High Energy Photon Source Research Articles

High-precision spatial measurement method of accelerator pre-alignment based on multiple total stations

Abstract With the development of accelerator technology, the scale of accelerators is becoming larger, ranging from hundreds of meters to several kilometers. For stable operation of accelerators, high-precision alignment, positioning, and installation are crucial. Installing all equipment inside the tunnel poses safety risks as personnel would be in a closed environment with potential radiation exposure for prolonged periods. To address the challenges of long adjustment and maintenance periods inside the tunnel due to the installation of equipment for large-scale accelerators, most accelerator devices under construction or in research have pre-alignment assemblies. Each assembly consists of a certain number of magnets distributed on girders. The magnets in one unit are pre-aligned with high precision in the laboratory and then transported to the tunnel. Aligning the entire magnet girder can significantly improve installation efficiency inside the tunnel. To meet the pre-alignment accuracy requirement of 10 μm in the horizontal and vertical directions for the magnet units in the high energy photon source (HEPS) storage ring, a system for high-precision pre-alignment of accelerator units using four total stations for angle observation has been designed in this paper. By employing different instrument layout configurations and incorporating reliable distance benchmarks, high-precision pre-alignment of the magnet are achieved. By arranging targets and utilizing recognition for automatic targeting, real-time point calculations during pre-alignment enhance efficiency. Subsequently, based on this system, pre-alignment simulation calculations and experimental verification of eight magnet focusing–defocusing units in the HEPS storage ring are conducted and ultimately realizing the 10 μm transverse and vertical pre-alignment measuring error within the units. This method, based on high-precision measurements in a small-scale space, reduces the period required for personnel on-site and improves pre-alignment efficiency. It also provides a reference for pre-alignment of multiple magnet units in large accelerators such as the Southern Advanced Photon Source and Circular Electron Positron Collider.

Development of silicon drift detectors for synchrotron radiation sources

Synchrotron radiation facilities are essential interdisciplinary research platforms, with performance and efficiency closely tied to detector technology. To meet future requirements, especially the High Energy Photon Source (HEPS), we have conducted key technological research and development on single-element and array Silicon Drift Detectors (SDDs). The research and testing were conducted at the Platform of Advanced Photon Source Technology (PAPS). The test results indicate that the single-element SDD has achieved an energy resolution of 143 eV@5.9 keV (−35 °C), and the 20-unit array-SDD has reached an energy resolution of better than 300 eV@13.96 keV (−40 °C).

Development of high energy resolution crystal analyzers based on microporous ceramics for resonant inelastic x‐ray scattering program at High Energy Photon Source

AbstractThe spherically bent x‐ray crystal analyzer is one of the key optical elements for performing high energy resolution hard x‐ray spectroscopies based on Rowland circle geometry. To meet the requirements of Resonant Inelastic X‐ray Scattering (RIXS) program at High Energy Photon Source (HEPS), the fourth‐generation high energy synchrotron in Beijing, China, high energy resolution crystal analyzers were fabricated. The fabrication processes of vacuum‐mounted flat‐diced crystal analyzers using home‐designed devices with microporous ceramics are presented. The energy resolution of the vacuum‐mounted crystal analyzers, for measuring Cu K‐edge RIXS, is benchmarked with that of the glued flat‐diced crystal analyzers. Both the gluing and vacuum‐mounting are proven to be reliable techniques for the routine production of spherical bent diced crystal analyzers with energy resolution of tens of meV, and with good focal properties and efficiency. In particular, the vacuum‐mounted technique will be beneficial for the RIXS techniques to target multiple elements of interest.

