Laser-driven plasma accelerators inherently produce very high electron bunch currents which can reach the 10 kA level. Even at modest energy monochromaticity levels, these bunches therefore have great potential to be used as drivers in subsequent PWFA stages. Such compact, inherently synchronized, “all-optical” systems are practically dephasing-free and can for example power Trojan Horse stages, which in turn can be used to transform the brightness, quality and the stability of the system.
Within the last decade, laser driven plasma accelerator R&D achieved breakthroughs as regards total beam energy, charge, and energy spreads. An inherent great advantage of laser-plasma-accelerators is that they produce ultrashort bunches and therefore high (peak) currents. This natural feature is a key requirement for beam-driven PWFA stages. A combined hybrid system of a laser driven stage and a subsequent beam driven, dephasing-free stage can be used e.g. to realise driver/witness type PWFA systems as in  or to drive Trojan Horse underdense plasma photocathode stages as in . The latter profits from inherent synchronization between electron and Trojan laser in such ultimately all-optical incarnations, and from the fact that the hereby produced witness bunch quality can exceed the drive beam quality substantially and its generation is to a large degree decoupled from the drive beam, allowing to exploit the full advantages of Trojan Horse. Such a beam quality transformer and booster -- a “plasma-CLIC” -- can improve the energy, energy spread, emittance and brightness by orders of magnitude. At the same time, the entire system is relatively immune as regards shot-to-shot variations of the drive beam from the LWFA stage, which is an experimental reality. Also, even high energy spreads of the drive beam can be tolerated to some extent, the more so, the higher the electron energies are. Theoretical considerations and start-to-end simulations are used to demonstrate the feasibility of the process and to explore its limitations. Experimental challenges are identified and first experimental results are discussed. This adds a new application to the arsenal of laser-plasma-accelerators, and the optimization of the LWFA process aiming at the production of PWFA-capable beams adds a new flavour to LWFA research, as the the optimization goals are substantially different from what one usually aims at with LWFA.
 B. Hidding, T. Königstein, J. Osterholz, S. Karsch, O. Willi, and G. Pretzler, PRL 104, 195002, 2010.
 B. Hidding, G. Pretzler, J.B. Rosenzweig, T. Königstein, D. Schiller, D.L. Bruhwiler, PRL 108, 035001, 2012
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