We present an experimental study of coherent high-power wakefield generation in a metamaterial (MTM) structure at 11.7 GHz by 65 MeV electron bunch trains at the Argonne Wakefield Accelerator (AWA), following a previous experiment, the Stage-I experiment, at the AWA. Both the Stage-II experiment, reported in this paper, and the Stage-I experiment were conducted using MTM structures, which are all-metal periodic structures with the period being much smaller than the wavelength. Differences between the two experiments include (1) structure length (Stage-I 8 cm and Stage-II 20 cm); (2) number of bunches used to excite the structure (Stage-I with two bunches, up to 85 nC of total charge; Stage-II with eight bunches, up to 224 nC of total charge); and (3) highest peak power measured (Stage-I 80 MW in a 2 ns pulse and Stage-II 380 MW in a 10 ns pulse). High-power radio frequency pulses were generated by reversed Cherenkov radiation of the electron beam due to the negative group velocity in the MTM structures. Because the radiation is coherent, a train of bunches with a proper spacing can build up to achieve a high peak power. The observed output power levels are very promising for future applications in direct collinear wakefield acceleration or in transfer to a second accelerator for two-beam acceleration.

中文翻译：

---

超材料结构中电子束列产生的相干高功率射频尾场

我们提出了在 11.7 GHz 的超材料 (MTM) 结构中通过 65 MeV 电子束在阿​​贡尾波场加速器 (AWA) 中产生相干高功率尾流场的实验研究，继之前的实验，第一阶段实验之后，在阿华。本文报道的第二阶段实验和第一阶段实验都是使用 MTM 结构进行的，MTM 结构是周期远小于波长的全金属周期结构。两个实验之间的差异包括（1）结构长度（Stage-I 8 cm和Stage-II 20 cm）；(2) 用于激发结构的束数（Stage-I 有两个束，总电荷高达 85 nC；Stage-II 有 8 个束，总电荷高达 224 nC）；(3) 测得的最高峰值功率（Stage-I 80 MW，2 ns 脉冲，Stage-II 380 MW，10 ns 脉冲）。由于 MTM 结构中的负群速度，电子束的反向切伦科夫辐射产生了高功率射频脉冲。由于辐射是相干的，因此可以建立一串具有适当间距的束以实现高峰值功率。观察到的输出功率水平对于直接共线尾流场加速或转移到第二个加速器以进行双光束加速的未来应用非常有希望。