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Physics Physics Accelerator Physics

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Tuesday 29 September

Accelerator Physics

Liquid xenon positron target flow optimizations

Max Varverakis, Spencer Gessner, Silviu Covrig Dusa et al. (+3 more)

In a previous work, we explored liquid xenon (LXe)-based positron targets as an alternative to conventional high-Z metallic targets for high energy physics applications. In this paper, we apply computational fluid dynamics simulations to the LXe target and containment vessel, including entrance and exit windows. We design a flow geometry that is able to quickly move heated LXe from previous beam pulses out of the target volume without significant boil-off. While our simulations indicate that the temperature of the exit window can be kept stable, the peak energy deposition density exceeds the widely accepted damage threshold of 35 Jg$^{-1}$ for ILC-like conditions.
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All authors Max Varverakis, Spencer Gessner, Silviu Covrig Dusa, Joseph Grames, Nathan Majernik, Sanjeev Chauhan

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

Laser-Polarization Dependence of Betatron X-Ray Production and Angular Collection in Laser-Wakefield Acceleration

Andrei Ciprian Berceanu, Vojtěch Horný, Dan Stutman et al. (+1 more)

Laser polarization affects both the production of betatron x rays and their angular distribution, which together determine the photon yield collected within a fixed angular acceptance. We investigate these effects using particle-in-cell simulations of laser-wakefield acceleration with linearly polarized (LP) and circularly polarized (CP) pulses of equal energy in helium–nitrogen targets of two different lengths. In the longer target, CP produces more photons early in propagation, whereas LP produces more later. For 20–60-keV photons transmitted through 2 mm of aluminum, the LP/CP yield ratio before angular selection changes from 0.88 early on to 1.91 in a late stage. Late-emitting LP electrons develop pronounced transverse oscillations along the laser polarization direction, accompanied by angular broadening of the radiation. This broadening largely removes the late LP production advantage within a central $\pm5$-mrad acceptance, where the two yields are nearly equal. Integrated over the full interaction, however, LP supplies more central photons, while CP provides more uniform illumination. In the shorter target, the extracted charges above 100 MeV are nearly equal, yet transport through a quadrupole triplet delivers 750 pC for LP and 500 pC for CP in the 350–500-MeV energy band within a radius of 5 mm. Collected photon and electron yields are thus shaped by propagation length and collection acceptance.
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All authors Andrei Ciprian Berceanu, Vojtěch Horný, Dan Stutman, Paolo Tomassini

Accelerator Physics

Input to the SCAC Facilities Subcommittee from the U.S. Muon Collider Collaboration

S.Jindariani, T.Holmes, P.Meade et al. (+5 more)

This document presents input from the U.S. Muon Collider Collaboration to the SCAC Facilities Subcommittee. It outlines the scientific motivation for a future Muon Collider, the R&D and demonstration program needed to establish its feasibility, and its relevance to U.S. facilities planning for 2026-2036. It also discusses opportunities for leveraging existing U.S. capabilities, developing the accelerator workforce, and building synergies with other DOE programs and international efforts.
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All authors S.Jindariani, T.Holmes, P.Meade, K.DiPetrillo, K.Kennedy, L.Lee, S.Pagan Griso, D.Stratakis

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

Electron Rephasing in a Truncated Tunable Plasma Channel

Arujash Mohanty, Santhosh Krishnamurthy, Yinren Shou et al. (+6 more)

We report the acceleration of stable electron beams with energies up to 1.5 GeV using a 50 TW laser pulse guided in a preformed plasma channel generated by an axiparabola-focused heater pulse. Varying the channel length changes the plasma density beyond the channel end and produces distinct electron spectra. A short channel causes a large decrease in bubble size after the truncated channel, leaving only part of the electron bunch in the accelerating phase and resulting in a quasi-monoenergetic peak. For a longer channel ending near the target density down-ramp, the smaller density increase rephases and further accelerates a larger fraction of the bunch, producing a continuous high-charge spectrum. Hydrodynamic and particle-in-cell simulations reproduce the observed spectral evolution. Together, the measurements and simulations identify channel length as a key control parameter in guided laser-wakefield acceleration.
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All authors Arujash Mohanty, Santhosh Krishnamurthy, Yinren Shou, Sheroy Tata, Anton Golovanov, Anda-Maria Talposi, Aaron Liberman, Eyal Kroupp, Victor Malka

Accelerator Physics

Calculation of the temporal structure for a pulsed slow positron beam based on superconducting accelerator

