MOPP :: Monday Afternoon Poster Session

Date/Time: 22-Aug-05 :: 13:45—15:45
Chair: C. Pellegrini, UCLA, Los Angeles, California

Paper Title Page
MOPP001 Coherence Improvement of the BESSY HGHG FEL Radiation 19
 
  • M. Abo-Bakr, R. Follath, A. Meseck
    BESSY GmbH, Berlin
 
 

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

BESSY proposes a soft X-ray free electron laser (FEL) multi-user facility. It will consist of three undulator lines, each based on a cascaded High-Gain Harmonic-Generation (HGHG) scheme. With a seed laser, tunable between 230 nm and 460 nm, the desired output radiation wavelength range from 1.24 nm to 51 nm can be covered. Signal to noise ratio and coherence of the HGHG FEL radiation degrades quadratically with the harmonic number. For the short-wavelength BESSY-FEL line, operating on the 225th harmonic of the seed, a cure to this effect and maintaining the coherence is to improve the spectral purity of the output radiation by implementation of a "non-dispersive double-monochromator" system between two HGHG stages. Layout and parameters of such a monochromator section are described. To separate the electron beam path from the optical devices a bypass section is needed. Its design is presented and influences on the electron beam dynamics are discussed. Simulations of the full cascaded HGHG FEL, using the restored seed radiation and the bypassed electron beam, are presented.

 
   
MOPP002 Prospects of the BESSY High-Energy FEL 23
 
  • K. Goldammer, M. Abo-Bakr, R. Follath, A. Meseck
    BESSY GmbH, Berlin
 
 

Funding: Funded by the Bundesministrium für Bildung, und Forschung, the state Berlin and the Zukunftsfonds Berlin

BESSY proposes a linac-based High-Gain Harmonic-Generation (HGHG) free electron laser (FEL) facility with three independent FEL lines. In the BESSY High-Energy-FEL (HE-FEL), a seed laser wavelength of 280nm is downconverted to 1.24nm by a cascade of four HGHG-stages. This procedure requires a high brightness electron beam and a high power seed laser. With the nominal set of beam parameters, radiation power in the range of GWs can be achieved. However, the signal to noise ratio degrades in each HGHG stage. This motivated intensive studies on the possibilities to further optimize the performance of the BESSY HE-FEL. In this paper, we report on three methods aiming to control the signal to noise ratio. They include simulation studies of new seeding schemes with HHG-lasers at shorter wavelengths and seeding with higher seed powers. Also, a concept for the integration of monochromators between two HGHG-stages has been worked out, see also [1]. All methods were studied extensively with regard to their influence on FEL output power, pulse duration and spectral bandwidth.

[1] M. Abo-Bakr et al., these Proceedings

 
   
MOPP003 Benefits from the BESSY FEL Higher Harmonic Radiation 27
 
  • K. Goldammer, A. Meseck
    BESSY GmbH, Berlin
 
 

In the FEL process, bunching and coherent radiation is produced at the fundamental frequency as well as its higher harmonics. BESSY proposes a linac-based cascaded High-Gain Harmonic-Generation (HGHG) free electron laser (FEL) multi-user facility. The BESSY soft X-ray FEL will be seeded by three lasers spanning the spectral range of 230nm to 460nm. Two to four HGHG stages downconvert the seed wavelength to the desired radiation range of 1.24nm to 51nm using higher harmonic bunching. As a surplus, higher harmonic radiation is intrinsically produced in each FEL stage. Radiation on a higher harmonic of the FEL frequency is of high interest because it yields the possibility to reduce the number of FEL stages. This paper details extensive studies of the higher harmonic content of the BESSY FEL radiation. Important aspects of FEL interaction on higher harmonics as resulting from theory and from numerical simulations are discussed. For the case of the BESSY FEL, methods for improving the harmonic content are presented. These methods are examined as to their influence on FEL output power, pulse duration and spectral bandwidth. Focus is laid on the application of higher harmonic radiation to seeding.

Funded by the Bundesministerium für Bildung und Forschung, the state of Berlin and the Zukunftsfonds Berlin

 
   
MOPP004 Effects of Tapered Betafunction in the LCLS Undulators 31
 
  • K. Goldammer
    BESSY GmbH, Berlin
  • P. Emma, Z. Huang
    SLAC, Menlo Park, California
 
 

The Linac coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) project based on the SLAC linac. With its nominal set of electron beam, focusing and undulator parameters, it is designed to achieve SASE saturation at an undulator length of about 100m with an average power of 10GW. In order to keep the electron beam focused in the undulators, a FODO lattice is integrated along the entire length of the undulators. Nominally, the quadrupoles strengths are chosen to produce nearly constant beta function and beam size along the undulator, optimized for the FEL interaction in the exponential growth regime. Since these quadrupoles are electromagnetic, it is possible to adjust the individual quadrupole strength to vary the beta function and the beam size along the undulator, tailoring the FEL interaction in the startup and the saturation regimes. In this paper, we present simulation studies of the tapered beta function in the LCLS undulator and discuss the generated x-ray properties.

 
   
MOPP005 Impact of Realistic Bunch Profiles and Timing Jitter on the Output of the BESSY Low Energy FEL Line 35
 
  • B.C. Kuske, M. Abo-Bakr, A. Meseck
    BESSY GmbH, Berlin
 
 

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

In present FEL designs, undulators are usually optimized for an electron bunch with properties constant along the bunch length. The central energy, emittance and other parameters are assumed not to vary from slice to slice. Unavoidable timing jitter of the photo cathode laser, and phase and amplitude errors of the RF fields in the injector and the linac result in variations in emittance, energy spread and beam dimensions along the bunch, causing a jitter in the arrival time of the electron bunch. Due to the passage through bunch compressors, the bunch shows a considerable residual energy chirp. Even assuming a perfect and on-time seed laser pulse, the changing properties along the bunch in combination with the arrival time jitter cause varying conditions for the interaction of the electron bunch with the seed laser radiation. This paper talks about how far the BESSY-FEL radiation is affected by the expected time jitter and the realistic bunch profile, and investigates counter measures. The studies are confined to the low energy FEL line generating output at l = 10nm.

