The photon flux resulting from high-energy electron beam interactions with high-field systems, such as those found in the upcoming FACET-II experiments at the SLAC National Accelerator Laboratory, yields deep insight into the electron beam’s underlying dynamics during the interaction. However, extracting this information is an intricate process. To demonstrate how to approach this challenge using modern methods, this paper utilizes simulated data that models plasma wakefield acceleration-derived betatron radiation in experiments to determine reliable methods of reconstructing key beam and beam-plasma interaction properties. For betatron radiation measurements, translating the observed $200\mathrm{keV}$ to $30\mathrm{MeV}$ photon double-differential energy-angle spectra obtained from an advanced Compton spectrometer requires testing multiple methods to optimize the pipeline from its response to incident electron beam information. The paper compares maximum likelihood estimation and machine learning to refine the translation of photon spectra into precise electron beam metrics, such as spot size, energy, and emittance, enhancing the understanding of beam behavior within these dense, high-field environments. We also introduce machine learning and the expected maximization algorithm to reconstruct the primary photon spectrum, employing a multilayer neural network for regression analysis of the energy and angle spectra. With appropriate modifications, the advanced methods reproduce relevant incident beam parameters with high accuracy, even for beam sizes in the $<10\mathrm{\mu }\mathrm{m}$ range. This capacity is critical to understanding intense beam propagation and its optimization in plasma.

The Electron-Ion Collider (EIC), to be built at Brookhaven National Laboratory, will collide a polarized high-energy electron beam with polarized proton and light ion beams in the center-of-mass energy range of 20–140 GeV, achieving a maximum peak luminosity of up to $1\times {10}^{34}{\text{cm}}^{-2}{\mathrm{s}}^{-1}$ for the proton and electron collisions. To achieve such a high luminosity, the EIC will employ small, flat beams at the interaction point, which requires a transverse emittance ratio of about 11:1. Since 2017, we have carried out a series of beam experiments to test the feasibility of achieving such a large emittance ratio in the Relativistic Heavy Ion Collider (RHIC). Thanks to the existing stochastic cooling and decoupling feedback system in RHIC, we successfully demonstrated a large transverse emittance ratio of 11:1 with gold ion beams in 2023. In this article, we will present more details and data analysis for these experiments, along with analytical estimates and numerical multiparticle simulations, and provide an outlook for future EIC coupling compensation.

The Advanced Virtual Accelerator Software (avas) has been developed to simulate beam transport processes in high-intensity linear accelerators and has been used in the China Initiative Accelerator Driven System (CiADS) project. In the study of beam dynamics for high-intensity linear accelerators, 3D multiparticle simulations are required due to numerous nonlinear effects caused by strong space charge effects. However, the use of multiparticle simulation is often limited by the computational speed of the particle-in-cell (PIC) algorithm. To achieve fast large-scale multiparticle simulation, avas uses a parallel framework implemented in c++ and improves related algorithms. Specifically, the PIC algorithm has been modified based on symmetry, resulting in the S-PICNIC algorithm. Under the test conditions described in this paper, compared to the standard algorithm, the S-PICNIC algorithm can accelerate the process of solving the space charge field by 4 times while maintaining the simulation accuracy. In addition, avas uses a combined particle motion mode that switches between two modes (using either time or position as the independent variable) based on the element type. This adaptive switching effectively balances the accuracy and speed of numerical simulation. This method has enabled the fast simulation of over 100 million macroparticles. Furthermore, avas uses object-oriented programming methods, where objects are designed based on real physical objects. This design allows avas to preset operating parameters through numerical simulation. In the test, avas successfully preset the operating parameters of the superconducting section of the Chinese ADS front-end demonstration linear Accelerator, resulting in a negligible beam loss and a deviation between the energy set value and the actual measured value of about 0.5%. This paper introduces the structure of the program and related physical models. Benchmark results are also discussed to verify the reliability of the code.

