Hollow plasma channels are attractive for lepton acceleration because they provide intrinsic emittance preservation regimes. However, beam breakup instabilities dominate the dynamics. Here, we show that thin, warm hollow channels can sustain large-amplitude plasma waves ready for high-quality positron acceleration. We verify that the combination of warm electrons and thin hollow channels enables positron focusing structures. Such focusing wakefields unlock beam breakup damping mechanisms. We demonstrate that such channels emerge self-consistently during the long-term plasma dynamics in the blowout's regime aftermath, allowing for experimental demonstration.
Metre-scale plasma wakefield accelerators have imparted energy gain approaching 10 gigaelectronvolts to single nano-Coulomb electron bunches. To reach useful average currents, however, the enormous energy density that the driver deposits into the wake must be removed efficiently between shots. Yet mechanisms by which wakes dissipate their energy into surrounding plasma remain poorly understood. Here, we report picosecond-time-resolved, grazing-angle optical shadowgraphic measurements and large-scale particle-in-cell simulations of ion channels emerging from broken wakes that electron bunches from the SLAC linac generate in tenuous lithium plasma. Measurements show the channel boundary expands radially at 1 million metres-per-second for over a nanosecond. Simulations show that ions and electrons that the original wake propels outward, carrying 90 percent of its energy, drive this expansion by impact-ionizing surrounding neutral lithium. The results provide a basis for understanding global thermodynamics of multi-GeV plasma accelerators, which underlie their viability for applications demanding high average beam current.
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. Particlein-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 the 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 the European Plasma Research Accelerator with eXcellence in Applications, 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 <100nm emittance.
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