Speaker
Description
The maximum accelerating gradient, Eacc,max, of a superconducting radio- frequency (SRF) cavity is limited by the surface magnetic field at which a vortex avalanche occurs on the inner cavity surface. Theoretical studies predict that a superconducting–insulator–superconducting (S′–I–S) multilayer structure can effectively enhance the threshold field for vortex avalanche. Furthermore, an optimal combination of superconducting- and insulating-layer thicknesses is expected to maximize the threshold field.
We aim to fabricate an Nb3Sn–I–Nb structure on the inner surface of a 3 GHz elliptical bulk-niobium SRF cavity and thereby increase Eacc,max by a factor of two or more, as theoretically predicted. Nb3Sn thin films are generally synthesized by heat-treating precursor materials containing Nb and Sn at 900–1100 °C for several hours. We therefore are developing a specialized cathode for depositing an Nb–Sn precursor layer on the inner surface of the SRF cavity by DC magnetron sputtering method. The cathode is designed to achieve the Nb-to-Sn atomic ratio of 3:1.
In this presentation, we report progress in the following areas: (1) particle- in-cell/Monte Carlo simulations used to design a DC magnetron-sputtering system capable of producing a uniform film-thickness distribution and the desired Nb-to-Sn atomic ratio inside the cavity, and (2) sputtering tests using a prototype cathode designed for the simultaneous deposition of two different metallic targets onto the inner surface of a coupon cavity.