FEL2015 - Table of Session: WEP (Poster Session)

Paper	Title	Page
WEP001	RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS	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	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	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	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	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	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	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	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	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	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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WEP023	Two Bunches with ns-Separation with LCLS	634
	F.-J. Decker, S. Gilevich, Z. Huang, H. Loos, A. Marinelli, C.A. Stan, J.L. Turner, Z. Van Hoover, S. Vetter SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) delivers typically one bunch. Two bunches are interesting for pump / probe experiments. Two electron bunches with ps separation have been already produced using a split and delay in the laser which produces them on the gun cathode. Here we present the combination of two lasers with a combiner, this allows any time separation and is it limited to RF bucket spacing so far to about 40 ns limited by the setup of our beam containment system. Different beam energies were also provided and the most challenging part was a transverse separation of a few σs for the two beams. Although this setup was very jittery a successful user experiment was accomplished.
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WEP025	Effect of Microbunching on Seeding Schemes for LCLS-II	639
	G. Penn, J. Qiang LBNL, Berkeley, California, USA P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, California, USA
	Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.
	Poster WEP025 [0.962 MB]
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WEP029	Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance	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	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	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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WEP037	Development Activites Related to RF Cables for Good Phase Stability	654
	J. Hu, H.-S. Kang, H.-S. Lee PAL, Pohang, Kyungbuk, Republic of Korea
	XFEL systems reqiure extreme RF stabilities in amplitude and phase. RF cables as parts of the systems also require very high stabilites. RF cable measurement is performed to choose good cables. Simple measurement method and test results are presented. To enhance the phase stability of RF cables a prototype jacket surrounding a RF cable is constructed and the test result is described. Finally, a modification for phase measurement of RF cables is presented.
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WEP038	Production Status of Accelerator Components	658
	N. Shigeoka, M. Kimura, S. Miura, K. Okihira MHI, Hiroshima, Japan
	Mitsubishi Heavy Industries, LTD. (MHI) has been delivered various kind of accelerator components to multiple FEL facilities. Recently we completed production of S-band accelerating structures for PAL-XFEL. Currently we are manufacturing C-band waveguide network for SwissFEL. Production status and result of above-mentioned products will be presented in the presentation.
	Poster WEP038 [2.189 MB]
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WEP042	Commissioning and First Performance of the LINAC-based Injector Applied in the HUST THz-FEL	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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WEP045	Study on Beam Modulation Technique using a Masked Chicane at FAST (Fermilab Accelerator Science and Technology) Facility	665
	Y.-M. Shin, D.R. Broemmelsiek, D.J. Crawford, A.H. Lumpkin Fermilab, Batavia, Illinois, USA A.T. Green Northern Illinois Univerity, Dekalb, Illinois, USA
	Funding: This work was supported by the DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC. Longitudinal density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The sub-ps beam modulation has been studied with a masked chicane by the analytic model and simulations with the beam parameters of the Advanced Superconducting Test Accelerator (ASTA) in Fermilab. With the chicane design parameters (bending angle of 18 degree, bending radius of 0.95 m and R56 ~ - 0.19 m) and a nominal beam of 3-ps bunch length, the analytic model showed that a slit-mask with slit period 900 microns and aperture width 300 microns generates about 100 microns modulation periodicity with 2.4% correlated energy spread. With the designed slit mask and a 3- ps bunch, particle-in-cell simulations (CST-PS), including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in ~ 100 microns of longitudinal modulation. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by extended 3D tracking simulations (Elegant). The modulated bunch generation will be tested by a slit-mask installed at the chicane of the ASTA 50-MeV-injector beamline for beam-driven acceleration experiments.
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WEP047	Femtosecond Timing Distribution at the European XFEL	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	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.	677
	I.V. Davidyuk NSU, Novosibirsk, Russia O.A. Shevchenko, V.G. Tcheskidov BINP SB RAS, Novosibirsk, Russia N. Vinokurov KAERI, Daejon, Republic of Korea
