MOPD —  Status Report / FEL Theory / FEL Technology -1-   (27-Aug-12   16:00—17:30)
Paper Title Page
MOPD01 Status of the FLASH Facility 37
 
  • S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch, M. Vogt
    DESY, Hamburg, Germany
 
  FLASH at DESY, Hamburg is a soft X-ray free-electron laser user facility. After a 3.5 months shutdown in autumn 2011 required for civil construction for a second undulator beamline, beam operation started as scheduled in January 2012. FLASH shows again an improvement in performance with even higher single and average photon pulse energies, better stability, and significant improvements in operation procedures. The 4th user period started end of March 2012. A 4 months shutdown is scheduled early 2013 to connect the second undulator beamline to the FLASH accelerator.  
 
MOPD02 Pulse-front Tilt Caused by the Use of a Grating Monochromator and Self-seeding of Soft X-ray FELs 41
 
  • G. Geloni, V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
 
  Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. The development of such schemes in the soft X-ray wavelength range necessarily involves gratings as dispersive elements. These introduce, in general, a pulse-front tilt, which is directly proportional to the angular dispersion. Pulse-front tilt may easily lead to a seed signal decrease by a factor two or more. Suggestions on how to minimize the pulse-front tilt effect in the self-seeding setup are given.  
 
MOPD03 Harmonic Lasing in X-ray FELs 45
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  Contrary to nonlinear harmonic generation, harmonic lasing in a high-gain FEL can provide much more intense, stable,and narrow-band FEL beam which is easier to handle if the fundamental is suppressed. We propose efficient methods for suppression of the fundamental. We perform a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics, and present explicit expression for FEL gain length, taking into account all essential effects. We conclude that harmonic lasing is much more robust than usually thought, and can be widely used in the existing or planned X-ray FEL facilities. LCLS after a minor modification can lase at the 3rd harmonic up to the photon energy of 25-30 keV providing multi-gigawatt power level. At the European XFEL the harmonic lasing would allow to extend operating range (ultimately up to 100 keV), to increase brilliance, to enable two-color operation for pump-probe experiments,and to provide more flexible operation at different electron energies. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities, harmonics can grow faster than the fundamental.  
 
MOPD04 Fitting Formulas for Harmonic Lasing in FEL Amplifiers 49
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  One of the most important subjects of the high-gain FEL engineering is the calculation of the gain length, and fitting formulas are frequently used for this purpose. Here we refer to Ming Xie fitting formulas [1] and fitting formulas for optimized FEL written down in an explicit form in terms of the electron beam and undulator parameters [2]. In this paper we perform generalization of these fitting formulas to the case of harmonic lasing.
[1] M. Xie, Nucl. Instrum. and Methods A445(2000)59
[2] E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov,
Opt. Commun. 235(2004)415
 
 
MOPD05 Harmonic Lasing of Thin Electron Beam 53
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  For a typical operating range of hard X-ray FELs the condition 2π ε/λ ~ 1 is usually a design goal for the shortest wavelength. In the case of the simultaneous lasing the fundamental mode has shorter gain length than harmonics. If the same electron beam is used to drive an FEL in a soft X-ray beamline, the regime with 2π ε/λ << 1 is realized which corresponds to the case of a small value of diffraction parameter. Here we present a detailed study of this regime. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities (like SASE3 beamline of the European XFEL), harmonics can grow faster than the fundamental wavelength. This feature can be used in some experiments, but might also be an unwanted phenomenon, and we discuss possible measures to diminish it.  
 
MOPD06 Spatial Properties of the Radiation from SASE FELs at the European XFEL 57
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  Recently DESY and the European XFEL GmbH performed revision of the baseline parameters for the electron beam. Operating range of bunch charges has been extended from 20 pC to 1 nC. Different modes of FEL operation become possible with essentially different properties of the radiation. Radiation from SASE FEL with planar undulator contains visible contribution of higher odd harmonics. Knowledge of spatial properties of harmonics is of great practical interest for planning user experiments. In this report we present results of the studies of spatial properties of the radiation from SASE FELs at the European XFEL. We consider nonlinear mechanism of harmonic generation and trace spatial properties of the odd harmonics up to deep nonlinear regime.  
 
