FEL2015 - List of Keywords (radiation)

Paper	Title	Other Keywords	Page
MOA02	First Lasing of the Third Stage of Novosibirsk FEL	FEL, undulator, 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, undulator, 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, undulator, electron, photon	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, undulator, 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, undulator, 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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MOP004	Influence of Horizantal Constant Magnetic Field on Harmonic Undulator Radiations and Gain	undulator, 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	undulator, FEL, electron, 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	undulator, electron, 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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MOP012	Present Status of Source Development Station at UVSOR-III	laser, experiment, undulator, 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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MOP030	Study of Smith-Purcell Free Electron Laser Using Electron Bunch Produced By Micro-Pulse Electron Gun	electron, bunching, simulation, cavity	93
	J. Zhao, X.Y. Lu, W.W. Tan, D.Y. Yang, Y. Yang, Z.Q. Yang PKU, Beijing, People's Republic of China
	A Micro-Pulse electron Gun (MPG) with the frequency of 2856 MHz has been designed, constructed and tested. Some primary experimental studies have been carried out and electron beam with the average current of 6 mA has been detected which holds promise to use as an electron source of Smith-Purcell Free Electron Laser (SP-FEL) to produced Coherent Radiation. It is well known that Smith-Purcell radiation is one of the achievable ways to produce FEL. After many years study in theory and experiment, lots of new mechanisms and appearances have been discovered. Coherent Smith-Purcell Radiation was discovered in 1990s as well. Compared with incoherent Smith-Purcell Radiation, It can generate a more powerful and frequency locked coherent emission due to displaying all three of these enhancements, Ng (the number of grating periods), Ne (the number of electrons in the bunch), Nb (the number of electron bunch). Obviously, MPG is one of ideal electron sources of CSPR for that (1) S-band electron source can increase energy density at these frequencies, (2) picosecond or subpicosecond pulse can generate THz radiation, (3) low emittance makes the interactions between electron beam and granting more stable. All of the above will be displayed in the simulation of this article. The progress of the experiment with beam energy of 80 Kev, the average current of 6 mA is also introduced.
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MOP033	Numerical Simulations of a Sub-THz Coherent Transition Radiation Source at PITZ	electron, simulation, laser, booster	97
	P. Boonpornprasert, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany B. Marchetti DESY, Hamburg, Germany
	The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can be considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments at the European XFEL. For this reason, the radiation generated by high-gain FEL and Coherent Transition Radiation (CTR) produced by the PITZ electron beam has been studied. In this paper, numerical simulations on the generation of CTR based on the PITZ accelerator are presented. The beam dynamics simulations of electron bunches compressed by velocity bunching are performed by using the ASTRA code. The characteristics of CTR are calculated numerically by using the generalized Ginzburg-Frank formula. The details and results of the simulations are described and discussed.
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MOP050	Development of Coherent Terahertz Wave Sources using LEBRA and KU-FEL S-band Linacs	FEL, electron, vacuum, synchrotron-radiation	143
	N. Sei, H. Ogawa AIST, Tsukuba, Ibaraki, Japan K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka LEBRA, Funabashi, Japan H. Ohgaki, H. Zen Kyoto University, Kyoto, Japan
	Funding: This work is supported by the "ZE Research Program, IAE ZE27B-6". In an infrared free-electron laser (FEL) facility using an S-band linac, a short-bunched electron beam is required to obtain a high FEL gain. Generally, the bunch length of the electron beam is compressed to 1 ps or less before interaction with the photons accumulated in the FEL resonator. This suggests that the electron beam dedicated to the FEL oscillation is suitable for generation of high-peak-power coherent radiation in terahertz (THz) wave region. Using the compressed electron beams, the coherent THz-wave sources have been developed at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University and Kyoto University Free Electron Laser (KU-FEL). The observed powers have been higher than 100 micro-joule per macropulse. In this presentation, the properties of the high-power coherent THz waves generated at the bending magnets will be reported. N. Sei et al., J. Opt. Soc. Am. B 31 (2014) 2150.
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MOP060	RFTweak 5 - An Efficient Longitudinal Beam Dynamics Code	GUI, controls, diagnostics, space-charge	176
	B. Beutner, H. Dinter, M. Dohlus DESY, Hamburg, Germany
	The shaping of the longitudinal phase space in bunch compression systems is essential for efficient FEL operation. RF systems and self-field interactions contribute to the overall phase space structure. The design of the various facilities relies on extensive beam dynamics simulations to define the longitudinal dynamics. However, in everyday control room applications such techniques are often not fast enough for efficient operation, e.g. for SASE tuning. Therefore efficient longitudinal beam dynamics codes are required while still maintaining reasonable accuracy. Our approach is to pre-calculate most of the required data for self-field interactions and store them on disc to reduce required online calculation time to a minimum. In this paper we present the fast longitudinal tracking code RFTweak 5, which includes wakes, space charge, and CSR interactions. With this code the full European XFEL with a 1M particles bunch is calculated on the order of minutes on a standard laptop. Neglecting CSR effects this time reduces to seconds.
	Poster MOP060 [0.799 MB]
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MOP068	First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators	undulator, 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, undulator, electron, 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, undulator, 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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MOP074	Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser	wiggler, electron, resonance, FEL	209
	N.S. Mirian UVSOR, Okazaki, Japan B. Maraghechi, E. Salehi AUT, Tehran, Iran
	The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Thermal effects in the form of longitudinal velocity spread are also investigated. The second wiggler field decreases linearly and nonlinearly at the point where the radiation of the third harmonic saturates to enhance the efficiency. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably.
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MOP075	Three-dimensional Simulation of a Harmonic Lasing Free-Electron Laser Amplifier	wiggler, electron, resonance, FEL	213
	E. Salehi, B. Maraghechi AUT, Tehran, Iran N.S. Mirian UVSOR, Okazaki, Japan
	Three-dimensional simulation of harmonic lasing Free-electron laser is represented in the steady-state regime. Here, the third harmonic of the first wiggler is adjusted at the fundamental resonance of the second wiggler by reducing the magnetic field strength of the second wiggler. The hyperbolic wave equations can be transformed into parabolic diffusion equations by using the slowly varying envelope approximation. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system is solved numerically by CYRUS3D code. This set of equations describes self-consistently the longitudinal spatial dependence of the radiation waists, curvatures, and amplitudes together with the evaluation of the electron beam. Thermal effects in the form of longitudinal velocity spread are also investigated. In order to reduce the length of the wiggler, the prebunched electron beam is considered.
