Minimizing energy spread and divergence is essential for using electron beams from laser-wakefield accelerators (LWFA) in applications such as compact free-electron lasers. Here the authors report the first experimental demonstration of dechirping of an LWFA beam, combined with a plasma lensing effect within a single tailored plasma density profile. These mechanisms take place in a down-ramp followed by a long, low-density plasma tail, and generate electron beams with a FWHM charge of 40 pC, 3.4% energy spread, and 0.46 mrad divergence, reaching a peak spectral brightness of 8 pC/MeV/mrad.

Online optimization of nonlinear beam dynamics in operating accelerators remains challenging because it requires a measurable chaos indicator capable of distinguishing irregular beam motion from radiation damping, beam decoherence, and measurement noise. We experimentally demonstrate the first online optimization of a storage-ring nonlinear lattice using a data-driven chaos indicator derived from the predictability of turn-by-turn beam motion. Implementation at the NSLS-II storage ring enlarges the dynamic aperture and improves off-axis injection efficiency, establishing a model-independent framework for accelerator optimization based solely on measured beam dynamics.

This paper proves that the longitudinal variation of third-order resonance driving terms, quantified by their RMS value at sextupole locations, forms a special convex function in the space of sextupole strengths. The iso-surfaces of this quantity are a series of concentric and coaxial ellipsoidal surfaces, and its distribution shows strong consistency with that of the dynamic aperture (DA) in the sextupole strength space. This finding suggests that the inherently non-convex DA optimization problem can be treated as a roughly approximate convex one. Based on the convexity, a fast DA optimization method is developed.

Conventional undulator tapering methods, such as gap variation or electromagnetic control, often involve complex mechanical structures or power supply systems. This work presents a beat frequency undulator composed of two permanent magnet arrays with slightly different periods, whose magnetic field superposition generates a longitudinal beat frequency envelope. By longitudinally shifting one array, the taper strength and direction can be dynamically controlled without gap adjustment or electromagnetic tuning, providing a robust and flexible solution for undulator tapering.

Enhanced SASE (ESASE) operation of an FEL uses a train of current spikes to locally enhance the electron beam current for improved FEL performance. However, these current spikes generate a strong space charge field, which builds up a linear chirp over each current spike. This effect must be compensated by a positive taper of the undulator field, but measurements at SwissFEL show a much stronger optimum taper than anticipated. Elongation of each current spike under its own space charge force spreads the already-induced microbunches of the FEL amplification apart, causing an adiabatic red shift in the emitted radiation. This effect is visible in the plot which shows matching simulations.

This paper develops an efficient nonlinear optimization method that minimizes on- and off-momentum ring-averaged resonance driving terms, which is applied to the SOLEIL storage ring. One optimized solution achieves a dynamic aperture comparable to that obtained from tracking-based nonlinear optimization while improving beam lifetime, as experimentally validated. It is also found that reducing ring-averaged resonance driving terms helps optimize working point and control tune shifts with momentum.

Inverse Compton scattering (ICS) is a promising method for generating coherent and tunable x-rays in a compact setup. Optimizing ICS x-ray sources is often left to simulations, which can be time consuming and not always provide a physical understanding of the limitations. This paper presents a closed form analytical framework to optimize the output of an ICS x-ray source at arbitrary interaction angles between pulsed electron and laser beams. We find that a co-propagating, grazing angle geometry is especially useful for soft x-ray generation.

Free-electron laser oscillators exhibit rich dynamics that can strongly affect pulse stability and output power. Using a three-dimensional, time-dependent simulation framework for the University of Hawai‘i FEL oscillator, we characterize its saturation, temporal and spectral evolution, and response to cavity desynchronization. We find that modest desynchronization can enhance pulse energy, while larger detuning suppresses spiking and improves robustness to timing jitter, providing guidance for future operation of the facility.

Laser-induced energy modulation and demodulation play a critical role in advanced beam-manipulation schemes for coherent radiation generation, while residual energy modulation can degrade electron-beam quality and limit scheme performance. Here, we systematically investigate the transition from modulation to demodulation through theory and three-dimensional simulations, explore a route toward complete demodulation, and develop diagnostics for weak residual modulation, followed by preliminary experiments at SXFEL. This work reports the first experimental observation of energy demodulation in a seeded FEL and establishes diagnostics for resolving weak residual modulation.

