Top-up Operation Research Articles

Rectifying unexpected injection issues due to an elliptically polarizing undulator

Top-up operation requires high efficiency injection with insertion devices at small gaps. We present a case study of one elliptically polarizing undulator at the Canadian Light Source that unexpectedly began having a detrimental impact on injection efficiency after operating for many years without issue. By performing beam-based measurements in the storage ring and magnetic measurements in our magnetic measurement laboratory, we built a model that provided an explanation and a remedy. An unrelated change in the vertical limiting physical aperture coupled to an octupole resonance caused a loss of dynamic aperture that explained the decreased injection efficiency. The remedy was to change the on-axis tunes of the storage ring, avoiding the resonance. We hope this detailed and thorough case study may help other laboratories to maintain high injection efficiency while requiring a minimum of restrictions on insertion device operating ranges.

10 years of Aichi Synchrotron Radiation Center Impact on industrial and academic research and developments

The synchrotron light source with the electron energy of 1.2 GeV is operated by Aichi Synchrotron Radiation Centre (AichiSR) in Aichi prefecture, Japan. The light has been offered to industrial and academic users since March 2013 in the top-up operation mode to maintain a constant current of 300 mA. This facility was established by Aichi prefecture, universities, and industries with support of government. Major purpose of the light source is to support research and development activities of industries and academia mostly in the area, which is the heart land of manufacturing of Japan. This paper describes evolution of the beamlines and recent research results and their impact to the society.

Development of a real-time cavity-based injection efficiency monitor system at SSRF

Injection efficiency is a critical parameter for synchrotron radiation facilities, especially those operating in top-up mode. The Shanghai Synchrotron Radiation Facility (SSRF) started top-up operation in 2012 committed to providing users with higher-quality light sources. During the top-up operation, a regular injection from the booster to the storage ring is required. A low-efficiency injection system will massively increase the radiation dose and seriously threaten the health of users. To evaluate the performance of the injection system, a real-time injection efficiency measurement system with high-resolution and high reliability is indispensable. Instead of using an integrating current transformer (ICT) that requires extremely careful shielding and grounding, a new system uses a novel dual-cavity monitor that can generate a high signal-to-noise ratio (SNR) and narrowband signal to detect bunch charges. It aims to reduce the influence of electromagnetic interference on the system and improve the reliability and resolution of the system. This paper describes the establishment of a cavity-based injection efficiency measurement system and focuses on bunch charge calibration and tests of the system resolution and injection efficiency. The test results show that the system resolution is 0.34% and the average injection efficiency is close to 90% at regular top-up operation.

Impacto ambiental y económico de las fugas de SF6 en las subestaciones de ENEL-CODENSA

This paper analyzes data provided by ENEL-CODENSA with information about substation assets, including sulphur hexafluoride (SF{\displaystyle _{6}}) containing equipment and its top-up operations over the last ten years. The information has been used to estimate the total SF{\displaystyle _{6}} mass in the current fleet and to determine historical emissions. The environmental and economic impacts are evaluated using the obtained results on simple models. Recommendations are made in order to mitigate the estimated impacts.

Low-Emittance Lattice Design with Reverse Bend and Longitudinal Gradient Bend for the PLS-III

With novel schemes using reverse bends and longitudinal gradient bends, the 4th generation low-emittance storage ring was designed for the Pohange Light Source-III: the upgrade of PLSII. A unit cell with one homogeneous bending magnet, designed by using a genetic algorithm, is commonly used in the design of multi-bend achromatic lattices to realize an extremely low natural emittance (100 pm) for a 3-GeV and 280-m ring. In order to obtain enough dynamic aperture for accumulating off-axis injected beam from the existing PLS-II linear accelerator, we optimized the nonlinear dynamics with a genetic algorithm after a tune scan along the dynamic aperture. As a result, enough dynamic aperture for off-axis injection and long lifetime for stable top-up operation were achieved.

Study on beam-induced heating in injection section of Hefei Light Source

Ceramic chambers distributed with metal striplines on the inner surface are installed in the injection section at Hefei Light Source (HLS). Heating on the ceramics chambers has been observed during machine operation. An air compressor is used to cool these chambers due to concerns of overheating during top-up operation mode. To understand the sources of the heating, a series of experiments are performed with various beam currents and bunch filling patterns. The study shows that the heating is mainly caused by the narrow-band impedances of the ceramic chambers and their adjacent vacuum components.

