FEL2015 - List of Keywords (FEL)

Paper	Title	Other Keywords	Page
MOA02	First Lasing of the Third Stage of Novosibirsk FEL	undulator, radiation, electron, linac	1
	O.A. Shevchenko, V.S. Arbuzov, K.N. Chernov, I.V. Davidyuk, E.N. Dementyev, B.A. Dovzhenko, Ya.V. Getmanov, B.A. Knyazev, E.I. Kolobanov, A.A. Kondakov, V.R. Kozak, E.V. Kozyrev, V.V. Kubarev, G.N. Kulipanov, E.A. Kuper, I.V. Kuptsov, G.Y. Kurkin, L.E. Medvedev, S.V. Motygin, V.N. Osipov, V.K. Ovchar, V.M. Petrov, A.M. Pilan, V.M. Popik, V.V. Repkov, T.V. Salikova, M.A. Scheglov, I.K. Sedlyarov, G.V. Serdobintsev, S.S. Serednyakov, A.N. Skrinsky, S.V. Tararyshkin, V.G. Tcheskidov, A.G. Tribendis, N. Vinokurov, P. Vobly BINP SB RAS, Novosibirsk, Russia
	Novosibirsk FEL facility is based on the first in the world multi-turn energy recovery linac (ERL). It comprises three FELs (stages). FELs on the first and the second tracks were commissioned in 2004 and 2009 respectively and operate for users now. The third stage FEL is installed on the fourth track of the ERL. It includes three undulator sections and 40-meters-long optical cavity. The design tuning range of this FEL is from 5 to 20 microns and the design average power at bunch repetition rate 3.74 MHz is about 1 kW. Recent results of the third stage FEL commissioning are reported.
	Slides MOA02 [4.901 MB]
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MOB01	Three-Plus Decades of Tapered Undulator FEL Physics	electron, radiation, 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	undulator, electron, photon, radiation	7
	Z. Huang SLAC, Menlo Park, California, USA
	The X-ray free-electron lasers (FELs), with nine to ten orders of magnitude improvement in peak brightness over the third-generation light sources, have demonstrated remarkable scientific capabilities. Despite the early success, X-ray FELs can still undergo dramatic transformations with accelerator and FEL R&D. In this talk, I will show examples of recent R&D efforts to increase X-ray coherence and brightness, to obtain better control of X-ray temporal and spectral properties, and to develop concepts for compact coherent sources.
	Slides MOB02 [18.004 MB]
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MOB03	Transforming the FEL: Coherence, Complex Structures, and Exotic Beams	laser, undulator, radiation, electron	10
	E. Hemsing SLAC, Menlo Park, California, USA
	Modern high brightness electron beams used in FELs are extremely versatile and highly malleable. This flexibility can be used to precisely tailor the properties of the FEL light for improved temporal coherence (as in external seeding), but can also be exploited in new ways to generate exotic FEL modes of twisted light that carry orbital angular momentum (OAM) for new science. In this talk, I will describe how lasers and undulator harmonics can be combined to produce both simple and complex e-beam distributions that emit intense, coherent, and highly tunable OAM light in future FELs.
	Slides MOB03 [12.208 MB]
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MOC02	Optimization of a High Efficiency Free Electron Laser Amplifier	electron, undulator, radiation, brilliance	17
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Technique of undulator tapering in the post-saturation regime is used at the existing X-ray FELs for increasing the radiation power. We present comprehensive analysis of the problem in the framework of one-dimensional and three-dimensional theory. We find that diffraction effects essentially influence on the choice of the tapering strategy. Our studies resulted in a general law of the undulator tapering for a seeded FEL amplifier as well as for SASE FEL.
	Slides MOC02 [24.462 MB]
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MOC03	Estimate of Free-Electron Laser Gain Length in the Presence of Electron Beam Collective Effects	emittance, electron, undulator, collective-effects	24
	S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom
	A novel definition for the three-dimensional free electron laser gain length is proposed, which takes into account the increase of electron beam projected emittance as due, for example, to geometric transverse wakefield and coherent synchrotron radiation developing in linear accelerators. The analysis shows that the gain length is affected by an increase of the electron beam projected emittance, even though the slice (local) emittance is preserved, and found to be in agreement with Genesis code simulation results. It is then shown that the minimum gain length and the maximum of output power may notably differ from the ones derived when collective effects are neglected. The proposed model turns out to be handy for a parametric study of electron beam six-dimensional brightness and FEL performance as function, e.g., of bunch length compression factor, accelerator alignment tolerances and optics design. S. Di Mitri, S. Spampinati, Phys. Rev. Special Topics Accel. Beams, 17, 110702 (2014)
	Slides MOC03 [2.528 MB]
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MOC04	Operating of SXFEL in a Single Stage High Gain Harmonic Generation Scheme	laser, bunching, electron, linac	29
	G.L. Wang, D.X. Dai, G.R. Wu, X.M. Yang, W.Q. Zhang DICP, Dalian, People's Republic of China
	The beam energy spread at the entrance of undulator system is of paramount importance for efficient density modulation in high-gain seeded free-electron lasers (FELs). In this paper, the dependencies of high harmonic bunching efficiency in the high-gain harmonic generation (HGHG) schemes on the electron energy spread distribution are studied. Theoretical investigations and multi-dimensional numerical simulations are applied to the cases of uniform and saddle beam energy distributions and compared to a traditional Gaussian distribution. It shows that the uniform and saddle electron energy distributions significantly enhance the performance of HGHG-FELs. A numerical example demonstrates that, with the saddle distribution of sliced beam energy spread controlled by a laser heater, the 30th harmonic radiation can be directly generated by a single-stage seeding scheme for a soft x-ray FEL facility.
	Slides MOC04 [3.345 MB]
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MOP004	Influence of Horizantal Constant Magnetic Field on Harmonic Undulator Radiations and Gain	undulator, radiation, electron, 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, electron, radiation, polarization	38
	G. Geloni XFEL. EU, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We show that radiation pulses from an X-ray Free-Electron Laser (XFEL) with a planar undulator, which are mainly polarized in the horizontal direction, exhibit a suppression of the vertical polarization component of the power at least by a factor λ_w²/(4 pi L_g)², where λ_w is the length of the undulator period and L_g is the FEL field gain length. We illustrate this fact by examining the XFEL operation under the steady state assumption. In our calculations we considered only resonance terms: in fact, non resonance terms are suppressed by a factor λ_w³/(4 pi L_g)³ and can be neglected. While finding a situation for making quantitative comparison between analytical and experimental results may not be straightforward, the qualitative aspects of the suppression of the vertical polarization rate at XFELs should be easy to observe. We remark that our exact results can potentially be useful to developers of new generation FEL codes for cross-checking their results.
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MOP010	Linac Design of the IR-FEL Project in CHINA	electron, gun, linac, beam-transport	46
	Z.G. He, Q.K. Jia, L. Wang, W. Xu, S.C. Zhang USTC/NSRL, Hefei, Anhui, People's Republic of China
	We are building an infrared free-electron laser (IR-FEL) facility that will operate from 5 um to 200 um. This FEL source is drived by a linac, which is composed of a triode electron gun, a subharmonic prebuncher, a buncher, two accelerators, and a beam transport line. The linac is required to operate from 15 to 60 MeV at 1 nC charge, while delivering a transverse rms emittance of smaller than 30 mm-mrad in a 5 ps rms length, smaller than 240 keV rms energy spread bunch at the Far-infrared and Mid-infrared undulators. In this article, the preliminary Linac design studies are described.
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MOP011	Status of CLARA, a New FEL Test Facility	laser, undulator, electron, gun	49
	J.A. Clarke, D. Angal-Kalinin, A.D. Brynes, R.K. Buckley, S.R. Buckley, L.S. Cowie, D.J. Dunning, B.D. Fell, P. Goudket, A.R. Goulden, P.C. Hornickel, F. Jackson, S.P. Jamison, J.K. Jones, K.B. Marinov, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, M.D. Roper, L.K. Rudge, Y.M. Saveliev, B.J.A. Shepherd, R.J. Smith, S.L. Smith, E.W. Snedden, M. Surman, T.T. Thakker, N. Thompson, R. Valizadeh, A.E. Wheelhouse, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom R.B. Appleby, K. Hanahoe, O. Mete Apsimon, H.L. Owen, G.X. Xia UMAN, Manchester, United Kingdom P. Atkinson, N. Bliss, R.J. Cash, N.A. Collomb, G. Cox, G.P. Diakun, S. Dobson, A. Gallagher, S.A. Griffiths, C. Hill, C. Hodgkinson, D.M.P. Holland, T.J. Jones, B.G. Martlew, J. Williams STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom R. Bartolini, I.P.S. Martin DLS, Oxfordshire, United Kingdom S.T. Boogert, E. Yamakawa Royal Holloway, University of London, Surrey, United Kingdom G. Burt, P.N. Ratoff Lancaster University, Lancaster, United Kingdom L.T. Campbell, A.J.T. Colin, J. Henderson, B. Hidding, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom A.M. Kolano University of Huddersfield, Huddersfield, United Kingdom A. Lyapin JAI, Egham, Surrey, United Kingdom V.V. Paramonov, A.K. Skasyrskaya RAS/INR, Moscow, Russia J.D.A. Smith TXUK, Warrington, United Kingdom S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom Y. Wei, C.P. Welsch, A. Wolski The University of Liverpool, Liverpool, United Kingdom
	CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK. The main motivation for CLARA is to test new FEL schemes that can later be implemented on existing and future short wavelength FELs. Particular focus will be on ultra-short pulse generation, pulse stability, and synchronisation with external sources. The project is now underway and the Front End section (photoinjector and first linac) installation will begin later this year. This paper will discuss the progress with the Front End assembly and also highlighting other topics which are currently receiving significant attention.
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MOP013	The Fermi Seeded FEL Facility: Operational Experience and Future Perspectives	experiment, laser, electron, photon	57
	L. Giannessi, E. Allaria, L. Badano, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, M. Coreno, R. Cucini, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, E. Ferrari, P. Finetti, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, F. Iazzourene, M. Kiskinova, S. Krecic, M. Lonza, N. Mahne, M. Manfredda, C. Masciovecchio, M. Milloch, F. Parmigiani, E. Pedersoli, G. Penco, L. Pivetta, O. Plekan, M. Predonzani, K.C. Prince, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, E. Roussel, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, M. Svandrlik, C. Svetina, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	FERMI is the seeded FEL user facility in Trieste, Italy, producing photons from the VUV to the soft X-rays with a high degree of coherence and spectral stability. Both FEL lines, FEL-1 and FEL-2, are available for users, down to the shortest wavelength of 4 nm. We report on the completion of the commissioning of the high energy FEL line, FEL-2, on the most recent progress obtained on FEL-1 and on the operational experience for users, in particular those requiring specific FEL configurations, such as two-colour experiments. We will also give a perspective on the improvements and upgrades which have been triggered based on our experience, aiming to maintain as well as to constantly improve the performance of the facility for our user community.
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MOP014	Status of the Soft X-Ray FEL User Facility FLASH	photon, electron, operation, experiment	61
	K. Honkavaara, B. Faatz, J. Feldhaus, S. Schreiber, R. Treusch, M. Vogt DESY, Hamburg, Germany
	Since 10 years FLASH at DESY (Hamburg, Germany) has provided high brilliance FEL radiation at XUV and soft X-ray wavelengths for user experiments. Recently FLASH has been upgraded with a second undulator beamline, FLASH2, whose commissioning takes place in parallel of the user operation on FLASH1. This paper summarizes the performance of the FLASH facility during the last user period from January 2014 to April 2015.
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MOP017	Beam Commissioning Plan for the SwissFEL Hard-X-Ray Facility	linac, undulator, electron, operation	69
	T. Schietinger PSI, Villigen PSI, Switzerland
	The SwissFEL facility currently being assembled at the Paul Scherrer Institute is designed to provide FEL radiation in the photon wavelength range between 0.1 and 7 nm. The commissioning of the first phase, comprising the electron injector, the main electron linear accelerator and the first undulator line, named Aramis and dedicated to the production of hard X-rays, is planned for the years 2016 and 2017. We present an overview of the beam commissioning plan elaborated in accordance with the installation schedule to bring into operation the various subsystems and establish beam parameters compatible with first pilot user experiments in late 2017.
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MOP034	Beam Optics Measurements at FERMI by using Wire-Scanner	optics, emittance, linac, quadrupole	101
	G. Penco, A. Abrami, I. Cudin, S. Di Mitri, M. Ferianis, E. Ferrari, G. Gaio, L. Giannessi, S. Grulja, R. Sauro, L. Sturari Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy G.L. Orlandi, C. Ozkan Loch PSI, Villigen PSI, Switzerland
	Measuring and controlling the electron beam optics is an important ingredient to guarantee high performance of a free-electron laser. In the FERMI linac, the Twiss parameters and the transverse emittances are routinely measured by detecting the beam spot size as a function of a scanning quadrupole placed upstream (i.e. quadrupole scan method). The beam spot size is usually measured with an OTR screen that unfortunately suffers from coherent optical transition radiation (C-OTR) that introduces spurious light and corrupts the image. Moreover, the beam size at the end of the FERMI linac is focused to a few tens of microns and this makes it difficult to precisely measure it with the OTR system, which has an estimated resolution of 20um. For this reason, a wire-scanner system has been installed at the end of the linac just in the waist of the optics channel. The wire-scanner is a SwissFEL prototype installed in FERMI in order to study the hardware and beam loss monitor performances at the GeV energy scale. The beam optics measurements performed with the wire-scanner is here presented, and the obtained results are more in agreement with the theoretical expectations. A more reliable beam optics estimation at the end of the linac has allowed to better match it to the nominal lattice and transport it up to the undulator chain, providing important benefits to the FEL performance.
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MOP036	Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator	laser, timing, detector, electron	105
	H. Yang, C. Jeon, K. Jung, J. Kim KAIST, Daejeon, Republic of Korea H. Chung Korea University Sejong Campus, Sejong, Republic of Korea B. Han, Y.U. Jeong KAERI, Daejon, Republic of Korea
	Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.
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MOP038	Stabilization of Magnetron Frequency for a Microtron-Driven FEL	controls, cavity, microtron, electron	107