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MOP078	Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam	electron, undulator, 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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MOP081	Generating a Single-Spike SASE Pulse in the Soft X-Ray Regime by Velocity Bunching	FEL, electron, linac, undulator	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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MOP083	FEL Operation Modes of the MAX IV Short Pulse Facility	undulator, electron, 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, undulator, simulation, 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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MOP086	Novel Opportunities for Sub-meV Inelastic X-Ray Scattering Experiments at High-Repetition Rate Self-seeded XFELs	undulator, 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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MOD02	Overview of Alternative Bunching and Current-shaping Techniques for Low-Energy Electron Beams	electron, laser, bunching, wakefield	274
	P. Piot Fermilab, Batavia, Illinois, USA P. Piot Northern Illinois University, DeKalb, Illinois, USA
	Funding: This work was supported by the U.S. Department of Energy contracts No. DE-SC0011831 to Northern Illinois University and No. DE-AC02-07CH11359 with the Fermi Research Alliance, LLC Techniques to bunch or shape an electron beam at low energies (E <15 MeV) have important implications toward the realization of table-top radiation sources [1] or to the design of compact multi-user free-electron lasers[2]. This paper provides an overview of alternative methods recently developed including techniques such as wakefield-based bunching, space-charge-driven microbunching via wave-breaking [3], ab-initio shaping of the electron-emission process [4], and phase space exchangers. Practical applications of some of these methods to foreseen free-electron-laser configurations are also briefly discussed [5]. [1] W. S. Graves, PRL 108, 263904 (2012) [2] A. Zholents, FEL14, 993 (2014) [3] P. Musumeci, PRL 106, 184801 (2011) [4] F. Lemery, PRSTAB 17, 112804 (2014) [5] G. Penco, PRL 112, 044801 (2014)
	Slides MOD02 [5.426 MB]
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TUB02	Distributed Seeding for Narrow-band X-ray Free-Electron Lasers	undulator, 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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TUB05	Tunable High-power Terahertz Free-Electron Laser Amplifier	FEL, laser, electron, simulation	305
	G. Zhao, S. Huang, K.X. Liu, W. Qin, L. Zeng PKU, Beijing, People's Republic of China C.H. Chen, Y.C. Chiu, Y.-C. Huang NTHU, Hsinchu, Taiwan
	In the THz spectrum, radiation sources are relatively scarce. Although recent advancement on optical technologies has enabled THz radiation generation covering a broad spectral range, free-electron laser (FEL) continues to be the most importance source for generating high-power THz radiation. Here we present an ongoing collaboration between Peking University (PKU) and National Tsinghua University (NTHU) to demonstrate high peak and average powers from a THz free-electron laser amplifier driven by a superconducting accelerator system at PKU. The superconducting accelerator comprises the DC-SRF photoinjector and a linac utilizing two 1.3 GHz Tesla-type cavities. It is expected to deliver high repetition rate electron beam with the energy of 10-25 MeV and rms bunch length of about 3 ps. The driver laser of the photoinjector is a mode-locked frequency-quadrupled Nd:YVO4 laser at 266 nm. We use the remaining gun driver laser power at 1064 nm to pump a THz parametric amplifier (TPA) which designed at NTHU and generate the THz seed radiation for the FEL amplifier. The signal laser of the TPA is tunable over 2 THz, permitting generation of radiation between 0.5 and 2.5 THz to seed the FEL amplifier. With our design parameters and computer simulation in GENESIS, we expect to generate narrow-band, wavelength-tunable THz radiation with sub-MW peak power and Watt-level average power.
	Slides TUB05 [2.349 MB]
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TUP001	THz Photo-Injector FEM Based on Spontaneous Coherent Emission from a Bunch of Negative-Mass Electrons	electron, undulator, 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	undulator, simulation, electron, 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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TUP003	Threshold of a Mirror-less Photonic Free Electron Laser Oscillator Pumped by One or More Electron Beams	electron, laser, free-electron-laser, plasma	327
	P.J.M. van der Slot, K.-J. Boller, A. Strooisma Mesa+, Enschede, The Netherlands
	Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs Transmitting electrons through a photonic crystal can result in stimulated emission and the generation of coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide. By appropriately tapering the bars at both ends of the slab, we numerically show that an electromagnetic wave can be transmitted through the waveguide filled with the photonic-crystal slab with close to zero reflection. Furthermore, the photonic-crystal slab allows transmission of electrons in the form of one or more beams. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron-beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we discuss the dynamics of the laser oscillator near threshold and numerically show that the threshold current can be distributed over multiple electron beams, resulting in a lower current per beam.
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TUP005	A Mirror-Less, Multi-Beam Photonic Free-Electron Laser Oscillator Pumped Far Beyond Threshold	electron, laser, free-electron-laser, feedback	334
	P.J.M. van der Slot, K.-J. Boller, A. Strooisma Mesa+, Enschede, The Netherlands
	Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs In a photonic free-electron laser electrons are transmitted through a photonic crystal in the form of one or multiple electron beams to generate coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide, with both ends tapered to provide complete transmission of an electromagnetic wave. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we numerically study the dynamics of the laser oscillator when pumped far beyond threshold with one or multiple electron beams. We show that using multiple beams with the same total current provide better suppression of higher-order modes and can produce more output power, compared to the laser pumped by a single beam of the same total current.
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TUP006	Quantum Nature of Electrons in Classical X-ray FELs	FEL, electron, undulator, 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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TUP009	Coherent Thomson Scattering Using the PEHG	laser, scattering, electron, simulation	351
	S. Chen, K. Ohmi, D. Zhou KEK, Ibaraki, Japan
	Electron beam is density modulated by the phase-merging effect to obtain ultra-short longitudinal structures in the phase space. Coherent radiations are then generated by the coherent Thomson scattering between the phase-merged beam and a long wavelength laser pulse.
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TUP012	Plans for an EEHG-based Short-Pulse Facility at the DELTA Storage Ring	laser, electron, storage-ring, synchrotron	363
	S. Hilbrich, F.H. Bahnsen, M. Bolsinger, M.A. Jebramcik, S. Khan, C. Mai, A. Meyer auf der Heide, R. Molo, H. Rast, G. Shayeganrad, P. Ungelenk DELTA, Dortmund, Germany
	Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Federal State NRW. The 1.5-GeV synchrotron light source DELTA, operated by the TU Dortmund University, comprises a short-pulse facility based on the coherent harmonic generation (CHG) technique, which allows for the generation of radiation pulses with wavelengths down to 50 nm and a duration of 50 fs. In order to reach even shorter wavelengths, the present setup will be modified to employ the echo-enabled harmonic generation (EEHG) and femtoslicing techniques. In this paper, recent developments including an improved lattice design and a concept for the new vacuum chambers will be presented.
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TUP015	Status of the ALICE IR-FEL: from ERL Demonstrator to User Facility	FEL, laser, cavity, operation	379
	N. Thompson, J.A. Clarke, D.J. Dunning, A.J. Moss, Y.M. Saveliev, M. Surman STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom T. Craig, M.R.F. Siggel-King, P. Weightman The University of Liverpool, Liverpool, United Kingdom O.V. Kolosov, P.D. Tovee Lancaster University, Lancaster, United Kingdom M.R.F. Siggel-King Cockcroft Institute, Warrington, Cheshire, United Kingdom
