Maximum efficiency of a stable collinear structure wakefield accelerator
In plain words
A driving bunch hands energy to a trailing bunch through the wake it leaves; taking more energy also makes the trailing bunch wobble sideways and break up.
Precise statement
For a collinear dielectric or corrugated-pipe wakefield accelerator, a relation between drive-to-witness energy-transfer efficiency $\eta$ and the transverse wake that drives beam breakup was derived around 2017-2018. Determine the maximal $\eta$ achievable at transformer ratio $R \ge 5$ with witness emittance growth below 10 percent over the full accelerator length, including BNS damping (energy-chirp detuning of the transverse motion) and quadrupole-wake focusing, or prove an upper bound on $\eta$.
What would settle it
An analytic bound or a converged start-to-end simulation with full $3\mathrm{D}$ wakes, checked by a multi-meter experiment at the stated $R$ and $\eta$.