	B.A. Gudkov, S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov KAERI, Daejon, Republic of Korea S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Under KAERI WCI program we develop a compact pulsed microtron-driven FEL. Electron bunches trains are accelerated in the microtron and transported by the beamline to the undulator. The RF cavity in the microtron is fed by a magnetron. Any accelerator driver for a FEL should provide an electron beam having very stable parameters such as electron energy, current, and especially the bunch repetition rate in a train. All mentioned parameters depend on magnetron current. It means that special attention should be paid for the shape of the current pulse, supplied to the magnetron from the modulator. We developed the modulator project with a computer control that will provide an arbitrary shape of the magnetron current. A simplified prototype was fabricated and tested. The methods of controlling of the pulse shape are considered. Simulation and experimental results are presented.
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MOP040	Implementation of MTCA.4-based Controls for the Pulsed Optical Synchronization Systems at DESY	controls, laser, FPGA, hardware	115
	M. Felber, L. Butkowski, M.K. Czwalinna, M. Fenner, C. Gerth, M. Heuer, E. Janas, M. Killenberg, T. Lamb, U. Mavrič, J.M. Müller, P. Peier, K.P. Przygoda, S. Ruzin, H. Schlarb, C. Sydlo, M. Titberidze, F. Zummack DESY, Hamburg, Germany T. Kozak, P. Prędki TUL-DMCS, Łódź, Poland
	Funding: This work has partly been funded by the Helmholtz Validation Fund Project MTCA.4 for Industry (HVF-0016) With the current state of the synchronization system at FLASH (Free-electron Laser in Hamburg) the arrival time between electron bunches and optical laser pulses can be synchronized to a level of 30 fs rms, e.g. for pump-probe experiments. In the course of the development of an up-scaled system for the European XFEL and the migration of control hardware to the modern MTCA.4 (Micro Telecommunications Computing Architecture) platform, all involved components of the system will be replaced with new developments. The front-end devices are upgraded. FPGAs (Field Programmable Gate Arrays) are performing the data processing and feedback calculations. In order to facilitate the firmware development, a toolset (Rapid-X) was established which allows application engineers to develop, simulate, and generate their code without help from FPGA experts in a simple and efficient way. A software tool kit (MTCA4U) provides drivers and tools for direct register access e.g. via Matlab or Python and a control system adapter, which allows the server applications to be written control system independent. In this paper, an overview on the synchronization setups and their upgrades as well as an introduction to the new hardware is given. The Rapid-X and MTCA4U tool kits are presented followed by a status report on the implementation of the new developments.
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MOP044	A Laser Heater for CLARA	laser, electron, undulator, linac	129
	S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom B.D. Muratori, N. Thompson, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	CLARA is a new FEL test facility, being developed at STFC Daresbury Laboratory in UK, based on a high brightness electron linac. The electron beam of CLARA can potentially be affected by the longitudinal microbunching instability leading to a degradation of the beam quality. The inclusion of a laser heater in the linac design can allow control of the microbunching instability, the study of microbunching and deliberate increase of the final energy spread to study energy spread requirements of the FEL schemes tested at CLARA. We present the initial design and layout of the laser heater system for CLARA and its expected performance.
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MOP050	Development of Coherent Terahertz Wave Sources using LEBRA and KU-FEL S-band Linacs	electron, radiation, 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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MOP054	Wake Field Potentials of 'Dechirpers'	wakefield, experiment, focusing, electron	157
	A. Novokhatski SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515. A corrugated structure, which is used on 'dechirpers' is usually a pipe or two plates with small corrugations (bumps) on the walls. There is a good single-mode description of the wake potentials excited by a relativistic bunch if the wave length of the mode is much longer than the distance between the bumps in the pipe. However, ultra-short bunches, which are now used in FELs, excite much higher frequency fields and the corresponding wake potentials will be very different from single-mode description. We made analyzes of these wake potentials based on a numerical solution of Maxwell's equations. The behavior of the wake fields of ultra-short bunches in corrugated structures is not much different from the fields excited usually in accelerating structures where the wake potentials are described by the exponential function. As we increase the bunch length, the wake potentials slowly transform to the form of a single mode. For a practical application we present results for a 'dechirper', which will be soon installed at LCLS. We also carried out calculations for a similar device, that was installed and measured at the Pohang Accelerator Laboratory, Korea. We find very good agreement with the experimental results.
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MOP055	The Effect of Wakefields on the FEL Performance	emittance, wakefield, linac, undulator	161
	A. Novokhatski, F.-J. Decker, Y. Nosochkov, M.K. Sullivan SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515. If a beam travels near collimator jaws or other discontinuities of the beam pipe, it gets the energy loss and the transverse kick due to the back reaction of the beam field diffracted on the collimator's jaws. The wake field effect from collimators may not only bring an additional energy jitter and change the trajectory of the beam, but may also lead to degradation of the performance of Free Electron Laser (FEL) It may be possible due to the special character of the wake fields: the response reaction depends on the longitudinal position of the particles in the bunch. We describe a model of the wake field radiation, simulation results and comparison with measurements.
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MOP062	Technology Maturation for the MaRIE 1.0 X-FEL	linac, emittance, simulation, laser	181
	J.W. Lewellen, K. Bishofberger, B.E. Carlsten, L.D. Duffy, F.L. Krawczyk, Q.R. Marksteiner, D.C. Nguyen, S.J. Russell, R.L. Sheffield, N.A. Yampolsky LANL, Los Alamos, New Mexico, USA
	Funding: This research was funded by the Matter-Radiation Interactions in Extremes program at Los Alamos National Laboratory, under contract DE-AC52-06NA25396. Los Alamos National Laboratory is proposing a high-energy XFEL, named MaRIE, to meet its mission needs. MaRIE will be required to generate coherent 42+ keV photons, and, due to space constraints at the LANSCE accelerator complex at Los Alamos, MaRIE's design electron beam energy is 12 GeV. This combination places significant restrictions upon the MaRIE electron beam parameters, in particular the transverse emittance and energy spread at the undulator entrance. We are developing approaches to meet these requirements, but these often require solutions extending beyond the current state-of-the-art in X-FEL design. To reduce overall project risk, therefore, we have identified a number of key experimental and modeling / simulation efforts intended to address both the areas of greatest uncertainty in the preliminary MaRIE design, and the areas of largest known risk. This paper describes the general requirements for the MaRIE X-FEL, our current areas of greatest concern with the preliminary design concept, and our corresponding Technology Maturation Plan (TMP). MaRIE website: http://www.lanl.gov/science-innovation/science-facilities/marie/index.php
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MOP067	Transverse Emittance-Preserving Transfer Line and Arc Compressor for High Brightness Electron Sources	emittance, dipole, optics, electron	191
	S. Di Mitri, M. Cornacchia, S. Spampinati Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Minimizing transverse emittance is essential in single- or few-passes accelerators designed to deliver high brightness electron beams. Emission of coherent synchrotron radiation (CSR) is an important factor of emittance degradation. We have demonstrated, with analytical and experimental results, that this perturbation may be cancelled by imposing certain conditions on the electron optics when the bunch length is constant along the line. This scheme of CSR suppression is then enlarged, analytically and numerically, to cover the case of varying bunch length in a periodic arc compressor. The proposed solution hold the promise of cost-saving of compact transfer lines with large bending angles, and new schemes for beam longitudinal gymnastics both in recirculating and in single-pass accelerators driving free electron lasers. S. Di Mitri, M. Cornacchia, S. Spampinati, Phys. Rev. Letters, 110, 014801 (2013) ** S. Di Mitri, M. Cornacchia, Europhys. Letters, 109, 62002 (2015)
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MOP068	First Simulation Results on Free Electron Laser Radiation in Displaced Phase-combined Undulators	undulator, radiation, electron, resonance	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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MOP074	Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser	wiggler, electron, radiation, resonance	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, radiation, electron, resonance	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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MOP076	Free-Electron Laser Driven by a 500 MeV Laser Plasma Accelerator Beam	undulator, laser, emittance, plasma	217
	W. Qin, J.E. Chen, S. Huang, K.X. Liu, X.Q. Yan, L. Zeng PKU, Beijing, People's Republic of China Y. Ding, Z. Huang SLAC, Menlo Park, California, USA
	A laser plasma accelerator is under construction at Peking University and several hundred MeV electron beams are expected. In this paper we discuss applying a 500 MeV beam with 1% relative energy spread to FEL. Bunch decompression method is considered to deal with the large energy spread of the beam. Emittance growth induced by large divergence and energy spread in electron beam transport has been treated with the chromatic matching manipulation. Simulation shows that 100 MW level, 6.3 fs , 0.008 bandwidth output can be obtained for 30 nm FEL. TGU method with assumed matched beam is also discussed as a comparison.
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MOP079	On the Importance of Electron Beam Brightness in High Gain Free Electron Lasers	electron, emittance, undulator, brightness	227
	S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Linear accelerators delivering high brightness electron beams are essential for driving short wavelength, high gain free-electron lasers (FELs). The FEL radiation output efficiency is often parametrized through the power gain length that relates FEL performance to the electron beam quality at the undulator. Experimental data and simulation results of existing and planned FEL facilities are used to explicit the relationship between the FEL output wavelength and the electron beam six-dimensional brightness. Practical formulas are provided that show the dependence of the exponential gain length on the beam brightness. S. Di Mitri, M. Cornacchia, Phys. Reports, 539 (2014) 1~48. ** S. Di Mitri, Photonics, 2 (2015) 317~341
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MOP081	Generating a Single-Spike SASE Pulse in the Soft X-Ray Regime by Velocity Bunching	radiation, 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, radiation, simulation	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	undulator, simulation, radiation, electron	246
	G. Feng, W. Decking, M. Dohlus, T. Limberg, I. Zagorodnov DESY, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany T. Plath Uni HH, Hamburg, Germany
	The free electron laser (FEL) facility at DESY in Hamburg (FLASH) is the world's first FEL user facility which can produce extreme ultraviolet (XUV) and soft X-ray photons. In order to increase beam time delivered to users, a major upgrade named FLASH II is in progress. As a possibility, a seeding undulator section can be installed between the extraction arc section and the SASE undulator of FLASH2. In this paper, a possible seeding scheme for the cascaded HGHG option for FLASH2 is given. The SASE undulator can be used as the second radiator of the cascaded HGHG. Parameters optimization for the accelerating modules and the bunch compressors has been done to meet the requirement of the electron bunches. In the beam dynamics simulation, collective effects were taken into account. Particle distribution generated from the beam dynamics simulation was used for the seeded FEL study. Space charge and CSR impacts on the microbunches were taken into account during the seeded FEL simulation. The simulation results show that FEL radiation with the wavelength of a few nms and with high monochromaticity can be seeded at FLASH2.
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MOP085	Scheme to Increase the Output Average Spectral Flux of the European XFEL at 14.4 keV	undulator, electron, photon, scattering	251
	V. Kocharyan, E. Saldin DESY, Hamburg, Germany G. Geloni XFEL. EU, Hamburg, Germany
	Inelastic X-ray scattering and nuclear resonance scattering are limited by the photon flux available at SR sources, up to 10¹⁰ ph/s/meV at 14.4 keV. A thousand-fold increase may be obtained by exploiting high repetition rate self-seeded pulses at the European XFEL. We report on a feasibility study for an optimized configuration of the SASE2 beamline combining self-seeding and undulator tapering at 14.4 keV. One should perform monochromatization at 7.2 keV by self-seeding, and amplify the seed in the first part of the output undulator. Before saturation, the electron beam is considerably bunched at the 2nd harmonic. A second part of the output undulator tuned to 14.4 keV can thus be used to obtain saturation at this energy. One can further prolong the exchange of energy between the photon and the electron beam by tapering the last part of the output undulator. Start-to-end simulations demonstrate that self-seeding, combined with undulator tapering, allows one to achieve more than a hundred-fold increase in average spectral flux compared with the nominal SASE regime at saturation, resulting in a spectral flux of order 10¹³ ph/s/meV. A more detailed description of this study can be found in. G. Geloni, V. Kocharyan and E.~Saldin, "Scheme to increase the output average spectral flux of the European XFEL at 14.4 keV", DESY 15-141 (2015).
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MOD01	Review of Experimental Results from High Brightness DC Guns: Highlights in FEL Applications	gun, cathode, emittance, brightness	269
	N. Nishimori JAEA, Ibaraki-ken, Japan
	Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15H03594). Future ERL light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photoinjector with a 350 kV photoemission gun [1,2]. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage [3]. This technique led to generation of 500 keV beam from the JAEA gun with 160mm acceleration gap [4], conditioning voltage more than 500 kV at the Cornell gun with gap < 50 mm [5], and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap [6]. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications. [1] Dunham, APL 102, 034105. [2] Gulliford, PRSTAB 16, 073401. [3] Nagai, RSI 81, 033304. [4] Nishimori, APL 102, 234103. [5] Maxson, RSI 85, 093306. [6] Yamamoto, private communication.
	Slides MOD01 [3.051 MB]
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TUA02	Suppression of FEL Lasing by a Seeded Microbunching Instability	electron, laser, undulator, photon	289
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school GRK1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brightness electron bunches driving free-electron lasers (FELs). In this contribution, we demonstrate suppression of FEL lasing induced by a laser-triggered microbunching instability at the free-electron laser FLASH. The interaction between the electron bunches and the 800-nm laser pulses takes place in an undulator upstream of the FEL undulators. A significant decrease of XUV photon pulse energies has been observed in coincidence with the laser-electron overlap in the modulator. We discuss the underlying mechanisms based on longitudinal space charge amplification (LSCA) [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.
	Slides TUA02 [14.298 MB]
