undulator
MOI7M01
Development of low period cryogenic permanent magnet undulators
40
Undulators are widely employed on accelerator-based light sources. The length of these devices is usually constrained by the length of the straight sections, and this will become even more critical for Diffraction Limited Storage Rings based on existing Synchrotrons, where the number of magnets required to store the electron beam is huge. Thus, to reach high brightness and flux, the total number of periods of undulators must remain large and the magnetic period values will be reduced. Cryogenic Permanent Magnets Undulators (CPMU) are a solution to keep a high peak field value while decreasing the magnetic period. Planar CPMUs have become widely adopted in Synchrotrons worldwide and some laboratories are developing equivalent devices providing also elliptical polarizations. A review of low period CPMU installed on accelerator-based light sources will be presented and sustainability of these sources will also be discussed.
Paper: MOI7M01
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOI7M01
About: Received: 16 May 2026 — Revised: 20 May 2026 — Issue date: 22 May 2026
MOP6318
Deterministic methods and bayesian optimization algorithms applied to the UH Mānoa linac
373
The University of Hawai‘I at Mānoa (UHM) linac delivers up to 45 MeV electron beams to a Free-Electron Laser(FEL) oscillator. As the linac is being recommissioned for renewed FEL operation, we are developing simulation and optimization tools to recover operational settings and to explore the landscape of beam-manipulation techniques for future experimental apparatus. This paper benchmarks classical deterministic methods and Bayesian optimization (BO) algorithms on three representative beam-optics tuning scenarios using a beam dynamics simulation model developed inhouse. For problems with only a few free parameters, classical methods converge reliably, while finite-difference derivative information improves the performance of constrained gradient-based solvers. For the higher-dimensional case, BO with a Gaussian Process (GP) surrogate and SOBOL initialization provides a more robust path toward convergence. The emphasis is on the number of optimization iterations required for each scenario, in order to anticipate the computational cost of applying the same workflow to higher-fidelity models.
Paper: MOP6318
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP6318
About: Received: 13 May 2026 — Revised: 16 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
MOP6660
Design and integration of motion control for the Iut24 in-vacuum undulator at TPS
556
The In-Vacuum Tapered Undulator (IUT24) was developed for the Phase-III beamline project at the Taiwan Photon Source (TPS). To counteract strong, non-linear magnetic attraction forces while maintaining precise synchronization between magnet arrays, a robust motion control architecture was implemented. This system integrates an EPICS-based supervisory layer with EtherCAT field I/O and BiSS-C absolute linear encoders (50 nm resolution) in a closed-loop pulse command configuration. Experimental results demonstrate that during dynamic gap transitions, the tracking error is strictly maintained within ± 2.5 𝜇m, and inter-axial synchronization remains within 0.5 𝜇m. Furthermore, long-term position stability was measured at ±150 nm over 200 minutes. This paper details the hardware integration, advanced motion control strategies, and comprehensive performance evaluations that confirm the system’s readiness for high-precision beamline operations.
Paper: MOP6660
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP6660
About: Received: 15 Apr 2026 — Revised: 17 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
MOP6685
Integrating FPGA into epics for on-the-fly scan control at the TPS 35A beamline
601
The growing demand for high-throughput XAS measurements at next-generation synchrotron light sources makes On-the-Fly Scan indispensable. Original software-based implementations improved efficiency but were limited by slow PC communication (~8 Hz) and soft-trigger jitter (<10 ms), restricting precise synchronization for multi-axis, non-linear trajectories and long-range energy scans. This work introduces a hardware-level fly-scan architecture that deeply integrates a Field-Programmable Gate Array (FPGA) into the EPICS control system at the TPS 35A beamline. Acting as a hardware acceleration core, the FPGA eliminates OS-induced latency and leverages high-speed parallel processing to achieve deterministic control. The system synchronously encapsulates ADC detector data, precise time tags, and high-speed position encoder feedback with nanosecond-level precision, enabling real-time trajectory compensation. This capability supports nano- to micro-second–scale measurements, opening new opportunities for time-resolved XAS. By replacing software delays with hardwired logic, this EPICS-FPGA paradigm delivers a standardized, stable, and highly efficient XAS measurement platform, critical for photon dose-sensitive samples. It fully realizes the hardware upgrade envisioned by previous software-based solutions, setting a new benchmark for high-performance beamline control.
Paper: MOP6685
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP6685
About: Received: 13 May 2026 — Revised: 15 May 2026 — Accepted: 16 May 2026 — Issue date: 22 May 2026
MOP7113
Swiss Light Source 2.0 vacuum system conditioning and first year of operation
901
After more than two decades of user operation, the Swiss Light Source (SLS) entered a major upgrade phase in October 2023, targeting a 40-fold reduction of electron-beam emittance via a new 7-bend achromat lattice at 2.7 GeV. The vacuum system, central to machine performance, was completely rebuilt to meet the stringent requirements imposed by the compact lattice. The new storage ring vacuum consists of an 18 mm aperture, 288 m long system assembled from over 500 chambers. Following 14 months of installation, first beam was achieved in January 2025. Vacuum conditioning represented a critical milestone, enabling delivery of light, with nominal beam current, to the first experiments in April. This contribution presents the vacuum conditioning of the SLS 2.0 storage ring during this first year of operation, from initial commissioning to user operation.
Paper: MOP7113
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7113
About: Received: 12 Apr 2026 — Revised: 17 May 2026 — Issue date: 22 May 2026
MOP7120
KIT superconducting undulator and magnet developments - overview and state of the art R&D on HTS technology
904
Undulators are widely used in synchrotron storage rings and free-electron laser facilities. With the advent of low-temperature superconductors (LTS), a new generation of superconducting undulators (SCUs) emerged, including the recent new THz LTS undulator for FLUTE. At KIT, state-of-the-art magnetic and cryogenic measurement capabilities — provided by the Magnet and Cryogenics Facilities (MCF) and the Accelerator Technology Platform (ATP) — form a foundation for the development and characterization of these systems. Building on this experience, KIT is now advancing magnets and undulators based on high-temperature superconductors (HTS), aiming for compact, sustainable, energy- and resource-efficient solutions. These activities are driven by in-house research and providing the full value chain of HTS technology from tape development via structuring to prototypes and tests in real-world environments at KIT. In this contribution, we provide an overview of our current developments and the supporting experimental infrastructure.
Paper: MOP7120
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7120
About: Received: 11 May 2026 — Revised: 15 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
MOP7121
In-Vacuum Undulators for BESSY II
908
Since 2018, the BESSY II storage ring has operated a cryogenic permanent magnet undulator (CPMU), which was developed and constructed in-house. With a period of 17 mm, CPMU17 was the first in-vacuum undulator to be installed at BESSY II. Another CPMU (CPMU20) and the world’s first in-vacuum APPLE II undulator (IVUE32) are currently under construction and will be installed at BESSY II within the next few years. To meet the needs of its diverse and ever-evolving user community, BESSY II has pioneered innovative operating modes, such as low-alpha and TRIBS, in addition to the hybrid mode. These special operating modes are based on phase space manipulation, which is enabled by the accelerator lattice's great flexibility and tight tolerances for the insertion devices. Accordingly, there are also tight tolerances on in-vacuum IDs. This paper discusses some of the main challenges, as well as the key developments and strategies, involved in meeting tolerance requirements.
