In current beam simulation software, there is no functionality specifically designed for the generation and tracking calculation of secondary particles produced during beam transport. These secondary particles are produced from collisions between the beam and background gas, as well as collisions with the electrodes. These processes can lead to beam particle loss, energy dissipation, electrode overheating, and device arcing issues. This paper addresses this challenge using Lua code based on simion. It enables the complete calculation of particle generation, transport, and loss processes. It overcomes four shortcomings of EAMCC and comsol, enabling it to simulate various beam types and processes beyond just the extraction of negative hydrogen ions. To demonstrate the application of this code, we investigated the neutral beam overdose issue in ion implanters, thermal deposition in large-scale ion sources, and arcing problems in electrostatic low-energy beam transport.

We present a new method for minimizing the effects of radiative depolarization in electron storage rings by use of a minimal number of special vertical orbit bumps. The bumps can be used to minimize the effects of radiative depolarization while simultaneously maintaining other common benefits of vertical orbits, e.g., transverse coupling and vertical dispersion control. Because simultaneously optimizing the large number of vertical correctors in a ring is operationally infeasible, we use dimensionality reduction to define a minimal number of the most effective groups of vertical correctors that can be optimized during operation, motivating the name “Best Adjustment Groups for ELectron Spin” (BAGELS). The method is streamlined by using suitable “basis bumps” instead of all individual vertical correctors. We define three types of basis bumps for different purposes: (i) generates no delocalized transverse coupling nor delocalized vertical dispersion, (ii) generates no delocalized vertical dispersion, and (iii) generates no delocalized transverse coupling. BAGELS has been essential in the design of the Electron Storage Ring (ESR) of the Electron-Ion Collider (EIC) and will be beneficial for any polarized electron ring, including FCC-ee. HERA and LEP would have likely benefitted as well. We use BAGELS to significantly increase polarization in the 18 GeV EIC-ESR, beyond what is achievable with conventional methods; in the 1-IP lattice, we nearly double the asymptotic polarization, and in the 2-IP lattice, we more than triple the asymptotic polarization. We also use BAGELS to construct knobs that can be used for global coupling correction, and knobs that generate vertical emittance for beam size matching, all while having minimal impacts on the polarization and orbit/optics.

A critical technology for high-volume manufacturing of nanoscale integrated circuits is a high-power extreme ultraviolet (EUV) light source. Over the past decades, laser-produced plasma (LPP) sources have been actively utilized in this field. However, current LPP light sources may provide insufficient average power to enable future manufacturing at the 3 nm node and below. In this context, accelerator-based light sources are considered to be promising tools for EUV lithography. This paper proposes a regenerative amplifier free-electron laser EUV source with harmonic lasing, driven by a superconducting energy-recovery linac (ERL). By utilizing the $n$th harmonic, the required electron beam energy is reduced to $1/\sqrt{n}$ of that in conventional schemes. The proposed configuration, employing an electron beam energy of approximately 0.33 GeV with a short-period (16 mm) undulator, is estimated to provide an average EUV power of about 2 kW. This approach significantly reduces the required electron energy and facility size relative to other accelerator-based proposals, thereby offering new possibilities for constructing high-power EUV sources with low-energy ERLs.

The concept of the coaxial cascade-line rectangular-pulse generator is put forward, the basic idea of which is to cascade two coaxial lines of equal impedance together and make one line turn around to let the two lines use a common middle tube. The obvious feature of this kind of generator is that it can form a rectangular pulse with a width of 4 times the electrical length of one line. Compared with the conventional single-tube generator, the total stored energy is doubled. Namely, the output pulse width of the coaxial cascade-line generator is doubled for the same output voltage, which is beneficial for miniaturization. The principle of the cascade pulse forming line is first introduced; then the coaxial cascade-line rectangular-pulse generator is suggested. The simulation results prove the feasibility of the cascade-line generators. Finally, the design of a Tesla-type generator with an output power of 20 GW and a pulse width of 40 ns is presented based on the coaxial cascade-line method.

