Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14-km 163.5 in AREA Science Park 34149 Basovizza, Trieste, Italy.
Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14-km 163.5 in AREA Science Park 34149 Basovizza, Trieste, Italy and University of Nova Gorica, 5000 Nova Gorica, Slovenia.
Phys Rev Lett. 2014 Jan 31;112(4):044801. doi: 10.1103/PhysRevLett.112.044801.
Control of the electron-beam longitudinal-phase-space distribution is of crucial importance in a number of accelerator applications, such as linac-driven free-electron lasers, colliders and energy recovery linacs. Some longitudinal-phase-space features produced by nonlinear electron beam self- fields, such as a quadratic energy chirp introduced by geometric longitudinal wakefields in radio-frequency (rf) accelerator structures, cannot be compensated by ordinary tuning of the linac rf phases nor corrected by a single high harmonic accelerating cavity. In this Letter we report an experimental demonstration of the removal of the quadratic energy chirp by properly shaping the electron beam current at the photoinjector. Specifically, a longitudinal ramp in the current distribution at the cathode linearizes the longitudinal wakefields in the downstream linac, resulting in a flat electron current and energy distribution. We present longitudinal-phase-space measurements in this novel configuration compared to those typically obtained without longitudinal current shaping at the FERMI linac.
在许多加速器应用中，如直线感应加速器驱动的自由电子激光器、对撞机和能量回收直线加速器，控制电子束的纵向相空间分布至关重要。一些由非线性电子束自场产生的纵向相空间特征，如射频（rf）加速器结构中的几何纵向尾场引入的二次能量啁啾，不能通过普通的直线加速器 rf 相位调谐或单个高次谐波加速腔来补偿。在这封信中，我们报告了通过在光电发射机处适当成形电子束电流来消除二次能量啁啾的实验演示。具体来说，在阴极处的电流分布中引入纵向斜坡使下游直线加速器中的纵向尾场线性化，从而产生平坦的电子电流和能量分布。我们在这个新颖的配置中展示了纵向相空间测量结果，与在 FERMI 直线加速器中没有纵向电流成形时通常获得的结果进行了比较。
