.O. Muller, S. Schnepp, T. Weiland
  TEMF, Darmstadt
• D. Alesini, M. Boscolo, G. Di Pirro, M. Ferrario, D. Filippetto, L. Palumbo, C. Vicario
  INFN/LNF, Frascati (Roma)
• V. Boccone
  Humboldt Universität zu Berlin, Berlin
• L. Catani, E. Chiadroni, A. Cianchi
  INFN-Roma II, Roma
• K. Floettmann, S. Schreiber
  DESY, Hamburg
• T. Garvey
  LAL, Orsay
• M.V. Hartrott, E. Jaeschke, D. Kraemer, D. Lipka, F. Marhauser, R. Richter
  BESSY GmbH, Berlin
• P. Michelato, L. Monaco, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)
• V.V. Paramonov
  RAS/INR, Moscow
• N. Pavel
  Humboldt University Berlin, Institut für Physik, Berlin
• J.R. Roensch, J. Rossbach
  Uni HH, Hamburg
• W. Sandner, I. Will
  MBI, Berlin
• I. Tsakov
  INRNE, Sofia

Funding: This work has been partly supported by the European Community, contract numbers RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds" of the Helmholtz Association, contract number VH-FZ-05.

Since December 2004, the photo injector test facility at DESY in Zeuthen (PITZ) has been upgraded. A normal conducting copper booster cavity has been installed and the diagnostics beamline has been strongly modified. An extended water cooling system has been installed and was successfully taken into operation. Actually, the new diagnostics elements are being commissioned. After the installation of the new 10 MW klystron in June/July, the gun can be conditioned towards higher average power, and the whole beamline including the booster will be taken into operation. First results from the commissioning phase including gun and booster conditioning are reported.

• P. Craievich, S. Di Mitri
  ELETTRA, Basovizza, Trieste

The FEL project FERMI@ELETTRA will use the existing Linac, upgraded to 1.2 GeV, to produce VUV radiation between 100-10 nm. FEL operations require a high quality beam in terms of the bunch energy spread and emittance. In this paper we present an analytical study based on a continuum model to describe the transverse motion of a single bunch. Such a study allows predicting the emittance growth under the combined influence of short-range transverse wakefields, injection offset, initial emittance and misaligned accelerating sections. We also report a comparison between analytical and numerical (tracking code) results.

• M. Ferianis, P. Craievich, G. D'Auria, S. Di Mitri
  ELETTRA, Basovizza, Trieste
• P. Emma
  SLAC, Menlo Park, California
• W. Graves
  MIT, Middleton, Massachusetts
• M. Poggi
  INFN/LNL, Legnaro, Padova
• A. Zholents
  LBNL, Berkeley, California

Fermi is the fourth generation light source currently under design at ELETTRA: based on the Harmonic Generation (HG) scheme it will generate FEL radiation in the 100-10nm range. The successful implementation of the HG scheme calls also for precise knowledge of electron beam emittances and energy spread as well as for very accurate control on the photon to electron interaction, in the Undulator sections. In this paper we present our design for two fundamental Diagnostics foreseen for the new FERMI LINAC: the Beam Position Monitors (BPM) and the Transverse Deflecting cavity set-up. Sensitivity studies on transverse beam displacement effects on global stability of FEL output radiation dictate the ultimate performance to be provided by the BPM system. Due to non negligible longitudinal occupancy of a cavity type BPM, some efforts have been put to study compact cavity BPM configuration. A proper set-up of RF deflecting cavity combined with the vertical ramp foreseen at the end of the LINAC provide a powerful tool for multiple beam measurement. Furthermore, by implementing the two bunch compressors in the vertical plane the effect of the Coherent Synchrotron Radiation (CSR) on the vertical emittance can be checked for.