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TUA04	First Simultaneous Operation of Two Sase Beamlines in FLASH	undulator, photon, operation, electron	297
	M. Scholz, B. Faatz, S. Schreiber, J. Zemella DESY, Hamburg, Germany
	FLASH2, the second undulator beamline of the FLASH FEL user facility at DESY (Hamburg, Germany) is under commissioning. Its first lasing was achieved in August 2014. FLASH is the first soft X-ray FEL operating two undulator beamlines simultaneously. Both undulator beamlines are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. Fast kickers and a septum are installed to distribute one part of the electron bunch train to FLASH1 and the other part to FLASH2 with full repetition rate. The commissioning of FLASH2 takes place primarily in parallel to FLASH1 user operation. Various beam optics measurements has been carried out in order to ensure the required electron beam quality for efficient SASE generation. This paper reports the status of the FLASH2 commissioning.
	Slides TUA04 [9.655 MB]
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TUB02	Distributed Seeding for Narrow-band X-ray Free-Electron Lasers	undulator, radiation, electron, 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	laser, electron, radiation, 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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TUC01	The Microbunching Instability and LCLS-II Lattice Design	simulation, laser, bunching, linac	308
	M. Venturini LBNL, Berkeley, California, USA
	The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.
	Slides TUC01 [4.206 MB]
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TUP004	Three-dimensional, Time-dependent Simulation of Free-Electron Lasers	undulator, simulation, electron, experiment	331
	P.J.M. van der Slot Mesa+, Enschede, The Netherlands H. Freund, P.J.M. van der Slot CSU, Fort Collins, Colorado, USA
	Minerva is a simulation code that models the interaction of electrons with an optical field inside an undulator. Minerva uses a modal expansion for the optical field and the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to mode, for example, FEL oscillators. As there exists a large variety of FELs ranging from long-wavelength oscillators to soft and hard X-ray FELs that are either seeded or starting from noise, a simulation code, such as Minerva, should be capable of modelling this huge variety of FEL configurations. Here we present a validation of the Minerva code against experimental data for various FEL configurations, ranging from long wavelength FEL oscillators to hard X-ray SASE FEL.
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TUP006	Quantum Nature of Electrons in Classical X-ray FELs	electron, undulator, radiation, laser	338
	P.M. Anisimov LANL, Los Alamos, New Mexico, USA
	X-ray FELs built to date are well described by the classical theory. This theory in its simplest form is expressed as a system of pendulum equations for electrons coupled to the electromagnetic field. The FEL interaction requires bunching of the electrons on a scale less than radiation wavelength. The progress in the development of FELs and the need to reach even shorter laser radiation wavelength with low energy electrons require that the quantum characteristic of the FEL interaction to be properly considered. Quantum theories have been already proposed by a number of authors. These theories, however, have been developed for regimes that are not relevant for modern/planned X-ray FELs. Here, we focus on quantum effects in modern/future X-ray FELs and stop treating an electron as a point-particle. This results in quantum reduction of the bunching! Starting with the analysis of the free space dispersion for the electron wave packet, we will present a modified 1D FEL theory that takes into account the quantum uncertainty of the electron position in X-ray FELs. This theory allows for a unified classification of FELs with respect to the wave nature of an electron that shows a planned FEL at Los Alamos National Lab to be most affected. The Genesis simulation code has been modified in order to include quantum reduction of the bunching that lead to interesting results. LA-UR-15-26276
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TUP007	High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II	undulator, electron, simulation, emittance	342
	G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, California, USA J. Qiang, M. Venturini LBNL, Berkeley, California, USA
	High fidelity numerical particle simulations that leverage a number of accelerator and FEL codes have been used to analyze the LCLS-II FEL performance. Together, the physics models that are included in these codes have been crucial in identifying, understanding, and mitigating a number of potential hazards that can adversely affect the FEL performance, some of which are discussed in papers submitted to this conference[, ]. Here, we present a broad overview of the LCLS-II FEL performance, based on these start-to-end simulations, for both the soft X-ray and hard X-ray undulators including both SASE and self-seeded operational modes. M. Venturini, et al., The microbunching instability and LCLS-II lattice design: lessons learned, FEL'15 ** Z. Zhang, et al., Microbunching-induced sidebands in a seeded free-electron laser, FEL'15
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TUP008	High-Gain FEL in the Space-Charge Dominated Raman Limit	space-charge, undulator, electron, simulation	347
	I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig UCLA, Los Angeles, USA
	While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.
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TUP010	Recent Progress in Upgrade of the High-Intensity THz-FEL at Osaka University	electron, linac, klystron, operation	354
	G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, A. Tokuchi, R. Tsutsumi, M. Yaguchi ISIR, Osaka, Japan
	We are upgrading the THz-FEL at Osaka University for its applications to high intensity THz sciences, which originally generated the high intensity FEL with the macropulse energy up to 3.7 mJ and the micropulse energy up to ~10 uJ at a wavelength around 70 um. To increase the micropulse energy, charge in electron bunches is increased four time higher and the bunch intervals are expanded four times longer to maintain the average current in the linac unchanged. In the new operation mode, the macropulse energy increases up to 26 mJ and the micropulse energy to ~0.2 mJ, which is 20 times higher than the energy previously obtained in the conventional mode. We have developed a solid-state switch for the klystron modulator to highly stabilize the klystron voltage, so that the output power of the FEL becomes stable. We are conducting basic studies on FEL for further improvement of its performance, including measurement of power evolution from start-up to saturation, time structures of FEL micropulses measured with a Michelson interferometer, and time structures of macropulses measured with a Schottky diode detector. We will report results of these studies on the THz-FEL at Osaka University.
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TUP011	Performance and Tolerance Studies of the X-Ray Production for the X-Band FEL Collaboration	undulator, simulation, electron, operation	359
	J. Pfingstner, E. Adli University of Oslo, Oslo, Norway
	The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied.
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TUP013	The X-Band FEL Collaboration	undulator, linac, electron, emittance	368
	J. Pfingstner, E. Adli University of Oslo, Oslo, Norway A.A. Aksoy, O. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey D. Angal-Kalinin, J.A. Clarke STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C.J. Bocchetta, A.I. Wawrzyniak Solaris, Kraków, Poland M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc, Y.E. Tan, K.P. Wootton, D. Zhu SLSA, Clayton, Australia G. Burt Lancaster University, Lancaster, United Kingdom N. Catalán Lasheras, A. Grudiev, A. Latina, D. Schulte, S. Stapnes, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland A. Charitonidis NTUA, Athens, Greece G. D'Auria, S. Di Mitri, C. Serpico Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy T.J.C. Ekelöf, M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden W. Fang, Q. Gu SINAP, Shanghai, People's Republic of China E.N. Gazis National Technical University of Athens, Athens, Greece X.J.A. Janssen VDL ETG, Eindhoven, The Netherlands Z. Nergiz Nigde University, Nigde, Turkey
	The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. Due to the higher accelerating gradients achievable with X-band technology, a X-band normal conducting linac can be shorter and therefore potentially cost efficient than what is achievable with lower frequency structures. This cost reduction of future FEL facilities addresses the growing demand of the user community for coherent X-rays. The X-band FEL collaboration consists of 12 institutes and universities that jointly work on the preparation of design reports for the specific FEL projects. In this paper, we report on the on-going activities, the basic parameter choice, and the integrated simulation results. We also outline the interest of the X-band FEL collaboration to use the electron linac CALIFES at CERN to test FEL concepts and technologies relevant for the X-band FEL collaboration.
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TUP015	Status of the ALICE IR-FEL: from ERL Demonstrator to User Facility	laser, cavity, radiation, 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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TUP017	HPC Simulation Suite for Future FELs	simulation, electron, software, plasma	384
	L.T. Campbell, A.J.T. Colin, B.W.J. MᶜNeil, P. Traczykowski USTRAT/SUPA, Glasgow, United Kingdom R.J. Allan The Hartree Centre, Science and Technology Facilities Council (STFC/DL), Warrington, United Kingdom D.J. Dunning, N. Thompson, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom D.J. Dunning, B.D. Muratori, N. Thompson, P.H. Williams Cockcroft Institute, Warrington, Cheshire, United Kingdom J.D.A. Smith Tech-X, Boulder, Colorado, USA
	A new HPC simulation suite, intended to aid in both the investigation of novel FEL physics and the design of new FEL facilities, is described. The integrated start-to-end suite, currently under development, incorporates both plasma (VSim) and linac (ELEGANT, ASTRA) accelerator codes, and will include the 3D unaveraged FEL code Puffin to probe novel FEL effects.
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TUP019	Time Locking Options for the Soft X-Ray Beamline of SwissFEL	laser, electron, undulator, radiation	388
	E. Prat, S. Reiche PSI, Villigen PSI, Switzerland
	SwissFEL is an FEL facility presently under construction at the Paul Scherrer institute that will serve two beamlines: Aramis, a hard X-ray beamline which is in construction phase and will provide FEL radiation in 2017 with a wavelength between 0.1 and 0.7 nm; and Athos, a soft X-ray beamline which is in design phase and it is expected to offer FEL light in 2021 for radiation wavelengths between 0.7 and 7 nm. A passive synchronization of the FEL signal to a laser source is fundamental for key experiments at Athos, such as the time-resolved resonant inelastic X-ray scattering (RIXS) experiments. In this paper we explore different options to achieve this time synchronization by means of energy modulating the electron beam with an external laser.
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TUP020	Recent Study in iSASE	electron, distributed, laser, undulator	393
	K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA C. Emma, C. Pellegrini UCLA, Los Angeles, USA S. Hsu University of California, San Diego (UCSD), La Jolla, California, USA
	The Improved Self-Amplified Spontaneous Radiation (iSASE) scheme has potential to reduce SASE FEL bandwidth. This is achieved by repeatedly delaying the electrons with respect to the radiation pulse using phase shifters in the undulator break sections. It has been shown that the strength, locations and sequences of phase shifters are important to the iSASE performance. Particle swarm optimization algorithm is used to explore the phase shifters configuration space globally.
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TUP021	Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability	radiation, 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, electron, detector, radiation	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	laser, electron, radiation, 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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TUP025	Studies of Undulator Tapering for the CLARA FEL	electron, undulator, laser, brightness	412
	I.P.S. Martin, R. Bartolini DLS, Oxfordshire, United Kingdom R. Bartolini JAI, Oxford, United Kingdom D.J. Dunning, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Undulator tapering is a well-known method for enhancing the performance of free-electron lasers [1]. It works by keeping the resonant wavelength constant, despite variation in the electron beam energy. Both the energy-extraction efficiency and the spectral brightness of the FEL can be improved using this technique. In this paper we present recent studies of undulator tapering for the CLARA FEL in both SASE and seeded modes. The methods used to optimise the taper profile are described, and the properties of the final FEL pulses are compared. [1] N.M. Kroll, P.L. Morton, M.N. Rosenbluth, J. Quantum Electronics 17, 8 (1981).
	Poster TUP025 [0.919 MB]
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TUP026	Measurment Uncertainties in Gas-Based Monitors for High Repetition Rate X-Ray FEL Operations	undulator, simulation, detector, linac	417
	Y. Feng, M.L. Campell, J. Krzywinski, E. Ortiz, T.O. Raubenheimer, M. Rowen, D.W. Schafer SLAC, Menlo Park, California, USA
	Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University. Thermodynamic simulations using a finite difference method were carried out to investigate the measurement uncertainties in gas-based X-ray FEL diagnostic monitors under high repetition rate operations such as planned for the future LCLS-II soft and hard X-ray FEL's. For monitors using relatively high gas pressures for obtaining sufficient signals, the absorbed thermal power becomes non-negligible as repetition rate increases while keeping pulse energy constant. The fluctuations in the absorbed power were shown to induce significant measurements uncertainties, especially in the single-pulse mode. The magnitude of this thermal effect depends nonlinearly on the absorbed power and can be minimized by using a more efficient detection scheme in which the gas pressure can be set sufficiently low
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TUP028	DESIGN OF THE MID-INFRARED FEL OSCILLATOR IN CHINA	electron, undulator, cavity, laser	427
	H.T. Li, Q.K. Jia, L. Wang, S.C. Zhang USTC/NSRL, Hefei, Anhui, People's Republic of China
	In 2014, Xiamen University and other three research organizations received the approval to realize an infrared free electron laser (IR-FEL) for fundamental of energy chemistry. The IR-FEL covers the spectral range of 2.5-200 μm and will be built in NSRL. Two FEL oscillators driven by one Linac will be used to generate mid- infrared and far-infrared lasers. In this article we describe the design studies for the mid-infrared FEL oscillator.
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TUP029	Single Picosecond THz Pulse Extraction from the FEL Macropulse using a Laser Activating Semiconductor Reflective Switch	laser, radiation, 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, radiation	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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TUP050	Extension of Existing Pulse Analysis Methods to High-Repetition Rate Operation: Studies of the "Time-Stretch Strategy"	electron, laser, detector, storage-ring	483