	The ALICE (Accelerators and Lasers In Combined Experiments) accelerator at STFC Daresbury Laboratory in the UK was conceived in 2003 and constructed as a short-term Energy Recovery Linac demonstrator to develop the underpinning technology and expertise required for a proposed 600MeV ERL-based FEL facility. In this paper we present an update on the performance and status of ALICE which now operates as a funded IR-FEL user facility. We discuss the challenges of evolving a short-term demonstrator into a stable, reliable user facility and present a summary of the current scientific programme.
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TUP019	Time Locking Options for the Soft X-Ray Beamline of SwissFEL	laser, FEL, electron, undulator	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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TUP021	Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability	FEL, emittance, electron, undulator	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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TUP022	Measurement of Spatial Displacement of X-rays in Crystals for Self-Seeding Applications	experiment, FEL, electron, detector	405
	A. Rodriguez-Fernandez, B. Pedrini, S. Reiche PSI, Villigen PSI, Switzerland K. Finkelstein Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Free-electron laser (FEL) radiation arises from shot noise in the electron bunch, which is amplified along the undulator section and results in X-ray pulses consisting of many longitudinal modes [1]. The output bandwidth of FELs can be decreased by seeding the FEL process with longitudinally coherent radiation. In the hard x-ray region, there are no suitable external sources. This obstacle can be overcome by self-seeding. The X-ray beam is separated from the electrons using a magnetic chicane, and then monochromatized. The monochromatized X-rays serve as a narrowband seed, after recombination with the electron bunch, along the downstream undulators. This scheme generates longitudinally coherent FEL pulses.[2] have proposed monochromatization based on Forward Bragg Diffraction (FBD), which introduces a delay of the narrowband X-rays pulse of the order of femtoseconds that can be matched to the delay of the electron bunch due to the chicane. Unfortunately, the FBD process produces a small transverse displacement of the X-ray beam, which results in the loss of efficiency of the seeding process [3]. Preliminary results from an experiment performed at Cornell High Energy Synchrotron Source seem to confirm the predicted transverse displacement, which is therefore to be taken into account in the design of self-seeding infrastructure for optimizing the FEL performance. [1] J.S. Wark et al., J. Apply. Crystallogr. 32, 692 (1999) [2] G. Geloni et al., DESY report 10-053 (2010). [3] Y. Shvyd'ko et al., Phys. Rev. ST Accel. Beams 15, 100702 (2012)
	Poster TUP022 [5.503 MB]
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TUP023	A Modified Self-Seeded X-ray FEL Scheme Towards Shorter Wavelengths	FEL, laser, electron, undulator	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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TUP027	Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA	laser, undulator, 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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TUP029	Single Picosecond THz Pulse Extraction from the FEL Macropulse using a Laser Activating Semiconductor Reflective Switch	FEL, laser, extraction, linac	430
	K. Kawase, M. Fujimoto, K. Furukawa, A. Irizawa, G. Isoyama, R. Kato, K. Kubo ISIR, Osaka, Japan
	The THz-FEL at the Institute of Scientific and Industrial Research, Osaka University can generate high-intensity THz pulses or FEL macropulses, which comprise approximately 100 micropulses at 37 ns intervals in the 27 MHz mode or 400 micropulses at 9.2 ns intervals in the 108 MHz mode. The maximum macropulse energy in the 27 MHz mode reaches 26 mJ at a frequency of 4.5 THz and the micropulse energy is estimated to be 0.2 mJ. To open new areas of studies with high intensity THz radiation for user experiments, we are developing a single pulse extraction system from the pulse train using a laser activating semiconductor reflective switch. We have succeeded in extracting a single THz pulse, duration of which is estimated to be less than 20 ps, from the FEL macropulse using a gallium arsenide wafer for the switch. We will report on the THz pulse extraction system and its performance.
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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, undulator, 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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TUP053	Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion	polarization, FEL, undulator, 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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TUP056	Design Challenge and Strategy for the LCLS-II High Repetition Rate X-ray FEL Photon Stoppers	photon, FEL, simulation, synchrotron	493
	Y. Feng, J.T. Delor, J. Krzywinski, P.A. Montanez, E. Ortiz, T.O. Raubenheimer, M. Rowen 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. Future high repetition rate X-ray FELs such as the European XFEL and LCLS-II presents new challenges to photon diagnostics as well as essential beamline components. In addition to these devices having to sustain the high peak power of a single-pulse FEL radiation, they must also be capable of handling the enormous power density of tens to hundreds of watts over an area as small as 0.1 mm X mm. In this talk, I will discuss the potential impact of high power FEL operation on performance of a gas attenuator and the design challenges to beam intercepting components such as a collimator or stopper.
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TUP057	The Highly Adjustable Magnet Undulator	undulator, simulation, electron, permanent-magnet	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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TUP074	Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility	laser, undulator, 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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TUP080	Terahertz Source Utilizing Resonant Coherent Diffraction Radiation at KEK ERL Test Accelerator	cavity, photon, extraction, operation	547
	Y. Honda, A. Aryshev, M. Shevelev, M. Shimada KEK, Ibaraki, Japan
	An energy recovery linac test accelerator, cERL, has been developing at KEK. It can produce a high repetition rate short bunched electron beam in a continuous operation mode. We propose to develop a high power THz radiation source at the return loop of the cERL. Coherent diffraction radiation of THz regime is emitted when an electron bunch passes through a conductive mirror with a beam hole at the center. If we form an optical cavity using two mirrors facing each other and the cavity length coincides with the bunch repetition rate, the coherent diffraction radiation of multiple bunches adds up coherently in the cavity. By extracting the power through transmission of one of the mirrors, we can realize a high power and high efficiency THz source. We discuss performance of the source assuming the beam parameters of cERL.
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TUP085	Lebra Free-Electron Laser Elicits Electrical Spikes from the Retina and Optic Nerve of the Slugs Limax Valentianus	FEL, site, experiment, electron	550
	F. Shishikura, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka LEBRA, Funabashi, Japan Y. Komatsuzaki Nihon University, Tokyo, Japan
	Since 2001, the Laboratory for Electron Beam Research and Application (LEBRA) has been providing tunable free-electron lasers (FELs) encompassing the near-IR region and some of the mid-IR region (0.9-6 microns), and generating visible wavelengths up to 400 nm by means of nonlinear optical crystals. We are investigating the efficiency of LEBRA-FELs for triggering photoreactions in living organisms. Last year we described the effects of LEBRA-FELs in controlling the photoreaction of lettuce seeds; red FEL (660 nm) and far-red FEL (740 nm) activate and inhibit germination, respectively. Here we used LEBRA-FEL to illuminate the retina of slugs (Limax valentianus), and determined which FEL wavelengths generate electrical spikes from the retina-optic nerve. Blue FEL light (wavelength: 470 nm) efficiently produced electrical spikes from the retina. The results are consistent with a previous study, where a xenon arc lamp with interference filters was used to produce monochromatic visible light. We plan to extend the wavelengths to the near- and mid-IR regions of LEBRA-FEL. We summarize our current results for the use of FEL in investigating the electrophysiology of the retina of slugs. We thank Mr. T. Kuwabara (a graduate of Departments of Physics, College of Science and Technolgy, Nihon University) for helpful assistance.
