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Physics Physics Accelerator Physics

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Wednesday 14 October · still arriving

Accelerator Physics · Cross-listed from nucl-ex

Physics with Radioactive Ion Beams at the Nuclear Science Laboratory

W.S. Porter, D.W. Bardayan, M. Brodeur et al. (+13 more)

The University of Notre Dame is home to a rich history of nuclear science efforts, including some of the earliest developments in the production and creation of radioactive ion beams (RIBs). The resulting TwinSol facility stands as the longest continuously-operating RIB facility in the United States, and has enabled a wide range of experimental efforts in nuclear structure, astrophysics and fundamental symmetries through in-flight RIBs one to two nucleons from stability. A recent upgrade to TwinSol via a third solenoid constituted the founding of the TriSol facility, which provides cleaner, better-focused RIBs to downstream experiments. In this paper, we present a summary of RIB science at the Nuclear Science Laboratory (NSL) with both TwinSol and TriSol and discuss recent upgrades and future experimental plans at the facilities.
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All authors W.S. Porter, D.W. Bardayan, M. Brodeur, C. Dembski, P.D. O'Malley, F. Rivero, W.W. von Seeger, C. Boomershine, O. Bruce, S.R. Carmichael, S. Coil, A.M. Houff, J.J. Kolata, D. Schroeder, A.A. Valverde, R. Zite

Tuesday 13 October · still arriving

Accelerator Physics

Phase Memory Controls Radiative Depolarization Near an Isolated Spin Resonance

Zhe Duan

Radiative depolarization near spin resonances in electron storage rings is conventionally described by correlated-sideband and local resonance-density theories, but a quantitative description of the crossover between them has remained lacking. Here we derive a unified finite-memory response from stochastic spin dynamics near an isolated resonance. By separating the coherent resonance contribution from stochastic fluctuations, we show that the connected correlation of the accumulated resonance-relative spin phase determines the leading off-center weak-resonance depolarization rate. Both conventional theories emerge as controlled asymptotic limits of this response, which also captures the surviving synchrotron phase memory governing the crossover. Monte Carlo spin tracking validates the predicted rates throughout the crossover and reproduces the recurrence-induced generalized-sideband structure. More broadly, the connected-correlation formulation provides a basis for extending radiative depolarization theory to more general stochastic spin-orbit dynamics in storage rings.
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Accelerator Physics

A modern particle-in-cell code for beam-beam simulations of future colliders

Arianna Formenti, Remi Lehe, Axel Huebl et al. (+10 more)

A key challenge in the design of next-generation colliders is predicting the effects of beam-beam interactions and using these predictions to optimize machine performance. Beam-beam interactions are characterized by strong focusing forces, radiative effects, and the generation of background particles. While analytical formulas provide insight into the dynamics of beam-beam interactions, these nonlinear, coupled effects are most accurately described with numerical methods. In this paper, we introduce the open-source particle-in-cell code WarpX as a modern tool for modeling the interaction point in future lepton colliders. WarpX provides high-performance execution on distributed GPU architectures within an open-source and actively maintained code base. We present convergence scans and benchmarks against the established beam-beam codes GUINEA-PIG (v1.2.2) and CAIN (v2.42) for luminosity spectra, photon emission, and secondary-particle production under a wide range of beam parameters corresponding to different collider concepts. Our results show that WarpX (v26.09) reproduces the benchmark beam-beam observables while enabling GPU-portable, extensible simulations. These results establish WarpX as a scalable platform for high-fidelity beam-beam modeling in future collider studies.
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All authors Arianna Formenti, Remi Lehe, Axel Huebl, Stepan S. Bulanov, Jens Osterhoff, Andrew Myers, Weiqun Zhang, Spencer Gessner, Peter Kicsiny, Anna Kinderman, Bao Nguyen, Jinseo Park, Jean-Luc Vay

Monday 12 October

Accelerator Physics

HOM Mitigation

Nicoleta Baboi

Higher Order Modes (HOMs) in accelerating structures are resonant electromagnetic fields excited and left behind by charged particle bunches. They can severely degrade the beam quality in accelerators, such as the multi-bunch energy spread and transverse emittance, and therefore one must carefully study and mitigate them. In this lecture, various methods of HOM mitigation are reviewed. On one hand, one tries to avoid their existence, for example by careful design of the accelerating structures and damping systems. On the other hand, one can reduce the effect of the excited HOM fields, for example by means of fast feedbacks or beam alignment. Additionally, a few ways to make HOM signals useful are referred to, such as diagnostics of the beam or of accelerating structures.
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Accelerator Physics

Anomaly Detection in Bunch Oscillations for Early Warning of Sudden Beam Loss at SuperKEKB

