FLS 2006 - List of Sessions

WG3 — Working Group 3 (16-May-06 11:00—18:00)

Paper	Title	Page
WG301	A Versatile UV-VUV Light Source Based upon a High Gain Distributed Optical Klystron FEL
	Y. K. Wu DU/FEL, Durham, North Carolina N. Vinokurov BINP SB RAS, Novosibirsk
	Funding: This work is supported by the medical FEL grant F49620-001-0370 from the Air Force Office of Scientific Research and by U. S. Department of Energy grant DE-FG05-91ER40665. The FEL gain can be significantly increased using a distributed optical klystron (DOK) FEL with multiple wigglers and bunchers. The enhanced FEL gain of DOK FELs opens the door for storage ring based FEL oscillators to operate in the VUV region toward 150 nm and beyond. This presentation reports the first experimental results from the world's first distributed optical klystron FEL, the DOK-1 FEL, at Duke University. The DOK-1 FEL is a hybrid system, comprised of four wigglers: two horizontal and two helical. With the DOK-1 FEL, we have obtained the highest FEL gain among all storage ring based FELs at 47.8% (±2.7%) per pass at 450 nm. We have also realized controlled polarization switches of the FEL beam by a non-optical means through the manipulation of a buncher magnet. DOK FELs are promising light sources capable of rapid polarization switch in UV and VUV. Furthermore, DOK FELs can be used as a multi-color light source with phase synchronization which can be realized through the generation of coherent harmonic radiation using DOK FELs.
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WG302	Experimental Studies of Optical Guiding, Efficiency Improvement and Pulse Length Control in a laser seeded FEL Amplifier at the NSLS SDL*
	X. J. Wang, J. B. Murphy, J. Rose, Y. Shen, T. Tsang, T. Watanabe BNL, Upton, Long Island, New York
	*Funding: Work supported by the Office of Naval Research and U. S. Department of Energy under contract No. DE-AC02-98CH1-886.** The Source Development Lab (SDL) at the NSLS of Brookhaven National Laboratory (BNL) is the only facility in the world now capable of performing the laser seeded FEL R&D, such as high gain harmonic generation (HGHG) and direct laser seeded FEL amplifier. A laser seeded FEL amplifier experiment @ 800 nm was initiated at the SDL to demonstrate the critical FEL amplifier technologies for high average power applications. The recent experimental results of the laser seeded FEL amplifier will be presented in this talk. We have achieved more than 4 orders of magnitude of the FEL gain over the seed laser, and measured record FEL output energy of more than 500 μJ. We experimentally demonstrated the FEL guiding and efficiency improvement by frequency detuning. We have experimentally observed nonlinear evolution of the femto-seconds FEL pulse both in exponential gain and superradiance regimes.
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WG303	Beam Dynamics Experiments and Analysis in FLASH on CSR and Space Charge Effects
	B. Beutner, M. Dohlus, M. Roehrs DESY, Hamburg
	High peak currents at the FLASH linac gives rise to strong self interactions like space charge fields and coherent synchrotron radiation wakes. These forces leads to distorted electron bunches. Simulations and measurements are presented to demonstrate the beam dynamics at FLASH. The projections into the longitudinal horizontal plane are observed with a transverse deflecting cavity. Measurements of CSR induced transverse displacements are presented and compared with simulations.
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WG304	Dispersion measurement and correction in the VUV-FEL
	E. Prat, W. Decking, T. Limberg DESY, Hamburg
	Increase in transverse beam size in the undulator caused by dispersive effects is one of the major limitations for the operation of the VUV-FEL at DESY. Sources of the (spurious) dispersion are field errors and stray magnet fields in the undulator beam line as well as spurious dispersion created upstream of the undulator by, for instance, rf coupler kicks, magnet misalignments and field errors. In this contribution, a procedure for dispersion measurement and correction is described and simulations and first experimental results for the VUV-FEL are presented.
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WG305	Operational Experience and Recent Results from FLASH
	E. Saldin, E. Schneidmiller, M. V. Yurkov DESY, Hamburg
	Experience from comissioning and operating the user facility at FLASH is discussed. Recent results (lasing at 13 nm) are presented.
