Beam Orbit Research Articles

Optimization stability and performance of the TPS storage ring dipole magnet power supply

This article focuses on the current status of the dipole magnet power supply (DMPS) and improvement in the Taiwan Photon Source (TPS) storage ring. The DMPS provides a stable and precise magnetic field for the storage ring operation. Appropriate wiring methods are employed to minimize magnetic field interference across the entire TPS area to meet the demands of high-energy output and overcome the challenges of operating at high currents. The target energy is set at 850 V and 750 A, utilizing a single-pole switching voltage regulator as a high-precision constant current source output structure. The system incorporates a closed control loop that uses the Direct Current Current Transducer (DCCT) to provide current signal feedback to the system. FPGA (Field-Programmable Gate Array) calculates PID (Proportional-Integral-Derivative) compensation values, generating a 2.1 kHz pulse width modulation (PWM) signal to regulate the output current. At the same time, insulated gate bipolar transistor (IGBT) modules are switching components. However, even after several years of practical operation, the stability and performance of the DMPS in the storage ring still require improvements. To enhance long-term output current stability and address peripheral issues, the current TPS utilizes the Beam Orbit Feedback (FOFB) system to suppress and fine-tune the magnetic field and compensate for the impact of temperature drift on the DMPS's output current. This improvement ensures a more stable circulation of the photon beam within the storage ring. By optimizing the temperature control circuit of the main control card, the long-term output current stability has been successfully enhanced to within ± 10 ppm. Simultaneously, the FOFB system reduces uncertainties in adjusting the X-axis beam position, improving beam stability and quality. Furthermore, relevant protective measures have been implemented to ensure robust system operation. Ultimately, these improvement measures have successfully met TPS's stringent requirements for the DMPS, enabling the synchrotron accelerator light source to operate at higher performance levels and fostering advanced scientific research. The results of these upgrades underscore the success of the power supply enhancements, making significant contributions to the overall improvement of the Taiwan Photon Source facility.

Analysis of Beam Orbit Stability at the SKIF

Analysis of Beam Orbit Stability at the SKIF

Enhanced beam extraction system at the U-120M cyclotron

Since its commissioning in 1977, the U-120M cyclotron was initially equipped with a single pair of harmonic coils aimed at optimizing beam quality at lower accelerating radii. In 2022, a significant upgrade introduced a second pair of harmonic coils, positioned at a radius of approximately 50 cm, aligning with the outermost beam orbit. This addition is essential for the efficient extraction of positively accelerated ions and serves as the basis for the newly developed extraction system, which, unlike the original fully electrostatic system, consists of electrostatic deflectors and magnetic channels. This paper describes the design and installation of new harmonic coils in the accelerator vacuum chamber and presents a new extraction system using precession and linear integer resonance methods. Basic properties of these two extraction methods are given and finally, an evaluation of their advantages and limitations concerning their possible use in the cyclotron and an estimation of the efficiency of the new extraction system is made.

Beam test results of the orbit correction at the low-energy superconducting accelerator section in the RAON accelerator

The RAON accelerator has been constructed for various science programs with stable ions and rare isotopes since 2011. After the installation of the injector section was completed in 2020, the low-energy superconducting accelerator (SCL3) section was also installed consecutively until 2022, and the beam commissioning using an argon beam is in progress from the injector section to the SCL3 section. For successful beam commissioning, various beam dynamics studies have been carried out, and the research of the orbit correction has been also conducted to determine the location and the number of steering magnets and BPMs for safe and efficient beam operation. In the SCL3 section, the orbit correction simulation was carried out as varying the number of steering magnets for the consideration of the correction of distorted beam orbit and the economic benefits, and then the beam test was carried out based on the simulation results during the beam commissioning. Here we will present the results of simulations and experiments for the orbit correction at the SCL3 section in the RAON accelerator.

New techniques method for improving the performance of the ALPI Linac

The superconductive quarter wave cavities hadron linac ALPI is the final acceleration stage at the Legnaro National Laboratories. It can accelerate heavy ions from carbon to uranium up to 10 MeV/u for nuclear and applied physics experiments. It is also planned to use it for re-acceleration of the radioactive ion beams for the SPES (Selective Production of Exotic Species) project. In this article, we will present the innovative results obtained with swarm intelligence algorithms, in simulations and measurements. In particular, the increment of the longitudinal acceptance for RIB (Radioactive Ion Beams) acceleration, and beam orbit correction without the beam first-order measurements will be discussed.

