Author: Huang, D.
Paper Title Page
TUPEA035 Plasma Effect in the Longitudinal Space Charge Induced Microbunching Instability 1220
  • D. Huang, Q. Gu
    SINAP, Shanghai, People's Republic of China
  • K.Y. Ng
    Fermilab, Batavia, USA
  Funding: National Science Foundation of China (NSFC), grant No. 11275253, and US DOE, contract DE-FG02-92ER40747.
In many cases, the longitudinal space charge (LSC) is a dominant factor to bring in the microbunching instability in the LINAC of a Free-Electron-Laser (FEL) facility. The current model of LSC impedance* derived from the fundamental electromagnetic theor** is widely used to explain the physics of the LSC-induced microbunching instability***. However, in the case of highly bright electron beams, the plasma effect starts to play a role. In this paper, the basic model of the LSC impedance including the plasma effect is built up by solving the Vlasov and Poisson equations in 6 dimensional phase space, and the investigation is done to study the modification to the gain of the instability based on the model. The solutions indicate that the gain does not only depend on the spatial information of the beam, but also on the velocity (momentum) and time information. The comparison of the gains of the microbunching instability in the LINAC of Shanghai soft X-ray Free Electron Laser Facility (SXFEL) computed by various methods is also given and the discrepancy is illustrated.
* Marco Venturini, Phys. Rev. ST Accel. Beams 11, 034401 (2008)
** J. D. Jackson, Classical Electrodynamics (Wiley, 1999)
*** Z. Huang, et. al., Phys, Rev. ST Accel. Beams 7, 074401 (2004)
TUPWO030 Beam-based Alignment Simulation on Flash-I Undulator 1940
  • D. Gu, Q. Gu, D. Huang, M. Zhang, M.H. Zhao
    SINAP, Shanghai, People's Republic of China
  • M. Vogt, N.J. Walker
    DESY, Hamburg, Germany
  In order to ensure the SASE process can take place in the whole FLASH-I undulator section, a straight beam trajectory is mandatory which can only be achieved through beam-based alignment (BBA) method based on electron energy variations. In this paper, a detailed result of simulation is presented which demonstrate that the alignment can be achieved within accuracy of a few 10 μm after several iterations. The influence of Quadrupole and BPM offsets, magnet-mover calibration errors, quadrupole gradient errors are also discussed.