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.

Local chromatic correction optics are proposed for the Future Circular $e^{+}-e^{-}$ Collider. These new optics assume an identical layout of the magnets at all operation energies and include a new design for the arcs, for the straight sections, and for the final focus. The arcs design is a step forward from the classic FODO lattice that achieves near cancellation up to the fourth order of chromatic and geometric aberrations. Straight sections and the final focus benefit from the application of transparency conditions and are thus minimally impacting the global beam dynamics. The final focus design includes both vertical and horizontal chromaticity correction sections, crab sextupoles, and additional specific sextupoles and decapoles for the optimization of the dynamics off-energy. Decapoles are very effective in mitigating the reduction of dynamic aperture due to synchrotron radiation. Nonlinear magnet settings are further optimized with multiobjective algorithms. The overall properties of the new optics proposed are analyzed in the presence of errors and compared to other optics designs.

It is a truth universally acknowledged that space-charge effects in ultrarelativistic electron storage rings are irrelevant due to the steep inverse dependence of their strength on the Lorentz factor. Yet, with the push toward the diffraction limit, the state-of-the-art light sources are approaching the point where their emittance becomes so small that the space-charge force can no longer be ignored. In this paper, we demonstrate how space-charge effects influence the injection dynamics, dynamical aperture, and collective beam stability using the example of fourth-generation light sources PETRA IV and SOLEIL II.

Coherent synchrotron radiation (CSR) in dipoles can degrade beam quality by increasing energy spread and transverse emittance. A simple one-dimensional CSR-kick model was developed to analyze CSR effects in dipoles and derive conditions for CSR suppression [Jiao et al. Phys. Rev. ST Accel. Beams 17, 060701 (2014)]. However, this model assumes a constant bunch length within the dipole, limiting its accuracy in scenarios involving bunch compression, where the bunch length typically varies. This limitation requires numerical corrections, which may reduce the general applicability of the model. We present a modified CSR-kick model that accounts for bunch length variations within dipoles. The modified model is validated through simulations and consistently reproduces CSR suppression conditions for double-bend achromat (DBA) compressors, showing excellent agreement with previously numerically corrected results. Further analysis of the DBA compressor under CSR suppression conditions is also provided.

The accurate knowledge of the beam coupling impedance in particle accelerators is important in order to address potential impedance-driven instabilities and for planning machine upgrades. While simple models exist for various components (e.g., beam pipes, step transitions, and collimators), they are often insufficient to correctly describe the overall machine impedance with the necessary precision. Numerical 3D simulations, such as those performed with CST wakefield and eigenmode solvers, are typically used to improve the impedance model accuracy accounting for the accelerator device’s detailed geometry. Nevertheless, for structures exhibiting low ohmic losses in low energy machines, where the beam velocity is not yet ultrarelativistic, existing 3D codes face computational challenges. Specifically, wakefield simulation times can become excessively long, and the eigenmode resonator model is not physically valid for nonultrarelativistic cases. To overcome these limitations, the mode matching technique, previously applied exclusively to canonical geometries, has been extended to arbitrary 3D particle accelerator structures by numerically computing the eigenmodes within their volume. With appropriate field manipulation at the beam pipe interfaces, the impedance of resonant structures can be accurately calculated without being affected by ohmic losses or particle velocity. Additionally, being combined with CST eigenmode simulations, this method takes advantage of the underlying tetrahedral mesh, providing a more accurate representation of device geometry compared to the hexahedral mesh used in wakefield simulations. In this work, we present the theory, development, and results of this generalized method, with a particular focus on the longitudinal impedance computation for a buncher of the High Brightness Beams Test Facility, where the effects of low wall losses and low beam velocity play a significant role.