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.

The collective behavior of an ion cloud confined in a linear Paul trap is physically almost equivalent to that of a relativistic beam traveling in a particle accelerator. This fact provides a new possibility for experimental beam-dynamics studies that can be done without relying on large-scale machines. We have constructed a compact ion trap to explore various accelerator-physics issues in a local tabletop environment. The present trap system is designed particularly for the study of high-intensity short hadron bunches typical in linear accelerators. Resonance-induced ion losses are measured and plotted as a function of the betatron and synchrotron phase advances over a wide range, which offers a piece of indisputable experimental evidence for the presence of various betatron and synchrobetatron resonance stop bands. We confirm that these instability bands shift in the stability map depending on the ion density. The recently proposed stop-band diagram, free from the conventional concept of incoherent tune spread, is employed to explain the experimental observations.

The interaction of dust particles with the LHC proton beams accounts for a major fraction of irregular beam loss events observed in LHC physics operation. The events cease after a few beam revolutions because of the expulsion of dust particles from the beam once they become ionized in the transverse beam tails. Despite the transient nature of these events, the resulting beam losses can trigger beam aborts or provoke quenches of superconducting magnets. In this paper, we study the characteristics of beam-dust particle interactions in the cryogenic arcs by reconstructing key observables like nuclear collision rates, loss durations and integral losses per event. The study is based on events recorded during 6.5 TeV operation with stored beam intensities of up to $\sim 3\times {10}^{14}$ protons per beam. We show that inelastic collision rates can reach almost ${10}^{12}$ collisions per second, resulting in a loss of up to $\sim 1.6\times {10}^8$ protons per event. We demonstrate that the experimental distributions and their dependence on beam parameters can be described quantitatively by a previously developed simulation model if dust particles are assumed to be attracted by the beam. The latter finding is consistent with recent time profile studies and yields further evidence that dust particles carry a negative charge when entering the beam. We also develop different hypotheses regarding the absence of higher-loss events in the measurements, although such events are theoretically not excluded by the simulation model. The results provide grounds for predicting dust-induced beam losses in the presence of higher-intensity beams in future runs of the High-Luminosity LHC.

The high intensity polarized electron source is a critical component for future nuclear physics facilities. The electron-ion collider requires a polarized electron gun with higher voltage and higher bunch charge compared to any existing polarized electron source. At Brookhaven National Laboratory, we have built an inverted high voltage direct current (HVDC) photoemission gun with a large cathode size. We report on the performance of GaAs photocathodes in a high gradient with up to 16 nC bunch charge. The measurements were performed at a stable operating gap voltage of 300 kV—demonstrating outstanding lifetime and robustness. We observed obvious lifetime enhancement by biasing the anode. The gun also integrated a cathode cooling system for potential application on high current electron sources. The various novel features implemented and demonstrated in this polarized HVDC gun will open the door toward future high intensity-high average current electron accelerator facilities.

Regenerative multibunch beam breakup instabilities are a well-known phenomenon in recirculating linacs where particle bunches pass multiple times through the same superconducting rf cavities with extremely high quality factor. This is in particular true for energy recovery linacs. Parasitic electromagnetic modes excited in the cavities can affect bunch dynamics in such a way, that on its subsequent passes it excites the modes further and a positive feedback loop is formed. Direct bunch tracking and a stability analysis technique can be used to study the instability. Usually only dipole modes are considered. In the present work, similar approaches are applied to monopole and quadrupole modes and illustrated with simulation results for the S-DALINAC and MESA facilities. An approximated stability analysis technique with better performance for the case of multiple recirculations is proposed. Countermeasures including betatron phase advance adjustment and additional betatron coupling are considered and a universal criterion for assessment of their effectiveness is proposed. A simple model of a damped oscillator with feedback is proposed as a universal example illustrating the phenomenon in general.