Seeding FELs
Paper Title Page
WEPSO02 Results and Perspectives on the FEL Seeding Activities at FLASH 491
 
  • J. Bödewadt, C. Lechner
    Uni HH, Hamburg, Germany
  
  In recent years, several methods of free-electron laser (FEL) seeding, such as high-gain harmonic generation (HGHG), self-seeding, or direct FEL amplification of external seed pulses, have proven to generate intense, highly coherent radiation pulses in the extreme ultraviolet (XUV), soft- (SXR) and hard (HXR) X-ray spectral range. At DESY in Hamburg, the FEL facility FLASH is currently being upgraded by a second undulator beamline (FLASH2) which allows for the implementation of various seeding schemes. The development of high repetition-rate, high-power laser systems allows for the production of seed sources which match the bunch-train pattern of FLASH. Furthermore, the FLASH1 beamline arrangement is well suited for testing various seeding schemes including HGHG, EEHG, HHG-seeding, and hybrid schemes. In this contribution, we* give an overview of latest results and planned FEL seeding activities at FLASH.
*Joern Boedewadt on behalf of the FLASH seeding collaboration (DESY, U Hamburg, TU Dortmund, U Uppsala, U Stockholm) 		 
 
WEPSO04 The Conceptual Design of CLARA, a Novel FEL Test Facility for Ultra-short Pulse Generation 496
 
  • J.A. Clarke, D. Angal-Kalinin, R.K. Buckley, S.R. Buckley, P.A. Corlett, L.S. Cowie, D.J. Dunning, B.D. Fell, P. Goudket, A.R. Goulden, S.P. Jamison, J.K. Jones, A. Kalinin, B.P.M. Liggins, L. Ma, K.B. Marinov, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, H.L. Owen, R.N.C. Santer, Y.M. Saveliev, R.J. Smith, S.L. Smith, E.W. Snedden, M. Surman, T.T. Thakker, N. Thompson, R. Valizadeh, A.E. Wheelhouse, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • R. Appleby, R.J. Barlow, H.L. Owen, M. Serluca, G.X. Xia
    UMAN, Manchester, United Kingdom
  • R. Appleby, G. Burt, S. Chattopadhyay, D. Newton, A. Wolski
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • R. Bartolini, S.T. Boogert, A. Lyapin
    JAI, Oxford, United Kingdom
  • N. Bliss, R.J. Cash, G. Cox, G.P. Diakun, A. Gallagher, D.M.P. Holland, B.G. Martlew, M.D. Roper
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • S.T. Boogert
    Royal Holloway, University of London, Surrey, United Kingdom
  • G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • L.T. Campbell, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • A.M. Kolano
    University of Huddersfield, Huddersfield, United Kingdom
  • I.P.S. Martin
    Diamond, Oxfordshire, United Kingdom
  • D. Newton, A. Wolski
    The University of Liverpool, Liverpool, United Kingdom
  • V.V. Paramonov
    RAS/INR, Moscow, Russia
  
  The conceptual design of CLARA, a novel FEL test facility focussed on the generation of ultra-short photon pulses with extreme levels of stability and synchronisation is described. The ultimate aim of CLARA is to experimentally demonstrate that sub-coherence length pulse generation with FELs is viable, and to compare the various schemes being championed. The results will translate directly to existing and future X-ray FELs, enabling them to generate attosecond pulses, thereby extending the science capabilities of these intense light sources. This paper will describe the design of CLARA, pointing out the flexible features that will be incorporated to allow multiple novel FEL schemes to be proven.  
 
WEPSO06 The Test-FEL at MAX-lab: Implementation of the HHG Source and First Results 507
 
  • F. Curbis, N. Čutić, F. Lindau, E. Mansten, S. Werin
    MAX-lab, Lund, Sweden
  • F. Brizuela, B. Kim, A. L'Huillier
    Lund University, Division of Atomic Physics, Lund, Sweden
  • M. Gisselbrecht
    SLF, Lund, Sweden
  
  The test-FEL at MAX-lab is a development set-up for seeding techniques. After the successful demonstration of coherent harmonic generation from a conventional laser, the new layout now presents a gas target for generation of harmonics. The drive laser will be up-converted and the low harmonics (around 100 nm) will seed the electron beam. The energy modulated electrons will then be bunched in the dispersive section and will radiate in the second undulator. We will detect the second harmonic of the HHG radiation around 50 nm. This experiment has several challenges never tried before: co-propagation of the electron beam and the drive laser, interaction of the electron beam with the gas in the target, no-focusing of the harmonics and no drive laser removal. The commissioning will show if this kind of in-line chamber has advantages with respect to more traditional approaches with optical beam transport. The results are relevant for many facilities that are planning to implement HHG seeding in the near future.  
 
