MOPB
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Monday Poster Session: MOPB
02 Jun 2025, 16:00 -
18:00
MOPB001
Beam dynamics studies and vacuum diagnostics in the Solaris storage ring
69
Since 2015, the National Synchrotron Radiation Center SOLARIS has operated a light source supporting eight experimental beamlines. Following vacuum chamber replacements and beamline upgrades, the total beam lifetime at 400 mA has reached 13 hours in decay mode operation. Regular lifetime measurements are conducted to monitor vacuum quality, residual gas composition, and potential stability issues arising from machine aging. Beam dynamics studies involve measuring electron beam lifetimes at 400 mA, 300 mA, and low currents (as low as 10 mA) under both multibunch and single-bunch operating modes. A particular focus is placed on intra-beam electron interactions influencing the Touschek lifetime and the effects of residual gas on beam scattering. These investigations provide valuable insights into vacuum performance, electron bunch behavior, and overall storage ring dynamics.
Paper: MOPB001
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB001
About: Received: 27 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB002
An IGBT pulser for the nonlinear in-vacuum kicker at Taiwan Photon Source
72
A test unit pulser for the proposed NIK (nonlinear in-vacuum kicker) project at TPS (Taiwan Photon Source) was fabricated in order to provide uniform kick strength applying onto the injected bunch train. This newly built flattop pulser gives much improved drive current pulse shape in comparison with previously used half-sine pulser. This flattop pulser will result in high injection efficiency and provide adjustable capability in terms of bunch train filling pattern.
Paper: MOPB002
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB002
About: Received: 20 Apr 2025 — Revised: 14 Jun 2025 — Accepted: 14 Jun 2025 — Issue date: 10 Jul 2025
MOPB004
The data acquisition system on vibration evaluation and predictive maintenance for cooling water pumps system in TPS
75
The purpose of this paper is evaluating vibration status for cooling water pump system in TPS. The utility systems operate continuously since TPS commission in 2014. The predictive maintenance based on vibration level and spectrum became more important, especially for those unstoppable operate water pump systems. The vibration monitoring system started to construct in 2017 and upgraded in 2023. After vibration test over several months and years, some components of the cooling water pumps found abrasion and mismatched. The recorded data showed vibration level increase irregularly over ISO 10816 standard. The spectrum showed the detail status in the pump system. The cooling water pump systems repaired and maintained base on vibration evaluation after vibration evaluation. The utility systems could prevent malfunction at least over one month through regular vibration inspection and daily data acquisition. The data acquisition system for pump systems on vibration evaluation provided the predictive maintenance enough time to solve the problem and avoid system suddenly shutdown.
Paper: MOPB004
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB004
About: Received: 27 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB005
SLS 2.0 storage ring upgrade overview
79
The Swiss Light Source, SLS, storage ring has been rebuilt as SLS2.0, to improve the radiation brightness by about two orders of magnitude. All components of the storage ring lattice and its supporting infrastructure are newly constructed and were installed during a 15-month shutdown that began in October 2023. The linac and booster synchrotron received only small modifications with the exception of a new power supply for the main magnet circuit with its 3 Hz current ramp. The new 7 bend achromat arcs had to fit the existing tunnel footprint and the location of the beamline exit ports resulting in tiny distances between magnets. In addition, all bends (and reverse bends) are based on permanent magnets necessitating thorough cross-talk studies due to larger stray magnetic field. The high density of magnets prevented the installation of vacuum bellows required for in-situ bake-out, so the twelve vacuum arc strings, of 18 m in length each, were installed in the ring after activation and pumping to a pressure around 1.e-11 mbar. Four HOM damped RF cavities at 500 MHz are installed in a row and supplied by four solid-state amplifiers of 150kW each. Two beamlines are dedicated to beam diagnostics and newly developed BPM and feedback systems monitor and stabilize the beam. This paper describes the main challenges faced during the SLS storage ring upgrade and gives an overview of the presently achieved performance. Beam commissioning details are described in a companion paper.
Paper: MOPB005
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB005
About: Received: 23 May 2025 — Revised: 04 Jun 2025 — Accepted: 06 Jun 2025 — Issue date: 10 Jul 2025
MOPB006
Optimal beam energy for ultra low emittance storage rings
83
As new synchrotron light sources push for lower emittances, intra-beam scattering (IBS) becomes an increasingly more important factor in determining the final beam distribution properties. Because IBS depends strongly on beam energy, in the regime of ultra-low emittance rings, beam energy is a parameter to be optimized for best beam performance. In this report, we study the optimal beam energy for various lattices and its dependence on bunch lengthening and damping wigglers.
Paper: MOPB006
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB006
About: Received: 25 May 2025 — Revised: 31 May 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB007
Echo-enabled harmonic generation at the DELTA storage ring
87
Echo-enabled harmonic generation (EEHG) has been proposed as a seeding method for free-electron lasers but can also be employed to generate ultrashort radiation pulses at electron storage rings. With a twofold laser-electron interaction in two undulators ("modulators"), each followed by a magnetic chicane, an electron phase space structure with high harmonic content is produced, which gives rise to coherent emission of radiation at short wavelengths. The duration of the coherently emitted pulses in a third undulator ("radiator") is given by the laser pulse durations. Thus, EEHG pulses can be three orders of magnitude shorter but still more intense than conventional synchrotron light pulses. The worldwide first storage ring implementation of EEHG was undertaken at the 1.5-GeV synchrotron light source DELTA at TU Dortmund University by reconfiguring an electromagnetic undulator. With a total length of only 4.75 m, the setup is very compact and fits in a single straight section. The paper presents technical aspects of the EEHG implementation as well as first results.
Paper: MOPB007
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB007
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB008
Higher order mode assessment in a single mode accelerating cavity
91
With the upgrade from PETRA III to PETRA IV the requirements concerning the beam parameters increase. Thus, a special focus is placed on the suppression of higher order modes (HOMs) in the accelerating systems. An Investigation of the already presented single mode structure showed the emergence of certain higher order modes. These cavity eigenmodes are now examined by evaluating and assessing their degrading influence on the particle beam by calculating kick and loss factors. Subsequently, the cavity geometry is changed to attenuate the HOMs’ influences or even supress them entirely. In this paper the optimization process using numerical simulations together with the achieved results and cavity structure are presented.
Paper: MOPB008
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB008
About: Received: 03 Jun 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
The high harmonic radiation with mild energy modulation based on storage ring
The synchrotron radiation generated by storage rings offers numerous advantages, including high stability, a broad photon energy range, and the capacity to support multiple users simultaneously. However, one notable limitation is its poor radiation coherence. Achieving coherent harmonic generation (CHG) in storage rings would not only significantly enhance the coherence of the emitted light but also dramatically improve specific spectral ranges, internal luminous flux, brightness, and energy resolution. However, the realization of higher order harmonic radiation usually requires higher energy modulation. In this paper, a relatively mild energy modulation scheme is proposed to generate higher harmonic radiation based on storage rings. Lower energy modulation is achieved by using a lower power laser, and then an additional self-modulation section is introduced to enhance the bunching factor of harmonics. Three-dimensional time-dependent simulation results based on the parameters of Hefei light source-II show that the modulation amplitude is reduced by half under the same harmonic radiation power, which can greatly improve the tolerance of the modulation to the momentum aperture in the ring and reduce the damping time to achieve coherent radiation with higher repetition rate.
Lattice design and optimization of the HALF storage ring with superbend
The HALF storage ring is a 2.2 GeV diffraction limited storage ring, with radiation photons mainly in the vacuum ultraviolet (VUV) to soft X-ray wavelength ranges. In order to meet the demand for high brightness hard X-rays, HALF plans to replace 0.9 T normally bending magnet with 6 T superbend. This paper reports two lattice design schemes, replacing one bend and two bends respectively. The beam dynamics effects of storage ring lattice with superbends has been also discussed.
Studies on virtual platform for the HALF beamline
The autonomous alignment and optimization of syn-chrotron beamlines pose significant challenges. Tradi-tionally, manual alignment is a time-consuming and ex-perience-dependent process, often requiring extensive diagnostic efforts and data collection. With the construc-tion of the Hefei Advanced Light Facility (HALF) under-way, the development of a virtual platform for beamlines will be an invaluable tool for beamline scientists and users. This platform will enable software testing and im-prove the prediction of optical element parameters in advance. In this paper, we present the development and comprehensive study of a virtual platform representing beamline BL10 at HALF. Additionally, we explore the integration of an AI-driven control system for optical element control in next-generation synchrotron radiation beamlines within the virtual platform.
MOPB014
Relativistic strophotron free electron laser
95
The scheme with quadrupole lenses is presented for realization relativistic strophotron type Free electron laser. Equations of motion are solved and trajectories are found. It is shown, that movement of electrons in presented scheme is stable in both transverse directions.
Paper: MOPB014
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB014
About: Received: 24 Apr 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB015
Tapering enhanced superradiance - tapering rate optimization using analytical magnetic field maps
98
THz sources are typically very limited in power, making high-power sources scarce. One of the most promising THz sources are the Free Electron Lasers (FELs), which can generate high-power THz radiation using an undulator structure. Undulator radiation is an incoherent synchrotron spontaneous emission whose energy is proportional to the number of particles in the beam (𝑁). By longitudinally bunching the charged particle beam, a coherent spontaneous emission is generated and referred to as a super-radiant emission. Unlike spontaneous emission, super-radiant energy yield is proportional to N^2. However, like typical FELs, the energy conversion efficiency is rather low. Here, we demonstrate a novel THz source structure based on a radiative interaction scheme of super-radiance – Tapered Enhanced Super-radiance (TES), which employs a tapered (amplitude) undulator in the zero-slippage condition. This method yields a significantly more powerful and efficient THz radiation source. An optimization algorithm was developed to obtain a tapering rate that yields the most efficient energy conversion from the electron beam to the radiation field.
