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TUP039 |
Meissner Screening at Hot (Unbaked) and Cold (Baked) Spots in Electropolished Cavities Studied by Low Energy Muon Spectroscopy | |
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Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. While there is a number of recent structural investigations, which shed light on possible underlying mechanisms of the high field Q slope and 120C baking effect [], there is fewer explicit superconducting investigations exploring the microscopic superconducting properties at the locations of "hot" spots in unbaked cavities. Furthermore, while the nature of the magnetic field penetration in the Meissner state into bulk niobium is predicted by BCS theory and its strong coupling extensions, it was never directly observed. Here we present a direct measurement of the magnetic field profile B(z) in the Meissner state inside a "hot" spot cutout from the electropolished cavity, and compare it to a "cold" spot from the baked electropolished cavity. We demonstrate the presence of a dead layer, a non-exponential B(z) profile, and a drastic change introduced by the 120C baking. [*] A. Romanenko, F. Barkov, L.D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26, 035003 (2013) [**]A. Romanenko, C.J. Edwardson, P.G. Coleman, P.J. Simpson, Appl. Phys. Lett. 102, 232601 (2013) |
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