Paper: MOP7121
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7121
About: Received: 12 May 2026 — Revised: 15 May 2026 — Accepted: 20 May 2026 — Issue date: 22 May 2026
MOP7123
A Hall-probe calibration setup in the temperature range from 300 K to 4 K at European XFEL
912
Precise magnetic-field measurements are essential for the characterization of both superconducting (SC) and permanent-magnet (PM) undulators. Since the accurate characterization of these devices relies directly on precisely calibrated Hall probes, a dedicated Hall-probe calibration setup for magnetic fields from -2T to +2T has been developed, produced, and commissioned at European XFEL, capable of operating over a broad temperature range from 300 K down to 4 K. This contribution presents the setup and first results.
Paper: MOP7123
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7123
About: Received: 18 May 2026 — Revised: 19 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
MOP7124
Overview of superconducting undulator development at the European XFEL
916
This contribution describes the recent progress of the European XFEL superconducting undulators (SCUs) program. This includes: an industrially-produced NbTi-based SCU afterburner foreseen for one of the two hard X-ray lines; a prototype SCU module (S-PRESSO) in production by Bilfinger; two magnetic measurement test stands to perform quality assurance; and further development of SCU technology to reach even larger magnetic fields, by leveraging recent developments in High Temperature Superconducting (HTS) tapes for future upgrades.
Paper: MOP7124
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7124
About: Received: 11 May 2026 — Revised: 17 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
MOP7125
First results from the SUNDAE1 test stand at European XFEL
920
European XFEL is planning the installation of superconducting undulators as afterburners downstream with respect to SASE2, one of the hard X-ray undulator lines, to provide even harder X-ray photon energies and a larger tuning range. The Superconducting undulator PRE-SerieS mOdule (S-PRESSO) consisting of two pair of coils, a phase shifter, and correction coils is in production by Bilfinger Nuclear & Energy Transition GmbH. In order to perform quality assurance of the superconducting coils a vertical test stand SUNDAE 1 (Superconducting UNDulAtor Experiment) has been developed. SUNDAE1 allows to train the superconducting coils, as well as to measure the magnetic peak field profile by means of Hall probes. We report here on first results.
Paper: MOP7125
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-MOP7125
About: Received: 12 May 2026 — Revised: 17 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
TUP2337
SIRIUS storage ring emittance measurement
1324
The SIRIUS is a fourth-generation Brazilian synchrotron light source whose high brilliance performance is determined by its low nominal electron beam emittance. The measurement of this parameter is crucial to validate the machine design, perform diagnostics, and guarantee beam quality for users. This work presents a methodology to measure the emittance at SIRIUS, combining spectral and spatial analysis of insertion device radiation. Three independent methods were applied: harmonic ratio, profile projection (peak-to-valley), and full 2D spatial profile minimization. Measurements were conducted simultaneously at the EMA (low beta section) and MANACA (high beta section) beamlines. The beta function, required for the final fitting, was measured with its uncertainty (≈ ±10%) incorporated into the analysis. The strategy aids in decoupling emittance from the ring's optical parameters with a certain level of confidence in the beta values. The results for the emittance are around 250-260 pm.rad, consistent with the design value, and demonstrate the effectiveness of the employed techniques. The study confirms the low emittance of SIRIUS and validates a set of methods for its continuous monitoring, advancing the knowledge on emittance measurement techniques.
Paper: TUP2337
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2337
About: Received: 13 May 2026 — Revised: 18 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP2338
Impact of VPU on beam dynamics in the SIRIUS storage ring
1328
This work evaluates the effects of the first vertical polarization undulators (VPUs) installed in the SIRIUS storage ring on electron-beam dynamics. These insertion devices (IDs) are light sources for the CARNAÚBA and CATERETÊ beamlines at the Brazilian Synchrotron Light Laboratory (LNLS). The analysis combines numerical simulations and beam-based measurements to quantify static and dynamic orbit distortions, optics perturbations (beta-beating and tune shifts), effects on injection efficiency, and changes in equilibrium beam parameters, including beam lifetime. The effectiveness of ID feed-forward compensation in mitigating these effects is assessed. Results characterize the operational impact of the VPUs on storage ring performance, providing safe conditions for beamline operation.
Paper: TUP2338
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2338
About: Received: 13 May 2026 — Revised: 18 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP2606
Feasibility of a Compact X-ray Free-Electron Laser Oscillator based on Diffraction Limited Storage Ring
1371
X-ray Free-Electron Laser Oscillators (XFELOs) utilize Bragg crystal-based x-ray cavities to generate high-brightness x-ray pulses with ultra-fine bandwidth. The successful realization of XFELOs would greatly benefit high-resolution photon-hungry experiments, such as nuclear resonant scattering and inelastic x-ray scattering. Existing XFELO proposals, constrained by either the electron beam repetition rate or limited single-pass gain in the undulator, typically require long undulators and long cavities. In this work, we investigate the feasibility of a compact XFELO design, utilizing the 6-meter straight sections of a Diffraction Limited Storage Ring (DLSR) and a cavity path length well below 100 meters. We show that sufficient single-pass gain can be achieved by optimizing the undulator and electron beam parameters. We present the projected performance of the proposed scheme based on the parameters of the High Energy Photon Source (HEPS) and discuss the practical challenges associated with its implementation.
Paper: TUP2606
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2606
About: Received: 13 May 2026 — Revised: 22 May 2026 — Issue date: 22 May 2026
TUP2635
Multi-objective bayesian optimization of multi-stage OK-SASE for efficient high-energy XFEL operation
1422
Femtosecond hard X-ray radiation beyond 12.4 keV enables unprecedented opportunities for probing matter at atomic scales, however, its generation remains challenging for self-amplified spontaneous emission (SASE)-based XFELs due to reduced FEL gain, leading to extended undulator requirements and limited radiation efficiency. To address this issue, we investigate a multi-stage optical-klystron SASE (OK-SASE) scheme that enhances microbunching through dispersive sections and shortens the gain length. A multi-objective Bayesian optimization (MOBO) framework is introduced to systematically optimize the configuration. Using SHINE as a representative case, steady-state simulations at 15 keV show that the optimized setup reduces the required undulator length relative to conventional SASE by about 7% to 22%, depending on the electron-beam energy spread. The optimization indicates that several chicanes can remain effectively inactive, enabling a more compact beamline layout. Time-dependent simulations also demonstrate the feasibility of multi-stage OK-SASE for efficient high-energy XFEL operation.
