Keyword: simulation
Paper Title Other Keywords Page
MOP009 Efficient Electron Sources of Coherent Spontaneous Radiation with Combined Helical and Uniform Magnetic Fields undulator, electron, radiation, solenoid 43
 
  • N. Balal, V.L. Bratman, E. Magori
    Ariel University, Ariel, Israel
  • V.L. Bratman
    IAP/RAS, Nizhny Novgorod, Russia
  
  We discuss two methods to mitigate repulsion of particles in dense electron bunches from photo-injectors and to enhance the power of terahertz radiation. First, the repulsion may be reduced with both very short bunches and undulator periods, reducing the length of a radiation section. According to simulations bunches with duration (50-100) fs, charge (50-200) pC, and energy 6 MeV could fairly effectively radiate at frequencies up to (10-20) THz. The undulator for such a source can be formed by means of redistribution of a solenoid field by a non-magnetized iron helix and a permanently magnetized helix. The second source is based on an idea proposed by A.V. Savilov for electron bunching under conditions when the cyclotron electron frequency is larger than the undulator frequency, and an increase of particle energy in the bunch Coulomb field leads to a decrease in longitudinal momentum and attraction of particles (this effect is analogous to the cyclotron negative-mass instability). A large value of the required uniform field can be used to easily obtain the needed undulator field by placing a simple iron helix inside a pulsed solenoid. Simulations confirm that the corresponding particle attraction can provide a powerful and narrowband radiation at the frequencies (1-3) THz.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP018 Comparison of Astra Simulations With Beam Parameter Measurements at the Kaeri Ultrashort Pulse Facility electron, laser, quadrupole, emittance 74
 
  • H.W. Kim, I.H. Baek, M.S. Chae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, Y. Kim, K. Lee, S.V. Miginsky, S. H. Park, S. Park, S. Setiniyaz, N. Vinokurov
    KAERI, Daejon, Republic of Korea
  • K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, S. H. Park, N. Vinokurov
    University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
  • S.V. Miginsky, N. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  
  An RF-photogun-based linear accelerator for ultra-short electron beam generation is under construction at Korea Atomic Energy Research Institute (KAERI). This facility are mainly composed of an 1.5 cell S-band (2856 MHz) RF gun, a travelling wave type linac 3 m long and 90-degree achromatic bends. The emitted electron beams are accelerated in high RF field to ~ 3 MeV. The electrons can be deflected by a first bending magnet installed right after the RF gun. Each beamline has second bending magnet similar to the first one and three quadrupoles between the bending magnets. Two bending and three quadrupole magnets compose the 90-degree achromatic bend. The deflected electron beams will be used for ultrafast electron diffraction (UED) experiments. We have performed computer simulation using ASTRA code to investigate the electron beam dynamics in the system with the input data of bead tested gun electric field distribution and the magnetic fields of the magnets. We will present the simulated and experimental electron beam parameters.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP030 Study of Smith-Purcell Free Electron Laser Using Electron Bunch Produced By Micro-Pulse Electron Gun electron, bunching, radiation, cavity 93
 
  • J. Zhao, X.Y. Lu, W.W. Tan, D.Y. Yang, Y. Yang, Z.Q. Yang
    PKU, Beijing, People's Republic of China
  
  A Micro-Pulse electron Gun (MPG) with the frequency of 2856 MHz has been designed, constructed and tested. Some primary experimental studies have been carried out and electron beam with the average current of 6 mA has been detected which holds promise to use as an electron source of Smith-Purcell Free Electron Laser (SP-FEL) to produced Coherent Radiation. It is well known that Smith-Purcell radiation is one of the achievable ways to produce FEL. After many years study in theory and experiment, lots of new mechanisms and appearances have been discovered. Coherent Smith-Purcell Radiation was discovered in 1990s as well. Compared with incoherent Smith-Purcell Radiation, It can generate a more powerful and frequency locked coherent emission due to displaying all three of these enhancements, Ng (the number of grating periods), Ne (the number of electrons in the bunch), Nb (the number of electron bunch). Obviously, MPG is one of ideal electron sources of CSPR for that (1) S-band electron source can increase energy density at these frequencies, (2) picosecond or subpicosecond pulse can generate THz radiation, (3) low emittance makes the interactions between electron beam and granting more stable. All of the above will be displayed in the simulation of this article. The progress of the experiment with beam energy of 80 Kev, the average current of 6 mA is also introduced.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP033 Numerical Simulations of a Sub-THz Coherent Transition Radiation Source at PITZ radiation, electron, laser, booster 97
 
  • P. Boonpornprasert, M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • B. Marchetti
    DESY, Hamburg, Germany
  
  The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can be considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments at the European XFEL. For this reason, the radiation generated by high-gain FEL and Coherent Transition Radiation (CTR) produced by the PITZ electron beam has been studied. In this paper, numerical simulations on the generation of CTR based on the PITZ accelerator are presented. The beam dynamics simulations of electron bunches compressed by velocity bunching are performed by using the ASTRA code. The characteristics of CTR are calculated numerically by using the generalized Ginzburg-Frank formula. The details and results of the simulations are described and discussed.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP039 First Results of Commissioning of the PITZ Transverse Deflecting Structure electron, laser, klystron, emittance 110
 