Paper: MOPB015
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB015
About: Received: 02 Jun 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Multi-dimensional phase space reconstruction based on neural network and polarizable transverse deflecting cavity
High-dimensional phase space reconstruction is an important tool for achieving precise beam simulation and optimization. We adopt a machine learning approach with a polarizable transverse deflecting cavity to reconstruct the multi-dimensional phase space of electron beam. By scanning the strength of the quadrupole magnets and the polarizations of the deflecting cavity, projections of the multi-dimensional phase space in different directions are obtained. A neural network is first trained with a large dataset, and the trained model is then applied to reconstruct the phase space. The result shows that the reconstructed phase space is good agreement with the original one. This report will describe the methods and results in detail.
Design of beam spreader system at S3FEL
Shenzhen Superconducting Soft X-Ray Free Electron Laser (S3FEL) is a high-repetition-rate and high-brightness soft X-ray facility under construction. It is designed to support multiple user experiments simultaneously, each requiring different undulator lines and FEL parameters. This capability is made possible by the beam spreader system, which plays a pivotal role in transporting the electron beam from the exit of the LINAC to multiple undulator lines, predominantly facilitated by the Kicker-Septum system. The system eliminates transverse dispersion, coherent synchrotron radiation, and adopts an isochronous design, all critical for preserving beam quality. This paper outlines the basic layout and lattice design of the beam spreader, presenting the corresponding simulation results.
Combining SASE and external seeding at high repetition rate: FLASH upgrade status
The FLASH facility generates XUV and soft X-ray radiation in two FEL beamlines based on SASE and powered simultaneously by a single superconducting linac. To enable next generation user experiments a series of upgrades is coordinated within the FLASH2020+ project. Upgrades on the linac have been performed in a preparatory 9 month shutdown in 2021/2022 and have demonstrated to deliver an improved electron beam quality and parameter range for operation. Right now the upgrades are targeted towards the FLASH1 FEL beamline and will transit the FEL from SASE to external seeding at MHz repetition rate with near transform limited pulses at superb stability. With an APPLE3 design, the radiators will enable full polarisation control which, together with a THz radiator, new pump-probe lasers and the corresponding beamlines, will enable new experiments on e.g. circular dichroism of magnetic materials, chirality and resonant excitations. In this contribution, we report on the FLASH2020+ incorporated existing and upcoming alterations to the FLASH facility as well as to project progress with respect to the current as well as following near- and midterm installations.
MOPB019
Flash status 2024 - FEL operation for users and upgrade shutdown
102
FLASH, the XUV and soft X-ray free-electron laser at DESY, is currently undergoing the 2nd of two long upgrade shutdowns within the FLASH2020+ project. The 1st half of 2024 was dedicated to user operation. The upgrade shutdown started in June 2024, and we plan to come back to beam operation in August 2025. Here we will discuss the operational highlights of the first half of 2024, briefly describe the new features being implemented, and report on the shutdown status.
Paper: MOPB019
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB019
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Exploring second harmonic generation in hard X-ray self-seeding FEL
Recently, the Hard X-ray Self-Seeding (HXRSS) setup at the European XFEL has been successfully demonstrated, achieving routinely pulse energies in the seeded signal of several hundreds of microjoules at various wavelengths. However, the shorter wavelengths pose a challenge to the impulse response of crystal, limiting output radiation and spectral performance. To address these challenges, a strategy combining HXRSS with second harmonic generation and tapering has been proposed. We have condcuted the Start-to-end simulations at 15keV and compared the output of the pulses with direct seeding at fundamental harmonic and seeding combined with 2nd harmonic. Tapering further improves energy conversion efficiency, leading to increased pulse energy and enhanced signal to noise ratio.
MOPB021
Commissioning of the soft X-ray variable polarization afterburner at the European XFEL
106
Following the successful commissioning of the soft X-ray planar undulator system (SASE3), the European XFEL user community expressed a strong demand to extend the radiation properties and provide the possibility to obtain variable polarization modes. It was therefore decided to build a helical afterburner behind the SASE3 system in collaboration with Paul Scherrer Institute (PSI). The final installation of the undulators in the tunnel took place at the beginning of 2024. Since then, a series of measures have been taken to commission four APPLE-X undulators, which form the base for the helical afterburner. The main objective is to maximally suppress the linear polarization of planar undulators in order to obtain the purest radiation from helical undulators. The methods and results of the optimization to achieve a maximum contrast between the pulse intensity generated by planar and helical undulators as well as the operating experience are presented.
Paper: MOPB021
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB021
About: Received: 26 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
MOPB022
Design of beam transport system integrating active plasma lens for laser-plasma-driven EUV free-electron lasers
110
Laser-plasma accelerators (LPAs) produce high-quality electron beams with the GeV-level of the energy, the high peak currents and low emittance, making them ideal for compact novel free-electron lasers (FELs). However, the large angular divergence and energy spread of these beams pose challenges for efficient beam transport and overall FEL performance. This study explores the use of an active plasma lens (APL) as a capture block to improve the transport of LPA-generated beams into an undulator. Initial beam parameters were based on published results from LWFA studies. In this report, we present the results of the modeling conducted to design an efficient LPA-based electron beamline and optimize the FEL regime for the extreme ultraviolet (EUV) range. Our goal is to achieve saturation of the photon beam power within a single unit. The results show that the APL enables efficient beam transport and facilitates the generation of high-brightness coherent X-rays. This work underscores the potential of APLs in developing compact FELs and advancing LPA beams. This technology is essential for creating a new generation of FELs at ELI-ERIC in the Czech Republic and within the EuPRAXIA project.
Paper: MOPB022
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB022
About: Received: 27 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB023
Concept and preliminary design of the DALI accelerator lattice
114
The Dresden Advanced Light Infrastructure (DALI) project at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a visionary initiative to establish a state-of-the-art light source facility, catering to cutting-edge research in materials science, biology, and other interdisciplinary fields. A cornerstone of this ambitious project is the development of an advanced accelerator lattice tailored to meet the unique demands of high-intensity, ultra-bright photon production. This presentation introduces the conceptual framework and preliminary design of the DALI accelerator lattice. Key features include a modular design optimized for stability, flexibility, and scalability, ensuring compatibility with diverse experimental setups. The lattice must integrate advanced beam dynamics solutions to achieve precise control over beam quality, energy spread, and emittance, crucial for generating high-brightness radiation. Early design studies highlight the potential of DALI to set new benchmarks in light source performance. This presentation seeks to engage the accelerator community in refining the lattice design and exploring its applications in cutting-edge research.
Paper: MOPB023
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB023
About: Received: 23 May 2025 — Revised: 31 May 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
VPuRD: virtual pulse reconstruction diagnostic for single-shot measurement of free electron laser
Accurate characterization of radiation pulse profiles is crucial for optimizing beam quality and enhancing experimental outcomes in Free Electron Laser (FEL) research. In this paper, we present a novel approach that employs machine learning techniques for real-time virtual diagnostics of FEL radiation pulses. Our advanced artificial intelligence (AI)-based diagnostic tool utilizes longitudinal phase space data obtained from the X-band transverse deflecting structure to reconstruct the temporal profile of FEL pulses in real time. Unlike traditional single-shot methods, this AI-driven solution provides a non-invasive, highly efficient alternative for pulse characterization. By leveraging state-of-the-art machine learning models, our method facilitates precise single-shot measurements of FEL pulse power, offering significant advantages for FEL science research. This work outlines the conceptual framework, methodology, and validation results of our virtual diagnostic tool, demonstrating its potential to significantly impact FEL research.
MOPB025
Plasma based optics for electron beam fast micro-bunching
118
The utilization of plasma devices in beam transport is slowly being accepted as a worthy alternative thanks to its potential in maintaining or even reducing particle beams emittance but also for its compactness which supplements the recent advances in compact laser plasma acceleration systems. However, their use can go beyond the substitution of magnets. In this work, the utilization of a low density plasma device to micro-bunch electron beams through a "cascade focusing" caused by the beam generated wake inside the plasma. In addition, specialized particle in cell tools to study such phenomena over long distance (>cm) taking advantage of relativistic reference frames is swiftly presented. Such devices present a great potential for shortening future FEL facilities and increasing the efficiency of current.
Paper: MOPB025
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB025
About: Received: 29 May 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
The generation of ultrafast seeded free-electron lasers at S3FEL
The field of ultrafast science has seen substantial growth over the past decade. High-power, ultrafast free-electron lasers (FELs) have become essential tools across various scientific disciplines, including physics, chemistry, and biology. The shorter pulse durations enable enhanced temporal resolution in pump-probe experiments. This paper introduces methods for generating ultrafast seeded free-electron lasers at the Shenzhen Superconducting Soft X-Ray Free-Electron Laser (S3FEL). The mechanisms underlying the proposed approaches are discussed in detail, along with corresponding simulation results.
