Experimental study of coaxial free-electron maser based on two-dimensional distributed feedback

Area of Science:

• Physics
• Electrical Engineering
• Materials Science

Background:

• Free-electron masers (FEMs) are vacuum electronic devices that generate coherent electromagnetic radiation.
• Two-dimensional (2D) photonic band gap (PBG) structures offer unique electromagnetic properties for controlling wave propagation.
• Coaxial cavities provide a geometry suitable for high-power microwave generation.

Purpose of the Study:

• To experimentally demonstrate a novel coaxial free-electron maser (FEM) utilizing 2D surface photonic band gap (PBG) structures.
• To investigate the excitation of different modes within the PBG cavity by tuning magnetic fields.
• To evaluate the performance of the coaxial FEM in terms of generated power and conversion efficiency.

Main Methods:

• Fabrication of a coaxial cavity incorporating 2D surface PBG structures.
• Operation of the FEM using a high-current (500 A), high-energy (475 keV) annular electron beam with a 7 cm diameter.
• Tuning of the undulator and guide magnetic fields to excite specific modes.
• Measurement of the generated radiation power and efficiency.

Main Results:

• Successful experimental demonstration of a coaxial FEM based on 2D PBG structures.
• Excitation of various modes by adjusting magnetic field parameters, corresponding to different band gaps.
• Generation of 15 MW of radiation power.
• Achieved a 6% conversion efficiency, which closely matched theoretical calculations.

Conclusions:

• The study presents the first experimental validation of a coaxial FEM employing 2D PBG structures.
• The results confirm the capability of 2D PBG structures to control mode selection and enhance FEM performance.
• The demonstrated device shows excellent agreement with theoretical models, paving the way for future high-power maser development.