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TUD01	COTR Resistant Profile Monitor	electron, laser, diagnostics, bunching	554
	H. Loos SLAC, Menlo Park, California, USA
	Funding: Work supported by DOE contract DE-AC02-76SF00515 Electron beam accelerators used as drivers for short wavelength FELs need ultra-high brightness beams with small emittances and highly compressed bunch lengths. The acceleration and beam transport process of such beams leads to micro-bunching instabilities which cause the emergence of coherent optical transition radiation (COTR). The effect of COTR on profile monitors based on OTR or fluorescent screens can be quite detrimental to their intended use to measure beam sizes and profiles. This presentation will review past observations of the beam diagnostics issues due to COTR and discuss various mitigation schemes for profile monitors as well as present experience with such implementations.
	Slides TUD01 [1.536 MB]
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TUD02	Diffraction Radiation Monitor	electron, target, beam-diagnostic, diagnostics	561
	Y. Taira AIST, Tsukuba, Japan
	Non-invasive beam diagnostics using a diffraction radiation (DR) has been developed at several electron accelerator facilities. Generation process of DR is similar to that of transition radiation (TR). TR is emitted when a charged particle passes through the boundary between two media with different dielectric constants. On the other hand, DR is emitted when it passes through in the vicinity of a boundary between two media. In the generation process of DR, the charged particle doesn't intersect the medium but its electric field intersects the medium. An aperture, a slit, and an edge are used for DR target. Optical wavelength of DR is usually used for beam diagnostics. One can evaluate energy, a transverse beam size, and a divergence of an electron beam by measuring a spatial distribution of DR. Moreover, coherent diffraction radiation with the wavelength of less than millimeter range is used for a bunch length measurement. In this conference, a theoretical background of DR and experimental results carried out at several facilities will be presented.
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WEP001	RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS	undulator, 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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WEP025	Effect of Microbunching on Seeding Schemes for LCLS-II	laser, electron, undulator, 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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WEP062	Study on Undulator Radiation from Femtosecond Electron Bunches	undulator, electron, 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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WEP067	Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility	bunching, space-charge, simulation, impedance	707
	A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University. Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4]) [1] M. Dohlus, PRSTAB, 14 090702 (2011). [2] A. Marinelli, PRL, 110 264802 (2013). [3] M. Borland, Advanced Photon Source, LS-287, 2000. [4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015).
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WEP073	Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser	electron, undulator, FEL, 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, undulator, 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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WEP079	Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs	FEL, electron, target, undulator	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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WEP082	High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses	polarization, electron, timing, laser	739
	J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov KAERI, Daejon, Republic of Korea B.A. Gudkov, S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method. Phys. Rev. Lett. 110, 064805.
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WEP085	Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance	electron, wiggler, FEL, free-electron-laser	746
	A. Gover, R. Ianconescu University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel C. Emma, P. Musumeci UCLA, Los Angeles, USA A. Friedman Ariel University, Ariel, Israel
	Funding: We acknowledge partial support by the U.S. Israel Binational Science Foundation (BSF)Jerusalem, Israel In the context of radiation emission from an electron beam Dicke's superradiance (SR) is the enhanced radiation emission from a pre-bunched beam. Stimulated Superradiance (ST-SR) is the further enhanced emission of the bunched beam in the presence of a phase-matched radiation wave. These processes were analyzed for Undulator radiation in the framework of radiation field mode-excitation theory[1]. In the nonlinear saturation regime the synchronism of the bunched beam and an injected radiation wave may be sustained by wiggler tapering [2]. Same processes are instrumental also in enhancing the radiative emission in the tapered wiggler section of seeded FEL[3]. In a long tapered wiggler the diffraction of the emitted radiation wave is not negligible even at Angstroms wavelengths (as in LCLS). A Fresnel diffraction model was provided in [4] for the SR process only. Here we outline the fundamental physical concepts of Spontaneous Superradiadce (SR), Stimulated Superradiance (ST-SR), Taper-Enhanced Superradiance (TES) and Taper-Enhanced Stimulated Superradiance Amplification (TESSA), and compare their Fourier and Phasor formulations in the radiation mode expansion and free-diffraction models. Detailed further analysis can provide better design concepts of high power FELs and improved tapering strategy for enhancing the power of seeded short wavelength FELs 1. A. Gover, PR ST-AB 8, (030701) ; (030702) (2005) 2. J. Duris et al., arxiv 2015. 3. Y. Jiao et al., PR ST-AB 15 050704 2012 4. E.A. Schneidmiller, M.V. Yurkov, PR ST-AB 18, 030705 (2015)
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WEP087	Smith-Purcell Radiation from Microbunched Beams Modulated after Passing the Undulators in FELs	FEL, target, undulator, 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	undulator, polarization, 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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WED03	Photon Diagnostics and Photon Beamlines Installations at the European XFEL	diagnostics, photon, beam-transport, vacuum	764
	J. Grünert, B. Baranasic, J. Buck, F. Dietrich, M. Dommach, W. Freund, A. Koch, N.G. Kujala, J. Liu, S. Molodtsov, M. Planas, H. Sinn XFEL. EU, Hamburg, Germany
	The European X-ray Free-Electron-Laser (XFEL. EU) is a new a 4th generation light facility which will deliver radiation with femtosecond and sub-Ångström resolution at MHz repetition rates, and is currently under construction in the Hamburg metropolitan area in Germany. Special diagnostics [1,2] for spontaneous radiation analysis is required to tune towards the lasing condition. Once lasing is achieved, diagnostic imagers [3], online monitors [4], and the photon beam transport system [5] need to cope with extreme radiation intensities. In 2015 the installation of machine equipment in the photon area of the facility is in full swing. This contribution presents the progress on final assemblies of photon diagnostics, the installation status of these devices as well as of the beam transport system, and recent design developments for diagnostic spectrometers and temporal diagnostics. [1] J. Grünert, XFEL. EU TR-2012-003(2012) [2] W. Freund, XFEL. EU TN-2014-001-01(2014) [3] A. Koch, Proc. SPIE 95121R(2015) [4] J. Buck et al., Proc. SPIE 85040U(2012) [5] H. Sinn et al., XFEL. EU TR-2012-006(2012)
	Slides WED03 [14.557 MB]
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WED04	Status Report of PAL-XFEL Undulator Program	undulator, FEL, electron, 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, undulator, 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, undulator, 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, undulator, electron, photon

