Hefei Light Source Research Articles

Research on datumn transformation model in particle accelerator component installation

When the important components of the particle accelerator are installed, it is required to locate the instrument in the global coordinate system by measuring the control points of the surrounding tunnels, which involves the datumn transformation between the global coordinate system and the station coordinate system, and the selection of the transformation model has gradually become a potential breakthrough in solving the problem. Four different models euler angle, Rodrigues matrix, dual quaternion and twelve parameters are used to analyze and compare the solution parameters, accuracy index, iteration efficiency, and the number of selected common points of the four models with the measured data of 2022 Hefei Light Source summer. The results show that the deviation of the four model parameters from the SpatialAnalyzer commercial software is no more than 3 μm for the translation parameters, and no more than 0.6” for the rotation angle. Among them, the twelve-parameters and dual quaternion two models are theoretically rigorous, with high and stable accuracy indexes, and the twelve parameters posteriori unit weight mean error shows obvious advantages. The twelve parameters and Rodrigues models have fewer iterations and higher efficiency. In summary, the dual quaternion model and twelve parameters method are preferred in the absence of better initial values. In addition, in the process of datumn transformation, along with the increase of the number of common points, the accuracies of all four model solutions show an increasing trend of first fast and then slow.

Research on methods to suppress the error accumulation in the elevation direction for accelerator tunnel control network

In recent years, the 4th generation synchrotron radiation light sources have gradually emerged. However, the accumulated errors in Laser Tracker multi-station measurements make it challenging to meet the accuracy requirements for the control network measurement, especially in the direction of elevation. To address this issue, this paper proposes to utilize the Hydrostatic Leveling System (HLS) to provide high-precision external constraints for the control network measurement. Firstly, based on the measurement principle of capacitive HLS sensor, a system is designed and constructed which was used to optimize the measurement accuracy of the HLS for level difference between difference points and to obtain the external reference. Comparison of the HLS measured values with the nominal values measured by the CMM shows that the optimized HLS can achieve a level difference measurement accuracy of 5 μm. On this basis, some constraint methods are proposed, which have been verified by simulations and measurements. The results show that the error accumulation in the elevation direction is suppressed compared with the classical adjustment. For the 70 m linear tunnel control network of Hefei Light Source, the maximum error of the measurement is reduced by 90 μm (23% improvement in accuracy) and the standard deviation of the error is reduced by 26 μm (35% improvement in accuracy) after adding constraint.

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.

Robust 3D coordinate transformation based on genetic algorithm intelligent weighting

In order to improve the solution quality of 3D coordinate transformation parameters, a robust optimization model is obtained by integrating the 3D coordinate transformation model within the overall framework of the genetic algorithm in this paper. The minimum of the weighted sum of squares of the point residuals of the common points is taken as the objective function for optimization, and the parallel search is started from the initial population, and the updating process of the solution set is used to generate new and better individuals, and the adaptive weight combination corresponding to the optimum of the fitness function is obtained at the end of the generation iteration. The generated simulated data and measured data were analyzed using the Hefei Light Source tunnel control network as an application scenario. The results show that the method in this paper can automatically reduce the influence of low-quality data on the model, and compared with the two robust conversion models of IGG III iterative weighting, the method in this paper is not affected by the empirical parameters in determining the weight combinations and the weighted sum of squares of the residuals of the solved points are smaller, so it can effectively improve the quality of the solved conversion parameters.

The HLS-II alarm system optimization for removing nuisance alarms

Hefei Light Source II (HLS-II) is a vacuum ultraviolet synchrotron light source. The HLS-II alarm system is responsible for monitoring the alarms of the process variables and distributing the alarm events in time. Nuisance alarms reduce the functionality, credibility and trustworthiness of the alarm system. This paper proposes a method for design alarm deadband and delay timers to remove the nuisance alarm events to the expected ratio. An optimal deadband width is calculated to reduce the alarm events while balancing the effects of reducing the occurrence number of alarm events and increasing the duration of alarm events. If the expected ratio is not met after using the optimal deadband width, the delay timers are set additionally. The Bayesian estimation approach is used to estimate the probability that the delay timers eliminate the alarm events. This method is based on statistical properties of the process variables and can effectively remove nuisance alarm events. Two examples of the HLS-II alarm system are provided to illustrate the proposed method. In the two examples, the optimal deadband removed 99.27% and 88.92% of nuisance alarms respectively.

