Beam Position Monitor Research Articles

Frequency Map Measurements at the TPS

The Taiwan Photon Source (TPS) has been operated now for several years since its successful commissioning in December 2014 and has achieved reliable routine operation up to 500 mA with more than 10 hrs beam lifetime. Dynamic aperture (DA) measurements and associated frequency map analyses (FMA) at the TPS reveal beam dynamics behavior with and without insertion devices. A preliminary study based on turn-by-turn beam position monitor (BPMs) is presented in this paper.

Beam Dynamics And Diagnostics For The High Energy Beam Transport Line of Minerva Project At Sck-Cen

MYRRHA will be a research infrastructure highlighted by the first prototype of a sub-critical nuclear reactor driven by a 600 MeV particle accelerator (ADS). This project aims at exploring the transmutation of long-lived nuclear wastes. A first phase is planned to validate the reliability of a 100 MeV/4 mA Protons LINAC carrying the beam toward an ISOL facility, prefiguring the real MYRRHA demonstrator at 600 MeV [1]. This project is called MINERVA [2]. This paper presents the status of the beam dynamic studies for the high energy beam transport lines at 100 MeV. In agreement with the project requirements, we describe the specificities of these beam lines for which it is needed to implement a fast kicker-septum. This system will separate the beam between two main lines: toward the beam dump or the ISOL facility [3]. We also describe the studies on the Beam Position Monitor (BPM) selected for MYRRHA. Part of this work was support by the MYRTE project of the European Union [4].

A rotation method to calibrate BPM electric offsets

Beam position monitor is a key instrument for machine commissioning. To measure beam position accurately, offline calibrations to acquire the sensitivity and offsets of the BPM are essential prerequisites. A new method to calibrate the BPM electric offset is proposed in this paper. By measuring the location variation of the BPM electric center after rotating the BPM 180 degrees, the BPM offset can be derived. The method is more convenient, universal and accurate than the traditional methods. The method is successfully applied to calibrate the button BPM of Xi’an Proton Application Facility. The repetitive measurement error is 20.8μm.

Beam momentum spread measurement using two beam position monitors at Xi’an Proton Application Facility

Beam momentum spread is a key parameter of the linac injector at the Xi’an Proton Application Facility (XiPAF), China. A momentum spread measurement method using multiple beam position monitors (BPM) was successfully developed recently at Tsinghua University, China. This work is an extension of the method. The original method requires at least three BPMs to perform the measurement, and the BPMs should be installed far from the accelerator exit, causing long measurement space and low BPM signals. The new method only needs two BPMs, and a much shorter measurement space is proposed for the low-current linac in this paper. The new method was successfully tested at XiPAF. The measured rms momentum spread at the Radio Frequency Quadrupole exit is (5.05 ± 0.06) × 10−3, which agrees well with the spectrometer measured value (5.09 ± 0.05) × 10−3.

Optimization of a phase-space beam position and size monitor for low-emittance light sources.

The recently developed vertical phase-space beam position and size monitor (ps-BPM) system has proven to be able to measure the electron-source position, angle, size and divergence simultaneously in the vertical plane at a single location of a beamline. The optimization of the ps-BPM system is performed by ray-tracing simulation to maximize the instrument sensitivity and resolution. The contribution of each element is studied, including the monochromator, the K-edge filter, the detector and the source-to-detector distance. An optimized system is proposed for diffraction-limited storage rings, such as the Advanced Photon Source Upgrade project. The simulation results show that the ps-BPM system can precisely monitor the source position and angle at high speed. Precise measurements of the source size and divergence will require adequate resolution with relatively longer integration time.

Stripline beam position monitor for X-ray free electron laser of Pohang Accelerator Laboratory.

Beam position monitors (BPMs) are important instruments even in the case of an X-ray free-electron laser (XFEL). Pohang Accelerator Laboratory (PAL) finished the construction of an XFEL (PAL-XFEL) in 2015, and new stripline BPMs were installed in PAL-XFEL. New BPMs were designed to have a strong signal and a high resolution. In addition, the impedance matching was considered to reduce a signal reflection. These features of the BPM design were confirmed with a simulation study as well. Fabricated BPMs were tested by using a wire test stand. Two-dimensional position errors and offsets were measured to select best BPMs for PAL-XFEL. Finally, a real beam test was tried to check the BPM performance and a better resolution than the requirement was obtained.