H. Q. Zhang, P. Kuang, Y. H. Hu et al. (+4 more)

The development of superconducting accelerator (SCA) provides a novel approach to generating pulsed slow positron beams with high time resolution and high intensity. SCAs can produce electron beams with repetition frequencies on the order of MHz and pulse widths of less than 100 ps. A pulsed positron beam based on SCA can, to a certain extent, preserve the excellent temporal structure of the primary electron beam. However, thermalization, diffusion, and surface re-emission of positrons in the moderator will inevitably lead to time broadening of positron pulses. In this paper, a calculation model coupling Geant4 Monte Carlo simulations with positron diffusion theory is established to evaluate the effect of the positron moderation process on time broadening. After being moderated by a tungsten foil, the initial time broadening of the pulsed slow positron beam is approximately 320 ps. By combining the time broadening calculation of pulsed beam during its transport, it is expected that the pulsed slow positron beam generated by the SCA, can be directly applied to the measurement of positron annihilation lifetime.
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All authors H. Q. Zhang, P. Kuang, Y. H. Hu, F. Y. Liu, X. Z. Cao, B. Y. Wang, X. P. Li

Monday 28 September

Accelerator Physics

Terahertz-driven electron acceleration from subrelativistic to fully relativistic energies in stepped dielectric-lined waveguides

Filip J. Peczek, Laurence J. R. Nix, Graeme Burt et al. (+6 more)

The short wavelength of terahertz (THz) waves makes the acceleration of electrons, from typical electron gun energies to fully relativistic energies, challenging due to the need to match the velocities over comparably long distances. However, the inherent laser synchronisation of a photogun to the THz drive laser offers significant advantage in applications where timing is critical. We present a novel design process for high-gradient THz-driven dielectric-lined waveguide injectors and demonstrate designs for rectangular and cylindrical geometries. These structures utilize novel tapering and stepping schemes to manipulate the phase velocity, controlling the position of the electron bunch relative to the phase of the accelerating field. We demonstrate a hybrid optimisation method utilizing firstly a multi-objective genetic algorithm based on analytic models of the waveguide accelerating modes, and then high-detail particle-in-cell simulations. Our example designs achieve electron acceleration from 100 keV to 1 MeV over a distance of 20 mm by interacting with a multicycle 0.5 mJ, 0.2 THz pulse, paving the way for the realisation of THz-based injectors. The exit beam shows excellent beam quality with 50 fs bunch lengths, sub 0.5% energy spread and emittances of under 0.15 {\mu}rad. We also present an analysis of the robustness of the designs to errors in machining and operational parameters demonstrating the feasibility of the concept. We show that using multi-objective genetic algorithm optimization and robust design process, we can achieve high-quality 1 MeV beams.
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All authors Filip J. Peczek, Laurence J. R. Nix, Graeme Burt, Rosa Letizia, Joseph T. Bradbury, Darren M. Graham, Morgan T. Hibberd, Steven P. Jamison, Robert B. Appleby

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

Electrons with Anomalous Energy Generated in Vacuum Diodes with Different Pulse Duration

Vasily Kozhevnikov, Victor Tarasenko, Maxim Vorobyov et al. (+2 more)

This paper presents results from an experimental study in which anomalous energy electrons (AEE) appear in vacuum diodes under varying amplitude and pulse-duration conditions. AEE refer to high-energy discharge electrons with kinetic energy $T$ exceeding $eU$ values (where $e$ is the electron charge and $U$ is the amplitude gap voltage). Here, two experimental setups were used to generate electron beams with different pulse durations. The electron energy spectra were reconstructed from the beam attenuation curves using an AI-driven methodology for solving an ill-posed inverse problem for the Fredholm equation. This confirms that vacuum diodes generate electron beams with a significant AEE fraction (up to 25~%) only when operating with nanosecond-long voltage pulses. It has been confirmed that AEE in vacuum is generated using nanosecond- or sub-nanosecond voltage pulses. Experiments also indicate that photoelectric absorption of bremsstrahlung cannot produce significant AEE in vacuum discharges.
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All authors Vasily Kozhevnikov, Victor Tarasenko, Maxim Vorobyov, Evgenii Baksht, Andrey Kozyrev

Sunday 27 September

Accelerator Physics

Circular-Mode Optics for High-Intensity Beams and High-Luminosity Colliders

Onur Gilanliogullari, Brahim Mustapha and Pavel Snopok

We study circular-mode optics as a framework for transporting and accelerating intrinsically flat beams while maintaining a round transverse projection in physical space. Motivated by the strong degradation of flat beams under low-energy space-charge forces, we develop a coupled-optics description of circular modes, analyze their formation and preservation, and derive lattice design conditions for conserving canonical angular momentum and coupling phase. These conditions motivate rotationally invariant transport and ring cells based on solenoids, symmetric alternating-gradient structures, and indexed dipoles. We further derive space-charge tune-shift and tune-spread expressions for circular-mode beams in uncoupled and coupled lattices, showing that they preserve the leading-order space-charge behavior of round beams while retaining intrinsic eigenemittance flatness. Particle-in-cell simulations with TRACK and ImpactX confirm the generation, transport, and acceleration of circular-mode beams in representative lattices, including regimes with strong space charge. Circular-mode optics therefore provides a promising route toward high-intensity hadron beams and high-luminosity collider applications.
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Accelerator Physics

Magnetizing nonlinear plasma wakefields for positron acceleration: mechanism and operating limits