Intensity-energy response function of Al/Cr-K[formula omitted] x-ray photoemission instruments: An inter-laboratory study

The question of the intensity-energy response of photoemission spectrometers has been approached through a round-robin involving 13 instruments working with low (Al/Mg-Kα) and high (Cr-Kα) energy photon sources. An algorithm based on the analysis of inelastic background previously proposed [S. Guilet et al., J. Electron Spectrosc. Relat. Phenom. 285 (2022) 147225)] was intensively tested against calibrated Al/Mg-Kα instruments and calculated relative sensitivity factors (RSFs) over the 15 core level peaks of coinage metals (Ag, Au, Cu). In both cases, the linear correlation within ±10 %, over two orders of magnitude in intensity and for kinetic energies ranging from ∼400 to 1400eV, showed the consistency of the approach. All the contributions to RSFs (e.g. non-dipolar terms in the photo-ionization cross section, elastic scattering effects, surface excitations, beam polarization by the monochromator) were critically reviewed and taken into account using the state-of-the-art modellings and databases. Strong variations were evidenced among instruments, regarding not only the response functions, but also the theoretical RSFs due to different measurement geometries. For the Cr-Kα hard x-ray instruments, the same analysis was performed with a set of different materials (Al, Si, Ge, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ag, W, Au). A ±10 % satisfactory agreement against theoretical RSFs over 69 core levels spanning a large kinetic energy range (300–4000 eV) could be achieved with a common response function. Despite limitations that are reviewed, this work opens interesting perspectives for a systematic calibration of photoemission instruments.

A new dual-thickness semi-transparent beamstop for small-angle X-ray scattering.

An innovative dual-thickness semi-transparent beamstop designed to enhance the performance of small-angle X-ray scattering (SAXS) experiments is introduced. This design integrates two absorbers of differing thicknesses side by side into a single attenuator, known as a beamstop. Instead of completely stopping the direct beam, it attenuates it, allowing the SAXS detector to measure the transmitted beam through the sample. This approach achieves true synchronization in measuring both scattered and transmitted signals and effectively eliminates higher-order harmonic contributions when determining the transmission light intensity through the sample. This facilitates and optimizes signal detection and background subtraction. This contribution details the theoretical basis and practical implementation of this solution at the SAXS station on the 1W2A beamline at the Beijing Synchrotron Radiation Facility. It also anticipates its application at other SAXS stations, including that at the forthcoming High Energy Photon Source, providing an effective solution for high-precision SAXS experiments.

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.

Design, construction and testing of the prototype cryogenic circulation centrifugal pump for the high energy photon source

A cryogenic circulation pump (CCP) with the small flow rate and low heat leakage, which is thekeyequipment of the cooling system for the cryogenic permanent magnet undulator (CPMU)and synchrotron monochromator in High Energy Photon Source(HEPS), is developed according to the design parameters and operation experiences. The mechanic structure of the CCP including a motor at room temperature, an impeller and a volute in the cryogenic environment is designed, and numerical simulation on the rotating shaft and internal flows are performed to predict the mechanical and hydrodynamic performances of the pump. Meanwhile, the experimental investigation of the CCP is carried out in the liquid nitrogen (LN2) cryogenic system, and the hydrodynamic performances of the CCP are verified experimentally. The results are shown that the calculated performances of the CCP are in reasonable agreement with the experimental results, which indicates that the numerical calculation model of the CCP is more effective. Moreover, the deviations of pressure drop and efficiency between the calculation and measurement are analyzed in this paper.

Beam coupling impedance measurement based on Goubau line method

The Goubau line method has been recently proposed and used for the longitudinal beam coupling impedance measurement of vacuum components. To extend the application of this method, the measurement of transverse impedance using the Goubau line method is proposed in this work. The feasibility of measuring the transverse impedance using the Goubau line method has been tested using a pillbox cavity. Additionally, the frequency shift induced by the dielectric-coated wire in the Goubau line measurements has been investigated analytically. The contribution of the dielectric coating to the frequency shift has been studied. Finally, the Goubau line setup has been optimized and used to evaluate the longitudinal and transverse beam coupling impedance of key vacuum components in the High Energy Photon Source.

