Bright Electron Source for X-ray Free Electron Lasers

The Basic Energy Sciences Report on DOE Facility Upgrades has identified The Linear Coherent Light Source II High Energy Upgrade LCLS II-HE) as “absolutely central to contribute to world leading science”. LCLS II-HE will provide X-ray energies above 5 keV. Even harder X-rays are necessary to study atomic structure dynamics, electronic and nuclear coupling in biological and chemical processes, and energy materials in situ. LCLS II-HE could potentially reach 20 keV, but it requires a factor of ten improvement in electron beam brightness. The ultimate beam brightness is limited by the least mean transverse energy or low emittance) of the electrons injected from the photocathode. Unfortunately, the currently-grown photocathodes for LCLS-II are inadequate to meet the future requirements because of their rough surfaces and poor chemical composition. RMD seeks to address the needs of the LCLS-II upgrade by growing the photocathode by sputtering technique in stark departure from the traditional evaporation technique. These cathodes will have a surface roughness 40% QE in a consistent manner, which will enable manufacturing of such cathodes in the United States. The technology will enable cost effective photocathode deposition over large areas, which will impact the realization of cost competitive new detectors such as the Large Area Picosecond Photo Detectors LAPPDs). Availability of such detectors will have a profound impact on full body scanners for medical investigations using PET, tomographic x-ray imaging, border security investigations, scattering neutron detectors for spallation sources to perform basic sciences, deep underground neutrino experiments DUNE), or the large water neutrino detection systems.