| Title |
Nanostructure of the Penetration Depth in Nb Cavities: Debunking the Myths and New Findings |
| Authors |
- Y. Trenikhina, A. Romanenko
Fermilab, Batavia, Illinois, USA
- J. Kwon, J.-M. Zuo
UIUC, Urbana, USA
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| Abstract |
Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency (SRF) cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls at both room and cryogenic temperatures, we directly discover the existence of nanoscale hydrides in SRF cavities limited by the high field Q slope, and show the decreased hydride formation after 120C baking. Crucially, in extended studies we demonstrate that adding 800C hydrogen degassing - both with AND without light BCP afterwards - restores the hydride formation to the pre-120C bake level correlating perfectly with the observed high field Q slope behavior. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120C bake, which contradicts some of the widely used models of niobium surface.
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| Paper |
download WEA1A05.PDF [1.160 MB / 6 pages] |
| Slides |
download WEA1A05_TALK.PDF [31.773 MB] |
| Conference |
SRF2015, Whistler, BC, Canada |
| Series |
International Conference on RF Superconductivity (17th) |
| Proceedings |
Link to full SRF2015 Proccedings |
| Session |
Fundamentals III - Frequency dependence |
| Date |
16-Sep-15 08:00–09:20 |
| Main Classification |
Fundamental SRF R&D - Bulk Nb |
| Keywords |
niobium, cavity, electron, cryogenics, SRF |
| Publisher |
JACoW, Geneva, Switzerland |
| Editors |
Robert E. Laxdal (TRIUMF, Vancouver, BC, Canada); Jana Thomson (TRIUMF, Vancouver, BC, Canada); Volker RW Schaa (GSI, Darmstadt, Germany) |
| ISBN |
978-3-95450-178-6 |
| Published |
December 2015 |
| Copyright |
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