Author: Raubenheimer, T.O.
Paper Title Page
MOP050
 The Collimation System for LCLS-II*  
 
  • J.J. Welch, E. Marín, T.O. Raubenheimer, M. Santana-Leitner, G.R. White
    SLAC, Menlo Park, California, USA
  • C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: * Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.
Minimizing beam loss is particularly important for LCLS-II because of very high average power beams, radiation sensitive undulators, and the high cost of adding shielding to existing accelerator enclosures. For example, for acceptable undulator magnet lifetime, dark current originating at the cathode must be attenuated by approximately a factor of 10-7 in a single pass before it reaches the undulator. Multi-stage, high-efficiency collimation is necessary. The system is described in this paper. A model of beam halo and dark current is developed that includes sources due to Touschek, intra-beam, and beam-gas scattering, as well as field emission from superconducting cavities, photo-emission from stray light on the cathode, and cathode field emission. The location and gap of the collimators is optimized using tracking analysis and other tools developed and validated at Cornell. Collimator efficiency is estimated by tracking secondaries using a modified version of Lucretia which call GEANT4. Finally collimator jaw design is optimized to produce a minimum leakage using FLUKA. These topics are discussed in this paper. 		 
 
MOP054 Harmonic Lasing Options for LCLS-II 148
 
  • G. Marcus, Y. Ding, Z. Huang, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • G. Penn
    LBNL, Berkeley, California, USA
  
  Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline. Furthermore, in comparison to nonlinear harmonics, harmonic lasing can provide a beam that is more intense, stable, and narrow-band. This paper explores the application of the harmonic lasing concept at LCLS-II using various combinations of phase shifters and attenuators. In addition, a scheme by which individual undulator modules are tuned to amplify either the third or fifth harmonic in different configurations is presented in detail.  
 
MOP075 Laser Seeding Schemes for Soft X-rays at LCLS-II 223
 
  • G. Penn
    LBNL, Berkeley, California, USA
  • P. Emma, E. Hemsing, G. Marcus, T.O. Raubenheimer, L. Wang
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515.
The initial design for LCLS-II incorporates both SASE and self-seeded configurations. Increased stability and/or coherence than is possible with either configuration may be provided by seeding with external lasers followed by one or more stages of harmonic generation, especially in the soft x-ray regime. External seeding also allows for increased flexibility, for example the ability to quickly vary the pulse duration. Studies of schemes based on high-gain harmonic generation and echo-enabled harmonic generation are presented, including realistic electron distributions based on tracking through the injector and linac. 		 
 
TUP032 FEL Simulation and Performance Studies for LCLS-II 456
 
  • G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang, J. Wu
    SLAC, Menlo Park, California, USA
  
  The design and performance of the LCLS-II free-electron laser beamlines are presented using start-to-end numerical particle simulations. The particular beamline geometries were chosen to cover a large photon energy tuning range with x-ray pulse length and bandwidth flexibility. Results for self-amplified spontaneous emission and self-seeded operational modes are described in detail for both hard and soft x-ray beamlines in the baseline design.  
 
WEB01
 The LCLS-II, a New FEL Facility at SLAC  
 
  • T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  
  Funding: This work supported under DOE Contract DE-AC02-76SF00515.
The LCLS-II is a new FEL facility at SLAC based on the existing LCLS-I and a new CW superconducting RF linac. Using two undulators, the LCLS-II will generate X-rays between 0.2 and 5 keV at rates up to 1 MHz and X-rays as high as 25 keV at 120 Hz. The SCRF linac will have an rf frequency of 1.3 GHz and is based heavily on the technology developed for the EuFEL and the International Linear Collider. The facility is being constructed by a collaboration consisting of SLAC, LBNL, Jefferson Lab, Fermilab and Cornell University. This talk will describe the LCLS-II layout and expected performance along with the major challenges. 		 
slides icon Slides WEB01 [20.316 MB]  
 
THB04 Electron Beam Diagnostics and Feedback for the LCLS-II 666
 
  • J.C. Frisch, P. Emma, A.S. Fisher, P. Krejcik, H. Loos, T.J. Maxwell, T.O. Raubenheimer, S.R. Smith
    SLAC, Menlo Park, California, USA
  
  Funding: work supported by DOE contract DE-AC02-76-SF00515
The LCLSII is a CW superconducting accelerator driven, hard and soft X-ray Free Electron Laser which is planned to be constructed at SLAC. It will operate with a variety of beam modes from single shot to approximately 1 MHz CW at bunch charges from 10pc to 300pC with average beam powers up to 1.2 MW. A variety of types of beam instrumentation will be used, including stripline and cavity BPMS, fluorescent and OTR based beam profile monitors, fast wire scanners and transverse deflection cavities. The beam diagnostics system is designed to allow tuning and continuous measurement of beam parameters, and to provide signals for fast beam feedbacks. 		 
slides icon Slides THB04 [1.501 MB]  
 