  • H. Huck, P. Boonpornprasert, A. Donat, J.D. Good, M. Groß, I.I. Isaev, L. Jachmann, D.K. Kalantaryan, M. Khojoyan, W. Köhler, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, M. Pohl, Y. Renier, T. Rublack, J. Schultze, F. Stephan, G. Trowitzsch, G. Vashchenko, R.W. Wenndorff, Q.T. Zhao
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. A. Bakr
    Assiut University, Assiut, Egypt
  • D. Churanov, L.V. Kravchuk, V.V. Paramonov, I.V. Rybakov, A.A. Zavadtsev, D.A. Zavadtsev
    RAS/INR, Moscow, Russia
  • C. Gerth, M. Hoffmann, M. Hüning
    DESY, Hamburg, Germany
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • M.V. Lalayan, A.Yu. Smirnov, N.P. Sobenin
    MEPhI, Moscow, Russia
  • O. Lishilin, G. Pathak
    Uni HH, Hamburg, Germany
  
  For successful operation of X-ray Free Electron Lasers, one crucial parameter is the ultrashort electron bunch length yielding a high peak current and a short saturation length. In order to effectively compress the bunches during the acceleration process, a detailed understanding of the full longitudinal phase space distribution already in the injector is required. Transverse deflecting RF structures (TDS) can shear the bunch transversely, mapping the longitudinal coordinate to a transverse axis on an observation screen downstream. In addition to the bunch length, the slice emittance along the bunch as well as the full longitudinal phase space can be obtained. At the Photo Injector Test Facility at DESY, Zeuthen site (PITZ), an S-band traveling wave TDS is under commissioning since 2015. This cavity is a prototype for the TDS in the injector part of the European XFEL and has been designed and manufactured by the Institute for Nuclear Research (INR, Moscow, Russia). In this paper, first commissioning results of the system at PITZ are presented and discussed.  
poster icon Poster MOP039 [0.893 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP052 Linear Vlasov Solver For Microbunching Gain Estimation with Inclusion of CSR, LSC, And Linac Geometric Impedances linac, impedance, dipole, electron 147
 
  • C.-Y. Tsai
    Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
  • D. Douglas, R. Li, C. Tennant
    JLab, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding CSR impedances, the LSC and linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs.
[1] C. -Y. Tsai et al., FEL'14 (THP022), IPAC'15 (MOPMA028) and ERL2015 (TUICLH2034)
[2] M. Venturini, Phys. Rev. ST Accel. Beams 10, 104401 (2007)
[3] D. Douglas et al., arXiv: 1403.2318v1 [physics.acc-ph]
[4] M. Borland, APS Light Source Note LS-287 (2000) 		 
poster icon Poster MOP052 [4.934 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP057 Front End Simulations and Design for the CLARA FEL Test Facility laser, emittance, gun, linac 171
 
  • J.W. McKenzie, A.D. Brynes, B.L. Militsyn
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  We present the design and simulations of the Front End for CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. This is based around an S-band RF photocathode gun. Initially this will be the 2.5 cell gun, currently used on VELA facility at Daresbury, which is limited to 10 Hz repetition rate. Later, this will be up-graded to a 1.5 cell gun, currently under development, which will allow repetition rates of up to 400 Hz to be reached. The beam will be accelerated up to 50 MeV with a booster linac which will be operated in both bunching and boosting modes for different operating regimes of CLARA. Simulations are presented for a currently achieved performance of the RF system and drive laser with optimisation of the laser pulse lengths for various operational modes of CLARA.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP062 Technology Maturation for the MaRIE 1.0 X-FEL linac, emittance, FEL, laser 181
 
  • J.W. Lewellen, K. Bishofberger, B.E. Carlsten, L.D. Duffy, F.L. Krawczyk, Q.R. Marksteiner, D.C. Nguyen, S.J. Russell, R.L. Sheffield, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  
  Funding: This research was funded by the Matter-Radiation Interactions in Extremes program at Los Alamos National Laboratory, under contract DE-AC52-06NA25396.
Los Alamos National Laboratory is proposing a high-energy XFEL, named MaRIE*, to meet its mission needs. MaRIE will be required to generate coherent 42+ keV photons, and, due to space constraints at the LANSCE accelerator complex at Los Alamos, MaRIE's design electron beam energy is 12 GeV. This combination places significant restrictions upon the MaRIE electron beam parameters, in particular the transverse emittance and energy spread at the undulator entrance. We are developing approaches to meet these requirements, but these often require solutions extending beyond the current state-of-the-art in X-FEL design. To reduce overall project risk, therefore, we have identified a number of key experimental and modeling / simulation efforts intended to address both the areas of greatest uncertainty in the preliminary MaRIE design, and the areas of largest known risk. This paper describes the general requirements for the MaRIE X-FEL, our current areas of greatest concern with the preliminary design concept, and our corresponding Technology Maturation Plan (TMP).
* MaRIE website: http://www.lanl.gov/science-innovation/science-facilities/marie/index.php 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP066 Electron Bunch Length Measurement using an RF Deflecting Cavity cavity, electron, resonance, space-charge 188
 
  • S. Park, E.-S. Kim
    Kyungpook National University, Daegu, Republic of Korea
  • S. Bae, K.H. Jang, Y.U. Jeong, H.W. Kim, J. Mun, N. Vinokurov
    KAERI, Daejon, Republic of Korea
  
  Recently, the RF photogun based-ultrafast electron diffraction (UED) system has been developed in KAERI. In the system, the emitted electron bunches are experimentally confirmed to be accelerated up to 3 MeV at 5MW of RF power. And the time duration of the each bunch is initially designed to be less than 50 fs at the sample position. To analyses the performance of the system and to measure exactly the length of the electron bunches, we developed a rectangular type of S-band deflecting cavity working on TM120 mode. The principle of electron deflecting in the cavity, design & mechanical fabrication process and test results will be present in the conference.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP070 Harmonic Generation in Two Orthogonal Undulators polarization, undulator, electron, radiation 200
 