Optimizing the injection process in particle accelerators is crucial for enhancing beam quality and operational efficiency. This paper presents a framework for utilizing reinforcement learning (RL) to optimize the injection process at accelerator facilities. By framing the optimization challenge as an RL problem, we developed an agent capable of dynamically aligning the beam’s transverse space with desired targets. Our methodology leverages the soft actor-critic algorithm, enhanced with domain randomization and dense neural networks, to train the agent in simulated environments with varying dynamics promoting it to learn a generalized robust policy. The agent was evaluated in live runs at the cooler synchrotron COSY and it has successfully optimized the beam cross section reaching human operator level but in notably less time. An empirical study further validated the importance of each architecture component in achieving a robust and generalized optimization strategy. The results demonstrate the potential of RL in automating and improving optimization tasks at particle acceleration facilities.

Efficient steering of particle beams in accelerators by means of bent crystals has been pursued over the last decades. Recent achievements in their operational deployment at CERN has resulted in a renewed interest in their exploitation for advanced accelerator and high energy physics concepts. Efforts to date have been focused on establishing planar channeling, given the intrinsic complexity of the process. However, the know-how developed with operation of bent crystals at the Large Hadron Collider has allowed this to be pushed a step further, demonstrating that axial channeling can also be used in the multi-TeV regime. Present results were achieved through a combination of mechanical crystal rotation and local orbit bump, proving that incorporating an additional degree of freedom in the design of future goniometers could enable the operational deployment of axial channeling, opening up the possibility for new and more efficient particle steering applications with bent crystals.

Laser-driven (LD) ion acceleration has been explored in a newly constructed short focal length laser beamline at the BELLA petawatt facility (interaction point 2, iP2). For applications utilizing such LD ion beams, a beam transport system is required, which for reasons of compactness be ideally contained within 3 m. While they are generated from a micron-scale source, large divergence and energy spread of LD ion beams present a unique challenge to transporting them compared to beams from conventional accelerators. This study gives an overview of proposed compact transport designs using permanent magnets satisfying different requirements depending on the application for the iP2 laser beamline such as radiation biology, material science, and high-energy density science. These designs are optimized for different parameters such as energy spread and peak proton density according to the application’s need. The various designs consist solely of permanent magnet elements, which can provide high magnetic field gradients on a small footprint. While the field strengths are fixed, we have shown that the beam size is able to be tuned effectively by varying the placement of the magnets. The performance of each design was evaluated based on high-order particle tracking simulations of typical LD proton beams. We also examine the ability of certain configurations to tune and select beam energies, critical for specific applications. A more detailed investigation was carried out for a design to deliver 10 MeV LD accelerated ions for radiation biology applications. With these transport system designs, the iP2 laser beamline is ready to house various application experiments.

We report on the operation of the first high peak and average power single-pass terahertz free-electron laser (THz FEL) based on a high-brightness photoinjector for developing a THz source for pump-probe experiments at advanced x-ray FELs (XFELs). Electron beams with $17\mathrm{MeV}/\mathrm{c}$ momentum and charge up to 2.4 nC were used to generate narrow-band 3 THz radiation with pulse energies of more than 0.1 mJ. The novelty of the realized method is that the undulator radiation by electron beams is much longer than the radiation wavelength, with FEL starting from coherent beam contribution rather than shot noise. This proved to be not a simple scaling of the XFEL mechanism due to the significant role of the bunching factor in the considered case.

Plasma can support extremely high-gradient strong electromagnetic fields, making it suitable not only for laser acceleration but also for short-distance manipulation of the charged particle beams, thereby enabling the miniaturization of particle accelerators. Straight capillary discharge plasma lenses have previously garnered widespread attention from researchers for their excellent focusing capabilities. We introduced the theory of using a curved capillary discharge plasma channel to deflect charged particle beams [Phys. Rev. Accel. Beams 24, 031301 (2021)] and, in this paper, present the first experimental demonstration of plasma-based deflection and focusing of laser-accelerated proton beams. Combined with a dipole magnet, the emittance after transmission was measured, revealing that magnetic field nonlinearity and multiple Coulomb scattering tend to increase the proton beam’s emittance. This work is of great significance for the development of compact beam transport systems.

In recent years, the field of positron acceleration in plasma wakefield accelerators has witnessed rapid theoretical advancements, and several effective schemes have been proposed. In these studies, longitudinally uniform plasma is taken into account, with the positron beam located at the start of the second wakefield bubble. The electron filament near the positron beam provides Coulomb attraction force for the guiding of the positron beam. However, the influence of vacuum-plasma transition on positron beams has not been considered yet, where wakefield bubble is larger than that in the density plateau region, and the positron beam is in the defocusing region. In this paper, we study the evolution of positron beam size in the vacuum-plasma transition region and find out that the transition is detrimental to low-energy positron beams. Wide drive beams with relatively large transverse sizes are proposed as a possible solution to this difficulty.

