• 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.

• P. Michel, P. Evtushenko, U. Lehnert, Ch. Schneider, R. Schurig, W. Seidel, J. Teichert, D. Wohlfarth
  FZR, Dresden

A FEL in the mid infrared range is one of the applications of the ELBE cw-electron accelerator. The successful operation of the lasing process for the different wavelength is mainly determined by the alignment of the optical cavities, the bunch length and the energy spread of the electron beam so as the transversal adjustment of the beam through the FEL. The energy spread and the bunch length of the electron beam have their minima at different phase conditions of the accelerator. For various energy settings of the accelerator a special adjustment of both parameters has to be found for the lasing process. The presentation describes the diagnostic tools used at ELBE for the correct alignment of the optical cavity, the steering of the electron beam through the FEL and the adjustment of the electron beam parameters with respect to energy spread and bunch length.

• 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.

• 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.

• R. Bonifacio
  INFN-Milano, Milano
• N. Piovella
  Universita' degli Studi di Milano, MILANO

We formulate a quantum linear theory of the N-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion, in the steady state regime. Quantum effects such as frequency shift, line narrowing, quantum limitation for bunching and energy spread and minimum uncertainty states are described. Using a second quantization formalism we demonstrate quantum entanglement between the recoiling electrons and the radiation field.

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

In a Storage Ring Free Electron Laser (FEL), the saturation mechanism results from the so-called "bunch heating” phenomenon. The periodic interaction between the electron bunch and the laser pulse within the cavity is responsible of the enhancement of the energy spread of the bunch correlated with a bunch lengthening. Recently, new electron beam optics aiming at achieving low emittance with distributed dispersive function  revealed a particular interest for the FEL. In the undulator straight section, these optics lead also to an increase of the transverse sizes of the beam, and to a significant change of the Touschek lifetime. Experimental results obtained on the Super-ACO and UVSORII FELs illustrating the change of saturation process according to the chromatic or achromatic optics will be given. They will be compared with simulations performed with the LAS model, which has been modified to represent this new saturation process.

• 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).

• 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.

• 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.

• 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.

• 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.

• 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).

• 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.