FEL2015 - List of Keywords (undulator)

Paper	Title	Other Keywords	Page
MOA02	First Lasing of the Third Stage of Novosibirsk FEL	FEL, radiation, electron, linac	1
	O.A. Shevchenko, V.S. Arbuzov, K.N. Chernov, I.V. Davidyuk, E.N. Dementyev, B.A. Dovzhenko, Ya.V. Getmanov, B.A. Knyazev, E.I. Kolobanov, A.A. Kondakov, V.R. Kozak, E.V. Kozyrev, V.V. Kubarev, G.N. Kulipanov, E.A. Kuper, I.V. Kuptsov, G.Y. Kurkin, L.E. Medvedev, S.V. Motygin, V.N. Osipov, V.K. Ovchar, V.M. Petrov, A.M. Pilan, V.M. Popik, V.V. Repkov, T.V. Salikova, M.A. Scheglov, I.K. Sedlyarov, G.V. Serdobintsev, S.S. Serednyakov, A.N. Skrinsky, S.V. Tararyshkin, V.G. Tcheskidov, A.G. Tribendis, N. Vinokurov, P. Vobly BINP SB RAS, Novosibirsk, Russia
	Novosibirsk FEL facility is based on the first in the world multi-turn energy recovery linac (ERL). It comprises three FELs (stages). FELs on the first and the second tracks were commissioned in 2004 and 2009 respectively and operate for users now. The third stage FEL is installed on the fourth track of the ERL. It includes three undulator sections and 40-meters-long optical cavity. The design tuning range of this FEL is from 5 to 20 microns and the design average power at bunch repetition rate 3.74 MHz is about 1 kW. Recent results of the third stage FEL commissioning are reported.
	Slides MOA02 [4.901 MB]
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MOB01	Three-Plus Decades of Tapered Undulator FEL Physics	FEL, electron, radiation, controls	5
	W.M. Fawley Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy W.M. Fawley SLAC, Menlo Park, California, USA
	Beginning with the classic 1981 work of Kroll-Morton-Rosenbluth (), multiple generations of FEL scientists have studied and used experimentally undulator tapering to improve and optimize the radiation output of both amplifier and oscillator FELs. Tapering has undergone a renaissance of interest, in part to make possible TW instantaneous power levels from x-ray FELs. In this talk, I will give a highly personalized (and undoubtedly strongly biased) historical survey of tapering studies beginning with the ELF 35-GHz experiments at Livermore in the mid-1980's and continuing up to quite recent studies at the LCLS at both soft and hard x-ray wavelengths. () N.M. Kroll, P.L. Morton, and M.N. Rosenbluth, IEEE J. Quantum Elec., QE-17, 1436 (1981).
	Slides MOB01 [2.106 MB]
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MOB02	X-Ray FEL R&D: Brighter, Better and Cheaper	FEL, electron, photon, radiation	7
	Z. Huang SLAC, Menlo Park, California, USA
	The X-ray free-electron lasers (FELs), with nine to ten orders of magnitude improvement in peak brightness over the third-generation light sources, have demonstrated remarkable scientific capabilities. Despite the early success, X-ray FELs can still undergo dramatic transformations with accelerator and FEL R&D. In this talk, I will show examples of recent R&D efforts to increase X-ray coherence and brightness, to obtain better control of X-ray temporal and spectral properties, and to develop concepts for compact coherent sources.
	Slides MOB02 [18.004 MB]
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MOB03	Transforming the FEL: Coherence, Complex Structures, and Exotic Beams	FEL, laser, radiation, electron	10
	E. Hemsing SLAC, Menlo Park, California, USA
	Modern high brightness electron beams used in FELs are extremely versatile and highly malleable. This flexibility can be used to precisely tailor the properties of the FEL light for improved temporal coherence (as in external seeding), but can also be exploited in new ways to generate exotic FEL modes of twisted light that carry orbital angular momentum (OAM) for new science. In this talk, I will describe how lasers and undulator harmonics can be combined to produce both simple and complex e-beam distributions that emit intense, coherent, and highly tunable OAM light in future FELs.
	Slides MOB03 [12.208 MB]
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MOC02	Optimization of a High Efficiency Free Electron Laser Amplifier	electron, FEL, radiation, brilliance	17
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Technique of undulator tapering in the post-saturation regime is used at the existing X-ray FELs for increasing the radiation power. We present comprehensive analysis of the problem in the framework of one-dimensional and three-dimensional theory. We find that diffraction effects essentially influence on the choice of the tapering strategy. Our studies resulted in a general law of the undulator tapering for a seeded FEL amplifier as well as for SASE FEL.
	Slides MOC02 [24.462 MB]
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MOC03	Estimate of Free-Electron Laser Gain Length in the Presence of Electron Beam Collective Effects	emittance, FEL, electron, collective-effects	24
	S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom
	A novel definition for the three-dimensional free electron laser gain length is proposed, which takes into account the increase of electron beam projected emittance as due, for example, to geometric transverse wakefield and coherent synchrotron radiation developing in linear accelerators. The analysis shows that the gain length is affected by an increase of the electron beam projected emittance, even though the slice (local) emittance is preserved, and found to be in agreement with Genesis code simulation results. It is then shown that the minimum gain length and the maximum of output power may notably differ from the ones derived when collective effects are neglected. The proposed model turns out to be handy for a parametric study of electron beam six-dimensional brightness and FEL performance as function, e.g., of bunch length compression factor, accelerator alignment tolerances and optics design. S. Di Mitri, S. Spampinati, Phys. Rev. Special Topics Accel. Beams, 17, 110702 (2014)
	Slides MOC03 [2.528 MB]
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MOP004	Influence of Horizantal Constant Magnetic Field on Harmonic Undulator Radiations and Gain	radiation, electron, FEL, resonance	34
	H. Jeevakhan, P.K. Purohit NITTTR, Bhopal, India G. Mishra Devi Ahilya University, Indore, India
	Harmonic undulators has been analyzed in the presence of constant magnetic field along the direction perpendicular to the main undulator field. Effect of constant magnetic field magnitude on trajectory of electron beam , intensity of radiation and FEL gain at fundamental and third harmonics has been evaluated. Performance of harmonic undulator in the presence horizontal component of earth's magnetic field is the practical realization of the suggested scheme.
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MOP008	Theoretical Computation of the Polarization Characteristics of an X-Ray Free-Electron Laser with Planar Undulator	FEL, electron, radiation, polarization	38
	G. Geloni XFEL. EU, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λ_w²/(4 pi L_g)², where λ_w is the length of the undulator period and L_g is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λ_w³/(4 pi L_g)³ and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.
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MOP009	Efficient Electron Sources of Coherent Spontaneous Radiation with Combined Helical and Uniform Magnetic Fields	electron, radiation, solenoid, simulation	43
	N. Balal, V.L. Bratman, E. Magori Ariel University, Ariel, Israel V.L. Bratman IAP/RAS, Nizhny Novgorod, Russia
	We discuss two methods to mitigate repulsion of particles in dense electron bunches from photo-injectors and to enhance the power of terahertz radiation. First, the repulsion may be reduced with both very short bunches and undulator periods, reducing the length of a radiation section. According to simulations bunches with duration (50-100) fs, charge (50-200) pC, and energy 6 MeV could fairly effectively radiate at frequencies up to (10-20) THz. The undulator for such a source can be formed by means of redistribution of a solenoid field by a non-magnetized iron helix and a permanently magnetized helix. The second source is based on an idea proposed by A.V. Savilov for electron bunching under conditions when the cyclotron electron frequency is larger than the undulator frequency, and an increase of particle energy in the bunch Coulomb field leads to a decrease in longitudinal momentum and attraction of particles (this effect is analogous to the cyclotron negative-mass instability). A large value of the required uniform field can be used to easily obtain the needed undulator field by placing a simple iron helix inside a pulsed solenoid. Simulations confirm that the corresponding particle attraction can provide a powerful and narrowband radiation at the frequencies (1-3) THz.
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MOP011	Status of CLARA, a New FEL Test Facility	FEL, laser, electron, gun	49
	J.A. Clarke, D. Angal-Kalinin, A.D. Brynes, R.K. Buckley, S.R. Buckley, L.S. Cowie, D.J. Dunning, B.D. Fell, P. Goudket, A.R. Goulden, P.C. Hornickel, F. Jackson, S.P. Jamison, J.K. Jones, K.B. Marinov, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, M.D. Roper, L.K. Rudge, Y.M. Saveliev, B.J.A. Shepherd, 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.B. Appleby, K. Hanahoe, O. Mete Apsimon, H.L. Owen, G.X. Xia UMAN, Manchester, United Kingdom P. Atkinson, N. Bliss, R.J. Cash, N.A. Collomb, G. Cox, G.P. Diakun, S. Dobson, A. Gallagher, S.A. Griffiths, C. Hill, C. Hodgkinson, D.M.P. Holland, T.J. Jones, B.G. Martlew, J. Williams STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom R. Bartolini, I.P.S. Martin DLS, Oxfordshire, United Kingdom S.T. Boogert, E. Yamakawa Royal Holloway, University of London, Surrey, United Kingdom G. Burt, P.N. Ratoff Lancaster University, Lancaster, United Kingdom L.T. Campbell, A.J.T. Colin, J. Henderson, B. Hidding, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom A.M. Kolano University of Huddersfield, Huddersfield, United Kingdom A. Lyapin JAI, Egham, Surrey, United Kingdom V.V. Paramonov, A.K. Skasyrskaya RAS/INR, Moscow, Russia J.D.A. Smith TXUK, Warrington, United Kingdom S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom Y. Wei, C.P. Welsch, A. Wolski The University of Liverpool, Liverpool, United Kingdom
	CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK. The main motivation for CLARA is to test new FEL schemes that can later be implemented on existing and future short wavelength FELs. Particular focus will be on ultra-short pulse generation, pulse stability, and synchronisation with external sources. The project is now underway and the Front End section (photoinjector and first linac) installation will begin later this year. This paper will discuss the progress with the Front End assembly and also highlighting other topics which are currently receiving significant attention.
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MOP012	Present Status of Source Development Station at UVSOR-III	laser, radiation, experiment, electron	54
	N.S. Mirian, K. Hayashi, M. Katoh, J. Yamazaki UVSOR, Okazaki, Japan M. Hosaka, Y. Takashima Nagoya University, Nagoya, Japan T. Konomi, N. Yamamoto KEK, Ibaraki, Japan H. Zen Kyoto University, Kyoto, Japan
	Construction and development of a source development station are in progress at UVSOR-III, a 750 MeV electron storage ring. It is equipped with an optical klystron type undulator system, a mode lock Ti:Sa Laser system, a dedicated beam-line for visible-VUV radiation and a parasitic beam-line for THz radiation. New light port to extract edge radiation was constructed recently. An optical cavity for a resonator free electron laser is currently being reconstructed. Some experiments such as coherent THz radiation, coherent harmonic radiation, laser Compton Scattering gamma-rays and optical vortices are in progress.
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MOP017	Beam Commissioning Plan for the SwissFEL Hard-X-Ray Facility	linac, electron, FEL, operation	69
	T. Schietinger PSI, Villigen PSI, Switzerland
	The SwissFEL facility currently being assembled at the Paul Scherrer Institute is designed to provide FEL radiation in the photon wavelength range between 0.1 and 7 nm. The commissioning of the first phase, comprising the electron injector, the main electron linear accelerator and the first undulator line, named Aramis and dedicated to the production of hard X-rays, is planned for the years 2016 and 2017. We present an overview of the beam commissioning plan elaborated in accordance with the installation schedule to bring into operation the various subsystems and establish beam parameters compatible with first pilot user experiments in late 2017.
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MOP044	A Laser Heater for CLARA	laser, electron, FEL, linac	129
	S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom B.D. Muratori, N. Thompson, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	CLARA is a new FEL test facility, being developed at STFC Daresbury Laboratory in UK, based on a high brightness electron linac. The electron beam of CLARA can potentially be affected by the longitudinal microbunching instability leading to a degradation of the beam quality. The inclusion of a laser heater in the linac design can allow control of the microbunching instability, the study of microbunching and deliberate increase of the final energy spread to study energy spread requirements of the FEL schemes tested at CLARA. We present the initial design and layout of the laser heater system for CLARA and its expected performance.
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MOP049	Design, Development and Test of the Magnets for PAL-XFEL	quadrupole, dipole, multipole, status	139
	H.S. Suh, M.-H. Cho, S.-H. Jeong, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park PAL, Pohang, Kyungbuk, Republic of Korea
	PAL-XFEL is now being constructed with the goal of 0.1 nm hard X-ray in Pohang, Korea. As the first phase we will construct 10 GeV linac, one hard X-ray and one soft X-ray beamlines which require 6 different families of 55 dipole magnets, 11 families of 209 quadrupole magnets, and 3 families of 48 corrector magnets. We have designed these magnets with considering the efficient production and the proper power supplies. This paper describes an outline of the design and test results of the magnets until now.
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MOP055	The Effect of Wakefields on the FEL Performance	emittance, wakefield, linac, FEL	161
	A. Novokhatski, F.-J. Decker, Y. Nosochkov, M.K. Sullivan SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515. If a beam travels near collimator jaws or other discontinuities of the beam pipe, it gets the energy loss and the transverse kick due to the back reaction of the beam field diffracted on the collimator's jaws. The wake field effect from collimators may not only bring an additional energy jitter and change the trajectory of the beam, but may also lead to degradation of the performance of Free Electron Laser (FEL) It may be possible due to the special character of the wake fields: the response reaction depends on the longitudinal position of the particles in the bunch. We describe a model of the wake field radiation, simulation results and comparison with measurements.
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MOP068	First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators	radiation, electron, resonance, FEL	196
	N.S. Mirian UVSOR, Okazaki, Japan E. Salehi AUT, Tehran, Iran
	This report deals with self amplified spontaneous emission free electron laser (FEL) amplifier where the FEL emission is obtained from displaced phase combined undulators. Magnetic field of this adjustment methods in three dimensions is presented. The electron dynamics is investigated. The simulation method and results are explained. The radiation properties of the fundamental resonance and third harmonic through the phase combined undulators are compared with the normal undulator with the same undulator deflection parameter
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MOP070	Harmonic Generation in Two Orthogonal Undulators	polarization, electron, radiation, simulation	200
	N.S. Mirian UVSOR, Okazaki, Japan
	In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.
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MOP071	Carrier-Envelope-Phase Stable Linearly and Circularly Polarized Attosecond Pulse Sources	laser, electron, radiation, simulation	205
	Z. Tibai, G. Almási, Zs. Csiha-Nagy, J.A. Fülöp, J. Hebling University of Pecs, Pécs, Hungary J.A. Fülöp, Gy. Tóth MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary
	Recently, we proposed a robust method for producing waveform-controlled attosecond pulses in the EUV spectral range.* In our scheme the relativistic electron beam, provided by a LINAC, is sent through a modulator undulator where a TW-power laser beam is superimposed on it in order to generate nanobunches. The nanobunched electron beam passes through a single- or few-period radiator undulator (RU). The waveform of the generated attosecond pulses closely resembles the longitudinal distribution of the magnetic field. According to our calculations, at 20 nm (60 nm) wavelength carrier-envelope-phase (CEP) stable pulses with 23 nJ (80 nJ) energy, 80 as (240 as) duration, and 31 mrad (13 mrad) CEP fluctuation (standard deviation) can be achieved at K=0.5. More than 500 nJ energy is predicted at longer wavelengths and larger K. The energy fluctuation of the EUV pulse is 2.5 times higher than that of the laser. By using a helical RU, even circularly polarized attosecond pulses with 30/300 nJ energy can be generated, depending on the wavelength. To the best of our knowledge, no other presently available technique enables the generation of arbitrary-waveform, CEP-controlled attosecond pulses. The predicted pulse energies are sufficiently high to be used as pump pulses in attosecond pump-probe measurements. * Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014).
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MOP076	Free-Electron Laser Driven by a 500 MeV Laser Plasma Accelerator Beam	FEL, laser, emittance, plasma	217
	W. Qin, J.E. Chen, S. Huang, K.X. Liu, X.Q. Yan, L. Zeng PKU, Beijing, People's Republic of China Y. Ding, Z. Huang SLAC, Menlo Park, California, USA
	A laser plasma accelerator is under construction at Peking University and several hundred MeV electron beams are expected. In this paper we discuss applying a 500 MeV beam with 1% relative energy spread to FEL. Bunch decompression method is considered to deal with the large energy spread of the beam. Emittance growth induced by large divergence and energy spread in electron beam transport has been treated with the chromatic matching manipulation. Simulation shows that 100 MW level, 6.3 fs , 0.008 bandwidth output can be obtained for 30 nm FEL. TGU method with assumed matched beam is also discussed as a comparison.
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MOP078	Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam	electron, radiation, simulation, wiggler	221
	R. Ianconescu Shenkar College of Engineering and Design, Ramat Gan, Israel A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel E. Hemsing, A. Marinelli SLAC, Menlo Park, California, USA A. Nause UCLA, Los Angeles, USA
	Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF) The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1]. [1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015) [2] E. Allaria et al., Nat. Photonics 7, 913 (2013) [3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)
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MOP079	On the Importance of Electron Beam Brightness in High Gain Free Electron Lasers	FEL, electron, emittance, brightness	227
	S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Linear accelerators delivering high brightness electron beams are essential for driving short wavelength, high gain free-electron lasers (FELs). The FEL radiation output efficiency is often parametrized through the power gain length that relates FEL performance to the electron beam quality at the undulator. Experimental data and simulation results of existing and planned FEL facilities are used to explicit the relationship between the FEL output wavelength and the electron beam six-dimensional brightness. Practical formulas are provided that show the dependence of the exponential gain length on the beam brightness. S. Di Mitri, M. Cornacchia, Phys. Reports, 539 (2014) 1~48. ** S. Di Mitri, Photonics, 2 (2015) 317~341
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MOP081	Generating a Single-Spike SASE Pulse in the Soft X-Ray Regime by Velocity Bunching	FEL, radiation, electron, linac	233
	J. Lee, B.H. Oh, M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	A bright ultrashort X-ray pulse emerges as a valuable tool for many fields of research nowadays. The single-spike operation of X-ray FEL is one way of making a bright ultrashort X-ray pulse. It requires extreme bunching and a magnetic chicane is a conventional compressor. In a low charge range, a magnetic chicane can be replaced by the velocity bunching technique. In this paper, we present the result of particle tracking simulation generating a single-spike soft X-ray SASE pulse without a magnetic chicane. We also investigate the error effects and show that this scheme is feasible under current technology.
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MOP082	New Soft X-Ray Undulator Line Using 10 GeV Electron Beam in PAL-XFEL	photon, electron, linac, simulation	237
	C.H. Shim, I.S. Ko POSTECH, Pohang, Kyungbuk, Republic of Korea Y.W. Parc PAL, Pohang, Kyungbuk, Republic of Korea
	PAL-XFEL is designed to have five undulator lines and only two undulator lines, the HXR undulator line with 10 GeV electron beam and the SXR undulator line with 3.15 GeV electron beam, will be installed during phase I. A photon beam energy from 0.28 to 1.24 keV will be provided at the SXR undulator line and different range from 2 to 20 keV will be supplied at the HXR undulator line. According to existing schedule, however, photon beam energy from 1.24 to 2 keV won't be provided in PAL-XFEL. In this research, new soft X-ray undulator line for PAL-XFEL using 10 GeV electron beam in main linac is proposed to cover the vacant photon energy. Four candidates are evaluated by estimating and comparing FEL performances using Ming Xie's formula.
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MOP083	FEL Operation Modes of the MAX IV Short Pulse Facility	electron, radiation, simulation, FEL	241
	A. Mak, F. Curbis, S. Werin MAX-lab, Lund, Sweden
	The Short Pulse Facility (SPF) of the MAX IV Laboratory in Lund, Sweden features the production of ultrashort, incoherent x-ray pulses. It is driven by a 3-GeV linac and comprises two 5-metre undulator modules. While the SPF is designed for spontaneous radiation, we explore alternative operation modes in which the SPF functions as a simple free-electron laser (FEL). In this article, we characterize two of them in time-dependent numerical simulations. We perform a sensitivity study on the electron beam parameters and examine the technique of single-step tapering.
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MOP084	Seeded FEL Study for the Cascaded HGHG option for FLASH2	FEL, simulation, radiation, electron	246
	G. Feng, W. Decking, M. Dohlus, T. Limberg, I. Zagorodnov DESY, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany T. Plath Uni HH, Hamburg, Germany
	The free electron laser (FEL) facility at DESY in Hamburg (FLASH) is the world's first FEL user facility which can produce extreme ultraviolet (XUV) and soft X-ray photons. In order to increase beam time delivered to users, a major upgrade named FLASH II is in progress. As a possibility, a seeding undulator section can be installed between the extraction arc section and the SASE undulator of FLASH2. In this paper, a possible seeding scheme for the cascaded HGHG option for FLASH2 is given. The SASE undulator can be used as the second radiator of the cascaded HGHG. Parameters optimization for the accelerating modules and the bunch compressors has been done to meet the requirement of the electron bunches. In the beam dynamics simulation, collective effects were taken into account. Particle distribution generated from the beam dynamics simulation was used for the seeded FEL study. Space charge and CSR impacts on the microbunches were taken into account during the seeded FEL simulation. The simulation results show that FEL radiation with the wavelength of a few nms and with high monochromaticity can be seeded at FLASH2.
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MOP085	Scheme to Increase the Output Average Spectral Flux of the European XFEL at 14.4 keV	FEL, electron, photon, scattering	251
	V. Kocharyan, E. Saldin DESY, Hamburg, Germany G. Geloni XFEL. EU, Hamburg, Germany
	Inelastic X-ray scattering and nuclear resonance scattering are limited by the photon flux available at SR sources, up to 10¹⁰ ph/s/meV at 14.4 keV. A thousand-fold increase may be obtained by exploiting high repetition rate self-seeded pulses at the European XFEL. We report on a feasibility study for an optimized configuration of the SASE2 beamline combining self-seeding and undulator tapering at 14.4 keV. One should perform monochromatization at 7.2 keV by self-seeding, and amplify the seed in the first part of the output undulator. Before saturation, the electron beam is considerably bunched at the 2nd harmonic. A second part of the output undulator tuned to 14.4 keV can thus be used to obtain saturation at this energy. One can further prolong the exchange of energy between the photon and the electron beam by tapering the last part of the output undulator. Start-to-end simulations demonstrate that self-seeding, combined with undulator tapering, allows one to achieve more than a hundred-fold increase in average spectral flux compared with the nominal SASE regime at saturation, resulting in a spectral flux of order 10¹³ ph/s/meV. A more detailed description of this study can be found in. G. Geloni, V. Kocharyan and E.~Saldin, "Scheme to increase the output average spectral flux of the European XFEL at 14.4 keV", DESY 15-141 (2015).
