Author: Dhanak, V. R.
Paper Title Page
THPAL095 Metal Photocathodes Preparation for Compact Linear Accelerator at Daresbury Laboratory 3865
  • A.N. Hannah, J.A. Conlon, L.B. Jones, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • V. R. Dhanak
    The University of Liverpool, Liverpool, United Kingdom
  • L.B. Jones, B.L. Militsyn
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • S. Lederer
    DESY Zeuthen, Zeuthen, Germany
  • S. Lederer
    DESY, Hamburg, Germany
  The photoinjector of the CLARA FEL test facility Front End at Daresbury Laboratory is based on a S-band 10 Hz photocathode RF-gun operating with a copper photocath-ode which is driven by the third harmonic of a Ti:Sapphire laser (266 nm). The main aim of this study was to establish a procedure to prepare the Cu surface prior to installation so a Quantum Efficiency (QE) of 10-5 or higher can be achieved at laser power density below the ablation threshold of copper. The best results have been obtained by ex-situ chemical cleaning. This removed the surface oxide layer whilst at the same time producing a surface buffer layer. This inhibited the regrowth of native oxide for up to a week when exposed to normal ambient atmospheric conditions. With either chemical cleaning or Ar plasma cleaning after heating the sample in-situ to 150 °C for 90 minutes or 250 °C for 40 hours, almost all of the surface oxide was removed. For these surfaces a QE of 4.10-5 or better was measured. Oxygen plasma cleaning at 100% and 20% power produced CuO layer with surface carbon contaminant to 3 atomic %, however in-situ thermal cycling resulted in at best a QE of 3·10-6.  
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