WEPSO09 Two-Color Self-seeding and Scanning the Energy of Seeded Beams at LCLS 514
 
  • F.-J. Decker, Y. Ding, Y. Feng, M. Gibbs, J.B. Hastings, Z. Huang, H. Lemke, A.A. Lutman, A. Marinelli, A. Robert, J.L. Turner, J.J. Welch, D.H. Zhang, D. Zhu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) produces typically SASE FEL pulses with an intensity of up to 5 mJ and at high photon energy a spread of 0.2% (FWHM). Self seeding with a diamond crystal reduces the energy spread by a factor of 10 to 40. The range depends on which Bragg reflection is used, or the special setup of the electron beam like over-compression. The peak intensity level is lower by a factor of about five, giving the seeded beam an advantage of about 2.5 in average intensity over the use of a monochromator with SASE. Some experiments want to scan the photon energy, which requires that the crystal angle be carefully tracked. At certain energies and crystal angles different lines are crossing which allows seeding at two or even three different colors inside the bandwidth of the SASE pulse. Out-off plane lines come in pairs, like [1 -1 1] and [-1 1 1], which can be split by using the yaw angle adjustments of the crystal, allowing a two-color seeding for all energies above 4.83 keV. 		 
 
WEPSO11 Coherent X-Ray Seeding Source for Driving FELs 522
 
  • A. Novokhatski, F.-J. Decker, R.O. Hettel, Z. Huang, H.-D. Nuhn, M.K. Sullivan
    SLAC, Menlo Park, California, USA
  
  Funding: "Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515
The success of the hard X-ray self-seeding experiment at the LCLS is very important in that it provided narrow, nearly transform-limited bandwidth from the FEL, fulfilling a beam quality requirement for experimental applications requiring highly monochromatic X-rays. Yet, because the HXRSS signal is generated random spikes of noise, it is not a truly continuous monochromatic seed signal and even higher FEL performance would be achieved using a continuous seed source. We propose developing such a source using an X-ray cavity to achieve a continuous, narrow band X-ray seed signal. This cavity consists of four crystals with corresponding Bragg angles of about 45 degrees for each. We will analyze and the interaction of X-rays and electron beams with this cavity. This source uses a train of electron bunches initially accelerated in a linear accelerator which then pass through a radiator element situated within an X-ray cavity. The number of bunches is proportional to the achievable Q-value of the X-ray cavity and may be in the range of 10-100. We do not need a high output power of X-ray beams, which leads to relaxed electron beam requirements. We will consider several options. 		 
 
WEPSO17 High-resolution Seeding Monochromator Design for NGLS 529
 
  • Y. Feng, J.B. Hastings, J. Wu
    SLAC, Menlo Park, California, USA
  • P. Emma, R.W. Schoenlein, T. Warwick
    LBNL, Berkeley, California, USA
  
  Funding: DOE/BES
A high-resolution soft X-ray seeding monochromator has been designed for self-seeding the Next-Generation Light Source (NGLS). The seeding monochromator system consists of a single variable-line-spacing grating, three mirrors and an exit slit and operates in the “fixed-focus” mode to achieve complete tuning of the seeding energy in range from 200 to 2000 eV with a nearly constant resolving power of over 2x104. The optical delay is less than 1 ps. The design is based upon a fully coherent treatment of the SASE FEL beam propagating from the upstream SASE undulator through the entire seeding monochromator system. This approach guides the design optimization in order to preserve the transverse beam profile entering the seeding undulator to ensure maximum efficiency. 		 
 
