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Hannon, F. E.

Paper Title Page
TUPMS020 Thermal Emittance Measurements from Negative Electron Affinity Photocathodes 1221
  • C. K. Sinclair, I. V. Bazarov, B. M. Dunham, Y. Li, X. G. Liu, D. G. Ouzounov
    Cornell University, Department of Physics, Ithaca, New York
  • F. E. Hannon
    Cockcroft Institute, Lancaster University, Lancaster
  • T. Miyajima
    KEK, Ibaraki
  Funding: Work supported by the National Science Foundation under contract PHY 0131508

Recent computational optimizations have demonstrated that it should be possible to construct electron injectors based on photoemission cathodes in very high voltage DC electron guns in which the beam emittance is dominated by the thermal emittance from the cathode. Negative electron affinity photocathodes have been shown to have a naturally low thermal emittance. However, the thermal emittance depends on the illuminating wavelength; the degree of negative affinity; and the band structure of the photocathode material. As part of the development of a high brightness, high average current photoemission electron gun for the injector of an ERL light source, we have measured the thermal emittance from negative affinity GaAs and GaAsP photocathodes. The measurements were made by measuring the electron beam spot size downstream of a counter-wound solenoid lens as a function of the lens strength. Electron beam spot sizes were measured by two techniques - a 20 micron wire scanner, and a CVD diamond screen. Both Gaussian and 'tophat' spatial profiles were used, and measurements were made at several wavelengths. Results will be presented for both cathode types.