SAP2025 - the 15th Symposium on Accelerator Physics

2 Sept 2025, 09:00 → 5 Sept 2025, 18:45 Asia/Shanghai

Urumqi, Xinjiang, China

Renkai Li (Tsinghua University)

Tuesday 2 September

10:00 → 21:00 Registration

Wednesday 3 September

10:50 → 12:05 Plenary Talk Session 1: WEAI

12:30 → 14:10 Plenary Talk Session 2: WEBI

16:00 → 16:50 Parallel Talk Session 1: WEMI

16:00 → 16:50 Parallel Talk Session 1: WENI

16:50 → 17:50 Parallel Talk Session 1: WEMC

16:50 Generation of coherent pulses via multiple-echo-enabled harmonic generation in storage rings

In comparison to free electron lasers, storage ring light sources (SRLS) can reuse a single electron beam to serve multiple users, offering high repetition rates and cost efficiency. However, despite the transverse emittance reaching the X-ray diffraction limit in fourth-generation SRLS, the storage ring suffers from limited longitudinal coherence. Enhancing longitudinal coherence has been shown to significantly improve spectral brightness, time resolution, and energy resolution. Laser modulation schemes for SRLS have been explored for their potential to induce strong micro-bunching, thereby enhancing spectral power and coherence. However, these methods modulate each bunch only once per revolution, limiting their application to a single beamline and underutilizing the multi-user capacity of storage rings. To enable coherent radiation delivery to multiple beamlines, we propose a multiple-echo-enabled harmonic generation scheme. This approach modulates the electron beam multiple times, generating coherent pulses at different wavelengths. By leveraging the multi-user capability of storage rings while simultaneously improving longitudinal coherence, our method enhances both spectral and temporal performance.

Speaker: Weihang Liu (Institute of High Energy Physics)

16:50 → 17:50 Parallel Talk Session 1: WENC

16:50 Modeling of CSR and its cancellation in DBA/Chicane type compressors

In advanced accelerator-based light sources and colliders, bunch compressors like arc-type (DBA) and linear-type (chicane) are widely used to generate high-quality electron beams with kiloampere (kA)-level peak currents. However, a serious problem in increasing the peak current even higher is the significant degradation of beam quality caused by the Coherent Synchrotron Radiation (CSR) effect. To tackle this, we develop a new analytical model for CSR that can describe beam transport with varying bunch lengths, establish a practical framework for analyzing CSR in both DBA and chicane-type compressors, and design CSR-suppressed DBA compressors (arc-type) as well as non-symmetric C- and S-shaped chicanes (linear-type). General analytical conditions for CSR cancellation are derived for these designs. Simulations show that, with these new compressors, high beam quality can be maintained even when the peak current is increased up to 10 kA. This work provides important guidance for enhancing the performance of existing accelerator facilities, as well as for the development of next-generation accelerator-based light sources and colliders.

Speaker: Fancong Zeng (Chinese Academy of Sciences)

18:05 → 18:30 Parallel Talk Session 2: WEXI

18:05 → 18:55 Parallel Talk Session 2: WEYI

18:30 → 20:10 Parallel Talk Session 2: WEXC

19:50 Beam extraction and darkcurrent study of a C-band RF photo gun

C-band RF photo gun is being developed worldwide for better electron bunch emittance, aiming to be used in advanced light sources such as diffraction-limited storage rings and free electron lasers. Initial beam tests of a 3.6-cell C-band RF photo gun achieved 6.6 MeV beam energy at 137 MV/m cathode gradient were conducted, along with high dark current; Surface checks revealed electron damage on cathodes and disk apertures after these tests. To understand and suppress the dark current, surface cleaning methods and preliminary numerical simulations have also been conducted, and the results are discussed.

Speaker: Xingguang Liu (Institute of High Energy Physics, Chinese Academy of Sciences, China Spallation Neutron Source)

18:55 → 19:55 Parallel Talk Session 2: WEYC

Thursday 4 September

10:30 → 12:10 Plenary Talk Session 3: THAI

11:20 Steady state microbunching high power light source

Steady state microbunching (SSMB) proposed by Alexander Chao and Daniel Ratner is a new concept of accelerator light source, which means to maintain the microbunching in storage rings for coherent radiation production. By combining the high coherence and high repetition rate, SSMB can provide very high average power radiation. And the radiation wavelength can cover THz to soft X-ray.
To promote the SSMB physics research and develop a SSMB-EUV light source, a taskforce has been established in Tsinghua University since 2017. Recently, we are continuing the proof of principle experiment and have observed multi-turn coherent radiation by modulating the electron bunch with laser single-turn on MLS storage ring. The experiment results are in very good agreement with theoretical prediction, which proof this kind of mechanism (maintain micro-bunch in storage ring) can work well.
We have also proposed a complete design for high average power EUV radiation based on SSMB. The proposal will provide kW EUV average power at the radiation wavelength of 13.5 nm within 2% bandwidth. We have done the start to end study for this proposal and the researches on the key technologies are also underway. This kind of EUV light source may open a new roadmap to meet the requirements of EUV lithography.

Speaker: Zhilong Pan (Institute of Theoretical Physics)

12:25 → 13:40 Plenary Talk Session 4: THBI

13:40 → 14:10 Plenary Talk Session 4: THBC

16:00 → 17:20 Parallel Talk Session 3: THMC

16:00 Energy stablization of high-charge electron bunches from Plasma Wakefield Acceleration

Plasma Wakefield Acceleration (PWA) promises to reduce the scales of advanced light sources and high-energy colliders due to its ultrahigh accelerating gradients. However, the relatively large energy jitter and energy spread (typically 1~10% level) of the electron bunches generated by PWAs remain a major obstacle for practical applications. In this work, we propose two independent schemes: 1) a combination of a laser-driven active plasma dechirper and a passive plasma dechirper with two magnetic chicanes; and 2) a beam-driven active plasma dechirper integrated with a magnetic chicane. The simulation results demonstrate that these schemes can reduce both energy jitter and energy spread of PWA-generated electron beams with charges ranging from hundreds of pC to several nC from the 1% level to 0.1% or lower. In addition, we preliminarily study the transverse coordinate offsets induced by the coherent synchrotron radiation effect in chicanes, as well as the feasibility and experimental design of these schemes.

Speaker: Xueyan Shi (Chinese Academy of Sciences)

16:00 → 17:20 Parallel Talk Session 3: THNC

16:20 CEPC accelerator physics challenges and research progress

The Circular Electron-Positron Collider (CEPC) is a dual-ring accelerator with a design circumference of 100 kilometers, prioritizing operation at the Higgs particle energy (center-of-mass energy of 240 GeV). To achieve its high-luminosity collision goals, the CEPC accelerator physics team addresses core challenges through design optimization, including beam optics design under strong radiation effects to ensure sufficient beam lifetime, simulation and mitigation of collective effects and nonlinear dynamics from intense beam-beam interactions, development of efficient injection methods despite short beam lifetimes, luminosity optimization for ultra-high energy beams, self-consistent handling of compound effects with precise component modeling and improved computational efficiency, and high-polarization collision design. The team is now conducting more rigorous and comprehensive performance assessments for the physical design, alongside beam physics experimental validation and specialized software development tailored for CEPC.

Speaker: Yiwei Wang (Institute of High Energy Physics)

16:40 Preliminary design of the beam transport system for the Super Tau-Charm Facility

TThe injector of the Super Tau-Charm Facility (STCF) should provide high-quality electron and positron beams for the collider ring according to different injection schemes, which is one of the key systems to ensure the high brightness of STCF. This paper presents the preliminary physical design and beam dynamics optimization of the complex beam transport system, which interconnects the main accelerator components over approximately 550 meters. The design encompasses three major segments: the injection line from the positron linac to the damping ring (PL2DR), the extraction and transport line from the damping ring to the main linac (DR2ML), and the final transport lines from the main linac to the collider rings (ML2CR). Each segment addresses unique challenges, including transverse emittance preservation, Twiss parameter matching, sophisticated phase-space manipulation and tight restrictions on the geometrical conditions. Through detailed optics design and particle tracking simulations, these results demonstrate the feasibility of the transport system in maintaining the high beam quality essential for the STCF's physics program.

Speaker: Ruixuan Huang (University of Science and Technology of China)

17:35 → 18:55 Parallel Talk Session 4: THXC

18:35 Dr. Cai, Han-Jie

A high-intensity muon source named MuST has been proposed for several years at CiADS. Utilizing the 5-mA proton beam of CiADS linac on targets, multiple muon beamlines can be fed, and the intensity of the DC muon beam is expected to be record-breaking. Here, the conceptual layout of MuST, including the tandem targets, the muon beamlines, and the terminals, is presented. The development plan and the conceptual design progress are reported. The study of the liquid jet target, which is more efficient in producing surface muons than graphite and has the potential to withstand a 3-MW proton beam, is presented. The design details and overall performance of the muon beam lines are introduced. The key beam parameters of the surface muons and decay muons are given.

Speaker: Han-Jie Cai (Institute of Modern Physics, Chinese Academy of Sciences)

17:35 → 18:55 Parallel Talk Session 4: THYC

18:55 → 20:30 Poster Session: THP

18:55 A universal numerical optimization framework for studying seeded free-electron laser schemes

Seeded free-electron lasers (FELs) have become indispensable tools across numerous scientific fields, owing to their high coherence and stability. To facilitate the discovery and optimization of such FELs, we propose a general-purpose framework utilizing intelligent optimization algorithms for identifying high-performance seeded FELs. In this paper, we demonstrate that our framework can automatically reproduce established seeded FELs, eliminating the need for prior physical analysis. Furthermore, this framework has the potential to discover novel schemes through the systematic incorporation of additional physical elements.

Speaker: Zihan Wang (University of Science and Technology of China)

18:55 Analytical Study of Fringe Fields and Nonlinear Transport in a Sector-based Energy Analysis System

Energy Analysis (EA) systems based on sector magnets are widely applied in accelerators. Nevertheless, for low-energy electron beams below 15 MeV, extra measurement errors introduced by fringe fields of the sector magnet cannot be neglected. Moreover, initial beams with large momentum spread will encounter system errors arising from nonlinear transport. Such fringe-field-induced aberrations and their impact on momentum spectrum are studied analytically and a compensation scheme considering high-order momentum spread terms is proposed. Further, the theoretical derivation is validated with simulations, and correction of second-order aberration errors is explored via data processing. These methods and conclusions improve the accuracy of built/operational EA systems without extra costs.

Speaker: Yan Wang (Huazhong University of Science and Technology)

18:55 Bunched-beam theory of microbunching instability

Conventional theory of single-pass microbunching instability (MBI) is primarily based on the coasting-beam approximation, which assumes that the modulation wavelength is much shorter than the bunch length. However, in isochronous beamlines, the characteristic modulation wavelength may sometimes become comparable to the bunch length, rendering the coasting-beam assumption invalid. In this paper we develop a bunched-beam theory of MBI, starting from the linearized Vlasov equation, aiming to quantify the impact of finite bunch length on the evolution of density modulations. Our analysis reveals that the final MBI gain, or the amplified bunching factor, exhibits a dependence on the initial modulation phase, a feature absent in the existing coasting-beam model. The proposed bunched-beam formulation may offer additional physical insights into the underlying mechanism of MBI, particularly in regimes where the finite extent of the bunch plays a non-negligible role.

Speaker: Cheng-Ying Tsai (Huazhong University of Science and Technology)

18:55 Coherent kW THz radiation from an SSMB storage ring via self-sustained laser modulation

Due to the unique role of terahertz (THz) radiation in the electromagnetic spectrum, it possesses significant scientific value and potential applications in fundamental science, biomedical research, spectroscopy, and etc. This paper proposes a novel mechanism for generating continuous kilowatt-level coherent terahertz radiation in steady-state microbunching storage rings, based on self-sustaining laser modulation processes. The analysis employs the transfer matrix method from accelerator physics, considering the dynamical evolution of electron beams during multiple passes through the laser modulator, as well as radiation damping and quantum excitation effects in the storage ring. Numerical tracking results demonstrate the feasibility of this mechanism. In a demonstrative case, we show that 1 kW continuous coherent radiation can be achieved at 5 THz frequency, corresponding to electric field strengths on the order of MV/m. Since this scheme is based on free electrons, its radiation output characteristics can be tuned over a broad frequency range of 1-10 THz, offering extremely high application value in scientific research.

Speaker: Cheng-Ying Tsai (Huazhong University of Science and Technology)

18:55 Design and preliminary implementation of the laser Compton polarimeter for BEPCII

As a key R&D project for polarized lepton beams at future colliders, a laser Compton polarimeter has been designed for the electron storage ring of BEPCII, utilizing the X-ray beamline and experimental hutch from a dismantled wiggler source. As of July 2025, we have preliminary completed laser transmission, focusing, circular polarization adjustment, and observed laser and electron beam collision signals on beam less monitors. However, laser focusing and detector still need to be improved, the potential modifications in the near future also be discussed in this article.

Speaker: Mengyu Su (Institute of High Energy Physics)

18:55 Exponential Sum Fitting of the Long-Range Transverse Resistive-Wall Wakefield

In high-intensity storage rings, long-range transverse
resistive-wall (RW) wakefield is a dominant source of
coupled-bunch instability. Conventional particle tracking
algorithms handling this wakefield require storing bunch-
by-bunch and turn-by-turn centroid position histories, re-
sulting in excessive memory consumption, which leads to
computational inefficiency. This study proposes fitting the
long-range transverse RW wakefield through a sum of expo-
nentials. This method eliminates the need for bunch centroid
histories during tracking computations while facilitating
GPU-based parallel implementation, thereby significantly
enhancing computational efficiency. This work demonstrates
the dependence of the fitting performance on the number of
exponential functions and the fitting interval.

Speaker: Xin Huang (National Synchrotron Radiation Laboratory)

18:55 GPU-accelerated simulation of longitudinal single-bunch instability in electron storage rings

Longitudinal single-bunch instability driven by high-frequency impedance is a major challenge for achieving optimal performance in fourth-generation synchrotron light sources and future electron-positron colliders. Accurate simulations of this instability are critical, yet computationally intensive, often requiring millions of macro-particles and fine slicing to resolve bunch density distributions. To address this, we have developed a GPU-accelerated tracking code that enables efficient simulations of longitudinal single-bunch instability. Our solution is specifically designed to run on a desktop computer equipped with a high-performance GPU, providing an accessible and cost-effective alternative to computing clusters.

Speaker: Tianlong He (University of Science and Technology of China)

18:55 Lattice design optimization of the interaction region for a super tau-charm facility

The Super Tau-Charm Facility (STCF), a new-generation high luminosity e+/e− collider of in the low-energy region of 1-3.5 GeV. To achieve the target luminosity of larger than 5×10^34 cm^−2s^−1, the collision scheme combining a large crossing angle and crab-waist correction is applied. However, the strong nonlinearity within the interaction region (IR), significantly decreases both dynamic and momentum apertures and limiting Touschek lifetime. Consequently, designing as a transparent (achromatic) IR as possible holds critical importance in enhancing the Touschek lifetime. In this paper, the modular linear lattice design for the STCF IR is designed to facilitate nonlinear optimization. The H-invariant is constrained less than 0.02m to help increase the local momentum acceptance. Up to third-order local chromaticity correction is implemented by using Montague function as indicator to broaden the momentum aperture, thereby improving the Touschek lifetime. Fringe field and detector solenoid effects on beam dynamics is designed and optimized.

Speaker: Linhao Zhang (University of Science and Technology of China)

18:55 Longitudinal collective dynamics in laser modulators of an SSMB storage ring based on macroparticle model

The mechanism of the steady-state microbunching (SSMB) storage ring is being actively investigated. In the conceptual design, a laser modulator used to modulate the electron beam include the co-propagating laser beam, undulator magnets and potential cavity mirrors, forming a laser modulator cavity. In this work the longitudinal single-bunch and multi-bunch collective dynamics are studied that may arise due to coherent undulator radiation, based on the macroparticle model. For multi-bunch multi-turn case, the dispersion equation is derived, and a detuning parameter is introduced to characterize the frequency deviation between the external laser and the resonant undulator radiation, and solve for the instability growth rates of different multibunch modes. When the detuning approaches a specific multi-bunch mode divided by the number of total microbunches, this instability mechanism tends to amplify that mode. Furthermore, possible mitigation effect of the potential well on the instability is discussed. This work may shed light on the underlying physical mechanisms of longitudinal collective beam dynamics in the laser cavity modulators of an SSMB storage ring.

Speaker: Cheng-Ying Tsai (Huazhong University of Science and Technology)

18:55 Minimizing the fluctuations of storage ring resonance driving terms using the step-by-step chromaticity compensation method

Our recent studies showed that reducing the fluctuations of resonance driving terms (RDTs) can enlarge the dynamic aperture (DA) of a storage ring very effectively. In this paper, we use the step-by-step chromaticity compensation method to minimize RDT fluctuations for DA optimization. For the minimization of third-order RDT fluctuations, this method yields the same optimization result as evolutionary algorithms. Crucially, however, this method exhibits faster convergence than evolutionary algorithms.

Speaker: Wanbin Li (University of Science and Technology of China)

18:55 Modeling and Optimization of Transverse Trapped-Mode Impedance for In-Vacuum Undulators of HALF

The in-vacuum undulator (IVU) exhibits exceptionally strong trapped-mode impedance due to its distinctive ridge-loaded waveguide structure and narrow magnetic gap design, which may lead to beam instability issues. This study primarily use the CST wakefield solver to investigate the trapped-mode impedance of the IVUs of the Hefei Advanced Light Facility (HALF). The trapped-mode impedance in the vertical direction is evaluated for both structures, with and without pump ports. Based on the impedance results, two mitigation strategies are proposed: ferrite damping and transition section optimization. Simulation results demonstrate that both strategies effectively reduce the impedance, with the transition section optimization strategy showing superior suppression performance.

Speaker: Haiyan Yao (University of Science and Technology of China)

18:55 Physical design of microwave electron gun optimized for carbon nanotube cathodes

Since the maximum electric field strength that a carbon nanotube field-emission cathode can withstand is less than 13 MV/m, the optimization scheme of shortening the length of the first cavity based on the traditional 1/2+1 cavity-type microwave electron gun fails to solve the problems of electron phase slippage and back-bombardment. Therefore, in accordance with the emission characteristics of the carbon nanotube field-emission cathode, beam dynamics optimization was conducted on different cavity structures to select a more suitable cavity structure. Subsequently, the radio frequency (RF) design of the electron gun was completed through fine parameter adjustment of the cavity structure. Finally, the engineering design of the electron gun was accomplished after considering multiple aspects such as the gun's assembly, cathode structure, microwave feed-in structure, and electron beam output structure.

Speaker: Tianhui He (China Academy of Engineering Physics)

18:55 Physical design study of the main magnet for the CIAE 75 MeV cyclotron

A 75 MeV cyclotron is currently under development at the China Institute of Atomic Energy (CIAE). This machine is designed to extract a beam with a rated power exceeding 60 kW for the production of medical radioisotopes, such as ⁶⁸Ge, ²²³Ra, and ²²⁵Ac, aiming to meet the growing domestic demand for diagnostic and therapeutic radionuclides. This paper addresses key challenges and solutions in the design and computational analysis of the main magnet. The magnet poles adopt a structural design scheme featuring integrated straight-edged sectors with a slight spiral angle at the trailing edges. The isochronous magnetic field distribution is achieved through an axial shimming method. Magnetic field optimization was performed using the numerical simulation software OPERA-3D, thereby enhancing the acceleration efficiency of the cyclotron. Furthermore, deformation simulation and mechanical structural optimization were carried out for the main magnet. Under the premise of ensuring overall performance, the deformation of the main magnet, which has a diameter of 4.4 meters and a weight of 130 tons, was controlled within acceptable engineering tolerances.

Speaker: Jinrong Lu (China Institute of Atomic Energy)

18:55 Position-phase error cancellation effects in beam-based linac alignment and synchronization

As prerequisites for automatic phase setting and fault compensation, precise longitudinal alignment and RF phase calibration are critical for high-intensity superconducting hadron linacs. While multiple facilities have successfully aligned or synchronized their linacs with time-of-flight (TOF) beam-based methods, existing error analyses typically assume uncorrelated position and phase uncertainties. This work rigorously derives intrinsic correlations between position and phase errors in beam-calibrated linacs. We demonstrate how these correlations can induce error cancellation effects that improve the accuracy of energy measurements and phase setting. Having validated these effects through simulations, we analyzed their implications for beam-based calibration experiments with applications to HIAF and CiADS commissioning.

Speaker: Haoyu Zhou (Institute of Modern Physics, Chinese Academy of Sciences)

18:55 Preliminary scheme for electron cooling using longitudinal hollow electron beam

The intra-beam scattering in high charge state intense heavy ion beams is a problem worth considering. By controlling the longitudinal distribution of the ion beam, it may be possible to alleviate the ion beam loss and improve the lifetime of the ion beam caused by intra-beam scattering. Unlike the traditional cooling process of direct current electron beams or longitudinal uniform distribution electron bunch beams, a longitudinal hollow electron beam is used to cool heavy ion beams. Ions at the edge of the ion beam will receive stronger cooling, while ions at the center of the ion beam will receive weaker cooling, avoiding overcooling at the center of the ion beam. This paper discusses the generation, measure-ment, and related issues of longitudinal hollow electron beams. Corresponding solutions and suggestions have been proposed for the problems and challenges that may be encountered in the research. The cooling process of longitudinal hollow electron beams will be simulated and experimentally studied in the future, with the hope of obtaining beneficial effects.

Speaker: Prof. Xiaodong Yang (Institute of Modern Physics, Chinese Academy of Sciences)

18:55 Quantifying differences between high dimensional beam phase space distributions with f-divergences

Quantifying differences between high-dimensional phase space distributions is essential for analyzing beam measurements and simulations. While f-divergences such as KL or JS divergence are increasingly used for this purpose, including in machine learning applications, their values lack physical interpretability. This work conducts the first systematic study of the difference quantification characteristics of several typical f-divergences for high-dimensional beam distributions commonly used in accelerators. The aims are to identify the most suitable f-divergence metric for the field of accelerator beam physics and to reveal the physical meanings represented by f-divergences values within this field. We first study the f-divergences properties among different types of beam distributions with the same covariance matrix. Subsequently, we demonstrate that various f-divergences between these distributions exhibit definite correspondences with the mismatch factors and the emittance differences. Finally, based on these correspondences, we establish assessment standards for f-divergences, which can interpret the specific meanings represented by their values in the context of beam phase space distributions. These findings provide guidance for selecting statistical divergences to quantify differences in high-dimensional phase space beam distributions.

Speaker: Yu Du (Institute of Modern Physics, Chinese Academy of Sciences)

18:55 Quasi-linear theory of single-pass microbunching instability

The existing theoretical treatment of single-pass microbunching instability (MBI) typically assumes a coasting beam and adopts a linear framework, within which the microbunching gain may grow without bound. While the inclusion of intrabeam scattering (IBS) introduces damping effects that may suppress excessive gain, these models remain fundamentally linear and do not capture saturation behavior. In this work, we develop a quasi-linear theory of MBI based on the Vlasov equation, incorporating the evolution of beam energy spread induced by the instability itself. The quasi-linear formulation yields a set of coupled equations describing the evolution of the bunching factor and energy spread, still under the coasting beam approximation where different modulation wavelengths evolve independently. This approach provides a more realistic description of the nonlinear evolution of MBI and offers insight into its natural saturation mechanism.

Speaker: Cheng-Ying Tsai (Huazhong University of Science and Technology)

18:55 Quick estimate of CSR-induced microbunching Instability in a multibend transport beamline

Microbunching instability (MBI) driven by short-range wakefields in high-brightness electron beams has been an active area of research over the past decade. While most existing studies focus on single-pass or linear accelerators --- particularly few-dipole bunch compressor chicanes --- MBI studies in multi-bend transport lines has relied predominantly on time-consuming numerical simulations. In this work, we present a quick estimate for evaluating MBI gain in generic multi-bend beamlines, thereby avoiding computational costs. Starting from Volterra integral equation governing the bunching factor, we first find the optimal wavelength and introduce physically motivated simplifications to derive the maximum gain. A gain spectrum is then constructed based on physical insights into MBI amplification mechanisms. The results show good agreement with detailed numerical calculations from Vlasov solver. The developed approach enables quick and reasonably accurate estimates of the MBI gain using only the lattice optics functions and the initial beam parameters, offering a practical tool for beamline design and mitigation of MBI.

Speaker: Cheng-Ying Tsai (Huazhong University of Science and Technology)

18:55 Research on higher-order mode suppression in CEPC electrostatic separators

The electrostatic separator is a key component of circular colliders (such as the CEPC), but the unique geometry of its vacuum chamber excites higher-order modes (HOMs), leading to significant narrow-band impedance. Previous studies have shown that adding absorbing materials at the feedthrough (holder) terminals of the electrostatic separator can effectively suppress HOMs, thereby improving the multibunch coupled instability threshold in the CEPC. However, since the electrostatic separator of the CEPC must operate in the magnetic field environment generated by bending dipoles magnets, the solution of adding absorbing materials at the feedthrough cannot be implemented. Therefore, new damping schemes must be explored, and non-magnetic materials must be used for the damping material. Based on the CST simulation software, this paper systematically investigates the approach of loading non-magnetic SiC absorbing rings at different positions of the electrostatic separator. Through simulation analysis, the suppression effects of different schemes on the quality factor (Q value) of HOMs and the transverse impedance are quantitatively evaluated, providing a basis for optimizing the design of the CEPC electrostatic separator and reducing the risk of beam instability.