A new design technique combining the improved Kyhl method with the improved Kroll method has been developed to efficiently match couplers for traveling-wave (TW) accelerating structures [Z. Huang et al., Phys. Rev. Accel. Beams 27, 082001 (2024)]. However, such a new technique requires some complicated modifications for the TW deflecting structure operating at HEM mode. This paper proposes a more efficient and universal approach for designing couplers in any TW structures including accelerating and deflecting structures. This approach is based on a new criterion $|R_c|\to 0$ and an equivalent circuit model to facilitate fast and accurate optimizations. By using this new approach, the optimizations on couplers for any TW structures with arbitrary starting dimensions can converge in just several iterations, significantly simplifying the overall design process while maintaining a high accuracy.

The proposed pulse compression system for the klystron-based Compact Linear Collider (CLIC) is based on individual cavities that are defined as a storage cavity and several correction cavities. The correction cavities modulate the amplitudes of the input rf pulses, while the storage cavity compresses the modulated rf pulses and generates rf pulses with a high peak rf power. The essential requisites for the cavities are easy fabrication, optimal rf performance, and cost effectiveness. We have identified two novel rf-cavity-system types that can be used as correction cavities for klystron-based CLIC pulse compression systems, characterized by their compactness, advantageous large passband or low surface fields, and ease of fabrication. Both rf-cavity-system types adopt a cylindrical resonant cavity with ${\mathrm{TE}}_{132}$ mode, employing four coupling holes to induce ${\mathrm{TE}}_{132}$ modes with dual polarizations. The power flow direction is facilitated by a U-shaped waveguide and a 3-dB hybrid in two layouts. A comprehensive discussion on the principles underlying these rf-cavity-system types is provided. In addition, we elucidate the rf designs of the individual cavities for principle demonstration. Furthermore, these two rf-cavity-system types can be readily adapted to other operational frequencies, such as C-band and S-band.

The baseline configuration of the Compact Linear Collider’s rings-to-main-linac sections has been optimized for the 380 GeV center-of-mass energy stage, and some outstanding issues in previous designs have been resolved. In particular, the bunch compressors have been redesigned to reduce power consumption and cost. The impact of the bunch phase error from the damping ring to the main linac has been investigated and optimized. A complete and improved set of beam-based alignment methods is outlined, and detailed realistic simulations showing its effectiveness in addressing static imperfections such as element misalignment and magnet strength errors are presented.

We report on the recovery of both linear and nonlinear optics in a hadron synchrotron using the novel deep Lie map network (DLMN) approach. The DLMN enables the construction of a detailed accelerator model by integrating charged particle dynamics with machine learning methods within a data-driven framework. The primary observable is the centroid motion over a limited number of turns, captured by beam position monitors. The DLMN generates an updated description of the accelerator in terms of magnetic multipole components, which can be directly utilized in established accelerator physics tools and tracking codes for further analysis. In this study, the DLMN approach is employed to recover a linear optics model, including gradient errors, from a single measured trajectory. Nonlinear optics, including sextupole errors, are recovered using three measured trajectories. We assess the validity of these results by comparison with the linear optics from closed orbits algorithm and through estimates of resonance driving terms. Additionally, we illustrate an application of the deep Lie map network and the predicted synchrotron optics by comparing measured and simulated tune scans.

Superconducting linear accelerator (SCL) is commonly used to boost the negative hydrogen ion (${\mathrm{H}}^{-}$) beam energy above the medium-$\beta$ range. Stripped proton beam loss in SCL is one of the heat and radioactive source, which could threaten the operation of the SCL. This paper describes a novel technique for removing stripped protons produced in the low-energy beam transport section, the main area of ${\mathrm{H}}^{-}$ beam stripping in the linac. The experiment is conducted at the China Spallation Neutron Source. The ${\mathrm{H}}^{-}$ beam is bent by 1.8° before being focused into the radio-frequency quadrupole (RFQ) entrance. As a result of the differential pumping and optimized beam optics design, the bending magnet effectively removes over 99% of the stripped protons, resulting in a significant reduction of stripped protons captured by the RFQ and downstream linac.

