Commissioning of SLS 2.0, the first light-source storage ring employing a substantial number of permanent magnets to realize a compact multi-bend achromat lattice, began in January 2025. As reported at IPAC'25, the nominal beam current of 400 mA was achieved within the first three months of accelerator-dedicated commissioning. Since then, significant additional progress has been made, such as beamline commissioning during the subsequent three-month period, realignment of the storage ring, and commissioning of the fast orbit feedback system. The Swiss Light Source facility upgraded to fourth-generation has reached a level of availability sufficient to begin user operation, delivering high-brightness photon beams to twelve operational beamlines. Two weeks of friendly user operation in July and one month of external user service in November–December were successfully completed. It is currently in shutdown for the further installation of planned photon sources and is scheduled to resume operation in spring 2026. We present the commissioning results, lessons learned, and experience gained during the initial user operations.

The most updated complex bend achromat lattice for the high-brightness upgrade of NSLSII provides a record-low electron beam emittance of 23 pm at 3 GeV. However, collective effects of beam dynamics, especially intra-beam scattering, are the main limiting factors of emittance and brightness at operational beam Intensity. Since the emittance and collective effects are strongly dependent on the beam energy, we estimated the lowest possible emittance scaled with energy and intensity, taking into account intrabeam scattering, vacuum chamber impedance, and bunch lengthening by higher-harmonic RF cavities.

We report on the development of an advanced storage ring lattice, the Stanford Diffraction-Limited Light Source (SDLS), tailored for installation in the existing PEP-II tunnel at SLAC. The design is based on the hybrid 6-bend achromat (H6BA) architecture optimized for ultra-low emittance while maintaining robust nonlinear dynamics, essential for diffraction-limited synchrotron radiation production. To accommodate long straight sections required for insertion devices and injection systems, we implement the mmodified transparency conditions that mitigate periodicity-breaking effects and preserve dynamic aperture and momentum acceptance. This latest design advances the SDLS concept by combining a new compact (insertion device-less) cell in half of the arcs and the H6BA in the remaining half of arcs. Nonlinear optimization—via multi-objective algorithms incorporating tune footprint control, frequency map analysis, and chromatic detuning minimization—yields a dynamic aperture sufficient for off-axis injection and a Touschek lifetime exceeding those of contemporary third-generation sources.

The High Energy Photon Source (HEPS) is a 35-pm, 1360-m storage ring light source being built in the suburb of Beijing, China. The HEPS construction started in 2019, with the main civil construction finished at the end of 2021. In the past two years, the beam commissioning of the HEPS storage ring had been started and bascially finished. In this paper, we will briefly introduce commissioning of the HEPS storage ring, and relavent physics studies.

X-ray Free-Electron Laser Oscillators (XFELOs) driven by Diffraction Limited Storage Rings (DLSRs) promise ultra-narrow-bandwidth X-rays at high repetition rates. However, simulating the multi-pass laser build-up and saturation is a severe computational bottleneck. We present a simplified and highly efficient fast modeling framework for DLSR-XFELOs, which is capable of capturing power growth, temporal and spectral evolution of the radiation as well as beam quality change from pass to pass. We show the characteristic behavior of the longitudinal mode growth of such coupled system for long and short electron pulses.

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.

In modern storage ring light source, large offset of quadrupoles will degrade the beam quality in the ring. Beam based alignment(BBA) methods have been used widely in storage rings, to correct the orbit of the beam to the magnetic center of quadrupoles. The BBA algorithm and commissioning procedure at HEPS is described in this paper

The High Energy Photon Source is the first fourth-generation synchrotron light source in Asia. As a green-field facility, HEPS began construction in 2019 and now the commissioning of the storage ring has been basically finished. The booster synchrotron, serving as the second-stage accelerator, completed its initial beam commission-ing between July and November 2023 and was officially put into operation in July 2024 to support the storage ring commissioning. This paper presents the beam per-formance of the booster since the start of operation, key upgrades and optimizations implemented, major opera-tional challenges encountered, and the ongoing plans for further performance enhancement

In this paper, we propose to use longitudinal strong focusing principle to lower particle beam energy spread locally in a storage ring. An example application of the proposed scheme in reversible Echo SSMB for high-power EUV radiation generation is presented. We believe strong focusing in the longitudinal dimension has a wide application potential.

