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Persistent URL http://purl.org/net/epubs/work/58259585
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Record Id 58259585
Title Report on Photocathode Options for a UK X-ray Free-Electron Laser
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Abstract This report summarises the photocathode options for a UK X–ray Free-Electron Laser (UK XFEL). It draws on the reports of photocathode solutions and their measured performance from a number of laboratories around the world to deliver high brightness and/or high repetition rate electron beams. Initially the UK XFEL baseline design considered operation at a low electron bunch repetition rate (‘LRR’: 1 – 100 kHz in a normal–conducting NcRF gun), or at a high repetition rate (‘HRR’: 1 MHz or more in a normal–conducting [NCRF] or a super–conducting [SRF] gun). The project now focuses on the delivery of a HRR machine with up to 300 pC electron bunches at MHz bunch rate (0.30 mA beam current, or more), with slice emittance of 0.3 µm at 8 GeV beam energy for a 250 pC bunch charge. Such a beam can be used to generate coherent 20 keV X–ray photons which will meet the experimental requirements of a substantial majority of the potential user community. The final machine design may incorporate an energy recovery linac (ERL), and the corresponding need for a cryogenic plant supports the possible development of an SRF injector to deliver the beam. There are several photocathode technologies which have the potential to meet these beam requirements, most notably the semiconductor Cs2Te and bare metals such as Cu, Mg or Mo under illumination at UV wavelengths (typically 266 nm), or bi–alkali semiconductors such as CsKSb, NaKSb or CsSb under illumination at visible ‘green’ wavelengths (532 nm). While the green photocathodes are generally more attractive due to their high quantum efficiency and the corresponding simplification in the required drive laser technology, there are potential issues with the operational lifetime of these technologies in a high–current injector. The Cs2Te and plain metals are demonstrably more robust, but carry the penalty of a more complex and expensive drive laser system.
Organisation ASTeC , ASTeC-AP , STFC
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Language English (EN)
Type Details URI(s) Local file(s) Year
Report ASTEC-AP-2023-001 v.1.0. 2023. 2023 Jones - UK X…ocathode Options.pdf 2023