A new 7 TeV Beam Delivery System for CLIC achieves a total luminosity of $1.28\times {10}^{35}$cm${}^{-2}$s${}^{-1}$, offering a 27% improvement over previous designs, while improving the overall compactness of the system. The design provides a potential baseline for future multi-TeV e+e− colliders, including a proposed 10 TeV plasma-wakefield acceleration-based collider.

Nanometer-scale beams are essential for high luminosity in future electron-positron linear colliders, but even small kicks can strongly distort the beam at the interaction point. Transverse wakefields have mainly been interpreted as static effects caused by orbit distortion and misalignment; this work presents the first direct experimental and quantitative evaluation of dynamic wakefields arising from pulse-to- pulse orbit fluctuations. Measurements at the KEK Accelerator Test Facility, together with simulations including all beamline wakefield sources, show that these effects can significantly increase the beam size and must be considered to maintain stable nanometer-scale beams.

Electron cloud buildup limits the performance of high-intensity proton accelerators like the LHC, driving beam instabilities and cryogenic heat loads. Existing methods to measure the maximum secondary electron yield (δmax) typically require dedicated instrumentation and beam-time interruptions. This work introduces a novel in situ technique that extracts δmax directly from routine electron cloud current measurements during standard LHC operation, using the transition to a linear regime with the number of injected bunches. Applied to Vacuum Pilot Sector data, it enables noninvasive, long-term monitoring of vacuum-surface conditioning.

Adding a relativistic ionization front to electron beam seeding is an effective way to control the self-modulation of an entire proton bunch in plasma. By using the relativistic ionization front to truncate an available electron seed bunch, reproducible seeding of self-modulation is demonstrated at plasma densities seven times higher than previously achieved, while simultaneously increasing the seed wakefield amplitude. This opens a route to controlled, high-gradient plasma wakefield acceleration with long proton drivers.

Dielectric laser accelerators (DLAs) achieve ultrahigh acceleration gradients on silicon chips, promising compact tabletop accelerators. However, subrelativistic operation is hindered by phase slippage from velocity changes and transverse beam loss in microscale channels. Inverse Cherenkov (ICR) DLAs offer high efficiency through fundamental mode fields, but strict phase matching requires precision tapered structures. This work proposes a dynamic phase-driven cascaded ICR-DLA with a four-stage tapered prism driven by a single laser pulse. Phase slippage is leveraged to alternate electrons between focusing and defocusing during acceleration, achieving stable long-range beam confinement.

We present a new formalism for designing secondary particle beamlines that captures realistic beam distributions and particle decay losses, going beyond the simplified assumptions of traditional collimator-only acceptance models. The approach avoids costly HPC tracking studies while enabling fast, powerful optimization of magnet parameters, beamline length, and even target design. Applied to the SBN-nuSCOPE neutrino beamline, a transmission-optimized solution beyond manual design capabilities is obtained. The results are validated end-to-end with BDSIM/GEANT4 simulations.

A dedicated model for x-ray reflection on solid surfaces has been developed and implemented in the general-purpose particle-transport code FLUKA. Relying on atomic scattering factors from evaluated databases, the model computes x-ray reflectivity as a function of the photon energy, its incidence angle, and linear polarization, while also accounting for surface roughness effects. The enhanced capabilities simplify simulations involving multilayer mirrors at synchrotron-light beamlines and allow the study of the role of x-ray reflectivity in high-energy electron/positron colliders.

The lattice design for the Super Tau-Charm Facility (STCF), a high-luminosity, low-energy electron-positron collider, is challenging. This work presents the design and nonlinear optimization of a one-fold STCF lattice and provides a framework for high-luminosity low-energy electron-positron colliders. The design procedure comprises lattice-independent global parameter optimization, interaction region design with local chromatic correction and crab-waist sextupoles, and full-ring nonlinear optimization with a two-stage strategy. The optimized lattice achieves target luminosity while maintaining sufficient dynamic aperture, momentum acceptance, and Touschek lifetime.

Beam loading effects in high-current linear accelerators can significantly degrade the energy stability of the accelerated beam by reducing the accelerating field along a bunch train. We propose a novel scheme that combines microwave pulse compression with beam loading compensation in a traveling-wave acceleration structure. By tailoring the temporal profile of the compressed microwave pulse, the proposed method compensates for beam-induced field variations while enhancing RF power utilization. This approach provides a promising pathway toward high-gradient, high-efficiency accelerator systems requiring stable high-current beams.