Continuous-wave photocathode guns are capable of delivering electron beams with high repetition rates and high average currents. However, they are limited by relatively low accelerating gradients and cathode fields. This limitation leads to a larger beam size at the gun exit due to space-charge forces, making the beam more sensitive to optical aberrations and posing challenges for low-emittance electron beam transmission. This paper focuses on the aberrations induced by multipole fields. We analyze the effects of quadrupole, sextupole, and higher-order fields on beam profile and transverse emittance and propose a beam-based method for the rapid characterization and correction of these multipole fields. Furthermore, we present an experimental study conducted on the DC-SRF-II photocathode gun equipped with dedicated correctors. Both simulation and experimental results demonstrate that our approach effectively mitigates beam aberrations caused by multipole fields, resulting in improved beam symmetry and reduced emittance.

For the first time at the Beam Test Facility (BTF) of the $\mathrm{DA}\mathrm{\Phi }\mathrm{NE}$ accelerator complex at the Laboratori Nazionali di Frascati of INFN, 450 MeV positrons have been deflected with high efficiency, using the planar channeling process in a bent silicon crystal. The deflection angle obtained is beyond 1 mrad. This interesting result finds several applications for manipulation of this kind of beams, in particular for ultraslow extraction from lepton circular accelerators like $\mathrm{DA}\mathrm{\Phi }\mathrm{NE}$. In this work, the experimental apparatus, the measurement procedure, and the experimental results are reported.

The development of red-shifted free electron lasers (FELs), based on strongly chirped electron beams, emerged a few years ago. Here we present a thorough study of the tunability of a seeded red-shifted FEL. An analytical model is introduced to describe the complex FEL resonance condition and its consequence for the FEL emission wavelength. This model is then benchmarked with experimental data from the COXINEL (COherence Xray source INferred from Electrons accelerated by Laser) FEL beamline driven by a laser plasma accelerator at Helmholtz-Zentrum Dresden-Rossendorf. We show that the FEL emission wavelength can be tuned not only with the undulator gap and taper geometry but also with the time delay between the seed laser pulse and the electron beam. Particularly a combination of individually chirped electron and seed beams promotes a wider tuning range compared with the usual undulator gap. This could serve as an additional yet simple tuning knob to tailor the FEL emission wavelength.

The Electron-Ion Collider (EIC), to be built at Brookhaven National Laboratory, will be a high luminosity ($\sim {10}^{34}{\text{cm}}^{-2}{\mathrm{s}}^{-1}$) nuclear science facility. To facilitate EIC experiments, the existing yellow ring of the Relativistic Heavy Ion Collider (RHIC) will be reconfigured to serve as the Hadron Storage Ring (HSR). Designing a stripline injection kicker for the HSR beams, with high magnetic rigidity ($\sim 82\mathrm{Tm}$), poses some technical challenges due to the required large pulsed voltage with long flattop duration, very fast rise time, expected shorter bunch spacing, and potential heating due to higher peak current. In addition, minimizing impedance mismatch in the transition region between the feedthrough and the stripline electrode is challenging. This paper focuses on the mechanical design and optimization of the HSR injection kicker, highlighting a novel impedance tuning capability achieved through an innovative kicker aperture adjustment mechanism. We comprehensively cover the design, including impedance optimization (both beam coupling and characteristic), beam-induced heating, and thermal analysis, and investigation of the maximum electric field due to high voltage signal excitation to ensure safe and reliable operation.

NanoTerasu, a new 3 GeV synchrotron light source in Japan, began user operation in April 2024. It provides high-brilliance soft to tender x-rays and covers a wide spectral range from ultraviolet to tender x-rays. Its compact storage ring with a circumference of 349 m is based on a four-bend achromat lattice to provide two straight sections in each cell for insertion devices with a natural horizontal emittance of 1.14 nm rad, which is small enough for soft x-rays users. The NanoTerasu accelerator incorporates several innovative technologies, including a full-energy injector C-band linear accelerator with a length of 110 m, an in-vacuum off-axis injection system, a four-bend achromat with B-Q combined bending magnets, and a TM020-mode accelerating cavity with built-in higher-order-mode dampers in the storage ring. This paper presents the accelerator machine commissioning over a half-year period and our model-consistent ring optics correction. The first user operation with a stored beam current of 160 mA is also reported. We summarize the storage ring parameters obtained from the commissioning. This is helpful for estimating the effective optical properties of synchrotron radiation at NanoTerasu.