Yung-Kun Liu, Pisin Chen, Ching-En Lin et al. (+2 more)

Positron acceleration is possible in linear plasma wakes, but the nonlinear electron-driven blowout regime confines simultaneous acceleration and focusing to narrow regions of returning plasma electrons. Here we investigate how an axial magnetic field reorganizes this nonlinear return to open an operating regime for sustained positron acceleration in a uniform plasma. Using quasi-3D and full-3D particle-in-cell simulations, we connect the formation of finite-radius electron columns, or gyro images, to witness transport and its operating limits. The image spacing is governed by the quasi-static invariant, while canonical angular momentum limits the return radius. Modified by the orbit-sampled wake potential, this mechanism yields a positioning law that accurately predicts the density peaks across a wide range of magnetic field strengths. At a plasma density of $10^{16} cm^-3$ and a 35 T axial field, the reorganized structure expands the usable accelerating and focusing interval by more than a factor of four compared to the unmagnetized case. A positron witness bunch placed at the settled phase of this band achieves 92% capture over a 60 mm stage, with the normalized emittance saturating at 83 mm mrad. Independent codes confirm sustained transport, yielding energy gains between 99 and 150 MeV, though numerical convergence on the exact energy gain remains an open challenge. Together with beam loading, alignment, and driver-energy scaling tests, these results establish magnetic control of the nonlinear electron return as a route to single-stage positron acceleration. Beam quality preservation, formation-transient control, and solenoid integration define the necessary next development steps.
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All authors Yung-Kun Liu, Pisin Chen, Ching-En Lin, Spencer Gessner, Bernhard Hidding

Saturday 26 September

Accelerator Physics · Cross-listed from cond-mat.other

Physics-based logarithmic description of electrostatic field enhancement in hemisphere-on-cylindrical-post structures for high-field applications

Thiago A. de Assis, Fernando F. Dall-Agnol and Richard G. Forbes

Electrostatic (ES) field enhancement at sharp conducting structures plays a central role in lightning protection, corona discharge, electrical breakdown in vacuum (for example in particle accelerators), and more generally in technological applications of field electron emitters. A canonical geometry for studying this ES effect is the hemisphere-on-cylindrical-post (HCP) model, in the regime where the structure stands on a planar conductor of large lateral extent, and a large gap exists between the structure and the counter-electrode. A parameter of major interest is the apex field enhancement factor (AFEF) (apex-ES-field/background-ES-field). For this (and other) structures, a formula for the AFEF can be written in the form AFEF = ASC x ASR, where the apex sharpness ratio (ASR) is given by the ratio (post-height/apex-radius-of-curvature), and the apex sharpness coefficient (ASC) depends on the post shape. For the HCP model, no exact analytical formulas for the ASC or the AFEF are currently known. (Quite possibly none exist.) This paper develops a compact analytical approximation for the ASC and hence for the AFEF. This compact formula has a logarithmic-style structure, rather than the power-style structure used in previous approximations. When compared with precise finite-element analyses of the HCP model, over the computationally accessible range 1 to 1000 for the ASR, this logarithmic-style formula has a maximum error-magnitude of 0.15 percent, which is significantly better than older approximations.
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Accelerator Physics · Cross-listed from physics.soc-ph

Hydrogen mon amour

Christophe Grojean and Patrick Janot

The FCC's projected average electricity consumption is 1.3 TWh per year. If supplied entirely by nuclear power, this would represent about 10% of the annual output of a large third-generation nuclear reactor, together with a corresponding share of its radioactive waste. By 2050, however, renewable sources could provide up to 80% of this electricity on a substantially decarbonised European grid, supported by long-term power-purchase agreements and flexible operation. This could reduce the residual nuclear requirement, and its associated waste, by up to a factor of five. This essay asks whether hydrogen could help bridge the remaining periods of low wind and solar generation. It examines production from renewable electricity, transport as hydrogen or ammonia, storage and conversion back into electricity, together with their efficiency losses and carbon footprints. It then considers the still uncertain prospect of naturally occurring hydrogen. None of these routes offers a ready-made solution. But the decades before the FCC begins operation leave time to develop one–and CERN could help accelerate that development by becoming a credible long-term customer.
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Friday 25 September

Accelerator Physics

Incorporating Heightened Scrutiny into a Large HEP Software Project

Philippe Canal, Chris Green, Kyle Knoepfel et al. (+5 more)

