Storage Ring Research Articles

Investigation of the neutron radiation fields inside the accelerator tunnel during operation of the Swiss Light Source (SLS)

The Swiss Light Source (SLS) is a third-generation synchrotron light source with an electron energy of 2.4 GeV. It consists of a linear accelerator, a booster and a storage ring providing light for various applications. As SLS is a high-energy accelerator, its operation is accompanied with production of ionizing radiation fields, including neutrons. This leads to additional challenges from a radiation protection point of view. The long-term investigation of the radiation fields at this accelerator facility can provide useful information for the residual activation studies and optimization of shielding. This work describes measurements of the neutron radiation fields inside the tunnel and results of this study.

Development of a 166.6MHz β = 1 higher-order-mode-damped superconducting cavity.

The storage ring of the high energy photon source will be driven by five 166.6MHz β = 1 quarter-wave superconducting cavities operating at 4K. A higher-order-mode-damped superconducting cavity was designed with excellent rf and mechanical properties based on the successful development of the proof-of-principle cavity. The mechanical design of the dressed cavity was focused on addressing stress safety throughout the processes, tunability, frequency detuning due to pressure fluctuation, and Lorentz force, among other factors. A new liquid helium vessel was designed along with a comprehensive stiffening scheme to mitigate the surging peak stress on the cavity resulting from the significantly unequal beam pipe size. In the first batch, three cavities were manufactured, and surface preparations were carefully conducted to eliminate defects and etching traces while ensuring cleanliness. The cavity's Q0 at the design voltage of 1.5 MV reached 3.8 × 109 at 4K, comfortably surpassing the design goal. Field emission onset was not observed during the entire test up to a peak electric field of 60 MV/m, thanks to the optimized processing procedures. Subsequently, one cavity was welded with the newly designed helium vessel and vertically tested at 2K, achieving an rf performance comparable to the bare cavities, demonstrating the success of the jacketed cavity. This paper presents the design, fabrication, surface preparation, and cryogenic tests of the first higher-order-mode-damped 166.6MHz β = 1 superconducting cavity.

Dedicated beam position monitor pair for model-independent lattice characterization at NSLS-II

This paper reports recent lattice characterization results obtained at the National Synchrotron Light Source II (NSLS-II) storage ring, conducted without reliance on a lattice model. A pair of beam position monitors (BPMs) with bunch-by-bunch (B×B) resolution, were recently installed in a section of the storage ring free of magnetic fields. The new BPM pair measured the beam, or bunch’s transverse Poincaré map precisely after the beam was excited. Linear one-turn-matrices (OTM) were then derived, and from these, the 4-dimensional coupled Twiss parameters were extracted at the locations of the BPM pair. By normalizing beam oscillation amplitudes with the Twiss parameters, the global action-variables were obtained. These action-variables facilitated the measurement of the local Twiss parameters observed by other BPMs independent on lattice model. This method is general, and particularly useful in certain scenarios such as a round beam mode in a diffraction-limited light source ring. We applied it to assess both weakly and strongly coupled lattices at the NSLS-II ring. Through analysis of the strongly coupled lattice, the quadrupole tilt errors were estimated to be less than 400 μrad. Utilizing the BPMs’ B×B resolution, for the first time we observed the variations of the linear lattice along a long bunch-train.

Nonlinear optimization for a low-emittance storage ring.

A multi-objective genetic algorithm (MOGA) is a powerful global optimization tool, but its results are considerably affected by the crossover parameter ηc. Finding an appropriate ηc demands too much computing time because MOGA needs be run several times in order to find a good ηc. In this paper, a self-adaptive crossover parameter is introduced in a strategy to adopt a new ηc for every generation while running MOGA. This new scheme has also been adopted for a multi-generation Gaussian process optimization (MGGPO) when producing trial solutions. Compared with the existing MGGPO and MOGA, the MGGPO and MOGA with the new strategy show better performance in nonlinear optimization for the design of low-emittance storage rings.

