Recently, the experimental discovery of a new type of wakefield effect, the “skewed wake effect,” has been reported. We provide an explanation of the nature of the skewed wake effect based on a simple three-particle model that we have developed. Taking a step forward, we analyze this effect for the case of a highly elliptical beam, provide a simple estimate of the skew angle, and analyze the wake amplitude effects associated with this effect.

We describe a simple and robust method for particle beam visualization using a general-purpose position-sensitive photodiode as a time- and position-sensitive particle detector. The detector and data acquisition system were characterized using an Am-241 source and tested in an accelerator experiment using a high-energy ion beam at beam intensities of ${10}^4{\mathrm{s}}^{-1}$ region. With an FPGA-based digital signal processing, the pulse height and timing of the photodiode signal allow the observation of the spatial and temporal profile of the beam, i.e., the real-time movie of the particle beam, with fairly good spatial and temporal resolutions. The 3D imaging of the beam clearly visualized the temporal profile of the beam spill as well as the long-term shot-by-shot stability of the beam without significant damage on the detector. This simple technique is quite useful for beam diagnosis in high-energy beam experiments and a variety of applications.

In this paper, we investigate incoherent quadrupolar synchrobetatron resonances caused by beam-beam collisions and their interplay with longitudinal wakefields in the context of crab-waist colliders. We present a comprehensive theoretical review of the established theory of synchrobetatron resonances and extend the formalism to explore horizontal synchrobetatron resonances specific to crab-waist colliders. As a case study, we examine incoherent horizontal emittance growth at the SuperKEKB and demonstrate through simulations that the interplay between beam-beam and longitudinal wakefields leads to a horizontal blowup of the bunch size and that the study of the dynamics can be reduced to the horizontal-longitudinal plane, independent of the motion in the vertical dimension. We present extensive simulation results using the codes bbws, pyheadtail, and xsuite, connect our analytical findings with these findings, and propose strategies to mitigate horizontal blowup.

The design of a linear electron accelerator and transport system enabling simultaneous two-beamline operation of an Inverse Compton Source (ICS) is presented. This novel option for an ICS is enabled by an all-C-band linear accelerator and an innovative electron beam selection switchyard. The proposed accelerator and laser box configuration allows the exploitation of x-ray to gamma-ray photon energies with custom-selectable repetition patterns and one additional direct high-brightness electron beamline. Start-to-end simulations from the photocathode to the interaction points are supported by the engineering design of nonstandard components of the light source.

The European Synchrotron Radiation Facility is now operating a fourth generation light source, which has a reduced horizontal emittance compared to its predecessor. Since it was first commissioned, systematic fluctuations of the beam position monitor (BPM) vertical readings have rendered some BPMs to be unusable, strongly affecting the orbit stability for the nearby bending magnet beamlines. A detailed study into the vacuum chamber close to the BPM revealed two possible sources of similar type; a break in electrical continuity via a gap on the order of several micrometers close to the BPM that creates a resonant frequency within the bandpass filter frequency of the BPMs. Electromagnetic simulations have been performed and confirm that the gap generates a resonance that could be the source of the BPM reading fluctuations. A solution to the problem has been implemented; the resonance has now been suppressed and the BPMs have been returned to general operation. Some guidelines on how to avoid this type of problem for future fourth generation light sources will then be proposed.

Generating a monoenergetic, high-energy muon beam using accelerator facilities can be very attractive for many purposes, for example, improving muon tomography currently limited by the low flux and wide energy spread of cosmic ray muons, and searching for muon related new physics beyond the Standard Model. One potential accelerator facility is the High Intensity Heavy-Ion Accelerator Facility (HIAF), which is currently under construction in Huizhou City, China. Considering the projectile energy and beamline length, a high-intensity and GeV-energy muon flux could be produced and delivered by the High energy FRagment Separator beamline of the HIAF facility. In this paper, the flux intensity and purity of the muon beam based on HIAF are discussed in detail. For the ${\mu }^{+}$ beam, the highest muon yield reaches $8.2\times {10}^6\mathrm{\mu }/\mathrm{s}$ with a purity of approximately 2% at a momentum of 3.5 GeV/c; meanwhile, for the ${\mu }^{-}$ beam, the maximum muon yield is $4.2\times {10}^6\mathrm{\mu }/\mathrm{s}$ with a purity of around 20% at a momentum of $1.5\mathrm{GeV}/\mathrm{c}$. The results also indicate that, for muon beams with an energy of several GeV, by applying a suitable purification strategy, we can get a muon beam with a purity of 100% and an intensity of the order of ${10}^5\mathrm{\mu }/\mathrm{s}$.