 
   
MOPP006 Start-to-End Simulations for the BESSY Low and Medium Energy FEL Line Including Errors 39
 
  • B.C. Kuske, M. Abo-Bakr, K. Goldammer, A. Meseck
    BESSY GmbH, Berlin
 
 

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

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

 
   
MOPP007 Source Characterization of BESSY Soft X-Ray FEL 43
 
  • A. Meseck, M. Abo-Bakr, J. Bahrdt, B.C. Kuske
    BESSY GmbH, Berlin
 
 

Funding: Funded by the Bundesministrium für Bildung, und Forschung, the state Berlin and the Zukunftsfonds Berlin

BESSY proposes a soft X-ray free electron laser (FEL) multi-user facility. It will consist of three undulator lines, each based on cascaded High-Gain Harmonic-Generation (HGHG) scheme delivering photons in energy range of 24 eV to 1 keV. Start-to-end Simulations including error sources from the injector, and linac structure have been performed to provide realistic information about the expected radiation field (B. Kuske, FEL2005). However, the beamline designer needs to know the exact location and the size of the photon beam waist to maximize the brightness at the sample. This information can be derived from results of longitudinal propagation of the electric field distribution, which can be extracted from simulation results using the code GENESIS. The results of the Start-to-End simulation are used for realistic prediction of the photon beam properties of the BESSY Soft X-ray FEL.

 
   
MOPP008 Tolerance Studies of a Seeded REVOLVER-Undulator FEL 47
 
  • A. Meseck, J. Bahrdt
    BESSY GmbH, Berlin
 
 

Funding: Funded by the Bundesministrium für Bildung, und Forschung, the state Berlin and the Zukunftsfonds Berlin

Wide-range wavelength-tunability is one of the key aspects of proposed FEL facilities. Once the electron beam energy and undulator period length is given, the span of the available K-values determines the achievable wavelength range, according to the resonance condition. As the usable range of the K-values is limited by technical considerations like minimum acceptable gap or permanent magnet technology etc, alternatives to enlarge the output wavelength range are of high interest. Using revolver-undulator design, different magnetic structures can be incorporated in the same undulator segment. Thus it is possible to switch between different undulator periods, covering a wider wavelength range at a given FEL-line. Because of the transverse-positions dependency of the magnetic field, the alignment reproducibility of the revolver-undulators is of concern, in particular for the APPEL type devices. Simulation studies have been performed taking the BESSY FEL-lines as examples to investigate the alignment tolerances of these devices, to reveal their limits of applicability.

 
   
MOPP010 Properties of the Third Harmonic of the SASE FEL Radiation 51
 
  • E. Saldin, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg
 
 

Recent theoretical and experimental studies have shown that SASE FEL with a planar undulator holds a potential for generation of relatively strong coherent radiation at the third harmonic of the fundamental frequency. Here we present detailed study of the nonlinear harmonic generation in SASE FEL obtained with time-dependent FEL simulation code FAST. Using similarity techniques we present universal dependencies for temporal, spectral, and statistical properties of the third harmonic radiation from SASE FEL.

 
   
MOPP011 The ARC-EN-CIEL FEL Proposal 55
 
  • M.-E. Couprie, M. LABAT
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
  • B. Carre, D. Garzella, G. Lambert
    CEA/Saclay, Gif-sur-Yvette
  • O.V. Chubar, A. Loulergue, L. Nahon
    SOLEIL, Gif-sur-Yvette
  • M. Jablonka, F. Meot, A. Mosnier
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • J.-R. Marques
    LULI, Palaiseaux
  • P. Monot
    CEA/DSM, Gif-sur-Yvette
  • J.-M. Ortega
    LURE, Orsay
  • A. Rousse
    LOA, Palaiseau
 
 

ARC-EN-CIEL (Accelerator-Radiation for Enhanced Coherent Intense Extended Light), the French project of a fourth generation light source aims at providing the user community with coherent femtosecond light pulses covering from UV to soft X ray. It is based on a CW 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches with a high repetition rate. The FEL is based on in the injection of High Harmonics in Gases in a High Gain Harmonic Generation scheme, leading to a rather compact solution. The produced radiation extending down to 0.8 nm with the Non Linear Harmonic reproduces the good longitudinal and transverse coherence of the harmonics in gas. Optional beam loops are foreseen to increase the beam current or the energy. They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges and a FEL oscillator in the 10 nm range. An important synergy is expected between accelerator and laser communities. Indeed, electron plasma acceleration will be tested for possible future compact electron beam sources for Xray FEL. Fs hard X ray can also be produced by Thomson Scattering. An overview of the user scientific case will also be given.

 
   
MOPP012 Seeding the FEL of the SCSS Phase 1 Facility with the 13th Laser Harmonic of a Ti:Sa Laser Produced in Xe Gas
 
  • G. Lambert
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
 
 

In order to reach very short wavelengths in systems based on Free Electrons Laser (FEL), and to have a more compact, fully coherent and tunable source, a particular seeding configuration is studied here. It is foreseen to test it as a demonstration experiment in 2006 into the SCSS phase 1 facility (Spring-8 Compact Sase Source, Japan). SCSS phase 1 is a linac-based FEL project, providing a compact SASE source with high brightness in the X-ray range. The external laser source, which is employed, is straightfully in the XUV range, the 13th harmonic of a Ti:Sa femtosecond laser (61.5 nm), generated in Xe gas. This harmonic can be now easily generated by focusing the Ti: Sa laser (25 mJ, 10 Hz, 100 fs) on a 10 Hz pulsed Xe gas cell. This High order Harmonics Generation (HHG) process provides us with a VUV beam with intense (1 μJ) and ultra-short (50 fs) properties.

 
   
MOPP013 Optimization Studies of the FERMI at ELETTRA FEL Design 59
 
  • G. De Ninno
    ELETTRA, Basovizza, Trieste
  • W.M. Fawley
    LBNL, Berkeley, California
  • W. Graves
    MIT, Middleton, Massachusetts
 
 

The FERMI at ELETTRA project at Sincotrone Trieste involves two FEL's, each based upon the principle of a seeded harmonic cascade and using the existing ELETTRA injection linac at 1.2 GeV beam energy. Scheduled to be completed in 2008, FEL-1 will operate in the 40-100 nm wavelength range and will involve one stage of harmonic up-conversion. The second phase, FEL-2, will begin operation two years later in the 10-40 nm wavelength range and will involve two cascade stages. FEL design assumes wavelength tunability over the full wavelength range and polarization tunability of the output radiation including helical polarization. The design considers focusing properties and segmentation of realizable undulators and available input seed lasers. We discuss how the interplay between various limitations and self-consistent accelerator simulations [1,2] have led to our current design. We present results of simulations using GENESIS and GINGER simulation codes including studies of various shot-to-shot fluctuations and undulator errors. Findings for the expected output radiation in terms of the power, transverse and longitudinal coherence for the short pulse (50-200 fs) and long pulse (~1 ps) modes of operation are reported.

[1] S. Lidia et al. in these proceedings. [2] S. Di Mitri et al. in these proceedings.

