BEAMS
In the literature: open
Can a Nb3Sn cavity exceed the gradient of the best niobium cavities
In plain words
The goal of Nb3Sn is to go beyond niobium, but so far niobium still holds the gradient record. The question is whether any Nb3Sn cavity can beat it.
Precise statement
Determine whether a Nb3Sn-coated 1.3 GHz elliptical cavity can sustain $E_{\mathrm{acc}}>0.45\,\mathrm{MV}/\mathrm{cm}$ ($B_{\mathrm{pk}}>1900\,\mathrm{G}$) at any temperature with $Q_{0}>1e10$, or whether intrinsic film properties (grain boundaries, thin-film thermal limits) forbid it.
What would settle it
A Nb3Sn cavity test exceeding the Nb record gradient, or a demonstrated intrinsic bound below it.