Beam Loss Monitor Research Articles

Estimation for the intensity of beam loss by the optical fiber based Cherenkov beam loss monitor at SACLA

From the issues of radiation safety and radiation damage of accelerator equipments, it is useful to detect the beam loss immediately at high-energy and high intensity particle accelerator facilities. In the undulator section of Spring-8 Angstrom Compact free electron LAser (SACLA) [1], beam loss monitors have been installed in order to control beam losses and to prevent demagnetization of permanent magnets due to electron hitting [2]. Since the commissioning phase of SACLA, this monitor has been successfully working. This beam loss monitor consists of a quartz fiber with 400 μm core diameter and a photomultiplier tube (PMT) which is connected with the upstream end of the fiber. The Cherenkov radiation which is produced in the fiber due to the passing of secondary electrons and positrons (Cherenkov emitters) is detected by the photomultiplier tube. With the detection time of the monitor signals, the position of the beam loss point can be measured. In addition, the use of two monitors with different gains allows measuring intensity of the beam loss over the wide dynamic range. While it is expected that the waveform of the monitor signal corresponds to the spatial distribution of the electron flux or absorbed dose due to the beam loss, if this monitor is used for the beam loss control, it is necessary to calibrate the magnitude of the monitor signal to a value such as the number of electrons or the absorbed dose in order to set an appropriate threshold level. In this study, the electron beam loss was measured by the beam loss monitor and thermo luminescent dosimeters (TLD), and the correlation among the signal of the beam loss monitor, the absorbed dose and electron flux was investigated.

BEPCⅡ储存环逐束团丢束监测系统及应用

BEPCⅡ储存环逐束团丢束监测系统及应用

Estimation of the radiation field distribution induced by beam loss at the 100-MeV proton linear accelerator

The Proton Engineering Frontier Project has been constructing a 100-MeV Proton Linear accelerator for completion in 2013 and the accelerator design has been carried out with the objective of limiting beam losses to less than 1 W/m during normal operation. If accidental beam loss is to be prevented a beam loss monitor has to be installed along to the linear accelerator. Thus, to determine the dynamic ranges and the installation intervals of the beam loss monitors, we calculated the radiation field distribution by using the Monte Carlo Method not only during continuous beam loss for normal operation but also dose during accidental beam loss. The calculation results show that the intensity of neutron dose was higher than that of the gamma. The lateral distribution of neutrons was wider than that of photons.

Longitudinal beam halo measurement with an RF chopper system

It is of practical importance in a high intensity linac to measure the longitudinal beam tail width with sufficient sensitivity to a tenuous halo. In this paper, we propose a newly devised method of diagnosing the longitudinal beam tail width utilizing an RF chopper system and a downstream beam loss monitor. We have conducted a demonstration experiment at a linac to successfully show the feasibility of the measurement method. The beam loss monitor has the sensitivity to detect the fractional beam loss in the order of 10−7, which enables us to detect the width of the corresponding highly tenuous beam tail. We can also deduce the information on the longitudinal beam profile by extending the method. Although saturation calibration is required for a quantitative analysis, we have experimentally confirmed that the measurement is sensitive to provide a qualitative picture of the longitudinal beam profile.

Radiation damage in the diamond based beam condition monitors of the CMS experiment at the Large Hadron Collider (LHC) at CERN

The Beam Condition Monitor (BCM) of the CMS detector at the LHC is a protection device similar to the LHC Beam Loss Monitor system. While the electronics used is the same, poly-crystalline Chemical Vapor Deposition (pCVD) diamonds are used instead of ionization chambers as the BCM sensor material. The main purpose of the system is the protection of the silicon Pixel and Strip tracking detectors by inducing a beam dump, if the beam losses are too high in the CMS detector. By comparing the detector current with the instantaneous luminosity, the BCM detector efficiency can be monitored. The number of radiation-induced defects in the diamond, reduces the charge collection distance, and hence lowers the signal. The number of these induced defects can be simulated using the FLUKA Monte Carlo simulation. The cross-section for creating defects increases with decreasing energies of the impinging particles. This explains, why diamond sensors mounted close to heavy calorimeters experience more radiation damage, because of the high number of low energy neutrons in these regions. The signal decrease was stronger than expected from the number of simulated defects. Here polarization from trapped charge carriers in the defects is a likely candidate for explaining the difference, as suggested by Transient Current Technique (TCT) measurements. A single-crystalline (sCVD) diamond sensor shows a faster relative signal decrease than a pCVD sensor mounted at the same location. This is expected, since the relative increase in the number of defects is larger in sCVD than in pCVD sensors.

