Ring Light Source Research Articles

Development of high-level applications for High Energy Photon Source booster

The High Energy Photon Source (HEPS), is the first fourth-generation storage ring light source being built in the suburb of Beijing, China. The storage ring was designed with the emittance lower than 60 pm.rad with a circumference of 1.36 km and beam energy of 6 GeV. Its injector contains a 500 MeV S-band Linac and a 454 m booster which was designed as an accumulator at the extraction energy. In the energy ramping control design of HEPS booster, the ramping process was programed to be able to stop and stay at any energy between the injection energy and the extraction energy. This feature enables us to conduct energy-dependent machine studies and ramping curve optimization. The beam commissioning of HEPS Linac finished in June, 2023. And the beam commissioning of booster started in the end of July, 2023. In November 17, main target values proposed in the preliminary design report has been reached. The high-level applications (HLAs) are essential tools for beam commissioning. The development of HLAs, which are based on the framework named Python accelerator physics application set (Pyapas), started in the end of 2021. The HEPS physics team spent more than one year to develop and test the HLAs to meet the requirements of beam commissioning of the booster. Thanks to the modular design, the principle based on physical quantities, and the ability of running simulation models online from the Pyapas, the development efficiency and reliability of the HLAs have been greatly improved. In particular, the principle based on physical quantities allows us to control the beam more intuitively.

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.

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

Off-energy operation for the Extremely Brilliant Source at the European Synchrotron Radiation Facility

The European Synchrotron Radiation Facility Extremely Brilliant Source (ESRF-EBS) is the first fourth generation 6 GeV storage ring (SR) light source making use of the hybrid multibend achromat lattice, reaching a natural horizontal emittance of 140 pm rad. Further, reducing the horizontal emittance would provide a more brilliant and a higher quality photon source for the EBS users. One way of achieving this is to operate the SR off-energy. The first approach reduces the electron beam energy by −1%, which gives a 121 pm rad natural horizontal emittance. To fulfill operation requirements, the full ring had to be rematched, including both the quadrupoles and the sextupoles in the linear optics correction. The off-energy settings are then tested in the SR in terms of lifetime, injection efficiency, and operability. Published by the American Physical Society 2024

Physics Design of a 200-MeV Electron Injector Linac With a Thermionic Electron Gun for the Korean Fourth-Generation Storage Ring Light Source

Physics Design of a 200-MeV Electron Injector Linac With a Thermionic Electron Gun for the Korean Fourth-Generation Storage Ring Light Source

Design and experimental research of UHV flanges for the Hefei Advanced Light Facility

The Hefei Advanced Light Facility (HALF) is a diffrac-tion-limited storage ring (DLSR) light source based on the compact multi-bend achromat (MBA) lattice. There-fore, the gaps between those focusing magnets are small. The commonly used ConFlat® flange, with a large axis dimension, is not suitable for the compact lattice in HALF. In this work, a stainless steel tapered flange fas-tened by a chain clamp has been designed for its smaller axis dimension. Two types of sealing structures are used, which are knife-edge and spring-energized metal C-ring structures, respectively. The copper gaskets with and without silver coating are used for knife-edge flange, respectively. Besides, the spring-energized metal C-ring is manufactured by SUS 304 with a tin layer of 50 μm. These flanges and chain clamps were made of SUS 304, and their vacuum properties were tested. The results indi-cate that these UHV flanges can meet the demands for the vacuum system of HALF.

Bimodal design of 500MHz and 1.5GHz normal conducting RF cavity for advanced synchrotron radiation facilities

The advanced storage ring light source needs to realize ultra-low emissivity beam operation, and improving the Touschek lifetime puts forward higher requirements for the performance of RF cavity. In this paper, a novel bimodal normal conducting RF cavity is proposed. In one cavity, two power sources will be connected at the same time to realize the simultaneous operation of the two frequencies. The TM010 mode with the frequency of 500 MHz is used for acceleration, and the TM020 mode with the frequency of 1.5 GHz is used as the third harmonic to improve the height of the RF bucket and achieve the purpose of lengthening the beam bunch. Two couplers are designed to adapt to the working characteristics of bimodal RF cavity.