Paper: TUP2635
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2635
About: Received: 30 Mar 2026 — Revised: 21 Apr 2026 — Accepted: 15 May 2026 — Issue date: 22 May 2026
TUP2657
Off-axis hollow-channel plasma tailoring for generating two-color x-ray free-electron lasers
1448
Plasma-wakefield-based acceleration offers a route to realize compact X-ray free-electron lasers, but its application is currently limited by beam quality. Two-color X-ray FEL pulses provide a powerful tool for probing ultrafast dynamics. Here we propose a scheme for generating such pulses by using an off-axis elliptical hollow-channel plasma to tailor the electron-beam phase space while preserving its quality. In this approach, the plasma wakefield imprints a time-dependent transverse tilt along the bunch, while the elliptical channel geometry effectively suppresses the quadrupole wakefield and minimizes the induced mismatch. This enables fresh-slice lasing control at different wavelengths in two undulator sections. Simulations show the feasibility of generating femtosecond-scale, high-power two-color pulses with tunable temporal separation at the Shanghai Soft X-ray Free Electron Laser facility.
Paper: TUP2657
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2657
About: Received: 16 Apr 2026 — Revised: 14 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP2675
Optimizing a low-gain FEL oscillator for the SAPS Storage Ring: a parameter study
1478
Achieving higher spectral brightness in fourth-generation light sources like the Southern Advanced Photon Source (SAPS) through integrated free-electron laser (FEL) oscillators presents significant challenges. In response, we present a systematic optimization of the parameters for a low-gain FEL oscillator on the SAPS storage ring. Our work quantitatively evaluates how a transverse gradient undulator (TGU) modifies the ring's equilibrium beam parameters and analyzes the effects of harmonic operation and undulator length on FEL gain. These findings offer essential design guidance for implementing such FEL oscillators in storage rings.
Paper: TUP2675
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2675
About: Received: 13 May 2026 — Revised: 18 May 2026 — Accepted: 20 May 2026 — Issue date: 22 May 2026
TUP2686
Investigation and diagnostic potential of off-axis resonance in THz Free-Electron Lasers
1504
We study undulator radiation observed away from the beam axis for terahertz (THz) free-electron laser (FEL) beams. Earlier work on a single short bunch relates the continuous off-axis spectrum to the longitudinal bunch profile , without a discrete angular ‘resonance’ tied to micro-bunch harmonics. For a pre-bunched pulse-train beam, the bunching factor develops narrow spectral lines at the fundamental frequency and its integer harmonics. Off-axis phase matching selects a specific resonant polar angle for each line, producing pronounced, spatially separated ring-like intensity patterns in the coherent far field. We utilize the non-averaged 3D FEL code PUFFIN to simulate single-bunch radiation—reproducing non-integer harmonic patterns consistent with analytical Lié-nard-Wiechert (LW) results—and to demonstrate the expected off-axis resonance for pulse-train beams.
Paper: TUP2686
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2686
About: Received: 17 May 2026 — Revised: 18 May 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
TUP2691
Using Stretching-Modulation-Compression effect to generate isolated few-femtosecond MeV electron bunches
1512
Femtosecond electron beams serve as effective tools for investigating ultrafast dynamic processes in matter, providing complementary capabilities to femtosecond laser beams. We propose and demonstrate the feasibility of a scheme combining an undulator with THz modulation to generate isolated few-femtosecond electron bunches. We have developed a theoretical method that incorporates the transport dynamics of low-energy relativistic electrons interacting with the THz modulation field in the undulator and the space charge effects within the bunch itself. The results indicate that the proposed scheme can generate single isolated ultrafast electron bunches with kinetic energy 3 MeV, bunch length about 6 fs (rms) with core charge up to 0.1 pC. We have also evaluated the potential influence of several relevant physical quantities on the final bunch length and arrival time, and provided some scaling relations with respect to the initial bunch charges. The proposed scheme and the developed theoretical model presented may provide useful insights for generating few-femtosecond electron bunches or even shorter attosecond electron bunches in accelerator-based ultrafast electron facilities.
Paper: TUP2691
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2691
About: Received: 07 May 2026 — Revised: 15 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
TUP2707
Study on polarization control of planar undulator system based on magnetic field modulation
1535
The fast polarization switching of undulator radiation has attracted more and more attention in recent years. Recently, a new method has been proposed for fast polarization switching up to kilohertz of undulator radiation by using magnetic field modulation generated from low-current electromagnetic coils. Through fast switching the power of coils, the radiation spectra of two undulators can be rapidly shifted into and out of the bandpass of a monochromator, enabling fast polarization switching for the user beamline. In this paper, we have studied the performance of the scheme using planar undulators. The performance of related parameters, such as photon flux, polarization degree, and spot distribution, will be reported.
Paper: TUP2707
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2707
About: Received: 18 May 2026 — Revised: 21 May 2026 — Accepted: 22 May 2026 — Issue date: 22 May 2026
TUP2708
The essence factor to deteriorate the circular polarization radiation performance in APPLE-KNOT undulator
1539
The APPLE-KNOT undulator forms composite magnetic fields by superimposing APPLE and KNOT fields with different period lengths. In this configuration, in which the APPLE field serves as the dominant component to approximate the target photon energy, while the KNOT field acts as an additional component to transversely deflect the electron beam off-axis. Although variable polarization modes can be realized with a low on-axis heat load, previous studies have observed a sharp reduction in flux and significant degradation of the polarization degree in the circular polarization (CP) mode. This paper discusses this phenomenon in detail from a theoretical perspective. The analysis reveals that the presence of an additional field with a longer period is the essence factor that inherently suppresses the radiation performance of CP mode. Theoretical findings are highly consistent with simulation results, demonstrating that selecting the KNOT field as the dominant component can effectively improve CP characteristics without significantly compromising the linear polarization performance.
Paper: TUP2708
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2708
About: Received: 15 Apr 2026 — Revised: 18 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP2716
Development of in-situ field measurement system for Korea-4GSR in-vacuum undulators
1550
Precise magnetic-field characterization of in-vacuum undulators is essential for achieving stable beam dynamics in synchrotron light sources. This work presents an in-situ measurement platform that integrates a SAFALI-based Hall probe scanner with a stretched-wire measurement system. The Hall probe unit measures the local magnetic-field distribution along the undulator, achieving micrometer-level positioning accuracy through laser interferometry and optical feedback. In parallel, the stretched-wire system enables reliable determination of the first and second magnetic-field integrals. To minimize magnetic distortion, most mechanical structures are fabricated from low-permeability materials. The system is designed to characterize in-vacuum undulators with magnetic lengths of up to 3 m, allowing comprehensive field mapping without removing the vacuum chamber. The integrated platform is currently under construction for application to in-vacuum undulators at the Korea-4GSR Facility and is expected to improve phase-error reproducibility while providing direct verification of undulator magnetic performance.