3D small-gain formula allowing strong focusing and harmonic lasing for a ring-based x-ray free electron laser oscillator

We present a detailed derivation of a formula for the small-gain calculation for an x-ray free electron laser oscillator (XFELO) based on a medium-energy (3–4 GeV) storage ring. We found harmonic lasing and strong focusing are essential for this beam energy range. Taking the small-signal low-gain formula developed by Kim and his colleagues, we modified it in such a way that the gain can be calculated without the “no focusing approximation,” and a strong focusing can be applied, as well as harmonic lasing. In this formula, the gain is represented as a product of two factors with one of them depending only on the harmonic number, undulator period, and gap. Using this factor, we show that it is favorable to use harmonic lasing to achieve hard x-ray FEL working in the small-signal low-gain regime with the medium-energy electron beam. Our formula also allows FEL optimization by varying the vertical gradient of the undulator, the vertical dispersion, and the horizontal and vertical focusing, independently. As an example, we applied this formula to study the feasibility of an XFELO option for the National Synchrotron Light Source II (NSLS-II) upgrade. Since a quite high peak current is required for the FEL, collective effects of beam dynamics in medium-energy synchrotrons significantly affect the electron beam parameters. We carried out a multiparameter optimization taking collective effects into account. Note, even though our example is for a ring-based XFELO at 3 to 4 GeV, the formula and, in particular, the approach developed here may be applied to other types of FELs. Published by the American Physical Society 2024

Research on particle accelerator control network deformation prediction algorithm with machine learning

Regular measurement of particle accelerators is imperative to ensure their long-term, stable operation and to meet future construction needs. The aim of this study is to minimise unplanned downtime and to provide data analysis and predictive insights for the remeasurement of similar particle accelerators. The focus is on the three-dimensional coordinate prediction and performance evaluation of a control network for a particle accelerator. The study uses observational data from the laser tracker in the Hefei Light Source storage ring control network, gathered from 2013 to 2023. Innovative use of the linear regression model, hyperbolic model, grey prediction model, and backpropagation neural network model has been made in the alignment of particle accelerators. A comparative analysis with measured data reveals that various deformation prediction methods can achieve a prediction accuracy of 0.25 mm. We recommend using the linear regression model for predicting the plumb direction, and the grey prediction model for predicting the horizontal direction. In addition, reducing the number of backward iteration steps can further improve the prediction accuracy. This study offers guidance for the deformation prediction of particle accelerators, and provides scientific data support and a basis for decision making on their long-term, stable operation.

Nonlinear analysis and control with nonlinear driving terms for small-emittance storage ring

Storage rings that use the hybrid multi-bend achromat (MBA) lattice concept [1] have been realized. The main characteristics of hybrid MBA as a typical lattice for a 4th generation storage ring are to adopt two large dispersion bumps in cell, and to make a -I-transformation between two dispersion bumps to cancel nonlinear effects. To increase the effectiveness of nonlinear control, analytical investigation of nonlinear phenomenon is essential. In this paper, we describe analytical investigation with a nonlinear driving term and simple model. We obtained similar results to the existing time-consuming MOGA optimization, but use a simplex optimizer with fewer nonlinear control knobs.

Design study of a low emittance complex bend achromat lattice

Light sources worldwide have experienced rapid growth in the last decades, pushing toward higher brightness with lower emittance to meet growing demands from the user community. The quest for higher brightness motivates the development of low-emittance ring lattices. At this point, all fourth-generation storage ring light sources employ variations of the multibend achromat (MBA) lattice. In this paper, we discuss an extension of this approach, known as complex bend achromat lattice in relation to the future NSLS-II upgrade. A detailed approach for the lattice design will be described and the developed lattice will be presented. The advantages of using our complex bend approach are evident in reaching a natural emittance as low as 23 pm at a beam energy of 3 GeV, providing a straight section of 8.4 m for long insertion devices, and acquiring a ratio of about 50% of free space with respect to the ring circumference. The design includes the use of permanent magnets largely reducing the need for power supplies. Our new approach provides an extension to the MBA concept for the next-generation light source lattice design. Published by the American Physical Society 2024

