FEL 2006 - List of Keywords (simulation)

A B C D E F G H I K L M O P Q R S T U V W

simulation

Paper	Title	Other Keywords	Page
MOBAU04	Optical Klystron Enhancement to SASE X-Ray FELs	klystron, undulator, electron, radiation	29
	Y. T. Ding, P. Emma, Z. Huang SLAC, Menlo Park, California V. Kumar RRCAT, Indore (M. P.)
	The optical klystron enhancement to self-amplified spontaneous emission (SASE) free electron lasers (FELs) is studied in theory and in simulations. In contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not sensitive to any phase mismatch between the radiation and the microbunched electron beam. The FEL performance with the addition of four optical klystrons located at the undulator long breaks in the Linac Coherent Light Source (LCLS) shows significant improvement if the uncorrelated energy spread at the undulator entrance can be controlled to a very small level. In addition, FEL saturation at shorter x-ray wavelengths (around 1.0 angstrom) within the LCLS undulator length becomes possible. We also discuss the application of the optical klystron in a compact x-ray FEL design that employs relatively low electron beam energy together with a shorter-period undulator.
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	Talk

MOPPH006	Extracting Information from Smith-Purcell FEL Simulations	radiation, multipole, bunching, electron	45
	J. T. Donohue CENBG, Gradignan J. Gardelle CESTA, Le Barp
	Simulations of Smith-Purcell radiation using 2D particle-in-cell codes have provided insight into the behavior of such devices, and have generally provided support to the viewpoint of the Vanderbilt University group. However, if one is interested in Terahertz frequencies, the need for small meshes and short time intervals makes the calculations exceedingly long. In particular, the S-P correlation between frequency and angle is only valid at distances large compared to the grating size, and may not be apparent if the simulation area is too small. With the help of the multipole expansion, we show how simulation data obtained with a small area may be extended to an area of arbitrary size. This enables us to confirm the presence of coherent higher order S-P peaks at the appropriate angles. H. L. Andrews, C. H. Boulware, C. A. Brau, and J. D. Jarvis, Phys. Rev. ST Accel. Beams 8, 050703 (2005)

MOPPH007	Simulation of Smith-Purcell FELs at Terahertz Frequencies	radiation, electron, bunching, resonance	49
	J. T. Donohue CENBG, Gradignan J. Gardelle CESTA, Le Barp
	Our previous work on the 2D simulation of a coherent Smith-Purcell FEL operating in the Terahertz domain is extended to a systematic study of the dependence on various parameters. The important question of the starting current reqired to produce coherent radiation is addressed, and our new results will be presented. As in our previous work we concentrate on two configurations, one similar to the Dartmouth S-P FEL, with a low energy continuous beam, and the other similar to the MIT experiment which uses a pre-bunched 15 MeV beam. A Bakhtyari, J. E. Walsh, and J. H. Brownell, Phys. Rev. Lett. E 65, 066503 (2002).** S. E. Korbly, A. S. Kesar, J. R. Sirigiri, and R. J. Temkin, Phys. Rev. Lett. 94, 054803 (2005)

MOPPH009	Beam Dynamics Experiments and Analysis on CSR Effects at FLASH	space-charge, electron, RF-structure, linac	56
	B. Beutner, W. Decking, M. Dohlus, T. Limberg, M. Roehrs DESY, Hamburg
	High peak currents at the FLASH linac are produced using magnetic bunch compressor chicanes. In these magnetic chicanes, the energy distribution along an electron bunch is changed by the emission of coherent synchrotron radiation (CSR). Due to dispersion, these energy changes lead to transverse displacements along the bunch. The projection into the longitudinal horizontal plane is observed with a transverse deflecting rf-structure. Measurements of CSR induced transverse displacements are presented and compared with simulations.

MOPPH011	FELO: A One-Dimensional Time-Dependent FEL Oscillator Code	electron, radiation, emittance, undulator	59
	B. W.J. McNeil, G. R.M. Robb USTRAT/SUPA, Glasgow D. J. Dunning, N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
	A one-dimensional, SDDS compliant time-dependent FEL oscillator code has been developed in Fortran 90. The code, FELO, solves universally-scaled FEL equations to simulate oscillator FELs operating from the low to high gain regime. The code can simulate start-up from shot noise, different electron pulse current distributions, the effects of cavity length detuning and temporal jitter between electron bunches. Cavity detuning curves for both the low-gain IR-FEL and the regenerative amplifier VUV-FEL of the 4th Generation Light Source (4GLS) proposal at Daresbury Laboratory are modelled. The code predictions for the VUV-FEL output are compared with simulations performed with the parallel implementation of Genesis 1.3 and are found to be in good agreement.

MOPPH012	The Conceptual Design of the 4GLS XUV-FEL	undulator, electron, photon, lattice	63
	B. W.J. McNeil USTRAT/SUPA, Glasgow B. Sheehy Sheehy Scientific Consulting, Wading River, New York N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
	The Conceptual Design Report for the 4th Generation Light Source (4GLS) at Daresbury Laboratory in the UK was published in Spring 2006. A key component of the proposal is an XUV-FEL amplifier directly seeded by a High Harmonic source and operating in the photon energy range 8-100eV. Numerical modelling shows the FEL may generate ~50fs (FWHM) pulses of variably-polarised, temporally-coherent radiation with peak powers in the range 2-8 GW.

