Keyword: emittance
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MOP028 Extraction of the Longitudinal Profile of the Transverse Emittance From Single-Shot RF Deflector Measurements at sFLASH ion, electron, FEL, laser 98
 
  • T. Plath, Ph. Amstutz, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • J. Bödewadt, N. Ekanayake, T. Laarmann, C. Lechner
    DESY, Hamburg, Germany
  • S. Khan
    DELTA, Dortmund, Germany
 
  The gain length of the free-electron laser (FEL) process strongly depends on the slice energy spread, slice emittance, and current of the electron bunch. At an FEL with only moderately compressed electron bunches, the slice energy spread is mainly determined by the compression process. In this regime, single-shot measurements using a transverse deflecting rf cavity enable the extraction of the longitudinal profile of the transverse emittance. At the free-electron laser FLASH at DESY, this technique was used to determine the slice properties of the electron bunch set up for seeded operation in the sFLASH experiment. Thereby, the performance of the seeded FEL process as a function of laser-electron timing can be predicted from these slice properties with the semi-analytical Ming-Xie model where only confined fractions of the electron bunch are stimulated to lase. The prediction is well in line with the FEL peak power observed during an experimental laser-electron timing scan. The power profiles of the FEL pulses were reconstructed from the longitudinal phase-space measurements of the seeded electron bunch that was measured with the rf deflector.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP028  
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TUB03 ASU Compact XFEL ion, FEL, electron, laser 225
 
  • W.S. Graves, J.P.J. Chen, P. Fromme, M.R. Holl, R. Kirian, L.E. Malin, K.E. Schmidt, J. Spence, M. Underhill, U. Weierstall, N.A. Zatsepin, C. Zhang
    Arizona State University, Tempe, USA
  • K.-H. Hong, D.E. Moncton
    MIT, Cambridge, Massachusetts, USA
  • C. Limborg-Deprey, E.A. Nanni
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by NSF Accelerator Science award 1632780, NSF BioXFEL STC award 1231306 and DOE contract DE-AC02-76SF00515.
ASU is pursuing a concept for a compact x-ray FEL (CXFEL) that uses nanopatterning of the electron beam via electron diffraction and emittance exchange to enable fully coherent x-ray output from electron beams with an energy of a few tens of MeV. This low energy is enabled by nanobunching and use of a short-pulse laser field as an undulator, resulting in an XFEL with 10 m total length and modest cost. The method of electron bunching is deterministic and flexible, rather than dependent on SASE amplification, so that the x-ray output is coherent in time and frequency. The phase of the x-ray pulse can be controlled and manipulated with this method so that new opportunities for ultrafast x-ray science are enabled using e.g. attosecond pulses, very narrow linewidths, or extremely precise timing among multiple pulses with different colors. These properties may be transferred to large XFELs through seeding with the CXFEL beam. Construction of the CXFEL accelerator and laboratory are underway, along with initial experiments to demonstrate nanopatterning via electron diffraction. An overview of the methods, project, and new science enabled are presented.
 
slides icon Slides TUB03 [5.933 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUB03  
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TUP009 The Effect of Transverse Space Charge on Beam Evolution and Photon Coherence ion, electron, space-charge, focusing 266
 
  • Q.R. Marksteiner
    LANL, Los Alamos, New Mexico, USA
 
  An electron beam experiences a transverse electric field which tends to act like a defocusing force on the electron beam. This defocusing force will act with different strengths at different locations in the electron beam because the current varies along the beam. A simple, quasi-analytic method is presented to calculate the impact of this force on beam projected emittance. In addition, estimates are made regarding the degree to which this could degrade the transverse coherence of x-rays in an XFEL.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP009  
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TUP027 Cancellation of Coherent Synchrotron Radiation Kicks at LCLS ion, electron, radiation, linac 296
 
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
 
  In this paper, we look at the cancellation of Coherent Synchrotron Radiation (CSR) induced emittance growth using a phase-advance manipulation technique pioneered by R. Hajima, and extended in the Courant-Snyder formalism by S. Di Mitri. Bending systems in a linear accelerator are essential for beam transport and bunch compression. With the ever-growing demands of high-energy, short wavelength free electron laser (FEL) drivers, the CSR effect has emerged to be a detrimental factor in emittance stability. Under linear approximation, it is showed that the CSR driven dispersive kicks in successive bending magnet systems can, with proper balancing of the linac optics, cancel each other to nullify transverse emittance growth. This technique of optics balancing in the constant bunch length regime is the focus of this paper. We will present our findings for the emittance measurements generated in Elegant simulations for the current LCLS-I dogleg system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP027  
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TUP030 An Emittance-Preservation Study of a Five-Bend Chicane for the LCLS-II-HE Beamline ion, electron, FEL, simulation 305
 
