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TY - CONF AU - Noakes, T.C.Q. AU - Angal-Kalinin, D. AU - Cowie, L.S. AU - Jackson, F. AU - McKenzie, J.W. AU - Middleman, K.J. AU - Militsyn, B.L. AU - Roper, M.D. AU - Snedden, E.W. AU - Valizadeh, R. AU - Walsh, D.A. ED - Koscielniak, Shane ED - Satogata, Todd ED - Schaa, Volker RW ED - Thomson, Jana TI - Photocathode Preparation and Characteristics of the Electron Source for the VELA/CLARA Facility J2 - Proc. of IPAC2018, Vancouver, BC, Canada, April 29-May 4, 2018 C1 - Vancouver, BC, Canada T2 - International Particle Accelerator Conference T3 - 9 LA - english AB - The VELA and CLARA front end accelerators at Daresbury are test facilities with a focus on FEL research and industrial applications of electron beams. Recently the CLARA injector has been commissioned with acceleration of beam to 50 MeV. For several years a normal conducting 2.5 cell S-band cavity RF gun operated at up to 80 MV/m has been used as the electron source for both VELA and CLARA. For further beam acceleration an S-band travelling wave 2m long cavity has been used. The gun has used several different copper cathodes throughout its operational life, employing different preparation techniques. Oxygen plasma treatment is a well-known procedure for removing hydrocarbon contamination from surfaces whereas Argon plasma treatment also removes contaminants and typically leaves a thinner oxide at the surface. In this study we compare dark current (from field emission), as measured directly after the gun, for these alternate surface preparations and also present results from post-use electron microscopy analysis of the photocathodes. Electromagnetic simulations are used to help explain the results. PB - JACoW Publishing CP - Geneva, Switzerland SP - 4442 EP - 4445 KW - cathode KW - plasma KW - laser KW - electron KW - operation DA - 2018/06 PY - 2018 SN - 978-3-95450-184-7 DO - 10.18429/JACoW-IPAC2018-THPMK063 UR - http://jacow.org/ipac2018/papers/thpmk063.pdf ER -