Terahertz Acceleration Technology Towards Compact Light Sources

Abstract: The concepts in this thesis comprise three groups focusing on: (1) fast electron sources, (2) THz injectors, and (3) THz linacs. First, the feasibility of ultrafast, high-yield electron emitters based on nanostructured cathodes is demonstrated. Benefitting from field enhancement effects, namely tip-enhancement and plasmonic enhancement, laser-induced field emission is realized over large, dense and highly uniform field emitter arrays. The theoretical principles of these field emitter arrays are studied and their suitability for pico-Coulomb charge production over femtosecond time-scales is confirmed. In the framework of THz injectors, two ground-breaking concepts including ultrafast single-cycle THz guns and segmented THz electron accelerator and manipulator (STEAM) devices are developed and tested. The possibility of using transient fields to realize ultrahigh acceleration gradients close to 0.5 GeV/m is confirmed. Specifically, a STEAM device capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches is demonstrated. With this single device, powered by few-micro-Joule, single-cycle, 0.3 THz pulses, we demonstrated record THz-acceleration of >30 keV, streaking with <10fs resolution, focusing with >2 kT/m strength, compression to ~ 100 fs as well as real-time switching between these modes of operation. Travelling wave THz linacs based on dielectric-loaded metallic waveguides operating under few-cycle excitations are proposed. Based on this concept, keV-level energy gain through a linear accelerator using optically-generated THz pulses is demonstrated. Moreover, the possibility of electron acceleration to tens of MeV with millijoule level THz pulses is theoretically shown. The final goal of the above studies is a fully THz-driven compact light source facility, whose start-to-end simulation is fulfilled in this thesis.