Proposal and numerical studies of a terahertz Cherenkov free electron laser driven by a non-ultra relativistic bunched electron beam

摘要

Corrugated and dielectric structures have been widely used for producing terahertz radiation source. Recently, a novel scheme of sub-terahertz free electron laser (FEL) from a metallic pipe with corrugated walls driven by a non-ultra-relativistic (10 MeV) picosecond electron beam was proposed and analyzed by using the Vlasov-Maxwell equations which can only provide crude estimates of the expected parameters of the FEL. It offers a promising candidate for compact accelerator-based high power terahertz source which can be realized with relatively low energy and low peak-current electron beams. In this paper, we propose a terahertz Cherenkov free electron laser scheme by using the cylindrical dielectric loaded waveguide (DLW) instead, and the new device scheme is studied numerically using both one-dimensional (1D) numerical model and particle in cell (PIC) simulations. The 1D model is developed in specialty for the longitudinal beam dynamics and electromagnetic simulations of the new Cherenkov FEL scheme. The basic idea of the approach is to use the analytic expressions of the longitudinal mode fields steady-state solution using Green function) to compute the wakefields at each time step using the macro particle currents as sources, while the Lorentz equations of the particles can be integrated numerically. The transitive effects in electromagnetic field (related to the group velocity of the wakefield) are modeled only approximately even in 1D case. It allows fast and accurate time-dependent calculation of the interaction between the wakefields and the electron beam. Good agreement is obtained comparing with particle in cell (PIC) simulation results.