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MOP086	Novel Opportunities for Sub-meV Inelastic X-Ray Scattering Experiments at High-Repetition Rate Self-seeded XFELs	radiation, photon, optics, scattering	257
	O.V. Chubar BNL, Upton, Long Island, New York, USA G. Geloni, A. Madsen XFEL. EU, Hamburg, Germany V. Kocharyan, E. Saldin, S. Serkez DESY, Hamburg, Germany Yu. Shvyd'ko ANL, Argonne, Ilinois, USA J. Sutter DLS, Oxfordshire, United Kingdom
	Inelastic x-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25/nm spectral and momentum Transfer resolutions, respectively. However, further improvements down to 0.1 meV and 0.02/nm are required to close the gap in energy-momentum space between high and low frequency probes. We Show that this goal can be achieved by further improvements in x-ray optics and by increasing the spectral flux of the incident x-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE2 beamline of the European XFEL promises up to a hundred-fold increase in average spectral flux compared to nominal SASE pulses at saturation, or three orders of magnitude more than possible with storage-ring based radiation sources. Wave-optics propagation shows that about 7·10¹² ph/s in a 90-microeV bandwidth can be achieved on the sample. This will provide unique new possibilities for IXS. Extended information about our work can be found in. Y. Shvyd'ko et al., Nature Communications 5:4219 (2014). ** O. Chubar et al., ‘Novel opportunities for sub-meV inelastic X-ray scattering at high-repetition rate self-seeded X-ray free-electron lasers', http://arxiv.org/abs/1508.02632, DESY 15-140, (2015).
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TUA02	Suppression of FEL Lasing by a Seeded Microbunching Instability	electron, laser, FEL, photon	289
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school GRK1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brightness electron bunches driving free-electron lasers (FELs). In this contribution, we demonstrate suppression of FEL lasing induced by a laser-triggered microbunching instability at the free-electron laser FLASH. The interaction between the electron bunches and the 800-nm laser pulses takes place in an undulator upstream of the FEL undulators. A significant decrease of XUV photon pulse energies has been observed in coincidence with the laser-electron overlap in the modulator. We discuss the underlying mechanisms based on longitudinal space charge amplification (LSCA) [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.
	Slides TUA02 [14.298 MB]
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TUA03	Multi-beamline Operation Test at SACLA	electron, operation, kicker, laser	293
	T. Hara, T. Inagaki, R. Kinjo, C. Kondo, Y. Otake, H. Takebe, H. Tanaka, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan K. Fukami JASRI/SPring-8, Hyogo-ken, Japan
	A new undulator beamline (BL2) was installed in September 2014 at SACLA. Following the installation of this second beamline, a DC switching magnet was replaced by a kicker magnet and a DC septum magnet for bunch-to-bunch multi-beamline operation. The commissioning of the new beamline and bunch-to-bunch operation was started early this year. Since SACLA has been operated with much higher peak currents around 10 kA compared to its original design value of 3 kA, the CSR effect in the beam transport line to BL2, where the electron beam is deflected twice by 3 degree, turns out to be non-negligible. BL2 is currently operated with reduced peak currents and the photon pulse energies of 100-150 μJ are obtained with increased undulator K-values around 2.6-2.85. Although the photon pulse energies of BL2 are still smaller than those of the existing beamline (BL3), the expected stability of the electron beam orbit after the bunch-to-bunch BL switching was achieved and simultaneous lasing at the two beamlines was demonstrated with 8 GeV electron beams. We will report the status and operational issues related to the multi-beamline operation at SACLA.
	Slides TUA03 [7.095 MB]
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TUA04	First Simultaneous Operation of Two Sase Beamlines in FLASH	photon, operation, electron, FEL	297
	M. Scholz, B. Faatz, S. Schreiber, J. Zemella DESY, Hamburg, Germany
	FLASH2, the second undulator beamline of the FLASH FEL user facility at DESY (Hamburg, Germany) is under commissioning. Its first lasing was achieved in August 2014. FLASH is the first soft X-ray FEL operating two undulator beamlines simultaneously. Both undulator beamlines are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. Fast kickers and a septum are installed to distribute one part of the electron bunch train to FLASH1 and the other part to FLASH2 with full repetition rate. The commissioning of FLASH2 takes place primarily in parallel to FLASH1 user operation. Various beam optics measurements has been carried out in order to ensure the required electron beam quality for efficient SASE generation. This paper reports the status of the FLASH2 commissioning.
	Slides TUA04 [9.655 MB]
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TUB02	Distributed Seeding for Narrow-band X-ray Free-Electron Lasers	radiation, electron, FEL, simulation	301
	D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner LANL, Los Alamos, New Mexico, USA
	Funding: We thank Bruce Carlsten, John Lewellen, Steve Russell, and Rich Sheffield (LANL), Craig Ogata and Yuri Shvyd'ko (ANL) for helpful discussion, and the MaRIE project for financial support. The MaRIE XFEL is the proposed XFEL driven by a 12-GeV electron beam to generate coherent 42-keV photons based on a new seeding technique called distributed seeding (DS). This paper presents details of the distributed seeding technique using Si(111) Bragg crystals as the spectral filters. DS differs from self-seeding in three important aspects. First, DS relies on spectral filtering of the undulator radiation at more than one location early in the exponential gain curve. This leads to an FEL output that is dominated by the coherent seed signal, not SASE noise. Secondly, DS affords the ability to select a wavelength longer than the peak of the SASE gain curve, which leads to improved spectral contrast of the seeded FEL over the SASE background. Lastly, the power growth curves in successive DS stages exhibit the behavior of an FEL amplifier, i.e. a lethargy region followed by the exponential growth region. This behavior results in FEL output pulses that are less spiky than the SASE pulses. Using 3D Genesis simulations, we show that DS with two filters provides a 12X enhancement in spectral brightness relative to SASE and that DS with three filters produces negligible SASE background. The DS FEL spectrum has a relative spectral bandwidth (FWHM) of 8 X 10^-5 with about 9 spectral modes.
	Slides TUB02 [1.241 MB]
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TUP001	THz Photo-Injector FEM Based on Spontaneous Coherent Emission from a Bunch of Negative-Mass Electrons	electron, radiation, cyclotron, simulation	317
	A.V. Savilov, I.V. Bandurkin IAP/RAS, Nizhny Novgorod, Russia
	The use of short dense electron bunches produced form a photo-injector gun is attractive for realization of a THz FEL based on spontaneous coherent emission from such bunches. This type of emission is realized, when the axial length of bunches is shorter that the wavelength of the radiated wave. Therefore, the length of the operating region of such a FEL is strictly limited by degradation (an increase in the axial size) of the e-bunch caused by both the Coulomb repulsion and the velocity spread. The use of the regime of the 'negative mass' can be a way to provide stabilization of the axial size of e-bunches. Such a regime is realized in a magnetostatic undulator with a guiding homogeneous axial magnetic field. If the electron cyclotron frequency (corresponding to the guiding magnetic field) exceeds the bounce-frequency of electron oscillations in the periodic undulator field, then the abnormal dependence of the axial velocity of electrons on their energy takes place (an increase in the energy leads to a decrease in the axial velocity). In such regime, axial Coulomb repulsion of the electrons leads to their mutual attraction which slows down bunch degradation. The use of this regime results in a substantial increase in the length of the spontaneous coherent emission, and, therefore, in an increase in both the duration and the power of the output radiation pulse. The work was supported by the Russian Scientific Foundation (RSCF), Project no. 14-19-01723
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TUP002	Further Studies of Undulator Tapering in X-Ray FELs	simulation, electron, radiation, laser	321
	A. Mak, F. Curbis, S. Werin MAX-lab, Lund, Sweden
	We further the studies of the model-based optimization of tapered free-electron lasers presented in a recent publication [Phys. Rev. ST Accel. Beams 18, 040702 (2015)]. Departing from the ideal case, wherein the taper profile is a smooth and continuous function, we consider the more realistic case, with individual undulator segments separated by break sections. Using the simulation code GENESIS, we apply our taper optimization method to a case, which closely resembles the FLASH2 facility in Hamburg, Germany. By comparing steady-state and time-dependent simulations, we examine how time-dependent effects alter the optimal taper scenario. From the simulation results, we also deduce that the "traditional" empirical method, whereby the intermediate radiation power is maximized after closing every undulator gap, does not necessarily produce the highest final power at the exit of the undulator line.
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TUP004	Three-dimensional, Time-dependent Simulation of Free-Electron Lasers	simulation, electron, FEL, experiment	331
	P.J.M. van der Slot Mesa+, Enschede, The Netherlands H. Freund, P.J.M. van der Slot CSU, Fort Collins, Colorado, USA
	Minerva is a simulation code that models the interaction of electrons with an optical field inside an undulator. Minerva uses a modal expansion for the optical field and the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to mode, for example, FEL oscillators. As there exists a large variety of FELs ranging from long-wavelength oscillators to soft and hard X-ray FELs that are either seeded or starting from noise, a simulation code, such as Minerva, should be capable of modelling this huge variety of FEL configurations. Here we present a validation of the Minerva code against experimental data for various FEL configurations, ranging from long wavelength FEL oscillators to hard X-ray SASE FEL.
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TUP006	Quantum Nature of Electrons in Classical X-ray FELs	FEL, electron, radiation, laser	338
	P.M. Anisimov LANL, Los Alamos, New Mexico, USA
	X-ray FELs built to date are well described by the classical theory. This theory in its simplest form is expressed as a system of pendulum equations for electrons coupled to the electromagnetic field. The FEL interaction requires bunching of the electrons on a scale less than radiation wavelength. The progress in the development of FELs and the need to reach even shorter laser radiation wavelength with low energy electrons require that the quantum characteristic of the FEL interaction to be properly considered. Quantum theories have been already proposed by a number of authors. These theories, however, have been developed for regimes that are not relevant for modern/planned X-ray FELs. Here, we focus on quantum effects in modern/future X-ray FELs and stop treating an electron as a point-particle. This results in quantum reduction of the bunching! Starting with the analysis of the free space dispersion for the electron wave packet, we will present a modified 1D FEL theory that takes into account the quantum uncertainty of the electron position in X-ray FELs. This theory allows for a unified classification of FELs with respect to the wave nature of an electron that shows a planned FEL at Los Alamos National Lab to be most affected. The Genesis simulation code has been modified in order to include quantum reduction of the bunching that lead to interesting results. LA-UR-15-26276
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TUP007	High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II	electron, FEL, simulation, emittance	342
	G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, California, USA J. Qiang, M. Venturini LBNL, Berkeley, California, USA
	High fidelity numerical particle simulations that leverage a number of accelerator and FEL codes have been used to analyze the LCLS-II FEL performance. Together, the physics models that are included in these codes have been crucial in identifying, understanding, and mitigating a number of potential hazards that can adversely affect the FEL performance, some of which are discussed in papers submitted to this conference[, ]. Here, we present a broad overview of the LCLS-II FEL performance, based on these start-to-end simulations, for both the soft X-ray and hard X-ray undulators including both SASE and self-seeded operational modes. M. Venturini, et al., The microbunching instability and LCLS-II lattice design: lessons learned, FEL'15 ** Z. Zhang, et al., Microbunching-induced sidebands in a seeded free-electron laser, FEL'15
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TUP008	High-Gain FEL in the Space-Charge Dominated Raman Limit	FEL, space-charge, electron, simulation	347
	I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig UCLA, Los Angeles, USA
	While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.
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TUP011	Performance and Tolerance Studies of the X-Ray Production for the X-Band FEL Collaboration	simulation, electron, FEL, operation	359
	J. Pfingstner, E. Adli University of Oslo, Oslo, Norway
	The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied.
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TUP013	The X-Band FEL Collaboration	FEL, linac, electron, emittance	368
	J. Pfingstner, E. Adli University of Oslo, Oslo, Norway A.A. Aksoy, O. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey D. Angal-Kalinin, J.A. Clarke STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C.J. Bocchetta, A.I. Wawrzyniak Solaris, Kraków, Poland M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc, Y.E. Tan, K.P. Wootton, D. Zhu SLSA, Clayton, Australia G. Burt Lancaster University, Lancaster, United Kingdom N. Catalán Lasheras, A. Grudiev, A. Latina, D. Schulte, S. Stapnes, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland A. Charitonidis NTUA, Athens, Greece G. D'Auria, S. Di Mitri, C. Serpico Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy T.J.C. Ekelöf, M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden W. Fang, Q. Gu SINAP, Shanghai, People's Republic of China E.N. Gazis National Technical University of Athens, Athens, Greece X.J.A. Janssen VDL ETG, Eindhoven, The Netherlands Z. Nergiz Nigde University, Nigde, Turkey
	The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. Due to the higher accelerating gradients achievable with X-band technology, a X-band normal conducting linac can be shorter and therefore potentially cost efficient than what is achievable with lower frequency structures. This cost reduction of future FEL facilities addresses the growing demand of the user community for coherent X-rays. The X-band FEL collaboration consists of 12 institutes and universities that jointly work on the preparation of design reports for the specific FEL projects. In this paper, we report on the on-going activities, the basic parameter choice, and the integrated simulation results. We also outline the interest of the X-band FEL collaboration to use the electron linac CALIFES at CERN to test FEL concepts and technologies relevant for the X-band FEL collaboration.
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TUP019	Time Locking Options for the Soft X-Ray Beamline of SwissFEL	laser, FEL, electron, radiation	388
	E. Prat, S. Reiche PSI, Villigen PSI, Switzerland
	SwissFEL is an FEL facility presently under construction at the Paul Scherrer institute that will serve two beamlines: Aramis, a hard X-ray beamline which is in construction phase and will provide FEL radiation in 2017 with a wavelength between 0.1 and 0.7 nm; and Athos, a soft X-ray beamline which is in design phase and it is expected to offer FEL light in 2021 for radiation wavelengths between 0.7 and 7 nm. A passive synchronization of the FEL signal to a laser source is fundamental for key experiments at Athos, such as the time-resolved resonant inelastic X-ray scattering (RIXS) experiments. In this paper we explore different options to achieve this time synchronization by means of energy modulating the electron beam with an external laser.
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TUP020	Recent Study in iSASE	FEL, electron, distributed, laser	393
	K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA C. Emma, C. Pellegrini UCLA, Los Angeles, USA S. Hsu University of California, San Diego (UCSD), La Jolla, California, USA
	The Improved Self-Amplified Spontaneous Radiation (iSASE) scheme has potential to reduce SASE FEL bandwidth. This is achieved by repeatedly delaying the electrons with respect to the radiation pulse using phase shifters in the undulator break sections. It has been shown that the strength, locations and sequences of phase shifters are important to the iSASE performance. Particle swarm optimization algorithm is used to explore the phase shifters configuration space globally.
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TUP021	Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability	FEL, radiation, emittance, electron	397
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	The radiation from SASE FEL has always limited value of the degree of transverse coherence. Two effects define the spatial coherence of the radiation: the mode competition effect, and the effect of poor longitudinal coherence. For the diffraction limited case we deal mainly with the effect of the poor longitudinal coherence leading to significant degradation of the spatial coherence in the post-saturation regime. When transverse size of the electron beam significantly exceeds diffraction limit, the mode competition effect does not provide the selection of the fundamental FEL mode, and spatial coherence degrades due to contribution of the higher azimuthal modes. Another consequence of this effect are fluctuations of the spot size and pointing stability of the photon beam. These fluctuations are fundamental and originate from the shot noise in the electron beam. The effect of pointing instability becomes more pronouncing for shorter wavelengths. Our study is devoted to the fundamental analysis of the effect and description of possible means for improving the degree of transverse coherence and the pointing stability.
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TUP023	A Modified Self-Seeded X-ray FEL Scheme Towards Shorter Wavelengths	FEL, laser, electron, radiation	409
	L. Zeng, J.E. Chen, S. Huang, K.X. Liu, W. Qin PKU, Beijing, People's Republic of China Y. Ding, Z. Huang, G. Marcus SLAC, Menlo Park, California, USA
	We present a modified self-seeded FEL scheme for harmonic generation. Different from classical HGHG scheme whose seed laser is a conventional laser with longer wavelength, this scheme first uses a regular self-seeding monochromator to generate a seed laser, followed by a HGHG configuration to produce shorter-wavelength radiations. As an example, we perform start-to-end simulations to demonstrate the second and third harmonic FELs from a soft x-ray self-seeding case at the fundumental wavelength of 1.72 nm. The harmonic performance results will be discussed.
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TUP025	Studies of Undulator Tapering for the CLARA FEL	FEL, electron, laser, brightness	412
	I.P.S. Martin, R. Bartolini DLS, Oxfordshire, United Kingdom R. Bartolini JAI, Oxford, United Kingdom D.J. Dunning, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Undulator tapering is a well-known method for enhancing the performance of free-electron lasers [1]. It works by keeping the resonant wavelength constant, despite variation in the electron beam energy. Both the energy-extraction efficiency and the spectral brightness of the FEL can be improved using this technique. In this paper we present recent studies of undulator tapering for the CLARA FEL in both SASE and seeded modes. The methods used to optimise the taper profile are described, and the properties of the final FEL pulses are compared. [1] N.M. Kroll, P.L. Morton, M.N. Rosenbluth, J. Quantum Electronics 17, 8 (1981).
	Poster TUP025 [0.919 MB]
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TUP026	Measurment Uncertainties in Gas-Based Monitors for High Repetition Rate X-Ray FEL Operations	FEL, simulation, detector, linac	417
	Y. Feng, M.L. Campell, J. Krzywinski, E. Ortiz, T.O. Raubenheimer, M. Rowen, D.W. Schafer SLAC, Menlo Park, California, USA
	Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University. Thermodynamic simulations using a finite difference method were carried out to investigate the measurement uncertainties in gas-based X-ray FEL diagnostic monitors under high repetition rate operations such as planned for the future LCLS-II soft and hard X-ray FEL's. For monitors using relatively high gas pressures for obtaining sufficient signals, the absorbed thermal power becomes non-negligible as repetition rate increases while keeping pulse energy constant. The fluctuations in the absorbed power were shown to induce significant measurements uncertainties, especially in the single-pulse mode. The magnitude of this thermal effect depends nonlinearly on the absorbed power and can be minimized by using a more efficient detection scheme in which the gas pressure can be set sufficiently low
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TUP027	Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA	laser, radiation, electron, focusing	422
	B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer SLAC, Menlo Park, California, USA D. Xiang Shanghai Jiao Tong University, Shanghai, People's Republic of China
	The Echo program currently underway at SLAC's NLCTA test accelerator aims to use Echo-Enabled Harmonic Generation (EEHG) to produce considerable bunching in the electron beam at high harmonics of a 2.4um seed laser. The production of such high harmonics in the EUV wavelength range necessitates an efficient radiator and associated light diagnostics to accurately characterize and tune the echo effect. We have installed and commissioned the Visible to Infrared SASE Amplifier (VISA) undulator, a strong focusing two meter long planar undulator of Halbach array design with 1.8cm period length. To characterize the output radiation, we have designed, built, and calibrated a grazing incidence EUV spectrometer which operates between 12-120nm with resolution sufficient to resolve individual harmonics. An absolute wavelength calibration is achieved by using both EEHG and High Gain Harmonic Generation (HGHG) signals from the undulator.
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TUP028	DESIGN OF THE MID-INFRARED FEL OSCILLATOR IN CHINA	FEL, electron, cavity, laser	427
	H.T. Li, Q.K. Jia, L. Wang, S.C. Zhang USTC/NSRL, Hefei, Anhui, People's Republic of China
	In 2014, Xiamen University and other three research organizations received the approval to realize an infrared free electron laser (IR-FEL) for fundamental of energy chemistry. The IR-FEL covers the spectral range of 2.5-200 μm and will be built in NSRL. Two FEL oscillators driven by one Linac will be used to generate mid- infrared and far-infrared lasers. In this article we describe the design studies for the mid-infrared FEL oscillator.
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TUP030	Time Dependent Study for an X-ray FEL Oscillator at LCLS-II	cavity, electron, photon, free-electron-laser	433
	J. Zemella DESY, Hamburg, Germany W.M. Fawley, T.J. Maxwell SLAC, Menlo Park, California, USA R.R. Lindberg ANL, Argonne, Illinois, USA
	The LCLS-II with its high repetition rate and high quality beam will be capable of driving an X-ray free electron laser oscillator at higher harmonics in the hard X-ray regime (0.1 nm). The oscillator consists of a low loss X-ray crystal cavity using diamond Bragg crystals with meV bandwidth. The expected average spectral flux has been estimated to be at least two orders of magnitude greater than present synchrotron-based sources with highly stable, coherent pulses of duration 1 ps or less for applications in Mössbauer spectroscopy and inelastic x-ray scattering. A more detailed study of the start up of a fifth-harmonic X-ray FEL oscillator at LCLS-II will be presented with full, time-dependent simulations.
	Poster TUP030 [0.619 MB]
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TUP032	Numerical Studies of the Influence of the Electron Bunch Arrival Time Jitter on the Gain Process of an XFEL-Oscillator for the European XFEL	electron, simulation, radiation, FEL	436
	C.P. Maag, J. Zemella DESY, Hamburg, Germany J. Roßbach Uni HH, Hamburg, Germany
	The superconducting linac of the European XFEL Laboratory in Hamburg will produce electron bunch trains with a time structure that allow in principle the operation of an XFELO (X-ray FEL-Oscillator). The electron bunches of the European XFEL have an expected length between 2 and 180 fs (FWHM) with an expected arrival time jitter of about 30 fs (RMS). A jitter of the electron bunch arrival time leads to a detuning between the electron and photon pulse. Since an XFEL-Oscillator relies on a spatial overlap of electron and photon pulse, the influence of a lack of longitudinal overlap is studied. The simulations are performed for different bunch lengths and levels of arrival time jitter. The results of a simulation are presented where angular, transversal and arrival time jitter are taken into account simultaneously, assuming parameters expected for the European XFEL Linac.
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TUP038	Construction of the EU-XFEL Laser Heater	laser, vacuum, electron, ion	452