Measurement and analysis of fast transient instabilities

Abstract A novel beam diagnostics technique to detect fast beam transient instabilities and glitches has been developed at National Synchrotron Light Source II (NSLS-II). Vertical spikes of beam size and centroid have been observed occasionally and randomly during high current operations. These spikes are believed to be caused by ion instabilities associated with vacuum activity localized in the ring. With the functionality of gated beam position monitor (BPM), the newly developed technique utilizes turn-by-turn (TBT) data to detect beam centroid glitches. Whenever one turn trajectory deviates from a predefined window, a global control event is generated to trigger an online TBT data acquisition. The data acquisition is synchronized for all BPMs around the ring. In the meantime, the bunch-by-bunch (BxB) data, which is acquired from a single dedicated feedback BPM, has also been collected for analyzing possible coupled bunch instabilities (CBI). In addition to CBI caused mainly by ion bursts, other types of fast transient motions, such as, the top-off residual disturbance and fast orbit disturbance, have been captured with the new tool. The sources of the glitches can be approximately localized with the synchronized TBT data from multiple BPMs around the ring.

Device for source position stabilization and beam parameter monitoring at inverse Compton X-ray sources.

Compact X-ray sources based on inverse Compton scattering provide brilliant and partially coherent X-rays in a laboratory environment. The cross section for inverse Compton scattering is very small, requiring high-power laser systems as well as small laser and electron beam sizes at the interaction point to generate sufficient flux. Therefore, these systems are very sensitive to distortions which change the overlap between the two beams. In order to monitor X-ray source position, size and flux in parallel to experiments, the beam-position monitor proposed here comprises a small knife edge whose image is acquired with an X-ray camera specifically designed to intercept only a very small fraction of the X-ray beam. Based on the source position drift recorded with the monitor, a closed-loop feedback stabilizes the X-ray source position by adjusting the laser beam trajectory. A decrease of long-term source position drifts by more than one order of magnitude is demonstrated with this device. Consequently, such a closed-loop feedback system which enables stabilization of source position drifts and flux of inverse Compton sources in parallel to experiments has a significant impact on the performance of these sources.

Refined betatron tune measurements by mixing beam position data

The measurement of the betatron tunes in a circular accelerator is of paramount importance due to their impact on beam dynamics. The resolution of the these measurements, when using turn by turn (TbT) data from beam position monitors (BPMs), is greatly limited by the available number of turns in the signal. Due to decoherence from finite chromaticity and/or amplitude detuning, the transverse betatron oscillations appear to be damped in the TbT signal. On the other hand, an adequate number of samples is needed, if precise and accurate tune measurements are desired. In this paper, a method is presented that allows for very precise tune measurements within a very small number of turns. The theoretical foundation of this method is presented with results from numerical and tracking simulations but also from experimental TbT data which are recorded at electron and proton circular accelerators.

A method to detect multiple error sources and suppression of periodic beam motion with feedforward correction

A high electron beam stability at the source points of synchrotron radiation is required for the preservation of the low emittance to generate highly brilliant photon beams to users. To improve beam stability, a method based on the response matrix between corrector magnets and beam orbit distortion at beam position monitors (BPMs) is used to detect multiple error sources at a particular frequency or a malfunction of power supplies after a beam trip. Horizontal beam motions with dispersion-like patterns, can be dealt with separately. This method has been used at the Taiwan Photon Source (TPS) to detect different types of error sources and to obtain simultaneously their relative phases and amplitudes. By employing a predefined current waveform obtained from error induced beam position variations in a feedforward correction method, a 3 Hz beam motion caused by booster stray fields could be reduced to one fifth. Furthermore, a 60 Hz beam motion due to stray fields from electric devices powered by the mains could be reduced to one-third compared to applying fast orbit feedback only.