Interference of harmonics observed in a free-electron laser oscillator
In an FEL oscillator with a planar undulator, odd harmonics appear as either spontaneous emission or as linear and nonlinear harmonics associated with the FEL pulse evolution. Additionally, misalignment of the electron beam or the resonator can lead to off-axis gain, generating even harmonics. We conducted an experiment at KU-FEL, operated at 5 µm, to measure the 6th- and 7th-harmonic spectra using a spectrometer equipped with an intensified CCD. Scanning the gate timing enabled us to capture the time evolution of the harmonic spectrum within the macro pulse. The results revealed that the harmonic spectra broaden as the macropulse intensity rises, with interference observed between the harmonics. Such interference between adjacent-order harmonics has also been observed in high-harmonic generation from solid-state targets and utilized to measure the carrier-envelope phase (CEP) of optical pulses. Based on the results of our FEL harmonic measurements and numerical simulations, we will discuss the potential for CEP measurement using FEL harmonics, highlighting the implications for further developments in FEL-based attosecond X-ray sources via high-harmonic generation.
MOPB028
Maximizing the hard-X-ray performance of SwissFEL by systematic re-alignment and recalibration of the Aramis undulator line
122
Aramis, the hard-X-ray undulator line at the free-electron laser SwissFEL at the Paul Scherrer Institute, has been in user operation at full beam energy since the end of 2018. After steady improvements of the performance until 2022, it proved difficult to maintain the achieved performance level in recent years. Now, after a systematic re-alignment and recalibration of the undulator line and a subsequent optimization of all relevant machine parameters, we have reached a new record photon pulse energy of 1 mJ at 12 keV photon energy. This contribution describes the steps taken and lessons learned to achieve and maintain this high level of performance.
Paper: MOPB028
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB028
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
Status of the seeding upgrade for FLASH2020+ project
In the framework of the FLASH2020+ project, the FLASH1 beamline will be upgraded to deliver seeded FEL pulses for users. This upgrade will be achieved by combining high gain harmonic generation and echo-enabled harmonic generation with a wide-range wavelength-tunable seed laser, to efficiently cover the 60<sup>-4</sup> nm wavelength range. The undulator chain will also be refurbished entirely using new radiators based on the APPLE-III design, allowing for polarization control of the generated light beams. With the superconducting linac of FLASH delivering electron beams at MHz repetition rate in burst mode, laser systems are being developed to seed at full repetition rates. In the contribution, we will report about the progress of the project.
MOPB030
Averaged FEL algorithm to simulate an arbitrary FEL polarization
126
FEL simulation codes are essential tools for simulating various FEL scenarios. Among the algorithms, the orbit-averaged algorithm is the most widely used due to its speed and low computational cost. The averaged algorithm simplifies physics model, so present codes such as GENESIS and SIMPLEX have limitations to model accurate features like FEL polarization and variations in electron beam current. Such details are possible when using an unaveraged algorithm (like PUFFIN). In this presentation we introduce an approach based on the averaged algorithm to simulate arbitrary FEL polarization and non-fixed electron beam current. Our method involves initializing all particles at the beginning of the simulation and performing particle calculations at each simulation step to account for the non-fixed electron beam. Additionally, arbitrary FEL polarization is calculated by modifying the FEL equations using the elliptical undulator formula and the GENESIS algorithm. Finally some demonstration will be shown comparing the performance of PAL-XFEL and results from other simulation codes to highlight the capabilities of this approach.
Paper: MOPB030
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB030
About: Received: 29 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Study on the characteristics of the XFEL beam source in the hard X-ray beamline at PAL-XFEL
Understanding the characteristics of the beam source is crucial for designing optimal beamline optics. During the construction of PAL-XFEL, simulation studies on the characteristics of the XFEL beam source were conducted in advance to aid in the design of beamline optics and experimental instruments. However, since the facility began providing user services in 2017, the performance of PAL-XFEL has been continuously improving. Consequently, it is anticipated that the characteristics of the XFEL beam source have changed from those at the time of initial construction. Despite this, measurement-based studies on the XFEL beam characteristics have not yet been conducted. Recent experimental results have revealed discrepancies between the design values and the observed focal position and size of the XFEL beam when it is focused using the compound refractive lens installed in the experimental hutch of the beamline. In this presentation, the current characteristics of the XFEL beam source in the hard X-ray beamline at PAL-XFEL will be discussed based on simulations and experiments. The characteristics of the XFEL beam source in the planned hard X-ray beamline will also be addressed.
Optimization of the longitudinal phase space of the electron beam for generating attosecond soft X-ray pulses at PAL-XFEL
At the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a scheme for generating attosecond XFEL pulses in the soft X-ray undulator line is under development using the Enhanced Self-Amplified Spontaneous Emission (E-SASE) method with an external laser pulse. To account for the slippage effect in the soft X-ray region, a mid-wavelength infrared (IR) laser pulse will be employed in the E-SASE section to create a sufficiently wide current spike. Following the E-SASE section, an additional wiggler will be used to introduce a strong energy chirp within the current spike via longitudinal space charge effects. This approach enables lasing exclusively within the current spike when applying strong reverse tapering in the undulator line, effectively suppressing background radiation. In this presentation, the optimization of the longitudinal phase space of the electron beam will be discussed by exploring the condition of the E-SASE section and wiggler for the attosecond soft X-ray pulses generation at PAL-XFEL.
MOPB033
A novel design of a magnetic chicane with positive R56
130
It has been attracting attention that the energy chirp, which is formed by the space-charge effect of the electron beam and the beam wake field when the beam passes through the accelerator tube, can be used to generate short-pulse XFELs. Since the energy chirp produced by this phenomenon is such that the energy of electrons in the rear of the bunch is lower than at the front, compression requires a magnetic chicane with a positive R56, which shortens the path of the lower energy electrons. On the other hand, a normal simple electromagnetic chicane would have a negative R56, not applicable to this bunch compression. In this presentation, we report on the idea of a compact R56-positive magnetic chicane that can be inserted in a straight section and the results of its design study.
Paper: MOPB033
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB033
About: Received: 27 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB034
Numerical simulation of on-axis helical undulator radiation using SCILAB-Xcos model
134
Abstract—A SCILAB Xcos model, developed using SCILAB software version 6.1.1, was implemented to simulate the on-axis radiation intensity of a helical undulator, (undulator parameter= 1, undulator wavelength 5cm, number of periods= 10, device length 0.6 m) with an electron beam (1, 2, & 3 GeV) and beam current as Ib = 3–6 × 10⁻⁶ Ampere. A numerical approach is utilized to perform the undulator radiation intensity calculations. The computed results were validated by comparing the on-axis undulator radiation intensity with those obtained from SPECTRA, an open-source synchrotron radiation (SR) calculation software.
Paper: MOPB034
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB034
About: Received: 13 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB035
Towards gamma-ray free-electron lasers
138
The free-electron laser (FEL), powered by an accelerator and equipped with an undulator, produces intense coherent radiation at ever-shorter wavelengths. Whilst the hard x-ray regime represents the current state of the art, the gamma-ray regime remains the next objective. Gamma-ray lasers, deemed one of the most profound and intriguing challenges in physics by the 2003 Nobel Laureate, hold the key to unlocking the largely unexplored nuclear domain. This article introduces a novel scheme that harnesses FEL harmonics, offering a pathway for existing x-ray FELs to operate as gamma-ray lasers.
Paper: MOPB035
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB035
About: Received: 15 May 2025 — Revised: 01 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
X-ray frequency combs generation using echoenabled harmonic generation free electron laser
Optical frequency comb (OFC) technology provides precise measurement tools for optical frequencies, leading to revolutionary changes in the field of optics.OFCs consist of a series of uniformly spaced spectral lines resembling the teeth of a comb, and they have found widespread applications in timing, precision spectroscopy, and fundamental physics.Extending this technology into the EUV to X-ray domain to achieve ultra-high precision detection of molecular and atomic structures has been a significant challenge faced by the scientific community.The next generation of light sources—free electron lasers—holds promise for addressing this challenge.By positioning different groups of undulators at various harmonic resonances within the EEHG-FEL, periodic modulation of the electron beam will be formed, which, with the appropriate parameter settings, will enable the generation of fully coherent optical frequency combs.
MOPB037
Orbit alignment study in the collimation section at the European XFEL
142
Orbit alignment plays an important role in free-electron laser (FEL) facilities, particularly in the collimation section, where multipoles are strategically positioned near the collimators as part of the specialized optics design. At the European XFEL, a strong dependence of lasing performance on the orbit in the collimation section has been observed. This study focuses on calibrating the central positions of the collimators using an orbit bump scanning technique combined with beam loss detection. Additionally, the influence of orbit alignment in the collimation section on lasing performance was systematically investigated, offering valuable insights into optimizing FEL operation.
Paper: MOPB037
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB037
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB038
Bayesian optimization for generating attosecond X-ray FEL pulses
146
Ångström and attosecond represent fundamental spatiotemporal scales for studying electron dynamics in various materials. Recently, high-power attosecond hard X-ray pulses have been successfully demonstrated at the European XFEL using the self-chirping operation mode. However, the current process heavily depends on manual tuning by experienced operators, which is time-intensive and less scalable. In this work, we report recent advancements in automating and optimizing the generation of high-power attosecond X-ray pulses using Bayesian optimization techniques. By leveraging machine-learning-based approach, we aim to enhance pulse energy, spectral quality, and operational efficiency, paving the way for more accessible and reproducible attosecond X-ray experiments.