MOPD07 On Disruption of the Fundamental Harmonic in SASE FEL with Phase Shifters 61
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  A method to disrupt the fundamental harmonic with phase shifters installed between undulator modules (while keeping the lasing at the third harmonic undisturbed) was proposed in [*]. If phase shifters are tuned such that the phase delay is 2π/3 (or 4π/3) for the fundamental, then its amplification is disrupted. At the same time the phase shift is equal to 2π for the third harmonic, i.e. it continues to get amplified without being affected by phase shifters. We note that simulations in [*] were done for the case of a monochromatic seed, and the results cannot be applied for a SASE FEL. The reason is that in the latter case the amplified frequencies are defined self-consistently, i.e. there is frequency shift (red or blue) depending on positions and magnitudes of phase kicks. This leads to a significantly weaker suppression effect. In particular, we found out that a consecutive use of phase shifters with the same phase kicks 2π/3 (as proposed in [*] is inefficient, i.e. it does not lead to a sufficiently strong suppression of the fundamental wavelength. In the present report we propose a modification of phase shifters method that can work in the case of a SASE FEL.
[*] B.W.J. McNeil et al., Phy. Rev. Lett. 96, 084801 (2006).
 
 
MOPD08 Coherence Properties of the Odd Harmonics of the Radiation from SASE FEL with Planar Undulator 65
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  We present a comprehensive analysis of coherence properties of odd harmonics radiated from a SASE FEL with planar undulator. Nonlinear mechanism of harmonic generation is under study. Temporal and space correlation functions, coherence time and degree of transverse coherence are calculated by means of numerical simulations with the code FAST. Similarity techniques have been used to derive general coherence properties of the radiation in the saturation regime.  
 
MOPD10 Nonlinear Harmonic Selection in an FEL Undulator System 69
 
  • S. Biedron, L. Giannessi, K. Horovitz, S.V. Milton
    CSU, Fort Collins, Colorado, USA
 
  Sandra Biedron1, William Fawley1,2, Luca Giannessi1,2,3, Karen Horovitz1, Stephen Milton1 1Colorado State University, Department of Electrical and Computer Engineering, 1373 Campus Delivery, Fort Collins, Colorado 80523 2 and Sincrotrone Trieste 34149 Basovizza (Trieste) Italy 3and ENEA, C.R. Frascati Via Enrico Fermi, 45 - 00044 Frascati (Roma) Italy The area of harmonic selection in undulator magnets is an important area of free electron laser (FEL) research. Within the undulator section of an FEL system, a wiggling electron beam emits coherent radiation at multiple wavelengths (harmonics), but in some cases the output should only be in the desired region for application purposes. Dispersion sections and unique undulators can be tailored in order to select harmonics and control their power levels. GINGER and PERSEO code were used for simulations. This research will lead to a better understanding of the emission process as well as the interaction of beam density distribution, the frequency and phase relationship of emission, and the amplitude of the emission as a function of time. Furthermore, harmonic control has applications within oscillator or amplifier-based FEL systems.  
 
MOPD12 Puffin: A Three Dimensional, Unaveraged Free Electron Laser Simulation Code 73
 
  • L.T. Campbell, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
 
  The broadband, 3D FEL code Puffin is presented. The analytical model is derived in absence of the Slowly Varying Envelope Approximation, and can model undulators of any polarisation. Due to the enhanced resolution, the memory and processing requirements are greater than equivalent unaveraged codes. The numerical code to solve the system of equations is therefore written for a parallel computing environment utilizing MPI. Some example simulations are presented.  
 
MOPD17 Nonlinear effects in FEL theory and their role in coherent electron cooling 77
 
  • A. Elizarov
    SUNY SB, Stony Brook, New York, USA
  • V. Litvinenko
    BNL, Upton, Long Island, New York, USA
 
  The novel cooling technique, the coherent electron cooling [1] relies on the amplification of the interaction between hadrons and electrons by an FEL. The linearity of the amplification process is essential for operation of such cooler. In this paper we propose a theoretical method of taking into account nonlinear effects in computation of evolution of charge perturbation in an FEL. This will allow to explore the limits of the FEL gain with special attention to the smearing of the phase caused by nonlinear and saturation effects.
[1] V. N. Litvinenko, Y. S. Derbenev, Phys. Rev. Lett. 102, 114801 (2009).
 
 
MOPD22 A General Method for Analyzing 3-D Effects in FEL Amplifiers 81
 
  • P. Baxevanis, Z. Huang, R.D. Ruth
    SLAC, Menlo Park, California, USA
 
  FEL configurations in which the parameters of the electron beam vary along the undulator become relevant when considering new aspects of existing FELs or when exploring novel concepts. This paper describes a fully three-dimensional, analytical method suitable for studying such systems. As an example, we consider a seeded FEL driven by a beam with varying transverse sizes. In the context of the Vlasov-Maxwell formalism, a self-consistent equation governing the evolution of the radiation field amplitude is derived. An approximate solution to this equation is then obtained by employing an orthogonal expansion technique. This approach yields accurate estimates for both the amplified power and the radiation beam size. Specific numerical results are presented for two different sets of X-ray FEL parameters.  
 