	M. Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden
	Funding: We thank the Swedish research council under Project number DNR-828-2008-1093 for financial support. Installation of the laser heater for the EU-XFEL is completed and first commissioning runs are imminent. We discuss the installation of the key elements and provide an outlook of the commissioning phase.
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TUP053	Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion	polarization, FEL, radiation, diagnostics	486
	W.M. Fawley, E. Allaria, E. Ferrari Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy
	Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators. [1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013). [2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014).
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TUP057	The Highly Adjustable Magnet Undulator	simulation, electron, permanent-magnet, radiation	499
	M. Hamberg Uppsala University, Uppsala, Sweden
	The highly adjustable magnet undulator is a concept aiming for flexibility and extensive tunability of undulator settings in the linear as well as the helical regime. I report about suggested layout, magnetic simulations.
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TUP066	Benchmark of ELEGANT and IMPACT	space-charge, wakefield, linac, optics	505
	L. Wang, P. Emma, T.O. Raubenheimer SLAC, Menlo Park, California, USA J. Qiang LBNL, Berkeley, California, USA
	The beam dynamics codes ELEGANT and IMAPCT have many users. We use these two codes for the design of LCLSII. Both codes use a 1D model for the coherent synchrotron radiation (CSR) in bend magnets. In addition, IMPACT has a 3D space-charge model, while ELEGANT uses a 1D model. To compare the two codes, especially the space-charge effects, we systematically benchmark the two codes with different physics aspects: wakefields, CSR and space-charge forces.
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TUP069	THz Based Phase-Space Manipulation in a Guided IFEL	electron, laser, simulation, coupling	519
	E.J. Curry, S. Fabbri, P. Musumeci UCLA, Los Angeles, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
	Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583. We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10^-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude.
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TUP074	Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility	laser, radiation, electron, experiment	540
	N.S. Sudar, J.P. Duris, I.I. Gadjev, P. Musumeci UCLA, Los Angeles, USA M. Babzien, M.G. Fedurin, K. Kusche, I. Pogorelsky, M.N. Polyanskiy, C. Swinson BNL, Upton, Long Island, New York, USA
	Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility.
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WEA03	SwissFEL Status Report	linac, FEL, vacuum, electron	567
	R. Ganter PSI, Villigen PSI, Switzerland
	SwissFEL is a 5.8 GeV linac which sends electron bunches at 100 Hz into a 60 m long in-vacuum undulator line to produce hard X-rays between 0.1 nm and 0.7 nm. The SwissFEL accelerator design is based on a low emittance beam with tight tolerances on RF stability. The first lasing of SwissFEL is planned for early 2017 and two end-stations should then be brought into operation in the same year. The delivery of the SwissFEL building to PSI is planned for fall this year, but some rooms are already completed and currently in use for components assembly. The production of the C-band RF accelerating structures has now reach the nominal rate of 5 structures/month. Two different RF solid state modulator prototypes could demonstrate jitter lower than 20 ppm but stability and reliability tests are still going on. The undulators assembly and measurement sequence have started and 13 undulators are planned to be ready in the tunnel by October 2016. Large series of components like magnets, vacuum systems and mechanical supports are already in house and under assembly. Photonics components for two beamlines and two end stations are ordered and planned to be ready for 2017.
	Slides WEA03 [36.505 MB]
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WEB01	A Two-Color Storage Ring FEL	FEL, electron, cavity, operation	571
	J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA S. Huang PKU, Beijing, People's Republic of China J.Y. Li USTC/NSRL, Hefei, Anhui, People's Republic of China N. Vinokurov BINP SB RAS, Novosibirsk, Russia J. Wu SLAC, Menlo Park, California, USA
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. Using different undulator configurations on the Duke storage ring, we have successfully achieved lasing with a novel two-color storage ring FEL. Using a pair of dual-band FEL mirrors, simultaneous lasing was realized in IR (around 720 nm) and in UV (around 360 nm). With this two-color FEL, we have demonstrated independent wavelength tuning of either IR or UV lasing. With careful tuning, we have also realized harmonic lasing with the UV lasing tuned to the second harmonic of the IR lasing. The tuning of harmonic two-color lasing has also been demonstrated with the locked wavelengths. Furthermore, we have demonstrated good control of the FEL power sharing between the two colors. The two-color FEL has created new opportunities to drive a two-color Compton gamma-ray beam at the High Intensity gamma-ray Source at Duke.
	Slides WEB01 [18.975 MB]
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WEB02	Waveguide THz FEL Oscillators	FEL, injection, electron, extraction	576
	S.V. Miginsky, S. Bae, B.A. Gudkov, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov KAERI, Daejon, Republic of Korea S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	In today's world there is a significant demand for FEL-based THz radiation sources. They have a wide tuning range, a narrow band of radiation, and comparably high peak and average emission power. There are a significant number of these machines in the world, operating or in the development. The main difference between a long-wave FEL, of THz or a millimeter band, and a conventional one is a too big transverse size of the fundamental mode of an open optical resonator. It claims a large gap in an undulator that dramatically decreases its strength. Both factors sorely decrease the amplification and the efficiency, and often make lasing impossible. The main way to solve this problem is to use a waveguide optical resonator. It decreases and controls the transverse size of the fundamental mode. However, the waveguide causes a number of problems: power absorption in its walls; higher modes generation by inhomogeneities, as it is not ideal; electron beam injection into a FEL is more sophisticated; also outcoupling is more complicated; finally, the resonator detuning control claims some special solutions. The waveguide dispersion relation differs from one in the free space. It shifts up the wavelength of the FEL, changes the optimal detuning, and creates a parasitic mode near the critical wavelength of the waveguide. These problems and possible solutions to them are considered.
	Slides WEB02 [20.394 MB]
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WEP001	RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS	radiation, FEL, cavity, gun	583
	J.R. Lewandowski, R.C. Field, A.S. Fisher, H.-D. Nuhn, J.J. Welch SLAC, Menlo Park, California, USA
	Funding: Work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A significant source of radiation signals in the LCLS Undulator have been identified as being generated by dark current emitted from the LCLS RF Photocathode Gun. Radiation damage to magnets over time can lead to degraded performance and significant cost for replacement. A method of using an existing transverse deflector cavity with a modified RF pulse has been tested and shows promise for eliminating the radiation dose from RF gun dark current that is generated in time before and after the production beam pulse. UNDULATOR RADIATION DAMAGE EXPERIENCE AT LCLS: H.-D. Nuhn, C. Field, S. Mao, Y. Levashov, M. Santana, J.N. Welch, Z. Wolf, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, U.S.A
	Poster WEP001 [1.631 MB]
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WEP004	Energy Spread Constraints on Field Suppression in a Reverse Tapered Undulator	laser, FEL, bunching, simulation	597
	J.P. MacArthur, Z. Huang, A.A. Lutman, A. Marinelli, H.-D. Nuhn SLAC, Menlo Park, California, USA
	A 3.2 m variable polarization Delta undulator[1] has been installed at the end of the LCLS undulator line. The Delta undulator acts an an afterburner in this configuration, using bunching from upstream planar undulators to produce radiation with arbitrary polarization. To optimize the degree of polarization from this device, a reverse taper[2] has been proposed to suppress background radiation produced in upstream undulators while still microbunching the beam. Here we extend previous work on free electron lasers with a slowly varying undulator parameter[3] to show there is a strong energy spread dependence to the maximum allowable detune from resonance. At LCLS, this energy spread limitation keeps the reverse taper slope in the slowly varying regime and limits the achievable degree of circular polarization. [1] A. B. Temnykh, PRST-AB, 11, 120702, (2008). [2] E. A. Schneidmiller and M. V. Yurkov, PRST-AB, 16, 110702, (2013). [3] Z. Huang and G. Stupakov, PRST-AB, 8, 040702, (2005).
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WEP005	Laser Heater Transverse Shaping to Improve Microbunching Suppresion for X-ray FELs	laser, electron, FEL, linac	602
	S. Li Stanford University, Stanford, California, USA A.R. Fry, S. Gilevich, Z. Huang, A. Marinelli, D.F. Ratner, J. Robinson SLAC, Menlo Park, California, USA
	In X-ray free electron lasers (FELs), a small amount of initial density or energy modulation in the electron beam will be amplified through acceleration and bunch compression process. The undesired microbunching on the electron bunch will increase slice energy spread and degrade the FEL performance. The Linac Coherent Light Source (LCLS) laser heater (LH) system was installed to increase the uncorrelated energy spread in the electron beam in order to suppress the microbunching instability. The distribution of the induced energy spread depends strongly on the transverse profile of the heater laser and has a large effect on the microbunching suppression. In this paper we discuss strategies to shape the laser profile in order to obtain better suppression of microbunching. We present analysis to achieve the Gaussian-like energy spread using a Laguerre-Gaussian laser mode and study the efficiency and alignment tolerance for implementation.
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WEP008	Four-Dimensional Models of FEL Amplifiers and Oscillators	electron, FEL, simulation, laser	607
	J. Blau, K. R. Cohn, W.B. Colson NPS, Monterey, California, USA
	Funding: This work has been supported by the High Energy Laser Joint Technology Office. New four-dimensional models of free electron lasers (FELs) are described, for both amplifier and oscillator configurations. Model validation and benchmarking results are shown, including comparisons to theoretical formulas and experiments.
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WEP014	LCLS-II: Status of the CW X-ray FEL Upgrade to the LCLS Facility	linac, FEL, gun, electron	618
	T.O. Raubenheimer SLAC, Menlo Park, California, USA
	Funding: Work supported by Department of Energy contract DE-AC02-76SF00515 The LCLS-II is a CW X-ray FEL based on a 4 GeV superconducting RF linac that will upgrade the LCLS facility at the SLAC National Accelerator Laboratory. The upgrade is being constructed by a collaboration including ANL, Cornell, Fermilab, JLab, LBNL, and SLAC. This talk will describe the status of the LCLS-II project as well as the major technical issues and R&D to address them. Presented on behalf of the LCLS-II collaboration
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WEP016	Free Electron Lasers in 2015	FEL, electron, laser, free-electron-laser	625
	K. R. Cohn, J. Blau, W.B. Colson, J.W. Ng, M.J. Price NPS, Monterey, California, USA
	Funding: This work has been supported by the High Energy Laser Joint Technology Office. Thirty-nine years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.
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WEP025	Effect of Microbunching on Seeding Schemes for LCLS-II	laser, electron, radiation, photon	639
	G. Penn, J. Qiang LBNL, Berkeley, California, USA P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, 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. External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.
	Poster WEP025 [0.962 MB]
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WEP029	Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance	laser, FEL, simulation, electron	643
	T. Plath, C. Lechner Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt DESY, Hamburg, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355. To enhance the spectral and temporal properties of a free-electron laser the FEL process can be seeded by an external light field. The quality of this light field strongly influences the final characteristics of the seeded FEL pulse. To push the limits of a seeding experiment and reach the smallest possible wavelengths it is therefore crucial to have a thorough understanding of relations between laser parameters and seeding performance. In this contribution we numerically study the influence of laser wavefront imperfections on high-gain harmonic generation seeding at the seeding experiment at FLASH.
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WEP051	The Prototype of New Variable Period Undulator for Novosibirsk Free Electron Laser.	simulation, permanent-magnet, FEL, electron	677
	I.V. Davidyuk NSU, Novosibirsk, Russia O.A. Shevchenko, V.G. Tcheskidov BINP SB RAS, Novosibirsk, Russia N. Vinokurov KAERI, Daejon, Republic of Korea
	To improve the parameters of the second stage Novosibirsk free electron laser one plans to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles for shorter periods with constant undulator length. Both these advantages will be realized in the new undulator under development in Budker INP. The idea of the permanent-magnet VPU was proposed just several years ago and it has not been properly tested yet. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.
	Poster WEP051 [3.821 MB]
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WEP052	Studies of LCLS FEL Divergence	simulation, electron, photon, quadrupole	681
	J.L. Turner, P. Baxevanis, F.-J. Decker, Y. Ding, Z. Huang, J. Krzywinski, H. Loos, G. Marcus, N.P. Norvell SLAC, Menlo Park, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 Simulations show various impacts on x-ray divergence. With the motivation to maximize intensity at the focus, these beam studies were designed to study parameter space and beam qualities impacting divergence, and therefore aperture related clipping and diffraction. With multiple simultaneous users, beam constraints increase, requiring an improving knowledge of the mechanism of impact of changing parameters. These studies have that goal in order to improve beam control.
	Poster WEP052 [1.010 MB]
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WEP054	Control of Gap Dependent Phase Errors on the Undulator Segments for the European XFEL	laser, electron, free-electron-laser, FEL	685
	Y. Li, J. Pflüger XFEL. EU, Hamburg, Germany
	Strong magnetic forces in long undulators always result in some girder deformation. This problem gets more serious in long gap tuneable undulators. In addition the deformation varies with changing forces at different gaps resulting in gap dependent phase errors. For the undulators for the European XFEL this problem has been studied thoroughly and quantitatively. A compensation method is presented which uses a combination of suitable shims and pole height tuning. It is exemplified by tuning one of the undulator segments for the European XFEL back to specs.
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WEP062	Study on Undulator Radiation from Femtosecond Electron Bunches	electron, radiation, linac, brightness	702
	N. Chaisueb, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand
	Funding: This work has been supported by the CMU Junior Research Fellowship Program, the Department of Physics and Material Science, Faculty of science, Chiang Mai University, and SAST Scholarship. Linac based terahertz (THz) source at the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, consists of a thermionic RF electron gun, an alpha magnet for magnetic bunch compressor, a travelling wave S-band accelerating structure for post acceleration, and various beam diagnostic instruments. The PBP-CMU linac can produce relativistic femtosecond electron bunches, which are used to generate coherent THz radiation via transition radiation technique. To increase the radiation intensity, an electromagnetic undulator will be added in the beam transport line. The designed electromagnetic undulator has 40.5 periods with a period length of 56 mm and a pole gap of 15 mm. Numerical calculation result shows that the brightness of the undulator radiation, which is produced from electron bunches with an energy of 10 MeV, a peak current of 300 A, and an effective bunch length of 120 fs, is about 10 thousand times higher than the brightness of the transition radiation. This study investigates the dependence of the electron beam energy, electron bunch charge, and electron bunch length on the coherent undulator radiation by using the PARMELA code. The numerical simulation and procedure to generate the undulator radiation in the terahertz regime by using femtosecond electron bunches produced at the PBP research facility is reported and discussed in this contribution. The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Material Science and the Graduate School, Chiang Mai University.
	Poster WEP062 [8.172 MB]
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WEP073	Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser	electron, FEL, radiation, plasma	718
	L.T. Campbell USTRAT/SUPA, Glasgow, United Kingdom A.R. Maier CFEL, Hamburg, Germany
	The effect of a correlated linear energy chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate linear taper of the undulator magnetic field have previously been investigated considering relatively small chirps. In the following, it is shown that larger linear energy chirps, such as those found in beams produced by laser-plasma accelerators, exhibit dispersive effects in the undulator, and require a non-linear taper on the undulator field to properly optimise.
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WEP075	Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam	electron, radiation, simulation, FEL	722
	C. Emma, C. Pellegrini UCLA, Los Angeles, USA Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini SLAC, Menlo Park, California, USA
	We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.
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WEP076	Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing	FEL, electron, simulation, extraction	726
	C. Emma UCLA, Los Angeles, USA K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy DE-SC0009983. Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented.
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WEP079	Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs	FEL, electron, radiation, target	735
	P. Niknejadi, J. Madey University of Hawaii, Honolulu,, USA
	The efforts in realizing x-ray free electron lasers (FELs) and enhancing their performance has stimulated remarkable theoretical developments and experimental advances in the field. Yet, the successful operation of x-ray FELs based on the self-amplified spontaneous emission (SASE) principle which has made them a powerful new tool, has beckoned our attention for better understanding a comprehensive physical basis of the theory that has the potential to improve the temporal structure and spectral optimization of these sources. We have previously explained the advantages of including the coherent radiation reaction force as a part of the solution to the boundary value problem for FELs that radiate into "free space" (SASE FELs) and discussed how the advanced field of the absorber can interact with the radiating particles at the time of emission.(, ) Here we present the outline of our theoretical approach which follows from eigenmode analysis of optical guiding in FELs. We will also discuss in some detail the experimental setup that could verify and/or further our understanding of the the underlying physics of these devices. P. Niknejadi et al., Phys. Rev. D 91 096006 (2015) ** P. Niknejadi and J.M.J. Madey, in Proceedings of Free Electron Laser Conference, JACoW, Basel, Switzerland (2014)
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WEP084	Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser	FEL, simulation, electron, bunching	741
	Z. Zhang TUB, Beijing, People's Republic of China Y. Ding, W.M. Fawley, Z. Huang, J. Krzywinski, A.A. Lutman, G. Marcus, A. Marinelli, D.F. Ratner SLAC, Menlo Park, California, USA
	The measured, self-seeded soft X-ray radiation spectrum corresponding to multiple effective undulator lengths of the LCLS exhibits a pedestal-like distribution around the seeded frequency. In the absence of a post-undulator monochromator, this contamination limits the spectral purity and may seriously degrade certain user applications. In general for either externally- or self-seeded FELs, such pedestals may originate with any time-varying property of the electron beam that can modulate the complex gain function. In this paper we specifically focus on the contributions of electron beam microbunching prior to the undulator. We show that both energy and density modulations can induce sidebands in a seeded FEL configuration. Analytic FEL theory and numerical simulations are used to analyze the sideband content relative to the amplified seeded signal, and to compare with experimental results.
	Poster WEP084 [1.263 MB]
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WEP087	Smith-Purcell Radiation from Microbunched Beams Modulated after Passing the Undulators in FELs	radiation, FEL, target, polarization	752
	A. Potylitsyn TPU, Tomsk, Russia D.Yu. Sergeeva, M.N. Strikhanov, A.A. Tishchenko MEPhI, Moscow, Russia
	We suggest using the Smith-Purcell effect from microbunched beams modulated after passing the undulators in FELs as an extra source of monochromatic radiation. We investigate theoretically characteristics of Smith-Purcell radiation in THz and X-ray frequency regions for two types of distribution of the particles in the beam. The expression for spectral-angular distribution of such radiation is obtained and analyzed, both for fully and partially modulated beams. The intensity of Smith-Purcell radiation is shown to be able to increase both due to the periodicity of the beam and the periodicity of the target. The numerical results prove that such radiation source can be an effective instrument for different FEL users, supplementary for the main FEL source.
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WED01	Commissioning of the Delta Polarizing Undulator at LCLS	polarization, radiation, bunching, electron	757
	H.-D. Nuhn, S.D. Anderson, R.N. Coffee, Y. Ding, Z. Huang, M. Ilchen, Yu.I. Levashov, A.A. Lutman, J.P. MacArthur, A. Marinelli, S.P. Moeller, F. Peters, Z.R. Wolf SLAC, Menlo Park, California, USA J. Buck XFEL. EU, Hamburg, Germany G. Hartmann, J. Viefhaus DESY, Hamburg, Germany A.O. Lindahl University of Gothenburg, Gothenburg, Sweden A.B. Temnykh Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work was supported by U.S. DOE, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A.B. Temnykh is supported U.S. National Science Foundation awards DMR-0807731 and DMR-DMR-0936384. The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators, which provides only limited taper capability and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new 3.2-m-long compact undulator (based on the Cornell University fixed-gap Delta design) has been developed and installed as the last LCLS undulator segment (U33) in October 2014. The Delta undulator provides full control of the polarization degree and K parameter through array position adjustments. Used on its own, it produces fully polarized spontaneous radiation in the selected state (linear, circular or elliptical). To increase the output power by orders of magnitude, the electron beam is micro-bunched by several (5-15) upstream LCLS undulator segments operated in the linear FEL regime. This micro-bunching process produces horizontally linear polarized (background) radiation. This unwanted radiation component has been greatly reduced by a reversed taper configuration, as suggested by Schneidmiller. Full elimination of the linear polarized component was achieved through spatial separation combined with transverse collimation. The paper will describe the methods tested during commissioning and will also present results of polarization measurements showing high degrees of circular polarization in the soft x-ray wavelength range.
	Slides WED01 [10.165 MB]
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WED04	Status Report of PAL-XFEL Undulator Program	FEL, electron, radiation, controls	769
	D.E. Kim, M.-H. Cho, Y.-G. Jung, H.-S. Kang, I.S. Ko, H.-G. Lee, S.B. Lee, W.W. Lee, B.G. Oh, K.-H. Park, H.S. Suh PAL, Pohang, Kyungbuk, Republic of Korea S. Karabekyan, J. Pflüger XFEL. EU, Hamburg, Germany
	PAL-XFEL is a SASE based FEL using S-band linear accelerator, photo cathode RF Gun, and hybrid undulator system for final lazing. The undulator system is based on EU-XFEL undulator design with necessary modifications. The changes include new magnetic geometry reflecting changed magnetic requirements, and EPICs based control system. The undulator system is in measurement and tuning stage targeting to finish installation within 2015. In this report, the development, tuning, measurement efforts for PAL-XFEL undulator system will be reported.
	Slides WED04 [3.317 MB]
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MOA02