Paper: MOPB038
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB038
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB040
Leveraging the capabilities of LCLS-II: linking adaptable photoinjector laser shaping to x-ray diagnostics through start-to-end simulation
150
SLAC’s LCLS-II is advancing towards MHz repetition rate attosecond X-ray pulses, creating opportunities to optimize X-ray generation through machine-driven controls and diagnostics via start-to-end simulation. Advanced laser shaping and upconversion techniques at the photoinjector, such as spatial light modulator-based pre-amplifier pulse shaping linked to nonlinear methods such as dispersion-controlled nonlinear synthesis or four-wave mixing, enable precise electron bunch control at the source. Downstream, diagnostics like the Multi-Resolution COokiebox (MRCO)—a 16-channel time-of-flight spectrometer—characterize X-ray pulse profiles, providing real-time feedback on attosecond X-ray pulses or attosecond X-ray substructure. We present developments towards a framework linking programmable photoinjector laser shaping to X-ray diagnostics, enabling data-driven optimization of the X-ray source. This approach combines machine learning, high-throughput feedback, and advanced control to align LCLS-II capabilities with experimental goals, laying the foundation for optimization of attosecond-scale precision in X-ray experiments.
Paper: MOPB040
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB040
About: Received: 30 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB041
CW SRF gun generating beam parameters sufficient for CW hard-X-ray FEL
154
SRF CW accelerator constructed for Coherent electron Cooling project at Brookhaven National Laboratory frequently demonstrated record parameters using 1.5 nC 350 psec long electron bunches, typically compressed to FWHM of 30 psec using ballistic compression. In this paper we report experimental demonstration of CW electron beam with parameters fully satisfying all requirements for hard-X-ray FEL and significantly exceeding those demonstrated by APEX LCLS II electron gun. The most remarkable part of this achievement in this experiment that we used 10-years old SRF gun with modest accelerating gradient ~ 15 MV/m, a bunching cavity followed by basilic compression to generate 50 pC, 15 psec electron bunches with normalized emittance of 0.15 mm mrad and normalized project emittance of 0.2 mm mrad. In other words, we are presenting alternative method of generating CW electron beams needed for hard-X-ray FELs using existing and proven accelerator technology. We present description of the accelerator system setting, details of projected and slice emittance measurements as well as relevant beam dynamics simulations.
Paper: MOPB041
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB041
About: Received: 30 May 2025 — Revised: 02 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB042
Conclusions from the UK XFEL conceptual design and options analysis study
157
UK XFEL is a multi-stage project to pursue ‘next-generation’ XFEL capabilities, either through developing a new facility in the UK or by investing at existing machines. The project’s Science Case envisages a step-change increase in the number of simultaneous experiments, with transform-limited (‘laser-like’) x-rays across a wide range of pulse durations and photon energies (up to ~20 keV) being delivered together with an array of synchronised sources, at high repetition rate to approximately ten FELs (evenly spaced pulses at approximately 100 kHz per experiment, with flexibility). A subset of applications require increased pulse energy and higher photon energies at low repetition rate or in short bursts. The project is now in the final year of its three-year conceptual design and options analysis phase, in which it has produced a conceptual design to efficiently meet these requirements, as well as conducting an analysis of the costs, socio-economic factors, and sustainability of the different investment options. The conclusions of this study are expected to be of general interest to the community.
Paper: MOPB042
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB042
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Pulsed Compton gamma-ray beam generation using pulsed FEL beam
Gamma-ray induced nuclear physics experiments rely on good signal-to-noise ratio, requiring accurate rejection of detector background. One source of this background is the interaction of cosmic rays with nuclear detectors. The Duke High Intensity Gamma-ray Source (HIGS) is typically operated in quasi-CW mode, requiring background measurements to be conducted independently of data production runs. A pulsed mode of HIGS beam operation enables improved rejection counts by allowing time discrimination between detector counts in coincidence with the gamam beam and detector counts out of coincidence with the beam. To achieve a HIGS beam with good pulse quality, a fast steering magnet has been used to decouple the FEL beam from the HIGS beam in the interaction region. By periodically overlapping the electron and FEL beams, gamma production can be limited to only the periods of overlap. Gating on these gamma pulses has been shown to reduce signal to noise ratio by at least 3 orders of magnitude.\*,\**,\*** However, this technique produces poor results at low energies, requiring development of more sophisticated gating techniques.
MOPB044
Free electron laser optical axis measurement system
161
The polarization of the gamma-ray beam plays a critical role in experimental photonuclear research by probing angular momentum. For example, the multipolarities of the 80Se(g,n)79Se reaction can be assigned by measuring cross-sections relative to the plane of polarization*. Dynamic control over gamma beam polarization will open new opportunities in nuclear research, particularly by allowing relative asymmetries to be calculated without the uncertainty introduced by relative detector efficiency. A gamma-ray beam with rotational linear poarization and high polarization purity (Plin ~ .99) has been demonstrated at the High Intensity Gamma-ray Source (HIGS)**. Without active tuning by an accelerator physicist, polarization quality is degraded due to decoupling of the free-electron laser (FEL) axis and the electron beam orbit. The FOAMS is an active feedback system that is sensitive to the small centroid motions of the FEL optical axis. Measurement uncertainty characterization has been conducted. Ongoing work will utilize this feedback system to automatically sustain controllable gamma-ray polarization for nuclear physics experiments.
Paper: MOPB044
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB044
About: Received: 02 Jun 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Study of the phase jump method for FEL oscillator
We propose a phase jump method to improve the electron beam conversion efficiency in FEL oscillator. A fast phase shifter is put between two undulator segments to kick the phase of the electron beam at saturation. The theoretical and simulation results are given based on FELiChEM which is built in Hefei. They indicate that a phase jump value of approximately π at saturation can significantly increase the gain and thus improving the FEL power. Taking 30μm wavelength as an example, the output power is increased by about 2.75 times than before.
Flat beam generation in photoinjectors for high brightness electron beams
The Energy Recovery Linac (ERL) combines the high repetition frequency of synchrotron radiation with the high brightness of FELs, showing great potential. Despite recent breakthroughs, the electron beam quality still fails to meet the requirements for driving short-wavelength FELs. The method combining ERL with Angular Dispersion-induced Microbunching (ADM), proposed by the Shanghai Light Source team, to generate a fully coherent light source with GHz repetition frequency and MeV-level energy resolution, supporting multiple users. In this scheme, microbunching is generated by ADM, and its radiation intensity is limited by the vertical emittance of the electron beam. To enhance brightness, flat beam technology is employed to reduce vertical emittance and increase horizontal emittance through lateral emittance exchange, also aiding control of the ERL bending section emittance. The round-to-flat beam conversion significantly reduces vertical emittance. This study focuses on flat beam theory, lattice design, and optimization.
Recent status and plan of ERL test accelerator at KEK
The compact ERL (cERL) is a test accelerator operating at KEK. Its main purposes are to develop key technologies related to energy-recovery linacs and high-current superconducting accelerators for industrial applications. An important goal of our activity is to realize a high power FEL source for future EUV lithography. In recent years, we have been working on demonstrating high current beam operation in energy-recovery mode. We will summarize the status of the facility and lessons learned in recent beam operations, and discuss our development plan for the future project.
MOPB049
Characterisation of beam dynamics sensitivity to misalignments in the PERLE injector
165
High current linear accelerators require the precise alignment of accelerating cavities to maintain a high beam quality. The PERLE (Powerful Energy Recovery Linac for Experiments) injector cryomodule is composed of four single-cell cavities, each of which can be independently tuned to allow greater control of the beam at this crucial point. Misalignments can lead to perturbations in the beam trajectory and contribute to an increased emittance and energy spread. Here we present a characterisation of the beam dynamics when various misalignments are applied in the injector. Various misalignments are applied, three in the translation axis (x, y, z), and two rotationally, yaw and pitch (𝚽, 𝚹). A study was conducted to determine the tolerances required misalignments to ensure an acceptable beam quality is maintained at. The results indicate that particular combinations of rotational and translational misalignments are especially detrimental to emittance. These findings provide an important guide for the subsequent design of the booster linac and alignment procedure.
Paper: MOPB049
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB049
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB053
Preliminary beta beating correction at the Canadian Light Source
169
The Canadian Light Source does not currently correct beta beating driven by its insertions devices. However, it has been known for some time that insertion device correlated vertical beam size changes can cause large reduction in flux at the VESPERS beamline. In this work we discuss our preliminary explorations to control the vertical beam size and correct beta beating.
Paper: MOPB053
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB053
About: Received: 27 May 2025 — Revised: 03 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB054
Evaluation of coating thickness and thermal deposited power for nonlinear in-vacuum kicker
173
This paper presents a comprehensive evaluation of the relationship between titanium coating thickness and thermal deposited power in the ceramic chambers of the Nonlinear In-vacuum Kicker (NIK) system, a critical component in synchrotron light sources. The study focuses on optimizing the coating thickness to minimize magnetic field attenuation and thermal load, thereby enhancing the performance of the NIK system. Through simulation analysis, we demonstrate that a titanium coating thickness of 5 μm provides an optimal balance between magnetic field attenuation and thermal load management. Additionally, the uniformity of the coating layer is found to significantly impact the system's stability and efficiency. The findings offer valuable insights for the design and operation of NIK systems in synchrotron facilities, particularly for the Taiwan Photon Source (TPS).
Paper: MOPB054
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB054
About: Received: 07 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
MOPB055
Exploring lattice candidates for TPS upgrade
176
The design of lattice candidates for the Taiwan Photon Source (TPS) upgrade is under investigation, focusing on Multi-Bend Achromat (MBA) and Hybrid Multi-Bend Achromat (HMBA) configurations. A 5BA lattice, which offers relaxed hardware requirements, can achieve a natural beam emittance in the hundred pm-rad range for a 3 GeV storage ring. The 6BA configuration shows promise in achieving phase cancellation without the need for harmonic sextupoles but presents challenges due to limited available space. The HMBA scheme is attractive for its simpler configuration and reduced reliance on nonlinear magnets. Preliminary results highlight the characteristics and trade-offs of each configuration, providing guidance for the future TPS upgrade.