  • N.S. Mirian
    UVSOR, Okazaki, Japan
  
  In this report, the harmonic generation in two orthogonal undulators is under discussion. There is a possibility of generation of the even and odd harmonics as well as no-integer harmonics in two orthogonal undulators. By considering the first order of electron velocity, the total energy radiated per unit solid angle per unit frequency interval for a single electron traveling along the undulators is derived. Also a numerical simulation of one-dimensional non-averaged equations is conducted to present the self amplified spontaneous emission of harmonic generation in two orthogonal undulators.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP071 Carrier-Envelope-Phase Stable Linearly and Circularly Polarized Attosecond Pulse Sources laser, electron, undulator, radiation 205
 
  • Z. Tibai, G. Almási, Zs. Csiha-Nagy, J.A. Fülöp, J. Hebling
    University of Pecs, Pécs, Hungary
  • J.A. Fülöp, Gy. Tóth
    MTA-PTE High-Field Terahertz Research Group, Pecs, Hungary
  
  Recently, we proposed a robust method for producing waveform-controlled attosecond pulses in the EUV spectral range.* In our scheme the relativistic electron beam, provided by a LINAC, is sent through a modulator undulator where a TW-power laser beam is superimposed on it in order to generate nanobunches. The nanobunched electron beam passes through a single- or few-period radiator undulator (RU). The waveform of the generated attosecond pulses closely resembles the longitudinal distribution of the magnetic field. According to our calculations, at 20 nm (60 nm) wavelength carrier-envelope-phase (CEP) stable pulses with 23 nJ (80 nJ) energy, 80 as (240 as) duration, and 31 mrad (13 mrad) CEP fluctuation (standard deviation) can be achieved at K=0.5. More than 500 nJ energy is predicted at longer wavelengths and larger K. The energy fluctuation of the EUV pulse is 2.5 times higher than that of the laser. By using a helical RU, even circularly polarized attosecond pulses with 30/300 nJ energy can be generated, depending on the wavelength. To the best of our knowledge, no other presently available technique enables the generation of arbitrary-waveform, CEP-controlled attosecond pulses. The predicted pulse energies are sufficiently high to be used as pump pulses in attosecond pump-probe measurements.
* Z. Tibai et al., Phys. Rev. Lett. 113, 104801 (2014). 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP078 Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam electron, radiation, undulator, wiggler 221
 
  • R. Ianconescu
    Shenkar College of Engineering and Design, Ramat Gan, Israel
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • E. Hemsing, A. Marinelli
    SLAC, Menlo Park, California, USA
  • A. Nause
    UCLA, Los Angeles, USA
  
  Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF)
The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1].
[1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015)
[2] E. Allaria et al., Nat. Photonics 7, 913 (2013)
[3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)
 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP082 New Soft X-Ray Undulator Line Using 10 GeV Electron Beam in PAL-XFEL undulator, photon, electron, linac 237
 
  • C.H. Shim, I.S. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • Y.W. Parc
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  PAL-XFEL is designed to have five undulator lines and only two undulator lines, the HXR undulator line with 10 GeV electron beam and the SXR undulator line with 3.15 GeV electron beam, will be installed during phase I. A photon beam energy from 0.28 to 1.24 keV will be provided at the SXR undulator line and different range from 2 to 20 keV will be supplied at the HXR undulator line. According to existing schedule, however, photon beam energy from 1.24 to 2 keV won't be provided in PAL-XFEL. In this research, new soft X-ray undulator line for PAL-XFEL using 10 GeV electron beam in main linac is proposed to cover the vacant photon energy. Four candidates are evaluated by estimating and comparing FEL performances using Ming Xie's formula.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP083 FEL Operation Modes of the MAX IV Short Pulse Facility undulator, electron, radiation, FEL 241
 
  • A. Mak, F. Curbis, S. Werin
    MAX-lab, Lund, Sweden
  
  The Short Pulse Facility (SPF) of the MAX IV Laboratory in Lund, Sweden features the production of ultrashort, incoherent x-ray pulses. It is driven by a 3-GeV linac and comprises two 5-metre undulator modules. While the SPF is designed for spontaneous radiation, we explore alternative operation modes in which the SPF functions as a simple free-electron laser (FEL). In this article, we characterize two of them in time-dependent numerical simulations. We perform a sensitivity study on the electron beam parameters and examine the technique of single-step tapering.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOP084 Seeded FEL Study for the Cascaded HGHG option for FLASH2 FEL, undulator, radiation, electron 246
 
  • G. Feng, W. Decking, M. Dohlus, T. Limberg, I. Zagorodnov
    DESY, Hamburg, Germany
  • K.E. Hacker
    DELTA, Dortmund, Germany
  • T. Plath
    Uni HH, Hamburg, Germany
  
  The free electron laser (FEL) facility at DESY in Hamburg (FLASH) is the world's first FEL user facility which can produce extreme ultraviolet (XUV) and soft X-ray photons. In order to increase beam time delivered to users, a major upgrade named FLASH II is in progress. As a possibility, a seeding undulator section can be installed between the extraction arc section and the SASE undulator of FLASH2. In this paper, a possible seeding scheme for the cascaded HGHG option for FLASH2 is given. The SASE undulator can be used as the second radiator of the cascaded HGHG. Parameters optimization for the accelerating modules and the bunch compressors has been done to meet the requirement of the electron bunches. In the beam dynamics simulation, collective effects were taken into account. Particle distribution generated from the beam dynamics simulation was used for the seeded FEL study. Space charge and CSR impacts on the microbunches were taken into account during the seeded FEL simulation. The simulation results show that FEL radiation with the wavelength of a few nms and with high monochromaticity can be seeded at FLASH2.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
MOD04 Emittance Measurements of the Electron Beam at PITZ for the Commissioning Phase of the European X-FEL laser, electron, emittance, gun 285
 