First Lasing of the Third Stage of Novosibirsk FEL

FEL, radiation, electron, linac

1

O.A. Shevchenko, V.S. Arbuzov, K.N. Chernov, I.V. Davidyuk, E.N. Dementyev, B.A. Dovzhenko, Ya.V. Getmanov, B.A. Knyazev, E.I. Kolobanov, A.A. Kondakov, V.R. Kozak, E.V. Kozyrev, V.V. Kubarev, G.N. Kulipanov, E.A. Kuper, I.V. Kuptsov, G.Y. Kurkin, L.E. Medvedev, S.V. Motygin, V.N. Osipov, V.K. Ovchar, V.M. Petrov, A.M. Pilan, V.M. Popik, V.V. Repkov, T.V. Salikova, M.A. Scheglov, I.K. Sedlyarov, G.V. Serdobintsev, S.S. Serednyakov, A.N. Skrinsky, S.V. Tararyshkin, V.G. Tcheskidov, A.G. Tribendis, N. Vinokurov, P. Vobly
BINP SB RAS, Novosibirsk, Russia

Novosibirsk FEL facility is based on the first in the world multi-turn energy recovery linac (ERL). It comprises three FELs (stages). FELs on the first and the second tracks were commissioned in 2004 and 2009 respectively and operate for users now. The third stage FEL is installed on the fourth track of the ERL. It includes three undulator sections and 40-meters-long optical cavity. The design tuning range of this FEL is from 5 to 20 microns and the design average power at bunch repetition rate 3.74 MHz is about 1 kW. Recent results of the third stage FEL commissioning are reported.