WEPSO19 A Full Beam 1D Simulation Code for Modeling Hybrid HGHG/EEHG Seeding Schemes for Evaluating the Dependence of Bunching Factor Bandwidth on Multiple Parameters 533
 
  • C.M. Fortgang, B.E. Carlsten, Q.R. Marksteiner, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  
  Multiple seeding schemes are available for design of narrow-band, short-wavelength FELs. Analysis of such schemes often focus on the amplitude of the final bunching factor b, and how far it is above shot noise. Only under ideal conditions is the bandwidth of b FT limited. We have developed a 1D simulation tool that models complex hybrid seeding schemes using macro properties of the entire beam bunch to assess effects on both the amplitude and bandwidth of b. In particular the effects on bunching factor from using non-ideal beam driven radiators for downstream modulators, energy slew and curvature, and energy spread are investigated with the 1D tool.  
 
WEPSO20 Wake Monochromator in Asymmetric and Symmetric Bragg and Laue Geometry for Self-seeding the European X-ray FEL 538
 
  • G. Geloni, V. Kocharyan, E. Saldin, S. Serkez, M. Tolkiehn
    DESY, Hamburg, Germany
  
  We discuss the use of self-seeding schemes with wake monochromators to produce TW power, fully coherent pulses for applications at the dedicated bio-imaging bealine at the European X-ray FEL, a concept for an upgrade of the facility beyond the baseline previously proposed by the authors. We exploit the asymmetric and symmetric Bragg and Laue reflections (σ polarization) in diamond crystal. Optimization of the bio-imaging beamline is performed with extensive start-to-end simulations, which also take into account effects such as the spatio-temporal coupling caused by the wake monochromator. The spatial shift is maximal in the range for small Bragg angles. A geometry with Bragg angles close to pi/2 would be a more advantageous option from this viewpoint, albeit with decrease of the spectral tunability. We show that it will be possible to cover the photon energy range from 3 keV to 13 keV by using four different planes of the same crystal with one rotational degree of freedom.  
 
WEPSO22 FERMI@Elettra Status Report 546
 
  • L. Giannessi, E. Allaria, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, P. Craievich, I. Cudin, G. D'Auria, M. Dal Forno, M.B. Danailov, R. De Monte, G. De Ninno, A.A. Demidovich, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, E. Ferrari, L. Fröhlich, P. Furlan Radivo, G. Gaio, M. Kiskinova, M. Lonza, B. Mahieu, N. Mahne, C. Masciovecchio, F. Parmigiani, G. Penco, M. Predonzani, E. Principi, L. Raimondi, F. Rossi, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, S. Spampinati, C. Spezzani, M. Svandrlik, C. Svetina, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • P. Craievich
    PSI, Villigen PSI, Switzerland
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • B. Mahieu
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
  
  Funding: Work supported in part by the Italian Ministry of University and Research under grants FIRB-RBAP045JF2 and FIRB-RBAP06AWK3
In this paper we report about the status of FERMI, the seeded Free Electron Laser located at the Elettra laboratory in Trieste, Italy. The facility welcomed the first external users on FEL-1 between December 2012 and March 2013, operating at wavelengths between 65 and 20 nm. Variable polarization and tunability of the radiation wavelength were widely used. Photon energies attained up to 200 microJoule, depending on the grade of spectral purity requested and on the selected wavelength. Pump-probe experiments were performed, both by double FEL pulses obtained via double pulse seeding of the electron beam and by providing part of the seed laser to the experimental stations as user laser. The FEL-2 line, covering the lower wavelength range between 20 and 4 nm thanks to a double stage cascaded HGHG scheme, operating in the "fresh bunch injection” mode, generated its first coherent photons in October 2012 and has seen further progress during the commissioning phases in 2013, at higher electron beam energy. In fact we will also report on the linac energy increase to 1.5 GeV and on the repetition rate upgrade from 10 to 50 Hz and eventually comment on the FEL operability and uptime. 		 
 
WEPSO34 Proposal for a Scheme to Generate a 10 tw Power Level, Femtosecond X-ray Pulses for Bio-imaging of Single Protein Molecules at the European XFEL 574
 
  • V. Kocharyan, G. Geloni, E. Saldin, S. Serkez, I. Zagorodnov
    DESY, Hamburg, Germany
  • O. Yefanov
    CFEL, Hamburg, Germany
  
  Crucial parameters for bio-imaging experiments are photon energy range, peak power and pulse duration. For a fixed resolution, the largest diffraction signals are achieved at the longest wavelength supporting that resolution. In order to perform these experiments at the European XFEL, we propose to use a novel configuration combining self-seeding and undulator tapering techniques with the emittance-spoiler method. Experiments at the LCLS confirmed the feasibility of these three techniques. Their combination allows obtaining a dramatic increase the XFEL output peak power and a shortening of the photon pulse duration to levels sufficient for performing bio-imaging of single protein molecules at the optimal photon-energy range between 3 keV and 5 keV. We show here that it is possible to achieve up to a 100-fold increase in peak-power of the X-ray pulses at the European XFEL: the X-ray beam would be delivered in 10 fs-long pulses with 50 mJ energy each at a photon energy around 4 keV. We confirm by simulations that one can achieve diffraction before destruction with a resolution of 0.25 nm resolution.  
 
WEPSO41 Feasibility Studies for Echo-enabled Harmonic Generation on CLARA 588
 
  • I.P.S. Martin, R. Bartolini
    Diamond, Oxfordshire, United Kingdom
  • R. Bartolini
    JAI, Oxford, United Kingdom
  • N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  The Compact Linear Accelerator for Research and Applications (CLARA) is a proposed single-pass FEL test facility, designed to facilitate experimental studies of advanced FEL techniques applicable to the next generation of light source facilities. One such scheme under consideration is Echo-Enabled Harmonic Generation (EEHG). In this paper we explore the suitability of CLARA for carrying out studies of this scheme, combining analytical and numerical calculations to determine likely hardware operating ranges, parameters tolerances and estimated FEL performance. A possible adaptation to convert EEHG into a short-pulse scheme is also considered.  
 
WEPSO43 EEHG and Femtoslicing at DELTA 594
 
  • R. Molo, H. Huck, M. Huck, M. Höner, S. Khan, A. Schick, P. Ungelenk
    DELTA, Dortmund, Germany
  
  The ultrashort-pulse facility at DELTA (a 1.5-GeV synchrotron light source operated by the TU Dortmund University) based on the coherent harmonic generation (CHG) technique will be upgraded using echo-enabled harmonic generation (EEHG) in order to reach shorter wavelengths. A laser-induced energy modulation is employed in the CHG and EEHG schemes to create a periodic electron density modulation, but can also be used to generate ultrashort pulses of incoherent radiation at arbitrary wavelengths by transversely displacing the off-energy electrons(femtoslicing). A new storage-ring lattice for DELTA will be presented that not only offers enough free straight sections for an EEHG and femtoslicing setup, but also allows to operate both radiation sources simultaneously.  
 
WEPSO47 Simulation Results of Self-seeding Scheme in PAL-XFEL 606
 
  • Y.W. Parc, J.H. Han, I. Hwang, H.-S. Kang
    PAL, Pohang, Kyungbuk, Republic of Korea
  • I.S. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • J. Wu
    SLAC, Menlo Park, California, USA
  
  There are two major undulator lines in Pohang Accelerator Laboratory XFEL (PAL XFEL), soft X-ray and hard X-ray. For the hard X-ray undulator line, self-seeding is the most promising approach to supply narrow bandwidth radiation to the users. The electron energy at hard X-ray undulator is 10 GeV and the central wavelength is 0.1 nm. We plan to provide the self-seeding option in the Phase I operation of PAL-XFEL. In this talk, the simulation results for the self-seeding scheme of hard X-ray undulator line in PAL XFEL will be presented.  
 
WEPSO48 Simulation Studies of FELs for a Next Generation Light Source 609
 
  • G. Penn, P. Emma, G. Marcus, J. Qiang, M.W. Reinsch
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Several possible FEL beamlines for a Next Generation Light Source are studied. These beamlines collectively cover a wide range of photon energies and pulse lengths. Microbunching and transverse offsets within the electron beam, generated through the linac, have the potential to significantly impact the longitudinal and transverse coherence of the x-ray pulses. We evaluate these effects and set tolerances on beam properties required to obtain the desired properties of the x-ray pulses. 		 
 
WEPSO51 Self-seeding Design for SwissFEL 618
 
  • E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  
  The SwissFEL facility, planned at the Paul Scherrer Institute, will provide SASE and self-seeded FEL radiation at a hard (1-7 Å) and soft (7-70 Å) X-ray FEL beamlines. This paper presents the current status of the self-seeding design for SwissFEL. The layout and full 6D start-to-end simulation results are presented for the hard X-ray beamline. Studies for different charges and optimization of the first and second undulator stages are shown.  
 
