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| THPMK062 | Transverse Energy Distribution Measurements for Polycrystalline and (100) Copper Photocathodes with Known Levels of Surface Roughness | 4438 |
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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. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK062 | |
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| THPAL095 | Metal Photocathodes Preparation for Compact Linear Accelerator at Daresbury Laboratory | 3865 |
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| 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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| THPMK059 | Commissioning of Front End of CLARA Facility at Daresbury Laboratory | 4426 |
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| CLARA (Compact Linear Accelerator for Research and Applications) is a Free Electron Laser (FEL) test facility being developed at STFC Daresbury Laboratory. The principal aim of CLARA is to test advanced FEL schemes which can later be implemented on existing and future short wavelength FELs. The installation of the Front End (FE) section of CLARA, a S-bend merging with existing VELA (Versatile Electron Linear Accelerator) beam line and installation of a high repetition rate RF gun on VELA was completed in 2017. First beam commissioning results and high level software developments are presented in this paper. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK059 | |
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| THPMK063 | Photocathode Preparation and Characteristics of the Electron Source for the VELA/CLARA Facility | 4442 |
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| 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. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK063 | |
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