Development of the second prototype C-band accelerator structure for SuperKEKB

Research and development of the C-band accelerating section has been in progress at KEK since 2002. This paper reports on the development of the second prototype accelerating section. Both input/output couplers have a single port and their cell lengths are the same as the waveguide width. The coupler irises are thicker than the first prototype for reducing the rf breakdown at the iris edge. The coupler cavity diameters and the coupling irises were optimized by using the iteration of the rf measurements and the manufacturing which is based on the nodal shift method. The high-power test of the accelerating section at the test stand has been performed for a month. Rf breakdown frequency has been reduced. (author)