TOP counter prototype R&D

We have been developing a Cherenkov ring-imaging counter, named TOP counter, as a particle-identification device of the Belle-II detector for the super B-factory at KEK. In this presentation, we show the R&D status of the TOP counter prototype. We performed a beam test using 2 m long quartz radiator and MCP-PMTs, and evaluated the number of detected photons, time resolution and chromatic effects. We developed a square-shape MCP-PMT with Hamamatsu photonics, so as to obtain a sufficient lifetime under the Belle-II environment. We improved the lifetime of the quantum efficiency by changing the internal structure and production process, and then obtained a lifetime of > 350 mC / cm 2 .