Author: Jones, L.B.
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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL095  
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THPMK062 Transverse Energy Distribution Measurements for Polycrystalline and (100) Copper Photocathodes with Known Levels of Surface Roughness 4438
 
  • L.B. Jones, B.L. Militsyn, T.C.Q. Noakes
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • L.B. Jones, D.P. Juarez-Lopez, B.L. Militsyn, T.C.Q. Noakes, C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • D.P. Juarez-Lopez, C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  
  Funding: This work is part of EuCARD-2, partly-funded by the European Commission, GA 312453.
The minimum achievable emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. This is measureable as the mean longitudinal and transverse energy spreads in the photoemitted electrons. ASTeC's Transverse Energy Spread Spectrometer (TESS)* experimental facility can be used with III-V semiconductor, multi-alkali and metal photocathodes to measure transverse and longitudinal energy distributions. Our R&D facilities also include in-vacuum quantum efficiency measurement, XPS, STM, plus ex-vacuum optical and STM microscopy for surface metrology. Intrinsic emittance is strongly affected by the photocathode surface roughness**, and the development of techniques to manufacture the smoothest photocathode is a priority for the electron source community. We present energy distribution measurements for electrons emitted from copper photocathodes with both defined single-crystal (100) and polycrystalline surfaces with measured levels of surface roughness.
* Proc. FEL'13, TUPPS033, pp. 290-293.
** Proc. FEL'06, THPPH013, pp. 583-586. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK062  
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