FEL 2006 - List of Keywords (laser)

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laser

Paper	Title	Other Keywords	Page
MOAAU01	FEL Prize Lecture: Coherent Electron-Beam Radiation Sources and FELs: A Theoretical Overview	radiation, electron, bunching, undulator	1
	A. Gover, E. Dyunin University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
	The theory of Coherent electron beam radiation devices in general, and FEL in particular, is reviewed in terms of a general simple formulation based on modal expansion of the radiation field. A variety of e-beam radiation mechanisms (FEL, TWT, Cerenkov Radiation) have common features. All these radiation mechanisms can emit coherent or partially coherent radiation by means of three basic kinds of radiation processes: Spontaneous emission (shot-noise radiation), Superradiance (bunched-beam coherent radiation) and Stimulated emission. The common radiation processes and their relations are explained, in both frequency and time domains, in terms of the radiation modes expansion formulation. It is shown that the coherence properties of the emitted radiation, in each radiation process, depend on the phase relations between the radiation wave-packets, emitted by the individual electrons and their entrance distribution statistics. In the high gain linear regime all these radiation mechanisms satisfy the Pierce dispersion equation, and all radiation characteristics are derived from the Pierce transfer functions. I employ the formulation to delineate limits of coherence of electron beam radiation sources, and particularly examine possible schemes for turning SASE FELs to operate as coherent radiation sources.
	Slides
	Talk

MOAAU05	The First Lasing of 193 nm SASE, 4th Harmonic HGHG and ESASE at the NSLS SDL	electron, undulator, diagnostics, linac	18
	X. J. Wang, J. B. Murphy, J. Rose, Y. Shen, T. Tsang, T. Watanabe BNL, Upton, Long Island, New York
	After successfully achieving SASE lasing at 198 nm on April 20, 2006, we have also observed the first 4th harmonic High Gain Harmonic Generation (HGHG) with a 795 nm seed laser. We will report the progress and experimental characterization of the 198 nm SASE and 4th harmonic HGHG.
	Slides
	Talk

MOPPH001	Coherent Harmonic Generation on UVSOR-II Storage Ring	electron, storage-ring, radiation, undulator	37
	M. Labat, G. Lambert CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara RIKEN Spring-8 Harima, Hyogo M. Hosaka, M. Katoh, A. Mochihashi, M. Shimada, J. Yamazaki UVSOR, Okazaki D. Nutarelli LAC, Orsay Y. Takashima Nagoya University, Nagoya
	In the Coherent Harmonic Generation Free Electron Laser configuration, an external seed signal, a commercial laser source, is focused inside the first undulator. The interaction between the electron beam and this seed leads to a more coherent light emission. Such devices are very promising for short wavelength operation with a rather compact facility. Experiments have been performed on the UVSOR-II Storage Ring (Okazaki, Japan) with electrons stored at 600 MeV, and using a 2.5 mJ Ti:Sa laser at 800 nm wavelength, 1 kHz repetition rate, and 100 fs up to 2 ps pulse duration, allowing emission at 266 nm. This third harmonic has been characterised versus various parameters. Optimizations have been realized on the electron beam and laser synchronisation, seed characteristics (focussing point, energy, and pulse duration). The dependency of the harmonic signal on the gain (undulator gap, magnetic functions) has also been studied. Theory is compared to experiment using both analytical models and simulation. These encouraging results make UVSOR-II storage ring an active test facility for Coherent Harmonic Generation scheme, as well as a potential VUV source for users experiments.

MOPPH008	A Beam Shaper for the Optical Beamline of RF Photoinjectors	cathode, radiation, electron, controls	53
	G. Klemz MBI, Berlin I. Will FZR, Dresden
	The transversal beam profile of a laser beam irradiating the photocathode has a significant influence on the emittance of the generated electron beam. Achieving the lowest emittance requires a flat-top beam profile. A typical laser, however, produces an intensity profile which is close to a Gaussian. That is why a special optical element, the so-called beam shaper, is required. We compare different technical solutions for the critical beam-shaping element. The demands on the design of the beamline resulting from the insertion of the beam shaper will be outlined. An aspherical lens pair of the Galilean type seems to be a favourable solution. It permits to precisely control the final intensity profile, it maintains both the temporal shape of the pulse and the coherence of the laser beam. Simulation of the propagation of the beam profile are presented. The described refractive beam-shaper significantly improves the energy efficiency of the complete beamline. It therefore allows to reduce the requirements regarding the energy of the laser pulses. Consequently, the application of an appropriately designed beam shaper can lead to a significant reduction of the overall costs of the laser.

MOPPH014	Optimization of Parameters of Smith-Purcell BWO	electron, emittance, space-charge, free-electron-laser	67
	V. Kumar RRCAT, Indore (M. P.) K.-J. Kim ANL, Argonne, Illinois
	We perform a detailed study of the dependence of start current in Smith-Purcell Backward Wave Oscillators (SP-BWO) on grating parameters and electron beam parameters. In our analysis, we include the attenuation due to finite conductivity of the grating material into account and also include three-dimensional effects approximately. We perform numerical simulation to optimize the parameters of an SP-BWO in order to generate intense THz-radiation.

MOPPH022	Control of the Intensity of a Wave Interacting with Charged Particles	controls, electron, plasma, resonance	83
	D. Fanelli, A. Antoniazzi Università di Firenze, Florence R. Bachelard, C. Chandre, X. Leoncini, M. Vittot CNRS/CPT, Marseille
	The interaction between a wave and a bunch of charged particles is encountered in many branches of applied physics ranging from particle accelerators to laser physics (Free Electron Laser). Generically, this self-consistent interaction leads to an exponential increase of the intensity of the wave, followed by an oscillating saturation. It is an interesting problem to regularize the saturated dynamics and thus improve the performance of the device. The aim of this paper is to show that it is possible to influence by external perturbation the dynamics of the particles in order to enhance the stability of the system resulting in a reduction of the oscillations of the waves. We apply a Hamiltonian control technique based on a small and apt modification of the potential to recreate or break up invariant (KAM) tori in phase space. We show that an appropriate tuning of the control parameters is able to reduce by an order of magnitude the amplitude of the oscillations without affecting the total power of the wave. This technique has been successfully implemented on a Travelling Wave Tube in the test-particle regime. C. Chandre et al., Phys. Rev. Lett. 94, 074101 (2005)

MOPPH025	Free Electron Laser as Paradigmatic Example of Systems with Long-Range Interactions	electron, coupling, free-electron-laser, bunching	87
	D. Fanelli, A. Antoniazzi, S. Ruffo Università di Firenze, Florence J. Barre' Université de Nice Sophia-Antipolis, Nice T. Dauxois ENS LYON, Lyon G. De Ninno ELETTRA, Basovizza, Trieste
	Long range interactions are such that the two-body interaction potential decreases at large distance with a power which is smaller or equal to the space dimension. Examples include gravitational forces, unshielded Coulombic interaction. In presence of long-range interactions, physics is very peculiar and a wide range of striking phenomena appears. In particular energy is non additive, hence the system under scrutiny cannot be divided into independent macroscopic parts, as it is usually the case for short-range interactions. These unexpected features are systematically detected, independently of the specific nature of the long-range interactions involved. FEL are one of the most interesting examples of systems with long-range interactions, where the interplay between collective (wave) and individual (particles) degrees of freedom is well known to be central and, in this respect, provides a unique experimental ground to investigate such universal pecularities. In this presentation I will review the main characteristics of such systems and dicuss the statistical theory of the Vlasov equation, a wide general approach that enables to analytically investigate the laser saturated regime.

MOPPH028	Future Seeding Experiments at SPARC	undulator, radiation, resonance, electron	95
	L. Giannessi, S. Ambrogio, F. Ciocci, G. Dattoli, A. Doria, G. P. Gallerano, E. Giovenale, M. Quattromini, A. Renieri, C. Ronsivalle, I. P. Spassovsky ENEA C. R. Frascati, Frascati (Roma) D. Alesini, M. E. Biagini, R. Boni, M. Castellano, A. Clozza, A. Drago, M. Ferrario, V. Fusco, A. Gallo, A. Ghigo, M. Migliorati, L. Palumbo, C. Sanelli, F. Sgamma, B. Spataro, S. Tomassini, C. Vaccarezza, C. Vicario INFN/LNF, Frascati (Roma) M. Bougeard, B. Carré, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Salieres, O. Tcherbakoff CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette A. Dipace, E. Sabia ENEA Portici, Portici (Napoli) M. Mattioli Università di Roma I La Sapienza, Roma P. Musumeci, M. Petrarca INFN-Roma, Roma M. Nisoli, G. Sansone, S. Stagira, S. de Silvestri Politecnico/Milano, Milano P. L. Ottaviani, S. Pagnutti, M. Rosetti ENEA-Bologna, Bologna L. P. Poletto, G. T. Tondello Univ. degli Studi di Padova, Padova L. Serafini INFN-Milano, Milano
	Sources based on high order harmonics generated in gas with high power Ti:Sa lasers pulses represent promising candidates as seed for FEL amplifiers for several reasons, as spatial and temporal coherence, wavelength tunability and spectral range, which extends down to the 10^-9m wavelength scale. This communication is devoted to the description of a research work plan that is under implementation at the SPARC FEL facility in the framework of the EUROFEL programme. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in crystal (400nm and 266 nm) and in gas (266nm, 160nm, 114nm) from a high intensity Ti:Sa laser pulse.

MOPPH030	X-Rays Generation with a FEL Based on an Optical Wiggler	electron, radiation, emittance, bunching	99
	A. Bacci, C. Maroli, L. Serafini INFN-Milano, Milano M. Ferrario INFN/LNF, Frascati (Roma) V. Petrillo Universita' degli Studi di Milano, Milano
	The interaction between high-brilliance electron beams and counter-propagating laser pulses produces X rays via Thomson back-scattering. If the laser source is long and intense enough, the electron beam can bunch on the scale of the X-ray wavelength and a regime of collective effects can establish. In this case the FEL instability can develop and the system behaves like a FEL based on an optical undulator. Coherent X-rays can be irradiated, with a bandwidth thinner than that of the corresponding incoherent emission. The emittance of the electron beam and the non-uniformity of the laser energy limit the growth of the X-ray signal. We analyse with a 3-D code the transverse effects in the emission. The scalings typical of the optical wiggler make possible considerable emission also in violation of the Pellegrini criterion for static wigglers. A generalized form of this criterion is validated on the basis of the numerical evidence. An optimization of the radiation intensity has been done shifting the focus of the beam. The dependence of the radiation on the stability of the laser pulse has been studied. INFN, Section of MIlan, Via Celoria,16 20133 Milano (Italy)

MOPPH031	The Saturated Regime of a Seeded Single-Pass Free Electron Laser: a Theoretical Investigation through the Statistical Mechanics of the Vlasov Equation	electron, undulator, bunching, radiation	103
	F. Curbis, F. Curbis Università degli Studi di Trieste, Trieste A. Antoniazzi, D. Fanelli Università di Firenze, Florence G. De Ninno ELETTRA, Basovizza, Trieste
	The quasi-stationary state characterizing the saturation of a single-pass free-electron laser is governed by the Vlasov equation obtained by performing the continuum limit of the Colson-Bonifacio model. By means of a statistical treatment, this approach allows to predict analytically the saturated laser intensity as well as the final electron-beam energy distribution. In this paper we consider the case of coherent harmonic generation obtained from a seeded free-electron laser and present predictions for the first stage of the project FERMI at Elettra project at Sincrotrone Trieste.

MOPPH032	Analysis of FEL Oscillations in a Perfectly Synchronized Optical Cavity	electron, undulator, radiation, linac	107
	N. Nishimori JAEA/FEL, Ibaraki-ken
	We analyze free electron laser (FEL) oscillations in a perfectly synchronized optical cavity by solving the one dimensional FEL equations. The radiation stored in the cavity is shown to finally evolve into an intense few-cycle optical pulse in the high gain and low loss regime. The evolution of the leading slope of the optical pulse, which is defined from the front edge toward the primary peak, is found to play an important role in generating the intense few-cycle pulse. The phase space evolution of electrons on the second pass which interact with the leading slope of a SASE output pulse is obtained in a perturbation method similar to that used in our previous study for a SASE FEL. The resulting analytical solution of the leading slope in the 2nd pass is shown to be approximated by that of a SASE FEL with FEL parameter greater than rho. The same perturbation method can thus be used to the subsequent passes. The peak amplitude and the pulse length at saturation are found to scale with the electron beam density and optical cavity loss. Those scalings accounts for the intense few-cycle FEL pulses observed in a high power FEL. N. Nishimori, Phys. Rev. ST-AB 8, 100701 (2005).

MOPPH033	Two-Stream Smith-Purcell Free-Electron Laser Using a Dual-Grating: Linear Analysis	electron, free-electron-laser, radiation, simulation	111
	D. Li, K. Imasaki ILT, Suita, Osaka Z. Liang, W. Liu, Z. Yang UESTC, Chengdu, Sichuan
	We present a linear analysis of two-stream Smith-Purcell Free-Electron Laser (SP-FEL). In this system, two electron-beams with velocity separation pass a rectangular dual-grating. The dispersion relation is derived employing the linear fluid theory and the growth rate is investigated through the numerical solutions. The instability of two-stream is obtained at an optimize separation velocity, and the effects of separation velocity , distance between the dual-grating, groove-depth, groove-width, beams energy on growth rate and bandwidth are studied in detail.

MOPPH034	Production of 'Giant' Pulses of Scattered Radiation from Pump Wave Spot Runing over the Electron Beam	electron, radiation, scattering, simulation	115
	N. S. Ginzburg, V. R. Baryshev, A. Sergeev, I. V. Zotova IAP/RAS, Nizhny Novgorod
	To generate ultrashort electromagnetic pulses it is suggested to use the superradiance (SR) effects in the process of stimulatted scattering when the spot illuminated by pump wave shifts along the electron beam with group velocity of scattered radiation. According to theoretical consideration it is shown that in such conditions the amplitude of scattered SR pulse is proportional to interaction distance. This process is not sensitive to the dispersion of beam parameters due to extremely short time of wave interaction with every electron. In the case of scattering of laser radiation by a moderately relativistic electron beam it is possible to produce intense SR pulses either at terahertz (down conversion) or at UV (up conversion) frequency band depending on direction of pump wave propagation with respect to electron beam. In principle, to shift the illuminated spot along the electron beam, reflection of the pump wave by rotating mirror can be used. More realistic method is the transmission of the frequency-modulated pump wave through an optical prism.