• F. Banfi, G. Ferrini, P.G. Galimberti, C. Giannetti, S. Pagliara, F. Parmigiani, E. Pedersoli
  Universita Cattolica-Brescia, Brescia
• J.N. Corlett, S.M. Lidia
  LBNL, Berkeley, California
• B. Ressel
  ELETTRA, Basovizza, Trieste

Funding: U.S. DOE, Office of Science, under Contract No. DE-AC03-76SF00098

A Monte Carlo study of electron transport in Cs2Te films is performed to investigate the transverse emittance epsilon at the cathode surface. We find the photoemitted electron angular distribution and explain the physical mechanism involved in the process, a mechanism hindered by the statistical nature of the Monte Carlo method. The effects of electron-phonon scattering are discussed. The transverse emittance is calculated for different radiation wavelengths and a laser spot size of 1.5*10(-3) m. For a laser radiation at 265 nm we find epsilon = 0.56 mm-mrad. The dependence of epsilon and the quantum yield on the electron affinity Ea is also investigated. The data shows the importance of aging/contamination on the material.

• F. Banfi, G. Ferrini, P.G. Galimberti, C. Giannetti, S. Pagliara, F. Parmigiani, E. Pedersoli
  Universita Cattolica-Brescia, Brescia
• J.N. Corlett, S.M. Lidia
  LBNL, Berkeley, California
• B. Ressel
  ELETTRA, Basovizza, Trieste

Funding: U.S Department of Energy, Office of Science under Contract No. DE-AC03-76SF00098.

Quantum Efficiency (QE) measurements of single photon photoemission from a Cu(111) single crystal and a Cu polycrystal photocathodes, irradiated by 150~fs-6.28~eV laser pulses, are reported over a broad range of incidence angle in both s and p polarizations. The maximum value of QE for the Cu polycrystal sample is Y~4*10(-4), obtained with p polarization at an angle of incidence theta=65°. Our data confirm the vectorial photoemission model. Issues concerning surface roughness and symmetry considerations are addressed. An explanation in terms of non local conductivity tensor is proposed. Advantages of a 6.28~eV photon as compared to the standard 4.71~eV photon in use with Cu photocathodes are discussed.

• G.L. Orlandi
  ENEA C.R. Frascati, Frascati (Roma)

In the electromagnetic radiative phenomena originated by relativistic charged beams, angular distortions as well as variations of the photon flux are commonly observed as a function of the ratio between the beam transverse size and the observed wavelength, even at a wavelength shorter than the longitudinal bunch length. In the framework of a single particle theory of the transition radiation, diffractive alterations of the spectrum due, for instance, to the finite size of the radiator screen are already known. For relativistic three-dimensional charged beams, it could be interesting to check if the transition radiation emission undergoes modifications depending on the finite value of the beam transverse size with respect to the observed wavelength. Taking into account the beam diagnostics applications of the transition radiation in a linear accelerator, such an experimental check can offer promising perspectives. The theoretical background and physical basis of the spatial coherence effects affecting the spectral distribution of the transition radiation intensity in conditions of temporal incoherence will be presented. The main beam diagnostics applications will be also contoured.

• 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.

• T. Kii, T. Fukui, K. Kusukame, K. Masuda, Y. Nakai, H. Ohgaki, T. Yamazaki, K. Yoshikawa, H. Zen
  Kyoto IAE, Kyoto

We have studied on improvement of electron beam macropulse properties from a thermionic RF gun. Though a thermionic RF gun has many salient features, there is a serious problem that back-bombardment effect worsens quality of the beam. To reduce beam energy degradation by this effect, we tried to feed non-flat RF power into the gun. As a result, we successfully obtained about 1.5 times longer macropulse and two times larger total charge per macropulse. On the other hand, we calculated transient evolution of RF power considering non-constant beam loading. The beam loading is evaluated from time evolution of cathode temperature, by use of one dimensional heat conduction model and electron trajectories' calculations by a particle simulation code. Then we found good agreement between the experimental and calculation results. Furthermore, with the same way, we studied the electron beam output dependence on the cathode radius.