	To improve the parameters of the second stage Novosibirsk free electron laser one plans to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles for shorter periods with constant undulator length. Both these advantages will be realized in the new undulator under development in Budker INP. The idea of the permanent-magnet VPU was proposed just several years ago and it has not been properly tested yet. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.
	Poster WEP051 [3.821 MB]
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WEP052	Studies of LCLS FEL Divergence	681
	J.L. Turner, P. Baxevanis, F.-J. Decker, Y. Ding, Z. Huang, J. Krzywinski, H. Loos, G. Marcus, N.P. Norvell SLAC, Menlo Park, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 Simulations show various impacts on x-ray divergence. With the motivation to maximize intensity at the focus, these beam studies were designed to study parameter space and beam qualities impacting divergence, and therefore aperture related clipping and diffraction. With multiple simultaneous users, beam constraints increase, requiring an improving knowledge of the mechanism of impact of changing parameters. These studies have that goal in order to improve beam control.
	Poster WEP052 [1.010 MB]
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WEP054	Control of Gap Dependent Phase Errors on the Undulator Segments for the European XFEL	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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WEP058	Emittance Measurements at the PAL-XFEL Injector Test Facility	690
	J. Lee POSTECH, Pohang, Kyungbuk, Republic of Korea J.H. Han, J.H. Hong, C.H. Kim, I.S. Ko, S.J. Lee, S.J. Park, H. Yang PAL, Pohang, Kyungbuk, Republic of Korea
	The PAL-XFEL Injector Test Facility (ITF) at PAL has been operating for experimental optimization of electron beam parameters and for beam test of various accelerator components. It consists of a photocathode RF gun, two S-band accelerating structures, a laser heater system, and beam diagnostics such as ICTs, BPMs, screens, beam energy spectrometers and an RF deflector. Projected and slice emittance measurements were carried out by using single quadrupole scan. In this paper, we present the emittance measurements.
	Poster WEP058 [0.646 MB]
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WEP060	Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF	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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WEP061	Numerical and Experimental Studies on Electron Beam Properties from Asymmetric RF-gun	698
	S. Rimjaem, N. Chaisueb, J. Saisut, C. Thongbai, W. Thongpakdi Chiang Mai University, Chiang Mai, Thailand N. Kangrang FNRF, Chiang Mai, Thailand E. Kongmon, K. Kosaentor, P. Wichaisirimongkol IST, Chiang Mai, Thailand
	Funding: This work has been supported by the CMU Junior Research Fellowship Program, and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University. The electron linear accelerator at the Plasma and Beam Physics Research Facility (PBP-CMU Linac), Chiang Mai University, Thailand, is used to produce femtosecond electron bunches for generation of THz radiation. The main components of the PBP-CMU Linac are a thermionic RF electron gun, an alpha magnet, a travelling wave linac structure, quadrupole lens, steering magnets, and various diagnostic components. The RF-gun consists of a 1.6 S-band standing wave structure and a side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a rectangular waveguide input-port. Both the RF input-port and the side-coupling cavity cause an asymmetric electromagnetic field distribution inside the gun. The electron beam from the RF-gun has asymmetric transverse shape with an emittance value, which is higher than the beam from the symmetric fields. The problems are increased when the beam is transported from the gun through the whole accelerator system. Beam dynamic simulations are performed to investigate the effect of the asymmetric fields on the electron properties by using the codes PARMELA and ELEGANT. An integrated electron beam diagnostic station to measure the beam properties will be installed in the system to investigate these effects. Results from numerical and experimental studies are reported in this contribution.
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WEP062	Study on Undulator Radiation from Femtosecond Electron Bunches	702
	N. Chaisueb, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand
	Funding: This work has been supported by the CMU Junior Research Fellowship Program, the Department of Physics and Material Science, Faculty of science, Chiang Mai University, and SAST Scholarship. Linac based terahertz (THz) source at the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, consists of a thermionic RF electron gun, an alpha magnet for magnetic bunch compressor, a travelling wave S-band accelerating structure for post acceleration, and various beam diagnostic instruments. The PBP-CMU linac can produce relativistic femtosecond electron bunches, which are used to generate coherent THz radiation via transition radiation technique. To increase the radiation intensity, an electromagnetic undulator will be added in the beam transport line. The designed electromagnetic undulator has 40.5 periods with a period length of 56 mm and a pole gap of 15 mm. Numerical calculation result shows that the brightness of the undulator radiation, which is produced from electron bunches with an energy of 10 MeV, a peak current of 300 A, and an effective bunch length of 120 fs, is about 10 thousand times higher than the brightness of the transition radiation. This study investigates the dependence of the electron beam energy, electron bunch charge, and electron bunch length on the coherent undulator radiation by using the PARMELA code. The numerical simulation and procedure to generate the undulator radiation in the terahertz regime by using femtosecond electron bunches produced at the PBP research facility is reported and discussed in this contribution. The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Material Science and the Graduate School, Chiang Mai University.