Field emission can cause significant problems in superconducting radio-frequency linear accelerators (linacs). When cavity gradients are pushed higher, radiation levels within the linacs may rise exponentially, causing degradation of many nearby systems. This research aims to utilize machine learning with uncertainty quantification to predict radiation levels at multiple locations throughout the linacs and ultimately optimize cavity gradients to reduce field emission-induced radiation while maintaining the total linac energy gain necessary for the experimental physics program. The optimized solutions show over 40% reductions for both neutron and gamma radiation from the standard operational settings.

During the third run of the Large Hadron Collider in 2023, which had the highest intensity bunch population compared to previous runs, a beam dump incident with operational delays occurred due to increased losses attributed to pressure spikes within a warm vacuum sector. Subsequent inspections revealed localized annealing and plasticization of the tension spring in the sliding contact radio frequency finger of a 212 mm diameter vacuum module, alongside traces of vapor deposition on the various module components with the stainless steel spring material. A comprehensive analysis involving vacuum and beam impedance studies was conducted to investigate the triggering mechanisms behind the warm vacuum module failure. The findings indicate localized beam-induced heating, which could lead to the annealing of the spring with a consequent cascade of effects. Systematic studies of a similar possible failure mechanism for other sizes of vacuum modules were also conducted. Additionally, investigations into potential mitigation measures were performed.

The systematic comparison of two semianalytical models of microbunching instability affecting electron beams in single pass or recirculating linear accelerators is reported. The comparison is comprehensive of numerous features of the instability, such as low and high gain contributions, either linearized or at second order, coherent synchrotron and edge radiation, and Landau damping by transverse emittance and laser heater, investigated for single and double magnetic bunch length compression. The comparison is enriched by three different expressions—one of which is new—to calculate intrabeam scattering. The inclusion of this effect allows the recovery of agreement with published experimental observations, to date either in disagreement with theory or in partial agreement by virtue of blind fitting of parameters. The study is complemented by the evaluation of beam heating for oblique electron-laser interaction, this scheme being relevant for high repetition rate free-electron lasers, space constrained, or subject to perturbations by the laser heater chicane.

An envelope equation is used to explore the propagation of a focused electron beam through dense conductive media like partially ionized high-pressure gas, metal vapor plumes from beam-target interactions, or low-density solid-phase targets. Envelope equations have been a most useful tool for predicting experimental results of beam propagation in gas, and they are refined for the general problem of propagation through a dense medium. The envelope equation is modified to account for the large beam divergence resulting from multiple scattering. The envelope code results are in qualitative agreement with published experimental data.

Accelerator physics presents unique challenges for natural language processing (NLP) due to its specialized terminology and complex concepts. A key component in overcoming these challenges is the development of robust text embedding models that transform textual data into dense vector representations, facilitating efficient information retrieval and semantic understanding. In this work, we introduce AccPhysBERT, a sentence embedding model fine-tuned specifically for accelerator physics. Our model demonstrates superior performance across a range of downstream NLP tasks, surpassing existing models in capturing the domain-specific nuances of the field. We further showcase its practical applications, including semantic paper-reviewer matching and integration into retrieval-augmented generation systems, highlighting its potential to enhance information retrieval and knowledge discovery in accelerator physics.

We investigate a slow-wave THz free-electron laser consisting of axially or helically corrugated waveguides driven by an annular electron beam. When the device is driven by a 10-mA electron beam at 30 keV, we numerically demonstrated backward-wave oscillation at 0.2212 and 0.2651 THz in axially and helically corrugated waveguides, respectively, without a solenoid field within a submillimeter aperture. We developed a unified theoretical framework for the two types of waveguides and successfully explained the observed backward-wave resonances. In our theory, azimuthal-symmetry breaking in a helically corrugated waveguide couples the synchronous transverse-magnetic radiation mode to a transverse-electric mode, resulting in radiation loss for the oscillation. Therefore, this study concludes superior radiation performance for the axially corrugated waveguide as a slow-wave THz free-electron laser. Furthermore, we show the opportunity of exciting self-started cyclotron resonance maser oscillations at THz frequencies from a helically corrugated waveguide without a solenoid field.

