Decoupling acceleration and wiggling in a laser-produced Betatron source

Betatron radiation is produced in laser plasma accelerators when the electrons are accelerated and simultaneously wiggle across the propagation axis [Rousse et al., Phys. Rev. Lett. 93, 135005 (2004)]. The mechanisms of electron acceleration and x-ray radiation production follow different scaling laws [Corde et al., Rev. Mod. Phys. 85, 1-48 (2013)], and the brightest x-ray radiation is often produced for an electron beam with a lower quality in terms of energy and divergence. Here, we report a laser-driven betatron x-ray source where the plasma density profile is tailored in order to separate the acceleration and wiggler stages, which allows for the independent optimizations of acceleration and x-ray production. We demonstrate this concept experimentally and show that the betatron photon energy can be controlled by adjusting the length of the plasma wiggler. This scheme offers a path to overcome the limitations of conventional betatron sources, enabling the production of bright, stable, energetic, and collimated x-ray beams.