Recent results of CERN RD39 collaboration on development of radiation hard Si detectors operated at low to cryogenic temperatures

Recent results of CERN RD39 collaboration on the development of radiation hard Si detectors operated at low to cryogenic temperatures will be presented in this paper. It has been found, in comparisons of results of simulation and charge collection data of pad and strip detectors, the charge-injected-diode (CID) operation mode of Si detectors reduces the free carrier trapping, resulting in a much higher charge collection at the SLHC fluence than that in a standard Si detector. The reduction in free carrier trapping by almost a factor of 3 is due to the fact that the CID mode pre-fills the traps, making them neutral and not active in trapping of particle-induced free carriers (signal). It has been found that, electron traps can be pre-filled by injection of electrons from the n+ contact. The CID mode of detector operation can be achieved by a modestly low temperature of ≤−40°C and a operation bias of <600V. Results of one CID detector application as LHC beam-loss-monitor (BLM) will be presented. Non-irradiated Si detectors has been shown, with tests by laser using our cryogenic transient-current-technique (TCT), to work quite well at LHe temperature (4K), which are very stable with no polarization and good charge collection efficiency.

Short and long term ionizing radiation effects on charge-coupled devices in radiation environment of high-intensity heavy ion accelerators

Radiation effects on semiconductor devices is a topical issue for high-intensity accelerator projects. In particular it concerns Charge-Coupled Device (CCD) cameras, which are widely used for beam profile monitoring and surveillance in high radiation environment. One should have a clear idea of short and long term radiation effects on such devices. To study these effects, a CCD camera was placed in positions less than half meter away from beam loss point. Primary heavy ion beam of 0.95GeV/n Uranium was dumped into a thick aluminium target creating high fluences of secondary particles (e.g., gammas, neutrons, protons). Effects of these particles on CCD camera were scored with LabView based acquisition software. Monte Carlo calculations with FLUKA code were performed to obtain fluence distributions for different particles and make relevant comparisons. Long term total ionising dose effects are represented by dark current increase, which was scored throughout experiment. Instant radiation effects are represented by creation of charge in CCD cells by ionising particles. Relation of this charge to beam intensity was obtained for different camera positions and fluences within 5 orders of magnitude ranges. With high intensities this charge is so high that it may dramatically influence data obtained from CCD camera used in high radiation environment. The linearity of described above relation confirms linear response of CCD to ionizing radiation. It gives an opportunity to find a new application to CCD cameras as beam loss monitors (BLM).

Improved design and construction of an ionization chamber for the CSNS beam loss monitor (BLM)

Based on the first ionization chamber (IC) prototype, the structure, working gas component and electrode material of the IC are improved. The test of the improved IC shows that the plateau length is about 2000 V, the plateau slope is less than 0.2%/100 V, the sensitivity is 19.6 pA/rad·h−1, the up-limitation of the linearity can be up to 3.6 × 105 rad/h, and the applied voltage can be operated to 3500 V. The test results show that the performance of the improved IC meets the requirements of the beam loss monitor.

First calibration of a Cherenkov beam loss sensor at ALICE using SiPM

The need for real-time monitoring of beam losses, including evaluation of their intensity and localization of their exact position, together with the possibility to overcome the limitations due to the reduced space for the diagnostics, makes exploitation of the Cherenkov effect in optical fibres, one of the most suitable candidates for beam loss monitoring.In this article, we report on the first tests of an optical fibre beam loss monitor based on large numerical aperture pure silica fibres and silicon photomultipliers. The tests were carried out at the ALICE accelerator research and development facility, Daresbury Laboratories, UK.In contrast to the results already published where the fibres are longitudinally placed with respect to the accelerator beam path and the losses are multidirectional charged particle showers, for the first time a dedicated set-up with an incident accelerator beam impinging directly on the optical fibre was used for optimizing the collection efficiency of the Cherenkov effect as a function of the incident angle by changing the fibre direction. For this purpose large core fibres were used together with the latest generation silicon detector instead of the standard photomultiplier tubes commonly used for Cherenkov beam loss monitoring.The experiments described in this contribution aim to demonstrate the suitability of the optical fibre sensor for loss monitoring, to optimize the Collection Efficiency (CE) of the Cherenkov photons inside the fibre as a function of the particle incident angle, to calibrate the sensor and calculate its sensitivity, and to understand the limits of temporal resolution of losses from different bunches in the accelerator.