 
   
MOPP014 Status of the Seeding Experiment at SPARC 63
 
  • L. Giannessi, M.C. Carpanese, F. Ciocci, G. Dattoli, A. Dipace, A. Doria, G.P. Gallerano, E. Giovenale, G. Parisi, M. Quattromini, A. Renieri, C. Ronsivalle, E. Sabia, S. Spampinati, I.P. Spassovsky
    ENEA C.R. Frascati, Frascati (Roma)
  • D. Alesini, M.E. Biagini, A. Drago, M. Ferrario, V. Fusco, A. Ghigo, B. Spataro, C. Vaccarezza, C. Vicario
    INFN/LNF, Frascati (Roma)
  • M. Bougeard, B. Carre, M.-E. Couprie, D. Garzella, M. LABAT, G. Lambert, H. Merdji, P. Salieres
    CEA/Saclay, Gif-sur-Yvette
  • M. Mattioli, P. Musumeci, M. Petrarca
    Universita di Roma I La Sapienza, Roma
  • M.  Migliorati, L. Palumbo
    Rome University La Sapienza, Roma
  • M. Nisoli, S. Stagira, S. de Silvestri
    Politecnico/Milano, Milano
  • L. P. Poletto, G. T. Tondello
    Univ. degli Studi di Padova, Padova
 
 

Funding: Work supported by the EU Commission in the sixth framework programme, contract no. 011935 – EUROFEL.

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(-9)m wavelength scale. This communication is devoted to the description of a research work plan that will be implemented 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.

 
   
MOPP015 Beam Dynamics Studies for the SPARXINO Linac 67
 
  • M. Boscolo, M. Ferrario, V. Fusco, B. Spataro, C. Vaccarezza
    INFN/LNF, Frascati (Roma)
  • L. Giannessi, M. Quattromini, C. Ronsivalle
    ENEA C.R. Frascati, Frascati (Roma)
  • M.  Migliorati, L. Palumbo
    Rome University La Sapienza, Roma
  • L. Serafini
    INFN-Milano, Milano
 
 

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

 
   
MOPP016 Quantum SASE FEL with a Laser Wiggler 71
 
  • R. Bonifacio, R. Bonifacio
    Universidade Federal de Alagoas, Maceio
  • M. Ferrario
    INFN/LNF, Frascati (Roma)
  • N. Piovella
    Universita' degli Studi di Milano, MILANO
  • G.R.M. Robb
    Strathclyde University, Glasgow
  • A. Schiavi
    Rome University La Sapienza, Roma
  • L. Serafini
    INFN-Milano, Milano
 
 

Funding: Istituto Nazionale di Fisica Nucleare (INFN), Italy

Quantum effects in high-gain FELs become relevant when ρ'=ρ(mcγ/ ћ k)<1. The quantum FEL parameter ρ' rules the maximum number of photons emitted per electrons. It has been shown that when ρ'<1 a "quantum purification" of the SASE regime occurs: in fact, the spectrum of the emitted radiation (randomly spiky in the usual classical SASE regime) shrinks to a very narrow single line, leading to a high degree of temporal coherence. From the definition of ρ it appears that in order to achieve the quantum regime, small values of ρ, beam energy and radiation wavelength are necessary. These requirements can be met only using a laser wiggler. In this work we state the scaling laws necessary to operate a SASE FEL in the Angstrom region. All physical quantities are expressed in terms of the normalized emittance and of two parameters: the ratio between laser and electron beam spot sizes and the ratio between Rayleigh range and electron β-function. The feasibility study of a Quantum SASE FEL experiment using parameters as those foreseen in the SPARC/PLASMONX projects in construction at the INFN Frascati is explicitly discussed.

 
   
MOPP017 Velocity Shot-Noise Contribution and Collective Effects in SASE-FEL Radiation
 
  • A. Gover, E. Dyunin
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
 
 

The conventional analytical descriptions SASE-FEL do not take into account the electron velocity noise and collective effects. We use the general gain-dispersion relation for pre-bunched FEL in the linear regime [1] to define the FEL transfer function response to density and velocity modulation (initial condition problem) allowing for possible collective effect. This is used to derive expressions for SASE radiation line to velocity noise (random velocity modulation which exists even in the cold beam regime), in addition to the conventional shot noise (random density modulation). We find out for the realizable SASE FEL parameters [2] that the contribution of the velocity noise is not negligible relative to the shot noise. Also unexpectedly, collective effects may not be negligible in FELs even at short (UV) wavelength because the high beam current is being used.

[1] I.Schnitzer, A.Gover Nucl.Inst&Meth. Vol.A237. n.1-2, pp.124-140, 1985. [2]. R.Treusch, J.Feldhaus Eur. Phys. J. D, 26 pp.119-122, 2003

 
   
MOPP018 Status of R&D for SCSS Project 75
 
  • T. Tanaka
    RIKEN Spring-8, Hyogo
  • Y. Asano
    JAEA, Ibaraki-ken
  • H. Baba, T. Bizen, Z. Chao, H. Ego, S. Eguchi, S. Goto, T. Inagaki, S. Inoue, D. Iwaki, K. Kase, Y. Kawashima, H. Kimura, S. Kojima, T. Kudo, N. Kumagai, X. Marechal, S. Matsui, T. Ohata, K. Onoe, Y. Otake, T. Seike, K. Shirasawa, N. Shusuke, T. Takagi, T. Takashima, K. Tamasaku, R. Tanaka, K. Togawa, R. Tsuru, S. Wu, M. Yabashi, S. Yoshihiro
    JASRI/SPring-8, Hyogo
  • T. Fukui
    Kyoto IAE, Kyoto
  • T. Hara, T. Ishikawa, H. Kitamura, T. Shintake
    RIKEN Spring-8 Harima, Hyogo
  • H. Matsumoto
    KEK, Ibaraki
  • S. Takahashi
    LNS, Sendai
 
 

Funding: Representing the SCSS project team

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

 
   
MOPP020 Design Study of Beijing XFEL Test Facility
 
  • J.P. Dai
    IHEP, Beijing
 
 

As R&D of X-ray Free Electron Laser facility in China, the construction of Beijing XFEL Test Facility (BTF) has been proposed. And the start to end simulation of BTF was made with codes PARMELA, ELEGANT and TDA. This paper presents the motivation, the scheme and the simulation results of BTF.

 
   
MOPP021 Harmonic Operation of the SDUV HGHG-FEL
 
  • Z.M. Dai, D.G. Li, Y. Xu, X.F. Zhao, Z. Zhao
    SINAP, Shanghai
 
 

In this paper, we study the harmonic operation of the SDUV HGHG-FEL (Phase-I), which consists of 160MeV linac, and two undulators separated by a dispersion section. A laser light at 352nm is injected into the first undulator to modulate the energy of the electron beam. This is followed by a dispersion section to produce spatial bunching at 352nm, and a second undulator which fundamental is resonant to 264nm and 3rd harmonic is resonant to 88nm. Upon passing through the second undulator, the prebunched electron beam first radiates coherently at 88nm (i.e., the 3rd harmonic of the second undulator which is integer times of the seeding laser), and then this radiation is exponentially amplified, while the fundamental of the second undulator is allowed to grow from noise. Under proper condition, the output power of the 3rd harmonic may be much higher than that of the fundamental.