• K. Kusukame, T. Fukui, T. Kii, K. Masuda, Y. Nakai, H. Ohgaki, T. Yamazaki, K. Yoshikawa, H. Zen
  Kyoto IAE, Kyoto

Funding: Kyoto University,Institute of Advanced Energy

Thermionic RF guns show advantageous features compared with photocathode ones such as easy operation and much higher repetition rate of micropulses, both of which are suitable for their application to high average power FELs. They however suffer from the back-bombardment effect [1], i.e., in conventional RF guns, electrons are extracted from cathode also in the latter half of accelerating phase and tend to back-stream to hit the cathode, and as a result the macropulse duration is limited down to severalμsec Against this adverse effect in thermionic RF guns, introduction of the triode structure has been proposed [2], where the accelerating phase and amplitude nearby the cathode can be controlled regardless of the phase of the first accelerating cell in the conventional RF gun. Our one-dimensional particle simulation results predict that the back-bombardment power can be reduced by 99 % only with 30-40 kW RF power fed to the grid in the present triode structure with an optimal phase difference from the RF induced in the main accelerating cavities. We also carried out two-dimensional particle simulations to evaluate emittance of the refined RF gun.

[1] T.Kii et al.,Nuclear Instruments and Methods in Physics Research A 507 (2003) 340-344. [2] E. Tanabe et al., Proc. of 27th Linear Accelerator Meeting in Japan, Aug 7-9, 2002, Kyoto, Japan (in Japanese).

• H. Zen, T. Fukui, T. Kii, K. Kusukame, K. Masuda, Y. Nakai, H. Ohgaki, T. Yamazaki, K. Yoshikawa
  Kyoto IAE, Kyoto

Transverse phase space tomography [1] using a quadrupole magnet and a beam profile monitor is very useful for emittance measurements especially for non-Gaussian beams, since this method directly gives transverse phase space distributions. We have tried to apply the method to measure the beam emittance of our FEL driver Linac [2]. We found, however, this method suffers from both the energy spread of the beam and the reconstruction noise which deeply depends on the reconstruction algorithm. To obtain reliable results, numerical evaluation using PARMELA which simulates the beam profile in each rotation angle has been carried out. Several image reconstruction method, such as FBP method, ART method, and Ordered Subsets - Expectation Maximization (OS-EM) algorithm [3], have been applied to reconstruct the phase space distribution. We also have introduced a noise cut procedure, and evaluation of a tolerable energy spread where this method can be applied.

[1] C.B. McKee, et al., NIM A 358 (1995) 264. [2] K. Masuda, et al., Proceedings of the 2004 FEL Conference 450. [3] H.M. Hudson and R.S. Larkin, IEEE Trans. Med. Imaging, 13:601 (1994).

• 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.

• S.J. Park, J.Y. Huang, I.S. Ko, J.-S. Oh, Y.W. Parc, P.C.D. Park, J.H. Park
  PAL, Pohang, Kyungbuk
• C. Kim
  POSTECH, Pohang, Kyungbuk
• X.J. Wang
  BNL, Upton, Long Island, New York
• D. Xiang
  TUB, Beijing

Funding: Work supported by the MOST and the POSCO.

The PAL XFEL, an X-Ray Free Electron Laser (XFEL) project based on the Self-Amplified Spontaneous Emission (SASE), is under progress at the Pohang Accelerator Laboratory (PAL). Successful completion of the project is expected to impose stringent requirements on the beam qualities such as the normalized emittance (< 1.2 mm-mrad) and the un-correlated energy spread (~10(-5)). This requires careful and systematic planning for ensuring the generation and the preservation of high-brightness beams in the whole machine. The PPI (Pohang Photo-Injector) is to achieve these requirements with high reliability and stability. In this article, we discuss various physics and engineering issues involved in the design and construction of the PPI. We also report on the R&D status of photo-cathode RF gun at the PAL.

