Beam Orbit Research Articles

Phase-merging enhanced harmonic generation free-electron laser with a normal modulator.

A phase-merging enhanced harmonic generation free-electron laser (FEL) was proposed to increase the harmonic conversion efficiency of seeded FELs and promote the radiation wavelength towards the X-ray spectral region. However, this requires a specially designed transverse gradient undulator (TGU) as the modulator to couple the transverse and longitudinal phase space of the electron beam. In this paper, the generation of the phase-merging effect is explored using the natural field gradient of a normal planar undulator. In this method, a vertical dispersion on the electron beam is introduced and then the dispersed beam travels through a normal modulator in a vertical off-axis orbit where the vertical field gradient is selected properly in terms of the vertical dispersion strength and modulation amplitude. The phase-merging effect will be generated after passing through the dispersive chicane. Theoretical analysis and numerical simulations for a seeded soft X-ray FEL based on parameters of the Shanghai Soft X-ray FEL project are presented. Compared with a TGU modulator, using the natural gradient of a normal planar modulator has the distinct advantage that the gradient can be conveniently tuned in quite a large range by adjusting the beam orbit offset.

Orbit and dispersion tool at European XFEL injector

Trajectory and electron beam size play an essential role in Free Electron Laser (FEL) obtainment. Since transverse dispersion changes off-energy particle trajectories and increases the effective beam size, dispersion and orbit must constantly be controlled and corrected along the whole lattice. In this paper the principles underlying the orbit and dispersion correction tool, developed at DESY, are described. The results of its testing on European XFEL injector are presented.

Anomaly Detection for Beam Loss Maps in the Large Hadron Collider

In the LHC, beam loss maps are used to validate collimator settings for cleaning and machine protection. This is done by monitoring the loss distribution in the ring during infrequent controlled loss map campaigns, as well as in standard operation. Due to the complexity of the system, consisting of more than 50 collimators per beam, it is difficult to identify small changes in the collimation hierarchy, which may be due to setting errors or beam orbit drifts with such methods. A technique based on Principal Component Analysis and Local Outlier Factor is presented to detect anomalies in the loss maps and therefore provide an automatic check of the collimation hierarchy.

SRF cavity alignment detection method using beam-induced HOM with curved beam orbit

We have developed a method to obtain mechanical centers of nine cell superconducting radio frequency (SRF) cavities from localized dipole modes, that is one of the higher order modes (HOM) induced by low-energy beams. It is to be noted that low-energy beams, which are used as alignment probes, are easy to bend in fringe fields of accelerator cavities. The estimation of the beam passing orbit is important because only information about the beam positions measured by beam position monitors outside the cavities is available. In this case, the alignment information about the cavities can be obtained by optimizing the parameters of the acceleration components over the beam orbit simulation to consistently represent the position of the beam position monitors measured at every beam sweep. We discuss details of the orbit estimation method, and estimate the mechanical center of the localized modes through experiments performed at the STF accelerator. The mechanical center is determined as x,y=(0.44±0.56mm,−1.95±0.40mm). We also discuss the error and the applicable range of this method.

Hi-Lumi LHC Twin-Aperture Orbit Correctors Magnet System Optimisation

Abstract: The large hadron collider (LHC) upgrade, called high luminosity LHC (HL-LHC) is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin-aperture beam orbit correctors positioned on the approaches to the ATLAS and CMS experiments. This twin-aperture magnet system comprising 16 magnets, approximately 2 m long, with large 105 mm clear aperture coils. Each aperture will independently deliver 5 T·m integral field, between apertures the field vectors are rotated by 90° from each other, individually powered, crosstalk between apertures is controlled to give good field quality independent of aperture powering status. This paper presents the sequence of magnet optimisations performed that determine optimal coil geometry for the canted cosine theta coil design, to achieve good field quality between the individually powered large apertures, quench optimization, integration of the magnet with the adjacent magnetic objects, and radiation hard robust design. Finally the design focuses on low system cost with minimal tooling.

