Dissipation of electron-beam-driven plasma wakes

Abstract

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 ps-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.

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• Ion dynamics driven by a strongly nonlinear plasma wake
• Advanced quasistatic approximation
• Lattice Boltzmann method for warm fluid simulations of plasma wakefield acceleration
• Recovery of hydrogen plasma at the sub-nanosecond timescale in a plasma-wakefield accelerator
• Longitudinally resolved measurement of energy-transfer efficiency in a plasma-wakefield accelerator
• Correlations between X-rays, Visible Light and Drive-Beam Energy Loss Observed in Plasma Wakefield Acceleration Experiments at FACET-II
• Thermal fluid closures and pressure anisotropies in numerical simulations of plasma wakefield acceleration