  • G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, Y. Renier, T. Rublack, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. A. Bakr
    Assiut University, Assiut, Egypt
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • O. Lishilin, G. Pathak
    Uni HH, Hamburg, Germany
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  
  For the operation of free electron lasers (FELs) like the European X-FEL and FLASH located at DESY, Hamburg Site, high quality electron beams are required already from the source. The Photo Injector Test facility at DESY, Zeuthen Site (PITZ) was established to develop, characterize and optimize electron sources for such FELs. Last year the work at PITZ focused on the optimization of a photo injector operated with the startup parameters of the European X-FEL. This implies photocathode laser pulses with a Gaussian temporal profile of about 11-12 ps FWHM to drive the photo gun operated at a gradient of 53 MV/m. Significant effort was spent on the electron beam characterization and optimization for various bunch charges. Emittance measurements were performed as a function of major accelerator parameters such as main solenoid current, laser spot size on the cathode and the gun launching phase. The requirement on the beam emittance for bunch charge of 500 pC for the European XFEL commissioning phase has been demonstrated. Results of these studies accompanied with the corresponding simulations are presented in this paper.  
slides icon Slides MOD04 [1.603 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUB02 Distributed Seeding for Narrow-band X-ray Free-Electron Lasers undulator, radiation, electron, FEL 301
 
  • D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner
    LANL, Los Alamos, New Mexico, USA
  
  Funding: We thank Bruce Carlsten, John Lewellen, Steve Russell, and Rich Sheffield (LANL), Craig Ogata and Yuri Shvyd'ko (ANL) for helpful discussion, and the MaRIE project for financial support.
The MaRIE XFEL is the proposed XFEL driven by a 12-GeV electron beam to generate coherent 42-keV photons based on a new seeding technique called distributed seeding (DS). This paper presents details of the distributed seeding technique using Si(111) Bragg crystals as the spectral filters. DS differs from self-seeding in three important aspects. First, DS relies on spectral filtering of the undulator radiation at more than one location early in the exponential gain curve. This leads to an FEL output that is dominated by the coherent seed signal, not SASE noise. Secondly, DS affords the ability to select a wavelength longer than the peak of the SASE gain curve, which leads to improved spectral contrast of the seeded FEL over the SASE background. Lastly, the power growth curves in successive DS stages exhibit the behavior of an FEL amplifier, i.e. a lethargy region followed by the exponential growth region. This behavior results in FEL output pulses that are less spiky than the SASE pulses. Using 3D Genesis simulations, we show that DS with two filters provides a 12X enhancement in spectral brightness relative to SASE and that DS with three filters produces negligible SASE background. The DS FEL spectrum has a relative spectral bandwidth (FWHM) of 8 X 10-5 with about 9 spectral modes. 		 
slides icon Slides TUB02 [1.241 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUB05 Tunable High-power Terahertz Free-Electron Laser Amplifier FEL, laser, electron, radiation 305
 
  • G. Zhao, S. Huang, K.X. Liu, W. Qin, L. Zeng
    PKU, Beijing, People's Republic of China
  • C.H. Chen, Y.C. Chiu, Y.-C. Huang
    NTHU, Hsinchu, Taiwan
  
  In the THz spectrum, radiation sources are relatively scarce. Although recent advancement on optical technologies has enabled THz radiation generation covering a broad spectral range, free-electron laser (FEL) continues to be the most importance source for generating high-power THz radiation. Here we present an ongoing collaboration between Peking University (PKU) and National Tsinghua University (NTHU) to demonstrate high peak and average powers from a THz free-electron laser amplifier driven by a superconducting accelerator system at PKU. The superconducting accelerator comprises the DC-SRF photoinjector and a linac utilizing two 1.3 GHz Tesla-type cavities. It is expected to deliver high repetition rate electron beam with the energy of 10-25 MeV and rms bunch length of about 3 ps. The driver laser of the photoinjector is a mode-locked frequency-quadrupled Nd:YVO4 laser at 266 nm. We use the remaining gun driver laser power at 1064 nm to pump a THz parametric amplifier (TPA) which designed at NTHU and generate the THz seed radiation for the FEL amplifier. The signal laser of the TPA is tunable over 2 THz, permitting generation of radiation between 0.5 and 2.5 THz to seed the FEL amplifier. With our design parameters and computer simulation in GENESIS, we expect to generate narrow-band, wavelength-tunable THz radiation with sub-MW peak power and Watt-level average power.  
slides icon Slides TUB05 [2.349 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUC01 The Microbunching Instability and LCLS-II Lattice Design laser, bunching, FEL, linac 308
 
  • M. Venturini
    LBNL, Berkeley, California, USA
  
  The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.  
slides icon Slides TUC01 [4.206 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP001 THz Photo-Injector FEM Based on Spontaneous Coherent Emission from a Bunch of Negative-Mass Electrons electron, undulator, radiation, cyclotron 317
 
