National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA.
Phys Rev Lett. 2013 Jul 19;111(3):034803. doi: 10.1103/PhysRevLett.111.034803.
Advanced light sources using relativistic electrons rely on coherent emission from high-density (compressed) beams. These beams, typically produced by photoinjected linear accelerators, can suffer from uncontrolled microbunching instabilities that are difficult to manage, since a complete understanding of their growth due to space charge and other wakefields is lacking. Here we present the first systematic measurements of microbunching instability using electron beams premodulated in a controlled fashion. By comparing beams having various modulation depths and wavelengths with unmodulated beams, we are able to benchmark, for the first time, the analytical calculations for the microbunching instability. In addition, our results give a proof of principle demonstration of a longitudinal space charge amplifier (LSCA), where a specific beam density pattern develops and grows. A potential application of this particular LSCA scheme is for controlling waveforms and enhancing the spectral content of linac-based sources of coherent terahertz radiation.
利用相对论电子的先进光源依赖于高密度（压缩）束的相干发射。这些束，通常由光注入线性加速器产生，可能会受到难以控制的微束不稳定性的影响，因为由于空间电荷和其他尾场，它们的增长完全无法理解。在这里，我们首次使用以受控方式预调制的电子束进行了微束不稳定性的系统测量。通过将具有不同调制深度和波长的束与未调制的束进行比较，我们首次能够对微束不稳定性的分析计算进行基准测试。此外，我们的结果还首次证明了纵向空间电荷放大器（LSCA）的原理，其中会形成和增长特定的束密度模式。这种特殊的 LSCA 方案的一个潜在应用是控制波形并增强相干太赫兹辐射的基于线性加速器的源的光谱内容。