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, undulator, 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, undulator, 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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MOP004

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

undulator, 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

undulator, FEL, electron, 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

undulator, electron, 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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MOP012

Present Status of Source Development Station at UVSOR-III

laser, experiment, undulator, 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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MOP030

Study of Smith-Purcell Free Electron Laser Using Electron Bunch Produced By Micro-Pulse Electron Gun

electron, bunching, simulation, cavity

93

J. Zhao, X.Y. Lu, W.W. Tan, D.Y. Yang, Y. Yang, Z.Q. Yang
PKU, Beijing, People's Republic of China

A Micro-Pulse electron Gun (MPG) with the frequency of 2856 MHz has been designed, constructed and tested. Some primary experimental studies have been carried out and electron beam with the average current of 6 mA has been detected which holds promise to use as an electron source of Smith-Purcell Free Electron Laser (SP-FEL) to produced Coherent Radiation. It is well known that Smith-Purcell radiation is one of the achievable ways to produce FEL. After many years study in theory and experiment, lots of new mechanisms and appearances have been discovered. Coherent Smith-Purcell Radiation was discovered in 1990s as well. Compared with incoherent Smith-Purcell Radiation, It can generate a more powerful and frequency locked coherent emission due to displaying all three of these enhancements, Ng (the number of grating periods), Ne (the number of electrons in the bunch), Nb (the number of electron bunch). Obviously, MPG is one of ideal electron sources of CSPR for that (1) S-band electron source can increase energy density at these frequencies, (2) picosecond or subpicosecond pulse can generate THz radiation, (3) low emittance makes the interactions between electron beam and granting more stable. All of the above will be displayed in the simulation of this article. The progress of the experiment with beam energy of 80 Kev, the average current of 6 mA is also introduced.

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MOP033

Numerical Simulations of a Sub-THz Coherent Transition Radiation Source at PITZ

electron, simulation, laser, booster

97

P. Boonpornprasert, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
B. Marchetti
DESY, Hamburg, Germany

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can be considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments at the European XFEL. For this reason, the radiation generated by high-gain FEL and Coherent Transition Radiation (CTR) produced by the PITZ electron beam has been studied. In this paper, numerical simulations on the generation of CTR based on the PITZ accelerator are presented. The beam dynamics simulations of electron bunches compressed by velocity bunching are performed by using the ASTRA code. The characteristics of CTR are calculated numerically by using the generalized Ginzburg-Frank formula. The details and results of the simulations are described and discussed.

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MOP050

Development of Coherent Terahertz Wave Sources using LEBRA and KU-FEL S-band Linacs

FEL, electron, vacuum, synchrotron-radiation

143

N. Sei, H. Ogawa
AIST, Tsukuba, Ibaraki, Japan
K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka
LEBRA, Funabashi, Japan
H. Ohgaki, H. Zen
Kyoto University, Kyoto, Japan

Funding: This work is supported by the "ZE Research Program, IAE ZE27B-6".
In an infrared free-electron laser (FEL) facility using an S-band linac, a short-bunched electron beam is required to obtain a high FEL gain. Generally, the bunch length of the electron beam is compressed to 1 ps or less before interaction with the photons accumulated in the FEL resonator. This suggests that the electron beam dedicated to the FEL oscillation is suitable for generation of high-peak-power coherent radiation in terahertz (THz) wave region. Using the compressed electron beams, the coherent THz-wave sources have been developed at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University and Kyoto University Free Electron Laser (KU-FEL). The observed powers have been higher than 100 micro-joule per macropulse*. In this presentation, the properties of the high-power coherent THz waves generated at the bending magnets will be reported.
* N. Sei et al., J. Opt. Soc. Am. B 31 (2014) 2150.

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MOP060

RFTweak 5 - An Efficient Longitudinal Beam Dynamics Code

GUI, controls, diagnostics, space-charge

176

B. Beutner, H. Dinter, M. Dohlus
DESY, Hamburg, Germany

The shaping of the longitudinal phase space in bunch compression systems is essential for efficient FEL operation. RF systems and self-field interactions contribute to the overall phase space structure. The design of the various facilities relies on extensive beam dynamics simulations to define the longitudinal dynamics. However, in everyday control room applications such techniques are often not fast enough for efficient operation, e.g. for SASE tuning. Therefore efficient longitudinal beam dynamics codes are required while still maintaining reasonable accuracy. Our approach is to pre-calculate most of the required data for self-field interactions and store them on disc to reduce required online calculation time to a minimum. In this paper we present the fast longitudinal tracking code RFTweak 5, which includes wakes, space charge, and CSR interactions. With this code the full European XFEL with a 1M particles bunch is calculated on the order of minutes on a standard laptop. Neglecting CSR effects this time reduces to seconds.

Poster MOP060 [0.799 MB]

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MOP068

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

undulator, 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, undulator, electron, 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, undulator, 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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MOP074

Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser

wiggler, electron, resonance, FEL

209

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

The harmonic lasing free-electron laser amplifier, in which two wigglers is employed in order for the fundamental resonance of the second wiggler to coincide with the third harmonic of the first wiggler to generate ultraviolet radiation, is studied. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system, for a long electron bunch, is solved numerically by CYRUS code. Thermal effects in the form of longitudinal velocity spread are also investigated. The second wiggler field decreases linearly and nonlinearly at the point where the radiation of the third harmonic saturates to enhance the efficiency. The optimum starting point and the slope of the tapering of the amplitude of the wiggler are found by a successive run of the code. It is found that tapering can increase the saturated power of the third harmonic considerably.

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MOP075

Three-dimensional Simulation of a Harmonic Lasing Free-Electron Laser Amplifier

wiggler, electron, resonance, FEL

213

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

Three-dimensional simulation of harmonic lasing Free-electron laser is represented in the steady-state regime. Here, the third harmonic of the first wiggler is adjusted at the fundamental resonance of the second wiggler by reducing the magnetic field strength of the second wiggler. The hyperbolic wave equations can be transformed into parabolic diffusion equations by using the slowly varying envelope approximation. A set of coupled nonlinear first-order differential equations describing the nonlinear evolution of the system is solved numerically by CYRUS3D code. This set of equations describes self-consistently the longitudinal spatial dependence of the radiation waists, curvatures, and amplitudes together with the evaluation of the electron beam. Thermal effects in the form of longitudinal velocity spread are also investigated. In order to reduce the length of the wiggler, the prebunched electron beam is considered.