Paper: MOPB055
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB055
About: Received: 27 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
Optimization of PLS-II
PLS-II has been faithfully fulfilling its role for 13 years since it launched its user service in 2012. As the 4GSR project is currently underway in South Korea, upgrading PLS-II to PLS-III is expected to take a significant amount of time. Therefore, how PLS-II can be optimized and used well over a significant time in the future is an important question. In this presentation, we present how to improve the performance of the linear accelerator and the storage ring for PLS-II optimization. First, in the PLS-II linear accelerator, we consider using a Sub-Harmonic Buncher to generate a single bunch electron beam. For beam injection, we consider introducing a Nonlinear Kicker instead of the 4-Kicker in use. In the storage ring, we propose to improve the speed of a Fast Orbit Feedback System, which is presently limited from 800 Hz to a few kHz.
Canting schemes design for Korea-4GSR storage ring
In Korea-4GSR, a beamline utilizing a canted ID is planned to be built. The impact of the electron beam resulting from the canting structure were investigated, and design modifications were implemented to minimize these effects. Simulation results show that the impact on the beam is negligible.
MOPB058
SPS-II machine imperfections and optimization
180
SPS-II was designed for low emittance storage ring with compact Double-Triple Bend Achromat (DTBA) cell. To ensure sufficient machine performance, realistic machine imperfections were simulated and incorporated into the optimization process.Thus the lattice solutions were made robust against imperfections, thereby reducing the machine’s sensitivity. The solution with sufficient dynamic aperture and lifetime can be found in the presence of imperfections. The simulation steps and optimization will be discussed in this work.
Paper: MOPB058
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB058
About: Received: 26 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
MOPB059
Improvements in FLASH operation through the use of the laser heater
183
FLASH is an XUV and soft X-ray free-electron laser (FEL) facility that comprises a superconducting linear accelerator with a beam energy of up to 1.35 GeV which drives two FEL beamlines in parallel and the plasma wakefield accelerator experiment FLASHForward. Within the upgrade program FLASH2020+, a laser heater was installed upstream of the first bunch compression chicane to mitigate microbunching instability in the linear accelerator by a controlled increase of the uncorrelated energy spread. The effect of the laser heater on microbunching instability and final energy spread has been verified with a transverse deflecting structure. In this paper, we describe the layout of the laser heater and report on improved operational aspects. It has been shown that the laser heater eliminates coherent contributions to visible transition radiation in transverse beam size measurements and, thus, contributes to better electron beam matching. In addition, an increase in the FEL output power is demonstrated, especially for first operation of the 3rd harmonic afterburner with variable polarisation.
Paper: MOPB059
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB059
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB060
Generation of short current spikes by laser modulation at FLASH
187
Generating few- or sub-femtosecond radiation pulses in a free-electron laser (FEL) requires precise control of the longitudinal phase space density of the driving electron bunch, as the FEL process depends strongly on the bunch current and energy spread profile. In an experiment conducted at FLASH in Hamburg, Germany, an energy modulation with linearly changing amplitude is imprinted onto part of the bunch by a laser pulse in an undulator upstream of the first bunch compression chicane. In subsequent longitudinally dispersive sections, a short current spike is created, as the linearly modulated region is compressed more strongly than the rest of the bunch. Measurements with a transverse-deflecting X-band cavity verify the creation of a short current spike, whose duration falls below the temporal resolution of the measurement setup of approximately 7 fs.
Paper: MOPB060
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB060
About: Received: 28 May 2025 — Revised: 30 May 2025 — Accepted: 30 May 2025 — Issue date: 10 Jul 2025
MOPB061
Experimental study on soft X-ray generation via Inverse Compton Scattering at CERN
190
This study explores the feasibility of using Compton Backscattering (CBS) as a compact source for generating photons in the extreme ultraviolet (EUV) to soft X-ray range, with potential applications in biological imaging and modern lithography. A CBS experiment was conducted at the AWAKE Run 2c test injector (ARTI), where electron bunches, accelerated up to 6 MeV by a high-gradient, brazing-free S-band photogun were collided with 1030 nm infrared pulses from the PHAROS femtosecond laser. The electron and laser beamlines were optimised for maximum CBS photon flux.
Paper: MOPB061
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB061
About: Received: 15 Apr 2025 — Revised: 01 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Electron beam and laser-Compton X-ray parameters stabilization simulation study at KEK Laser-Undulator Compact X-ray facility
Electron beam and laser-Compton X-ray parameters stabilization simulation study at KEK Laser-Undulator Compact X-ray facilityis a normal conductivity multi-bunch electron linear accelerator devoted to develop an intense monochromatic source of laser-Compton X-ray for tomography applications. The electron beam parameters absolute values and its stability were simulated at the ASTRA tracking code, while laser-Compton X-ray beam stability was simulated at CAIN. In reverse, this stability values allows to define the accelerating field stability requirements for the linear accelerator based laser- Compton X-ray sources. This report demonstrates the electron beam parameters and laser-Compton X-ray stability simulation results. Also, the accelerating field stability requirements are discussed in this report.
MOPB063
Spatial polarization distribution measurements of gamma rays produced by inverse Compton scattering
194
Highly polarized MeV gamma rays, produced by Laser Compton Scattered (LCS) of a polarized laser with an electron beam, offer a unique probe for basic and applied physics research. As the polarization characteristics of these gamma rays vary with the position of the beam cross section, it is essential to understand the polarization properties when using polarized gamma rays * . However, detailed measurements of the two-dimensional spatial polarization distribution have not yet been conducted. In the UVSOR synchrotron facility, a polarimeter was developed to measure the spatial polarization distribution of linearly polarized gamma rays. The polarimeter is based on asymmetry measurements of the Compton scattering cross section. In this conference, we will report on measurement results of the spatial polarization distribution of linearly and circularly polarized LCS gamma-rays. The polarization axis of the polarized gamma rays was clearly measured to vary with scattering and azimuth angle. In the near future, we plan to use the developed polarimeter to also measure the spatial polarization distribution of gamma rays generated by an axially symmetric polarized laser ** .
Paper: MOPB063
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB063
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
MOPB065
Application of fast algorithms to calculate dynamic and momentum aperture to the design of ALBA II
197
In synchrotron light sources, the non-linear magnetic fields and Touschek scattering limit the stability of electron motion, determining the dynamic aperture (DA) and the momentum acceptance (MA). Optimizing both the DA and the MA is crucial to maximize injection efficiency and the beam's lifetime, but it is numerically expensive. We implement recently developed algorithms that speed-up their calculation in CPUs: Flood Fill and Fast Touschek Tracking (FTT). Applying these to the analysis of the ALBA II lattice and comparing them to the existing methods, we obtain rigorous and faster results using Flood Fill, and ones with a slight loss of accuracy for FTT.
Paper: MOPB065
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB065
About: Received: 31 Mar 2025 — Revised: 30 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
MOPB066
Compensation of an elliptically polarizing undulator in the HLS-II storage ring
201
The insertion devices (IDs) can severely affect the beam dynamics of a storage ring. Recently, a new elliptically polarizing undulator(EPU) is installed in the Hefei Light Source II (HLS-II) storage ring. The effects of this EPU can be modeled using the kick map method. In this paper, we present the kick map of the EPU with vertical mode and how it affects the beam dynamics. Since the HLS-II storage ring is compact, only four quadrupoles in the same straight section can be used to compensated the ID effect. The compensation result is also reported in this paper.
Paper: MOPB066
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB066
About: Received: 21 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
Investigation of new collimator head material candidates for SuperKEKB and future collider
Currently, SuperKEKB faces the challenge of sudden beam loss (SBL), which occurs with almost no prior sign. The causes of SBL are not fully understood. A damaged collimator reduces its ability to suppress beam background noise compared to an undamaged one. In cases that the beam background noise reduction decrease, it is necessary to stop the operation and replace the collimator jaw. Therefore, a robust collimator head material is required. In this conference, we report the results of our investigation of copper-carbide graphite (CuGr), which is a candidate as a new collimator head material for SuperKEKB. Measurements of electrical conductivity in the high-frequency region, secondary electron yield, outgassing rate due to photon stimulated desorption, and the amount of dust generated by ultrasonic cleaning of CuGr, along with simulation results of beam background with CuGr, are presented.
Realizing steady-state microbunching with Optical Stochastic Crystallization
Optical Stochastic Cooling (OSC) is a state-of-the-art beam cooling technology first demonstrated in 2021 at the IOTA storage ring at Fermilab's FAST facility. A second phase of the research program is planned to run in 2025 and will incorporate an optical amplifier to enable increased cooling rates and greater operational flexibility. In addition to beam cooling, an OSC system can be configured to enable advanced control over the phase space of the beam. An example operational mode could enable crystallization, where the particles in a bunch are locked into a self-reinforcing, regular microstructure at the OSC fundamental wavelength; we refer to this as Optical Stochastic Crystallization (OSX). OSX represents a new path toward Steady-State Microbunching (SSMB), which may enable light sources combining the high brightness of an FEL with the high repetition rate of a storage ring. Such a source has applications from the terahertz to the extreme ultraviolet (EUV), including high-power EUV generation for semiconductor lithography. This contribution will discuss the development of OSX within the OSC program at IOTA, including the design of the experiment and simulations results.