MOPPH015	Analysis of Smith-Purcell BWO with End Reflections	electron, damping, interaction-region, undulator	71
	V. Kumar RRCAT, Indore (M. P.) K.-J. Kim ANL, Argonne, Illinois
	All the previous analyses of Smith-Purcell Backward Wave Oscillator (SP-BWO) have assumed that there is no reflection at the end of the grating. We present an analysis of SP-BWO taking the reflection at the end of the grating into account. We study the dependence of start current on end reflection, taking the attenuation due to finite conductivity into account.

MOPPH020	Enhancement of a Coherent (Super Radiant) Emission in FEL by Means of Energy Modulation of an Emitting Short Electron Bunch	electron, radiation, electromagnetic-fields, wiggler	79
	Yu. Lurie, Y. Pinhasi CJS, Ariel A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
	The developing techniques for generation of short bunches of relativistic electron beams enable construction of high-power, compact super-radiant free-electron lasers (FELs). Optimal efficiency of the super-radiant emission is achieved with ultra-short pulses (the beam duration is much less then the period of radiation). Unfortunately, the minimum duration of the pulse that can be achieved in practice is technologically limited, restricting the frequency of the radiation. We demonstrate that a super-radiant emission can be strongly enhanced by means of a proper energy modulation of the driving beam pulse, as suggested by A. Doria et al.. In this way, a THz FEL source driven by short electron bunches generated by photo-cathode injection can be realized. Numerical simulations carried out using the WB3D code* show that linear energy modulation of a driving electron bunch enables one to increase the power of the super-radiant emission by a few orders of magnitude, approaching the power that can be achieved if ultra-short e-beam bunches are available. Possible limitations for the application of this method are also discussed, as well as the spectral purity of enhanced radiation. * A. Doria et al., Phys. Rev. Lett. 80, 2841 (1998).** Y. Pinhasi, Yu. Lurie and A. Yahalom, Nucl. Instr. and Meth. in Phys. Res. A 475, 147 (2001).

MOPPH026	Overview of Perseo, a System for Simulating FEL Dynamics in Mathcad	undulator, coupling, electron, resonance	91
	L. Giannessi ENEA C. R. Frascati, Frascati (Roma)
	The computing performances of today's personal computers are sufficient for executing interactively one dimensional FEL simulations. Mathcad is a versatile tool for implementing math expressions, plotting data and analysing results with the main prerogative of the simplicity of the user-interface. This suggested to develope a set of functions devoted to the simulation of FEL dynamics that can be accessed from the Mathcad environment. The result is Perseo, a flexible tool that can be simply programmed to set up FEL simulations in a wide variety of practical configurations. Perseo allows the time dependent simulation of SASE and seeded FEL configurations, oscillator configurations and exhotic configurations like master oscillator power amplifier or multiple stages cascaded FELs. The model include higher order harmonics and startup from shot-noise. Perseo is freely available at http://www.perseo.enea.it

MOPPH033	Two-Stream Smith-Purcell Free-Electron Laser Using a Dual-Grating: Linear Analysis	electron, laser, free-electron-laser, radiation	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, laser, scattering	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.

MOPPH040	Transverse Coherence Properties of the LCLS X-Ray Beam	radiation, undulator, electron, laser	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.

MOPPH044	Optical Beam Quality in Free-Electron Lasers	wiggler, electron, laser, 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.	laser, undulator, focusing, radiation	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.

MOPPH050	The Properties of the FEL Output for Different Seeding Schemes	undulator, radiation, optics, electron	150
	J. Bahrdt BESSY GmbH, Berlin B. Faatz, R. Treusch DESY, Hamburg V. Miltchev Uni HH, Hamburg R. Reininger New Affiliation Request Pending, -TBS-
	Several seeding schemes, like self seeding for FLASH or seeded HGHG cascades for BESSY soft X-ray FEL, are proposed for existing or planned free electron laser facilities. The simulation of these schemes requires the detailed knowledge of the properties of the seeding radiation and the implementation of these properties in the Codes. Time dependent simulations with the 3D code GENESIS calculate the electric field distribution in and at the end of the undulator. The physical optics code PHASE permits the propagation of wave fronts across grazing incidence optics. Using the combination GENESIS PHASE GENESIS, the properties of the FEL output for different seeding schemes can be obtained. For example, the radiation quality of a SASE FEL can be improved in a self seeding scheme. Here, the radiation is monochromatized after a first undulator section and reflected back to the second Undulator modules. We present simulation studies for the self seeding option of FLASH.

MOPPH051	Development and Application of Figures of Merit to Evaluate the Output of HGHG FEL Cascades	radiation, background, linac, electron	154
	B. C. Kuske, R. Follath, A. Meseck BESSY GmbH, Berlin
	In the design of Free Electron Lasers, parameters like the peak power and the spectral power were established as figures of merit to evaluate the FEL output quality. However, spectra obtained with FEL studies using bunches from start-to-end simulations do not have a purely Gaussian profile, so that these simple parameters can no longer be used as figures of merit. Furthermore, criteria such as the signal-to-noise ratio and the stability of the source point, which is of extreme importance for the transport of the radiation to the user experiment, should be included in the design considerations. This paper suggests different criteria and parameters to describe and compare the FEL output, which are not readily provided by the common FEL codes. An IDL code has been written, that extracts this information from the regular GENESIS output. This procedure will be used to analyze the output of the BESSY FEL.

