Coherent terahertz generation in storage rings is typically limited in repetition rate by the time required for radiation damping to restore the electron beam. We propose an active demodulation scheme that uses a phase-reversed laser interaction to rapidly compensate the induced energy modulation after THz emission. Simulations for HLS-II indicate that coherent 10-THz radiation could be generated at repetition rates on the order of 100 kHz.

[Phys. Rev. Accel. Beams 29, 093403] Published Tue Sep 15, 2026

Sudden beam loss (SBL)—the loss of much of the stored beam within a few turns—has limited SuperKEKB’s luminosity for nearly five years, damaging collimators and the Belle II detector. Reproduction experiments and laboratory analysis pin SBL on dust–beam interactions. Such interactions occur at many accelerators, but SuperKEKB’s tiny vertical aperture (nano-beam scheme) and high stored current make the damage uniquely severe. One dust source was vacuum sealant degraded into black stains; removing them sharply reduced SBL. Yet because discharges also produce dust, SBL cannot be fully eliminated in high-current, nano-beam machines—a key lesson for future colliders like FCC-ee and CEPC.

[Phys. Rev. Accel. Beams 29, 093501] Published Tue Sep 15, 2026

Scaling fixed-field alternating gradient (FFA) accelerators offer strong potential for high-intensity proton drivers but face complex nonlinear dynamics under tight spatial limits. Through large-sample tracking of over 360,000 configurations under engineering errors, a 300–600 MeV scaling-FFA lattice is established for the CSNS Phase-II upgrade. A spiral FD doublet lattice (N=16) is identified as the optimal baseline, mitigating parameter bottlenecks and expanding dynamic aperture. Machine learning feature attribution further reveals the critical role of vertical edge focusing in beam survivability.

[Phys. Rev. Accel. Beams 29, 093701] Published Tue Sep 15, 2026

We propose a versatile electron-optical system featuring a semi-immersed electron gun and a magnetic coil that generates a nonadiabatic magnetic field for an electron-beam ion source (EBIS). The system is capable of producing electron beams over a wide operating range, with beam currents of 0.2–3.0 A, current densities of 200–1900 A/cm², and electron energies of 2–20 keV. This flexible design is ideally suited for carbon-ion cancer therapy accelerator facilities, charge breeding of radioactive ions, and other accelerator systems requiring highly charged ions.

[Phys. Rev. Accel. Beams 29, 094501] Published Tue Sep 15, 2026

The storage ring proton Electric Dipole Moment (sr-pEDM) experiment uses a novel symmetric-hybrid frozen-spin storage ring with radial electric bending and alternate magnetic focusing to minimize systematics, enabling precise measurement of the vertical rotation of the polarization of polarized stored proton beams. We present a detailed analysis of second-order effects arising from the interplay of stray radial magnetic fields with electric quadrupole and sextupole fields, and show how the ring’s symmetries—beam reversal and magnetic quadrupole polarity switching—suppress these effects below the sr-pEDM experiment’s targeted sensitivity.

[Phys. Rev. Accel. Beams 29, 094701] Published Tue Sep 15, 2026

A new type of fast pulse generator which utilizes wideband RF amplifiers and a new chopper chamber with high-impedance strip-line electrodes has been developed to reliably and accurately cut out a short bunch from the long-pulsed beam emitted from a single-crystal CeB${}_6$ hot cathode at the X-ray free-electron laser (XFEL) facility SACLA. Using these apparatuses, we succeeded in forming a nanosecond multi-bunch structure in the thermionic electron beam and generating a double-bunch XFEL pulse with a total pulse energy of 1mJ at 10 keV. The results will provide new possibilities for XFEL beams: higher intensity, higher coherence, and higher pulse repetition rate.

[Phys. Rev. Accel. Beams 29, 093401] Published Wed Sep 09, 2026

This paper proposes a novel emittance compensation scheme for the HALF diffraction-limited storage ring based on the quantum excitation effect. The proposed quantum-excitation-based scheme achieves emittance compensation comparable to the usually used radiation-damping-based scheme, even though the compensation wiggler is significantly shorter. It also yields significantly smaller energy spread variations and thus very small effective emittance variations at dispersive straight sections, with the effective emittance considered basically compensated.

[Phys. Rev. Accel. Beams 29, 093402] Published Wed Sep 09, 2026

Laser Wakefield Acceleration offers the potential for more compact and cost-effective electron accelerators. Significant efforts are being made to improve electron beam quality for various applications, particularly through the design of suitable gas targets and optimization of laser and target parameters. The present study investigates LWFA in a specially designed capillary gas-cell setup for generating high-quality, GeV-scale electron beams using combined hydrodynamic and Particle-In-Cell (PIC) simulations. The results reveal the impact of tailored gas-density profiles on LWFA and beam quality, with multiple injection mechanisms identified and analyzed.

[Phys. Rev. Accel. Beams 29, 093601] Published Wed Sep 09, 2026

Precise measurements of the muon anomalous magnetic moment motivate the development of a low-emittance muon beam at J-PARC using rf linacs. Positive muons have so far been accelerated only through the radio-frequency quadrupole (RFQ) stage. We report the first full-size 324-MHz interdigital H-mode drift tube linac dedicated to muon acceleration. Designed to follow the RFQ and accelerate muons from 0.34 to 4.26 MeV, it uses a cost-effective three-piece copper cavity with monolithic drift tubes. Low-power tuning reduced the peak-to-peak on-axis field error to 1.4%. The cavity operated stably at the nominal peak power of 390 kW and reached an accelerating field 10% above the design value.

