Author: Marinelli, A.
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MOPOW040 High Efficiency, High Brightness X-ray Free Electron Lasers via Fresh Bunch Self-Seeding 805
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • M.W. Guetg, A.A. Lutman, A. Marinelli, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  High efficiency, terawatt peak power X-ray Free Electron Lasers are a promising tool for enabling single molecule imaging and nonlinear science using X-rays. Increasing the efficiency of XFELs while achieving good longitudinal coherence can be achieved via self-seeding and undulator tapering. The efficiency of self-seeded XFELs is limited by two factors: the ratio of seed power to beam energy spread and the ratio of seed power to shot noise power. We present a method to overcome these limitations by producing a strong X-ray seed and amplifying it with a small energy spread beam. This is achieved by selectively suppressing lasing for part of the bunch in the SASE section. In this manner we can saturate with the seeding electrons and amplify the strong seed with 'fresh' electrons downstream of the monochromator. Simulations of this scenario are presented for two systems, an optimal superconducting undulator design and the LCLS. In the case of the LCLS we examine how betatron oscillations leading to selective suppression are induced by using the transverse wakefield of a parallel plate dechirper. We also discuss extending the selective suppression scheme to chirped electron bunches.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOW040  
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TUZA02 Twin-bunch Two-colour FEL at LCLS 1032
  • A. Marinelli, R.N. Coffee, F.-J. Decker, Y. Ding, R.C. Field, S. Gilevich, Z. Huang, D. Kharakh, H. Loos, A.A. Lutman, T.J. Maxwell, J.L. Turner, S. Vetter
    SLAC, Menlo Park, California, USA
  Twin electron bunches have been the subject of much investigation at the Linac Coherent Light Source, due to their many applications to X-ray free-electron lasers (X-FEL). Twin bunches are trains of two electron bunches that are accelerated and compressed within the same accelerating RF period. At LCLS, these bunches are used in the downstream FEL undulator to generate two X-ray pulses of different energies for pump/probe applications or de novo phase determination of protein crystals. The spectral and temporal shaping of the two bunches requires exquisite control of the compression system to vary the main parameters of the system in a controlled way (peak current, temporal delay and energy separation). I will discuss recent experimental and theoretical results on this subject. In particular I will focus on the demonstration of mJ-level two-color X-ray pulses using twin bunches, as well as the temporal and spectral control of this new mode of operation. Finally, I will discuss our experience with user experiments as well as our future directions of investigation.  
slides icon Slides TUZA02 [5.738 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUZA02  
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TUOCA01 LCLS Bunch Compressor Configuration Study for Soft X-ray Operation 1037
  • S. Li, Y. Ding, Z. Huang, A. Marinelli, T.J. Maxwell, D.F. Ratner, F. Zhou
    SLAC, Menlo Park, California, USA
  • C. Behrens
    DESY, Hamburg, Germany
  The microbunching instability (MBI) is a well-known problem for high brightness electron beams and has been observed at accelerator facilities around the world. Free-electron lasers (FELs) are particularly susceptible to MBI, which can distort the longitudinal phase space and increase the beam's slice energy spread (SES). Past studies of MBI at the Linac Coherent Light Source (LCLS) relied on optical transition radiation to infer the existence of microbunching. With the development of the x-band transverse deflecting cavity (XTCAV), we can for the first time directly image the longitudinal phase space at the end of the accelerator and complete a comprehensive study of MBI, revealing both detailed MBI behavior as well as insights into mitigation schemes [1]. The fine time resolution of the XTCAV also provides the first LCLS measurements of the final SES, a critical parameter for many advanced FEL schemes. Detailed MBI and SES measurements can aid in understanding MBI mechanisms, benchmarking simulation codes, and designing future high-brightness accelerators.  
slides icon Slides TUOCA01 [4.436 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOCA01  
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TUPOW017 Twin Bunches at the FACET-II 1778
  • Z. Zhang
    TUB, Beijing, People's Republic of China
  • M.J. Hogan, Z. Huang, A. Marinelli
    SLAC, Menlo Park, California, USA
  Twin electron bunches, generated, accelerated and compressed in the same acceleration bucket, have attracted a lot of interest in the free-electron lasers and wakefield acceleration. The recent successful experiment at the LCLS used twin bunches to generate two-color two x-ray pulses with tunable time delay and energy separation. In this note, we apply the twin bunches to the plasma wakefield acceleration. Numerical simulations show that based on the beamline of the FACET-II, we can generate high-intensity two electron bunches with time delay from  ∼ 100 fs to picoseconds, which will benefit the control of high-gradient witness bunch acceleration in a plasma.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOW017  
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