The FCC-ee collider complex relies on continuous top-up injection to maintain the high bunch charge and luminosity required to achieve its physics objectives. The injector complex will generate and accelerate electron and positron beams up to 20 GeV using linear accelerators, while a damping ring is foreseen to reach the emittance levels demanded by the high-energy booster. This contribution presents the first concept for the injection and extraction systems of the damping ring, including the layout, optics design, and hardware constraints. A possible implementation of the newly introduced polariser ring and its associated beam transfer scheme is also outlined. The beam dynamics and operational scenarios of these transfer systems are discussed, together with the next steps towards defining a baseline layout within the injector complex.

The Beam Accumulator Ring (BAR) in the EIC injector chain accumulates charge from multiple linac pulses to provide the high-intensity polarized electron beam required for ESR injection. At the design single-bunch charge, beam–impedance effects become a key performance and stability limit, so initial broadband-resonator estimates must be refined with a realistic impedance budget. We use the 3D EM solver GdfidL to compute the longitudinal and transverse geometric impedances of the main vacuum components and combine them with the resistive-wall contribution in a ring-wide model.

High single-bunch charge in the EIC Beam Accumulator Ring (BAR) leads to strong impedance-induced bunch lengthening that exceeds the requirements for injection into the Rapid Cycling Synchrotron. Using geometric and resistive-wall impedance model and multi-particle tracking with ELEGANT, we study RF phase-jump schemes that rotate the longitudinal phase space to transiently shorten the bunch before extraction. The simulations show that an appropriately timed phase jump can compress the bunch into the required bunch-length and energy-spread window while maintaining transverse stability.

A dedicated electron transfer line from Rapid Cycling Synchrotron (RCS) to Electron Storage Ring (ESR), referred to as the RTE line has been designed for the Electron-Ion Collider (EIC). The beamline follows a straight-line geometry, with a length of 133 m, and is consists with two matching sections and a FODO section for beam diagnostics. Imperfections with magnet alignments introduce orbit distortions, making orbit correction scheme a critical component in the design. To facilitate orbit correction, each quadrupole magnet is equipped with a pair of beam position monitors (BPMs) and kickers. The Singular Value Decomposition (SVD) algorithm is used for orbit correction and tolerance studies. This paper presents the ongoing progress in the optics design and error correction scheme of the RTE line.

The electron injector for the Electron-Ion Collider (EIC) consists of a linear accelerator, a beam accumulation ring, and the Rapid Cycling Synchrotron (RCS) before the electrons are injected into the Electron Storage Ring (ESR) and collided. Extraction out of the RCS is complicated by limited space and the nominal beam pipe aperture, while injection into the ESR is complicated due to the limitation of kicker strength, so that the kickers will not impact the proton beam in the adjacent Hadron Storage Ring (HSR); additionally, the ESR kickers must also provide enough kick to the stored bunch for the swap-out scheme. This paper covers the injection into and extraction out of the RCS, as well as injection into the ESR, detailing layout, optics, and anticipated parameters of the septa and different kickers.

The Super Tau-Charm Facility (STCF) is a tau–charm electron-positron collider currently under design, with a projected single-bunch charge of up to 8 nC and an average beam current as high as 2 A. On-axis swapping injection is one of the feasible injection schemes; however, the high-current beam can induce severe heating effects on the electrodes of the stripline kicker. Based on theoretical derivations and CST simulations, this work systematically evaluates the longitudinal beam coupling impedance, effective impedance, loss factor, total parasitic power loss, and electrode thermal power deposition of the kicker, and subsequently performs an impedance-optimization study. The results show that both the total parasitic power loss and the electrode thermal power deposition are significantly reduced after structural optimization, with the loss factor notably improved for various bunch lengths. Further temperature-rise and mechanical-deformation analyses indicate that the maximum electrode temperature remains below the safe operating threshold for copper electrodes, and that the deformation induced by thermal expansion has a negligible impact on the electromagnetic field. In summary, the optimized stripline kicker continues to satisfy the design requirements under the high-current operation conditions of the STCF.

The Super Tau-Charm Facility is a high-luminosity electron–positron collider operating at a center-of-mass energy range of 2–7 GeV. The stringent requirements for beam brightness and stability pose significant challenges to the injector transport system, especially the positron transport lines of the damping ring. Beam transverse emittance is one of the primary parameters, which is influenced by a mass of components in the lattice design. In this study, a newly developed multistage optimization method is employed to optimize multiple sets of quadrupole strengths along the transport line. The optimized results effectively suppress the emittance growth and maintain compliance of other parameters with damping ring requirements. These results provide a practical reference for the optical design of high-brightness transport systems in next-generation electron–positron colliders.

The Super Tau-Charm Facility (STCF), a new-generation electron-positron collider proposed in China, is a major international scientific facility designed to operate in the center-of-mass energy range of 2–7 GeV, with luminosity at 4 GeV beyond 5x1034 cm-2s-1. It adopts third-generation collider design concepts, including ultra-small beam size, a large Piwinski angle, and the crab waist scheme. However, these features introduce challenges such as a limited dynamic aperture and a short beam lifetime, which significantly complicate beam injection. Two injection schemes are currently under investigation. The first is off-axis injection, which is technologically mature but requires a large horizontal dynamic aperture and is characterized by low injection efficiency and considerable beam loss. The second is swap-out injection, with stored bunches replaced by injected ones using ultra-fast kickers, improving injection efficiency and easing aperture constraints, but imposing stringent technical requirements and high costs on the injector system. To address these challenges, we propose an injection design compatible with both schemes, reserving upgrade potential from off-axis injection in Phase I to swap-out injection in Phase II.