 
   
MOPP022 Numerical Simulation of HGHG Operation for the SDUV-FEL
 
  • D.G. Li, Z.M. Dai, Q. Gu, Y. Xu, X.F. Zhao, Z. Zhao
    SINAP, Shanghai
 
 

In this paper, we present the numerical simulation for HGHG operation of the Shanghai deep ultra-violet free electron laser source (SDUV-FEL). In this operation, a 264nm seed laser interacts with a 277MeV, 400A, normalized emittance 4mm.rad and local energy spread 0.1% electron beam in the first wiggler(modulator) with period 5cm, total length 0.8m and parameter K=2.03, where the energy of the electron beam is modulated. Then through a dispersion section with dy/dg~6.3, the energy modulation is converted to spatial bunching. In the second wiggler (radiator) with period 2.5cm, total length 10m and parameter K=1.45, the 88nm coherent radiation is generated in the first two gain lengths and its radiation power is exponentially amplified after two gain lengths. The simulation indicates that about several hundred MW 88nm and about few MW 29.3nm radiation can be produced.

 
   
MOPP023 Status of the SDUV-FEL Facility
 
  • Z. Zhao, Z.M. Dai, Q. Gu, D.G. Li
    SINAP, Shanghai
 
 

The SDUV-FEL based on a 300MeV S-band normal conducting Linac has been designed as an HGHG type high gain FEL facility. Since last December its first 100MeV Linac section has been being commissioned with a thermionic gun injector and will pass its acceptance this Autumn. After that, a photocathode injector will replace the existing the thermionic gun and bunchers of the 100MeV Linac. The photocathode gun, the magnetic bunch compressor, the FEL required beam diagnostics are under manufacture. A two-period radiator undulator prototype has been fabricated and measured, and six 1.5m radiator sections are now under manufacture. In this paper, we also briefly introduce the design optimization on the SDUV-FEL facility.

 
   
MOPP024 A VUV-FEL for 4GLS: Design Concept and Simulation Results 79
 
  • N. Thompson, M.W. Poole
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • B.W.J. McNeil
    Strathclyde University, Glasgow
 
 

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

A Free-Electron Laser operating in the photon energy range 3-10eV is a component of the 4th Generation Light Source (4GLS) proposal at Daresbury Laboratory in the UK. In this paper we present a current design proposal which is based on the Regenerative Amplifier Free-Electron Laser (RAFEL) concept. We also present simulation results which illustrate the potential performance of the device.

 
   
MOPP025 Gain Calculations and Analysis of a FWTWT for THz Regime
 
  • A.I. Al-Shamma'a, J. Lucas, R.A. Stuart, C.C. Wright
    University of Liverpool, Liverpool
 
 

In this paper, the small signal gain of a folded waveguide travelling wave tube (FWTWT) is calculated by means of Madey's theorem. The results of this analysis were compared with a single particle simulation carried out with MATLAB. The results were in excellent agreement. The calculations indicate the great potential of this device as an oscillator in the terahertz regime.

 
   
MOPP026 Simulations, Diagnostics and Recent Results of the VISA II Experiment 83
 
  • G. Andonian, A.Y. Murokh, C. Pellegrini, S. Reiche, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • M. Babzien, I. Ben-Zvi, V. Litvinenko, V. Yakimenko
    BNL, Upton, Long Island, New York
  • I. Boscolo, S. Cialdi, A.F. Flacco
    INFN-Milano, Milano
  • M. Ferrario, L. Palumbo, C. Vicario
    INFN/LNF, Frascati (Roma)
  • J.Y. Huang
    POSTECH, Pohang, Kyungbuk
 
 

The VISA II experiment entails use of a chirped beam to drive a high gain SASE FEL. The output radiation is diagnosed with a modified frequency resolved optical gating (FROG) technique. Sextupoles are implemented to correct the lonigtudinal aberrations affecting the high energy spread chirped beam during transport to the undulator. The double differential energy spectrum is measured with a pair of slits and a set of gratings. In this paper, we report on start-to-end simulations, radiation diagnostics, as well as intial experimental results; experimental methods are described.

 
   
MOPP027 High-gain Seeded FEL Amplifier Tunable in the Terahertz Range 87
 
  • C. Sung, C. Joshi, C. Pellegrini, J.E. Ralph, S. Reiche, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California
 
 

The lack of a high-power, relatively low-cost and compact terahertz (THz) source in the range 0.3-3x10(12) Hz is the major obstacle in progressing on biomedical and material studies at these wavelengths. A high-gain, single pass seeded FEL technique allows to obtain high power THz pulses of a high spectral brightness. We describe an ongoing project at the Neptune laboratory where a ~ 1kW seed pulse generated by difference frequency mixing of CO2 laser lines in a GaAs nonlinear crystal is injected into a waveguide FEL amplifier. The FEL is driven by a 5 ps (r.m.s) long electron pulse with a peak current up to 100A provided by a regular S-band photoinjector. According to 3-D, time dependent simulations, up to ~ 10 MW THz power can be generated using a 2 meter long planar undulator. By mixing different pairs of CO2 laser lines and matching resonant energy of the electron beam, tunability in the 100-400 mm range is expected. A tunable Fabri-Perot interferometer will be used to select a high-power 5ps THz pulse. This pulse is synchronized both with 1mm (photoinjector driver) and 10 mm lasers allowing time resolved pump-probe measurements.

 
   
MOPP028 Comparative Design Studies for the BESSY FEL Program using the MEDUSA and GENESIS Simulation Codes 91
 
  • H. Freund
    SAIC, McLean
  • M. Abo-Bakr, K. Goldammer, D. Kraemer, B.C. Kuske, A. Meseck
    BESSY GmbH, Berlin
  • S. Biedron
    ANL, Argonne, Illinois
 
 

The BESSY FEL is based on a seeded cascade of High Gain Harmonic Generation (HGHG) sections followed by an amplifier to produce coherent and stable short wavelength output. Here, we report on comparative design studies carried out using the MEDUSA [1], and GENESIS [2] simulation codes. These two codes have each been used to successfully predict a variety of FEL designs and have agreed well with a number of important experiments. In addition, they were included in a comparative study of FEL simulation [3] that reported substantial agreement between the codes for the specific configurations studied. However, these codes are based on different assumptions. GENESIS treats the particle dynamics using a wiggler-averaged orbit approximation, the transverse electromagnetic field is treated using a field solver, and harmonics are not included. MEDUSA does not use the wiggler-averaged orbit approximation to treat particle dynamics, the transverse fields are treated using a Gaussian modal superposition, and harmonics are included self-consistently. Hence, the comparative study for an HGHG cascade is important. We report the results where the parameters of each stage have been optimized.

