Phase-locked laser-wakefield electron acceleration

A Laser-Plasma Accelerator (LPA) uses accelerating fields (wakefield) that are typically 3 orders of magnitude higher than in radio-frequency accelerators. These extreme fields could allow for a drastic decrease of accelerator sizes for scientific, medical or industrial applications and make of LPAs promising candidates for future high-energy colliders. Producing a very large accelerating field is however not sufficient for reaching high energies; electron bunches trapped in the wakefield have also to experience acceleration on long distances, which remains challenging in a LPA because of 3 phenomena: diffraction, pump depletion and dephasing.

 We proposed an acceleration concept that allows us to tackle simultaneously these three phenomena, leading to new favorable energy scaling for LPA. It associates high-intensity quasi-Bessel beams for generating the plasma wave and spatio-temporal couplings (i.e. dependencies in the laser field requiring a non-separable time-space description) for controlling its velocity. This concept leads to a new regime, dephasing-free, where the electron beam energy gain increases by more than one order of magnitude compared to a regular LPA.

 C. Caizergues, S. Smartsev, V. Malka and C. Thaury. Phase-locked laser-wakefield electron acceleration. Nature Photonics (2020).

Schematic view of laser plasma acceleration with a regular LPA (upper part) or a phase-locked LPA (lower part). In the lower part, the electron beam in orange remains in the region (blue) where the accelerating field is maximum while in the upper part it shifts towards the decelerating region (red).