H. Haigh, P. Horak, G. Inguglia et al. (+5 more)

Sudden beam loss (SBL) events at the SuperKEKB collider result in the loss of a large fraction of the stored beam within just a few revolutions, on a timescale comparable to or shorter than the 20-30 {\mu}s latency of the existing abort system. Such events have damaged collimators and threaten Belle II subdetectors. Bunch Oscillation Recorders (BORs) capture transverse bunch positions at each revolution, which often show sizable oscillations that precede significant beam current loss. We test whether these precursors can be detected earlier than a charge-based reference that mimics the existing abort sensors. We apply several oscillation-based anomaly detection algorithms to 208 SBL events recorded in the low-energy ring during the 2024 run period, ranging from simple rolling statistics to machine learning models trained to forecast bunch oscillation. On 173 events not used for training or calibration, the best-balanced model (DeepLSTM) triggers before the charge-based reference in 86-90% of events across five training seeds, with a mean lead time of 25-30 {\mu}s. The only trigger classified as a false alarm fires on an oscillation that begins about 60 turns before the abort and persists until the beam is lost, making it more likely an early precursor than a spurious trigger. These results establish bunch oscillations as a viable early abort trigger and motivate a shadow-mode deployment to measure the false-alarm rate in continuous operation.
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All authors H. Haigh, P. Horak, G. Inguglia, C. Krause, G. Mitsuka, H. Nakayama, R. Nomaru, M. Tobiyama

Accelerator Physics · Cross-listed from physics.optics

Programmable Hard-X-Ray Spectral Comb Generation via Laser-Compton Scattering

Hao Zhang, 1Ji Qiang, Shukui Zhang et al. (+1 more)

Independent control of line spacing and offset underpins programmable frequency-comb spectroscopy, yet it has not been established for hard-X-ray sources based on inverse Compton scattering after electron transport and angular collection. Self-consistent multi-particle tracking and Li'enard-Wiechert radiation calculations model a transported 10 pC beam and its angle-integrated spectrum near 11 keV. Laser pulse separation programs the comb spacing, while pulse-to-pulse phase translates the entire line grid at fixed spacing. The spacing model agrees within 0.52%, while transport and optics change the phase-transfer slope by less than 0.2%. At fixed electron spot size, the largest resolvable separation scales as the inverse square of normalized emittance; subnanometer bunches also produce a mode-locked train with 13.9 as spacing. This two-coordinate programmability enables phase-stepped multicolor measurements and offers routes to hard-X-ray Ramsey interferometry, coherent control of core and nuclear excitations, and attosecond nonlinear spectroscopy.
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All authors Hao Zhang, 1Ji Qiang, Shukui Zhang, Sergio Carbajo

Sunday 11 October

Accelerator Physics

Brilliance: toward autonomous computational research in particle accelerator physics

Jinyu Wan, Yu Zhao, Wei Bao et al. (+4 more)

Computational research in physics requires continuous interplay between simulation and scientific interpretation, demanding substantial specialist effort. Here we introduce Brilliance, a research agent that combines large language models, reusable physics knowledge and numerical simulation to conduct adaptive investigations in accelerator physics. Given a single user prompt, Brilliance designs a fourth-generation synchrotron light source that meets coupled emittance and nonlinear-acceptance requirements. Further exploration yields a design combining sub-10-pm emittance with a large dynamic aperture under realistic engineering constraints, suggesting a route towards hard-X-ray diffraction-limited operation, although the momentum-acceptance target remains unmet. Brilliance also calibrates a model of an operating light source against measured responses, accurately inferring its lattice and calibration errors. Across these studies, Brilliance autonomously revises its computational strategies in response to numerical evidence. These results demonstrate a route towards delegating sustained scientific investigations to agents equipped with domain expertise and numerical tools.
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All authors Jinyu Wan, Yu Zhao, Wei Bao, Ying Li, Hao Zhong, Xiaohan Lu, Yi Jiao

Saturday 10 October

Accelerator Physics

Multi-Objective Design of C-Shaped Targets for Energy–Divergence Control in Laser-Driven Proton Acceleration

Mohammad Rezaei-Pandari, Mahdi Shayganmanesh and Mohammad Hossein Mahdieh

We optimize the energy-divergence trade-off of laser-driven protons from a C-shaped target using two-dimensional particle-in-cell simulations and constrained multi-objective Bayesian optimization. Five geometry and focusing parameters are varied to maximize proton cutoff energy and minimize the RMS divergence of forward protons with E_k >= 5 MeV under a proton-only conversion-efficiency constraint of eta_H >= 9%. Of 82 designs, 60 are feasible and 15 Pareto-optimal. The Max-Energy and Min-Divergence endpoints yield 28.64 MeV at 52.51 degrees and 11.47 MeV at 11.13 degrees, respectively; a representative compromise yields 21.44 MeV at 38.44 degrees. Matched-stage diagnostics link these regimes to optical-field buildup, electron energization, charge separation, and outer-sheath organization. Numerical tests support the principal trends. Reflection timing does not support a monotonic trapping-duration law, and the charge-sheath relation remains non-local. These results establish a design-resolved route to controlling proton energy and angular quality.
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Accelerator Physics

Learn the Dynamics, Enforce the Physics: Generative Latent Operators for High-Dimensional Beam Evolution