[Phys. Rev. Accel. Beams 29, 093201] Published Tue Sep 01, 2026

In the Z-pinch pulsed-power accelerators, multi-MA currents rapidly heat the electrodes above the threshold for plasma formation. The stability and dynamics of an electron sheath emitted from the highly magnetized electrode plasmas are investigated using semi-analytic theory and kinetic particle-in-cell simulation which show strong resistive plasma instability (RPI) growth. The nonlinear evolution of the RPI drives electron vortices and uncovers sufficient ion charge for plasma transport across the gap in several nanoseconds with plasma densities sufficient to generate published current losses via a Hall mechanism.

[Phys. Rev. Accel. Beams 29, 093301] Published Tue Sep 01, 2026

We present a more accurate formula for calculating the intra-beam scattering (IBS)-induced path length deviation of an electron beam traversing the lattice, which can aid in lattice optimization. Additionally, we have developed a tool to simulate IBS-kick effects on beam dynamics. The tool can directly compute the IBS equilibrium emittance in storage rings and efficiently evaluate the associated path length deviations for an electron beam traversing a lattice. These capabilities are important for applications such as optical stochastic cooling and steady-state microbunching, which strictly require the isochronicity of lattice.

[Phys. Rev. Accel. Beams 29, 094901] Published Tue Sep 01, 2026

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.

[Phys. Rev. Accel. Beams 29, 083405] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, 083406] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, 083407] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, 083503] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, 083601] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, L080501] Published Mon Aug 31, 2026

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.

[Phys. Rev. Accel. Beams 29, 083404] Published Fri Aug 28, 2026

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.

[Phys. Rev. Accel. Beams 29, 083703] Published Fri Aug 28, 2026

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.

[Phys. Rev. Accel. Beams 29, 083403] Published Mon Aug 24, 2026

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.

[Phys. Rev. Accel. Beams 29, 083803] Published Mon Aug 24, 2026

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.

[Phys. Rev. Accel. Beams 29, 084302] Published Mon Aug 24, 2026

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.

[Phys. Rev. Accel. Beams 29, 083902] Published Fri Aug 14, 2026

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.

[Phys. Rev. Accel. Beams 29, 085101] Published Thu Aug 13, 2026

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.

[Phys. Rev. Accel. Beams 29, 083901] Published Wed Aug 12, 2026

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.

[Phys. Rev. Accel. Beams 29, L081601] Published Wed Aug 12, 2026

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.

[Phys. Rev. Accel. Beams 29, 083402] Published Tue Aug 11, 2026

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.

[Phys. Rev. Accel. Beams 29, 083602] Published Tue Aug 11, 2026

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.

[Phys. Rev. Accel. Beams 29, 084301] Published Tue Aug 11, 2026

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.

[Phys. Rev. Accel. Beams 29, 084501] Published Tue Aug 11, 2026

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.

[Phys. Rev. Accel. Beams 29, 083401] Published Fri Aug 07, 2026

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.

[Phys. Rev. Accel. Beams 29, 083502] Published Fri Aug 07, 2026

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.

[Phys. Rev. Accel. Beams 29, 083702] Published Fri Aug 07, 2026

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.

[Phys. Rev. Accel. Beams 29, 083802] Published Fri Aug 07, 2026

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.

[Phys. Rev. Accel. Beams 29, 083501] Published Thu Aug 06, 2026

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.

[Phys. Rev. Accel. Beams 29, 083701] Published Thu Aug 06, 2026

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.

[Phys. Rev. Accel. Beams 29, 083801] Published Thu Aug 06, 2026

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.

[Phys. Rev. Accel. Beams 29, 084901] Published Thu Aug 06, 2026

How much data does a machine really need to understand itself? For pulsed accelerator systems, the answer may be just one waveform. A kernel-based Dynamic Mode Decomposition framework exploits Takens’ delay embedding to learn complete system dynamics from a single reference pulse, constructing a physics-aligned ordinary differential equation surrogate using only 5–10% of the available phase-space states. Validated on five beam kicker and pulse-forming network (PFN) modulator systems at SSRL/SLAC across three years, the approach achieves sub-percent reconstruction error, outperforms conventional methods by up to 100 times, and detects hardware anomalies automatically.

[Phys. Rev. Accel. Beams 29, L072001] Published Fri Jul 31, 2026

Fixed Field alternating gradient Accelerators (FFA) remove the need for a time varying magnetic field and enable highly intense beam pulses in a flexible time structure, limited only by the acceleration system. Beam stacking allows an FFA to accumulate beam and reach the space-charge limit at the extraction energy, making FFAs promising candidates for next-generation spallation neutron sources such as ISIS-II. However, RF knockout can cause significant beam loss during stacking. To make beam stacking viable in high-intensity FFAs, this loss must be mitigated. Here, we show that a symmetric arrangement of RF cavities cancels the RF knockout perturbation, enabling lossless beam stacking.

[Phys. Rev. Accel. Beams 29, 074001] Published Thu Jul 30, 2026

High-luminosity electron–positron colliders require ampere-level beam currents, rendering coupled-bunch instabilities driven by RF-cavity accelerating modes a critical concern. For the Super Tau-Charm Facility, we demonstrate that these instabilities can be effectively suppressed over the full 1–3.5 GeV energy range using solely the baseline low-level RF (LLRF) proportional-integral (PI) loop. The combination of a unity proportional gain and half-revolution loop delay produces a notch-filter response that strongly attenuates the most dangerous odd modes. Analytical calculations, particle tracking, and Nyquist analysis collectively confirm the robustness of both beam and loop stability.

[Phys. Rev. Accel. Beams 29, 074902] Published Thu Jul 30, 2026

Multipactor (MP) discharge is a major factor limiting the performance of superconducting RF cavities. We propose a novel scheme for MP suppression based on the controlled excitation of higher-order quadrupole modes in a superconducting spoke resonator. Analytical symmetry arguments and simulation studies show these quadrupole fields suppress MP while imparting zero net transverse kick and negligible emittance growth to the proton beam in the MEHIPA-II linac, over the energy range of 40 to 200 MeV. This flexible approach offers an effective alternative to control persistent electron activity, enabling more stable and uninterrupted operation of a high‑gradient SRF linac.