Paper: TUP2716
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP2716
About: Received: 07 May 2026 — Revised: 15 May 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
TUP3019
Betatron radiation studies as a path to plasma undulators
1580
The emission of betatron radiation from the beam-driven plasma wakefield acceleration is under consideration at SPARC_LAB [1], as a test-bed for the study and development of a plasma-based undulator device. In the framework of the EuPRAXIA ESFRI facility [2] and EuPRAXIA@SPARC_LAB project [3], there is a deep interest in developing a compact plasma-based user facility, not only for what concerns the acceleration module, but also for what is ancillary to the delivery of FEL radiation. In this regard, great efforts have been made to miniaturize for instance diagnostic stations, detection devices and transfer lines, e.g. based on active plasma lenses [4]. However, conventional undulators are still too cumbersome and expensive to meet the requirements of compactness and sustainability. Nowadays, advanced undulator concepts arouse great interest in pushing the frontier beyond conventional, magnet-based undulators. In this regard, a promising, alternative is represented by the betatron motion of electrons in an ion-channel to emulate an undulator device. This work will present a case study at SPARC_LAB. [1] M. Ferrario et al., Nucl. Instr. and Meth. B 309, 183–188 (2013). [2] Assmann, R. W. et al., Eur. Phys. J. Spec. Top. 229, 3675–4284 (2020). [3] M. Ferrario et al., Nucl. Instr. and Meth. A 909, 134–138 (2018). [4] R. Pompili et al., Phys. Rev. Accel. Beams, 22:121302, Dec 2019.
Paper: TUP3019
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP3019
About: Received: 21 May 2026 — Revised: 21 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP7358
Reconfiguration options for reusing a permanent magnet undulator as a low-field wiggler source
1778
The Canadian Light Source (CLS) currently operates a 1.9 T superconducting wiggler (SCW) that has been in service since 2005. As the risk of failure and maintenance requirements for this aging device increase, and funding for a permanent replacement remains pending, an interim solution is needed to ensure continued beamline operation. Reconfiguring a decommissioned permanent magnet undulator offers a cost-effective alternative that could minimize downtime. Several approaches to modifying the magnetic layout to enhance wiggler performance are under consideration, with the goal of reusing existing mechanical supports, permanent magnets, and vacuum chambers. Proposed modifications include reducing the gap and halving the magnetic period to achieve the desired field characteristics.
Paper: TUP7358
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7358
About: Received: 08 May 2026 — Revised: 18 May 2026 — Accepted: 21 May 2026 — Issue date: 22 May 2026
TUP7360
A novel magnetic measurement system for cryogenic permanent magnet undulator
1781
A standardized magnetic measurement system exists for evaluating the field characteristics of conventional insertion devices, including in-vacuum undulators designed for NSLS-II, which employ a rectangular measurement window. A In-Vacuum Magnetic Measurement System (IVMMS) valid for 1.5 m long CPMU was developed during the NSLS-II project. However, in the case of cryogenic permanent magnet undulators (CPMUs), each facility implements its own design, and no commercially available measurement apparatus currently exists. At NSLS-II, we intend to retain a side rectangular window for room-temperature characterization. Consequently, a completely new in-vacuum Hall probe system good for longer devices than 1.5 m has been developed to interface with this window. This paper presents a preliminary design of the in-vacuum Hall probe measurement bench, designed to characterize a 3 m-long CPMU planned for the NEXT-III (NSLS-II Experimental Tools III) project beamline.
Paper: TUP7360
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7360
About: Received: 05 May 2026 — Revised: 07 May 2026 — Accepted: 16 May 2026 — Issue date: 22 May 2026
TUP7698
Analysis and refurbishment of a radiation-damaged undulator
1971
Synchrotron radiation facilities impose stringent requirements on the magnetic field quality, stability, and lifetime of undulators. During long-term operation of a beamline at the Shanghai Synchrotron Radiation Facility (SSRF), a gradual degradation of photon-beam performance was observed. To identify the cause, the cryogenic permanent magnet undulator of this beamline was warmed up and re-measured at room temperature during the summer shutdown. The on-axis field was found to be most strongly attenuated in the upstream region, with a maximum reduction of about 20% that gradually relaxed towards the downstream end. In addition, several sharp local drops of the magnetic field were detected in the central section. Visual inspection revealed pronounced melting holes in the copper foil in this area, indicating localized electron-beam impacts that likely damaged the underlying magnets and led to the abnormal field reduction. This paper presents the magnetic measurement results and the longitudinal attenuation pattern of the radiation-damaged undulator, and describes how local magnet replacement, re-shimming, and re-measurement were used to refurbish the device, providing a reference for future operation, maintenance, and radiation-protection design of similar undulators.
Paper: TUP7698
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7698
About: Received: 15 Apr 2026 — Revised: 16 May 2026 — Accepted: 16 May 2026 — Issue date: 22 May 2026
TUP7699
Design of a Compact Hybrid Planar Undulator
1974
Undulators are key insertion devices in synchrotron radiation and free-electron laser (FEL) facilities, where shortening the magnetic period is a crucial technical route to achieving compact machines and short-wavelength radiation. In our previous work, we proposed and experimentally validated an ultra-compact planar undulator that provides about a 48% increase in magnetic field strength compared with a conventional planar undulator under the same period length and gap, but its field strength is fixed and not tunable, limiting its engineering applicability. Building on that work, this paper proposes a compact hybrid planar undulator design that deliberately sacrifices part of the magnetic field strength to achieve tunability over a practical working gap range. To reduce the demagnetizing field experienced by the magnets under operating conditions, permanent magnets with different grades are combined in the structure, effectively mitigating the demagnetization risk in critical regions. Using three-dimensional magnetic-field simulations and optimization, we systematically investigate the effective field, field roll-off characteristics, and integrated field errors. The results show that the proposed compact hybrid planar undulator maintains a short period and relatively high field strength while providing magnetic-field tunability, offering a useful reference for the design of next-generation compact, high-performance undulators for advanced light sources.
Paper: TUP7699
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7699
About: Received: 15 Apr 2026 — Revised: 30 Apr 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
TUP7704
Improvement and optimization of a permanent-magnet phase shifter
1978
A permanent-magnet (PM) phase shifter for phase matching between tandem elliptically polarizing undulators (EPUs) at the Taiwan Photon Source (TPS) has been developed, and its initial version has already been installed in the storage ring. Current efforts focus on improving the device by enhancing the mechanical precision of the gap-adjustment system, maintaining magnetic-field quality, and minimizing beam-orbit perturbations within the limited installation space. Magnet sorting and shimming techniques were used to refine the magnetic performance of the first version. At small operating gaps, strong magnetic forces introduce substantial mechanical loading and can affect the field directionality. To overcome this limitation, an upgraded design incorporating a spring-assisted mechanism is under development. This work presents the optimization approach and the resulting improvements achieved through the integration of the spring system, demonstrating enhanced structural stability and improved reproducibility under high-force operating conditions.