Haohan Zou, Alexander Scheinker and Yuanyuan Shi

Particle-in-cell (PIC) simulation is indispensable for modeling beam dynamics in particle accelerators, but its computational cost limits many-query workflows, such as configuration exploration, virtual diagnostics, and controller design. We introduce GLOBE, a physics-constrained Generative Latent Operator for Beam Evolution, modeling the nonlinear, control-dependent, multiscale evolution of 3D beam–field dynamics covering $10^7$ spatial cells. GLOBE compresses beam–field states into a compact latent space and factors their evolution into two components. A control-conditioned neural operator learns the dominant dynamics, while an amplitude-normalized generative model captures the residual distribution, recovering fine-scale structures and conditional variations. GLOBE enforces field constraints by regime-specific, parameter-free operators: a Poisson solve reconstructs the electric field in the electrostatic regime, and a spectral projection imposes Gauss's law and a divergence-free magnetic field in the electromagnetic regime. On two high-resolution 3D particle-accelerator benchmarks, bunched-beam transport and plasma-wakefield acceleration, GLOBE lowers relative-$L_2$ error by 9% and 13%, low-frequency spectral error by 69% and 51%, and mid-frequency spectral error by 54% and 20% relative to the strongest baseline (DPOT), satisfies field constraints, and reduces hours of PIC simulation to a minute per rollout.
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Friday 9 October

Accelerator Physics

AI Acceleration of Muon Collider R&D: A Report from the AI4MuC Workshop

J. Scott Berg, David Bizzozero, Tulika Bose et al. (+27 more)

A Muon Collider is one of the most attractive routes to multi-TeV lepton collisions, but it requires the accelerator and detector communities to solve a tightly coupled set of problems that have no close precedent in an operating collider. Muons must be produced, captured, cooled, accelerated, and collided before they decay. The detector must then extract clean physics from an environment dominated by decay products from the beamline. Artificial intelligence is not a substitute for accelerator physics, detector design, or engineering validation. It is, however, unusually well matched to several of the central obstacles: high-dimensional design spaces, expensive simulations, coupled subsystem trade-offs, and workflows that are currently too slow or too fragile to support broad design exploration. This report distills the AI4MuC workshop into a summary of AI use cases with the potential to change the pace of Muon Collider R&D, organized around the following physics bottlenecks: muon production and capture, ionization cooling, magnet and RF technology, detector design in beam-induced background, background simulation and generation, reconstruction, and software.
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All authors J. Scott Berg, David Bizzozero, Tulika Bose, Lance Cooley, John Dervan, Auralee Edelen, Peter Elmer, Cristiano Fanelli, Tova Holmes, Walter Hopkins, Sergo Jindariani, Michael Kagan, Maira Khan, Young-Kee Kim, Matt LeBlanc, Lawrence Lee, Matthias Liepe, Radha Mastandrea, Patrick Meade, Federico Meloni, Chad Mitchell, Linh Nguyen, Isobel Ojalvo, Ryan Roberts, Nicholas Smith, Jean-Luc Vay, Gordon Watts, Drew Winder, Chenran Xu, Katsuya Yonehara

Accelerator Physics

Physics of stabilization and dynamic control of CW magnetrons for superconducting accelerators

G. Kazakevich, R.P. Johnson, I. Gonin et al. (+2 more)

Powerful CW magnetrons were suggested for feeding RF cavities of superconducting accelerators because they provide higher efficiency and lower RF power cost than the traditionally used klystrons, IOTs, or solid-state amplifiers. RF amplifiers driven by a master oscillator serve as coherent RF sources. CW magnetrons are regenerative RF self-oscillators with a huge regenerative gain. This causes regenerative instability with notable noise when a magnetron operates as a self-oscillator, i.e., with the anode voltage above the threshold of self-excitation. An injection locking by a small signal was proposed for phase stabilization of magnetrons. In this case, CW magnetrons with injection-locked (coherent) oscillations generate a notable level of noise. This may preclude the use of CW magnetrons in this mode in superconducting RF (SRF) accelerators. This work discusses our analytical results, PIC simulations, and previously obtained analytical and experimental data regarding the operation and control of CW magnetrons. These results led to the development of methods which are most suitable for SRF accelerators.
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All authors G. Kazakevich, R.P. Johnson, I. Gonin, V. Yakovlev, Ya. Derbenev

Accelerator Physics · Cross-listed from math.NA

Global Optimization of Beam Profiles for Suppressing the Bump-On-Tail Instability

Sandro Mignelli and Lukas Einkemmer

A particle beam with constant intensity that propagates into a plasma triggers a bump-on-tail instability. It has been demonstrated that beam modulation can be used to significantly reduce this instability. However, finding the optimal beam profiles that accomplish this is a complex optimization problem that suffers from an extremely rugged optimization landscape and a relatively high-dimensional parameter space. In this paper, we evaluate a number of optimization algorithms and find that population based methods (in particular, CMA-ES and Differential Evolution) perform best. In particular, we investigate beam profiles where the beam is either completely turned ON or OFF. This configuration is easier to accomplish experimentally, but leads to a higher-dimensional and thus more challenging optimization problem. We obtain ON/OFF beam profiles that reduce the instability by more than 80% and thus perform significantly better than what has been reported in the literature.
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Thursday 8 October

