Beams of radioactive heavy ions allow researchers to study rare and unstable atomic nuclei, shedding light on the internal structure of exotic nuclei and on how chemical elements are formed in stars. However, the extraction and transport of radioactive beams rely on time consuming expert-driven tuning methods, where hundreds of parameters are manually optimized. Here, we introduce a system that employs artificial intelligence (AI), specifically utilizing Bayesian optimization, to assist in the transport process of radioactive beams. We apply our methodology to real-life scenarios showing advantages when compared with standard tuning methods. This AI-assisted approach can be extended to other radioactive beam facilities around the world to improve operational efficiency and enhance scientific output.

The most significant advances in accelerator-based light sources (i.e., x-ray free electron lasers) are driven by the production of a kiloampere-level peak current. As a prerequisite to achieve the desired high peak current, multistage symmetric C-chicane compressors are widely utilized due to their simple geometry and effectiveness. However, during the bunch compression process, coherent synchrotron radiation (CSR) effects may lead to transverse emittance dilution, eventually hindering progress toward achieving a higher peak current. Therefore, suppressing or even canceling the CSR effects in chicane compressors is essential. In this paper, we consider a general model of a four-bend chicane and conduct an explicit point-kick analysis of the coherent synchrotron radiation (CSR) effects, based on which we derive the conditions for completely canceling the steady-state CSR (ss-CSR) kicks using analytical formulas. These results yield two novel ss-CSR-immune chicanes that feature nonsymmetric C-shape and S-shape layouts, respectively. We also demonstrate their excellent emittance preservation capabilities with particle tracking simulations. By utilizing the proposed chicanes instead of the widely used C-chicane, the CSR-induced emittance growth can be reduced by about 1 order of magnitude in an almost identical bunch compression scenario.

Angular streaking experiments enable for experimentation in the attosecond regions. However, the deployed time-of-flight (TOF) detectors are susceptible to noise and failure. These shortcomings make the outputs of the TOF detectors hard to understand for humans and further processing, such as, for example, the extraction of beam properties. In this article, we present an approach to remove high noise levels and reconstruct up to three failed TOF detectors from an arrangement of 16 TOF detectors. Due to its fast evaluation time, the presented method is applicable online during a running experiment. It is trained with simulation data, and we show the results of denoising and reconstruction of our method on real-world experiment data.

In typical studies of collective effects in a storage ring, an important assumption is that the longitudinal bunch length remains constant over one turn, which is referred to as the adiabatic approximation. This approximation is reasonable for conventional storage rings. However, for extremely short bunch length storage rings, such as steady-state microbunching storage ring, the global phase slippage is very small, and the local or partial phase slippage can significantly influence the longitudinal dynamics of the bunch. Consequently, the bunch length can vary greatly around the ring, and the adiabatic approximation no longer holds. In this work, we investigate the microwave instability caused by the coherent synchrotron radiation, which represents one of the dominant collective effects in short bunch storage rings, beyond the adiabatic approximation. We present a general formula for the instability threshold considering the variation of longitudinal optics around the ring and offer valuable guidance for the design of extremely short bunch storage rings. Our results show that depending on the distribution of the partial phase slippage, the instability threshold of a real lattice can be increased by a factor of 2 or even more compared to the classical prediction.

High-intensity proton accelerators are utilized for neutron, neutrino, and hadron sources. Increasing the beam intensity is important for science that utilizes these particles. However, as beam intensity increases in these proton accelerators, beam instability has emerged as a limiting factor. Coupled-bunch instability, resulting from impedance with frequency components near or below the revolution frequency, stemming from the electrical resistance of beam chambers, ceramic chambers in rapid cycling synchrotrons, and kicker magnets, poses a significant challenge in these proton accelerators. The oscillation frequency of beams observed during operation with chromaticity is considerably higher than the impedance frequency. Space charge forces exhibit significant strength, with a tune shift exceeding 0.1 as an absolute value. In single-bunch behavior, space charge forces dominate, influencing the oscillation modes of instability. It is inevitable that the effect will extend to coupled-bunch modes. This paper provides a theoretical discussion on the coupled-bunch instability of beams subjected to intense space charge forces.

