WEPS
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Wednesday Poster Session: WEPS
04 Jun 2025, 16:00 -
18:00
WEPS002
Performance of the diode stack with resistors to suppress beam instability at the J-PARC RCS
2240
The main source of beam instability in the J-PARC 3-GeV RCS is the impedance of the eight installed kickers. This arises because one end of each kicker magnet is shorted while the other end is left open during beam acceleration. The shorted-end configuration provides the benefit of power savings during beam extraction from the RCS. However, it also excites beam instability. To retain the energy-saving benefit while suppressing beam instability, we developed a diode stack with resistors and inserted it at the open ends of four kickers. This configuration effectively suppresses beam instability for smaller-emittance beams, which are delivered to the MR at J-PARC.
Paper: WEPS002
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS002
About: Received: 26 May 2025 — Revised: 31 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS003
Study of operation above half-integer random resonance in the J-PARC RCS
2244
In the 3-GeV Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), the beam power ramp-up aiming to surpass the design of 1 MW enhances the space charge effect. It pushes the beam toward the structure resonance. To mitigate the beam loss, the operating point is required to be apart from the structure resonance as the beam power ramp-up. However, large beam loss was observed when the operating point was set near the half-integer resonance. Thus, the maximum beam power of the RCS is currently limited so that the beam does not overlap the structure resonance or half-integer random resonance. To address this issue and achieve the beam power ramp-up, we experimentally studied the half-integer resonance compensation using trim quadrupole magnets. In addition, detailed numerical simulations were performed to develop a better understanding. The experimental and numerical results of the operation above half-integer random resonance are presented.
Paper: WEPS003
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS003
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
Coherent synchrotron radiation instability in steady-state microbunching ring
We study the coherent synchrotron radiation instability in a novel synchrotron light source concept, steady-state microbunching storage ring.
Dynamic simulation of collective physics in SSMB storage ring
We simulated the dynamic problems in the SSMB storage ring, such as TMCI, through the dynamic simulation software elegant and discovered its instability threshold current intensity.
GPU-Accelerated Study of Longitudinal Single-Bunch Instability in Electron Storage Rings
Longitudinal single-bunch instability caused by high-frequency impedance poses a major challenge for achieving optimal performance in fourth-generation synchrotron light sources and future electron-positron colliders. Accurate simulations of this instability are critical but computationally intensive, requiring millions of macro-particles and dense slicing to resolve bunch density distributions. To address this, we present a GPU-accelerated tracking code that enables efficient longitudinal single-bunch instability simulations. Designed for high-performance GPUs on desktop computers, our approach provides an accessible, cost-effective alternative to computing clusters.
WEPS007
Measurement of coherent synchrotron frequencies under conditions close to the Robinson limit at the Aichi Synchrotron Radiation Center
2248
Past measurements* of coherent synchrotron frequencies at the Photon Factory storage ring revealed that the behavior of measured coherent frequencies could not be well explained with standard 4th-order characteristic equation under conditions close to the Robinson limit. To investigate whether similar phenomenon occurs in other storage rings, we measured the coherent synchrotron frequencies at a 1.2-GeV electron storage ring of Aichi Synchrotron Radiation Center as a function of the cavity voltage and the beam current. At beam currents higher than about 200 mA, we observed double peaks, one with a frequency higher than the incoherent synchrotron frequency and one with a lower frequency, that can correspond to two independent solutions of the 4th-order characteristic equation. Our preliminary analysis indicated that the frequencies of lower-frequency peak did not agree well with those predicted by the characteristic equation. We also observed that under a condition very close to the Robinson limit, the beam exhibited strong longitudinal coherent self-excited oscillation without beam dump. We present these measurement results and updated analysis.
Paper: WEPS007
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS007
About: Received: 27 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
WEPS008
Longitudinal microwave instability in the J-PARC Main Ring
2252
Longitudinal microwave instability has been observed in the J-PARC Main Ring. The longitudinal microwave instability was observed during the debunching process for the slow extraction. This led to electron cloud formation, which can cause transverse beam instability and beam losses. Longitudinal microwave instability was also observed during the latter part of the acceleration for the fast extraction operation, even though no loss or transverse instability related to the longitudinal microwave instability was observed. To investigate the source of the longitudinal microwave instability, spectral analysis was used on the waveform recorded by a high-speed oscilloscope. The spectral analysis suggests the RF cavity and its structure as a possible source of the longitudinal microwave instability. A beam longitudinal dynamics simulation with measured longitudinal impedance of the RF cavity was performed, and its result is compared with the measurement for various beam intensities. In this paper, we present the result of the simulation and measurement of the longitudinal microwave instabilities for various beam intensities.
Paper: WEPS008
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS008
About: Received: 28 May 2025 — Revised: 31 May 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS009
Interaction of intrabeam scattering, longitudinal wakefield, and a passive harmonic RF cavity in SOLEIL II
2256
Synchrotron light sources worldwide are transforming into next-generation facilities with ultralow transverse emittances at the diffraction limits. With these parameters, intrabeam scattering (IBS) becomes significant and can spoil the light quality by increasing emittance. A harmonic cavity can be installed to mitigate this effect by increasing the bunch length. Another way to reduce the impact of IBS is to operate with the full transverse coupling. This contribution considers the IBS effect on SOLEIL II performance with an up-to-date impedance model, passive harmonic cavity, different insertion device gap configurations (open, close), and full transverse coupling for all foreseen operation modes. The combined effect of IBS and microwave instability (MWI) on the energy spread is reported. It is demonstrated that the contribution of IBS to energy spread increase is as important as that of MWI.
Paper: WEPS009
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS009
About: Received: 24 Apr 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS010
Photoinjector beam halo formation due to a secondary picosecond time-delayed laser pulse
2260
Beam halo formation is a significant challenge for high-intensity accelerators, as it can lead to performance degradation and radiation safety risks. This study investigates the formation and mitigation of beam halos caused by a picosecond time-delayed laser pulse, which generates a secondary electron bunch in the same RF bucket as the main bunch. The energy difference between the two bunches creates a defocusing effect, leading to the halo generation. Experimental validation of RF-Track simulations was conducted at the AWAKE Run 2c test injector (ARTI). The research outlines methods for identifying, analyzing, and mitigating laser-driven beam halo formation, contributing to more effective control of beam halos in accelerator operations.
Paper: WEPS010
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS010
About: Received: 16 May 2025 — Revised: 31 May 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS011
Machine learning-based symplectic model for space-charge effect simulation
2264
Symplectic simulation of space-charge effects is important for high-intensity particle accelerators. In this work, we propose to use a generative model to efficiently simulate space-charge effects in JuTrack, a Julia-based particle tracking code. The one-step symplectic transverse transfer map of the particles is obtained by differentiating the predicted space-charge Hamiltonian. This model effectively preserves the phase-space structure and reduces non-physical effects in long-term simulations by ensuring symplecticity in the calculation.
Paper: WEPS011
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS011
About: Received: 16 May 2025 — Revised: 01 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS012
Beam loss simulations with space charge and octupoles for the SIS100 magnet quality assessment
2267
The components of the SIS100 synchrotron (FAIR facility) are presently under installation in the accelerator tunnel. The superconducting dipole magnets have been produced and the magnet field errors up to 7th order have been measured for all magnets. The superconducting quadrupole magnets are under production, the field error data for a part of the magnets is available. As a part of the magnet quality assessment, the particle tracking simulations are used to study the beam losses during the 1 sec beam accumulation at the injection energy. The tune settings for the slow extraction operation are considered. Direct space-charge effects and the Landau damping octupole magnets, which dominate the incoherent tune distribution, are included. In order to reduce the computational load and to increase the parameter resolution, a machine learning based optimizer is used in the accelerator and beam parameter studies.
Paper: WEPS012
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS012
About: Received: 23 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Advancing beam dynamics for high current cyclotrons
This study explores beam dynamics in the development of high intensity cyclotrons, focusing on the challenges posed by space charge effects at high beam intensities. Space charge forces, which become significant in high-current operations, can lead to emittance growth, beam loss, and instability, compromising cyclotron performance. Advanced modeling techniques are employed to analyze and mitigate these effects, ensuring stable beam transport and acceleration throughout the cyclotron. By optimizing field configurations and beam trajectories, the study achieves improved beam quality and reduced particle losses. These findings contribute to the development of cyclotrons capable of delivering high-intensity beams for applications such as BNCT.
Beam Dynamic study of the accelerating cavity of the dual energy NSTRI-eLinac
The side-coupled standing wave accelerator tubes have a wide range of applications in linear electron accelerators due to their relatively high acceleration gradient and relatively low sensitivity to manufacturing errors. In the NSTRI-eLinac project, a dual energy electron linear accelerator is defined for cargo applications. In this accelerator, a side-coupled standing wave tube accelerates electrons to energies of 4 and 6 MeV. This tube operates at a frequency of 2998.5 MHz in the π/2 mode, fed by a magnetron with a maximum power of 2.6 MW. The most important issue in designing the accelerating tube is the interaction between the electron beam and the RF electromagnetic field to deliver the electron bunch at the desired energy with maximum efficiency and suitable output beam quality. Beam dynamics studies are essential for determining the specifications of the output beam. In this paper, the output beam characteristics for the NSTRI accelerating tube have been investigated using the STRA code. The results estimate the output beam characteristics in energies of 4 and 6 MeV at the end of the constructed tube.
WEPS015
Simulation of electron beam transport through the coherent electron cooling amplification section using real number of electrons
2271
Coherent electron cooling plays an important role in the Electron Ion Collider (EIC) by providing a fast cooling rate at collision energy to counter the emittance growth driven by intrabeam scattering effects. In this paper, we report on the high-fidelity simulation of the electron beam transport through the amplification section of the cooling channel. We will show the amplification of the initial modulation in the electron beam from the protons and present the study of collective effects such as the space-charge and CSR effects on the process of modulation amplification.
Paper: WEPS015
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS015
About: Received: 20 May 2025 — Revised: 31 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS016
Experimental investigation of longitudinal scraping of H- bunches via photo-detachment
2275
Longitudinal emittance growth is a significant challenge in RF linacs, especially for poorly bunched beams. This stems from particles occupying outer synchrotron oscillation orbits in the LBET, causing unwanted bunch-bunch interactions and degraded beam quality. To address this, we proposed using temporally spaced laser pulses to selectively photo-detach electrons from the longitudinal head and tail regions of H- ion bunches. This approach aims to reduce particle density in extreme orbits, enhancing beam uniformity and limiting emittance growth. Our experiments employed Fermilab's 'LaserNotcher' system at the font end of the linac, delivering 1.6 MW peak power with sub-nanosecond precision. By neutralizing the first and last half-nanosecond of several H- bunches, we measured their propagation injection into the booster. Measurements of pulse width, average height, and temporal spacing over booster cycles were compared between the scraped and unscraped bunches. Statistical analysis evaluated the results’ significance, highlighting the feasibility of laser-based scraping for future linac designs to achieve higher beam energies with improved emittance control.