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WG311	Quantum Regime of SASE FELS
	R. Bonifacio INFN-Milano, Milano N. Piovella Universita' degli Studi di Milano, Milano G. R.M. Robb USTRAT/SUPA, Glasgow A. Schiavi Rome University La Sapienza, Roma
	The novel quantum regime of an high-gain FEL operating in the SASE mode is expected to produce high coherent X-ray radiation, with a narrow spectrum. The theory, based on a Schroedinger-like equation coupled self-consistently to the Maxwell equations, shows that the dynamics depends on a single quantum parameter r, interpreted as the ratio between the classical momentum spread and the photon recoil momentum. In the quantum regime, r < 1, the spectrum is a series of narrow lines, associated to transitions between discrete momentum eigenstates and resulting in high temporal coherence. The classical SASE regime, with random spiking behavior and broad spectrum, is obtained increasing r until the linewidth becomes larger than the frequency separation. We intend to investigate the feasibility of a future experiment of quantum SASE using an e.m. wiggler, by developing a 3D numerical code which will take into account transverse and emittance effects.
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WG312	Optical Klystron Enhancement to SASE X-ray FELs
	Z. Huang, Y. T. Ding, P. Emma SLAC, Menlo Park, California V. Kumar ANL, Argonne, Illinois
	We study the optical klystron enhancement to SASE FELs in theory and simulations. In contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not sensitive to any phase mismatch between the radiation and the microbunched electron beam. The FEL performance with the addition of four optical klystrons located at the undulator long breaks in the Linac Coherent Light Source (LCLS) shows significant improvement if the uncorrelated energy spread at the undulator entrance can be controlled to a very small level. In addition, FEL saturation at shorter X-ray wavelengths (around 1.0 Angstrom) within the LCLS undulator length becomes possible.
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WG313	Beam Physics Highlights of the FERMI@ELETTRA Project	27
	S. Di Mitri, M. Cornacchia, P. Craievich, G. Penco, M. Trovo ELETTRA, Basovizza, Trieste P. Emma, Z. Huang, J. Wu SLAC, Menlo Park, California D. Wang MIT, Middleton, Massachusetts A. Zholents LBNL, Berkeley, California
	The electron beam dynamics in the Fermi Linac has been studied in the framework of the design of a single-pass free electron laser (fel) based on a seeded harmonic cascade. The wakefields of some accelerating sections represent a challenge for the preservation of a small beam emittance and for achieving a small final energy spread. Various analytical techniques and tracking codes have been employed in order to minimize the quadratic and the cubic energy chirps in the longitudinal phase space, since they may cause a degradation of the fel bandwidth. As for the transverse motion, the beam breakup (bbu) instability has been recognized as the main source of emittance dilution; the simulations show the validity of local and non-local correction methods in order to counteract the typical “banana” shape distortion of the beam caused by the instability.
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WG314	Start-To-End Simulations for the European XFEL
	M. Dohlus, I. Zagorodnov DESY, Hamburg
	The lattice and optics data of the s2e simulations are based on an Excel table with the XFEL component list [1]. The simulation tools are ASTRA, CSRtrack, GENESIS and ELEGANT. Utility programms are used to convert particle files and to consider wake fields of cavities (calculated with ECHO) or due to space charge, surface effects and the undulator geometry. The simulations [2] for the XFEL STI review meeting (15/16 March 2006) are based on ASTRA calculations for the low energy part (including the first module) and on semianalytic estimations of space charge effects and particle propagation based on transport matrices for all non dispersive sections upstream of the undulator. Dispersive sections as the two bunch compressors are computed with the 1d model of CSRtrack. GENESIS is used for the SASE-FEL process in the undulator. The s2e simulation reported on the XFEL-s2e web page [3] uses ASTRA calculations for all non-dispersive parts of the XFEL before the second bunch compressor and even for the following eight rf modules. The injector dogleg as well as both bunch compressors are simulated with CSRtrack using a 3D sub-bunch approach. The rest of the machine before the undulator is treated with ELEGANT and semianalytic space charge wakes. SASE simulations are so far not available. There is a considerable difference in the numerical effort of the start-to-undulator simulations for [2] and [3]. The later simulation is intended as a reference solution. A method that is efficient and precise is probably based on the use of ELEGANT in combination with the semianalytic space charge estimation for parts of the XFEL even before the first bunch compressor and on the 1d CSR model in CSRtrack. This is subject of further investigations. [1] http://www.desy.de/xfel-beam/data/component_list.xls [2] TESLA-FEL Report 2005-10 [3] http://www.desy.de/xfel-beam/s2e/xfel_v4.html
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WG315	Experience with Start-to-End Tolerance Studies in HGHG FEL Cascades
	B. C. Kuske, M. Abo-Bakr, K. Goldammer, A. Meseck BESSY GmbH, Berlin
	*Funding: Funded by the Bundesministerium für Bildung und Forschung (BMBF), the State of Berlin and the Zukunftsfond Berlin** Start-to-end simulations for today's FEL projects are tedious and time consuming. Tolerance studies easily extend the efforts to weeks of computation time. Comparisons between start-to-end simulations and perfect bunches show how important these studies are. Special emphasis is put on HGHG FEL cascades, where results of start-to-end simulations have direct impact on the hardware layout. Examples are given for the BESSY FEL, especially the 2 stage low energy FEL line.