Damping of injection perturbations at the European Synchrotron Radiation Facility

Top-up operation was recently introduced at the European Synchrotron Radiation Facility (ESRF) to provide constant beam current to the beam line users. This mode of operation involves frequent injections that can be the source of significant perturbations on the stored beam. Beam lines running experiments with a timescale longer than the injection period may be impacted by such perturbations. The ESRF storage ring injection systems and layout were not designed to allow for transparent injection, i.e., without visible perturbations on the stored beam. These perturbations are driven directly or indirectly by rapidly pulsing elements, the effect of which cannot be corrected by standard methods such as feedback loops. Major efforts were put into the development of mitigation measures at the ESRF. Depending on the source of perturbation different approaches were used. They all contribute to the achievement of transparent injections and unperturbed continuous data acquisition for the beam lines. After a review of the ESRF injection systems, these developments and the resulting reduction of the injection perturbations are described in this paper.

Energy feedback system for the PLS-II linac

The upgraded Pohang-Light-Source (PLS-II) was opened to the public in 2012. Among many improvements of the PLS-II, a top-up operation was one of the highlights of them, and the stability of the electron beam was improved significantly. For the top-up operation, a stable injection from the linac to the storage ring was critically important, so that an energy feedback system was introduced to reduce the energy jitter of the linac electron beam. The result of the feedback system was successful and the measured energy jitter was less than ±0.1% (rms). In this work, the details of the energy feedback system are presented. It includes the setup for the energy feedback system, measurement results in the optimization process, and the future work for a better performance.

Top-up injection schemes for future circular lepton collider

Top-up injection is an essential ingredient for the future circular lepton collider (FCC-ee) to maximize the integrated luminosity and it determines the design performance. In ttbar operation mode, with a beam energy of 175 GeV, the design lifetime of ∼1 h is the shortest of the four anticipated operational modes, and the beam lifetime may be even shorter in actual operation. A highly robust top-up injection scheme is consequently imperative. Various top-up methods are investigated and a number of suitable schemes are considered in developing alternative designs for the injection straight section of the collider ring. For the first time, we consider multipole-kicker off-energy injection, for minimizing detector background in top-up operation, and the use of a thin wire septum in a lepton storage ring, for maximizing the luminosity.

Active and passive compensation of APPLE II-introduced multipole errors through beam-based measurement

The effect of an APPLE II-type elliptically polarized undulator (EPU) on the beam dynamics were investigated using active and passive methods. To reduce the tune shift and improve the injection efficiency, dynamic multipole errors were compensated using L-shaped iron shims, which resulted in stable top-up operation for a minimum gap. The skew quadrupole error was compensated using a multipole corrector, which was located downstream of the EPU for minimizing betatron coupling, and it ensured the enhancement of the synchrotron radiation brightness. The investigation methods, a numerical simulation algorithm, a multipole error correction method, and the beam-based measurement results are discussed.

The crystallography stations at the Alba synchrotron

Alba is a 3rd-generation 3 GeV synchrotron facility with an emittance of 4.6nm·rad which has been operational since 2011 and has recently started top-up operation. Photons in a broad energy range of 0.08-80 keV are served to seven beamlines dedicated to a large variety of scientific fields. The portfolio includes two beamlines, XALOC and MSPD, fully dedicated to X-ray crystallography. BL13-XALOC is currently the only macromolecular crystallography beamline. The end-station includes a high-accuracy single-axis diffractometer with a removable minikappa stage, a sample-mounting robot and a large-area, photon-counting detector. The beamline optics, fed by an in-vacuum undulator, deliver a tunable photon beam between 5.5 and 22 keV. The beam size at the sample position can be adjusted by defocusing the mirrors in a range of 50-300μm in the horizontal direction and 5.5-300μm in the vertical direction. Beamline BL04-MSPD, which is fed by a superconducting wiggler, has two in-line end-stations. The first station is devoted to high-pressure/microdiffraction. It offers a \( 15\times 15\) μm beam in the range 20-50 keV, particularly suited for powder diffraction studies requiring a very small beam, e.g. mapping of cultural heritage samples and high-pressures studies. The second station is dedicated to high-resolution/high-throughput powder diffraction. It covers the 8-50 keV range and includes a heavy-duty 3-circle diffractometer equipped with a 13-channel multianalyzer detector with high-angular resolution ( \( \Delta 2\theta=0.004^{\circ}\) FWHM) and a high-throughput, position-sensitive detector spanning \( 40^{\circ}\) in 2\( \theta\) range allowing millisecond data acquisitions.

