High-resolution sampling of beam-driven plasma wakefields

Abstract

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.

Multiparameter-controlled laser ionization within a plasma wave for wakefield acceleration

“…Both schemes have been realized experimentally at various facilities. Especially the regime of beam-driven nonlinear wakefields has been reached and well controlled recently [5,6] and future experiments are initiated [7]. Whereas accelerating electron bunches that are already at relativistic velocities even more has been demonstrated using external injection schemes [1,8], the acceleration of electrons starting from rest is also of huge interest due to the possible exceptional parameters of those bunches.…”

Progress of the FLASHForward X-2 high-beam-quality, high-efficiency plasma-accelerator experiment

“…Exploiting the near-linear chirp in longitudinal phase space, the high-energy (tail) collimator could be used to sample the wake at 15 fs resolution at percent-level accuracy, as reported in Ref. [25]. Comparing the measurement with particle-in-cell simulations required a detailed 6D reconstruction of the bunch, combining the BPM-based technique with TDS measurements and quadrupole scans, as well as longitudinally resolved plasma-density measurements-a process that resulted in a greatly increased understanding of many subtleties of the FLASHForward setup.…”

Free electron lasers driven by plasma accelerators: status and near-term prospects

“…This is made possible at FLASHForward in large part due to the exquisite stability of the FEL-standard FLASH front end. Great progress has been made in this direction in recent years via multiple branches: developing techniques to improve beam quality after plasma acceleration [ 55 ] , diagnostics to better understand the plasma-wakefield process in order to optimize it [ 56 ] , and finally demonstrator experiments utilizing these techniques for the preservation of beam quality [ 12 ] . This combined pillar of research will continue until a single highly efficient stage capable of simultaneous preservation of transverse (normalized emittance) and longitudinal (energy spread) quality over large energy gain is demonstrated.…”