The design and application of magnetic landmark used for magnetic fiducialization of HEPS insertion devices*

Abstract Achieving high performance in synchrotron radiation light sources demands increased precision in fiducialization and alignment of insertion devices (IDs). Conventional sensor systems utilizing Hall probes for high-precision magnetic field measurements face limitations in determining the absolute position of the magnetic center of IDs. In this paper, the Magnetic Landmark (MLK), a novel solution based on a magnetized block structure, is designed to address this challenge. The MLK serves as an intermediary, establishing contact between the magnetic center of IDs and their externally accessible fiducials, thus enabling high-precision alignment. Through analysis of magnetic field distribution, self-calibration precision, and practical application of the MLK, the following conclusions are drawn: when the Hall probe is positioned within 0.5 mm of the magnetic field zero point inside the MLK, the measurement accuracy of the zero point for normal and skew quadrupole magnetic fields reaches 7 and 2 μm, respectively. Additionally, the self-measurement accuracy of the MLK is 10 and 4 μm in the transverse and vertical directions, respectively. These accuracies meet our usage requirements. The MLK demonstrates efficacy in aligning the magnetic center of High Energy Photon Source (HEPS) In-air undulators, achieving alignment accuracies of 16 μm in the transverse direction and 11 μm in the vertical direction, surpassing the 30 μm accuracy stipulated in the physical design. Furthermore, the device proves applicable for measuring the magnetic center of other types of HEPS insertion devices, including Cryogenic undulators.

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.

The HEPS synchrotron unleashes new medical frontiers.

The High Energy Photon Source (HEPS) in Beijing achieved a beam energy of 6 GeV. This milestone enables groundbreaking advances in health sciences and various research fields, promising new insights into biological and quantum processes.

Mango wiggler as a novel insertion device providing a large and symmetrical imaging field of view.

A novel insertion device is introduced, designated as the Mango wiggler, designed for synchrotron radiation (SR) imaging that provides a large field of view. This innovative device is constructed from two orthogonal planar wigglers with a small difference in their period lengths, eliciting the phase difference of the magnetic fields to incrementally transitions from 0 to π/2. Such a configuration enlarges the vertical divergence of the light source, as with the horizontal divergence. The appellation `Mango wiggler' derives from the distinctive mango-shaped contour of its radiation field. A comprehensive suite of theoretical analyses and simulations has been executed to elucidate the radiation properties of the Mango wiggler, employing SPECTRA and Mathematica as calculation tools. In conjunction with the ongoing construction of the High Energy Photon Source in Beijing a practical Mango wiggler device has been fabricated for utilization in SR imaging applications. Theoretical analyses were applied to this particular Mango wiggler to yield several theoretical conclusions, and several simulations were performed according to the measured magnetic field results.

A study of the latest updates of the readout system for the hybird-pixel detector at HEPS

The High Energy Photon Source (HEPS) represents a fourth-generation light source. This facility has made unprecedented advancements in accelerator technology, necessitating the development of new detectors to satisfy physical requirements such as single-photon resolution, large dynamic range, and high frame rates. Since 2016, the Institute of High Energy Physics has introduced the first user-experimental hybrid pixel detector, progressing to the fourth-generation million-pixel detector designed for challenging conditions, with the dual-threshold single-photon detector HEPS-Beijing PIXel (HEPS-BPIX) set as the next-generation target. HEPS-BPIX will employ the entirely new Application-Specific Integrated Circuit (ASIC) BP40 for pixel information readout. Data flow will be managed and controlled through readout electronics based on a two-tier Field-Programmable Gate Array (FPGA) system: the Front-End Electronics (FEE) and the Input-Output Board (IOB) handle the fan-out for 12 ASICs, and the μ4FCP is tasked with processing serial data on high-speed links, transferring pixel-level data to the back-end RTM and μTCA chassis, or independently outputting through a network port, enabling remote control of the entire detector. The new HEPS-BPIX firmware has undergone a comprehensive redesign and update to meet the electronic characteristics of the new chip and to improve the overall performance of the detector. We provide an overview of the core subunits of HEPS-BPIX, emphasizing the readout system, evaluating the new hardware and firmware, and highlighting some of its innovative features and characteristics.