The present investigation reports the design and development of an advanced material with a high figure of merit (FoM) for beampipe applications in particle accelerators by bringing synergy between computational and experimental approaches. Machine-learning algorithms have been used to predict the phase(s), low density, and high radiation length of the designed Al-Ti-V alloys. Al-Ti-V alloys with various compositions for single-phase and dual-phase mixtures, liquidus temperature, and density values were obtained using the latin hypercube sampling method in TC Python Thermo-Calc software. The obtained dataset was utilized to train the machine-learning algorithms. Classification algorithms such as XGBoost and regression models such as linear regression and random forest regressor have been used to compute the number of phases, radiation length, and density, respectively. The XGBoost algorithm shows an accuracy of 98%, the linear regression model shows an accuracy of 94%, and the random forest regressor model is accurate up to 99%. The developed Al-Ti-V alloys exhibit high radiation length as well as a good combination of high elastic modulus and toughness due to the synergistic effect of the presence of hard ${\mathrm{Al}}_3\mathrm{Ti}$ phase along with a minor volume fraction of FCC $(\mathrm{Al}{)}_{\mathrm{ss}}$ solid solution phase mixture. The comparison of our alloys, alloy-1 (${\mathrm{Al}}_{75.2}{\mathrm{Ti}}_{22.8}{\mathrm{V}}_2$) and alloy-2 (${\mathrm{Al}}_{89}{\mathrm{Ti}}_{10}{\mathrm{V}}_1$) shows an increase in the radiation length by 7 times and a decrease in the density by 2 to 3 times as compared to stainless steel 304, the preferred material for constructing beampipes in low-energy particle accelerators. Further, we experimentally verify the elastic modulus of the alloy-1 and compute the FoM equal to 0.416, which is better than other existing materials for beampipes in low-energy experiments.

Orbit stability is a critical performance metric for modern synchrotron radiation facilities and colliders, necessitating effective orbit correction and slow orbit feedback systems. In recent years, innovative orbit feedback methods leveraging neural networks have been progressively implemented, demonstrating improved performance. BEPCII has also attempted to implement an orbit feedback system based on neural networks. Furthermore, we have noted that orbit stability is significantly affected by noises. To address the impact of noises, we introduced the Kalman filtering method into the orbit feedback system and combined it with the existing neural network framework, creating a dual neural network orbit feedback system. This innovative approach has led to further improvements in overall orbit stability.

The room temperature continuous wave (cw) very-high-frequency (VHF) gun is one of the candidates for the electron gun of the high-repetition-rate free-electron lasers (FELs). The VHF gun operates with a cathode gradient of $\sim 20\mathrm{MV}/\mathrm{m}$ and an accelerating voltage of $\sim 750\text{kV}$. The gun dark current emission leads to beam loss along the FEL machine, therefore, it is a critical parameter for the performance of the cw gun. In this paper, we present a systematic study of the dark current reduction of the VHF gun, including cathode region optimizations, dark current tracking simulations, and measurements. Over-inserted cathode plugs were tested in two VHF guns of different acceleration gap sizes, and both demonstrated significant dark current reduction ratios of more than two orders of magnitude.