In 2023, DUNE began re-evaluating the requirements of its data-processing framework, which led to commissioning a new design that would better fit neutrino physics than the existing reconstruction frameworks designed for collider physics. Due to the radical changes expected, significant multi-institutional effort has been directed toward the creation of the Phlex framework. In addition, the tight timelines in which to implement such a framework have invited scrutiny from various parties, including DUNE itself, the host laboratory Fermilab, and the US Department of Energy. After briefly discussing the unique needs of neutrino physics, we will recount how the Phlex development team has approached the design and development of a framework in the context of this heightened scrutiny. This process began with a systems-engineering approach to formally manage the requirements DUNE has of its framework. What followed was, for the first time in the HEP community, a review of the framework's conceptual design by a panel of external framework experts before developers proceeded to the implementation. The implementation efforts have led to a series of prototypes that are being used to provide rapid feedback from Phlex users to framework developers. We will discuss how each of these steps has resulted in a strong design that has the backing of the DUNE experiment, Fermilab, and the US Department of Energy.
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All authors Philippe Canal, Chris Green, Kyle Knoepfel, Wim Lavrijsen, Adam Lyon, Marc Paterno, Saba Sehrish, Beojan Stanislaus

Accelerator Physics

Generation of 10-TW Attosecond X-Ray Pulses in a Free Electron Laser

E.A.Schneidmiller, S.Serkez, I.Zagorodnov et al. (+35 more)

Attosecond pulses provide direct access to electron dynamics in atoms, molecules, and solids on their natural timescales. While table-top sources have achieved attosecond pulse durations at moderate intensities, extending attosecond science to high peak powers in the x-ray regime requires free-electron lasers (FELs). Here we report the generation of soft-x-ray pulses with a duration of $\sim\!100$ as and peak power on the order of 10 TW at the European XFEL. The unprecedented combination of pulse duration and peak power is enabled by operation of a soft-x-ray undulator at high electron energy together with five-stage bunch compression, producing ultrahigh peak currents. These millijoule-level attosecond x-ray pulses establish a new regime for attosecond science.
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All authors E.A.Schneidmiller, S.Serkez, I.Zagorodnov, N.Gerasimova, M.Scholz, N.Golubeva, M.Guetg, G.Geloni, S.Karabekyan, F.Sottocorona, A.Trebushinin, G.Perosa, S.Tomin, F.Mayet, Th.Maltezopoulos, J.Gruenert, J.Laksman, H.Ahmadi Rashtabadi, T.M.Baumann, R.Boll, F.Calegari, G.Catacchio, S.Dold, D.E.Ferreira de Lima, L.Funke, W.Helml, M.Ilchen, T.Mazza, M.Meyer, T.Mullins, M.Robinson, S.Savio, K.Scharei, Ph.Schmidt, A.Thiel, S.Usenko, L.Wuelfing, W.Decking

Accelerator Physics

Fabry-Pérot Resonance Shifts as a Novel Non-destructive In Situ Surface Damage Diagnostic

Gregory Blume, Colin Kirk, Sushil Poudel et al. (+6 more)

Current surface damage evaluation for nanostructured electronic devices requires specialized equipment or conditions outside the designed operating environment and cannot be used for in situ evaluation of surface damage. In this work, we developed a non-destructive method to probe the surface sublimation of a semiconductor heterostructure which can be applied to other semiconductor damage mechanisms. This approach employs shifts in the resonances of an optical cavity comprising the surface and an integrated distributed Bragg reflector fabricated below the semiconductor heterostructure undergoing sublimation. We performed the demonstration of this technique under vacuum, but surface damage effects can be observed in any operational environment either in situ or ex situ.
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All authors Gregory Blume, Colin Kirk, Sushil Poudel, John Hill, Alimohammed Kachwala, Joseph Grames, Marcy L. Stutzman, Matt Grau, Sylvain Marsillac

Thursday 24 September

Accelerator Physics · Cross-listed from eess.SY

From Routing Delay Shifts to Silent Data Corruption: Neutron-Induced SEU Effects in AXI-Based Zynq UltraScale+ MPSoCs

Mostafa Darvishi

SRAM-based FPGA system-on-chip devices are vulnerable to single-event upsets (SEUs) in configuration memory, which may perturb programmable routing resources and degrade communication fabrics. In modern Zynq UltraScale+ MPSoCs, such routing disturbances can introduce small propagation delay shifts that remain logically transparent yet compromise AXI-based data transfers and lead to silent data corruption. Although routing delay degradation and AXI interconnect failures have been studied independently, their experimental correlation under neutron irradiation has not been established. This work presents a cross-layer investigation on a ZCU104 platform integrating routing-dominated delay sensors with an AXI interconnect benchmark comprising replicated accelerators. Neutron irradiation experiments were conducted on the fully operational system, while a frame-level configuration fault injector implemented via the internal configuration access port enables controlled upset emulation. Measured routing delay events are statistically correlated with communication failures, and cross-sections for both timing shifts and AXI malfunctions are derived. The results experimentally demonstrate how neutron-induced routing perturbations propagate into system-level silent data corruption in UltraScale+ MPSoCs, providing insight for resilience-oriented AXI-based design in neutron-rich environments.
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Accelerator Physics · Cross-listed from hep-ex

Climate, Science, and the FCC: Think Clearly, Choose Wisely, Act Swiftly

Patrick Janot and Christophe Grojean

Could a collider become the symbol of everything that must be abandoned to save the climate? In the summer of 2026, this question ran through discussions within the Particles and Fields Division of the French Physical Society. An unacceptable carbon footprint, two EPR nuclear reactors, five hundred deaths, billions to be reallocated and, to top it all, unclear scientific objectives: the objections to CERN's Future Circular Collider (FCC) appeared to form an overwhelming indictment. This essay examines each charge in turn. Grounded in a clear and compelling scientific vision, it confronts emotionally charged imagery with orders of magnitude, distinguishes a project's footprint from its full balance sheet, considers the costs of postponing or abandoning it, and explores ways of reducing its impacts-including the still uncertain prospect of natural hydrogen. The climate alone does not decide the future of the FCC; it requires us to judge the available choices by their real consequences. Developed for the public debate organised by France's National Commission for Public Debate (CNDP) and for the Swiss consultation, this essay is intended for the broadest possible readership, well beyond particle physics and the scientific community. It frames the FCC debate as a choice about the kind of society we want to build: should we organise society around renunciation and ever-shrinking horizons, or transform how we produce and choose a future worth wanting?
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2609.30180 · 24 Sep · The present text expands and unifies eight earlier essays arising from discussions on climate change and the FCC held in summer 2026 within the Particles and Fields Division of the French Physical Society (SFP). Version 2 includes the arXiv reference to the companion paper 'Hydrogen mon amour' (arXiv:2609.32307) and a few formulation improvements

Abstract PDF $CLIM ×3$CLDR ×2$VISN ×1

Accelerator Physics

Production of a Titanium Ion Beam Using Fluorides and Fluorine-Forming Precursors in an ECR Ion Source

D.K. Pugachev, K.I. Berestov, A.E. Bondarchenko et al. (+7 more)

The production of multiply charged titanium ions is of significant interest for accelerator-based experiments, surface modification technologies, and applications in nuclear physics. Due to the low saturated vapor pressure of titanium at temperatures below 1000 {\deg}C, the generation of titanium ion beams from an electron cyclotron resonance ion source (ECRIS) remains a challenging task. The choice of titanium vapor injection methods into the ECR plasma plays a key role in achieving high ionization efficiency, plasma stability, and reliable long-term source operation. In this work, alternative approaches for the injection of neutral titanium atoms into the ECR plasma are investigated, focusing on the use of fluorine-containing compounds. Titanium fluorides (TiF3, TiF4) possess a relatively high saturated vapor pressure at moderate temperatures, allowing to use standard resistively heated ovens operating up to 1000 {\deg}C. Another method involves the in-situ formation of titanium fluorides inside the plasma chamber via chemical reactions between metal titanium and the dissociation products of sulfur hexafluoride (SF6). These approaches enable controlled and efficient titanium injection into the ECRIS plasma with satisfactory extracted ion beam stability.
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All authors D.K. Pugachev, K.I. Berestov, A.E. Bondarchenko, V.N. Loginov, A.N. Lebedev, E.Yu. Kidanova, K.I. Kuzmenkov, V.E. Mironov, D.S. Podoinikov, D.S. Yakovlev

Wednesday 23 September

Accelerator Physics

Imaging with GeV muons produced via laser-wakefield-accelerated electrons

M. Dobre, P. Ghenuche, A. Balaceanu et al. (+15 more)

Artificially generated muon beams, with tunable parameters, are highly valuable in imaging objects that are opaque to any other scanning technique. Lower-energy muon beams are currently produced at accelerator facilities, while higher energies have only recently been observed as a result of the interaction of laser-wakefield-accelerated electrons and solid targets. This work focuses on using muography imaging detectors to measure the profile of a muon beam generated via the Bethe-Heitler process and to perform muon imaging in an experimental setup extending up to 42 meters from the muon source. By comparing the data with Monte Carlo simulations, we confirm that the measured beam profile and object imaging are consistent with artificially produced muons of energy of a few GeV. To our knowledge, this represents the first demonstration of imaging dominated by an artificial, laser-driven muon beam.
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All authors M. Dobre, P. Ghenuche, A. Balaceanu, D. Catana, M.O. Cernaianu, D. Dorobantu, R. Lica, V. Malka, D. Martello, I. Mitu, M. Niculescu-Oglinzanu, L. Stan, D. Stanca, P. Tomassini, C.A. Ur, C. Vancea, A. Saftoiu, D. Doria

Accelerator Physics

Development and Testing of Tools for ORM Measurements and Quadrupole Centering

A. Pathak, E. Chen and A. Shemyakin

In preparation for the commissioning of Linac2 (formerly referred to as the {PIP-II} linac) at Fermilab, we are developing high-level applications that automate Orbit Response Matrix (ORM) measurement and beam-based localization of quadrupole magnetic centers. Both procedures are designed to run in a low-amplitude mode compatible with otherwise regular operation. The ORM is measured by exciting multiple dipole correctors simultaneously at low amplitude, each at a distinct frequency, and applying a Discrete Fourier Transform to the recorded BPM signals to extract per-element transfer function with quantified noise. One application of the measured ORM is to predict the corrector coefficients that form local orbit perturbations (bumps). To center the trajectory in a quadrupole, such a bump is created around it, the quadrupole current is oscillated, and the responses of the downstream BPMs are recorded and analyzed. Repeating this at several beam positions inside the quadrupole – each set by the bump – the dependence of the BPM signal on beam position provides information about the quadrupole center. The applications are being tested at the Fermilab 400\,MeV Linac during regular production runs, and the lessons learned are fed back into their improvement.
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Accelerator Physics

Vector Potential-based Beam Current Sensors: Applications for Mu2e, and Picosecond Bunch Substructure

P. W. Gorham, M. T. Hedges, R. Kim et al. (+8 more)

We report on a new beam current monitor system based on work originally done to develop timing planes for future collider detectors. In contrast to sensors based on wall currents or toroid inductance, we make use of electric field induced by the electromagnetic vector potential of the beam current as it passes near or through a transmission line (TL), arranged with its dominant TEM or TE10 fields aligned with the current, thus directly coupling to TL modes. For resonantly extracted proton pulses currently being commissioned at the Fermilab Delivery Ring, we utilized a TEM parallel-plate TL geometry, since the requirements included measuring the structure of the bunch over $\sim{}200~\rm{ns}$ time scales. We present the design and results of simulated and realized sensors now deployed at Fermilab for future use as pulse-to-pulse proton intensity monitors at the Mu2e experiment. In addition, inspired by this and prior work, we investigate the use of broadband mm-wave dual-ridge waveguides as a means of measuring substructure of nanosecond bunches down to the tens of picosecond level for future use at the Long Baseline Neutrino Facility (LBNF).
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All authors P. W. Gorham, M. T. Hedges, R. Kim, P. M. Lewis, K. Lynch, C. Miki, J. Morgan, N. Nyza, D. Pang, T. Polischuk, D. Still

Accelerator Physics

Integration of Retrieval-Augmented Generation for Knowledge Access in the ELBE Accelerator Control System

Najmeh Mirian

The efficient operation of accelerator facilities increas- ingly relies on rapid access to heterogeneous operational knowledge, including logbooks, interlock reports, machine parameters, and historical archive data. At ELBE, we pro- posed a Retrieval-Augmented Generation (RAG) frame- work that integrates facility documentation and operational records into a unified AI-assisted support tool for operators. The system is expected to index electronic logbooks, ma- chine archive time-series data, and subsystem manuals using domain-adapted embeddings stored in a vector database. User queries will be expected to be processed through a large language model that retrieves the most relevant oper- ational context and generates structured, operator-oriented responses with traceable source references. This contribu- tion presents the system architecture, data integration strat- egy, and challenges toward real-time AI-assisted accelerator operation
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Tuesday 22 September

Accelerator Physics

Thermomechanical rf breakdown from magnetically focused field emission in high-gradient normal-conducting cavities

Dillon Merenich, Xueying Lu and Tianhuan Luo

Normal-conducting radiofrequency (rf) cavities for muon-collider ionization cooling must operate at high accelerating gradients in strong solenoidal magnetic fields, where rf breakdown can be enhanced by the magnetic focusing of field-emitted electrons. In this work, field-emitted electrons were tracked in the realistic field maps of rectilinear cooling-lattice cavities to test the validity of the previously developed localized-bombardment picture with simplified field maps. Under comparable reduced-field assumptions, the tracking results show good agreement with previous results. The full rf eigenmode fields and nonuniform solenoidal fields modify the idealized beamlet structure, producing rf phase dependent centroid shifts and broadened impact distributions from solenoid fringe fields. Nevertheless, the original model remains a useful framework for estimating limits on operating gradients. The thermal response is evaluated analytically using this model, with material properties varied to assess the coupled effects of heat transport and thermomechanical damage threshold. These results can inform cavity testing in strong solenoidal fields, muon ionization cooling channel designs, and other applications requiring high-gradient rf operation in magnetic fields.
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Accelerator Physics

Stable 50 MeV Beams from a 100 Hz Laser-Wakefield Accelerator Driven by an OPCPA Laser

S. Smartsev, J. Wheeler, O. Lundh et al. (+12 more)

We demonstrate a laser-wakefield accelerator driven by a high-repetition-rate optical parametric chirped-pulse amplification (OPCPA) laser, producing stable, quasi-monoenergetic electron beams at 100 Hz. Using 70 mJ, 8.1 fs laser pulses, we obtain 47 MeV electron beams with 15 pC charge and an intrinsic energy spread below 10%. Measurements over 10,000 consecutive shots show rms fluctuations of only 1.4% in peak energy and 12% in charge, together with low pointing jitter. Principal-component analysis reveals that the beam fluctuations are described by five physically interpretable modes, dominated by slow variations below 1 Hz. Particle-in-cell simulations reproduce the measured spectrum and show that nonlinear self-focusing localizes ionization injection, resulting in the observed narrow energy distribution. The demonstrated combination of electron energy, charge, beam quality, and stability represents a significant step toward high-average-power laser-plasma accelerators.
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All authors S. Smartsev, J. Wheeler, O. Lundh, I. A. Andriyash, S. Tchetovsky, V. Tomkus, M. Mackeviciute, P. Gecys, G. Raciukaitis, P. P. Gheeta, J. Csontos, M. Samir, C. Kamperidis, D. Papp, J. Faure

Accelerator Physics · Cross-listed from gr-qc

Spacetimes of maximal proper acceleration and muon mean lifetime

Ricardo Gallego Torromé

In this paper, it is shown that in spacetimes of maximal proper acceleration, there is a reduction of the mean lifetime of the muon. We consider several candidates for the maximal proper acceleration. For all of them, the induced corrections are small, but for the case when the maximal proper acceleration is identified with the Schwinger's acceleration, the effect is detectable in future muon collider facilities.
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Monday 21 September

Accelerator Physics

Bayesian Optimization of The Relativistic Heavy Ion Collider Luminosity via $s^*$ Control

Xiaofeng Gu, Benjamin Coe, Guillaume Robert-Demolaize et al. (+7 more)

Maximizing luminosity at the interaction point (IP) requires the collision location $s_{IP}$ to coincide with the longitudinal position of the minimum beta function, $s^$. Accurate optics measurements and control of $s^$ are therefore essential for luminosity optimization. At the Relativistic Heavy Ion Collider (RHIC), average horizontal beta-beat measurements between operating IPs are approximately $20%$, with significant variation in measured $s^*$. Precise control of the beam waist position $s^$ is particularly challenging for modern high-energy colliders with short bunch lengths and large crossing angles. We present an online Bayesian optimization (BO) application using the GPTune framework to optimize sPHENIX luminosity through $s^$ control at RHIC. GPTune was first validated at the RHIC Electron Beam Ion Source (EBIS), where it achieved up to a $70%$ increase in beam intensity over the baseline, although experienced operators could reach similar performance with longer manual tuning. The framework was subsequently deployed during sPHENIX operations. Using an intensity-normalized Zero-Degree Calorimeter (ZDC) signal as the optimization objective, due to the unavailability of the live sPHENIX MVTX signal, GPTune identified local luminosity maxima, recovered from intentionally degraded $s^$ configurations, and revealed residual horizontal and vertical waist offsets in the interaction region. These results demonstrate the robustness and efficiency of Bayesian optimization for real-time collider tuning under noisy, time-varying conditions. The $s^$ control methodology provides a promising tool for precision luminosity optimization and is particularly relevant to next-generation short-bunch colliders such as the Electron-Ion Collider (EIC).
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All authors Xiaofeng Gu, Benjamin Coe, Guillaume Robert-Demolaize, Takeshi Kanesue, Masahiro Okamura, William Fung, Yue Hao, Ji Qiang, Xiaoye S. Li, Yang Liu

Sunday 20 September

Accelerator Physics

Design and Operation of a 3-Crystal Multi-Volume Reflection Array for Loss Reduction in CERN SPS Slow Extraction

F. M. Velotti, M. Bay, T. Calvet et al. (+10 more)

The flux of protons slow-extracted from the CERN Super Proton Synchrotron (SPS) to the North Area experiments is limited by the induced radioactivity of the beam lost on the electrostatic septum during the third-integer resonant extraction. Crystal shadowing, in which a thin bent silicon crystal deflects the portion of beam that would otherwise impinge on the septum wires, has been in operation at the SPS since 2021, and a single crystal at a non-local position halved the extraction losses, short of the fourfold reduction that the activation budget of the future high-intensity operation calls for. In this paper, the design, deployment and operation of a 3-crystal Multi-Volume Reflection Array (MVRA) at the non-local position in the fourth long straight section (LSS4) are presented. The array geometry was designed by Multi-Fidelity Bayesian Optimization (MFBO), combining a multilayer-perceptron surrogate with full particle tracking, which predicts a fourfold loss reduction with three crystals and up to tenfold with an ideally aligned array of four to five. Measurements with beam confirm the prediction: at its optimum the as-built array reduces the losses by the predicted factor of four, and beam dynamics simulations matched to the measured position and angle scans reproduce them to a few per cent. The array has since been used in physics production, held on its operating plateau by an extremum-seeking controller, with a median loss reduction by a factor of 3.6 over 0.1 million extraction cycles relative to the pre-shadowing baseline. The remaining margin to the target, the limitations of the present installation and the upgrade to a 4- or 5-crystal array are discussed.
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All authors F. M. Velotti, M. Bay, T. Calvet, M. Calviani, G. Daher, L. S. Esposito, M. A. Fraser, B. Goddard, M. Howes, V. Kain, E. Matheson, A. Perillo Marcone, R. Seidenbinder