[1] H.P. Freund et al., IEEE JQE 36, 275 (2000). [2] S. Reiche, NIMA 429, 243 (1999). [3] S.G. Biedron et al., NIMA 445, 110 (2000).

 
   
MOPP030 On the Definition of the Number of Temporal Modes in the SASE Output 94
 
  • S. Krinsky
    BNL, Upton, Long Island, New York
 
 

Funding: Work supported by DOE contract number DE-AC02-98CH10886.

We consider three definitions of the number of temporal modes in SASE output. These are defined in terms of: (1) the number of minimum area phase space cells occupied by the radiation; (2) the pulse energy fluctuation; and (3) the Wigner function. The conditions under which these definitions are equivalent is discussed.

 
   
MOPP031 Experimental Characterization of the Seeded FEL Amplifier at the BNL SDL 98
 
  • T. Watanabe, D.F.L. Liu, J.B. Murphy, J. Rose, T.V. Shaftan, T. Tsang, X.J. Wang, L.-H. Yu
    BNL, Upton, Long Island, New York
  • P. Sprangle
    NRL, Washington, DC
 
 

Funding: Work supported by the Office of Naval Research.

A laser seeded near IR FEL amplifier experiment was initiated at the BNL SDL [1] to explore various schemes of FEL efficiency improvement and generation of short Rayleigh length (SRL) FEL output. The FEL achieved first SASE lasing at 0.8 μm on May 6, 2005. The experimental characterization of the laser seeded FEL output power, spectrum and transverse mode structure evolution will be presented.

[1] A. Doyuran et al., PRSTAB, Vol. 7, 050701 (2004).

 
   
MOPP032 Diagnostic Tools for Operation and Optimization of the ELBE-FEL 102
 
  • P. Michel, P. Evtushenko, U. Lehnert, Ch. Schneider, R. Schurig, W. Seidel, J. Teichert, D. Wohlfarth
    FZR, Dresden
 
 

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

 
   
MOPP033 Detector Response and Beam Line Transmission Measurements with Far-Infrared Radiation 106
 
  • O. Grimm, H. Delsim-Hashemi, L. Fröhlich
    DESY, Hamburg
  • E. Chiadroni
    Universita di Roma II Tor Vergata, Roma
 
 

Various activities at the TTF linear accelerator at DESY, Hamburg, that drives the VUV-FEL are geared towards measuring the longitudinal charge distribution of electron bunches with coherent far-infrared radiation. Examples are beam lines transporting synchrotron or transition radiation to interferometers mounted inside or outside the tunnel, and studies of single-shot grating spectrometers. All such approaches require a good understanding of the radiation generation and transport mechanism and of the detector characteristics to extract useful information on the charge distribution. Simulations and measurements of the expected transverse intensity distribution and polarization of synchrotron radiation emitted at the first bunch compressor of TTF have been performed. The transverse intensity scanning provided for the first time at DESY a visual image of the footprint of terahertz radiation. Detector response measurements have been performed at the FELIX facility, Netherlands, for wavelengths between 100-160 microns, and first studies with blackbody radiation and band pass filters in the terahertz regime have been done at PTB, Berlin. The paper will summarize these results.

 
   
MOPP034 Upgrades of the Laser Beam-line at PITZ 110
 
  • J.W. Baehr
    DESY, Hamburg
  • K. Abrahamyan
    YerPhI, Yerevan
  • G. Asova, G. Dimitrov
    INRNE, Sofia
  • V. Boccone
    Humboldt Universität zu Berlin, Berlin
  • H.-J. Grabosch, J.H. Han, S. Khodyachykh, G. Klemz, M. Krasilnikov, S. Liu, H.L. Luedecke, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan, M. Winde, O. kalekin
    DESY Zeuthen, Zeuthen
  • M.V. Hartrott, R. Richter
    BESSY GmbH, Berlin
  • J.R. Roensch
    Uni HH, Hamburg
  • I. Will
    MBI, Berlin
 
 

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

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

 
   
MOPP035 Bunch Length Measurements Using a Martin-Puplett Interferometer at the VUV-FEL 114
 
  • L. Fröhlich, O. Grimm
    DESY, Hamburg
 
 

The longitudinal charge distribution of short electron bunches can be characterized by a measurement of their coherent far-infrared radiation spectrum. This paper will present the results obtained at the DESY VUV-FEL linear accelerator by observation of synchrotron radiation with a Martin-Puplett interferometer. The reconstructed bunch shapes are strongly asymmetric with a full width at half maximum of about 1 ps.

 
   
MOPP036 Next Generation Synchronization System for the VUV-FEL at DESY 118
 
  • H. Schlarb, V. Ayvazyan, F. Ludwig, D. Noelle, B. Schmidt, S. Simrock
    DESY, Hamburg
  • F.X. Kaertner
    MIT, Cambridge, Massachusetts
  • A. Winter
    Uni HH, Hamburg
 
 

The control and stabilization of the longitudinal beam profile and the bunch arrival time in linac driven VUV or X-ray Free-Electron Lasers require special effort and new developments in the fields of low level RF controls, global synchronization systems and longitudinal beam feedbacks. In this paper we describe the required upgrades for the VUV-FEL at DESY to synchronize the FEL pulse and optical lasers to the level of hundred femtoseconds (FWHM).

 
   
MOPP037 Femtosecond Timing Distribution Using Optical Pulses
 
  • A. Winter, P. Schmuser, A. Winter
    Uni HH, Hamburg
  • J. Chen, F.O. Ilday, F.X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
  • H. Schlarb
    DESY, Hamburg
 
 

Fourth-generation light sources, such as the European X-ray Free Electron Laser (XFEL) require timing signals distributed over distances of several kilometers with a stability in the order of femtoseconds. A promising approach is the use of a mode-locked laser that generates sub-picosecond pulses which are distributed in timing stabilized optical fiber links. A good candidate for a laser master oscillator (LMO) is a mode-locked Erbium-doped fiber laser, featuring extremely low phase noise far from the carrier. Results on the development of the LMO locked to an external reference microwave oscillator to suppress low frequency jitter, the distribution via timing stabilized optical fiber links and the reconversion of the optical pulses to a low phase noise microwave RF signals with overall femtosecond stability are presented.