A third harmonic system is planned for PETRA IV. One possible option for the third harmonic cavity is a novel single-mode cavity based on the choke-mode principle. The DESY device developed on this basis offers the following advantages over alternative designs: a) Very strong suppression of all unwanted modes. b) Coupling factor adjustable during operation. c) The wall currents induced by the fundamental mode are not disturbed by weld seams. This has a favourable effect on the shunt impedance and quality factor. d) The simple geometry of the cavity results in the smallest possible number of independent cooling circuits. The presentation describes the development work, introduces the design and highlights some of the cavity's outstanding features. It a also discusses the current construction of the cavity.

The SOLARIS 1.5 GeV storage ring featuring a compact 96 m circumference design, operates at currents up to 500 mA with a horizontal emittance of ~6 nm·rad, delivering high-brightness synchrotron radiation from the soft X-ray to ultraviolet range. Head–tail instabilities remain a significant limitation for the stable operation of modern synchrotron light sources, particularly as facilities push toward ultra-low emittance and higher single-bunch currents. In these regimes, strong transverse focusing and reduced momentum compaction significantly increase the sensitivity of betatron motion to both chromaticity and short-range impedance. In this work, we investigate the onset and evolution of head–tail modes in a third-generation storage-ring light source using a high-resolution bunch-by-bunch diagnostics. Growth rates of first- and higher-order head–tail modes are mapped as a function of key parameters including beam current and bunch length. Furthermore, the response of the magnetic lattice is analyzed via Linear Optics for Closed Orbits (LOCO) complemented by single bunch lifetime measurements for different chromaticity settings. These studies provide insight into instability thresholds and lattice behavior, supporting strategies for enhanced operational stability.

ALBA is working on the upgrade project that shall transform the actual storage ring, in operation since 2012, into a 4th generation light source, in which the soft X-rays part of the spectrum shall be diffraction limited. The project was launched in 2021 with an R&D budget to build prototypes of the more critical components. The storage ring upgrade is based on a MBA lattice which has to comply with several constraints imposed by the decision of maintaining the same circumference (269m), the same number of cells (16), the same beam energy (3GeV), and as many of the source points as possible unperturbed. At present, the lattice optimization, iterating with the technical constraints of space and performance, is ongoing. This paper presents the situation of the project, with the present proposed lattice and equipment design; the status of the prototyping of magnets, pulsed elements. vacuum chambers, buttons BPMs, and girders; the proposed RF system with fundamental and harmonics cavities; and the general context of the upgrade.

Multi-bend achromat lattices allow for the design of extremely low-emittance electron storage rings and are a cornerstone of the performance of storage-ring-based synchrotron light sources. As part of the proposed MAX IV upgrade, MAX4U, we revise the impact of the insertion devices (IDs) on the beam. We extend the kickmap-based tracking analysis by including the effects of radiation and quantify the resilience of the proposed achromats to the different ID settings and configurations. Finally, we present mitigation strategies, both local to each ID and global, that may be tested experimentally in the current MAX IV 3 GeV ring.

The alignment of girders and individual magnetic elements according to the tight design specifications is of paramount importance for achieving the ultimate performance of the SLS 2.0 storage ring (SR) which is consisting of a large number of SR optics defining permanent magnets. As a result, alignment errors can easily overstrain the very limited capabilities of the electromagnetic dipole corrector magnets. In order to enable a fast realignment during commissioning the girders are vertically remote adjustable allowing for a realignment within +-0.5mm (backed by simulation) with stored beam and running fast orbit feedback based on previously taken survey data (Beam-Assisted Girder Alignment). A linear encoder based vertical positioning system monitors the relative girder-to-girder motion. In addition, the orbit correction system helps to identify errors of individual magnets on the girders.