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WG316	Analysis of Spontaneous Emission and its Self-Amplification in Free-Electron Laser
	Q. K. Jia USTC/NSRL, Hefei, Anhui
	The spontaneous emission and the self-amplified spontaneous emission (SASE) in free-electron laser are investigated from the one-dimensional Maxwell wave equation in the time domain. The explicit expressions of the incoherent spontaneous emission and the coherent spontaneous emission are deduced for an arbitrary electron pulse profile, it show that both are related to the slippage distance. The effective start-up power of SASE for a long electron bunch is obtained with the time domain approach, it is composed of the shot noise term and the super radiant term, corresponding the incoherent spontaneous emission and the coherent spontaneous emission respectively. The shot noise term is found to be equal to the usual spontaneous undulator radiation in the one power gain length. An analytical estimation of saturation power and saturation length of SASE is presented.
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WG317	An Analysis of Nonlinear Harmonic Generation
	Q. K. Jia USTC/NSRL, Hefei, Anhui
	The nonlinear harmonic generation in high gain free electron laser is analysed in a perspicuous way. The harmonic interactions and evolution is shown explicitly. One-dimensional analytical equations for nonlinear harmonic generation in both SASE FEL and HGHG FEL are given.
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WG321	Commissioning Plans for the LCLS
	J. J. Welch SLAC, Menlo Park, California
	The Linear Coherent Light Source (LCLS), an XFEL presently under construction at SLAC, will begin commissioning this fall, starting with the drive laser, the injector, and the first bunch compressor section of the linac. In this paper, we describe the overall commissioning plans for the entire LCLS up to and including commissioning the FEL beam. Work supported in part by the DOE Contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC.
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WG322	Status of the SPARX FEL Project	30
	C. Vaccarezza INFN/LNF, Frascati (Roma)
	SPARX is a proposal for a X-ray-FEL facility jointly funded by MIUR (Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and Rome University Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1 and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5–6 nm and 6–1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC [1] high brightness photoinjector presently under installation at Frascati INFN-LNF Laboratories. The use of superconducting and exotic undulator sections will be also exploited. In this paper we discuss the present status of the collaboration. on behalf of the SPARX team
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WG323	Shanghai DUV-FEL Progress
	Z. Zhao, Y. Cao, M. Chen, Z. M. Dai, H. X. Deng, Q. Gu, D. M. Li, D. G. Li, D. K. Liu, K. R. Ye, M. H. Zhao, X. F. Zhao, Q. G. Zhou SINAP, Shanghai S. Y. Chen IHEP Beijing, Beijing J. P. Dai IHEP, Beijing H. He, Q. K. Jia USTC/NSRL, Hefei, Anhui
	Funding: Supported by the Major State Basic Research Development Programme of China under Grant No. 2002CB713600, the Chinese Academy of Sciences, and the National Natural Science Foundation of China. The SDUV-FEL has been designed as an HGHG type high gain FEL facility to provide high power coherent radiation from 262 nm to 88 nm, which consists of a 300 MeV S-band Linac, seeding laser, six sections of 1.5 m radiator undulator, one 0.8 m modulator undulator and one dispersion section. Its first 100 MeV Linac section has been successfully commissioned with a ns grid gun injector in 2005. A photocathode injector will replace the existing gun and buncher of the 100 MeV Linac in this year. The magnetic bunch compressor has been completed and will be installed in this year. The first 1.5 m radiator undulator has been fabricated and measured, and other five sections of radiator undulator are being under manufacture. The laser system for photocathode has been installed and commissioned. The photocathode RF gun and the FEL required beam diagnostics are under manufacture. In this paper, we also present the design optimization on the SDUV-FEL facility.