THP025 Linear Accelerator Design for the LCLS-II FEL Facility 743
 
  • P. Emma, J.C. Frisch, Z. Huang, H. Loos, A. Marinelli, T.J. Maxwell, Y. Nosochkov, T.O. Raubenheimer, L. Wang, J.J. Welch, M. Woodley
    SLAC, Menlo Park, California, USA
  • J. Qiang, M. Venturini
    LBNL, Berkeley, California, USA
  • A. Saini, N. Solyak
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
The LCLS-II is an FEL facility proposed in response to the July 2013 BESAC advisory committee, which recommended the construction of a new FEL light source with a high-repetition rate and a broad photon energy range from 0.2 keV to at least 5 keV. A new CW 4-GeV electron linac is being designed to meet this need, using a superconducting (SC) L-band (1.3 GHz) linear accelerator capable of operating with a continuous bunch repetition rate up to 1 MHz at ~16 MV/m. This new 700-m linac is to be built at SLAC in the existing tunnel, making use of existing facilities and providing two separate FELs, preserving the operation of the existing FEL, which can be fed from either the existing copper or the new SC linac. We briefly describe the acceleration, bunch compression, beam transport, beam switching, and electron beam diagnostics. The high-power and low-level RF, and cryogenic systems are described elsewhere. 		 
poster icon Poster THP025 [0.627 MB]  
 
THP027 LCLS-II Bunch Compressor Study: 5-Bend Chicane 755
 
  • D. Khan, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  
  In this paper, we present a potential design for a bunch compressor consisting of 5 bend magnets which is designed to compensate the transverse emittance growth due to Coherent Synchrotron Radiation (CSR). A specific implementation for the second bunch compressor in the LCLS-II is considered. The design has been optimized using the particle tracking code, ELEGANT. Comparisons of the 5-bend chicane’s performance with that of a symmetric 4-bend chicane are shown for various compression ratios and bunch charges. Additionally, a one-dimensional, longitudinal CSR model for the 5-bend design is developed and its accuracy compared against ELEGANT simulations.  
poster icon Poster THP027 [0.881 MB]  
 
THP029 MOGA OPTIMIZATION DESIGN OF LCLS-II LINAC CONFIGURATIONS 763
 
  • L. Wang, P. Emma, Y. Nosochkov, T.O. Raubenheimer, M. Woodley, F. Zhou
    SLAC, Menlo Park, California, USA
  • C. F. Papadopoulos, J. Qiang, M. Venturini
    LBNL, Berkeley, California, USA
  
  The Linac Coherent Light Source II (LCLS-II) will generate extremely intense X-ray flashes to be used by researchers from all over the world. The FEL is powered by 4 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. LCLS-II will provide large flexibility in bunch charge and peak current. Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters including bunch compressors system, linearizer, de-chirper, RF phase and laser heater, in order to minimize the energy spread, collective effects and emittance. The strong resistive wall wake field along the 2km bypass beam line acts as a natural de-chirper. This paper summarizes the optimization of various configurations.  
poster icon Poster THP029 [0.702 MB]  
 
THP042 The LCLS-II Injector Design 815
 
  • J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, California, USA
  • A. Lunin, N. Solyak, A. Vivoli
    Fermilab, Batavia, Illinois, USA
  
  The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.  
 
THP057 Longitudinal and Transverse Optimization for a High Repetition Rate Injector 864
 
  • C. F. Papadopoulos, D. Filippetto, R. Huang, G.J. Portmann, H.J. Qian, F. Sannibale, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, California, USA
  • A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • A. Brachmann, D. Dowell, P. Emma, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • A. Vivoli
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The injector is the low energy part of a linac, where space charge and kinematic effects may affect the electron beam quality significantly, and in the case of single pass systems determines the brightness in the downstream components. Following the increasing demand for high repetition rate user facilities, the VHF-gun, a normal conducting, high repetition rate (1 MHz) RF gun operating at 186 MHz has been constructed at LBNL within the APEX project and is under operation. In the current paper, we report on the status of the beam dynamics studies. For this, a multi-objected approach is used, where both the transverse and the longitudinal phase space quality is optimized, as quantified by the transverse emittance and the bunch length and energy spread respectively. We also report on different bunch charge operating modes.