Physics design of the HEPS LINAC

The High Energy Photon Source (HEPS) is a synchrotron radiation source with an ultrahigh brightness and under construction in China. Its accelerator system is comprised of a 6-GeV storage ring, a full energy booster, a 500-meV Linac and three transport lines. With deepening investigations on the physics designs of the storage ring and the booster, the physics scheme of the Linac has evolved through multiple versions. The final version of the Linac, including the electron gun, bunching system and main accelerator, has been determined. The Linac is an s-band normal conducting electron linear accelerator with a very high bunch charge and a large bunch charge range. Based on simulations, the Linac could provide electron bunches with charge greater than 8.5-nC, meeting the energy spread and emittance requirements. This paper first reviews the evolution and main considerations for different design versions and then describes the physics design and dynamic simulation results of the final scheme in detail.