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WG324	Single Bunch Emittance Preservation in XFEL Linac	33
	V. M. Tsakanov, G. A. Amatuni CANDLE, Yerevan R. Brinkmann, W. Decking DESY, Hamburg
	The single bunch emittance preservation in booster and main linacs of European XFEL project is presented. The wakefield and chromatic dilution of the beam emittance caused by free betatron oscillations, cavity and modules offset misalignments and random tilts are evaluated. The effects of cavities misalignments correlation along the linac are discussed. The effects of quadrupole misalignments and the corresponding trajectory steering based on one-to-one correction technique are given. The residual chromatic emittance dilution of the corrected trajectory is evaluated.
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WG331	Simulation Studies on the Self-Seeding Option at FLASH
	V. Miltchev, J. Rossbach Uni HH, Hamburg B. Faatz, R. Treusch DESY, Hamburg
	Funding: This work has been partially supported by the EU Commission in the Sixth Framework Program, Contract No. 011935 – EUROFEL. In order to improve the temporal coherence of the radiation generated by FLASH, a two-stage seeding scheme [1] is presently being realized. It consists of two undulator stages and a magnetic chicane and a monochromator located between them. In this contribution we investigate various configurations of the electron optics of the seeding set-up. The optimization of the lattice in the first seeding stage and the parameters of the magnetic chicane will be discussed. Simulation results for the performance of the seeded FEL at different resonant wavelengths will be presented. [1] J. Feldhaus et. al. "Possible application of X-ray optical elements for reducing the spectral bandwidth of an X-ray SASE FEL". Optics Communications, Volume 140, Pages 341–352
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WG332	Fully Coherent X-Ray Pulses from a Regenerative-Amplifier FEL
	Z. Huang, R. D. Ruth SLAC, Menlo Park, California
	We propose and analyze a regenerative-amplifier FEL to produce fully coherent, hard X-ray pulses [1]. The method makes use of narrow-bandwidth Bragg crystals to form an X-ray feedback loop around a relatively short undulator. Self-amplified spontaneous emission (SASE) from the leading electron bunch in a bunch train is spectrally filtered by the Bragg reflectors and is brought back to the beginning of the undulator to interact repeatedly with subsequent bunches in the bunch train. The FEL interaction with these short bunches regeneratively amplifies the radiation intensity and broadens its spectrum, allowing for effective transmission of the X-rays outside the crystal bandwidth. The spectral brightness of these X-ray pulses is about 2 to 3 orders of magnitude higher than that from a single-pass SASE FEL. [1] Z. Huang and R. Ruth, Phys. Rev. Lett. 96, 144801 (2006).
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WG333	High Harmonic Seeding and the 4GLS XUV-FEL	36
	B. Sheehy Sheehy Scientific Consulting, Wading River, New York J. A. Clarke, D. J. Dunning, N. Thompson CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire B. W.J. McNeil USTRAT/SUPA, Glasgow
	The Fourth Generation Light Source (4GLS) project, proposed by the CCLRC in the U. K., will include free electron lasers in the XUV, VUV, and IR. It is proposed that the XUV-FEL, operating between 8–100 eV, be seeded by a high harmonic (HH) source, driven by an ultrafast laser system. This offers advantages in longitudinal coherence, synchronization, and the potential for chirped pulse amplification and pulse shaping. In this talk we discuss the issues of HH generation relevant to its use as a seed (energy, spectrum, tunability, synchronization and time structure) and the current planned implementation in the 4GLS XUV-FEL.
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WG334	Femtosecond Synchronism of X-Rays and Light in an X-Ray Free-Electron Laser
	B. W. Adams ANL, Argonne, Illinois
	Funding: This work was supported by the U. S. Department of Energy, Office of Basic Energy Sciences under contract W-31-109-ENG-38. An important tool to study the fundamental processes of chemistry and solid-state physics is the femtosecond-resolving visible/IR pump, X-ray probe technique. It requires ultrashort pulses of light and X-rays in few-femtosecond synchronism with each other. Here, a scheme is proposed to derive both types of radiation from the same electrons in an emittance-sliced XFEL [1]. For this, the same emittance contrast that is imposed onto the bunches in an XFEL to modulate the SASE process is also used to generate a coherence enhancement of transition undulator radiation [2] (TUR). This results in an intense single-cycle pulse of near-infrared, coherent TUR (CTUR) light that is perfectly synchronized to the SASE X-rays, and has about 100 μJ of energy (based upon LCLS parameters). The idea will be presented and conceptual issues will be discussed, such as near-field effects in the CTUR. Furthermore, practical issues arising from the integration into an XFEL facility will be adressed, such as impact on beam-position monitoring, direct use of the CTUR for pumping vs. cross-correlation with a short-pulse laser, and scanning delays. [1] P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004) [2] K.-J. Kim, Phys. Rev. Lett. 76, 1244 (1996) [3] B. W. Adams, Rev. Sci. Instrum. 76, 063304 (2005)
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WG341	Flat Electron Beams for a Smith-Purcell Backward Wave Oscillator for Intense Terahertz Radiation
	K.-J. Kim ANL, Argonne, Illinois V. Kumar RRCAT, Indore (M. P.)