• 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.H. Lumpkin, W. Berg, M. Borland, N. Sereno
  ANL, Argonne, Illinois

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

The interest in bunch compression to generate higher peak current electron beams with low emittance continues in the free-electron laser (FEL) community. At the Advanced Photon source (APS) we have both an rf thermionic gun and an rf photocathode (PC) gun on the S-band linac. At the 150-MeV point in the linac, we have a flexible chicane bunch compressor whose four dipoles bend the beam in the horizontal plane. There is also a vertical bend dipole after the chicane that allows measurement of energy and horizontal beam size at the imaging screen station to study possible effects on emittance due to coherent synchrotron radiation (CSR) in the chicane. A far-infrared (FIR) coherent radiation monitor is located downstream of the chicane as well. We have begun recommissioning of this device with coherent transition radiation (CTR), but we also have directly observed CSR from the bunch-compressed beam as it transits the vertical dipole and goes into the down leg. The unique geometry allows simultaneous tracking of bunch length, horizontal emittance, and energy distribution effects. Initial measurements of the CSR and CTR as a function of linac phase are described.

• S. Biedron, J.W. Lewellen, M. Virgo
  ANL, Argonne, Illinois

Funding: Air Force Research Laboratory, HEL-JTO Program Office

There is increasing interest in high-average-power (>100 kW), um-range FELs. These machines require high peak current (~1 kA), modest transverse emittance, and beam energies of ~100 MeV. High average currents (~1 A) place additional constraints on the design of the injector. We present a design for an injector intended to produce the required peak currents at the injector, eliminating the need for magnetic compression within the linac. This reduces the potential for beam quality degradation due to CSR and space charge effects within magnetic chicanes.

• J.W. Lewellen, J. Noonan
  ANL, Argonne, Illinois

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

Conventional pi-mode rf photoinjectors typically use magnetic solenoids for emittance compensation. This provides independent focusing strength, but can complicate rf power feed placement, introduce asymmetries (due to coil crossovers), and greatly increase the cost of the photoinjector. Cathode-region focusing can also provide for a form of emittance compensation. Typically this method strongly couples focusing strength to the field gradient on the cathode, however, and also requires altering the longitudinal position of the cathode to change the focusing. We propose a new method for achieving cathode-region variable-strength focusing for emittance compensation. The new method reduces the coupling to the gradient on the cathode, and does not require a change in the longitudinal position of the cathode. Expected performance for an S-band system is similar to conventional solenoid-based designs. This paper presents the results of rf cavity and beam dynamics simulations of the new design.

• M. Trovo, M.B. Danailov, G. Penco
  ELETTRA, Basovizza, Trieste
• W. Graves
  MIT, Middleton, Massachusetts
• S.M. Lidia
  LBNL, Berkeley, California

In the framework of the FERMI@ELETTRA project, aimed to build an X-ray FEL source, a crucial role is played by the electron source, which has to produce a very high quality bunch, in terms of low emittance and uncorrelated energy spread. We have investigated the effects of low- (100-300 5m) and high- ( 10^-50 5m) frequency modulation of the beam charge deriving from intensity modulation of the laser pulse incident on the photocathode on the downstream beam distribution. Following other proposals, we have investigated the use of a short laser 'heater' to increase the effective incoherent energy spread and reduce the gain in the longitudinal density modulation instability. We present results from simulation of the beam generation at the photocathode, and transport through the photoinjector, initial acceleration modules and the laser heater.