Hefei Advanced Light Facility: Empowering research of correlated electron systems

The Hefei Advanced Light Facility is the fourth-generation diffraction-limited storage ring light source, scheduled to begin operation in 2028. With its high-brightness and highly coherent X-rays, it will break through the current spatiotemporal resolution bottlenecks of X-ray techniques in studying correlated electron systems, providing crucial information for understanding the nature and microscopic origins of novel physical properties in these materials. This article introduces the main scientific goals and technical advantages of the Hefei Advanced Light Facility, focusing on the application perspectives of advanced technologies such as angle-resolved photoemission spectroscopy, magnetic circular dichroism, coherent X-ray scattering, and coherent X-ray imaging in researches of quantum materials and correlated electron systems. These techniques will enable the detailed analysis of the distribution and dynamics of electronic/spin/orbital states, reveal various novel quantum phenomena, and elucidate the fluctuations of order parameters in correlated electron systems. The completion of the Hefei Advanced Light Facility will provide advanced technical supports for decoding complex quantum states and non-equilibrium properties, ultimately promoting the application of quantum materials and correlated electron systems in frontier fields such as energy and information.

Design strategies and technology of Elettra 2.0 for a versatile offer to the user community

Elettra 2.0 will be a fourth generation storage ring light source replacing the existing Elettra synchrotron. This article illustrates design strategies, physical investigations and technical choices to meet multiple and sometimes conflicting requirements. These include to make Elettra 2.0 a fully transversely coherent source up to 0.5 keV-photon energy, diversify the type of experiments through a very broad range of photon energies, from infrared to hard x-rays, maximize the number of photon beamlines in excess of 2-times the machine periodicity, and be able to produce picosecond-long light pulses at MHz repetition rate without interference to the standard multi-bunch operation. Most recent advancements in beam physics, technical systems and installation plan are reported with some detail.

Applications of vertical damping wigglers in an X-ray diffraction limited storage ring

This study presents a lattice design for an X-ray diffraction limited storage ring (DLSR) light source with a circumference of 864 m and achieving an ultralow natural emittance of 25.6 pm·rad (N-IBS). However, the ultra-low emittance and long damping times lead to significant intra-beam scattering (IBS) effects. To address this issue, the study explores the implementation of vertical damping wigglers (VDWs) to decrease damping times, reduce beam horizontal emittance, and generate vertical emittance to achieve a “round beam” in the 864mDLSR. Through theoretical analysis and accelerator toolbox (AT) simulations, the impacts of VDWs with varied parameters were investigated, and the optimal period length, peak field, and total length were determined. Additionally, the twelve quadrupole magnets in both the front and rear cells of the VDWs were employed to correct linear optics. The findings demonstrate that VDWs could significantly reduce the beam's equilibrium emittance and damping times of the 864mDLSR. Furthermore, a comparison between the spectral brightness and flux of the 864mDLSR with and without VDWs revealed that the 864mDLSR employing VDWs yielded higher brightness and flux.

Method for solving bunch head-tail overlapping in HLS-II using a new trigger scanning module of streak-camera measurement system

This study proposed a trigger scanning module for a streak camera to overcome head–tail overlapping of bunch to achieve absolute bunch length monitoring based on the unique machine properties of the Hefei Light Source-II (HLS-II). Furthermore, precise measurement of longitudinal bunch characteristic parameters and study of longitudinal beam dynamics is crucial, and this significantly contributes for observing longitudinal bunch behavior and evolution associated with current potential-well distortion and microwave instability. First, the scanning module is calibrated thoroughly to test its performance and applicability. Afterward, the module is applied to measure the dependence of bunch length on current under single-bunch operation. Moreover, potential-well distortion and bunch lengthening are observed. Results showed that the designed trigger scanning module is appropriate for the exploration of the physical mechanism of single-bunch beam behavior, which is crucial for the investigation of bunch characteristics and beam instability in storage ring light sources.

Non-equilibrium magnetic compression for picosecond-long X-ray pulses at a diffraction limited storage ring light source

Picosecond-long x-ray pulses of moderate intensity and high repetition rate are highly sought after by the light sources community, e.g. for time-resolved investigations of matter in the linear response regime. We investigate the upgrade of a diffraction-limited storage ring light source to a short X-ray pulse scheme. Short pulses are emitted by electron bunches magnetically compressed in the injection chain, with no impact on the simultaneous standard emission from long bunches. The ultimate performance, limits and operational aspects of the scheme are discussed in terms of soft X-ray undulator emission.

Data synchronization module for multi-dimensional bunch-by-bunch measurement in a storage ring.