WEPSO57 Optimization of a Dedicated Bio-imaging Beamline at the European X-ray Fel 632
 
  • E. Saldin, G. Geloni, V. Kocharyan, S. Serkez
    DESY, Hamburg, Germany
  
  We recently proposed a basic concept for design and layout of a dedicated undulator source for bio-imaging experiments at the European XFEL. Here we present an optimization of that concept. The core of the scheme is composed by soft and hard X-ray self-seeding setups. Using an improved design for both monochromators it is possible to increase the design electron energy up to 17.5 GeV in photon energy range between 2 keV and 13 keV, which is the most preferable for life science experiments. Operating at such high electron energy one increases the X-ray output peak power. Moreover, 17.5 GeV is the preferred operation energy for SASE1 and SASE2 users. This choice will reduce the interference with other undulator lines. We include a study of the performance of the self-seeding scheme accounting for spatiotemporal coupling caused by the use of a single crystal monochromator. This distortion can be easily suppressed by the right choice of diamond crystal planes. The proposed undulator source yields about the same performance as in the case for a X-ray seed pulse with no coupling. Simulations show that the FEL power reaches 2 TW in the 3 keV - 5 keV photon energy range.  
 
WEPSO58 Status Report of the Short-pulse Facility at the Delta Storage Ring 642
 
  • A. Schick, H. Huck, M. Huck, M. Höner, S. Khan, R. Molo, P. Ungelenk
    DELTA, Dortmund, Germany
  
  Funding: * Work supported by DFG, BMBF and by the Federal State NRW.
At DELTA, a 1.5-GeV synchrotron light source operated by the TU Dortmund university, a short-pulse facility employing the CHG (Coherent Harmonic Generation) principle is in operation. Here, the interaction of an intense, ultrashort laser pulse and electrons in an undulator leads to microbunching of a small fraction of the electrons in the bunch. As a consequence, ultrashort, coherent synchrotron-radiation pulses in the VUV regime are emitted at harmonics of the incident laser wavelength. In addition, coherent THz pulses on the sub-ps timescale are generated. In this paper, the latest improvements of the facility and recent measurements are presented, including investigation of the transverse coherence and detection of the CHG radiation using photoemission spectroscopy in a VUV beamline. 		 
 
WEPSO64 Grating Monochromator for Soft X-ray Self-seeding the European XFEL 667
 
  • S. Serkez, G. Geloni, V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  Self-seeding implementation in the soft X-ray wavelength range involves gratings as dispersive elements. We study a very compact self-seeding scheme with a grating monochromator originally designed at SLAC, which can be straightforwardly installed in the SASE3 undulator beamline at the European XFEL. The design is based on a toroidal VLS grating at a fixed incidence angle, and without entrance slit. It covers the spectral range from 300 eV to 1000 eV. The performance was evaluated using wave optics method vs ray tracing methods. Wave optics analysis takes into account the actual beam wavefront of the radiation from the FEL source, third order aberrations, and errors from optical elements. We show that, without exit slit, the self-seeding scheme gives the same resolving power (about 7000) as with an exit slit. Wave optics is also naturally applicable to calculations of the scheme efficiency, which include the monochromator transmittance and the effect of the mismatching between seed beam and electron beam. Simulations show that the FEL power reaches 1 TW, with a spectral density about two orders of magnitude higher than that for the SASE pulse at saturation.  
 
WEPSO70 Fully Phase Matched High Harmonics Generation in a Hollow Waveguide for Free Electron Laser Seeding 693
 
  • C. Vicario
    INFN/LNF, Frascati (Roma), Italy
  • F. Ardana-Lamas, C.P. Hauri, A. Trisorio
    PSI, Villigen PSI, Switzerland
  • C.P. Hauri
    EPFL, Lausanne, Switzerland
  • G. Lambert, V. Malka, B. Vodungbo, P. Zeitoun
    LOA, Palaiseau, France
  
  Funding: LASERLAB-EUROPE, grant n◦ 228334 PARIS ERC project (Contract No. 226424) Swiss National Science Foundation under grant PP00P2_128493
A bright high harmonic source is presented delivering up to 1011 photons per second around a central photon energy of 120 eV. Fully phase matched harmonics are generated in an elongated capillary reaching a cut-off energy of 160 eV. The high HHG fluence opens new perspectives towards seeding FELs at shorter wavelengths than the state of the art. Characterization of the phase matching conditions in the capillary is presented. 		 
 
