Our work studies the transient beam instability caused by beam loading within the macropulse in standing-wave (SW) low-energy electron linacs. A general model is presented to predict the transient outcomes of SW linacs by combining the power conversion relationship and beam dynamics simulation results under steady conditions, calculating outcomes of current waveform and energy spectrum with arbitrary inputs. The model was verified by a beam test with an X-band (9.3 GHz) 6 MeV SW electron linac, revealing causes of the observed beam instability. This work could provide guidance on the design, commissioning, and operation in industrial and medical low-energy electron linac applications.

Simulations are used to investigate electron beam dynamics in a diffraction limited storage ring with a high-gain free electron laser as a combined and coupled system. We found that the exponential radiation power is reduced approximately to linear with respect to the undulator length due to the large increase of the energy spread from the free electron laser, resulting in much less radiative power than the values found in previous works.

Systematic errors were observed on some beam position monitor (BPM) readings at the ESRF. All diagnostic measurements were indicating that an electromagnetic resonance with a frequency of 352 MHz was the cause, but the vacuum chamber profile is far too small to support a mode with such a frequency. The mode origin was surprising. During the vacuum bake-out, a small gap on the order of 3 micrometers was formed on the rf gasket next to the BPM. Gaps of this size can create low frequency capacitive modes in small spaces. This can pose major issues for the design of 4th generation light sources, whose magnetic lattices are becoming more compact.

Free-electron lasers (FELs) based on self-amplified spontaneous emission (SASE) are key sources of high-power, coherent radiation. However, pulse energy fluctuations during the exponential growth phase can hinder experimental precision. This study presents a stabilization scheme using a magnetic chicane introduced in this regime to exploit the developed energy modulation of the electron beam for controlling bunching factor variations, thereby significantly enhancing pulse energy stability and ensuring more reliable, consistent SASE FEL output.

The collimation system of High-Luminosity Large Hadron Collider (HL-LHC) was upgraded to address severe limitations from halo collimation with lead ion beams of unprecedented beam stored energies of 17 MJ at 6.8Z TeV. Planar channeling in bent crystals is effective forhigh-energy heavy ions. Four newly produced bent crystals, installed in state-of-the-art goniometers for sub-μrad angular control, are used as primary collimators of the multi-stage collimation system. For the first time, a crystal collimation scheme was deployed operationally during a lead ion beam run in 2023, demonstrating an improvement by factors of 5 to 13 compared to the conventional collimation scheme.

A new theory has been developed to describe incoherent horizontal emittance growth in crab-waist colliders due to the interplay of beam-beam with a large crossing angle and longitudinal wakefield, building upon existing work on synchrobetatron resonances. It has been applied to study incoherent horizontal emittance blowup at the SuperKEKB, where the predictions compare well with results obtained using various numerical tracking codes. Decreasing the horizontal betastar or adjusting the rf system phase which in turn adjusts the arrival time of the beam are proposed as mitigation techniques.

The study analyzes recently discovered skewed wake effect in slab structures, focusing on its dependence on beam tilt ($\alpha$) and ellipticity ($\kappa$). For highly elliptical beams ($\kappa \gg 1$), the skew angle $\varphi$ approaches $-\frac{3}{2}\alpha$, while the scaling factor $\lambda$ decreases. Low-$\kappa$ beams show increased $\lambda$ and $\varphi$ scaling with ${\kappa }^2$ and $\sin 2\alpha$. The skew wake arises geometrically from beam asymmetry and misalignment, persisting even when $\lambda$ is suppressed. Its stochastic nature, tied to random tilt, complicates mitigation strategies used for quadrupole wakes, posing risks of instabilities and emittance growth in colliders and wakefield accelerators. The findings highlight the need for advanced diagnostics and feedback systems to manage this effect in accelerator design and operation.