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
 
  The Linac Coherent Light Source II (LCLS-II) is an upgrade intended to advance the great success of its predecessor, LCLS-I, to maintain its position at the forefront of X-ray science. The introduction of a niobium-metal superconducting linac for LCLS-II not only increases the repetition rate to the MHz level (from 120 Hz), but also boasts an average brightness many orders higher (~10,000) than that of LCLS-I. Though, these improvements do not come without a price: the peak brightness suffers by a factor of 10, owing its degradation to the impact of Coherent Synchrotron Radiation (CSR) diminishing the peak current of the beam in the second bunch compressor (BC2). In this paper, we discuss the impact of implementing a plug-compatible 5-bend chicane for BC2 on the beam's emittance dilution for a high-energy, low-emittance configuration of LCLS-II (LCLS-II-HE). The results are compared with that of a standard 4-bend chicane under various settings in Elegant and CSRTrack.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP030  
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TUP054 Preparations for Installation of the Double Emittance-Exchange Beamline at the Argonne Wakefield Accelerator Facility ion, wakefield, simulation, experiment 340
 
  • G. Ha
    PAL, Pohang, Republic of Korea
  • M.E. Conde, D.S. Doran, W. Gai, J.G. Power
    ANL, Argonne, Illinois, USA
 
  Funding: This work is supported by Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Preparations to upgrade the single EEX beamline at the Argonne Wakefield Accelerator (AWA) facility to a double EEX beamline are underway. The single EEX beamline recently demonstrated exchange-based longitudinal bunch shaping (LBS) which has numerous applications including high-energy physics linear colliders, x-ray FELs, and intense radiation sources. The exchange-based method can generate arbitrary LBS in the ideal case but has limitations in the real case. The double EEX beamline was proposed as a means to overcome the limitations of single EEX due to transverse jitter and large horizontal emittance. In this paper, we present the current status of beamline design and installation and simulation results for the planned experiments: collinear wakefield acceleration with tailored beams and tunable bunch compression without the double-horn feature.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP054  
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WEA01 European XFEL Injector Commissioning Results ion, FEL, gun, operation 389
 
  • B. Beutner
    DESY, Hamburg, Germany
 
  In the first commissioning phase of the European XFEL SASE FEL driver linac, we demonstrated the design goals for the injector section. These goals include reliable operation of sub-systems and feasible beam parameters like emittance and bunch length of the beam produced by the RF gun. Of particular interest is the operation of long bunch trains with up to 2700 bunches with a 4.5 MHz repetition rate. In this presentation we will provide an overview of our experiences from the injector commissioning run including beam dynamics studies, diagnostics, and system performance.  
slides icon Slides WEA01 [4.633 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEA01  
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WEA02 Model of Photocathode for CW Electron Gun ion, electron, cathode, scattering 394
 
  • P.W. Huang, W.-H. Huang, C.-X. Tang
    TUB, Beijing, People's Republic of China
 
  Most of the proposed CW guns for free electron lasers use semiconductors as the photocathode due to their high quantum efficiency and potentially low thermal emittance. We manage to establish a model to explain the photoemission of semiconductors with incident photon energy above or below the theoretical threshold and derive the expression for quantum efficiency and thermal emittance. For the incident photon energy near or below the threshold of the cathode, things will be subtle and we should be careful to consider the details we used to neglect. The results of quantum efficiency and thermal emittance agree well with the published work. We also focus on the degradation of the semiconductors and propose a model to examine the development of the thermal emittance. We mainly consider the effect brought by the surface reactions with poisoning gases. The variation of quantum efficiency with time is well-consistent with experiment data. We also present the calculated results of thermal emittance, showing a decline with time. Similar results are presented with typical value of electric field in DC gun and RF gun.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEA02  
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WEP006 Preliminary On-Table and Photoelectron Results from the PITZ Quasi-Ellipsoidal Photocathode Laser System ion, laser, cathode, electron 426
 
  • J.D. Good, G. Asova, P. Boonpornprasert, Y. Chen, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, D.M. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, T. Rublack, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
    IAP/RAS, Nizhny Novgorod, Russia
  • I. Hartl, S. Schreiber
    DESY, Hamburg, Germany
  • E. Syresin
    JINR, Dubna, Moscow Region, Russia
 