MOPPH052	Study of a Deflecting Dispersive Chicane for BESSY Soft X-Ray FEL	radiation, electron, dipole, coupling	158
	A. Meseck, G. Wuestefeld BESSY GmbH, Berlin
	High power, short pulse lengths and full coherence are the main parameters of the second generation free electron lasers like BESSY soft X-ray FEL. To provide radiation with these properties, cascades of HGHG stages are planned. In these stages an energy modulation is imprinted on the electron beam by seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The following radiator is tuned to this harmonic and generates radiation with high power. The separation of the electron beam and seeding radiation after the modulation is desirable, as not only the quality of the radiator improves but also the seeding radiation itself can be used for diagnostics. A simple bending magnet leads to the separation but it causes a coupling of the longitudinal and transverse motion and could spoil the longitudinal modulation. Based on an exact linear model, a dispersive chicane is designed for one stage of the BESSY FEL which bends the electron beam without the coupling effects. The linear model will be presented and used to design a chicane. Simulations of the spatial modulation will also be discussed.

MOPPH053	Simulation Studies on the Self-Seeding Option at FLASH	undulator, electron, radiation, optics	162
	V. Miltchev, J. Rossbach Uni HH, Hamburg B. Faatz, R. Treusch DESY, Hamburg
	In order to improve the temporal coherence of the radiation generated by FLASH, a two-stage seeding scheme* is presently being realized. It consists of two undulator stages and a magnetic chicane and a monochromator located between them. In this contribution we investigate various configurations of the electron optics of the seeding set-up. The optimization of the lattice in the first seeding stage and the parameters of the magnetic chicane will be discussed. Simulation results for the performance of the seeded FEL at different resonant wavelengths will be presented. * J. Feldhaus et. al. "Possible application of X-ray optical elements for reducing the spectral bandwidth of an X-ray SASE FEL". Optics Communications, Volume 140, Pages 341-352

MOPPH055	Coherent Harmonic Emission of the Elettra Storage-Ring Free-Electron Laser in Single-Pass Configuration: a Numerical Study for Different Undulator Polarizations	undulator, laser, 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, photon, laser	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

MOPPH058	Start-to-end Time-Dependent Study of FEL Output Sensitivity to Electron-beam Jitters for the First Stage of the FERMI@Elettra Project	electron, photon, linac, emittance	178
	G. De Ninno, E. Allaria, M. Trovo ELETTRA, Basovizza, Trieste
	Sensitivity of the output laser pulse to electron-beam jitters is one of the major issues affecting the expected performance of both SASE and seeded FEL's. Focusing on the first stage of the FERMI@Elettra project, in this paper we present results of time-dependent numerical simulations in which the codes GENESIS and GINGER have been used to process a large number of electron-beam distributions generated at the gun using the code GPT and propagated through the linac using the code ELEGANT.

MOPPH065	The First Experimental Observation of FEL Amplifier Efficiency Improvement using Electron Beam Energy Detuning at the NSLS SDL	electron, laser, resonance, radiation	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.

MOPPH067	Issues in High Harmonic Seeding of the 4GLS XUV-FEL	optics, laser, controls, 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, laser, 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.

MOPPH069	Transverse and Longitudinal Coherence Properties of the Radiation from X-Ray SASE FELs	radiation, electron, undulator, emittance	206
	E. Saldin, E. Schneidmiller, M. V. Yurkov DESY, Hamburg
	We present the results of comprehensive numerical studies on transverse and longitudinal coherence of SASE FEL radiation. Development of coherence in exponential gain regime and saturation is studied with the help of similarity techniques. Expected coherence properties of X-ray sourses at the European XFEL, LCLS and SCSS are compared. The simulations were performed with the three-dimensional time-dependent code FAST using a real number of particles in the electron bunch.

MOPPH073	An Enhanced GINGER Simulation Code with Harmonic Emission and HDF5 IO Capabilities	radiation, undulator, vacuum, diagnostics	218
	W. M. Fawley LBNL, Berkeley, California
	GINGER* is an axisymmetric, polychromatic (r-z-t) FEL simulation code originally developed in the mid-1980's to model the performance of single-pass amplifiers. Over the past 15 years GINGER's capabilities have been extended to include more complicated configurations such as undulators with drift spaces, dispersive sections, and vacuum chamber wakefield effects; multi-pass oscillators; and multi-stage harmonic cascades. Its coding base has been tuned to permit running effectively on platforms ranging from desktop PC's to massively parallel processors such as the IBM-SP. Recently, we have made significant changes to GINGER by replacing the original predictor-corrector field solver with a new direct implicit algorithm, adding harmonic emission capability, and switching to the HDF5 IO library** for output diagnostics. In this paper, we discuss some details regarding these changes and also present simulation results for a number of test cases ranging from LCLS SASE emission to performance of the FERMI@ELETTRA two-stage, harmonic cascade. * http://www-ssrl.slac.stanford.edu/lcls/technotes/LCLS-TN-04-3.pdf (also LBNL-49625-Rev. 1) ** http://hdf.ncsa.uiuc.edu/HDF5/

MOPPH075	Simulations of High Power-FEL Amplifiers	electron, undulator, extraction, laser	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.