Initial Application of Machine Learning for Beam Parameter Optimization at the Hefei Light Source II

Machine learning (ML) has become a valuable tool in particle accelerator control, with growing potential for beam parameter correction. In this study, we present preliminary ML applications at HLS-II, using Lasso regression for online tune correction and a neural network (NN) for beta function simulation correction. Both models were trained with supervised learning on measured beam parameter data, while an improved genetic algorithm optimized the NN structure. Our results show that the ML-based approach achieves competitive correction quality with fewer steps, making it a promising method for future particle accelerator applications and other fields.

Study on beam position measurement based on diode detection in HLS-II

In order to improve the sensitivity and long-term stability of beam position measurement for Hefei Light Source – II (HLS-II), it is necessary to improve the measurement method. The beam position monitor (BPM) electronics is used to measure the beam position and is an important part of the beam position measurement system. In this paper, a beam position measurement system based on the compensated diode detection (CDD) technology for electron storage ring was proposed. Since HALF under construction, the parameters of HLS-II were used to design the system and simulate the system circuits to verify its feasibility.

Study on Beam Orbit Shift due to Synchrotron Radiation

The beam orbit stability is the crucial indicator to evaluate the performance of the synchrotron radiation source. In order to obtain higher beam quality, higher stability requirements are placed on the beam orbit. The stability can be improved through accurate measurement of beam orbit by beam position monitors (BPMs) and appropriate feedback system. However, due to radiation of the synchrotron beams on the vacuum chamber, the thermal effect of synchrotron radiation causes the thermal deformation of the vacuum chamber. The thermal deformation drives the BPM fixed on the vacuum chamber to move, which will induce error to the beam orbit. We analyze the effect of beam current on the vacuum chamber movement and the effect of vacuum chamber movement on the beam orbit. We also built an online vacuum chamber displacement measurement system on Hefei Light Source II (HLS II), which is used to validate and correct our analysis. After analysis and verification, the vacuum chamber moves with the change of current. The larger the change of current, the larger the vacuum chamber displacement. The vacuum chamber displacement has a hysteresis compared to the current change.

Neural network structure optimization for Hefei Light Source II β function correction

In this study, we address the design challenges related to hyperparameters, such as the number of layers and nodes in deep neural networks, by introducing an Improved Genetic Algorithm-based method for optimizing neural network structures (IGA-DNN). We apply this method to the practical problem of β function correction in particle accelerators and develop a storage ring β function correction scheme based on IGA-DNN. We compare our approach with traditional genetic algorithm-optimized neural networks to evaluate its performance. Our results reveal that the neural network optimized by the improved genetic algorithm reduces the number of layers by three and decreases training time by a factor of three, leading to a more efficient model. Moreover, the accuracy of β function simulation correction is enhanced using the IGA-DNN method. This approach can also be extended to optimize other optical parameters and tackle multi-parameter optimization problems, showcasing its versatility and potential for broader applications across various fields.

Beam reference orbit compensation for the HLS-II storage ring

The stability of the beam orbit is essential for a storage ring based light source. An orbit feedback system is usually adopted to help maintain the beam circulating on a reference orbit. The movement and deformation of the Beam Position Monitor (BPM) chambers due to thermal effect can affect the BPM readings. The BPM misreading leads to shift of the reference orbit for the orbit feedback system. The feedback system then corrects the beam to a different closed orbit, resulting in a change in the real beam orbit. Online experiments are carried out to measure the BPM readings dependency on the temperature of BPM chambers in the Hefei Light Source II (HLS-II) storage ring. To improve the beam orbit stability, a compensation system is developed to mitigate the reference orbit shift accordingly. With this compensation system, the stability of the reference orbit is improved to be better than 10 μm in the horizontal plane and 5 μm in the vertical plane. This paper reports our work on the measurement of BPM readings dependency and the development of the reference orbit compensation system for the HLS-II storage ring. The online compensation results are also presented.

Integrated optical design method for the synchrotron radiation beamlines

In this paper, a new beamline optical system design method is reported in which the calculation of synchrotron radiation source flux distribution, monochromator spectral resolving power, mirror reflectance and grating diffraction efficiency are integrated together in one program to evaluate the whole beamline optical system performance. We demonstrate the advantage of this method by applying it to the Surface Physics beamline at Hefei Light Source to find out better optical system parameters. By using this method, a higher photon flux with the same spectral resolving power than the original design is achieved. The integrated optical system design method provides a great promising application in the beamline optical design and optimization in the future.