Paper: WEPS016
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS016
About: Received: 03 Jun 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Simulation of three-dimensional magnetic confinement of a Coulomb crystal in a ring
A novel storage ring is proposed in which the bunch maintains a fixed orientation relative to the outside world (does not rotate with the ring as usual). In this geometry, magnetic focussing can confine all three dimensions of the bunch without RF. The application of this ring to ultra-low emittance Coulomb crystals is investigated, where the focussing force balances the space charge to give zero phase advance and the crystal structure can be preserved for tens of milliseconds. The dynamics is highly coupled and dominated by weak focussing. Some different instabilities are observed, one of which appears to be suppressed by adding nonlinear components to the ring field.
WEPS018
Bunch length regulation in the LHC during controlled emittance blow-up
2279
Controlled longitudinal emittance blow-up is indispensable for the operation of the Large Hadron Collider (LHC) to counteract single-bunch loss of Landau damping during the acceleration ramp. The blow-up is performed by injecting RF phase noise in a narrow frequency band into the beam phase loop, with bunch-length feedback regulating the noise amplitude. In 2024, the variation of the bunch length due to imperfect regulation caused unacceptable beam-induced heating of certain accelerator components. In this contribution, we present the results of extensive simulation scans that have been used to optimize the feedback parameters. We show how this optimization, along with a reduction of the feedback delay on the controls side, has been implemented in the LHC and significantly improved the bunch length evolution during acceleration. Finally, we discuss the results of a measurement scan performed during an operational period of five weeks to fine-tune the blow-up feedback settings.
Paper: WEPS018
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS018
About: Received: 26 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
Analysis of higher order modes of QWR cavity for in-situ plasma processing
SRF cavities deteriorate in efficiency over time and need for inexpensive cleaning methods that are effective is apparent. Plasma Processing is one such cleaning method that can be implemented in-situ, reducing the processing time taken drastically. In this work we present our analysis of the higher order modes of the 72 MHz QWR at ATLAS, ANL for use in igniting plasma for cavity processing.
WEPS020
Preliminary study of higher-order mode based scheme for bunch length compression in SRF Electron guns
2283
Higher-Order Modes (HOMs) in superconducting radiofrequency (SRF) cavities are traditionally considered detrimental to efficient operation. They are often associated with beam instabilities and are actively damped. However, these “harmful” HOMs, if used strategically, can be transformed into a tool for providing extra control over the beam, which can introduce new opportunities that are not easily achievable by conventional SRF cavity-based systems. Particularly, we have investigated the feasibility of boosting ballistic bunch compression using HOMs in SRF gun. The proposed idea will be presented with preliminary simulation results. The 185 MHz SRF gun cavity used for the simulation study was modelled using the ACE3P software suite and further modelling of the compression scheme was performed using the GPT code.
Paper: WEPS020
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS020
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS021
Simulation study on attosecond bunch generation using reversed chicane at Argonne Wakefield Accelerator (AWA)
2286
Capability for generating an attosecond bunch can provide interesting opportunities to wakefield accelerator research. We have been studying requirements and challenges in beam dynamics to produce an attosecond bunch using an existing beamline at Argonne Wakefield Accelerator (AWA) facility. One unavoidable limitation of this study is that conventional C-typed chicane is not available. Thus, a modified version of a chicane-like compressor, called a reversed chicane, is designed and running at the AWA facility. AWA’s injector and beamline were simulated using ASTRA and ELEGANT respectively. The study provided guidance toward the attosecond bunch generation. We present the simulation results and propose the modified design and operation conditions to generate the attosecond bunch at AWA facility.
Paper: WEPS021
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS021
About: Received: 28 May 2025 — Revised: 31 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS022
Progress on experimental efforts to investigate CSR shielding effects
2290
A collaboration is underway to investigate the impact of CSR and shielding on the beam of various shapes as it passes through a chicane. Experimental efforts are being made at the Argonne Wakefield Accelerator (AWA) facility. Currently, the facility is equipped with two identical doglegs with reversing quadrupoles that allow doglegs to function as a chicane, and manually adjustable shielding gaps in dipole magnet chambers. A 6.4-ps-long flattop laser pulse is generated using alpha-BBO crystals, and linac phase is adjusted to either preserve the bunch length or slightly compress it through the chicane. While the expected beam behavior was observed during the initial experiment, the current chicane’s exceptionally large R56 (=0.45 m) rendered it sensitive to modulations from the alpha-BBO configuration. We have confirmed a new beam-based tuning procedure for BBO crystals at the AWA facility and its effect on modulations. We present the summary of experimental efforts to date and outline future plans.
Paper: WEPS022
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS022
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS023
Study for limiting factors in transverse wiggler-based arbitrary correlation generation
2294
Recently proposed transverse wiggler is an intriguing tool for imparting designed correlations in phase space. While several simulations have demonstrated its feasibility, the method using the transverse wiggler has several concerns need to be addressed. Beam evolution along the wiggler can introduce errors in the designed correlation. Wiggler fields have strong vertical position dependence, which can introduce unwanted horizontal and vertical couplings. The transverse wiggler generates both horizontal and vertical sinusoidal fields, which can significantly degrade the beam quality. Additionally, its applicability to heavy particles remains uncertain. We will present results from a preliminary study aimed at addressing these concerns.
Paper: WEPS023
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS023
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
WEPS025
Design, manufacturing and validation of fast-ramping alpha magnet for interleaving operation at ANL APS
2298
RadiaBeam has designed and manufactured a fast-ramping alpha magnet (FRAM) that is developed for interleaved operation at the Advanced Photon Source (APS) at Argonne National Laboratory. This interleaving operation requires the alpha magnet to stably complete a 5 s long cycle with a 100 ms ramp-up, 1s nominal field output and a 100 ms ramp-down. A laminated yoke is used to minimize eddy currents, ensure fast field response times and reduce core-loss during operation. The magnet has been measured by a Hall probe at Radiabeam and at Argonne, demonstrating 2.75 T/m maximum field gradi-ent within a 10 cm x 14 cm good field region in both DC and pulse modes.
Paper: WEPS025
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS025
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Simultaneous electron beam acceleration and compression with a radiofrequency cavity in ultrafast electron diffraction experiments
In ultrafast electron diffraction experiments, the scattering cross-section, q-range, and space-charge effects are critically influenced by the electron beam energy, which is constrained by the high-voltage breakdown. By integrating a 100 kV DC electron gun with a 3 GHz radiofrequency cavity powered with a 400 W amplifier, we demonstrate a net energy gain of up to 31 keV. Here we present simulation and experimental results highlighting the simultaneous compression and accelerating capabilities using a radiofrequency cavity, demonstrating that significant energy gains are attainable without compromising femtosecond scale time resolution.
WEPS028
Quadrupole pumping for bunch shortening in the Proton Synchrotron and Super Proton Synchrotron at CERN
2302
Quadrupole pumping is a longitudinal manipulation technique for bunch shortening, which works by modulating the RF voltage at twice the synchrotron frequency to excite bunch length oscillations. These controlled oscillations rotate the bunch in longitudinal phase space, with extraction set for when the bunch is shortest. Higher RF harmonics can also be used to linearise the synchrotron frequency distribution, reducing the formation of tails. Recently, quadrupole pumping has been proposed as a method for achieving ultra short bunches for proton-driven plasma wakefield accelerators such as the AWAKE experiment. In this contribution, we assess the performance of quadrupole pumping for the first time in the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS) at CERN. Using simulations and beam measurements, we compare the effectiveness of this technique (without linearisation) against other bunch-shortening methods, including the unstable phase jump and the non-adiabatic voltage jump.
Paper: WEPS028
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS028
About: Received: 27 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS029
Predicting losses in the SPS using longitudinal tomography during bunch shortening in the PS
2306
The efficient transfer of protons from the Proton Synchrotron (PS) to the Super Proton Synchrotron (SPS) is crucial for beams in the Large Hadron Collider (LHC). A particular challenge at the intensities required for the High-Luminosity LHC is the handover from a 40 MHz to a 200 MHz RF system. This requires a non-adiabatic bunch shortening in the PS triggered by a fast RF voltage jump. However, nonlinearity of the synchrotron frequency distribution causes tails to emerge during rotation, resulting in uncaptured beam in the SPS. The uncaptured particles lost at the start of acceleration in the SPS, and the additional flat bottom losses, can currently only be evaluated with the beam intensity and loss monitors. In this work, detailed studies of the bunch rotation in the PS were carried out both in simulations and in measurements. A tomography-based tool was developed to predict uncaptured losses in the SPS from bunch profile measurements in the PS during bunch shortening. This tool enables detailed monitoring of the PS-to-SPS transfer of LHC-type beams by identifying potential losses due to uncaptured beam, before injection into the SPS.
Paper: WEPS029
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS029
About: Received: 27 May 2025 — Revised: 01 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS031
Longitudinal beam coupling impedance of unshielded pumping manifolds at the CERN PS
2310
The High-Luminosity LHC (HL-LHC) project aims at increasing beam intensity, hence posing tight constraints on its injector chain. A critical issue in the Proton Synchrotron (PS) is the contribution of numerous pumping manifolds to the longitudinal beam coupling impedance at high frequencies. It causes microwave instabilities that particularly affect ion beams and limit the longitudinal density of proton bunches close to transition energy. This contribution characterizes the impedance of these vacuum components through detailed electromagnetic simulations, examining configurations with and without a pick-up head inserted in the manifold. The effect of damping resistors on the impedance behavior is also investigated. Mitigation strategies, including shielding to prevent beam coupling with the manifold's volume, are evaluated for their effectiveness using electromagnetic simulations, offering solutions for improved beam performance.
Paper: WEPS031
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS031
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
An electron beam manipulated by circularly polarized Laguerre-Gaussian modes
Manipulation of an electron beam by Laguerre-Gaussian (LG) modes is investigated using finite-difference time-domain particle-in-cell (FDTD-PIC) simulations. The azimuthal velocity profiles of macro-particles exhibit a 3-D spiral pattern with the number of strands equal to a sum of the state number of spin angular momentum and the orbital angular momentum of LG modes. These spiral patterns move along with the electron beam like a helical traveling wave. The electrons also exhibit both an orbit revolution and a small rotation motion. The former is very similar to the gyromotion of electrons under an external magnetic field. The small rotation motion has the same frequency as that of the LG mode while the orbit revolution frequency or gyrofrequency is far lower. This gyrofrequency can be manipulated by the frequency, electric field strength, and beam waist size of the LG mode. Furthermore, a larger-current electron beam can be confined within the LG mode by increasing the electric field strength. It is demonstrated that the manipulation of an electron beam can be realized by using circularly polarized LG modes. The fundamental mechanism and simulation results will be presented.