  • A.V. Savilov, I.V. Bandurkin
    IAP/RAS, Nizhny Novgorod, Russia
  
  The use of short dense electron bunches produced form a photo-injector gun is attractive for realization of a THz FEL based on spontaneous coherent emission from such bunches. This type of emission is realized, when the axial length of bunches is shorter that the wavelength of the radiated wave. Therefore, the length of the operating region of such a FEL is strictly limited by degradation (an increase in the axial size) of the e-bunch caused by both the Coulomb repulsion and the velocity spread. The use of the regime of the 'negative mass' can be a way to provide stabilization of the axial size of e-bunches. Such a regime is realized in a magnetostatic undulator with a guiding homogeneous axial magnetic field. If the electron cyclotron frequency (corresponding to the guiding magnetic field) exceeds the bounce-frequency of electron oscillations in the periodic undulator field, then the abnormal dependence of the axial velocity of electrons on their energy takes place (an increase in the energy leads to a decrease in the axial velocity). In such regime, axial Coulomb repulsion of the electrons leads to their mutual attraction which slows down bunch degradation. The use of this regime results in a substantial increase in the length of the spontaneous coherent emission, and, therefore, in an increase in both the duration and the power of the output radiation pulse.
The work was supported by the Russian Scientific Foundation (RSCF), Project no. 14-19-01723 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP002 Further Studies of Undulator Tapering in X-Ray FELs undulator, electron, radiation, laser 321
 
  • A. Mak, F. Curbis, S. Werin
    MAX-lab, Lund, Sweden
  
  We further the studies of the model-based optimization of tapered free-electron lasers presented in a recent publication [Phys. Rev. ST Accel. Beams 18, 040702 (2015)]. Departing from the ideal case, wherein the taper profile is a smooth and continuous function, we consider the more realistic case, with individual undulator segments separated by break sections. Using the simulation code GENESIS, we apply our taper optimization method to a case, which closely resembles the FLASH2 facility in Hamburg, Germany. By comparing steady-state and time-dependent simulations, we examine how time-dependent effects alter the optimal taper scenario. From the simulation results, we also deduce that the "traditional" empirical method, whereby the intermediate radiation power is maximized after closing every undulator gap, does not necessarily produce the highest final power at the exit of the undulator line.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP004 Three-dimensional, Time-dependent Simulation of Free-Electron Lasers undulator, electron, FEL, experiment 331
 
  • P.J.M. van der Slot
    Mesa+, Enschede, The Netherlands
  • H. Freund, P.J.M. van der Slot
    CSU, Fort Collins, Colorado, USA
  
  Minerva is a simulation code that models the interaction of electrons with an optical field inside an undulator. Minerva uses a modal expansion for the optical field and the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to mode, for example, FEL oscillators. As there exists a large variety of FELs ranging from long-wavelength oscillators to soft and hard X-ray FELs that are either seeded or starting from noise, a simulation code, such as Minerva, should be capable of modelling this huge variety of FEL configurations. Here we present a validation of the Minerva code against experimental data for various FEL configurations, ranging from long wavelength FEL oscillators to hard X-ray SASE FEL.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP007 High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II undulator, electron, FEL, emittance 342
 
  • G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang
    SLAC, Menlo Park, California, USA
  • J. Qiang, M. Venturini
    LBNL, Berkeley, California, USA
  
  High fidelity numerical particle simulations that leverage a number of accelerator and FEL codes have been used to analyze the LCLS-II FEL performance. Together, the physics models that are included in these codes have been crucial in identifying, understanding, and mitigating a number of potential hazards that can adversely affect the FEL performance, some of which are discussed in papers submitted to this conference[*, **]. Here, we present a broad overview of the LCLS-II FEL performance, based on these start-to-end simulations, for both the soft X-ray and hard X-ray undulators including both SASE and self-seeded operational modes.
* M. Venturini, et al., The microbunching instability and LCLS-II lattice design: lessons learned, FEL'15
** Z. Zhang, et al., Microbunching-induced sidebands in a seeded free-electron laser, FEL'15 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP008 High-Gain FEL in the Space-Charge Dominated Raman Limit FEL, space-charge, undulator, electron 347
 
  • I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig
    UCLA, Los Angeles, USA
  
  While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP009 Coherent Thomson Scattering Using the PEHG radiation, laser, scattering, electron 351
 
  • S. Chen, K. Ohmi, D. Zhou
    KEK, Ibaraki, Japan
  
  Electron beam is density modulated by the phase-merging effect to obtain ultra-short longitudinal structures in the phase space. Coherent radiations are then generated by the coherent Thomson scattering between the phase-merged beam and a long wavelength laser pulse.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP011 Performance and Tolerance Studies of the X-Ray Production for the X-Band FEL Collaboration undulator, electron, FEL, operation 359
 
  • J. Pfingstner, E. Adli
    University of Oslo, Oslo, Norway
  
  The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP017 HPC Simulation Suite for Future FELs FEL, electron, software, plasma 384
 
  • L.T. Campbell, A.J.T. Colin, B.W.J. MᶜNeil, P. Traczykowski
    USTRAT/SUPA, Glasgow, United Kingdom
  • R.J. Allan
    The Hartree Centre, Science and Technology Facilities Council (STFC/DL), Warrington, United Kingdom
  • D.J. Dunning, N. Thompson, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • D.J. Dunning, B.D. Muratori, N. Thompson, P.H. Williams
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • J.D.A. Smith
    Tech-X, Boulder, Colorado, USA
  
  A new HPC simulation suite, intended to aid in both the investigation of novel FEL physics and the design of new FEL facilities, is described. The integrated start-to-end suite, currently under development, incorporates both plasma (VSim) and linac (ELEGANT, ASTRA) accelerator codes, and will include the 3D unaveraged FEL code Puffin to probe novel FEL effects.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP026 Measurment Uncertainties in Gas-Based Monitors for High Repetition Rate X-Ray FEL Operations FEL, undulator, detector, linac 417
 