MOPD28 Theoretical Study of Smith-Purcell Free-Electron Lasers 85
 
  • D. Li, K. Imasaki
    ILT, Suita, Osaka, Japan
  • M.R. Asakawa, Y. Tsunawaki
    Kansai University, Osaka, Japan
  • M. Hangyo
    ILE Osaka, Suita, Japan
  • S. Miyamoto
    LASTI, Hyogo, Japan
  • Y. Wei, Z. Yang
    UESTC, Chengdu, Sichuan, People's Republic of China
 
  We report here a theory to calculate the growth rate and start current of a Smith-Purcell free-electron lase. The mechanism of the interaction between a sheet electron beam and the surface wave above a lamellar grating is well investigated. After deriving the growth rate from the dispersion equation, the start current is dexterously worked out by considering the energy flow above the grating. The predictions of our theory agree with the results from the particle-in-cell simulations.  
 
MOPD31 Injector Optimization for a High-repetition Rate X-ray FEL 89
 
  • C. F. Papadopoulos, J.N. Corlett, P. Emma, D. Filippetto, G. Penn, J. Qiang, M.W. Reinsch, F. Sannibale, M. Venturini
    LBNL, Berkeley, California, USA
 
  Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
In linac driven free electron lasers, the final electron beam quality is constrained by the low energy (<100 MeV) beam dynamics at the injector. In this paper, we present studies and the optimized design for a high-repetition (>1 MHz) injector in order to provide a high brightness electron beam. The design effort is also extended to multiple modes of operation, in particular different bunch charges. The effects of space charge and low energy compression on the electron beam brightness are also discussed for the different modes.
 
 
MOPD32 Theory of the Quantum FEL in a Nutshell 93
 
  • P. Preiss, R. Sauerbrey
    HZDR, Dresden, Germany
  • R. Endrich, E.A. Giese, P. Kling, M. Knobl, W.P. Schleich
    Uni Ulm, Ulm, Germany
  • S.M. Zubairy
    Texas A&M University, College Station, Texas, USA
 
  New developments in accelerator and laser physics raise hope for the so-called QFEL, a free-electron laser operating in the quantum mechanical regime. We develop a fully quantized single-particle theory describing the dynamics of the interaction between the electron, the wiggler and the laser field. In the quantum mechanical regime the dynamics are reminiscent of the standard laser theory with a two-level atom. Indeed, we find oscillations between two entangled states - where the entanglement appears between the electron momentum state and the Fock states of the laser and wiggler field. Compared to a two-level system with one internal degree of freedom (e.g. an atom with a ground and one excited state) the state of our system is mainly determined by the momentum of the electron in the co-moving Bambini-Renieri frame. In contrast to the classical regime here the electron propagating through the wiggler field can only emit or absorb a single laser photon. Transitions including the emission or absorption of many photons are substantially much suppressed.  
 
MOPD33 Saturation in Free Electron Laser with Quadrupole Wiggler and Axial Magnetic Field 97
 
  • P. Yahyaee, A.A. Kordbacheh
    IUST, Narmac, Tehran, Iran
 
  In this paper, we study the nonlinear evolution of a quadrupole wiggler free electron laser, in the presence of a helical wiggler, which increases adiabatically from zero to a constant level. To focus the electron beam, we apply an axial magnetic field. By using Maxwell equations and Lorentz force equation of motion for electrons, a set of coupled nonlinear equation is derived and solved numerically. The beam is cold and propagates with a relativistic velocity. Results are compared with dipole wiggler FEL.  
 
MOPD35 Detailed Modeling of Seeded Free-electron Lasers 101
 
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  • M. Carlà
    UNIFI, Sesto Fiorentino (FI), Italy
 
  Seeding schemes for Free Electron Lasers have mostly a strong impact on the electron distribution by either a conversion of an energy modulation into a current modulation with high harmonic content (HGHG seeding) or an over-compression of this energy modulation to induce energy bands (EEHG seeding) or smear out any bunching in the electron beam (self-seeding). Most codes follow an approach to use thin electron slices, which are carefully generated to provide the correct shot-noise but which also prevents them from mixing and re-sorting the macro-particle distribution. The FEL code Genesis 1.3 has been modified to allow resolution of each individual electron. Using this approach the correct shot noise at all frequencies is provided and permits "re-binning" of the particles to the 3D radiation grid at any time. The results for self-seeding and HGHG seeding are discussed.  
 
