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TY - UNPB AU - Junginger, T. AU - Hall, D.L. AU - Laxdal, R.E. AU - Liepe, M. AU - Posen, S. AU - Prokscha, T. AU - Salman, Z. AU - Storey, D.W. AU - Suter, A. AU - Tan, T. AU - Thoeng, E. AU - Valente-Feliciano, A-M. AU - Wasserman, W.W. AU - Withanage, W.K. AU - Wolak, M.A. AU - Xi, X. ED - Schaa, Volker RW ED - He, Yuan ED - Li, Lu ED - Zhao, Ning TI - Dirty Layers, Bi-layers and Multi-layers: Insights from Muon Spin Rotation Experiments J2 - Proc. of SRF2017, Lanzhou, China, July 17-21, 2017 C1 - Lanzhou, China T2 - International Conference on RF Superconductivity T3 - 18 LA - english AB - The multilayer approach is being investigated for SRF applications since 2006 "*". More recently the option of using a bilayer system of two superconductors has been considered as an alternative approach to reach accelerating gradients beyond bulk niobium or to explain the gradient enhancement from a 120°C bake by introduction of a 'dirty layer "**"'. In this talk results are presented from two muon spin rotation experiments at TRIUMF and PSI. The former measures the field of first entry Hentry. It will be shown that MgB2 and Nb3Sn on top of Nb both push Hentry above Hc1 to a value consistent with Hsh, independent of the layer thickness. 120°C baking increases Hentry slightly but significantly above Hc1. Using the low energy muon beam at PSI we show that there is a long range proximity effect in a bilayer system of NbTiN on Nb. This effect yields a stronger decay of the RF field with depth as expected for pure NbTiN, opposite to what has been predicted for a bi-layer system due to counter current flow at the superconductor-superconductor interface "***". An insulating layer suppresses this proximity effect. PB - JACoW CP - Geneva, Switzerland ER -