The collimators in the SuperKEKB rings are indispensable for reducing beam background noise in the Belle II particle detectors and protecting essential components, such as the final focusing superconducting quadrupole magnets, from beams that may deviate into abnormal orbits. This study developed a new robust collimator using a carbon-fiber composite (CFC) as the head material to receive a beam kicked by the accidental firing of the injection kicker. Simulation results confirmed that the new CFC collimator suppressed the temperature rise in the collimator head caused by a beam hit through accidental firing of an injection kicker more effectively than the conventional tungsten collimator. Additionally, radiation damage to the particle detector was reduced to a sufficiently low level with the new CFC collimator. When CFC was adopted as the head material, the head length was longer, and thus the impedance was higher than that of tungsten. Calculations confirmed that using CFC as the head material of the D06H3 horizontal collimator did not result in beam instability for a head length of up to 160 mm. Further, these calculations also verified that the temperature of the surface of collimator jaws irradiated by synchrotron radiation remained within $100°\mathrm{C}$, despite the steeper taper angle owing to the 160 mm head length. Initial copper and CFC bonding tests revealed cracks in the CFC caused by stress owing to the difference in thermal expansion. In subsequent bonding tests, slits were made in the copper to alleviate this stress and prevent the formation of cracks in the CFC. A sample with copper slits exhibited no cracks in the CFC. Based on these measurements and calculations, we manufactured a collimator using CFC as the head material and installed it within the SuperKEKB LER ring as a countermeasure against accidental kicker fires. The installed collimators were also evaluated for issues resulting from factors such as beam impedance, the ability to protect the Belle II particle detectors during accidental fires, and the ability to cool the high-intensity synchrotron radiation surface. All evaluated items indicated no major issues.

In this paper, we present a novel scheme for the controlled generation of tunable narrowband $\gamma$-ray radiation by ultrarelativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which the excitation of a silicon single crystal along the (100) planar direction by a piezoelectric transducer periodically modulates the crystal lattice in the [100] axial direction. An ultrarelativistic positron beam is directed diagonally into the crystal and propagates along the (110) planes. The lattice modulation forces the positrons to follow periodic trajectories, resulting in the emission of undulator radiation in the MeV range. A computational methodology for the design and development of such acoustically based light sources is presented together with the results of simulations demonstrating the favorable properties of the proposed technology. The longitudinal acoustic strains induced in the crystal by high-frequency piezoelectric elements are calculated by finite element simulations. The resulting bending profiles of the deformed crystal planes are used as geometrical conditions for the relativistic molecular dynamics simulations that calculate the positron trajectories and the spectral distribution of the emitted radiation. The results show a strong enhancement of the emitted radiation within a narrow spectral band defined by the bending period, demonstrating the feasibility and potential of the proposed technology.

A measurable chaos indicator is used as the online optimization objective in tuning a complicated nonlinear system—the National Synchrotron Light Source-II storage ring. Through analyzing the Shannon entropy in measured Poincaré maps, not only can the commonly used nonlinear characterizations be extracted, but more importantly, the chaos can be quantified and then used for an online regularization of these maps. The method itself is general and applicable to other tunable nonlinear systems as well.

We present an unsupervised learning framework for detecting anomalous superconducting radio-frequency (SRF) cavity behavior at the Continuous Electron Beam Accelerator Facility (CEBAF), emphasizing its initial performance and effectiveness. Key to the system’s success was the development of data acquisition systems (DAQs) that capture fast-sampled, information-rich signals, essential for detecting transient effects. The approach involves creating daily cavity-specific models using principal component analysis to handle variations in rf signal behavior and mitigate performance degradation from data drift. This unsupervised method eliminates the need for expensive labeling by continuously updating models with recent data. Deployed and operational for 3 months before a scheduled shutdown, the system successfully identified several issues with DAQ signals, confirming its effectiveness. Despite access to only a fraction of CEBAF’s SRF cavity signals, the framework efficiently detected several instances requiring intervention, demonstrating a significant improvement over traditional, labor-intensive methods of manual plot inspection.

