Keyword: polarization
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TUPB041 Scattering of  H Stripped Electrons  from SEM Grids and Wire Scanners at the CERN LINAC4 electron, simulation, scattering, linac 567
  • F. Roncarolo, E. Chevallay, M. Duraffourg, G.J. Focker, C. Heßler, U. Raich, VC. Vuitton, F. Zocca
    CERN, Geneva, Switzerland
  • B. Cheymol
    ESS, Lund, Sweden
  At the CERN LINAC4, wire grids and scanners will be used to characterize the H beam transverse profile at different stages along the acceleration to 160 MeV. The wire signal will be determined by the balance between secondary emission and number of charges stopped in the wire, which will depend on the wire material and diameter, the possible choice of biasing (DC) the wires and the beam energy. The outermost electrons of H ions impinging on a wire are stripped in the first nanometers of material. A portion of such electrons are scattered away from the wire and can reach the neighboring wires.  In addition, scattered electrons hitting the surrounding beam pipe generate secondary electrons that can also perturb the measurement. Monte Carlo simulations, analytical calculations and a laboratory experiment allowed quantifying the amount of scattering and the scattered particles distributions. The experiment was based on 70 keV electrons, well reproducing the case of 128 MeV H ions. For all the LINAC4 simulated cases the predicted effect on the beam size reconstruction results in a relative error of less than 5%.  
THPB068 First Observation of Photoemission Enhancement from Copper Cathode Illuminated by Z-Polarized Laser Pulse laser, cathode, gun, focusing 996
  • H. Tomizawa, H. Dewa, A. Mizuno, T. Taniuchi
    JASRI/SPring-8, Hyogo, Japan
  Since 2006, we have developed a novel photocathode gun gated by laser-induced Schottky-effect. This new type of gun utilizes a laser’s coherency to aim at a compact femtosecond laser oscillator as an IR laser source using Z-polarization on the photocathode. This Z-polarization scheme reduces the laser photon energy (making it possible to excite the cathode with a longer wavelength) by reducing the work function of cathode due to Schottky effect. A hollow laser incidence is applied with a hollow convex lens in a vacuum that is focused after passing the laser beam through a radial polarizer. According to our calculations (convex lens: NA=0.15), a Z-field of 1 GV/m needs 1.26 MW at peak power for the fundamental wavelength (792 nm). In the first demonstration of Z-field emission, enhancement was done with a copper cathode at THG (264 nm). Consequently, we observed 1.4 times enhancement of photoemission at 1.6 GV/m of an averaged laser Z-field on the cathode surface. We report the first observation and analysis of the emission enhancements with this laser-induced Schottky-effect on metal copper photocathodes by comparing radial and azimuthal polarizations of the incident laser pulses.