Slides MOA02 [4.901 MB]

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MOB01

Three-Plus Decades of Tapered Undulator FEL Physics

FEL, electron, radiation, controls

5

W.M. Fawley
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
W.M. Fawley
SLAC, Menlo Park, California, USA

Beginning with the classic 1981 work of Kroll-Morton-Rosenbluth (*), multiple generations of FEL scientists have studied and used experimentally undulator tapering to improve and optimize the radiation output of both amplifier and oscillator FELs. Tapering has undergone a renaissance of interest, in part to make possible TW instantaneous power levels from x-ray FELs. In this talk, I will give a highly personalized (and undoubtedly strongly biased) historical survey of tapering studies beginning with the ELF 35-GHz experiments at Livermore in the mid-1980's and continuing up to quite recent studies at the LCLS at both soft and hard x-ray wavelengths.
(*) N.M. Kroll, P.L. Morton, and M.N. Rosenbluth, IEEE J. Quantum Elec., QE-17, 1436 (1981).

Slides MOB01 [2.106 MB]

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MOB02

X-Ray FEL R&D: Brighter, Better and Cheaper

FEL, electron, photon, radiation

7

Z. Huang
SLAC, Menlo Park, California, USA

The X-ray free-electron lasers (FELs), with nine to ten orders of magnitude improvement in peak brightness over the third-generation light sources, have demonstrated remarkable scientific capabilities. Despite the early success, X-ray FELs can still undergo dramatic transformations with accelerator and FEL R&D. In this talk, I will show examples of recent R&D efforts to increase X-ray coherence and brightness, to obtain better control of X-ray temporal and spectral properties, and to develop concepts for compact coherent sources.

Slides MOB02 [18.004 MB]

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MOB03

Transforming the FEL: Coherence, Complex Structures, and Exotic Beams

FEL, laser, radiation, electron

10

E. Hemsing
SLAC, Menlo Park, California, USA

Modern high brightness electron beams used in FELs are extremely versatile and highly malleable. This flexibility can be used to precisely tailor the properties of the FEL light for improved temporal coherence (as in external seeding), but can also be exploited in new ways to generate exotic FEL modes of twisted light that carry orbital angular momentum (OAM) for new science. In this talk, I will describe how lasers and undulator harmonics can be combined to produce both simple and complex e-beam distributions that emit intense, coherent, and highly tunable OAM light in future FELs.

Slides MOB03 [12.208 MB]

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MOC02

Optimization of a High Efficiency Free Electron Laser Amplifier

electron, FEL, radiation, brilliance

17

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Technique of undulator tapering in the post-saturation regime is used at the existing X-ray FELs for increasing the radiation power. We present comprehensive analysis of the problem in the framework of one-dimensional and three-dimensional theory. We find that diffraction effects essentially influence on the choice of the tapering strategy. Our studies resulted in a general law of the undulator tapering for a seeded FEL amplifier as well as for SASE FEL.

Slides MOC02 [24.462 MB]

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MOC03

Estimate of Free-Electron Laser Gain Length in the Presence of Electron Beam Collective Effects

emittance, FEL, electron, collective-effects

24

S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom

A novel definition for the three-dimensional free electron laser gain length is proposed*, which takes into account the increase of electron beam projected emittance as due, for example, to geometric transverse wakefield and coherent synchrotron radiation developing in linear accelerators. The analysis shows that the gain length is affected by an increase of the electron beam projected emittance, even though the slice (local) emittance is preserved, and found to be in agreement with Genesis code simulation results. It is then shown that the minimum gain length and the maximum of output power may notably differ from the ones derived when collective effects are neglected. The proposed model turns out to be handy for a parametric study of electron beam six-dimensional brightness and FEL performance as function, e.g., of bunch length compression factor, accelerator alignment tolerances and optics design.
* S. Di Mitri, S. Spampinati, Phys. Rev. Special Topics Accel. Beams, 17, 110702 (2014)

Slides MOC03 [2.528 MB]

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MOP004

Influence of Horizantal Constant Magnetic Field on Harmonic Undulator Radiations and Gain

radiation, electron, FEL, resonance

34

H. Jeevakhan, P.K. Purohit
NITTTR, Bhopal, India
G. Mishra
Devi Ahilya University, Indore, India

Harmonic undulators has been analyzed in the presence of constant magnetic field along the direction perpendicular to the main undulator field. Effect of constant magnetic field magnitude on trajectory of electron beam , intensity of radiation and FEL gain at fundamental and third harmonics has been evaluated. Performance of harmonic undulator in the presence horizontal component of earth's magnetic field is the practical realization of the suggested scheme.

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MOP008

Theoretical Computation of the Polarization Characteristics of an X-Ray Free-Electron Laser with Planar Undulator

FEL, electron, radiation, polarization

38

G. Geloni
XFEL. EU, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λ_w²/(4 pi L_g)², where λ_w is the length of the undulator period and L_g is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λ_w³/(4 pi L_g)³ and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.

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MOP009

Efficient Electron Sources of Coherent Spontaneous Radiation with Combined Helical and Uniform Magnetic Fields

electron, radiation, solenoid, simulation

43

N. Balal, V.L. Bratman, E. Magori
Ariel University, Ariel, Israel
V.L. Bratman
IAP/RAS, Nizhny Novgorod, Russia

We discuss two methods to mitigate repulsion of particles in dense electron bunches from photo-injectors and to enhance the power of terahertz radiation. First, the repulsion may be reduced with both very short bunches and undulator periods, reducing the length of a radiation section. According to simulations bunches with duration (50-100) fs, charge (50-200) pC, and energy 6 MeV could fairly effectively radiate at frequencies up to (10-20) THz. The undulator for such a source can be formed by means of redistribution of a solenoid field by a non-magnetized iron helix and a permanently magnetized helix. The second source is based on an idea proposed by A.V. Savilov for electron bunching under conditions when the cyclotron electron frequency is larger than the undulator frequency, and an increase of particle energy in the bunch Coulomb field leads to a decrease in longitudinal momentum and attraction of particles (this effect is analogous to the cyclotron negative-mass instability). A large value of the required uniform field can be used to easily obtain the needed undulator field by placing a simple iron helix inside a pulsed solenoid. Simulations confirm that the corresponding particle attraction can provide a powerful and narrowband radiation at the frequencies (1-3) THz.

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MOP011

Status of CLARA, a New FEL Test Facility

FEL, laser, electron, gun

49

J.A. Clarke, D. Angal-Kalinin, A.D. Brynes, R.K. Buckley, S.R. Buckley, L.S. Cowie, D.J. Dunning, B.D. Fell, P. Goudket, A.R. Goulden, P.C. Hornickel, F. Jackson, S.P. Jamison, J.K. Jones, K.B. Marinov, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, M.D. Roper, L.K. Rudge, Y.M. Saveliev, B.J.A. Shepherd, 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.B. Appleby, K. Hanahoe, O. Mete Apsimon, H.L. Owen, G.X. Xia
UMAN, Manchester, United Kingdom
P. Atkinson, N. Bliss, R.J. Cash, N.A. Collomb, G. Cox, G.P. Diakun, S. Dobson, A. Gallagher, S.A. Griffiths, C. Hill, C. Hodgkinson, D.M.P. Holland, T.J. Jones, B.G. Martlew, J. Williams
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
R. Bartolini, I.P.S. Martin
DLS, Oxfordshire, United Kingdom
S.T. Boogert, E. Yamakawa
Royal Holloway, University of London, Surrey, United Kingdom
G. Burt, P.N. Ratoff
Lancaster University, Lancaster, United Kingdom
L.T. Campbell, A.J.T. Colin, J. Henderson, B. Hidding, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
A.M. Kolano
University of Huddersfield, Huddersfield, United Kingdom
A. Lyapin
JAI, Egham, Surrey, United Kingdom
V.V. Paramonov, A.K. Skasyrskaya
RAS/INR, Moscow, Russia
J.D.A. Smith
TXUK, Warrington, United Kingdom
S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
Y. Wei, C.P. Welsch, A. Wolski
The University of Liverpool, Liverpool, United Kingdom

CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK. The main motivation for CLARA is to test new FEL schemes that can later be implemented on existing and future short wavelength FELs. Particular focus will be on ultra-short pulse generation, pulse stability, and synchronisation with external sources. The project is now underway and the Front End section (photoinjector and first linac) installation will begin later this year. This paper will discuss the progress with the Front End assembly and also highlighting other topics which are currently receiving significant attention.

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MOP012

Present Status of Source Development Station at UVSOR-III

laser, radiation, experiment, electron

54

N.S. Mirian, K. Hayashi, M. Katoh, J. Yamazaki
UVSOR, Okazaki, Japan
M. Hosaka, Y. Takashima
Nagoya University, Nagoya, Japan
T. Konomi, N. Yamamoto
KEK, Ibaraki, Japan
H. Zen
Kyoto University, Kyoto, Japan

Construction and development of a source development station are in progress at UVSOR-III, a 750 MeV electron storage ring. It is equipped with an optical klystron type undulator system, a mode lock Ti:Sa Laser system, a dedicated beam-line for visible-VUV radiation and a parasitic beam-line for THz radiation. New light port to extract edge radiation was constructed recently. An optical cavity for a resonator free electron laser is currently being reconstructed. Some experiments such as coherent THz radiation, coherent harmonic radiation, laser Compton Scattering gamma-rays and optical vortices are in progress.

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MOP017

Beam Commissioning Plan for the SwissFEL Hard-X-Ray Facility

linac, electron, FEL, operation

69

T. Schietinger
PSI, Villigen PSI, Switzerland

The SwissFEL facility currently being assembled at the Paul Scherrer Institute is designed to provide FEL radiation in the photon wavelength range between 0.1 and 7 nm. The commissioning of the first phase, comprising the electron injector, the main electron linear accelerator and the first undulator line, named Aramis and dedicated to the production of hard X-rays, is planned for the years 2016 and 2017. We present an overview of the beam commissioning plan elaborated in accordance with the installation schedule to bring into operation the various subsystems and establish beam parameters compatible with first pilot user experiments in late 2017.

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MOP044

A Laser Heater for CLARA

laser, electron, FEL, linac

129

S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
B.D. Muratori, N. Thompson, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

CLARA is a new FEL test facility, being developed at STFC Daresbury Laboratory in UK, based on a high brightness electron linac. The electron beam of CLARA can potentially be affected by the longitudinal microbunching instability leading to a degradation of the beam quality. The inclusion of a laser heater in the linac design can allow control of the microbunching instability, the study of microbunching and deliberate increase of the final energy spread to study energy spread requirements of the FEL schemes tested at CLARA. We present the initial design and layout of the laser heater system for CLARA and its expected performance.

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MOP049

Design, Development and Test of the Magnets for PAL-XFEL

quadrupole, dipole, multipole, status

139

H.S. Suh, M.-H. Cho, S.-H. Jeong, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park
PAL, Pohang, Kyungbuk, Republic of Korea

PAL-XFEL is now being constructed with the goal of 0.1 nm hard X-ray in Pohang, Korea. As the first phase we will construct 10 GeV linac, one hard X-ray and one soft X-ray beamlines which require 6 different families of 55 dipole magnets, 11 families of 209 quadrupole magnets, and 3 families of 48 corrector magnets. We have designed these magnets with considering the efficient production and the proper power supplies. This paper describes an outline of the design and test results of the magnets until now.

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MOP055

The Effect of Wakefields on the FEL Performance

emittance, wakefield, linac, FEL

161

A. Novokhatski, F.-J. Decker, Y. Nosochkov, M.K. Sullivan
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515.
If a beam travels near collimator jaws or other discontinuities of the beam pipe, it gets the energy loss and the transverse kick due to the back reaction of the beam field diffracted on the collimator's jaws. The wake field effect from collimators may not only bring an additional energy jitter and change the trajectory of the beam, but may also lead to degradation of the performance of Free Electron Laser (FEL) It may be possible due to the special character of the wake fields: the response reaction depends on the longitudinal position of the particles in the bunch. We describe a model of the wake field radiation, simulation results and comparison with measurements.

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MOP068

First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators

radiation, electron, resonance, FEL

196

N.S. Mirian
UVSOR, Okazaki, Japan
E. Salehi
AUT, Tehran, Iran

This report deals with self amplified spontaneous emission free electron laser (FEL) amplifier where the FEL emission is obtained from displaced phase combined undulators. Magnetic field of this adjustment methods in three dimensions is presented. The electron dynamics is investigated. The simulation method and results are explained. The radiation properties of the fundamental resonance and third harmonic through the phase combined undulators are compared with the normal undulator with the same undulator deflection parameter

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MOP070

Harmonic Generation in Two Orthogonal Undulators

polarization, electron, radiation, simulation

200

N.S. Mirian
UVSOR, Okazaki, Japan

In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.

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MOP071

Carrier-Envelope-Phase Stable Linearly and Circularly Polarized Attosecond Pulse Sources

laser, electron, radiation, simulation

205

Z. Tibai, G. Almási, Zs. Csiha-Nagy, J.A. Fülöp, J. Hebling
University of Pecs, Pécs, Hungary
J.A. Fülöp, Gy. Tóth
MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary

Recently, we proposed a robust method for producing waveform-controlled attosecond pulses in the EUV spectral range.* In our scheme the relativistic electron beam, provided by a LINAC, is sent through a modulator undulator where a TW-power laser beam is superimposed on it in order to generate nanobunches. The nanobunched electron beam passes through a single- or few-period radiator undulator (RU). The waveform of the generated attosecond pulses closely resembles the longitudinal distribution of the magnetic field. According to our calculations, at 20 nm (60 nm) wavelength carrier-envelope-phase (CEP) stable pulses with 23 nJ (80 nJ) energy, 80 as (240 as) duration, and 31 mrad (13 mrad) CEP fluctuation (standard deviation) can be achieved at K=0.5. More than 500 nJ energy is predicted at longer wavelengths and larger K. The energy fluctuation of the EUV pulse is 2.5 times higher than that of the laser. By using a helical RU, even circularly polarized attosecond pulses with 30/300 nJ energy can be generated, depending on the wavelength. To the best of our knowledge, no other presently available technique enables the generation of arbitrary-waveform, CEP-controlled attosecond pulses. The predicted pulse energies are sufficiently high to be used as pump pulses in attosecond pump-probe measurements.
* Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014).

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MOP076

Free-Electron Laser Driven by a 500 MeV Laser Plasma Accelerator Beam

FEL, laser, emittance, plasma

217

W. Qin, J.E. Chen, S. Huang, K.X. Liu, X.Q. Yan, L. Zeng
PKU, Beijing, People's Republic of China
Y. Ding, Z. Huang
SLAC, Menlo Park, California, USA

A laser plasma accelerator is under construction at Peking University and several hundred MeV electron beams are expected. In this paper we discuss applying a 500 MeV beam with 1% relative energy spread to FEL. Bunch decompression method is considered to deal with the large energy spread of the beam. Emittance growth induced by large divergence and energy spread in electron beam transport has been treated with the chromatic matching manipulation. Simulation shows that 100 MW level, 6.3 fs , 0.008 bandwidth output can be obtained for 30 nm FEL. TGU method with assumed matched beam is also discussed as a comparison.