MOPD36 Dark Current Studies for SwissFEL 105
 
  • F. Le Pimpec, A. Adelmann, S. Reiche, R. Zennaro
    PSI, Villigen PSI, Switzerland
  • B. Grigoryan
    CANDLE, Yerevan, Armenia
 
  Activation of the surrounding of an accelerator must be quantified and those data provided to the official agencies, This is a necessary step for obtaining the appropriate authorization to operate such accelerator. The SwissFEL, being a 4th generation light source, will produce more accelerated charges, which are dumped or lost, than any conventional 3rd generation light source, like the Swiss Light Source. We have simulated the propagation of a dark current beam produced in the photoelectron gun using tracking codes like ASTRA and Elegant for the current layout of the SwissFEL. Detailed experimental study have been carried out at the SwissFEL test facilities at PSI (C-Band RF Stand and SwissFEL Injector Test Facility), in order to provide necessary input data for detailed study of components using the simulation code OPAL. A summary of these studies are presented.  
 
MOPD37 Switchyard Design: Athos 109
 
  • N. Milas, S. Reiche
    PSI, Villigen PSI, Switzerland
 
  The SwissFEL facility will produce coherent, ultrabright and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance of 0.43 mm mrad or better. In order to provide electrons to the soft X-ray beam line a switchyard is necessary. This beamline will switch the electron bunch coming from the SwissFEL linac, with an energy of 3.0 GeV, and transport it to Athos. The switchyard has to be designed in such a way to guarantee that beam properties like low emittance, high peak charge and small bunch length will not be spoiled. In order to keep the switchyard as versatile as possible it can work for a range of values of R56 from isochronous up to 6 mm, when the bunch is stretched by a factor two, and also be able to transport the beam in the so called "large bandwidth" mode. In this paper we present the schematics for the switchyard, discuss its many modes of operation, sextupole correction scheme and positioning of energy collimator for machine protection.  
 
MOPD38 Investigation of Non-rectangular RF Pules influence in Emitted Electron Beam of Thermionic RF-gun at the Linac-based THz Facility in Thailand 113
 
  • K. Damminsek, S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
 
  Funding: Department of Physics and Materials Science at Chiang Mai University, Thailand Center of Excellence in Physics and the Development and Promotion of Science and Technology talents project.
An electron gun of a linac based THz source at the Plasma and Beam Physics (PBP) Research facility, Chiang Mai University in Thailand is a 1-1/2 cell S-band standing wave RF cavity with an Os/Ru coating dispenser cathode. The electron current density of a few amperes per square centimeter can be achieved from zero-field thermionic emission using this cathode type at a desired operating temperature. However, Non-Rectangular RF pulse have significant influence on the emitted electron current in a thermionic RF-gun. Numerical and experimental studies of the contribution of the effect have been carried out. Results of the investigation together with a proposed model to improve the performance of the thermionic RF-gun will be presented and discussed in this contribution.
 
 
MOPD40 Simulation for New Injector Test Facility of PAL-XFEL 117
 
  • M.S. Chae, I.S. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • J.H. Han, J.H. Hong, S.J. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  As a part of the preparation plan of PAL-XFEL, Injector Test Facility (ITF) has been constructed and now required beamline components are being installed for the test of injector system. ITF components includes RF gun, two accelerating columes, solenoids and basic diagnostic components such as spectrometers, quad scan system, BPMs, wire scanner, etc. Main diagnostics will be installed until October this year and deflecting cavity and laser heater will be installed next year. This facility will generate 135 MeV electron beam with the emittance under 0.5 mm-mrad. Simulation for the optimized operation of the ITF has been carried out with ASTRA code and its results are given in this paper.  
 
MOPD41 Low Emittance Injector Development for the PAL-XFEL Project 121
 
  • J.H. Han, J.H. Hong, I. Hwang, H.-S. Kang, I.S. Ko, S.J. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
  • M.S. Chae
    POSTECH, Pohang, Kyungbuk, Republic of Korea
 
  Funding: The Ministry of Education, Science and Technology of the Korean Government
An injector designed for low emittance beam generation as well we high repetition rate and more reliable operation is under development at PAL. By adopting a coaxial high power RF coupler at the gun exit, the gun solenoid can be positioned at an optimum location for low emittance and the cooling water channels can fully surround the gun cavity cylinder for high cooling capacity. With an exchangeable photocathode plug, high quantum efficiency cathode can be used for reducing the drive-laser power requirement and a damaged cathode can be easily replaced with a fresh one. Injector beam dynamics optimization with this gun is presented.
 
 
MOPD42 Microbunching Instability Study for the PAL-XFEL Linac 125
 
  • J.H. Han, I. Hwang, H.-S. Kang
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  Funding: The Ministry of Education, Science and Technology of the Korean Government
PAL-XFEL is designed to generate X-ray FEL radiation in a range of 0.1 and 10 nm for users. The machine consists of a 10 GeV linear accelerator and five undulator beamlines. An electron beam is generated at a low emittance S-band photocathode RF gun and accelerated through an S-band normal conducting linac. Microbunching instability may occur when the beam goes through magnetic bunch compressors and beam spreaders. We discuss microbunching instability issues at PAL-XFEL.
 