MOPB071
Simulation study on fast beam-based alignment for commissioning of light sources
204
Beam based alignment (BBA) plays an important role in the commissioning of the light sources. To speed up the BBA, a BBA method using AC excitation, called fast BBA (FBBA), has been proposed and is tested in several existing light sources. In the FBBA, the beam orbit is sinusoidally modulated at around 10Hz by AC correctors, and the change in the beam response when a target quadrupole magnet strength is changed is measured using fast beam position monitors (BPM) at about 10kHz. To apply FBBA to light source commissioning, a simulation study of FBBA using random variables as response functions was performed to calculate the optimal corrector strength and variation of the strength of a quadrupole as a function of the BPM noise. We also improved the FBBA and found that a new FBBA scheme using two AC correctors of different frequencies separated by 1/2π betatron phase for one plane (horizontal or vertical) can suppress the BPM offset error by up to 10.
Paper: MOPB071
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB071
About: Received: 28 May 2025 — Revised: 01 Jun 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
MOPB072
Magnet crosstalk in highly-compact light-source storage ring
208
Electron storage rings based on multi-bend achromat (MBA) lattice can achieve very low natural emittances. Several fourth generation light sources have been built and operating, the natural emittances of which are a few 100 pm or even lower than 100 pm, providing high brightness photon beams to users. Since the lattice of MBA storage ring tends to be highly compact, the field of a magnet may be affected by the neighboring magnets. This effect turned out to be significant in the new Swiss Light Source storage ring with 7-BA lattice during its design study: the integral fields of magnets are altered by a few percent due to the magnet cross talk at locations, which is an order of magnitude larger than the field precision typically required. We present how we managed to reproduce the design magnetic fields and optics including the cross talk effects
Paper: MOPB072
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB072
About: Received: 24 May 2025 — Revised: 30 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
MOPB074
SOLEIL II project: entrance in the construction phase
212
SOLEIL II is the French upgrade project to build the science of tomorrow with synchrotron light radiation. Providing the highest brilliance in its class while maintaining the radiation range from IR to hard X-rays, the project is an ambitious triple upgrade of the SOLEIL facility: accelerators (new booster and storage ring), 29 beamlines and 3 laboratories, and an information technology transformation plan. High Order Achromat based on multi-bend achromat lattices will be used to replace both the storage (SR) and booster rings of the Synchrotron SOLEIL. The achieved equilibrium emittance of the SR (below 100 pm.rad, 354 m, 2.75 GeV) is about 50 times smaller than that of the existing Storage Ring (4000 pm.rad). To ensure the technical feasibility, an intensive R&D phase based on extensive numerical simulations, prototyping and measurements has been carried out. This paper presents the latest status of the project, the updated timeline, and describes the main results obtained so far in terms of performance and the prototypes launched in many technical domains (lattice, magnets, insertion device, vacuum, alignment…).
Paper: MOPB074
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB074
About: Received: 03 Jun 2025 — Revised: 03 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
MOPB075
SOLEIL synchrotron light source lastest news
216
The synchrotron SOLEIL is France's 2.75 GeV third-generation synchrotron light source and serves as a cutting-edge research laboratory dedicated to advanced experimental techniques for matter analysis at the atomic scale. It also functions as a service platform accessible to both scientific and industrial communities. This abstract highlights the performance of the accelerators, which deliver exceptionally stable photon beams to 29 beamlines. Key figures of merit from the past year are reported, along with a review of several incidents and the lessons learned to prevent recurrence. Additionally, major research and development efforts addressing component obsolescence are outlined. The status of the LINAC upgrade is also discussed, alongside plans to use SOLEIL's current accelerator as a test bench to validate and precommission critical equipment for the forthcoming SOLEIL upgrade.
Paper: MOPB075
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB075
About: Received: 02 Jun 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Design of RF system for 4th generation storage ring at Korea
A new 4th Generation Storage Ring (4GSR) will be constructed in Ochang, South Korea, by the end of 2029. A technical design review for the Korea 4GSR was completed at the end of 2023. The storage ring has a circumference of 799 meters and is designed for a maximum current of 400 mA at 4 GeV electron beam energy. The target emittance is below 100 pm-rad, with a calculated emittance of 62 pm-rad—100 times smaller than that of PLS-II, a 3rd-generation storage ring in Korea. The RF system for the Korea 4GSR comprises 10 normal-conducting cavities, a low-level RF (LLRF) system, a high-power RF (HPRF) system, and additional components. To ensure beam stability, Higher Order Mode (HOM)-damped cavities have been implemented. Additionally, we plan to install harmonic cavities to improve beam lifetime and reduce wakefields. For the LLRF system, we aim to apply a new digital feedback control scheme and implement FPGA chips. For the HPRF system, we have chosen to use a solid-state RF power amplifier (SSPA). This presentation highlights the design results of the RF system for the Korea 4GSR, as well as prototypes of the 3rd harmonic cavity and SSPA.
Present status of Kyoto University free electron laser
Kyoto University Free Electron Laser (KU-FEL) has been developed for promoting energy related researches in Institute of Advanced Energy, Kyoto University. Currently two accelerator based infrared light sources, a mid-infrared FEL (MIR-FEL) and THz coherent undulator radiation (THz-CUR) are available. MIR-FEL covers the wavelength region from 3.4 to 26 micro-m and THz-CUR covers the frequency region from 0.1 to 0.45 THz. Present status and perspectives of those light sources will be presented in the conference.
MOPB080
Study of DESY II as an injector option for PETRA IV storage ring
220
PETRA IV is the storage ring light source currently under design at DESY in Germany. The baseline injector is a 6-GeV synchrotron DESY IV, an upgrade to the existing injector DESY II. Even if the project progresses in developing the DESY IV, we studied the intensity limit of DESY II to investigate the feasibility of reusing the existing injector chain, in view of a possible upgrade to a laser plasma injector in the coming years. We identified the microwave instability-induced energy spread and the transient beam loading as a limiting mechanism of single-bunch intensity in a 12.5 Hz cycle synchrotron. This paper reports the numerical simulation, its analysis, and its follow-up experiments of high charge acceleration at DESY II and its subsequent injection into PETRA III. The injection efficiency of DESY II's beam into future PETRA IV is also computed assuming imperfect lattices with 5% beta-beating. To overcome the intensity limit set by the pre-accelerator PIA, we investigated the possibility of multi-cycle accumulation at low energy. In this regard, we measured the lifetime and emittance over cycles and the chromaticities of the lattice. These are also reported in the paper.
Paper: MOPB080
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB080
About: Received: 28 May 2025 — Revised: 31 May 2025 — Accepted: 31 May 2025 — Issue date: 10 Jul 2025
Study on the linear model of the wiggler in the storage ring
As proposed in Ref[1], a fully coherent synchrotron light source requires a high-current, low-emittance storage ring with very short damping time to deliver a high-quality beam for the bypass line, ultimately producing high average power EUV radiation. The initial design adopts 8 TBA (Triple Bend Achromat) cells, with four cells forming one superperiod. The straight sections on either side of each super-period are designed with high beta functions, while the internal straight sections feature low beta functions. Each low-beta straight section includes three super-conducting sandwich-type damping wigglers to facilitate the I transformation, which increases radiation losses and significantly reduces the damping time. Overall, the ring is equipped with 18 superconducting damping wigglers.
Realisation of a 1.5 GHz single mode cavity for PETRA IV
In the period from October 2021 to August 2024, a cavity was developed for the 3rd harmonic system of PETRA IV. The development has progressed so far that a complete CAD model already exists. The cavity design has been reviewed by an external expert and approved. The project team is now working on clarifying the final details of the design and preparing all the technical documentation for the production of the cavity. This article reports on the issues that need to be addressed in order to turn the simulation and CAD model into a real, fully functional cavity.
MOPB088
Exploratory tests for the design of a Python accelerator middle layer
224
Several laboratories and facilities recently started joined efforts towards the realization of a python accelerator middle layer (pyAML) for control, tuning and optimization. This software is intended as a successor to matlab middle layer (MML), inheriting its features but also expanding to new ones (e.g., nonlinear optics and machine learning tools). Presently, several codes are available that provide some of the desired features. These codes have been adapted and tested at several of the participating laboratories to give input to the design of the pyAML. The most relevant features and results have been analyzed and are presented here together with the implications for the pyAML design.
Paper: MOPB088
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB088
About: Received: 23 May 2025 — Revised: 01 Jun 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
MOPB089
Status of Sirius operation with users
228
SIRIUS is a state-of-the-art synchrotron light source facility, featuring a 3 GeV electron storage ring with a 518 m circumference and 250 pm·rad emittance. Built and operated by the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, Brazil, SIRIUS has undergone significant upgrades over the past year. These include the installation of a cryogenic plant, superconducting RF cavities, in-vacuum undulators, and new orbit feedforward systems, among others. This report summarizes these developments, highlights improvements in beam stability, and provides an overview of the facility’s operational status over the past year.
Paper: MOPB089
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB089
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Switchable X-ray orbital angular momentum from a cavity-based free electron laser
X-ray vortices carrying tunable Orbital Angular Momentum (OAM) are an emerging tool for X-ray characterization technology. However, in contrast to the generation of vortex beams in the visible wavelength region, the generation of X-ray vortices in a controlled manner has proved challenging. Here, we demonstrate an X-ray free-electron laser oscillator (XFELO) can adjust only the kinetic energy of the electron beam to produce vortex beams that can be programmed to dynamically change between different OAM modes, without the need for additional optical elements. With the nominal parameters of currently constructing 1 MHz repetition rate facility (i.e. SHINE), the active formation of the OAM modes of l = ±1 and l = ±2 and the rapid switching between them by detuning the electron beam energy of the XFELO are numerically illustrated. The real-time switching can be achieved within 200 μs, while the output pulse energy can reach the 100 μJ level. This result extends the capabilities of XFELOs, and paves the way for advanced at-source applications using X-ray vortex beams.