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MOP078

Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam

electron, radiation, simulation, wiggler

221

R. Ianconescu
Shenkar College of Engineering and Design, Ramat Gan, Israel
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
E. Hemsing, A. Marinelli
SLAC, Menlo Park, California, USA
A. Nause
UCLA, Los Angeles, USA

Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF)
The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1].
[1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015)
[2] E. Allaria et al., Nat. Photonics 7, 913 (2013)
[3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)

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MOP079

On the Importance of Electron Beam Brightness in High Gain Free Electron Lasers

FEL, electron, emittance, brightness

227

S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Linear accelerators delivering high brightness electron beams are essential for driving short wavelength, high gain free-electron lasers (FELs). The FEL radiation output efficiency is often parametrized through the power gain length that relates FEL performance to the electron beam quality at the undulator. Experimental data and simulation results of existing and planned FEL facilities are used to explicit the relationship between the FEL output wavelength and the electron beam six-dimensional brightness*. Practical formulas are provided that show the dependence of the exponential gain length on the beam brightness**.
* S. Di Mitri, M. Cornacchia, Phys. Reports, 539 (2014) 1~48.
** S. Di Mitri, Photonics, 2 (2015) 317~341

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MOP081

Generating a Single-Spike SASE Pulse in the Soft X-Ray Regime by Velocity Bunching

FEL, radiation, electron, linac

233

J. Lee, B.H. Oh, M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

A bright ultrashort X-ray pulse emerges as a valuable tool for many fields of research nowadays. The single-spike operation of X-ray FEL is one way of making a bright ultrashort X-ray pulse. It requires extreme bunching and a magnetic chicane is a conventional compressor. In a low charge range, a magnetic chicane can be replaced by the velocity bunching technique. In this paper, we present the result of particle tracking simulation generating a single-spike soft X-ray SASE pulse without a magnetic chicane. We also investigate the error effects and show that this scheme is feasible under current technology.

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MOP082

New Soft X-Ray Undulator Line Using 10 GeV Electron Beam in PAL-XFEL

photon, electron, linac, simulation

237

C.H. Shim, I.S. Ko
POSTECH, Pohang, Kyungbuk, Republic of Korea
Y.W. Parc
PAL, Pohang, Kyungbuk, Republic of Korea

PAL-XFEL is designed to have five undulator lines and only two undulator lines, the HXR undulator line with 10 GeV electron beam and the SXR undulator line with 3.15 GeV electron beam, will be installed during phase I. A photon beam energy from 0.28 to 1.24 keV will be provided at the SXR undulator line and different range from 2 to 20 keV will be supplied at the HXR undulator line. According to existing schedule, however, photon beam energy from 1.24 to 2 keV won't be provided in PAL-XFEL. In this research, new soft X-ray undulator line for PAL-XFEL using 10 GeV electron beam in main linac is proposed to cover the vacant photon energy. Four candidates are evaluated by estimating and comparing FEL performances using Ming Xie's formula.

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MOP083

FEL Operation Modes of the MAX IV Short Pulse Facility

electron, radiation, simulation, FEL

241

A. Mak, F. Curbis, S. Werin
MAX-lab, Lund, Sweden

The Short Pulse Facility (SPF) of the MAX IV Laboratory in Lund, Sweden features the production of ultrashort, incoherent x-ray pulses. It is driven by a 3-GeV linac and comprises two 5-metre undulator modules. While the SPF is designed for spontaneous radiation, we explore alternative operation modes in which the SPF functions as a simple free-electron laser (FEL). In this article, we characterize two of them in time-dependent numerical simulations. We perform a sensitivity study on the electron beam parameters and examine the technique of single-step tapering.

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MOP084

Seeded FEL Study for the Cascaded HGHG option for FLASH2

FEL, simulation, radiation, electron

246

G. Feng, W. Decking, M. Dohlus, T. Limberg, I. Zagorodnov
DESY, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany
T. Plath
Uni HH, Hamburg, Germany

The free electron laser (FEL) facility at DESY in Hamburg (FLASH) is the world's first FEL user facility which can produce extreme ultraviolet (XUV) and soft X-ray photons. In order to increase beam time delivered to users, a major upgrade named FLASH II is in progress. As a possibility, a seeding undulator section can be installed between the extraction arc section and the SASE undulator of FLASH2. In this paper, a possible seeding scheme for the cascaded HGHG option for FLASH2 is given. The SASE undulator can be used as the second radiator of the cascaded HGHG. Parameters optimization for the accelerating modules and the bunch compressors has been done to meet the requirement of the electron bunches. In the beam dynamics simulation, collective effects were taken into account. Particle distribution generated from the beam dynamics simulation was used for the seeded FEL study. Space charge and CSR impacts on the microbunches were taken into account during the seeded FEL simulation. The simulation results show that FEL radiation with the wavelength of a few nms and with high monochromaticity can be seeded at FLASH2.

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MOP085

Scheme to Increase the Output Average Spectral Flux of the European XFEL at 14.4 keV

FEL, electron, photon, scattering

251

V. Kocharyan, E. Saldin
DESY, Hamburg, Germany
G. Geloni
XFEL. EU, Hamburg, Germany

Inelastic X-ray scattering and nuclear resonance scattering are limited by the photon flux available at SR sources, up to 10¹⁰ ph/s/meV at 14.4 keV. A thousand-fold increase may be obtained by exploiting high repetition rate self-seeded pulses at the European XFEL. We report on a feasibility study for an optimized configuration of the SASE2 beamline combining self-seeding and undulator tapering at 14.4 keV. One should perform monochromatization at 7.2 keV by self-seeding, and amplify the seed in the first part of the output undulator. Before saturation, the electron beam is considerably bunched at the 2nd harmonic. A second part of the output undulator tuned to 14.4 keV can thus be used to obtain saturation at this energy. One can further prolong the exchange of energy between the photon and the electron beam by tapering the last part of the output undulator. Start-to-end simulations demonstrate that self-seeding, combined with undulator tapering, allows one to achieve more than a hundred-fold increase in average spectral flux compared with the nominal SASE regime at saturation, resulting in a spectral flux of order 10¹³ ph/s/meV. A more detailed description of this study can be found in*.
* G. Geloni, V. Kocharyan and E.~Saldin, "Scheme to increase the output average spectral flux of the European XFEL at 14.4 keV", DESY 15-141 (2015).

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MOP086

Novel Opportunities for Sub-meV Inelastic X-Ray Scattering Experiments at High-Repetition Rate Self-seeded XFELs

radiation, photon, optics, scattering

257

O.V. Chubar
BNL, Upton, Long Island, New York, USA
G. Geloni, A. Madsen
XFEL. EU, Hamburg, Germany
V. Kocharyan, E. Saldin, S. Serkez
DESY, Hamburg, Germany
Yu. Shvyd'ko
ANL, Argonne, Ilinois, USA
J. Sutter
DLS, Oxfordshire, United Kingdom

Inelastic x-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25/nm spectral and momentum Transfer resolutions, respectively*. However, further improvements down to 0.1 meV and 0.02/nm are required to close the gap in energy-momentum space between high and low frequency probes. We Show that this goal can be achieved by further improvements in x-ray optics and by increasing the spectral flux of the incident x-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE2 beamline of the European XFEL promises up to a hundred-fold increase in average spectral flux compared to nominal SASE pulses at saturation, or three orders of magnitude more than possible with storage-ring based radiation sources. Wave-optics propagation shows that about 7·10¹² ph/s in a 90-microeV bandwidth can be achieved on the sample. This will provide unique new possibilities for IXS. Extended information about our work can be found in**.
* Y. Shvyd'ko et al., Nature Communications 5:4219 (2014).
** O. Chubar et al., ‘Novel opportunities for sub-meV inelastic X-ray scattering at high-repetition rate self-seeded X-ray free-electron lasers', http://arxiv.org/abs/1508.02632, DESY 15-140, (2015).

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TUA02

Suppression of FEL Lasing by a Seeded Microbunching Instability

electron, laser, FEL, photon

289

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov
DESY, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school GRK1355.
Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brightness electron bunches driving free-electron lasers (FELs). In this contribution, we demonstrate suppression of FEL lasing induced by a laser-triggered microbunching instability at the free-electron laser FLASH. The interaction between the electron bunches and the 800-nm laser pulses takes place in an undulator upstream of the FEL undulators. A significant decrease of XUV photon pulse energies has been observed in coincidence with the laser-electron overlap in the modulator. We discuss the underlying mechanisms based on longitudinal space charge amplification (LSCA) [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

Slides TUA02 [14.298 MB]

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TUA03

Multi-beamline Operation Test at SACLA

electron, operation, kicker, laser

293

T. Hara, T. Inagaki, R. Kinjo, C. Kondo, Y. Otake, H. Takebe, H. Tanaka, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
K. Fukami
JASRI/SPring-8, Hyogo-ken, Japan

A new undulator beamline (BL2) was installed in September 2014 at SACLA. Following the installation of this second beamline, a DC switching magnet was replaced by a kicker magnet and a DC septum magnet for bunch-to-bunch multi-beamline operation. The commissioning of the new beamline and bunch-to-bunch operation was started early this year. Since SACLA has been operated with much higher peak currents around 10 kA compared to its original design value of 3 kA, the CSR effect in the beam transport line to BL2, where the electron beam is deflected twice by 3 degree, turns out to be non-negligible. BL2 is currently operated with reduced peak currents and the photon pulse energies of 100-150 μJ are obtained with increased undulator K-values around 2.6-2.85. Although the photon pulse energies of BL2 are still smaller than those of the existing beamline (BL3), the expected stability of the electron beam orbit after the bunch-to-bunch BL switching was achieved and simultaneous lasing at the two beamlines was demonstrated with 8 GeV electron beams. We will report the status and operational issues related to the multi-beamline operation at SACLA.

Slides TUA03 [7.095 MB]

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TUA04

First Simultaneous Operation of Two Sase Beamlines in FLASH

photon, operation, electron, FEL

297

M. Scholz, B. Faatz, S. Schreiber, J. Zemella
DESY, Hamburg, Germany

FLASH2, the second undulator beamline of the FLASH FEL user facility at DESY (Hamburg, Germany) is under commissioning. Its first lasing was achieved in August 2014. FLASH is the first soft X-ray FEL operating two undulator beamlines simultaneously. Both undulator beamlines are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. Fast kickers and a septum are installed to distribute one part of the electron bunch train to FLASH1 and the other part to FLASH2 with full repetition rate. The commissioning of FLASH2 takes place primarily in parallel to FLASH1 user operation. Various beam optics measurements has been carried out in order to ensure the required electron beam quality for efficient SASE generation. This paper reports the status of the FLASH2 commissioning.

Slides TUA04 [9.655 MB]

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TUB02

Distributed Seeding for Narrow-band X-ray Free-Electron Lasers

radiation, electron, FEL, simulation

301

D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner
LANL, Los Alamos, New Mexico, USA

Funding: We thank Bruce Carlsten, John Lewellen, Steve Russell, and Rich Sheffield (LANL), Craig Ogata and Yuri Shvyd'ko (ANL) for helpful discussion, and the MaRIE project for financial support.
The MaRIE XFEL is the proposed XFEL driven by a 12-GeV electron beam to generate coherent 42-keV photons based on a new seeding technique called distributed seeding (DS). This paper presents details of the distributed seeding technique using Si(111) Bragg crystals as the spectral filters. DS differs from self-seeding in three important aspects. First, DS relies on spectral filtering of the undulator radiation at more than one location early in the exponential gain curve. This leads to an FEL output that is dominated by the coherent seed signal, not SASE noise. Secondly, DS affords the ability to select a wavelength longer than the peak of the SASE gain curve, which leads to improved spectral contrast of the seeded FEL over the SASE background. Lastly, the power growth curves in successive DS stages exhibit the behavior of an FEL amplifier, i.e. a lethargy region followed by the exponential growth region. This behavior results in FEL output pulses that are less spiky than the SASE pulses. Using 3D Genesis simulations, we show that DS with two filters provides a 12X enhancement in spectral brightness relative to SASE and that DS with three filters produces negligible SASE background. The DS FEL spectrum has a relative spectral bandwidth (FWHM) of 8 X 10^-5 with about 9 spectral modes.

Slides TUB02 [1.241 MB]

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TUP001

THz Photo-Injector FEM Based on Spontaneous Coherent Emission from a Bunch of Negative-Mass Electrons

electron, radiation, cyclotron, simulation

317

A.V. Savilov, I.V. Bandurkin
IAP/RAS, Nizhny Novgorod, Russia

The use of short dense electron bunches produced form a photo-injector gun is attractive for realization of a THz FEL based on spontaneous coherent emission from such bunches. This type of emission is realized, when the axial length of bunches is shorter that the wavelength of the radiated wave. Therefore, the length of the operating region of such a FEL is strictly limited by degradation (an increase in the axial size) of the e-bunch caused by both the Coulomb repulsion and the velocity spread. The use of the regime of the 'negative mass' can be a way to provide stabilization of the axial size of e-bunches. Such a regime is realized in a magnetostatic undulator with a guiding homogeneous axial magnetic field. If the electron cyclotron frequency (corresponding to the guiding magnetic field) exceeds the bounce-frequency of electron oscillations in the periodic undulator field, then the abnormal dependence of the axial velocity of electrons on their energy takes place (an increase in the energy leads to a decrease in the axial velocity). In such regime, axial Coulomb repulsion of the electrons leads to their mutual attraction which slows down bunch degradation. The use of this regime results in a substantial increase in the length of the spontaneous coherent emission, and, therefore, in an increase in both the duration and the power of the output radiation pulse.
The work was supported by the Russian Scientific Foundation (RSCF), Project no. 14-19-01723

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TUP002

Further Studies of Undulator Tapering in X-Ray FELs

simulation, electron, radiation, laser

321

A. Mak, F. Curbis, S. Werin
MAX-lab, Lund, Sweden

We further the studies of the model-based optimization of tapered free-electron lasers presented in a recent publication [Phys. Rev. ST Accel. Beams 18, 040702 (2015)]. Departing from the ideal case, wherein the taper profile is a smooth and continuous function, we consider the more realistic case, with individual undulator segments separated by break sections. Using the simulation code GENESIS, we apply our taper optimization method to a case, which closely resembles the FLASH2 facility in Hamburg, Germany. By comparing steady-state and time-dependent simulations, we examine how time-dependent effects alter the optimal taper scenario. From the simulation results, we also deduce that the "traditional" empirical method, whereby the intermediate radiation power is maximized after closing every undulator gap, does not necessarily produce the highest final power at the exit of the undulator line.

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TUP004

Three-dimensional, Time-dependent Simulation of Free-Electron Lasers

simulation, electron, FEL, experiment

331

P.J.M. van der Slot
Mesa+, Enschede, The Netherlands
H. Freund, P.J.M. van der Slot
CSU, Fort Collins, Colorado, USA

Minerva is a simulation code that models the interaction of electrons with an optical field inside an undulator. Minerva uses a modal expansion for the optical field and the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to mode, for example, FEL oscillators. As there exists a large variety of FELs ranging from long-wavelength oscillators to soft and hard X-ray FELs that are either seeded or starting from noise, a simulation code, such as Minerva, should be capable of modelling this huge variety of FEL configurations. Here we present a validation of the Minerva code against experimental data for various FEL configurations, ranging from long wavelength FEL oscillators to hard X-ray SASE FEL.