	A Smith-Purcell device can operate as a backward wave oscillator (BWO) producing a few watts of narrow bandwidth, CW Terahertz radiation. We discuss the requirements on electron beam properties for achieving the operation of such a device based on the results of a 2-D theory of Smith-Purcell BWO [1]. It is found that a specially designed non-relativistic electron beam is necessary with the current exceeding a certain threshold value and a flat transverse profile. Two methods for producing electron beams of required characteristics are discussed, one based on a line source and one employing the flat beam technique. [1] V. Kumar and K.-J. Kim, Physical Review E 73, 026501 (2006).
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WG342	Design of the Thomson Source at SPARC/PLASMONX for Incoherent and Coherent X-Rays
	L. Serafini INFN-Milano, Milano
	The SPARC Project, presently commissioning its photo-injector, will be upgraded, in the frame of the Project PLASMONX, by installing at LNF an ultra-high intensity Ti:Sa laser system, delivering 30 fs laser pulses, synchronized to the SPARC electron beam, carrying up to 200 TW. The collision of the two beams will produce X-rays by Thomson back-scattering with unprecedented characteristics of: monochromaticity (in the range 1–10 % bandwidth), tunability in the 20–500 keV spectral region, rapidity (from 100 fs to 10 ps pulses) and brilliance, which is comparable to the one of synchrotron light sources. Applications of this Thomson X-ray Source range from advanced radiological imaging to radio-therapy with micro-beams, from X-ray microscopy to national security applications. Studies are under way to assess the existence of FEL collective instabilities, in the classical and quantum regime, by operating the Thomson Source either with extremely high brightness beams or with very high laser pulse energies: we will discuss the experimental conditions under which the FEL instability can be driven and observed. This would produce coherent X-rays with much higher brilliance.
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WG343	Production of Coherent X-Rays with a Free-Electron Laser Based on Optical Wiggler	39
	C. Maroli, V. Petrillo Universita' degli Studi di Milano, Milano A. Bacci INFN/LASA, Segrate (MI) M. Ferrario INFN/LNF, Frascati (Roma) L. Serafini INFN-Milano, Milano
	Funding: Istituto Nazionale di Fisica Nucleare(INFN) - Sezione di milano The interaction between high-brightness electron beams and counter-propagating laser pulses produces X-rays via Thomson scattering. If the laser source is long enough the electrons bunch on the scale of the emitted X-ray wavelength and a regime of collective (coherent) emission can be established. The emitted radiation grows exponentially and the system behaves as a FEL with optical undulator. The bandwidth of the emitted X-rays is sharper than that of the usual incoherent emission. Emittance of the beam and gradients and irregularities of the laser intensity spatial distribution are the principal factors that limit the growth of the X-ray signal. The characters of the emission and the corresponding X-ray spectra are analyzed on the basis of a 3D code. The scalings typical of the optical wiggler with very short gain lengths and short time duration of the ineteraction allow considerable emissions also in violation of criteria valid for static wigglers. The parameters chosen in the cases examined allow a classical treatment of the lasing process.
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WG344	The 4GLS VUV-FEL: A Regenerative Amplifier FEL Design
	N. Thompson, D. J. Dunning CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire J. G. Karssenberg, I. Volokhine, P. J.M. van der Slot Twente University, Laser Physics and Non-Linear Optics Group, Enschede B. W.J. McNeil USTRAT/SUPA, Glasgow B. Sheehy Sheehy Scientific Consulting, Wading River, New York
	A VUV-FEL operating over the photon energy range 3–10 eV is a component of the 4th Generation Light Source (4GLS) proposal by Daresbury Laboratory in the United Kingdom. This presentation gives an overview of the design of the 4GLS VUV-FEL, which is based on the concept of the Regenerative Amplifier FEL (RAFEL). A 3D optical propagation code which allows FEL codes such as Genesis 1.3 to be used in combination with full wavefront propagation through cavity elements has been developed at the University of Twente. This code has been used for initial transverse cavity mode analysis of the VUV-FEL and simulation results are presented in this contribution.
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