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Moody, N. A.

Paper Title Page
TUPMS091 A Theoretical Photocathode Emittance Model Including Temperature and Field Effects 1377
 
  • K. Jensen
    NRL, Washington, DC
  • D. W. Feldman, P. G. O'Shea
    UMD, College Park, Maryland
  • N. A. Moody
    LANL, Los Alamos, New Mexico
  • J. J. Petillo
    SAIC, Burlington, Massachusetts
 
  Funding: We gratefully acknowledge funding by the Joint Technology Office and the Office of Naval Research.

A recently developed model* of the emittance and brightness of a photocathode based on the evaluation of the moments of the electron emission distribution function admits an analytical solution for the zero-field and zero-temperature asymptotic model. Here, the model has been extended to account for the critical modifications of temperature and field dependence, which are tied to material issues with the cathode. Temperature impacts the nature of scattering within the photoemitter material and therefore affects quantum efficiency significantly. Field changes the emission probability at the surface barrier, and is particularly important for low work function coatings, as occur for the cesiated surfaces characteristic of our controlled porosity dispenser photocathodes. Extensions of the theoretical models shall be given, followed by an analysis of their comparison with numerical simulations of the intrinsic emittance and brightness of a photocathode. The methodology is designed to facilitate the development of photoemission models into comprehensive particle-in-cell (PIC) codes to address issues otherwise not readily treated, e.g., variation in surface coverage and topology.

* K. L. Jensen, P. G. O'Shea, D. W. Feldman, and N. A. Moody, Applied Physics Letters 89, 224103 (2006).

 
TUPMS010 Fabrication and Measurement of Efficient, Robust Cesiated Dispenser Photocathodes 1206
 
  • E. J. Montgomery, D. W. Feldman, N. A. Moody, P. G. O'Shea, Z. Pan
    UMD, College Park, Maryland
  • K. Jensen
    NRL, Washington, DC
 
  Funding: This work is funded by the Office of Naval Research and the Joint Technology Office.

Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications.