Design of the positron accelerators for STCF

Abstract The Super Tau-Charm Facility (STCF) is a new generation electron-positron collider designed to explore frontier physics in the tau-charm energy region, with a center-of-mass energy range of 2–7 GeV and a luminosity of 0.5× 10 35 cm -2 s -1 . The positron injector is a critical component of circular colliders. It employs a 2.5 GeV electron beam to strike a tungsten target, thereby generating positron beams. After production, the positrons are captured and initially accelerated to 260 MeV in the pre-acceleration section, followed by further acceleration to 1 GeV in Positron Linac 1. This study focuses on optimizing the production, transport, and acceleration of positrons to maximize the yield, ensuring it meets the requirements for injection into the accumulation ring. The STCF positron source system has successfully achieved a 2.5 nC positron beam at the 1 GeV exit, featuring a rms geometric emittance below 1400 nm·rad, an energy spread of 0.5%, and an bunch length of 0.5 ps.