Particle-in-cell simulations are widely used in most fields of physics to investigate known and new phenomena which cannot be directly observed or measured yet. However, the computational and time resources needed for PICs make them impractical when high resolution and long time/distance simulations are required. In this work, we present a new PIC simulation code that takes advantage of the use of a relativistic reference frame and consequent time dilation and length contraction. These properties make a simulation capable of long (meter length) and high resolution simulations without the need for supercomputers. This new code is a step forward with regard to the previous tries enabling complex multiple body situations without additional filtering and smoothing of fields and currents. The usefulness of the relativistic frame PIC code is displayed by simulating electron beam bunching obtained in long undulator propagation and also the potential as a beam ”buncher” of 10 s of cm long low-density plasmas.

The pursuit of coherent radiation generation remains a key direction in the advancement of storage ring light sources. Despite the potential of laser modulation in achieving this goal, it leads to a significant decline in the quality of the electron beam. Efforts to mitigate this decline have resulted in the proposal of demodulation schemes. However, implementing modulation and demodulation within the storage ring presents significant challenges due to dynamical and spatial constraints within straight sections. In this study, we propose a straightforward and easily implementable method for achieving reversible laser modulation in a storage ring. Notably, our approach circumvents the need for lengthy straight sections or bypass section. Simulation results show a substantial restoration of beam quality following demodulation. This innovative scheme holds great promise for the realization of high repetition rate coherent storage ring light sources.

The RFQ accelerator, often the initial rf component in a hadron accelerator, focuses, bunches, and accelerates the beam from several keV to MeV across a several-meter quadrupole channel. Due to the significant application potential of high-power RFQs, research efforts have grown substantially in recent years. This paper reviews global advancements in high-power RFQ technology. The stable operation of these high-power RFQs faces many design challenges and technological limitations. The experiences and lessons learned from the recent design, fabrication, high-power rf conditioning, and beam commissioning processes have been summarized. Key issues related to thermal effects, multipacting, sparking, stability, and frequency detuning in the components of the RFQ system are presented, and the proposed solutions are discussed.

We present a simulation configuration for the electron beam profile consistent with experiments on the linear accelerator UERL-10-15S2, focusing on determining electron energy and beam size. Two essential aspects of the electron beam described in the simulation configuration are the initial energy distribution and the initial beam size with the flux distribution. Notably, we introduce a new mathematical function by modifying the approximated Landau distribution. This new function offers a better fit than our previous mathematical function and, more importantly, accurately reflects the physical nature of the energy spectrum of electrons passing through a thin layer of matter. Using this configuration, we have simulated the irradiation of zeolite ETS-10 by the electron beam. This irradiated simulation was set up with various electron energy distributions, yielding results on the dose rate distribution (2D dose map) and the mean absolute percentage deviation of the absorbed dose rate within the irradiated titanosilicate. With the improvements in this paper, we have provided a solution to enhance the linear accelerator’s application in scientific research besides conventional industrial irradiation applications.

The University of New Mexico, in collaboration with the Naval Research Laboratory, has developed and characterized a fast rise time air-insulated linear transformer driver (LTD) for use in high power microwave (HPM), high energy density physics (HEDP), as well as shock physics experiments. The LTD cavity is a fast rise time—high current pulsed power rectangular device that is composed of four “wings” each containing three bricks, situated on the perimeter of a central spool containing the load. Each brick has two distinct capacitors and a rail switch composed of a six-by-six arrangement of spherical electrodes. This paper provides a full characterization of the device with relevant operational parameters, experimental results of load currents from various loads at various voltages, and currents and timing relationships from individual bricks and wings.

This paper presents the successful application of a phase-lock feedback system to maintain the resonance condition of a radio frequency (rf) spin rotator (specifically, an rf Wien filter) with respect to a 120 kHz spin precession in the Cooler Synchrotron (COSY) storage ring. Real-time monitoring of the spin precession and the rf Wien filter signal allows the relative phase between the two to be stabilized at an arbitrary setpoint. The feedback system compensates for deviations in the relative phase by adjusting the frequency and/or phase of the rf device as needed. With this method, a variation in the phase relative to the demanded value with a standard deviation of ${\sigma }_{\mathrm{\Delta }\phi }\approx 0.2\mathrm{rad}$ could be achieved. The system was implemented in two runs aiming at a first direct measurement of the deuteron electric dipole moment in 2018 and 2021. In addition, the difference between a single-bunch beam affected by the spin rotator and a two-bunch system in which only one bunch is exposed to the spin rotator fields is discussed. Both methods have been used during these beam times. The ability to keep the spin precession and the rf fields synchronized is crucial for future investigations of electric dipole moments of charged particles using storage rings.

Tsinghua University has designed an X-band (11.424 GHz) slow-wave parallel-coupled ten-cell standing-wave accelerator structure, operated it at a high gradient with 40-ns-long rf pulses. Unexpected bead-pull results were observed during the cold testing, which we attribute to intercavity coupling. To explain these results, a multicell coupling circuit model was developed and used to analyze the data. High-power testing was conducted on the TPOT-X platform, achieving a highest gradient of $130\mathrm{MV}/\mathrm{m}$ after $1.1\times {10}^7$ conditioning pulses. Compared to conventional multicavity high-gradient structures, the distributed power feeding system offers a shorter conditioning period and demonstrates the potential to achieve higher accelerating gradients under short-pulse operation.

The Diamond-II storage ring upgrade will provide users with 1–2 orders of magnitude increase in brightness over the existing Diamond facility, as well as double the number of straight sections to allow for the installation of additional beamlines. A key performance requirement for the upgrade will be to provide a quasitransparent top-up injection scheme. The ring was originally designed to use a single-bunch aperture sharing injection scheme, in which short stripline kickers are used to kick the injected bunch into the storage ring’s dynamic aperture, while the kick remains weak enough to avoid displacing the existing stored bunch outside the acceptance. This scheme has been modified to implement a kick-and-cancel method to place the stored bunch back on axis and leave only the injected bunch to oscillate. The kicker power supplies are thus required to provide a double pulse with a few-microsecond pulse spacing. This new method is expected to significantly improve the transparency of the injection process and reduce the recovery time for the targeted bunch, along with minimizing the transverse wakefield effects and any interactions with the transverse multibunch feedback and harmonic cavity.

The self-amplified spontaneous emission (SASE) mechanism, the fundamental operating principle of numerous free-electron laser (FEL) facilities, is driven by electron beam shot noise and leads to significant fluctuations in the output pulse energy. This study presents a robust method for improving pulse energy stability by incorporating a dispersion element that introduces longitudinal dispersion into the electron beam during the exponential growth phase of the SASE process. At this phase, the density modulation of the electron beam, characterized by the bunching factor, undergoes large fluctuations, resulting in substantial variations in the emitted radiation power. The introduction of longitudinal dispersion allows for controlled manipulation of the bunching distribution, suppressing fluctuations and enhancing pulse energy stability. The stabilization mechanism is explained in this paper, and its impact on the radiation properties is analyzed for both the standard SASE scheme and advanced lasing setups, such as a two-stage lasing process for two-color pulse generation, with the initial stage operating in SASE mode.

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.