Rigorous mathematical modelling for a Fast Corrector Power Supply in TPS

To enhance the stability of beam orbit, a Fast Orbit Feedback System (FOFB) eliminating undesired disturbances was installed and tested in the 3rd generation synchrotron light source of Taiwan Photon Source (TPS) of National Synchrotron Radiation Research Center (NSRRC). The effectiveness of the FOFB greatly depends on the output performance of Fast Corrector Power Supply (FCPS); therefore, the design and implementation of an accurate FCPS is essential. A rigorous mathematical modelling is very useful to shorten design time and improve design performance of a FCPS. A rigorous mathematical modelling derived by the state-space averaging method for a FCPS in the FOFB of TPS composed of a full-bridge topology is therefore proposed in this paper. The MATLAB/SIMULINK software is used to construct the proposed mathematical modelling and to conduct the simulations of the FCPS. Simulations for the effects of the different resolutions of ADC on the output accuracy of the FCPS are investigated. A FCPS prototype is realized to demonstrate the effectiveness of the proposed rigorous mathematical modelling for the FCPS. Simulation and experimental results show that the proposed mathematical modelling is helpful for selecting the appropriate components to meet the accuracy requirements of a FCPS.

Design and commissioning of the RIKEN cryogenic electrostatic ring (RICE).

A new electrostatic ion storage ring, the RIKEN cryogenic electrostatic ring, has been commissioned with a 15-keV ion beam under cryogenic conditions. The ring was designed with a closed ion beam orbit of about 2.9 m, where the ion beam is guided entirely by electrostatic components. The vacuum chamber of the ring is cooled using a liquid-He-free cooling system to 4.2 K with a temperature difference of 0.4 K at most within all the positions measured by calibrated silicon diode sensors. The first cryogenic operation with a 15-keV Ne+ beam was successfully performed in August 2014. During the measurement, the Ne+ beam was stored under a ring temperature of 4.2 K with a residual-gas lifetime of more than 10 min. This permits an estimation of the residual gas density at a few 104 cm-3, which corresponds to a room-temperature-equivalent pressure of around 1×10-10 Pa. An effect of longitudinal pulse compression at the bunching cavity in the ring was clearly identified by monitoring the pick-up beam detector. The detailed design and mechanical structure of the storage ring, as well as the results from the commissioning run, are reported.

Designing of the low energy beam lines with achromatic condition in the RAON accelerator

The RAON accelerator has been built to create and accelerate stable heavy-ion beams and rare isotope beams. The stable heavy-ion beams are generated by the superconducting electron cyclotron resonance ion source and accelerated by the low energy superconducting linac SCL1. The beams accelerated by the SCL1 are re-accelerated by the high energy superconducting linac SCL2 for the generation of rare isotope beams by using the in-flight fragmentation system or are put to use in the low energy experimental halls, which include the neutron science facility and the KOrea Broad acceptance Recoil spectrometer and Apparatus after having passed through the low energy beam lines which have long deflecting sections. At the end of each beam line in the low energy experimental halls, the beams should meet the targets of the two facilities with the specific requirements satisfied. Namely, if the beam is to be sent safely and accurately to the targets and simultaneously, satisfy the requirements, an achromatic lattice design needs to be applied in each beam line. In this paper, we will present the lattice design of the low energy beam lines and describe the results of the beam dynamics simulations. In addition, the correction of the beam orbit, which is distorted by machine imperfections, will be discussed.

Study of the one-way speed of light anisotropy with particle beams

Concepts of high precision studies of the one-way speed of light anisotropy are discussed. The high energy particle beam allows measurement of a one-way speed of light anisotropy (SOLA) via analysis of the beam momentum variation with sidereal phase without the use of synchronized clocks. High precision beam position monitors could provide accurate monitoring of the beam orbit and determination of the particle beam momentum with relative accuracy on the level of $10^{-10}$, which corresponds to a limit on SOLA of $10^{-18}$ with existing storage rings. A few additional versions of the experiment are also presented.

Compensation for booster leakage field in the Duke storage ring**Supported by National Natural Science Foundation of China (11175180, 11475167) and US DOE (DE-FG02-97ER41033)

The High Intensity Gamma-ray Source (HIGS) at Duke University is an accelerator-driven Compton gamma-ray source, providing high flux gamma-ray beam from 1 MeV to 100 MeV for photo-nuclear physics research. The HIGS facility operates three accelerators, a linac pre-injector (0.16 GeV), a booster injector (0.16—1.2 GeV), and an electron storage ring (0.24—1.2 GeV). Because of the proximity of the booster injector to the storage ring, the magnetic field of the booster dipoles close to the ring can significantly alter the closed orbit in the storage ring being operated in the low energy region. This type of orbit distortion can be a problem for certain precision experiments which demand a high degree of energy consistency of the gamma-ray beam. This energy consistency can be achieved by maintaining consistent aiming of the gamma-ray beam, and therefore a steady electron beam orbit and angle at the Compton collision point. To overcome the booster leakage field problem, we have developed an orbit compensation scheme. This scheme is developed using two fast orbit correctors and implemented as a feedforward which is operated transparently together with the slow orbit feedback system. In this paper, we will describe the development of this leakage field compensation scheme, and report the measurement results, which demonstrate the effectiveness of the scheme.