 
MOPD43 New RF-Gun Design for The PAL-XFEL 129
 
  • J.H. Hong, K.H. Gil, J.H. Han, H.-S. Kang, S.J. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
  • M.S. Chae, I.S. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
 
  We are developing an S-band photocathode RF-gun for the X-ray free electron laser (XFEL) at the Pohang Accelerator Laboratory (PAL). This RF-gun is a 1.6-cell RF-gun with dual-feed waveguide ports and two pumping ports. We have done the complete RF and thermal analysis of a new gun. The new RF-gun is designed to operate at a maximum field gradient of 130MV/m with a RF pulse width of 3 μs, a repetition rate of 120Hz. In this paper we present features and RF simulation results and thermal analysis results.  
 
MOPD44 Design of Magnets for PAL-XFEL 133
 
  • H.S. Suh, M.-H. Cho, H.S. Han, J.Y. Huang, S.T. Jung, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, T.-Y. Lee, K.-H. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  Pohang Accelerator Laboratory (PAL) is starting the X-ray Free Electron Laser of 10 GeV. PAL-XFEL has the hard X-ray and soft X-ray branches. The linac contains dipole magnets, quadrupole magnets and corrector magnets. The kicker magnet followed by the septum magnet is needed to extract the beam from the linac to the soft X-ray undulator line. In this presentation, we describe the design and analysis of the magnets.  
 
MOPD45 Present Status of Thermionic RF-Gun for Terahertz Source Project at Tohoku University 137
 
  • F. Hinode, H. Hama, N.Y. Huang, S. Kashiwagi, M. Kawai, T. Muto, I. Nagasawa, K. Nanbu, Y. Shibasaki, K. Takahashi
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • X. Li
    TUB, Beijing, People's Republic of China
 
  Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A thermionic RF gun for an acceleratora-based terahertz source has been commissioned at Electron Light Science Centre, Tohoku University*. The RF gun consisting of two independently-tunable cells (ITC RF gun) can be operated so as to optimize the phase space distribution of the extracted electrons for the further manipulation in an alpha magnet and a 3 m accelerating structure for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching in the accelerating structure. In the early result of the gun commissioning, it was shown that the back-bombardment (B-B) effect was rather serious for the beam quality in spite of the operation with the short pulse length and slow repetition rate. The simulation study for the B-B effect with the 2D heat transfer model turned out that low energy electrons coming back in the cathode cell have the significant contribution for the additional cathode heating rather than the higher energy electrons**. We will show the recent results of beam commissioning of the ITC RF gun and the current status of t-ACTS project.
*H. Hama et al., New J. Phys. 8 (2006) 292,
**X. Li et al., Proc. of FEL'11, (2011) THPA17
 
 
MOPD46 Design Study of the LINAC of the Shanghai Soft X-ray Free Electron Laser Facility 141
 
  • D. Huang, W. Fang, D. Gu, Q. Gu, G.Q. Lin, M. Zhang
    SINAP, Shanghai, People's Republic of China
 
  Shanghai soft X-ray Free Electron Laser Facility (SXFEL), which is planned to start construction by the end of 2012, will be the first X-ray free electron laser facility in China. As of today, the physical design of it has been done and optimized. In this article, the design process and the key physical parameters will be discussed in details, including RF structures, microbunching instability, jitter analysis, etc. The goal and the expected performance of the LINAC will also be given.  
 
MOPD47 Enhancement of the Electron Energy by using a Linearly Tapered Density in the Laser Wakefield Acceleration 145
 
  • J. Kim
    KERI, Changwon, Republic of Korea
 
  Due to the capability of making a compact accelerator and the ability to generate an ultra-short bunch electron beam, a laser wakefield acceleration(LWFA) is widely studied. In LWFA, a dephasing effect is the main limitation of the electron energy. To overcome the dephasing effect and increase the electron energy, we studied the linearly tapered density. A 2D particle in cell simulation and the experimental results show that with linearly tapered density, we could increase the electron energy with the same laser power. The details of the work will be presented.  
 
MOPD48 Overall Performance Comparison of S-band, C-band, and X-band Based Compact XFEL Facilities 149
 
  • Y. Kim
    IAC, Pocatello, IDAHO, USA
  • K.H. Jang
    KAERI, Daejon, Republic of Korea
  • S. Setiniyaz, M. Titberidze
    ISU, Pocatello, Idaho, USA
 
  After successful demonstration of XFEL lasing from C-band based XFEL facility at SPring-8, demand on compact XFEL facilities becomes much stronger. Recently, there were several activities to build much more compact XFEL facilities, which are based on X-band RF linac technology. But up to now, there was no detailed research to compare the performance of S-band, C-band, and X-band RF linac based XFEL facilities. To compare the performance, recently, ISU accelerator and FEL physics group has designed three different XFEL facilities where the S-band, C-band, and X-band RF linac technologies are used for the main FEL driving linacs. In this paper, we describe layouts, start-to-end simulations, and comparison of overall performance of those three XFEL facilities. Finally, we also describe control of energy chirp, RF jitter tolerances, alignment and transverse wakefield issue, and bandwidth of XFEL photon beam in C-band or X-band based XFEL facilities.  
 