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. For the recent upgrade project of Xi’an 200 MeV Proton Application Facility (XiPAF) hadron synchrotron, the incoherent space-charge-driven resonances are very significant, especially in the beam injection stage. In this paper, we represent a novel analytical method to identify the exact order of space-charge-driven structural resonances. The analytical method can be employed to calculate the resonance phase space structure driven by the incoherent space charge. The feasibility of this method has been verified by taking the XiPAF-Upgrading synchrotron as the example synchrotron. It is shown that during the resonance crossing, the phase space structure can be obtained and analyzed via the proposed analytical method. The analytical results are compared to particle-in-cell simulations and show good agreement. In addition, we discuss beam loss induced by multiple factors including space charge, magnet errors, power supply ripple, and chromatic effects.

This work studies the transient beam instability caused by beam loading within the macropulse in standing-wave (SW) low-energy electron linear accelerators (linacs). A general model is presented to predict the transient outcomes of SW linacs with arbitrary input conditions, such as input power and voltage of the electron gun. In this approach, main outcomes including the current waveform and the energy spectrum can be calculated by combing the power conversion relationship and beam dynamics simulation results under steady conditions. A beam test was performed with an X-band (9.3 GHz) 6 MeV SW electron linac, which indicated that the calculation agreed well with the measurement results. In addition, the proposed method demonstrates that the observed beam instability was caused by beam loading in the test. This work could provide guidance on the design, commissioning, and operation in industrial and medical low-energy electron linac applications.

High average current and high-brightness electron bunch trains enable a broad range of accelerator-based facilities to explore scientific frontiers with higher resolution and efficiency. The beam loading effect induced by high beam currents strongly influences the beam dynamics and is a critical challenge for normal-conducting linacs operating in burst mode. Effective compensation methods are essential for enhancing beam quality. Traditional compensation techniques often require the addition of extra compensation structures or dedicated power supply components, which increases both the cost and complexity of the accelerator system. In this paper, we propose a novel beam loading compensation method by employing chicanes, which are commonly utilized in accelerator-based facilities, to adjust the spacing between bunches for optimal phase tuning during acceleration. Simulation results for an electron injector design show a root mean square energy spread of less than $2\times {10}^{-4}$ and a transverse normalized emittance below 0.5 mm mrad for a 1 A bunch train.

In this paper, we study the dynamics of the electron beam in a diffraction limited storage ring with a high-gain free-electron laser. We present in detail the design, including lattice, dynamic aperture, intrabeam scattering, and coherent synchrotron radiation. The simulation of the electron storage ring combined with the free-electron laser is carried out until the electron beam reaches its equilibrium. We find that the initial 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.

Double rf systems are critical for achieving the parameters of fourth-generation light sources. These systems, comprising both main and harmonic rf cavities, relax statistical collective effects but also introduce instabilities, such as Robinson and periodic transient beam loading (PTBL) instabilities. In this paper, we provide semianalytical algorithms designed to predict and analyze these instabilities with improved accuracy and robustness. The algorithms leverage recent advancements in the field, offering a computationally efficient and accurate complement to multibunch tracking simulations. Using the SOLEIL II project as a case study, we demonstrate how these algorithms can optimize rf cavity parameters in high-dimensional parameter spaces, thereby maximizing the Touschek lifetime. An open-source Python package, ALBuMS (Algorithms for Longitudinal Multibunch Beam Stability), is provided as an accessible tool for double rf system stability analysis.