[Phys. Rev. Accel. Beams 29, 073201] Published Wed Jul 29, 2026

We study an electromagnetic field of a thin extended bunch of charged particles forming over some finite time. We show that the radiation field is the main part of the total field in the relatively thin spherical layer. The energy characteristics of the radiation are calculated and analyzed. The radiation under consideration is compared with the radiation of a point variable charge moving with a constant velocity, as well as with bremsstrahlung of a point charge having constant magnitude.

[Phys. Rev. Accel. Beams 29, 073802] Published Wed Jul 29, 2026

Coherent Transition Radiation Michelson Interferometry (CTRI) is a compact technique for measuring the temporal profiles of electron bunches, but accurate reconstruction of ultrashort electron bunch profiles is hindered by optical filtering and phase ambiguity. This work develops an imaging-based numerical frequency-filter model and a genetic-algorithm (GA) forward-fitting method to reconstruct bunch profiles directly from time-domain interferograms. The approach provides a practical framework for advanced electron bunch diagnostics in accelerator experiments.

[Phys. Rev. Accel. Beams 29, 074101] Published Wed Jul 29, 2026

High-current electron storage rings require efficient collimation to protect superconducting magnets and minimize detector backgrounds. We present the first baseline collimation system design for the Electron-Ion Collider electron ring, combining optimized lattice integration with multi-turn particle tracking simulations. The proposed system localizes beam losses and reduces interaction-region losses by up to two orders of magnitude while preserving machine acceptance and beam lifetime, establishing a robust foundation for future EIC operations.

[Phys. Rev. Accel. Beams 29, 074202] Published Wed Jul 29, 2026

Ultrafast science demands ultrashort electron beams, yet generating such high-brightness electron bunches remains challenging. In this paper we propose using tailored THz modulation within an undulator to sculpt MeV electrons into sub-femtosecond microbunch trains, achieving a few fs pulses with up to fC charge and tunable spacing. Downstream dispersion further compresses pulses, while upstream dispersion can engineer periodic comb-like structures with satellite features. This scheme may enable time-resolved structural probing and mark a step toward capturing real-time electron dynamics in matter.

[Phys. Rev. Accel. Beams 29, 074901] Published Wed Jul 29, 2026

In storage rings, focusing perturbations break lattice periodicity and degrade nonlinear performance. We introduce asymmetry parameters from Fourier harmonics of beta functions and resonance driving terms to quantify this symmetry breaking. Compared to the commonly used beta-beat, these parameters show stronger relationships with dynamic aperture reduction, further enhanced when considering the frequency diffusion rate. The beta-beat serving as a reasonable indicator of dynamic aperture reduction is also physically explained based on the longitudinal variation of resonance driving terms.

[Phys. Rev. Accel. Beams 29, 074701] Published Mon Jul 27, 2026

Accelerating spin-polarized beams in circular accelerators is difficult because the beam’s polarization can be significantly reduced when its spin motion is in resonance with its orbital motion. For constant-speed resonance crossings, the corresponding depolarization can be estimated using the Froissart-Stora formula. However, higher-order resonances, which are the dominant depolarization mechanisms in colliders with Siberian snakes, typically involve a change in crossing speed at the moment of crossing. This work introduces an extension of the Froissart-Stora formula to this case with comparisons to numerical integration and tracking in the Relativistic Heavy Ion Collider.

[Phys. Rev. Accel. Beams 29, 074702] Published Mon Jul 27, 2026

This study demonstrates the significance of magnetic fields in vacuum arc initiation, which can be a major design limitation in numerous devices operating at high electric fields in vacuum. Most previous studies on vacuum arcing have neglected the magnetic field or used simplified theoretical models, while high magnetic fields have been demonstrated to contribute significantly to arc occurrence. Our study examines the electron emission and heating processes by simulation, which provides more accurate details on the processes involved. This benefits understanding of the phenomenon itself, as well as its influence on applications.

[Phys. Rev. Accel. Beams 29, 074301] Published Wed Jul 22, 2026

Understanding photoemission from electron sources in typical accelerator environments requires an easily accessible diagnostic method that can probe the position and momentum of electrons at the moment of emission. We experimentally demonstrate a method that uses a beam phase space diagnostic to compute the transfer matrix of a beamline and reconstruct the source 4D transverse phase space of a spatially structured photocathode. This method can uncover local correlations that other diagnostics might miss and aid in particle source design.

[Phys. Rev. Accel. Beams 29, 074501] Published Tue Jul 21, 2026

Efficient positron injection in plasma wakefield acceleration is challenging because it requires a field structure that can both focus and accelerate positrons. Here, we propose a self-adaptive catch-up injection scheme, in which a positron source placed in front of a hollow, positively charged driver is naturally captured as the wake catches up. Analytical modeling and 3D PIC simulations show that positrons with broad initial conditions can be injected into similar accelerating phases and further accelerated to multi-GeV energies.These results provide a proof-of-principle demonstration for a new positron injection and acceleration scheme in plasma wakefields.

[Phys. Rev. Accel. Beams 29, L070501] Published Fri Jul 17, 2026

Conventional laser-driven proton acceleration suffers from a trade-off between maximum energy and conversion efficiency as the accelerating field and the ion bunch quickly lose synchronization. We overcome this by combining two laser pulses with a micronozzle structure. With precise timing control, the proton bunch remains phase-locked to the co-moving field, enabling sustained acceleration with far higher efficiency. Our simulations show that sub-GeV-class proton energies can be achieved with a total laser-to-proton conversion efficiency of approximately 20%. Over 13% of the laser energy is transferred to protons above 100 MeV, useful for applications such as neutron and muon sources.