Accelerator Physics · Cross-listed from physics.bio-ph

Femtosecond Three-Dimensional Imaging of Single-Protein with Hard X-ray Laser

Paul Lourdu Xavier, Andrew J. Morgan, Johan Bielecki et al. (+66 more)

The extremely intense pulses of X-ray free-electron lasers (XFELs) have enabled imaging of radiation-sensitive samples, such as macromolecular microcrystals, beyond radiation damage limits. These sources have the potential to deliver biomolecular single-particle imaging, similar to cryo-electron microscopy but without the need for cryo-fixation and with temporal resolution from femtoseconds to milliseconds. While this possibility was recognized before XFELs were built, the biological single-particle imaging work-flow has previously only been demonstrated on large virus particles. Based on decades of improvements in X-ray beam focusing, particle delivery, diffraction detection, and advanced analysis, here we demonstrate imaging of a single molecular complex, the giant-hemoglobin erythrocruorin (Ery) with X-ray laser pulses. Two-dimensional classes of diffraction patterns could be reconstructed to 15 Angstrom resolution, and 3D images to approximately 20 Angstrom, while the 3D merged intensity in reciprocal space extended beyond 20 Angstrom. The resolution discrepancy is likely due to heterogeneity caused by gas-phase compaction of the complexes. With increased throughput, this approach could be used to reveal in-situ structural details during mass spectrometry studies of biomolecules, while improvements in sample delivery may provide ultrafast snapshot imaging of biological single-particles in their native-state beyond the limitations of radiation damage.
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All authors Paul Lourdu Xavier, Andrew J. Morgan, Johan Bielecki, Amit K. Samanta, Simon Dold, Chufeng Li, Xinyue Gao, Spencer K. Passmore, Ruslan P. Kurta, Tim B. Berberich, Emiliano De Santis, Wenhui Zhang, Juncheng E, Faisal H. M. Koua, Romain Letrun, Luca Gelisio, Oleksii Turkot, Egor Sobolev, Lukas V. Haas, Jannik Lübke, Jingxuan He, Madeline B. F. Memovich, Kevin Janson, Stefanie Lenzen, Safi Rafie-Zinedine, Mansi Butola, Oleksandr Yefanov, Fabian Trost, Chan Kim, Tomas Popelar, Tokushi Sato, Yevheniy Ovcharenko, Rebecca Boll, Sergey Usenko, Thomas M. Baumann, Alberto De Fanis, Björn Senftleben, Matteo Porro, Andrea Castoldi, Ibrahym Dourki, Cyril Danilevski, Ekaterina Round, Christina Schmidt, Huijong Han, Roberto Alvarez, Ervin Chia, Cornelia Cazey, Carolin Seuring, Ruojie Sha, Maia Azubel, David A. Bushnell, Sébastien Boutet, Sergey Ovchinnikov, Adrian P. Mancuso, Michael Meyer, Richard Bean, Anton Barty, Filipe R. N. C. Maia, Richard A. Kirian, Thomas D. Grant, N. Duane Loh, Carl Caleman, Erik G. Marklund, Nadia Zatsepin, Andrew V. Martin, Saša Bajt, Roger D. Kornberg, Jochen Küpper, Henry N. Chapman

Wednesday 7 October

Accelerator Physics · Cross-listed from physics.optics

Start-to-end simulations of non-relativistic electron acceleration along reflective grating structure by front-tilted laser pulse

I.V. Beznosenko, A.V. Vasyliev, S.M. Kovalov et al. (+2 more)

A comprehensive (start-to-end) simulation was performed regarding the formation of a front-tilted laser pulse and the subsequent acceleration of non-relativistic electrons moving along a reflective grating structure. The laser pulse tilt was formed using another diffraction grating – either reflective or transmissive. The pulse had a spectral range (FWHM) of 803–863 nm and an initial duration of approximately 17 fs. Acceleration under normal laser pulse incidence was also calculated for comparison. Research results indicate that the use of a femtosecond laser pulse with a front, tilted by means of a reflective diffraction grating, significantly enhances the efficiency of laser acceleration of non-relativistic electrons compared to the case of a pulse at normal incidence. Furthermore, it was found that using a transmissive diffraction grating to shape the tilted pulse front also increases acceleration efficiency relative to normal incidence on the accelerating grating, although the acceleration rate is lower than when a reflective diffraction grating is used.
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All authors I.V. Beznosenko, A.V. Vasyliev, S.M. Kovalov, R.R. Kniaziev, G.V. Sotnikov

2610.10193 · 7 Oct · 10 pages, 6 figures, 2 tables. Start-to-end PIC simulations of non-relativistic electron acceleration along a reflective grating structure driven by a front-tilted femtosecond laser pulse; comparison of pulse-front tilting by transmissive vs. reflective diffraction gratings