MOCAU03	The Use of HHG at 4GLS	undulator, radiation, electron, photon	234
	B. W.J. McNeil USTRAT/SUPA, Glasgow D. J. Dunning, N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire B. Sheehy Sheehy Scientific Consulting, Wading River, New York
	4GLS is a facility proposed for the Daresbury Laboratory in the UK* which will offer users a suite of high brightness synchronised sources from THz frequencies into the XUV. In the current design, photon energies from 8-100eV will be generated in a variable polarisation FEL amplifier directly seeded by a High Harmonic Gain system. The reasoning behind this choice will be discussed and characterisation of the sources based on the present design presented. *http://www.4gls.ac.uk/documents.htm#CDR
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MOCAU05	Analysis of the Process of Amplification in a Single Pass FEL of High Order Harmonics Generated in a Gas Jet	electron, laser, 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.
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TUAAU05	Optical Design of the Energy Recovery Linac FEL at Peking University	linac, undulator, emittance, space-charge	277
	Z. C. Liu, J.-E. Chen, J. K. Hao, K. X. Liu, X. Y. Lu, S. W. Quan, B. C. Zhang, K. Zhao, G. M. wang PKU/IHIP, Beijing
	Peking University is currently building an Energy Recovery Linac FEL (PERFEL). The system is consisted of the DC-SC photocathode injector, the superconducting main linac which is composed of two nine cell TESLA-type cavities and the beam transport system. The objective of the PERFEL is to build a testbed for the study of beam dynamics and accelerator technology for energy recovery except to provide infrared FEL. In this paper the main parameters of the PERFEL are described and the optical design for the beam transport of PERFEL is presented. The simulation is carried out using the typical particle tracking codes such as elegant. *Corresponding author. Tel: +86-10-6275-8528; Fax: +86-10-6275-1875. Email address: kxliu@pku.edu.cn
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TUBAU04	Inverse Free Electron Lasers for Advanced Light Sources	undulator, laser, electron, radiation	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.
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TUPPH001	A 3D Model of the 4GLS VUV-FEL Conceptual Design Including Improved Modelling of the Optical Cavity	undulator, radiation, electron, optics	304
	N. Thompson, D. J. Dunning CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire K.-J. Boller, J. G. Karssenberg, P. J.M. van der Slot Twente University, Laser Physics and Non-Linear Optics Group, Enschede B. W.J. McNeil USTRAT/SUPA, Glasgow
	The Conceptual Design Report for the 4th Generation Light Source (4GLS) at Daresbury Laboratory in the UK was published in Spring 2006. The proposal includes a low-Q cavity (also called a regenerative amplifier) FEL to generate variably-polarised, temporally-coherent radiation in the photon energy range 3-10eV. A new simulation code has been developed that incorporates the 3D FEL code Genesis 1.3 and which simulates in 3D the optical components and radiation propagation within the non-amplifying sections of an optical cavity. This code is used to estimate the optimum low-Q cavity design and characterise the output from the 4GLS VUV-FEL. J. G. Karstenberg, P. J.M. van der Slot, J. W.J. Verschuur, I. V. Volohkin, K.-J. Boller (ibid)

TUPPH002	Development of Frequency-Resolved Optical Gating for Measurement of Correlation between Time and Frequency of Chirped FEL	laser, 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.

TUPPH008	Harmonic Lasing Characterization at Jefferson Lab	laser, electron, wiggler, 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.

TUPPH024	Super Coherent THz Light Source Based on an Isochronous Ring with Very Short Electron Bunches	gun, lattice, radiation, electron	371
	H. Hama, K. Akiyama, F. Hinode, K. Kasamsook, M. Kawai, T. Muto, K. Nanbu, T. Tanaka, M. Yasuda Laboratory of Nuclear Science, Tohoku University, Sendai H. Tanaka JASRI/SPring-8, Hyogo-ken
	A project to develop a coherent Teraherz (THz) light has been progressed at Laboratory of Nuclear Science, Tohoku University. The coherent synchrotron light at the frequency region of THz is emitted from electron bunches of several tens femto-second bunch length created by a thermionic RF gun and a sophisticated bunch compressor. In addition, the beam is circulating a ring consisted of nearly complete isochronous optics for many turns, so that the average power of the radiation may be considerably enhanced. Forgetting about the amount of the charge, thermionic RF gun is quite suitable to produce such a very short bunch. We have developed an ITC (Independently-Tunabel-Cells) RF gun, which is consisted with two independent cavities in order to manipulate the longitudinal phase space. In addition to expected performance of the ITC RF gun and the bunch compressor, the paper describes the latest version of the lattice design of the isochronous ring and results of tracking simulations as well. Possibility of long wavelength SASE mode and superradiant on the isochronous ring are also discussed. H. Hama, Proc. the 27th Int. Free Electron Laser Conf., Stanford, CA (2005) 1-7. ** T. Tanaka, F. Hinode, M Kawai, A. Miyamoto, K. Shinto, H. Hama, Proc. PAC2005, Knoxville, TN (2005) 3499-3501.

TUPPH026	Dispersion Effects in Short Pulse Waveguide FEL	electron, radiation, undulator, free-electron-laser	378
	N. S. Ginzburg, A. Sergeev IAP/RAS, Nizhny Novgorod E. R. Kocharovskaya New Affiliation Request Pending, -TBS-
	The influence of waveguide dispersion on the FEL operation driven by short electron bunches is studied. Under the assumption of a high quality resonator a parabolic equation for the evolution of electromagnetic pulse profile is derived. Based on an analytical theory describing the linear stage of generation a starting condition is determined. A structure of supermodes representing the sum of resonator eigenmodes with locked phases is found as well. It is demonstrated that due to waveguide dispersion FEL is able to generate not only for positive but also for negative cavity detuning. The computer simulation of a nonlinear regime taking into account electromagnetic pulse dispersion defines a stationary profile of electromagnetic pulse in good agreement with experimental results,. It is shown that regimes with periodic and chaotic self-modulation of the pulse profile are realized for considerable exceeding of the length of interaction region over the threshold. A superradiant (transient) regime of short pulse generation is found for small cavity detuning. Jeong Y. U., et al. Proc. of the 2004 FEL Conference, Trieste, Italy, 2004, P.667. ** Doria A., Bartolini R., Feinstein J. IEEE J. Quantum Electron., 1993, V.29, P.1428.

