Advanced Accelerator Research: Photocathode Sources

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Particle accelerators and light sources are important tools for scientific discovery across many disciplines such as biomedical, biological, chemical, and physical sciences. Photocathodes with improved emission properties are desirable for certain next generation light sources, such as those based on Free Electron Laser (FEL) or Energy Recovery Linac (ERL) technologies. They are also needed for high-resolution microscopy tools such as Dynamic Transmission Electron Microscopy (DTEM) devices. Accelerators are also used by industry for a variety of manufacturing tasks. Thermionic cathodes are typically used for industrial accelerators, although the beam properties of photocathodes would in some applications be more desirable. Some examples are medical radiological accelerators, and electron beam machining and welding. The cost and complication of photocathode operation discourages their use in industry. A goal of this award is to apply a multidisciplinary research approach to discover methods to modify the photocathode surface to manipulate emission properties, making them cheaper to operate, or else improve their performance.With this award, an investigation of the use of thin film deposition to modify photo-emissive surface properties in a systematic way will be carried out. Specifically, development of novel photocathodes including plasmonic cathodes with thin coatings, and thin epitaxial multilayered MgO/Ag/MgO structures is planned. It may be possible to make robust, high quantum efficiency metallic plasmonic nanostructured cathodes by deposition of a thin layer of material such as BaO on the surface. The goal is to manipulate the photocathode to operate at visible, rather than ultra-violet wavelengths, making the technology more accessible for industrial applications. The thin flanking layers of MgO utilized in multilayered MgO/Ag/MgO structures modify the surface band structure; and emission properties vary systematically with layer thickness. Previous research can be continued, both to investigate how robust these structures are in an accelerator environment, and to determine more fully how performance depends on properties such as the surface roughness.