Abstract PDF $LASR ×6

Accelerator Physics

AloHEP Software: A luminosity optimizer for High Energy Physics colliders

Burak Dagli and Yigitali Karaca

The luminosity quoted for proposed particle colliders is usually derived from the analytic geometric formula, which assumes head-on collisions of identical, rigid Gaussian bunches. For the new generation of asymmetric machines—in particular lepton–hadron colliders such as the EIC, LHeC and FCC-eh—this assumption can misestimate the luminosity, because it ignores a few coupled effects that act in the interaction region such as hourglass effect, crossing angle, and mutual electromagnetic (beam–beam) deformation of the colliding bunches. We present AloHEP (A luminosity optimizer for High Energy Physics), an open-source, cross-platform Java application that simulates the interaction region of both symmetric and asymmetric colliders. AloHEP represents each bunch by an ensemble of macroparticles deposited on the grid with a cloud-in-cell scheme, and slices the crossing longitudinally. On each transverse slice it solves the two-dimensional electrostatic problem by a direct Green's-function convolution, then obtains the beam–beam forces by finite differencing and continuous bicubic interpolation. The hourglass effect, finite crossing angle and beam–beam pinch/disruption can be enabled independently, and the two colliding beams may consist of entirely different species (leptons, protons, heavy ions). A JSON-backed parameter database and an interactive graphical interface make AloHEP a flexible tool for the rapid prototyping of realistic luminosity estimates. We verify that the code reproduces the analytic geometric luminosity in the appropriate limit and present scaling, grid-convergence and asymmetric-collider benchmarks.
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Tuesday 6 October

Accelerator Physics · Cross-listed from physics.optics

Synthesizing free-electron wave functions by stimulated near-field interactions

Álvaro Rodríguez Echarri and Albert Polman

Stimulated electron-optical-near-field interactions imprint a coherent, phase-coherent modulation on the wave function of a free electron, of which the free-space dispersion subsequently converts into a train of attosecond density peaks. Light thereby becomes a tool for synthesizing the electron wave function itself, setting when, where, and how narrowly the electron density concentrates. Here we study photon-induced near-field electron microscopy (PINEM) to gain control over that synthesis in two stages: first for a single PINEM interaction, whose design parameters we obtain in closed form, and then for multiple PINEM interactions acting in parallel, which extends the control across space and time. The design rules follow from decomposing the propagated density into temporal harmonics, which we classify into three: (i) the arrival time of the attosecond train, fixed by the optical phase of the coupling; (ii) the distance at which the train forms, set by diffraction at the point where all classical trajectories converge; and (iii) the pulse duration, fixed by the imprinted energy spread. We evaluate these parameters for a scanning-electron-microscope (SEM) configuration at 10~keV, where the compression completes within tens of micrometers from the interaction region, with results 20% better than previous approaches. Letting the electron then interact with several spatially separated near fields in parallel, normal to the trajectory, each pathway carrying its own coupling strength and optical phase, we show that retaining or erasing which-path information changes both the propagated density and the measurable energy spectrum, the latter providing in turn a measure of the mutual coherence of the driving fields. These results establish PINEM as a quantitative synthesis tool for free-electron wave functions in compact, low-voltage electron microscopes.
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Accelerator Physics

Development of a continuous-wave photocathode very-high-frequency electron gun for $\rm S^3FEL$

Lianmin Zheng, Yitong Duan, Yuanyuan Qin et al. (+11 more)

A very-high-frequency (VHF) electron gun operating at a resonant frequency of 216.667 MHz has been developed at Tsinghua University for the Shenzhen Superconducting Soft X-ray Free-Electron Laser ($\rm S^3FEL$) facility. Building upon the SHINE gun design, the cavity profile was optimized to achieve a higher cathode electric-field gradient and a higher accelerating voltage at comparable input power. The revised cavity geometry also yields improved multipacting performance. In addition, thermal analysis was carried out to guide the water-cooling design, and enhanced cooling was implemented in the vicinity of the cathode. During high-power conditioning, 82 kW of continuous-wave radio-frequency power was successfully coupled into the gun, corresponding to a cathode gradient of 29.9 MV/m and an accelerating voltage of 856 kV. The gun voltage surpasses the previous world record for room-temperature VHF guns. The maximum dark current measured by the Faraday cup at the gun exit was only 6.8 nA.
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All authors Lianmin Zheng, Yitong Duan, Yuanyuan Qin, Baiting Song, Yang Yu, Zixuan Dong, Yijiang Zhu, Yanqing Jia, Jiaru Shi, Renkai Li, Wenhui Huang, Huaibi Chen, Chuanxiang Tang, Yingchao Du

Monday 5 October

Accelerator Physics

Limits on energy recovery for positron acceleration in a warm plasma column

Max Varverakis, Spencer Gessner, Severin Diederichs et al. (+1 more)

Beam-driven plasma wakefield acceleration (PWFA) is a promising candidate for realizing a future linear collider, owing to the extremely high field gradients that are produced in plasmas. Despite recent success in high-gradient and high-efficiency electron PWFA, efficient positron PWFA remains a challenge. The warm plasma column regime offers stable, high-quality acceleration of positron beams in a plasma electron filament, albeit at low energy-transfer efficiencies. We explore the possibility of employing an electron energy recovery beam to extract residual energy from the plasma wakefield and increase the efficiency of this scheme. Our particle-in-cell simulations reveal that certain mechanisms, including higher-order ionization and ion motion, limit our ability to further extract energy from the plasma wakefield.
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All authors Max Varverakis, Spencer Gessner, Severin Diederichs, Carl A. Lindstrøm

