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Shaping trailing beams for beam loading via beam-induced-ionization injection at FACET

Recent progress in plasma based accelerator technology has demonstrated its ability to deliver high energy (GeV) beams in compact structures (centimeter to meter scale plasmas). Current developments of that technology are oriented toward producing beams with quality and energy spread comparable to those obtained using standard accelerating structures. In plasma based accelerators, the beam energy spread can be improved during the acceleration process through beam loading. To achieve optimum beam loading, the beam has to be shaped such that the superposition of its space charge fields and plasma fields result in a uniform accelerating field. In this work we show how beam-induced-ionization injection can be used to shape and inject a trailing beam suitable for beam loading. Our particle-in-cell numerical simulations done with OSIRIS show the ionization injection of a shaped 340 pC, 13 kA and 3  μm long electron beam accelerated to 900 MeV in less than 3 cm of plasma. The configurations considered numerically were based on the beams and plasmas that have been and will be available at the FACET facility.