Beam optics distortion caused by orbit deviation at strong sextupole magnets in SuperKEKB

The SuperKEKB is an electron-positron double-ring asymmetric-energy collider at the High Energy Accelerator Research Organization (KEK) in Japan. It uses a novel collision method referred to as the nano-beam scheme to avoid the so-called hourglass effect. The highest peak luminosity achieved thus far is 4.65 × 1034 cm-2s-1, which was reached on June 8th, 2022. Although the SuperKEKB holds the record for the world's highest instantaneous luminosity, several unresolved issues prevent a further increase in luminosity. One of the major issues is inadequate stability and reproducibility of the beam orbit and optics. This paper discusses optics distortion caused by orbit deviation near strong sextupole magnets. Numerical estimations indicate that a horizontal orbit deviation of a few tens of micrometers induces a sizable distortion of the optical functions at the interaction point. Analyses of the amount of betatron tune feedback and orbit at sextupole magnets used for crab waist and vertical local chromaticity correction indicate that the beam-current dependence of the vertical tune shift is attributable to the change of the beam orbit at the sextupoles. The orbit fluctuation at the sextupoles causes beta-beating and makes stable operation at high beam currents more difficult. The results show that orbit tuning at the sextupoles improves both the injection efficiency and the detector background level. Optics deterioration within a few days is another urgent issue in high-beam-current operation. A vertical orbit change of a few tens of microns at sextupole magnets installed in arc cells is a matter of concern according to numerical estimations.

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.

Effects of a 4.3T superconducting wiggler on the electron beam optics and dynamics at NSLS-II

A superconducting wiggler (SCW) with a peak field of 4.3 T has recently been installed at NSLS-II. The wiggler generates a high-flux X-ray beam with a photon energy range from 20 keV to 200 keV for the High Energy Engineering X-ray Scattering beamline. This device induces significant distortions in the electron beam orbit and optics. We have corrected these adverse effects using feed-forward tables. The effects of the SCW on the electron beam emittance, energy spread, and bunch length were calculated and measured. The beam-induced heating of the cryogenic vacuum chamber was also studied. Finally, the superconducting wiggler has been commissioned for user operations.

The effect of ground motion on the LHC and HL-LHC beam orbit

The High Luminosity Large Hadron Collider (HL-LHC) will require unprecedented orbit stability at the low-beta experiments, ATLAS and CMS. Because the effect of seismic noise might become a relevant source of luminosity loss, several studies have been conducted to characterise the actual ground motion in the LHC tunnel. In preparation for the official groundbreaking of the civil engineering work for the high luminosity upgrade, that started on 15 June 2018 in parallel to LHC beam operation, seismic sensors were installed to permanently monitor the ground stability close to these experiments. Compactor work and shaft excavation were expected to induce vibrations in the accelerator magnets that would cause orbit disturbance, beam loss and potentially premature beam dumps. This paper summarises the observations made on the LHC beams and uses this data to benchmark estimates of the impact of low frequency vibrations on the closed orbit at the main interaction points and collimators. The impact of ground motion on HL-LHC operation is then estimated using the expected operational scenario and the estimated mechanical stability of the new HL-LHC triplet magnets that is based on recent measurements of mechanical magnet transfer functions.

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.

Twin delayed deep deterministic policy gradient for free-electron laser online optimization

X-ray free-electron lasers (FEL) have contributed to many frontier applications of nanoscale science which benefit from its extraordinary properties. During FEL commissioning, the beam status optimization especially orbits correction is particularly significant for FEL amplification. For example, the deviation between beam orbit and the magnetic center of undulator can affect the interaction between the electron beam and the FEL pulse. Usually, FEL commissioning requires a lot of effort for multi-dimensional parameters optimization in a time-varying system. Therefore, advanced algorithms are needed to facilitate the commissioning procedure. In this paper, we propose an online method to optimize the FEL power and transverse coherence by using a twin delayed deep deterministic policy gradient (TD3) algorithm. The algorithm exhibits more stable learning convergence and improves learning performance because the overestimation bias of policy gradient methods is suppressed.

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).

