Particle-in-cell simulation of coherent and superradiant Smith-Purcell radiation
Particle-in-cell simulation of coherent and superradiant Smith-Purcell radiation
复制标题
DOI：
10.1103/physrevstab.9.040701
复制
发表时间：
2006-04
影响因子：
--
通讯作者：
Dazhi Li;Z. Yang;K. Imasaki;G. Park
中科院分区：
文献类型：
--
作者：
Dazhi Li;Z. Yang;K. Imasaki;G. Park
本文借助二维细胞内粒子 (PIC) 模拟对相干和超辐射史密斯-珀塞尔 (SP) 辐射进行了研究。仿真模型假设周期长度为 $173\text{ }\ensuremath{\mu}\mathrm{m}$ 的矩形光栅分别由单个电子束、周期性束串和连续束驱动。我们选择 40 keV 作为电子的初始能量，因此 SP 辐射频率落在太赫兹范围内。从我们的单束模拟中，我们区分了在时间上分离的真实 SP 辐射与倏逝波的发射。倏逝波从光栅的两端辐射，其特征在于与角度无关的频率低于允许的最小SP频率。为了避免最初连续光束形成光束聚集，我们使用一系列周期性光束来激发光栅并观察超辐射现象。空间周期性束的重复频率假设为 300 GHz。我们发现超辐射辐射仅在该频率的高次谐波和相应的 SP 角处发射。这一结果符合安德鲁斯和同事的观点。连续束的模拟显示了输出功率对束电流的依赖性。功率曲线显示了两种状态，一种是非相干 SP 辐射，另一种是超辐射，类似于达特茅斯实验结果。此外，两种制度的频谱显示出明显的差异，这与浦田和同事的观察结果相反。
This paper presents a study of coherent and superradiant Smith-Purcell (SP) radiation with the help of a two-dimensional particle-in-cell (PIC) simulation. The simulation model supposes a rectangular grating with period length of $173\text{ }\ensuremath{\mu}\mathrm{m}$ to be driven by a single electron bunch, a train of periodic bunches and a continuous beam, respectively. We chose 40 keV as the initial energy of electrons and therefore the SP radiation frequency falls in the THz regime. From our single bunch simulation we distinguish the true SP radiation separated in time from the emission of the evanescent wave. The evanescent wave radiates from both ends of the grating and is characterized by an angle independent frequency lower than the minimum allowed SP frequency. In order to avoid the buildup of beam bunching from an initially continuous beam, we use a train of periodic bunches to excite the grating and observe the superradiant phenomenon. The repetition frequency of the spatially periodic bunches is assumed to be 300 GHz. We find that the superradiant radiation is only emitted at higher harmonics of this frequency and at the corresponding SP angles. This result conforms to the viewpoint of Andrews and co-workers. The simulation with a continuous beam shows the dependence of the output power on the beam current. The power curve shows two regimes, one for the incoherent SP radiation and the other for the superradiance, which resembles the Dartmouth experimental result. And furthermore, the frequency spectrum shows an apparent difference for the two regimes, which is in contrast to the observations of Urata and co-workers.