Why Nb_3Sn cavities quench far below their predicted field · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title · changed
Revision 1: Why Nb3Sn cavities quench far below their predicted field
Revision 2: Why $\mathrm{Nb_3Sn}$ cavities quench far below their predicted field
Plain · changed
Revision 1: Nb3Sn should hold about twice the field of niobium, but real cavities fail at roughly half of niobium's best.
Revision 2: $\mathrm{Nb_3Sn}$ should hold about twice the field of niobium, but real cavities fail at roughly half of niobium's best.
Precise · changed · core
Revision 1: Vapor-diffusion Nb3Sn films ($\sim 2e-4\,\mathrm{cm}$ thick) on Nb cavities quench at $H_{\mathrm{pk}} \sim 800\text{-}1200\,\mathrm{G}$, compared with a predicted $H_{\mathrm{sh}}$ near $4000\,\mathrm{G}$. Identify the limiting mechanism (thin-grain regions, tin-depleted patches with low $H_c$, vortex entry at grain boundaries, thermal runaway in the low-conductivity film) and predict the quench field from measured film microstructure.
Revision 2: Vapor-diffusion $\mathrm{Nb_3Sn}$ films ($\sim 2 \times 10^{-4}\,\mathrm{cm}$ thick) on Nb cavities quench at $H_{\mathrm{pk}} \sim 800\text{-}1200\,\mathrm{G}$, compared with a predicted $H_{\mathrm{sh}}$ near $4000\,\mathrm{G}$. Identify the limiting mechanism (thin-grain regions, tin-depleted patches with low $H_c$, vortex entry at grain boundaries, thermal runaway in the low-conductivity film) and predict the quench field from measured film microstructure.
Settled by
Temperature mapping and post-test microscopy of quench sites in several cavities showing a single microstructural cause whose predicted threshold matches the quench field.
Kind
well-posed
Answer type
mechanism
References
(empty)
Literature status
open
Status note · changed
Revision 1: Single-cell Nb3Sn cavities reached accelerating gradients of approximately $0.24\,\mathrm{MeV}/\mathrm{cm}$ by the early 2020s; the gap to the predicted superheating field remained.
Revision 2: Single-cell $\mathrm{Nb_3Sn}$ cavities reached accelerating gradients of approximately $0.24\,\mathrm{MeV}/\mathrm{cm}$ by the early 2020s; the gap to the predicted superheating field remained.
Posed since
(empty)

Decisions