• 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.

• T. Tanaka
  RIKEN Spring-8, Hyogo
• Y. Asano
  JAEA, Ibaraki-ken
• H. Baba, T. Bizen, Z. Chao, H. Ego, S. Eguchi, S. Goto, T. Inagaki, S. Inoue, D. Iwaki, K. Kase, Y. Kawashima, H. Kimura, S. Kojima, T. Kudo, N. Kumagai, X. Marechal, S. Matsui, T. Ohata, K. Onoe, Y. Otake, T. Seike, K. Shirasawa, N. Shusuke, T. Takagi, T. Takashima, K. Tamasaku, R. Tanaka, K. Togawa, R. Tsuru, S. Wu, M. Yabashi, S. Yoshihiro
  JASRI/SPring-8, Hyogo
• T. Fukui
  Kyoto IAE, Kyoto
• T. Hara, T. Ishikawa, H. Kitamura, T. Shintake
  RIKEN Spring-8 Harima, Hyogo
• H. Matsumoto
  KEK, Ibaraki
• S. Takahashi
  LNS, Sendai

Funding: Representing the SCSS project team

SCSS, an acronym of "SPring-8 Compact SASE Source", is an X-ray FEL project under planning to be build at the SPring-8 site. R&Ds for accelerator components such as the pulsed-DC electron gun, C-band main linac, and in-vacuum short period undulator have been performed and almost completed. Before construction of the X-ray FEL facility, a prototype accelerator with the electron energy of 250 MeV is being built to demonstrate the concept of SCSS. In this presentation, status of the R&Ds for each accelerator component will be presented together with an overview of the 250-Mev prototype accelerator.

• J.W. Baehr
  DESY, Hamburg
• K. Abrahamyan
  YerPhI, Yerevan
• G. Asova, G. Dimitrov
  INRNE, Sofia
• V. Boccone
  Humboldt Universität zu Berlin, Berlin
• H.-J. Grabosch, J.H. Han, S. Khodyachykh, G. Klemz, M. Krasilnikov, S. Liu, H.L. Luedecke, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan, M. Winde, O. kalekin
  DESY Zeuthen, Zeuthen
• M.V. Hartrott, R. Richter
  BESSY GmbH, Berlin
• J.R. Roensch
  Uni HH, Hamburg
• I. Will
  MBI, Berlin

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

In spring of 2005 an essential upgrade of the photocathode laser and of the 27 m long laser beam-line took place at PITZ. A detectable improvement of the laser beam profile at the photocathode is expected. This improvement should lead to an additional reduction of the transverse emittance of the electron beam. The upgraded laser consists of a fully laser diode pumped scheme of pulse train oscillator, pre-amplifiers and booster amplifiers. The main advantages of this upgrade are improved stability, easier maintenance and long-term operations at 10 Hz repetition rate. In addition, the scheme of the optical beam-line was changed: The distance between the beam shaping aperture and the cathode was strongly reduced. Therefore a further improvement of the laser beam profile at the photocathode is expected. The laser beam-line is upgraded by an enlarged number of remotely controlled optical elements that allows the fine tuning of the laser beam characteristics during the running. New diagnostics tools are included in the laser beam-line. The paper focuses on the design of the new optical beam-line. It describes the results of electron beam measurements using the upgraded laser and the new PITZ2 electron beam-line in detail.

• 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.

• 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.

• H. Tomizawa, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, K. Yanagida
  JASRI/SPring-8, Hyogo
• F. Matsui
  ,

We have been studying photocathode single-cell pillbox rf gun for future light sources since 1996. We achieved a rmaximum field gradient of 187 MV/m with chemical-etching processed cavity. We have been developed stable and highly qualified UV-laser source for the rf gun intensively last 3 years. The UV-laser pulse (10 Hz) energy is up to 850 uJ/pulse. The energy stability (rms) of laser has been improved down to 0.2~0.3 % at the fundamental and 0.7~1.3% at the third harmonic generation. This stability is held for two months continuously. In this improvement, we just passively stabilized the system in a humidity-controlled clean room. On the other hand, the ideal spatial and temporal profiles of a shot-by-shot single laser pulse are essential to suppress the emittance growth of the electron beam from the rf gun. We prepared a deformable mirror for spatial shaping, and a spatial light modulator based on fused-silica plates for temporal shaping. With a deformable mirror, we obtained an emittance of1.6<pi> mm mrad with beam energy of 28 MeV, holding its net charge to 0.1 nC/bunch. The both adaptive optics automatically optimize electron beam for lower emittance with a feedback routine.