Microbunched electron cooling (MBEC, Ratner, Phys. Rev. Lett. 111, 084802 (2013)), a special category of coherent electron cooling, has been under consideration as a candidate method for the strong hadron cooling component of the Electron Ion Collider (EIC) at BNL. Most of the theoretical treatments of this scheme so far have been based on simplified models for the key space charge effect in which electrons and/or hadrons are approximated by charged disks. Although such disk-based models provide a flexible tool that captures a good part of the underlying physics, they lack the fidelity and robustness of a rigorous analysis that explicitly treats the hadron and cooler electron beams as collections of point charges. In this paper, we present such a rigorous, three-dimensional (3D) model, both from a theory-based and a simulation perspective. Specifically, we calculate the generalized wakefield (or Green’s function) of the cooling system—a crucial quantity that determines the overall performance—paying special attention to the dependence of the wake on the hadron transverse positions. Additionally, our treatment takes into account previously neglected 3D effects that can cause damping of the plasma oscillations in the amplification section of the cooler, such as focusing and the angular spread of the electron beam.

We present a theoretical framework for analyzing longitudinal coupled-bunch instabilities in double-rf systems with even filling patterns, accounting for potential-well distortion and multiple azimuthal modes. The linearized Vlasov equation is solved in the frequency domain for an arbitrary rf potential to derive the Lebedev equation. We unified different formulations, obtaining results from recent publications as particular cases. Applications to Robinson dipole-quadrupole mode coupling and the periodic transient beam loading (PTBL)/mode-1 instability are presented. Notably, for the first time, theoretical predictions of the mode-1 thresholds show excellent agreement with experimental data. The analysis reveals that the PTBL instability is triggered when coherent focusing is lost for the dipole motion of the coupled-bunch mode-1. We also confirm that this instability is dependent on azimuthal mode interactions and resistant to Landau damping, providing new insights into its mechanism. The methods are implemented in the open-source package pycolleff, offering a useful semianalytical tool for studying instabilities in electron storage rings with harmonic cavities.

Accurate characterization of radiation pulse profiles is crucial for optimizing beam quality and enhancing experimental outcomes in free electron laser (FEL) research. In this paper, we present a unique approach that employs machine learning techniques for real-time virtual diagnostics of FEL radiation pulses. Our simple artificial intelligence (AI)-based diagnostic tool utilizes longitudinal phase space data obtained from the X-band transverse deflecting structure to reconstruct the temporal profile of FEL pulses in real time. Unlike traditional single-shot methods, this AI-driven solution provides a noninvasive, highly efficient alternative for pulse characterization. By leveraging state-of-the-art machine learning models, our method facilitates precise, single-shot measurements of FEL pulse power, offering significant advantages for FEL science research. This work outlines the conceptual framework, methodology, and validation results of our virtual diagnostic tool, demonstrating its potential to significantly impact FEL research.

Hadrontherapy utilizes accelerated ion beams to deliver precise and effective cancer treatments, depositing energy at specific depths while sparing healthy tissues. Gantries are large rotating structures that direct beams at various angles around the patient, improving dose conformity to tumors and the robustness of the treatment plan while minimizing radiation exposure to surrounding organs. While proton gantries are widespread and commercially available, the diffusion of carbon ion gantries is limited due to more demanding technological challenges and financial investments. This paper presents the magnetic design of the scanning magnets for the EuroSIG (European Superconducting Ion Gantry) project, aimed at developing a novel superconducting gantry for hadrontherapy. The chosen layout foresees the positioning of the scanning magnets downstream of the last bending section. This simplifies the production of the superconducting dipole but increases the complexity of the scanning system in terms of integrated fields, bending angles, and ramp rates. To address this challenge, analytical models and optimization tools were employed to achieve balanced configurations for the scanning magnets, improving compatibility with power converters. Three-dimensional numerical simulations were implemented to evaluate and improve the steady-state field quality of horizontal and vertical scanning magnets. Particle tracking was used to validate the effective beam deflection in both magnets and assess beam position errors at the isocenter. Furthermore, quasistatic simulations were carried out to evaluate integral field errors due to the hysteretic behavior of the yoke alloy. Continuing the analysis of dynamic phenomena, the generation of eddy currents in the laminated yoke was investigated, highlighting the delay of the generated field with respect to the imposed current profile. The studies reported in this manuscript confirmed the design’s feasibility, posing a solid base for the construction of the first scanning magnet prototype.