  The optimization of photoinjectors is crucial for the successful operation of linac-based free electron lasers, and beam dynamics simulations have shown that ellipsoidal photocathode laser pulses result in significantly lower electron beam emittance than that of conventional cylindrical pulses. Therefore, in collaboration with the Institute of Applied Physics (Nizhny Novgorod, Russia) and the Joint Institute of Nuclear Research (Dubna, Russia), a laser system capable of generating quasi-ellipsoidal laser pulses has been developed and installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). The pulse shaping has been realized using the spatial light modulator technique, characterized by cross-correlation and spectrographic measurements, and is demonstrated with electron beam measurements. In this contribution the overall setup, operating principles, and results of first regular electron beam measurements will be presented together with corresponding beam dynamics simulations. Furthermore, the numerous improvements of the simplified re-design currently under construction shall be detailed.  
poster icon Poster WEP006 [1.766 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP006  
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WEP007 Electron Beam Asymmetry Compensation with Gun Quadrupoles at PITZ ion, gun, quadrupole, electron 429
 
  • M. Krasilnikov, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, X. Li, O. Lishilin, G. Loisch, D.M. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan, Q.T. Zhao
    DESY Zeuthen, Zeuthen, Germany
  • G.A. Amatuni, B. Grigoryan
    CANDLE SRI, Yerevan, Armenia
  • G. Asova
    INRNE, Sofia, Bulgaria
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
 
  The electron beam asymmetry observed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) was traced back to multipole kicks in the gun section, namely around the location of the coaxial power coupler and the main solenoid. Several dedicated studies have been performed to quantify the kick location and strength. Based on these studies, two designs of correction quadrupole coils were proposed. The coils were fabricated and tested with an electron beam. The second updated design implies a two quadrupole setup on a frame installed around the gun coaxial coupler close to the main solenoid centre location. Skew and normal quadrupole magnets are powered independently, enabling flexibility in electron beam manipulations. By means of this setup, a more symmetric beam was obtained at several screens. This led also to more equal measured horizontal and vertical phase spaces and to even smaller overall emittance values. Some details of the gun quadrupole designs, magnetic measurements, and results of electron beam measurements including emittance optimization will be reported.  
poster icon Poster WEP007 [1.997 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP007  
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WEP008 Beam Brightness Improvement by Ellipsoidal Laser Shaping for CW Photoinjectors ion, gun, laser, cathode 432
 
  • H.J. Qian, M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  High-brightness photoinjectors operating in a continuous wave (CW) mode are required for many advanced applications, such as CW X-ray FEL, ERL light source, electron coolers for hadron beams and electron-ion colliders and so on. Now, three types of CW electron guns are available: DC gun, SRF gun and normal conducting RF gun, which are under intense development in different institutes based on local expertise and application demands. Compared to pulsed guns, both beam energy and brightness from CW guns are compromised due to a lower acceleration gradient. Flattop laser shaping has been applied in both pulsed and CW guns to improve beam emittance. In this paper, ellipsoidal laser shaping is applied in CW photoinjectors to improve beam brightness, and preliminary ASTRA simulations are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP008  
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WEP025 Emittance Measurements from SRF Gun in CeC Accelerator ion, gun, solenoid, cathode 470
 
  • K. Mihara
    Stony Brook University, Stony Brook, USA
  • Y.C. Jing, V. Litvinenko, I. Pinayev, G. Wang
    BNL, Upton, Long Island, New York, USA
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
 
  Funding: DoE NP office, grant DE-FOA-0000632 and NSF grant PHY-1415252
In this paper we report on extremely good performance of 113 MHz SRF CW gun. This gun is a part of the system built to test coherent electron cooling concept and was aimed to generate trains of 78 kHz pulses with large 1 nC to 5 nC charge per bunch. While it was not built for attaining record low emittances, the machine can achieve very low normalized emittances ~ 0.3 mm mrad with 0.5 nC charge per bunch using CsK2Sb photocathode. In addition to excellent performance, this gun provides for very long lifetime of these high QE photocathodes, with a typical using time of 2 months.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP025  
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WEP043 Tune-Up Simulations for LCLS-II ion, simulation, quadrupole, linac 507
 
  • M.W. Guetg, P. Emma
    SLAC, Menlo Park, California, USA
 
  The planned superconducting LCLS-II linac poses new operational constraints with respect to the existing copper linac currently operated for LCLS. We present the results of exhaustive accelerator simulations, including realistic machine errors and exploring beam tune-up strategies. The results are used to pin-point the required beam diagnostics and the key correction elements. Specifically, these simulations concentrate on longitudinal and transverse beam matching as well as orbit and dispersion control through the new linac and up to the hard x-ray FEL. Dispersion control is achieved by a novel method presented within this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP043  
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