MOPD50
Quantum Efficiency and Emission Mechanisms of Electrons from Flat Metallic Cathodes under Varying Electric Fields and Tunable Laser Illumination  
 
  • S. Mingels, B. Bornmann, D. Lützenkirchen-Hecht, G. Müller
    Bergische Universität Wuppertal, Wuppertal, Germany
 
  Funding: German Federal Ministry of Education and Research BMBF (contract number 05K10PXA)
Highly brilliant electron sources are crucial for the performance of future free electron lasers[1]. Photo-induced field emission (PFE) might combine the high peak currents of photo cathodes with the low emittance of field emitted electrons. Previous investigations of PFE were performed on tip cathodes and yielded a high brilliance B ≤ 1x1013 A/m2rad2 but only low currents I ≤ 2.9 A and parasitic field emission [2]. We are investigating PFE from flat cathodes in an UHV system for PFE spectroscopy with a resolution of less than 50 meV [3]. Electric fields of up to 400 MV/m can be applied, and pulsed tunable laser illumination of the cathode (0.5 - 5.9 eV photon energy, 1-15 mJ in 3.5 ns pulses, 10 Hz repetition rate) are available. First indications of Schottky-induced photo emission and PFE on flat polycrystalline Au samples were obtained. Measurements of quantum efficiency at continuously varied photon energies revealed strong resonances, which hint for certain band structure transitions. Detailed measurements on single-crystalline Au and Ag samples including electron spectra are ongoing, and the results will be presented at the conference.
[1] D.H. Dowell et al., Nucl. Instr. And Meth. Phys. A 622, 685-697 (2010)
[2] R. Ganter et al., PRL 100, 064801 (2008)
[3] B. Bornmann et al., Rev. Sci. Instrum. 83, 013302 (2012)
 
poster icon Poster MOPD50 [1.572 MB]  
 
MOPD51 Developing S-band Accelerating Structures 153
 
  • S. Miura
    MHI, Hiroshima, Japan
  • T. Inagaki, H. Maesaka
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • H.-S. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
  • H. Matsumoto
    KEK, Ibaraki, Japan
  • T. Shintake
    OIST, Onna-son, Okinawa, Japan
 
  We have supplied more than fifty high gradient S-band accelerating structures to KEK/ATF, SPring-8, PAL/Korea and INFN/Italy. Maximum accelerating garinent of these structures reaches in 30MV/m. Now we are developing new S-band accelerating structures. This time we report manufacturing of these structures.  
 
MOPD52 Beam Dynamics Calculations for the SPring-8 Photoinjector System using Multiple Beam Envelope Equations 157
 
  • A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
    JASRI/SPring-8, Hyogo-ken, Japan
  • E. Hotta
    Department of Energy Sciences, Tokyo Institute of Technology, Yokohama, Japan
 
  A new semi-analytical method of investigating the beam dynamics for electron injectors was developed. In this method, a short bunched electron beam is assumed to be an ensemble of several segmentation pieces in both the longitudinal and transverse directions. The trajectory of each electron in the segmentation pieces is solved by the beam envelope equations. The shape of the entire bunch is consequently calculated, and thus the emittances can be obtained from weighted mean values of the solutions for the obtained electron trajectories. Using this method, dynamics calculation for the SPring-8 RF gun system was performed while taking into account the space charge fields, the image charge fields at a cathode surface,the electromagnetic fields of the RF gun cavity and the following accelerator structure, and the solenoidal coils. In this paper, we discuss applicable conditions for this method by comparing calculation results of this method and that of the particle simulation code.  
 
MOPD53 Development of a Photoemission DC Gun at JAEA 161
 
  • N. Nishimori
    JAEA/FEL, Ibaraki-ken, Japan
  • R. Hajima, S.M. Matsuba, R. Nagai
    JAEA, Ibaraki-ken, Japan
  • Y. Honda, T. Miyajima, M. Yamamoto
    KEK, Ibaraki, Japan
  • H. Iijima, M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
  • M. Kuwahara, T. Nakanishi, S. Okumi
    Nagoya University, Nagoya, Japan
 
  Funding: This work is supported by MEXT Quantum Beam Technology Program and partially supported by JSPS Grants-in-Aid for Scientific Research in Japan (23540353).
The next generation light source such as X-ray FEL oscillator requires high brightness electron gun with megahertz repetition rate. We have developed a photoemission DC gun at JAEA. By employing a segmented insulator with rings which guard the ceramics from field emission, we successfully applied 500-kV on the ceramics with a center stem electrode for eight hours without any discharge in 2009. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. In 2011 we reached 526kV with NEG pumps and electrodes, before suffering another field emission problem from the cathode electrode. The problem may be attributed to small dust inside our gun chamber. We found wiping the cathode electrode with a lint free tissue could remove the field emission site effectively. Noble gas conditioning is also planned to remove the emission site without air exposure of the gun chamber.
 
