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Title: Collider-quality positron acceleration in plasma
Plain: The usual plasma wake focuses electrons but pushes positrons apart, so positrons cannot be accelerated in it with good quality. A collider needs both, and no scheme yet works for positrons in experiment.
Precise: In the nonlinear blowout regime, plasma electrons are expelled and the ion column focuses electrons but defocuses positrons. Find a wake configuration (hollow channel, finite-radius plasma, electron filament, magnetized wake, quasi-linear wake) that simultaneously gives gradient above $1e7\,\mathrm{eV}/\mathrm{cm}$, energy-transfer efficiency above 30 percent, rms energy spread below 1 percent and collider-level emittance preservation. An answer is a demonstrated configuration or a proof that the requirements are incompatible.
Settled by: An experiment accelerating a positron bunch meeting all four metrics simultaneously.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: Several schemes meet subsets of the requirements in simulation (2023-2026, e.g. magnetized wakes, arXiv:2608.30455); none meets all in experiment.
Posed since: (empty)