MOPPH036	Influence of Linear Fluctuations on Low- and High-Gain Cherenkov FELs	electron, radiation, free-electron-laser, bunching	118
	I. de la Fuente, K.-J. Boller, P. J.M. van der Slot Twente University, Laser Physics and Non-Linear Optics Group, Enschede
	In a previous study* it was shown that irregularities in the liner result in phase fluctuations of the ponderomotive potential which affects the gain of a low energy Cerenkov FEL. Here we investigate numerically how sensitive a Cerenkov FEL is to such fluctuations when operating in different gain regimes. For this study we considered an increased transverse dimensions of the liner and electron beam as compared to the study presented in, while the resonance frequency and beam voltage are held constant around 50 GHz and 80 kV respectively. The different gain regimes then correspond to different electron beam currents ranging from 0.8 A to 20 A. Without liner fluctuations, these beam currents result in a single pass saturated output power of approx. 200 W to 25 kW respectively, where the laser output saturates in a much shorter distance for the higher beam current. We have found that the low gain system (I=0.8 A) shows a much higher sensitivity to liner fluctuations than the high gain system (I=20 A). I de la Fuente, PJM van der Slot and K-J Boller. Proceedings of the 26th International Free-Electron Laser Conference and the 11th FEL User-Workshop. Trieste, Italy, p53-56 (2004)

MOPPH037	Theory of Radiation of Electrons in the Field of a Linear Polarized Stationary Electromagnetic Wave	electron, radiation, polarization	122
	I. V. Drebot, Yu. N. Grigor'ev, A. Y. Zelinsky NSC/KIPT, Kharkov
	In the paper the results of exact integration of Lorentz equation for a free electron in the field of a linear polarized stationery electromagnetic wave are presented. Stationary wave is considered as a sum of two running in opposite directions linear polarized waves. Single integration of projections of equations on coordinate axes allows to reduce the task to solution of nonlinear equation of the second order for electron coordinate. The axis of projection coincides with a wave line. For approximate integration of the second order equation the expansion on two small parameters are used. Velocity and coordinate of electron in parametric form are presented in the paper. It is shown that under interaction of a relativistic electron with stationary wave there is a motion, which has a beat character. The amplitude and period of the beating were calculated.

MOPPH040	Transverse Coherence Properties of the LCLS X-Ray Beam	radiation, undulator, electron, simulation	126
	S. Reiche UCLA, Los Angeles, California H.-D. Nuhn SLAC, Menlo Park, California
	Self-amplifying spontaneous radiation free-electron lasers, such as the LCLS or the European XFEL, rely on the incoherent, spontaneous radiation as the seed for the amplifying process. Though this method overcomes the need for an external seed source one drawback is the incoherence of the effective seed signal. The FEL process allows for a natural growth of the coherence because the radiation phase information is spread out within the bunch due to slippage and diffraction of the radiation field. However, at short wavelengths this spreading is not sufficient to achieve complete coherence. In this presentation we report on the results of numerical simulations of the LCLS X-ray FEL. From the obtained radiation field distribution the coherence properties are extracted to help to characterize the FEL as a light source.

MOPPH042	An Analysis of Shot Noise Propagation and Amplification in Harmonic Cascade FELs	electron, bunching, undulator, radiation	130
	Z. Huang SLAC, Menlo Park, California
	The harmonic generation process in a harmonic cascade (HC) FEL is subject to noise degradation which is proportional to the square of the total harmonic order. In this paper, we study the shot noise evolution in the first-stage modulator and radiator of a HC FEL that produces the dominant noise contributions. We derive the effective input noise for a modulator operating in the low-gain regime, and analyze the radiator noise for a density-modulated beam. The significance of these noise sources in different harmonic cascade designs is also discussed. E. Saldin, E. Schneidmiller, M. Yurkov, Opt. Commun. 202, 169 (2002).

MOPPH044	Optical Beam Quality in Free-Electron Lasers	wiggler, simulation, electron, higher-order-mode	134
	P. Sprangle, J. Penano NRL, Washington, DC H. Freund SAIC, McLean B. Hafizi Icarus Research, Inc., Bethesda, Maryland
	The quality of the FEL optical beam is an important consideration for many applications. The quantity M-squared is a single parameter that is used to quantify the higher-order transverse mode content of the beam. For steady state propagation in the paraxial limit, equations for the axial variation of the laser spot size and M-squared are derived. The quantity M-squared for the output of an FEL can also be determined by making measurements of the spot size at three locations and making use of the parabolic propagation law. We consider the optical beam quality for a MW-class amplifier. In this configuration the radiation is optically guided, maintaining a constant spot size through the wiggler, and is pinched at the wiggler exit. This leads to a relatively good optical beam quality, short growth length, short wiggler length, and good efficiency. Diffractive spreading of the FEL output beam can be sufficiently large to allow the first relay mirror to be close to the exit of the wiggler without exceeding the mirror damage intensity threshold, particularly in a grazing incidence configuration. The minimum distance to the relay mirror is shown to be inversely proportional to M-squared.

MOPPH046	Seeding the FEL of the SCSS Prototype Accelerator with Harmonics of a Ti:Sa Laser Produced in Gas.	undulator, focusing, radiation, simulation	138
	G. Lambert, M. Bougeard, W. Boutu, B. Carré, D. Garzella, M. Labat CEA, Gif-sur-Yvette O. V. Chubar, M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara, H. Kitamura, T. Shintake RIKEN Spring-8 Harima, Hyogo
	A particular seeded configuration will be tested in 2006 on the SCSS test facility (SPring-8 Compact Sase Source, Japan). This facility is based on a thermionic cathode electron gun (1 nC), a C-band LINAC (5712 MHz, 35 MV/m) and two in-vacuum undulators (15 mm of period). The maximum electron beam energy is 250 MeV and the SASE emission from visible to 60 nm can be obtained. The external source, obtained by the High order Harmonic Generation (HHG) process, can be tuned from the 3th (260 nm) to the 13th harmonic (60 nm) of a Ti: Sa laser generated in a gas cell. The experiment contains a first chamber, dedicated to harmonic generation and a second one for harmonic beam diagnostics and adaptation of the harmonic waist in the modulator. The tests have been performed in Saclay (15 mJ, 10 Hz, 50 fs). An energy of 2e-6J with a high stability for the 3th harmonic and a good transversal shape with an optimized energy level and a high stability for the 13th harmonic have been obtained at the modulator center place. The performances using PERSEO, GENESIS and SRW will be updated. The chambers will be installed on the SCSS test facility in the beginning of July for seeding tests during summer.

MOPPH047	Seeding SPARC Facility with Harmonic Generation in Gases: Preliminary Tests of the Harmonic Generation in Gas Chamber	undulator, electron, photon, focusing	142
	O. Tcherbakoff, M. Bougeard, P. Breger, B. Carré, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Monchicourt, P. Salieres CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette A. Doria, L. Giannessi ENEA C. R. Frascati, Frascati (Roma)
	A coherent short wavelength source can be realised with a Free Electron Laser by using High Gain Harmonic Generation configuration. The injection of an external light source in the first part of an undulator results in a coherent light emission in its second part. The SPARC FEL (Frascati, Italy), delivering an electron beam at 200 MeV passing through an undulator of 6 sections, can be configured to test such schemes. We propose to use High order Harmonic Generation (HHG) in gases process as the seed. HHG produces a coherent XUV source by focusing an intense laser pulse into a gas medium. This beam, composed of odd harmonics of the fundamental laser, is then shaped using a telescope of two spherical mirrors, allowing the focusing at a given position, in the SPARC undulator. Appropriate tuning of the undulator gaps will amplify the 3rd and 5th harmonics seeded, and non-linear harmonics of those wavelengths, allowing the perspective of producing VUV coherent radiation. The chambers for harmonic generation and shaping have been realised and tested at the CEA (Saclay, France). We present these tests as well as simulations of the expected performances of the SPARC FEL with this seed.

MOPPH048	The ARC-EN-CIEL FEL Proposal	emittance, radiation, undulator, electron	146
	C. Bruni, O. V. Chubar, J.-M. Filhol, A. Loulergue, L. Nahon SOLEIL, Gif-sur-Yvette P. Bosland, B. Carré, M.-E. Couprie, G. Devanz, D. Garzella, O. Gobert, Ph. Hollander, M. Jablonka, M. Labat, G. Lambert, M. Luong, F. Meot, P. Monot, A. Mosnier, G. Petite, O. Tcherbakoff, B. Visentin CEA, Gif-sur-Yvette J.-R. Marquès LULI, Palaiseaux H. Monard, J.-M. Ortega CLIO/ELYSE/LCP, Orsay A. Rousse LOA, Palaiseau
	ARC-EN-CIEL (Accelerator-Radiation for Enhanced Coherent Intense Extended Light aims at providing the user community with coherent femtosecond light pulses covering from UV to soft X ray in France. Phase 1 aims at exploiting the different sources of seeding, in particular Harmonic generation in Gas (HHG), to improve the longitudinal coherence and shortening the output radiation wavelength in a rather compact device. Phase 2 uses a CW 10 KHz 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches for HHG seeded High Gain harmonic Generation extending to 1 nm. In phase 3, fs undulator sources in the IR, VUV and X ray and a FEL oscillator in the 10 nm range will be implemented on ERL beam loops for beam current or energy enhancement. Electron plasma acceleration and fs hard X ray produced by Thomson Scattering are also foreseen. Preliminary studies are carried out in the frame of the EUROFEL collaboration, concerning the electro-optical measurement at ELYSE, carbon nanotubes, synchronisation and beam shaping for the gun, seeding with high harmonics produced in gas on SPARC and compensation of microphonics for the Linac.

MOPPH054	FERMI @ Elettra: A Seeded FEL Facility for EUV and Soft X-Rays	electron, linac, undulator, radiation	166
	J. N. Corlett, L. R. Doolittle, W. M. Fawley, S. M. Lidia, G. Penn, I. V. Pogorelov, J. Qiang, A. Ratti, J. W. Staples, R. B. Wilcox, A. Zholents LBNL, Berkeley, California E. Allaria, C. J. Bocchetta, D. Bulfone, F. C. Cargnello, D. Cocco, P. Craievich, G. D'Auria, M. B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, M. Ferianis, A. Galimberti, A. Gambitta, M. Giannini, F. Iazzourene, E. Karantzoulis, M. Lonza, F. M. Mazzolini, G. Penco, L. Rumiz, S. Spampinati, G. Tromba, M. Trovo, A. Vascotto, M. Veronese, M. Zangrando ELETTRA, Basovizza, Trieste M. Cornacchia, P. Emma, Z. Huang, J. Wu SLAC, Menlo Park, California W. Graves, F. X. Kaertner, D. Wang MIT, Middleton, Massachusetts
	We describe the conceptual design and major performance parameters for the FERMI FEL project funded for construction at the Sincrotrone Trieste, Italy. This user facility complements the existing storage ring light source at Sincrotrone Trieste, and will be the first facility to be based on seeded harmonic cascade FELs. Seeded FELs provide high peak-power pulses, with controlled temporal duration of the coherent output allowing tailored x-ray output for time-domain explorations with short pulses of 100 fs or less, and high resolution with output bandwidths of the order of meV. The facility uses the existing 1.2 GeV S-band linac, driven by electron beam from a new high-brightness rf photocathode gun, and will provide tunable output over a range from ~100 nm to ~10 nm, and APPLE undulator radiators allow control of x-ray polarization. Initially, two FEL cascades are planned, a single-stage harmonic generation to operate over ~100 nm to ~40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelengh, each with spatially and temporally coherent output, and peak power in the GW range.

MOPPH055	Coherent Harmonic Emission of the Elettra Storage-Ring Free-Electron Laser in Single-Pass Configuration: a Numerical Study for Different Undulator Polarizations	undulator, simulation, electron, storage-ring	170
	F. Curbis, F. Curbis Università degli Studi di Trieste, Trieste G. De Ninno ELETTRA, Basovizza, Trieste H. Freund SAIC, McLean
	The optical klystron installed on the Elettra storage-ring is normally used as interaction region for an oscillator free-electron laser, but, removing the optical cavity and using an external seed laser, one obtains an effective scheme for the single-pass harmonic generation. In this configuration, which is presently under development, the high-power external laser is synchronized with the electron beam entering the first undulator of the optical klystron. The laser-electron beam interaction produces a spatial partition of electrons in micro-bunches separated by the seed wavelength. The micro-bunching is then exploited in the second undulator (radiator) to produce coherent light at the harmonics of the seed wavelength. The Elettra radiator is an APPLE type undulator and this allows to explore different configurations of polarization. We present here numerical results obtained using the code Medusa for both planar and helical configurations. We also draw a comparison with predictions of the numerical code Genesis.

MOPPH057	Design and Performance of the FERMI at Elettra FEL	undulator, electron, simulation, photon	174
	G. De Ninno, E. Allaria ELETTRA, Basovizza, Trieste W. M. Fawley, G. Penn LBNL, Berkeley, California
	The FERMI project* at Sincrotrone Trieste is the first user facility based on seeded, harmonic cascade FELs. The second stage FEL will produce tunable output in the 10-40nm wavelength range and will rely upon two stages of harmonic up-conversion. A major goal for this FEL is good longitudinal output coherence (i.e., small spectral bandwidth). At present, we are examining the performance characteristics of two possible configurations. The first "fresh bunch" option is a classic harmonic cascade, where the output radiation from the first radiator is used to seed a fresh part of the electron bunch in the second-stage modulator. The second "whole bunch" scheme seeds the entire e-beam pulse, uses a much shorter first radiator and completely eliminates the second modulator, with the second radiator involving many e-folds of gain. Relying both upon time-steady input parameter sensitivity studies and full start-to-end time-dependent simulations*, we examine the predicted performance of the two configurations and compare with users requirements. C. Bocchetta et al., this meeting ** S. Di Mitri et al., this meeting

MOPPH061	The Test Facility for Harmonic Generation at the MAX-lab Injector Linac	undulator, electron, gun, linac	182
	S. Werin, M. Brandin, T. Hansen, S. Thorin MAX-lab, Lund M. Abo-Bakr, J. Bahrdt, K. Goldammer BESSY GmbH, Berlin A. L'Huillier, J. Larsson, A. Persson, C.-G. Wahlstrom New Affiliation Request Pending, -TBS-
	The MAX-lab injector linac system will be used in a test set-up for developing and testing techniques important for the designs of the BESSY FEL and the MAX IV FEL proposals. The first goal is using a 400 MeV electron beam to generate third harmonic photons at 90 nm from a 266 nm seed laser. The installations at MAX-lab are being improved by a new photo cathode RF gun (to improve emittance and peak current), an optical klystron (2 undulators + chicane, supplied by BESSY) and a combined synchronised laser system for both the RF-gun and the seeding system. The injector optics and transport system are also being retuned to allow the necessary electron beam compression. The project is a part of the EUROFEL collaboration.