FEL performance enhancement with phase shifters at Dalian Coherent Light Source
A phase shifter collocated with an undulator is an efficient method to enhance the lasing performance of free-electron laser (FEL), particularly for seeded FEL. Dalian Coherent Light Source (DCLS) is a seeded FEL facility operating in high-gain harmonic generation (HGHG) mode to produce fully coherent vacuum ultraviolet laser. To achieve high FEL lasing performance, five phase shifters are interspersed among six undulators to match the phase of the electron beam and the FEL radiation field. This paper presents the commissioning results of these five phase shifters, with a primary focus on their impact on FEL lasing performance.
Ultrafast free-electron laser generation with optical beat note
As one of the most important frontiers of international science and technology, the development of ultrafast science has provided important research tools for many disciplines. Free-electron laser (FEL) has the unique advantages of high power and short wavelength in generating ultrafast pulses. In this paper, the theoretical simulations were performed to produce the ultrafast pulses, utilizing an electron beam compressed by an optical beat note. The main parameters used in the simulation are from Shanghai Soft X-ray Free Electron Laser Facility (SXFEL). The results show that an isolated FEL pulse with the peak power of 700 MW and the pulse duration of ~1 femtoseconds can be generated. In addition, we discuss the effect of the relative delay jitter of optical beating laser on ultrafast radiation. The result shows that the scheme is very sensitive to time delay jitter.
MOPB093
Study on pre-bunched free electron laser in the terahertz wavelength range
232
We have been studying about a pre-bunched FEL in the THz region. In the pre-bunched FEL, the electron bunches being compressed shorter than the oscillation laser wavelength, it is expected that we can generate short-pulse THz laser pulses with high peak intensity. A broadband spectrum and high-intensity characteristics, which cannot be realized by conventional FEL, are expected. The pre-bunched FEL experiments were conducted using the THz-CUR at Kyoto University Free Electron Laser (KU-FEL) consists of an existing electron rf gun (ECC-RF-Gun), which can produce short electron bunches adequate for pre-bunched FEL, and a 10-period undulator. We installed an optical cavity and performed beam tests at the lasing frequency of 0.2 to 0.4 THz. As the results of beam test, we observed the coherent stacking of coherent THz pulses inside the cavity, however, FEL oscillation has not been achieved yet. We will report on our pre-bunched FEL project, experimental setup, beam test results and future prospects.
Paper: MOPB093
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB093
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 04 Jun 2025 — Issue date: 10 Jul 2025
Progress in CBXFEL construction at SLAC
Cavity-based XFEL - CBXFEL - is an ongoing experiment at SLAC Accelerator National Laboratory. It utilizes first seven LCLS hard x-ray undulators, wrapped into a rectangular Bragg cavity. CBXFEL is expected to operate at 9.831 keV, and serve as a proof-of-principle device for future large scale cavity-based systems. We report on the recent status and preliminary experimental results.
X-ray laser oscillator - new results
X-ray Laser Oscillator (XLO) is an ongoing project at SLAC National Accelerator Laboratory. The project aims to construct world's first population inversion x-ray laser, using LCLS XFEL as a pump. XLO also utilizes the multi-bunch mode of LCLS copper linac, and a Bragg cavity arranged in a bow-tie configuration. When built, XLO will be able to generate x-ray pulses of very high quality. In this proceeding, we report on the new findings and design updates of the XLO.
Enhanced self-seeding - first experiments
Enhanced self-seeding (proposed in Phys. Rev. Lett. 125, 044801, 2020) is a concept for more stable, laser-like XFEL operation. The principle of enhanced self-seeding lies in strong lasing on the current spike in the SASE section, and picking the seed pulse with the flat, lower current portion of the beam. Recently, we performed experimental studies of this scheme with the existing hard x-ray self-seeding (HXRSS) at LCLS. We report on our findings and possible new self-seeding schemes.
Study on optimization of FEL generation in HX and SX lines for two-bunch operation
PAL-XFEL comprises two lines: Hard X-ray (HX) line for 2.5-15 keV FEL and Soft X-ray (SX) line for 0.25~1.1 keV FEL. Both lines share accelerator sections L1, L2, L3A, and two Bunch Compressors (BCs). The electron bunch is accelerated to 2.8 GeV and compressed to a peak current of 400-500A using accelerators and two BCs, then it is directed into either the HX or SX line at the branch line. Since the optimal RF phase settings for the two lines are different in the shared sections, we perform simultaneous operation by adjusting the LLRF settings of shared accelerator sections on a pulse-by-pulse basis. We are preparing for simultaneous operation using the two-bunch operation method to fully utilize the repetition rate for both lines. This method involves injecting two GUN lasers with a 25 ns delay into a single pulse, generating two bunches per pulse, and sending them simultaneously to the HX and SX lines. For two-bunch operation, the device settings of shared sections must be identical, we have re-optimized the HXFEL and SXFEL to have identical device settings for the shared sections. In this paper, we present the detailed optimization process and the final optimized parameters.
MOPB098
Simulation studies on optimization of hard and soft X-ray beamlines for parallel user service at the PAL-XFEL
235
PAL-XFEL (Pohang Accelerator Laboratory X-ray Free Electron Laser) is a facility that generates high-brightness FEL for users to perform the FEL-based sciences. Currently hard and soft X-ray (HX/SX) beamlines are operational, but the parallel operation can be done with less than 60 Hz using a single electron bunch from the electron injector. Therefore, for the user service with maximum repetition rate of 60 Hz on both HX and SX beamlines, a scheme that uses two bunches from the injector with an exact single cycle of 2.856 GHz frequency is under consideration. Particularly, simulation study is necessary to understand the optimal accelerator condition for both HX and SX since the SX shares the same accelerator condition up to the third accelerating column with the HX beamline. In this study, we show discussions using the particle tracking simulations showing the optimal conditions for both beamlines. We also present the potential issues to be considered in the actual operations such as error of RF cavity amplitude.
Paper: MOPB098
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB098
About: Received: 28 May 2025 — Revised: 02 Jun 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
MOPB100
An alternative lattice for the ZIPS storage ring
239
Since synchrotron radiation sources have many advanced characteristics such as high radiation power, high brightness, broad spectral range, transverse coherence, and excellent time structure, they have become powerful tools for exploring microscopic material structures. With the growing demand for industrial researches, several dedicated industrial light sources are under operation or construction around the world. Zhejiang Industrial Photon Source (ZIPS) is designed to provide a scientific platform for industrial applications within the X-ray region in China. As a preliminary design, the ZIPS storage ring adopts a modified Triple-Bend Achromat (TBA) lattice with an energy of 2.6 GeV and a low emittance of 3.88 nm · rad. Details of the lattice design are presented in this paper.
Paper: MOPB100
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB100
About: Received: 10 Apr 2025 — Revised: 30 May 2025 — Accepted: 02 Jun 2025 — Issue date: 10 Jul 2025
MOPB101
Bayesian optimization for the local bump injection in the HLS-II storage ring
242
Currently, a conventional local bump injection system with four pulsed dipole kicker magnets is adopted in the Hefei Light Source II (HLS-II) storage ring to achieve topoff operation. Due to the multipole magnets located between the kickers in the injection section, the local bump injection presents technical challenges in forming a perfect closed bump, which causes oscillation to the stored beam. In order to reduce the injection disturbance on the stored beam, the Bayesian Optimization (BO) method is employed to determine the kick angles of the four bump kickers.
Paper: MOPB101
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB101
About: Received: 09 Apr 2025 — Revised: 31 May 2025 — Accepted: 01 Jun 2025 — Issue date: 10 Jul 2025
Single spike hard x-ray free-electron laser pulses generated by photocathode laser shaping
We report the generation of single spike hard x-ray pulses at the Linac Coherent Light Source enabled by temporal shaping of the photocathode laser. The pulses were produced with typical pulse energies of 10 uJ and full-width at half-maximum spectral bandwidths averaging 30 eV, corresponding to a 60 attosecond Fourier-limited pulse duration. These pulses open new doors in electronic-damage-free probing of ultrafast phenomena and, eventually, attosecond hard x-ray scattering experiments. We discuss future plans to characterize the pulse in the time domain using hard x-ray angular streaking and a hard x-ray split and delay device.
Analytical model for the transition to superradiance in seeded free-electron lasers
Free-electron lasers (FEL) seeded by short radiation pulses can exhibit superradiant behavior. In the superradiant regime, the pulse simultaneously compresses and amplifies as it propagates through the FEL, making superradiance very promising for pushing the performance limits of attosecond x-ray FELs. To date, this regime has been studied in asymptotic limits, but there is no model for how the initially linear dynamics of the seeded FEL transition into the nonlinear superradiant behavior. We derive an analytical model for the 1D FEL seeded by a short pulse which accurately captures the linear dynamics, the nonlinear superradiant evolution, and the smooth transition between them. Our model fills a critical gap in our understanding of FEL superradiance and nonlinear time-dependent FEL physics more broadly, and may provide a bridge to the corresponding problem in three-dimensions, and analogous problems in other fields exhibiting soliton behavior.