Speaker: Yuzhe Liu (Institute of High Energy Physics)

18:55 SOFT: Single-Optics 4D phase space Tomography via double-rotated 2D measurements

Detailed knowledge of high-dimensional phase space distributions is crucial for predicting and controlling the evolution of intense beams. Conventional beam tomography techniques require measurements under multiple beamline configurations, introducing reconstruction errors due to transport nonlinearities and model uncertainties while complicating the beamline design. This paper introduces SOFT (Single-Optics Four-dimensional Tomography) , a novel technique that reconstructs the complete 4D distribution using measurements from a single beamline setting. SOFT conducts 2D phase space scans with two independently rotatable slits to extract otherwise inaccessible cross-plane information. We present a rigorous proof demonstrating SOFT’s ability to acquire sufficient data for full 4D reconstruction. Physics-informed analytical tools based on 4D geometry were developed to optimize the design and minimize measurement errors. SOFT’s efficacy is validated through simulations, and the status of the prototype experiment is discussed.

Speaker: Binghui Ma (Institute of Modern Physics, Chinese Academy of Sciences)

18:55 Spectral form function with applications in beam physics

To describe longitudinal fine structure within a particle beam like microbunching, a classical approach is to define a bunching factor or form factor which is the Fourier transform of the particle density distribution in longitudinal dimension. Such a 1D definition of form factor can be generalized to 6D spectral form function (SFF) to describe more complicated structure in phase space. The complex SFF is another complete description of beam in spectral domain and can offer complementary and valuable insight in beam dynamics study which usually invokes the real particle density distribution. The basic property and Fokker-Planck equation of the SFF is presented, along with its solution in a general coupled linear lattice. The example applications of SFF in electron storage ring physics and laser-induced microbunching are presented.

Speaker: Xiujie Deng (Tsinghua University)

18:55 Study of bunch lengthening with harmonic cavities for HLS-III

NSRL recently proposed a future plan to further upgrade the HLS to an EUV diffraction-limited storage ring, named HLS-III. To improve the Touschek lifetime and suppress beam instabilities, HLS-III will employ a bunch-lengthening harmonic cavity system. Based on theoretical analysis, this work evaluates the bunch lengthening performance under five distinct double RF configurations involving different frequencies and harmonic orders, identifies the required harmonic cavity voltage to achieve the target bunch lengthening, and quantifies the corresponding improvement factor in Touschek lifetime. These findings provide valuable guidance for the selection of RF frequencies and the design of harmonic cavity parameters for HLS-III.

Speaker: Wenshu Liang (University of Science and Technology of China)

18:55 Suppression of emittance variation for the HALF storage ring

The Hefei Advanced Light Facility (HALF) is a diffraction-limited storage ring light source. The HALF storage ring lattice has relatively long damping times, which can result in substantial variations in beam emittance when the gaps of insertion devices change. In this paper, we study different ways to suppress the emittance variation of the HALF storage ring, including the usage of damping wigglers in long straight sections, wigglers in short dispersive straight sections and leaked dispersion in long straight sections.

Speaker: Mr Xiaoyu Liu (University of Science and Technology of China)

18:55 Tracking simulation of longitudinal beam dynamics in a triple RF system for electron storage rings

For diffraction-limited storage rings, a triple RF system scheme has been proposed, aimed at achieving longer bunch lengthening or meeting the specific requirements of longitudinal injection. In such a system, the choice of RF cavity parameters plays a critical role in the longitudinal beam dynamics, which typically requires precise analysis through macroparticle tracking simulations. This paper extends STABLE code [T. He et al., Phys. Rev. Accel. Beams 24, 104401 (2021)] to investigate the longitudinal dynamics of the triple RF system proposed for the Hefei Advanced Light Facility (HALF) storage ring. The simulation results reveal that two key factors limit bunch lengthening.