 
MOPD55 RF DESIGN AND HIGH POWER TESTS OF A NEW TSINGHUA PHOTOCATHODE RF GUN 165
 
  • H.J. Qian, Y.-C. Du, J.F. Hua, W.-H. Huang, C. Li, C.-X. Tang, L.X. Yan
    TUB, Beijing, People's Republic of China
 
  A new photocathode RF gun has been designed and fabricated to meet beam brightness requirements (0.5-1 nC, 1-2 mm mrad) of Tsinghua Thomson scattering project (TTX) and Shanghai soft X-ray free electron laser test facillity (SXFEL). Compared with classical BNL type gun, the new Tsinghua gun features improved cathode sealing structure, 0-mode and multipole field suppression, and higher quality factor. Single RF feed is kept in the new gun for simplicity, and beam dynamics due to single RF feed are investigated theoretically, which predict negligible emittance growth. After high power conditioning, the new gun operates stably with a peak acceleration gradient of ~120 MV/m. Measurements of dark current, Quantum Efficiency (QE), and transverse emittance are presented and discussed in this paper.  
 
MOPD56 Design and Commission of the Driven Laser System for Advanced Superconducting Test Accelerator 169
 
  • J. Ruan, M.D. Church, J.K. Santucci
    Fermilab, Batavia, USA
 
  Currently an advanced superconducting test accelerator (ASTA) is being built at Fermilab. The accelerator will consist of an photo electron gun, injector, ILC-type cryomodules, multiple downstream beam lines for testing cryomodules and carrying advanced accelerator researches. In this paper we will describe the design and commissioning of the drive laser system for this facility. It consists of a fiber laser system properly locked to the master frequency, a regen-amplifier, several power amplifier and final wavelength conversion stage. We will also report the initial characterization of the fiber laser system and the current commissioning status of the laser system.  
 
MOPD57 Development of Multi-bunch Laser System for Photocathode RF Gun in KU - FEL 173
 
  • K. Shimahashi, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, T. Konstantin, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Yoshida, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  • R. Kuroda
    AIST, Tsukuba, Ibaraki, Japan
 
  We have been developing mid-infrared FEL (MIR-FEL) system, KU-FEL (Kyoto University-FEL), which utilizes a 4.5-cell S-band thermionic RF gun, in Institute of Advanced Energy, Kyoto University. We plan to introduce a BNL-type 1.6-cell photocathode RF gun to generate higher peak power MIR-FEL. The purpose of this work is to develop the multi-bunch laser system which excites the photocathode in the RF gun. The target values of the system are bunch number of 300 and pulse energy of 10 uJ perμpulse in 266 nm. The laser system consists of a mode-locked Nd:YVO4 laser as the oscillator, an acousto-optic modulator, a laser beam pointing stabilization system, a flash lamp pumped amplifier and 4th harmonic generation crystals. We will report the current status of multi-bunch laser in this conference.  
 
MOPD58 Commissioning of the FERMI@ELETTRA Laser Heater 177
 
  • S. Spampinati, E. Allaria, L. Badano, S. Bassanese, D. Castronovo, M.B. Danailov, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, L. Giannessi, G. Penco, C. Spezzani, M. Trovò
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. De Ninno, E. Ferrari
    University of Nova Gorica, Nova Gorica, Slovenia
 
  The linac of the FERMI seeded free electron laser includes a laser heater to control the longitudinal microbunching instability, which otherwise is expected to degrade the quality of high brightness electron beam sufficiently to reduce the FEL power. The laser heater consists of an short undulator located in a small magnetic chicane through which an external laser pulse enters to the electron beam both temporally and spatially. The resulting interaction within the undulator produces an energy modulation of the electron beam on the scale of the optical wavelength. This modulation together with the effective R52 transport term of the chicane increases the incoherent energy spread (i.e., e-beam heating). We present the first commissioning results of this system and its impact on the electron density and energy distribution and on FEL output quality.  
 
