Author: Noakes, T.C.Q.
Paper Title Page
Energy Distribution and Work Function Measurements for Metal Photocathodes With Measured Levels of Surface Roughness  
  • T.S. Beaver, L.B. Jones, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S. Mistry
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  Funding: The work is part of EuCARD2, partly funded by the European Commission, GA 312453. Funded by the Science and Technology Facilities Council.
The minimum achievable emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source which is measureable as the mean longitudinal and transverse energy spreads in the photoemitted electrons. Reducing emittance in an accelerator driving a Free Electron Laser (FEL) delivers significant reduction in the saturation length for an X-ray FEL, reducing machine cost and increasing X-ray beam brightness. There are many parameters which affect the intrinsic emittance of a photocathode. Surface roughness is a significant factor*, and consequently the development of techniques to manufacture low roughness photocathodes with optimum emission properties is a priority for the electron source community. In this work, we present transverse energy distribution and work function measurements made using our TESS facility** for electrons emitted from copper and molybdenum photocathodes with differing levels of measured surface roughness.
* Proc. FEL '06, THPPH013, 583586
** Proc. FEL '13, TUPPS033, 290293
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