	Poster WEP062 [8.172 MB]
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WEP067	Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility	707
	A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University. Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4]) [1] M. Dohlus, PRSTAB, 14 090702 (2011). [2] A. Marinelli, PRL, 110 264802 (2013). [3] M. Borland, Advanced Photon Source, LS-287, 2000. [4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015).
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WEP069	Minimization of the Emittance Growth Induced by Coherent Synchrotron Radiation in Arc Compressor	711
	X.Y. Huang, X. Cui, Y. Jiao, G. Xu IHEP, Beijing, People's Republic of China
	Funding: Supported by National Natural Science Foundation of China (11475202, 11405187). Coherent synchrotron radiation (CSR) is a critical issue when electron bunches with short bunch length and high peak current transporting through a bending system in high-brightness light sources and linear colliders. For example, a high peak current of electron beam can be achieved by using magnetic bunch compressor, however, CSR induced transverse emittance growth will limit the performance of bunch compressor. In this paper, based on our 'two-dimensional point-kick analysis', an arc compressor with high compression factor is studied. Through analytical and numerical research, an easy optics design technique is introduced that could minimize the emittance dilution within this compressor. It is demonstrated that the strong compression of bunch length and the transverse emittance preservation can be achieved at the same time.
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WEP070	Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons	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	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	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	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	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	735
	P. Niknejadi, J. Madey University of Hawaii, Honolulu,, USA
	The efforts in realizing x-ray free electron lasers (FELs) and enhancing their performance has stimulated remarkable theoretical developments and experimental advances in the field. Yet, the successful operation of x-ray FELs based on the self-amplified spontaneous emission (SASE) principle which has made them a powerful new tool, has beckoned our attention for better understanding a comprehensive physical basis of the theory that has the potential to improve the temporal structure and spectral optimization of these sources. We have previously explained the advantages of including the coherent radiation reaction force as a part of the solution to the boundary value problem for FELs that radiate into "free space" (SASE FELs) and discussed how the advanced field of the absorber can interact with the radiating particles at the time of emission.(, ) Here we present the outline of our theoretical approach which follows from eigenmode analysis of optical guiding in FELs. We will also discuss in some detail the experimental setup that could verify and/or further our understanding of the the underlying physics of these devices. P. Niknejadi et al., Phys. Rev. D 91 096006 (2015) ** P. Niknejadi and J.M.J. Madey, in Proceedings of Free Electron Laser Conference, JACoW, Basel, Switzerland (2014)
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WEP082	High-Power Ultrashort Terahertz Pulses generated by a Multi-foil Radiator with Laser-Accelerated Electron Pulses	739
	J.S. Jo, B.A. Gudkov, Y.U. Jeong, H.N. Kim, K.N. Kim, K. Lee, S.V. Miginsky, S. H. Park, W.J. Ryu, N. Vinokurov KAERI, Daejon, Republic of Korea B.A. Gudkov, S.V. Miginsky, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Terahertz (THz) wave is an attractive source for a variety of research including imaging, spectroscopy, security, etc. We proposed a new scheme of high-power and ultrashort THz generation by using the coherent transition radiation from a cone-shaped multi-foil radiator [] and a rectangle-shaped multi-foil radiator. To perform the proof-of-principle of the multi-foil THz radiator, we used 80~100 MeV electron bunches from laser-plasma acceleration. While a cone-shaped multi-foil radiator has a circular polarization with a conic wave, we made a rectangle-shaped multi-foil radiator that has a linear polarization in a plane-like wave, which can be used more widely for various applications. We can easily control the power of multi-foil radiator by adjusting the number of foils. We compare the THz power ratio between 1 sheet and multi sheets using cooled bolometer. We will measure the pulse duration and bandwidth of the THz wave from the multi-foil radiators in a single-shot by using electro-optic sampling and cross-correlation method. Phys. Rev. Lett. 110, 064805.
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WEP084	Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser	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	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	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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Paper

Title

Page

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

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

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

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

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

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

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

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

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

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

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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WEP023

Two Bunches with ns-Separation with LCLS

634

F.-J. Decker, S. Gilevich, Z. Huang, H. Loos, A. Marinelli, C.A. Stan, J.L. Turner, Z. Van Hoover, S. Vetter
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) delivers typically one bunch. Two bunches are interesting for pump / probe experiments. Two electron bunches with ps separation have been already produced using a split and delay in the laser which produces them on the gun cathode. Here we present the combination of two lasers with a combiner, this allows any time separation and is it limited to RF bucket spacing so far to about 40 ns limited by the setup of our beam containment system. Different beam energies were also provided and the most challenging part was a transverse separation of a few σs for the two beams. Although this setup was very jittery a successful user experiment was accomplished.

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WEP025

Effect of Microbunching on Seeding Schemes for LCLS-II

639

G. Penn, J. Qiang
LBNL, Berkeley, California, USA
P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, California, USA

Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.

Poster WEP025 [0.962 MB]

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WEP029

Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance

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

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

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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WEP037

Development Activites Related to RF Cables for Good Phase Stability

654

J. Hu, H.-S. Kang, H.-S. Lee
PAL, Pohang, Kyungbuk, Republic of Korea

XFEL systems reqiure extreme RF stabilities in amplitude and phase. RF cables as parts of the systems also require very high stabilites. RF cable measurement is performed to choose good cables. Simple measurement method and test results are presented. To enhance the phase stability of RF cables a prototype jacket surrounding a RF cable is constructed and the test result is described. Finally, a modification for phase measurement of RF cables is presented.

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WEP038

Production Status of Accelerator Components

658

N. Shigeoka, M. Kimura, S. Miura, K. Okihira
MHI, Hiroshima, Japan

Mitsubishi Heavy Industries, LTD. (MHI) has been delivered various kind of accelerator components to multiple FEL facilities. Recently we completed production of S-band accelerating structures for PAL-XFEL. Currently we are manufacturing C-band waveguide network for SwissFEL. Production status and result of above-mentioned products will be presented in the presentation.

Poster WEP038 [2.189 MB]

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WEP042

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

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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WEP045

Study on Beam Modulation Technique using a Masked Chicane at FAST (Fermilab Accelerator Science and Technology) Facility

665

Y.-M. Shin, D.R. Broemmelsiek, D.J. Crawford, A.H. Lumpkin
Fermilab, Batavia, Illinois, USA
A.T. Green
Northern Illinois Univerity, Dekalb, Illinois, USA

Funding: This work was supported by the DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC.
Longitudinal density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The sub-ps beam modulation has been studied with a masked chicane by the analytic model and simulations with the beam parameters of the Advanced Superconducting Test Accelerator (ASTA) in Fermilab. With the chicane design parameters (bending angle of 18 degree, bending radius of 0.95 m and R56 ~ - 0.19 m) and a nominal beam of 3-ps bunch length, the analytic model showed that a slit-mask with slit period 900 microns and aperture width 300 microns generates about 100 microns modulation periodicity with 2.4% correlated energy spread. With the designed slit mask and a 3- ps bunch, particle-in-cell simulations (CST-PS), including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in ~ 100 microns of longitudinal modulation. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by extended 3D tracking simulations (Elegant). The modulated bunch generation will be tested by a slit-mask installed at the chicane of the ASTA 50-MeV-injector beamline for beam-driven acceleration experiments.