Multi-dimensional bunch-by-bunch (BbB) measurements are an efficient tool to research beam dynamics induced by wakefields in storage ring light sources, yet they can have data misplacement problems on high-speed acquisition boards. Hence, a data synchronization module (DSM) was designed to solve the issue of data misplacement. We analyzed different synchronization states in the DSM and conducted testing of the DSM on a field programmable gate array to evaluate its performance. Test results indicate the synchronized DSM data from multiple high-speed acquisition boards corresponds to the bucket number in the bunch filling pattern. We found that the resolution of the longitudinal phase in three-dimensional BbB measurements can be improved with DSM and propose a scheme for multi-dimensional BbB measurements. In this paper, we will detail the structure of DSM and its limitations.

Multi-objective optimization of longitudinal injection based on a multi-frequency RF system for fourth-generation storage ring-based light sources

In the fourth-generation storage ring light sources (4GLSs), associated with the extremely strong nonlinearities inherent in the multi-bend achromat design, the dynamic acceptance is usually small and it is difficult to implement traditional off-axis local-bump injection. To release the requirement on dynamic acceptance, on-axis longitudinal injection schemes have been explored. In this paper, we present a multi-objective optimization of longitudinal injection with a multi-frequency RF system, based on the parameters of the Southern Advanced Photon Source, a 4GLS proposed in China. We show that by treating the optimal bunch lengthening condition as an optimizing objective rather than a condition that must be satisfied, a plethora of feasible candidate solutions can be found, showing different trade-offs among multi-objectives. From these candidate solutions, one can find an optimal RF parameter setting that is most adapted to a specific 4GLS physics design and the available technical level of injection kicker. Especially, it would be feasible to realize longitudinal injection within a static bucket enabled by a double-frequency RF system, suggesting an attractive longitudinal injection option for 4GLSs.

Lattice design for an improved angular dispersion-induced microbunching scheme

In this paper, an improved angular dispersion-induced microbunching (ADM) scheme [1] is studied to generate fully coherent soft x-ray radiation pulses in an electron storage ring light source with a limited energy modulation amplitude. This scheme releases the coupling between the dispersion function and the momentum compaction in the original ADM scheme. The lattice structure of the improved ADM is simple, which only adds a chicane following the dogleg compared to the original one. With the chicane, even higher harmonic radiation can be generated. Numerical simulation results show that soft x-ray radiation with photon energy covering the water window range can be produced.

Broad band waveguide to coaxial transition for HOM suppression in RF cavities for future synchrotron light sources

In the modern storage ring light sources, exploiting multi-bunch beams, the longitudinal and transverse coupled bunch instabilities are predominantly driven by higher order modes (HOM) of the accelerator RF cavities. In order to suppress the HOM to a harmless level, we propose using a modified broadband waveguide to coaxial line transitions placed on the cavity body, similar to those used for the DAΦNE collider RF cavities. Such a solution has a simple design that avoids the application of the ferrite materials under the ultra-high vacuum and dissipates the HOM power on the external loadings. Different from DAΦNE with a single cavity per ring, where the damping waveguides are placed laterally on the cavity body, we consider the possibility of allocating the waveguides vertically. Since the modern synchrotron light sources require using more RF cavities to compensate for the synchrotron radiation losses, such a solution helps to save the occupied space when placing the cavities in a row next to each other. This paper describes the design optimization process and discusses the obtained results concerning the effectiveness of the HOM suppression and minimization of the impact of the transitions on the fundamental mode parameters.

Hemispherical Surface Defect Classification of Valve Core with a Noval Semi-supervised Learning

