WEA —  Electron Guns, RF Lasers, Cathodes   (23-Aug-17   08:30—10:00)
Chair: F. Stephan, DESY Zeuthen, Zeuthen, Germany
Paper Title Page
European XFEL Injector Commissioning Results  
  • B. Beutner
    DESY, Hamburg, Germany
  In the first commissioning phase of the European XFEL SASE FEL driver linac, we demonstrated the design goals for the injector section. These goals include reliable operation of sub-systems and feasible beam parameters like emittance and bunch length of the beam produced by the RF gun. Of particular interest is the operation of long bunch trains with up to 2700 bunches with a 4.5 MHz repetition rate. In this presentation we will provide an overview of our experiences from the injector commissioning run including beam dynamics studies, diagnostics, and system performance.  
slides icon Slides WEA01 [4.628 MB]  
WEA02 Model of Photocathode for CW Electron Gun 1
  • P.W. Huang, W.-H. Huang, C.-X. Tang
    TUB, Beijing, People's Republic of China
  Most of the proposed CW guns for free electron lasers use semiconductors as the photocathode due to their high quantum efficiency and potentially low thermal emittance. We manage to establish a model to explain the photoemission of semiconductors with incident photon energy above or below the theoretical threshold and derive the expression for quantum efficiency and thermal emittance. For the incident photon energy near or below the threshold of the cathode, things will be subtle and we should be careful to consider the details we used to neglect. The results of quantum efficiency and thermal emittance agree well with the published work. We also focus on the degradation of the semiconductors and propose a model to examine the development of the thermal emittance. We mainly consider the effect brought by the surface reactions with poisoning gases. The variation of quantum efficiency with time is well-consistent with experiment data. We also present the calculated results of thermal emittance, showing a decline with time. Similar results are presented with typical value of electric field in DC gun and RF gun.  
Simulation Optimization of DC-SRF Photoinjector for Low-Emittance Electron Beam Generation  
  • K.X. Liu, J.E. Chen, W. Cheng, L.W. Feng, J.K. Hao, S. Huang, L. Lin, W. Qin, S.W. Quan, F. Wang, H.M. Xie, F. Zhu
    PKU, Beijing, People's Republic of China
  A DC and superconducting rf (SRF) combined photoinjector, DC-SRF photoinjector, has been developed at Peking University to generate high repetition-rate electron bunches. At present stable operation of the DC-SRF photoinjector has been realized and the electron beam has been delivered to a SRF linac with two 9-cell TESLA-type cavities for further acceleration and experiments. Here we will present our latest progress on the DC-SRF photoinjector. We will also present our recent simulation work to decrease the emittance. The purpose is to build an upgraded DC-SRF photoinjector capable of driving CW X-ray free-electron lasers.  
WEA04 Novel Concepts of a High-Brightness Photoinjector RF Gun 1
  • S.V. Kuzikov, O.A. Ivanov, A.A. Vikharev, A.L. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  • S.P. Antipov
    Euclid Beamlabs LLC, Bolingbrook, USA
  • S.P. Antipov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  We propose here a program to design and manufacture a high performance, advanced source of electrons having high beam brightness (>1016 A/m2) and high bunch charge (~100 pC). Three innovations are being considered: 1) the use of a high peak cathode field, short-pulse RF gun; 2) the use of multi-layered diamond photocathode at low temperature; and 3) the utilization of THz ultrafast field emission gating. High peak cathode field is necessary to achieve a high brightness (low emittance) beam to be accelerated to relativistic energies before space-charge effects lengthen the bunch. The multilayered diamond photocathode is needed to obtain high QE with long wavelength laser in the first doped layer, beam cooling in the next layer, and negative electron affinity at the emission layer. High field single cycle THz pulses, produced by means of laser light rectification in a nonlinear crystal, allow to avoid a UV laser, provide high field emission charge (up to nC) and ~1 GV/m pre-acceleration of subpicosecond bunches.  
WEA05 Higher Fields and Beam Energies in Continuous-Wave Room-Temperature VHF RF Guns 1
  • F. Sannibale, J.M. Byrd, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, J.W. Staples, S.P. Virostek
    LBNL, Berkeley, California, USA
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The development in the last decade of MHz-class repetition rate free electron lasers (FELs), and ultrafast electron diffraction and microscopy (UED/UEM) applications, required new gun schemes capable of generating high-brightness beams at such high rates. The VHF-Gun, a 186 MHz room-temperature continuous-wave RF photogun developed at the Lawrence Berkeley Lab (LBNL) was an answer to that need. The VHF-Gun was constructed and tested in the APEX facility at LBNL successfully demonstrating all design parameters and the generation of FEL-quality electron beams. A close version of the APEX gun is in the final phase of fabrication at LBNL to operate as the electron source for the LCLS-II, the new SLAC X-ray FEL. The recently approved upgrade of the LCLS-II towards higher energies (LCLS-II HE) and the brightness-dependent UED and UEM applications would greatly benefit from an increased brightness of the electron source. Such performance upgrade can be obtained by increasing the electric field at the cathode and the beam energy at the gun exit. In this paper, we present and discuss possible upgrade options that would allow us to extend the VHF-Gun technology towards these new goals.
slides icon Slides WEA05 [4.320 MB]