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The SIS structure which consists of alternative thin lay- ers of superconductors and insulators on a bulk niobium has been proposed to shield niobium cavity surface from high magnetic field and hence increase the accelerating gradient. The study of the behavior of multilayer supercon- ductors in an external magnetic field is essential to opti- mize their SRF performance. In this work we report the de- velopment of a simple and efficient technique to measure penetration of magnetic field into bulk, thin film and mul- tilayer superconductors. Experimental setup contains a small superconducting solenoid which can produce a par- allel surface magnetic field up to 0.5 T and Hall probes to detect penetrated magnetic field across the superconduct- ing sample. This system was calibrated and used to study the effect of niobium sample thickness on the field of full magnetic flux penetration. We determined the optimum thickness of the niobium substrate to fabricate the multi- layer structure for the measurements in our setup. This technique was used to measure penetration fields of Nb 3 Sn thin films and Nb 3 Sn/Al 2 O 3 multilayers deposited on Al 2 O 3 wafers. The system was optimized to mitigate thermo- magnetic flux jumps at low temperatures. 

The magnetic field at which first flux penetrates is a fundamental parameter characterizing superconducting materials for SRF cavities. Therefore, an accurate technique is needed to measure the penetration of the magnetic field directly. The conventional magnetometers are inconvenient for thin superconducting film measurements because these measurements are strongly influenced by orientation, edge and shape effects. In order to measure the onset of field penetration in bulk, thin films and multi-layered superconductors, we have designed, built and calibrated a system combining a small superconducting solenoid capable of generating surface magnetic field higher than 500 mT and Hall probe to detect the first entry of vortices. This setup can be used to study various promising alternative materials to Nb, especially SIS multilayer coatings on Nb that have been recently proposed to delay the vortex penetration in Nb surface. In this paper, the system will be described, and calibration will be presented.