  • Y. Feng, M.L. Campell, J. Krzywinski, E. Ortiz, T.O. Raubenheimer, M. Rowen, D.W. Schafer
    SLAC, Menlo Park, California, USA
  
  Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University.
Thermodynamic simulations using a finite difference method were carried out to investigate the measurement uncertainties in gas-based X-ray FEL diagnostic monitors under high repetition rate operations such as planned for the future LCLS-II soft and hard X-ray FEL's. For monitors using relatively high gas pressures for obtaining sufficient signals, the absorbed thermal power becomes non-negligible as repetition rate increases while keeping pulse energy constant. The fluctuations in the absorbed power were shown to induce significant measurements uncertainties, especially in the single-pulse mode. The magnitude of this thermal effect depends nonlinearly on the absorbed power and can be minimized by using a more efficient detection scheme in which the gas pressure can be set sufficiently low 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP032 Numerical Studies of the Influence of the Electron Bunch Arrival Time Jitter on the Gain Process of an XFEL-Oscillator for the European XFEL electron, undulator, radiation, FEL 436
 
  • C.P. Maag, J. Zemella
    DESY, Hamburg, Germany
  • J. Roßbach
    Uni HH, Hamburg, Germany
  
  The superconducting linac of the European XFEL Laboratory in Hamburg will produce electron bunch trains with a time structure that allow in principle the operation of an XFELO (X-ray FEL-Oscillator). The electron bunches of the European XFEL have an expected length between 2 and 180 fs (FWHM) with an expected arrival time jitter of about 30 fs (RMS). A jitter of the electron bunch arrival time leads to a detuning between the electron and photon pulse. Since an XFEL-Oscillator relies on a spatial overlap of electron and photon pulse, the influence of a lack of longitudinal overlap is studied. The simulations are performed for different bunch lengths and levels of arrival time jitter. The results of a simulation are presented where angular, transversal and arrival time jitter are taken into account simultaneously, assuming parameters expected for the European XFEL Linac.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP034 New Ellipsoidal Photocathode Laser Pulses at the Upgraded PITZ Facility gun, laser, cathode, electron 439
 
  • J.D. Good, P. Boonpornprasert, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, G. Kourkafas, M. Krasilnikov, D. Melkumyan, A. Oppelt, M. Otevřel, Y. Renier, T. Rublack, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
    IAP/RAS, Nizhny Novgorod, Russia
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. A. Bakr
    Assiut University, Assiut, Egypt
  • I. Hartl, S. Schreiber
    DESY, Hamburg, Germany
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • M. Khojoyan
    SOLEIL, Gif-sur-Yvette, France
  • O. Lishilin, G. Pathak
    Uni HH, Hamburg, Germany
  • D. Malyutin
    HZB, Berlin, Germany
  • E. Syresin
    JINR, Dubna, Moscow Region, Russia
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  
  High brightness electron sources for free electron lasers like FLASH and the European XFEL are developed, optimized and characterized at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Last year the facility was significantly upgraded with a new prototype photocathode laser capable of producing homogeneous ellipsoidal pulses. Previous simulations have shown that the corresponding pulses produce high brightness electron bunches with minimized emittance. Furthermore, a new normal conducting RF gun cavity was installed with a modified two-window waveguide RF feed layout for stability and reliability tests, as required for the European XFEL. Other relevant additions to the facility include beamline modifications for improved electron beam transport through the PITZ accelerator, refinement of both the cooling and RF systems for improved parameter stability, and preparations for the installation of a plasma cell. This paper describes the facility upgrades and reports on the operational experience with the new components.  
poster icon Poster TUP034 [1.211 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP043 PAL-XFEL Cavity BPM Prototype Beam Test at ITF cavity, pick-up, electron, dipole 468
 
  • S.J. Lee, J.H. Han, H.-S. Kang, C. Kim, S.H. Kim, I.S. Ko, Y.J. Park, D.C. Shin
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  To achieve sub-micrometer resolution, PAL-XFEL undulator section will use X-band Cavity beam position monitor (BPM) systems. The prototype cavity BPM pick-up was designed and fabricated to test the performance of the cavity BPM system. The fabricated prototype cavity BPM pick-up was installed at Pohang Accelerator Laboratory injector test facility (PAL ITF) for the beam test. Under 200 pC beam charge condition, the signal properties of the cavity BPM pick-up were measured. Also, the dynamic range of the cavity BPM pick-up was measured by using the corrector magnet. In this paper, the design and beam test results of the prototype cavity BPM pick-up will be discussed.  
poster icon Poster TUP043 [0.695 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP056 Design Challenge and Strategy for the LCLS-II High Repetition Rate X-ray FEL Photon Stoppers photon, FEL, radiation, synchrotron 493
 
  • Y. Feng, J.T. Delor, J. Krzywinski, P.A. Montanez, E. Ortiz, T.O. Raubenheimer, M. Rowen
    SLAC, Menlo Park, California, USA
  
  Funding: Portions of this research were carried out at the LCLS at the SLAC National Accelerator Laboratory. LCLS is an User Facility operated for the US DOE Office of Science by Stanford University.
Future high repetition rate X-ray FELs such as the European XFEL and LCLS-II presents new challenges to photon diagnostics as well as essential beamline components. In addition to these devices having to sustain the high peak power of a single-pulse FEL radiation, they must also be capable of handling the enormous power density of tens to hundreds of watts over an area as small as 0.1 mm X mm. In this talk, I will discuss the potential impact of high power FEL operation on performance of a gas attenuator and the design challenges to beam intercepting components such as a collimator or stopper. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP057 The Highly Adjustable Magnet Undulator undulator, electron, permanent-magnet, radiation 499
 