Paper: TUP7704
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7704
About: Received: 13 May 2026 — Revised: 16 May 2026 — Accepted: 16 May 2026 — Issue date: 22 May 2026
TUP7705
Sustainability-oriented cryogenic permanent magnet undulator (LN₂-enabled C³-CPMU)
1981
A sustainability-oriented cryogenic permanent magnet undulator, the LN₂-enabled C³-CPMU, has been success-fully demonstrated at the Taiwan Photon Source (TPS). The system is designed to address cryogenic performance, thermal stability, and cost efficiency for high-current storage ring operation (up to 500 mA). The undulator employs a conduction-cooled architecture combined with an LN₂ reservoir-based cooling scheme with simplified flow and pressure control, eliminating the need for dedi-cated cryogenic units. Operating at an intermediate tem-perature of 150–160 K, the system consumes approxi-mately 8 L/h of LN₂. Active temperature control main-tains the magnet temperature within ± 0.08 K under vary-ing beam conditions, ensuring stable magnetic field per-formance. The enhanced magnetic properties at cryogenic temperatures enable shorter undulator periods, while integration with existing facility LN₂ infrastructure sig-nificantly reduces system complexity and operational overhead. These results demonstrate a scalable and ener-gy-efficient solution for next-generation synchrotron and XFEL light sources.
Paper: TUP7705
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7705
About: Received: 08 May 2026 — Revised: 14 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
TUP7733
Magnetic design of a prototype hybrid in-vacuum undulator and passive force cancellation system for SPS-II
2028
This paper presents the comprehensive magnetic design and simulation-based optimization of a prototype hybrid in-vacuum undulator (IVU), developed as a proof-of-concept for the 4th generation synchrotron light source (SPS-II) at the Synchrotron Light Research Institute (SLRI). Synchrotron radiation spectra simulations were performed using SPECTRA to calculate the expected photon flux for a configuration featuring a 20 mm period length and a 4.2 mm minimum gap at a 3 GeV electron beam energy. The magnetic structure was subsequently modeled in 3D using RADIA, employing NdFeB permanent magnets and FeCo-V poles. To ensure high-quality field distribution and beam stability, four distinct end-termination configurations were evaluated. The optimal configuration was selected based on its superior effectiveness in minimizing field integrals and beam trajectory deviations. A significant engineering challenge involving a peak attraction force of 18.8 kN was addressed through a Pure Permanent Magnet (PPM) force cancellation system. Through systematic parameter tuning and curve-fitting analysis, an optimized 16 mm period for the PPM array was determined. Furthermore, it was found that a 0.5 mm vertical installation offset relative to the main magnets is required to achieve precise force compensation. Simulation results demonstrate that this optimized system reduces the mechanical load by 99%, resulting in a residual force of only -166.1 N.
Paper: TUP7733
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-TUP7733
About: Received: 11 May 2026 — Revised: 16 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
WEP5026
Tracking-Based linear symplectic parameterization of insertion devices
2618
Accurate linear models of insertion devices (IDs) are essential for optics correction, coupling control, and feed-forward strategies in modern light sources. We present a systematic framework that builds a linear transverse symplectic parameterization, including leading-order chromatic effects, directly from Radia’s Runge–Kutta (RK) particle tracking. We compare the resulting matrices with those obtained using the standard kick maps approach for planar and elliptic IDs. The resulting parameterized symplectic models are well suited for constructing feed-forward tables across ID operating ranges.
Paper: WEP5026
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-WEP5026
About: Received: 06 May 2026 — Revised: 07 May 2026 — Accepted: 14 May 2026 — Issue date: 22 May 2026
WEP6116
Tune Compensation for Insertion Devices Motion at the SOLARIS Storage Ring
3192
Precise control of betatron tune is essential for maintaining beam stability in modern synchrotron light sources. At the SOLARIS storage ring, tune perturbations induced by undulator gap and phase present a significant operational challenge. This study presents a method for local tune compensation during the gap and phase motion of Apple II type undulator, installed upstream of a dedicated beamline. The approach employs a tune-feedback system based on two local quadrupoles and two global magnet families driven by a feed-forward table generated from a systematic scan of the undulator parameters (gap, phase) and the corresponding tune shifts. Prior to table generation, the magnets' response matrices for both tune planes were independently obtained. The proposed method ensures effective and reproducible mitigation of tune perturbations during undulator motion, enabling stable machine performance and improved beam quality at SOLARIS.
Paper: WEP6116
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-WEP6116
About: Received: 13 May 2026 — Revised: 17 May 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
WEP6123
Beam Loss Study for the L-shaped Corrugated Structure at European XFEL
3215
The European XFEL is a free-electron laser facility based on a superconducting linac with high bunch repetition rates of up to 4.5 MHz. An L-shaped corrugated structure has been installed upstream of the SASE1 undulator for fresh-slice operation and ultrashort-pulse generation. As the electron beam passes through the structure, strong longitudinal and transverse wakefields are excited which induce a correlated energy chirp and transverse kicks along the bunch. Since the gap between the corrugated structure and the beam is typically less than 1 mm, any beam misalignment or tail expansion may result in particles hitting the corrugated surfaces. For the L-shaped geometry this may occur on both the horizontal and vertical surfaces. Such interactions lead to energy deposition and secondary radiation that may cause damage to the downstream undulators. For this reason, studies have been carried out using BDSIM to simulate the losses caused by the L-shaped corrugated structure. Simulation results have been compared with in-situ radiation measurements using an autonomous robot.
Paper: WEP6123
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-WEP6123
About: Received: 13 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THO2M02
Results of the first interferometric measurements of undulator radiation from single electrons
3391
The aims of the CLARA experiment at the Fermilab Integrable Optics Test Accelerator (IOTA) were to directly measure the coherence length of undulator radiation emitted by a single electron and to test whether the radiation is in a pure classical Glauber coherent state or in a quantum mixture of coherent and Fock states. We used a Mach-Zehnder interferometer (MZI) to study visible radiation generated by 150-MeV electrons circulating in the ring. The relative delay between the two arms of the MZI was adjusted by varying the length of one of them with a resolution of 10 nm. The intensity of the circulating beam spanned several orders of magnitude, down to single electrons. A pair of single-photon avalanche diodes (SPADs) was placed at the output of the MZI arms to detect photocounts with high efficiency and timing resolution. We describe the observed interference patterns and photocount rates as a function of interferometer delay. The arrival time distributions of photocounts of undulator radiation, lasers and chaotic light are compared. The implications for the quantum-optical nature of the radiation are discussed. To our knowledge, these are the first direct measurements of this kind.
