• H. Hama
  LNS, Sendai

More than 20 years ago, D.A.G. Deacon proposed an isochronous storage ring for FEL to avoid bunch heating and decreasing instantaneous gain [1]. Some of low momentum compaction (alpha) operations have been carried out, and recently coherent infrared radiation are observed on a 3rd generation light source. Because the 3rd generation rings are optimized to obtain very low emittance beam, the dispersion function in the arc sections are much reduced by introducing large bending radius, so that those are very big machines. Meanwhile N.A. Vinokurov et al. recently proposed a ring type SASE FEL based on a complete isochronous bending transport [2]. At least, experimental and theoretical study of the isochronous ring so far suggests nonlinear effects resulted from higher order dispersion and chromaticity declines the "complete" isochronous system. On the other hand, in a wavelength region of THz, tolerance of the path length along a turn of the ring seems to be within our reach. A concept to preserve of a form factor of microbunch or very short bunch by using no-dispersion bend for a ring source of THz coherent radiation and its extension toward short wavelength and SASE FEL will be discussed.

[1] D.A.G. Deacon, Phys. Rep. 76 (1981) 349. [2] N.A. Vinokurov, O.A. Shevchenko, Nucl. Instr. and Meth. A 528 (2004) 491.

• B.C. Kuske, M. Abo-Bakr, K. Goldammer, A. Meseck
  BESSY GmbH, Berlin

Funding: Bundesministerium für Bildung und Forschung, the state of Berlin and the Zukunftsfonds Berlin

Contrary to storage rings, where the electron bunch properties are damped to equilibrium values due to the repeated passages through identical structures, every bunch in a single pass FEL will show individual imprints of it's passage through the linac. Based on ASTRA and ELEGANT tracking studies, realistic bunches were tracked through the BESSY-FEL undulators; the effect of timing errors of the photo cathode laser, and phase and amplitude errors of the RF fields in the injector and the linac on the FEL radiation were studied. The fluctuations of the bunch parameter due to these errors are of the order of magnitude of their variation over the bunch length, reflecting the initial electron distribution and the impact of the passed optics. The unavoidable residual energy chirp in connection with the timing jitter is of concern. The expected shot to shot variations in the FEL output are discussed.

• M. Boscolo, M. Ferrario, V. Fusco, B. Spataro, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• L. Giannessi, M. Quattromini, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• M.  Migliorati, L. Palumbo
  Rome University La Sapienza, Roma
• L. Serafini
  INFN-Milano, Milano

The first phase of the SPARX project is essentially an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. The SPARXINO test facility will generate ultra-high peak brightness electron beams at 1 GeV, thanks to the upgrade of the existing Frascati 800 MeV linac. This facility will allow driving a single pass FEL experiment in the range of 3-5 nm, both in SASE and SEEDED FEL configurations. A peculiarity of this linac design is the choice of integrating a rectilinear RF compressor in the early stage of the acceleration, producing a 300-500 A beam, with a magnetic chicane afterwards, for a further compression up to 1 kA. In this paper we discuss the dynamics of the beam, which is in the space charge dominated regime throughout almost all the linac. Start to end simulations and preliminary stability studies taking into account some significant parameter fluctuations are also reported.

• K. Honkavaara, F. Loehl
  Uni HH, Hamburg
• M. Castellano, G. Di Pirro
  INFN/LNF, Frascati (Roma)
• L. Catani, A. Cianchi
  INFN-Roma II, Roma
• D. Noelle, S. Schreiber
  DESY, Hamburg
• M. Sachwitz, E.S. sombrowski
  DESY Zeuthen, Zeuthen

The VUV-FEL is a new free electron laser user facility under commissioning at DESY. High demands on the electron beam quality require sophisticated beam diagnostics tools and methods. At the VUV-FEL, the transverse characterization of the electron beam is performed using optical transition radiation (OTR) monitors and wirescanners. This paper refers the concepts, analysis, and results of these measurements. The main emphasis is put on the emittance measurements, in which we have regularly observed small rms emittances around 1.4 mm mrad for 90% of a 1 nC bunch at 127 MeV beam energy.

• G. D'Auria, P. Craievich, M. Ferianis, M.M. Milloch
  ELETTRA, Basovizza, Trieste
• dc. Cheever, T. Zwart
  MIT, Middleton, Massachusetts
• L.R. Doolittle, A. Ratti
  LBNL, Berkeley, California

The VUV soft x-ray FEL user facility, FERMI@Elettra, will use the existing 1.2 GeV linac to produce, in two separate phases, 100-40 nm and 40-10 nm, intense photon beams with single stage and double stage harmonic generation schemes respectively. To fulfill the stringent requirements of the project the present RF systems will be completely revised and upgraded. The work presented here describes the present performances of the system and plans for the linac upgrades to meet the required system specifications for FEL operation.