A real-time phase-space beam emittance monitoring system.

An electron beam position and angle monitoring system, ps-BPM, has been shown to be able to measure the electron source position and angle at a single location in a beamline at a synchrotron source. This system uses a monochromator to prepare a photon beam whose energy is at that of the K-edge of an absorber filter. The divergence of the beam from the source gives an energy range that will encompass the K-edge of the filter. A measurement of the centre of the monochromatic beam and the K-edge location through the absorber filter gives the position and angle of the electron source. Here, it is shown that this system is also capable of measuring the source size and divergence at the same time. This capability is validated by measurement as the beam size in the storage ring was changed and by ray-tracing simulations. The system operates by measuring the photon beam spatial distribution as well as a K-edge filtered beam distribution. These additional measurements result in the ability to also determine the electron source size and divergence.

An X-ray gas monitor for free-electron lasers.

A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays. The XGM covers a wide dynamic range from spontaneous undulator radiation to FEL radiation and provides a temporal resolution of better than 200 ns. The XGM consists of two X-ray gas-monitor detectors (XGMDs) and two huge-aperture open electron multipliers (HAMPs). The HAMP enhances the detection efficiency of the XGM for low-intensity radiation down to 105 photons per pulse and for FEL radiation in the hard X-ray spectral range, while the XGMD operates in higher-intensity regimes. The relative standard uncertainty for measurements of the absolute photon pulse energy is well below 10%, and down to 1% for measurements of relative pulse-to-pulse intensity on pulses with more than 1010 photons per pulse. The accuracy of beam-position monitoring in the vertical and horizontal directions is of the order of 10 µm.

Operation of X-ray gas monitors at the European XFEL.

X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. They are used for tuning and maintaining the self-amplified spontaneous emission (SASE) operation and for sorting single-shot experimental data according to the pulse-resolved energy monitor data. The XGMs were developed at DESY based on the specific requirements for the European XFEL. In total, six XGM units are continuously in operation. Here, the main principle and experimental setup of an XGM are summarized, and the locations of the six XGMs at the facility are shown. Pulse energy measurements at 0.134 nm wavelength are presented, exceeding 1 mJ obtained with an absolute measurement uncertainty of 7-10%; correlations between different XGMs are shown, from which a SASE1 beamline transmission of 97% is deduced. Additionally, simultaneous position measurements close to the undulator and at the end of the tunnel are shown, along with the correlation of beam position data simultaneously acquired by an XGM and an imager.

Design and simulation of cavity BPM for BEPCII

In the linac of Beijing Electron Positron Collider II (BEPCII), the resolution of existing BPMs is several hundred microns. But the requirement of transverse position resolution of BPM for future top-up injection needs to be more precise. This paper is mainly concerned about the design and simulation of the cavity beam position monitor (CBPM) for BEPCII linac and free electron laser (FEL). The requirement of beam transverse position resolution for linac is several microns, even a few nanometers for FEL. When the beam bunch goes through the CBPM, it can excite different electromagnetic field modes in resonator. In these modes, TM110 is the most sensitive to beam transverse position offset. The design of CBPM is aim to analyze the relationship between TM110 and beam transverse position by CST Studio and Ansys HFSS. In this research, we design a pair of rectangular slots for position cavity to revise the direction of electromagnetic field. The simulation result of theoretical resolution is able to reach 15 nm@1nC with the operating frequency 2500 MHz. It is obviously that CBPM has more excellent resolution than all of operating BPM in BEPCII. Meanwhile, the research of CBPM improves the application of beam detection technology in BEPCII and accumulates technology for future design of HEPS and FEL. The mechanical design of the prototype is being fabricated.