Updates to the differentiable accelerator simulation code Cheetah
The design and operation of modern accelerators demand advanced simulation tools capable of addressing complex challenges. Differentiable simulations are particularly valuable, as they enable gradient-based optimization techniques that significantly reduce computational costs and efficiently tackle high-dimensional problems. The PyTorch-based simulation code Cheetah was developed to combine high-speed, differentiable simulations with seamless integration into machine learning workflows. In this work, we present recent updates to Cheetah, developed collaboratively by DESY, KIT, SLAC, and LBNL, which extend its capabilities and enhance its performance. Key advancements include support for vectorized execution, enabling simultaneous simulations across large parameter spaces; the addition of space charge modeling and higher-order transfer maps for more accurate beam dynamics; and expanded support for multiple particle species and additional accelerator components, broadening its applicability to other systems. By enabling faster, more precise, and scalable simulations, Cheetah is poised to become a valuable tool for meeting the growing demands of the accelerator physics community.
WEPS035
Characterizing proton beam properties for cell irradiation study using GEANT4 simulation
2314
The purpose of this research is to characterize proton beam properties - beam energy, energy spread, beam size, and transverse emittance - to establish the initial setup for simulation in planning cancer cell culture experiments at the Cyclotron Medical Accelerator at King Chulalongkorn Memorial Hospital in Bangkok, Thailand. The characterization was performed using GEANT4 Monte Carlo (MC) simulations. Proton energies of 70 MeV, 100 MeV, 150 MeV, and 220 MeV were selected, and the 80%-20% distal fall-off of the depth profile was utilized to determine the energy spread. The simulated results were then verified against experimental data and compared with the Treatment Planning System (TPS). The details of the validating procedure, as well as results on the optimized energy spread, beam size, and emittance, and the irradiated setup for cell irradiation, will be discussed in this contribution.
Paper: WEPS035
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS035
About: Received: 26 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
WEPS036
First proton crabbing at the LHC via head-on beam-beam interaction
2317
The first experimental observation of a 10 $\mu$m crabbing orbit at 1~$\sigma_z$ induced by head-on collisions with a non-zero crossing angle ($\theta_c$) in a high-energy proton beam at the LHC is presented. This challenging measurement required both the design of a dedicated experiment and a careful calibration and optimization of the beam instrumentation to produce and detect such a subtle effect. By varying the crossing angle from positive to negative values the reversibility of the effect and its dependence on the crossing angle were also demonstrated. Lattice simulations were performed to corroborate the experimental results, showing excellent agreement with the measured crabbing amplitudes. This experiment highlights the potential of the existing wideband beam-position monitors to diagnose crabbing effects, which will be crucial in the HL-LHC upgrade.
Paper: WEPS036
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS036
About: Received: 19 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS038
Python FLUKA beam line, a python library to create FLUKA simulations of accelerators
2321
FLUKA simulations of beamlines are important for un- derstanding numerous different aspects of accelerators, in- cluding beam losses, particle backgrounds, activation and shielding. Creating a beam-line simulation using FLUKA is a time consuming and potentially error prone process. This paper describes a set of python tools called pyflubl (Python FLUKA beam-line) which can create a FLUKA simulation using input from MAD-X, MAD8, Transport or BDSIM. pyflubl is based on multiple stable and advanced python packages created to make BDSIM (Geant4) beamline simu- lations as simple as possible, these are pymadx (an interface to MAD-X output), pymad8 (an interface to MAD8 out- put), pybdsim (interface to BDSIM) and most importantly pyg4ometry (a geometry engine for Monte Carlo geometry creation). The magnetic fields required for FLUKA are im- plemented in C++ via BDSIM, thus keeping fields consistent between Geant4 and FLUKA beamline simulations. This paper describes pyflubl design and implementation and ex- ample results for an idealised electron beam-line. Particular attention is given to geometry, fields and scoring.
Paper: WEPS038
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS038
About: Received: 28 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
WEPS039
Progress & developments of beam delivery simulation (BDSIM)
2325
BDSIM (Beam Delivery Simulation) is a Monte Carlo particle tracking tool for accelerator beamline modelling. It integrates particle transport with detailed geometry and physics using Geant4 for precise modelling of particle-matter interactions in 3D models of particle accelerators. Primarily for energy deposition studies and beam loss simulations, BDSIM allows a high degree of control and customisation, and is ideal for understanding and enhancing the performance of beamline designs. BDSIM has numerous modelling applications, including high-energy physics facilities, particle detection experiments, synchrotron light sources, medical accelerators, and novel acceleration experiments. Here, we present recent developments of BDSIM. This includes improved custom inverse-Compton scattering processes for laserwire and polarimeter simulations and extending the process to model polarization & electron spin; improved acceleration including transverse focussing in RF elements with implementation of 3D transverse magnetic and electric modes; custom elements for modelling muon cooling channels; and updates to interfacing with Xsuite via improved code couplings and BDSIM distribution methods.
Paper: WEPS039
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS039
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
AtomicAndPhysicalConstants.jl – a package for managing physical constants atomic and subatomic data in Julia
AtomicAndPhysicalConstants.jl is a Julia package designed to provide atomic and physical constants including the speed of light, subatomic particle properties, atomic isotope properties, etc. Values are obtained from CODATA (Committee on Data of the International Science Council), NIST (National Institute of Standards and Technology), and PDG (Particle Data Group) datasets for physical constants, atomic and subatomic particles for scientific computations, particularly in fields such as particle and accelerator physics. Key features include a macro for users to access and customize units for constants, dynamic updates to integrate the latest scientific data, and compatibility with Julia's Unitful.jl library for convenient unit manipulation. These capabilities make the package ideal for applications requiring rigorous physical accuracy and reproducibility.
WEPS041
GPU accelerated longitudinal phase space tomography
2329
Longitudinal tomography is widely used in the CERN synchrotrons as an essential beam diagnostics tool. In recent years, more complex applications of phase space tomography, such as voltage calibration and multi-bunch tomography, have been explored. For these applications, large numbers of reconstructions are required, and computation time has a significant impact on usability. The current implementation is Python based, with the numerically intensive components written in C++. To further increase performance, a GPU-accelerated version has been developed using CuPy and CUDA. The most computationally demanding parts of the algorithm can now be run on the GPU, whilst maintaining the Python interface for maximum flexibility. Performance benchmarks showed speedups up to a factor of 35 in the scope of the entire application and even higher values when only considering the computationally intensive parts. This contribution discusses the implementation of GPU tomography as well as the additional performance improvements it enables.
Paper: WEPS041
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS041
About: Received: 15 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS042
Benchmarking Intrabeam Scattering with RF-Track
2333
Intra-beam scattering (IBS) has recently gained significant interest in the community of free electron lasers (FELs), as it is believed to produce an increment in the sliced energy spread (SES), which is detrimental to FEL performance. To control and contain this phenomenon, it is important to include IBS in the design phase of an FEL through appropriate numerical simulation. Most existing codes that simulate IBS were developed for long-term tracking in circular lattices, assuming Gaussian bunches. Unfortunately, this assumption doesn’t capture the rapid bunch evolution of electron bunches in photoinjectors. To address this limitation, the tracking code RF-Track has recently been updated to include IBS, using a novel hybrid-kinetic Monte Carlo method. This paper presents benchmarks performed to verify the implementation. The predicted SES increment in the beam due to IBS using RF-Track has been compared against a kinetic approach used in a different tracking code and, secondly, against a semi-analytical model. The results showed a good agreement, setting RF-Track as a tool to understand and control the SES growth in photoinjectors and, in particular, in FEL.
Paper: WEPS042
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS042
About: Received: 04 Apr 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS043
Achieving diverse beam modes with modelling and optimisation for the versatile SRF photoelectron gun at SEALab
2337
The SEALab facility in Berlin is home to an R\&D superconducting radio-frequency (SRF)photoinjector setup and beamline. Designed to support multiple varied applications - ranging from Energy Recovery Linac (ERL) to Ultrafast Electron Diffraction (UED) and Electron-Beam Water Treatment (EBWT) - SEALab requires flexible, high-precision tuning to support these diverse beam modes. These applications span over three orders of magnitude in bunch charge, emittance, and current, alongside sub-picosecond pulse lengths. This makes injector setup and tuning a significant challenge. With the world's first beam achieved at SEALab from a Na-K-Sb cathode in our SRF gun, a suite of beam dynamics models has been developed to support understanding of the beam behaviours in the gun, where no observations are possible, and operation of the commissioning process. This is comprised of a first-order analytical model, particle-in-cell (PIC) ASTRA simulations, and a machine-learning surrogate model trained for current commissioning operation ranges. These models are coupled with a Multi-Objective Bayesian Optimisation (MOBO) algorithm to enable rapid tuning across multiple beam modes. This combination of surrogate modelling and optimisation algorithm reduces optimisation timescales from hundreds of hours to minutes, allowing near-real-time tuning for the accelerator. This work presents the modelling framework, its validation, and its application to SEALab's many-mode optimisation challenges.
Paper: WEPS043
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS043
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
Fast and efficient modeling of structure-based wakefield accelerators
Structure-based wakefield accelerators (SWFA) have been identified as a candidate technology for future applications ranging from free electron lasers to colliders. However, achieving the desired beam energy and quality requires meter-scale structures with tight tolerances, placing constraints on structure and beam characteristics to minimize emittance growth and combat transverse instabilities. High fidelity and self-consistent simulations over these lengths necessitate enormous computational resources, making parametric studies of novel structures or instability-mitigation schemes unfeasible with standard practices. We present a technique for decomposing high dimensional wakefield systems into a set of lower dimensional components, capable of accurately reconstructing the structure response in a fraction of the time. We discuss the approach and implementation of this technique using Green’s Functions for common structure geometries. We demonstrate the potential for significant reduction in computation times and memory footprint using such representations. Finally, we discuss the application of machine learning in generating these representations for novel structure geometries.
WEPS045
Investigating the Impact of alternative LHC optics on accelerator backgrounds at FASER using BDSIM
2341
Alternative configurations around the ATLAS experiment are investigated aiming to reduce muon rates at forward physics experiments such as FASER and SND@LHC. The Geant4 toolkit BDSIM is used to propagate muons through a model of a section of the LHC and the TI12 tunnel, where the FASER experiment is located. We compare the muon rates in BDSIM with FASER data collected during dedicated tests in the LHC. Results show a significant worsening of the background with the non-nominal polarity configuration of the triplet quadrupoles, used in 2024. The horizontal crossing angle further increased the background, however a partial mitigation of approximately 10% was found using a set of orbit corrector magnets. Additionally, nominal triplet polarity was favorable for both vertical and horizontal crossing angles. This work served as benchmark of simulations that will be used to validate future configurations.
Paper: WEPS045
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS045
About: Received: 28 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Extracting symplectic maps for space-charge dominated beams
Symplecticity of the transfer maps is important for reliable evaluation of space-charge dominated beams in accelerators. Unfortunately, most simulation codes that include collective effects, such as space charge, do not use canonical phase-space variables and therefore are not symplectic in the presence of electromagnetic fields. In this paper, we present a numerical method to extract symplectic transfer maps using particle tracking simulation code IMPACT-T for space-charge dominated beams. We demonstrate this method by obtaining symplectic transfer maps in the photo-injector (113 MHz SRF gun) section of the Coherent electron Cooling (CeC) Proof of Principle (POP) experiment.
WEPS047
Report on Opera-3D hands-on session in the 7th International School on Beam Dynamics and Accelerator Technology (ISBA24)
2345
The 7th International School on Beam Dynamics and Accelerator Technology (ISBA24) held in Chiangmai University during November 1-9, 2024, encompasses seven days opportunities where the foundation of accelerator physics is applied during hands-on sessions with simulation software including ASTRA, ELEGANT, Opera-3D and CST Studio Suite. Opera-3D, a finite element-based Maxwell’s equations solver, is known for its powerful low frequency simulation capabilities and is appropriate for magnet design. Instructed by two lecturers from Synchrotron Light Research Institute, 15 students from China, Japan, India and Thailand were trained on the Opera-3D software fundamentals in the application of magnet design for particle accelerator. The students showcase their knowledge in the group assignments including the design of H-shape dipole, C-shape dipole and combined horizontal and vertical corrector with success. Thanks to the generous support of the ISBA24 sponsors and Sigma Solutions Co., Ltd., who provided the software licenses during the school. This article reports on the completion of the ISBA24 Opera-3D hands-on session provided to graduate students and young researchers from the Asian region.
Paper: WEPS047
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS047
About: Received: 18 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS048
Design of non-linear kicker for Siam Photon Source II
2348
A non-linear kicker (NLK) is designed for the beam injection into the storage ring of Siam Photon Source II. The required deflection angle is 4 mrad, the effective length is 400 mm and the peak field is 100 mT at the horizontal position of 9 mm from the magnet center. The design is based on 8-wire configuration where the conductor position is symmetric along the xz and yz planes. The vertical size of ceramics chamber is determined by the vertical beam stay-clear at the magnet position, available space for magnet installation and feasibility of conductive coating process. Magnetic field calculation of the NLK is performed in Radia and Opera-3D. The octupole-like magnetic field with the field-free region at the magnet center minimizes perturbation on the stored beam. Nevertheless, position error of the conductors leads to excess dipole and quadrupole field components at the magnet center. Magnetic field distortion is also caused by Eddy current induced in the conductive coating in transient analysis. In this work, magnetic design and magnetic field calculation of the NLK is presented.
Paper: WEPS048
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS048
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
WEPS049
Development of stretched wire system for magnetic field measurement of magnets for Siam Photon Source II
2351
A stretched wire measurement system was developed for magnetic field measurement of magnet prototype for Siam Photon Source II. It is used for magnetic field integral measurement for characterization of multipole field errors, magnet centering and fiducialization of multipole magnets. The wire trajectory across magnet aperture can be either linear or circular. The maximum wire movement is ±100 mm in both horizontal and vertical directions with the positioning accuracy of ±2 µm. The system is built on a 3.2-m granite support which allows the maximum magnet length of 2.2 m and magnet weight of 2,500 kg to be measured. Effects of wire tension, scan region, pause time between measurements, wire movement speed, number of repeated measurements and number of data points have been studied. With the optimized measurement parameters, the repeatability of 3E-4 or better can be achieved for the normalized multipole components measured using the circular scan.
Paper: WEPS049
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS049
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
WEPS050
Electron cloud mitigation techniques for the FCC-ee
2354
The Future Circular Collider (FCC)-ee is a planned electron-positron collider under development. The future collider would be built in an about 91 km ring-shaped underground tunnel located beneath the French departments of Haute-Savoie and Ain, and the Swiss canton of Geneva. The FCC-ee may face challenges from electron cloud (e-cloud). The strongest effects are foreseen for the Z configuration, due to the highest number of bunches, which corresponds to the smallest bunch spacing, which is a key parameter for the e-cloud formation process. A high electron density in the beam pipe could limit the accelerator’s achievable performance through various mechanisms, such as transverse instabilities, transverse emittance growth, particle losses, vacuum degradation and additional heat loads on the inner surface of the vacuum chambers. In the design phase, the objective is to suppress the e-cloud effects in the FCC-ee. Therefore, effective e-cloud mitigation techniques, to avoid the e-cloud avalanche multiplication and its deleterious effects, are discussed in the paper.
Paper: WEPS050
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS050
About: Received: 27 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS051
Filling pattern with non-uniform bunch spacing to mitigate e-cloud for the FCC-ee
2358
The Future Circular Collider (FCC) study is developing designs for higher performance particle colliders that could follow on from the Large Hadron Collider once it reaches the end of its high-luminosity phase. In particular, the FCC-ee is a proposed electron-positron collider that may face challenges from the electron cloud (e-cloud). Specifically, the Z configuration foresees the highest number of bunches. Consequently, this configuration could suffer more form the deleterious effects of the e-cloud, such as transverse instabilities, transverse emittance growth, particle losses, vacuum degradation and additional heat loads on the inner surface of the vacuum chambers. The e-cloud effects have been observed in several circular accelerators all over the world and it is much more commonly in those operated with positively charged particles. Presently, it is among the major performance limitations for high energy collider. Therefore, the study of e-cloud mitigation techniques is crucial during the accelerator's design stage to suppress the e-cloud avalanche multiplication. This paper analyses the use of non-uniform bunch spacing patterns as a potential e-cloud mitigation strategy.
Paper: WEPS051
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS051
About: Received: 27 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
WEPS052
Investigating electron cloud formation in FCC-ee nested magnet designs
2362
The Future Circular Collider is an ambitious international proposal for a next-generation particle accelerator complex, building upon the successes of CERN’s Large Hadron Collider. Specifically, the FCC-ee is a future circular lepton collider. The baseline design for the FCC-ee features four modes of operation, with beam energies ranging from 45.6 GeV to 182.5 GeV. Electron cloud (e-cloud) could be a concern for the FCC-ee due to the high number of bunches foreseen for the Z configuration, which results in small bunch spacing. The bunch spacing is a key parameter for the e-cloud formation process, as very small bunch spacing could lead to the avalanche multiplication and its deleterious effects. Moreover, electron trajectories are strongly influenced by externally applied magnetic fields, which could trap electrons and alter their survival time inside the vacuum chamber. The concept of nested magnets, which involves overlapping dipole fields with quadrupolar and/or sextupolar gradients, is under investigation. This approach aims to increase the dipole filling factor and reduce the synchrotron radiation. In this paper, the nested magnets are studied from the e-cloud point of view.
Paper: WEPS052
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS052
About: Received: 27 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Preliminary results on the electron cloud build-up in the booster of the FCC-ee
The presence of the electron cloud inside the chamber of high energy accelerators with positively charged circulating beams has been reported and studied by several facilities. Those studies intend to describe and predict which scenarios may present a mayor risk to operating the machine. The electron cloud build-up inside the vacuum chambers might generate critical effects that diminish the performance of the machine and beam quality. Due to these reasons, it is important to review the possible scenarios to operate at injection and extraction of the beam inside the booster proposed for the FCC-ee. This work reports preliminary studies on electron cloud evolution inside the booster, considering some variations in strategic design parameters, such as the bunch spacing, and secondary emission yield. We compare the simulated electron distribution across the two stages of the beam.
Atomic layer deposited ZnMgO multilayered coatings for TEEY and electrical conductivity optimization
Total electron emission yield (TEEY), defined as the number of electrons emitted per incident electron of a given energy, is potentially the source of two major problems: electrostatic discharges (ESD) in vacuum and multipacting effect. To mitigate these risks, a possible solution could be to coat the surfaces prone to ESD or multipacting originate with a thin film with tunable TEEY and electrical conductivity. In order to be able to control both properties independently, a possible solution is to develop a thin film heterostructure based on the mixing of a low TEEY, electrical conductor material with a high TEEY, dielectric material in order, for instance, to obtain a low TEEY, dielectric coating that will prevent both Multipacting and a decrease of surface losses quality factor. We choose the Atomic Layer Deposition (ALD) method to achieve that goal and we will present results obtained with coatings made of multiple layers of ZnO and MgO to verify that this solution is relevant. Electrical conductivity and TEEY measurements carried out on these multimaterial multilayered coatings have shown that both properties vary according to their composition and their structure.
WEPS059
Simulation study on power loss in the coupling cavity damper of the accelerating π/2 mode for the SuperKEKB ARES cavity
2366
In the SuperKEKB electron-positron collider, the coupled-bunch instability caused by the accelerating mode of RF cavities becomes severe in high beam current. To suppress it, the ARES cavities have been used. The accelerating cavity is coupled with an energy storage cavity via a coupling cavity between them. While the beam is accelerated by the π/2 mode, the parasitic 0 and π modes are damped by a coaxial damper at the coupling cavity without damping the π/2 mode. However, as the beam current becomes higher, some of the accelerating field of the π/2 mode is absorbed by the damper. This is because the π/2-mode field is deformed when two frequency tuners in the accelerating and storage cavities are moved for the optimum tuning condition. This effect increases power load of the damper, which can be an issue at higher beam current. Our high-power test showed that the power loss was higher than a prediction of the equivalent circuit model. Thus, using the CST MW Studio, we simulated the power loss and studied the relation between the power loss and the detuning frequency. We compare the simulation and high-power test results and discuss the possibility of new frequency tuning schemes.
Paper: WEPS059
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS059
About: Received: 26 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
Design of High Gradient, Fast Response, Broadband RF System for HIAF
The high broadband field-gradient RF system based on direct oil-cooling magnetic alloy cavity for High Intensity Heavy-ion Accelerator Facility (HIAF) Bost Ring (BRing) has been successfully reached and developed in Oct. 2022. The RF system consists of a three gaps cavity which loaded by 24 domestic nanocrystalline soft magnetic alloy (MA) ring cores, a RF power amplifier with an output power of 500 kW and digital LLRF. The acceleration voltage reached 66kV (gradient > 30kV/m) with a frequency swing from 290kHz to 2.1MHz, amplitude stability |△A/A|≤1% and phase stability |△φ|≤ 1°. In 2011, we collaborated with Chinese companies to begin the R&D of ultra-thin amorphous metal ribbon and magnetic ring core manufacturing process, in the meanwhile also established a MA core test platform. After ten years’ effort, 780(OD)×350(ID)×35 (TH) mm MA core with broadband characteristics in the frequency range of 0.1MHz to 20MHz has been successfully developed using domestic 14μm ribbon in 2021. The key performance μQf and Q at 0.3MHz are 6.5GHz and 0.9, respectively. In addtion, in order to further improve the acceleration gradient, we are still working hard to enhance the performance of MA core.
