Closed Orbit Distortion Research Articles

Closed-orbit Distortion study of XiPAF upgrading project synchrotron

Xi’an 200 MeV proton application facility (XiPAF) upgrading project is now in the design phase. A six super periods synchrotron is the main component of this project. Using MADX program, a statical analysis of the relationship between closed-orbit distortion (COD) and different types of magnet errors was carried out. Because we do not know the exact error in the design phase, we use rms value to represent errors and CODs. The results show that COD is in direct proportion to magnet error in some cases while the others are square proportional. We regard all the cases as direct proportional since the errors are usually small and find that the error amplification factors differ a lot. These results can give us some meaningful guide in lattice design and magnet error control.

Orbit stabilization for the new insertion devices in SSRF

During the Shanghai Synchrotron Radiation Facility (SSRF) beamline project, fourteen new insertion devices (IDs) have been successfully installed and transitioned to operation. However, these new IDs led to considerable closed orbit distortions in the SSRF storage ring. In the canted beamlines, the theoretical current values of dipoles required for the closed dual-canted angle were established, however, errors in the actual machine make a significant effect on closed orbit. To address this, an adjustment configuration, based on the response matrix, was developed for the closed dual-canted angles. Additionally, an orbit feedforward compensation system equipped with corrector coils, was employed. As a result, the maximum horizontal and vertical orbit distortions induced by the IDs were successfully decreased to less than 5.0 μm and 3.5 μm, respectively. Furthermore, a specialized local fast feedback system was designed to maintain the precise orbit and angle stability for the Hard X-ray Nanoprobe beamline.

Linear Optics Calibration in a Storage Ring Based on Machine Learning

Inevitably, various errors occur in an actual storage ring, such as magnetic field errors, magnet misalignments, and ground settlement deformation, which cause closed orbit distortion and tuning shift. Therefore, linear optics calibration is an essential procedure for storage rings. In this paper, we introduce a new method using machine learning to calibrate linear optics. This method is different from the traditional linear optics from closed orbit (LOCO) method, which is based on singular value decomposition (SVD). The machine learning model does not need to be computed by SVD. Our study shows that the machine-learning-based method can significantly reduce the difference between the model response matrix and the measurement response matrix by adjusting the strength of the quadrupoles.

Adaptive feedforward control of closed orbit distortion caused by fast helicity-switching undulators.

A new correction algorithm for closed orbit distortion based on an adaptive feedforward control (AFC) has been developed. At SPring-8, two helicity-switching twin-helical undulators (THUs) had been implemented with conventional feedforward corrections. However, the validity of these corrections turned out to be expiring due to unforeseen variation in the error magnetic fields with time. The developed AFC system has been applied to the THUs dynamically updating the feedforward table without stopping the helicity switching amid user experiments. The error sources in the two THUs are successfully resolved and corrected even while the two THUs are switching simultaneously with the same repetition period. The actual operation of the new AFC system enables us to keep the orbit variations suppressed with an accuracy at the sub-micrometre level in a transparent way for light source users.

Closed orbit correction of the HIMM synchrotron

In this paper the closed orbit correction of the Heavy Ion Medical Machine (HIMM) synchrotron is described. Results of simulations and measurements are presented. Consistently with simulations, it is possible to correct the maximum closed orbit distortion of the HIMM synchrotron down to 2.4mm in the horizontal direction and 0.7mm in the vertical one. The errors of dipole magnets, especially the longitudinal alignment errors (Δs), have large impact on the horizontal correction results. A Singular Value Decomposition (SVD) algorithm is adopted for computing the correction. The residual orbits and the effects of reducing the number of singular values are analytically expressed and simulated. In addition, the influences of BPM reading errors as well as corrector setting errors are analyzed. For further optimization, the method to estimate the dipole errors is studied. In the commissioning, the maximum closed orbits at BPMs can also be well corrected to within 1mm through SVD algorithm.

The magnet sorting of APTRON.