WEPSO73 High Average Power Seed Laser Design for High Reprate FELs 697
 
  • R.B. Wilcox, G. Marcus, G. Penn
    LBNL, Berkeley, California, USA
  • T. Metzger, M. Schultze
    TRUMPF Scientific Lasers GmbH + Co. KG, Munchen-Unterfoehring, Germany
  
  Funding: US Department of Energy, under Contract Numbers DE-AC02-0SCH11231.
In the proposed Next Generation Light Source (NGLS), FEL designs use lasers to seed the FEL in an HGHG scheme or bunch the electron beam in an E-SASE scheme. The FELs would run at 100kHz to 1MHz, requiring high average power lasers. For the seeded FEL, laser modulation is applied at 200-240nm, with 250-700MW peak power depending on pulse length, which can vary from 100-10fs. The laser consists of a broadband oscillator and amplitude/phase shaper seeding an optical parametric amplifier (OPA). After recompression, the ~800nm pulse is converted to the fourth harmonic. Losses could be high enough to require 250W at 100kHz, making the OPA ~100x more powerful than existing femtosecond OPAs. In the E-SASE scheme, a single cycle of 5 micron light bunches the beam, which then radiates a short X-ray burst. This requires 100% fractional bandwidth, and precise phase control of the e-field within the pulse, as well as broad band compensation of dispersion throughout the laser path. Bandwidth can be increased by splitting the amplified spectrum into segments and coherently recombining. We present design concepts that are expected to meet requirements, and identify R&D needs. 		 
 
THIANO01 Double Stage Seeded FEL with Fresh Bunch Injection Technique at FERMI 723
 
  • E. Allaria, D. Castronovo, P. Cinquegrana, G. D'Auria, M. Dal Forno, M.B. Danailov, G. De Ninno, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, E. Ferrari, L. Fröhlich, G. Gaio, L. Giannessi, R. Ivanov, B. Mahieu, N. Mahne, I. Nikolov, F. Parmigiani, G. Penco, L. Raimondi, C. Serpico, P. Sigalotti, C. Spezzani, M. Svandrlik, C. Svetina, M. Trovò, M. Veronese, D. Zangrando, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • M. Dal Forno
    DEEI, Trieste, Italy
  • G. De Ninno, D. Gauthier
    University of Nova Gorica, Nova Gorica, Slovenia
  • E. Ferrari, F. Parmigiani
    Università degli Studi di Trieste, Trieste, Italy
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • B. Mahieu
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
  • M. Zangrando
    IOM-CNR, Trieste, Italy
  
  Seeding a FEL with an external coherent source has been extensively studied in the last decades as it can provide a way to enhance the radiation brightness and stability, with respect to that available from SASE. An efficient scheme for seed a VUV-soft x ray FEL uses, a powerful, long wavelength external laser to induce on the electron beam coherent bunching at the harmonics of the laser wavelength. When the bunching is further amplified by FEL interaction in the radiator, the scheme is called high gain harmonic generation (HGHG). The need of high power seed sources and of small energy spread are at the main limits for a direct extension of the HGHG scheme to short wavelengths. The fresh bunch scheme was proposed as a way to overcome these limitations; the scheme foresees the FEL radiation produced by one HGHG stage as an external seed in a second HGHG stage. We report the latest results obtained at FERMI that uses the two-stage HGHG scheme for generation of FEL pulses in the soft x-ray. A characterization of the FEL performance in terms of power, bandwidth and stability is reported. Starting from the FERMI results we will discuss extension of the scheme toward shorter wavelengths.  
slides icon Slides THIANO01 [9.355 MB]  
 
THOANO01 Stable Operation of HHG-Seeded EUV-FEL at the SCSS Test Accelerator 728
 
  • H. Tomizawa, T. Hara, T. Ishikawa, K. Ogawa, H. Tanaka, T. Tanaka, T. Togashi, K. Togawa, M. Yabashi
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • M. Aoyama, K. Yamakawa
    JAEA/Kansai, Kyoto, Japan
  • A. Iwasaki, S. Owada, T. Sato, K. Yamanouchi
    The University of Tokyo, Tokyo, Japan
  • S. Matsubara, Y. Okayasu, T. Watanabe
    JASRI/SPring-8, Hyogo, Japan
  • K. Midorikawa, E. Takahashi
    RIKEN, Saitama, Japan
  