Photon Diagnostic for FLASH2020+: Analysis of Spontaneous Radiation for Undulator Alignment

Within the FLASH2020+ program, DESY is aiming to significantly improve the flexibility and availability of its pioneering FEL FLASH for users. Increasing the electron beam energy to 1.35GeV will make wavelengths available up to the oxygen K-edge on the fundamental harmonic. Exchanging the current fixed gap undulators in the FLASH1 branch for variable gap devices will allow for fully independent operation of both branches in the future. The 11 new Apple III type variable polarization undulator segments will have a period length of 33mm and a length of 2.5m each.This paper presents the development of a photon diagnostic station for FLASH2020+, an additional tool for alignment and commissioning of the undulators. The diagnostic station will be located about 50m downstream from the last undulator. It will allow for the measurement and correction of the electron beam orbit as well as for the measurement of the undulator K-values. In addition, the system can be used to investigate the phasing of the undulators in two adjacent cells by analysing their spontaneous radiation.

A digitally controlled linear power supply for HALF fast orbit correctors

The fourth-generation synchrotron radiation source Hefei Advanced Light Facility (HALF) requires higher stability of the beam orbit. The corrector power supply with fast response and high stability can effectively reduce the latency of the Fast Orbit FeedBack (FOFB) system and improve the beam quality. In this paper, an FPGA-based, fully digitally controlled linear power supply based on H-bridge topology is proposed. Multiple buck circuits are cascaded as the front stage power supply, and the linear amplification of the H-bridge MOSFETs provides the power for the corrector load. The PI closed loop is calculated by the FPGA and finally drives the MOSFETs through the high precision Digital to Analog Converter (DAC) chip. As a result, the response bandwidth of the power supply can reach 5 kHz, and the long-term stability and current ripple are better than 20 ppm, which will improve the beam quality of HALF. The design can also be easily extended to other magnet power supply and fast power conversion technologies.

Study on support for HALF beam position monitor displacement measurement system

Hefei Advanced Light Facility (HALF), is a fourth-generation vacuum ultraviolet and X-ray diffraction limit synchrotron radiation (DLSR) light source under preliminary research and construction. Beam position monitor (BPM) displacement measurement system with nanometer resolution is used to correct the BPM data and achieve sub-micron beam orbit stability. In order to make full use of the performance and meet the requirement of HALF’s beam orbit stability, the supports of the system are particularly crucial. The purpose of this paper is to develop a set of support for the BPM displacement system that meet the stability requirements of HALF. A hybrid support with Invar 36 and carbon fiber/epoxy is creatively proposed to achieve stability requirements. Through the calculation of thermal expansion, the analysis of mechanical vibration and finite element analysis (FEA), the hybrid support is adjusted to higher stability. Experiments are conducted and show that the hybrid support has higher stability than traditional support. On the existing experimental platform, the vibration RMS of the hybrid support was measured at 42.6 nm in horizontal and 29.9 nm in vertical and the hybrid support could meet the requirement of HALF’s beam orbit stability.

Magnetic Measurements on the Twin Aperture Orbit Correctors for HL-LHC at IMP

The Large Hadron Collider (LHC) upgrade, namely, High Luminosity LHC (HL-LHC) is planned for the next decade. A set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS & CMS experiments will be developed. Two Chinese Academy of Sciences institutes, i.e., IHEP (Institute of High Energy Physics) and IMP (Institute of Modern Physics), and one company in China will work on the magnet R&D and series production. IMP is in charge of the performance test both at ambient and cryogenic temperatures, and the first China-built model (MCBRDP2) has been tested recently. In this paper, the test setup for magnetic measurements, the room temperature bore, and the rotating coil probe being system used at IMP are presented. The quench record and the measurement results, such as integral field, multipoles, cross-talk, are given and discussed.

Online beam orbit correction of MEBT in CiADS based on multi-agent reinforcement learning algorithm

The proton linac accelerator has been the mostly appropriate equipment applied to radioactive waste disposal and cancer treatment. However, beam offset is a particularly significant problem during proton acceleration, which not only produces a halo and causes orbital distortion of the beam to make the beam injection inefficient. In exceptionally complex accelerator systems, accurate correction of beam offset is very difficult. The traditional method is based on manual experience and manual adjustment to achieve beam trajectory correction, the automation level is low and the adjustment speed is slow. Therefore, this paper proposes a new method of beam orbit correction based on Multi-Agent Reinforcement Learning. In order to verify the feasibility of the algorithm in beam orbit correction, this method takes the MEBT section of the virtual accelerator as the control object, and uses three agents to control the beam orbit of Medium Energy Beam Transport (MEBT) in sections. Each agent is designed based on the Reinforcement Learning of the Deep Deterministic Policy Gradient (DDPG) algorithm, the deterministic strategy is used to explore the large state and action space to realize discretization, and the training model convergence is successfully realized. The experimental results show that the final calibrated average beam offset of this method is about 0.39 mm, which achieves the expected experimental goal. It can control the beam orbit of MEBT, and has application value and competitiveness in the beam orbit correction of linac.