	S. Bielawski PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France J.B. Brubach, L. Cassinari, M.-E. Couprie, M. Labat, L. Manceron, J.P. Ricaud, P. Roy, M.-A. Tordeux SOLEIL, Gif-sur-Yvette, France C. Evain, C. Szwaj PhLAM/CERLA, Villeneuve d'Ascq, France M. Le Parquier CERLA, Villeneuve d'Ascq, France E. Roussel Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Funding: ANR (2010-042301, DYNACO), LABEX CEMPI project (ANR-11-LABX-0007), ERC grant COXINEL (340015), GENCI TGCC/IDRIS (x2014057057,i2015057057). Many single-shot recording setups are based on the encoding of the information onto a laser pulse. This concerns in particular electro-optic sampling of bunch shapes, and VUV/X pulse monitors using transient reflectivity. The upgrade of these methods to high repetition rates presents challenging issues, that are due to the limited speed of the recording cameras. Recently [1], we demonstrated that multi-MHz repetition rates can be achieved using a relatively simple upgrade of existing setups, using the so-called "photonic time-stretch" technique. Here we present guidelines for the practical realization in the case of electro-optic sampling. We also present a performance analysis, and compare it to the spectral encoding case. The technique is potentially applicable to other cases where the information can be encoded on a chirped laser pulse, as, e.g., transient reflectivity diagnostics of XUV pulses. [1] Observing microscopic structures of a relativistic object using a time-stretch strategy, E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E Couprie, and P. Roy, Scientific Reports 5, 10330 (2015).
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TUP053	Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion	polarization, undulator, radiation, diagnostics	486
	W.M. Fawley, E. Allaria, E. Ferrari Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy
	Cross-polarized (X-POL) configurations are a means to produce circularly-polarized radiation output from purely planar-polarized undulators. Recent polarization results from both the FERMI FEL-1 [1] at XUV wavelengths and Shanghai DUV FEL [2] at visible wavelengths have confirmed that such configurations do work for single pass FELs. However, analysis of both FERMI and SINAP results indicate that the quantitative degree of planar to circular conversion can be significantly affected by several experimental details. Full conversion requires not only equal intensity of the two cross-polarized beams but also perfect overlap in space and time of their far-field amplitude and phase patterns. From both simple theoretical analysis and more detailed simulation modeling, we examine a number of possible factors that can degrade the net linear to circular conversion efficiency. In addition to the previous suggestions by Ferrari et al. of problems with unbalanced powers and transverse phase variation arising from different effective emission z locations for the two cross-polarized radiation pulses, we also consider separate degradation effects of imperfect downstream overlap of the two linearly-polarized beams arising from different emission tilt angles and mode sizes. We also discuss optimizing the conversion efficiency by aperturing the radiation pulses downstream of the undulators. [1] E. Ferrari et al., Paper THA02, Proc. FEL2013 (2013). [2] H. Deng et al., Phys. Rev. ST Accel. Beams 17, 020704 (2014).
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TUP056	Design Challenge and Strategy for the LCLS-II High Repetition Rate X-ray FEL Photon Stoppers	photon, simulation, radiation, 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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TUP085	Lebra Free-Electron Laser Elicits Electrical Spikes from the Retina and Optic Nerve of the Slugs Limax Valentianus	site, experiment, electron, radiation	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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WEA03	SwissFEL Status Report	undulator, linac, vacuum, electron	567
	R. Ganter PSI, Villigen PSI, Switzerland
	SwissFEL is a 5.8 GeV linac which sends electron bunches at 100 Hz into a 60 m long in-vacuum undulator line to produce hard X-rays between 0.1 nm and 0.7 nm. The SwissFEL accelerator design is based on a low emittance beam with tight tolerances on RF stability. The first lasing of SwissFEL is planned for early 2017 and two end-stations should then be brought into operation in the same year. The delivery of the SwissFEL building to PSI is planned for fall this year, but some rooms are already completed and currently in use for components assembly. The production of the C-band RF accelerating structures has now reach the nominal rate of 5 structures/month. Two different RF solid state modulator prototypes could demonstrate jitter lower than 20 ppm but stability and reliability tests are still going on. The undulators assembly and measurement sequence have started and 13 undulators are planned to be ready in the tunnel by October 2016. Large series of components like magnets, vacuum systems and mechanical supports are already in house and under assembly. Photonics components for two beamlines and two end stations are ordered and planned to be ready for 2017.
	Slides WEA03 [36.505 MB]
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WEB01	A Two-Color Storage Ring FEL	undulator, electron, cavity, operation	571
	J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA S. Huang PKU, Beijing, People's Republic of China J.Y. Li USTC/NSRL, Hefei, Anhui, People's Republic of China N. Vinokurov BINP SB RAS, Novosibirsk, Russia J. Wu SLAC, Menlo Park, California, USA
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. Using different undulator configurations on the Duke storage ring, we have successfully achieved lasing with a novel two-color storage ring FEL. Using a pair of dual-band FEL mirrors, simultaneous lasing was realized in IR (around 720 nm) and in UV (around 360 nm). With this two-color FEL, we have demonstrated independent wavelength tuning of either IR or UV lasing. With careful tuning, we have also realized harmonic lasing with the UV lasing tuned to the second harmonic of the IR lasing. The tuning of harmonic two-color lasing has also been demonstrated with the locked wavelengths. Furthermore, we have demonstrated good control of the FEL power sharing between the two colors. The two-color FEL has created new opportunities to drive a two-color Compton gamma-ray beam at the High Intensity gamma-ray Source at Duke.
	Slides WEB01 [18.975 MB]
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WEB02	Waveguide THz FEL Oscillators	injection, electron, extraction, undulator	576
	S.V. Miginsky, S. Bae, B.A. Gudkov, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov KAERI, Daejon, Republic of Korea S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	In today's world there is a significant demand for FEL-based THz radiation sources. They have a wide tuning range, a narrow band of radiation, and comparably high peak and average emission power. There are a significant number of these machines in the world, operating or in the development. The main difference between a long-wave FEL, of THz or a millimeter band, and a conventional one is a too big transverse size of the fundamental mode of an open optical resonator. It claims a large gap in an undulator that dramatically decreases its strength. Both factors sorely decrease the amplification and the efficiency, and often make lasing impossible. The main way to solve this problem is to use a waveguide optical resonator. It decreases and controls the transverse size of the fundamental mode. However, the waveguide causes a number of problems: power absorption in its walls; higher modes generation by inhomogeneities, as it is not ideal; electron beam injection into a FEL is more sophisticated; also outcoupling is more complicated; finally, the resonator detuning control claims some special solutions. The waveguide dispersion relation differs from one in the free space. It shifts up the wavelength of the FEL, changes the optimal detuning, and creates a parasitic mode near the critical wavelength of the waveguide. These problems and possible solutions to them are considered.
	Slides WEB02 [20.394 MB]
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WEB04	Saturation Dynamics, Fine Spectrum, and Chirp Control in a CW FEL Oscillator	laser, electron, coupling, operation	580
	H. S. Marks, A. Gover, H. Kleinman University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel D. Borodin, A. Damti, A. Friedman, Y. Vashdi Ariel University, Ariel, Israel M. Einat, M. Kanter, Y. Lasser, Yu. Lurie, A. Yahalom Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel
	As in conventional laser physics, the saturation dynamics of a long-pulse Electrostatic Accelerator FEL (EA-FEL) oscillator consists of oscillations build-up, resonator modes competition, and establishment of narrow linewidth single mode lasing. In EA-FEL the gain curve drifts to lower frequencies during the long laser pulse due to inevitable droop in the acceleration voltage. This post-saturation drift renders fine chirp of the single mode laser frequency due to the oscillator frequency pulling effect. We have integrated a voltage-ramping element into the electrostatic accelerator terminal that makes it possible to control the acceleration voltage throughout the lasing pulse. This allows us to keep the voltage constant throughout the e-beam pulse, and so increase the single mode lasing time, avoiding mode-hopping during the pulse due to the drift of the gain curve. Furthermore, by adjusting the voltage ramp rate and polarity we obtained controllable positive/negative laser frequency chirp that can be used in a single pulse sweep for fine spectral line (10^-6) gas-spectroscopy. The study was conducted on the Israeli EA-FEL that operates at tunable frequencies between 95-110 GHz.
	Slides WEB04 [2.310 MB]
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WEP001	RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS	undulator, radiation, 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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WEP002	Simulating Single Crystal Copper Photocathode Emittance	emittance, simulation, electron, laser	587
	T. Vecchione SLAC, Menlo Park, California, USA
	Funding: US DOE contract DE-AC02-76SF00515 The performance of free-electron lasers depends on the quality of the electron beam used. In some cases this performance can be improved by optimizing the choice of photocathode with respect to emittance. With this in mind, electronic structure calculations have been included in photoemission simulations and used to predict the emittance from single crystal copper photocathodes. The results from different low-index surfaces are reported. Within the model assumptions the Cu(100) surface was identified as having minimal emittance, particularly when illuminated by 266 nm light and extracted in a 60 MV/m gradient. These findings may guide future experimental work, leading to improved machine performance.
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WEP003	Recent Understanding and Improvements of the LCLS Injector	laser, emittance, cathode, electron	592
	F. Zhou, D.K. Bohler, Y. Ding, S. Gilevich, Z. Huang, H. Loos, D.F. Ratner SLAC, Menlo Park, California, USA
	Funding: U.S. DOE contract No. DE-AC02-76SF00515. Ultraviolet drive laser and copper photocathode are the key systems for reliably delivering <0.4 micron of emittance and high brightness free electron laser (FEL) at the linac coherent light source (LCLS). Characterizing, optimizing and controlling laser distributions in both spatial and temporal directions are important for ultra-low emittance generation. Spatial truncated Gaussian laser profile has been demonstrated to produce better emittance than a spatial uniform beam. Sensitivity of the spatial laser distribution for the emittance is measured and analysed. Stacking two 2-ps Gaussian laser beams significantly improves emittance and eventually FEL performance at the LCLS in comparison to a single 2-ps Gaussian laser pulse. In addition, recent observations at the LCLS show that the micro-bunching effect depends strongly on the cathode spot locations. The dependence of the micro-bunching and FEL performance on the cathode spot location is mapped and discussed.
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WEP004	Energy Spread Constraints on Field Suppression in a Reverse Tapered Undulator	undulator, laser, bunching, simulation	597
	J.P. MacArthur, Z. Huang, A.A. Lutman, A. Marinelli, H.-D. Nuhn SLAC, Menlo Park, California, USA
	A 3.2 m variable polarization Delta undulator[1] has been installed at the end of the LCLS undulator line. The Delta undulator acts an an afterburner in this configuration, using bunching from upstream planar undulators to produce radiation with arbitrary polarization. To optimize the degree of polarization from this device, a reverse taper[2] has been proposed to suppress background radiation produced in upstream undulators while still microbunching the beam. Here we extend previous work on free electron lasers with a slowly varying undulator parameter[3] to show there is a strong energy spread dependence to the maximum allowable detune from resonance. At LCLS, this energy spread limitation keeps the reverse taper slope in the slowly varying regime and limits the achievable degree of circular polarization. [1] A. B. Temnykh, PRST-AB, 11, 120702, (2008). [2] E. A. Schneidmiller and M. V. Yurkov, PRST-AB, 16, 110702, (2013). [3] Z. Huang and G. Stupakov, PRST-AB, 8, 040702, (2005).
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WEP005	Laser Heater Transverse Shaping to Improve Microbunching Suppresion for X-ray FELs	laser, electron, undulator, linac	602
	S. Li Stanford University, Stanford, California, USA A.R. Fry, S. Gilevich, Z. Huang, A. Marinelli, D.F. Ratner, J. Robinson SLAC, Menlo Park, California, USA
	In X-ray free electron lasers (FELs), a small amount of initial density or energy modulation in the electron beam will be amplified through acceleration and bunch compression process. The undesired microbunching on the electron bunch will increase slice energy spread and degrade the FEL performance. The Linac Coherent Light Source (LCLS) laser heater (LH) system was installed to increase the uncorrelated energy spread in the electron beam in order to suppress the microbunching instability. The distribution of the induced energy spread depends strongly on the transverse profile of the heater laser and has a large effect on the microbunching suppression. In this paper we discuss strategies to shape the laser profile in order to obtain better suppression of microbunching. We present analysis to achieve the Gaussian-like energy spread using a Laguerre-Gaussian laser mode and study the efficiency and alignment tolerance for implementation.
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WEP008	Four-Dimensional Models of FEL Amplifiers and Oscillators	electron, undulator, simulation, laser	607
	J. Blau, K. R. Cohn, W.B. Colson NPS, Monterey, California, USA
	Funding: This work has been supported by the High Energy Laser Joint Technology Office. New four-dimensional models of free electron lasers (FELs) are described, for both amplifier and oscillator configurations. Model validation and benchmarking results are shown, including comparisons to theoretical formulas and experiments.
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WEP010	Development of Phonon Dynamics Measurement System by MIR-FEL and Pico-second Laser	laser, scattering, timing, lattice	615
	T. Murata, T. Katsurayama, T. Kii, T. Konstantin, K. Masuda, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Zen Kyoto University, Kyoto, Japan K. Hachiya Kyoto University Graduate School of Energy Science, Kyoto, Japan K. Yoshida Kumamoto University, Department of Applied Chemistry and Biochemistry, Kumamoto, Japan
	Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.
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WEP014	LCLS-II: Status of the CW X-ray FEL Upgrade to the LCLS Facility	undulator, linac, gun, electron	618
	T.O. Raubenheimer SLAC, Menlo Park, California, USA
	Funding: Work supported by Department of Energy contract DE-AC02-76SF00515 The LCLS-II is a CW X-ray FEL based on a 4 GeV superconducting RF linac that will upgrade the LCLS facility at the SLAC National Accelerator Laboratory. The upgrade is being constructed by a collaboration including ANL, Cornell, Fermilab, JLab, LBNL, and SLAC. This talk will describe the status of the LCLS-II project as well as the major technical issues and R&D to address them. Presented on behalf of the LCLS-II collaboration
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WEP016	Free Electron Lasers in 2015	electron, undulator, laser, free-electron-laser	625
