WEXA05
TRIUMF, Vancouver, Canada
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
HZB, Berlin, Germany
Fermilab, Batavia, Illinois, USA
PSI, Villigen PSI, Switzerland
Victoria University, Victoria, B.C., Canada
Temple University, Philadelphia, USA
UBC & TRIUMF, Vancouver, British Columbia, Canada
JLab, Newport News, Virginia, USA
UBC, Vancouver, B.C., Canada
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.
* Gurevich, A. APL 88.1 (2006)
** Checchin, M. Diss. Illinois Institute of Technology, 2016.
Kubo, T. Superconductor Science and Technology 30.2 (2016)
*** Kubo, T et al. APL 104.3 (2014)
