Plasma-wakefield accelerators driven by intense particle beams promise to significantly reduce the size of future high-energy facilities. Such applications require particle beams with a well-controlled energy spectrum, which necessitates detailed tailoring of the plasma wakefield. Precise measurements of the effective wakefield structure are therefore essential for optimising the acceleration process. Here we propose and demonstrate such a measurement technique that enables femtosecond-level (15 fs) sampling of longitudinal electric fields of order gigavolts-per-meter (0.8 GV m⁻¹). This method—based on energy collimation of the incoming bunch—made it possible to investigate the effect of beam and plasma parameters on the beam-loaded longitudinally integrated plasma wakefield, showing good agreement with particle-in-cell simulations. These results open the door to high-quality operation of future plasma accelerators through precise control of the acceleration process.

由强粒子束驱动的等离子-尾波加速器有望显着减小未来高能设施的规模。这样的应用需要具有良好控制的能谱的粒子束，这需要对等离子体尾流场进行详细的调整。因此，有效尾流场结构的精确测量对于优化加速过程至关重要。在这里，我们提出并演示了这样一种测量技术，该技术能够实现飞秒级（15 fs）的千兆米/米量级的纵向电场（0.8 GV m ^-1）。该方法基于入射束的能量准直，使得有可能研究射束和等离子体参数对射束加载的纵向积分等离子体尾波场的影响，与单元粒子模拟显示出良好的一致性。这些结果通过精确控制加速过程，为将来的等离子加速器的高质量运行打开了大门。