Reducing Starting Current of Smith-Purcell Radiation with a Two-Layer Grating Structure

Smith–Purcell radiation (SPR) is generated when an electron beam passes near a periodic structure [1]. Two-layer gratings are proposed to enhance SPR by improving electromagnetic coupling [2] [3]. Using particle-in-cell (PIC) simulations [4], two-layer gratings have been shown to enhance SPR growth rates and reduce Smith-Purcell backward wave oscillators' start currents.

This study presents a novel approach to enhance the coupling of evanescent waves with an electron beam in SPR by utilizing a two-layer grating structure. The operating frequency of SPR with the two-layer grating is determined through the derivation of a cold-tube dispersion relation, which is further validated by CST and PIC simulations [4]. PIC simulations reveal that the two-layer gratings exhibit significantly higher radiation intensity. Moreover, the two-layer metallic gratings demonstrate the generation of coherent SPR with a reduced beam starting current [3]. This reduction in beam current yields several advantageous effects for particle accelerators, such as minimizing beam loss, prolonging cathode lifetime, and mitigating the heating of beam-carrying components.

REFERENCE

[1] S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953).

[2] J. Shu, P. Zhang, M. Liang, S.-P. Yang, S.-M. Wang, and Y.-B. Gong, Chin. Phys. B 31, 044103 (2022).

[3] M. Arifuzzaman Faisal and P. Zhang, IEEE Trans. Electron Devices 70, 2860 (2023).

[4] J. P. Verboncoeur, A. B. Langdon, and N. T. Gladd, Comput. Phys. Commun. 87, 199 (1995).