• G. Penco, M. Trovo
  ELETTRA, Basovizza, Trieste
• S.M. Lidia
  LBNL, Berkeley, California

In the framework of the FERMI@ELETTRA project, aimed to build an x-ray FEL source based on laser-seeded harmonic generation, a crucial role is played by the electron source, which has to produce a very high quality beam, in terms of low emittance and uncorrelated energy spread. A very attractive solution is the SLAC/BNL/UCLA 1.6 cell s-band gun III based upon the demonstrated high performance of this design and its descendants. This paper describes the results of the optimization studies based on the gun III design and carried out with two space charge tracking codes (GPT and ASTRA) for nominal operating parameters. In particular two different bunch charge regimes has been explored: low (few hundreds of pC) and high (~1nC) . In the first case, the limited charge extracted from the photo-cathode allows to propagate a bunch with an initial higher density and to compress it along the linac down to a few hundreds of fs, attaining a high peak current bunch with a very low slice emittance. The second case has been investigated in order to verify the possibility to produce a "1 ps plateau" bunch with acceptable peak current and a slice emittance lower than 2 mm mrad. We present simulation results for both cases.

• D.R. Gillingham, T. M. Antonsen
  IREAP, College Park, Maryland

Funding: Work supported by the Office of Naval Research and the Joint Technology Office.

High power Free Electron Laser (FEL) designs require high-brightness beams. These beams may suffer beam quality degradation during transport through bending sections from effects that were previously insignificant at low bunch charges. Potential mechanisms include microbunching from longitudinal space-charge and transverse emittance dilution from coherent synchrotron radiation. The effects are not well-understood in the transient state, in the presence of conducting boundaries or when these effects operate together and in conjunction with the beam dynamics. A simulation method applicable under the conditions of a MW-class average power FEL driver has been developed that accounts for radiation, space-charge and boundary conditions in a self-consistent manner. This simulation may be useful in evaluating design concepts under consideration including chicane bunch compressors and energy recovery bending arcs.

• J.R. Harris
  University of Maryland, College Park, Maryland
• J.G. Neumann
  IREAP, College Park, Maryland
• P.G. O'Shea
  University Maryland, College Park, Maryland

Funding: Department of Energy, Office of Naval Research, Army Research Laboratory, and Directed Energy Professional Society

All beams are dominated by space charge forces when first created. After a beam is accelerated, space charge directly plays a less important role. However, at low energy space charge will drive changes in the beam which will become "frozen in" as the beam is accelerated, and may have adverse consequences even at high energy. In this paper, we report on the generation and evolution of modulated beams in the University of Maryland Electron Ring, a low energy (10 keV), high current (100 mA) electron recirculator for the study of beams in the extreme space charge dominated regime. Such intense, modulated beams have application to future high power FELs and novel light sources.

• S. Roychowdhury
  Duke University, Durham, North Carolina
• M. Babzien, V. Litvinenko, V. Yakimenko
  BNL, Upton, Long Island, New York

The brightness of electron beams from a photo injector is influenced by the transverse and longitudinal distribution of the laser beam illuminating the cathode. Previous studies at Brookhaven Accelerator Test Facility have shown that formation of an ideal e-beam with lowest transverse emittance requires uniform circular distribution of the emitted electrons. The use of the uniformly distributed power of the laser beam may not lead to that of the emitted electrons because of the non-uniform quantum efficiency. A proper shaping of the laser beam can compensate for this non-uniformity. In this paper we describe the use of digital light processing (DLP) technique based on digital mirror device (DMD) for spatial modulation of the laser beam, for measurements of the quantum efficiency map, and for creating the desirable e-beam density profiles. A DMD is aμelectronic mechanical system (MEMS) comprising of millions of highly reflectiveμmirrors controlled by underlying electronics. We present experimental results of the influence of the various spatial profiles on the e-beam emittance.

• H. Loos, J. Castro, D. Dowell, S.M. Gierman, J.F. Schmerge
  SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515

Understanding and optimizing the beam dynamics in high brightness electron accelerators not only requires the measurement of the 6-D beam ellipse, but also the details of the phase space distribution. By combining longitudinal and transverse phase space tomography in a dipole spectrometer the four-dimensional distribution can be resolved. We report on experiments at the Gun Test Facility (GTF) at SLAC where we measure the energy resolved horizontal beam distribution while simultaneously varying the longitudinal time-energy correlation and the horizontal phase advance to reconstruct the horizontal-longitudinal phase space distribution.