[Phys. Rev. Accel. Beams 29, 073601] Published Mon Jul 13, 2026

We developed a waveguide-type RF window with a simple structure to seal the vacuum for the cavity at continuous-wave RF frequency (509 MHz) and power (up to 250 kW) in the electron storage ring. This RF window can be replaced on-site quickly in the event of a ceramic plate puncture during beam operations. Although the high-power RF operations faced issues with abnormal heating due to a high loss tangent and multipactor discharges on the ceramic plate, we developed effective countermeasures. These RF windows were finally installed in NanoTerasu, a light source facility in Sendai, Japan, and have been operated without any problems.

[Phys. Rev. Accel. Beams 29, 073801] Published Fri Jul 10, 2026

To address the increasingly severe target damage of linear induction accelerators for flash radiography, this paper proposes a solution adopting an electromagnetically driven high-speed moving target. Preliminary physical design and verification experiments have been completed, which verify the feasibility of the proposed scheme. This method is expected to resolve the multi-pulse target issue of flash radiography accelerators.

[Phys. Rev. Accel. Beams 29, 074201] Published Fri Jul 10, 2026

Modern compact cyclotrons are generally equipped with spiral inflectors for axial injection of the beam. Until now, spiral inflectors have been electrostatic, which limits space charge neutralization of the beam, preventing higher beam currents from being achieved. A proposed solution has been to use a magnetic inflector, which has the added advantage of allowing higher energy injection due to the scaling of the magnetic force. Here we demonstrate the design, construction, and testing of the first proof-of-concept magnetic spiral inflector.

[Phys. Rev. Accel. Beams 29, 074602] Published Fri Jul 10, 2026

In the Hadron Storage Ring of the Electron-Ion Collider, preservation of helion polarization is especially challenging: a large anomalous magnetic moment and asymmetries in the magnetic optics drive a dense spectrum of strong spin resonances, unlike the more symmetric RHIC proton case. This work compares two snake-matching strategies, betatron phase optimization and Siberian-snake axis optimization, and finds a clear advantage for symmetry-based spin control. By introducing the Doubly Lee-Courant scheme, which enforces local $\pi$ spin phase advance across every consecutive snake pair, the study provides a robust foundation for high-polarization beams in the EIC and future facilities.

[Phys. Rev. Accel. Beams 29, 073501] Published Thu Jul 09, 2026

Medium-temperature (Mid-T) baking can significantly improve the quality factor of SRF cavities, reducing cryogenic losses and energy consumption. Conventionally, this treatment is performed in vacuum furnaces, introducing contamination risks and reoxidation of the niobium surface. We investigate an $in$ $situ$ approach in which a TESLA 9-cell cavity is heated directly by RF power via the TTF-III coupler in the fundamental passband. Combining experiments with a validated thermal model, we show that alternating modes can provide the temperature uniformity required for effective Mid-T baking, enabling furnace-free $in$ $situ$ processing of SRF cavities within accelerator modules.

[Phys. Rev. Accel. Beams 29, 074401] Published Thu Jul 09, 2026

In next-generation light sources, a key challenge common to off-axis injections based on both dipole kickers and nonlinear kickers still remains: mitigating the field distortion caused by eddy currents in the metallic coating of the ceramic vacuum chamber, while minimizing beam coupling impedance and induced heating. We prototyped a chamber with a strip-patterned titanium coating on its inner surface tailored to requirements of SPring-8-II and evaluated the eddy current effects.

[Phys. Rev. Accel. Beams 29, 074601] Published Thu Jul 09, 2026

Attosecond electron beams are essential for investigating ultrafast dynamics with atomic-scale resolution. However, conventional compression methods struggle to reach the sub-femtosecond regime without severe charge loss. We propose a novel multi-dimensional phase-space manipulation technique combining pulse-front-tilted photoemission, THz-driven chirping, and an angular dispersion beamline. This method effectively exchanges transverse emittance for robust attosecond longitudinal compression, paving the way for unprecedented resolution in ultrafast sciences.

[Phys. Rev. Accel. Beams 29, 060102] Published Tue Jun 30, 2026

The 3.8 nC/J low divergent electron bunch with energy up to 25 MeV is generated at 10 Hz by the 1.3 TW femtosecond laser pulse. The particles source is based on the efficient coupling of the pulse with an under-critical plasma slab formed by a nanosecond prepulse-induced breakdown of a thin, liquid ethanol microjet. The acceleration mechanism involves complex interplay between Direct Laser Acceleration (DLA) and Self-Modulated Laser Wakefield Acceleration (SM-LWFA) in the plasma density profile. Simple liquid target design has the advantage of robustness and suitability for long-term operation in vacuum for future kHz repetition rate laser-plasma applications.

[Phys. Rev. Accel. Beams 29, 061301] Published Mon Jun 29, 2026

The Super Tau-Charm Facility requires an injector capable of delivering high-charge and high-brightness electron beams. We present a segmented design strategy that employs multi-objective optimization in the low-energy section mainly to restrain space-charge effects, followed by sophisticated beam manipulation in the high-energy section mainly to mitigate wakefield effects. This approach reduces design complexity and is capable of yielding a 2 GeV beam with 0.22% energy spread and normalized emittance below 6.5 μmrad. The lattice supports both 8.5 nC swap-out and 1.5 nC off-axis injection without hardware intervention, providing a versatile platform for future high-intensity colliders.

