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| MOPPH010 | Three-Dimensional Analysis of the Surface Mode Supported by a Reflection Grating | 38 |
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| In a Smith-Purcell Free-Electron Laser (SP-FEL), the electron beam interacts with the surface mode supported by a metallic reflection grating to produce coherent radiation. All the previous analyses of SP-FEL had considered the localization of the surface mode only in the direction perpendicular to the grating surface and assumed translational invariance along the direction of grooves of the grating. In this paper, we include the localization of the surface mode along the direction of grooves and study the three-dimensional structure of the surface mode in order to include diffraction effects in the analysis of SP-FELs. Full three-dimensional Maxwell-Lorentz equations are derived for the self-consistent nonlinear analysis of SP-FELs. | ||
| TUBAU05 | One Angstrom FEL Oscillator using ERL Beams | |
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| An oscillator X-ray FEL for 1-Å is feasible with ERLs. We have studied a 1-Å FEL using electron beams extrapolated from the "high coherence" mode of the proposed Cornell ERL, using the electron energy = 7 GeV, the undulator parameter K=1.4, and period length=1.88 cm. With a 30-m undulator the small signal gain is about 20%, sufficient for "lasing" if one round trip reflectivity is greater than 90%. The gain will be higher for a higher bunch current achievable with further optimization of the gun. The peak power of the circulating optical beam at saturation is about 20 MW and its bandwidth 10-6. The increased energy spread of the electron beam due to the FEL interaction does not pose problem for the recirculation optics. Two possible schemes for optical cavity are possible. One is a cavity of regular triangle with three crystal reflectors. Another is to use a cavity consisting of two Bragg reflectors at near-backscattering configuration and a grazing incidence mirror in between. Parasitic diffraction in backscattering of a cubic crystal provides a convenient out-coupling mechanism. The fraction of parasitic diffraction can be set to a small, desired value while keeping the high reflectivity in the main diffraction by suitably orienting the crystals away from the exact backscattering geometry. The mirror serves also the important function of focusing the x-ray beam. | ||
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| WEAAU05 | A Compact Electron Spectrometer for an LWFA | 294 |
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The use of a laser wakefield accelerator (LWFA) beam as a driver for a compact Free-Electron Laser (FEL) has been proposed recently. A project is underway at Argonnne National Laboratory (ANL) to operate an LWFA in the bubble regime and to use the quasi-monoenergetic electron beam as a driver for a 3-m long undulator for generation of sub-ps UV radiation. The Terawatt Ultrafast High Field Facility (TUHFF) in the Chemistry division provides the 20 TW peak power laser. Towards this goal, a compact electron spectrometer whose initial fields of 0.45 T provide energy coverage of 30-200 MeV has been selected to characterize the electron beams. The system is based on the Ecole Polytechnique design* used for their LWFA and incorporates the 5-cm long permanent magnet dipole, the LANEX scintillator screen located at the dispersive plane, a Roper Scientific 16-bit MCP-intensified CCD camera, and a Bergoz ICT for complementary charge measurements. Test results on the magnets, the 16-bit camera, and the ICT will be described, and initial electron beam data will be presented as available.
*Y. Glinnec et al., "Broadrange Single Shot Electron Spectrometer", Report dated July 6, 2006, Ecole Polytechnique. |
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