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采用模拟和数值计算的方法,研究了THz波段的受激史密斯-帕塞尔辐射特性。实验装置以“上海电子束离子阱”为原型,采用紧凑型设计以便最终实现其可移动性。束流动力学模拟表明,此装置采用强磁场,可以得到平均流强为0.2 A、束流半径为75μm的高品质电子束,为电子束工作在自由电子激光模式下创造了条件。基于Andrews和Brau的理论,优化了光栅参数,保证了辐射角度在60°。其中消散场的计算频率为0.365 9 THz。采用particle-in-cell(PIC)程序模拟了光栅表面的辐射场以及电子的动力学特性。模拟结果表明电子有群聚效应,且二次谐波(0.723 THz,约为消散频率的2倍)得到增强。采用后处理方法计算了史密斯-帕塞尔辐射的功率空间分布。计算显示辐射角度与理论角度相一致,表明了方法的有效性。输出的功率约为2 mW。
The stimulated Smith-Pasarr radiation characteristics of THz band are studied by means of simulation and numerical calculation. The experimental setup is based on the Shanghai Electron Beam Ion Trap and uses a compact design for ultimate mobility. The beam dynamics simulation shows that the device can obtain the high quality electron beam with the average current of 0.2 A and the beam radius of 75 μm by using a strong magnetic field, which creates the conditions for the electron beam to operate in the free electron laser mode. Based on the theory of Andrews and Brau, the grating parameters are optimized to ensure that the radiation angle is 60 °. The dissipation field is calculated at 0.365 9 THz. The particle-in-cell (PIC) program was used to simulate the radiation field and the electron dynamics of the grating. The simulation results show that the electrons have a clustering effect and the second harmonic (0.723 THz, about twice the dissipation frequency) is enhanced. The post-processing method was used to calculate the power-space distribution of the Smith-Pasarr radiation. The calculation shows that the radiation angle is consistent with the theoretical angle, which shows the effectiveness of the method. The output power is about 2 mW.