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MOP078

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

electron, undulator, 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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MOP081

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

FEL, electron, linac, undulator

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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MOP083

FEL Operation Modes of the MAX IV Short Pulse Facility

undulator, electron, 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, undulator, simulation, 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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MOP086

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

undulator, 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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MOD02

Overview of Alternative Bunching and Current-shaping Techniques for Low-Energy Electron Beams

electron, laser, bunching, wakefield

274

P. Piot
Fermilab, Batavia, Illinois, USA
P. Piot
Northern Illinois University, DeKalb, Illinois, USA

Funding: This work was supported by the U.S. Department of Energy contracts No. DE-SC0011831 to Northern Illinois University and No. DE-AC02-07CH11359 with the Fermi Research Alliance, LLC
Techniques to bunch or shape an electron beam at low energies (E <15 MeV) have important implications toward the realization of table-top radiation sources [1] or to the design of compact multi-user free-electron lasers[2]. This paper provides an overview of alternative methods recently developed including techniques such as wakefield-based bunching, space-charge-driven microbunching via wave-breaking [3], ab-initio shaping of the electron-emission process [4], and phase space exchangers. Practical applications of some of these methods to foreseen free-electron-laser configurations are also briefly discussed [5].
[1] W. S. Graves, PRL 108, 263904 (2012)
[2] A. Zholents, FEL14, 993 (2014)
[3] P. Musumeci, PRL 106, 184801 (2011)
[4] F. Lemery, PRSTAB 17, 112804 (2014)
[5] G. Penco, PRL 112, 044801 (2014)

Slides MOD02 [5.426 MB]

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TUB02

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

undulator, 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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TUB05

Tunable High-power Terahertz Free-Electron Laser Amplifier

FEL, laser, electron, simulation

305

G. Zhao, S. Huang, K.X. Liu, W. Qin, L. Zeng
PKU, Beijing, People's Republic of China
C.H. Chen, Y.C. Chiu, Y.-C. Huang
NTHU, Hsinchu, Taiwan

In the THz spectrum, radiation sources are relatively scarce. Although recent advancement on optical technologies has enabled THz radiation generation covering a broad spectral range, free-electron laser (FEL) continues to be the most importance source for generating high-power THz radiation. Here we present an ongoing collaboration between Peking University (PKU) and National Tsinghua University (NTHU) to demonstrate high peak and average powers from a THz free-electron laser amplifier driven by a superconducting accelerator system at PKU. The superconducting accelerator comprises the DC-SRF photoinjector and a linac utilizing two 1.3 GHz Tesla-type cavities. It is expected to deliver high repetition rate electron beam with the energy of 10-25 MeV and rms bunch length of about 3 ps. The driver laser of the photoinjector is a mode-locked frequency-quadrupled Nd:YVO4 laser at 266 nm. We use the remaining gun driver laser power at 1064 nm to pump a THz parametric amplifier (TPA) which designed at NTHU and generate the THz seed radiation for the FEL amplifier. The signal laser of the TPA is tunable over 2 THz, permitting generation of radiation between 0.5 and 2.5 THz to seed the FEL amplifier. With our design parameters and computer simulation in GENESIS, we expect to generate narrow-band, wavelength-tunable THz radiation with sub-MW peak power and Watt-level average power.

Slides TUB05 [2.349 MB]

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TUP001

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

electron, undulator, 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

undulator, simulation, electron, 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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TUP003

Threshold of a Mirror-less Photonic Free Electron Laser Oscillator Pumped by One or More Electron Beams

electron, laser, free-electron-laser, plasma

327

P.J.M. van der Slot, K.-J. Boller, A. Strooisma
Mesa+, Enschede, The Netherlands

Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs
Transmitting electrons through a photonic crystal can result in stimulated emission and the generation of coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide. By appropriately tapering the bars at both ends of the slab, we numerically show that an electromagnetic wave can be transmitted through the waveguide filled with the photonic-crystal slab with close to zero reflection. Furthermore, the photonic-crystal slab allows transmission of electrons in the form of one or more beams. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron-beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we discuss the dynamics of the laser oscillator near threshold and numerically show that the threshold current can be distributed over multiple electron beams, resulting in a lower current per beam.

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TUP005

A Mirror-Less, Multi-Beam Photonic Free-Electron Laser Oscillator Pumped Far Beyond Threshold

electron, laser, free-electron-laser, feedback

334

P.J.M. van der Slot, K.-J. Boller, A. Strooisma
Mesa+, Enschede, The Netherlands

Funding: This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research, and which is partly funded by the Ministry of Economic Affairs
In a photonic free-electron laser electrons are transmitted through a photonic crystal in the form of one or multiple electron beams to generate coherent Cerenkov radiation. Here we consider a photonic-crystal slab consisting of a two-dimensional, periodic array of bars inside a rectangular waveguide, with both ends tapered to provide complete transmission of an electromagnetic wave. By appropriately designing the photonic-crystal slab, we obtain a backward wave interaction at low electron beam energy of around 15 kV, that results in distributed feedback of the radiation on the electrons without any external mirrors being present. Here we numerically study the dynamics of the laser oscillator when pumped far beyond threshold with one or multiple electron beams. We show that using multiple beams with the same total current provide better suppression of higher-order modes and can produce more output power, compared to the laser pumped by a single beam of the same total current.

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TUP006

Quantum Nature of Electrons in Classical X-ray FELs

FEL, electron, undulator, 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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TUP009

Coherent Thomson Scattering Using the PEHG

laser, scattering, electron, simulation

351

S. Chen, K. Ohmi, D. Zhou
KEK, Ibaraki, Japan

Electron beam is density modulated by the phase-merging effect to obtain ultra-short longitudinal structures in the phase space. Coherent radiations are then generated by the coherent Thomson scattering between the phase-merged beam and a long wavelength laser pulse.

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TUP012

Plans for an EEHG-based Short-Pulse Facility at the DELTA Storage Ring

laser, electron, storage-ring, synchrotron

363

S. Hilbrich, F.H. Bahnsen, M. Bolsinger, M.A. Jebramcik, S. Khan, C. Mai, A. Meyer auf der Heide, R. Molo, H. Rast, G. Shayeganrad, P. Ungelenk
DELTA, Dortmund, Germany

Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Federal State NRW.
The 1.5-GeV synchrotron light source DELTA, operated by the TU Dortmund University, comprises a short-pulse facility based on the coherent harmonic generation (CHG) technique, which allows for the generation of radiation pulses with wavelengths down to 50 nm and a duration of 50 fs. In order to reach even shorter wavelengths, the present setup will be modified to employ the echo-enabled harmonic generation (EEHG) and femtoslicing techniques. In this paper, recent developments including an improved lattice design and a concept for the new vacuum chambers will be presented.