MOPPH063	Coherent X-Ray Production by Cascading Stages of High Gain Harmonic Generation Free Electron Lasers Seeded by IR Laser Driven High-Order Harmonic Generation	radiation, electron, undulator, emittance	186
	J. Wu, P. R. Bolton SLAC, Menlo Park, California
	Coherent x-ray production achieved by seeded free electron lasing with cascaded high gain harmonic generation (HGHG) is important for next generation development of synchrotron light sources. We examine the feasibility and some features of FEL emission seeded by a high order harmonic of an intense infrared conventional laser source (HHG). In addition to the intrinsic FEL chirp phenomenon, the longitudinal profile and spectral bandwidth of the HHG seed are modified significantly by the FEL interaction well before saturation occurs. This smears out the original attosecond pulselet structure. As an example, we describe a cascaded HGHG scheme for coherent x-ray FEL generation that is seeded by the twenty-seventh harmonic of an ultrashort 800 nm laser pulse with 10 fs rms duration. Given the multiple order HHG spectrum, proof-of-principle experiments using lower order harmonics can also be considered.

MOPPH065	The First Experimental Observation of FEL Amplifier Efficiency Improvement using Electron Beam Energy Detuning at the NSLS SDL	electron, resonance, radiation, simulation	190
	T. Watanabe, J. B. Murphy, J. Rose, Y. Shen, T. Tsang, X. J. Wang BNL, Upton, Long Island, New York H. Freund SAIC, McLean
	We report on the first observation of efficiency enhancement in a single-pass laser seeded FEL amplifier by detuning electron beam energy away from resonance. The dependence of the output FEL energy on the electron energy was measured; a maximum and average enhancement of 100 % and 70 % were observed. The spectral output of the seeded FEL both with and without an energy detuning was also measured. It was verified that the peak wavelength was dominated by the seed laser. The experimental results are compared with the analytical theory and the numerical simulation code, GENESIS 1.3.

MOPPH066	Chirped Pulse Amplification Experiment at 800 nm	electron, undulator, linac, dipole	194
	L.-H. Yu, D. F.L. Liu, J. Rose, T. V. Shaftan, T. Tsang, X. J. Wang, T. Watanabe BNL, Upton, Long Island, New York
	We report the chirped pulse amplification (CPA) experiment carried out using 800 nm direct seed and NISUS undulator as free electron laser amplifier at SDL of BNL. The experiment indicated that due to saturation in the center part of the chirped electron bunch the output pulse shape has a dip in the middle, as result the edge of the bunch has higher power than the center. Hence the output spectrum also showed a dip in the center, resulting a larger FWHM bandwidth than the seed. An interesting result is that the output of the 800 nm chirped FEL pulse was compressed and generated a pulse length shorter than what the seed itself can be compressed to.

MOPPH067	Issues in High Harmonic Seeding of the 4GLS XUV-FEL	optics, controls, simulation, background	198
	B. Sheehy Sheehy Scientific Consulting, Wading River, New York J. A. Clarke, D. J. Dunning, N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire B. W.J. McNeil USTRAT/SUPA, Glasgow
	Using High Harmonics (HH) as a seed for free electron lasers is currently under consideration in a number of proposed facilities. An HH seed source is independent of machine dynamics, and allows for extensive manipulation of the seed pulse using well-established techniques of ultrafast laser physics. These allow for rapid tuning, and may enable the extension of chirped pulse amplification and even pulse shaping for coherent control to short wavelengths. In addition, there are advantages in terms of noise and synchronization. There are a number of issues involved in the implementation of HH seeding: energy, tunability, coherence, temporal structure, etc. We discuss these issues and their application in the 4GLS XUV-FEL

MOPPH068	Attosecond Pulses from X-Ray FEL with an Energy-Chirped Electron Beam and a Tapered Undulator	undulator, electron, simulation, radiation	202
	E. Saldin, E. Schneidmiller, M. V. Yurkov DESY, Hamburg
	We present a new scheme for generation of attosecond pulses in X-ray SASE FEL. A short slice in the electron beam is strongly modulated in energy by a few-cycle laser pulse in a short undulator, placed in front of the main undulator. Gain degradation within this slice is compensated by an appropriate undulator taper while the rest of the bunch suffers from this taper and does not lase. Three-dimensional simulations with the code FAST predict that short (200 attoseconds) high-power (up to 100 GW) pulses can be produced in Angstrom wavelength range with a high degree of contrast. A possibility to reduce pulse duration to sub-100 attosecond scale is discussed.

MOPPH075	Simulations of High Power-FEL Amplifiers	electron, undulator, simulation, extraction	222
	J. Blau, D. T. Burggraff, W. B. Colson, T. Voughs NPS, Monterey, California
	FEL amplifier simulations have been updated and parallelized, and system vibration effects have been added. The simulations are used to study proposed high-power amplifier FELs at LANL and BNL. We look at the single-pass gain and output power, including the effects of wiggler tapering, electron beam pinching, and shifting and tilting of the electron beam.

MOCAU01	The BESSY Soft X-Ray FEL: A Seeded HGHG FEL	electron, undulator, radiation, bunching	226
	A. Meseck BESSY GmbH, Berlin
	Reproducibility, high power and short pulse length combined with variable polarization and tunable wavelength are the requirements to open new frontiers for the soft X-ray users. To provide radiation with such extraordinary properties, BESSY has been designing a seeded FEL based on high-gain harmonic-generation (HGHG) concept. The seeding with an external tunable laser ensures the reproducibility of the full-coherent radiation. The combination of so-called HGHG stages, used to down-convert the seed wavelength, and a final amplifier provides for the high power and superior spectral properties. Furthermore, the HGHG concept and the fresh bunch techniques planned for BESSY FEL mitigate the effects of parameter variation along the bunch which are expected from realistic assumptions of the Gun and LINAC structure. The design concept of the BESSY soft X-ray FEL will be presented and the stabilizing effect of HGHG stages and the benefits from the fresh bunch techniques and final amplifier will be discussed.
	Slides
	Talk

MOCAU04	Focal Point Laser-Field as Optical Seeder	electron, cathode, radiation, coupling	242
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	Focusing optical laser into its wavlength size, and crossing the electron beam through the focal point, interaction of electron with laser field becomes non zero, as a result, creates velocity modulation. In contrast with modulation scheme using undulator, this method does not require energy resonance condition to the electron beam, thus works all energy, even with energy chirp. Using it in front of the bunch compressor, with energy chirp, the wavelength can be compressed by large factor with bunch length compression.
	Slides
	Talk

MOCAU05	Analysis of the Process of Amplification in a Single Pass FEL of High Order Harmonics Generated in a Gas Jet	electron, simulation, radiation, undulator	248
	L. Giannessi, M. Quattromini ENEA C. R. Frascati, Frascati (Roma) P. Musumeci INFN-Roma, Roma M. Nisoli, G. Sansone, S. Stagira, S. de Silvestri Politecnico/Milano, Milano
	We have studied the amplification of high harmonics generated by a short infrared pulse in a gas jet, injected in a free electron laser amplifier. The high-order harmonic spectra have been simulated using a 3D non-adiabatic model that includes both the single atom response and the effect of the propagation of the XUV field inside the gas jet. The response of a single atom to the IR field is calculated in the framework of the Strong Field Approximation (SFA); The nonlinear polarization associated to this process is evaluated as the acceleration of the nonlinear dipole moment. This term is used as source term in the propagation of the harmonic field inside the gas jet. The propagation effect are extremely relevant for the temporal structure of the XUV field as the coherent interference of the dipole emission of the different atoms leads to the selection of only one XUV pulse for each semi-cycle of the driving IR field. The amplification in the free electron laser has been simulated both in 1D and 3D with Perseo and GENESIS 1.3 respectively. The effects of filtering the seed spectrum have been analyzed and the coherence properties of the light are considered.
	Slides
	Talk

TUAAU01	Performance Achievements and Challenges for FELs Based on Energy Recovery Linacs	electron, linac, recirculation, radiation	252
	G. A. Krafft Jefferson Lab, Newport News, Virginia
	During the past decade several groups have assembled free electron lasers based on energy recovered linacs (ERLs). Such arrangements have been built to obtain high average power electron and photon beams, by using high repetition rate beam pulses driving FEL oscillators. In this talk the performance of many existing and several proposed facilities from around the world are analyzed and reviewed. Going forward, many questions must be addressed to achieve still better performance including: higher average current injectors, better optimized accelerating cavities, higher energy acceptance and lower loss beam recirculation systems, and better optical cavity designs for dealing with the optical beam power circulating in the ERL FELs. The talk presents some of the current thinking on each of these issues.
	Slides
	Talk

TUAAU02	Future Light Sources: Integration of Lasers, FELs and Accelerators at 4GLS	electron, linac, radiation, undulator	257
	J. A. Clarke CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
	4GLS is a novel next generation proposal for a UK national light source to be sited at Daresbury Laboratory, based on a superconducting energy recovery linac (ERL) with both high average current photon sources (undulators and bending magnets) and three high peak current free electron lasers. Key features are a high gain, seeded FEL amplifier to generate XUV radiation and the prospect of advanced research arising from unique combinations of sources with femtosecond pulse structure. The conceptual design is now completed and a CDR recently published. The 4GLS concept will be summarised, highlighting how the significant design challenges have been addressed, and the project status and plans explained.
	Slides
	Talk

TUAAU03	FEL Oscillation with a High Extraction Efficiency at JAEA ERL FEL	electron, undulator, quadrupole, linac	265
	N. Nishimori JAEA/FEL, Ibaraki-ken R. Hajima, H. Iijima, N. Kikuzawa, E. J. Minehara, R. Nagai, T. Nishitani, M. Sawamura JAEA/ERL, Ibaraki
	One of challenges that high power FEL oscillators with energy recovery linac (ERL) are facing is to increase the extraction FEL efficiency as high as possible. The high efficiency oscillation relaxes the total beam current needed for high power lasing and makes the FEL optical pulse length shorter, which is useful for various applications. A Bates type recovery loop with energy acceptance well in excess of 10% allows an ERL FEL at Jefferson Lab to operate with a high FEL efficiency. A triple bend achromat loop with energy acceptance of 7% has been used in an ERL FEL at Japan Atomic Energy Agency (JAEA). Recently we have achieved the efficiency exceeding 2%, which accompanies large energy spread beyond the energy acceptance of the loop, by doubling the electron bunch repetition rate*. The optical pulse can now interact with a fresh electron bunch every round trip, while it overlapped with an injected electron every two round trips before the doubling of the bunch repetition. This talk will summarize our recent development of a high power FEL with a high extraction efficiency at JAEA ERL FEL. S. Benson et al., in proceedings of the FEL2004, (2004) 229. R. Hajima et al., Nucl. Instr. and Meth. A445 (2000) 384. * R. Nagai et al., in these proceedings.
	Slides
	Talk

TUAAU04	On the Design Implications of Incorporating an FEL in an ERL	electron, controls, wiggler, acceleration	273
	G. Neil, S. V. Benson, D. Douglas, P. Evtushenko, T. Powers Jefferson Lab, Newport News, Virginia
	Encouraged by the successful operation of the JLab Demo in 1998, many high current ERLs are now being designed with not only short pulse synchrotron beamlines but also FELs. Such inclusion has major implications on magnet quality, rf feedback requirements, wiggler design, srf cavity Q_L, halo, etc. Measurements on the JLab ERL FEL have identified new challenges. The JLab Upgrade was designed with a 160 MeV beam of 10 mA in 75 MHz, 300 fs bunches. FEL designers set transverse emittance and longitudinal bunching, but to accommodate an FEL in our ERL also means setting stringent phase stability requirements of (<6x10^-9/fm rms) based on a desired FEL detuning tolerance of 1.2 microns. Recovered beam RF loading on the subsequent accelerated beam complicates satisfying these requirements. Gain in the rf feedback limits the accuracy of energy stability when loaded Qs are ~10⁷ . Energy recovery to <10 MeV sets magnetic field tolerances at 10^-4. We present measurements on the JLab ERL showing how to set system requirements to tolerate such FEL lasing.
	Slides
	Talk

TUBAU01	Prospects of Cascaded Harmonic Generation FELs	electron, bunching, undulator, radiation	281
	G. Penn LBNL, Berkeley, California
	Harmonic generation in Free Electron Lasers (FELs) encompasses many techniques for using an input seed laser to produce FEL radiation at a frequency that is multiples above that of the seed laser itself. This allows for the advantages of seeded FELs to be preserved, while extending the reach of these FELs to photon energies far above those produced by conventional laser sources. Many new projects are underway to make use of these methods, including the FERMI@Elettra* facility which envisions the use of two harmonic generation stages to reach photon energies above 100 eV. Different methods of harmonic generation are discussed, as well as the technical challenges to overcome in attempting to chain together multiple harmonic stages in an FEL. * C. Bocchetta et al., Proceedings of the 2005 FEL Conference, (2005) 682.
	Slides
	Talk

TUBAU02	Femtosecond Synchronization and Stabilization Techniques	electron, free-electron-laser, extraction, controls	287
	J. Kim, J. Chen, F. X. Kaertner MIT, Cambridge, Massachusetts F. Ludwig DESY, Hamburg Z. Zhang Peking University, School of Physics, Beijing
	Future seeded X-ray free electron laser facilities will be based on an intricate interplay between ultrafast lasers and RF-driven accelerators. To develop the full potential of these new ultrafast X-ray sources, tight synchronization between the laser pulses and the electron bunches on the scale of a few femtoseconds is necessary over several kilometres of distance. In this paper, we present optical synchronization and stabilization techniques that enable the implementation of a long-term stable femtosecond timing and synchronization system. For optical-to-RF synchronization, we demonstrate an optical-microwave phase detector that is capable to extract an RF-signal from an optical pulse train with less than 5 fs timing jitter [1 Hz, 10MHz]. Scaling of this component to sub-femtosecond resolution is discussed. Optical-to-optical synchronization of multiple femtosecond lasers with sub-femtosecond precision over more than 12 hours is demonstrated. In addition, first results on optically stabilized fiber links for timing distribution will be presented. Together with low noise mode-locked lasers, a flexible femtosecond timing distribution system can be constructed.
	Slides
	Talk