  • M. Hamberg
    Uppsala University, Uppsala, Sweden
  
  The highly adjustable magnet undulator is a concept aiming for flexibility and extensive tunability of undulator settings in the linear as well as the helical regime. I report about suggested layout, magnetic simulations.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP067 Effect of Hot Ions in LCLC-II ion, electron, linac, vacuum 508
 
  • L. Wang, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  
  The ions in a linac, such as ERL, draw more attention recently. LCLSII has a long linac with 1MHz repetition rate. The ions, in general, are not deeply trapped due to the long bunch spacing. The effect of ion thermal energy becomes important in this regime. The beam dynamics with ions are studied numerically. There is a linear growth in amplitude, but not exponential growth as traditional fast ion instability. This instability set a maximum bunch-train length to limit the beam amplitude to fractional beam σ. Theoretical works are also done to compare the simulations. We also extend our works to different regimes where the motions of ions from stable to unstable.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP069 THz Based Phase-Space Manipulation in a Guided IFEL electron, laser, coupling, undulator 519
 
  • E.J. Curry, S. Fabbri, P. Musumeci
    UCLA, Los Angeles, California, USA
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  
  Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583.
We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
TUP070 Energy Jitter Minimization at LCLS linac, timing, experiment, operation 523
 
  • L. Wang, A.L. Benwell, A. Brachmann, W.S. Colocho, F.-J. Decker, Z. Huang, T.J. Maxwell, T. Tao, J.L. Turner
    SLAC, Menlo Park, California, USA
  
  The energy jitters of the electron beam can affects the FEL in self-seeded modes if the jitter is large compared to the FEL parameter. We work in multiple ways to reduce the jitters, including hardware improvement, optimization linac set-up. This paper discusses the optimization of linac set-up. The solutions always suggest that we can largely reduce the energy jitter from a weak compression at BC1 and a stronger compression at BC2. Meanwhile a low beam energy at BC2 also reduce the energy jitter, which is confirmed by the experiment. The results can be explained by a simple model. Experimental results are also presented, demonstrating better than 20% and 40% relative energy jitter reduction for 13.6 and 4 GeV linac operation, respectively.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP002 Simulating Single Crystal Copper Photocathode Emittance emittance, electron, FEL, laser 587
 
  • T. Vecchione
    SLAC, Menlo Park, California, USA
  
  Funding: US DOE contract DE-AC02-76SF00515
The performance of free-electron lasers depends on the quality of the electron beam used. In some cases this performance can be improved by optimizing the choice of photocathode with respect to emittance. With this in mind, electronic structure calculations have been included in photoemission simulations and used to predict the emittance from single crystal copper photocathodes. The results from different low-index surfaces are reported. Within the model assumptions the Cu(100) surface was identified as having minimal emittance, particularly when illuminated by 266 nm light and extracted in a 60 MV/m gradient. These findings may guide future experimental work, leading to improved machine performance. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP004 Energy Spread Constraints on Field Suppression in a Reverse Tapered Undulator undulator, laser, FEL, bunching 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). 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP008 Four-Dimensional Models of FEL Amplifiers and Oscillators electron, FEL, undulator, laser 607
 
  • J. Blau, K. R. Cohn, W.B. Colson
    NPS, Monterey, California, USA
  
  Funding: This work has been supported by the High Energy Laser Joint Technology Office.
New four-dimensional models of free electron lasers (FELs) are described, for both amplifier and oscillator configurations. Model validation and benchmarking results are shown, including comparisons to theoretical formulas and experiments. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP029 Influence of Seed Laser Wavefront Imperfections on HGHG Seeding Performance laser, FEL, undulator, electron 643
 
  • T. Plath, C. Lechner
    Uni HH, Hamburg, Germany
  • S. Ackermann, J. Bödewadt
    DESY, Hamburg, Germany
  
  Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
To enhance the spectral and temporal properties of a free-electron laser the FEL process can be seeded by an external light field. The quality of this light field strongly influences the final characteristics of the seeded FEL pulse. To push the limits of a seeding experiment and reach the smallest possible wavelengths it is therefore crucial to have a thorough understanding of relations between laser parameters and seeding performance. In this contribution we numerically study the influence of laser wavefront imperfections on high-gain harmonic generation seeding at the seeding experiment at FLASH. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP031 Measurements and Simulations of Seeded Electron Microbunches with Collective Effects electron, laser, FEL, bunching 650
 
  • K.E. Hacker, S. Khan, R. Molo
    DELTA, Dortmund, Germany
  • S. Ackermann, J. Bödewadt, M. Dohlus, N. Ekanayake, T. Laarmann, H. Schlarb
    DESY, Hamburg, Germany
  • L.L. Lazzarino, C. Lechner, Th. Maltezopoulos, T. Plath, J. Roßbach
    Uni HH, Hamburg, Germany
  
  Funding: The experiments were carried out at FLASH at DESY. BMBF contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3, and the German Research Foundation program graduate school 1355.
Measurements of the longitudinal phase-space distribution of electron bunches seeded with an external laser were done in order to study the impact of collective effects on seeded microbunches in free-electron lasers. Velocity bunching of a seeded microbunch appears to be a viable alternative to compression with a magnetic chicane under high-gain harmonic generation seeding conditions when the collective effects of Coulomb forces in a drift space and coherent synchrotron radiation in a chicane are considered. Measurements of these effects on seeded electron microbunches were performed with an RF deflecting structure and a dipole magnet which streak out the electron bunch for single-shot images of the longitudinal phase-space distribution. Particle tracking simulations in 3D predicted the compression dynamics of the seeded microbunches with collective effects. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP045 Study on Beam Modulation Technique using a Masked Chicane at FAST (Fermilab Accelerator Science and Technology) Facility bunching, dipole, space-charge, linac 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. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP048 Electron Beam Diagnostics for FEL Studies at CLARA FEL, electron, diagnostics, laser 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). 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP051 The Prototype of New Variable Period Undulator for Novosibirsk Free Electron Laser. undulator, permanent-magnet, FEL, electron 677
 