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TUP015

Status of the ALICE IR-FEL: from ERL Demonstrator to User Facility

FEL, laser, cavity, operation

379

N. Thompson, J.A. Clarke, D.J. Dunning, A.J. Moss, Y.M. Saveliev, M. Surman
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T. Craig, M.R.F. Siggel-King, P. Weightman
The University of Liverpool, Liverpool, United Kingdom
O.V. Kolosov, P.D. Tovee
Lancaster University, Lancaster, United Kingdom
M.R.F. Siggel-King
Cockcroft Institute, Warrington, Cheshire, United Kingdom

The ALICE (Accelerators and Lasers In Combined Experiments) accelerator at STFC Daresbury Laboratory in the UK was conceived in 2003 and constructed as a short-term Energy Recovery Linac demonstrator to develop the underpinning technology and expertise required for a proposed 600MeV ERL-based FEL facility. In this paper we present an update on the performance and status of ALICE which now operates as a funded IR-FEL user facility. We discuss the challenges of evolving a short-term demonstrator into a stable, reliable user facility and present a summary of the current scientific programme.

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TUP019

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

laser, FEL, electron, undulator

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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TUP021

Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability

FEL, emittance, electron, undulator

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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TUP022

Measurement of Spatial Displacement of X-rays in Crystals for Self-Seeding Applications

experiment, FEL, electron, detector

405

A. Rodriguez-Fernandez, B. Pedrini, S. Reiche
PSI, Villigen PSI, Switzerland
K. Finkelstein
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Free-electron laser (FEL) radiation arises from shot noise in the electron bunch, which is amplified along the undulator section and results in X-ray pulses consisting of many longitudinal modes [1]. The output bandwidth of FELs can be decreased by seeding the FEL process with longitudinally coherent radiation. In the hard x-ray region, there are no suitable external sources. This obstacle can be overcome by self-seeding. The X-ray beam is separated from the electrons using a magnetic chicane, and then monochromatized. The monochromatized X-rays serve as a narrowband seed, after recombination with the electron bunch, along the downstream undulators. This scheme generates longitudinally coherent FEL pulses.[2] have proposed monochromatization based on Forward Bragg Diffraction (FBD), which introduces a delay of the narrowband X-rays pulse of the order of femtoseconds that can be matched to the delay of the electron bunch due to the chicane. Unfortunately, the FBD process produces a small transverse displacement of the X-ray beam, which results in the loss of efficiency of the seeding process [3]. Preliminary results from an experiment performed at Cornell High Energy Synchrotron Source seem to confirm the predicted transverse displacement, which is therefore to be taken into account in the design of self-seeding infrastructure for optimizing the FEL performance.
[1] J.S. Wark et al., J. Apply. Crystallogr. 32, 692 (1999)
[2] G. Geloni et al., DESY report 10-053 (2010).
[3] Y. Shvyd'ko et al., Phys. Rev. ST Accel. Beams 15, 100702 (2012)

Poster TUP022 [5.503 MB]

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TUP023

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

FEL, laser, electron, undulator

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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TUP027

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

laser, undulator, 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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TUP029

Single Picosecond THz Pulse Extraction from the FEL Macropulse using a Laser Activating Semiconductor Reflective Switch

FEL, laser, extraction, linac

430

K. Kawase, M. Fujimoto, K. Furukawa, A. Irizawa, G. Isoyama, R. Kato, K. Kubo
ISIR, Osaka, Japan

The THz-FEL at the Institute of Scientific and Industrial Research, Osaka University can generate high-intensity THz pulses or FEL macropulses, which comprise approximately 100 micropulses at 37 ns intervals in the 27 MHz mode or 400 micropulses at 9.2 ns intervals in the 108 MHz mode. The maximum macropulse energy in the 27 MHz mode reaches 26 mJ at a frequency of 4.5 THz and the micropulse energy is estimated to be 0.2 mJ. To open new areas of studies with high intensity THz radiation for user experiments, we are developing a single pulse extraction system from the pulse train using a laser activating semiconductor reflective switch. We have succeeded in extracting a single THz pulse, duration of which is estimated to be less than 20 ps, from the FEL macropulse using a gallium arsenide wafer for the switch. We will report on the THz pulse extraction system and its performance.

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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, undulator, 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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TUP053

Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion

polarization, FEL, undulator, 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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TUP056

Design Challenge and Strategy for the LCLS-II High Repetition Rate X-ray FEL Photon Stoppers

photon, FEL, simulation, synchrotron

493

Y. Feng, J.T. Delor, J. Krzywinski, P.A. Montanez, E. Ortiz, T.O. Raubenheimer, M. Rowen
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.
Future high repetition rate X-ray FELs such as the European XFEL and LCLS-II presents new challenges to photon diagnostics as well as essential beamline components. In addition to these devices having to sustain the high peak power of a single-pulse FEL radiation, they must also be capable of handling the enormous power density of tens to hundreds of watts over an area as small as 0.1 mm X mm. In this talk, I will discuss the potential impact of high power FEL operation on performance of a gas attenuator and the design challenges to beam intercepting components such as a collimator or stopper.

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TUP057

The Highly Adjustable Magnet Undulator

undulator, simulation, electron, permanent-magnet

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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TUP074

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

laser, undulator, 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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TUP080

Terahertz Source Utilizing Resonant Coherent Diffraction Radiation at KEK ERL Test Accelerator

cavity, photon, extraction, operation

547

Y. Honda, A. Aryshev, M. Shevelev, M. Shimada
KEK, Ibaraki, Japan

An energy recovery linac test accelerator, cERL, has been developing at KEK. It can produce a high repetition rate short bunched electron beam in a continuous operation mode. We propose to develop a high power THz radiation source at the return loop of the cERL. Coherent diffraction radiation of THz regime is emitted when an electron bunch passes through a conductive mirror with a beam hole at the center. If we form an optical cavity using two mirrors facing each other and the cavity length coincides with the bunch repetition rate, the coherent diffraction radiation of multiple bunches adds up coherently in the cavity. By extracting the power through transmission of one of the mirrors, we can realize a high power and high efficiency THz source. We discuss performance of the source assuming the beam parameters of cERL.

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TUP085

Lebra Free-Electron Laser Elicits Electrical Spikes from the Retina and Optic Nerve of the Slugs Limax Valentianus

FEL, site, experiment, electron

550

F. Shishikura, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka
LEBRA, Funabashi, Japan
Y. Komatsuzaki
Nihon University, Tokyo, Japan

Since 2001, the Laboratory for Electron Beam Research and Application (LEBRA) has been providing tunable free-electron lasers (FELs) encompassing the near-IR region and some of the mid-IR region (0.9-6 microns), and generating visible wavelengths up to 400 nm by means of nonlinear optical crystals. We are investigating the efficiency of LEBRA-FELs for triggering photoreactions in living organisms. Last year we described the effects of LEBRA-FELs in controlling the photoreaction of lettuce seeds; red FEL (660 nm) and far-red FEL (740 nm) activate and inhibit germination, respectively. Here we used LEBRA-FEL to illuminate the retina of slugs (Limax valentianus), and determined which FEL wavelengths generate electrical spikes from the retina-optic nerve. Blue FEL light (wavelength: 470 nm) efficiently produced electrical spikes from the retina. The results are consistent with a previous study, where a xenon arc lamp with interference filters was used to produce monochromatic visible light. We plan to extend the wavelengths to the near- and mid-IR regions of LEBRA-FEL. We summarize our current results for the use of FEL in investigating the electrophysiology of the retina of slugs.
We thank Mr. T. Kuwabara (a graduate of Departments of Physics, College of Science and Technolgy, Nihon University) for helpful assistance.