[Phys. Rev. Accel. Beams 29, 061604] Published Mon Jun 29, 2026

Scientists have successfully developed two new methods that act as real-time “heart monitors” for high-power particle accelerators, allowing continuous and safe measurement of particle beams without interrupting particle accelerators. To prevent dangerous beam losses, operators must constantly track the beam’s current (intensity) and phase (precise timing relative to driving radio-frequency waves). Traditionally, acquiring these details required either dedicating machine time for offline phase scans or running the machine in a risky “open-loop” mode with radio frequency (RF) feedback turned off. To solve this problem, the newly developed Virtual Open-Loop and Steady-State algorithms mathematically analyze the existing RF signals that power the accelerator, accurately extracting the beam-induced signature while the feedback loops remain fully active. Tested successfully at the European Spallation Source, these noninvasive techniques accurately parse out both beam current and phase using zero additional hardware. This breakthrough provides a crucial real-time diagnostic tool for the safe and efficient operation of the next generation of high-power accelerators worldwide.

[Phys. Rev. Accel. Beams 29, 062802] Published Mon Jun 29, 2026

The crab-waist collision scheme now defines the world’s highest-luminosity circular colliders, from SuperKEKB today to future machines such as FCC-ee and CEPC. Such colliders require collimators placed very close to the beam core, making them dominant impedance sources that can drive the transverse mode-coupling instability (TMCI). Using electromagnetic and particle-tracking simulations, this work shows how collimator jaw geometry controls the vertical dipolar wakefield. Hollowed, exponentially tapered jaws, especially in a one-sided layout, reduce the dipolar kick factor and raise the TMCI threshold by up to ~90% in the SuperKEKB Low Energy Ring, used here as a case study.

[Phys. Rev. Accel. Beams 29, 063001] Published Mon Jun 29, 2026

Schottky effects in photoinjectors are neglected in most computational codes due to minimal impact. However, for applications such as high brightness high charge photoinjectors in future colliders such as FCC-ee, these field effects on the photocathode surface become significant. We explore the charge production limitations under ultrafast illumination that arise directly from these surface field effects. By self consistently coupling microscopic barrier dynamics with macroscopic space field and charge effects, a new model captures complex collective dynamics while remaining exceptionally computationally efficient, enabling real time simulation and injector tuning.

[Phys. Rev. Accel. Beams 29, 063401] Published Mon Jun 29, 2026

Nonlinear resonances are known to significantly influence stability boundaries, producing island chains and separatrix intersections that are difficult to capture analytically over a wide parameter range. This work introduces a perturbative construction of approximate invariants directly from symplectic one-turn maps. Unlike isolated-resonance normal forms, the method yields a generic invariant expression and can track changes in phase-space topology across different machine configurations. Applications to Fermilab lattices show that the resulting invariant accurately describes nonlinear trajectories and can be used for stability estimates.

[Phys. Rev. Accel. Beams 29, L064001] Published Mon Jun 29, 2026

This work introduces a systematic and deterministic approach to designing the linear set up of multi-bend achromat lattices with distributed sextupoles based on their substructures. The method reveals key parameter dependencies, prepares a relaxed starting point for nonlinear optimization and reduces reliance on computationally intensive optimization algorithms. Applied to the BESSY III design, it leads to a physically motivated baseline lattice. The approach efficiently provides a transparent foundation for further nonlinear optimization.

[Phys. Rev. Accel. Beams 29, 061603] Published Fri Jun 26, 2026

This paper details the design, fabrication, and tuning methodology of a s-band cryogenic traveling-wave high-gradient accelerating structure with β = 0.3, targeting a theoretical accelerating gradient of 60 MV/m. For the first time, this work establishes a framework for tuning cryogenic traveling-wave copper cavities and for implementing conduction cooling in high-gradient, low-β copper cavities. These developments are significant for future high-gradient ultracompact linacs intended for hadron therapy and other applications.

[Phys. Rev. Accel. Beams 29, 061602] Published Tue Jun 23, 2026

Dynamic detuning, encompassing dynamic Lorentz force detuning (LFD) and Microphonics, significantly restricts the operational stability of superconducting radio-frequency (SRF) cavity modules. This paper proposes a novel semi-analytical method for calculating the dynamic detuning of SRF cavities, reducing computation time by several orders of magnitude compared to transient f inite element analysis (FEA). A key advancement of this method is the incorporation of a correction term for high-frequency mechanical modes, which enhances simulation accuracy relative to conventional approaches that neglect them.

[Phys. Rev. Accel. Beams 29, 062002] Published Thu Jun 18, 2026

Next-generation particle accelerators facilities will require diagnostic systems that can operate at multi-GHz repetition rates. We have designed and tested an ionizing-particle detection system that achieves a 4-5 GHz response rate over a dynamic range of over 1000. The system consists of a novel compact signal path mated to a co-designed custom IC, all developed by the collaboration that authored the article. The resulting ionizing particle detection system is the best-performing fast particle detection system ever built. In addition to accelerator physics, this system could find application in high energy physics, advanced laser system development, and fusion energy science.

[Phys. Rev. Accel. Beams 29, 062901] Published Tue Jun 16, 2026

In high-intensity proton accelerators, beam quality is strongly affected by space-charge effects, especially in the low energy beam transport (LEBT) region, where space-charge compensation (SCC) is essential for maintaining beam quality. In this work, we combine detailed simulations and experiments to study SCC dynamics in the LEHIPA LEBT, using PIC-MCC modelling along with dedicated diagnostics. A novel Particle Monitor Probe captures the time evolution of SCC, while a Retarding Field Analyzer measures the degree of compensation. In addition, a multiwire profiler is used to measure beam profiles under varying gas pressure, providing a comprehensive picture of the process.

[Phys. Rev. Accel. Beams 29, 064201] Published Fri Jun 12, 2026

We present a two-color XFEL scheme based on a self-seeding configuration. In this scheme, a chirped electron beam first generates a chirped x-ray pulse in the initial undulator. The electron beam is then directed through a chicane, while the chirped x-ray pulse is sent through a multilayer-based two-color filter to produce a two-color seed. Finally, the seed is amplified to saturation by the electron beam in the second undulator, yielding ultrashort two-color x-ray pulses that are separated both spectrally and temporally. This work offers a novel approach for the generation of ultrashort two-color XFEL pulses.

