Merging conventional and laser wakefield accelerators

Abstract

Laser wake field accelerators deliver high quality electron beams in terms of emittance and bunch length. However, there are also parameters which cannot compete with conventional machines, namely the spectral width as well as the shot-to-shot stability in terms of energy and pointing. The bunch formation in this new type of accelerators happens in a highly non-linear plasma wave and is a statistical process based on Coulomb scattering. However, there is no direct access to the injection mechanism of electrons into that plasma wake field. Injecting a well-characterized electron beam produced by a conventional accelerator into a plasma wake field could help to solve this problem: Measuring the difference in the electron spectrum in such a pump-probe type experiment should yield the possibility to directly reconstruct the electric field distribution. From that point on, comparisons with theoretical models as well as results from particle-in-cell (PIC) codes could lead to a better understanding of the injection process. At DESY in Hamburg there is a conventional accelerator suited for such a type of experiment: the Relativistic Electron Gun for Atomic Exploration (REGAE). We report on the status of the beam line extension to REGAE and the plans of the external injection project, with the goal to directly measure the wake field and further improve the stability of laser wake field accelerators.