 
   
MOPP038 Transverse Electron Beam Diagnostics at the VUV-FEL at DESY 122
 
  • K. Honkavaara, F. Loehl
    Uni HH, Hamburg
  • M. Castellano, G. Di Pirro
    INFN/LNF, Frascati (Roma)
  • L. Catani, A. Cianchi
    INFN-Roma II, Roma
  • D. Noelle, S. Schreiber
    DESY, Hamburg
  • M. Sachwitz, E.S. sombrowski
    DESY Zeuthen, Zeuthen
 
 

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

 
   
MOPP039 Present Performance and Future Requirements of the RF Plants for the FERMI Project 126
 
  • G. D'Auria, P. Craievich, M. Ferianis, M.M. Milloch
    ELETTRA, Basovizza, Trieste
  • dc. Cheever, T. Zwart
    MIT, Middleton, Massachusetts
  • L.R. Doolittle, A. Ratti
    LBNL, Berkeley, California
 
 

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

 
   
MOPP040 Optimization and Modeling of the Accelerator for the FERMI @ Elettra FEL 130
 
  • S. Di Mitri, P. Craievich
    ELETTRA, Basovizza, Trieste
  • M. Cornacchia, P. Emma, Z. Huang, J. Wu
    SLAC, Menlo Park, California
  • D. Wang
    MIT, Middleton, Massachusetts
  • A. Zholents
    LBNL, Berkeley, California
 
 

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

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

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

 
   
MOPP041 Generation and Distribution of Stable Timing Signals to Synchronize RF and Lasers at the FERMI FEL Facility 134
 
  • M. Ferianis
    ELETTRA, Basovizza, Trieste
  • J.M. Byrd, J.W.  Staples, R.B. Wilcox
    LBNL, Berkeley, California
  • J. Chen, F.O. Ilday, F.X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
  • A. Winter
    Uni HH, Hamburg
 
 

Fermi is the fourth generation light source that is currently being designed at ELETTRA, in the frame of a collaboration that includes LBNL and MIT. The timing system will play a crucial role in achieving the expected performance of this and other Linac based FELs due to the sub-ps electron bunch length and the expanded use of fs-lasers as key components in future light sources. Furthermore, the requirements of the timing system are also tightly linked to the applications of the generated ultrafast x-ray pulses. In this paper we present the requirements for the FERMI timing system, which will be based on optical timing distribution concepts, currently seen to be the only technique to enable an RMS jitter at the 10fs level. The timing system, intended for a user facility that is operated on a 24-h, 7-d basis, must operate stable and reliable. The fundamental components of the system are analyzed, such as the optical reference oscillator, the fiber optic stabilized links and the local optical to electrical (O/E) converters, needed for the RF plant synchronization. Furthermore, solutions for the synchronization of the diagnostic tools for the Linac as well as user related synchronization issues are presented and discussed.

 
   
MOPP042 Status of SPring-8 Photocathode Rf Gun for Future Light Sources 138
 
  • H. Tomizawa, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, K. Yanagida
    JASRI/SPring-8, Hyogo
  • F. Matsui
    ,
 
 

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

 
   
MOPP043 An Independently Tunable Cells Thermionic RF Gun (ITC-RF GUN) for Sub-Picosecond Short Pulse 142
 
  • H. Hama, F. Hinode, M. Kawai, T. Tanaka
    LNS, Sendai
 
 

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

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

 
   
MOPP044 Beam Diagnostic System for PAL-XFEL 146
 
  • J.Y. Huang, Y.S. Bae, M.-H. Chun, Y.J. Han, S.-H. Jeong, H.-S. Kang, D.T. Kim, S.H. Kim, S.-C. Kim, I.S. Ko, H.J. Park, I.-S. Park, S.J. Park, Y.J. Park, S.Y. Rah, J.-H. Suh
    PAL, Pohang, Kyungbuk
  • J.H. Hong, C. Kim
    POSTECH, Pohang, Kyungbuk
 
 

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

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

 
   
MOPP045 Preliminary RF Test in PLS 2.5GeV Linac for PAL-XFEL 150
 
  • W.H. Hwang, J. Choi, Y.J. Han, J.Y. Huang, H.-G. Kim, W.W. Lee
    PAL, Pohang, Kyungbuk
 
 

Funding: Work supported by MOST and POSCO.

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

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

 
   
MOPP046 Beam Transport Line Design for Emittance Adjustment PLS X-FEL 153
 
  • M. Kim, Y.S. Bae, J. Choi, H.-S. Kang, T.-Y. Lee
    PAL, Pohang, Kyungbuk
 
 

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

 
   
MOPP047 Development of an Ultra Stable Klystron-Modulator for PAL XFEL 157
 
  • J.-S. Oh, S. D. Jang, I.S. Ko, S. J. Kwon, W. Namkung, Y. G. Son, J.-H. Suh
    PAL, Pohang, Kyungbuk
 
 

Funding: Supported by the POSCO and the MOST, Korea

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

 
   
MOPP048 Experimental Progress of DC-SC Photoinjector at Peking University 161
 
  • G.M. wang, J.-E. Chen, Y.T. Ding, J. Hao, S.L. Huang, L. Lin, X.Y. Lu, S.W. Quan, L.F. Wang, R. Xiang, B.C. Zhang, K. Zhao, F. Jiao, D. Xie, L. Yang, F. Zhu, C. Liu, F. Wang, W. Xu, Z. Liu
    PKU/IHIP, Beijing
  • Y.G. Wang
    Peking University, School of Physics, Beijing
 
 

Funding: NSFC, MOST of China

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

 
   
MOPP049 Injection System for Microtron-Based Terahertz FEL 164
 
  • G.M. Kazakevich
    Fermilab, Batavia, Illinois
  • Y.U. Jeong, B.C. Lee, S.-H. Park
    KAERI, Daejon
  • G.I. Kuznetsov
    BINP SB RAS, Novosibirsk
  • V. M. Pavlov
    Strathclyde University, Glasgow
 
 

Funding: Budker Institute of Nuclear Physics RAS, Academician Lavrentyev 11, Novosibirsk, 630090, Russia; Laboratory for Quantum Optics, Korea Atomic Energy Research Institute, P. O. Box 105, Yusong, Taejon, 305-600, South Korea.

A reliable injection system of the widely tunable microtron-based terahertz Free Electron Laser (FEL) has been developed and during last few years provides stable operation of the FEL for users. The system is based on the long-life thermionic cathode assembly using 2.5 mm-in diameter monocrystalline LaB6 emitter, heated by the tungsten cylindrical filament with the power consumption less than 50 W. The cathode emits the macro-pulse current in the range of 1-1.4 A providing operation of the terahertz FEL during more than 1000 h. The cathode assembly is installed on the cover of the I-type microtron accelerating cavity in location providing an efficient injection for the acceleration with variable number of orbits. This variation widely changes the energy of the electron beam and allows on-the-fly retuning of the FEL in the range of 1-3 THz. Pulse-signal system stabilizing the emission current prevents randomized break-downs in the accelerating cavity and decreases macro-pulse power fluctuations of the FEL radiation. The fluctuations were measured to be less than 10% during long-time operation.