Paper: THO2M02
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THO2M02
About: Received: 13 May 2026 — Revised: 18 May 2026 — Accepted: 22 May 2026 — Issue date: 22 May 2026
THP2028
SOLEIL 2025 Operational Status
3483
SOLEIL, the French 2.75 GeV third-generation synchrotron light source, continues to operate as a high-performance research infrastructure supporting both academic and industrial communities. This contribution reviews the 2025 operational achievements, with emphasis on accelerator stability, availability, and the delivery of reliable photon beams to 29 beamlines. Key performance indicators and operational trends are presented, together with an analysis of major events and the mitigation strategies implemented to strengthen machine robustness. Significant progress in addressing component obsolescence is reported, including advances in BPM electronics, RF systems, and the global control-system upgrade. Updates on the LINAC modernization programme are provided, along with the use of the current SOLEIL accelerator as an integrated test platform to validate critical technologies for the forthcoming facility upgrade. Preparatory activities for SOLEIL II are outlined, including a progress report for bunch-per-bunch transverse feedback system, development and preparation to the qualification of new 352 MHz low-HOM RF cavities, the 1.4 GHz fourth-harmonic system, and upgraded control architectures, highlighting the technical readiness for the next-generation machine.
Paper: THP2028
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2028
About: Received: 20 May 2026 — Revised: 20 May 2026 — Issue date: 22 May 2026
THP2036
Echo-enabled harmonic generation at electron storage rings
3503
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 the interaction of electrons with femtosecond laser pulses in two undulators (”modulators”), each followed by a magnetic chicane, a longitudinal phase space structure with high harmonic content is produced, which gives rise to coherent emission of radiation at harmonics of the laser wavelength. 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. After reviewing proposals of EEHG at different storage rings, the latest results of a first demonstration experiment at the 1.5-GeV synchrotron light source DELTA at TU Dortmund University are presented.
Paper: THP2036
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2036
About: Received: 13 May 2026 — Revised: 20 May 2026 — Issue date: 22 May 2026
THP2038
Undulator radiation from a single electron in a storage ring
3511
A low-intensity double-slit experiment in the time domain has been undertaken by measuring the spectral distribution of synchrotron light from a single relativistic electron in a storage ring. In two consecutive undulators with a dispersive section between them (known as optical klystron), an electron beam emits two temporally separated light pulses leading to a spectrum with interference fringes - in close analogy to the angular distribution of light behind two spatially separated slits. Experiments at the electron storage rings DELTA in Dortmund, Germany, and UVSOR-III in Okazaki, Japan, show directly that the spectral distribution of accumulated synchrotron light from a single electron is essentially the same as the spectrum from a beam of many electrons. While the latter is usually explained by interference between simultaneous the light waves from the two undulators, the single-electron experiments demonstrate the uncertainty of the photon source point over several meters.
Paper: THP2038
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2038
About: Received: 13 May 2026 — Revised: 20 May 2026 — Issue date: 22 May 2026
THP2041
Chicane-free laser heater system for mitigation of microbunching instability in linac-FELs
3519
We introduce a closed-form, verified through numerical integration, of the beam energy spread induced by oblique electron-laser interaction in a short undulator, so-called chicane-free laser heater. This scheme is relevant for high repetition rate free-electron lasers, space constrained, or subject to microbunching instability induced by a standard laser heater chicane. A calculation of the instability gain with the proposed scheme is presented to demonstrate its feasibility.
Paper: THP2041
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2041
About: Received: 21 Apr 2026 — Revised: 19 May 2026 — Issue date: 22 May 2026
THP2051
Insertion devices characterization at the SLS 2.0
3544
Accurate measurement of high-order multipoles in insertion devices is crucial for meeting the beam-dynamics requirements of Swiss Light Source 2.0. A beam-based method using transverse tune-shift measurements can effectively identify sextupole, octupole, and higher-order magnetic components under normal operating conditions, avoiding the need for dedicated magnetic tests. Among the upgraded insertion devices—planar, in-vacuum, and knot-type—only the knot-type device shows significant multipole components beyond sextupole, reaching octupole order. This study focuses on the knot-type device, which is expected to be used in SLS 2.0 and in other modern synchrotron facilities, presenting measurements and comparisons with simulation results.
Paper: THP2051
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2051
About: Received: 22 Apr 2026 — Revised: 06 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
THP2065
Experimental study of reverse tapering and resonance detuning in a seeded X-ray FEL
3572
Reverse tapering can suppress the FEL field while preserving electron microbunching for downstream radiators over an appropriate range of taper strength. In a monochromatically seeded FEL, one-dimensional small-signal theory suggests that the response to reverse tapering can be compared with the response to an accumulated resonance detuning. Here, we report on an experimental investigation of the relationship between undulator reverse tapering and resonance detuning in a seeded hard X-ray FEL, where the fixed seed frequency eliminates the influence of SASE photon-energy jitter. A modulator-radiator configuration was used in which U19 to U24 were scanned either by changing the resonance setting or by applying reverse tapering, while U25 was kept as the downstream radiator. The scans were performed with U25 active, to characterize the bunching-driven radiator signal, and with U25 off, to characterize residual upstream radiation. The U25-active spectra comparison shows a good agreement between reverse tapering and resonance detuning. The U25-off spectra show a stronger reduction of residual upstream radiation on the negative-detuning side than the U25-active radiator signal, indicating that the radiation field is suppressed more efficiently than the bunching-related signal, as expected for reverse-taper operation.
Paper: THP2065
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2065
About: Received: 12 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THP2069
Compensating The Effect of Asymmetrically Placed Undulators in FODO Lattices
3580
The dynamical focusing of FEL undulators with variable gap in FODO lattices with varying but overall low energy is detrimental the FODO optics. In the absence of compensation by adjusting the FODO quadrupole strengths it may drive the cell unstable. Typical examples of FELs in the critical regime are FLASH at DESY and the SXFEL-SBP at the Shanghai Synchrotron Radiation Facility. Before, in our contributions to FEL 2024 and IPAC 2025 we have extensively discussed the case where the undulators are centered inside the FODO drift of a Lattice with symmetric FODO cells. Here we treat the fairly common case where the drifts on each side of the undulator are unequal, which has significant impact on the compensation strategy and stability issues.
Paper: THP2069
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2069
About: Received: 11 May 2026 — Revised: 13 May 2026 — Accepted: 14 May 2026 — Issue date: 22 May 2026
THP2084
SwissFELplus: a Mid-Term Upgrade Plan for the Swiss Free-Electron Laser
3606
SwissFEL, the free-electron laser facility at the Paul Scherrer Institute (PSI) in Switzerland, is about to complete its first decade of user operation. The knowledge gained during this period, together with important developments at FEL facilities worldwide, suggests a number of key upgrades to the accelerator and undulator complex that would substantially enhance the scientific capabilities of the two existing SwissFEL beamlines. The SwissFELplus project, planned for 2029-2032, aims to implement these upgrades - including full coherence in the hard- and soft-X-ray regimes via self- and external-laser seeding, as well as preparations for a new beamline - and thereby bring SwissFEL to a new level of scientific excellence ahead of its quantitative expansion with a third beamline. The resulting improvements in beam stability and coherence will benefit applications ranging from atomic physics to biology and will enable new approaches, such as quantum optics for X-rays, with its advantages in the management of radiation damage. This contribution describes the upgrade elements and their expected impact on SwissFEL’s photon-science capabilities.