Merged-Beams Study of the Reaction of Cold HD+ with C atoms Reveals a Pronounced Intramolecular Kinetic Isotope Effect

We present a merged-beams study of reactions between HD+ ions, stored in the Cryogenic Storage Ring (CSR), and laser-produced ground-term C atoms. The molecular ions are stored for up to 20 s in the extreme vacuum of the CSR, where they have time to relax radiatively until they reach their vibrational ground state (within 0.5 s of storage) and rotational states with J≤3 (after 5 s). We combine our experimental studies with quasiclassical trajectory calculations based on two reactive potential energy surfaces. In contrast to previous studies with internally excited H2+ and D2+ ions, our results reveal a pronounced isotope effect, favoring the production of CH+ over CD+ across all collision energies, and a significant increase in the absolute rate coefficient of the reaction. Our experimental results agree well with our theoretical calculations for vibrationally relaxed HD+ ions in their lowest rotational states. Published by the American Physical Society 2024

Absolute rate coefficient measurements of the reactions of vibrationally cold HD+ and H3+ ions with neutral C atoms

Ion-neutral reactions are driving the formation of small molecules in the gas phase of interstellar clouds, where hydrogen molecules and their ions are by far the most important collision partners for any species in the astrochemical network. Here we present absolute rate coefficient measurements for the reactions HD++C→CH+/CD++D/H and H3++C→CH+/CH2++H2/H obtained using a recently commissioned ion-neutral collision setup at the Cryogenic Storage Ring. Our measurements with vibrationally cold ions result in significantly higher rate coefficients when compared with previous studies using internally excited ions, bringing them in better agreement with classical capture theories. Moreover, we have performed detailed quasiclassical trajectory (QCT) calculations for the HD++C reaction, using new potential energy surfaces. Our experimental results and the QCT calculations show very good agreement for the absolute cross section of the reactions, as well as for the isotope effect. These results have great potential relevance for the chemistry of the interstellar medium and the onset of organic chemistry in space. Published by the American Physical Society 2024

Laser spectroscopy of highly charged ions at the storage ring CSRe: Schottky-based spectroscopic investigation and XUV fluorescence detector development

Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In this work, the fine-structure splitting 1s22s2S1/2−1s22p2P1/2 transition in lithium-like 16O5+ has been investigated in a laser spectroscopy experiment at the heavy-ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2S1/2−2P1/2 transition wavelength was determined to be λ0= 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high-precision divider to precisely measure the high-voltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off-axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole-forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger-scale scientific facility HIAF in China.

Incoherent tune measurement of an ion storage ring using single ions

The measurement of betatron tunes is important in the studies of beam dynamics in circular accelerators. Here, we report a new method to extract the fractional tune values using revolution times of single ions stored for a few hundred turns in a heavy-ion storage ring utilizing a single time-of-flight detector. The experiment was done at the experimental Cooler Storage Ring (CSRe) in Lanzhou. The unbunched cocktail secondary beam was injected into the ring and allowed to coast without further excitation. Since the average number of simultaneously stored ions inside the 128.8 m-circumference ring was merely ∼20, the obtained tune values are considered to be incoherent. Given that the revolution time of an individual ion is related to its momentum, the chromaticity of the ring could be addressed. Moreover, the data indicate a possible beam mismatch in vertical direction y^ at the injection into CSRe. The new method is developed for ultralow beam intensities and is thus a sensitive approach to tune measurements. Thanks to its simplicity, the method can straightforwardly be employed at other circular accelerators by applying the same detection approach. Published by the American Physical Society 2024

First Study of Antihyperon-Nucleon Scattering Λ[over ¯]p→Λ[over ¯]p and Measurement of Λp→Λp Cross Section.