Beam orbit shift due to BPM thermal deformation using machine learning

Stabilizing beam orbit is critical for advanced synchrotron radiation light sources. The beam orbit can be affected by many sources. To maintain a good orbit stability, global orbit feedback systems (OFB) has been widely used. However, the BPM thermal deformation would lead to BPM misreading, which can not be handled by OFB. Usually, extra diagnostics, such as position transducers, is needed to measure the deformation dependency of BPM readings. Here, an alternative approach by using the machine operation historic data, including BPM temperature, insertion device (ID) gaps and corrector currents, is presented. It is demonstrated at Hefei Light Source (HLS). The average orbit shift due to BPM thermal deformation is about 34.5 μm/°C (horizontal) and 20.0 μm/°C (vertical).

A one-time sampling method for the real-time measurement of bunch-by-bunch three-dimensional positions in storage rings

Bunch-by-bunch (BbB) technique, which allows accelerator physicists to monitor beam information on finer timescales, is an efficient tool for studying longitudinal and transverse beam dynamics. However, the real-time measurement in BbB technique can only monitor one beam parameter, thus focusing only on the longitudinal phase or transverse positions of bunches. Therefore, to solve this issue, we put forward a one-time sampling method (OSM) to evaluate the longitudinal phase and transverse positions of bunches simultaneously, taking as one way of the real-time measurement for BbB three-dimensional (3D) positions. And we carried out related experiments in Hefei Light Source II and Shanghai Synchrotron Radiation Facility. As a result, experiments show that OSM obtains 12 μm of x-direction resolution, 10 μm of y-direction resolution, 0.57 ps of z-direction resolution at Hefei Light Source II, and 10 μm of x-direction resolution, 10 μm of y-direction resolution, 0.35 ps of z-direction resolution at Shanghai Synchrotron Radiation Facility. All these experimental results reveal that OSM is feasible to measure the BbB 3D positions.

Modified double-double bend achromat lattice for an ultra-low emittance design of the HLS

The storage ring of the present Hefei Light Source (HLS) consists of four double-bend achromat lattice cells, each with two straight sections. In this paper, a modified double-double bend achromat (DDBA) lattice is proposed for an ultra-low emittance design of HLS, where the circumference of the storage ring and the lengths of all straight sections remain the same. Compared to the typical DDBA lattice, this modified lattice can obtain both lower emittance and lower dispersion in the mid-straight section, thus providing higher brightness of insertion device radiation. The natural emittance of the HLS designed with the modified DDBA lattice is 3.9 nm·rad, about one order of magnitude lower than that of the present HLS.

Research advances on X-ray pixel detectors

<p indent="0mm">Advanced light sources, represented by synchrotron radiation facilities, are important platforms for multi-discipline research. Several large-scale scientific facilities are under construction or being scheduled, including the High Energy Photon Source (HEPS), Shanghai high repetition rate XFEL and extreme light facility (SHINE), Hefei Light Source, and so on. This shows that they are the strategic directions from the national demands. However, detector technologies of the light source beamlines became the bottleneck problem for a long time. Among them, the X-ray pixel detector is a typical representative. Unfortunately, systematic studies were fully blank in this field in China before, and products were totally foreign-monopolized. To break through the dilemma, Wei Wei and his team made pioneer studies in the X-ray pixel detector field in China, and achieved two stages of key results through long-term research. (1) Realized the breakthrough and filled in the blanks in the field of high-end detectors for synchrotron radiation: Brought out the first domestic silicon pixel detector prototype machine, while the performance of the full system reached the level of advanced international products; the sub-project successfully passed the national acceptance inspection of HEPS-TF (High Energy Photon Source-Test Facility); the detector has been delivered for customer applications, while customers’ achievements have already begun to emerge. During the development work, key techniques of pixel detectors have been broken through, especially the techniques of pixel IC chips, sensors, and advanced packaging. Meanwhile, key technology localization has also been achieved and various innovations have been made. This proved the work generally solved the problem of “being strangled” in the field of pixel detectors. (2) Aiming at the international frontier: Led the development of the fine pitch pixel detector. Its spatial resolution reached the same level as the state-of-the-art research of the world, and filled in the blanks in the domestic field; Wei Wei proposed a novel 4-D detection mode and implemented it in the field of synchrotron radiation for the first time; a series of prototype chips were successfully developed for large-scale scientific facilities including vertex detectors for particle physics experiments, free-electron lasers, and so on. The work preliminarily realized “paralleling” with international studies while promoted from “pursuing”. The breakthrough of those key technologies can make beamlines in future light sources capable to realize customized detector design. Therefore, the restrictions from foreign products can be freed and a large number of national funds can be saved. Moreover, it also makes it possible to promote the beamline capabilities, or even explore brand new experimental methodologies to realize original innovations.