• H. Loos, P.R. Bolton, J.E. Clendenin, D. Dowell, S.M. Gierman, C. Limborg-Deprey, J.F. Schmerge
  SLAC, Menlo Park, California

Funding: Work supported by DOE contracts DE-AC02-76SF00515

The Gun Test Facility (GTF) at SLAC serves as a test bed for electron gun and high brightness photoinjector developement for future short wavelength light sources as well as new or improved diagnostics techniques. We report on measurements of longitudinal and projected as well as time-resolved transverse electron beam properies over a wide range of charge from 15 to 600 pC. The transverse and longitudinal phase space distributions are compared with simulation results.

• H. Loos, D. Dowell
  SLAC, Menlo Park, California
• M. Boscolo, M. Ferrario, C. Vicario
  INFN/LNF, Frascati (Roma)
• M. Petrarca
  INFN-Roma, Roma
• L. Serafini
  INFN-Milano, Milano
• B. Sheehy, Y. Shen, T. Tsang, X.J. Wang
  BNL, Upton, Long Island, New York

Funding: Work supported by DOE contracts DE-AC02-76SF00515 and DE-AC02-98CH10886

The photoinjectors for future short wavelength high brightness accelerator driven light sources need to produce an electron beam with ultra-low emittance. At the DUV-FEL facility at BNL, we studied the effect of longitudinally shaping the photocathode laser pulses on the electron beam dynamics. We report on measurements of transverse and longitudinal electron beam emittance and comparisons of the experimental results with simulations.

• J. Wu, P. Emma, Z. Huang
  SLAC, Menlo Park, California

Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.

Longitudinal space charge (LSC) force can be a main effect driving the microbunching instability in the linac for an x-ray free-electron laser (FEL). In this paper, the LSC-induced beam modulation is studied using an integral equation approach that takes into account the transverse (radial) variation of LSC field. Changes of beam energy and the transverse beam size can be also incorporated. We discuss the validity of this approach and compare it with other analyses as well as numerical simulations. We apply this approach to study the LSC effect in the LCLS accelerator

• W. Graves, F.O. Ilday, F.X. Kaertner, T. Zwart
  MIT, Middleton, Massachusetts
• M.B. Danailov, B. Diviacco, M. Ferianis, M. Marsi
  ELETTRA, Basovizza, Trieste
• Z. Huang
  SLAC, Menlo Park, California
• S.M. Lidia
  LBNL, Berkeley, California

The optical properties of an FEL amplifier are sensitively dependent on the electron beam current profile, energy spread, and transverse emittance. In this paper we consider using a short FEL amplifier operating on a low harmonic of a visible-IR input seed as a mildly destructive electron beam diagnostic able to measure these properties for sub-ps time slices. The optical methods are described as well as a planned implementation of the device for the FERMI@Elettra XUV FEL under construction at Sincrotrone Trieste, including its fiber-based seed laser closely coupled with the facility timing system, undulator parameters, and requirements on the electron and FEL pulses. This diagnostic is conveniently integrated with a "laser heater" designed to increase the very low electron beam energy spread produced by a photoinjector in order to avoid space charge and coherent synchrotron radiation instabilities.

• J.L. Coleman, S.V. Benson, R. Evans, A.G. Grippo, K. Jordan
  Jefferson Lab, Newport News, Virginia

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, The Army Night Vision Laboratory and by DOE Contract DEAC05-84ER40150

The Jefferson Lab FEL poses a number of challenges regarding laser safety. The IR FEL is designed to lase at powers in excess of 10 kWatt and at wavelengths from 1 to 10 microns and the UV FEL will lase at the kilowatt level from 1 micron to 250 nanometers. Additionally there are table top Class 4 lasers and a THz beam line that produces hundreds of watts. The FEL operation is further complicated by Class 4 powers in the coherent harmonics of the FEL. There are 3 modes that we operate in: alignment mode, hutch mode, and full power exclusionary. This paper describes the experience with our current Laser Safety System and the upgrades planned to allow safe operation with these many hazards.

