In-vacuum undulators for the first phase beamlines of Korea-4GSR

Korea-4GSR, a new synchrotron radiation facility currently under construction in Ochang, Chungbuk, South Korea, introduces three types of in-vacuum undulators (IVUs) for its first phase hard X-ray beamlines: IVU20, IVU22, and IVU24. These IVU types share a common 3-m-long framework capable of adjusting the magnetic gap size between 5 and 18 mm, but they differ in the undulator period length (λ_u). This study characterizes their photon beams in terms of brightness, spectral coverage, source size, angular divergence, coherent fraction, coherent flux, and total and central cone radiation powers, using undulator calculations. The three IVU types are comparable in brightness. IVU20 is the most coherent, although lacking spectral continuity at around 7.5 keV. IVU22 and IVU24 ensure spectral continuity, but their coherent flux is moderately compromised. The performance of the undulators is assessed in comparison to the Pohang Light Source-II (PLS-II) undulator and the U21 undulator at Advanced Photon Source Upgrade (APS-U).