Simultaneous top-up injection into five rings at KEK electron/positron injector linac

The 600-m-long KEK injector linac has delivered electron and positron beams for collider rings and light sources. It was upgraded for aiming at a low emittance beam with a high bunch charge towards the SuperKEKB project based on the nano-beam scheme. In this upgrade, many new components have been newly developed, such as a flux concentrator, a large aperture S-band accelerating structure, a pulsed magnet, a low emittance photo-cathode rf gun, a fast rf monitor, a fast BPM module, and so on. After many long years of upgrade work and beam commissioning, simultaneous top-up injection into five independent rings was successfully achieved in 2019. (author)