Paper: THP2084
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2084
About: Received: 13 May 2026 — Revised: 13 May 2026 — Accepted: 17 May 2026 — Issue date: 22 May 2026
THP2118
Superradiant THz generation and bunch compression at DALI
3668
The Dresden Advanced Light Infrastructure (DALI), a 50 MeV superconducting linac currently under development at Helmholtz-Zentrum Dresden-Rossendorf, aims to deliver from one of its sources high-brightness, few cycle THz radiation through superradiant emission in a dedicated undulator. Efficient superradiant generation requires electron bunches with a form factor matched to the desired wavelengths between 0.1 and 3 THz. Achieving such short bunches at the design charge of 1 nC, however, is constrained by space charge forces and coherent synchrotron radiation in the magnetic chicane used for compression. This work discusses the design of the superradiant THz beamline with emphasis on the attainable compression performance and the resulting impact on the THz output. Quantitative tradeoffs between compression strength, bunch quality, and expected radiation yield are discussed to guide the optimization of the DALI THz source.
Paper: THP2118
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2118
About: Received: 13 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THP2151
In-vacuum and cryogenic permanent-magnet undulators at the ESRF
3749
The European Synchrotron Radiation Facility (ESRF) operates a large number of in vacuum undulators (IVUs) and cryogenic permanent magnet undulators (CPMUs). Eight IVUs and nine CPMUs are currently in service, and a few more are under construction or planned. CPMU technology is used to build short period undulators with a wide tuning range. These insertion devices generate intense high order harmonics and can reach high photon energies — typically up to 100 keV at the ESRF. When a CPMU is installed at the centre of a straight section it can be set to a smaller gap, which allows the undulator period to be reduced. Two undulators can also be placed upstream and downstream of each other and phased with a phase shifter. A major limitation of this approach is the heat load on the photon front ends and on the optical elements of the beamlines. This problem can be mitigated by combining a tunable device with a short period, almost monochromatic in vacuum undulator dedicated to a single photon energy. The various layouts of the ESRF IVU/CPMU straight sections will be presented, together with the CPMU operating experience, construction and installation trends, and future developments.
Paper: THP2151
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2151
About: Received: 11 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THP2152
The SOLEIL II insertion devices
3753
The SOLEIL II insertion devices will be presented. They range from long period Adjustable Phase Undulator of long period, APPLE X, Dual undulators for the intermediate energy spectral range, and in vacuum undulators, cryogenic permanent magnet undulators and wigglers for hard X-rays.
Paper: THP2152
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2152
About: Received: 11 May 2026 — Revised: 18 May 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
THP2153
Wakefield studies of IVUE32
3757
The Helmhotz-Zentrum Berlin (HZB) is developing an elliptical in-vacuum undulator, IVUE32, following the APPLE-II design with a magnetic force compensation concept. The undulator will be installed in the BESSY II storage ring. It will feature a 7 mm minimum gap and four magnet rows that can be moved to adjust the polarization of the synchrotron radiation. This shift movement requires a complex taper structure and a longitudinal slit in the shielding foils. Extensive CST wakefield simulations have been conducted to investigate the interaction between the undulator and the beam. The impedance of the device on the beam is studied, as well as the heating of the undulator induced by the beam. The taper structure has to compensate for two axes of motion. The vertical gap movement and the longitudinal shift movement. The shift movement is different for each half of the shielding foil. Previously presented designs used separate foil tensioning systems to independently compensate for the two axes of motion. A length constraint due to the $\beta$-function might prohibit the separate compensation. Changing the gap while also compensating for the shift motion introduces an asymmetry in the taper, where the shielding foils have different gradients. Different asymmetric tapers are studied to find the limits for horizontal impedance for the BESSY II beam.
Paper: THP2153
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2153
About: Received: 13 May 2026 — Revised: 19 May 2026 — Accepted: 20 May 2026 — Issue date: 22 May 2026
THP2154
Design, training and magnetic field characterization of the superconducting THz-undulator coils for FLUTE
3761
FLUTE, a short-pulse linac and short-bunch THz test facility, serves as an accelerator test setup for a variety of accelerator physics studies. In its final stage of expansion, it is foreseen to provide coherent radiation in ultra-short, very intense light pulses in the terahertz and far-infrared spectral range. A superconducting undulator (SCU) at the end of the accelerator structure offers the possibility to generate photon radiation between 4 THz and 12 THz (energies between 16.5 meV and 50 meV) with a high pulse energy. This energy range, for instance, is of interest for studies of water-soluble interactions. The final undulator design was carried out by Bilfinger Nuclear & Energy Transition GmbH (BNET) in close collaboration with the Institute for Beam Physics and Technology (IBPT) of the Karlsruhe Institute of Technology (KIT). Before assembling the final undulator device the superconducting coils were trained and magnetically characterized in CASPER II, a magnetic measurement setup which is part of the Magnet and Cryogenics Facilities (MCF) at the IBPT at KIT. In this contribution we describe the general SCU layout, presenting the results of the coil training, the local magnetic field characterization and field integral minimization of the THz-undulator coils.
Paper: THP2154
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2154
About: Received: 12 May 2026 — Revised: 18 May 2026 — Accepted: 20 May 2026 — Issue date: 22 May 2026
THP2155
Upcoming insertion devices at MAX IV facility
3765
Currently, there are 17 Insertion Devices (ID) in operation at the MAX IV facility. The soft X-ray undulators are based on the 3 APPLE II undulator at the 3 GeV ring, 4 APPLE II and 1 planar undulators at the 1.5 GeV ring, and the hard X-ray IDs are based on room-temperature in-vacuum technology at the 3 GeV ring and the Short Pulse Facility. A recently funded Tomography beamline for materials science at the 3 GeV ring will utilize two sources within the same straight section: a short-period cryogenic permanent magnet undulator (CPMU) with a 14 mm period length for nano-tomography and a 3 T 3-pole wiggler for micro-tomography. Both IDs are currently in production, with installation planned for summer 2027. Further developments include a planned tender hard X-ray (2–20 keV) spectroscopy beamline and a new medical-imaging beamline covering an energy range of 15–80 keV at the 3 GeV ring. At the 1.5 GeV ring, a new APPLE II undulator providing polarization control from 50 eV photon energy is foreseen to replace an older planar undulator. In this paper, we present the parameters of these upcoming insertion devices and provide estimates of their expected performance.