Accelerator Physics

Construction of Approximate Invariants Across Nonlinear Resonances

Yongjun Li, Derong Xu, Yue Hao et al. (+1 more)

Our previous work [Y.~Li, D.~Xu, and Y.~Hao, Phys. Rev. Accel. Beams 28, 074001 (2025)] introduced a square-matrix method for constructing approximate invariants recursively, order by order, from the one-turn map of non-integrable Hamiltonian systems. At fourth and higher even orders, the recursive construction is intrinsically non-unique because rotationally invariant polynomials generate a null space in the corresponding homological equations. In the resonant regime, this ambiguity can lead to an incorrect description of the resonance-island topology and is therefore particularly relevant to accelerator applications that rely on stable resonance islands. In this work, we select the null-space contributions by explicitly incorporating the null-space basis vectors and determining their coefficients through an averaging procedure over a prescribed region of interest. The method is demonstrated using the Kobayashi map near a third-order resonance, extending the square-matrix construction to resonant Hamiltonian dynamics.
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All authors Yongjun Li, Derong Xu, Yue Hao, Sergei Nagaitsev

Accelerator Physics

Effect of transition layer on wakefield in plasma waveguide

Peter Markov, Kostyantyn Galaydych and Gennadiy Sotnikov

Using 2.5D particle-in-cell simulations, we investigate the parameters of a plasma wakefield accelerator (PWFA) for positrons and electrons in a layered plasma waveguide (LPW) in the presence of a transition layer (TL) between two layers of uniform plasma with different densities. The layered plasma is modeled as a combination of a near-wall tubular plasma of higher density and an on-axis plasma column of substantially lower density, separated by a TL in which the plasma density varies smoothly from the lower to the higher value according to a specified law. It is shown that using the PWFA parameters determined for a layered plasma waveguide without the transition layer changes the acceleration conditions when the TL is present, and that this change depends on the TL thickness. It is demonstrated that when the TL thickness exceeds the skin-layer depth in the tubular plasma, the positron acceleration rate decreases substantially. The methods are proposed for correcting the parameters of the plasma waveguide under consideration that compensate for the decrease in the energy gain of the accelerated bunches and ensure their stable transport.
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Accelerator Physics

Reveal normal form structure for nonlinear map in accelerator beam physics with symplectic neural network

Leo He and Yue Hao

Long-term multi-turn tracking is required to study nonlinear phenomena in circular accelerators, such as resonances, chaotic motion, and the dynamic aperture. General-purpose neural networks do not preserve the symplectic structure of Hamiltonian dynamics, so their errors can grow over many turns. Symplectic neural networks (SympNets) guarantee symplecticity through their architecture rather than through a loss penalty. In this work, we use a SympNet to learn the normal-form transformation of a nonlinear map from tracking data. In the learned coordinates, the dynamics become a rotation of each mode, whose amplitude-dependent phase advance is given by a second network. We demonstrate the method on a four-dimensional McMillan-type map. The model reproduces the one-turn dynamics, the learned phase advances stay constant along each trajectory to within $\sim 10^{-5}$~rad, and orbits become close to circles in the learned coordinates at small and moderate amplitude. At large amplitude the learned orbits spread noticeably, and the cause of this degradation is not yet established. The approach is a step toward fast, structure-preserving surrogate models for lattice analysis and online beam-dynamics applications in storage rings.
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Saturday 3 October

Accelerator Physics

Design of the Electron-Beam Collimator for the Electron-Ion Collider

Andrii Natochii, Elke-Caroline Aschenauer, Jay Best et al. (+5 more)

The design and optimization of a beam collimator for the Electron Storage Ring (ESR) of the Electron-Ion Collider (EIC) are presented. The collimator must efficiently intercept stray beam particles while maintaining acceptable beam coupling impedance, surviving rapid accidental beam impacts, and withstanding steady-state beam-induced heating. An integrated design approach combining beam-loss tracking, electromagnetic-shower simulations, thermomechanical analysis, and impedance calculations is developed and benchmarked against published simulations and beam-impact experiments. A comparison of candidate absorber materials identifies Al2219-T62 as providing a favorable balance of beam-impact robustness, thermal and electrical conductivity, mechanical strength, and ultra-high-vacuum compatibility. For the ultimate ESR bunch charge of 28 nC at 10 GeV, the Al2219-T62 jaw remains below the adopted practical thermal-shock threshold for approximately 50 fully intercepted bunches and below the localized melting threshold for approximately 100 bunches under the reference impact conditions considered. These results provide an engineering input to the machine-protection requirements, for which a complete protection response within several machine turns is required. Optimization of the absorber-tip length yields a 70 mm tapered jaw that balances collimation performance, beam-impact robustness, and impedance. The resulting design maintains acceptable impedance margins and remains below both the yield and ultimate tensile strengths under a conservative 3.6 kW beam-induced heating scenario. The results establish a baseline ESR collimator design and a benchmarked methodology for evaluating collimator robustness in high-current electron storage rings.
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All authors Andrii Natochii, Elke-Caroline Aschenauer, Jay Best, Alexei Blednykh, Xiaofeng Gu, Kuppan Gunavathi, Charles Hetzel, Christoph Montag