The magnetic field error caused by imperfection during the manufacturing process of magnets is inevitable. Therefore, the field error of both dipole and quadrupole magnets and their alignment errors will cause the synchrotron closed orbit distortion. In order to minimize the influence of the beam, a sorting method is applied to both dipole and quadrupole magnets with integral consideration of different excitation currents, covering both low and high field situations. The commissioning result shows that we can achieve the designed beam intensity.

Linear optics and coupling correction of ILSF storage ring lattice

The Iranian Light Source Facility (ILSF) is a 3 GeV synchrotron radiation facility, which is in the design stage. The ILSF storage ring design is based on a five-bend achromat lattice providing an ultralow horizontal beam emittance of 0.27 nm-rad. Inevitable errors like imperfection of magnetic field and misalignment of magnets will introduce various destructive effects on the performance of the machine. The possibility of correcting the errors should be thoroughly examined before settling the design. In this paper, we have tried to estimate the errors as realistic as possible based on the results obtained from the simulation of the elements and the accuracy of the predicted equipment for fabrication and alignment. The influence of errors on the lattice is investigated. Closed orbit distortion, beta beating and betatron coupling are corrected and improvement made in the lattice functions and machine performance will be presented.

Residual orbit of BC bump for CSNS/RCS

In a beam cycle, there is a chicane bump (BC bump) in the injection region of China Spallation Neutron Source (CSNS). It is a core part of the injection system and the important guarantee that the Linac beam injecting into the rapid cycling synchrotron (RCS). During the beam commissioning, the residual orbit of BC bump, i.e. the closedorbit distortion (COD) due to the imperfect BC bump, was an important problem which can affect the orbit correction and beam loss control of the RCS. In this paper, a method to measure the residual orbit of BC bump was studied and given. By using the three auxiliary powers of BC magnets, a method to correct the residual orbit of BC bump was developed. The numerical simulation results showed that the measurement and correction methods had worked well and they can be applied to the beam commissioning of CSNS/RCS. The measurement results in the machine study showed that the residual orbit of BC bump is not large and can be corrected by the three auxiliary powers of BC magnets.

Beam dynamics of the racetrack-shape fixed field induction accelerator

Beam dynamics of the racetrack-shape fixed field induction accelerator for giant cluster ions were established. Linear optics theory and Runge-Kutta particle tracking approaches were developed, and the consistency between two approaches was confirmed. Use of gradient field bending magnets with a reverse field strip and ramping quadrupole doublets were crucial to achieve the orbit stability. A physically limited size of the huge bending magnet in the longitudinal direction generated the inherent closed-orbit distortion that substantially affected the orbit stability. In addition, the inherent field component ${B}_{s}$ along the orbit coordinate ``$s$'' induced horizontal-vertical (H-V) couplings. A possible correction method of this closed-orbit distortion was proposed. A net effect of the H-V coupling was evaluated. Longitudinal motion with a time-varying transition energy, which is one of characteristic features in the racetrack-shape fixed field induction accelerator, was studied with the help of computer simulations.

Local impedance measurements from closed orbit distortion due to wake fields at CESR

Abstract Short range transverse wake fields are excited by charged particles passing through a vacuum chamber. The wake fields can act back on a bunch of particles and alter its trajectory. We have measured the distortion of the closed orbit due to transverse wake fields in the Cornell Electron–positron Storage Ring. A transverse monopole wake field is induced by an asymmetric impedance associated with the insertion of a single vertical scraper. A transverse dipole wake field is generated by displacing the bunch from the symmetry axis of the chamber. The orbit is offset vertically through the gap of a pair of symmetrically inserted scrapers and also in a narrow-gap undulator chamber. A fit to the distorted orbits yields the average kick of the transverse monopole wake of the asymmetric scrapers and the kick factor of the symmetric scrapers; the scraper results are in reasonable agreement with the values from numerical simulation of the wake fields. The kick factor extracted from the closed orbit distortion of the dipole wake induced by the narrow-gap undulator chamber is significantly greater than that predicted by the numerical simulation. Possible sources of the discrepancy are discussed.