 
   
MOPP050 Measurement of Low Workfunction Cesiated Metals for Use in Dispenser Photocathodes 168
 
  • N.A. Moody, D.W. Feldman, P.G. O'Shea
    IREAP, College Park, Maryland
  • A. Balter
    ,
  • K. Jensen
    NRL, Washington, DC
 
 

Funding: We gratefully acknowledge our funding agencies, Joint Technology Office (JTO) and the Office of Naval Research (ONR).

Photoinjector performance is a limiting factor in the continued development of high powered FELs. Presently available photocathodes have limited efficiency and short lifetime in an RF-gun environment, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode should have high efficiency at visible wavelengths, long lifetime in practical vacuum environments, and prompt emission. High efficiency cathodes typically have limited lifetime, and the needs of the photocathode are generally at odds with those of the drive laser. A potential solution is the low work function dispenser cathode, where short lifetimes are overcome by periodic in situ regeneration that restores the photosensitive surface layer, analogous to methods used in the power tube industry. This work reports on the fabrication techniques and performance of cesiated metal photocathodes and cesiated dispenser cathodes, with a focus on understanding and improving quantum efficiency and lifetime, analyzing issues of emission uniformity, and optimizing the activation procedure needed to rejuvenate the cathode. The efficiency versus coverage behavior of cesiated metals is discussed and closely matches that predicted by recent theory.

 
   
MOPP051 In-Situ Cleaning of Metal Cathodes Using a Hydrogen Ion Beam 172
 
  • D. Dowell, F. King, R.E. Kirby, J.F. Schmerge
    SLAC, Menlo Park, California
 
 

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

Improving and maintaining the quantum efficiency (qe) of a metal photocathode in an s-band RF gun requires a process for cleaning the surface. In this type of gun, the cathode is typically installed and the system is vacuum baked to ~200&deg;C. If the qe is too low, the cathode is cleaned with the UV-drive laser. While laser cleaning does increase the cathode qe, it requires fluences close to the damage threshold and rastering the small diameter beam, both of which can produce non-uniform electron emission and potentially damage the cathode. This paper investigates the efficacy of a low-energy hydrogen ion beam to produce high-qe metal cathodes. Measurements of the qe vs. wavelength, surface contaminants using x-ray photoelectron spectroscopy and surface roughness were performed on copper samples, and the results showed a significant increase in qe after cleaning with a 1keV hydrogen ion beam. The H-ion beam cleans an area approximately 1cm in diameter and has no effect on the surface roughness while significantly increasing the qe. These results and a comparison with theory as well as a scheme for installing a H-ion cleaner on an s-band gun are presented.

 
   
MOPP052 Using Nonlinear RF Acceleration for Beam Conditioning 176
 
  • G.V. Stupakov, Z. Huang
    SLAC, Menlo Park, California
 
 

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

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

 
   
MOPP053 Incorporation of a PbSe Array Based Spectrograph into EPICS using LabView at the JLab FEL Facility 180
 
  • D. Hardy, S.V. Benson, M.D. Shinn, S. Zhang
    Jefferson Lab, Newport News, Virginia
 
 

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, the Army Night Vision Lab, and by DOE Contract DE-AC05-84ER40150.

A real-time spectrograph with a 1Hz update rate was designed and installed at the JLab FEL facility using a Cal Sensors PbSe array and a Roper Scientific SpectraPro 300 monochrometer. This paper describes the implementation of EPICS channel access on a remote PC running LabView with modification of vendor supplied LabView VI's to allow display of FEL light spectra in real-time on a remote workstation. This allows PC based diagnostics to be used in EPICS

 
   
MOPP054 Electron Gun and Injector Designs for State-of-the-Art FELs
 
  • H. Bluem, A. Ambrosio, V. Christina, M.D. Cole, M. Falletta, D. Holmes, E. Peterson, J. Rathke, T. Schultheiss, A.M.M. Todd, R. Wong
    AES, Princeton, New Jersey
  • I. Ben-Zvi, A. Burrill, R. Calaga, P. Cameron, X.Y. Chang, H. Hahn, D. Kayran, J. Kewisch, V. Litvinenko, G.T. McIntyre, T. Nicoletti, J. Rank, T. Rao, J. Scaduto, K.-C. Wu, A. Zaltsman, Y. Zhao
    BNL, Upton, Long Island, New York
  • S.V. Benson, E. Daly, D. Douglas, H.F.D. Dylla, L. W. Funk, C. Hernandez-Garcia, J. Hogan, P. Kneisel, J. Mammosser, G. Neil, H.L. Phillips, J.P. Preble, R.A. Rimmer, C.H. Rode, T. Siggins, T. Whitlach, M. Wiseman
    Jefferson Lab, Newport News, Virginia
  • I.E. Campisi
    ORNL, Oak Ridge, Tennessee
  • P. Colestock, J.P. Kelley, S.S. Kurennoy, D.C. Nguyen, W. Reass, D. Rees, S.J. Russell, D.L. Schrage, R.L. Wood
    LANL, Los Alamos, New Mexico
  • D. Janssen
    FZR, Dresden
  • J.W. Lewellen
    ANL, Argonne, Illinois
  • J.S. Sekutowicz
    DESY, Hamburg
  • L.M. Young
    TechSource, Santa Fe, New Mexico
 
 

Funding: This work is supported by the Naval Sea Systems Command, the Office of Naval Research, the DoD Joint Technology Office, the Missile Defense Agency and the US Department of Energy.

Reliable, high-brightness, high-power injector operation is a critical technology issue for energy recovery linac drivers of high-power free electron lasers (FEL). Advanced Energy Systems is involved in three ongoing injector programs that target up to 0.5 Ampere current levels at emittance values consistent with the requirements of the FEL. One is a DC photocathode gun and superconducting RF (SRF) booster cryomodule. A 748.5 MHz injector of this type is being assembled and will be tested up to 100 mA at the Thomas Jefferson National Accelerator Facility (JLAB) beginning in 2007. The second approach being explored is a high-current normal-conducting RF photoinjector. A 700 MHz gun, presently under fabrication, will undergo thermal test in 2006 at Los Alamos National Laboratory (LANL). Finally, a half-cell 703.75 MHz SRF gun is presently being designed and will be tested to 0.5 Ampere at Brookhaven National Laboratory (BNL) in 2007. The status and projected performance for each of these injector projects is presented.