[Phys. Rev. Accel. Beams 29, 060701] Published Thu Jun 11, 2026

The electron–positron Future Circular Collider (FCC-ee) is an ambitious post-LHC project at CERN, designed to deliver collisions at four interaction points along a 91-km ring. At the experimental insertions, multiple radiation sources produce a challenging radiation environment exposing detectors and machine equipment. This work presents a comprehensive FLUKA model of the FCC-ee experimental insertions, characterizing the full radiation environment and identifying dominant sources in each region for the two extreme operational modes, at the Z pole and at the t$\overline{\mathrm{t}}$ threshold. The results crucially support the machine design, informing shielding strategies and technology choices.

[Phys. Rev. Accel. Beams 29, 061001] Published Mon Jun 08, 2026

Crab cavities are essential to the HL-LHC upgrade to restore geometrical luminosity loss at the main interaction points. Amplitude noise from their low-level RF systems drives both emittance growth and transverse beam tail evolution. In this CERN SPS experiment we demonstrate that crab cavity amplitude noise produces emittance growth with an unexpected dependence on octupole induced tune spread through beam-coupling impedance, while reducing the heavy-tail population of the beam profile. Through dedicated simulations we quantitatively reproduce both effects, establishing a validated framework to predict crab cavity noise impact in future operation.

[Phys. Rev. Accel. Beams 29, 061002] Published Mon Jun 08, 2026

We present a new embedded structure for nanocrystalline soft magnetic alloy (MA) cores in proton/heavy-ion synchrotron RF cavities. The design uses ribbons of different thicknesses in distinct radial regions, effectively transferring power loss from inner thicker ribbons to thinner ribbon regions, overcoming the drawback of conventional cores fabricated from uniformly thick ribbons, where power loss concentrates in inner diameters. The embedded structure effectively improves temperature distribution and increases shunt impedance, as validated by numerical simulations and experiments. These results provide a theoretical foundation for the performance optimization of MA cores.

[Phys. Rev. Accel. Beams 29, 062001] Published Mon Jun 08, 2026

Beam trajectory control in free-electron lasers relies on static response matrices (RM) that become outdated as machine conditions drift, degrading correction performance. We propose an online dictionary learning method that continuously refines the RM during routine operation with modest data requirements. Simulations demonstrate that this approach achieves a root-mean-square error of 0.2 m/rad or lower for RM elements using only ~1000 trajectory–excitation data pairs. Online experiments at the Shanghai Soft X-ray Free-Electron Laser confirm robust orbit stabilization with correction precision better than 0.01 mm, enabling real-time trajectory correction in low-repetition-rate linacs.

[Phys. Rev. Accel. Beams 29, 062801] Published Mon Jun 08, 2026

Additive manufacturing of pure copper enables the production of complex RF cavities with features such as internal cooling channels. We report the successful demonstration of proton-beam acceleration in an additively manufactured pure-copper Interdigital H-mode structure (IH-DTL). The 433 MHz six-gap cavity accelerated 1.4 MeV protons to 2.212 MeV at 25 kW RF power, realizing an effective accelerating gradient of 5.6 MV/m while reaching cavity peak fields up to 68 MV/m without RF breakdown. With RF performance and vacuum operation on par with conventionally manufactured IH-type cavities, this experiment demonstrates the viability of additive manufacturing for future efficient linac structures.

[Phys. Rev. Accel. Beams 29, 060101] Published Fri Jun 05, 2026

Measuring neutron-capture cross sections on radioactive nuclei is one of the main open challenges in nuclear astrophysics, yet no existing technique can reach most of the relevant isotopes. We present the conceptual design of a free-neutron target driven by a supercompact cyclotron, optimized for integration into a low-energy ion storage ring using readily available technologies. Monte Carlo simulations show that the design enables a proof-of-concept demonstration at the CRYRING storage ring and is scalable to high neutron densities at future dedicated facilities, opening the path toward direct neutron-induced reaction measurements in inverse kinematics on stored radioactive beams.

[Phys. Rev. Accel. Beams 29, 061601] Published Wed Jun 03, 2026

X-band high-gradient structures are critical enabling technology for compact linear accelerators and gamma-ray sources. We present tuning, conditioning, and performance of six identical XT72 structures for Tsinghua’s VIGAS gamma source. All reliably achieve 80 MV/m with breakdown rate below $1\times {10}^{-4}$ per pulse, revealing strong localization of breakdowns near high-field input coupler cells, a power-law decay of the normalized breakdown rate, and a dependence on input power waveform. These results provide key benchmarks for high-gradient structure conditioning and future compact facilities.

[Phys. Rev. Accel. Beams 29, 050401] Published Fri May 29, 2026

The Compact Linear Collider (CLIC) injector linacs must sustain high-gradient acceleration under strong beam loading and tight wakefield constraints. We present optimized 2 GHz traveling-wave structures combining iris tapering, RF pulse shaping, and a novel double-train RF operation scheme. Together, these enable stable acceleration with controlled wakefields and flat gradients across long bunch trains. The resulting design significantly reduces the required number of RF structures, klystrons, and peak RF power, yielding a more compact and energy-efficient injector complex compatible with future collider RF systems.

[Phys. Rev. Accel. Beams 29, 051603] Published Fri May 29, 2026

Ultrashort, high-current electron beams can drive advances in next-generation accelerators, ultrafast light sources, and attosecond science, yet conventional compression techniques are fundamentally limited by collective effects and beam degradation. Using simulations and analytical modeling, we demonstrate that plasma-based compression can achieve orders-of-magnitude stronger longitudinal compression while preserving beam quality. By imprinting energy chirps exceeding 500 MeV/μm onto an electron bunch, this approach can compress beams to durations approaching 10 nm and peak currents nearing 1 MA, enabling unprecedented beam brightness and new regimes of ultrafast beam-driven science.