Paper: THP2155
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2155
About: Received: 04 May 2026 — Revised: 18 May 2026 — Accepted: 18 May 2026 — Issue date: 22 May 2026
THP2156
Modeling of Insertion Devices in Xsuite
3768
Insertion devices with longitudinally periodic fields—such as undulators, damping wigglers, and polarizing wigglers—play a central role in several stages of the FCC-ee injection chain. Accurate field models and efficient long-term tracking are required, as the strong longitudinal field variation cannot be captured reliably with standard multipole expansions. We introduce in the Xsuite simulation toolkit a general model for such devices based on a Maxwell-consistent series expansion of the magnetic field. The expansion is constructed from the on-axis field and its transverse derivatives and is implemented in BPMETH, which provides a direct interface to Xsuite. Particle tracking is performed using the Boris integrator. We assess the approach by comparing Boris integration with a multipole expansion and compare the convergence of the resulting tracking. This framework enables detailed optics and beam-parameter studies for synchrotron light sources, damping rings, and polarization systems.
Paper: THP2156
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2156
About: Received: 07 May 2026 — Revised: 18 May 2026 — Issue date: 22 May 2026
THP2157
Demonstration of a transverse gradient undulator in an X-ray free-electron laser
3772
Modern synchrotron light sources employ various types of undulators to generate highly coherent and well collimated X-rays. A large and homogeneous magnetic field around the beam axis is typically the preferred configuration, since it simplifies both alignment and operation. Nevertheless, a nonhomogeneous field, such as that of a transverse gradient undulator (TGU), offers attractive possibilities for advanced operating modes, for example enabling large bandwidth operation in a free electron laser. In this contribution, we present the first beam-based characterization of such a TGU for various magnetic field gradients and X-ray polarization settings, and we compare the experimental results with corresponding simulation data. The measurements were carried out at Athos, the soft x-ray beamline of SwissFEL. This line employs Apple X undulators, whose independent radial and shift motion of all four magnetic arrays makes them uniquely capable of generating the required transverse gradients.
Paper: THP2157
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2157
About: Received: 18 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THP2158
The first APPLE X knot undulators: magnetic characterization and initial performance
3775
Concepts for reducing on-axis heat load become essential as photon flux increases in next-generation synchrotrons, especially in the soft X-ray regime. Therefore, APPLE “knot” undulators are promising insertion devices, as they divert most of the energy off-axis without compromising polarization purity. The first two APPLE X knot undulators, 2 m long and with a period of 36 mm, were designed and built at Paul Scherrer Institute (PSI) and installed into the newly upgraded Swiss Light Source (SLS2.0) electron storage ring. This contribution presents the final magnetic characterization results of the novel undulators and derives photon characteristics, including how effectively the radiation power is expected to be reduced on-axis in contrast to a regular elliptical undulator, especially in linear modes. Further, their initial performance with the beam is demonstrated, providing a glimpse of the ongoing beamline commissioning and operation.
Paper: THP2158
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP2158
About: Received: 13 May 2026 — Revised: 19 May 2026 — Accepted: 19 May 2026 — Issue date: 22 May 2026
THP5320
Symplectic integrator for insertion devices tracking at SIRIUS
4211
This paper presents the development of a symplectic integrator for particle tracking in insertion devices at SIRIUS. The method relies on analytical field representations specifically tailored to model the magnetic structure of the device accurately. Tracking results obtained with the new integrator are compared with those from traditional kickmaps, and the differences observed in dynamical aperture calculations and frequency map analyses are examined, showing the integrator’s effect on long-term beam dynamics predictions. The integrator is further applied to specify the field roll-off requirements for SIRIUS’s first CPMU, which will operate with a minimum gap of 4.65 mm at a high-beta section.
Paper: THP5320
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP5320
About: Received: 13 May 2026 — Revised: 22 May 2026 — Issue date: 22 May 2026
THP5339
Impedance analysis of long vacuum chambers via longitudinally reduced geometries
4247
Beamlines of modern synchrotron light sources demand the installation of long undulators with small gaps in the storage ring. The vacuum chamber of these devices requires time-consuming wakefield simulations for impedance estimation. Furthermore, these structures can exhibit trapped modes, demanding extensive eigenmode simulations for impedance characterization. This paper presents a method to estimate a conservative impedance envelope for trapped modes from a longitudinally reduced geometry, reducing both computational time and numerical artifacts inherent to long simulations. The proposed methodology is validated through the impedance analysis of the APPLE-2 undulator for the SIRIUS IPE beamline.
Paper: THP5339
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP5339
About: Received: 13 May 2026 — Revised: 21 May 2026 — Issue date: 22 May 2026
THP5627
Symplectic integration for storage ring based FEL in Genesis
4330
Symplectic integration is essential for simulating the long-term stability of systems such as storage rings. In contrast, it has traditionally been considered unnecessary for single-pass free-electron laser (FEL) simulations. Consequently, standard FEL simulation codes, like Genesis, have not fully incorporated symplectic methods in their treatment of the beam dynamics. However, with the growing interest in storage ring-based FELs, the requirement for symplectic tracking in the FEL dynamics process has emerged. This paper presents a modification of the Genesis code to implement a symplectic algorithm for its dynamical part. A comparative analysis between the symplectic and non-symplectic approaches is conducted. The results demonstrate that the symplectic Genesis preserves the symplecticity of beam dynamics without compromising the accuracy of the radiation simulation, thereby providing a more reliable tool for accurate storage ring FEL modeling.
Paper: THP5627
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP5627
About: Received: 13 May 2026 — Revised: 19 May 2026 — Accepted: 19 May 2026 — Issue date: 22 May 2026
THP5654
Longitudinal beam instability in SSMB laser modulators: a cavity mode decomposition approach
4378
Steady-state microbunching (SSMB) is a promising mechanism for generating high-average-power coherent radiation by maintaining microbunches in a storage ring. In an SSMB laser modulator (LM), the interaction between electron bunches and the recirculating coherent undulator radiation can drive longitudinal beam instabilities, which may limit the overall performance. In this work, we investigate the longitudinal single-bunch multi-turn instability using a cavity mode decomposition approach. The evolution of the longitudinal wakefield is derived by expanding the radiation into a complete set of cavity eigenmodes, accurately capturing the optical evolution of the field over multiple turns. The longitudinal beam dynamics equations are formulated to analyze the instability growth rates. Numerical simulations show excellent agreement with the theoretical model, validating the mode decomposition technique. These findings provide critical insights into the instability characteristics and suggest effective mitigation strategies for the design and operation of SSMB storage rings.
Paper: THP5654
DOI: reference for this paper: 10.18429/JACoW-IPAC2026-THP5654
About: Received: 11 May 2026 — Revised: 20 May 2026 — Issue date: 22 May 2026