THB —  Electron-Beam Dynamics   (24-Aug-17   10:30—12:00)
Chair: S.J. Russell, LANL, Los Alamos, New Mexico, USA
Paper Title Page
Beam Dynamics Optimization in High-Brightness Electron Injectors  
  • C.E. Mitchell, J. Qiang, F. Sannibale
    LBNL, Berkeley, California, USA
  Funding: This work was supported by the Office of Science of the U.S. Department of Energy under Contract Numbers DE-AC02-76SF00515, DE-AC02-05CH11231, and the LCLS-II project.
The next generation of X-ray free electron lasers requires beams with increasingly high peak current and low emittances at ~MHz repetition rates, placing increased demands on the performance of high-brightness electron photoinjector sources. To explore the high-dimensional parameter space associated with photoinjector design, global multiobjective optimization methods based on genetic algorithms or similar tools are playing an increasingly critical role. We review our experience with applying these tools both to understand and to optimize simulated injector beam performance for projects such as LCLS-II (at SLAC) and the Advanced Photoinjector EXperiment (at LBNL), including both challenges and successes.
slides icon Slides THB01 [13.103 MB]  
THB02 Non-Standard Use of Laser Heater for FEL Control and THz Generation 1
  • E. Allaria, L. Badano, M.B. Danailov, A.A. Demidovich, S. Di Mitri, D. Gauthier, L. Giannessi, G. Penco, E. Roussel, P. Sigalotti, S. Spampinati, M. Trovò, M. Veronese
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  The laser heater system is currently used at various FEL facilities for an accurate control of the electron beam energy spread in order to suppress the micro-bunching instabilities that can develop in high brightness electron beams. More recently, studies and experiments have shown that laser-electron interaction developing in the laser heater can open new possibilities for tailoring the electron beam properties to meet special requirements. A suitable time-shaping of the laser heater pulse opened the door to the generation of (tens of) femtosecond-long FEL pulses. Using standard laser techniques it is also possible to imprint onto the electron bunch, energy and density modulations in the THz frequency range that, properly sustained through the accelerator, can be exploited for generation of coherent THz radiation at GeV beam energies. Such recent results at the FERMI FEL are here reported, together with near future plans.  
High-Power, Narrow-Bandwidth THz Generation Using Laser-Electron Interaction in a Compact Accelerator  
  • Z. Huang, G. Marcus
    SLAC, Menlo Park, California, USA
  • K. Kan
    ISIR, Osaka, Japan
  • Z. Zhang
    TUB, Beijing, People's Republic of China
  We propose a method based on the slice energy-spread modulation to generate strong subpicosecond density bunching in high-intensity relativistic electron beams.* A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. In this paper, we study this method in a compact accelerator with electron energy on the order of 50 MeV. To interact with an infra-red laser, the modulation undulator is resonant with the laser at a harmonic frequency. We show the flexibility of this method to generate powerful, narrow-bandwidth radiation between 1-20 THz. The THz radiation can be generated at a very high-repetition rate that matches a high-repetition rate X-ray free-electron laser for pump-probe studies of novel materials.
* Z. Zhang et al., Phys. Rev. Accel. Beams 20, 050701 (2017).
Two-Color Beam Generation via Wakefield Excitation  
  • S. Bettoni, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  Several beam manipulation methods have been studied and experimentally tested to generate two-color photon beams in free electron laser facilities to accommodate the user requests. We propose to use the interaction of the beam with an oscillating longitudinal wakefield source to obtain a suitable electron beam structure. The bunch generates two sub-pulses with different energies and delays in time passing through a magnetic chicane after its longitudinal phase space has been modulated by the wakefield source. According to this approach, the power of the emitted radiation is not degraded compared to the monochromatic beam, and the set-up in the machine is quite simple because the bunch is manipulated only in the high energy section where the beam is more rigid. We present the design applied to SwissFEL. We identified the parameters and the corresponding range of tunability of the time and energy separation among the two sub-bunches.
Reference: Phys. Rev. Accel. Beams 19, 050702 (2016)
Ion Effects in LCLS and LCLS-II  
  • T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  Funding: This work supported in part by the Department of Energy Contract DE-AC02-76-SF00515.
The effect of ions are evaluated in LCLS and LCLS-II. X-ray FEL's require high-brightness beams, that generate very high internal beam fields which can potentially lead to tunneling ionization. The FEL performance is sensitive to betatron mismatches which can arise from the focusing due to ions. In LCLS, both collisional and tunneling ionization may have an impact on single electron bunches while LCLS-II will have the additional complication of trapped ions in the MHz-rate multi-bunch trains. Analytic and simulation results for the LCLS and LCLS-II are presented and scalings are described to estimate the effects in other X-ray FEL's.