TUPPH034	Generation of Narrow Band Short mm Wave Superradiance Pulses in a Non-uniform Planar Waveguide	electron, radiation, undulator, cyclotron	397
	N. S. Ginzburg, R. M. Rozental, A. Sergeev, I. V. Zotova IAP/RAS, Nizhny Novgorod
	Recently significant progress was achieved in production of ultrashort pulses in millimeter wave band based on intense electron bunch supperradiance,,*. One of the problems for advance similar mechanisms in shorter wave bands is spectrum broadening caused by the simultaneous bunch interaction with several waveguide modes. To suppress spurious interaction we suggest to use the non-uniform planar waveguide. In such a waveguide the phase velocities of the different modes varied over longitudinal coordinate, with the exception of the fundamental TEM mode. As a result it is possible to suppress interaction of the short electron bunch with higher-orders modes responsible for lower frequencies radiation including cut-off modes. We studied 200-500 GHz superradiance of a 2 MV, 100 A, 100-300 ps electron bunch in a planar regular wiggler. It is shown that narrow band superradiance pulses could be produced in the 2 m long planar waveguide with the gap between plates linear increasing from 1-2 to 5-8 wavelength. The peak power of the pulses amounted 3 MW and hundreds of kW for the 200 GHz and 500 GHz bands correspondingly. Ginzburg N. S, et al. // Nucl. Instr. Meth. Phys. Res., 1999, A429 (1), 94 N. S.Ginzburg, et al. // Opt. Comm., 2000, 175 (1-3), 139 *A. G.Reutova, et al. // JETP Lett., 2005, 82(5), 263

TUPPH035	Generation of Superradiant Pulses by Backscattering of Pumping Wave on the Intense Electron Bunch	electron, radiation, scattering, background	400
	N. S. Ginzburg JINR, Dubna, Moscow Region V. I. Belousov, G. G. Denisov, A. Sergeev, I. V. Zotova IAP/RAS, Nizhny Novgorod A. G. Reutova, K. A. Sharypov, V. G. Shpak, S. A. Shunailov, M. R. Ulmaskulov, M. I. Yalandin RAS/IEP, Ekaterinburg
	Recently significant progress was archived in the generation of multimegawatt subnanosecond pulses in millimeter wave band utilizing the cyclotron and Cherenkov mechanisms of superradiance (SR). We study the novel mechanism of SR when the powerful pumping wave undergoes the stimulated backscattering on the intense electron bunch. Due to the Doppler up shift the radiation frequency can significantly exceed the frequency of the pumping wave. With the relativistic microwave generator as a pumping wave source such a mechanism can be used for generation of the powerful pulse radiation in the short millimeter and submillimeter wave bands. Experiments on the observation of the stimulated scattering in the superradiance regime were carried out at Institute of Electrophysics RAS with two synchronized accelerators. The 4 ns electron beam from the first accelerator is used for generation of the 38 GHz 100 MW pumping wave which subsequently scattered on the subnanosecond 250 keV 1 kA electron bunch produced by the second accelerator. The SR pulses with duration 200 ps and peak power about 1 MW were generated. The spectrum of scattered signal included the frequencies up to 150 GHz.

TUPPH037	FEL-Oscillator Simulations with Genesis 1.3	undulator, radiation, laser, 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.

TUPPH047	Absolute and Convective Instability of Smith-Purcell Free Electron Laser	electron, feedback, radiation, free-electron-laser	431
	D. Li, K. Imasaki ILT, Suita, Osaka G. S. Park SNU, Seoul Z. Yang UESTC, Chengdu, Sichuan
	Smith-Purcell free electron laser can operate on two different modes. The low-energy electron excites the absolute instability and it operates in the manner of a backward-wave oscillator, while the high-energy electron induces the convective instability and it operates like a traveling-wave tube. In this paper, we demonstrate those two instabilities using a two-dimensional particle-in-cell simulation. The simulation model supposes a rectangular grating to be driven by a continuous beam, and the radiation is in the THz regime. The beam bunching and the evolution of the radiation field are observed. The variation of the gain is reported as well.

TUPPH048	Superradiant Smith-Purcell Radiation in the Terahertz-wave Region from Bunched Electron Beams	radiation, bunching, electron, laser	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.

TUPPH049	Study on Superradiant Smith-Purcell Radiation	radiation, electron, bunching, single-bunch	439
	D. Li, K. Imasaki ILT, Suita, Osaka S. Amano, S. Miyamoto, T. Mochizuki NewSUBARU/SPring-8, Laboratory of Advanced Science and Technology for Industry (LASTI), Hyogo G. S. Park, Z. Yang SNU, Seoul
	A simulation of coherent and superradiant Smith-Purcell radiation is performed in GHz regime using a three-dimensional particle-in-cell code. The simulation model supposes a rectangular grating to be driven by a single electron bunch,a train of periodic bunches and a continuous beam, respectively. The true Smith-Purcell radiation is distinguished from the evanescent wave, which has an angle independent frequency lower than the minimum allowed Smith-Purcell frequency. We also find that the superradiant radiations excited by periodic bunches are emitted at higher harmonics of the bunching frequency and at the corresponding Smith-Purcell angles. The "start current" is determined as well as the distributions of the radiation intensity are presented.

