Particle accelerators, and the light sources they enable at wavelength down to below the ångström, are incredible tools for human discoveries, providing a unique window into the subatomic world and our understanding of Nature, allowing the study of the building blocks of life at the molecular level, and opening countless societal applications, in medicine for therapy and diagnosis, in the semiconductor industry or in material processing and nondestructive inspection. Conventional accelerator technology has now reached its limit, and the idea of using an ionized gas –or plasma– as the medium sustaining the electric field used to accelerate particles, is very promising as accelerating fields few orders of magnitude higher are now possible. One class of plasma accelerators, that could become relevant to push the energy frontier of particle colliders, consists in using a particle beam, « the driver », to excite a plasma wave, that is then used to accelerate the main particle beam. Research in this area requires large facilities, and the project aims at powering these plasma accelerators with laser-accelerated electron beams, so as to miniaturize these beam-driven plasma accelerators. The project achieved a first proof-of-principle demonstration of a miniature beam-driven plasma accelerator, with a single electron beam and an optical visualization of the plasma accelerator structure, and then developed a dual beam configuration, where one bunch is the driver and the other one is the main beam to accelerate. This new plasma acceleration platform together with the development of novel methodologies were then used to address some of the key challenges in plasma accelerator research, such as energy efficiency or quality preservation. The project also showed the potential for the generation of bright electron beams and light sources with unprecedented brightness, and pushed our capabilities and understanding of plasma-based positron acceleration.