Background: In the industrial manufacturing process, manually labeling enough datasets is time-consuming, which hinders the training and deployment of defect detection models. Therefore, automatic defect detection and its classification is the premise of industrial production quality. Objectives: The study mainly discusses about the detection of the Hemispherical Surface of the valve core by machine vision method. Methods: The paper put forward a novel semi-supervised algorithm to detect the Hemispherical Surface of the Valve Core. Under the condition of the lack of labeled datasets, the paper used labeled and unlabeled samples for model training. This thesis proposed, for the first time, using the Mean Teacher semisupervised learning framework and then making changes to the model; firstly, this paper proposed to use the Stochastic Weight Average (SWA) algorithm to update the weight of the teaching model to enhance this model’s generalization ability. Furthermore, in order to select reliable datasets and calculate the consistency loss, this study also proposed an Uncertainty Filter (UF) method. Thirdly, the selection of hard-ware equipment, since the hemispherical surface is anisotropic, ring light source is used, which can lit the surface from top to bottom. Results: Experimental results show that in two different conditions, the classification accuracy can raise. On one hand, under the condition of training with a small amount of labeled datasets, the proposed semi-supervised learning model can achieve a classification accuracy of 90.51%; whereas, under the condition of the semi-supervised learning mechanism and a large amount of unlabeled datasets, the accuracy increases from 93.7% to 98.1%. Conclusion: This paper uses hemispherical metal surface as the dataset for the first time, and also innovatively optimizes the semi-supervised model. On the other hand, experimental comparative analysis indicates that the model proposed in this paper is significantly better than the comparison model, which lays the basic position for the defect detection of the hemispherical surface’s metal. At the same time, the novel semi-supervised algorithm can also be used to detect other metal part’s hemispherical surfaces.

Autoresonant excitation of nonlinear beam motion in storage rings

Understanding and controlling of nonlinear beam dynamics are essential to the performance of storage ring light sources. In order to measure and correct limitations due to nonlinear beam dynamics, an effective method is needed to excite the beam oscillation to large amplitudes. Autoresonance is a method that enables the control of the amplitude of a driven nonlinear oscillator by sweeping the frequency of the driver. In this study, autoresonant excitation of beam transverse oscillations in storage rings is studied. The threshold of the drive amplitude for autoresonance is theoretically obtained, for cases with or without damping. The results are in good agreement with simulations for a simple storage ring model, as well as for models of actual storage rings. Application of the theory to experimental data on the SPEAR3 storage ring also validates the results.

Experimental investigation of transverse quadrupolar beam oscillation in the Hefei Light Source-II storage ring

Research on the transverse beam dynamics issues and collective bunch behaviors in association with the higher-mode oscillation fields are important in analyzing beam properties and improving machine performance of particle accelerators. In this study, a simple effective excitation and detection scheme was developed to analyze the transverse quadrupole-mode beam oscillation in electron storage rings. Transverse quadrupole-mode beam oscillation was induced by the stripline transverse quadrupole kicker, and then, measured using the stripline beam position monitor in the Hefei Light Source-II storage ring. A spectrum analyzer was employed for the real-time detection of the excitation sidebands of the horizontal quadrupole-mode oscillation in both single-bunch and nominal multi-bunch operations. Additionally, the horizontal dipolar and quadrupolar kick factors are obtained as 6.992 × 1014 and −4.458 × 1014 V/mC with accuracy of 7.49% and 2.03%, respectively, for the single-bunch operation. The dipolar and quadrupolar kick factors in the nominal multi-bunch operation are −2.567 × 1013 and −2.344 × 1013 V/mC with accuracy of 3.53% and 4.91%, respectively. The experimental measurements thus validate the practicability and reliability of this scheme. Moreover, it is demonstrated that this excitation and detection method for the transverse quadrupole oscillation is valid for studying the properties of transverse higher-mode wakefields and related beam behaviors in storage ring light sources.

Manipulating the upconversion luminescence of Yb3+/Er3+ doped nanoparticles by the sheet-shaped nanocavity

Rare-earth doped upconversion luminescence is important for display and imaging field due to its narrow band, multicolor, long lifetime and high stability. However, low quantum yield of upconversion energy transfer, weak excited states absorption and slow spontaneous radiation rates lead to weak upconversion luminescence, which may dramatically limit the practical application of upconversion nanoparticles. Here, we report a metal-sheet-shaped plasmonic nanocavity consisting of gold and silver micro-sheets. It is found that the upconversion processes (including quantum yield of energy transfer, excited states absorption and spontaneous radiation rates) were enhanced by strong local electromagnetic field of the plasmonic nanocavity when RE3+ nanoparticles were filled in the plasmonic nanocavity. The significant enhancement of the luminescence and clear directional radiation were observed under 980 nm laser excitation. By adjusting the nanogap distance of the plasmonic nanocavity, we achieved a 75-fold enhancement in 654 nm emission. Benefiting from the plasmonic nanocavity, the upconversion luminescence exhibited a directional emission, which indicates the plasmonic near-field excitation contributed to the luminescence enhancement. These findings provide a candidate for ring light source and bio-imaging application.