Author: Marcus, G.
Paper Title Page
TUB03
Generating Femtosecond to Sub-Femtosecond X-Rays with a Modulated Chirped Beam in a Self-Seeded FEL  
 
  • S. Huang
    PKU, Beijing, People's Republic of China
  • Y. Ding, Z. Huang, G. Marcus
    SLAC, Menlo Park, California, USA
 
  We propose a scheme to generate ultrashort soft X-ray pulses in a self-seeded FEL. In this scheme, a time-energy chirped electron beam is first modulated by an infrared laser with the wavelength of a few microns. It is then used to drive the self-seeded FEL. During the selfseeding section, besides the regular functions of the self-seeding chicane and the grating monochromator, the chicane is also used to shear the previously modulated electron beam, leading to current spikes in the temporal profile. Since the seeded pulse length from the chirped beam is much shorter than the electron bunch, we can choose to align the seed with one of the current spikes for generating a single short pulse. Simulations indicate that soft X-ray pulses with a fwhm of less than 1 fs and peak power at 10 GW level can be obtained.  
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TUP007 High Fidelity Start-to-end Numerical Particle Simulations and Performance Studies for LCLS-II 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
 
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TUP023 A Modified Self-Seeded X-ray FEL Scheme Towards Shorter Wavelengths 409
 
  • L. Zeng, J.E. Chen, S. Huang, K.X. Liu, W. Qin
    PKU, Beijing, People's Republic of China
  • Y. Ding, Z. Huang, G. Marcus
    SLAC, Menlo Park, California, USA
 
  We present a modified self-seeded FEL scheme for harmonic generation. Different from classical HGHG scheme whose seed laser is a conventional laser with longer wavelength, this scheme first uses a regular self-seeding monochromator to generate a seed laser, followed by a HGHG configuration to produce shorter-wavelength radiations. As an example, we perform start-to-end simulations to demonstrate the second and third harmonic FELs from a soft x-ray self-seeding case at the fundumental wavelength of 1.72 nm. The harmonic performance results will be discussed.  
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WEB03
Progress Towards an X-ray FEL Oscillator  
 
  • K.-J. Kim, T. Kolodziej, R.R. Lindberg, D. Shu, Yu. Shvyd'ko, S. Stoupin
    ANL, Argonne, Ilinois, USA
  • J. Arthur, Y. Ding, W.M. Fawley, J.C. Frisch, J.B. Hastings, Z. Huang, J. Krzywinski, G. Marcus, T.J. Maxwell
    SLAC, Menlo Park, California, USA
 
  Funding: Work at ANL supported under US Department of Energy contract DE-AC02-76SF00515 and at SLAC by the U.S. Department of Energy, Office of Science, under Contract No. DE-ACO2-O6CH11357
Issues and progress in R&D toward realizing an X-ray FEL oscillator will be discussed, including electron injector optimization, X-ray power density evolution on Bragg crystals throughout the lasing process, experimental efforts for testing radiation damage, evaluating the performance of compound refractive lenses (CRLs) as the focusing elements, and the basic considerations for mechanical layout. These will be discussed in the context of a concrete implementation scheme [*] using the 4 GeV superconducting linac to be constructed at the LCLS-II. Time-dependent simulations of harmonic XFELO performance is discussed in another contribution to this conference by Zemella, et al.
[*] T. J. Maxwell et al., Feasibility study for an X-ray free electron laser oscillator, IPAC 2015, Richmond, Virginia, USA
 
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WEP025 Effect of Microbunching on Seeding Schemes for LCLS-II 639
 
  • G. Penn, J. Qiang
    LBNL, Berkeley, California, USA
  • P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.
 
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WEP052 Studies of LCLS FEL Divergence 681
 
  • J.L. Turner, P. Baxevanis, F.-J. Decker, Y. Ding, Z. Huang, J. Krzywinski, H. Loos, G. Marcus, N.P. Norvell
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Simulations show various impacts on x-ray divergence. With the motivation to maximize intensity at the focus, these beam studies were designed to study parameter space and beam qualities impacting divergence, and therefore aperture related clipping and diffraction. With multiple simultaneous users, beam constraints increase, requiring an improving knowledge of the mechanism of impact of changing parameters. These studies have that goal in order to improve beam control.
 
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WEP070 Start-to-End Simulation of the LCLS-II Beam Delivery System with Real Number of Electrons 714
 
  • J. Qiang, C.E. Mitchell, C. F. Papadopoulos, M. Venturini
    LBNL, Berkeley, California, USA
  • Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley
    SLAC, Menlo Park, California, USA
 
  The LCLS-II as a next generation high repetition rate FEL based X-ray light source will enable significant scientific discoveries. In this paper, we report on the progress in the design of the accelerator beam delivery system through start-to-end simulations. We will present simulation results for three cases, 20 pC, 100 pC and 300 pC that are transported through the hard X-ray line and the soft X-ray line for FEL radiation.  
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WEP075 Femtosecond X-ray Pulse Generation with an Energy Chirped Electron Beam 722
 
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • Y. Ding, Z. Huang, A.A. Lutman, G. Marcus, A. Marinelli, C. Pellegrini
    SLAC, Menlo Park, California, USA
 
  We study the generation of short (sub 10 fs) pulses in the X-ray spectral region using an energy chirped electron beam in a Self Amplified Spontaneous Emission Free Electron Laser (SASE FEL) and a self-seeding monochromator [1]-[2]. The monochromator filters a small bandwidth, short duration pulse from the frequency chirped SASE spectrum. This pulse is used to seed a small fraction of the long chirped beam, hence a short pulse with narrow bandwidth is amplified in the following undulators. We present start-to-end simulation results for LCLS operating in the soft X-ray self-seeded mode with an energy chirp of 1% over 30 fs and a bunch charge of 150pC. We demonstrate the potential to generate ~5 fs pulses with a bandwidth ~0.3eV. We also assess the possibility of further shortening the pulse by utilizing one more chicane after the self-seeding stage and shifting the radiation pulse to a 'fresh' part of the electron beam. Experimental study on this short pulse seeding mode has been planned at the LCLS.  
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WEP084 Microbunching-Instability-Induced Sidebands in a Seeded Free-Electron Laser 741
 
  • Z. Zhang
    TUB, Beijing, People's Republic of China
  • Y. Ding, W.M. Fawley, Z. Huang, J. Krzywinski, A.A. Lutman, G. Marcus, A. Marinelli, D.F. Ratner
    SLAC, Menlo Park, California, USA
 
  The measured, self-seeded soft X-ray radiation spectrum corresponding to multiple effective undulator lengths of the LCLS exhibits a pedestal-like distribution around the seeded frequency. In the absence of a post-undulator monochromator, this contamination limits the spectral purity and may seriously degrade certain user applications. In general for either externally- or self-seeded FELs, such pedestals may originate with any time-varying property of the electron beam that can modulate the complex gain function. In this paper we specifically focus on the contributions of electron beam microbunching prior to the undulator. We show that both energy and density modulations can induce sidebands in a seeded FEL configuration. Analytic FEL theory and numerical simulations are used to analyze the sideband content relative to the amplified seeded signal, and to compare with experimental results.  
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