On the use of the envelope model for down-ramp injection in laser-plasma accelerators

摘要： The path towards high 6D-brightness electron beams coming from plasma accelerators relies on numerical simulations to investigate and explain novel physics and parameter regimes. Particle-in-cell codes are a reliable tool for this purpose, but full-scale simulations can be computationally challenging, specifically when performing large parameter scans. Approximate models and solvers are an alternative to quickly assess new regimes, but one needs to understand the validity of these models for each specific problem. In this work, we investigate the usefulness of a ponderomotive guiding center solver to model density down-ramp injection in laser wakefield accelerators. We also report results for density down-ramp injection in the context of EuPRAXIA, where we find that this method can produce 250 MeV, 30 pC beams that fulfill all the requirements for the injector stage, with <1 % energy spread and <100 nm emittance.