Using (10.087±0.044)×10^{9} J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λ[over ¯]p→Λ[over ¯]p are studied, where the Λ/Λ[over ¯] baryons are produced in the process J/ψ→ΛΛ[over ¯] and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in -0.9≤cosθ_{Λ/Λ[over ¯]}≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6_{stat}±1.1_{syst}) and σ(Λ[over ¯]p→Λ[over ¯]p)=(17.5±2.1_{stat}±1.6_{syst}) mb at the Λ/Λ[over ¯] momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θ_{Λ/Λ[over ¯]} are the scattering angles of the Λ/Λ[over ¯] in the Λp/Λ[over ¯]p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λ[over ¯]p→Λ[over ¯]p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λ[over ¯]p→Λ[over ¯]p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.

High Harmonic Generation Seeding Echo-Enabled Harmonic Generation toward a Storage Ring-Based Tender and Hard X-ray-Free Electron Laser

To align with the global trend of integrating synchrotron light source (SLS) and free electron laser (FEL) facilities on one site, in line with examples such as SPring-8 and SACLA in Japan and ELETTRA and FERMI in Italy, we actively explore FEL options leveraging the ultralow-emittance electron beam of the NSLS-II upgrade. These options show promising potential for synergy with storage ring (SR) operations, thereby significantly enhancing our facility’s capabilities. Echo-enabled harmonic generation (EEHG) is well-suited to SR-based FELs, and has already been demonstrated with the capability of generating extremely narrow bandwidth as well as high brightness, realized using diffraction-limited short pulses in transverse planes and Fourier transform-limited bandwidth in the soft X-ray spectrum. However, regarding a conventional EEHG scheme, the combination of the shortest seed laser wavelength (256 nm) and highest harmonic (200) sets the short wavelength limit to λ = 1.28 nm. To further extend the short wavelength limit down to the tender and hard X-ray region, a vital option is to shorten the seed laser wavelength. Thanks to recent advances in high harmonic generation (HHG), packing 109 photons at one harmonic within a few-femtosecond pulse could turn such a novel HHG source into an ideal seeding for EEHG. Thus, compared to the cascaded EEHG, the HHG seeding option could not only lower the cost, but also free the SR space for accommodating more user beamlines. Moreover, to mitigate the SASE background noise on the sample and detector, we combine the HHG seeding EEHG with the crab cavity short pulse scheme for maximum benefit.

A novel generation design dipole magnet power supply of booster to storage ring transport line in NSRRC

The Taiwan Light Source (TLS) is a synchrotron radiation facility located in Taiwan. The booster ring at TLS injects electrons into the storage ring, which then circulates the electrons to produce synchrotron radiation for various experiments. The Taiwan Light Source (TLS) has been in service for more than 20 years, and some of the power supplies used in the facility are old and hard to maintain repair and the component are phase-out. The upgrade is specifically aimed at replacing the power supply for the BTS (Booster to Storage ring) transmission line with a new machine. During the regular shunt down time, dipole magnet power supply replacements were completed. The main reason for using the Chroma 62075H-30E power supply is commonality, for this machine is widely used in Taiwan Photon Source (TPS), and the output current of the power supply is paralleled to a dipole magnet. Therefore, a total of 17 power supplies are used in this upgrade planned to be executed. This novel generation upgrade design is important because the power supply for the BTS transmission line is critical for the operation of the facility, as it is responsible for maintaining the electron beam at a stable energy level as it is injected from the booster ring into the storage ring. A more reliable and efficient power supply can help improve the stability and quality of the electron beam, leading to better experimental results and more efficient use of the facility. Overall, this novel generation upgrade design is part of the ongoing effort to modernize and improve the infrastructure of the TLS, ensuring that it remains a state-of-the-art research facility for years to come.

Merits of atomic cascade computations

Atomic cascades refer—first and foremost—to the stepwise de-excitation of excited atoms owing to the emission of electrons or photons. Apart from dedicated experiments at storage rings and synchrotrons, such cascades frequently occur in astro and plasma physics, material research, surface science and at various places elsewhere. In addition, moreover, “atomic cascades” have been found a useful concept for modeling atomic behavior under different conditions, for instance, when dealing with the photoabsorption of matter, the generation of synthesized spectra, or for determining a rather wide class of (plasma) rate coefficients. We here compile and discuss several atomic cascades (schemes) that help predict cross sections, rate coefficients, electron and photon spectra, or ion distributions. We also demonstrate how readily these schemes have been implemented within JAC, the Jena Atomic Calculator. Emphasis is placed on the classification of atomic cascades and their (quite) natural breakdown into cascade computations, to deal with the electronic structure and transition amplitudes of atoms and ions, as well as the cascade simulation of those properties and spectra, that are experimentally accessible. As an example, we show and discuss the computation of dielectronic recombination plasma rate coefficients for beryllium-like gold ions. The concept of atomic cascades and its implementation into JAC can be applied for most ions across the periodic table and will facilitate the modeling and interpretation of many forthcoming observations.Graphical abstract