Study on the influence of gap dependent error on the cryogenic permanent magnet undulator performance

The mass production of the first stage of HEPS (High Energy Photon Source) is approaching its final stage. 6 CPMUs (cryogenic permanent magnet undulators) have been manufactured, with four successfully finalizing the tuning of the magnetic field. To ensure radiation performance, HEPS's CPMUs enforce stringent phase error protocols. Moreover, the contraction properties at cryogenic temperature lead to a decrease in phase error after cooling. In the process of CPMU commissioning, a technique for forecasting the change of magnetic errors from room to cryogenic temperature was discovered and studied, as will be demonstrated in this paper.

Experimental study on abrasive flow finishing of narrow inner cavity of alumina-dispersed copper absorber

Given the difficulties in processing and detecting the narrow and deep inner cavities of the diffusive copper absorber used by the High Energy Photon Source (HEPS), a regression equation prediction model for surface roughness and material removal depth based on abrasive flow machining was proposed through mixed-level orthogonal experiments. The influences of machining area pressure, machining cycle number, and abrasive mesh number on surface roughness and material removal were revealed. Subsequently, abrasive flow machining verification experiments were conducted on the narrow and deep inner cavities of the absorber, showing that the experimental results were within 15% error compared to the model predictions. After abrasive flow machining, the roughness decreased from about 4.4 μm to around 0.6 μm, significantly improving the surface quality of the workpiece. These research findings can provide a theoretical basis and technical support for the optical finishing of workpieces with narrow and deep variable cross-section inner cavities.

A 5.12-Gbps serializer circuit for front-end fast readout electronics of silicon pixelated detectors

Advanced synchrotron radiation sources are major facilities for analyzing the formation and evolution of material structure in multidisciplinary research, owing to their high luminosity, low emittance, wide energy bandwidth and other characteristics. In China, several advanced synchrotron radiation sources are under construction, including the HEPS (High Energy Photon Source) and SHINE (Shanghai high repetition rate X-ray Free Electron Laser and extreme light facility). These facilities are poised to become major multidisciplinary research platforms in China. To meet the requirements of pixel detectors in these facilities, dedicated pixel readout chips are being developed, including HEPS-BPIX and HYLITE. This paper presents a high-speed serializer circuit developed in a commercial 130-nm CMOS technology for the full-scale (128 × 128) pixel readout chip of HYLITE, which requires a data rate of 4 Gbps currently. The serializer consists of a 16-to-1 binary-tree multiplexer, a ring-oscillating-based phase-locked loop (RO-PLL) and a current-mode logic driving stage with a multi-stage pre-amplifier. Test results demonstrate its expected functionality within a wide operating range from 0.52 Gbps to 5.5 Gbps. At 5.12 Gbps, the measured jitter values are about 2 ps for random jitter, 20 ps for deterministic jitter, and 47 ps for total jitter with a 10−12 bit error rate. Additionally, the horizontal and vertical eye openings are 0.84 UI and 72%, respectively. These positive results indicate that the serializer meets the requirements of HYLITE.

QScatter: numerical framework for fast prediction of particle distributions in electron-laser scattering

The new generation of multi-PetaWatt laser facilities will allow tests of strong field quantum electrodynamics (QED), as well as provide an opportunity for novel photon and lepton sources. The first experiments are planned to study the (nearly) head-on scattering of intense, focused laser pulses with either relativistic electron beams or high-energy photon sources. In this work, we present a numerical framework that can provide fast predictions of the asymptotic particle and photon distributions after the scattering. The method detailed in this manuscript can include multiple features such as spatial and temporal misalignment between the laser and the scattering beam, broadband electron beams, and beam divergence. The expected mean energy, energy spread, divergence or other observables are calculated by combining an analytical description and numerical integration. This method can provide results within minutes on a personal computer, which would otherwise require full-scale 3D QED-PIC simulations using thousands of cores. The model, which has been compiled into an open-source code QScatter, may be used to support the analysis of large-size data sets from high-repetition rate experiments, leveraging its speed for optimization or reconstruction of experimental parameters.