[Phys. Rev. Accel. Beams 29, 052802] Published Fri May 29, 2026

Third-order resonances limit performance in high-intensity bunched beams. We experimentally demonstrate mitigation in the Fermilab Recycler Ring by minimizing resonance driving terms using sextupole correction. Measurements with bunched beams across low and high intensities show reduced beam loss, emittance growth, and halo population. These results establish resonance control as a key tool for intensity-frontier accelerator operation.

[Phys. Rev. Accel. Beams 29, 054001] Published Fri May 29, 2026

The concept of matched transport in periodic quadrupole focusing channels has been extended from uncoupled beams to those exhibiting significant correlations between the two transverse degrees of freedom.

In this paper, several rms-moment-matched transport solutions exhibiting substantial interplane coupling are derived analytically for a periodic solenoid focusing channel with alternating polarities. Particle tracking simulations, performed along this channel using the particle-in-cell Beampath code, confirm that the proposed rms-moment matching formalism remains accurate and robust even in the presence of strong nonlinear space-charge forces.

[Phys. Rev. Accel. Beams 29, 054401] Published Wed May 27, 2026

X-ray free-electron lasers provide new opportunities for probing ultrafast dynamical processes in matter. Here we present a four-color XFEL scheme for multiframe diffraction imaging, in which the whole electron beam is used to generate pulses with adjustable wavelength separation and controllable time delay. By introducing optical-klystron enhancement in split undulators, the scheme improves FEL intensity while reducing the total undulator length.

[Phys. Rev. Accel. Beams 29, 050704] Published Tue May 26, 2026

This paper presents a compact route to ultrashort, high-intensity THz light using unseeded optical-klystron free-electron lasers. Time-dependent 3D simulations at 10, 30, and 100 µm show how natural THz slippage can phase-align energy modulation, create strong microbunching, and drive coherent amplification without an external seed. The study demonstrates sub-picosecond pulses with multi-hundred-megawatt peak powers, examines dispersion, diffraction, and harmonic-bunching options, and introduces a chicane-embedded optical-delay scheme to restore beam-radiation overlap for staged amplification. These results point toward compact, powerful tunable THz FEL sources for science.

[Phys. Rev. Accel. Beams 29, 050703] Published Thu May 21, 2026

A simple yet effective scheme for spectral broadening is proposed which utilizes a plasma wakefield accelerator (PWFA) to impart a large energy chirp to an electron beam and a specifically designed transport system then selectively injects the portion of the beam meeting the lasing requirements. A start-to-end simulation demonstrates that a high-brightness X-ray FEL exhibiting a full-width bandwidth reaching 20% can be generated which is approximately five times greater than what is achievable with conventional accelerator technology.

[Phys. Rev. Accel. Beams 29, 050702] Published Wed May 20, 2026

The SPARC LAB facility, operating at the LNF-INFN laboratories in Frascati in Italy, has been recently upgraded with the aim to enable user-oriented applications by offering high-brightness electron beams and ultra-short light pulses from THz up to the soft X-rays range. The paper summarizes the electron beams and radiation parameters and describes the layout and main infrastructures available to external users.

[Phys. Rev. Accel. Beams 29, 051602] Published Tue May 19, 2026

We present a method for suppressing transverse single-bunch instabilities, using the combined action of longitudinal impedance, feedback, and chromaticity. The key stabilization mechanism arises from two effects: feedback and positive chromaticity shift the dominant modes of instabilities, while longitudinal impedance introduces a tune spread in these modes. The theory is applied to three electron storage rings. Both the analysis and simulation lead to consistent conclusions.

[Phys. Rev. Accel. Beams 29, 051001] Published Fri May 15, 2026

Transverse Electric (TE) RF cavities are important tools for beam manipulation and beam-quality improvement, but systematic methods for designing cavities with prescribed multipolar TE fields remain limited. This work presents a method for synthesizing such cavities by superimposing cylindrical standing-wave solutions and enforcing conducting boundary conditions through numerical optimization. CST eigenmode simulations validate the resulting hybrid geometries and show that the prescribed multipolar content is realized with high modal purity.

[Phys. Rev. Accel. Beams 29, 052801] Published Thu May 14, 2026

Laser wakefield acceleration (LWFA) studies commonly assume an ideal Gaussian laser driver, although real high-power laser pulses often exhibit complex transverse intensity and phase structures. We combine experiments and particle‑in‑cell simulations to show that actual laser profiles significantly modify the wakefield evolution and electron injection process. The nonideal laser distribution lowers the self‑focused intensity and broadens the plasma wake sheath, delaying injection. Incorporating the reconstructed laser profile in simulations reproduces experimentally observed ~200 pC, ~200 MeV electron beams, revealing the critical role of realistic laser structures in high‑charge LWFA.

[Phys. Rev. Accel. Beams 29, 051301] Published Wed May 13, 2026

Operation close to half-integer resonances can lead to significant beam quality degradation and beam loss in high-intensity/high-brightness synchrotrons. At the CERN Proton Synchrotron Booster, the controlled crossing of the $2Q_y=9$ half-integer resonance was experimentally investigated and benchmarked against six-dimensional self-consistent tracking simulations. The study demonstrates the role of incoherent space charge effects in shaping the beam profile evolution and beam losses. The observed dependence of beam losses on the resonance crossing rate, beam intensity, and resonance strength provides a basis for devising mitigation strategies.

[Phys. Rev. Accel. Beams 29, 054201] Published Tue May 12, 2026

Emittance minimization in high-brightness photoinjectors is a key challenge for x-ray free-electron lasers. We demonstrate a data- and model-guided framework combining physics-informed laser shaping with inverse emittance modeling. The approach achieves ~20% emittance reduction and enables reliable, stable shaped electron bunches for sustained high-intensity FEL operation at the European XFEL.

