The Super Tau-Charm Facility (STCF) was proposed as a third-generation circular electron-positron collider in the energy range of 2-7 GeV (CoM) and with a luminosity greater than 5*10^34 cm^-2s^-1 @4 GeV, aiming to explore charm physics and tau physics in the next decades. This presentation will introduce the facility design and R&D efforts for STCF, including the design goal, accelerator and detector schemes, and key technological R&D efforts, with focus on the accelerator. Under the financial support of the key technology R&D project by the local governments and other national funding agencies, the STCF accelerator team including international collaborators has completed the conceptual design of the accelerator, and started the technical design. The accelerator consists of a full-energy injector consisting of multi-section linacs and a positron accumulator ring and a double-ring collider with the crab-waist collision scheme. Key physics and technological challenges will be addressed. Ongoing R&D efforts and progresses will be summarized. The project planning will also be given. International collaboration is much welcome.

The Ghost Collider is a proposal for a 550 GeV center-of-mass (275 GeV per beam) linear collider with four interaction regions, each with the design luminosity. The primary innovation is the use of “ghost bunches” containing equal numbers of electrons and positrons, therefore being electrically neutral. In the linacs, energy is transferred between electrons and positrons in the same bunch, decelerating one type of particle and using the energy to accelerate the other; a new class of Energy Recovery Linac. At the interaction points (IPs), collisions between two neutral ghost bunches occur. Historically this approach has been referred to as "charge compensation of beam-beam". To avoid instabilities, round beams with small disruption parameter are arranged at the IPs, ensuring particles and their energy can be recycled with minimal loss. Four “serial IPs” are incorporated, where chromatic errors produced in one IP are canceled in the following IP. All interaction points have the nominal luminosity per IP of $2.8 \times 10^{34}$ cm$^{-2}$ s$^{-1}$ for a facility luminosity of $11 \times 10^{34}$ cm$^{-2}$ s$^{-1}$ @ 100 MW total electrical power for SR replacement, linac RF, cryogenic and damping ring systems. The result is a totally original concept for an electron-positron collider.

The PADME-X17 experiment is searching for a light dark matter candidate. The experiment would greatly benefit from the availability of a dedicated beam with long pulse duration and minimal instantaneous current. In this contribution, a third-order resonant slow-extraction scheme is considered, starting from the present lattice of the DAFNE damping ring. This solution, already integrated with the DAFNE complex, could provide the necessary positron-beam improvements within the existing facility. This study, currently aimed at improving the sensitivity of fixed-target experiments with positrons, could open new possibilities for beamlines based on the beam extracted from the damping ring.

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 layout of the FCC-ee collider requires the separa- tion of the electron and positron beams, which are circu- lating in opposite directions, on either side of the RF sys- tem. Only one of the two beams must be deflected, while the other one (the beam circulating in the direction of the RF) shall remain untouched to avoid synchrotron radiation being emitted toward the RF section. This functionality is achieved using a combination of an electric field and a perpendicular magnetic field, which must be matched to each other along the entire length of the separator to avoid synchrotron radiation (SR) emission toward the supercon- ducting RF cryomodules. In order to satisfy the matching condition 𝐵 = 𝐸/𝑐 for relativistic particles, an extremely weak magnetic field (5 mT) is required for a given achiev- able static electric field (1.5 MV/m). This article presents a separator concept that combines an under-vacuum electro- static system with a low-field large-aperture outside-vacuum dipole magnet to achieve the main separation functionality while providing excellent field matching and low SR produc- tion. In addition to the concept development, three critical aspects have been identified and are the subject of ongoing studies to assess feasibility by end of 2027: high-voltage (HV) breakdown, beam coupling impedance and machine protection.

The FCC-ee demands an injector complex capable of delivering high-current, high-brightness electron and positron beams with exceptional efficiency. Within the CHART/FCC-ee Injector Study collaboration, a revised injector layout has been developed to optimize performance, cost, and power consumption. A central pillar of this effort is the tuning-free, high-gradient normal-conducting RF structure technology pioneered at PSI for SwissFEL and since extended across S-, C-, and X-band systems. This scalable approach underpins future developments in the FCC-ee linacs, enabling reliable acceleration. In parallel, the P³ program at PSI is advancing the positron source, with commissioning foreseen in 2026, while upcoming work will enhance the electron source and refine RF requirements for the positron linac. This contribution presents the current injector complex status, key design highlights, and the outlook toward the FCC-ee injector technical design report.

The Future Circular Electron-Positron Collider (FCC-ee) is a proposed next-generation particle accelerator, planned as the first stage of the larger Future Circular Collider project at CERN. It is an electron-positron collider designed to be a precision instrument for studying fundamental physics. The PSI Positron Production (P$^{3}$) is the planned proof-of-principle experiment for the FCC-ee positron source. The main goal of this experiment is to test new technology and validate the envisioned positron production scheme. To this end, a prototype of the FCC-ee positron source will be hosted at the SwissFEL facility at the Paul Scherrer Institute in Switzerland. A dedicated bunker has been built inside the SwissFEL tunnel, and the experimental components are being installed. Simulations have been performed with the FLUKA.CERN Monte Carlo code to dimension the P$^{3}$ bunker and local shielding elements. Calculations have been repeated for various target models since different target options will be tested. This contribution briefly describes the ingredients of the P$^{3}$ experiment and details the dedicated bunker and the local shielding. It shows the expected dose rate distribution outside the P$^{3}$ bunker. The foreseen activation is also discussed.