Design and optimization of a multi-bend achromat lattice for 3.5 GeV synchrotron storage ring

In the past decades, the optimized design of light source array by use of multi-bend achromat has been considered to achieve high-quality photon beam for fundamental researches in different areas of science and technology. In this paper, we investigate a lattice design for a low emittance storage ring with intermediate energy of 3.5 GeV . We present the design results in detail for a five-bend achromat lattice with an emittance of 230 pm-rad, appropriate dynamic aperture, high brilliance photons near soft X-ray diffraction limited, the total lifetime of 11 hours and circumference of 448 m contains 20 straight sections of 6.1 meters in length. The results of closed orbit correction and misalignments errors on the dynamic aperture were also presented. The lattice provides sufficient dynamic aperture after closed orbit distortion correction. Furthermore, the variation of the emittance due to coupling and intra-beam scattering (IBS) effect has been calculated as a function of the energy and length of the bunch. Our designed storage ring shows an optimized five-bend achromat lattice for intermediate light sources.

Simulation of Closed Orbit Correction for the Nuclotron Booster

The quality of booster closed-orbit correction is estimated. The distribution of the maximum orbit distortion in both directions and the results of numerical simulation using the singular value decomposition method are given. The estimation of closed-orbit distortion with the worst correction quality is given.

Magnetic field errors tolerances of Nuclotron booster

Generation of magnetic field in units of booster synchrotron for the NICA project is one of the most important conditions for getting the required parameters and qualitative accelerator operation. Research of linear and nonlinear dynamics of ion beam 197Au31+ in the booster have carried out with MADX program. Analytical estimation of magnetic field errors tolerance and numerical computation of dynamic aperture of booster DFO-magnetic lattice are presented. Closed orbit distortion with random errors of magnetic fields and errors in layout of booster units was evaluated.

Beam based alignment and its relevance in Indus-2.

Initially in the Indus-2 storage ring, the closed orbit distortion (COD) could be best corrected to 1.3 mm rms in the horizontal and 0.43 mm rms in the vertical plane. The strength of the corrector magnets required high values for COD correction. This revealed that offsets in COD readout by the beam position monitors (BPMs) played a role in not achieving a rms COD lower than the above value. Thus, the offset between the electrical center of BPMs and the magnetic center of the nearest quadrupole magnet could be estimated using the beam based alignment (BBA) method. It prefers that the quadrupole magnet is able to be controlled individually and active shunt power supply (ASPS) system was designed for this purpose that works efficiently. This paper describes the methodology of BBA, topology of ASPS and its performance, and COD minimization using the measured BPM offsets. After BBA, the COD could be reduced to 0.45 mm rms and 0.2 mm rms in horizontal and vertical planes, respectively.

Observation of edge radiation from a straight section of SAGA-LS storage ring

Edge radiation generated by relativistic electrons passing between two bending magnets was investigated in a straight section of the SAGA-LS storage ring. Observations with correction of the closed orbit distortion (COD) and with large COD by single dipole kick were performed. Small but uncontrolled dipole kicks due to various magnets such as quadrupoles, sextupoles and steering magnets between the two bending magnets were considered to be non-negligible as a disturbance factor of the spatial distribution of the edge radiation. In addition, clear edge radiation was observed under the large COD due to a single dipole kick. The large COD was thought to generate a “pure” straight subsection, which contained no magnets and was clearly off-axis with respect to other subsections. Calculation based on this consideration showed good agreement with our observations.

Optimal placement of magnets in Indus-2 storage ring

In Indus-2, by optimizing the position of the magnetic elements, using the simulated annealing algorithm, at different locations in the ring with their field errors, the effects on beam parameters have been minimized. Closed orbit distortion and beta beat are considerably reduced by optimizing the dipole and quadrupole magnets positions in the ring. For the Indus-2 storage ring, sextupole optimization gives insignificant improvement in dynamic aperture with chromaticity-correcting sextupoles. The magnets have been placed in the ring with the optimized sequence and storage of the beam has been achieved at injection energy without energizing any corrector magnets. Magnet sorting has led to the easy beam current accumulation and the measurement of parameters such as closed orbit distortion, beta function, dispersion, dynamic aperture etc.