Comparison of two vacuum system technologies for the synchrotron storage ring: case study of Iranian Light Source Facility

The current study compares two vacuum system designs for the Iranian Light Source Facility (ILSF) storage ring: conventional vacuum system design with stainless-steel vacuum chambers that are pumped by Non-Evaporable Getter (NEG) cartridges and ion pumps. In this design, all synchrotron radiation is absorbed by the local photon absorbers. In the second design, the water-cooled copper tubes that are coated with NEG materials are used as the vacuum chambers. This study will illustrate the advantages of using the NEG-coated vacuum chambers over the conventional design with the stainless-steel chambers. Since the two designs for ILSF are now completed, some of the details of this comparison might be interesting to other light sources, especially those that have plans to upgrade to a 4th generation.

Emittance optimization under magnet strength limitation for a multi-bend achromat lattice

Diffraction-limited storage rings (DLSRs) based on multi-bend achromat (MBA) lattices are being developed towards much lower emittances. For instance, for the future development, MAX IV designed a 19BA lattice to replace the present 7BA lattice, achieving an emittance of 16 pm·rad. While this 19BA lattice, with a significantly increased number of unit cells, requires extremely strong quadrupoles and sextupoles, which will result in very small vacuum chambers and can thus significantly increase beam coupling impedance and potentially enhance beam instabilities. This issue raises a question of how we can reduce magnet strengths while achieving the emittance goal. In this paper, based on a simplified model where an MBA lattice is considered to consist of a number of identical unit cells, emittance optimization is numerically studied under magnet strength limitation. The studied results show that for a given arc length and emittance goal, choosing an appropriate number of unit cells with relatively large horizontal cell tunes can significantly reduce magnet strengths. As a practical example, an 11BA lattice with relatively large unit cell tunes is designed and compared with a 17BA lattice with smaller unit cell tunes. The two lattices have roughly the same emittance with the same energy, ring circumference and number of periods, while the magnets of the 11BA lattice are significantly weaker.

The concept for hard X-ray beamline optics atSLS2.0.

In the scope of the latest upgrade of the Swiss Light Source, five hard X-ray beamlines will be constructed or rebuilt. To use synergies between these beamline projects, a concept is developed here for hard X-ray beamlines that is tailored to the new storage ring. Herein, this concept is described from the source, via the front end, to the beamline optics. The latter will be outlined in detail, including a new and modular concept for hard X-ray monochromators, focusing optics and heat-load management. With a simple, easy-to-operate and robust beamline design, the new beamlines will greatly profit from the increased brilliance of the new storage ring. The performance increase is up to four orders of magnitude, while the beamline concept allows for the broad application of experimental techniques, from propagation-based methods, such as phase-contrast tomography, to imaging techniques with nanometre resolution. At the same time, spectroscopy experiments are possible as well as high-performance serial X-ray crystallography.

Status and Commissioning Plan of Korea-4GSR

Multipurpose Synchrotron Radiation Construction Project is in progress to construct 4th generation storage ring with a 800-m-long circumference in Ochang. Its beam parameter is 4 GeV electron beam energy, lower than 100 pm emittance, 100 mA beam current. Currently, Korea Basic Science Institute is in charge of construction and Pohang Accelerator Laboratory (PAL) is in charge of the accelerator complex and ten beamlines. Recently, PAL is finalizing technical design and producing prototypes. In this report we introduce status and commissioning plan of 4GSR project focusing on beam physics part.