The Low Energy Recirculator Facility (LERF) at Jefferson Lab, formerly operated for the Free-Electron Laser program, has been proposed as the injector complex for the planned 12 GeV CEBAF positron upgrade (Ce+BAF), with an additional pathway to support a potential 22 GeV CEBAF electron upgrade. In this configuration, LERF would generate and pre-accelerate positrons to 123 MeV, matching the present injection energy into the North Linac. Due to the relatively large emittance expected from the positron source, a comprehensive acceptance study has been performed from LERF through the CEBAF recirculating linacs and beam transport lines to the experimental halls. The objective is to establish the positron phase-space acceptance and provide design feedback to the positron production and capture systems. Furthermore, given CEBAF’s capability to deliver highly polarized beams, spin-tracking simulations have been carried out including magnet imperfections, alignment errors, and synchrotron-radiation–induced energy spread. Particular attention is given to the evolution of the spin tune and the corresponding depolarization mechanisms along the beam delivery path, especially for providing longitudinal polarization at the experimental halls. These results inform injector design choices and assess the overall feasibility of delivering high-polarization positron beams in CEBAF.

Super Tau Charm Facility (STCF) is the third-generation e+-e- collider under design and R&D with a circumference of about 800-900 m, a center-of-mass energy range from 2-7 GeV and design luminosity higher than 0.5 x 1035 cm-2 s-1, about 100 times higher than BEPC-II. To squeeze the beam for higher luminosity, compact twin-aperture high gradient interaction region superconducting magnet (IRSM) systems are required on both sides of interaction point (IP). The IRSM system consists of four twin-aperture superconducting quadrupole magnets. As part of the key R&D activities at accelerator CDR stage, full-scale twin-aperture QD1 quadrupole magnets were designed and constructed. The QD1 magnets have design field gradients of 50 T/m, field harmonics below 0.2‰, and site at 900 mm distance away from IP at beam crossing angle of 60 mrad. In this paper, details of QD1 design, construction and test are reported.

Abstract: The Super Taume-Charm Facility (STCF), a new generation of electron-positron collider led by the University of Science and Technology of China, requires a high-quality positron source to sustain high-luminosity continuous operation. The Adiabatic Matching Device (AMD) is a critical component for positron focusing, its excitation pulse source requires a peak current ≥15 kA and a pulse front edge ≤3.5 us. To reduce the significant power dissipation of pulse discharge system, an energy feedback circuit was designed. The optimized system achieved a dramatic reduction in losses, decreasing input power by 73.96% and enhancing long-term operational stability. This article provides a detailed account of the simulation of power loss in AMD excitation pulse sources, as well as the design, simulation, and offline debugging of energy feedback circuits. Key words: excitation pulse power for AMD; power loss; energy feedback; photoconductive semiconductor switch

The Super Tau-Charm Facility (STCF) is a next-generation electron-positron collider under development, with a designed center-of-mass energy of 2–7 GeV. Positrons generated by a high-energy electron beam striking a target are captured and accelerated to 200 MeV using large-aperture traveling-wave accelerating structures to reduce beam loss. A constant-aperture cavity geometry, in which the group velocity is controlled by the nose-cone length, is proposed to simplify fabrication while maintaining a high accelerating gradient. A pulse compressor is incorporated into the RF system to further enhance the effective RF power. This paper presents the RF design and optimization of 2 m and 3 m large-aperture accelerating structures, both achieving gradients above 15 MV/m.

The Super Tau-Charm Facility (STCF) is a next-generation electron-positron collider project proposed in China, designed to explore frontier physics in the tau-charm energy region. The facility's accelerator is required to provide electron and positron beams with tunable energies ranging from 1.0 to 3.5 GeV. This study presents the design of a traveling-wave accelerating structure for the STCF. By optimizing the regular-cell configuration, a high shunt impedance is achieved. The peak electric field in accelerating structure is reduced by adjusting the accelerating gradient profile, and an under-coupled output coupler design is adopted to enhance the performance of the accelerating structure. The objective is to achieve an accelerating gradient of 22.5 MV/m with an input power of 45.3 MW, and to further increase the power in pursuit of high-gradient operation in the S-band.

KEK-LINAC is an electron/positron linear accelerator used as the injector for the synchrotron radiation facilities (PF ring and PF-AR) and SuperKEKB. The stable operation of experiments at these facilities requires reliable beam supply from the LINAC. We have newly introduced an analytical method based on gradient boosting decision tree (GBDT) to further enhance our beam adjustment capability. GBDT is one of machine learning methods and has been used as an exceptionally effective model for tabular data. The GBDT analysis handling hundreds of LINAC operating parameters predicted accurately beam’s charge and position in the LINAC. Furthermore, by performing SHAP analysis, we have identified key parameters for the beam adjustment and correlations between the parameters. Furthermore, it was found that a model trained by the analyses can be utilized as a surrogate model for fast simulation of beam behavior in the LINAC. The results of beam adjustment with the GBDT analyses will be shown in this presentation.

The Super Tau-Charm Facility (STCF) is a new generation tau-charm factory designed to collect an enormous and unique dataset in the tau-charm energy region. In order to supply high-quality electron and positron beams to the collider, the STCF injector employs a compatible injector scheme that supports both off-axis and swap-out injection modes. This paper introduces the conceptual design of a combined damping and accumulator rings for positrons at the STCF, aimed at meeting low-emittance beam requirements.The damping ring (DR) and the accumulator ring (AR) share the same lattice, and aligned vertically to reduce construction costs. The detailed lattice design of the DR and AR are presented in this paper.

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.