Author: Gilevich, S.
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WEP003 Recent Understanding and Improvements of the LCLS Injector 592
  • F. Zhou, D.K. Bohler, Y. Ding, S. Gilevich, Z. Huang, H. Loos, D.F. Ratner
    SLAC, Menlo Park, California, USA
  Funding: U.S. DOE contract No. DE-AC02-76SF00515.
Ultraviolet drive laser and copper photocathode are the key systems for reliably delivering <0.4 micron of emittance and high brightness free electron laser (FEL) at the linac coherent light source (LCLS). Characterizing, optimizing and controlling laser distributions in both spatial and temporal directions are important for ultra-low emittance generation. Spatial truncated Gaussian laser profile has been demonstrated to produce better emittance than a spatial uniform beam. Sensitivity of the spatial laser distribution for the emittance is measured and analysed. Stacking two 2-ps Gaussian laser beams significantly improves emittance and eventually FEL performance at the LCLS in comparison to a single 2-ps Gaussian laser pulse. In addition, recent observations at the LCLS show that the micro-bunching effect depends strongly on the cathode spot locations. The dependence of the micro-bunching and FEL performance on the cathode spot location is mapped and discussed.
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WEP005 Laser Heater Transverse Shaping to Improve Microbunching Suppresion for X-ray FELs 602
  • S. Li
    Stanford University, Stanford, California, USA
  • A.R. Fry, S. Gilevich, Z. Huang, A. Marinelli, D.F. Ratner, J. Robinson
    SLAC, Menlo Park, California, USA
  In X-ray free electron lasers (FELs), a small amount of initial density or energy modulation in the electron beam will be amplified through acceleration and bunch compression process. The undesired microbunching on the electron bunch will increase slice energy spread and degrade the FEL performance. The Linac Coherent Light Source (LCLS) laser heater (LH) system was installed to increase the uncorrelated energy spread in the electron beam in order to suppress the microbunching instability. The distribution of the induced energy spread depends strongly on the transverse profile of the heater laser and has a large effect on the microbunching suppression. In this paper we discuss strategies to shape the laser profile in order to obtain better suppression of microbunching. We present analysis to achieve the Gaussian-like energy spread using a Laguerre-Gaussian laser mode and study the efficiency and alignment tolerance for implementation.  
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WEP023 Two Bunches with ns-Separation with LCLS 634
  • F.-J. Decker, S. Gilevich, Z. Huang, H. Loos, A. Marinelli, C.A. Stan, J.L. Turner, Z. Van Hoover, S. Vetter
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) delivers typically one bunch. Two bunches are interesting for pump / probe experiments. Two electron bunches with ps separation have been already produced using a split and delay in the laser which produces them on the gun cathode. Here we present the combination of two lasers with a combiner, this allows any time separation and is it limited to RF bucket spacing so far to about 40 ns limited by the setup of our beam containment system. Different beam energies were also provided and the most challenging part was a transverse separation of a few σs for the two beams. Although this setup was very jittery a successful user experiment was accomplished.
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