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WEP047

Femtosecond Timing Distribution at the European XFEL

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

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.

677

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

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

Poster WEP051 [3.821 MB]

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WEP052

Studies of LCLS FEL Divergence

681

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

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

Poster WEP052 [1.010 MB]

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WEP054

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

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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WEP058

Emittance Measurements at the PAL-XFEL Injector Test Facility

690

J. Lee
POSTECH, Pohang, Kyungbuk, Republic of Korea
J.H. Han, J.H. Hong, C.H. Kim, I.S. Ko, S.J. Lee, S.J. Park, H. Yang
PAL, Pohang, Kyungbuk, Republic of Korea

The PAL-XFEL Injector Test Facility (ITF) at PAL has been operating for experimental optimization of electron beam parameters and for beam test of various accelerator components. It consists of a photocathode RF gun, two S-band accelerating structures, a laser heater system, and beam diagnostics such as ICTs, BPMs, screens, beam energy spectrometers and an RF deflector. Projected and slice emittance measurements were carried out by using single quadrupole scan. In this paper, we present the emittance measurements.

Poster WEP058 [0.646 MB]

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WEP060

Longitudinal Electron Bunch Shaping Experiments at the PAL-ITF

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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WEP061

Numerical and Experimental Studies on Electron Beam Properties from Asymmetric RF-gun

698

S. Rimjaem, N. Chaisueb, J. Saisut, C. Thongbai, W. Thongpakdi
Chiang Mai University, Chiang Mai, Thailand
N. Kangrang
FNRF, Chiang Mai, Thailand
E. Kongmon, K. Kosaentor, P. Wichaisirimongkol
IST, Chiang Mai, Thailand

Funding: This work has been supported by the CMU Junior Research Fellowship Program, and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University.
The electron linear accelerator at the Plasma and Beam Physics Research Facility (PBP-CMU Linac), Chiang Mai University, Thailand, is used to produce femtosecond electron bunches for generation of THz radiation. The main components of the PBP-CMU Linac are a thermionic RF electron gun, an alpha magnet, a travelling wave linac structure, quadrupole lens, steering magnets, and various diagnostic components. The RF-gun consists of a 1.6 S-band standing wave structure and a side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a rectangular waveguide input-port. Both the RF input-port and the side-coupling cavity cause an asymmetric electromagnetic field distribution inside the gun. The electron beam from the RF-gun has asymmetric transverse shape with an emittance value, which is higher than the beam from the symmetric fields. The problems are increased when the beam is transported from the gun through the whole accelerator system. Beam dynamic simulations are performed to investigate the effect of the asymmetric fields on the electron properties by using the codes PARMELA and ELEGANT. An integrated electron beam diagnostic station to measure the beam properties will be installed in the system to investigate these effects. Results from numerical and experimental studies are reported in this contribution.

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WEP062

Study on Undulator Radiation from Femtosecond Electron Bunches

702

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

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

Poster WEP062 [8.172 MB]

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WEP067

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

707

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

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

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WEP069

Minimization of the Emittance Growth Induced by Coherent Synchrotron Radiation in Arc Compressor

711

X.Y. Huang, X. Cui, Y. Jiao, G. Xu
IHEP, Beijing, People's Republic of China

Funding: Supported by National Natural Science Foundation of China (11475202, 11405187).
Coherent synchrotron radiation (CSR) is a critical issue when electron bunches with short bunch length and high peak current transporting through a bending system in high-brightness light sources and linear colliders. For example, a high peak current of electron beam can be achieved by using magnetic bunch compressor, however, CSR induced transverse emittance growth will limit the performance of bunch compressor. In this paper, based on our 'two-dimensional point-kick analysis', an arc compressor with high compression factor is studied. Through analytical and numerical research, an easy optics design technique is introduced that could minimize the emittance dilution within this compressor. It is demonstrated that the strong compression of bunch length and the transverse emittance preservation can be achieved at the same time.

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WEP070

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

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

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

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

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

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

735

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

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

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WEP082

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

739

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

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

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WEP084

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

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

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

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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