Design, development, and operation of a fiber-based Cherenkov beam loss monitor at the SPring-8 Angstrom Compact Free Electron Laser

A fiber-based Cherenkov beam loss monitor (CBLM) consisting of large core (400μm), long (≥150m) multimode fibers, has been developed as an online long-range detection tool with high sensitivity and good position resolution for the 8GeV SPring-8 Angstrom Compact Free Electron Laser: primarily designed for radiation safety in order to limit the dose outside the shielding of the machine, this monitor also serves as an early warning tool to avoid radiation damages done by lost electrons to the undulator magnets. This paper presents the approach chosen to insure that the required sensitivity (≤1pC) could be obtained over more than 100m. A beam-based approach was used to characterize (attenuation and signal strength) different fibers (diameter, index profile, and numerical aperture) and to select the most appropriate one. The response of the detector has also been studied numerically for different geometries (vacuum pipe and in-vacuum type undulators), beam energies, and beam loss scenarios, to determine the optimum number of fibers and their position in order to achieve the required detection limit. The results of the first few months of operation show that the SPring-8 CBLM can detect beam losses of less than 0.5pC over the full 150m length of the fiber.

Beam Loss Monitoring for LHC Machine Protection

Abstract The energy stored in the nominal LHC beams is two times 362 MJ, 100 times the energy of the Tevatron. As little as 1 mJ/cm 3 deposited energy quenches a magnet at 7 TeV and 1 J/cm 3 causes magnet damage. The beam dumps are the only places to safely dispose of this beam. One of the key systems for machine protection is the beam loss monitoring (BLM) system. About 3600 ionization chambers are installed at likely or critical loss locations around the LHC ring. The losses are integrated in 12 time intervals ranging from 40 μs to 84 s and compared to threshold values defined in 32 energy ranges. A beam abort is requested when potentially dangerous losses are detected or when any of the numerous internal system validation tests fails. In addition, loss data are used for machine set-up and operational verifications. The collimation system for example uses the loss data for set-up and regular performance verification. Commissioning and operational experience of the BLM are presented: The machine protection functionality of the BLM system has been fully reliable; the LHC availability has not been compromised by false beam aborts.

Monitoring system experiments on beam loss at SSRF injector

Experiments on beam loss by using beam loss monitoring (BLM) system were carried out at Shanghai Synchrotron Radiation Facility (SSRF) injector. This system used highly sensitive and current-integrated Si-photodiode detectors and an Ethernet data acquisition (DAQ) system. The experimental results demonstrate that the Si-photodiode detectors are a useful tool that provides dynamic information on beam loss and investigates problems of machine operation. It also shows that the Si-photodiode BLM system is suitable for pulse-radiation of high-energy accelerators.

The upgraded data acquisition system for beam loss monitoring at the Fermilab Tevatron and Main Injector

A VME-based data acquisition system for beam-loss monitors has been developed and is in use in the Tevatron and Main Injector accelerators at the Fermilab complex. The need for enhanced beam-loss protection when the Tevatron is operating in collider-mode was the main driving force for the new design. Prior to the implementation of the present system, the beam-loss monitor system was disabled during collider operation and protection of the Tevatron magnets relied on the quench protection system. The new Beam-Loss Monitor system allows appropriate abort logic and thresholds to be set over the full set of collider operating conditions. The system also records a history of beam-loss data prior to a beam-abort event for post-abort analysis. Installation of the Main Injector system occurred in the fall of 2006 and the Tevatron system in the summer of 2007. Both systems were fully operation by the summer of 2008. In this paper we report on the overall system design, provide a description of its normal operation, and show a number of examples of its use in both the Main Injector and Tevatron.

First experiences with the LHC BLM sanity checks

The reliability concerns have driven the design of the Large Hardron Collider (LHC) Beam Loss Monitoring (BLM) system from the early stage of the studies up to the present commissioning and the latest development of diagnostic tools. To protect the system against non-conformities, new ways of automatic checking have been developed and implemented. These checks are regularly and systematically executed by the LHC operation team to ensure that the system status is after each test "as good as new". The sanity checks are part of this strategy. They are testing the electrical part of the detectors (ionisation chamber or secondary emission detector), their cable connections to the front-end electronics, further connections to the back-end electronics and their ability to request a beam abort. During the installation and in the early commissioning phase, these checks have shown their ability to find also non-conformities caused by unexpected failure event scenarios. In every day operation, a non-conformity discovered by this check inhibits any further injections into the LHC until the check confirms the absence of non-conformities.

