Powerful ERL for experiments (PERLE) is a novel energy recovery linac (ERL) test facility [1], designed to validate choices for a 50 GeV ERL foreseen in the design of the Large Hadron Electron Collider and the Future Circular Collider and to host dedicated nuclear and particle physics experiments. Its main goal is to demonstrate the high current, continuous wave, multipass operation with superconducting cavities at 802 MHz. With very high beam power (10 MW), PERLE offers an opportunity for controllable study of every beam dynamic effect of interest in the next generation of ERLs and becomes a “stepping stone” between the present state-of-the-art 1 MW ERLs and the future 100 MW scale applications.

Electrons in an x-ray free electron laser (XFEL) develop periodic density fluctuations, known as microbunches, which enable the exponential gain of x-ray power in an XFEL. When an electron beam microbunched at a hard x-ray wavelength is kicked, microbunches are often washed out due to the dispersion and $R_{56}$ of the bend. An achromatic (dispersion-free) bend with a small $R_{56}$, however, can preserve microbunches, which rotate to follow the new trajectory of the electron bunch. Rotated microbunches can subsequently interact in a repointed undulator to produce a new beam of off-axis x rays. In this work, we demonstrate hard x-ray multiplexing in the Linac Coherent Light Source hard x-ray undulator line using microbunch rotation through a $10\mathrm{\mu }\mathrm{rad}$ first-order-achromatic bend created by transversely offsetting quadrupole magnets in the FODO lattice. Quadrupole offsets are determined analytically from beam-matrix theory. We also discuss the application of microbunch rotation to out-coupling a cavity-based XFEL.

Superconducting magnets with noncircular aperture are desired for accelerators and many other high-field applications. This paper presents new methods for the analytic design of elliptic bore superconducting accelerator magnets. Part 1 of this work shares the derivation of current to field relations between a sheet current density on an elliptic cylinder and the magnetic field harmonics inside the aperture. This result is explored in the general context of elliptic bore magnet design with relevant scaling laws compared between elliptic and circular bore magnets. In part 2, this approach is applied to the specific geometry of canted-cosine-theta (CCT) accelerator magnets, enabling analytic winding design for single or mixed circular harmonics within elliptic aperture CCT magnets.

The concept of crystal collimation relies on the use of bent crystals to coherently deflect positively charged particles with suitable impact conditions by trapping them in the potential well generated by adjacent crystalline planes. The resulting deflection is much higher than what can be achieved by multiple scattering on amorphous materials. For this reason, this technique has been explored in the past decades for applications to particle accelerators. In particular, a full test stand was installed in the betatron collimation insertion of the Large Hadron Collider (LHC) to explore applications to hadron beam collimation. This setup was extensively studied in Run 2 (2015–2018), as a way to improve the cleaning performance of the machine in particular with Pb ion beams, in view of the more challenging parameters envisaged for the High Luminosity upgrade (HL-LHC). This paper reports the results of measurements performed with Pb ion beams, demonstrating the capability of crystal collimation to improve the cleaning performance at the LHC. These results supported the integration of this advanced technology in the baseline upgrade program for HL-LHC.

The PSI Positron Production (${\mathrm{P}}^3$ or P-cubed) experiment is a $e^{+}$ source and capture system with the potential to increase by an order of magnitude the state-of-the-art $e^{+}$ yield normalized to the drive linac energy, a highly desirable goal for future colliders. The experiment is framed in the FCC-ee injector study and will be hosted at SwissFEL, located at the Paul Scherrer Institute in Switzerland. This paper presents the ${\mathrm{P}}^3$ project at an advanced stage, with an emphasis on a capture system featuring a novel $e^{+}$ matching device based on high-temperature superconducting solenoids, followed by two large aperture rf cavities surrounded by normal-conducting solenoids. The diagnostics design is also introduced, including monitors of charge, energy spectrum, and bunch-by-bunch longitudinal profile simultaneously for secondary $e^{+}$ and $e^{-}$. The last chapter of the text overviews the currently ongoing installation at SwissFEL, including the beam transfer line, rf network, radiation protection, and other relevant activities toward the operation with $e^{+}$ in the coming years.