The CBETA Beam Position Monitor (BPM) System Design and Strategy for Measuring Multiple Simultaneous Beams in the Common Beam Pipe

The CBETA Beam Position Monitor (BPM) System Design and Strategy for Measuring Multiple Simultaneous Beams in the Common Beam Pipe

Design of Beam Position Monitoring System for IPM Low Energy Electron LINAC

Design of Beam Position Monitoring System for IPM Low Energy Electron LINAC

Fast beam–beam collisions monitor for experiments at NICA

Two compact detector systems are proposed to meet the challenges of the fast beam–beam collisions monitoring, event selection and the precise timing determination in proton–proton and nucleus–nucleus collisions at NICA. Beam Position Monitor (BPM) and Fast Beam–Beam Collision (FBBC) monitor are capable to provide the information for each bunch crossing both on the beams location and on the intensity of collisions, as well as on the azimuthal distribution of the particles in the event. The systems are using fast Micro Channel Plate detectors (MCPs). The ultra-high vacuum (UHV) compatibility and low-mass compact design of the BPM and FBBC components allow one to consider their application inside the vacuum beam line of NICA collider. The BPM is based on the effect of the residual gas ionization and provides the high accuracy, fast, bunch-by-bunch measurements of the beam location. The FBBC uses the concept of the fast isochronous timing for the multi-pad readout of short (∼1ns) MCP signals, produced by the particles in the collisions of the beams. Studies of the polarization phenomena in light- and heavy-ion interactions at NICA beams is another goal of research at NICA, and the FBBC is also considered for the local polarimetry at the SPD. In this report we present the results of model simulations and tests of the new prototypes of the fast MCP readout set-ups that are proposed for NICA.

Electrodes for Beam Position Monitors for Fourth Generation Synchrotron Radiation Source

Fourth-generation synchrotron radiation sources demand new quality for the electron beam diagnostic systems. Some of diagnostic system elements have to be accurately developed or redeveloped due to match the new requirements. Beam position monitor (BPM) is a most used detector and tens (even hundreds) BPMs are installed in numerous positions along beam transfer lines, booster and storage rings. Modern approach to this device development assumes such features as short transient time, wide bandwidth, high sampling rate, low noise architecture and reasonable production and maintenance price. As a part of the system, the BPM electrodes should meet all those requirements. In this article we describe a development procedure for high quality capacitive electrodes for the BPM. 3D electromagnetic model allows estimation of the sensitivity, frequency response and tolerance requirements for the manufacturing of hundreds of monitors. Presented here equivalent scheme for the electrodes is a basis for the BPM electronics design.

The Signal Processing Electronics for the Beam Position Monitors of Russian Fourth Generation Synchrotron Radiation Source

The project of fourth-generation Ultimate Source for Synchrotron Radiation (USSR-4) is under development in Russia by leading of National Research Center “Kurchatov institute”. Some of diagnostic systems required for the new facility have to be developed or redeveloped to satisfy the features of the new facility. Hundreds beam position monitors (BPM) are installed along beam transfer lines, booster and storage rings to control the electron beam position. In booster and storage ring the electronics of BPM has to provide both the normally beam circulation and the first beam turn operation. It has to provide beam position monitoring in the bunch-by-bunch option for all operational modes [1]. In this manuscript we discuss the architecture of the BPM electronics, important aspects of the analog front-end, available components and a resulting performance of designed electronic module.

A fast gain calibration algorithm for beam position monitoring

A stable, reliable and well-calibrated beam position monitor (BPM) system is essential for a safe and reproducible operation of accelerators. The BPM system enables the measurement of important machine and beam parameters, such as the Twiss parameters, and helps to avoid damage to accelerator components by high-energy particle beams or radiation. In this paper, we discuss a new BPM calibration scheme tested at the Taiwan Photon Source (TPS). By altering the current in a single horizontal or vertical corrector magnet, we generate an orbit distortion with respect to the nominal reference orbit. The difference orbit is measured by observing the change of the beam position at each BPM pickup location as a function of the corrector current. The analog BPM signals are digitized by analog-to-digital converters (ADC), giving raw, non-calibrated beam position data for each BPM. By comparison of the beam orbit response in terms of raw ADC data from each BPM with the expected beam displacement we can calibrate the beam position monitors. Moreover, because of limited setup time available after a long shutdown, this new procedure acts as a fast, easy way to calibrate the BPM system.