The Next SRF Technologies

In this talk, I introduce the proposed next superconducting radio-frequency (SRF) technologies that will make it possible to achieve much higher accelerating electric field than the present SRF technologies. Audiences are assumed to be non-experts. We start from a brief review of basics of SRF, history of the high gradient technologies and the layered structure behind it. The multiple benefit of the layered structure is introduced. We then move to the next SRF technologies: superconductor-superconductor (SS) structure and superconductor-insulator-superconductor (SIS) structure. We discuss the SS structure in detail. Experimental results are also introduced and compared with theoretical considerations.