MC5: Beam Dynamics and EM Fields
D01 Beam Optics - Lattices, Correction Schemes, Transport
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WEVIR01
Use of Reverse Bending Magnets in MBA Lattices  
 
  • A. Streun
    PSI, Villigen PSI, Switzerland
 
  Including reverse bending magnets further reduces the equilibrium emittance of multi-bend achromat (MBA) lattices through decoupling of dispersion and horizontal beta function. This coupling is a shortcoming of the classical theoretical minimum emittance (TME) cell preventing it from reaching lowest emittance at realistic, moderate focusing conditions. Rather small deflection angles of the reverse bends, in the order of 10% of the unit cell bending angle, are usually sufficient, and realized through down-feed by displacing the horizontally focusing quadrupoles of the unit cell by a small amount towards the storage ring inside. Reverse bends are indispensable in particular to enable emittance reduction from dipoles with longitudinal field variation, since these require very small dispersion at the central region of highest field strength. In past decades reverse bends were employed occasionally for isochronous lattices or to enhance damping. Now they are becoming an integral component of low emittance MBA lattices.  
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WEVIR03 Microbunch Rotation as an Outcoupling Mechanism for Cavity-based X-Ray Free Electron Lasers 35
 
  • R.A. Margraf, Z. Huang
    Stanford University, Stanford, California, USA
  • Z. Huang, J.P. MacArthur, G. Marcus
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Electron bunches in an undulator develop periodic density fluctuations, or microbunches, which enable the exponential gain of power in an X-ray free-electron laser (XFEL). For certain applications, one would like to preserve this microbunching structure of the electron bunch as it experiences a dipole kick which bends its trajectory. This process, called microbunch rotation, rotates the microbunches and aligns them perpendicular to the new direction of electron travel. Microbunch rotation was demonstrated experimentally by MacArthur et al. with soft x-rays* and additional unpublished data demonstrated microbunch rotation with hard x-rays. Further investigations into the magnetic lattice used to rotate these microbunches showed that microbunches can be rotated using an achromatic lattice with a small R56, connecting this technique to earlier studies of achromatic bends. Here, we propose and study a practical way to rotate Angstrom-level microbunching as an out-coupling mechanism for the Optical Cavity-Based X-ray FEL (CBXFEL) project at SLAC.
*J. P. MacArthur, A. A. Lutman, J. Krzywinski, and Z. Huang, "Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam", Physical Review X, vol. 8, no. 4, Nov. 2018.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2020-WEVIR03  
About • paper received ※ 01 June 2020       paper accepted ※ 12 June 2020       issue date ※ 11 August 2020  
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WEVIR04 On-Axis Beam Accumulation Based on a Triple-Frequency RF System 40
 
  • G. Xu, S.C. Jiang
    IHEP, Beijing, People’s Republic of China
 
  Considering the incompatible off-axis injection scheme on the newly constructed light sources, we have proposed a new on-axis accumulation scheme based on the so-called triple-frequency RF system [1]. By means of additional second harmonic cavities, the original static longitudinal acceptance will be lengthened, which will provide the sufficient time to raise a full-strength kicker pulse. Through imposing the specific restriction on the RF parameters, the final bunch length can also be stretched to satisfy the functions of the conventional bunch lengthening system. In this paper, we will move on to explain how to build this complex triple-frequency RF system, and present the relevant simulation works.
[1] S.C. Jiang, G. Xu, On-axis injection scheme based on a triplefrequency rf system for diffraction-limited storage rings. Phys.
Rev. ST Accel. Beams 21, 110701 (2018).
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2020-WEVIR04  
About • paper received ※ 26 May 2020       paper accepted ※ 14 June 2020       issue date ※ 25 June 2020  
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WEVIR06 Hollow Electron Beams in a Photoinjector 49
 
  • A. Halavanau, Y. Ding, C.E. Mayes
    SLAC, Menlo Park, California, USA
  • S. Baturin, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • P. Piot
    ANL, Lemont, Illinois, USA
 
  Photoinjectors have demonstrated the capability of electron beam transverse tailoring, enabled by the microlens array (MLA) setup. For instance, electron beams, transversely segmented into periodic beamlet formations, were successfully produced in several experiments at Argonne Wakefield Accelerator (AWA). In this proceeding, we discuss necessary steps to demonstrate the hollow electron beam generation, with an arbitrary diameter and width with the MLA. We also present beam dynamics simulations and highlight key features of the hollow beam transport in LCLS copper linac.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2020-WEVIR06  
About • paper received ※ 01 June 2020       paper accepted ※ 12 June 2020       issue date ※ 27 October 2020  
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WEVIR07
Mitigation of Microbunching Instability for Improved FEL Spectral Brightness  
 
  • S. Di Mitri
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
 
  Advances in electron beam optics control for suppression of the microbunching instability in high brightness linacs. Experimental demonstrations of the instability suppression confirm the validity of the theoretical model, and promise simple and robust schemes for improvement of the spectral brightness at x-ray FELs.  
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