MOPB105
Simulation and optimization of a sub-THz Cherenkov FEL at AREAL
246
A circular waveguide lined with a thin dielectric layer enables electron bunches propagating within the structure to radiate light in the (sub-)THz regime. In this work, we perform simulations of low-energy electron beams traversing extended waveguides to analyze the dynamics of beam bunching and lasing within the structure. By exploring the free-electron laser (FEL) process in this context, we demonstrate the potential of waveguides as a cost-effective alternative to undulator-based FELs. The study employs a simulated model of the AREAL LINAC at the CANDLE SRI to demonstrate these effects and provide realistic results. The simulations are performed using the space charge tracking algorithm ASTRA and the wakefield solver ECHO. For optimization of the system, the genetic optimization algorithm GIOTTO is applied to refine both the waveguide and accelerator variables. Using a 4 MeV electron beam with a charge of 300 pC, the optimized setup achieves a radiation frequency of 100 GHz with energy outputs exceeding 20 µJ in a waveguide of only 1.2 meters length. These results underscore the feasibility of this method, offering a innovative pathway to produce intense THz radiation.
Paper: MOPB105
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB105
About: Received: 28 May 2025 — Revised: 03 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
MOPB106
Optimizing Cherenkov waveguide seeding for THz SASE FELs towards stable, few-cycle pulses
250
The PITZ facility at DESY in Zeuthen has demonstrated the first operational high peak and average power THz self-amplified spontaneous emission (SASE) free electron laser (FEL). The current setup displays the onset of saturation at a central frequency of 3THz using a 3.5m long LCLS-I undulator. However, the THz user community has expressed the need for carrier-envelope phase (CEP) stability and the availability of few-cycle THz pulses to complement the currently demonstrated long pulses. In this work, simulations are conducted to evaluate and optimize FEL performance by incorporating a Cherenkov waveguide to seed the process. The waveguide parameter space is scanned to vary energy modulation depth and frequency, after which the performance is estimated using the space charge tracking algorithm, ASTRA, and the FEL simulation code, Genesis1.3. The optimized parameters allow saturation to be reached much earlier, while also significantly increasing the shot-to-shot stability. Down the line, the implementation of such a scheme would facilitate generation of few-cycle, CEP-stable THz pulses to be used in user experiments.
Paper: MOPB106
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB106
About: Received: 28 May 2025 — Revised: 05 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Isolated attosecond pulses generation with the microbunching synthesis
Attosecond x-ray pulses play a crucial role in the study of ultrafast phenomena involving inner and valence electrons. Especially isolated attosecond pulses with high photon energy and high peak power are of great significance in single-shot imaging in the soft x-ray region, life sciences, and attosecond pump-probe experiments. In modern accelerators, laser manipulation of electrons can be used to tailor the ultrafast properties of free-electron laser pulses. In this paper, we propose a novel laser manipulation technique that makes use of two many-cycle, obliquely incident laser beams with mutual delays to synthesize microbunching rotation on the scale of infrared laser wavelengths within the electron bunch. This synthesis microbunching rotation ultimately leads to an enhanced current contrast ratio between the main peak and the surrounding satellite peaks within the bunch. By properly accounting for the longitudinal space-charge fields within the undulator, a tapered undulator can further suppress the side peaks in the radiation pulse and enable the selection of an isolated, hundred-attosecond, GW-level soft x-ray pulse.
MOPB108
Coherent undulator radiation with account of the beam energy spread
254
When a microbunched beam is sent to a resonantly tuned undulator it radiates coherent radiation with the intensity propotional to the bunching squared of the beam. According to *, the radiated energy increases with the undulator length. This conclusion, however, is only valid if one ignores the energy spread of the beam (and also the beam angular spread). The finite energy spread smears the microbunching, ultimately suppressing coherent radiation beyond a certain distance. In this work, we calculate the radiation of a microbunced beam with an energy spread and find the maximum energy that it can radiate coherently.
Paper: MOPB108
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB108
About: Received: 22 May 2025 — Revised: 30 May 2025 — Accepted: 03 Jun 2025 — Issue date: 10 Jul 2025
Development of regenerative-amplifier FEL at the compact ERL
The compact ERL has been built in 2013 at High Energy Accelerator Research Organization (KEK) to a test machine of an energy recovery linac. Afterwards, two undulators have been installed in the compact ERL and a first light amplification (free-electron laser: FEL) in mid-infrared range has been observed in 2021. However, the intensity of light has not been achieved to the intensity saturation because of not enough undulator length. Since we are considering for industrial applications using it, the intensity has to be improved. There are several methods to improve the intensity, and we have decided to try a “regenerative-amplifier (RA) FEL” scheme and now it is under the construction. In this presentation, we will report the status and plan of RA-FEL development using the compact ERL.
MOPB110
Research plans for the University of Hawai’i Accelerator and Free-Electron Laser Lab
257
The accelerator and free-electron laser (FEL) laboratory at the University of Hawai’i at Manoa (UHM), established by John Madey, has been in standby since his passing in 2016, with operations further paused during the pandemic. Recent efforts aim to recommission the facility, which includes a thermionic gun, an S-band linear accelerator reaching 45 MeV, and a Mark III undulator FEL oscillator producing tunable infrared light. Previously, 3 μm infrared light from this undulator demonstrated the capability to generate 10 keV X-ray photons via inverse Compton scattering. Current upgrades include enhancements to vacuum systems and linac controls. Future plans focus on enhancing cathode performance, developing 3D FEL simulations for superradiance studies, achieving phase coherence with interferometer optics, and using waveguides for THz generation. Recent GINGER simulations explored FEL oscillator output under varying Desynchronization conditions, demonstrating pulse train formation. The revived UHM accelerator will advance FEL science and train the next generation of researchers.
Paper: MOPB110
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB110
About: Received: 23 May 2025 — Revised: 02 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025
Optimization of undulator tapering for the laser heater shaped electron bunch at PAL-XFEL
The pulse duration of the X-ray free-electron laser (XFEL) relies on the pulse duration of the electron bunch. The energy distribution of the electron bunch can be manipulated by using the laser heater in the purpose of generating attosecond pulse duration electron bunch current profile. Therefore, the resultant electron bunch current profile after the bunch compressor chicanes is programmable by the laser parameters. To obtain further bunch compression with the high current electron bunch profile, we investigate the hard X-ray beamline setup for the longitudinal space charge (LSC) field effect desired at the magnetic dogleg where is right before the hard X-ray undulator section. The hard X-ray undulator tapering is optimized for the linear energy chirp of the ultra-short electron bunch.
Design of a microbunched electron cooler energy recovery linac
Microbunched electron Cooling (MBEC) is a type of Coherent electron Cooling (CeC), suitable for cooling high energy protons; such an electron cooler can be driven by an energy recovery linac (ERL). The beam parameters of this design are based on cooling 275 and 100 GeV protons at the Electron-Ion Collider (EIC), requiring 150 and 55 MeV electrons, respectively. If implemented, a high energy cooler would serve to increase the average luminosity of the collider by mitigating the emittance growth due to degradation caused by various processes. This ERL is designed to deliver a bunch charge of 1 nC, an average current of 100 mA, and strict requirements on the transverse emittance, slice energy spread, and longitudinal distribution profile. This paper covers the current state of the design.
Design of bellows in HALF vacuum system
The fourth generation HALF light source is a kind of storage ring light source based on diffraction limit. On the one hand, the shielded bellows in the vacuum system is used to compensate the thermal expansion and cold contraction of the vacuum chamber, and to adjust the longitudinal and transverse offset of the vacuum chamber according to the requirements of installation and collimation, on the other hand, it provides continuous shielding in the adjacent vacuum chamber to reduce the impedance of the beam pipe. The shielded bellows consists of a shielding finger, a contact finger and an inner tube, the contact finger acts on the inner tube, and the contact force comes from the elastic force formed by pressing the spring finger on the contact finger. In the structure, the high temperature area of the shielding finger is separated from the high stress area, so as to improve the durability of the bellows. The main mechanical parameters are as follows: longitudinal compression: ≥ 8mm; stretching: ≥ 8mm; lateral offset: ≥ 1mm; overall permeability ≤ 1.02 after welding, so that it can meet the requirements of vacuum system.
MOPB118
Sub 100 keV hard X-ray inverse compton sattering experiment at BNL ATF
261
Recent progress on the experiments of Inverse Compton Scattering (ICS) at Brookhaven National Laboratory Accelerator Test Facility (BNL ATF) is introduced. Nominal e-beam parameters utilized are electron beam energy of 70 MeV, charge per pulse of 0.5 nC with normalized emittance of 2 mm mrad. Use of long wavelength TW CO2 laser, and short wavelength Nd: YAG or Ti: Sapphire lasers allows us to explore unique nonlinear dynamics of Compton scattering such as Bi-Harmonic interaction and emission of Orbital Angular Momentum of X-ray. Currently, up to 90 keV hard X-ray yield from counter collision of Nd: YAG laser and 70 MeV electron beam is in a range of 1E6 photons per single pulse. Planning to increase electron beam energy to achieve establishment of sub 100 keV ICS to provide sufficient photon flux density, in the range of 1E10 per pulse, owing to the long wavelength multi TW CO2 laser and tighter electron beam focus is underway.
Paper: MOPB118
DOI: reference for this paper: 10.18429/JACoW-IPAC25-MOPB118
About: Received: 28 May 2025 — Revised: 04 Jun 2025 — Accepted: 05 Jun 2025 — Issue date: 10 Jul 2025