	K. R. Cohn, J. Blau, W.B. Colson, J.W. Ng, M.J. Price NPS, Monterey, California, USA
	Funding: This work has been supported by the High Energy Laser Joint Technology Office. Thirty-nine years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.
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WEP022	Photon Energies beyond the Selenium K-Edge at LCLS	photon, electron, operation, linac	630
	F.-J. Decker, W.S. Colocho, Y. Ding, R.H. Iverson, H. Loos, J. Sheppard, H. Smith, J.L. Turner SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) was designed for a photon energies of 830 eV to 8.3 keV. This range was widened and up to 11.2 keV photons were already delivered for users. The Selenium K-edge at 12.6578 keV is very interesting since Selenium can replace Sulfur in biological structures and then that structure could be precisely measured. To reach this the electron energy would need to be raised by about 6% which initially didn't seem possible. The trick is to change the final compression scheme from a high correlated energy spread and moderate R56 in the compression chicane to moderate energy spread and high R56. The same bunch length can be achieved and RF energy is freed up, so the overall beam energy can be raised. Photons up to an energy of 12.82 keV (1.3% above the K-edge) with a pulse intensity of 0.93 mJ were achieved. The photon energy spread with this setup is wider at around 40-50 eV FWHM, since less correlated energy spread is left after the compression.
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WEP029	Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance	laser, undulator, simulation, electron	643
	T. Plath, C. Lechner Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt DESY, Hamburg, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355. To enhance the spectral and temporal properties of a free-electron laser the FEL process can be seeded by an external light field. The quality of this light field strongly influences the final characteristics of the seeded FEL pulse. To push the limits of a seeding experiment and reach the smallest possible wavelengths it is therefore crucial to have a thorough understanding of relations between laser parameters and seeding performance. In this contribution we numerically study the influence of laser wavefront imperfections on high-gain harmonic generation seeding at the seeding experiment at FLASH.
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WEP030	First Lasing of an HGHG Seeded FEL at FLASH	electron, laser, experiment, injection	646
	K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany S. Ackermann, Ph. Amstutz, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, T. Plath, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, R.W. Aßmann, J. Bödewadt, N. Ekanayake, B. Faatz, I. Hartl, R. Ivanov, T. Laarmann, J.M. Müller DESY, Hamburg, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355. The free-electron laser facility FLASH at DESY operates in SASE mode with MHz bunch trains of high-intensity extreme ultraviolet and soft X-ray FEL pulses. A seeded beamline which is designed to be operated parasitically to the main SASE beamline has been used to test different external FEL seeding methods. First lasing at the 7th harmonic of a 266 nm seed laser using high-gain harmonic generation has been demonstrated. Studies of the influence of the microbunching instability are being pursued.
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WEP031	Measurements and Simulations of Seeded Electron Microbunches with Collective Effects	electron, simulation, laser, bunching	650
	K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany S. Ackermann, J. Bödewadt, M. Dohlus, N. Ekanayake, T. Laarmann, H. Schlarb DESY, Hamburg, Germany L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, T. Plath, J. Roßbach Uni HH, Hamburg, Germany
	Funding: The experiments were carried out at FLASH at DESY. BMBF contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3, and the German Research Foundation program graduate school 1355. Measurements of the longitudinal phase-space distribution of electron bunches seeded with an external laser were done in order to study the impact of collective effects on seeded microbunches in free-electron lasers. Velocity bunching of a seeded microbunch appears to be a viable alternative to compression with a magnetic chicane under high-gain harmonic generation seeding conditions when the collective effects of Coulomb forces in a drift space and coherent synchrotron radiation in a chicane are considered. Measurements of these effects on seeded electron microbunches were performed with an RF deflecting structure and a dipole magnet which streak out the electron bunch for single-shot images of the longitudinal phase-space distribution. Particle tracking simulations in 3D predicted the compression dynamics of the seeded microbunches with collective effects.
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WEP042	Commissioning and First Performance of the LINAC-based Injector Applied in the HUST THz-FEL	linac, target, gun, beam-diagnostic	662
	T. Hu, Q.S. Chen, J. Li, B. Qin, P. Tan, Y.Q. Xiong HUST, Wuhan, People's Republic of China L. Cao, W. Chen Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China Y.J. Pei, Zh. X. Tang USTC/NSRL, Hefei, Anhui, People's Republic of China
	The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc.
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WEP047	Femtosecond Timing Distribution at the European XFEL	laser, timing, optics, electron	669
	C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack DESY, Hamburg, Germany S. Jabłoński Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.
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WEP048	Electron Beam Diagnostics for FEL Studies at CLARA	electron, diagnostics, laser, simulation	672
	S. Spampinati Cockcroft Institute, Warrington, Cheshire, United Kingdom D. Newton The University of Liverpool, Liverpool, United Kingdom
	CLARA (Compact Linear Accelerator for Research and Applications) is a proposed 250 MeV, 100-400 nm FEL test facility at Daresbury Laboratory [1]. The purpose of CLARA is to test and validate new FEL schemes in areas such as ultra-short pulse generation, temporal coherence and pulse-tailoring. Some of the schemes that can be tested at CLARA depend on a manipulation of the electron beam properties with characteristic scales shorter than the electron beam. In this article we describe the electron beam diagnostics required to carry on these experiments and simulations of FEL pulse and electron beam measurements. [1] J. A. Clarke et al., JINST 9, 05 (2014).
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WEP051	The Prototype of New Variable Period Undulator for Novosibirsk Free Electron Laser.	undulator, simulation, permanent-magnet, electron	677
	I.V. Davidyuk NSU, Novosibirsk, Russia O.A. Shevchenko, V.G. Tcheskidov BINP SB RAS, Novosibirsk, Russia N. Vinokurov KAERI, Daejon, Republic of Korea
	To improve the parameters of the second stage Novosibirsk free electron laser one plans to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles for shorter periods with constant undulator length. Both these advantages will be realized in the new undulator under development in Budker INP. The idea of the permanent-magnet VPU was proposed just several years ago and it has not been properly tested yet. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.
	Poster WEP051 [3.821 MB]
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WEP054	Control of Gap Dependent Phase Errors on the Undulator Segments for the European XFEL	undulator, laser, electron, free-electron-laser	685
	Y. Li, J. Pflüger XFEL. EU, Hamburg, Germany
	Strong magnetic forces in long undulators always result in some girder deformation. This problem gets more serious in long gap tuneable undulators. In addition the deformation varies with changing forces at different gaps resulting in gap dependent phase errors. For the undulators for the European XFEL this problem has been studied thoroughly and quantitatively. A compensation method is presented which uses a combination of suitable shims and pole height tuning. It is exemplified by tuning one of the undulator segments for the European XFEL back to specs.
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WEP060	Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF	laser, electron, cavity, experiment	694
	M. Chung, J.M. Seok UNIST, Ulsan, Republic of Korea J.H. Han, J.H. Hong, H.-S. Kang, C.H. Kim PAL, Pohang, Kyungbuk, Republic of Korea J.C.T. Thangaraj Fermilab, Batavia, Illinois, USA
	Longitudinal shaping of electron beam has received much attention recently, due to its potential applications to THz generation, dielectric wakefield acceleration, improvement of FEL performance, and controlled space-charge modulation. Using a set of alpha-BBO crystals, shaping of laser pulse and electron bunch on the order of ps is tested at the Injector Test Facility (ITF) of Pohang Accelerator Laboratory (PAL). In particular, we investigate the response of the longitudinally-modulated beam to a dechirper, which is a vacuum chamber of two corrugated, metallic plates. Initial experimental results will be presented with analytical theory and numerical simulations.
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WEP070	Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons	emittance, linac, electron, simulation	714
	J. Qiang, C.E. Mitchell, C. F. Papadopoulos, M. Venturini LBNL, Berkeley, California, USA Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley SLAC, Menlo Park, California, USA
	The LCLS-II as a next generation high repetition rate FEL based X-ray light source will enable significant scientific discoveries. In this paper, we report on the progress in the design of the accelerator beam delivery system through start-to-end simulations. We will present simulation results for three cases, 20 pC, 100 pC and 300 pC that are transported through the hard X-ray line and the soft X-ray line for FEL radiation.
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WEP073	Dispersion of Correlated Energy Spread Electron Beams in the Free Electron Laser	electron, undulator, radiation, plasma	718
	L.T. Campbell USTRAT/SUPA, Glasgow, United Kingdom A.R. Maier CFEL, Hamburg, Germany
	The effect of a correlated linear energy chirp in the electron beam in the FEL, and how to compensate for its effects by using an appropriate linear taper of the undulator magnetic field have previously been investigated considering relatively small chirps. In the following, it is shown that larger linear energy chirps, such as those found in beams produced by laser-plasma accelerators, exhibit dispersive effects in the undulator, and require a non-linear taper on the undulator field to properly optimise.
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WEP075	Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam	electron, radiation, undulator, simulation	722
	C. Emma, C. Pellegrini UCLA, Los Angeles, USA Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini SLAC, Menlo Park, California, USA
	We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.
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WEP076	Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing	undulator, electron, simulation, extraction	726
	C. Emma UCLA, Los Angeles, USA K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy DE-SC0009983. Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented.
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WEP078	Advances on the LUNEX5 and COXINEL Projects	laser, electron, operation, plasma	730
	M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, J.D. Bozek, F. Briquez, L. Cassinari, L. Chapuis, J. Da Silva, J. Daillant, D. Dennetière, Y. Dietrich, M. Diop, J.P. Duval, M.E. El Ajjouri, T.K. El Ajjouri, C. Herbeaux, N. Hubert, M. Khojoyan, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, J. Lüning, P. Marchand, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, A. Nadji, R. Nagaoka, F. Polack, F. Ribeiro, J.P. Ricaud, P. Rommeluère, P. Roy, G. Sharma, K.T. Tavakoli, M. Thomasset, M. Tilmont, M.-A. Tordeux, M. Valléau, J. Vétéran, W. Yang, D. Zerbib SOLEIL, Gif-sur-Yvette, France S. Bielawski, M. Le Parquier PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France X. Davoine CEA/DAM/DIF, Arpajon, France N. Delerue, M. El Khaldi, W. Kaabi, F. Wicek LAL, Orsay, France G. Devanz, C. Madec CEA/IRFU, Gif-sur-Yvette, France A. Dubois CCPMR, Paris, France C. Evain, C. Szwaj PhLAM/CERLA, Villeneuve d'Ascq, France D. Garzella CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France G. Lambert, V. Malka, A. Rousse, C. Thaury LOA, Palaiseau, France A. Mosnier CEA/DSM/IRFU, France E. Roussel Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Funding: ERC COXINEL 340015 LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating compact and advanced Free Electron Laser (FEL). It comprises one one hand a 400 MeV superconducting linac for studies of advanced FEL schemes, high repetition rate operation (10 kHz), multi-FEL lines, and one the other hand a Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, an undulator line enabling advanced seeding and pilot user applications in the 40-4 nm spectral range. Following the CDR completion, different R&D programs were launched, as for instance on FEL pulse duration measurement, high repetition rate electro-optical sampling. The COXINEL ERC Advanced Grant aims at demonstrating LWFA based FEL amplification, thanks to a proper electron beam manipulation, with a test experiment under preparation. As a specific hardware is also under development such as a cryo-ready 3 m long undulator of 15 mm period is under development.
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WEP079	Inclusion of Advanced Fields and Boundary Conditions in the Analytic Theory for High Gain FELs	electron, radiation, 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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WEP084	Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser	undulator, simulation, electron, bunching	741
	Z. Zhang TUB, Beijing, People's Republic of China Y. Ding, W.M. Fawley, Z. Huang, J. Krzywinski, A.A. Lutman, G. Marcus, A. Marinelli, D.F. Ratner SLAC, Menlo Park, California, USA
	The measured, self-seeded soft X-ray radiation spectrum corresponding to multiple effective undulator lengths of the LCLS exhibits a pedestal-like distribution around the seeded frequency. In the absence of a post-undulator monochromator, this contamination limits the spectral purity and may seriously degrade certain user applications. In general for either externally- or self-seeded FELs, such pedestals may originate with any time-varying property of the electron beam that can modulate the complex gain function. In this paper we specifically focus on the contributions of electron beam microbunching prior to the undulator. We show that both energy and density modulations can induce sidebands in a seeded FEL configuration. Analytic FEL theory and numerical simulations are used to analyze the sideband content relative to the amplified seeded signal, and to compare with experimental results.
	Poster WEP084 [1.263 MB]
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WEP085	Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance	radiation, electron, wiggler, 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	radiation, 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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WED04	Status Report of PAL-XFEL Undulator Program	undulator, electron, radiation, controls	769
	D.E. Kim, M.-H. Cho, Y.-G. Jung, H.-S. Kang, I.S. Ko, H.-G. Lee, S.B. Lee, W.W. Lee, B.G. Oh, K.-H. Park, H.S. Suh PAL, Pohang, Kyungbuk, Republic of Korea S. Karabekyan, J. Pflüger XFEL. EU, Hamburg, Germany
	PAL-XFEL is a SASE based FEL using S-band linear accelerator, photo cathode RF Gun, and hybrid undulator system for final lazing. The undulator system is based on EU-XFEL undulator design with necessary modifications. The changes include new magnetic geometry reflecting changed magnetic requirements, and EPICs based control system. The undulator system is in measurement and tuning stage targeting to finish installation within 2015. In this report, the development, tuning, measurement efforts for PAL-XFEL undulator system will be reported.
	Slides WED04 [3.317 MB]
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MOA02