• S. Di Mitri, P. Craievich
  ELETTRA, Basovizza, Trieste
• M. Cornacchia, P. Emma, Z. Huang, J. Wu
  SLAC, Menlo Park, California
• D. Wang
  MIT, Middleton, Massachusetts
• A. Zholents
  LBNL, Berkeley, California

Funding: Sincrotrone Trieste and Director, Office of Science, of the U.S. Department of Energy, under contract No. DE-AC03-76SF00098.

Design studies are in progress to use the existing FERMI@Elettra linear accelerator for a seeded harmonic cascade FEL facility [1]. This accelerator will be upgraded to 1.2 GeV and equipped with a low-emittance RF photocathode gun, laser heater, two bunch compressors, and beam delivery system. We present an optimization study for all the components following the gun, with the aim of achieving high peak current, low energy spread and low emittance electron beam necessary for the FEL. Various operational scenarios are discussed. Results of accelerator simulations including effects of space charge, coherent synchrotron radiation, and wakefields are reported.

[1] C. Bocchetta, et al., FERMI@Elettra - A Seeded Harmonic Cascaded FEL for EUV and Soft X-rays, this conference.

• J.Y. Huang, Y.S. Bae, M.-H. Chun, Y.J. Han, S.-H. Jeong, H.-S. Kang, D.T. Kim, S.H. Kim, S.-C. Kim, I.S. Ko, H.J. Park, I.-S. Park, S.J. Park, Y.J. Park, S.Y. Rah, J.-H. Suh
  PAL, Pohang, Kyungbuk
• J.H. Hong, C. Kim
  POSTECH, Pohang, Kyungbuk

Funding: Work supported by Ministry of Science and Technology (MOST)

Beam diagnostics for PAL-XFEL physics calls for precision of femto-second in time structure and sub-micrometer in beam position measurement(BPM). Existing instruments can be used for standard diagnostics such as single bunch charge measurement, wire scanner or optical transition radiator for beam size measurement. Instead, major R&D efforts should be focused on the measurement of femto-second bunch structure using electro-optic crystal, coherent radiation and transverse deflecting cavity. Nanometer BPM technique being developed in collaboration with linear collider group will also be utilized for sub-micrometer BPM. Overall plan and the ongoing R&D activities will be presented.

• W.H. Hwang, J. Choi, Y.J. Han, J.Y. Huang, H.-G. Kim, W.W. Lee
  PAL, Pohang, Kyungbuk

Funding: Work supported by MOST and POSCO.

In PALXFEL [1], the specification of the beam energy spread and rf phase is tighter than PLS Linac. We examined the rf performance in the present PLS 2.5GeV Linac. The beam energy is changed by cooling temperature, air condition, and modulator high voltage jitter. The main factor to change the beam energy is the rf phase drift by environmental conditions. We measured rf phase drift according to the variation of environmental condition and cooling temperature. We reduced the beam energy drift and the rf phase drift in long-term by improvement of cooling and air conditioning control system. Also, rf phase compensation system is needed for stable beam quality. This paper describes the microwave system for the PALXFEL the rf phase measurement and phase compensation system.

[1] Pohang Accelerator Laboratory, POSTECH Pohang 790-784, Korea

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

PLS W-FEL (1.2 GeV) and X-FEL (3.7 GeV) are designed to have large angle about 30 degree and 20 degree totally because of geometric restriction. This results in severe emittance growth. So PLS FEL BTL Design is focused to adjust emittance growth. This paper talks simulation results of emittance growth and another beam dynamic parameters.

• J.-S. Oh, S. D. Jang, I.S. Ko, S. J. Kwon, W. Namkung, Y. G. Son, J.-H. Suh
  PAL, Pohang, Kyungbuk

Funding: Supported by the POSCO and the MOST, Korea

The PAL (Pohang Accelerator Laboratory) is persuading to construct a SASE-XFEL facility (PAL XFEL) that supplies coherent X-rays. The bright and stable electron beam is essential for the PAL XEL. The electron beams has to have an emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.5 MeV. In order to provide reasonably stable SASE output, the RF stability of 0.02% rms is required for both RF phase and amplitude. This is a technologically challenging issue for PAL XFEL. An inverter technology is to be applied to charge the PFN of a new modulator. Therefore, a new inverter system should provide very stable charging performances. This paper presents the development of an ultra stable klystron-modulator with an inverter power supply.

• S. Sasaki, I. Vasserman
  ANL, Argonne, Illinois

Funding: Supported by the U.S. Dept. of Energy, BES-Office of Science, under Contract W-31-109-ENG-38.