[Phys. Rev. Accel. Beams 29, 050701] Published Fri May 08, 2026

A Luenberger state observer provides real-time estimates of detuning and half bandwidth in superconducting radio frequency (SRF) cavities, offering insight into parameters critical for safe and energy efficient operation. Based on a gain-scheduled linear cavity model with parameter-varying pole placement, it features stable and tunable estimation error dynamics. Differences from existing approaches are discussed and evaluated using experimental data, outlining the observers potential for future applications in resonance control and quench detection.

[Phys. Rev. Accel. Beams 29, 054601] Published Fri May 08, 2026

Laser wakefield acceleration offers an exciting route to the generation of bright, high-energy electron bunches, but these electrons are generated with large divergence and must be captured well. GeV-scale electrons need strong quadrupoles. In this paper we propose a Focusing-Defocusing (FODO) array of equal-strength Permanent-Magnet Quadrupoles (PMQs) to gradually capture such bunches. A modular array of fixed-strength PMQs can be readily tuned for different electron energies by adding or removing magnets; we have developed a practical arrangement for the 1 GeV electrons expected at the UK Extreme Photonics Application Center (EPAC) facility, and have constructed novel 350 T/m capture PMQs.

[Phys. Rev. Accel. Beams 29, 051601] Published Thu May 07, 2026

Heavy-ion storage rings with internal targets offer highly efficient production of rare events, but are severely limited by stochastic charge-state conversion at each target interaction, which drives rapid transverse emittance growth. We introduce a concept based on a scaling fixed-field alternating-gradient (FFA) lattice with an azimuthally modulated field index k to overcome this fundamental limitation. This approach is found to significantly suppress emittance growth, particularly in the horizontal plane. Six-dimensional beam-tracking simulations incorporating energy loss, scattering, and charge-state conversion are presented, demonstrating effectiveness under realistic conditions.

[Phys. Rev. Accel. Beams 29, 050101] Published Wed May 06, 2026

This work addresses the question of how precisely one can control the orbit of a single ion. A unique ion source based on a simple radio-frequency quadrupole trap is employed to provide an extremely narrow beam that enables one to irradiate a target with nanometer precision. This novel source is equipped with a Doppler laser cooler to reduce the temperature of a trapped ion cloud to near absolute zero, where a phase transition to a Coulomb crystalline state occurs. We demonstrate experimentally and numerically that it is possible to extract these ultracold ions one by one from the trap at arbitrary timing and transport them precisely along the design orbit.

[Phys. Rev. Accel. Beams 29, 053401] Published Tue May 05, 2026

Double-RF systems are widely used in advanced storage-ring light sources, but they are generally implemented with separate accelerating and harmonic cavities. Here we propose a compact normal-conducting bimodal cavity that supports the TM${}_{010}$ and TM${}_{020}$ modes in a single cavity. A low-pass filter suppresses harmonic power leakage through the fundamental-mode coupler, while tunable band-stop filters provide selective isolation for higher-order-mode damping to protect the harmonic mode. The two operating modes remain largely independently controllable, providing a practical design approach for compact bimodal RF cavities in storage rings.

[Phys. Rev. Accel. Beams 29, 042001] Published Thu Apr 30, 2026

he SHINE 3.9 GHz fundamental power coupler was improved from the original Eu-XFEL design by incorporating adjustable external quality factor $Q_{ext}$ and a double-braid copper strip for enhanced cooling. This paper details all aspects of coupler development, including requirements, design, RF simulations, fabrication techniques, power testing, cryomodule integration and RF conditioning. Sixteen production 3.9 GHz couplers were manufactured and integrated into two SHINE third harmonic cryomodules, which achieved maximum total cavity voltages of 63.6 MV and 59.8 MV, respectively. These cryomodules have since been successfully commissioned for online operation.

[Phys. Rev. Accel. Beams 29, 043501] Published Wed Apr 22, 2026

A comprehensive design is presented for the Booster-to-pEDM (BtP) injection line serving both clockwise and counterclockwise rings in the proposed proton Electron Dipole Moment (pEDM) experiment at BNL. The design builds upon a symmetric-hybrid lattice while reusing segments of the existing Booster-to-AGS transfer line, tackling key challenges in precision injection for pEDM searches—such as stringent optics matching, dispersion suppression, spin preservation within $\pm 20$ mrad, and systematic error control—required to reach the target sensitivity of ${10}^{-29}$ e$\cdot$cm. Multi-particle and spin tracking simulations validate beam containment and polarization stability, demonstrating design feasibility and robustness.

[Phys. Rev. Accel. Beams 29, 041601] Published Fri Apr 17, 2026

We present the results of analytical and numerical calculations of electromagnetic radiation generated by a charged particle bunch passing through two parallel grids composed of thin conductors. The longwave range of the radiation spectrum is studied, i.e., the wavelengths are assumed to be much greater than the cell size of each grid. We demonstrate, in particular, that the structure under consideration can be used for developing new methods of non-destructive bunch diagnostics.

[Phys. Rev. Accel. Beams 29, 042901] Published Fri Apr 17, 2026

Modern synchrotron light sources strive for extreme parameters, where the resulting lowered dynamic aperture could be mitigated by reducing the required sextupole strength through a negative momentum compaction factor. This strategy significantly changes the longitudinal beam dynamics which must be investigated in detail. At KARA, this operation mode was studied in a regime dominated by the coherent synchrotron radiation impedance. The results include significant deviations from the usual positive momentum compaction dynamics, particularly in terms of bunch length and the micro-bunching instability, challenging existing theoretical predictions of the threshold current.

[Phys. Rev. Accel. Beams 29, 044402] Published Thu Apr 16, 2026