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TUP006

Quantum Nature of Electrons in Classical X-ray FELs

FEL, electron, radiation, laser

338

P.M. Anisimov
LANL, Los Alamos, New Mexico, USA

X-ray FELs built to date are well described by the classical theory. This theory in its simplest form is expressed as a system of pendulum equations for electrons coupled to the electromagnetic field. The FEL interaction requires bunching of the electrons on a scale less than radiation wavelength. The progress in the development of FELs and the need to reach even shorter laser radiation wavelength with low energy electrons require that the quantum characteristic of the FEL interaction to be properly considered. Quantum theories have been already proposed by a number of authors. These theories, however, have been developed for regimes that are not relevant for modern/planned X-ray FELs. Here, we focus on quantum effects in modern/future X-ray FELs and stop treating an electron as a point-particle. This results in quantum reduction of the bunching! Starting with the analysis of the free space dispersion for the electron wave packet, we will present a modified 1D FEL theory that takes into account the quantum uncertainty of the electron position in X-ray FELs. This theory allows for a unified classification of FELs with respect to the wave nature of an electron that shows a planned FEL at Los Alamos National Lab to be most affected. The Genesis simulation code has been modified in order to include quantum reduction of the bunching that lead to interesting results. LA-UR-15-26276

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TUP007

High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II

electron, FEL, simulation, emittance

342

G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, California, USA
J. Qiang, M. Venturini
LBNL, Berkeley, California, USA

High fidelity numerical particle simulations that leverage a number of accelerator and FEL codes have been used to analyze the LCLS-II FEL performance. Together, the physics models that are included in these codes have been crucial in identifying, understanding, and mitigating a number of potential hazards that can adversely affect the FEL performance, some of which are discussed in papers submitted to this conference[*, **]. Here, we present a broad overview of the LCLS-II FEL performance, based on these start-to-end simulations, for both the soft X-ray and hard X-ray undulators including both SASE and self-seeded operational modes.
* M. Venturini, et al., The microbunching instability and LCLS-II lattice design: lessons learned, FEL'15
** Z. Zhang, et al., Microbunching-induced sidebands in a seeded free-electron laser, FEL'15

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TUP008

High-Gain FEL in the Space-Charge Dominated Raman Limit

FEL, space-charge, electron, simulation

347

I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig
UCLA, Los Angeles, USA

While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.

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TUP011

Performance and Tolerance Studies of the X-Ray Production for the X-Band FEL Collaboration

simulation, electron, FEL, operation

359

J. Pfingstner, E. Adli
University of Oslo, Oslo, Norway

The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied.

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TUP013

The X-Band FEL Collaboration

FEL, linac, electron, emittance

368

J. Pfingstner, E. Adli
University of Oslo, Oslo, Norway
A.A. Aksoy, O. Yavaş
Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey
D. Angal-Kalinin, J.A. Clarke
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C.J. Bocchetta, A.I. Wawrzyniak
Solaris, Kraków, Poland
M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc, Y.E. Tan, K.P. Wootton, D. Zhu
SLSA, Clayton, Australia
G. Burt
Lancaster University, Lancaster, United Kingdom
N. Catalán Lasheras, A. Grudiev, A. Latina, D. Schulte, S. Stapnes, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland
A. Charitonidis
NTUA, Athens, Greece
G. D'Auria, S. Di Mitri, C. Serpico
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
T.J.C. Ekelöf, M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden
W. Fang, Q. Gu
SINAP, Shanghai, People's Republic of China
E.N. Gazis
National Technical University of Athens, Athens, Greece
X.J.A. Janssen
VDL ETG, Eindhoven, The Netherlands
Z. Nergiz
Nigde University, Nigde, Turkey

The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. Due to the higher accelerating gradients achievable with X-band technology, a X-band normal conducting linac can be shorter and therefore potentially cost efficient than what is achievable with lower frequency structures. This cost reduction of future FEL facilities addresses the growing demand of the user community for coherent X-rays. The X-band FEL collaboration consists of 12 institutes and universities that jointly work on the preparation of design reports for the specific FEL projects. In this paper, we report on the on-going activities, the basic parameter choice, and the integrated simulation results. We also outline the interest of the X-band FEL collaboration to use the electron linac CALIFES at CERN to test FEL concepts and technologies relevant for the X-band FEL collaboration.

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TUP019

Time Locking Options for the Soft X-Ray Beamline of SwissFEL

laser, FEL, electron, radiation

388

E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland

SwissFEL is an FEL facility presently under construction at the Paul Scherrer institute that will serve two beamlines: Aramis, a hard X-ray beamline which is in construction phase and will provide FEL radiation in 2017 with a wavelength between 0.1 and 0.7 nm; and Athos, a soft X-ray beamline which is in design phase and it is expected to offer FEL light in 2021 for radiation wavelengths between 0.7 and 7 nm. A passive synchronization of the FEL signal to a laser source is fundamental for key experiments at Athos, such as the time-resolved resonant inelastic X-ray scattering (RIXS) experiments. In this paper we explore different options to achieve this time synchronization by means of energy modulating the electron beam with an external laser.

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TUP020

Recent Study in iSASE

FEL, electron, distributed, laser

393

K. Fang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
S. Hsu
University of California, San Diego (UCSD), La Jolla, California, USA

The Improved Self-Amplified Spontaneous Radiation (iSASE) scheme has potential to reduce SASE FEL bandwidth. This is achieved by repeatedly delaying the electrons with respect to the radiation pulse using phase shifters in the undulator break sections. It has been shown that the strength, locations and sequences of phase shifters are important to the iSASE performance. Particle swarm optimization algorithm is used to explore the phase shifters configuration space globally.

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TUP021

Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability

FEL, radiation, emittance, electron

397

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

The radiation from SASE FEL has always limited value of the degree of transverse coherence. Two effects define the spatial coherence of the radiation: the mode competition effect, and the effect of poor longitudinal coherence. For the diffraction limited case we deal mainly with the effect of the poor longitudinal coherence leading to significant degradation of the spatial coherence in the post-saturation regime. When transverse size of the electron beam significantly exceeds diffraction limit, the mode competition effect does not provide the selection of the fundamental FEL mode, and spatial coherence degrades due to contribution of the higher azimuthal modes. Another consequence of this effect are fluctuations of the spot size and pointing stability of the photon beam. These fluctuations are fundamental and originate from the shot noise in the electron beam. The effect of pointing instability becomes more pronouncing for shorter wavelengths. Our study is devoted to the fundamental analysis of the effect and description of possible means for improving the degree of transverse coherence and the pointing stability.

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TUP023

A Modified Self-Seeded X-ray FEL Scheme Towards Shorter Wavelengths

FEL, laser, electron, radiation

409

L. Zeng, J.E. Chen, S. Huang, K.X. Liu, W. Qin
PKU, Beijing, People's Republic of China
Y. Ding, Z. Huang, G. Marcus
SLAC, Menlo Park, California, USA

We present a modified self-seeded FEL scheme for harmonic generation. Different from classical HGHG scheme whose seed laser is a conventional laser with longer wavelength, this scheme first uses a regular self-seeding monochromator to generate a seed laser, followed by a HGHG configuration to produce shorter-wavelength radiations. As an example, we perform start-to-end simulations to demonstrate the second and third harmonic FELs from a soft x-ray self-seeding case at the fundumental wavelength of 1.72 nm. The harmonic performance results will be discussed.

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TUP025

Studies of Undulator Tapering for the CLARA FEL

FEL, electron, laser, brightness

412

I.P.S. Martin, R. Bartolini
DLS, Oxfordshire, United Kingdom
R. Bartolini
JAI, Oxford, United Kingdom
D.J. Dunning, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Undulator tapering is a well-known method for enhancing the performance of free-electron lasers [1]. It works by keeping the resonant wavelength constant, despite variation in the electron beam energy. Both the energy-extraction efficiency and the spectral brightness of the FEL can be improved using this technique. In this paper we present recent studies of undulator tapering for the CLARA FEL in both SASE and seeded modes. The methods used to optimise the taper profile are described, and the properties of the final FEL pulses are compared.
[1] N.M. Kroll, P.L. Morton, M.N. Rosenbluth, J. Quantum Electronics 17, 8 (1981).

Poster TUP025 [0.919 MB]

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TUP026

Measurment Uncertainties in Gas-Based Monitors for High Repetition Rate X-Ray FEL Operations

FEL, simulation, detector, linac

417

Y. Feng, M.L. Campell, J. Krzywinski, E. Ortiz, T.O. Raubenheimer, M. Rowen, D.W. Schafer
SLAC, Menlo Park, California, USA

Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University.
Thermodynamic simulations using a finite difference method were carried out to investigate the measurement uncertainties in gas-based X-ray FEL diagnostic monitors under high repetition rate operations such as planned for the future LCLS-II soft and hard X-ray FEL's. For monitors using relatively high gas pressures for obtaining sufficient signals, the absorbed thermal power becomes non-negligible as repetition rate increases while keeping pulse energy constant. The fluctuations in the absorbed power were shown to induce significant measurements uncertainties, especially in the single-pulse mode. The magnitude of this thermal effect depends nonlinearly on the absorbed power and can be minimized by using a more efficient detection scheme in which the gas pressure can be set sufficiently low

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TUP027

Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA

laser, radiation, electron, focusing

422

B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
D. Xiang
Shanghai Jiao Tong University, Shanghai, People's Republic of China

The Echo program currently underway at SLAC's NLCTA test accelerator aims to use Echo-Enabled Harmonic Generation (EEHG) to produce considerable bunching in the electron beam at high harmonics of a 2.4um seed laser. The production of such high harmonics in the EUV wavelength range necessitates an efficient radiator and associated light diagnostics to accurately characterize and tune the echo effect. We have installed and commissioned the Visible to Infrared SASE Amplifier (VISA) undulator, a strong focusing two meter long planar undulator of Halbach array design with 1.8cm period length. To characterize the output radiation, we have designed, built, and calibrated a grazing incidence EUV spectrometer which operates between 12-120nm with resolution sufficient to resolve individual harmonics. An absolute wavelength calibration is achieved by using both EEHG and High Gain Harmonic Generation (HGHG) signals from the undulator.

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TUP028

DESIGN OF THE MID-INFRARED FEL OSCILLATOR IN CHINA

FEL, electron, cavity, laser

427

H.T. Li, Q.K. Jia, L. Wang, S.C. Zhang
USTC/NSRL, Hefei, Anhui, People's Republic of China

In 2014, Xiamen University and other three research organizations received the approval to realize an infrared free electron laser (IR-FEL) for fundamental of energy chemistry. The IR-FEL covers the spectral range of 2.5-200 μm and will be built in NSRL. Two FEL oscillators driven by one Linac will be used to generate mid- infrared and far-infrared lasers. In this article we describe the design studies for the mid-infrared FEL oscillator.

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TUP030

Time Dependent Study for an X-ray FEL Oscillator at LCLS-II

cavity, electron, photon, free-electron-laser

433

J. Zemella
DESY, Hamburg, Germany
W.M. Fawley, T.J. Maxwell
SLAC, Menlo Park, California, USA
R.R. Lindberg
ANL, Argonne, Illinois, USA

The LCLS-II with its high repetition rate and high quality beam will be capable of driving an X-ray free electron laser oscillator at higher harmonics in the hard X-ray regime (0.1 nm). The oscillator consists of a low loss X-ray crystal cavity using diamond Bragg crystals with meV bandwidth. The expected average spectral flux has been estimated to be at least two orders of magnitude greater than present synchrotron-based sources with highly stable, coherent pulses of duration 1 ps or less for applications in Mössbauer spectroscopy and inelastic x-ray scattering. A more detailed study of the start up of a fifth-harmonic X-ray FEL oscillator at LCLS-II will be presented with full, time-dependent simulations.

Poster TUP030 [0.619 MB]

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TUP032

Numerical Studies of the Influence of the Electron Bunch Arrival Time Jitter on the Gain Process of an XFEL-Oscillator for the European XFEL

electron, simulation, radiation, FEL

436

C.P. Maag, J. Zemella
DESY, Hamburg, Germany
J. Roßbach
Uni HH, Hamburg, Germany

The superconducting linac of the European XFEL Laboratory in Hamburg will produce electron bunch trains with a time structure that allow in principle the operation of an XFELO (X-ray FEL-Oscillator). The electron bunches of the European XFEL have an expected length between 2 and 180 fs (FWHM) with an expected arrival time jitter of about 30 fs (RMS). A jitter of the electron bunch arrival time leads to a detuning between the electron and photon pulse. Since an XFEL-Oscillator relies on a spatial overlap of electron and photon pulse, the influence of a lack of longitudinal overlap is studied. The simulations are performed for different bunch lengths and levels of arrival time jitter. The results of a simulation are presented where angular, transversal and arrival time jitter are taken into account simultaneously, assuming parameters expected for the European XFEL Linac.

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TUP038

Construction of the EU-XFEL Laser Heater

laser, vacuum, electron, ion

452

M. Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden

Funding: We thank the Swedish research council under Project number DNR-828-2008-1093 for financial support.
Installation of the laser heater for the EU-XFEL is completed and first commissioning runs are imminent. We discuss the installation of the key elements and provide an outlook of the commissioning phase.

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TUP053

Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion

polarization, FEL, radiation, diagnostics

486

W.M. Fawley, E. Allaria, E. Ferrari
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy

Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators.
[1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013).
[2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014).

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TUP057

The Highly Adjustable Magnet Undulator

simulation, electron, permanent-magnet, radiation

499

M. Hamberg
Uppsala University, Uppsala, Sweden

The highly adjustable magnet undulator is a concept aiming for flexibility and extensive tunability of undulator settings in the linear as well as the helical regime. I report about suggested layout, magnetic simulations.

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TUP066

Benchmark of ELEGANT and IMPACT

space-charge, wakefield, linac, optics

505

L. Wang, P. Emma, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
J. Qiang
LBNL, Berkeley, California, USA

The beam dynamics codes ELEGANT and IMAPCT have many users. We use these two codes for the design of LCLSII. Both codes use a 1D model for the coherent synchrotron radiation (CSR) in bend magnets. In addition, IMPACT has a 3D space-charge model, while ELEGANT uses a 1D model. To compare the two codes, especially the space-charge effects, we systematically benchmark the two codes with different physics aspects: wakefields, CSR and space-charge forces.

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TUP069

THz Based Phase-Space Manipulation in a Guided IFEL

electron, laser, simulation, coupling

519

E.J. Curry, S. Fabbri, P. Musumeci
UCLA, Los Angeles, California, USA
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel

Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583.
We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10^-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude.

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TUP074

Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility

laser, radiation, electron, experiment

540

N.S. Sudar, J.P. Duris, I.I. Gadjev, P. Musumeci
UCLA, Los Angeles, USA
M. Babzien, M.G. Fedurin, K. Kusche, I. Pogorelsky, M.N. Polyanskiy, C. Swinson
BNL, Upton, Long Island, New York, USA

Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility.

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WEA03

SwissFEL Status Report

linac, FEL, vacuum, electron

567

R. Ganter
PSI, Villigen PSI, Switzerland

SwissFEL is a 5.8 GeV linac which sends electron bunches at 100 Hz into a 60 m long in-vacuum undulator line to produce hard X-rays between 0.1 nm and 0.7 nm. The SwissFEL accelerator design is based on a low emittance beam with tight tolerances on RF stability. The first lasing of SwissFEL is planned for early 2017 and two end-stations should then be brought into operation in the same year. The delivery of the SwissFEL building to PSI is planned for fall this year, but some rooms are already completed and currently in use for components assembly. The production of the C-band RF accelerating structures has now reach the nominal rate of 5 structures/month. Two different RF solid state modulator prototypes could demonstrate jitter lower than 20 ppm but stability and reliability tests are still going on. The undulators assembly and measurement sequence have started and 13 undulators are planned to be ready in the tunnel by October 2016. Large series of components like magnets, vacuum systems and mechanical supports are already in house and under assembly. Photonics components for two beamlines and two end stations are ordered and planned to be ready for 2017.

Slides WEA03 [36.505 MB]

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WEB01

A Two-Color Storage Ring FEL

FEL, electron, cavity, operation

571

J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA
S. Huang
PKU, Beijing, People's Republic of China
J.Y. Li
USTC/NSRL, Hefei, Anhui, People's Republic of China
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
J. Wu
SLAC, Menlo Park, California, USA

Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
Using different undulator configurations on the Duke storage ring, we have successfully achieved lasing with a novel two-color storage ring FEL. Using a pair of dual-band FEL mirrors, simultaneous lasing was realized in IR (around 720 nm) and in UV (around 360 nm). With this two-color FEL, we have demonstrated independent wavelength tuning of either IR or UV lasing. With careful tuning, we have also realized harmonic lasing with the UV lasing tuned to the second harmonic of the IR lasing. The tuning of harmonic two-color lasing has also been demonstrated with the locked wavelengths. Furthermore, we have demonstrated good control of the FEL power sharing between the two colors. The two-color FEL has created new opportunities to drive a two-color Compton gamma-ray beam at the High Intensity gamma-ray Source at Duke.

