Speaker
Description
Laser and plasma wakefield accelerators are promising for many applications such as future TeV electron-positron colliders and X-ray free electron lasers (XFELs). These applications, generally, require high beam quality in terms of energy spread, emittance, shot-to-shot stability, etc. To achieve high beam quality, one has to precisely diagnose the beam dynamics during acceleration. This is difficult owing to the highly nonlinear acceleration process and the sub-µm, sub-fs spatial-temporal diagnostic requirements. Here, we report on a single-shot longitudinal phase-space reconstruction diagnostic for electron beams in a laser wakefield accelerator via the experimental observation of distinct periodic modulations in the angularly resolved spectra. Such modulated angular spectra arise as a result of the direct interaction between the ultra-relativistic electron beam and the laser driver in the presence of the wakefield. A constrained theoretical model for the coupled oscillator, assisted by a genetic algorithm, was used to recreate the experimental electron spectra and fully reconstruct the longitudinal phase-space distribution of the electron beam with a temporal resolution of ∼1.3 fs. In particular, it revealed the slice energy spread of the electron beam, which is important to measure for applications such as XFELs. In our experiment, the root-mean-square slice energy spread retrieved is bounded at 9.9 MeV, corresponding to a 0.9-3.0% relative spread, despite the overall GeV energy beam having ∼100% relative energy spread. Particle-in-cell simulations demonstrate that our method also applies for electron beams from traditional accelerators. We show that periodically modulated electron spectra can be induced via either direct laser-electron interaction in vacuum or in a beam-driven plasma wakefield accelerator.
| Keyword-1 | Laser wakefield accelerator |
|---|---|
| Keyword-2 | Phase space |
| Keyword-3 | Electron diagnostics |