First Lasing of the Third Stage of Novosibirsk FEL

undulator, radiation, electron, linac

1

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

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

Slides MOA02 [4.901 MB]

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MOB01

Three-Plus Decades of Tapered Undulator FEL Physics

electron, radiation, 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

undulator, electron, photon, radiation

7

Z. Huang
SLAC, Menlo Park, California, USA

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

Slides MOB02 [18.004 MB]

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MOB03

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

laser, undulator, radiation, electron

10

E. Hemsing
SLAC, Menlo Park, California, USA

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

Slides MOB03 [12.208 MB]

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MOC02

Optimization of a High Efficiency Free Electron Laser Amplifier

electron, undulator, radiation, brilliance

17

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

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

Slides MOC02 [24.462 MB]

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MOC03

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

emittance, electron, undulator, collective-effects

24

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

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

Slides MOC03 [2.528 MB]

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MOC04

Operating of SXFEL in a Single Stage High Gain Harmonic Generation Scheme

laser, bunching, electron, linac

29

G.L. Wang, D.X. Dai, G.R. Wu, X.M. Yang, W.Q. Zhang
DICP, Dalian, People's Republic of China

The beam energy spread at the entrance of undulator system is of paramount importance for efficient density modulation in high-gain seeded free-electron lasers (FELs). In this paper, the dependencies of high harmonic bunching efficiency in the high-gain harmonic generation (HGHG) schemes on the electron energy spread distribution are studied. Theoretical investigations and multi-dimensional numerical simulations are applied to the cases of uniform and saddle beam energy distributions and compared to a traditional Gaussian distribution. It shows that the uniform and saddle electron energy distributions significantly enhance the performance of HGHG-FELs. A numerical example demonstrates that, with the saddle distribution of sliced beam energy spread controlled by a laser heater, the 30th harmonic radiation can be directly generated by a single-stage seeding scheme for a soft x-ray FEL facility.

Slides MOC04 [3.345 MB]

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MOP004

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

undulator, radiation, electron, 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, electron, radiation, polarization

38

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

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

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MOP010

Linac Design of the IR-FEL Project in CHINA

electron, gun, linac, beam-transport

46

Z.G. He, Q.K. Jia, L. Wang, W. Xu, S.C. Zhang
USTC/NSRL, Hefei, Anhui, People's Republic of China

We are building an infrared free-electron laser (IR-FEL) facility that will operate from 5 um to 200 um. This FEL source is drived by a linac, which is composed of a triode electron gun, a subharmonic prebuncher, a buncher, two accelerators, and a beam transport line. The linac is required to operate from 15 to 60 MeV at 1 nC charge, while delivering a transverse rms emittance of smaller than 30 mm-mrad in a 5 ps rms length, smaller than 240 keV rms energy spread bunch at the Far-infrared and Mid-infrared undulators. In this article, the preliminary Linac design studies are described.

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MOP011

Status of CLARA, a New FEL Test Facility

laser, undulator, electron, gun

49

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

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

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MOP013

The Fermi Seeded FEL Facility: Operational Experience and Future Perspectives

experiment, laser, electron, photon

57

L. Giannessi, E. Allaria, L. Badano, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, M. Coreno, R. Cucini, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, E. Ferrari, P. Finetti, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, F. Iazzourene, M. Kiskinova, S. Krecic, M. Lonza, N. Mahne, M. Manfredda, C. Masciovecchio, M. Milloch, F. Parmigiani, E. Pedersoli, G. Penco, L. Pivetta, O. Plekan, M. Predonzani, K.C. Prince, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, E. Roussel, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, M. Svandrlik, C. Svetina, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

FERMI is the seeded FEL user facility in Trieste, Italy, producing photons from the VUV to the soft X-rays with a high degree of coherence and spectral stability. Both FEL lines, FEL-1 and FEL-2, are available for users, down to the shortest wavelength of 4 nm. We report on the completion of the commissioning of the high energy FEL line, FEL-2, on the most recent progress obtained on FEL-1 and on the operational experience for users, in particular those requiring specific FEL configurations, such as two-colour experiments. We will also give a perspective on the improvements and upgrades which have been triggered based on our experience, aiming to maintain as well as to constantly improve the performance of the facility for our user community.

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MOP014

Status of the Soft X-Ray FEL User Facility FLASH

photon, electron, operation, experiment

61

K. Honkavaara, B. Faatz, J. Feldhaus, S. Schreiber, R. Treusch, M. Vogt
DESY, Hamburg, Germany

Since 10 years FLASH at DESY (Hamburg, Germany) has provided high brilliance FEL radiation at XUV and soft X-ray wavelengths for user experiments. Recently FLASH has been upgraded with a second undulator beamline, FLASH2, whose commissioning takes place in parallel of the user operation on FLASH1. This paper summarizes the performance of the FLASH facility during the last user period from January 2014 to April 2015.

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MOP017

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

linac, undulator, electron, operation

69

T. Schietinger
PSI, Villigen PSI, Switzerland

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

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MOP034

Beam Optics Measurements at FERMI by using Wire-Scanner

optics, emittance, linac, quadrupole

101

G. Penco, A. Abrami, I. Cudin, S. Di Mitri, M. Ferianis, E. Ferrari, G. Gaio, L. Giannessi, S. Grulja, R. Sauro, L. Sturari
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy
G.L. Orlandi, C. Ozkan Loch
PSI, Villigen PSI, Switzerland

Measuring and controlling the electron beam optics is an important ingredient to guarantee high performance of a free-electron laser. In the FERMI linac, the Twiss parameters and the transverse emittances are routinely measured by detecting the beam spot size as a function of a scanning quadrupole placed upstream (i.e. quadrupole scan method). The beam spot size is usually measured with an OTR screen that unfortunately suffers from coherent optical transition radiation (C-OTR) that introduces spurious light and corrupts the image. Moreover, the beam size at the end of the FERMI linac is focused to a few tens of microns and this makes it difficult to precisely measure it with the OTR system, which has an estimated resolution of 20um. For this reason, a wire-scanner system has been installed at the end of the linac just in the waist of the optics channel. The wire-scanner is a SwissFEL prototype installed in FERMI in order to study the hardware and beam loss monitor performances at the GeV energy scale. The beam optics measurements performed with the wire-scanner is here presented, and the obtained results are more in agreement with the theoretical expectations. A more reliable beam optics estimation at the end of the linac has allowed to better match it to the nominal lattice and transport it up to the undulator chain, providing important benefits to the FEL performance.

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MOP036

Femtosecond Synchronization of 80-MHz Ti:Sapphire Photocathode Laser Oscillator with S-Band RF Oscillator

laser, timing, detector, electron

105

H. Yang, C. Jeon, K. Jung, J. Kim
KAIST, Daejeon, Republic of Korea
H. Chung
Korea University Sejong Campus, Sejong, Republic of Korea
B. Han, Y.U. Jeong
KAERI, Daejon, Republic of Korea

Precision synchronization between lasers and RF sources in free-electron lasers (FELs) and ultrafast electron diffraction (UED) systems is becoming more important. There have been intense research and development toward femtosecond synchronization of lasers and RF sources in the last decade. Most of the previous approaches at large-scale FELs have used cw lasers or low-jitter mode-locked lasers at telecomm wavelength as the master oscillator and distributed the timing signals via stabilized fiber links. However, for smaller-scale FELs and UED, this approach may be a complex and high-cost method. In this work, we studied the possibility of using the commercial Ti:sapphire photocathode laser as the optical master oscillator as well. For its use in UED and FELs, we synchronized the 80-MHz Ti:sapphire photocathode laser oscillator to a 2.856-GHz RF source (used for RF-photogun) with 50-fs precision. Some interesting findings are following. First, intrinsic rms timing jitter of the used photocathode laser is 2.6 fs [10 kHz-10 MHz], which sets the fundamental limit in synchronization. Second, timing jitter in 100 Hz-1 kHz in photocathode laser is so severe (e.g., ~40 fs even feedback control is applied), so that it will require additional external-cavity control for achieving sub-10-fs precision. By addressing this issue, we are currently working toward 10-fs precision.

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MOP038

Stabilization of Magnetron Frequency for a Microtron-Driven FEL

controls, cavity, microtron, electron

107

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

Under KAERI WCI program we develop a compact pulsed microtron-driven FEL. Electron bunches trains are accelerated in the microtron and transported by the beamline to the undulator. The RF cavity in the microtron is fed by a magnetron. Any accelerator driver for a FEL should provide an electron beam having very stable parameters such as electron energy, current, and especially the bunch repetition rate in a train. All mentioned parameters depend on magnetron current. It means that special attention should be paid for the shape of the current pulse, supplied to the magnetron from the modulator. We developed the modulator project with a computer control that will provide an arbitrary shape of the magnetron current. A simplified prototype was fabricated and tested. The methods of controlling of the pulse shape are considered. Simulation and experimental results are presented.