Fast Corrector Magnets for Fast Orbit Feedback System of Indus-2 Synchrotron

Synchrotron users in Indus-2 require stable photon beams for performing various scientific experiments. At the source points of the photons, typical requirement of the beam position stability is ≤ 10% of the r.m.s size of the electron beam. This stability requirement demands correction of beam orbit disturbances in the range from DC to 100 Hz. The existing slow corrector magnets in Indus-2 are used for correction of very slow disturbances e.g. thermal drift. Therefore a separate set of combined function corrector magnets of high bandwidth were developed for correction of short term perturbations (from low to high frequency up to 100 Hz). These fast corrector magnets have relatively weak kick strengths of ≥ ± 50 μrad at ±15 A DC. The magnetic measurements show no appreciable attenuation in the field strength of these magnets up to 200 Hz. The design, development of the fast corrector magnets and the results achieved by using them in the fast orbit feedback system of Indus-2 will be discussed in this paper.

Smoothing analysis of HLSII storage ring magnets**Supported by National Natural Science Foundation of China (11275192) and the Upgrade Project of Hefei Light Source

Hefei Light Source (HLS) has been upgraded to improve the quality and stability of the synchrotron light, and the new facility is named HLSII. However, a final accurate adjustment is required to smooth the beam orbit after the initial instalment and alignment of the magnets. We implement a reliable smoothing method for the beam orbit of the HLSII storage ring. In addition to greatly smoothing and stabilizing the beam orbit, this method also doubles the work efficiency and significantly reduces the number of magnets adjusted and the range of the adjustments.

Beam dynamics and error study of the medium energy beam transport line in the Korea Heavy-Ion Medical Accelerator

The Korea Heavy Ion Medical Accelerator consists of an injector and a synchrotron for an ion medical accelerator that is the first carbon-ion therapy system in Korea. The medium energy beam transport(MEBT) line connects the interdigital H-mode drift tube linac and the synchrotron. We investigated the beam conditions after the charge stripper by using the LISE++ and the SRIM codes. The beam was stripped from C4+ into C6+ by using the charge stripper. We investigated the performance of a de-buncher in optimizing the energy spread and the beam distribution in z-dW/W (direction of beam progress-beam and energy) phase. We obtained the results of the tracking simulation and the error analysis by using the TRACK code. Possible misalignments and rotations of the magnets were considered in the simulations. States of the beam were examined when errors occurred in the magnets by the applying analytic fringe field model in TRACK code. The condition for the beam orbit was optimized by using correctors and profile monitors to correct the orbit. In this paper, we focus on the beam dynamics and the error studies dedicated to the MEBT beam line and show the optimized beam parameters for the MEBT.

Beam-based calibrations of the BPM offset at C-ADS Injector II**Supported by National Natural Science Foundation of China (91426303, 11525523)

Beam-based BPM offset calibration was carried out for Injector II at the C-ADS demonstration facility at the Institute of Modern Physics (IMP), Chinese Academy of Science (CAS). By using the steering coils integrated in the quadrupoles, the beam orbit can be effectively adjusted and BPM positions recorded at the Medium Energy Beam Transport of the Injector II Linac. The studies were done with a 2 mA, 2.1 MeV proton beam in pulsed mode. During the studies, the “null comparison method” was applied for the calibration. This method is less sensitive to errors compared with the traditional transmission matrix method. In addition, the quadrupole magnet’s center can also be calibrated with this method.

Magnetic Field Stability and Current Ripple of Collector Ring Dipole Magnets

The magnetic field stability of the collector ring dipole magnets has been studied with driving current ripple phenomena. The current ripple and corresponding magnetic field variation can be a cause of the beam orbit instability. We investigate the magnetic field variation due to the current ripple in the frequency range of 10 Hz to 10 kHz. The amplitude of magnetic field variation has the exponential decay with respect to the increasing current ripple frequency. This result explains the effect of the secondary magnetic field in the beam chamber. Although the dipole field variation is reduced, the higher odd-number multipoles by eddy current are not compensated. The multipole profiles depend on the beam chamber shape. We present the field stability simulation results including the secondary field harmonics with the vacuum beam chamber geometry.