We present a feasibility study, providing guidelines for the design of Inverse Compton Source (ICS)-based compact x-ray sources with large operational flexibility and extended energy tunability range. Applications of these sources range from advanced medical imaging to industrial nondestructive tests. Properties of the electron beam accelerated in an All-C-Band RF structure are optimized, introducing a short X-band RF cavity, while a fast-cycling bunch selection module allows for simultaneous three electron beam–two photon beamlines–operation. The x-ray energy can be doubled in one of the two arms, providing a wide range of tunability by adjusting electron energy and interaction angle.

Superconducting magnets with non-circular apertures are crucial for advanced accelerators handling unconventional beam profiles, yet a systematic analytical design approach has been lacking. This paper introduces a novel analytical framework, employing conformal mapping, to design superconducting magnets with quasi-polygonal apertures capable of generating precise circular field harmonics. We apply this derived methodology to the canted-cosine-theta (CCT) coil concept, demonstrating how CCT can be effectively extended to the complex geometries. This work enables the optimized design of magnets for specialized applications demanding enhanced spatial efficiency and beam acceptance.

We introduce a simple yet powerful method for visualizing high-energy ion beams in three dimensions using a general-purpose position-sensitive photodiode. Integrated with an FPGA-based signal processing system, the detector simultaneously records the time and position of incoming particles, allowing for full reconstruction of the beam’s spatiotemporal profile. The technique was demonstrated using 390 MeV/u Ar${}^{16+}$, Ar${}^{17+}$, and Ar${}^{18+}$, beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC). The data reveal the detailed structure of each spill and its shot-to-shot stability.

The High-Intensity Heavy-Ion Accelerator Facility (HIAF) is currently under construction in Huizhou, China. Its high-energy fragment separator beamline will be capable of producing and delivering a high-intensity, GeV-energy muon flux. This muon beam—with its controllable energy and high flux—holds significant potential for rapid, nondestructive testing of large-scale objects. Additionally, it offers a unique platform for exploring new physics, including studies of dark matter interactions, charged lepton flavor violation and so on.

Beam loading compensation in normal-conducting linacs for high-current electron bunch trains is critical for maintaining beam quality. This work proposes a chicane-based method for beam loading compensation by adjusting bunch-RF phase relationships without requiring additional structures or power systems. Simulations show the method achieves a root mean square relative energy spread below $2\times {10}^{-4}$ and normalized emittance under 0.5 mm·mrad for a 1 A bunch train in a 400 MeV injector. This approach simplifies burst-mode operations for facilities with chicanes already installed in the beamline.

For high-intensity and low-energy hadron synchrotrons, the resonance driven by the incoherent space charge is one of the main factors of emittance growth. In this paper, we present a novel analytical method to calculate the phase space structure and identify the exact order of space-charge driven structural resonances in alternating gradient focusing channels. The analytical results are compared to particle-in-cell simulations and show good agreement. One potential application of the analytical method is to design of the space-charge compensation scheme for high-intensity hadron synchrotrons. In addition, we discuss beam loss induced by multiple factors including space charge, magnet errors, power supply ripple, and chromatic effects.

This study presents advanced semi-analytical algorithms for predicting and analyzing longitudinal beam instabilities in double rf systems, which are critical for fourth-generation light sources. The algorithms take advantage of recent advances in the field and provide a computationally efficient and accurate complement to multibunch tracking simulations. We demonstrate how these algorithms can optimize rf cavity parameters in high-dimensional parameter spaces, thereby maximizing Touschek lifetime. An open-source Python package, ALBuMS (Algorithms for Longitudinal Multibunch Beam Stability), is provided as an accessible tool for the stability analysis of dual rf systems.

The growing demand for high-power, narrowband, and tunable THz radiation sources drives innovation in compact accelerator-based devices. This study presents a novel 3D emission-collection concept that significantly boosts the efficiency of Smith-Purcell radiation. A helically rotated grating, optimized via inverse design, enhances the radiated power by over an order of magnitude, reaching millijoule-level energies. This compact and manufacturable structure opens new paths for developing high-power, tunable THz sources.