Advanced accelerator-driven THz radiators: achieving high power and continuous tunability

The increasing demand for high-power, narrowband, and tunable THz radiation sources has driven the exploration of compact and efficient generation methods. Smith-Purcell radiation presents a promising approach for producing narrowband THz emission, but its power output remains a limiting factor. This work introduces a 3D emission-collection strategy that significantly enhances radiation efficiency, achieving a 20× boost in coherent power compared to conventional 2D designs. Through systematic simulations, a single-layer helically rotated structure, optimized via inverse design, is shown to outperform existing circumferentially closed gratings, reaching sub-millijoule radiated energy levels. Furthermore, a novel tuning mechanism is proposed, utilizing mechanical deformation of dielectric materials to modify the grating periodicity, enabling continuous tunability of THz emission from ultrarelativistic electron beams. The helix grating offers a practical and manufacturable solution for developing accelerator-based, high-power tunable THz radiators. These findings provide a pathway toward more efficient THz sources, with potential applications in free-electron laser facilities and advanced THz-driven technologies.