A facility for the characterisation of planar multilayer structures with preliminary niobium results

Abstract

Abstract The maximum accelerating gradient of superconducting radio frequency cavities are currently reaching their theoretical limits, due to the magnetic field entering the superconductor in the form of vortices. To overcome these limits, thin film coated superconducting materials are required, however these need to be tested to optimise their properties. A system has been designed, built, and commissioned at Daresbury Laboratory that applies a local DC magnetic field parallel to the surface, from one side of a sample, similar to that in cavity operation. A magnetic flux density (up to 600 mT) is generated parallel to the sample surface in the 2 mm gap of a C-shaped ferrite yoke. Two Hall probe sensors are used to measure both the applied and penetrated magnetic field. The system operates in a cryogen free environment, with a minimum temperature of approximately 2.6 K. A Pb foil has been used to characterise the system, and determine how the sample size affects the results. Nb thin film samples have been tested for varying thickness to determine how the depth effects the field of full flux penetration, B f p . The design, operation, methods of analysis and first results of this facility will be reported in this paper.