Beam dynamics design of a proton/heavy-ion injector for the synchrotron of the XiPAF upgrading project

Abstract

In the multi-turn injection process of proton and heavy-ion synchrotrons, reducing the transverse emittance of the injected beam enhances injection gain, thereby increasing the number of particles stored in the synchrotron. An injector with low emittance growth is advantageous for achieving a low-transverse-emittance beam at the injection point. This paper presents the results of the beam dynamics design for a low-transverse-emittance injector intended for a proton/heavy-ion synchrotron of the Xi'an 200 MeV Proton Application Facility (XiPAF) upgrading project. The injector comprises two dedicated injection lines that accelerate and transport the protons and heavy-ions, along with a shared line to direct the beams into the synchrotron. While the proton injection line is developed from upgrading of the existing H⁻ beam line, the heavy-ion injection line is newly constructed. A heavy-ion IH-DTL featuring negative phase acceleration and FODO focusing has been adopted. Its acceleration phase and acceleration voltage have been optimized to suppress the emittance growth. The beam dynamics of the linac-to-ring beam transport line (LRBT) has been optimized, employing three sets of beam scrapers to further reduce emittance. Simulations using the TraceWin code demonstrate that the normalized transverse emittances (99 % particles) at the injection point are ensured to be less than 1.2 π mm·mrad for the proton beam and 1.05 π mm·mrad for the heavy ion beams. A comprehensive error analysis, accounting for errors from the input beams, solenoids, quadrupoles, debunchers, RF fields inside the cavities, and machining, is conducted through the start-to-end simulations. With corrections to the quadrupoles, scrapers, and steering magnets, the results indicate a 95 % probability of achieving the required mismatch factor, and a certainty of 100 % that the required beam current, momentum spread, and normalized transverse emittance at the injection point can be attained.