Fourth generation storage ring light sources enabled by multibend achromat lattices and high-gradient magnets can reach unprecedented photon brightness. In this study, we show that, through the two-frequency crab cavity scheme, such machines also offer a unique opportunity to produce intense short x-ray pulses that are ideal for time-resolved user experiments. The short pulses and the high brightness photon beams are simultaneously available at all beamlines in a fully compatible operation mode. Owing to the small momentum compaction factor characteristic in fourth generation storage rings, the vertical emittance contribution due to coupling between the longitudinal and transverse planes by the crab cavities is small, which allows choosing a lower fractional vertical tune and in turn enables reaching the desired beam bunch tilting with a weaker deflecting voltage. However, bunch lengthening by the harmonic cavity is found to drastically increase the vertical emittance, which poses a serious hurdle to the scheme. We propose to use a half-integer harmonic cavity to simultaneously produce bunch lengthening and shortening in the bunch train to facilitate the compatible operation of the normal and short-pulse beams. A concrete case study based on the Advanced Photon Source Upgrade lattice is provided to demonstrate the system configuration and beam performance.

The beam longitudinal dynamics code blond, utilized tool, has been developed at CERN since 2014. It has emerged as a central tool for conducting longitudinal beam dynamics simulations. In this paper, we present this modular simulation suite and the various physics models that can be included and combined by the user. We detail the reference frame, the equations of motion, the plethora of options for radio-frequency parameters such as phase noise, fixed-field acceleration, and feedback models for the CERN accelerators, as well as the modeling of collective effects and synchrotron radiation. We also present various methods of generating multibunch distributions matched to a given impedance model. blond is furthermore a well tested and optimized simulation suite, which is demonstrated through examples, too.

Conventional direct-drive direct current (dc) septum magnets suffer from a high current density in the drive coil, which can cause magnet failures such as coil shorting due to the strong heat cycles, and result in large power consumption. Requirements for a thin septum and narrow gap in the magnet design naturally limit the space for coils, causing a high current density to be inevitably applied to the small cross-section coils. In this paper, we presented a new design for a dc septum magnet that largely decreased the current density and power consumption, while keeping an injection amplitude using a thin dogleg-shaped septum. According to our design comparison, the current density and power consumption were reduced from $145\mathrm{A}/{\mathrm{mm}}^2$ and 24.5 kW for the conventional direct-drive configuration to $4.5\mathrm{A}/{\mathrm{mm}}^2$ and 1.0 kW, respectively. The primary idea presented in paper leads to a power reduction of a factor of 25. We also detailed the fabrication process and magnet performance of the dc septum magnet developed for the next generation light source.

The LHCb (Large Hadron Collider beauty) experiment at CERN LHC aims at achieving a significantly higher luminosity than originally planned by means of two major upgrades: the Upgrade I that took place during the Long Shutdown 2 (LS2) and the Upgrade II proposed for LS4. Such an increase in instantaneous and integrated luminosity with respect to the design values requires to reassess the radiation exposure of LHC magnets, cryogenics, and electronic equipment placed in the insertion region 8 (IR8) around LHCb. Monte Carlo simulations are a powerful tool to understand and predict the interaction between particle showers and accelerator elements, especially in case of future scenarios. For this purpose, their validation through the comparison with available measurements is a relevant step. A detailed IR8 model, including the LHCb detector, has been implemented with the fluka code. The objective of this study is to evaluate radiation levels due to proton-proton collisions and benchmark the predicted dose values against beam loss monitor measurements performed in 2018. Finally, we comment on the upcoming LHC run (Run 3, from 2022 to 2025), featuring a first luminosity jump in LHCb.

At the Rapid Cycling Synchrotron (RCS) in Japan Proton Accelerator Research Complex (J-PARC), theoretical predictions have indicated that the kicker impedance would excite the beam instability. A 1-MW beam with large emittance can be delivered to the Material and Life Science Experimental Facility through suppression of the beam instabilities by choosing the appropriate machine parameters. However, we require other high-intensity and high-quality smaller emittance beams (than the 1-MW beam) for the main ring. Hence, we proposed a scheme for suppressing the kicker impedance by using prototype diodes and resistors, thereby demonstrating the effect on the kicker impedance reduction. However, the J-PARC RCS must be operated with a repetition rate of 25 Hz, which urged us to consider special diodes that are tolerant to heating. After developments, we have demonstrated that the special diodes with resistors can suppress the beam instability by reducing the kicker impedance. Enhanced durability of the prototype diodes and resistors for the 25-Hz operation was also realized. Moreover, the new diodes and the resistors have a negligible effect on the extracted beam from the RCS. From a simulation point of view, the scheme can be employed for at least 5-MW beam operation within the stipulated specifications.