High efficiency is essential for plasma-wakefield accelerators to be a cost-effective alternative in high-power applications, such as a linear collider. However, in a plasma-wakefield accelerator, the beam-breakup instability can be seeded by a transverse offset between the driver and trailing bunch. This instability, which rapidly increases the oscillation amplitude of the trailing bunch, grows with higher power-transfer efficiency from the driver to the trailing bunch [V. Lebedev et al., Phys. Rev. Accel. Beams 20, 121301 (2017)]. In this paper, we use particle-in-cell simulations to investigate the efficiency–instability relation that constrains the driver-to-trailing-bunch power-transfer efficiency in beam-driven plasma accelerators. We test the relation using a grid of simulations across all parameters that affect the beam-breakup instability, assuming a uniform accelerating field (optimal beam loading) and no ion motion. We find that the previously proposed efficiency–instability relation represents a lower limit on the strength of the instability for a given efficiency. For each normalized wake radius, only a certain accelerating field reaches this lowest value of the transverse instability; deviating from this point can increase the growth rate by several orders of magnitude. Finally, we highlight how the oscillation-amplitude growth of the trailing bunch can be reduced or damped with an initial uncorrelated energy spread and the presence of ion motion.

This paper presents the concept and design of a novel accelerator magnet consisting of two concentric rings of permanent magnets arranged in a Halbach layout. By replacing one component, the device can be converted to any transverse multipole configuration. By the individual rotation of the two rings, both the strength and the direction of the field pattern can be continuously tuned in a wide range, including the special case of polarity reversal. The tuning range can be changed by a parametric change of the design. The device is split into two halves and can be easily opened to allow for its installation and removal around an existing beampipe. The performance of a quadrupole demonstrator prototype is presented, including measurement results of field quality, integrated gradient and hysteresis, and discussion of sensitivity to the remanent magnetization of the permanent magnets.

The analysis of plasma wakefield acceleration experimental measurements, particularly in the characterization of photons emitted through the betatron radiation mechanism, requires the development of accurate numerical models. These computational models are crucial for supporting modern instrumentation designed to measure the single-shot, double-differential angular-energy radiation spectra resulting from interactions between beams and plasmas. Motivated by the needs of such applications, this paper presents detailed numerical models of betatron radiation generated in beam-plasma acceleration experiments. These models are based on the integration of the Liénard-Wiechert (LW) potentials, applied to computed particle trajectories. The particle trajectories are generated using three distinct methods: first, by tracking particles through idealized fields in the blowout regime of PWFA; second, by obtaining trajectories using the fast quasistatic particle-in-cell (PIC) code quickpic; and third, obtaining trajectories from the fully self-consistent PIC code osiris. To ensure the accuracy and reliability of these models, the paper includes various benchmark tests using analytical expressions, as well as employing the PIC code epoch, which takes an alternative approach by using a Monte Carlo quantum electrodynamics (QED)-based radiation model. Additionally, the paper presents simulations of the expected experimental betatron radiation spectra, taking into account parameters relevant to PWFA and plasma photocathode experiments at the SLAC FACET-II facility.

Transverse stabilization of the beam is crucial for optimizing the performance of a particle accelerator, regardless of its application. The most common method for minimizing transverse beam jitter is the Balakin-Novokhatsky-Smirnov (BNS) damping technique. Although this method has been successfully implemented worldwide, it has limitations since a significant fraction of the accelerating structures are operated off crest. In this work, we propose an alternative approach to induce the required energy spread, utilizing the natural curvature of the accelerating rf field in combination with a relatively long bunch and a longitudinal wakefield. This approach achieves strong damping of the transverse beam oscillations, similar to BNS damping, while simultaneously optimizing beam quality and maximizing acceleration efficiency. We have applied this method to the design of the Future Circular Collider injector linacs, designed to reach a beam energy of up to 20 GeV. However, this method is general and can be applied in principle to any accelerator.

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.