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TUD01

COTR Resistant Profile Monitor

electron, laser, diagnostics, bunching

554

H. Loos
SLAC, Menlo Park, California, USA

Funding: Work supported by DOE contract DE-AC02-76SF00515
Electron beam accelerators used as drivers for short wavelength FELs need ultra-high brightness beams with small emittances and highly compressed bunch lengths. The acceleration and beam transport process of such beams leads to micro-bunching instabilities which cause the emergence of coherent optical transition radiation (COTR). The effect of COTR on profile monitors based on OTR or fluorescent screens can be quite detrimental to their intended use to measure beam sizes and profiles. This presentation will review past observations of the beam diagnostics issues due to COTR and discuss various mitigation schemes for profile monitors as well as present experience with such implementations.

Slides TUD01 [1.536 MB]

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TUD02

Diffraction Radiation Monitor

electron, target, beam-diagnostic, diagnostics

561

Y. Taira
AIST, Tsukuba, Japan

Non-invasive beam diagnostics using a diffraction radiation (DR) has been developed at several electron accelerator facilities. Generation process of DR is similar to that of transition radiation (TR). TR is emitted when a charged particle passes through the boundary between two media with different dielectric constants. On the other hand, DR is emitted when it passes through in the vicinity of a boundary between two media. In the generation process of DR, the charged particle doesn't intersect the medium but its electric field intersects the medium. An aperture, a slit, and an edge are used for DR target. Optical wavelength of DR is usually used for beam diagnostics. One can evaluate energy, a transverse beam size, and a divergence of an electron beam by measuring a spatial distribution of DR. Moreover, coherent diffraction radiation with the wavelength of less than millimeter range is used for a bunch length measurement. In this conference, a theoretical background of DR and experimental results carried out at several facilities will be presented.

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WEP001

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

undulator, 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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WEP025

Effect of Microbunching on Seeding Schemes for LCLS-II

laser, electron, undulator, 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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WEP062

Study on Undulator Radiation from Femtosecond Electron Bunches

undulator, electron, 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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WEP067

Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility

bunching, space-charge, simulation, impedance

707

A. Halavanau, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University.
Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4])
[1] M. Dohlus, PRSTAB, 14 090702 (2011).
[2] A. Marinelli, PRL, 110 264802 (2013).
[3] M. Borland, Advanced Photon Source, LS-287, 2000.
[4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015).

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WEP073

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

electron, undulator, FEL, 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, undulator, 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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WEP079

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

FEL, electron, target, undulator

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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WEP082

High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses

polarization, electron, timing, laser

739

J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov
KAERI, Daejon, Republic of Korea
B.A. Gudkov, S.V. Miginsky, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [*] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method.
* Phys. Rev. Lett. 110, 064805.

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WEP085

Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance

electron, wiggler, FEL, free-electron-laser

746

A. Gover, R. Ianconescu
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
C. Emma, P. Musumeci
UCLA, Los Angeles, USA
A. Friedman
Ariel University, Ariel, Israel

Funding: We acknowledge partial support by the U.S. Israel Binational Science Foundation (BSF)Jerusalem, Israel
In the context of radiation emission from an electron beam Dicke's superradiance (SR) is the enhanced radiation emission from a pre-bunched beam. Stimulated Superradiance (ST-SR) is the further enhanced emission of the bunched beam in the presence of a phase-matched radiation wave. These processes were analyzed for Undulator radiation in the framework of radiation field mode-excitation theory[1]. In the nonlinear saturation regime the synchronism of the bunched beam and an injected radiation wave may be sustained by wiggler tapering [2]. Same processes are instrumental also in enhancing the radiative emission in the tapered wiggler section of seeded FEL[3]. In a long tapered wiggler the diffraction of the emitted radiation wave is not negligible even at Angstroms wavelengths (as in LCLS). A Fresnel diffraction model was provided in [4] for the SR process only. Here we outline the fundamental physical concepts of Spontaneous Superradiadce (SR), Stimulated Superradiance (ST-SR), Taper-Enhanced Superradiance (TES) and Taper-Enhanced Stimulated Superradiance Amplification (TESSA), and compare their Fourier and Phasor formulations in the radiation mode expansion and free-diffraction models. Detailed further analysis can provide better design concepts of high power FELs and improved tapering strategy for enhancing the power of seeded short wavelength FELs
1. A. Gover, PR ST-AB 8, (030701) ; (030702) (2005)
2. J. Duris et al., arxiv 2015.
3. Y. Jiao et al., PR ST-AB 15 050704 2012
4. E.A. Schneidmiller, M.V. Yurkov, PR ST-AB 18, 030705 (2015)

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WEP087

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

FEL, target, undulator, 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

undulator, polarization, 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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WED03

Photon Diagnostics and Photon Beamlines Installations at the European XFEL

diagnostics, photon, beam-transport, vacuum

764

J. Grünert, B. Baranasic, J. Buck, F. Dietrich, M. Dommach, W. Freund, A. Koch, N.G. Kujala, J. Liu, S. Molodtsov, M. Planas, H. Sinn
XFEL. EU, Hamburg, Germany

The European X-ray Free-Electron-Laser (XFEL. EU) is a new a 4th generation light facility which will deliver radiation with femtosecond and sub-Ångström resolution at MHz repetition rates, and is currently under construction in the Hamburg metropolitan area in Germany. Special diagnostics [1,2] for spontaneous radiation analysis is required to tune towards the lasing condition. Once lasing is achieved, diagnostic imagers [3], online monitors [4], and the photon beam transport system [5] need to cope with extreme radiation intensities. In 2015 the installation of machine equipment in the photon area of the facility is in full swing. This contribution presents the progress on final assemblies of photon diagnostics, the installation status of these devices as well as of the beam transport system, and recent design developments for diagnostic spectrometers and temporal diagnostics.
[1] J. Grünert, XFEL. EU TR-2012-003(2012)
[2] W. Freund, XFEL. EU TN-2014-001-01(2014)
[3] A. Koch, Proc. SPIE 95121R(2015)
[4] J. Buck et al., Proc. SPIE 85040U(2012)
[5] H. Sinn et al., XFEL. EU TR-2012-006(2012)

Slides WED03 [14.557 MB]

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WED04

Status Report of PAL-XFEL Undulator Program

undulator, FEL, electron, 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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