Development and application of high-performance MA core
From 2010, the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) carried out the relevant testing and research work on the RF Cavity loaded magnetic alloy materials firstly, and explored the development process of high-performance magnetic alloy (MA) cores with domestic manufacturers and research institutes jointly. Through the long-term exploration from small (diameter≤100mm), medium (diameter≤460mm) to large (diameter ≤ 1000mm) high-performance MA cores, breakthroughs have been made in many key processes, such as MA ribbon shearing, insulation silica coating, horizontal winding, atmosphere annealing and epoxy resin proof coating etc. Finally, liquid-cooled MA cores with high performances and large sizes were developed successfully. Its performance parameter value of μ'pQf is more than 30% higher than that of the same type of optimal MA cores, reported publicly in the world. Moreover, it reached the international advanced levels and realized the localization replacements. Meanwhile, the Institute of modern physics built a high-performance MA core production line with independent intellectual properties together with domestic enterprises. This realized the batch productions in high-performance MA cores. At present, the high-performance MA cores from this production lines were successfully applied in many projects
WEPS062
RF design of an integrated X-band mode-launcher for an open-structure TW LINAC
2370
In this paper, we present the RF design of a mode-launcher integrated with an open-type, multi-cell 12 GHz 4-sector structure. The electromagnetic design is carried out using the 3D full-wave electromagnetic solver CST-Microwave Studio. To ensure compactness, a key focus of the integration process is the minimization of the distance between the coupler cell and the accelerating open structure. We evaluate the feasibility of two solutions: two conventional couplers, and another configuration with two mode-launchers employed at both the input and output ends of the accelerating structure. A comparison is performed to assess the performance of the proposed design
Paper: WEPS062
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS062
About: Received: 29 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS063
Estimation of coupled-bunch instability induced by high-order modes of bell-shaped cavity in high current operation at SPring-8-II
2373
At the large synchrotron radiation facility SPring-8, the upgrade project “SPring-8-II” is underway to increase the radiation brightness by 100 times. In SPring-8-II, the beam energy will be reduced from 8 GeV to 6 GeV and the beam current will increase from 100 mA to 200 mA. The bell-shaped 509 MHz cavities will remain in place at SPring-8-II, with the number of cavities reduced from 32 to 16. Currently, the longitudinal coupled-bunch instability (CBI) is not observed. However, the CBI may occur due to high-order modes (HOMs) in some cavities because of the parameter changing at SPring-8-II. We estimated the threshold shunt impedance and Q-value for the CBI by using Ansys HFSS. Especially, TM011 mode at 900 MHz has a large impedance and the threshold impedance is 0.8 MΩ, which corresponds to QL~12,000 when R/Q=65Ω. On the other hand, we measured the actual QL-value of the cavities using single-bunch beam. The spectra and its Q-values of the HOM induced by the beam were measured. The results show that most cavities are below the threshold, but some cavities are over threshold. If the HOM causes instability, we plan to adjust two tuner plungers to shift them off the peak.
Paper: WEPS063
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS063
About: Received: 30 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
Performance of HOM dampers in the 100 MHz RF cavities in the MAX IV 3 GeV ring
Throughout 2023 and 2024, higher-order mode (HOM) dampers were designed, manufactured and installed on the 100 MHz RF cavities in the 3 GeV ring at MAX IV Laboratory. Cavity HOMs have been the main driving source of longitudinal coupled-bunch modes (LCBM) in the ring. This contribution presents the impact of the HOM dampers via measurements performed on the cavities at different operating temperatures. Measurements were made of the transmission between two probe antennas, the fields excited in the cavities by a single bunch stored in the ring and the damping rates of the LCBMs extracted using the drive-damp technique with a multibunch stored beam.
WEPS065
Development of C-band compact accelerating structure made of longitudinally-split two halves
2377
Our 6 MeV medical C-band accelerating structure is assembled using the disk-stacked method, where multiple oxygen-free copper components are stacked along the beam axis. The design incorporates the side-coupled (SC) structure and the re-entrant structure with an accelerating gap at the center of the cavity. Due to the complex shape and the large nunber of components, there are challenges in manufacturing efficiency. On the other hand, the longitudinally-split method divides the structure along a plane passing through the beam axis, independent of the number of cells, which significantly reduces the number of components. Based on the longitudinally-split X-band accelerating structure developed in the CLIC project, we have been working on the development of a compact, high-gradient, high-shunt impedance, longitudinally-split SC-type C-band accelerating structure. In this presentation, we will report the progress of our work, including manufacturing, RF testing, frequency tuning, and beam testing in the actual operating conditions.
Paper: WEPS065
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS065
About: Received: 27 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS066
Multi-objective optimization of ring cyclotron RF cavity using neural network ensembles with uncertainty quantification
2381
This study presents a multi-objective optimization scheme for ring cyclotron RF cavities, leveraging a neural network ensemble surrogate model. The cavity geometry is parameterized using Non-Uniform Rational B-Splines (NURBS), with control points and weights as design parameters. To reduce the computational cost of direct eigenmode simulations, an ensemble of neural networks trained using Ansys HFSS results is used to approximate performance metrics efficiently. The surrogate model also quantifies uncertainty, enabling Monte Carlo error propagation to account for potential manufacturing deviations. A multi-objective genetic algorithm (MOGA) explores the design space, using the surrogate model for efficient evaluations. The neural network ensemble are periodically retrained through HFSS simulations, iteratively improving the accuracy of surrogate model. This approach gives a robust and reliable RF cavity design optimization scheme.
Paper: WEPS066
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS066
About: Received: 27 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
WEPS067
Development of high-power RF components for an X-band transverse deflector system at SACLA
2385
We have been developing an X-band transverse deflector system (XB-TDS) with sub-fs time resolution, which will be installed after the undulator sections at SACLA. A sub-fs XFEL pulse is desirable for user experiments such as the measurements of structural disordering in an XFEL interaction with a matter, as the degree of damage depends on the pulse duration. The demand for a shorter and shorter XFEL pulse is increasing. The SACLA’s XFEL pulse duration is 6 fs at FWHM. In order to achieve a shorter XFEL pulse duration and to satisfy users’ needs, a diagnostic system of the longitudinal bunch distribution is essential. We adopt an X-band frequency to efficiently deflect an 8 GeV electron beam. We feed 20 MW to the pulse compressor, and the peak power is increased to around 100 MW, which is divided into four cavities, generating HEM11 horizontal mode. We utilize a dipole magnet before the beam dump to measure the energy-time distribution.The current status is to manufacture high-power RF components such as deflector cavity, pulse compressor, and dummy load. In this presentation, we will show the design, manufacturing method, and commissioning status of these components.
Paper: WEPS067
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS067
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
High power testing of 500MHz room temperature high-frequency cavity
The high-frequency cavity system of the Wuhan Advanced Light Source (WALS) utilizes a normal temperature single-cell cavity with heavily damped higher-order modes. The operating frequency of this cavity is 499.654 MHz. Power from a solid-state power source module passes through a circulator and then is fed into the main cavity via a waveguide. The coupler is designed to be compatible with both circular waveguides and coaxial waveguides, and the coupling coefficient can be continuously adjusted within the range of 1 to 3. This paper reports that in November 2024, the 500 MHz normal temperature high-frequency cavity of WALS has successfully completed a 50 kW high-power test, effectively validating the performance of the high-frequency cavity and the stability of the high-frequency system.
WEPS070
Analysis of coupled-bunch instabilities in Diamond-II
2388
The low-frequency components of the impedance drive coupled-bunch instabilities in electron synchrotrons. In the Diamond-II storage ring, the geometric component of the impedance of some vacuum vessels is comparable in strength to the resistive-wall impedance. This study compares the growth rates of all coupled-bunch modes obtained through simulations and analytical calculations. Self-consistent simulations, incorporating the harmonic cavity along with short-range wakefields and higher-order cavity modes, show that the beam can be stabilised with and without multi-bunch feedback by adjusting the chromaticity.
Paper: WEPS070
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS070
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS071
Microwave instability driven by terahertz-scale resistive-wall impedance in Diamond-II
2391
Vacuum vessels of the Diamond-II storage ring feature non-evaporable getter (NEG) coating which cause a resonator-like peak in the longitudinal impedance. This work demonstrates how different parameters of NEG can increase momentum-spread growth. It is shown that the spread of the coating-layer thickness amongst vacuum vessels results in significantly reduced momentum-spread growth. Insertion devices featuring rectangular geometry and NEG coating can cause a multi-peak structure of the longitudinal impedance which can drive additional momentum-spread growth.
Paper: WEPS071
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS071
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS075
A new method for the RFQ inter-vane voltage diagnostic
2395
Radio frequency quadrupole (RFQ) is one of the first cavities in a protons or ions accelerator. It aims to focus, bunch, and accelerate the beam, using a high-intensity electric field concentrated between rods or vanes. At CEA, similarly to other labs, a method to evaluate the inter-vane voltage and to tune the cavity (usually with 4 vanes) has been developed, based on the bead pull measurement. It consists of inserting a small bead in the back of each of the 4 quadrants. The induced magnetic field perturbation aims to evaluate the electric field close to the beam axis. This method requires the insertion of a bead along the cavity, whose length can be about several meters. In this paper, we propose to study the possibility of measuring and tuning the cavity using the insertion of slug tuners which would demonstrate the feasibility of obtaining this diagnostic, without opening the cavity.
Paper: WEPS075
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS075
About: Received: 20 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
WEPS076
Thresholds of longitudinal multi-bunch instabilities in double harmonic RF systems
2398
Multi-bunch instabilities, often driven by narrowband impedance sources such as higher-order modes, present significant intensity limitations in synchrotrons. One approach to mitigate these instabilities is applying a double harmonic radio frequency (RF) system, which can increase the intensity threshold by enlarging the synchrotron frequency spread. In this study, intensity thresholds are calculated for different RF parameters using stability diagrams derived from the Lebedev equation. We analysed configurations and beam characteristics relevant to the synchrotrons at CERN, particularly focusing on the Super Proton Synchrotron (SPS). The semi-analytical results were then compared to macroparticle simulations and measurements. The findings reveal an unexpected beam stabilisation even if a non-monotonic amplitude dependency of the synchrotron frequency is present. Further, techniques for deducing the driving impedance parameters are discussed.