TUBAU04	Inverse Free Electron Lasers for Advanced Light Sources	undulator, electron, radiation, simulation	292
	P. Musumeci, F. Germoni, M. Mattioli, M. Serluca INFN-Roma, Roma
	Laser accelerators hold the promise for high gradient acceleration and production of ultra short electron bunches. Among these, the inverse free-electron laser has recently demonstrated to be a mature and reliable scheme ready to step up from successful proof-of-principle experiments to cutting-edge applications. The very high gradient and the multi kAmp peak current of the output beam make it an attractive option in the hundreds of MeV to few GeV energy region. We examine the feasibility of using an IFEL driven by an high power Ti:Sa laser source to generate soft x-rays by FEL interaction in an undulator. A control of the slippage of the radiation over the ultrashort spikes of the IFEL-microbunched beam current is implemented to increase the gain and maintain the 200as-long pulse structure in the radiation profile.
	Slides
	Talk

TUBAU05	Technical Aspects of the Integration of the Optical Replica Synthesizer for the Diagnostics of Ultra-short Bunches into FLASH at DESY	electron, undulator, diagnostics, vacuum	296
	P. van der Meulen, N. X. Javahiraly, M. Larsson FYSIKUM, AlbaNova, Stockholm University, Stockholm E. Saldin, H. Schlarb, E. Schneidmiller, A. Winter, M. V. Yurkov DESY, Hamburg V. G. Ziemann UU/ISV, Uppsala
	Recently, Saldin et al.* introduced a novel scheme to characterise ultra-short electron bunches in a FEL. The method is based on producing an 'optical copy' of the electron bunch, which can then be easily analysed using well-known non-linear optical techniques. To this end, a near-IR laser beam is overlapped with the electron beam in the first undulator of an optical klystron. In the following dispersive section the laser-induced energy modulation is transformed into a density modulation . The modulated electron bunch then produces a strong optical pulse in the second undulator. Analysis of this near-IR pulse (the optical copy) then provides information about the length, the slice emittance and the slice energy spread of the original electron bunch. We discuss the implementation of such a measurement set-up at the VUV-FEL at DESY and investigate the influence of various parameters on the performance of the device. Topics we address include the electron beam optics of the undulators, quadrupoles and the dispersive chicane, as well as the requirements for the seed laser pulses. The detection and analysis of the near-IR pulse and an extension to the XUV-FEL are also covered. * E. Saldin, et al. "A simple method for the determination of the structure of ultrashort relativistic electron bunches," Nucl. Inst. and Methods A 539 (2005) 499.
	Slides
	Talk

TUPPH002	Development of Frequency-Resolved Optical Gating for Measurement of Correlation between Time and Frequency of Chirped FEL	simulation, polarization, electron, linac	308
	H. Iijima, R. Hajima, E. J. Minehara, R. Nagai, N. Nishimori JAEA/ERL, Ibaraki
	A femtosecond infrared-chirped FEL is an effective way of dissociating molecules without the intramolecular vibrational redistribution. At Japan Atomic Energy Agency (JAEA), an energy recovery linac (ERL) has been investigated to produce high power FEL at far-infrared region. Normally the long-pulse electron beam is operated by the ERL; therefore the high-power chirped pulse can be generated. Until now, the amount of chirp in the pulse was measured to be f/f₀ = 14% with the wavelength of 23 μm and the pulse width of 320 fs at FWHM. However the correlation between time and frequency in the chirped pulse was not measured. In order to measure the correlation between time and frequency in the chirped pulse directly, we have started to construct an FEL transport system and the frequency-resolved optical grating in new experimental room. The chirped pulse is guided to the experimental room by a 22-m vacuum duct which avoids the absorption of infrared radiation by water vapor. The optical focusing systems are located at the entrance and exit of the vacuum duct. Now we are measuring basic parameters of the chirped pulse (beam size, power and so on) in the experimental room.

TUPPH006	Performance of a Conventional Analog Phi-A Type Low-Level RF Controller	feedback, linac, free-electron-laser, monitoring	316
	R. Nagai, R. Hajima, H. Iijima, N. Kikuzawa, E. J. Minehara, N. Nishimori, T. Nishitani, M. Sawamura JAEA/ERL, Ibaraki
	For an FEL application and an ERL light source, high-stability of accelerator RF amplitude and phase is required. A low-level RF controller (LLC) of the JAEA-ERL has been improved to ensure high-stability accelerating RF field. The LLC is a conventional analog phi-A type controller with following functions: the feedback gain, loop-offset phase and time constant can be varied during operation to obtain optimum parameters for the high-stability RF field, all the circuits are contained in a temperature controlled oven. The LLC performance is tested for a 499.8MHz superconducting cavity and a 1300MHz copper cavity. The phase and amplitude stabilities of the 499.8MHz superconducting cavity within a 1ms macro-pulse are 0.0055deg-rms and 7.64×10^-5, respectively. For the 1300MHz copper cavity, pulse mode and CW mode were tested. In the case of pulse mode, the phase and amplitude stabilities are 0.011deg-rms and 7.64×10^-5, respectively. In the case of CW mode, the phase and amplitude stabilities are 0.011deg-rms and 6.68×10^-5, respectively.

TUPPH007	JAEA Photocathode DC-Gun for an ERL Injector	electron, gun, ion, vacuum	319
	T. Nishitani, R. Hajima, H. Iijima, N. Kikuzawa, E. J. Minehara, R. Nagai, N. Nishimori, M. Sawamura JAEA/ERL, Ibaraki H. Hayashitani, Y. Noritake, M. Tabuchi, Y. Takeda Nagoya University, Nagoya
	ERL light source and FEL require an electron beam of large current and small emittance. In order to realize an electron gun satisfying such requirements, we started developments of a photocathode DC-gun and a new-type NEA-photocathode. The DC-gun consists of a chamber to activate NEA-surface, a 250keV acceleration chamber, and a mode-locked Ti:Sapphire laser. Since extreme high vacuum is essential to obtain a long-life photocathode, we adopt a load-lock system for transporting a photocathode between the chambers, each of which is equipped with an NEG pump. Up to now, we fabricated an electrodes chamber and a high voltage terminal of 250kV and we succeeded in a 250kV high voltage test. We also have suggested a superlattice photocathode as a new-type photocathode with higher performance than an existing technology. Up to now, we fabricated photocathode samples by molecular beam epitaxy and measured quantum efficiency after NEA-surface activation.

TUPPH008	Harmonic Lasing Characterization at Jefferson Lab	electron, wiggler, simulation, free-electron-laser	323
	S. V. Benson, M. D. Shinn Jefferson Lab, Newport News, Virginia
	Harmonic lasing is normally suppressed because of lasing at the fundamental wavelength. It can, however, be achieved by using any of several methods that suppress fundamental lasing. In this paper we discuss two methods used at Jefferson Lab. The first is to use the characteristics of dielectric coatings to allow harmonic lasing at cavity lengths longer than the synchronous length for the fundamental. The second is to use a dielectric coating that has little reflectivity at the fundamental. This allows us to directly compare fundamental and harmonic lasing with the same optical resonator and electron beam. We present measurement carried out at Jefferson Lab using the IR Upgrade FEL operating at 0.54, 0.93, 1.04, 1.6, and 2.8 microns in which both schemes are used to produce lasing at both the 3rd and 5th harmonic of the fundamental.

TUPPH012	Experimental Study of a Volume Free Electron Laser with a ''Grid'' Resonator	radiation, electron, free-electron-laser, polarization	331
	V. G. Baryshevsky, N. A. Belous, A. Gurinovich, A. S. Lobko, P. V. Molchanov, V. I. Stolyarsky Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
	Volume Free Electron Laser (VFEL) uses volume distributed feedback formed by diffraction gratings with different patterns,. First lasing of a Volume Free Electron Laser with a ''grid'' resonator, built from periodically strained metallic threads, was observed in*. Structures of this kind are often referred to as photonic crystals. Experiments with ''grid'' VFEL are carried out. Radiation is detected in the frequency range about 10 GHz. Backward wave regime is tested. Dependence of the generation threshold on the resonator length is investigated. It is demonstrated that use of volume resonators of the described type provides to weaken requirements for the electron beam shape and guiding precision. Radiation frequency tuning, which is an advantage of VFEL, can be achieved in such a structure by change of threads tilt to the electron beam velocity. V. G.Baryshevsky, K. G. Batrakov, A. A. Gurinovich et al., NIM 483A (2002) 21. V. G. Baryshevsky, NIM A 445 (2000) 281. * V. G. Baryshevsky et.al. LANL e-print archive: physics/0409125

TUPPH013	Electrodynamical Properties of a Volume Free Electron Laser with a ''Grid'' Resonator	lattice, electron, wiggler, free-electron-laser	335
	A. Gurinovich, V. G. Baryshevsky Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
	The electrodynamical properties of a crystal-like artificial periodic structure (a photonic crystal), formed by a periodic structure built from the metallic threads ("grid" volume resonator) is considered. Peculiarities of passing of electromagnetic waves with different polarizations through such a volume resonator are discussed. It is shown that the frequency spectrum of diffraction (Smith-Purcell) radiation is such a resonator appears splitted due to the complex anomalous Doppler effect. Specific features of a Volume Free Electron Laser (VFEL),* with a ''grid'' resonator for different frequency ranges are analyzed. Possibility of development of tunable radiation source in THz range is particularly discussed. The equations, which describe lasing of VFEL with a ''grid'' resonator (photonic crystal)**, are obtained. Estimation of the resonator durability to the heating by the electron beam is done. V. G.Baryshevsky, K. G. Batrakov, A. A. Gurinovich et al., NIM 483A (2002) 21. V. G. Baryshevsky, NIM A 445 (2000) 281. * V. G. Baryshevsky et.al. LANL e-print archive: physics/0409125

TUPPH014	Laser Gain and Intra-Cavity Losses of the ELBE Mid-IR FEL	electron, radiation, undulator, optics	339
	U. Lehnert, P. Michel, W. Seidel, J. Teichert, R. Wuensch FZR, Dresden
	The the U27-FEL of the ELBE radiation source allows to choose between five mirrors with different outcoupling holes. This allows to adapt the optical resonator to the required wavelength range to ensure the needed laser gain and to optimize the outcoupled laser power. Another parameter which influences the achievable laser gain and output power is the detuning length of the optical cavity. While for CW operation often the minimum detuning point is choosen which maximizes the outcoupled power, for pulsed-mode operation about one wavelength of cavity detuning maximizes the laser gain and yields best stability of the laser. To gain some insight into the behavior of the optical resonator we have measured the round-trip losses and the net laser gain and compare both to calulations. For the measurements we have used a fast-readout MCT detector to measure the decay and rise-time of the outcoupled infrared beam caused by a 10μs break in the electron beam micro-pulse train. We show gain and loss for 5, 10 and 20μm wavelength with the typical detuning curves of an FEL.

TUPPH015	Remote Controlled IR-Diagnostic Station for the FEL at Rossendorf	diagnostics, plasma, radiation, electron	341
	W. Seidel, S. Friebel, R. Jainsch, M. Justus, K.-W. Leege, D. Proehl, D. Stehr, H. Weigelt, S. Winnerl, D. Wohlfarth FZR, Dresden
	The remote controlled diagnostic station delivers a small amount of the IR radiation by means of a system of relocatable mirrors and beam splitters to the spectrometer and to various power detectors working in different power ranges. Furthermore, a long wavelength MCT detector is integrated in the diagnostic station for gain and loss measurement in the whole wavelength range of the U27-FEL. The average radiation power available for the users can be reduced by a remote controlled attenuator. To characterize the optical micropulse duration we have built a non-collinear background-free autocorrelator as a part of the diagnostic station. By using a CdTe single-crystal for second-harmonic generation a broad wavelength coverage is obtained. Certain experiments require high pulse energies but moderate or low average power. For such experiments the repetition rate of the Rossendorf FEL can be reduced from 13 MHz to 1 kHz, in the future also to 1 Hz, by a semiconductor plasma switch excited with a synchronized Nd:YAG amplifier. This system is under commissioning and we will report on first results. Submitted as a poster to the FEL 2006 conference.

TUPPH016	The Partial-Waveguide Resonator of the U100-FEL at FZ Rossendorf	vacuum, undulator, alignment, electron	345
	R. Wuensch, M. Freitag, R. Schlenk, W. Seidel, U. Willkommen, D. Wohlfarth, B. Wustmann FZR, Dresden
	The U100-FEL, which is under construction at the Forschungszentrum Rossendorf, will be equipped with a parallel-plate waveguide which is 10 mm high (inside), almost 8 m long and covers more than two third of the total resonator length. Its horizontal width varies from 70 mm within the undulator up to 130 mm at the downstream resonator mirror. A special diagnostics had to be developed to align the electron and the IR beam within this waveguide. A drive system has been designed for the cylindrical downstream resonator mirror. It allows to shift and tilt the mirror, which is completely embedded in the waveguide. The size and the curvature of the bifocal upstream resonator mirror has been fitted to minimize the optical loss in the resonator. To adjust the outcoupling to the varying beam size on the mirror surface a set of three collocated, relocatable mirrors with different outcoupling hole sizes will be applied. We present various sophisticated design concepts which comply with the large wavelength range and the special requirements caused by the bulky waveguide construction and its small free space in vertical direction.

TUPPH020	Dynamics Control of the Elettra Storage Ring Free-Electron Laser with Digital Feedbacks	feedback, controls, electron, storage-ring	356
	E. Allaria, G. De Ninno ELETTRA, Basovizza, Trieste A. Antoniazzi, D. Fanelli Università di Firenze, Florence
	The laser dynamics of a storage-ring free-electron laser (FEL) has two main sources of instabilities. First of all, as it is known, dynamical instabilities are developed as the FEL is moved away from the exact tuning between the period of the electron bunch(es) circulating into the ring and that of the photon pulse stored in the optical cavity. In addition, external (low-frequency) noise sources have a strong influence on the dynamical behaviour of the system and can perturb its dynamic. Different feedback techniques have been proposed in order to control dynamical instabilities and stabilize the FEL output. We present here a numerical and experimental investigation on the control of the Elettra SRFEL dynamics using the simultaneous combination of different feedbacks techniques that have been experimentally implemented by means of a Field ProgrammableGate Aarray (FPGA).

