Stimulated Superradiance Emitted from Periodic Microbunches of Electrons

概要

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Electron bunches of a picosecond scale can emit terahertz waves superradiantly. Superradiant undulator radiation is considered for a train of periodic bunches injected into a resonating cavity. It is found that the cavity modes excited by successive bunches can be accumulated when they satisfy the accumulation condition, $[\Delta\omega_{n}/2\pi+(n + 2L/\lambda_{w})/T_{\text{R}}] T_{\text{b}} = \text{integer}$, where $\Delta\omega_{n}$ is the frequency mismatch, $n$ is the mode number, $L$ is the cavity length, $\lambda_{w}$ is the undulator period, $T_{\text{R}}$ is the round trip time, and $T_{\text{b}}$ is the bunch period. Numerical simulation shows growth of resonant modes ($\Delta\omega_{n}=0$) and specific off-resonant modes ($\Delta\omega_{n}=2\pi p/T_{\text{R}}$, $ p=\text{odd}$) when the accumulation condition is fulfilled. Also identified in simulation is stimulation of superradiant emission in the radiation pulses excited through grazing resonance. The radiative efficiency is observed to increase bunch after bunch until saturation is reached.
2010-11-25