TUPPH052	Future FEL Studies at the VISA Experiment in the SASE and Seeded Modes	radiation, undulator, electron, laser	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.

TUPPH053	Magnetic Chicane Radiation Studies at the BNL ATF	radiation, electron, polarization, synchrotron	447
	M. P. Dunning, G. Andonian, A. M. Cook, E. Hemsing, A. Y. Murokh, S. Reiche, J. B. Rosenzweig, D. Schiller UCLA, Los Angeles, California M. Babzien, K. Kusche, V. Yakimenko BNL, Upton, Long Island, New York
	Coherent edge radiation, emitted from the edges of chicane dipole magnets, has recently been observed at the Accelerator Test Facility at Brookhaven National Laboratory. Using the 60 MeV linac, a series of experiments has been performed to characterize the radiation, including measurements of the spectrum, angular distribution, and polarization. Details and results of the experiments and plans for future experiments are presented.

TUPPH054	Beam Pickup Designs Suited for an Optical Sampling Technique	pick-up, laser, 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.

TUPPH057	First Tolerance Studies for the 4GLS FEL Sources	electron, undulator, radiation, photon	462
	D. J. Dunning, J. A. Clarke, D. J. Scott, N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire B. W.J. McNeil USTRAT/SUPA, Glasgow
	The Conceptual Design Report for the 4th Generation Light Source (4GLS) at Daresbury Laboratory in the UK was published in Spring 2006. 4GLS features three distinct FEL designs, each operating in a different wavelength range: an externally seeded amplifier operating in the photon energy range 8-100eV (XUV-FEL); a low-Q cavity (regenerative amplifier) FEL operating over 3-10eV (VUV-FEL); a high-Q cavity FEL operating from 2.5-200μm (IR-FEL). Preliminary results of tolerance studies for the FELs designs are presented. In particular, the effects of the relative timing offset between the seed pulse of the XUV-FEL and the electron bunch, as well as the effects of electron bunch timing jitter in the VUV-FEL, are presented.

TUPPH071	Simulation of Mirror Distortion in Free-Electron LASER Oscillators	wiggler, electron, vacuum, emittance	477
	H. Freund SAIC, McLean S. V. Benson, M. D. Shinn Jefferson Lab, Newport News, Virginia
	Thermal distortion in cavity mirrors in high-power FELs can alter mode quality and degrade performance. Hence, it is important to be able to predict the character of the distortions to model their effect on FEL performance. To this end, we address these key issues by developing modeling and simulation tools that can accomplish these goals, and then benchmarking the simulation against observations on the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility. The modeling and simulation will rely on the MEDUSA code, which is a 3-D FEL simulation code capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. MEDUSA employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian resonantor modes and then analytically propagating these modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. Knowledge of the power loading on the mirrors allows us to model the mode distortions using Zernicke polynomials and this technique has been incorporated into MEDUSA.

THAAU03	A Scalloped Electron Beam Free-Electron Laser	wiggler, electron, radiation, emittance	509
	D. C. Nguyen LANL, Los Alamos, New Mexico W. B. Colson NPS, Monterey, California H. Freund SAIC, McLean
	Typical high-gain FEL amplifiers employ an electron beam that is matched to the wiggler so that the envelope remains constant throughout the wiggler. This paper describes a novel approach in which the electrons undergo natural betatron scalloping motion along the wiggler because the beams are deliberately mismatched at the wiggler entrance. We present an analysis of the electron scalloping motion and the FEL interaction with a scalloped electron beam. For a representative set of beam and wiggler parameters, we discuss the effect of the pinching the electron beams on the interaction in the FEL and on the focusing and propagation of the FEL radiation.
	Slides
	Talk

THAAU06	Parametric Optimization of a X-Ray FEL Based on a Thomson Source	laser, electron, radiation, 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

THBAU04	Stair-Step Tapered Wiggler for High-Efficiency FEL	wiggler, electron, extraction, synchrotron	545
	D. C. Nguyen LANL, Los Alamos, New Mexico H. Freund SAIC, McLean
	A new concept of a high-efficiency wiggler called the stair-step tapered wiggler is presented. The stair-step tapered wiggler differs from the traditional continuously tapered wigglers in that there are several uniform wiggler segments with decreasing wiggler periods (or decreasing Krms). Thanks to the relatively large ponderomotive potential in each segment, a substantial fraction of the electrons is captured while the electrons execute synchrotron motion down the energy scale. This leads to high FEL extraction efficiencies and partial optical guiding in the tapered wiggler sections. The stair-step tapered wiggler provides other advantages, such as ease of fabrication and flexibility in the taper rate. Numerical simulations using the code MEDUDA* will be presented to show the high-efficiency performance of a representative FEL with a stair-step tapered wiggler. * H. P. Freund, S. G. Biedron, and S. V. Milton, IEEE J. Quantum Electron. 36, 275 (2000)
	Slides
	Talk

THPPH002	Characterisation of Microphonics in HoBiCaT	resonance, cryogenics, feedback, klystron	556
	O. Kugeler, W. Anders, J. Knobloch, A. Neumann BESSY GmbH, Berlin
	The HoBiCaT test-facility at BESSY, which is designed for cryogenic testing of superconducting TESLA units has been equipped with a 9-cell TESLA-type cavity. Mechanical vibrations in the cryostat result in microphonic detuning of the cavity resonance. These microphonics have been characterized, and their sources analyzed, including the impact of operating conditions such as LHe pressure, cavity field and heater power. Furthermore, the mechanical transfer functions needed for the eventual compensation of the microphonics have been recorded.

