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Title: Origin of the field-dependent losses in Nb3Sn cavities
Plain: Even before stopping, Nb3Sn cavities lose more energy as the field grows. The source of this extra loss is unclear.
Precise: Nb3Sn cavities at 4.2 K and 1.3 GHz show $Q_{0}$ decreasing with $B_{\mathrm{pk}}$ above $\sim 300\ \text{to}\ 500\,\mathrm{G}$. Determine whether this arises from grain-boundary Josephson weak links, vortex penetration at local defects, tin-poor phases, or nonlinear BCS response, with a model predicting $Q_{0}(B_{\mathrm{pk}}, T)$.
Settled by: Measured $Q_{0}(B_{\mathrm{pk}})$ for cavities with controlled grain size and stoichiometry matched by a predictive model.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)