Paper: WEPS076
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS076
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS088
Wakefield and HOMs preliminary characterization of the four-quadrant multi-cell RF accelerating structure for the ASTERIX project
2402
The goal of the ASTERIX project, proposed at INFN-LNF and funded by the CSN5, is the first-time demonstration of a practical, meter-long X-band RF structure for real linear accelerators made of hard copper and four quadrants. Our joining technique will be the TIG welding for the prototype. During the feasibility study, in the first year, we will proceed to the RF cavity design of two full structures (~ 1m long and ~100 cells), one with optimized geometry for single-bunch and the other one for multi-bunch operation. We will perform the RF design optimization, including thermo-mechanical analysis, of the multi-cell TW cavity and the RF mode-launcher (which will be integrated with the cavity in the most compact way possible) for both structures’ geometries. In this paper, we show the preliminary characterization of the higher-order modes (HOMs) and wake-fields, which are detrimental for the particle beam with high-quality parameters typically accelerated in such structures, in the case of single-bunch operation. The electromagnetic designs will be performed by using the 3D numerical codes Ansys-HFSS and CST-Microwave Studio.
Paper: WEPS088
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS088
About: Received: 29 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
WEPS090
Touschek effect in Super Charm Tau factory
2405
Super Charm Tau factory is a proposed electron-positron double ring collider with crab waist collision scheme operating in wide beam energy range from 1.5 GeV to 3.5 GeV with peak luminosity of 10^35 cm^(-2) s^(-1). The polarized electron source and three Siberian Snakes provide 80% longitudinally polarized electron beam at 2 GeV. Superconducting wigglers decrease damping times, effects of intra-beam scattering and increase Touschek beam lifetime, particularly at low energy. This work presents studies of the Touschek effect in SCTF, as well as the results of a simulation of Touschek scattering, MOGA optimization of local momentum acceptance, and an investigation into the dependence of the dynamic aperture and the Touschek lifetime on the average orbit error.
Paper: WEPS090
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS090
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS091
Intrabeam scattering in SRF "SKIF" storage ring
2408
SKIF (Russian acronym for Siberian Circular Photon Source) – is a new fourth generation synchrotron light source under construction in Novosibirsk, Russian Federation. One of the most important characteristics of the synchrotron radiation source SRF "SKIF", which in turn determines its brightness, is the ultra-low emittance of the electron beam, which depends on the operating regime and parameters of the storage ring: the intensity of the electron beam, the insertion devices parameters, the coupling coefficient of linear betatron oscillations, the elongation of the bunches, etc. Intrabeam scattering (IBS) is a collective effect that causes bunch volume inflation and brightness decrease for high intensity beams. Described in this work are the results of study of IBS impact on beam emittance, energy spread, Touschek lifetime and geometrical brightness for different operating regimes of the SRF “SKIF” storage ring.
Paper: WEPS091
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS091
About: Received: 29 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
WEPS092
Touschek lifetime and periodic beam loading effect in the storage ring of SRF "SKIF"
2411
The collective effects observed in storage rings with high-intensity beams are numerous and diverse. One such effect is that of periodic beam loading of accelerating RF cavities. This effect is contingent upon the impedance of the fundamental mode of the RF cavities and the mode of filling pattern. In a multitude of configurations, the periodic beam loading effect in storage rings leads to a change in the Touschek lifetime along the beam. This work is dedicated to the calculation of this effect in the storage ring of SRF "SKIF", a novel fourth-generation synchrotron radiation source currently under construction in Novosibirsk. Analytical calculations of this effect have been carried out for the main filling mode of the storage ring. It has been demonstrated that bunches in this regime can exhibit significantly disparate Touschek lifetimes. Furthermore, it has been shown that the effect is negligible when the RF acceptance is equal to the energy acceptance of the storage ring.
Paper: WEPS092
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS092
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
Application of the nonlinear material solver in the ACE3P electromagnetic code suite
SLAC has been developing the parallel finite element electromagnetics simulation suite ACE3P (Advanced Computational Electromagnetics 3D Parallel) for accelerator modeling using high performance computing (HPC) platforms. In this work we present the current status of the development of the nonlinear EM solver, in ACE3P which includes nonlinear material with application to quantum nonlinear photonics. This utilizes parallel and scalable architecture to perform simulations on multiscale optical and quantum systems. We show examples of harmonic generation, and parametric interaction essential for THz generation. Also we show examples of using this code to design novel THz nonlinear deflecting structures used for developing a sub0femotosecon timing diagnostics for UED beamlines.
Design of a high-power X-band load with circular waveguide TE01 mode input
RF loads are critical components in any high-power rf system. There are two types of commonly used rf loads in multi-megawatt systems: water loads and dry loads. Water loads have a ceramic window separating vacuum from the water. Use of water loads in large scale rf systems is risky because of the possibility of water leaking into vacuum. At SLAC multi-megawatt dry loads were developed and used in S-band and X-Band applications. For example, a compact X-band load based on a tapered WR90 and circularly polarized TE11 mode has been in use for decades. To increase high power performance of a load beyond the state-of-the art, we designed an 11.424 GHz load fed by the TE01 circular waveguide mode. The load is of disk-loaded-waveguide type, built out of a set of cells. The cells are made of magnetic stainless-steel with bulk conductivity is 160000 S/m. The passband of the load is about 180 MHz. The load utilizes axially symmetric TE mode which has minimal surface electric fields. We show the design of the load and results of X-band resonant measurements of the load’s cells. The measurements allow us to determine conductivity of the 430 stainless steels after multiple brazing cycles.
High efficiency L-band IOT design and high power testing
Recent efforts at SLAC aim at developing high-power accelerators powered by compact, high-efficiency rf sources such as klystrons and Inductive output tubes (IOT). In particular, a high-efficiency IOT is an electron-beam-driven RF source employed in the UHF band that offers high efficiency at variable output power levels. In this talk, we show the progress of developing a 1.3 GHz HEIOT in terms of design, and manufacturing.
WEPS100
Impedance reduction of the beam wire scanners for the CERN LHC
2415
The beam wire scanners are instruments for precise transverse beam profile measurements by detecting the secondary particles generated from the interaction of the beam with a moving carbon wire. Following a completely new design of this device for the Large Hadron Collider (LHC), a detailed impedance calculation has been performed already in the design phase. This contribution presents the beam coupling impedance optimization and reduction strategy of the beam wire scanners for the High-Luminosity (HL) upgrade of the LHC. Prior to the construction of the prototype, extensive three-dimensional electromagnetic simulations of the proposed mechanical designs were performed to detect potential resonances and their sources. The mechanical model was improved to minimize the beam coupling impedance by geometrical modifications and coatings. We also present the beam-induced RF power loss calculation of the instrument.
Paper: WEPS100
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS100
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
Effects of chromaticity and space charge on coupled bunch instability in CSNS/RCS
Coupled bunch instability was observed during beam commissioning of CSNS/RCS. The instability was successfully suppressed by installing sextupoles to control chromaticity. The instability exhibits characteristics influenced by the strength of space charge. We conducted a theoretical study on the effects of chromaticity and space charge on coupled bunch instability and compared results with simulation and measurements. This work provides valuable insights for beam control in the second phase of CSNS.
WEPS102
Reconstructing wake functions using Haissinski distributions from multiple bunch charges
2419
Accurate knowledge of wake functions is crucial in accelerator physics, serving as the cornerstone for understanding intra-bunch interactions and for controlling or mitigating instabilities that limit accelerator performance. Haissinski distributions, which describe the steady-state longitudinal bunch density, are intrinsically determined by the wake function experienced by the bunch. While these distributions are typically computed from a given wake function, we investigate the inverse problem: extracting the wake function directly from measured Haissinski distributions. In this theoretical work, we introduce a novel method to reconstruct wake functions by utilizing Haissinski distributions obtained at multiple bunch charges. By combining these profiles into an overdetermined system, we address challenges posed by the inverse problem, which is sensitive to noise and discretization errors. Here, our preliminary results suggest that the use of regularization techniques may help achieve more stable reconstructions of the wake function.
Paper: WEPS102
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS102
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS103
Impedance estimation and instability analysis for Korea-4GSR storage ring
2423
Korea-4GSR is a future light source in Korea with a circumference of 800 m, an energy of 4 GeV, and a maximum current of 400 mA. Due to the small aperture of the vacuum chamber (12H x 9V octagonal) and the large number of normal-conducting cavities and beam position monitors (BPMs), impedance-induced instabilities are expected to pose challenges at 400 mA operation. In this study, we estimated the storage ring impedance of Korea-4GSR and investigated both single-bunch and multi-bunch instabilities to determine optimal operational conditions, including the analysis of fill patterns
Paper: WEPS103
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS103
About: Received: 04 Jun 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
WEPS105
Benchmark study of transverse instability driven by the resistive wall impedance in the PF-HLS 2.5 GeV storage ring
2427
Effect of the transverse instability driven by the resistive wall impedance in the PF-HLS (Photon Factory Hybrid Light Source) 2.5GeV storage ring* are investigated and compared with three methods: an analytical method with azimuthal modes**, a Vlasov solver DELPHI*** and beam tracking code MBTRACK2****. The PF-HLS is proposed as the successor machine to the PF-2.5GeV ring and the PF Advanced Ring at KEK. Its concept is a 2.5/5.0GeV energy switchable high-brightness storage ring with a circumference of 750m. A feature of this ring is the adoption of isochronous cells over a large part of the ring, which allow electrons having a bunch length shorter than one nano-second to pass through without significant bunch lengthening. However, in return for this feature, the momentum compaction factor becomes small, which is estimated to 3.24x10-5. In this case, the coherent beam motion may be sensitive to the ring chromaticity. As the results, it's suggested that the higher-order modes of the coherent beam motion determine the stability of the beam. In the paper, the chromaticity dependence of the instability growth rate for each method is compared and reported in detail.
Paper: WEPS105
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS105
About: Received: 25 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
Microbunching gain evaluation of bunch compressor designs
Many accelerators have to take microbunching gain into consideration during both design and operation; this typically involves beam parameters where space charge is negligible. However, there are some accelerator designs which involve bunch compression of low energy beams with very low slice energy spread - conditions which may be prone to both microbunching considerations as well as space charge. In this paper, we examine the impacts of space charge on the microbunching gain of bunch compressor chicanes of various designs.
WEPS108
Studies of resonances limiting the high-brightness LHC beams in the SPS
2431
Space charge effects in combination with betatron resonances limit the performance of high-brightness LHC beams in the CERN Super Proton Synchrotron (SPS). Here we report on experimental studies performed with single-bunch proton beams, monitoring transverse emittance evolution and particle losses while performing tune scans across the horizontal and vertical planes. Two significant resonances were identified: a coupled resonance leading to emittance growth in the horizontal plane and a corresponding emittance decrease in the vertical plane, and another coupled resonance directly associated with particle losses. The resonances identified in these studies could explain the limitations of the beam brightness encountered with the multi-bunch LHC-type beams in the SPS, thus providing valuable insights for the optimization of the high-intensity beams performance.