Intensity-sensitive and position-resolving cavity for heavy-ion storage rings

A heavy-ion storage ring can be adapted for use as an isochronous mass spectrometer if the ion velocity matches the transition energy of the ring. Due to the variety of stored ion species, the isochronous condition cannot be fulfilled for all the ions. In order to eliminate the measurement uncertainty stemming from the velocity spread, an intensity-sensitive and position-resolving cavity is proposed. In this paper we first briefly discuss the correction method for the anisochronism effect in the measurement with the cavity. Then we introduce a novel design, which is operated in the monopole mode and offset from the central beam orbit to one side. The geometrical parameters were optimized by analytic and numerical means in accordance with the beam dynamics of the future collector ring at FAIR. Afterwards, the electromagnetic properties of scaled prototypes were measured on a test bench. The results were in good agreement with the predictions.

Design Optimization for 10 MeV Cyclotron Magnets Employing Sequential Approximation and Automatic Boundary Shifting Techniques

Use of the systematic process of design optimization was proposed using the sequential approximation technique for the 10 MeV cyclotron magnet, which is a positron emission tomography cyclotron for producing radioactive isotopes. To design cyclotrons with the conventional routine approach, too much time and an iterative process are required, because even a very small change in the magnet shape is directly linked to success or failure, as verified using the beam orbit and energy level. To resolve this sensitive and tricky problem, designers need a systematic numerical approach for developing a new design. Until now, however, related research articles have not been seen in the literature. To build a systematic optimization process for the cyclotron magnet, we adopted the Latin hypercube sampling method, one of the design of experiments, and generated sampling data. On the basis of these data, an approximation model was modeled using the Kriging technique. To find the optimal shape, an iterative searching technique was implemented, which incorporates the approximation model, restricted evolution strategy, and boundary shifting technique. The initial magnet model was obtained from the conventional routine procedure for a cyclotron. To verify our proposed model, the final magnet model was tested with a beam simulation for checking the trajectory of $^{18}\text{F}$ at a level of 10 MeV at the extraction point.

Hybrid Magnet Wiggler for SR Research Program at VEPP-4M

A compact hybrid magnet wiggler is under development for the VEPP-4 SR research program. The wiggler allows increasing the photon flux two orders of magnitude at a beam energy of 4.5 GeV in the spectrum range of 60-100 keV. The magnet consists of conventional coils, which generate a magnetic field, and permanent magnet insertions, which concentrate the flux. This solution increases the field in the beam orbit up to 2.05 T. Here we present the design, magnetic calculations and analysis of the beam dynamics under the hybrid wiggler influence.

Beam dynamics at the main LEBT of RAON accelerator

The high-intensity rare isotope accelerator (RAON) of the Rare Isotope Science Project (RISP) in Daejeon, Korea, has been designed to accelerate multiple-charge-state beams. The ion beams, which are generated by using an electron cyclotron resonance ion source (ECR-IS), will be transported through the main low energy beam transport (LEBT) system to the radio frequency quadrupole (RFQ). While passing the beams through the LEBT, we should keep the transverse beam size and longitudinal emittance small. Furthermore, the matching of required twiss parameter at the RFQ entrance will be performed by using electro-static quadrupoles at the main LEBT matching section which is from the multi-harmonic buncher (MHB) to the entrance of the RFQ. We will briefly review the new aspects of the main LEBT lattice, and the beam matching at the main LEBT matching section will be presented. In addition, the effects of various errors on the beam orbit and the correction of a distorted orbit will be discussed.

Development of Front-end Software for Beam Parameters Measurement for Indus-2 Electron Synchrotron

electron synchrotron with high brilliance requires monitoring of the electron beam parameters continuously. The state of the machine may be identified by measuring the beam parameters like betatron tune, synchrotron tune, beam orbit, instabilities level etc. To measure the machine status for Indus-2, a synchrotron radiation source at RRCAT, Indore, India, an integrated measurement scheme has been developed. This work involves the design of six different measurement modules, interfacing the hardware to initialize the measurement and acquisition of the data from hardware into software. The software acquires the beam position and beam intensity data in time and frequency domains. Signal processing techniques like point invariant concatenation of acquired data, low pass filtering, curve fitting, multi-peak detection etc. are applied on the acquired data to measure the beam parameters simultaneously. With the development of this software, more than 800 parameters are monitored online and logged.