With the transition from machine commissioning to beamline commissioning and user operation, long-term reliability and high availability of the SLS 2.0 accelerator complex have become critical. Rapid, systematic fault handling is essential to minimize downtime and protect the accelerator. This contribution presents the architecture and implementation of key systems developed for fault management at SLS 2.0, including the Post Mortem framework, Injection Guard, and controlled emergency beam-dump procedure. The Post Mortem system captures and logs comprehensive fault data for analysis supporting root-cause identification, confirmation of a successful emergency beam dump and continuous improvement. The Injection Guard ensures safe and reliable injection by monitoring critical parameters and preventing injection when safety thresholds are violated. For severe fault scenarios, a controlled emergency beam dump using a fast beam dump controller, a fast beam dump magnet and a dedicated beam dump protects sensitive components such as the vacuum chamber. Together, these measures form an integrated approach to fault handling that enhances operational robustness and user reliability. Initial experience during early user operation demonstrates their effectiveness and lays the foundation for further optimization and long-term reliability.

Following successful machine commissioning, the Swiss Light Source upgrade, SLS 2.0, entered its first beamline commissioning and user operation phases. This contribution reports on the achieved storage-ring performance and operational stability during user operation. Storage-ring optics were tuned near design, achieving beta beating within a few percent and optimized dispersion. Sub-micron orbit stability was achieved through fast-orbit feedback supported by the in-house DBPM 3 system, permanent magnets, stable power supplies, and improved environmental control. The injector chain delivered highly reproducible bunch charge, stable energy and optics matching, and transmission exceeding requirements. User operation started with a stable baseline filling pattern and regular top-up injection under defined current-stability conditions. Beamline commissioning progressed in parallel with accelerator-performance optimization, and by the end of the first user period 14 beamlines were routinely operating with availability comparable to the final years of SLS. Operational statistics confirm that SLS 2.0 has rapidly reached a robust operational regime, paving the way for continued performance optimization and full scientific exploitation.

The Diamond-II booster ring is designed to reduce the emittance and the bunch length for efficient injection into the storage ring. Non-optimal commissioning of the injector might increase the dark-time period and the impact on the existing scientific program. This work explores the strategies for booster commissioning to predict and resolve possible issues. The results include tracking simulations with realistic errors such as alignment of magnets and precision of beam diagnostic devices, errors in the magnet gradients, eddy-current effects, measured multipole errors in magnets, pulsed-magnet and injected beam-jitter.

A beam-based alignment procedure is used to realign the beamt to the centres of the quadrupoles, enabling calibration of BPM offsets. Accurately determining these quadrupole centres is an important step that requires analyzing BPM data collected while modulating the nearby quadrupole and one or more corrector magnets in the ring. In this paper, several numerical methods to extract the quadrupole centres, with or without error analysis, are presented and their results are compared. This study is based on online experiments performed at Diamond.

This work demonstrates that periodic transient beam loading can affect bunch lengthening as well as cause its variation over time in Diamond-II. The instability can be eliminated by increasing the detuning of the harmonic cavity. The results suggest that introducing longer gaps in the filling pattern might eliminate the instability, but this will reduce the effectiveness of the passive harmonic cavity. Next, this study explores the option of creating a charge variation within the train of the hybrid-fill pattern. This technique can help to flatten the bunch-length variation as well as increase the bunch length in the timing bunch. Finally, the bunch-compression regime was explored using the standard-fill pattern without collective effects. It was found that the harmonic cavity can be detuned such that it shortens bunches instead of elongating them.

The PETRA IV project has finalised the engineering design for the construction of a new ultra-low emittance storage ring PETRA IV, based on hybrid 6-bend achromat lattice and the whole rebuild of the injector chain. We review here the latest development in the different technical subsystems, the status of the engineering integration and the plans for the implementation of the new ring in the existing PETRA III tunnel.