TUPPH021	Q-Switch Techniques Implemented at the ELETTRA Storage-Ring Free Electron Laser	electron, storage-ring, radiation, synchrotron	360
	F. Curbis, F. Curbis Università degli Studi di Trieste, Trieste M. B. Danailov, G. De Ninno, B. Diviacco, L. Romanzin, M. Trovo ELETTRA, Basovizza, Trieste
	In a storage-ring FEL the gain can be calculated measuring the rise-time of giant pulses, produced by the interaction between the light stored in the optical cavity and an electron beam with low energy-spread (cold beam). This interplay produces the heating of the beam. Therefore, after the generation of a single giant pulse, the overlap between electrons and radiation is periodically prevented for a time necessary to dump the energy spread and recover the cold-beam condition. For this purpose two different methods are implemented at Elettra. In the first, modifying the radio-frequency of the ring, the change of the revolution time of electrons avoids the temporal overlap between the electron beam and the optical field in the mirror cavity. The second method relies on a mechanical gating (chopper) which intercept the light produced during previous interactions, inducing a periodic emptying of the optical cavity. The gain can be also estimated using an indirect formula after measuring the electron-beam energy spread and bunch length. In this paper we compare the different techniques mentioned above for the case of the Elettra SR-FEL.

TUPPH022	Development of a Compact Cherenkov Free-Electron Laser in Terahertz Spectral Range	electron, cathode, focusing, radiation	364
	M. R. Asakawa, N. Miyabe Kansai University, Osaka M. Kusaba, K. Nakao, Y. Tsunawaki OSU, Daito, Osaka
	A Cherenkov free-electron laser (CFEL) generating terahertz radiation is now being developed under the joint research of Osaka Sangyo university and Kansai university. The main feature of this CFEL is its compactness. Electron beamlets emitted by a Spindt cathode are accelerated up to 60 keV in a D. C. electron gun and then are injected into 100μm-gaps between stacked plates of silicon, which acts as radiator. The radiation frequency will be ranged from 0.8 to 2 THz according to the acceleration voltage. In order to suppress diverging of the beamlet with a high current density about 1kA/cm², the electron gun and the radiator section are immersed in a longitudinal magnetic field produced by a super-conducting (SC) coil. The total length of the CFEL section, i.e., the distance between the cathode and beam dumper, is 4 cm and the diameter of this section is less than 2 cm. Such compact laser module is placed in the bore of SC coil. In spite of the large size of the cryostat and the power supply of the SC coil, the total footprint is about 1×1 m².

TUPPH023	High Power Deep UV Lasing on the UVSOR-II Storage Ring FEL	electron, storage-ring, radiation, synchrotron	368
	M. Hosaka, M. Katoh, A. Mochihashi, M. Shimada UVSOR, Okazaki T. Hara RIKEN Spring-8 Harima, Hyogo Y. Takashima Nagoya University, Nagoya
	Thanks to an improved quality of the electron beam at the UVSOR-II storage ring, we have obtained a high power FEL lasing of 0.25 W in the deep UV region around 215 nm. The beam emittance of the UVSOR-II storage ring are improved by factor 6 in 2002. Recently we have renewed an rf accelerating cavity, which can be operated in about 3 time higher cavity voltage ( 150 kV) than the previous cavity voltage. All these improvement increased the FEL gain and we have obtained FEL lasing around 215 nm using Al2O3/SiO2 multilayer mirrors. In the primarily lasing experiment, the storage ring was operated at an electron energy of 600 MeV, which is ordinary energy for FEL experiments. Then we increased the energy to 750 MeV and obtained an extracted power of 0.25 W. The deep UV FEL has been already applied to an users irradiation experiment. Two other application experiments are planned now. In the presentation, the latest status of UVSOR-II FEL will be reported.

TUPPH025	Recent Experiments and Prospect on the NIJI-IV VUV/IR FEL	beam-transport, electron, storage-ring, free-electron-laser	375
	H. Ogawa, N. Sei, K. Yagi-Watanabe, K. Y. Yamada, M. Y. Yasumoto AIST, Tsukuba, Ibaraki
	The NIJI-IV free electron laser (FEL) is being developed as a compact light source with very good optical quality and ultra-wideband tunability from the VUV to the IR. To obtain lasing at shorter wavelengths in the VUV region, continuous efforts to improve the cavity-mirror performance have been made. As a result, the original loss of Al2O3/SiO2 multilayer mirrors was recently decreased by 30% around 195nm, compared with that of previous ones. A new optical cavity system, composed of two sets of a heavy granite base and a stable mirror manipulator holding two in-vacuum interchangeable mirrors, was installed to stabilize the lasing and also to extend the tuning range. This will enable us to carry out reproducible FEL application experiments, such as real-time observation of surface chemical reactions. As for the IR FEL, modification of the beam transport system to make space for installation of the optical cavity was completed. Here we report recent progress in the NIJI-IV FEL.

TUPPH027	The Experimental Research of the SR-FEL Cavity Mirrors at 355nm and 248nm	free-electron-laser, storage-ring, radiation, synchrotron	382
	H. L. Gao, R. Q. Tan, D. L. Wang, Y. Wang, J. Wu Institute of Electronics, Chinese Academy of Sciences, Beijing N. Y. Wang CIAE, Beijing
	The cavity mirrors of the storage-ring free-electron laser (SR-FEL) at 355nm and 248nm central wavelengths have been investigated experimentally with the optical coating materials of Al2O3/HfO2/SiO2 on fused silica. They were deposited by the electron-beans evaporation technology and ion-beam sputtering technology, so that the mirror have high damage threshold to laser pulse and resist to the reflectance degeneration- induced by the synchrotron radiation. The experimental results show that the absolute reflectance of the broad-band mirror at reaches up to R=99.45%, the frequency-tunable range with reflectance higher 99.00% is 406nm-331nm=75nm. For the dual-central wavelength mirror, the absolute reflectance are R(248nm)=98.21% and R(355nm)= 99.69%. The frequency-tunable range is 373nm-314nm for 355nm central wavelength; 275nm-272nm and 240nm-234nm for 248nm central wavelength, it isn't continual due to the absorption of HfO2 optical materials. All of the samples have passed the high-temperature test under the condition 400°C-4hrs successfully, and shown very stable optical property.

TUPPH037	FEL-Oscillator Simulations with Genesis 1.3	undulator, simulation, radiation, optics	407
	J. G. Karssenberg, K.-J. Boller, J. W.J. Verschuur, P. J.M. van der Slot Twente University, Laser Physics and Non-Linear Optics Group, Enschede I. Volokhine Philips Research, Eindhoven
	We present a paraxial optical propagation code (OPC) as an extension to Genesis 1.3* for the theoretical description of FELs with an optical resonator. The OPC receives the optical output from a Genesis simulation, propagates it once through the resonator, and applies the result as the optical input pulse for a next run of Genesis. The OPC allows both the description of time dependent and steady state FEL operation. The propagation algorithms available are the Spectral algorithm, the Fresnel algorithm and a modified Fresnel algorithm. The latter enables a fast modelling of feedback via complex resonator designs that may include hard-edge elements (apertures) or hole-coupled mirrors with arbitrary shapes. The code enables to predict the output at each of the various optical elements which is of advantage for beam diagnostics and for designing suitable optics for a further propagation of the output beam. Finally, the OPC can be used to determine the far field output in connection with any Genesis 1.3 simulation, be it an oscillator or an amplifier FEL. As a test of the combined OPC and Genesis 1.3 codes we found good agreement with experimental data available for FELIX*. http://pbpl.physics.ucla.edu/~reiche/index.html** B. Faatz, Ph. D. Thesis, Nieuwegein, The Netherlands 1992.

TUPPH039	Bright Electron Beams and Smith-Purcell Free-Electron Lasers	electron, cathode, space-charge, radiation	415
	C. H. Boulware, H. L. Andrews, C. A. Brau, J. D. Jarvis Vanderbilt University, Nashville, Tennessee
	We have continued to develop the theory of Smith-Purcell free-electron lasers * by including the effects of losses in the grating and reflections of the evanescent wave at the ends of the grating. We estimate the magnitude of the reflection coefficient to be about 15 % based on published simulations*, and compute the effect on the start current and the frequency shift. Experiments to observe these effects are underway. H. L. Andrews, C. H. Boulware, C. A. Brau, and J. D. Jarvis, Phys. Rev. ST-AB 8, 050703 (2005). ** D. Li, Z. Yang, K. Imasaki, and G.-S. Park, Phys. Rev. ST-AB 9, 040701 (2006).

TUPPH044	Free Electron Laser Study of Free Carbon Clusters	photon, radiation, electron, background	423
	C. Spezzani, E. Allaria, F. Curbis, G. De Ninno, B. Diviacco, L. Romanzin, S. Tileva, M. Trovo ELETTRA, Basovizza, Trieste M. Amati, G. Bongiorno, C. Lenardi, T. Mazza, P. Milani, T. A. Mostefaoui, P. Piseri, L. Ravagnan Università degli Studi di Milano, Milano M. Coreno CNR - IMIP, Trieste
	UV absorption from carbon nanoparticles is a very interesting astrophysical topic. The prominent hump centered at 217.5nm is the most dominant feature in the interstellar extinction curve and also the most controversial and a long-standing problem in astrophysics. Actual models lack of experimental data about carbon dust in gas phase. At the University of Milano an experimental set-up based on a PulsedμPlasma Source has been developed for the investigation of free clusters at the Elettra Gas Phase beamline (CESyRA: Cluster Experiments with Synctrotron RAdiation). The cluster source produces very intense cluster beams with tunable size distribution. The design of the apparatus is extended with a chamber for gas phase reaction (water vapor, CO, H2…) providing a unique opportunity to study the gas phase properties of carbonaceous particles in different environment. We plan to investigate Resonant Raman scattering of free carbon particles tuning the high brilliance UV/VIS storage ring FEL of ELETTRA across the region of 217nm where the UV absorption hump in astrophysical data is observed and where a number of electronic transitions exist for variable size linear carbon chains.

TUPPH046	Free Electron Laser Pulse Control by Acousto-Optic Modulators	controls, electron, free-electron-laser, insertion	427
	T. Kanai, K. Awazu, S. Suzuki Osaka University, Suita
	The free electron laser (FEL) at Osaka University can be continuously varied over a range from 5.0 to 20.0 um when using the 30 MeV electron beam. The FEL has a double pulse structure. The structure consists of a train of macropulses with a pulse width of 15 us, and each macropulse contains a train of 330 micropulses with a pulse width of 5 ps. The FEL's tunability and short pulse make possible new medical applications, such as investigating protein dynamics and ablating soft tissues. Precise control of the micropulse train is essential for FEL medical applications because macropulses of long pulse duration lead to undesirable thermal effects. An FEL pulse control system, using an acousto-optic modulator (AOM), was developed to investigate the non-thermal effects of FEL on living tissues. This system provides efficiency (~ 70%) and a fast switching speed (> 200 ns), and we predict that FEL will serve as a novel tool in many new applications.

TUPPH048	Superradiant Smith-Purcell Radiation in the Terahertz-wave Region from Bunched Electron Beams	radiation, simulation, bunching, electron	435
	Z. Shi, Z. Liang, Z. Yang UESTC, Chengdu, Sichuan K. Imasaki, D. Li ILT, Suita, Osaka
	This paper presents a study of the characteristic of Smith-Purcell radiation (SPR) in the terahertz-wave (THz) region from bunched electron beams. The model consists of a grating with different period length and grating profile to be driven by a single electron bunch and a train of periodic bunches, respectively. The radiation efficiency and the angular distribution of SPR with various bunch distribution functions are investigated. According to the analysis, the coherent emission will occur when electron bunches are short compared with the radiation wavelength, and the coherent emission strongly depends on the longitudinal distribution of bunches. Some numerical results for the sinusoidal grating are compared with those for echellette grating .The results show that the THz radiation will be obtained using the reasonable parameters for the bunches and the grating. The results provide a basis for designing a superradiant SP free-electron laser in the THz wavelength region.

TUPPH052	Future FEL Studies at the VISA Experiment in the SASE and Seeded Modes	radiation, undulator, electron, simulation	443
	G. Andonian, M. P. Dunning, A. Y. Murokh, C. Pellegrini, S. Reiche, J. B. Rosenzweig UCLA, Los Angeles, California M. Babzien, I. Ben-Zvi, V. Yakimenko BNL, Upton, Long Island, New York
	The VISA (Visible to Infrared SASE Amplifier) experiment at BNL (Brookhaven National Laboratory) has previously demonstrated saturation at 840 nm in 2001. Further SASE studies, in 2003, have demonstrated an anomalously large bandwidth spread of the FEL spectrum due to off-angle emissions. This paper disseminates the current and future program of the VISA program at BNL. This includes a study of a seeded FEL, using a 1 micron YAG laser as a seed, and the accompanying diagnostics to characterize the radiation. Diagnostics include the double differential spectrometer, a mode converter to investigate the orbital angular momentum of light in the FEL, and an optical pepper-pot for coherence measurements. As usual, start-to-end simulations are presented.

TUPPH054	Beam Pickup Designs Suited for an Optical Sampling Technique	pick-up, simulation, electron, vacuum	451
	K. E. Hacker, F. Loehl, H. Schlarb DESY, Hamburg
	A beam position monitor with a large horizontal aperture is being developed for use in dispersive regions of magnetic chicanes as part of an energy measurement. It will have a horizontal detection range of 10 cm or more and a resolution of better than 30 um. This is achievable with a stripline design, mounted perpendicularly to the electron beam direction. A high-precision phase measurement at both ends of the stripline will allow for determination of the beam postion. The phase measurement of the short RF pulses from the stripline will be done with a technique that utilizes a timing laser that samples the RF pulse traveling though an electro-optical modulator.

TUPPH055	A Design for an XUV FEL Driven by the Laser-Plasma Accelerator at the LBNL LOASIS Facility	electron, undulator, radiation, plasma	455
	W. M. Fawley, E. Esarey, W. Leemans, C. B. Schroeder LBNL, Berkeley, California
	We present a design for a compact FEL source of ultra-fast, high-peak flux, soft x-ray pulses employing a high-current, GeV-energy electron beam from the existing laser-plasma accelerator at LBNL's LOASIS facility. The proposed ultra-fast source would be intrinsically temporally synchronized to the drive laser pulse, enabling pump-probe studies in ultra-fast science with pulse lengths of ~10–25 fs. Owing both to the high current (>10 kA) and reasonable charge/pulse (~0.1-0.5 nC) of the laser-plasma-accelerated electron beams, saturated output fluxes are potentially on the order of 10¹⁴ photons/pulse. We examine devices based both on SASE and high-harmonic generated input seeds to give improved coherence and reduced undulator length, presenting both analytic scalings and numerical simulation results for expected FEL performance. A successful source would result in a new class of compact laser-driven FELs in which a conventional RF accelerator is replaced by a GeV-class laser-plasma accelerator whose active acceleration region is only several cm in length.