Friday 2 October

Accelerator Physics

Quarter-wave shift for an extra pass in an energy recovery linac

Julien Michaud and Alex Fomin

Energy Recovery Linacs (ERLs) are advanced particle accelerators that recover the kinetic energy of the beam after interaction, significantly improving efficiency. In this paper we discuss an alternative operation mode for multi-pass ERLs with an extra pass at top energy, allowing a doubled beam current at the expense of an increased energy spread. We explain the theoretical concept behind this approach, detailing how the phase shift enables an extra acceleration pass without requiring additional hardware. Preliminary simulations on a lattice similar to the PERLE one explore the feasibility of this method. The results are discussed in the context of ERL performance optimization, and potential applications for future accelerator designs are explored.
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Thursday 1 October

Accelerator Physics

From Simulation to Fabrication: Realizing Silicon Crystalline Undulators with Silicon Nitride Stressor Layer Patterning

L. Malagutti, L. Bandiera, F. Bonafè et al. (+14 more)

A crystalline undulator is a crystal exhibiting periodic deformations that cause channeled particles to oscillate, generating coherent electromagnetic waves. In this study, stressor layer patterning has been employed to induce the desired deformations on a silicon substrate. Finite element method simulations were performed to optimize the geometric parameters of the undulator. The primary focus was on achieving sinusoidal deformation with sub-millimeter period and amplitude exceeding 1~nm, utilizing the silicon (110) plane for its superior channeling properties. Key parameters, such as substrate thickness and undulator period, were meticulously refined to ensure uniform deformation while minimizing the impact of higher harmonics, which could degrade performance. Based on the simulation results, a crystalline undulator, 160 $\mu$m thick and consisting of 10 periods with a period length of 334 $\mu$m, has been successfully fabricated. The final device demonstrates structural integrity and a uniform deformation extending up to 20 $\mu$m from the surface. Specifically designed for use with 5-30 GeV particle beams, the undulator is capable of generating gamma photons in the 5-15 MeV range. This work effectively integrates advanced simulation techniques with precise fabrication methods, demonstrating the feasibility of crystalline undulators as high-performance devices for generating gamma radiation.
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All authors L. Malagutti, L. Bandiera, F. Bonafè, N. Canale, D. De Salvador, P. Fedeli, V. Guidi, A. V. Korol, F. Mancarella, R. Negrello, Gianfranco Paternò, M. Romagnoni, F. Sgarbossa, A.V. Solov'yov, A. Sytov, D. Valzani, A.Mazzolari

Accelerator Physics

The JO&Minna Framework: A Method to Interpret Depth Profiles of Activation

Edil Mustafin

A novel analytical framework, designated as the JO&Minna method, is presented for interpreting the depth profiles of residual activation induced by heavy-ion beams in thick structural materials. By combining the limiting fragmentation and factorization principles, the JO-factor formalism rigorously links the spatial distribution of projectile-like fragments to the range derivatives and electronic stopping powers. Furthermore, the Minna procedure establishes a mathematical link via profile differentiation and convolution analysis to reconstruct the original energy spectrum and energy spread of the fragments from the measured activity profiles. The methodology is benchmarked using experimental data for $^{46}\text{Sc}$ production from $^{238}\text{U}$ irradiation in aluminum, demonstrating a reliable and straightforward approach for extracting fragment production kinematics and energy distributions in accelerator materials research.
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Accelerator Physics

High-Field Brightness Limits of Alkali-Antimonide Photocathodes

Peng-Wei Huang, Zhiyuan Wang, Xinlong Cao et al. (+6 more)

Pushing the brightness limit of electron sources requires simultaneously minimizing the intrinsic emittance and maximizing the accelerating field. Alkali-antimonide photocathodes exhibit excellent properties at low fields, yet their high-field photoemission physics remains poorly understood owing to acute vacuum sensitivity. Here, we demonstrate robust photoemission from alkali-antimonide photocathodes in a radio-frequency gun at peak fields exceeding 100 MV/m, with quantum efficiency maintained above 1% for more than two weeks, enabling the first systematic measurements of their high-field brightness limits. The measured field dependence of the intrinsic emittance provides direct insight into photoemission physics at high fields. Near-threshold photoemission further reduces the intrinsic emittance, increasing the attainable brightness, and reveals constraints imposed by surface roughness. This work opens the high-field regime for advanced photocathodes, extending the brightness limits of electron sources.
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All authors Peng-Wei Huang, Zhiyuan Wang, Xinlong Cao, Zhuoxuan Liu, Lianmin Zheng, Yingchao Du, Wenhui Huang, Chuanxiang Tang, Renkai Li