  • I.V. Davidyuk
    NSU, Novosibirsk, Russia
  • O.A. Shevchenko, V.G. Tcheskidov
    BINP SB RAS, Novosibirsk, Russia
  • N. Vinokurov
    KAERI, Daejon, Republic of Korea
  
  To improve the parameters of the second stage Novosibirsk free electron laser one plans to replace the existing electromagnetic undulator by permanent-magnet variable-period undulator (VPU). The VPUs have several advantages compared to conventional undulators, which include wider radiation wavelength tuning range and an option to increase the number of poles for shorter periods with constant undulator length. Both these advantages will be realized in the new undulator under development in Budker INP. The idea of the permanent-magnet VPU was proposed just several years ago and it has not been properly tested yet. There are some technical problems, which have to be solved before this idea can be implemented in practice. To check the solution of these problems we designed and manufactured a small undulator prototype, which has just several periods. In this paper, the results of mechanical and magnetic measurements of this undulator prototype are presented and compared with simulations.  
poster icon Poster WEP051 [3.821 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP052 Studies of LCLS FEL Divergence undulator, electron, photon, quadrupole 681
 
  • J.L. Turner, P. Baxevanis, F.-J. Decker, Y. Ding, Z. Huang, J. Krzywinski, H. Loos, G. Marcus, N.P. Norvell
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Simulations show various impacts on x-ray divergence. With the motivation to maximize intensity at the focus, these beam studies were designed to study parameter space and beam qualities impacting divergence, and therefore aperture related clipping and diffraction. With multiple simultaneous users, beam constraints increase, requiring an improving knowledge of the mechanism of impact of changing parameters. These studies have that goal in order to improve beam control. 		 
poster icon Poster WEP052 [1.010 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP061 Numerical and Experimental Studies on Electron Beam Properties from Asymmetric RF-gun gun, electron, linac, emittance 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. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP067 Simulation of Cascaded Longitudinal-Space-Charge Amplifier at the Fermilab Accelerator Science & Technology (Fast) Facility bunching, space-charge, radiation, impedance 707
 
  • A. Halavanau, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • P. Piot
    Fermilab, Batavia, Illinois, USA
  
  Funding: This work was supported by the US Department of Energy under contract DE-SC0011831 with Northern Illinois University.
Cascaded longitudinal space-charge amplifier (LSCA) have been proposed as a mechanism to generate density modulation over broadband.[1] The scheme was recently demonstrated in the optical regime and confirmed the production of broadband optical radiation.[2] In this paper we investigate, via numerical simulations, the performances of a cascaded LSCA beamline at the Fermilab's Advanced Superconducting Test Accelerator (ASTA) to produce broadband ultraviolet radiation. Our studies are carried using a three-dimensional space charge algorithm coupled with ELEGANT [3] and based on a tree-based space-charge algorithm (see details in Ref. [4])
[1] M. Dohlus, PRSTAB, 14 090702 (2011).
[2] A. Marinelli, PRL, 110 264802 (2013).
[3] M. Borland, Advanced Photon Source, LS-287, 2000.
[4] A. Halavanau, Proc. IPAC15, TUPMA007 (2015). 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP069 Minimization of the Emittance Growth Induced by Coherent Synchrotron Radiation in Arc Compressor emittance, dipole, synchrotron-radiation, synchrotron 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. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP070 Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons FEL, emittance, linac, electron 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.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP075 Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam electron, radiation, undulator, FEL 722
 
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, USA
  • Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini
    SLAC, Menlo Park, California, USA
  
  We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP076 Tapering Studies for TW Level X-ray FELs with a Superconducting Undulator and Built-in Focusing undulator, FEL, electron, extraction 726
 
  • C. Emma
    UCLA, Los Angeles, USA
  • K. Fang, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: U.S. Department of Energy DE-SC0009983.
Tapering optimization schemes for TeraWatt (TW) level X-ray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle de-trapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multi-frequency effects are included. A discussion of how to incorporate these effects in a revised model is presented. 		 
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
WEP084 Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser undulator, FEL, electron, bunching 741
 
  • Z. Zhang
    TUB, Beijing, People's Republic of China
  • Y. Ding, W.M. Fawley, Z. Huang, J. Krzywinski, A.A. Lutman, G. Marcus, A. Marinelli, D.F. Ratner
    SLAC, Menlo Park, California, USA
  
  The measured, self-seeded soft X-ray radiation spectrum corresponding to multiple effective undulator lengths of the LCLS exhibits a pedestal-like distribution around the seeded frequency. In the absence of a post-undulator monochromator, this contamination limits the spectral purity and may seriously degrade certain user applications. In general for either externally- or self-seeded FELs, such pedestals may originate with any time-varying property of the electron beam that can modulate the complex gain function. In this paper we specifically focus on the contributions of electron beam microbunching prior to the undulator. We show that both energy and density modulations can induce sidebands in a seeded FEL configuration. Analytic FEL theory and numerical simulations are used to analyze the sideband content relative to the amplified seeded signal, and to compare with experimental results.  
poster icon Poster WEP084 [1.263 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)