 
   
MOPP055 The Infrared Undulator Project at the VUV-FEL 183
 
  • O. Grimm, J. Feldhaus, J. Rossbach, E. Saldin, E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg
 
 

Funding: University of Hamburg

A special electromagnetic wiggler generating infrared radiation in the range 1-200 microns is planned to be installed at the DESY VUV-FEL in Hamburg by autumn 2006. The device is located after the FEL undulators, using the spent electron beam. The purpose is two-fold: first, it will serve longitudinal electron beam diagnostics, similar to other methods currently investigated using the coherent emission of radiation at wavelengths similar to the bunch length, and second it will be used as a powerful (100 MW peak) source for short (few ps) infrared radiation pulses. The natural, perfect synchronization with the VUV pulses will allow for pump-probe experiments with high timing precision. This paper will give an overview of the project, including the infrared beam transport line.

 
   
MOPP056 Phase Shifters for the SPARC Undulator System 187
 
  • G. Parisi, F. Ciocci, G. Dattoli, L. Giannessi, G. K. V. Voykov
    ENEA C.R. Frascati, Frascati (Roma)
 
 

In the framework of the SPARC FEL experiment, a 14-m long undulator divided into six sections is presently under construction (by ACCEL Instruments GmbH). In order to correct the phase difference between the electron beam and the radiation, a tunable device will be inserted at the end of each of the six sections of the undulator. In this paper a preliminary design of this device, performed with RADIA code, is proposed,. The phase shifter consists of two groups of a few permanent magnets, arranged as in the main undulator in a variable gap magnet assembly. Adjusting the gap allows to correct the electron-radiation phase difference. Results from beam dynamics simulation, performed with GENESIS code, show the impact of the phase shifter on the characteristics of the output laser field.

 
   
MOPP057 Adjustment of Adiabatic Transition Magnetic Field of Solenoid-Induced Helicla Wiggler 191
 
  • Y. Tsunawaki
    OSU, Daito, Osaka
  • M. Asakawa, N. Ohigashi
    Kansai University, Osaka
  • K. Imasaki
    ILT, Suita, Osaka
 
 

We have been constructed a solenoid-induced helical wiggler for a compact free electron maser operated in a usual small laboratory which does not have electric source capacity available enough. It consists of two staggered-iron arrays inserted perpendicularly to each other in a solenoid electromagnet. In order to lead/extract an electron beam into/from the wiggler, adiabatic transition (AT) field is necessary at both ends of the wiggler. In this work the AT field was produced by setting staggered-nickel plates with different thickness in the five periods. The thickness of each nickel plate was decided by the field analysis using the MAGTZ computational code based on a magnetic moment method. Exact thickness was, however, found by the precise measurement of the field distribution with the greatest circumspection to obtain a homogeneous increment of the AT field. The change of AT field distribution was studied by referring to an equivalent electric circuit of the wiggler.

 
   
MOPP058 Numerical Study on the Undulator in KU-FEL 195
 
  • T. Fukui, T. Kii, K. Kusukame, K. Masuda, Y. Nakai, H. Ohgaki, T. Yamazaki, K. Yoshikawa, H. Zen
    Kyoto IAE, Kyoto
 
 

We have constructed system for 3~20μmeter FEL oscillation for bio/chemical energy researches which consists of a thermionic RF gun and a 3-meter accelerating tube at the Institute of Advanced Energy, Kyoto University. [1] A 30 MeV electron beam has been successfully accelerated and studies on the beam characterization have also been carried out. [2] In parallel, evaluation of an FEL oscillation in KU-FEL has been performed. We will report our present expectations and future visions about undulators in KU-FEL. The former is the numerical studies on the expected FEL gain of the existing Halbach type undulator in KU-FEL based on experimental measurements of the undulator and beam parameters. The latter is the upgrade plan of the undulator and the design of a variable polarization undulator to obtain higher gain or circular polarized FEL. These undulator parameters are calculated by simulation code Radia and TDA3D.

[1] T. Kii, et al., Proceedings of the 2004 FEL conference, (2004) 447 [2] K. Masuda et al., Proceedings of the 2004 FEL conference, (2004) 450

 
   
MOPP059 Strong Focusing Wiggler for SASE and FEL in the Far-Infrared Region at ISIR, Osaka University 199
 
  • S. Kashiwagi, G. Isoyama, R. Kato, N. Noda
    ISIR, Osaka
  • K. Tsuchiya, S. Yamamoto
    KEK, Ibaraki
 
 

We apply the edge-focusing scheme to the wiggler for FEL and SASE in the far-infrared region at ISIR, Osaka University in order to make the gain length of SASE shorter by keeping the beam size small along the wiggler. As the electron beam energy is 10-30 MeV and the magnetic field of the wiggler is up to 0.4 T, the natural focusing force in the vertical direction is strong in the wiggler and it is strongly dependent on the electron energy and the wiggler gap. The focusing forces should be compatible to or higher than the strong natural focusing force, equally in the horizontal and vertical directions over the wide range of the electron beam energy and the wiggler gap. In order to meet this requirement, we adopt the strong focusing scheme using the EF wiggler. The wiggler consists of 4 FODO cells in the 1.938 m long (32 periods, period length: 60mm). A focusing element and defocusing element are incorporate with single wiggler periods with edge angles of +5 and -5 degrees, respectively, and they are separated by 3 normal wiggler periods. The strong focusing wiggler has been fabricated and magnetic field has been measured at KEK. We will report results of the magnetic field measurements of the strong focusing wiggler.

 
   
MOPP060 X-Band Microwave Undulators for Short Wavelength Free-Electron Lasers 203
 
  • C. Pellegrini
    UCLA, Los Angeles, California
 
 

Funding: Work funded by the US Department of Energy, grant 4-444025-PG-57689

We study the use of Radio Frequency electromagnetic waves as undulators for short wavelength FELs and undulator radiation sources. Magnetostatic undulators have a gap much smaller than the period, limiting how short a period we can use. The relation between period and gap can be overcome using electromagnetic waves to produce the force wiggling the electrons. The wave frequency is chosen to optimize the system performance. In the case of centimeters or mm waves a waveguide is used to propagate the field over a long distance. We call an undulator based on a waveguide a TWU. In this paper we show that a TWU using X-band RF is a practical and convenient device for short wavelength FELs, and to produce sub-nanometer undulator radiation circularly or linearly polarized.The recent development of high power X-band microwave sources make it possible today to build TWUs of practical interest. In this paper we will discuss the characteristic of the TWU, how to control the effects of RF power losses in the waveguide walls, and how to optimize a TWU and the associated electron transport system for use in a synchrotron radiation source or FEL.

 
   
MOPP061 Modeling the Effect of the Earth's Field and an Iron Plate on the LCLS Undulator Trajectory 207
 
  • S. Sasaki, I. Vasserman
    ANL, Argonne, Illinois
 
 

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

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