• S. Zhang, S.V. Benson, D. Douglas, D. Hardy, C. Hernandez-Garcia, K. Jordan, G. Neil, M.D. Shinn
  Jefferson Lab, Newport News, Virginia

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Army Night Vision Laboratory, the Air Force Research Laboratory, and by DOE Contract DE-AC05-84ER40150.

The design and construction of an optical transport that brings synchrotron radiation from electron bunches to a fast streak camera in a remote area has become a useful tool for online observation of bunch length and stability. This paper will report on the temporal measurements we have done, comparison with simulations, and the on-going work for another imaging optical transport system that will make possible the direct measurement of the longitudinal phase space by measuring the bunch length as a function of energy.

• D. Kayran, V. Litvinenko
  BNL, Upton, Long Island, New York

Funding: Work performed under the auspices of the U.S. Department of Energy

Energy recovery linacs (ERLs) are potential candidates for the high power and high brightness electron beams sources. The main advantages of ERL are that electron beam is generated at relatively low energy, injected and accelerated to the operational energy in a linac, and after the use is decelerated in the same linac down to injection energy, and, finally, dumped. A merging system, i.e. a system merging together high energy and low energy beams, is an intrinsic part of any ERL loop. One of the challenges for generating high charge, high brightness electron beams in an ERL is development of a merging system, which provides achromatic condition for space charge dominated beam and which is compatible with the emittance compensation scheme. In this paper we present the theory, the principles of operation and some designs (including simulations) of such merging systems. We use a specific implementation for R&D ERL at Brookhaven as the illustration.

• D. Suetterlin, V. Schlott, H. Sigg
  PSI, Villigen
• D. Erni, H. Jäckel
  ETH, Zurich
• A. Murk
  University of Berne, Institute of Applied Physics, Berne

The polarization dependent intensity distribution of coherent transition radiation (CTR) emission has been studied theoretically and experimentally at an optical beam port downstream the 100 MeV SLS pre-injector LINAC. Based on these analyses, a spatial interferometer using the vertically polarized lobes of CTR has been designed and installed at this location. While a proof of principle of this bunch length monitor was achieved by step-scan measurements with a Golay cell detector, the single shot capability has been demonstrated by electro-optical correlation of the spatial CTR interference pattern with the fairly long Nd:YAG laser pulses in a ZnTe crystal. In single-shot operation variations of the bunch length due to different settings of the LINACs bunching cavities have been observed.

• L. Catani, E. Chiadroni, A. Cianchi
  INFN-Roma II, Roma
• M. Castellano, G. Di Pirro, D. Filippetto, C. Vicario
  INFN/LNF, Frascati (Roma)
• M.V. Hartrott
  BESSY GmbH, Berlin
• M. Krasilnikov, A. Oppelt, F. Stephan
  DESY Zeuthen, Zeuthen

For the SPARC Project a novel diagnostic device, called "Emittance-meter", has been conceived and constructed to perform a detailed study of the emittance compensation process in the SPARC photo-injector and to optimize the RF-gun and the accelerator working point. It consists of a movable emittance measurement system, based on the 1D pepper-pot method, installed between two long bellows with the possibility to scan a region 1.5 m long downstream the RF-gun. The construction of the device was completed in the first part of this year and a series of laboratory tests, to evaluate its performances, were carried out in Spring 2005. At the beginning of the summer the complete system was moved to DESY at Zeuthen to be installed on the Photo Injector Test Facility PITZ. After the commissioning it will used for measurements of the PITZ electron beam in the framework of a collaboration between the SPARC and PITZ Projects aiming on studies and operations with photo injectors.