• H. Hama, F. Hinode, M. Kawai, T. Tanaka
  LNS, Sendai

Funding: Supported partly by a Grant-in Aid for Scientific Research from Japan Society for the Promotion of Science, #17360035

As a result of simulation study so far, a specific feature has been found in the longitudinal dynamics in thermionic RF guns. At the beginning of beam extraction, the head of the electrons from a cathode is followed immediately by the electrons just behind, which is extracted by the higher electric field than that at the head of the beam train. Thus later electrons would get velocity faster than the head of the electrons, so that the electrons are expected to concentrates onto the head of the beam under certain conditions such as the gun geometry and the strength of the RF field. In order to investigate this velocity-bunching like effect, a prototype thermionic RF gun was designed and its characteristics have been studied by a 3-D simulation code based on a FDTD (finite difference time demain) method. The gun is consists of two independentlly power feeding S-band RF cavities, and can be operated at modes with different power ratio and phase between two RFs. This paper report the thermionic RF gun is expected to produce several hundreds femtosecond pulse containing approximately 0.1 nC, which may be a powerful tool to generate THz coherent radiation or FELs driver.

• 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.

• G.M. wang, J.-E. Chen, Y.T. Ding, J. Hao, S.L. Huang, L. Lin, X.Y. Lu, S.W. Quan, L.F. Wang, R. Xiang, B.C. Zhang, K. Zhao, F. Jiao, D. Xie, L. Yang, F. Zhu, C. Liu, F. Wang, W. Xu, Z. Liu
  PKU/IHIP, Beijing
• Y.G. Wang
  Peking University, School of Physics, Beijing

Funding: NSFC, MOST of China

Beam loading experiments on DC-SC photoinjector test facility have been finished at 4.4 K. Upon the present experiments, the gradient of 6 MV/m is achieved. The maximum energy gain is 1.1 MeV at 4.4 K. With average beam current of 270 mA, the measured rms emittance is about 5 mm-mrad at the beam energy of 500 keV. Experiments on the test facility has validated that the DC-SC photoinjector is a good choice to provide moderate average current electron beams with low bunch charge and very high repetition rate.

• G.V. Stupakov, Z. Huang
  SLAC, Menlo Park, California

Funding: This work was supported by the Department of Energy, contract DE-AC02-76SF00515.

Several ideas have been proposed in the past to "condition" an electron beam prior to the undulator of a Free-Electron Laser (FEL) by increasing each particle's energy in proportion to the square of its transverse betatron amplitude. This conditioning enhances FEL gain by reducing the axial velocity spread within the electron bunch. Nevertheless, a practical solution for beam conditioning remains difficult. In this paper we consider a new approach to condition the beam using nonlinear effects in the RF field. We demonstrate that such effects can generate a radial variation of the particle's energy in the beam, and and calculate the induced energy spread in the limit of weak field. Methods to minimize the emittance growth in such a beam conditioner are also discussed.

• 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.

• J.-Y. Raguin, R.J. Bakker, K.S.B. Li, M. Pedrozzi
  PSI, Villigen

In the Low Emittance Gun (LEG) under development at PSI an extremely bright electron beam is produced from a field emission array and then rapidly accelerated in a diode configuration up to 1 MeV with gradients of the order of 250 to 500 MV/m. The electronic emission from such a cold cathode allows normalized intrinsic emittance below 0.1 mm.mrad well suited for X-ray FELs or linear collider applications. The diode is followed by an L-band RF-gun like cavity to further accelerate the beam. A third harmonic field is superposed to the fundamental [1] 1.5 GHz pi-mode field to minimize the RF emittance. We report here on the design of such a two-frequency RF cavity with some details on the RF coupling and possible tuning mechanisms. Beam dynamics studies, performed with PARMELA and the fully self-consistent code MAFIA, are presented and compared with the results obtained for an RF cavity excited with the fundamental frequency only.

[1] D.H. Dowell et al., Nucl. Instr. and Meth. A 528 (2004) 316.

• K. Honkavaara
  Uni HH, Hamburg

The VUV-FEL being commissioned at DESY Hamburg is a user facility for SASE FEL radiation in the VUV wavelength range. The quality of the high brightness electron beam driving the VUV-FEL plays an important role for the performance of the facility. Prior to installation, the electron photo-injector of the VUV-FEL has been fully tested and characterized at the PITZ photo injector test facility at DESY Zeuthen, dedicated to develop high brightness electron sources for FEL projects like the VUV-FEL and the XFEL. We summarize the results on transverse emittance optimization at PITZ and report on the upgrade of the PITZ facility presently under construction. Results on transverse emittance optimization and measurements at the VUV-FEL are presented. Projected emittances around 1.4 mm mrad for 90% of a 1 nC bunch have been regularly measured. In addition, recent measurements of the longitudinal bunch profile after compression using a transverse deflecting cavity are presented.

• C. Limborg-Deprey
  SLAC, Menlo Park, California

Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC02-76SF00515

If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for normal conducting RF guns the photo-electron distribution should approach a 3D-ellipsoidal shape. The emittance at the end of the injector would reduce to the combination of cathode emittance and RF emittance. We explore how the emittance and the brightness can be optimized for normal conducting photocathode RF gun depending on the peak current requirements. Techniques available to produce those ideal laser pulse shapes are also discussed.

• B.W. Adams
  ANL, Argonne, Illinois

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

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

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.