The ALPHA Collaboration, based at the CERN Antiproton Decelerator, has recently implemented a novel beamline for low energy ($\lesssim 100\mathrm{eV}$) positron and antiproton transport between cylindrical Penning traps that have strong axial magnetic fields. Here, we describe how a combination of semianalytical and numerical calculations was used to optimize the layout and design of this beamline. Using experimental measurements taken during the initial commissioning of the instrument, we evaluate its performance and validate the models used for its development. By combining data from a range of sources, we show that the beamline has a high transfer efficiency and estimate that the percentage of particles captured in the experiments from each bunch is $(78\pm 3)\%$ for up to ${10}^5$ antiprotons and $(71\pm 5)\%$ for bunches of up to ${10}^7$ positrons.

The static Robinson instability and associated coherent synchrotron frequencies were systematically studied at the Photon Factory (PF) 2.5-GeV storage ring at KEK. Under machine parameters close to an anticipated Robinson limit, we observed beam dumps at which the beam and related signals were recorded. The evolution of the beam phase and the threshold condition at the beam dumps were consistent with theoretical values calculated based on the uniformly filled point-bunch model. However, we found remarkable discrepancies from theoretical predictions with additional coherent-frequency measurements. Under conditions close to the Robinson limit, we observed an unpredicted sharp peak at a frequency of approximately 5.2 kHz, together with discrepancies in both the frequency and damping rate of the coherent oscillation. These results indicate the importance of further experimental and theoretical studies on the static Robinson instability.

This paper introduces a storage ring lattice design for synchrotron radiation sources which fulfills all the required features for the realization of a diffraction limited light source. Insertion devices half gaps of $2.5\mathrm{m}\mathrm{m}$ are assumed and enabled by the design of dedicated straight sections. The use of long straight sections is possible for such a lattice and led to the definition of a set of transparency conditions used to minimize the effect of such insertions for on- and off- energy beam dynamics. The design proposed enables an extremely long Touschek lifetime and beam accumulation. A real case study will be shown for large circumference storage ring upgrade lattices.

We report the development of a multileaf collimator (MLC) for charged particle beams, based on independently actuated tungsten strips that can selectively scatter unwanted particles. The MLC is used in conjunction with an emittance exchange beamline to rapidly generate highly variable longitudinal bunch profiles. The developed MLC consists of 40 independent leaves that are 2 mm wide and can move up to 10 mm and operates in an ultrahigh vacuum environment, enabled by novel features such as magnetically coupled actuation. An experiment at the Argonne Wakefield Accelerator, which previously used inflexible, laser-cut masks for beam shaping before an emittance exchange beamline, was conducted to test functionality. The experiment demonstrated myriad transverse mask silhouettes, as measured on a scintillator downstream of the MLC, and the corresponding longitudinal profiles after emittance exchange, as measured using a transverse-deflecting cavity. Rapidly changing between mask shapes enables expeditious execution of various experiments without the downtime associated with traditional methods. The many degrees of freedom of the MLC can enable the optimization of experimental figures of merit using feed-forward control and advanced machine learning methods.

The operation of the SuperKEKB has been ongoing since 2016. The vacuum systems of the main ring (MR) which consists of a 7-GeV electron ring (HER) and a 4-GeV positron ring (LER), the damping ring (DR) for 1.1 GeV positrons in the middle of the injector linac have been working well as a whole. As of June 2022, the maximum stored beam currents of MR are 1.46 and 1.14 A for the LER and the HER, respectively, and approximately 30 mA for the DR. The pressure increase per unit beam current is steadily decreasing and the new vacuum components developed for the SuperKEKB have been working as expected. No significant electron cloud effect has been observed in the LER after installing solenoids in drift spaces in 2017 which apply magnetic fields in the beam direction. The recent pressure behavior of the LER with increased beam current is explained by considering thermal gas desorption induced by the beam as well as photon-stimulated gas desorption. Currently, the beam lifetime is primarily limited by the Touschek effect rather than the vacuum pressure, and their degrees of contribution are evaluated. The challenges associated with high beam currents, such as damage to beam-collimator heads and excess heating of beam pipes at wiggler sections have become more apparent as beam currents are increased. The status of the SuperKEKB vacuum system and the experiences during the past 6 years of operation are presented here.