  We performed the higher-order harmonic (HH) seeded FEL operation at a 61.2 nm fundamental wavelength, using a seeding source of HH pulses from a Ti:sapphire laser at the SCSS (EUV-FEL) accelerator. It is important for the HH seeded FEL scheme to synchronize the seeding laser pulses to the electron bunches. We constructed the relative arrival timing monitor based on Electro-Optic sampling (EOS). Since the EOS-probe laser pulses were optically split from HH-driving laser pulses, the arrival time difference of the seeding laser pulses, with respect to the electron bunches, were measured bunch-by-bunch. This non-invasive EOS monitor made uninterrupted, real-time monitoring possible even during the seeded FEL operation. The EOS system was used for the arrival timing feedback with a few-hundred-femtosecond adjustability for continual operation of the HH-seeded FEL. By using the EOS-locking system, the HH seeded FEL was operated over half a day with a 20-30% hit rate. The output pulse energy reached 20uJ at the 61.2 nm wavelength. A user experiment was performed by using the seeded EUV-EL and a clear difference between the SASE-FEL and the seeded FEL was observed.  
slides icon Slides THOANO01 [11.493 MB]  
 
THOANO02
 Experimental Demonstration of Echo-enabled Harmonic Generation at the 14th Harmonic  
 
  • D. Xiang, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer, S.P. Weathersby
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. DOE under Contract No. DE-AC02-76SF00515.
Following the successful demonstration of echo-enabled harmonic generation [1] (EEHG [2]) with n=7 [3] at SLAC's NLCTA in 2011 [4], the beam line has been upgraded recently to benchmark EEHG theory at much higher harmonics. An optical parametric amplifier has been used to provide a seed with wavelength at 2.4 μm. Using an rf undulator as the radiator, coherent radiation at the 14th harmonic of the seed, i.e. with wavelength at 171 nm, has been generated using EEHG technique with a 120 MeV beam. We will present detailed experimental results on testing EEHG at n=14. Future plans in testing EEHG at n=30~75 in the coming year will be briefly discussed as well.
[1] G. Stupakov, PRL 102, 074801 (2009).
[2] D. Xiang and G. Stupakov, PRST-AB 12, 030702 (2009).
[3] D. Xiang et al., PRL 105, 114801 (2010).
[4] D. Xiang et al., PRL 108, 024802 (2012) 		 
slides icon Slides THOANO02 [2.288 MB]  
 
THOANO03
 Experimental Characterization of the Laser Heater Effects on a Seeded FEL  
 
  • E. Ferrari, E. Allaria, W.M. Fawley, L. Giannessi, G. Penco, S. Spampinati
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • W.M. Fawley
    LBNL, Berkeley, California, USA
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • Z. Huang
    SLAC, Menlo Park, California, USA
  
  High brightness electron beams necessary for high gain FEL usually require a laser heater in order to increase the local energy spread in the low energy part of the machine that can mitigate the microbunching instabilities developing in the compressors and in the rest of the linac. Microbunching suppression is essential for FEL operations both in SASE and in seeded mode since it can strongly affect the final electron beam properties. In the case of HGHG, due to the seeding mechanism, the FEL process is extremely sensitive to the amount of energy spread at the undulator entrance, and the FEL output may depend to the amount of heating. In this work we characterize the dependence of the FEL output as a function of the laser heater intensity in the case of FERMI FEL-1. Results also show that for a non Gaussian distribution of the electron beam energy the HGHG may produce significant radiation with an energy spread significantly higher than what expected for a simple Gaussian distribution.  
slides icon Slides THOANO03 [2.333 MB]  
 
THOANO04
 Experimental Studies of Echo-enabled HG FEL  
 
  • Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  • D. Xiang
    SLAC, Menlo Park, California, USA
  
  After echo-enabled HG FEL was studied theoretically and numerically, several experiments have been done to verify it. An overview of the experiments over the world and new understanding of it will be given in this talk.  
slides icon Slides THOANO04 [18.207 MB]