Author: Gadjev, I.I.
Paper Title Page
TUP008 High-Gain FEL in the Space-Charge Dominated Raman Limit 347
  • I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.  
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TUP074 Results from the Nocibur Experiment at Brookhaven National Laboratory's Accelerator Test Facility 540
  • N.S. Sudar, J.P. Duris, I.I. Gadjev, P. Musumeci
    UCLA, Los Angeles, California, USA
  • M. Babzien, M.G. Fedurin, K. Kusche, I. Pogorelsky, M.N. Polyanskiy, C. Swinson
    BNL, Upton, Long Island, New York, USA
  Conversion efficiencies of electrical to optical power in a Free Electron Laser are typically limited by their Pierce parameter, ρ ~0.1%. Introducing strong undulator tapering can increase this efficiency greatly, with simulations showing possible conversion efficiencies of ~40%. Recent experiments performed with the Rubicon Inverse Free Electron Laser have demonstrated acceleration gradients of ~ 100 MeV/m and high particle trapping efficiency by coupling a pre-bunched electron beam to a high power CO2 laser pulse in a strongly tapered helical undulator. By reversing the undulator period tapering and re-optimizing the field strength along the Rubicon undulator, we obtain an Inverse Free Electron Laser decelerator, which we have aptly renamed Nocibur. This tapering profile is chosen so that the change in beam energy defined by the ponderomotive decelerating gradient matches the change in resonant energy defined by the undulator parameters, allowing the conversion of a large fraction of the electron beam power into coherent narrow-band radiation. We discuss this mechanism as well as results from a recent experiment performed with the Nocibur undulator at Brookhaven National Laboratory's Accelerator Test Facility.  
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