TUPPH056	Comparative Study of Digital and Analog Synchronization Techniques for Lasers in Accelerators	feedback, resonance, diagnostics, controls	459
	A. Winter DESY, Hamburg W. J. Jalmuzna Warsaw University of Technology, Institute of Electronic Systems, Warsaw
	Laser systems play an important role in present and future light sources. These lasers need to be synchronized very precisely to the accelerator RF. One aproach is using an analog controller, which offers low-noise performance and has been demonstrated to achieve sub-50 fs stability. A digital controller based on a high-performance FPGA on the other hand offers great flexibility, for instancethe possibility to implement notch filters to evade the limitations of piezo resonances. This paper presents results obtained with both approaches.

TUPPH061	Phase Noise Comparision of Short Pulse Laser Systems	controls, feedback, electron, alignment	466
	S. Zhang, S. V. Benson, J. Hansknecht, D. Hardy, G. Neil, M. D. Shinn Jefferson Lab, Newport News, Virginia
	This paper describes the phase noise measurement on several different mode-locked laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on the state of the art short pulse lasers, especially the drive lasers for photocathode injectors. A comparison between the phase noise of the drive laser pulses, electron bunches and FEL pulses will also be presented.

TUPPH072	Generation and Characterization of the Microbunched Beams in the Range from 0.3 to 500 Femtoseconds	target, electron, radiation, linac	481
	V. Yakimenko, M. Babzien, K. Kusche BNL, Upton, Long Island, New York E. K. Kallos, P. Muggli UCLA, Los Angeles, California W. D. Kimura STI, Washington
	The presentation will cover recent experimental results on generation and measurement of the beams with the bunch lengthes from 0.3 to 500 fs at Brookhaven Accelerator Test Facility. Double beam structure is produced at 100 fs - 0.5 ps time scale using compression in the magnetic chicane - "dog leg" arrangement. The beam structure is characterized using interferometer and 6 mm long plasma wakefield channel with the controllable plasma density. Arbitrary number of 10-100 femtosecond microbunches is sliced out of 5 ps long beam using wire mesh. CSR interferometer is used for detailed characterization of the beams. Accuracy of the bunch length measurement using CSR energy is greatly improved for the 0.3 fs bunches by spectral measurements of multiple harmonics.

TUCAU01	Design of a Long Wavelength FEL for Experiments under High Magnetic Fields	electron, free-electron-laser, radiation, resonance	485
	W. J. van der Zande Nijmegen University, Physics Faculty, Nijmegen F. J.M. Harren, A. P.M. Kentgens, J. C. Maan, T. H.M. Rasing Radboud University Nijmegen, Institute of Molecules and Materials, Nijmegen
	At the University of Nijmegen, a novel collaboration has been established that combines a number of spectroscopic laboratories. These laboratories form a centre for advanced spectroscopy and constitute the spectroscopic department of the (Research) Institute for Molecules and Materials combining physical and chemical techniques. As part of the spectroscopic centre, a long-wavelength far-infrared free electron laser (FIR-FEL) operating between 100 um/3 THz and 1.5 mm/200 GHz will be designed and constucted in the coming years. The FIR-light should facilitate new experiments in the existing high field magnet laboratory (HFML), a large European Rerearch Infrastructure and in the NMR pavillion equipped with NMR instrumentation operating up to 800 MHz, especially for dynamic nuclear polarization technology.
	Slides
	Talk

TUCAU02	The Rossendorf IR-FEL ELBE	electron, radiation, undulator, linac	488
	P. Michel, H. Buettig, F. G. Gabriel, M. Helm, U. Lehnert, Ch. Schneider, R. Schurig, W. Seidel, D. Stehr, J. Teichert, S. Winnerl, R. Wuensch FZR, Dresden
	The radiation source ELBE is the central research facility in the Forschungszentrum Rossendorf. The machine is based on a 40 MeV superconducting RF Linac wich can be operated up to 1 mA in cw mode. After commissioning the Bremsstrahlung and the X-ray facilities in 2002, and 2003 respectively, and the first lasing of the mid-IR FEL (4-22 um) in 2004 about 7000 hours user beam-time have been provided. At present a second FEL for long IR waves (15-150 um) using a partial waveguide is under commissioning. Besides in-house users especially the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. In this talk the fundamental features of the ELBE IR FEL's and the parameters demanded by users are displayed. In addition, an overview about user experimental work and important machine date like availability are shown. Future projects like the combination of the new High Magnetic Field lab with the ELBE-IR beams will be described.
	Slides
	Talk

TUCAU03	Status of the Novosibirsk High Power Terahertz FEL	radiation, electron, undulator, linac	492
	N. Vinokurov, N. Gavrilov, B. A. Knyazev, E. I. Kolobanov, V. V. Kotenkov, V. V. Kubarev, G. Kulipanov, A. N. Matveenko, L. E. Medvedev, S. V. Miginsky, L. A. Mironenko, A. D. Oreshkov, A. V. Ovchar, V. Ovchar, V. M. Popik, T. V. Salikova, M. A. Scheglov, S. S. Serednyakov, O. A. Shevchenko, A. N. Skrinsky, V. G. Tcheskidov BINP SB RAS, Novosibirsk
	The first stage of Novosibirsk high power free electron laser (FEL) was commissioned in 2003. It is based on the normal conducting CW energy recovery linac (ERL). Now the FEL provides electromagnetic radiation in the wavelength range 120 - 230 micron. The maximum average power is 400 W. The minimum measured linewidth is 0.3%, which is close to the Fourier-transform limit. Four user stations are in operation now. Manufacturing of the second stage of the FEL (based on the four-turn ERL) is in progress.
	Slides
	Talk

THAAU02	Fourier Optics Treatment of Classical Relativistic Electrodynamics	radiation, undulator, electron, optics	501
	G. Geloni, E. Saldin, E. Schneidmiller, M. V. Yurkov DESY, Hamburg
	In this paper we present a critical re-examination of Transition Undulator radiation, that has been first investigated a decade ago. We study a realistic undulator setup, which includes an undulator, two straight sections and two bends, before and after the undulator. This allows us to underline an important physical fact: it does not make sense to study the intensity distribution of transition radiation from an undulator without a detailed knowledge of the complete setup. The present paper also helps to point out several misconceptions present in literature regarding Coherent Transition Undulator Radiation.
	Slides
	Talk

THAAU05	Space-Frequency Model of Ultra Wide-Band Interactions in Free-Electron Lasers	electron, radiation, free-electron-laser, acceleration	513
	Y. Pinhasi, Yu. Lurie, A. Yahalom CJS, Ariel
	The principle of operation of intense radiation devices such as microwave tubes, free-electron lasers (FELs) and masers, is based on a distributed interaction between an electron beam and radiation. We developed a three-dimensional, space-frequency theory for the analysis and simulation of radiation excitation and propagation in electron devices and free-electron lasers operating in an ultra wide range of frequencies. The total electromagnetic field is presented in the frequency domain as an expansion in terms of cavity eigen-modes. The mutual interaction between the electron beam and the field is fully described by coupled equations, expressing the evolution of mode amplitudes and electron beam dynamics. The approach is applied in a numerical particle code WB3D, simulating wide band interactions in free-electron lasers operating in the linear and non-linear regimes. The code is used to study the statistical and spectral characteristics of multimode radiation generation in a free-electron laser, operating in various operational parameters. The theory is demonstrated also in the case of "grazing", resulting in a wide-band interaction between the electron beam and the radiation. Y. Pinhasi, Yu. Lurie, A. Yahalom: Space-frequency model of ultra wide-band interactions in millimeter wave masers, Phys. Rev. E 71, (2005), 036503- 1-8
	Slides
	Talk

THAAU06	Parametric Optimization of a X-Ray FEL Based on a Thomson Source	electron, radiation, simulation, undulator	517
	L. Serafini, A. Bacci, C. Maroli, V. Petrillo, A. R. Rossi INFN-Milano, Milano M. Ferrario INFN/LNF, Frascati (Roma)
	We present a study based on a parametric optimization for a Thomson Source operated in FEL mode. This deals with the proposed scheme to use a high energy laser pulse colliding with a high brightness electron beam of low to medium energy electrons undulating in the incoming laser field may emit in a FEL coherent mode as far as some conditions are satisfied. A set of simple analytical formulas taking into account 3D effects is derived to express these conditions in terms of three free parameters, namely the wavelength of the laser, the amplitude of the ripples in the laser field, and the peak current of the eletron beam. A few examples of possible operating points are compared with results of 3D numerical simulations, showing the FEL coherent emission of X-rays in the 0.1 to 5 nm range with tens of MeV high brightness electron beams coliding with high energy laser pulses.
	Talk

THBAU03	How to Obtain High Quality Electron Bunches in the Presence of Normal Conducting LINAC Wake Fields	electron, emittance, linac, radiation	537
	S. Di Mitri ELETTRA, Basovizza, Trieste
	The dynamics of electron beams involved in Free Electron Lasers (FELs) projects is an interplay between sources of 6-dimensional emittance dilution and methods of emittance preservation. Relatively long bunches are required for harmonic cascade seeded FELs in order to accommodate the timing jitter and the seed provided by the bunch itself at each stage of the cascade. A high quality is required from such electron beams (small transverse emittance and energy spread) together with a uniform distribution in time along the usable part of the bunch; non-linearity in the longitudinal phase space and in the transverse planes are also issues. A complex longitudinal phase space dynamics characterizes the study often in presence of by the Coherent Synchrotron Radiation (CSR) generated in magnetic compressors. This paper reviews specific problems related to the electron beam dynamics dominated by bunches of kA peak current and varying length (0.1 to 2 ps) in the presence of normal conducting linac wakefields. Methods implemented to minimize the 6-dimensonal phase space degradation are discussed. Results of high beam quality performance are illustrated with particles tracking codes.
	Slides
	Talk

THPPH001	Temporal Analysis and Shape Control of UV High Energy Laser Pulses for Photoinjectors	target, electron, emittance, controls	552
	D. Garzella, O. Gobert, Ph. Hollander, F. Lepetit, M. Perdrix CEA, Gif-sur-Yvette T. Oksenhendler FASTLITE, Palaiseau
	In order to obtain high brightness electron bunches and generating high power, subpicosecond XUV radiation by SASE and/or seeded FEL, the laser pulses impinging onto the photocathode require special characteristics not only in terms of wavelength and delivered energy per pulse. Temporally and spatially shaped UV pulses are needed for preventing non linear space charge forces and then minimizing the electron emittance. In the EUROFEL program framework, our goal is to obtain few picosecond, 100 μJ laser pulses in the UV (266 nm) with a totally controlled and characterized longitudinal shape varying from the "beer can" profile to the "rotation ellipsoid" one. In this paper, a survey of the studies conceived for obtaining the desired goal on the KHz, Chirped Pulse Amplification (CPA)-based Ti:Sa laser system PLFA at CEA-Saclay, is shown. These latter deal with the amplitude and phase control of the stretched laser pulses issued from an amplifier before entering the compressor and the tripling unit. The work presents the theoretical background and stresses on the existing technological bottlenecks before showing various proposed experimental set-ups and preliminary promising results.

THPPH003	A High Average Power RF-Photoinjector Gun Cavity Developed for the BESSY Soft X-ray FEL	gun, emittance, electron, linac	560
	F. Marhauser, M. Dirsat, V. Duerr, A. Meseck, R. Richter, E. Weihreter BESSY GmbH, Berlin G. Asova, J. W. Baehr, H.-J. Grabosch, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, A. Oppelt, B. Petrosyan, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen O. Kalekin Humboldt Universität zu Berlin, Berlin J. R. Roensch Uni HH, Hamburg F. Tonisch DESY, Hamburg
	A 1.3-GHz, high duty factor, high-repetition-rate rf photoinjector gun cavity has been developed at BESSY. RF conditioning and high-power tests have been performed at the Photoinjector Test Facility at DESY Zeuthen (PITZ). The measurement results will be presented in this paper.

THPPH006	Photocathode Laser for the Superconducting Photo Injector at the Forschungszentrum Rossendorf	gun, emittance, focusing, radiation	564
	I. Will, G. Klemz MBI, Berlin F. Staufenbiel, J. Teichert FZR, Dresden
	We report on the design of the photocathode laser for a superconducting RF gun under development at the Forschungszentrum Rossendorf. The laser consists of a short-pulse oscillator, a pulse-picking Pockels cell, a linear amplifier chain and a frequency conversion stage. It generates pulses of about 5 ps duration with 13 MHz repetition rate and 1 W average power at 263 nm wavelength. Both the oscillator and the amplifiers are pumped by fiber-coupled semiconductor diodes. Nd:YLF is used as the gain medium of this laser. It introduces only small distortions on the optical wavefront of the laser beam and supports pulses of a few picoseconds duration. The beamline which transfers the laser beam to the photocathode of the RF gun has a large impact on the final beam profile. One can optimize the emittance of the electron beam by illuminating the cathode with a nearly flat-top beam profile. This is achieved by a pair of aspheric lenses and appropriate imaging optics in the beamline. Simulation of the beamline and its effect on the laser profile at the photocathode of the RF gun are also presented.

THPPH008	High Peak Current Design of a Superconducting Cavity for a SRF Photoinjector	emittance, gun, booster, cathode	571
	D. Janssen FZR, Dresden F. Marhauser BESSY GmbH, Berlin V. Volkov BINP SB RAS, Novosibirsk
	In collaboration between BESSY, DESY, FZR, MBI and BINP a SRF electron gun is under development. The progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity is the FEL project at BESSY. The electron injector of the linac should produce bunches with a charge of 2.5 nC and a transverse emittance of 1.5 mm mrad. In order to compensate the emittance expansion by space charge effects a large electric field on the cavity axis and a strong magnetic field near the cathode are necessary. The strengths of these fields are limited by the maximum magnetic surface field in superconducting cavities. We have designed a 1.5 cell gun cavity, where the magnetic field is realized by an additional RF mode (TE mode). In order to reduce third order effects of the RF fields, for the accelerating field a frequency below the linac frequency is used. The laser pulse, which creates the electron bunch, has a length of 20ps and a rise time of 2ps. In the tracking calculation the electrons start with an average energy of 1eV. For a bunch charge of 2.5 nC a transverse emittance of 1.8 mm mrad has been obtained. The maximal surface field is 160 mT.

