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...
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....
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...
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...
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)...
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...
The 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. The transport line of the injector mainly consists of the electron transport section, the injection and extraction section of the positron damping ring,...
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...
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...
Energy Analysis (EA) systems based on sector-magnets, with simple structure and high resolution, are widely applied in particle accelerators. As core components, sectors directly determine the accuracy of beam momentum spectra evaluations. However, for low-energy electron beams below 15 MeV, nonlinear-transport in large-dispersion sectors causes errors in results from linear-transport models;...
In high-intensity storage rings, long-range transverse resistive wall wake fields serve as the dominant source of coupled-bunch instabilities. Conventional particle tracking algorithms handling these wake fields require storing per-bunch, per-turn centroid position histories, resulting in excessive memory consumption and computational inefficiency. This paper proposes fitting the long-range...
Hefei Light Source II (HLS-II) is currently planned for an upgrade to Hefei Light Source III (HLS-III). To increase beam Touschek lifetime and suppress beam instabilities, HLS-III will employ harmonic cavities for bunch lengthening. This study evaluates bunch lengthening performance for different RF frequencies and harmonic cavity orders using theoretical analytical formulations, identifying...
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...
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...
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...
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...
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...
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...
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...
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 systematically investigates the trapped-mode impedance in the Hefei Advanced Light Facility's (HALF) IVU using both eigenmode and wakefield solvers in CST Studio Suite,...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