MOPD59 PITZ Status, Recent Measurements and Tests 181
 
  • M. Krasilnikov, H.-J. Grabosch, M. Groß, I.I. Isaev, Ye. Ivanisenko, M. Khojoyan, G. Klemz, G. Kourkafas, M. Mahgoub, D. Malyutin, B. Marchetti, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • K. Kusoljariyakul
    FNRF, Chiang Mai, Thailand
  • J. Li
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • D. Richter
    HZB, Berlin, Germany
  • S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
  • I. Will
    MBI, Berlin, Germany
 
  The photo injector test facility at DESY, Zeuthen site (PITZ) is dedicated to the development and optimization of a high-brightness electron source for the European XFEL. Recently a significant upgrade has been done at the facility. A new RF system has been installed for the PITZ gun, enabling higher attainable peak power in the cavity which is important for efficient LLRF regulation. First long-term tests for a stable gun operation at high duty cycle have been performed. Two major components for electron beam diagnostics - a transverse deflecting cavity for time resolved electron bunch characterization, and a second high energy dispersive arm for precise longitudinal phase space measurements - have been installed. First results of their commissioning will be reported.  
 
MOPD60 Optimization of the Transverse Projected Emittance of the Electron Beam at PITZ 185
 
  • G. Vashchenko, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, A. Shapovalov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. Khojoyan
    ANSL, Yerevan, Armenia
  • D. Richter
    HZB, Berlin, Germany
 
  High brightness electron sources for linac based free-electron lasers operating at short wavelength such as the Free-Electron Laser in Hamburg at DESY, Hamburg Site (FLASH) and the European X-Ray Laser Project XFEL (European XFEL) are characterized and optimized at the Photo Injector Test Facility at DESY, Zeuthen Site (PITZ). One of the most important parameters influencing the FEL process is the normalized transverse projected emittance of the electron beam. The major part of the experimental program at PITZ is devoted to its optimization. Detailed simulations of the present facility setup are performed for a 1 nC bunch charge in order to optimize the transverse projected emittance of the electron beam. Cathode laser pulse length and transverse spot size at the photo cathode, gun and booster accelerating gradients and their launching phases as well as the main solenoid current are optimized. Simulations results together with experimental data are presented.  
 
MOPD61 Laser Pulse Train Management with an Acousto-optic Modulator 189
 
  • M. Groß, H.-J. Grabosch, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M. Khojoyan, G. Klemz, G. Kourkafas, M. Krasilnikov, K. Kusoljariyakul, J. Li, M. Mahgoub, D. Malyutin, B. Marchetti, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • D. Richter
    HZB, Berlin, Germany
  • H. Schlarb, S. Schreiber
    DESY, Hamburg, Germany
 
  Photo injector laser systems for linac based FELs often have the capability of generating pulse trains with an adjustable length. For example, the currently installed laser at the Photo Injector Test Facility at DESY, Zeuthen Site (PITZ) can generate pulse trains containing up to 800 pulses. Repetition frequencies are 10 Hz for the pulse trains and 1 MHz for the pulses within a train, respectively. Mostly due to thermal effects caused by absorption in amplifier and frequency doubling crystals, pulse properties are changing slightly within a pulse train and also shot-to-shot, depending on the pulse train length. To increase stability and repeatability of the laser it is desirable to run it under constant conditions. To achieve this while still being able to freely choose pulse patterns a pulse picker to sort the wanted from the unwanted pulses can be installed at the laser output. A promising candidate for this functionality is an acousto-optic modulator which currently is being tested at PITZ. First experimental results will be presented and discussed towards the possibility of including this device into an FEL photo injector.  
 
MOPD62 High-brightness Electron Beam Evolution In Time Following Laser-Based Cleaning of the LCLS Cathode 193
 
  • F. Zhou, A. Brachmann, F.-J. Decker, P. Emma, R.H. Iverson, P. Stefan, J.L. Turner
    SLAC, Menlo Park, California, USA
 
  Funding: The work supported under DOE contract No. DE-AC02-76SF00515.
Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE). However, the impact of laser cleaning on the cathode uniformity and final quality of the electron beam is not understood. We are evaluating whether the technique can be applied to revive photocathodes used for electron beam sources of advanced x-ray free electron laser (FEL) facilities, such as the Linac Coherent Light Source (LCLS) at the SLAC. The laser-based cleaning was applied to two separate areas of the LCLS photocathode on July 4 and July 26, 2011, respectively. Since the cleaning performed, routine operation has shown a slow evolution of both the QE and the transverse emittance, with a significant improvement of both over 2-3 weeks. Currently, the LCLS photocathode QE is constant at about 1.2·10-4 with a normalized injector emittance of about 0.3 μm for a 150-pC bunch charge. The laser cleaning technique becomes a viable tool to revive the LCLS photocathode. We present these observations of the QE and emittance evolution after laser-based cleaning of the LCLS photocathode,and the thermal emittance for different QE.