Saturday 19 September

Accelerator Physics

Experimental Verification of Circumferential Bunch Length Variation and Head-Tail Exchange Affecting Microwave Instability in a Storage Ring

Jihong Bian, Xiujie Deng, Arne Hoehl et al. (+5 more)

Classical analyses of microwave instability are built upon the longitudinal adiabatic approximation, which assumes that the bunch length remains constant around the storage ring. However, in a storage ring with small global phase slippage, the bunch length can vary around the ring and some particles can experience head-tail exchange due to the partial phase slippage and transverse-longitudinal coupling. Our theoretical study reveals that these effects can be beneficial for suppressing microwave instability. A new microwave instability threshold evaluation method has been correspondingly proposed to account for these effects. Here we present the first experimental evidence supporting our theoretical analysis. The measurements confirm that the microwave instability threshold can be increased by a factor of up to six compared to the classical prediction in our cases. Our results can also provide practical guidance for the design of extremely short bunch storage rings.
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All authors Jihong Bian, Xiujie Deng, Arne Hoehl, Wenhui Huang, Arnold Kruschinski, Carsten Mai, Markus Ries, Chuanxiang Tang

Friday 18 September

Accelerator Physics

Persistent homology of Hamiltonian orbits with applications to beam physics: Euler-Betti classification and topological chaos indicators

D. Iglesias Tinoco and B. Erdélyi

Estimating the dynamic aperture of circular particle accelerators typically requires expensive long-term tracking. Using classical homology, we construct a two-dimensional theoretical classification of regular and chaotic orbits and use persistent homology for its numerical implementation on short orbit segments. In four dimensions, we introduce topological chaos indicators based on persistent homology and use normal-form theory to apply the classification to two symplectic-plane projections. The methods reproduce the expected organization of regular and chaotic motion in several canonical Hamiltonian systems. Applied to symplectified one-turn maps of a nonlinear lattice model of the Integrable Optics Test Accelerator, the results obtained from the first 200 turns identify the central connected stability region and its surrounding transition to chaos. They are consistent with the short-term dynamic aperture of the electron configuration obtained from $10^4$ turns and the long-term dynamic aperture of the proton configuration obtained from $10^8$ turns. For the configurations studied, persistent homology of short orbit segments predicts the dynamic aperture obtained by substantially longer tracking, potentially reducing the need for exhaustive simulations in studies of existing accelerators and the design of future facilities. The methods could also complement classical chaos indicators and modern approaches based on artificial intelligence.
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Accelerator Physics

Moderator Modeling for High Intensity Slow Positron Sources

Sophie Crisp, Ryland Goldman and Spencer Gessner

Slow positron beams enable diverse applications, from surface-sensitive materials studies to positronium physics, but progress is limited by source intensity and brightness. In linac-based sources, mono-energetic, slow positrons are produced by moderating the broad, divergent distribution of fast positrons produced by high-energy electrons incident on a high-Z target. This process is intrinsically inefficient. Conventional linac-based designs place the moderator close to the target. Tungsten moderators become less efficient when heated by high-power, fast positrons, leading to defect-related losses. Cryogenic moderators, like solid neon, melt when exposed to high-power, fast positrons. Following the method of O'Rourke et al., we use Monte Carlo simulations combined with a diffusion model to investigate how moderator geometry, material, and incident fast positron energy affect slow positron production. We compare single tungsten foil and multi-foil configurations with solid neon moderators in reflection and transmission geometries. We find that for fast positron energies below 300 keV, solid neon offers order-of-magnitude higher efficiency than tungsten due to its larger diffusion length, whereas at MeV-scale energies multi-foil tungsten has higher efficiency due to the maximization of scattering. We also find that including a target proxy in simulation increases low-energy efficiency up to fourfold by allowing a fraction of initially reflected positrons to return to the moderator. We conclude that substantial gains in start-to-end efficiency at linac sources will likely require combining a decelerating cavity with a decoupled cryogenic moderator.
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Accelerator Physics

Approximate solution of an adapted Bethe transport equation for electron scattering in foils

J.M. Corstens

A new semi-analytical model for electron scattering in foils is presented valid for thin foils and electron-beam kinetic energies up to roughly $100$ keV and from 20 keV at a dimensionless foil thickness of $20$, and higher energies for thinner foils. To perform calculations, an approximate solution is constructed by Hankel transforms of an adapted Bethe transport equation for electron scattering. The Wentzel differential cross section is used in the Bethe transport Eq. and resulting integrals are solved analytically or approximated. These approximate solutions of the transport Eq.'s were compared to the Goudsmit-Saunderson solutions in gold, for thin samples with dimensionless thicknesses $\lambda=5,10,20$. We also compare to the Kawrakow \cite{Kawr} model, which uses the small angle approximation. We show that in the regime of $20$ to $100$ keV beam energies, our model performs better than Kawrakow's model and this is opposite above about 100 keV. Exactly, some angularly distributed beams and the influence of energy loss of the beam can be simulated with our model.
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