Development of a Field Emitter Array Based High-Current Electron Injector

At present there exists a very significant science and technology gap for the production of photocathodes that have both high quantum efficiency (QE) and long lifetime. The National Academies has identified this as an area of critical importance to the development of high-power free-electron lasers (FEL). If the high-current electron injectors required are based on low-QE cathodes, then the required drive laser has a prohibitive average power requirement. Conversely, if existing high-QE cathodes are utilized then the operational lifetimes, which are on the order of hours, are outside of what is acceptable for user facilities or other applications. New cathode and injector technologies that obviate the need for high-QE photocathodes and complex drive lasers may be a key component in the future development of high-power free-electron laser. We propose a focused development program that integrates recent advances in field emission cathodes with new paradigms in radio-frequency (RF) gun design. Diamond field emission cathodes have demonstrated high-current capability, chemical inertness, excellent emission uniformity, and transverse emittance compatible with high-brightness performance. Phase I will involve performance optimization of diamond field emitter arrays through precise control of morphology, composition, and surface functionalization, and simulation, modeling and preliminary design of the gun concept that will be produced in phase II. The ultimate goal of phase II will be the demonstration and characterization of a field emission based high current RF injector. Should the program prove successful, not only would the cathodes provide improved economic and reliability performance for existing user facilities such as light sources and FELs, but could also allow penetration into markets presently restricted to thermionic cathodes such as environmental remediation systems for water remediation and flue gas scrubbing