BLM System for LINAC and Booster at SSRF

A beam loss monitoring (BLM) system for a linear accelerator (LINAC) and booster has been designed and implemented at the Shanghai Synchrotron Radiation Facility, which is under construction. It is a distributed system, constructed with 54 detectors, 11 data collectors, and a console personal computer. Several experiments were made at the National Synchrotron Radiation Laboratory to verify the performance of this system, and one comparison experiment with thermoluminescent dosimeters for dose rate measurement was also done. From preliminary experiments and commissioning, this BLM system is proving to be functional and a useful tool to study the machine status. Moreover, it is hoped that this can be developed into a new method to measure the radiation dose distribution around the LINAC and booster directly, which would help the shielding calculation for future facilities, although more quantitative experiments are needed.

Commissioning and first operational experience of the ATLAS beam conditions and loss monitors based on pCVD diamond sensors

Primary goal of ATLAS Beam Condition and Beam Loss Monitors based on polycrystalline chemical vapor deposition (pCVD) diamonds is to protect the ATLAS inner silicon detectors from beam incidents. The sensor material was chosen due to its radiation hardness. The first one, ATLAS Beam Condition Monitor (BCM) utilizes fast front end amplifiers and processing electronics capable of handling events in real time and storing data in circular buffer thousand LHC turns deep for post-mortem analysis. There are eight detectors installed, four on each side of interaction point (IP) of ATLAS spectrometer. Due to fast timing and high efficiency for detecting single particles BCM will also provide valuable information on instantaneous luminosity. The second system, ATLAS Beam Loss Monitor (BLM) is adopted after similar system developed in the LHC beam instrumentation group with detectors replaced with the pCVD diamonds, with six of such detectors on each side of the IP. In this contribution the design and commissioning of the above two systems will be presented and results of the first operational experience will be shown as obtained in combined ATLAS framework both with the first LHC beam and commissioning cosmic ray runs.

Design and construction of the first prototype ionization chamber for CSNS and PA beam loss monitor (BLM) system

Design and construction of the first prototype ionization chamber for CSNS and Proton Accelerator (PA) beam loss monitor (BLM) system is reported. The low leakage current (<0.1 pA), good plateau (≈800 V) and linearity range up to 200 Roentgen/h are obtained in the first prototype. All of these give us good experience for further improving the ionization chamber construction.

Beam Loss Monitor System for SSRF Storage Ring

A Beam Loss Monitor (BLM) system has been designed for Shanghai Synchrotron Radiation Facility (SSRF). The BLM system is utilized to detect beam loss around the electron storage ring. It will be helpful to find out the position of vacuum leakage, regulate the machine operation parameters, and study the beam lifetime. This paper will discuss some considerations in the BLM system design, including the detector selection, the beam loss mechanism, the detector location along the ring, and the structure of BLM system.

Simulations and Measurements of Secondary Electron Emission Beam Loss Monitors for LHC

Secondary Emission Monitor (SEM) is a part of the LHC Beam Loss Monitoring system, which is providing the number of particles lost from the primary hadron beam by measuring the radiation field induced by their interaction with matter surrounding the beam pipe. SEM detectors will be used in the high dose rate environments of LHC because of their low sensitivity and excellent linearity. The design of SEM consists of two bias electrodes separating the produced secondary electrons from the Ti signal electrode placed in a vacuum steel cylinder. The response of the chamber was tested with bunched and continuous proton beams and compared with a reference detector and GEANT4 simulations.

FLUKA Monte Carlo simulations and benchmark measurements for the LHC beam loss monitors

One of the crucial elements in terms of machine protection for CERN's Large Hadron Collider (LHC) is its beam loss monitoring (BLM) system. On-line loss measurements must prevent the superconducting magnets from quenching and protect the machine components from damages due to unforeseen critical beam losses. In order to ensure the BLM's design quality, in the final design phase of the LHC detailed FLUKA Monte Carlo simulations were performed for the betatron collimation insertion. In addition, benchmark measurements were carried out with LHC type BLMs installed at the CERN-EU high-energy Reference Field facility (CERF). This paper presents results of FLUKA calculations performed for BLMs installed in the collimation region, compares the results of the CERF measurement with FLUKA simulations and evaluates related uncertainties. This, together with the fact that the CERF source spectra at the respective BLM locations are comparable with those at the LHC, allows assessing the sensitivity of the performed LHC design studies.