Pre-Bunched Free Electron Maser

The free electron laser (PEL) is a source of microwave power which makes use of the interaction between the electron beam and electromagnetic radiation. In recent years, most effort in FEL research has been concentrated on producing high power sources of tuneable radiation using high relativistic electron beams. This approach requires accelerators operating at megavolts potential using pulsed-power techniques. Hence, typical FELs are produced in large-scale facilities. The purpose of this research is to bring the FEL back to the world of industrial processing, for which the FEL offers the prospect of a microwave source with a broad tuning range, high power and reasonable efficiency which is higher than the conventional FEL devices. At the University of Liverpool, we are developing a prototype pre-bunched free electron maser (pFEM) that is compact, powerful and efficient fOf industrial applications, using available and affordable technology. The design, set-up and experimental result of this novel X-band rectangular waveguide PFEM are presented. Our device operates at 10 GHz and employs two rectangular waveguide cavities (one for velocity modulation and the other for energy extraction). The electron beam used in this experiment is produced by thermionic electron gun which operates at 3 kV and produces beam current up to 5 rnA. The resonant cavity consists of a thin gap section of height 1.5 mm which reduces the beam energy required for beam wave interaction. EM wave is used to pre-bunch the electrons, instead of using permanent wiggler magnets in conventional FEL system. A phase shifter is installed to ensure the correct phase of the bunched electrons and the EM wave in the output cavity. This novel design allows the PFEM to operate at a low current and accelerating voltage, maintaining a compact design. The experimental result has demonstrated that coherent emission and gain with a beam current of up to 5 rnA can be achieved. The gain curve has an interference pattern due to the phase variations ofthe electrons relative to the EM wave.EThOS - Electronic Theses Online ServiceGBUnited Kingdo