Paper: WEPS108
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS108
About: Received: 27 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS110
An updated HL-LHC halo population model based on recent experimental measurements
2435
The transverse beam halo population in the Large Hadron Collider (LHC) has been found to carry a significant fraction of the total stored beam energy, potentially reaching several percent. With the anticipated increase in beam brightness for the High Luminosity LHC (HL-LHC), this poses an increasing risk to machine safety, particularly during abrupt orbit shifts or critical component failures. A comprehensive understanding and an accurate modelling of the transverse beam halo are crucial for simulations of beam losses around the ring as a consequence of such failure scenarios in the HL-LHC era. Various models, including Gaussian, double-Gaussian, and q-Gaussian distributions, have been used to describe the LHC beam halos for fitting the measured distributions. This paper provides an in-depth analysis of halo modelling based on collimator scraping measurements from the LHC operational Run 2 and Run 3, and evaluates the accuracy and representativeness of these different distribution models.
Paper: WEPS110
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS110
About: Received: 27 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Dynamics studies for advanced-compact and high repetition rate C-band injector for PWFA
C-band technology holds the potential to generate a high-energy, high-brightness electron beam by elevating the peak field of both the cathode and cavity within the machine. This proposed injector offers a promising avenue for achieving kHz operation. The conceptualization of this injector draws inspiration from the EuPRAXIA@SPARC_LAB S-band injector, wherein the gun is replaced with a 2.6-cell C-band RF gun. The entire beamline is proportionally scaled, reducing lengths by a factor of 2 while doubling electric and magnetic fields. Operating with brief RF pulses, the 2.6-cell C-band RF gun mitigates breakdown rates and power dissipation. By capitalizing on higher peak fields and applying established scaling laws to reduce laser spot size and duration, it becomes feasible to minimize both cathode and space charge emittance. A Ka-band HHC after the RF gun stabilizes the beam by pre-correcting its longitudinal phase space, flattening the charge distribution, and optimizing parameters at the photoinjector exit. The design of a C-band injector is within the framework of the EuPRAXIA@SPARC_LAB design study, aiming to produce high-quality beams for PWFA applications.
WEPS113
Update on multi-objective genetic optimizations of the photoinjector for CARIE
2439
We present updated simulation results on the maximum brightness achievable by a 1.6-cell cold copper C-band photoinjector, designed for testing and commissioning as part of the Cathodes and RF in Extremes project at Los Alamos National Laboratory. Previous simulations highlighted the high brightness attainable with a 250 pC bunch charge, attributed to the high accelerating gradients and the benefits of a radially symmetrized photoinjector design. However, these earlier simulations relied on idealized temporal beam profiles, overlooked the temporal evolution of the gradients, and did not account for the influence of cathode plug geometry on the gradients—factors that significantly affect the maximum achievable brightness. In this work, we report the results of Multi-Objective Genetic Optimizations that incorporate more realistic temporal beam profiles and gradients, accounting for both the cathode plug geometry and the effects of time-dependent gradient evolution.
Paper: WEPS113
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS113
About: Received: 28 May 2025 — Revised: 14 Jun 2025 — Accepted: 14 Jun 2025 — Issue date: 10 Jul 2025
Wakefield effects on dynamic aperture during RCS bunch merges
In order to achieve the necessary bunch charge, the Rapid Cycling Synchrotron utilizes bunch merging. The altered longitudinal motion during merges has the potential to reduce dynamic aperture and cause emittance growth. Tools for analyzing the effects of merging have been developed for the AGS using Bmad and a simplified tracking code in Julia. These tools are applied to the merges of the RCS, altered to include the important effects of wakefields. In this paper, dynamic aperture and emittance growth for current RCS merge parameters and their effective operational limits are analyzed.
Effects of dark current in high brightness RF photoguns
The behavior of high gradient rf cavity is improved via the reduction of RF breakdown rates by operating at cryogenic and temperatures. These studies are largely empirical but they present a new paradigm in the future of high gradient capital operation. Peak electric fields >200 MV/m are sustainable at S and C band frequencies. These fields while sustainable produce more dark current than is ideal for high brightness beam production. We present investigation into the dark current limits on high brightness beam performance, especially in the case of an RF photogun where beam dynamics is most sensitive. We also present mechanism for reducing the effects of dark current on bright low charge electron beams produced in high gradient photoguns. Specific interest is spent considering reentrant nosecone geometric for high shunt impedance cavities.
Beam-beam simulation with lattice and related researches of STCF
To achieve the design luminosity of $1 \times 10^{35}\ \text{cm}^{-2}\text{s}^{-1}$, the Super Tau-Charm Facility (STCF) adopts an extremely low $\beta_y^*$ and a crab waist (CW) collision design. The extremely small vertical beam size at the interaction point and low vertical emittance required to achieve a beam-beam parameter of around 0.1 make the CW colliders highly susceptible to beam instabilities arising from beam-beam interactions. Some of these instabilities need to be carefully assessed and optimized through strong-strong beam-beam simulations. The nonlinearity from lattice will further increase the need to circumvent these instabilities.In this paper, we investigate the luminosity stability of the STCF design parameters using strong-strong simulations with lattice. We also explore the influence of the CW scheme and various beam parameters on luminosity. These findings offer valuable insight to guide lattice design and optimize global parameters for STCF.
Ion effects on the space charge limited emission for particle-in-cell simulations
Space charge limited (SCL) emission is of fundamental importance to vacuum electronic devices, where the self-field of emitted charges limits the maximum current density being emitted from a cathode surface. Traditional modeling of SCL emission using the Child-Langmuir law primarily focuses on electron dynamics, neglecting the role of ions, which can significantly influence emission dynamics. In this work, we extend a previously developed simple SCL algorithm for implementing the Child-Langmuir law at the surface grid in particle-in-cell (PIC) simulations to study ion effects. The presence of ions introduces new dynamics, affecting the steady-state current, the evolution of surface electric fields, and the transient behavior of SCL emission. Using the 1-D electrostatic PIC code, XPDP1, developed by the Plasma Theory and Simulation Group (PTSG), we investigate these ion-induced modifications and test the influence of ions on the SCL emission algorithm. The extended algorithm ensures an accurate computation of the surface electric field via Gauss’s law to resolve the space charge contribution from both ion motion and electron emission, and the findings will be discussed in detail.
Enhanced G4beamline advanced GUI for accelerator modeling
Graphical user interfaces (GUIs) are sought to support particle accelerator and beamline modeling for both conventional and advanced accelerator concepts. Downloaded over 1500 times in the last 22 years, G4beamline (available gratis from Muons, Inc.) has been used for diverse applications in science and industry, representing over 50M$ of economic activity. Its strengths include ease of use compared to its underlying CERN Geant4 package, flexibility in modeling beamline elements (as well as other systems such as particle detectors), and use of the well tested Geant4 libraries to track particles in electromagnetic fields and in matter: of particular importance in simulating muon cooling and muon colliders. Its current GUI interface is however rudimentary. A more comprehensive and modern GUI would enhance the program’s utility and user appeal, attracting a wider community of users in accelerator science and related fields. Another valuable feature would be “hooks” in the GUI interface for additional commonly used simulation programs such as MCNP and MAD-X, easing comparisons among alternative accelerator modeling tools by providing a common geometry description and output format.
Full simulation model of crystal-based extraction from an accelerator using BDSim and Geant4 G4ChannelingFastSimModel
Oriented bent crystal planes can deflect charged particles as strongly as a magnetic field exceeding 100 T. As a result, beam extraction from an accelerator using oriented crystals offers significant opportunities for diverse applications, ranging from beam tests for particle detector R&D to high-energy fixed-target experiments. However, designing these applications requires a universal simulation tool that accurately describes the physics of crystals, beam dynamics in an accelerator, and particle interactions with materials. We present a new simulation model realized using the BDSIM * , built on the Geant4 toolkit ** , to simulate particle transport in accelerators and their interactions with materials. The model includes a bent crystal as a new BDSIM accelerator component, leveraging the latest Geant4 features, G4ChannelingFastSimModel *** and G4BaierKatkov, to incorporate channeling physics and radiation losses, respectively. This model was applied to simulate the crystal-based extraction of 6 GeV electrons from the DESY II Booster Synchrotron ****. We present the calculated parameters of the extracted beam and discuss the feasibility of a proof-of-principle experiment.
Error tolerances for a 4 GeV fourth-generation synchrotron light source
Recently, many new light source projects have been developed based on the Multi-Bend Achromat (MBA) magnet lattice. In general, the dynamic aperture and transverse emittance of synchrotron light sources are sensitive to errors in magnet fields, alignment, and momentum. A realistic estimation of error tolerances is crucial for the successful construction of a fourth-generation synchrotron light source. In this paper, we present a realistic estimation of the error tolerances for a 4 GeV, 800-meter-long fourth-generation synchrotron light source, based on numerous simulations performed using the ELEGANT code in conjunction with an MCP server and an Agentic AI.
Report on the hands-on training with the ELEGANT code at ISBA24
The 7th International School on Beam dynamics and Accelerator technology (ISBA24) took place over nine days, from November 1 to 9, 2024 at Chiang Mai University in Thailand. The school, part of the KEK-IINAS-NX series, was jointly hosted by Chiang Mai University and the Synchrotron Light Research Institute (SLRI). Out of 115 applicants who had submitted resumes and recommendation letters, 64 students from nine countries (Thailand, China, Japan, Indonesia, Korea, Taiwan, India, Germany, and Turkey) were selected to participate the school. During the ISBA24 school period, we opened four hands-on trainings with ASTRA, ELEGANT, CST, and OPERA codes to deepen students’ understanding of accelerator theory and improve their skills in accelerator design. All students chose one of the hands-on trainings according to their interests. In the ELEGANT hands-on training, approximately 20 students learned to use the ELEGANT code to design the various 4th generation synchrotron light sources with the Multi-Bend Achromat (MBA) magnet lattices. In this paper, we report details on the ELEGANT hands-on training conducted during ISBA24.
WEPS132
Estimation of the required current on the anode power supply for high power operation in the J-PARC Main Ring
2443
The J-PARC Main Ring (MR) RF system has been undergoing upgrades in preparation for the Hyper-Kamiokande (Hyper-K) neutrino experiment, which is scheduled to begin receiving a 1.3 MW proton beam in 2028. The beam will be accelerated from 3 GeV to 30 GeV within the MR over a reduced cycle time of 0.58 seconds, down from the current 0.65 seconds. Additionally, the number of protons will be increased from $2.3 \times 10^{14}$ to $3.1 \times 10^{14}$to support high power operation. To accommodate these enhancements, additional RF cavities equipped with 600 kW vacuum tubes will be installed, and the anode current will be increased accordingly. Maintaining a constant RF voltage under these conditions requires more anode current to supply the necessary voltage and to compensate for beam loading effects. This paper presents an estimation of the anode current required for high-power beam operation.
