Designing the Heart of an Accelerator: Korea-4GSR Beam Physics Design

Electron storage ring-based synchrotron light sources have become essential research infrastructure across a wide range of scientific and technological fields, offering high-brightness, broad-spectrum, and highly coherent photon beams. The brightness and quality of these photon beams are fundamentally determined by the emittance of the electron beam circulating in the ring. Fourth-generation storage rings, developed with multi-bend achromat (MBA) or hybrid MBA lattice structures (HMBA), achieve ultra-low emittance and represent a major leap in accelerator performance. Korea-4GSR is a new 4 GeV electron beam energy facility designed with HMBA lattice, enabling a low emittance of 62 pm within 800 m ring circumference. This article introduces the key design concepts, beam dynamics considerations, and technological components of Korea-4GSR as a representative case of a next-generation storage ring light source.