Speaker
Description
The material of choice for current SRF accelerators is bulk Nb which is reaching the theoretical limits in terms of maximum accelerating gradient, Eacc. One method to increase Eacc is to use superconductor-insulator-superconductor, SIS, structures, where the thin films on the surface are smaller than the London penetration depth to screen the applied field, Bapp, such that the thicker superconducting layer will see a lower B than on the surface. The screening allows Bapp to be increased resulting in a larger Eacc. Multilayer structures are challenging to fabricate and test. It is easier to deposit flat samples for multilayers than for 3D structures. Flat samples cannot be tested by commercial magnetometry such as a VSM without limitations, such as early flux penetration due to edge effects as the Bapp is larger than the sample, and B penetrating through the insulating layer so the screening effect will not be observed.
A field penetration facility has been designed, built, and commissioned at Daresbury laboratory. A DC magnetic field is applied from one side of the sample using a C-shaped dipole magnet. Hall probe sensors measure both Bapp and the penetrated field. Samples are mounted directly onto a cryocooler and can be tested at a range of temperatures from as low as 2.5K. The facility has been commissioned using a range of samples including Pb and Nb, which will be reported along with preliminary multilayer results.