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MOP040

Implementation of MTCA.4-based Controls for the Pulsed Optical Synchronization Systems at DESY

controls, laser, FPGA, hardware

115

M. Felber, L. Butkowski, M.K. Czwalinna, M. Fenner, C. Gerth, M. Heuer, E. Janas, M. Killenberg, T. Lamb, U. Mavrič, J.M. Müller, P. Peier, K.P. Przygoda, S. Ruzin, H. Schlarb, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany
T. Kozak, P. Prędki
TUL-DMCS, Łódź, Poland

Funding: This work has partly been funded by the Helmholtz Validation Fund Project MTCA.4 for Industry (HVF-0016)
With the current state of the synchronization system at FLASH (Free-electron Laser in Hamburg) the arrival time between electron bunches and optical laser pulses can be synchronized to a level of 30 fs rms, e.g. for pump-probe experiments. In the course of the development of an up-scaled system for the European XFEL and the migration of control hardware to the modern MTCA.4 (Micro Telecommunications Computing Architecture) platform, all involved components of the system will be replaced with new developments. The front-end devices are upgraded. FPGAs (Field Programmable Gate Arrays) are performing the data processing and feedback calculations. In order to facilitate the firmware development, a toolset (Rapid-X) was established which allows application engineers to develop, simulate, and generate their code without help from FPGA experts in a simple and efficient way. A software tool kit (MTCA4U) provides drivers and tools for direct register access e.g. via Matlab or Python and a control system adapter, which allows the server applications to be written control system independent. In this paper, an overview on the synchronization setups and their upgrades as well as an introduction to the new hardware is given. The Rapid-X and MTCA4U tool kits are presented followed by a status report on the implementation of the new developments.

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MOP044

A Laser Heater for CLARA

laser, electron, undulator, linac

129

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

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

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MOP050

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

electron, radiation, 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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MOP054

Wake Field Potentials of 'Dechirpers'

wakefield, experiment, focusing, electron

157

A. Novokhatski
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DOE-AC03-76SF00515.
A corrugated structure, which is used on 'dechirpers' is usually a pipe or two plates with small corrugations (bumps) on the walls. There is a good single-mode description of the wake potentials excited by a relativistic bunch if the wave length of the mode is much longer than the distance between the bumps in the pipe. However, ultra-short bunches, which are now used in FELs, excite much higher frequency fields and the corresponding wake potentials will be very different from single-mode description. We made analyzes of these wake potentials based on a numerical solution of Maxwell's equations. The behavior of the wake fields of ultra-short bunches in corrugated structures is not much different from the fields excited usually in accelerating structures where the wake potentials are described by the exponential function. As we increase the bunch length, the wake potentials slowly transform to the form of a single mode. For a practical application we present results for a 'dechirper', which will be soon installed at LCLS. We also carried out calculations for a similar device, that was installed and measured at the Pohang Accelerator Laboratory, Korea. We find very good agreement with the experimental results.

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MOP055

The Effect of Wakefields on the FEL Performance

emittance, wakefield, linac, undulator

161

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

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

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MOP062

Technology Maturation for the MaRIE 1.0 X-FEL

linac, emittance, simulation, laser

181

J.W. Lewellen, K. Bishofberger, B.E. Carlsten, L.D. Duffy, F.L. Krawczyk, Q.R. Marksteiner, D.C. Nguyen, S.J. Russell, R.L. Sheffield, N.A. Yampolsky
LANL, Los Alamos, New Mexico, USA

Funding: This research was funded by the Matter-Radiation Interactions in Extremes program at Los Alamos National Laboratory, under contract DE-AC52-06NA25396.
Los Alamos National Laboratory is proposing a high-energy XFEL, named MaRIE*, to meet its mission needs. MaRIE will be required to generate coherent 42+ keV photons, and, due to space constraints at the LANSCE accelerator complex at Los Alamos, MaRIE's design electron beam energy is 12 GeV. This combination places significant restrictions upon the MaRIE electron beam parameters, in particular the transverse emittance and energy spread at the undulator entrance. We are developing approaches to meet these requirements, but these often require solutions extending beyond the current state-of-the-art in X-FEL design. To reduce overall project risk, therefore, we have identified a number of key experimental and modeling / simulation efforts intended to address both the areas of greatest uncertainty in the preliminary MaRIE design, and the areas of largest known risk. This paper describes the general requirements for the MaRIE X-FEL, our current areas of greatest concern with the preliminary design concept, and our corresponding Technology Maturation Plan (TMP).
* MaRIE website: http://www.lanl.gov/science-innovation/science-facilities/marie/index.php

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MOP067

Transverse Emittance-Preserving Transfer Line and Arc Compressor for High Brightness Electron Sources

emittance, dipole, optics, electron

191

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

Minimizing transverse emittance is essential in single- or few-passes accelerators designed to deliver high brightness electron beams. Emission of coherent synchrotron radiation (CSR) is an important factor of emittance degradation. We have demonstrated, with analytical and experimental results, that this perturbation may be cancelled by imposing certain conditions on the electron optics when the bunch length is constant along the line*. This scheme of CSR suppression is then enlarged, analytically and numerically, to cover the case of varying bunch length in a periodic arc compressor**. The proposed solution hold the promise of cost-saving of compact transfer lines with large bending angles, and new schemes for beam longitudinal gymnastics both in recirculating and in single-pass accelerators driving free electron lasers.
* S. Di Mitri, M. Cornacchia, S. Spampinati, Phys. Rev. Letters, 110, 014801 (2013)
** S. Di Mitri, M. Cornacchia, Europhys. Letters, 109, 62002 (2015)

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MOP068

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

undulator, radiation, electron, resonance

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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MOP074

Efficiency Enhancement of a Harmonic Lasing Free-Electron Laser

wiggler, electron, radiation, resonance

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, radiation, electron, resonance

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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MOP076

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

undulator, laser, emittance, plasma

217

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

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

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MOP079

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

electron, emittance, undulator, brightness

227

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

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

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MOP081

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

radiation, 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, radiation, simulation

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

undulator, simulation, radiation, electron

246

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

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

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MOP085

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

undulator, electron, photon, scattering

251

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

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

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MOD01

Review of Experimental Results from High Brightness DC Guns: Highlights in FEL Applications

gun, cathode, emittance, brightness

269

N. Nishimori
JAEA, Ibaraki-ken, Japan

Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15H03594).
Future ERL light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photoinjector with a 350 kV photoemission gun [1,2]. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage [3]. This technique led to generation of 500 keV beam from the JAEA gun with 160mm acceleration gap [4], conditioning voltage more than 500 kV at the Cornell gun with gap < 50 mm [5], and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap [6]. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications.
[1] Dunham, APL 102, 034105.
[2] Gulliford, PRSTAB 16, 073401.
[3] Nagai, RSI 81, 033304.
[4] Nishimori, APL 102, 234103.
[5] Maxson, RSI 85, 093306.
[6] Yamamoto, private communication.

Slides MOD01 [3.051 MB]

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TUA02

Suppression of FEL Lasing by a Seeded Microbunching Instability

electron, laser, undulator, photon

289

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

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

Slides TUA02 [14.298 MB]

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TUA04

First Simultaneous Operation of Two Sase Beamlines in FLASH

undulator, photon, operation, electron

297

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

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

Slides TUA04 [9.655 MB]

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TUB02

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

undulator, radiation, electron, 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

laser, electron, radiation, 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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TUC01

The Microbunching Instability and LCLS-II Lattice Design

simulation, laser, bunching, linac

308

M. Venturini
LBNL, Berkeley, California, USA

The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.

Slides TUC01 [4.206 MB]

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TUP004

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

undulator, simulation, electron, experiment

331

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

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

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TUP006

Quantum Nature of Electrons in Classical X-ray FELs

electron, undulator, radiation, laser

338

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

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

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TUP007

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

undulator, electron, simulation, emittance

342

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

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

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TUP008

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

space-charge, undulator, electron, simulation

347

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

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

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TUP010

Recent Progress in Upgrade of the High-Intensity THz-FEL at Osaka University

electron, linac, klystron, operation

354

G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, A. Tokuchi, R. Tsutsumi, M. Yaguchi
ISIR, Osaka, Japan

We are upgrading the THz-FEL at Osaka University for its applications to high intensity THz sciences, which originally generated the high intensity FEL with the macropulse energy up to 3.7 mJ and the micropulse energy up to ~10 uJ at a wavelength around 70 um. To increase the micropulse energy, charge in electron bunches is increased four time higher and the bunch intervals are expanded four times longer to maintain the average current in the linac unchanged. In the new operation mode, the macropulse energy increases up to 26 mJ and the micropulse energy to ~0.2 mJ, which is 20 times higher than the energy previously obtained in the conventional mode. We have developed a solid-state switch for the klystron modulator to highly stabilize the klystron voltage, so that the output power of the FEL becomes stable. We are conducting basic studies on FEL for further improvement of its performance, including measurement of power evolution from start-up to saturation, time structures of FEL micropulses measured with a Michelson interferometer, and time structures of macropulses measured with a Schottky diode detector. We will report results of these studies on the THz-FEL at Osaka University.

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TUP011

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

undulator, simulation, electron, operation

359

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

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

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TUP013

The X-Band FEL Collaboration

undulator, linac, electron, emittance

368

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

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

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TUP015

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

laser, cavity, radiation, 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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TUP017

HPC Simulation Suite for Future FELs

simulation, electron, software, plasma

384

L.T. Campbell, A.J.T. Colin, B.W.J. MᶜNeil, P. Traczykowski
USTRAT/SUPA, Glasgow, United Kingdom
R.J. Allan
The Hartree Centre, Science and Technology Facilities Council (STFC/DL), Warrington, United Kingdom
D.J. Dunning, N. Thompson, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
D.J. Dunning, B.D. Muratori, N. Thompson, P.H. Williams
Cockcroft Institute, Warrington, Cheshire, United Kingdom
J.D.A. Smith
Tech-X, Boulder, Colorado, USA

A new HPC simulation suite, intended to aid in both the investigation of novel FEL physics and the design of new FEL facilities, is described. The integrated start-to-end suite, currently under development, incorporates both plasma (VSim) and linac (ELEGANT, ASTRA) accelerator codes, and will include the 3D unaveraged FEL code Puffin to probe novel FEL effects.

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TUP019

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

laser, electron, undulator, radiation

388

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

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

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TUP020

Recent Study in iSASE

electron, distributed, laser, undulator

393

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

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

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TUP021

Fundamental Limitations of the SASE FEL Photon Beam Pointing Stability

radiation, 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, electron, detector, radiation

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

laser, electron, radiation, 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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TUP025

Studies of Undulator Tapering for the CLARA FEL

electron, undulator, laser, brightness

412

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

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

Poster TUP025 [0.919 MB]

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TUP026

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

undulator, simulation, detector, linac

417

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

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

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TUP028

DESIGN OF THE MID-INFRARED FEL OSCILLATOR IN CHINA

electron, undulator, cavity, laser

427

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

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

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TUP029

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

laser, radiation, 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, radiation

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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TUP050

Extension of Existing Pulse Analysis Methods to High-Repetition Rate Operation: Studies of the "Time-Stretch Strategy"

electron, laser, detector, storage-ring

483

S. Bielawski
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
J.B. Brubach, L. Cassinari, M.-E. Couprie, M. Labat, L. Manceron, J.P. Ricaud, P. Roy, M.-A. Tordeux
SOLEIL, Gif-sur-Yvette, France
C. Evain, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
M. Le Parquier
CERLA, Villeneuve d'Ascq, France
E. Roussel
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Funding: ANR (2010-042301, DYNACO), LABEX CEMPI project (ANR-11-LABX-0007), ERC grant COXINEL (340015), GENCI TGCC/IDRIS (x2014057057,i2015057057).
Many single-shot recording setups are based on the encoding of the information onto a laser pulse. This concerns in particular electro-optic sampling of bunch shapes, and VUV/X pulse monitors using transient reflectivity. The upgrade of these methods to high repetition rates presents challenging issues, that are due to the limited speed of the recording cameras. Recently [1], we demonstrated that multi-MHz repetition rates can be achieved using a relatively simple upgrade of existing setups, using the so-called "photonic time-stretch" technique. Here we present guidelines for the practical realization in the case of electro-optic sampling. We also present a performance analysis, and compare it to the spectral encoding case. The technique is potentially applicable to other cases where the information can be encoded on a chirped laser pulse, as, e.g., transient reflectivity diagnostics of XUV pulses.
[1] Observing microscopic structures of a relativistic object using a time-stretch strategy, E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E Couprie, and P. Roy, Scientific Reports 5, 10330 (2015).

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TUP053

Real-World Considerations for Crossed-Polarized Undulator Radiation Conversion

polarization, undulator, radiation, diagnostics

486

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

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

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TUP056

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

photon, simulation, radiation, 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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TUP085

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

site, experiment, electron, radiation

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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WEA03

SwissFEL Status Report

undulator, linac, vacuum, electron

567

R. Ganter
PSI, Villigen PSI, Switzerland

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

Slides WEA03 [36.505 MB]

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WEB01

A Two-Color Storage Ring FEL

undulator, electron, cavity, operation

571

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

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

Slides WEB01 [18.975 MB]

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WEB02

Waveguide THz FEL Oscillators

injection, electron, extraction, undulator

576

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

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

Slides WEB02 [20.394 MB]

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WEB04

Saturation Dynamics, Fine Spectrum, and Chirp Control in a CW FEL Oscillator

laser, electron, coupling, operation

580

H. S. Marks, A. Gover, H. Kleinman
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
D. Borodin, A. Damti, A. Friedman, Y. Vashdi
Ariel University, Ariel, Israel
M. Einat, M. Kanter, Y. Lasser, Yu. Lurie, A. Yahalom
Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel

As in conventional laser physics, the saturation dynamics of a long-pulse Electrostatic Accelerator FEL (EA-FEL) oscillator consists of oscillations build-up, resonator modes competition, and establishment of narrow linewidth single mode lasing. In EA-FEL the gain curve drifts to lower frequencies during the long laser pulse due to inevitable droop in the acceleration voltage. This post-saturation drift renders fine chirp of the single mode laser frequency due to the oscillator frequency pulling effect. We have integrated a voltage-ramping element into the electrostatic accelerator terminal that makes it possible to control the acceleration voltage throughout the lasing pulse. This allows us to keep the voltage constant throughout the e-beam pulse, and so increase the single mode lasing time, avoiding mode-hopping during the pulse due to the drift of the gain curve. Furthermore, by adjusting the voltage ramp rate and polarity we obtained controllable positive/negative laser frequency chirp that can be used in a single pulse sweep for fine spectral line (10^-6) gas-spectroscopy. The study was conducted on the Israeli EA-FEL that operates at tunable frequencies between 95-110 GHz.