Development and testing of high precision and stability power supply for high energy photon source

Development and testing of high precision and stability power supply for high energy photon source

A new modular framework for high-level application development at HEPS.

As a representative of the fourth-generation light sources, the High Energy Photon Source (HEPS) in Beijing, China, utilizes a multi-bend achromat lattice to obtain an approximately 100 times emittance reduction compared with third-generation light sources. New technologies bring new challenges to operate the storage ring. In order to meet the beam commissioning requirements of HEPS, a new framework for the development of high-level applications (HLAs) has been created. The key part of the new framework is a dual-layer physical module to facilitate the seamless fusion of physical simulation models with the real machine, allowing for fast switching between different simulation models to accommodate the various simulation scenarios. As a framework designed for development of physical applications, all variables are based on physical quantities. This allows physicists to analytically assess measurement parameters and optimize machine parameters in a more intuitive manner. To enhance both extensibility and adaptability, a modular design strategy is utilized, partitioning the entire framework into discrete modules in alignment with the requirements of HLA development. This strategy not only facilitates the independent development of each module but also minimizes inter-module coupling, thereby simplifying the maintenance and expansion of the entire framework. To simplify the development complexity, the design of the new framework is implemented using Python and is called Python-based Accelerator Physics Application Set (Pyapas). Taking advantage of Python's flexibility and robust library support, we are able to develop and iterate quickly, while also allowing for seamless integration with other scientific computing applications. HLAs for both the HEPS linac and booster have been successfully developed. During the beam commissioning process at the linac, Pyapas's ease of use and reliability have significantly reduced the time required for the beam commissioning operators. As a development framework for HLA designed for the new-generation light sources, Pyapas has the versatility to be employed with HEPS, as well as with other comparable light sources, due to its adaptability.

A common points selection method based on the uniformity of FLTMMS for pre-alignment of particle accelerators

High-precision pre-alignment of a magnet is a crucial step in the construction of a particle accelerator such as the Hefei Advanced Light Facility (HALF) or High Energy Photon Source (HEPS). To improve the accuracy and efficiency of pre-alignment, there are plans to build a four-station laser tracker multilateration measurement system (FLTMMS) at HALF. In the coordinate conversion and self-calibration processes of a FLTMMS, an unreasonable distribution of common points can lead to a loss of accuracy. A method for selecting common points based on uniformity in the FLTMMS is therefore proposed. In this method, the coordinate transformation space is divided according to the uniformity in different directions. The feasibility of our method is compared and analysed through coordinate conversion and self-calibration experiments. Simulations show that with the same number of common points, this method leads to higher accuracy in coordinate conversion and self-calibration. The proposed method compensates for the loss of accuracy due to aggregation of common points. Comparative analyses show a clear positive relationship between the accuracy improvement effect and the difference in uniformity. The distribution of common points will change the accuracy distribution of FLTMMS. Our approach of providing essential references for pre-aligning HALF magnets has been applied to HEPS with extensive engineering experience, to verify the practicality of this method for engineering applications. In the actual measurements, self-calibration is performed using an edge measurement network, and coordinate conversion is conducted using angle measurements. Based on actual measurements, the self-calibration accuracy is 1.7 μm and a conversion accuracy is 14.8 μm. The results show that under the premise of satisfying precision, the method can reduce the number of common points, thus decreasing the cost of common points construction. Our study provides instructions for pre-alignment at HALF in the future.