High-power RF pulse compressors boost peak power while reducing system cost, but devices based on degenerate resonant modes remain notoriously difficult to characterize, especially when built as non-dismountable monolithic units. This work introduces a new analytical method that disentangles the coupled electromagnetic response, independently extracting resonant-mode and waveguide-network parameters. The result is a clearer understanding of device behavior, enabling more accurate diagnostics, tuning, and optimization of compact RF pulse compression systems.

High-gradient normal-conducting copper cavities equipped with beryllium windows are essential for enhancing muon cooling channel performance in a future muon collider. This study presents a comprehensive physics-based design framework including cavity optimization with an advanced hybrid frequency-time domain beam-loading analysis. The results demonstrate that local compensation schemes effectively mitigate single-bunch wakefield effects, providing critical design guidelines for high-intensity muon cooling applications.

To meet the extreme brightness requirements of fourth-generation light sources, HEPS has developed a family of quadrupole magnets employing saddle-shaped coils, customized pole profiles, and “Magic Finger” harmonic compensation. The magnets feature a 26 mm aperture, an 80 T/m gradient, and field harmonics below 4×10⁻⁴. Through finite-element simulations and high-precision field measurements, their saturation behavior, current-dependent harmonics, and batch-to-batch reproducibility were systematically characterized on both solid and laminated magnets. The validated design offers a proven engineering baseline for future low-emittance light source magnet systems.

Can high-temperature superconductors take accelerator dipoles past the limits of Nb-Ti and Nb₃Sn? The U.S. Magnet Development Program and industry partners tested C3, a canted-cosine-theta dipole wound with commercial REBCO CORC® wires, reaching 5.99 T in a 65 mm clear aperture at 4.2 K, with no measurable degradation after a thermal cycle. Field quality and energy loss were limited by strong conductor magnetization, yet the results reveal no fundamental showstopper on the path to 8–10 T. Alongside the magnet performance, the authors report fabrication incidents and open questions candidly and invite accelerator physicists to join as early adopters of this emerging technology.

High-efficiency, low-emittance photocathodes are essential for next-generation electron sources, free-electron lasers and advanced photodetectors. We present a 3D coupled finite-difference time domain (FDTD) Monte Carlo method for nanopatterned alkali photocathodes, showing that plasmonic gratings can boost quantum efficiency by 128% without degrading intrinsic emittance, while 2D gratings make the response polarization-independent. We achieved this by solving Maxwell’s equations for the full optical field and feeding the resulting absorption map into 3D Monte Carlo electron-transport simulations. These results can guide powerful, more robust photocathodes for accelerators and photonics.

Multilayer NbTiN coatings are a promising route toward superconducting RF cavities operating beyond the limits of bulk niobium. By combining XRD, optical profilometry, AFM, UPS, and field-emission scanning microscopy, we show that high-temperature annealing substantially improves the microstructure and suppresses field emission, increasing the onset field from below 60 MV/m to about 200 MV/m. The results establish thermal annealing as a key processing step for enhancing the performance and reliability of NbTiN thin films for next-generation SRF cavities.

Managing high reflected power in high-power standing-wave RF structures remains a critical challenge for next-generation accelerators. We propose two circulator-free RF topologies based on unequal-split hybrid networks. A newly developed single-objective optimization metric facilitates the systematic design of arbitrary multi-port hybrids with customized power ratios. Electromagnetic simulations and high-power experiments on C-band and X-band photoinjector systems provide validation. The results demonstrate robust suppression of reflected power under both steady-state and transient operation, offering a highly effective alternative to conventional circulator-based architectures.

High-quality, double-bunch electron beams are critical for beam-driven plasma wakefield accelerators; however, existing generation methods typically suffer from charge loss or degraded stability at high charge. To address this, we introduce a coherent synchrotron radiation–tolerant beam-merging scheme that employs twin isochronous beamlines sharing a common dipole magnet. Simulations confirm that this approach produces high-charge double bunches with no charge loss, low timing jitter, and small emittance growth, thereby offering a robust beam source for future plasma wakefield accelerator facilities.

At the 1.5-GeV synchrotron light source DELTA, ultrashort radiation pulses are produced via coherent harmonic generation (CHG), where femtosecond laser pulses modulate the electron energy and a magnetic chicane produces periodic density maxima, giving rise to coherent emission at harmonics of the laser wavelength. This paper investigates CHG spectra under variation of the chicane and laser parameters. By combining numerical simulations with a convolutional neural network, the group-delay dispersion and third-order dispersion of the laser pulses can be extracted from the data. Conversely, these tunable parameters can be used to control the spectrotemporal properties of the CHG pulses.