Paper: WEPS132
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS132
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
Development of test bench for 324 MHz superconducting cavity power couplers
The power coupler is one of the most important components for superconducting cavities. Different from the normal conducting cavity, the superconducting cavity has to keep an ultra-high cleanliness environment for operation. As the vacuum barrier, power couplers are welded by many different materials and maybe the gas source since they are installed to the cavities after vertical test, therefore, they should be high power conditioned before operation. Generally speaking, test bench equipment with two power couplers is often designed to improve the high conditioning efficiency. In this paper, different types of test benches are compared according to simulation and the cylindrical quarter-wavelength cavity is chosen. Besides, the detailed electromagnetic and mechanical design of the test bench is presented; to verify machining accuracy, two test pieces are also designed to measure the transmission of the test bench. Finally, limited by the output power of klystron, the test bench with a pair of couplers is high power conditioned to a standing power level of 500 kW with a repetition rate of 25 Hz and a pulse width of 1.2 ms.
Development of an online adjustable waveguide coupler for CSNS- Ⅱ debuncher cavity
The China Spallation Neutron Source Upgrade Project (CSNS-Ⅱ) will use two debuncher cavities to supplement the beam energy at the end of the linear accelerator. The PI mode structure operating at room temperature is chosen, and each debuncher cavity is equipped with an online adjustable waveguide coupler. The main body of the coupler is the WR1500 waveguide, and a hole on the narrow wall of the waveguide is opened to achieve the coupling between the cavity and the waveguide. Meanwhile, every coupler contains a removable waveguide window. In this paper, we will detail describe the electromagnetic, cooling and mechanical design of the coupler. Finally, the coupler is high-power conditioned to 1 MW with a duty factor of 2.25%, and the coupler factor of it can be online adjusted between 0.6˜3 without arc event.
WEPS135
RF window ghost mode analysis
2447
The RF window acts as a barrier between the vacuum and air, gas, or water while allowing RF power to pass through with minimal loss. Resonant modes (called "ghost modes") can occur within the ceramic disk of a window. The frequencies of these modes depend on the material and size of the ceramic. Ceramic disk dimensions must be carefully optimized to minimize reflections and avoid ghost mode resonances within the operating bandwidth. In this paper we present the design of an input window used in an X-band klystron. The dimensions of the window and ceramic disk are optimized to minimize insertion and reflection losses while preventing ghost mode resonances in the operating bandwidth. In addition to this, we ensure that the maximum electric field at the window surface is kept low to reduce the probability of RF breakdowns. Analytical analysis, numerical simulations and experimental measurements of the ghost modes of ceramic disks were carried out. The measured ghost mode frequency was used to evaluate the ceramic dielectric constant. In this article we present simulated and measured results.
Paper: WEPS135
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS135
About: Received: 29 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Design and simulation of high-power RF window for NSTRI e-Linac Project
The RF window has to withstand several megawatts of RF power without experiencing any physical deformity to maintain the pressure difference between vacuum and isolate gas sides. It must also have suitable and acceptable RF performance with minimum reflection and insertion loss. The design of an RF window depends on the window materials' dielectric characteristics, such as dielectric constant, permeability, and permittivity. The dielectric permittivity and permeability of window material affect the transmission of RF power. This paper presents the design and simulation of an RF window that works at a frequency of 2.998 MHz and performs thermal analyses to determine its structural stability. This RF window must withstand an average power of 3 kW. This window will used for NSTRI dual energy e-Linac Project.
Design and implementation of ridge waveguides for dual-mode microwave structure
The growing interest in dual-mode microwave structures has led to a surge in research efforts. A critical challenge in their application is the efficient transfer of microwave power with various frequencies. One approach to this issue involves the utilization of intricate waveguide components, such as a dual-mode electron gun that operates at both the fundamental and second harmonic frequencies. This gun is constructed by integrating a directional coupler with a mode launcher, which allows the S-band and C-band power to be transferred into a single waveguide, directing them to a dual-mode electron gun. An alternative method employs ridge waveguide technology to selectively transmit or block specific frequencies. The technology has been successfully integrated into dual-mode deflecting structure. This paper presents a C-band bandpass filter has been engineered to achieve a power reflection level of less than -30 dB at 5712 MHz and a power transmission level of less than -40 dB at 11424 MHz.
Magnetic properties of niobium processed with high- and low-temperature nitrogen baking for SRF applications
We systematically investigated the effects of various thermal treatments on the superconducting properties of niobium. In this study, niobium is utilized for fabricating nine-cell 1.3 GHz cavities used in particle accelerator facilities. Cylindrical niobium samples underwent the same chemical and thermal treatments applied to superconducting radiofrequency (SRF) cavities, including buffered chemical polishing (BCP), low-temperature baking (LTB), N-doping, and N-infusion. Magnetization curves and complex magnetic susceptibility were measured across a broad temperature range (2–9 K) and in dc magnetic fields up to 1 T. Bulk superconductivity parameters such as the critical temperature (Tc), thermodynamic critical field (Bc), and upper critical field (Bc2) were determined for samples subjected to different treatments. Notably, the Bc2 field exhibited significant variation depending on the treatment, reaching its highest value for N-doped niobium. Additionally, evidence of surface superconductivity at fields exceeding Bc2 was observed in all thermally treated samples, with the critical surface field surpassing the Ginzburg-Landau field in all cases.
In-situ XPS study of low-temperature baking of SRF niobium cavities
We investigated the effects of low-temperature baking, a standard treatment for superconducting radiofrequency (SRF) cavities, on niobium samples using synchrotron X-ray photoelectron spectroscopy. The study examined the chemical state of the niobium surface after chemical treatment with a buffered etching solution, which leaves a native oxide layer, fluorine impurities, and surface hydrocarbons. In-situ analysis was conducted during baking at 120°C for 48 hours in ultra-high vacuum. No significant changes in the core levels were observed; however, subtle variations were detected in the Nb 3d and C 1s spectra. Specifically, the most intense C 1s peak shifted to lower binding energies, indicating the formation of new chemical bonds. Additionally, partial transformation of Nb⁵⁺ to Nb⁴⁺ was observed, with no detectable oxygen depletion within the depth probed by XPS. The potential influence of X-ray exposure on the chemical state of these elements is also discussed.
Specification, design, and production schedule of cryomodule for SRF 5-year plan at KEK
A five-year project (MEXT advanced Accelerator element Technology Development (MEXT-ATD)) funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) began at KEK in FY2023. The goal is to manufacture and construct a cryomodule (CM) that satisfies the ILC (International Linear Collider Project) specifications and conduct cooling tests. The 3D model of the cryomodule will be based on the Type-4 CM adopted in the Technical Design Report (TDR) published in 2013, moreover will also reflect the latest technology and experience obtained from the construction and operation of the European XFEL in Europe and LCLS-II in the United States since the TDR. In addition, in anticipation of future prospects, it has been decided that the design and production of every cavity and CM will be based on the refrigeration regulations of the High Pressure Gas Safety (HPGS) Act in Japan. This is first for the iCASA SRF group in KEK. In this presentation, the basic specifications and design of the cryomodule as well as the overall manufacturing schedule and recent progress will be reported in detailed.
WEPS143
Ongoing vertical testing and high-pressure rinsing simulations of single-spoke resonator cavities
2450
Vertical tests of single-spoke resonator type 1 (SSR1) superconducting cavities were conducted in conjunction with high-pressure rinsing (HPR) simulations to assess and improve cavity performance. The quality factor (Q) was evaluated as a function of the accelerating field (Eacc), Lorentz force detuning (LFD), and pressure sensitivity. In the HPR simulations, water droplet dynamics emitted from a 0.5 mm diameter nozzle operating at 100 bar were analyzed as a function of travel distance. The simulations provided detailed estimates of the velocity and impact force of the water jet, which are critical for optimizing cavity surface cleaning.
Paper: WEPS143
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS143
About: Received: 26 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
WEPS144
Understanding superconducting cavities through the least action principle
2454
Superconducting cavities are indispensable elements in modern particle accelerators, utilizing the ultra-low sur-face resistance of superconductors to achieve exceptionally high quality factors. In this work, we apply the least action principle to derive an equivalent RLC circuit model, offering a unified theoretical framework to describe the electromagnetic behavior of superconducting cavities. Beyond the classical model, we examine the underlying heat dissipation mechanisms and identify quantized physical quantities that influence cavity performance. Particular attention is given to the quantum aspects of the quality factor, including its manifestation in decay time measurements. By bridging classical electrodynamics and quantum dissipation, this study provides a deeper under-standing of the fundamental principles governing super-conducting cavity dynamics.
Paper: WEPS144
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS144
About: Received: 26 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS145
Plasma processing of ESS elliptical cavities
2458
Plasma treatment has proven effective in recovering and reducing field emission in the affected superconducting radiofrequency (SRF) cavities. A joint effort is underway between CEA, ESS and INFN to apply this technique to the treatment of elliptical cavities in the ESS linac. This paper presents the work done so far, which aims at both the development of the plasma process for cavities in the cryomodule and the treatment of cavities in the vertical test configuration. The peculiarity of ESS cavities compared with typical cavities at 1.3 GHz is the absence of couplers for higher orders.
Paper: WEPS145
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS145
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
WEPS147
R&D on SRF cavities at INFN-LASA
2462
As part of its ongoing and future contributions to high-Q/high-G activities in major international projects such as PIP-II, ILC Technology Network, and the European Strategy for Particle Physics, INFN-LASA is upgrading its experimental facility for vertical cold tests of superconducting cavities. This upgrade will enable cavity performance characterization in a low residual magnetic field environment and with dedicated diagnostics for understanding possible performance limitation. In parallel, state-of-the-art surface treatments aimed at achieving high-Q and high-G performance are being developed and applied to single and multicell cavities at different frequencies. This paper presents the current status of the facility, its key features, an overview of cavities currently in production, and the experimental results obtained to date.
Paper: WEPS147
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS147
About: Received: 29 May 2025 — Revised: 31 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
WEPS148
INFN LASA in-kind contribution to PIP-II
2466
This paper reports the status and recent progress of INFN LASA’s in-kind contribution to the PIP-II project at Fermilab, with updates on key activities and major procurements. Production efforts for the 38 INFN LASA-designed, 5-cell cavities (β=0.61) for the LB650 section of the linac are underway and two pre-series prototypes are being realized as a first step to validate the manufacturing and treatment sequence. Concurrently, preliminary testing on existing prototypes is progressing to gain a deeper understanding of the surface preparation and qualification procedures, including cross-validation at different infrastructures. Series LB650 cavities will be industrially produced and surface-treated to achieve the stringent performance targets, qualified via vertical cold tests at DESY AMTF, and delivered installation-ready for string assembly.
Paper: WEPS148
DOI: reference for this paper: 10.18429/JACoW-IPAC25-WEPS148
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025