Slides WEB01 [18.975 MB]

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WEB02

Waveguide THz FEL Oscillators

FEL, injection, electron, extraction

576

S.V. Miginsky, S. Bae, B.A. Gudkov, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov
KAERI, Daejon, Republic of Korea
S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

In today's world there is a significant demand for FEL-based THz radiation sources. They have a wide tuning range, a narrow band of radiation, and comparably high peak and average emission power. There are a significant number of these machines in the world, operating or in the development. The main difference between a long-wave FEL, of THz or a millimeter band, and a conventional one is a too big transverse size of the fundamental mode of an open optical resonator. It claims a large gap in an undulator that dramatically decreases its strength. Both factors sorely decrease the amplification and the efficiency, and often make lasing impossible. The main way to solve this problem is to use a waveguide optical resonator. It decreases and controls the transverse size of the fundamental mode. However, the waveguide causes a number of problems: power absorption in its walls; higher modes generation by inhomogeneities, as it is not ideal; electron beam injection into a FEL is more sophisticated; also outcoupling is more complicated; finally, the resonator detuning control claims some special solutions. The waveguide dispersion relation differs from one in the free space. It shifts up the wavelength of the FEL, changes the optimal detuning, and creates a parasitic mode near the critical wavelength of the waveguide. These problems and possible solutions to them are considered.

Slides WEB02 [20.394 MB]

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WEP001

RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS

radiation, FEL, cavity, gun

583

J.R. Lewandowski, R.C. Field, A.S. Fisher, H.-D. Nuhn, J.J. Welch
SLAC, Menlo Park, California, USA

Funding: Work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A significant source of radiation signals in the LCLS Undulator have been identified as being generated by dark current emitted from the LCLS RF Photocathode Gun. Radiation damage to magnets over time can lead to degraded performance and significant cost for replacement. A method of using an existing transverse deflector cavity with a modified RF pulse has been tested and shows promise for eliminating the radiation dose from RF gun dark current that is generated in time before and after the production beam pulse.
UNDULATOR RADIATION DAMAGE EXPERIENCE AT LCLS: H.-D. Nuhn, C. Field, S. Mao, Y. Levashov, M. Santana, J.N. Welch, Z. Wolf,
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, U.S.A

Poster WEP001 [1.631 MB]

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WEP004

Energy Spread Constraints on Field Suppression in a Reverse Tapered Undulator

laser, FEL, bunching, simulation

597

J.P. MacArthur, Z. Huang, A.A. Lutman, A. Marinelli, H.-D. Nuhn
SLAC, Menlo Park, California, USA

A 3.2 m variable polarization Delta undulator[1] has been installed at the end of the LCLS undulator line. The Delta undulator acts an an afterburner in this configuration, using bunching from upstream planar undulators to produce radiation with arbitrary polarization. To optimize the degree of polarization from this device, a reverse taper[2] has been proposed to suppress background radiation produced in upstream undulators while still microbunching the beam. Here we extend previous work on free electron lasers with a slowly varying undulator parameter[3] to show there is a strong energy spread dependence to the maximum allowable detune from resonance. At LCLS, this energy spread limitation keeps the reverse taper slope in the slowly varying regime and limits the achievable degree of circular polarization.
[1] A. B. Temnykh, PRST-AB, 11, 120702, (2008).
[2] E. A. Schneidmiller and M. V. Yurkov, PRST-AB, 16, 110702, (2013).
[3] Z. Huang and G. Stupakov, PRST-AB, 8, 040702, (2005).

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WEP005

Laser Heater Transverse Shaping to Improve Microbunching Suppresion for X-ray FELs

laser, electron, FEL, linac

602

S. Li
Stanford University, Stanford, California, USA
A.R. Fry, S. Gilevich, Z. Huang, A. Marinelli, D.F. Ratner, J. Robinson
SLAC, Menlo Park, California, USA

In X-ray free electron lasers (FELs), a small amount of initial density or energy modulation in the electron beam will be amplified through acceleration and bunch compression process. The undesired microbunching on the electron bunch will increase slice energy spread and degrade the FEL performance. The Linac Coherent Light Source (LCLS) laser heater (LH) system was installed to increase the uncorrelated energy spread in the electron beam in order to suppress the microbunching instability. The distribution of the induced energy spread depends strongly on the transverse profile of the heater laser and has a large effect on the microbunching suppression. In this paper we discuss strategies to shape the laser profile in order to obtain better suppression of microbunching. We present analysis to achieve the Gaussian-like energy spread using a Laguerre-Gaussian laser mode and study the efficiency and alignment tolerance for implementation.

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WEP008

Four-Dimensional Models of FEL Amplifiers and Oscillators

electron, FEL, simulation, laser

607

J. Blau, K. R. Cohn, W.B. Colson
NPS, Monterey, California, USA

Funding: This work has been supported by the High Energy Laser Joint Technology Office.
New four-dimensional models of free electron lasers (FELs) are described, for both amplifier and oscillator configurations. Model validation and benchmarking results are shown, including comparisons to theoretical formulas and experiments.

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WEP014

LCLS-II: Status of the CW X-ray FEL Upgrade to the LCLS Facility

linac, FEL, gun, electron

618

T.O. Raubenheimer
SLAC, Menlo Park, California, USA

Funding: Work supported by Department of Energy contract DE-AC02-76SF00515
The LCLS-II is a CW X-ray FEL based on a 4 GeV superconducting RF linac that will upgrade the LCLS facility at the SLAC National Accelerator Laboratory. The upgrade is being constructed by a collaboration including ANL, Cornell, Fermilab, JLab, LBNL, and SLAC. This talk will describe the status of the LCLS-II project as well as the major technical issues and R&D to address them.
Presented on behalf of the LCLS-II collaboration

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WEP016

Free Electron Lasers in 2015

FEL, electron, laser, free-electron-laser

625

K. R. Cohn, J. Blau, W.B. Colson, J.W. Ng, M.J. Price
NPS, Monterey, California, USA

Funding: This work has been supported by the High Energy Laser Joint Technology Office.
Thirty-nine years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.

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WEP025

Effect of Microbunching on Seeding Schemes for LCLS-II

laser, electron, radiation, photon

639

G. Penn, J. Qiang
LBNL, Berkeley, California, USA
P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, 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.
External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.

Poster WEP025 [0.962 MB]

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WEP029

Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance

laser, FEL, simulation, electron

643

T. Plath, C. Lechner
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt
DESY, Hamburg, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
To enhance the spectral and temporal properties of a free-electron laser the FEL process can be seeded by an external light field. The quality of this light field strongly influences the final characteristics of the seeded FEL pulse. To push the limits of a seeding experiment and reach the smallest possible wavelengths it is therefore crucial to have a thorough understanding of relations between laser parameters and seeding performance. In this contribution we numerically study the influence of laser wavefront imperfections on high-gain harmonic generation seeding at the seeding experiment at FLASH.

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WEP051

The Prototype of New Variable Period Undulator for Novosibirsk Free Electron Laser.

simulation, permanent-magnet, FEL, electron

677

I.V. Davidyuk
NSU, Novosibirsk, Russia
O.A. Shevchenko, V.G. Tcheskidov
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
KAERI, Daejon, Republic of Korea

To improve the parameters of the second stage Novosibirsk free electron laser one plans to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles for shorter periods with constant undulator length. Both these advantages will be realized in the new undulator under development in Budker INP. The idea of the permanent-magnet VPU was proposed just several years ago and it has not been properly tested yet. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.

Poster WEP051 [3.821 MB]

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WEP052

Studies of LCLS FEL Divergence

simulation, electron, photon, quadrupole

681

J.L. Turner, P. Baxevanis, F.-J. Decker, Y. Ding, Z. Huang, J. Krzywinski, H. Loos, G. Marcus, N.P. Norvell
SLAC, Menlo Park, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Simulations show various impacts on x-ray divergence. With the motivation to maximize intensity at the focus, these beam studies were designed to study parameter space and beam qualities impacting divergence, and therefore aperture related clipping and diffraction. With multiple simultaneous users, beam constraints increase, requiring an improving knowledge of the mechanism of impact of changing parameters. These studies have that goal in order to improve beam control.

Poster WEP052 [1.010 MB]

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WEP054

Control of Gap Dependent Phase Errors on the Undulator Segments for the European XFEL

laser, electron, free-electron-laser, FEL

685

Y. Li, J. Pflüger
XFEL. EU, Hamburg, Germany

Strong magnetic forces in long undulators always result in some girder deformation. This problem gets more serious in long gap tuneable undulators. In addition the deformation varies with changing forces at different gaps resulting in gap dependent phase errors. For the undulators for the European XFEL this problem has been studied thoroughly and quantitatively. A compensation method is presented which uses a combination of suitable shims and pole height tuning. It is exemplified by tuning one of the undulator segments for the European XFEL back to specs.

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WEP062

Study on Undulator Radiation from Femtosecond Electron Bunches

electron, radiation, linac, brightness

702

N. Chaisueb, S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand

Funding: This work has been supported by the CMU Junior Research Fellowship Program, the Department of Physics and Material Science, Faculty of science, Chiang Mai University, and SAST Scholarship.
Linac based terahertz (THz) source at the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, consists of a thermionic RF electron gun, an alpha magnet for magnetic bunch compressor, a travelling wave S-band accelerating structure for post acceleration, and various beam diagnostic instruments. The PBP-CMU linac can produce relativistic femtosecond electron bunches, which are used to generate coherent THz radiation via transition radiation technique. To increase the radiation intensity, an electromagnetic undulator will be added in the beam transport line. The designed electromagnetic undulator has 40.5 periods with a period length of 56 mm and a pole gap of 15 mm. Numerical calculation result shows that the brightness of the undulator radiation, which is produced from electron bunches with an energy of 10 MeV, a peak current of 300 A, and an effective bunch length of 120 fs, is about 10 thousand times higher than the brightness of the transition radiation. This study investigates the dependence of the electron beam energy, electron bunch charge, and electron bunch length on the coherent undulator radiation by using the PARMELA code. The numerical simulation and procedure to generate the undulator radiation in the terahertz regime by using femtosecond electron bunches produced at the PBP research facility is reported and discussed in this contribution.
The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Material Science and the Graduate School, Chiang Mai University.

Poster WEP062 [8.172 MB]

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WEP073

Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser

electron, FEL, radiation, plasma

718

L.T. Campbell
USTRAT/SUPA, Glasgow, United Kingdom
A.R. Maier
CFEL, Hamburg, Germany

The effect of a correlated linear energy chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate linear taper of the undulator magnetic field have previously been investigated considering relatively small chirps. In the following, it is shown that larger linear energy chirps, such as those found in beams produced by laser-plasma accelerators, exhibit dispersive effects in the undulator, and require a non-linear taper on the undulator field to properly optimise.

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WEP075

Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam

electron, radiation, simulation, FEL

722

C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini
SLAC, Menlo Park, California, USA

We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.

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WEP076

Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing

FEL, electron, simulation, extraction

726

C. Emma
UCLA, Los Angeles, USA
K. Fang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy DE-SC0009983.
Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented.

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WEP079

Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs

FEL, electron, radiation, target

735

P. Niknejadi, J. Madey
University of Hawaii, Honolulu,, USA

The efforts in realizing x-ray free electron lasers (FELs) and enhancing their performance has stimulated remarkable theoretical developments and experimental advances in the field. Yet, the successful operation of x-ray FELs based on the self-amplified spontaneous emission (SASE) principle which has made them a powerful new tool, has beckoned our attention for better understanding a comprehensive physical basis of the theory that has the potential to improve the temporal structure and spectral optimization of these sources. We have previously explained the advantages of including the coherent radiation reaction force as a part of the solution to the boundary value problem for FELs that radiate into "free space" (SASE FELs) and discussed how the advanced field of the absorber can interact with the radiating particles at the time of emission.(*, **) Here we present the outline of our theoretical approach which follows from eigenmode analysis of optical guiding in FELs. We will also discuss in some detail the experimental setup that could verify and/or further our understanding of the the underlying physics of these devices.
* P. Niknejadi et al., Phys. Rev. D 91 096006 (2015)
** P. Niknejadi and J.M.J. Madey, in Proceedings of Free Electron Laser Conference, JACoW, Basel, Switzerland (2014)

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WEP084

Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser

FEL, simulation, electron, bunching

741

Z. Zhang
TUB, Beijing, People's Republic of China
Y. Ding, W.M. Fawley, Z. Huang, J. Krzywinski, A.A. Lutman, G. Marcus, A. Marinelli, D.F. Ratner
SLAC, Menlo Park, California, USA

The measured, self-seeded soft X-ray radiation spectrum corresponding to multiple effective undulator lengths of the LCLS exhibits a pedestal-like distribution around the seeded frequency. In the absence of a post-undulator monochromator, this contamination limits the spectral purity and may seriously degrade certain user applications. In general for either externally- or self-seeded FELs, such pedestals may originate with any time-varying property of the electron beam that can modulate the complex gain function. In this paper we specifically focus on the contributions of electron beam microbunching prior to the undulator. We show that both energy and density modulations can induce sidebands in a seeded FEL configuration. Analytic FEL theory and numerical simulations are used to analyze the sideband content relative to the amplified seeded signal, and to compare with experimental results.

Poster WEP084 [1.263 MB]

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WEP087

Smith-Purcell Radiation from Microbunched Beams Modulated after Passing the Undulators in FELs

radiation, FEL, target, polarization

752

A. Potylitsyn
TPU, Tomsk, Russia
D.Yu. Sergeeva, M.N. Strikhanov, A.A. Tishchenko
MEPhI, Moscow, Russia

We suggest using the Smith-Purcell effect from microbunched beams modulated after passing the undulators in FELs as an extra source of monochromatic radiation. We investigate theoretically characteristics of Smith-Purcell radiation in THz and X-ray frequency regions for two types of distribution of the particles in the beam. The expression for spectral-angular distribution of such radiation is obtained and analyzed, both for fully and partially modulated beams. The intensity of Smith-Purcell radiation is shown to be able to increase both due to the periodicity of the beam and the periodicity of the target. The numerical results prove that such radiation source can be an effective instrument for different FEL users, supplementary for the main FEL source.

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WED01

Commissioning of the Delta Polarizing Undulator at LCLS

polarization, radiation, bunching, electron

757

H.-D. Nuhn, S.D. Anderson, R.N. Coffee, Y. Ding, Z. Huang, M. Ilchen, Yu.I. Levashov, A.A. Lutman, J.P. MacArthur, A. Marinelli, S.P. Moeller, F. Peters, Z.R. Wolf
SLAC, Menlo Park, California, USA
J. Buck
XFEL. EU, Hamburg, Germany
G. Hartmann, J. Viefhaus
DESY, Hamburg, Germany
A.O. Lindahl
University of Gothenburg, Gothenburg, Sweden
A.B. Temnykh
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work was supported by U.S. DOE, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A.B. Temnykh is supported U.S. National Science Foundation awards DMR-0807731 and DMR-DMR-0936384.
The LCLS generates linearly polarized, intense, high brightness x-ray pulses from planar fixed-gap undulators, which provides only limited taper capability and lacks polarization control. The latter is of great importance for soft x-ray experiments. A new 3.2-m-long compact undulator (based on the Cornell University fixed-gap Delta design) has been developed and installed as the last LCLS undulator segment (U33) in October 2014. The Delta undulator provides full control of the polarization degree and K parameter through array position adjustments. Used on its own, it produces fully polarized spontaneous radiation in the selected state (linear, circular or elliptical). To increase the output power by orders of magnitude, the electron beam is micro-bunched by several (5-15) upstream LCLS undulator segments operated in the linear FEL regime. This micro-bunching process produces horizontally linear polarized (background) radiation. This unwanted radiation component has been greatly reduced by a reversed taper configuration, as suggested by Schneidmiller. Full elimination of the linear polarized component was achieved through spatial separation combined with transverse collimation. The paper will describe the methods tested during commissioning and will also present results of polarization measurements showing high degrees of circular polarization in the soft x-ray wavelength range.

Slides WED01 [10.165 MB]

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WED04

Status Report of PAL-XFEL Undulator Program

FEL, electron, radiation, controls

769

D.E. Kim, M.-H. Cho, Y.-G. Jung, H.-S. Kang, I.S. Ko, H.-G. Lee, S.B. Lee, W.W. Lee, B.G. Oh, K.-H. Park, H.S. Suh
PAL, Pohang, Kyungbuk, Republic of Korea
S. Karabekyan, J. Pflüger
XFEL. EU, Hamburg, Germany

PAL-XFEL is a SASE based FEL using S-band linear accelerator, photo cathode RF Gun, and hybrid undulator system for final lazing. The undulator system is based on EU-XFEL undulator design with necessary modifications. The changes include new magnetic geometry reflecting changed magnetic requirements, and EPICs based control system. The undulator system is in measurement and tuning stage targeting to finish installation within 2015. In this report, the development, tuning, measurement efforts for PAL-XFEL undulator system will be reported.

Slides WED04 [3.317 MB]

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