Present status of the electron beam diagnostics system of the PLS-II linac

The PLS-II, the upgraded PLS (Pohang Light Source), has been providing users with photon beams in the top-up mode since March 2013. The requirements for the PLS-II linac to achieve the top-up injection are very demanding because it is a full energy injector with a very limited energy margin. One of the requirements is to ensure high injection efficiency in order to minimize the beam loss at the storage ring injection point and the experimental hall during injection because loss leads to a high radiation level in the experimental hall. The energy stability and energy spread of the accelerated electron beam are fundamental parameters to monitor and manage for high injection efficiency. An energy feedback system consisting of a stripline-type beam position monitor and the last klystron was implemented. To diagnose the injected beam’s energy and energy spread in real time during top-up mode injection, we installed an optical transition radiation (OTR) monitor system upstream of the beam transport line (BTL) after the first bending magnet. The energy and the energy spread ranges can be controlled with a horizontal slit installed after the OTR monitor. The vertical beam size of the accelerated beam must be decreased for efficient injection because the electron beam is injected into the storage ring with many in-vacuum undulators of small gaps. For this purpose, two vertical slits were installed in the BTL region. We will describe mainly those instruments closely related to top-up operation, though other beam diagnostic instruments have been used since PLS.

Monte Carlo simulation study to calculate radiation dose under beam-loss scenarios in Top-up operation mode for HXMA beamline at Canadian Light Source

This study was conducted to analyze the radiological impact in the experimental area of the Hard X-Ray beamline at Canadian Light Source under beam loss scenario during Top-up injection. The radiation doses were calculated using Monte Carlo code: FLUKA. The physical size, location, and material of the beamline components were adopted from the technical drawings and were incorporated in the FLUKA model. Three (03) beam loss scenarios were simulated: (i) Beam was miss-steered in the storage ring (ii) Beam hit misaligned components inside the ring and (iii) Beam was lost inside the primary optical enclosure (POE). Total ambient dose was calculated at several observation points for each scenario considering the injected beam as the primary source. The results and impacts were discussed.

Studies and optimization of Pohang Light Source-II superconducting radio frequency system at stable top-up operation with beam current of 400 mA

After three years of upgrading work, the Pohang Light Source-II (PLS-II) is now successfully operating. The final quantitative goal of PLS-II is a top-up user-service operation with beam current of 400 mA to be completed by the end of 2014. During the beam store test up to 400 mA in the storage ring (SR), it was observed that the vacuum pressure around the radio frequency (RF) window of the superconducting cavity rapidly increases over the interlock level limiting the availability of the maximum beam current storing. Although available beam current is enhanced by setting a higher RF accelerating voltage, it is better to keep the RF accelerating voltage as low as possible in the long time top-up operation. We investigated the cause of the window vacuum pressure increment by studying the changes in the electric field distribution at the superconducting cavity and waveguide according to the beam current. In our simulation, an equivalent physical modeling was developed using a finite-difference time-domain code. The simulation revealed that the electric field amplitude at the RF window is exponentially increased as the beam current increases, thus this high electric field amplitude causes a RF breakdown at the RF window, which comes with the rapid increase of window vacuum pressure. The RF accelerating voltage of PLS-II RF system was set to 4.95 MV, which was estimated using the maximum available beam current that works as a function of RF voltage, and the top-up operation test with the beam current of 400 mA was successfully carried out.

Energy-efficient operation of a booster RF system for Taiwan light source operated in top-up mode

Contemporary light sources operate in a top-up mode to maintain their photon intensity quasi-constant so as to improve significantly the thermal stability of the photon beam and to maximize ultimately the average photon flux at a designed maximum operational beam current. Operating in a top-up mode requires frequent beam injection from the synchrotron booster to the storage ring of the light source, but the injection intervals occupy only a tiny portion of the operational time of the integrated machine. To maintain a high operational reliability, the booster RF system practically operates necessarily under injection conditions around the clock and consumes full electric power whether during top-up injection or not. How to decrease the power consumption of the booster RF system during its stand-by time but not to sacrifice the reliability and availability of the RF system is obviously of fundamental interest for routine operation of the light source in a top-up mode. Here, an energy-efficient operation of a booster RF system adaptive to top-up operation of a light source is proposed that has been developed, realized and integrated into the booster RF system of the Taiwan Light Source (TLS), and routinely operated since the end of year 2008. The klystron cathode current and RF gap voltage of the booster׳s accelerating RF cavity are both periodically modulated to adapt the injection rhythm during top-up operation, which results in decreased consumption of electric power of the booster RF system by more than 78%. The impact on the reliability and availability of the booster RF system has been carefully monitored during the past five operational years, delivering more than 5000h scheduled user beam time per year. The booster RF system retains its excellent reliability and availability as previously. Neither a decrease of the service time nor an induced reliability issue from the klystron or any high-power high-voltage component of the transmitter has been experienced. We conclude that our energy-efficient operation of the booster RF system is harmless for the operation of the light source but decreases significantly the consumption of electric power. Here we report our approach and operational results in detail.

The Sirius project.