THPPH016	First Experience with the Machine Protections System of FLASH	undulator, linac, beam-losses, radiation	587
	L. Fröhlich Uni HH, Hamburg M. Görler, P. Göttlicher, D. Noelle, D. Pugachov, H. Schlarb, S. Schreiber, M. Staack, M. Werner DESY, Hamburg A. Hamdi, M. Luong, J. Novo CEA, Gif-sur-Yvette
	Superconducting LINACs provide high brightness beams with substantial beam power. The design of the TTF2 machine is 70 kW beam power at the dump, XFEL will run 2 dump systems with 600 kW each. From this numbers is becomes very clear, that protections systems are required. This paper will present the design and implementation of the machine protection system of the FLASH facility, and will report on the first operational experience.

THPPH017	Experience with the Photoinjector Laser at FLASH	electron, cathode, controls, free-electron-laser	590
	S. Schreiber, M. Görler, K. Klose, M. Staack DESY, Hamburg L. Fröhlich Uni HH, Hamburg I. H. Templin, I. Will MBI, Berlin
	The photoinjector laser system of FLASH is a key element for the generation of high quality electron beams required for a stable and reliable operation of the facility. FLASH is the VUV and soft X-ray FEL user facilitry at DESY. FLASH is based on superconducting accelerating structures allowing to accelerate electron bunch trains of a length of up to 800 us with a repetition rate of 10 Hz. Based on the standard 1 MHz pattern, the laser provides to some extend a flexible bunch train structure. We report on operational issues and on the performance of the laser system with emphasis on its transverse and longitudinal properties, energy and timing stability.

THPPH018	Single-Shot Longitudinal Diagnostics with THz Radiation at the Free-Electron Laser FLASH	radiation, electron, diagnostics, free-electron-laser	594
	H. Delsim-Hashemi, J. Rossbach, P. Schmüser Uni HH, Hamburg O. Grimm, H. Schlarb, B. Schmidt DESY, Hamburg A. F.G. van der Meer FOM Rijnhuizen, Nieuwegein
	The longitudinal charge distribution in the electron bunches has a strong impact on the lasing process in a SASE-type FEL. The investigation of the longitudinal charge distribution in the electron bunches with very high resolution and on a bunch-by-bunch basis is enabled by a novel spectrometer which is based on diffraction gratings and multichannel signal detection. Measurements of coherent transition radiation with this spectrometer in both the scanning mode and the single-shot mode are presented. Structures in the electron bunches as short as 10 fs have been observed. Correlations between the measured FEL pulse energies and the signals in different wavelength channels of the single-shot spectrometer have been established. These data will be utilized to fine-tune the parameters of the bunch compression system at FLASH in order to optimize the gain in the SASE process.

THPPH023	Tuning, Conditioning, and Dark Current Measurements of a New Gun Cavity at PITZ	gun, cathode, resonance, electron	609
	A. Oppelt, K. Abrahamyan, O. A. Aldrian, G. Asova, J. W. Baehr, G. Dimitrov, H.-J. Grabosch, L. Hakobyan, Y. Ivanisenko, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, V. Miltchev, B. Petrosyan, R. I. Spesyvtsev, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen K. Floettmann, J. H. Han, C. Martens, R. Meyer, F. Tonisch DESY, Hamburg O. Kalekin Humboldt Universität zu Berlin, Berlin F. Marhauser, R. Richter, E. Weihreter BESSY GmbH, Berlin P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI) J. R. Roensch Uni HH, Hamburg
	In December 2005, a new gun cavity for the Photo Injector Test Facility at DESY in Zeuthen (PITZ) was tuned at Hamburg with the help of a specially designed tuning device. The tuning processus and its results as well as RF measurements will be presented. Meanwhile, the cavity was installed in the PITZ facility and conditioned. Dark current measurements with different cathodes were undertaken and will be described in the paper. Comparisons to former measurements will be made.

THPPH026	Design of a Two-Stage Laser Pulse Shaping System for FEL Photoinjectors	simulation, controls, insertion, gun	617
	M. B. Danailov, A. A. Demidovich, R. Ivanov ELETTRA, Basovizza, Trieste
	Temporal pulse shaping is one of the most important requirements to photoinjector lasers needed in the majority of FEL projects. The laser pulses commonly requested for excitation of the photocathode are in the UV (around 260 nm) and have flat-top shape of duration in the 5-10 ps range. More complex pulse shapes like "water-bags" and ramps have also been proposed recently, indicating that the pulse shaping scheme must offer flexibility in generating different shapes. In this paper we present an approach which combines the two main pulse shaping techniques, namely acousto -optic dispersive filter (DAZZLER) and Fourier-based 4-f system. The DAZZLER is inserted between the seed mode-locked oscillator and the amplifier and is used for preliminary shaping in the infrared, while the final pulse shape and duration are determined by a 4-f system incorporating deformable mirror positioned after the harmonic conversion to UV. The paper provides simulations and experimental results on designed and measured pulses of both flat-top and asymmetric (ramp) type, comparing solutions based on different distribution of amplitude and phase shaping between the two parts of the shaping setup.

THPPH028	Further Studies in the FERMI@ELETTRA Photoninjector Optimization	emittance, gun, linac, electron	625
	M. Trovo, G. Penco ELETTRA, Basovizza, Trieste S. M. Lidia LBNL, Berkeley, California
	In the framework of the FERMI@ELETTRA project we are presently studying an electron beam configuration satisfying the bunch energy requirements coming out from the FEL photon production system. The multi-particles tracking code results concerning the photoinjector set up which includes the RF gun and the first two accelerating sections are presented in this paper, describing two possible electron bunch configurations, which satisfy the FEL operation modes. Both injector configurations aim to match the linac requirements to have a ramped current profile at the exit of the photoinjector. Moreover sensitivity studies, time and energy jitters estimations are presented for both cases.

THPPH031	Commissioning of the SPARC Photo-Injector	gun, diagnostics, controls, emittance	637
	M. Bellaveglia, D. Alesini, S. Bertolucci, M. E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, S. Guiducci, M. Incurvati, C. Ligi, M. Migliorati, A. Mostacci, L. Palumbo, L. Pellegrino, M. A. Preger, R. Ricci, C. Sanelli, F. Sgamma, B. Spataro, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario INFN/LNF, Frascati (Roma) A. Bacci, I. Boscolo, F. Broggi, S. Cialdi, D. Giove, M. Mauri, A. R. Rossi, L. Serafini INFN-Milano, Milano L. Catani, E. Chiadroni, A. Cianchi, S. Tazzari INFN-Roma II, Roma L. Giannessi, M. Quattromini, A. Renieri, C. Ronsivalle ENEA C. R. Frascati, Frascati (Roma) M. Mattioli, P. Musumeci, M. Petrarca INFN-Roma, Roma A. Perrone INFN-Lecce, Lecce J. B. Rosenzweig UCLA, Los Angeles, California
	The SPARC project is born to perform R&D activity headed to realize SASE-FEL experiments at 500nm and higher harmonic generation. The project foresees the realization of a high brightness photo-injector able to produce a 150-200MeV electron beam to drive FEL process inside a dedicated 14m long undulator. The machine is going to be assembled at LNF and its final configuration is made up of an RF gun, driven by a Ti:Sa laser, injecting into three SLAC type accelerating sections. Nowadays we are working in a photo-injector test phase, aiming to characterize the main hardware components and to investigate the behavior of the e-beam dynamics in the first meters of drift. To do this we utilize the emittance-meter, a home designed diagnostic device placed just after the RF gun, able to move 1.2 meters along the longitudinal axis to measure beam parameters. In this paper we report a more accurate description of the project, the status of the single systems constituting the machine and the most important results we obtained in the e-meter phase.

THPPH032	Free Electron Laser Triggered Photo-Cathode	cathode, emittance, radiation, electron	641
	E. Sabia, A. Dipace ENEA Portici, Portici (Napoli) G. Dattoli ENEA C. R. Frascati, Frascati (Roma)
	The possibility of realizing a FEL triggered photocathode has been proposed long time ago and the advantages have been pointed out. In these devices the FEL can be exploited to extract electrons from a photocathode to provide a high quality e-beam. The device becomes even more appealing if photo-thermoionic cathodes can be exploited in two different phases. In the first the electrons are extracted from the cathode working as thermoionic and are used to drive a FEL oscillator, the FEL light is then used to flash the cathode which operates as a photo thermal assisted device. We comment on the possibility of using FEL triggered photocathodes to produce high quality e-beams for SASE or oscillator FEL devices. The use of the same e-beam driving the photocathode and the FEL makes the system naturally free of any synchronization problem arising when an external laser is used. Examples of interplay between the generation of electron and optical bursts are also investigated.

THPPH034	Laser Pulse Length Dependence of Beam Emittance of Photocathode RF-Gun	emittance, electron, gun, simulation	649
	H. Dewa, T. Asaka, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, H. Tomizawa, K. Yanagida JASRI/SPring-8, Hyogo-ken
	A pulse length of the UV laser is an important parameter of the Photocathode RFgun. Due to space charge effect, too short laser pulse increases the beam emittance. Therefore there should be an optimum pulse length if the electron beam charge is determined. To study the pulse length dependence of the beam emittance, the emittance was measured at several conditions of laser pulse length, which were prepared with a laser pulse stacker. The laser pulse can be stretched by dividing a laser pulse of a few pico second into two pulses and then combined them with time delay. The pulse stacker that consists of four sets of the divider and combiner could generate an arbitrary pulse length within 2 - 20 ps by changing delay time of each sets. The beam charge dependence was also measured. Beam emittance was measured with the magnetic quadrupole scanning technique. The results are compared with predictions of a 3-D beam tracking simulation that treats space charge effects.

THPPH037	Magnetic Field Measurement of the Undulator in KU-FEL	undulator, electron, radiation, gun	660
	M. Nakano, T. Kii, K. Masuda, H. Ohgaki, N. Okawachi, T. Yamazaki, K. Yoshikawa, H. Zen Kyoto IAE, Kyoto
	We have constructed an infrared FEL facility for advanced energy researches. In the last FEL conference, numerical studies on the undulator in KU-FEL by optimizing both for electron beam and for the optical cavity have been presented. On the other hand, since the undulator had been used in FELI, demagnetization has been anticipated. So we have measured the magnetic field of the undulator. In this conference, we will show the FEL gain and the spectrum of spontaneous emission by using the measurement data. T. Fukui, et al., Proc. of the 2005 FEL conference (2005) 195-198. ** E. Nishimura, et al., Nucl. Instr. and Methods, A341 (1994) 39-42.

THPPH045	Electro-Optic Sampling Method Using High DC Voltage Applying Setup	electron, gun, simulation, monitoring	692
	Y. W. Parc, J. Y. Huang, C. Kim, I. S. Ko, J. H. Park, S. J. Park PAL, Pohang, Kyungbuk X. Dao TUB, Beijing
	A RF photo-cathode (RF PC) gun with 1.6 cell cavity is installed at GTS(Gun Test Stand) being built at the Pohang Accelerator Laboratory (PAL). The short, intense, and low emittance electron beams are produced by the RF PC gun. For the successful construction of PAL-XFEL, the timing jitter and bunch length of the beam at the exit of the gun should be measured accurately. EOS (Electro-Optic Sampling) is a very promising method to measure the jitter without any interference with the electron beam. The spatially resolved method will be used in this experiment, which is a single shot measurement using cooled CCD carmera due to very low energy. Before the measurement with the beam at the exit of the gun, the calibration experiment is done with DC high voltage applying setup with 1mm thick ZnTe crystal. The broadening of our laser pulse by the ZnTe crystal is measured with auto-correlation method to know the resolution limit in this experiment and to do data analysis properly. In this presentation, the result of calibration experiment will be presented with a description of the experiment in detail.

THPPH046	Preliminary Measurement of Emittance Evolution Using Emittance Meter at the PAL	emittance, gun, cathode, space-charge	695
	J. H. Park, J. Y. Huang, C. Kim, I. S. Ko, Y. W. Parc, S. J. Park PAL, Pohang, Kyungbuk X. Dao TUB, Beijing X. J. Wang BNL, Upton, Long Island, New York
	A high-brightness electron beam is emitted from a RF photocatoode gun with 1.6 cell cavity from October 2005 at the Pohang Accereator Laboratory (PAL). The project of 4th Generation Light Source (4GLS) with the Spontaneous Amplification Sponteneous Emission Free-electron Laser (SASE FEL) in the PAL is called Pohang Accereator Laboratory X-ray Free-electron Laser (PAL-XFEL). In order to success of the PAL-XFEL project, it is necessary to research the high-brightness electron beam at the injector. A emittance meter (E-Meter) is installed for the high-brightness research in GTS (Gun Test Stand). The measurement of transverse emittance and beam size profile along the longitudinal direction was done by the E-Meter. Precise measurement of the emittance profile will provide powerful tool for the commissioning of the 4GLS injectors based on the emittance compensation principle. We are going to achieve this with the use of slit-based E-Meter that can be moved along the longitudinal direction. In this article, we present a preliminary measurement of the emittance evolution with the E-Meter for the commissioning of the RF photocathode gun.

THPPH050	Beat-Wave Laser-Driven Photoinjector for Superradiance Free-Electron Laser	electron, beat-wave, radiation, gun	699
	Y.-C. Huang, H.-L. Chang, A.-C. Chiang NTHU, Hsinchu
	Electron bunching plays a crucial role in a radiative emission process. Every free-electron laser (FEL) more or less relies on periodic bunching of electrons to build up radiation power. In this paper, we present our study on the generation and acceleration of periodically bunched electrons in a photo-injector. The idea is to use a laser beat wave to induce a density modulated photocurrent from a photocathode, which is subsequently accelerated to a relativistic speed. The electron micro-bunches in the density modulated current repeat at the laser beat frequency. Our computer simulations using the ASTRA* code show remarkable modulation contrast in > 50 A output current of a 4 MeV RF photocathode gun and a 20 MeV photocathode accelerator. With slight modifications to a conventional photocathode-gun driver laser, a UV beat-wave laser with a variable beat frequency can be implemented by combining two chirped laser pulses with a variable time delay. We will report our experimental progress toward realizing such a new technique in a compact superradiance Smith-Purcell FEL at THz frequencies. * K. Floettmann, ASTRA User Manual, http://www.desy.de/mpyflo/Astra\_dokumentation

THPPH053	3-D Laser Pulse Shaping for Photoinjector Drive Lasers	simulation, emittance, electron, gun	703
	YL. Li ANL, Argonne, Illinois X. Chang BNL, Upton, Long Island, New York
	We discuss techniques for 3-D laser pulse shaping aimed at improving the performance of photoinjectors and hence free-electron lasers seeded by the electron beams from such photoinjectors. These techniques are based on laser phase-space manipulation in conjunction with refractive/diffractive optics. We present a few schemes for 3-D laser pulse shaping that can be used to generate ellipsoidal laser pulses. Simulation results based on physical optics will be given.