The development of the alarm system for HLS-II

Hefei Light Source II (HLS-II) is a vacuum ultraviolet synchrotron light source. The control system of HLS-II is a distributed system based on the experimental physics and industrial control system (EPICS). The alarm system of HLS-II is responsible for monitoring the alarm state of the facility and distributing the alarm message in time. It facilitates the operator to troubleshoot problem efficiently, so as to improve the availability of HLS-II. Phoebus/Alarms (Alarms) is the latest alarm software released in EPICS community. Based on Alarms, the alarm system of HLS-II is designed, developed and deployed. The alarm distribution strategy is designed from the perspective of the HLS-II operation mode, alarm severity and alarm representative to overcome alarm floods. The 3 ways to distribute the alarm message are added to the HLS-II alarm system, which include WeChat, SMS and web-based GUI. In order to configure alarm options efficiently and conveniently, an alarm configuration management tool is developed based on the MySQL database and Browser/Server architecture. The alarm system of HLS-II has been deployed since November 2021. The result indicates that the alarm system is effective and convenient to operate.

Design of an interference system for measuring the transverse beam size in HLS-II

In this paper, a horizontal and vertical double-slits interferometer using visible light are designed to measure the transverse beam size of Hefei Light Source II (HLS-II). For the given initial structural parameters of the two interferometers, a series of numerical simulations and analyses are carried out by using the Synchrotron Radiation Workshop (SRW) code. Furthermore, the core parameters of the double-slits components in the interferometers are optimized. In the end, the visibilities of the horizontal and vertical interferometer we designed are 0.345 and 0.548 respectively, which are in the range of 0.2–0.6. And simulation results meet the requirement of theoretical relative measurement error of less than 10%.

Research on tune feedback of the Hefei Light Source II based on machine learning

The theory of tune feedback correction and the principle of a feedback algorithm based on machine learning are introduced, with a focus on the application of lasso regression for tune feedback correction. Simulation verification and online feedback correction results are presented. The results show that, after applying machine learning, the feedback accuracy of the tune feedback system was higher, and the betatron tune stability was further improved.

Micro telecom computing architecture.4-based beam position monitor electronics design for storage ring of Hefei advanced light facility.

The Hefei Advanced Light Facility (HALF) is a fourth-generation vacuum ultraviolet and x-ray diffraction limit synchrotron radiation (DLSR) light source now under preliminary research. To achieve ultralow beam emittance and small beam size, the orbit of the beam in the DLSR storage ring should meet the stability requirement at submicrometer scale. The beam position monitor (BPM) electronics measures the orbit and is hence an essential part of the beam orbit control system. In this article, we designa BPM electronics based on the MicroTCA.4 (Micro Telecom Computing Architecture) standards platform, which consists of a MicroTCA.4 module (including a chassis, a power supply, and a digital board), a customized RF front end module, and a frequency synthesizer. In-phase and quadrature sampling and digital signal processing algorithms are implemented to obtain turn-by-turn data, fast acquisition data at a 10 kHz rate, and slow acquisition data at a 10Hz rate. To evaluate the performance and function of BPM electronics, we conducted offline tests in the laboratory and beam tests based on the storage ring of Hefei Light Source II (HLS II), a light source similar to the HALF as an alternative. Test results indicate that the performance of MicroTCA.4-based BPM electronics can meet the requirements of the HALF storage ring.

Design and simulation of interferometer for synchrotron radiation beam size measurement

The interferometric measurement of the transverse beam size based on synchrotron radiation is a non-intercepting high precision measurement method. Compared with the imaging method, the interferometric method can measure smaller beam size and get better resolution. It is expected to obtain submicron resolution at shorter measurement wavelength, so it is widely used in synchrotron radiation sources. The upgraded scheme of current interference device in Hefei Light Source HLS-II is presented in this paper. It is proposed to replace the first focusing lens in the original interference light path with an RC structure focusing mirror, and the second single lens with a doublet lens. The design goal of this paper is to reduce dispersion and geometric aberration without changing the optical axis of the optical path, so as to improve the imaging quality of the optical path. The geometrical optical path design is used to evaluate the imaging quality of the optical path, and physical optical simulation is performed to obtain the interference fringes of the measurement system. The simulation results show that the radius of Airy spot is reduced by about 35%, the root mean square radius of dot array is reduced by about 99%, the wavefront difference is reduced by about 75%, and the cutoff frequency of MTF function is increased by about 65%, using a focusing mirror to replace the original focusing lens can greatly improve the image quality of the optical path.