The demand for high-power, narrowband, and tunable THz radiation sources is steadily increasing. Smith-Purcell radiation offers a compact method for resonantly generating narrowband THz sources with notable advantages over other approaches, though the power output still requires improvement. This work introduces a novel 3D emission-collection concept that enhances the efficiency of THz radiators, achieving an enhancement of over an order of magnitude in coherent radiation power compared to the 2D approach. Systematic simulations reveal that the single-layer helically rotated structure, optimized through inverse design, emits stronger THz radiation than other reported circumferentially closed gratings, achieving millijoule radiated energy. Helix gratings exhibit significant potential for developing accelerator-based high-power and tunable THz radiators and are easy to manufacture. Some methods concerning optimizing beam-grating properties are employed to improve the radiated THz intensity. These results provide new insights into developing high-power THz radiators, which may provide an alternative THz source for free-electron laser facilities.

Superconducting magnets with noncircular apertures are important for handling unconventional beam profiles and specialized accelerator applications. This paper presents an analytical framework for designing superconducting accelerator magnets with quasipolygonal apertures, aimed at generating precise circular field harmonics. In part 1, we explore the relationship between current distributions on quasipolygonal formers and their corresponding magnetic field harmonics. By employing conformal mapping techniques, we establish a connection between the design of quasipolygonal bore magnets and traditional circular bore configurations, facilitating the simplification of complex mathematical formulations. Part 2 applies the derived current distributions to the canted cosine-theta (CCT) coil magnet concept, focusing on designing analytic winding schemes that generate single or mixed circular harmonics within quasipolygonal apertures. This work not only advances the design of superconducting magnets but also broadens the scope of CCT technology to accommodate more complex geometries.

An important upgrade has been deployed for the collimation system of the Large Hadron Collider (LHC) for lead-ion beams that are already planned to reach their high-luminosity target intensity upgrade in the ongoing LHC Run 3 (2022–2026). While certain effects like e-cloud, beam-beam, impedance, injection, and dump protection are relaxed with ion beams, halo collimation becomes an increasing challenge, as the conventional multistage collimation system is about two orders of magnitude less efficient than that for proton beams. Ion fragments scattered out of the collimators in the betatron cleaning insertion risk quenching the cold dipole magnets downstream and may represent performance limitations. Planar channeling in bent crystals has been proven effective for high-energy heavy ions. A crystal collimation system was integrated into the LHC as a baseline solution for collimation in the High-Luminosity LHC (HL-LHC) era. In this paper, simulation and measurement results demonstrating the observation of channeling of heavy-ion beams and improvement in collimation cleaning in the multi-TeV energy regime are presented. The efficiency of the collimation scheme foreseen for the HL-LHC is presented. The highlights of the collimation performance in 2023, when crystal collimation was successfully deployed operationally for the first time, are also presented.

An inductive voltage adder named “Mi2” has been built at Commissariat à l’Énergie Atomique et aux Energies Alternatives to produce two intense pulsed electron beams of 2 kA, 700 keV, and 80 ns full width at half maximum from a cold velvet cathode. In a coupling of experimental and simulation studies, we aim to evaluate the emittance value of those beams. This study focuses on the first beam modelization. Multidimensional particle-in-cell simulation models are used to demonstrate the necessity of taking into account the discrete nature of the electronic emission in order to model a beam consistent with the experimental studies. This study also shows the influence of the emissive surface geometry on the beam current density and emittance and provides a numerical model matching the first beam structure.

Ultrashort broadband THz radiation is an essential tool for investigating nonlinear phenomena and other frontier scientific research. Here, we propose a novel scheme that leverages the nonlinear longitudinal space-charge oscillation process to amplify the chirped density modulation amplitude of the electron beam, which is then utilized to generate ultrashort THz radiation. In this scheme, by controlling the charge density during the beam transport process, the initial chirped density modulation is converted into current peaks with higher amplitude, thereby enabling subsequent ultrashort broadband THz radiation in an optimally tapered undulator. We analyze the key parameters affecting nonlinear longitudinal oscillations of the electron beam with initial chirped density modulation. Furthermore, simulation results verify the feasibility of enhancing the chirped density modulation via the space-charge oscillation. It shows the generation of a microbunched electron beam with a peak current exceeding 370 A, while maintaining the chirped characteristics of the density modulation. Consequently, ultrashort broadband radiation with a full width at half maximum pulse duration of 250 fs and a frequency range covering 1.5 to 5 THz can be produced in the subsequent undulator.