THPPH059	Energy Modulation of the Electrons by the Laser Field in the Wiggler Magnet: Analysis and Experiment	electron, wiggler, radiation, resonance	725
	K. Holldack BESSY GmbH, Berlin A. Zholents LBNL, Berkeley, California
	Energy modulation of the electron beam after the interaction with the laser field in the wiggler magnet can be calculated using interference of the laser field and the field of spontaneous emission in the far field region of wiggler radiation. Quite often this approach gives a deeper insight on the process than traditional calculations where the effect of the laser field on the electron energy is integrated along the electron trajectory in the wiggler. We demonstrate it by showing the agreement between the analytical model and the experiment involving wiggler scan measurements with large detuning from the FEL resonance producing more than one order of magnitude variations in the amplitude of the energy modulation. The high sensitivity was achieved using the THz radiation from a sub-mm density variations that energy modulated electron leave behind while propagating the storage ring lattice. All measurements were performed at the BESSY-II electron storage ring.

THPPH063	In-Situ Cleaning of Metal Photo-Cathodes in RF Guns	gun, cathode, ion, electron	732
	J. F. Schmerge, J. Castro, J. E. Clendenin, E. R. Colby, D. Dowell, S. M. Gierman, H. Loos, M. Nalls, W. E. White SLAC, Menlo Park, California
	Cu cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to "clean" the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and the laser is scanned across the cathode. However, this can also damage the cathode since the laser is operated near the damage threshold and the QE degrades over days and must be cleaned regularly. Alternatively Hydrogen ion beams can be used to clean the cathode and improve the QE but this cleans only the area exposed to the ion beam. In this paper we measure the QE and the dark current emitted from a cathode before and after exposing the gun to a hydrogen plasma created with an rf discharge. With this technique the entire surface of the gun is cleaned simultaneously with no apparent detrimental effects.

THPPH064	Bunch Length Measurements at JLab FEL	radiation, electron, synchrotron, synchrotron-radiation	736
	P. Evtushenko, J. L. Coleman, K. Jordan, J. M. Klopf, G. Neil, G. P. Williams Jefferson Lab, Newport News, Virginia
	The JLab FEL is routinely operated with sub-picosecond bunches. The short bunch length is important for high gain of the FEL. Coherent transition radiation has been used for the bunch length measurements for many years. This diagnostic can be used only in the pulsed beam mode. It is our goal to run FEL with CW beam and 74.85 MHz micropulse repetition rate. Hence it is very desirable to have the possibility of doing the bunch length measurements when running CW beam with any micropulse frequency. We use a Fourier transform infrared interferometer, which is essentially a Michelson interferometer, to measure the spectrum of the coherent synchrotron radiation generated in the last dipole of the magnetic bunch compressor upstream of the FEL wiggler. This noninvasive diagnostic provides the bunch length measurements for CW beam operation at any micropulse frequency. We also compare the measurements made with the help of the FTIR interferometer with the data obtained by the Martin-Puplett interferometer. Results of the two diagnostics are usually agree within 15%. Here we present a description of the experimental setup, data evaluation procedure and results of the beam measurements.

THPPH066	Longitudinal Phase Space Characterization of Electron Bunches At the JLab FEL Facility	electron, linac, diagnostics, monitoring	740
	S. Zhang, S. V. Benson, D. Douglas, D. Hardy, G. Neil, M. D. Shinn Jefferson Lab, Newport News, Virginia
	We report the latest measurement of the longitudinal phase space of electron bunches on our 10kW free-electron laser facility. The design and construction of an all reflective optical transport has made it possible to make full use of broadband synchrotron radiation and perform a high-efficiency dispersion-free measurement with a remote fast streak camera. The evolution of the longitudinal phase space can be observed live when the accelerating RF phase is tuned. The results for different beam setups including low and high current will be presented.

THPPH068	The Development and Application of a Photoemission Model for Cesiated Photocathode Surfaces	scattering, emittance, brightness, electron	744
	K. Jensen, J. L. Shaw, J. E. Yater NRL, Washington, DC D. W. Feldman, N. A. Moody IREAP, College Park, Maryland P. G. O'Shea University Maryland, College Park, Maryland
	A photoemitter capable of in situ rejuvenation with a high quantum efficiency (QE) is a photocathode candidate of FELs and linear accelerators. Our program to develop a controlled porosity dispenser (CPD) photocathode* led to the development and validation of a theoretical model that accounts for low work function surfaces from submonolayer coverage of alkali (and alkali earth) metals. Here, we substantially modify our previous theoretical thermal photoemission model by: first, considering the impact of electron-electron and electron-lattice scattering; second, by the development of an integrated absorption-transport-emission model developed to evaluate the moments of the electron emission distribution function; and third, by the inclusion of quantum effects and surface features on the emission probability. For the experimental conditions to which we compare the resultant theory, there are no adjustable parameters. We discuss the performance of the model in the prediction of the QE of bare metals and coated surfaces, project the performance to regimes of interest to FELs, and use elements of the model to assess theoretical quantities of interest such as emittance. N. A. Moody, et al. (this conf.); K. L. Jensen, et al., (to be published in JAP99); * K. L. Jensen, et al., APL88, 154105 (2006), ibid, 164105.

THPPH069	Experimental Progress Toward Low Workfunction Controlled Porosity Dispenser Photocathodes	cathode, ion, electron, photon	748
	N. A. Moody, D. W. Feldman, P. G. O'Shea IREAP, College Park, Maryland K. Jensen, J. L. Shaw, J. E. Yater NRL, Washington, DC
	High efficiency, long-lived photocathodes are crucial for continued development of high power FELs. Most photocathodes with high quantum efficiency in the visible range suffer from short lifetime, due to chemical instability of the photosensitive surface layer that evaporates or is contaminated during operation in a RF-injector environment. We propose a controlled porosity dispenser (CPD) concept as a means of rejuvenating photosensitivity and performance. In many high-QE photocathodes, degradation over time is due to the loss of a surface coating of cesium. In CPD cathodes, cesium is replaced at near-room temperature via diffusion, maintaining high QE and extending effective lifetime. Measurements of increasingly complex photoemitting surfaces were performed, yielding QE as a function of cesium coating thickness, temperature, and photon wavelength. These measurements validate a photoemission model* that allows calculation of emission distribution, photocathode performance, and surface conditions of the cathode. Techniques for room-temperature cleaning of the CPD surface were determined and a prototype CPD photocathode based on cesiated sintered tungsten was evaluated. * K. L. Jensen, et al., (this conference)

THPPH070	Optimum Beam Creation In Photoinjectors Using Space-Charge Expansion	emittance, simulation, space-charge, linac	752
	M. P. Dunning, A. M. Cook, R. J. England, J. B. Rosenzweig UCLA, Los Angeles, California M. Bellaveglia, M. Boscolo, L. Catani, A. Cianchi, G. Di Pirro, M. Ferrario, D. Filippetto, G. Gatti, L. Palumbo, C. Vicario INFN/LNF, Frascati (Roma) S. M. Jones Jet Propulsion Laboratory, Pasadena, California P. Musumeci INFN-Roma, Roma
	It has recently been shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Frascati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed, and prospects for using the very low longitudinal emittance beam in a future bunch compressor to produce 10 micron long beams are evaluated.

THPPH071	Free Electron Lasers in 2006	electron, undulator, free-electron-laser, storage-ring	756
	W. B. Colson, J. Blau, A. Kampouridis NPS, Monterey, California
	Twenty-nine years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are listed and discussed.

THCAU01	Overview on Diagnostics for X- and XUV-FELs	radiation, diagnostics, electron, emittance	761
	B. Schmidt DESY, Hamburg
	Controlling and optimizing the SASE process of X-FELs and XUV-FELs requires detailed knowledge and information about the parameters of the driving electron beam which are of critical influence on the laser performance. Due to the very high peak current, collective phenomena have to be carefully measured and controlled while integral (projected) parameters are of limited use. This necessitates the development of a variety of diagnostics tools to monitor the electron bunch parameters in detailedness beyond the capabilities of conventional systems. Longitudinal bunch structures can be derived from time domain methods like electro optic techniques or using transverse deflecting RF-structures, and from frequency domain methods using coherent radiation. The talk will report on recent developments with special emphasis on single shot and online monitoring capabilities in this field. Other topics will be new concepts and experience in measuring the projected and time-sliced emittance of the beam, high precision beam position monitors and sub-picosecond beam phase and arrival time monitor systems.
	Slides
	Talk

THCAU03	Operational Experience with the Emittance-Meter at SPARC	emittance, cathode, gun, simulation	777
	L. Catani, E. Chiadroni, A. Cianchi INFN-Roma II, Roma M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, L. Cultrera, G. Di Pirro, A. Drago, M. Ferrario, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario INFN/LNF, Frascati (Roma) M. Migliorati, L. Palumbo Rome University La Sapienza, Roma P. Musumeci, M. Petrarca INFN-Roma, Roma C. Ronsivalle ENEA C. R. Frascati, Frascati (Roma)
	We report the operational experience of the movable emittance meter at SPARC. This device is based on the well-known technique of pepper pot (1-D slits in our case) but it allows moving the measuring device along the beam line from about 840 mm to 2200 mm from the cathode, following the emittance oscillations. More than a simple improvement over conventional, though non-trivial, beam diagnostic tools this device defines a new strategy for the characterization of high performance photoinjectors, providing a tool for detailed analysis of the beam dynamics, over a section of the accelerator where emittance compensation take place. With this device we performed detailed and systematic studies on beam dynamics with particular attention to the transverse parameters as well as longitudinal. We report also the operating experience at the PITZ facility.
	Slides
	Talk

THCAU04	Peak Current Performances from Electron Sources based on Field Emission (Single Tip and Field Emitter Arrays (FEAs))	electron, emittance, vacuum, gun	781
	R. Ganter, R. J. Bakker, M. Dehler, G. J. Gobrecht, C. Gough, E. Kirk, F. Le Pimpec, S. C. Leemann, K. L. Li, M. Paraliev, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, V. Schlott, H. Sehr, S. Tsujino, A. F. Wrulich PSI, Villigen
	Reducing beam emittance while keeping high brightness is the most direct way to reduce the cost and size of Free Electron Lasers (FELs). Ultimately, beam emittance is limited by the thermal emittance at the electron source. In order to find electron sources with low thermal emittance (<5.10^-8 m.rad) and high brightness (>5.10¹³ A.m^-2.rad^-2), cathodes based on single tip field emitter as well as field emitters arrays (FEAs) are investigated. Maximum peak current, measured from single tip in ZrC with a typical apex radius around one micrometer, are presented. Voltage pulses of two nanoseconds duration and up to 50 kilovolts amplitude lead to field emission current up to 470 mA from one ZrC tip. Combination of high applied electric field with laser illumination gives the possibility to modulate the emission with laser pulses. Sub-nanoseconds current pulses have been emitted with laser pulses at 1064nm illuminating a ZrC tip under high electric field. The dependence of photo-field emitted current with the applied voltage can be explained by the Schottky effect.
	Slides
	Talk

FRAAU03	Wave-Front Observations at FLASH	diagnostics, alignment, optics, focusing	794
	M. Kuhlmann, E. Plönjes, K. I. Tiedtke, S. Toleikis DESY, Hamburg P. Mercere SOLEIL, Gif-sur-Yvette P. Zeitoun LOA, Palaiseau
	During the first user operation of the Free-Electron Laser in Hamburg (FLASH) wavefront measurements have been recorded in the vacuum-ultraviolet region using a Hartmann sensor (by Imagine Optic). The Hartmann principle is based on a pinhole array, which divides the incoming beam into a large number of sub-rays monitored in intensity and position of individual spots. The identification of the local slope of the incident wavefront makes the aberrations from a perfect spherical wavefront visible. Ray tracing in upstream direction accesses the beam focal point in size and position. The intense and coherent vacuum-ultraviolet FEL beam leads to unique requirements for the wavefront sensor setup. We report an optimized setup to observe the metrology of flat and curved mirrors at FLASH beamlines. The effects of solid and gaseous filters are selectively described in the wavelength regime of 10nm to 32nm. The use of wavefront measurements to provide reliable machine parameter is discussed. The wavefront sensor proved to be a valuable tool to observe the FEL beam quality and the performance of optical elements, filters and diagnostic tools.
	Slides
	Talk

FRBAU03	Ultrafast Coherent Diffraction Imaging with X-ray Free Electron Lasers	electron, photon, radiation, scattering	805
	H. Chapman, S. P. Hau-Riege LLNL, Livermore, California J. Hajdu Uppsala University, Biomedical Centre, Uppsala
	The ultrafast pulses of X-ray FELs allow high-resolution imaging of biological and other soft matter without limitations imposed by radiation damage. A collaboration between LLNL, University of Uppsala, SLAC, TU Berlin, and DESY has carried out high-resolution diffraction imaging of structures using single 25 fs duration, 32 nm wavelength pulses generated by FLASH at DESY. Our objects were placed in the focused FEL beam, with peak intensities up to 10¹⁴ W/cm². The objects were heated to about 60,000 K by the pulse, but destruction only occurred after the pulse traversed the sample. We reconstructed images from the finely-sampled coherent diffraction patterns by phase retrieval using our Shrinkwrap algorithm. These show no evidence of the effects of the pulse on the structure. We also performed quantitative measurements of the explosion of test particles in the focused FEL pulse, by recording their diffraction patterns. No motion occurred during the pulse and we followed the evolution of the explosion with a novel holographic time-resolved technique. Our results confirm the basic principles of flash imaging and lend great confidence to achieving molecular imaging at future short-wavelength X-ray FELs.
	Slides
	Talk