We introduce a quasistatic particle-in-cell (PIC) code—wand-pic—which does not suffer from some of the common limitations of many quasistatic PICs, such as the need for a predictor-corrector method in solving electromagnetic fields. We derive the field equations under quasistatic (QS) approximation and find the explicit form of the “time” derivative of the transverse plasma current. After that, equations for the magnetic fields can be solved exactly without using the predictor-corrector method. Algorithm design and code structure are thus greatly simplified. With the help of explicit quasistatic equations and our adaptive step size, plasma bubbles driven by the large beam charges can be simulated efficiently without suffering from the numerical instabilities associated with the predictor-corrector method. In addition, wand-pic is able to simulate the sophisticated interactions between high-frequency laser fields and beam particles through the method of subcycling. Comparisons between the wand-pic and a first-principle full PIC code (vlpl) are presented. wand-pic is open-source, fully three-dimensional, and parallelized with the in-house multigrid solver. Scalability, time complexity, and parallelization efficiency up to thousands of cores are also discussed in this work.

A new parasitic, mixed-field, neutron-dominated irradiation station has been recently commissioned at the European Laboratory for Particle Physics (CERN). The station is installed within the neutron time-of-flight (n_TOF) facility, taking advantage of the secondary radiation produced by the neutron spallation target, with neutrons ranging from 0.025 eV to several hundreds of MeV. The new station allows radiation damage studies to be performed in irradiation conditions that are closer to the ones encountered during the operation of particle accelerators; the irradiation tests carried out in the station will be complementary to the standard tests on materials, usually performed with gamma sources. Samples will be exposed to neutron-dominated doses in the MGy range per year, with minimal impact on the n_TOF facility operation. The station has 24 irradiation positions, each hosting up to $100{\mathrm{cm}}^3$ of sample material. In view of its proximity to the n_TOF target, inside protective shielding, the irradiation station and its operating procedures have been carefully developed taking into account the safety of personnel and to avoid any unwanted impact on the operation of the n_TOF facility and experiments. Due to the residual radioactivity of the whole area around the n_TOF target and of the irradiated samples, access to the irradiation station is forbidden to human operators even when the n_TOF facility is not in operation. Robots are used for the remote installation and retrieval of the samples, and other optimizations of the handling procedures were developed in compliance with radiation protection regulations and the aim of minimizing doses to personnel. The sample containers were designed to be radiation tolerant, compatible with remote handling, and subject to detailed risk analysis and testing during their development. The whole life cycle of the irradiated materials, including their post-irradiation examinations and final disposal, was considered and optimized.

SPIRAL2 is a high power linear accelerator part of the GANIL laboratory. This superconducting (SC) linac can accelerate cw light ions to heavy ions at energies up to $40\mathrm{MeV}/\mathrm{nucleon}$ and $14.5\mathrm{MeV}/\mathrm{nucleon}$, respectively. In July 2019, the authorization to fully operate the SPIRAL2 SC linac permitted to start the commissioning of the medium energy beam transport line and SC linac. The main milestone of the commissioning in 2020 was to validate the transport and linac design by increasing the duty cycle up to 10% with a proton beam. This paper presents the strategy used by the commissioning team to increase the beam power, as well as the results obtained using different diagnostics. The extrapolation from obtained measurements to 100% duty cycle was also performed; the results are presented.

During the 2018 proton run, a new radio-frequency beam manipulation has been studied and successfully implemented at the CERN Proton Synchrotron (PS) for the first time. This technique is used to deplete a well-defined fraction of a continuous longitudinal beam distribution by creating a so-called barrier bucket. We propose a new application of the barrier bucket gymnastics in the multiturn extraction scheme used at CERN. These two exotic techniques are combined into a highly sophisticated procedure that dramatically reduces the beam losses at PS extraction, thus paving the way to high-intensity proton beams for future fixed-target experiments at the CERN Super Proton Synchrotron (SPS). In this paper, the expected performance of the PS and SPS is analyzed in detail to define a road map for making this novel extraction scheme operational.