Shanghai Synchrotron Radiation Facility (SSRF)/Shanghai soft X-ray FEL facility (SXFEL) has developed an advanced transverse deflecting structure two-mode transverse deflecting structure (TTDS) to deflect beams at any angle. The rf design of the TTDS uses a two-mode structure utilizing both the ${\mathrm{H}\mathrm{E}\mathrm{M}}_{11}$ and ${\mathrm{H}\mathrm{E}\mathrm{M}}_{12}$ modes for simultaneous vertical and horizontal deflections, operating at 2856 and 5712 MHz, respectively. The design was published in Physical Review Accelerators and Beams in April 2024. A TTDS prototype with 14 regular cells and 2 coupler cells was fabricated at SSRF/SXFEL. Because of the differences in electromagnetic field distributions between the two modes of the TTDS, the nonresonant perturbation measurement was studied by taking the coexisting two modes in mind. Based on an independent tuning process between the modes, a sequential tuning process was designed and established. Using the existing measurement system in the Microwave Laboratory at SSRF, all necessary measurements and tuning have been completed, and the TTDS prototype is ready for high-power tests.

A fundamental comparison between a magnetic undulator and an ion channel, or betatron, radiation from relativistic electrons is presented. While conventional theories nominally range from the undulator ($K<1$) to the wiggler ($K>1$) regime, they are only applicable for sufficiently large Lorentz factors (${\gamma }_0\gg K$). They therefore do not account for high $K/{\gamma }_0$ cases, for which we show that particle trajectories and radiation characteristics strongly deviate from the linear predictions in both magnetic undulators and ion channels. This problem arises from the fundamental differences between a magnetostatically and electrostatically induced oscillation. A reformulation of both the ion channel betatron wavelength and amplitude, as well as the same parameters in a magnetic undulator, permits us to compare cases with equivalent oscillation period and amplitude in the two different scenarios. The notable differences in spectral features of the two radiation mechanisms can then be addressed via numerical simulations of single particle as well as full beam dynamics. Additionally, we identify and quantify a novel transverse orbit precession effect in ion channels for particles with initial angular momentum relative to the device axis. This effect, which is significant in cases of strong transverse kinetic energy oscillations, alters both the radiation divergence and the beam emittance. In this paper, we present this new theoretical framework and compare its results with numerical simulation applied to realizable experimental tests of such radiation sources.

The muon collider has the potential to be a powerful tool for the exploration of frontiers in particle physics. In order to reach high luminosity, the 6D emittance of the muon beam needs to be reduced by several orders of magnitude. The cooling process for a muon collider involves two parts: initial six-dimensional cooling and final transverse cooling. This paper focuses on the former and proposes a conceptual design of the rectilinear cooling channel with additional dipole magnets. We first introduce a general method for designing the rectilinear cooling channel. Subsequently, we apply this method to develop two rectilinear cooling channels before and after a bunch merge system. Furthermore, we investigate the impact on cooling performance of employing $\pi$-mode rf cavities and the effect of errors in the magnetic and rf fields.

Coherent synchrotron radiation (CSR) is known for its detrimental effects on the performance of free electron lasers (FEL). While it is commonly considered a source of beam quality degradation in linacs, in externally seeded FEL schemes, CSR is known to spoil the bandwidth of the FEL radiation. Investigating CSR’s effect on seeded FELs requires a realistic estimation of CSR-induced energy modulations, known as wakes. Several models exist for calculating CSR wakes, differing in their treatment of transient and shielding effects. This work applies various models to compute CSR wakes in a magnetic chicane. In particular, it highlights the importance of the chicane chamber shielding for relatively long electron bunches used in seeded FELs. We use the practical example of the echo-enabled harmonic generation (EEHG) seeding technique to establish that proper consideration of transient and shielding effects is essential for estimating the impact of CSR on seeded FEL performance. This corrected estimate is vital for reaching the near-Fourier limit bandwidth of EEHG by the currently available methods.