THPPH007	First RF-Measurements at the 3.5-Cell SRF-Photo-Gun Cavity in Rossendorf	gun, cathode, electron, coupling	567
	A. Arnold, H. Buettig, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, J. Teichert, R. Xiang FZR, Dresden T. Kamps, D. Lipka, F. Marhauser BESSY GmbH, Berlin G. Klemz DESY Zeuthen, Zeuthen W.-D. Lehmann IfE, Dresden A. Matheisen, B. van der Horst DESY, Hamburg J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk I. Will MBI, Berlin
	At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attention was focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results. Submitted as poster to the 2006 FEL conference

THPPH021	Design Consideration of the RF Deflector to Optimize the Photo Injector at PITZ	emittance, diagnostics, kicker, single-bunch	605
	S. A. Korepanov, S. Khodyachykh, M. Krasilnikov, A. Oppelt, F. Stephan DESY Zeuthen, Zeuthen V. V. Paramonov RAS/INR, Moscow
	In order to optimize photo injectors for Free Electron Laser (FEL) applications, a detailed characterization of the longitudinal and transverse phase space of the electron beam provided by the Photo Injector Test Facility at DESY in Zeuthen (PITZ) is required. Design considerations of the RF deflecting cavity for transverse slice emittance and longitudinal phase space measurements are presented in the paper.

THPPH025	Design of the Cavity BPM for FERMI@ELETTRA	dipole, coupling, undulator, electron	613
	P. Craievich, D. Castronovo, M. Ferianis ELETTRA, Basovizza, Trieste M. Poggi INFN/LNL, Legnaro, Padova
	The Beam Position Monitors (BPM) are fundamental diagnostics for a seeded FEL, like FERMI@ELETTRA, as they allow to measure the electron beam trajectory non destructively and on a shot-by shot basis. A cavity BPM provides sub-micrometer resolution relying on excitation of the TM110 dipoles modes by beam when it passes through the cavity off axis. Therefore for the seeded FEL FERMI, we adopted a set of cavity BPMs to be located upstream the modulating undulator to correct the electron beam trajectory to the micrometer level. In this paper we first discuss the requirements for this cavity BPM including that for beam based alignment. The scaling from an X-band design to the final C-band design is presented. The resolution to stay below one micrometer has been cross-checked both analytically and numerically, The losses of the common mode TM010 have been checked for too, leading to the final dimensions preserving the losses of the X-band cavity BPM.

THPPH026	Design of a Two-Stage Laser Pulse Shaping System for FEL Photoinjectors	laser, 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.

THPPH030	Main High Voltage Solid State Gyrotron Power Supply 60kV / 80A	power-supply, cathode, controls, electron	633
	M. P.C. Pretelli, L. Rinaldi, V. R. Rossi, L. Sita, G. Taddia O. C.E. M. S.p. A., Bologna T. Bonicelli, P. L. Mondino EFDA, Garching R. Claesen, M. Santinelli ENEA C. R. Frascati, Frascati (Roma) D. Fasel EPFL, Lausanne
	This paper describes the design of a 4.8MW Main High Voltage Power Supply, rated 60kV/80A, conceived to supply the voltage between Cathode and grounded Collector of a Gyrotron. The PS is being procured for the EC Test Facility in Lausanne for the development and testing of CPD type 170GHz Gyrotrons. The PS specifications include the requirement of fast and repetitive switch on and off of the current up to 5kHz in order to reduce the average power dissipation on the Collector during modulation of the RF power. A full solid state technology, named SWM (Stair-Way Modulation) has been adopted. The 60kV output voltage is reached by adding 128 high voltage modules in series connection, with ad hoc control criteria to allow a regulation at full performances in the range of 45-60kV, a square wave modulation and a fast switch-off in less than 10us. This solution can be extended to several applications in the High Voltage domain and is aimed to enhance the reliability, decrease costs, provide redundancy and plug-in modularity. In the paper, the technical implications of extending similar topologies to the ITER EC system as alternative to the present ITER reference design will be considered.

THPPH034	Laser Pulse Length Dependence of Beam Emittance of Photocathode RF-Gun	laser, emittance, electron, gun	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.

THPPH036	Design Study of RF Triode Structure for the KU-FEL Thermionic RF Gun	gun, emittance, cathode, electron	656
	K. Masuda, T. Kii, K. Kusukame, H. Ohgaki, T. Shiiyama, T. Yamazaki, K. Yoshikawa, H. Zen Kyoto IAE, Kyoto
	Thermionic rf guns show advantageous features compared with photocathode ones such as easy operation, low cost and high averaged current, which are suitable for their application to FELs for various uses. They however suffer from the back-bombardment effect, resulting in limited macro-pulse duration of severalμseconds. Against this adverse effect, we plan to introduce the triode structure,* in the 4.5-cell rf gun for the KU-FEL by replacing the thermionic cathode by an assembly of a cathode with an additional coaxial cavity. Two-dimensional simulations have predicted a significant reduction of the back-bombardment power by 99% with a moderate rf power of several tens kW fed to the additional extraction cavity. Moreover an improved energy spread and peak current are expected at the same time with an optimal geometry and operating conditions. * E. Tanabe et al., Proc. of 27th Linear Accelerator Meeting in Japan (2002) 57, in Japanese. ** K. Masuda et al., Proc. of 27th Intnl. FEL Conf. 2005 (2006) 588.