Slides WEB04 [2.310 MB]

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WEP001

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

undulator, radiation, 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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WEP002

Simulating Single Crystal Copper Photocathode Emittance

emittance, simulation, electron, laser

587

T. Vecchione
SLAC, Menlo Park, California, USA

Funding: US DOE contract DE-AC02-76SF00515
The performance of free-electron lasers depends on the quality of the electron beam used. In some cases this performance can be improved by optimizing the choice of photocathode with respect to emittance. With this in mind, electronic structure calculations have been included in photoemission simulations and used to predict the emittance from single crystal copper photocathodes. The results from different low-index surfaces are reported. Within the model assumptions the Cu(100) surface was identified as having minimal emittance, particularly when illuminated by 266 nm light and extracted in a 60 MV/m gradient. These findings may guide future experimental work, leading to improved machine performance.

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WEP003

Recent Understanding and Improvements of the LCLS Injector

laser, emittance, cathode, electron

592

F. Zhou, D.K. Bohler, Y. Ding, S. Gilevich, Z. Huang, H. Loos, D.F. Ratner
SLAC, Menlo Park, California, USA

Funding: U.S. DOE contract No. DE-AC02-76SF00515.
Ultraviolet drive laser and copper photocathode are the key systems for reliably delivering <0.4 micron of emittance and high brightness free electron laser (FEL) at the linac coherent light source (LCLS). Characterizing, optimizing and controlling laser distributions in both spatial and temporal directions are important for ultra-low emittance generation. Spatial truncated Gaussian laser profile has been demonstrated to produce better emittance than a spatial uniform beam. Sensitivity of the spatial laser distribution for the emittance is measured and analysed. Stacking two 2-ps Gaussian laser beams significantly improves emittance and eventually FEL performance at the LCLS in comparison to a single 2-ps Gaussian laser pulse. In addition, recent observations at the LCLS show that the micro-bunching effect depends strongly on the cathode spot locations. The dependence of the micro-bunching and FEL performance on the cathode spot location is mapped and discussed.

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WEP004

Energy Spread Constraints on Field Suppression in a Reverse Tapered Undulator

undulator, laser, bunching, simulation

597

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

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

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WEP005

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

laser, electron, undulator, linac

602

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

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

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WEP008

Four-Dimensional Models of FEL Amplifiers and Oscillators

electron, undulator, simulation, laser

607

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

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

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WEP010

Development of Phonon Dynamics Measurement System by MIR-FEL and Pico-second Laser

laser, scattering, timing, lattice

615

T. Murata, T. Katsurayama, T. Kii, T. Konstantin, K. Masuda, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Zen
Kyoto University, Kyoto, Japan
K. Hachiya
Kyoto University Graduate School of Energy Science, Kyoto, Japan
K. Yoshida
Kumamoto University, Department of Applied Chemistry and Biochemistry, Kumamoto, Japan

Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.

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WEP014

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

undulator, linac, gun, electron

618

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

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

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WEP016

Free Electron Lasers in 2015

electron, undulator, laser, free-electron-laser

625

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

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

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WEP022

Photon Energies beyond the Selenium K-Edge at LCLS

photon, electron, operation, linac

630

F.-J. Decker, W.S. Colocho, Y. Ding, R.H. Iverson, H. Loos, J. Sheppard, H. Smith, J.L. Turner
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) was designed for a photon energies of 830 eV to 8.3 keV. This range was widened and up to 11.2 keV photons were already delivered for users. The Selenium K-edge at 12.6578 keV is very interesting since Selenium can replace Sulfur in biological structures and then that structure could be precisely measured. To reach this the electron energy would need to be raised by about 6% which initially didn't seem possible. The trick is to change the final compression scheme from a high correlated energy spread and moderate R56 in the compression chicane to moderate energy spread and high R56. The same bunch length can be achieved and RF energy is freed up, so the overall beam energy can be raised. Photons up to an energy of 12.82 keV (1.3% above the K-edge) with a pulse intensity of 0.93 mJ were achieved. The photon energy spread with this setup is wider at around 40-50 eV FWHM, since less correlated energy spread is left after the compression.

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WEP029

Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance

laser, undulator, simulation, electron

643

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

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

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WEP030

First Lasing of an HGHG Seeded FEL at FLASH

electron, laser, experiment, injection

646

K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany
S. Ackermann, Ph. Amstutz, A. Azima, M. Drescher, L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, T. Plath, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, R.W. Aßmann, J. Bödewadt, N. Ekanayake, B. Faatz, I. Hartl, R. Ivanov, T. Laarmann, J.M. Müller
DESY, Hamburg, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
The free-electron laser facility FLASH at DESY operates in SASE mode with MHz bunch trains of high-intensity extreme ultraviolet and soft X-ray FEL pulses. A seeded beamline which is designed to be operated parasitically to the main SASE beamline has been used to test different external FEL seeding methods. First lasing at the 7th harmonic of a 266 nm seed laser using high-gain harmonic generation has been demonstrated. Studies of the influence of the microbunching instability are being pursued.

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WEP031

Measurements and Simulations of Seeded Electron Microbunches with Collective Effects

electron, simulation, laser, bunching

650

K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany
S. Ackermann, J. Bödewadt, M. Dohlus, N. Ekanayake, T. Laarmann, H. Schlarb
DESY, Hamburg, Germany
L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, T. Plath, J. Roßbach
Uni HH, Hamburg, Germany

Funding: The experiments were carried out at FLASH at DESY. BMBF contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3, and the German Research Foundation program graduate school 1355.
Measurements of the longitudinal phase-space distribution of electron bunches seeded with an external laser were done in order to study the impact of collective effects on seeded microbunches in free-electron lasers. Velocity bunching of a seeded microbunch appears to be a viable alternative to compression with a magnetic chicane under high-gain harmonic generation seeding conditions when the collective effects of Coulomb forces in a drift space and coherent synchrotron radiation in a chicane are considered. Measurements of these effects on seeded electron microbunches were performed with an RF deflecting structure and a dipole magnet which streak out the electron bunch for single-shot images of the longitudinal phase-space distribution. Particle tracking simulations in 3D predicted the compression dynamics of the seeded microbunches with collective effects.

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WEP042

Commissioning and First Performance of the LINAC-based Injector Applied in the HUST THz-FEL

linac, target, gun, beam-diagnostic

662

T. Hu, Q.S. Chen, J. Li, B. Qin, P. Tan, Y.Q. Xiong
HUST, Wuhan, People's Republic of China
L. Cao, W. Chen
Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China
Y.J. Pei, Zh. X. Tang
USTC/NSRL, Hefei, Anhui, People's Republic of China

The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc.

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WEP047

Femtosecond Timing Distribution at the European XFEL

laser, timing, optics, electron

669

C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, J.M. Müller, H. Schlarb, F. Zummack
DESY, Hamburg, Germany
S. Jabłoński
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results.

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WEP048

Electron Beam Diagnostics for FEL Studies at CLARA

electron, diagnostics, laser, simulation

672

S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
D. Newton
The University of Liverpool, Liverpool, United Kingdom

CLARA (Compact Linear Accelerator for Research and Applications) is a proposed 250 MeV, 100-400 nm FEL test facility at Daresbury Laboratory [1]. The purpose of CLARA is to test and validate new FEL schemes in areas such as ultra-short pulse generation, temporal coherence and pulse-tailoring. Some of the schemes that can be tested at CLARA depend on a manipulation of the electron beam properties with characteristic scales shorter than the electron beam. In this article we describe the electron beam diagnostics required to carry on these experiments and simulations of FEL pulse and electron beam measurements.
[1] J. A. Clarke et al., JINST 9, 05 (2014).

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WEP051

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

undulator, simulation, permanent-magnet, electron

677

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

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

Poster WEP051 [3.821 MB]

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WEP054

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

undulator, laser, electron, free-electron-laser

685

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

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

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WEP060

Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF

laser, electron, cavity, experiment

694

M. Chung, J.M. Seok
UNIST, Ulsan, Republic of Korea
J.H. Han, J.H. Hong, H.-S. Kang, C.H. Kim
PAL, Pohang, Kyungbuk, Republic of Korea
J.C.T. Thangaraj
Fermilab, Batavia, Illinois, USA

Longitudinal shaping of electron beam has received much attention recently, due to its potential applications to THz generation, dielectric wakefield acceleration, improvement of FEL performance, and controlled space-charge modulation. Using a set of alpha-BBO crystals, shaping of laser pulse and electron bunch on the order of ps is tested at the Injector Test Facility (ITF) of Pohang Accelerator Laboratory (PAL). In particular, we investigate the response of the longitudinally-modulated beam to a dechirper, which is a vacuum chamber of two corrugated, metallic plates. Initial experimental results will be presented with analytical theory and numerical simulations.

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WEP070

Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons

emittance, linac, electron, simulation

714

J. Qiang, C.E. Mitchell, C. F. Papadopoulos, M. Venturini
LBNL, Berkeley, California, USA
Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley
SLAC, Menlo Park, California, USA

The LCLS-II as a next generation high repetition rate FEL based X-ray light source will enable significant scientific discoveries. In this paper, we report on the progress in the design of the accelerator beam delivery system through start-to-end simulations. We will present simulation results for three cases, 20 pC, 100 pC and 300 pC that are transported through the hard X-ray line and the soft X-ray line for FEL radiation.

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WEP073

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

electron, undulator, radiation, plasma

718

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

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

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WEP075

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

electron, radiation, undulator, simulation

722

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

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

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WEP076

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

undulator, electron, simulation, extraction

726

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

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

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WEP078

Advances on the LUNEX5 and COXINEL Projects

laser, electron, operation, plasma

730

M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, J.D. Bozek, F. Briquez, L. Cassinari, L. Chapuis, J. Da Silva, J. Daillant, D. Dennetière, Y. Dietrich, M. Diop, J.P. Duval, M.E. El Ajjouri, T.K. El Ajjouri, C. Herbeaux, N. Hubert, M. Khojoyan, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, J. Lüning, P. Marchand, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, A. Nadji, R. Nagaoka, F. Polack, F. Ribeiro, J.P. Ricaud, P. Rommeluère, P. Roy, G. Sharma, K.T. Tavakoli, M. Thomasset, M. Tilmont, M.-A. Tordeux, M. Valléau, J. Vétéran, W. Yang, D. Zerbib
SOLEIL, Gif-sur-Yvette, France
S. Bielawski, M. Le Parquier
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
X. Davoine
CEA/DAM/DIF, Arpajon, France
N. Delerue, M. El Khaldi, W. Kaabi, F. Wicek
LAL, Orsay, France
G. Devanz, C. Madec
CEA/IRFU, Gif-sur-Yvette, France
A. Dubois
CCPMR, Paris, France
C. Evain, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
D. Garzella
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
G. Lambert, V. Malka, A. Rousse, C. Thaury
LOA, Palaiseau, France
A. Mosnier
CEA/DSM/IRFU, France
E. Roussel
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Funding: ERC COXINEL 340015
LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating compact and advanced Free Electron Laser (FEL). It comprises one one hand a 400 MeV superconducting linac for studies of advanced FEL schemes, high repetition rate operation (10 kHz), multi-FEL lines, and one the other hand a Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, an undulator line enabling advanced seeding and pilot user applications in the 40-4 nm spectral range. Following the CDR completion, different R&D programs were launched, as for instance on FEL pulse duration measurement, high repetition rate electro-optical sampling. The COXINEL ERC Advanced Grant aims at demonstrating LWFA based FEL amplification, thanks to a proper electron beam manipulation, with a test experiment under preparation. As a specific hardware is also under development such as a cryo-ready 3 m long undulator of 15 mm period is under development.

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WEP079

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

electron, radiation, 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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WEP084

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

undulator, simulation, electron, bunching

741

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

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

Poster WEP084 [1.263 MB]

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WEP085

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

radiation, electron, wiggler, 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

radiation, 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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WED04

Status Report of PAL-XFEL Undulator Program

undulator, electron, radiation, controls

769

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

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

Slides WED04 [3.317 MB]

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