Speaker: Jincheng Xiao (University of Science and Technology of China)

Friday 5 September

10:30 → 12:00 Parallel Talk Session 5: FRMC

11:45 Real-time comprehensive electron beam diagnostics through machine learning in ultrafast electron diffraction system

Ultrafast electron diffraction (UED) is a powerful technique for observing atomic-scale structural dynamics in materials. Electron beam parameters—beam size, divergence, energy spread, and bunch length—determine spatio-temporal resolution. Traditional diagnostic methods require complex instrumentation that cannot be integrated into routine workflows, particularly for high-repetition-rate facilities. We present a machine learning approach enabling comprehensive, non-invasive extraction of electron beam parameters directly from diffraction patterns. Deep neural networks trained on physics-based simulations decode signatures that beam parameters imprint on diffraction images. The method exploits distinct physical mechanisms: geometric effects from beam size, angular distortions from divergence, chromatic aberrations from energy spread, and temporal convolution from bunch length. This enables bunch length measurement without dedicated temporal diagnostics—traditionally one of the most challenging parameters to access non-invasively. The trained models can be deployed across UED facilities using standard imaging detectors, democratizing access to advanced diagnostics. This approach eliminates expensive specialized equipment and enables real-time beam monitoring and optimization, enhancing experimental throughput and data quality for ultrafast materials characterization.

Speaker: Jiapeng Li (Huazhong University of Science and Technology)

10:30 → 12:10 Parallel Talk Session 5: FRNC

10:50 The start-to-end beam dynamics simulation study and its application in the high-intensity cyclotron of CIAE

The neutron yield of the neutron source based on the 18MeV/1mA high-intensity cyclotron developed by the China Institute of Atomic Energy (CIAE) has reached 7×10^13 n/s and has been successfully applied in high-resolution neutron imaging and Boron Neutron Capture Therapy (BNCT) experiments. Precise and quantitative start-to-end beam dynamics simulations facilitate a better understanding of the complex beam dynamics behavior of high-intensity beams, which is one of the key technologies for high-intensity cyclotrons. The beam dynamics simulation technology for cyclotrons is relatively mature. However, it is typically implemented independently in each subsystem. During the simulation process, assumed initial conditions are introduced multiple times, making it difficult to obtain quantitative results and carry out a global optimization design of beam dynamics. Start-to-end beam dynamics simulation is used in the 18MeV/1mA high-intensity cyclotron. It quantitatively simulates the beam dynamics behavior of high-intensity beams in each subsystem, including the injection line, spiral inflector, central region, acceleration region, extraction region, and uniform beam transport line.

Speaker: Tianjian Bian (China Institute of Atomic Energy)

11:50 AVASX: a GPU-based high-performance beam dynamics simulation code using hybrid tracking methods for ion linear accelerators

In high-intensity ion accelerators, particle dynamics is significantly influenced by nonlinear collective effects, particularly the space charge effects. The Particle-in-Cell (PIC) method is widely used to study these effects, but the computational burden restricts the applications in accelerator design, failure compensation, and machine learning dataset generation. In this work, a high-performance beam dynamcs code, named AVASX (Advanced Virtual Accelerator Software X), was developed with CUDA (Compute Unified Device Architecture) and performed on NVIDIA GPUs (Graphics Processing Units). The AVASX framework implements an adaptive particle tracking method that alternates between time and position as the independent variable. This switching mechanism optimizes the trade-off between the simulation accuracy and the computational efficiency. For the purpose of improving computing performance in charge deposition with atomic operations performed on GPU global memory, three optimization schemes, such as the thread aggregation method, the strategy of scattering data processing scopes, and the use of duplicate memory instances, were employed in this work and profiled using NVIDIA Nsight Compute to prove their effectiveness. According to the test results of simulating different beamlines, the GPU-based code is reliable and achieves 320 ~ 450 times faster than the CPU-based code performed on 56 cores.

Speaker: Chao Jin (Institute of Modern Physics, Chinese Academy of Sciences)

12:25 → 13:40 Parallel Talk Session 6: FRXC

12:25 → 13:45 Parallel Talk Session 6: FRYC

16:00 → 17:15 Plenary Talk Session 5: FRAI

17:30 → 18:45 Plenary Talk Session 6: FRBI