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Noonan, J.

Paper Title Page
THPMS010 Polarized Pulsed Beam Source for Electron Microscopy 3011
  • N. Vinogradov, C. L. Bohn, P. Piot
    Northern Illinois University, DeKalb, Illinois
  • J. W. Lewellen, J. Noonan
    ANL, Argonne, Illinois
  A novel source of polarized pulsed electron beam is discussed. Unlike conventional devices based either on a thermionic cathodes or field-emission needle cathodes, in this source the electrons are produced by a laser beam hitting the cathode surface. Using a combination of gallium arsenide (GaAs) planar cathode and a suitable laser one can obtain a polarized picosecond electron bunch. Numerical simulations of the electron dynamics in the optimized cathode-anode geometry have shown that the beam with initial transverse size of a few mm can be focused down to 1 mm RMS at a distance of about 4 cm from the cathode. The suggested source can be installed instead of a tungsten filament source in an existing electron microscope with no modification of any column elements. The main advantages of this approach are that the beam can be easily pulsed, the beam is polarized which makes it an effective probe of some magnetic phenomena, and the laser can be used to provide larger beam intensity. The design of the source and subsequent fabrication has been completed. The paper presents numerical studies, conceptual design of the device, and results of beam measurements.