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Title: Evaluation of FEL performance with a longer injector drive laser pulse at the LCLS

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SLAC National Accelerator Lab., Menlo Park, CA (United States)
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Resource Type:
Program Document
Country of Publication:
United States

Citation Formats

None. Evaluation of FEL performance with a longer injector drive laser pulse at the LCLS. United States: N. p., 2017. Web.
None. Evaluation of FEL performance with a longer injector drive laser pulse at the LCLS. United States.
None. 2017. "Evaluation of FEL performance with a longer injector drive laser pulse at the LCLS". United States. doi:.
title = {Evaluation of FEL performance with a longer injector drive laser pulse at the LCLS},
author = {None},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 8

Program Document:
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  • Requirements for the LCLS injector drive laser present significant challenges to the design of the system. While progress has been demonstrated in spatial shape, temporal shape, UV generation and rep-rate, a laser that meets all of the LCLS specifications simultaneously has yet to be demonstrated. These challenges are compounded by the stability and reliability requirements. The drive laser and transport system has been installed and tested. We will report on the current operational state of the laser and plans for future improvements.
  • The temporal profile of the uv drive laser pulse for the LCLS injector is specified by the duration, the rise/fall time, and the maximum rms amplitude (for all frequencies) of residual modulation in the plateau region. The bandwidth of the uv laser system should accommodate pulses with a rise/fall time as low as 0.7 ps and an rms residual amplitude modulation (on the plateau) below 0.5% in the absence of a laser heater. Computations including the laser heater [3] relax this requirement to the 5% level. Numerical analyses of Fourier transform limited uv pulses show that the extent of frequencymore » sidebands should extend to at least 1.5 THz on either side of the central uv frequency. For simplicity, we assume that the emitted electron beam profile matches the laser profile. The evolution of those electron beam distributions in the longitudinal phase space along the beamline as calculated with PARMELA/ASTRA are shown. Related spectral and shaping requirements on the fundamental ir pulses are briefly addressed.« less
  • Kinetic simulations of break-out-afterburner (BOA) ion acceleration from nm-scale targets are examined in a longer pulse length regime than studied previously. It is shown that when the target becomes relativistically transparent to the laser, an epoch of dramatic acceleration of ions occurs that lasts until the electron density in the expanding target reduces to the critical density in the non-relativistic limit. For given laser parameters, the optimal target thickness yielding the highest maximum ion energy is one in which this time window for ion acceleration overlaps with the intensity peak of the laser pulse. A simple analytic model of relativisticallymore » induced transparency is presented for plasma expansion at the time-evolving sound speed, from which these times may be estimated. The maximum ion energy attainable is controlled by the finite acceleration volume and time over which the BOA acts.« less
  • The high quality LCLS electron beam generated in the photoinjector is subject to many instabilities in the downstream acceleration and compression. The instability can be initiated by any density modulation of the electron beam generated at the photocathode. In this paper, we prescribe the tolerance on the initial electron beam density modulation possibly introduced by the ultraviolet (uv) laser at the cathode. Our study shows that with a matched Landau damping laser-heater, the initial rms density modulation of the electron beam at the photocathode must be less than 5% to ensure the FEL lasing and saturation.
  • No abstract prepared.