THPPH038	Production of Electron Beam with Constant Energy by Controlling Input Power into a Thermionic RF Gun	cathode, electron, gun, beam-loading	664
	N. Okawachi, T. Kii, K. Masuda, M. Nakano, H. Ohgaki, T. Yamazaki, K. Yoshikawa, H. Zen Kyoto IAE, Kyoto
	We have studied on performance of a thermionic RF gun. Though a thermionic RF gun is a compact and economical electron gun, a backbombardment effect makes it difficult to produce electron beam with constant energy. The backbombardment effect depends on cavity voltage of the RF gun (Vc) and cathode current density (Jc). We tried to keep beam energy constant in macro pulse duration by feeding modulated RF power in experiment. We have succeeded to produce a 4 μs macro pulse electron beam. We also tried to perform transient analysis with equivalent circuit including the time evolution of beam loading depending on the Vc and Jc, By using this analysis we have succeeded to reproduce the measured time evolution of electron beam energy and the pulse shape of reflected RF power in case a constant RF power was fed and a modulated RF power was fed. Moreover we found the condition in which we could produce a 6 μs macro pulse electron beam. In this conference we will discuss the comparison between the experimental results and the calculation results.

THPPH039	Experimental Study on Effect of Energy Distribution on Transverse Phase Space Tomography	electron, emittance, gun, quadrupole	668
	H. Zen, T. Kii, K. Masuda, M. Nakano, H. Ohgaki, N. Okawachi, S. Sasaki, T. Shiiyama, T. Yamazaki, K. Yoshikawa Kyoto IAE, Kyoto
	Tomographic method * using a quadrupole magnet and a beam profile monitor is useful method of transverse phase space measurement. However the method is suffered from energy distribution. Therefore we have evaluated the effects numerically. As the result, the low energy tail of the beam distorted the result of tomographic method even with a small amount of the tail *.To confirm the numerical evaluation, measurements have been performed with single slit method, whose result is free from energy distribution. In this conference, the experimental result of two methods will be shown and a new tomographic analysis, which mitigates the effect of energy distribution, is proposed. C. B.McKee, et al, NIM A 358 (1995) 264** H. Zen, et al, Proc. of FEL2005 (2006) 592

THPPH042	A Compact Low Emittance DC Gun Employing Single Crystal Cathode of LaB6	cathode, emittance, electron, gun	680
	K. Kasamsook, K. Akiyama, H. Hama, F. Hinode, M. Kawai, T. Muto, K. Nanbu, T. Tanaka, M. Yasuda Laboratory of Nuclear Science, Tohoku University, Sendai
	Development of an electron gun capable of producing low emittance is in the interests of further applications of high brightness electron beam such as Smith-Purcell radiation for examples. A prominent point of this DC gun is that operation high voltage is very low and the emittance is, however, sufficiently low because of a short distance between the wehnelt and the anode. A pulsed high voltage of 50 kV is supplied, and pulse duration is variable from 1 to 5 sec. Since a higher beam current of the macropulse is required in general, a cathode should have higher current density, while the smaller size of the cathode is preferred for lower emittance. Consequently we have chosen single crystal LaB6 as the cathode, which can provide higher current with good homogeneity emission. In additon, a floating bias voltage can be applied between the cathode and the wehnelt to optimize the electric field for achieving the lowest emittance. Numerical calculations using EGUN shows a better normalized rms emittance is expected to be less than 5 mm mrad. A state-of-the-art electron source will possibly open new scientific opportunities in the many fields.

THPPH045	Electro-Optic Sampling Method Using High DC Voltage Applying Setup	electron, laser, gun, 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.

THPPH053	3-D Laser Pulse Shaping for Photoinjector Drive Lasers	laser, 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.

THPPH057	Modeling and Measurement of Mu-Metal Shielding Effect on the Magnetic Performance of an LCLS Undulator*	undulator, shielding, linac, dipole	718
	S. Sasaki, E. Trakhtenberg, I. Vasserman ANL, Argonne, Illinois
	In a previous paper (FEL05), we presented results showing that the Earth's field might give a significant effect on the LCLS undulator performance due to a large concentration of the field by the undulator poles. Based on the result of model calculation, we decided to shield the Earth's field by surrounding the undulator backing structure with a 1-mm-thick mu-metal sheet. First, the effect of the shield was modeled using the code RADIA. According to the calculation, the shielding factor of a C-shape mu-metal shield was better than a factor of 8. Second, we measured the Earth's field shielding effect without an undulator. In our measurement laboratory, the vertical component of the Earth's field was 0.5 gauss. It was suppressed to smaller than 0.1 gauss with the shield. After these background measurements, we examined the effect of the shield with an undulator in place. The measurement results show very good agreement with the model calculation.

THPPH070	Optimum Beam Creation In Photoinjectors Using Space-Charge Expansion	emittance, laser, 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.

THCAU03	Operational Experience with the Emittance-Meter at SPARC	emittance, cathode, laser, gun	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.
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