Wednesday 30 September

Accelerator Physics

Recent radiological studies at NSLS-II using the Monte Carlo code FLUKA

Ricardo dos Santos Augusto and Robert J. Lee

This work details some of the recent radiological studies performed at National Synchrotron Light Source II (NSLS-II) using the Monte Carlo (MC) particle transport code FLUKA. In particular, it assesses the radiation protection challenges posed by the anticipated NSLS-II facility upgrade, taking into consideration various upgrade options. Also, it evaluates the impact related to the use of different shielding materials and the employment of ambient dose H* as the external radiation exposure estimator of effective dose. Lastly, a demonstration of synchrotron radiation transport is provided for an in-silico beamline, all the way from the radiation source to end-station, utilizing FLUKA's recent X-ray reflectivity capabilities.
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Accelerator Physics

Compact ultrafast intense LWFA-driven crystal-based source of $\gamma$-radiation, positrons and neutrons

Alexei Sytov, Hyeon Myung Jeong, Leejin Bae et al. (+5 more)

Compact sources of intense $\gamma$-rays, positrons and neutrons can bring radiation and particle-beam capabilities to small university-scale laboratories that would otherwise rely on large accelerator facilities. Here we propose and simulate a compact, laser-driven source that combines laser plasma wakefield acceleration (LWFA) with oriented crystalline targets to enhance the conversion of relativistic electron beams into high-energy photons and secondary particles. Electrons aligned with major crystallographic directions undergo coherent interactions, including channeling radiation and coherent bremsstrahlung, producing substantially enhanced photon emission compared with amorphous targets. Moreover, the strong angular-spectral correlation of the emitted radiation enables the generation of collimated $\gamma$-ray beams with reduced spectral bandwidth. Consequently, crystal-enhanced emission can increase particle-production efficiency, namely that of positrons through $\gamma$ conversion into electron-positron pairs and of neutrons through photonuclear reactions. Using Geant4 simulations, we investigate electron energies of 300 MeV, 1 GeV and 3 GeV interacting with an oriented tungsten crystal. Crystal orientation increases the $\gamma$-ray, positron and neutron yields by up to a factor of $\sim2$, reaching production rates of $\sim10^{24}\gamma/s$, $\sim10^{23}e^+/s$ and $\sim10^{21}neutrons/s$ for a 200 pC electron bunch with a duration of a few fs. The collimated $\gamma$-ray brightness reaches $\sim10^{24}\gamma/s/mm^2/mrad^2/0.1\%BW$, with an enhancement of 6-8 compared with random crystal alignment. We further demonstrate tunable quasi-monochromatic radiation through coherent bremsstrahlung in a thin diamond crystal, reaching a brilliance of $\sim3.5\cdot10^{20}\gamma/s/mm^2/mrad^2/0.1\%BW$. Furthermore, we discuss the potential applications of the technique proposed.
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All authors Alexei Sytov, Hyeon Myung Jeong, Leejin Bae, Iryna Chaikovska, Hyoeun Choi, Gianfranco Paternò, Laura Bandiera, Inhyuk Nam

Accelerator Physics

Beam Tracking I & II

Helga Timko

Longitudinal beam dynamics simulations are an essential tool for the design and operation of circular and linear accelerators alike, fundamentally supporting everything from RF system design to the interpretation of beam-based measurements. This paper gives a practical, self-contained introduction to longitudinal beam tracking, aimed at newcomers to the field who wish to build, or better understand, their simulation tools. Starting from the analogy between beam tracking and particle-in-cell plasma simulations, the basic equations of motion, their discretisation, and the choice of phase-space coordinates are introduced, followed by the collective effects driven by the machine impedance. The modelling of the RF system and its associated control loops, and the generation and matching of realistic particle distributions are discussed thereafter. Selected topics that require a fully six-dimensional treatment are briefly touched upon, before closing with practical guidance on the design, optimisation, and benchmarking of longitudinal tracking codes.
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Accelerator Physics

Emittance tuning of the FCC-ee high energy booster ring

Quentin Bruant, B Dalena, A Chance et al. (+4 more)

The Future Circular Collider (FCC), in its leptonic configuration has been chosen by CERN as main proposition for the next high-energy collider. This project aims to achieve luminosities one to two orders of magnitude higher than ever. Feasibility studies have led to the definition of tolerances on magnet imperfections and correction strategies. This is crucial for ensuring the performance of one of the main elements of the acceleration chain, the High Energy Booster (HEB) ring. The efficiency and overall performance of these strategies greatly influence new magnet specifications and tolerances, affecting main optic functions. Horizontal and vertical orbit corrections use horizontal and vertical kickers, respectively. Skew quadrupoles address vertical dispersion and transverse coupling. Normal quadrupoles correct the horizontal and vertical phase advances. This study simulates the distribution of these four corrector types to minimize the equilibrium emittance at the extraction energy of 45.6 GeV. The calculated strengths of these correctors and the associated misalignments are presented. The study also discusses the limitations and drawbacks of the proposed correction strategy.
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All authors Quentin Bruant, B Dalena, A Chance, V Gautard, F Bugiotti, Adnan Ghribi, R Tomas