Trajectory straightness through the undulator is critical for the success of the LCLS project. Environmental fields, including the earth’s field, will affect the trajectory. The earth’s field works as an external dipole field and, unless it is shielded or corrected, causes a bend in the electron trajectory through an undulator. We investigated the effects of the earth’s field and an iron plate which might be used as part of a girder. Modeling and calculation were performed using the code RADIA. A model with a large solenoid surrounding a seven-period undulator was used for the simulation. According to the calculations, the vertical component of the earth’s field at the undulator axis is enhanced by the undulator poles by a factor of 2.5. The horizontal on-axis component, however, is well shielded by the undulator poles and falls to less than 3% of its original strength. The effect of an iron plate located 200 mm below the undulator axis is negligibly small, so final Hall probe measurements can be done without the girder in place. However, the magnetic tuning of the undulator field must take into account the amplification of the vertical component of the environmental field in the LCLS tunnel.

• 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.

• T. Limberg, M. Dohlus
  DESY, Hamburg

In present designs for FEL's with high electron peak currents and short bunch lengths, higher harmonic RF systems are often used to optimize the final longitudinal charge distributions. This opens degrees of freedom for the choice of RF phases and amplitudes to achieve the necessary peak current with a reasonable longitudinal bunch shape. It had been found empirically that different working points result in different tolerances for phases and amplitudes. We give an analytical expression for the sensitivity of the compression factor on phase and amplitude jitter for a bunch compression scheme involving two RF systems and two magnetic chicanes as well numerical results for the case of the European XFEL.

• E.J. Minehara, R. Hajima, H. Iijima, N. Kikuzawa, R. Nagai, N. Nishimori, T. Nishitani, M. Sawamura, T. Yamauchi
  JAEA/FEL, Ibaraki-ken

The JAERI high power ERL-FEL has been extended to the more powerful and efficient free-electron laser (FEL) than 10kW for nuclear energy industries, and other heavy industries like defense, shipbuilding, chemical industries, environmental sciences, space-debris, and power beaming and so on. In order to realize such a tunable, highly-efficient, high average power, high peak power and ultra-short pulse FEL, we need the efficient and powerful FEL driven by the JAERI compact, stand-alone and zero boil-off super-conducting RF linac with an energy-recovery geometry. Our discussions on the ERL-FEL will cover the current status of the 10kW upgrading and its applications of non-thermal peeling, cutting, and drilling to decommission the nuclear power plants, and to demonstrate successfully the proof of principle prevention of cold-worked stress-corrosion cracking failures in nuclear power reactors under routine operation using small cubic low-Carbon stainless steel samples.

• S.-H. Lee, S. Sasaki, I. Vasserman, D.R. Walters
  ANL, Argonne, Illinois
• D.E. Kim
  PAL, Pohang, Kyungbuk

Funding: Work supported by DOE under contract no. W-31-109-Eng-38.

A prototype vacuum chamber is being designed for use in the Linac Coherent Light Source at Stanford Linear Accelerator Center under development at the Advanced Photon Source. The chamber will be fabricated from the austenite stainless steels. In general, the magnetic properties of austenite stainless steels are affected by their compositions, processing methods and physical conditions. Austenite stainless steels are generally regarded as non-magnetic in the annealed condition and not attracted significantly by a magnet. However, cold working or welding will change their magnetic properties. This paper presents measurements use to choose a proper chamber material for LCLS undulator, to examine the fabrication processes, and to investigate the relative magnetic permeabilities of the stainless steels such as 316LN, 20Cb-3, Nitronic 33, Nitronic 40 and 310S. This paper presents the results of fabricating of 3"-long vacuum chambers along with their permeability measurements. In addition, the magnetic field variations with/without vacuum chamber under APS undulator A and numerical studies of magnetic field to the permeability of the flat/cylindrical chambers are presented.

• 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.

• 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.

• 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)

• 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).

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• I. Will
  MBI, Berlin
• S. Düsterer, J. Feldhaus, E. Plönjes, H. Redlin
  DESY, Hamburg

Funding: This work was funded by the European Commission under Contract no. HPRI-CT-1999-50009

The VUV-FEL at DESY provides ultra-short pulses with pulse durations below 50 fs. To explore a wider field of time resolved experiments a complex laser system has been installed delivering 150 fs pulses at a wavelength of 800 nm with 50 μJ pulse energy at 1MHz repetition rate during the FEL burst (of 800 μs). In order to perform two color pump-probe experiments the laser has to be synchronized to the FEL. To ensure precise and reliable synchronized operation of the laser, various diagnostic experiments have been developed. Concepts as well as first results of the synchronization will be shown.