The lattice design and beam dynamics optimization for Sirius, a new low-emittance synchrotron light source presently under construction at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, Brazil, is presented. The electron storage ring is based on a five-bend achromat (5BA) design achieving a bare lattice emittance of 0.28 nm rad for a 3 GeV beam. The circumference of 518 m contains 20 achromatic straight sections of alternating 7 m and 6 m in length. An innovative approach is adopted to enhance the performance of the storage ring dipoles by combining low-field (0.58 T) magnets for the main beam deflection with a very short 2 T permanent-magnet superbend sandwiched in the center dipole. This superbend creates 12 keV critical photon energy dipole sources with modest total energy loss from dipoles. In addition it also creates a longitudinal dipole field gradient that reduces the emittance by about 10%. The optimized dynamic aperture allows for top-up operation with off-axis injection and the optimized energy acceptance allows for a total beam lifetime of around 11 h at nominal current with a third-harmonic cavity.

Top-up operation at Pohang Light Source-II.

After three years of upgrading work, PLS-II (S. Shin, Commissioning of the PLS-II, JINST, January 2013) is now successfully operating. The top-up operation of the 3 GeV linear accelerator had to be delayed because of some challenges encountered, and PLS-II was run in decay mode at the beginning in March 2012. The main difficulties encountered in the top-up operation of PLS-II are different levels between the linear accelerator and the storage ring, the 14 narrow gap in-vacuum undulators in operation, and the full energy injection by 3 GeV linear accelerator. Large vertical emittance and energy jitter of the linac were the major obstacles that called for careful control of injected beam to reduce beam loss in the storage ring during injection. The following measures were taken to resolve these problems: (1) The high resolution Libera BPM (see http://www.i-tech.si) was implemented to measure the beam trajectory and energy. (2) Three slit systems were installed to filter the beam edge. (3) De-Qing circuit was applied to the modulator system to improve the energy stability of injected beam. As a result, the radiation by beam loss during injection is reduced drastically, and the top-up mode has been successfully operating since 19th March 2013. In this paper, we describe the experimental results of the PLS-II top-up operation and the improvement plan.

Impact of the Lambertson septum magnet on the photon beam flux in the PLS-II beam line experiment

The Pohang Light Source II (PLS-II) has been operating successfully since the completion on March 21, 2012 of the PLS-II project to upgrade the PLS. Because top-up injection is becoming a general operation mode in the 3 rd generation light source, top-up operation using full energy injection from the 3 GeV linear accelerator is one of the main goals of the PLS-II. In the PLS-II topup operation, small beam loss of the injected beam in the storage ring and stored beam oscillation during injection are two main issues to be solved. The top-up mode has been successfully operated since March 19, 2013, because the beam loss of injected beam in the storage ring was reduced. As a result, the flux stability, excepting injection time, in the beam line has been dramatically improved. During injection, a systematic dip pattern occurs in the photon beam flux due to oscillation of the vertical stored beam. The main source of the oscillation of the vertical stored beam is the leakage field of Lambertson septum magnet. In this paper, the impact of lambertson septum magnet on the stored beam oscillation will be described and an improvement plan will be presented.

Tracking study of transient behaviors at beam injection of the PLS-II ring

The PLS-II project to upgrade the Pohang Light Source (PLS) has been completed. In PLS-II, top-up operation with full energy injection from a 3 GeV linear accelerator is planned. Therefore, detailed studies of transient behaviors at beam injection are required. This paper present the results of a simulation study of PLS-II beam dynamics at beam injection. Particle tracking software, ELEGANT, was used to study several useful and interesting effects at beam injection. The timing and the energy of the injected beam and the error allowance tolerance of the kickers were investigated. Based on simulation results, the commissioning was successfully carried out, and the results will be described in this paper.

Lattice design and beam dynamics studies for the PLS-II

Pohang Light Source (PLS) [1] had operated for 14 year successfully. To meet the request of the increasing user community, the PLS-II that is the upgrade project of PLS have been carried out. Main design goals of the PLS-II lattice are to increase beam energy to 3 GeV, to increase number of insertion devices by factor of two (20 IDs), to increase beam current to 400 mA and to reduce beam emittance below 10 nm with existing PLS tunnel and injection system. Following the desired design criteria, DBA lattice had been chosen such that the full storage ring includes 12 long straight sections and 12 short straight sections for installation of insertion devices with keeping beam emittance as small as possible. Through the six months of commissioning in the later half of 2011 and user operation in full period of 2012, we have successfully operated 14 insertion devices operation and top-up operation with 200 mA beam current and 5.8 nm beam emittance. It is especially important that good understanding of the machine operation and limitations can be achieved by comparison of experimental and simulation data during realizing final PLS-II goal and stable operation. Therefore, this paper describes the results of lattice design and beam dynamics studies for the PLS-II [2,3].