Shot-to-shot two-dimensional photon intensity diagnostics within megahertz pulse-trains at the European XFEL.

Characterizing the properties of X-ray free-electron laser (XFEL) sources is a critical step for optimization of performance and experiment planning. The recent availability of MHz XFELs has opened up a range of new opportunities for novel experiments but also highlighted the need for systematic measurements of the source properties. Here, MHz-enabled beam imaging diagnostics developed for the SPB/SFX instrument at the European XFEL are exploited to measure the shot-to-shot intensity statistics of X-ray pulses. The ability to record pulse-integrated two-dimensional transverse intensity measurements at multiple planes along an XFEL beamline at MHz rates yields an improved understanding of the shot-to-shot photon beam intensity variations. These variations can play a critical role, for example, in determining the outcome of single-particle imaging experiments and other experiments that are sensitive to the transverse profile of the incident beam. It is observed that shot-to-shot variations in the statistical properties of a recorded ensemble of radiant intensity distributions are sensitive to changes in electron beam current density. These changes typically occur during pulse-distribution to the instrument and are currently not accounted for by the existing suite of imaging diagnostics. Modulations of the electron beam orbit in the accelerator are observed to induce a time-dependence in the statistics of individual pulses - this is demonstrated by applying radio-frequency trajectory tilts to electron bunch-trains delivered to the instrument. We discuss how these modifications of the beam trajectory might be used to modify the statistical properties of the source and potential future applications.

Analysis and modeling of laser-driven ion-beam trace probe diagnostics of poloidal magnetic fields in field-reversed configurations

The field-reversed configuration (FRC) is a promising magnetic confinement fusion concept [M. Tuszewski, Nucl. Fusion 28, 2033 (1988)] and is often chosen as the target plasma for magneto inertial fusion [S. A. Slutz and M. R. Gomez, Phys. Plasmas 28, 042707 (2021)]. In FRCs, the toroidal magnetic field is essentially zero, and the poloidal magnetic field (Bp) pressure is comparable with the plasma pressure. Applying the traditional Bp diagnostics to FRCs is a major challenge because Bp is small, and reversal occurs across the core region of FRCs. The laser-driven ion-beam trace probe (LITP) is a newly developing diagnostic method to measure Bp and the radial electric field (Er) in tokamak. Here, the principles of using LITP to diagnose Bp in FRCs are proposed, verified, and numerically implemented using an iterative method to reconstruct the Bp profile. Least square tomography employing a dissipative term is used to solve the nonlinear tomography problem, which arises when applying LITP to the unique FRC magnetic topology. Numerical modeling results show that the relative errors of the reconstruction are mostly below 10%, verifying the feasibility of LITP diagnostics for FRC internal magnetic field measurements. Ion beam orbits and detector arrangements are optimized to meet the experimental requirements of FRCs. LITP can still be applied to diagnose Bp in FRCs when there is 5% measurement errors.

Transverse force in a relativistic beam moving along a curved trajectory

When a relativistic beam moves along a curved trajectory it loses energy on coherent radiation. The effect of this radiation on the beam dynamics is described by the so call coherent synchrotron radiation (CSR) longitudinal wake field. Among different models of the CSR wake, the simplest is the one-dimensional (1D) one where the beam is treated as a line-charge. The self-field of the beam on a curved trajectory also creates a transverse component of the force. Unfortunately, there is a confusion in the literature as to whether a 1D model can be worked out for the transverse force inside the beam. In this paper, we show how such a 1D model can be consistently derived for a general curvilinear beam orbit if one formulates the equations of motion for the beam particles in Hamiltonian form and uses a renormalized transverse force. Unfortunately, this scheme cannot be applied to the classical problem of relativistic beam passing through a single bending magnet, because the scalar potential in the initial conditions for the Hamiltonian variables cannot be defined in the 1D model. In this case, one should use the 3D transverse force, for which we derive analytical expressions. For the steady state, our calculations show an excellent agreement with computer simulations. We also calculate the transient effects for this force at the entrance to and the exit from the bend. Our results provide a new way to accommodate the transverse force into the existing and new simulation codes which is important for many applications of the high-current, small-emittance relativistic beams.