Orbit correction in a linear nonscaling fixed field alternating gradient accelerator

In a linear nonscaling fixed field alternating gradient accelerator, the large natural chromaticity of the machine results in a betatron tune that varies by several integers over the momentum range. Orbit correction is complicated by the consequent variation of the phase advance between lattice elements. Here we investigate how the correction of multiple closed orbit harmonics allows correction of both the closed orbit distortion and the accelerated orbit distortion over the momentum range.

Beam loss reduction by magnetic shielding using beam pipes and bellows of soft magnetic materials

One of the main sources of beam loss in high power accelerators is unwanted stray magnetic fields from magnets near the beam line, which can distort the beam orbit. The most effective way to shield such magnetic fields is to perfectly surround the beam region without any gaps with a soft magnetic high permeability material. This leads to the manufacture of vacuum chambers (beam pipes and bellows) with soft magnetic materials. A Ni–Fe alloy (permalloy) was selected for the material of the pipe parts and outer bellows parts, while a ferritic stainless steel was selected for the flanges. An austenitic stainless steel, which is non-magnetic material, was used for the inner bellows for vacuum tightness. To achieve good magnetic shielding and vacuum performances, a heat treatment under high vacuum was applied during the manufacturing process of the vacuum chambers. Using this heat treatment, the ratio of the integrated magnetic flux density along the beam orbit between the inside and outside of the beam pipe and bellows became small enough to suppress beam orbit distortion. The outgassing rate of the materials with this heat treatment was reduced by one order magnitude compared to that without heat treatment. By installing the beam pipes and bellows of soft magnetic materials as part of the Japan Proton Accelerator Research Complex 3GeV rapid cycling synchrotron beam line, the closed orbit distortion (COD) was reduced by more than 80%. In addition, a 95.5% beam survival ratio was achieved by this COD improvement.

Amplitude dependent shift of betatron oscillation center

We have analytically calculated and measured the amplitude-dependent shift of the betatron oscillation center at the electron storage ring, NewSUBARU. The shift is due to nonzero average horizontal deflections at the normal sextupole magnets. The shifted center forms a displaced closed orbit and is measured by a closed orbit distortion measurement system, although no single electron runs on this orbit. The measured shifts by betatron oscillations agreed with the theoretical calculation except the variation of data points, which did not obey the ring symmetry. Additional measurements, whose results included the effect of the circumference shift, experimentally proved the amplitude dependent circumference shift for the first time. We also discuss some applications of the shift, which has never been previously analyzed.

Design of a low-emittance lattice for 3.5 GeV synchrotron light source

We investigate a lattice design for a low-emittance, high-brilliance intermediate energy synchrotron light source that is being intensively performed in the world. We present the design results in detail for a non-achromatic double bend achromat lattice with an emittance of 1.1 nm and 597.6 m circumference. Each superperiod has 4 straight sections, 7 m, 5.4 m, and 2 × 2.8 m in length, giving a total of 60 straight sections in the ring. The lattice is designed to be flexible and also provides an achromatic optics with an emittance of 3.2 nm. The lattice provides high brilliance at a photon energy of a few tens of keV, which meets the requirements of hard X-ray synchrotron radiation users. We investigated the dynamic aperture in the lattice with machine errors using a simulation method that achieves the optimal tune for the ring. The low-emittance lattice provides sufficient dynamic aperture after closed orbit distortion correction. We show an estimate of variations of emittance, energy spread, and dynamic aperture due to a wiggler in the straight sections. We present the design of an injection scheme for full energy injection, the space allocation in injection section, and the particle dynamics of injected beam. Particle tracking after beam injection was performed to examine the validity of the injection scheme. Our design lattice shows good optimization in terms of the emittance, number of straight sections, brilliance, and circumference as a light source for 3.5 GeV beam energy.