CERN, Geneva
The diamond beam monitor is a solid-state ionization chamber that stands out due to its fast and efficient charge collection and its high radiation tolerance. The diamond technology gives a charge collection time of less than 1 ns and lifetime studies made at CERN with 24 GeV protons showed a decrease in performance of only 50% at 10 MGy, which make this device particularly well adapted to applications in particle accelerators. A poly-crystalline CVD diamond beam monitor has been evaluated as a beam halo loss monitor for the CERN LHC accelerator. Despite the read-out being made through 250 m of cable, the tests showed a good signal-to-noise ratio of 6.8, an excellent double-pulse resolution of less than 5 ns and a high dynamic range basically unlimited except by the electronics. A single-crystalline CVD diamond beam monitor was built and tested in cooperation with Bergoz Instrumentation for ISOLDE at CERN for the HIE-REX upgrade. This device was used to measure the beam intensity for particle counting and for measuring the beam energy spectrum. An energy resolution of 0.6% and a time resolution of 39 ps were measured for a carbon ion energy of 22.8 MeV.
DESY, Hamburg
PETRA III is a high brilliant synchrotron light-source operating at 6GeV. The commissioning of the machine began in April 2009 *. In the first months of operation the Machine Protection System (MPS) ran on basic requirements to protect absorbers and vacuum chambers in the damping wiggler section and the undulator section against synchrotron light. Therefore several alarms distributed along the machine are identified and within 100us a dump command is created. The beam is dumped within 300us by switching of the rf system **. Prior the first user runs different improvements increasing the reliability and availability are planned and partly implemented in the MPS. This paper presents first commissioning results of the system and gives an overview of these new implementations as well as a more detailed discussion of some alarm conditions and the dump procedure. Additionally some key aspects of the Temperature Interlock as one major alarm-deliverer are described.
ANL, Argonne
For reliable radiation dosimetry of undulator magnets, a beam loss monitor (BLM) covering a large solid angle from the point of beam losses is highly desirable. A BLM that uses a Cherenkov radiator plate wrapping around the beam pipe is utilized in the Linac Coherent Light Source (LCLS) undulator systems, and a similar BLM geometry is currently being tested for the Advanced Photon Source (APS) undulators. We report on measurements made with large solid-angle BLMs recently installed in the APS storage ring (SR) and the booster-to-SR transfer line (BTS) to assess the following design and performance characteristics: (1) relative sensitivity of the Cherenkov detector as a function of the transverse position of electron entry into the quartz radiator; (2) signal intensity as a function of the detector distance from the nominal beam loss location at the undulator vacuum chamber entrance; and (3) the effect of incorporating different tungsten/lead enhancers upstream of the radiator. The measured data will be compared with numerical simulation of the beam loss processes.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
The introduction of Silicon Photomultipliers (SiPMs) as single photon sensitive detectors represents a promising alternative to traditional photomultiplier tubes. This is especially true in applications in which it is compulsory to attain magnetic field insensitivity, low photon flux detection, quantum efficiency in the blue region that is comparable to standard photomultipliers, high timing resolution, dimensions comparable to the dimensions of an optical fiber diameters, and low costs. The structure of the SiPM is based on an array of independent avalanche photodiodes (APDs) working in Geiger-mode at a low bias voltage with a high gain. The output signal is proportional to the number of pixels "fired" by impacting photons. The detection efficiency for state-of-the-art devices is in the order of 20% at 500 nm. In this contribution, the measured dark count rates of different SiPMs are compared and the influence of this noise on the real signal is presented. These results are then used to correct the photon count and determine the optimized working parameters for a future beam loss monitor at CTF3/CLIC.
GSI, Darmstadt
To avoid beam losses of intense beams stored at the GSI heavy ion synchrotron SIS-18 a precise tune measurement during a whole acceleration cycle is required. This contribution presents a sensitive method of tune determination using data of Beam Position Monitor (BPM) measured in bunch-by-bunch manner. The signals induced in the BPM electrodes were digitized by 125 MS/s and integrated for each individual bunch. The tune was determined by Fourier transformation of the position data for typically 512 subsequent turns. Coherent betatron oscillations were excited with bandwidth-limited white noise. The presented method allows for tune measurements with satisfactory signal-to-noise ratio already at relatively low beam excitation i.e. without a significant increase of transverse beam emittance. In parallel the evolution of transverse beam emittance was monitored by means of Ionization Profile Monitor. The system for online tune measurement is an integral part of the new digital BPM System, presently under commissioning.
SLAC, Menlo Park, California
The LCLS Undulator Beam Loss Monitor System is required to detect any loss radiation seen by the FEL undulators. The undulator segments consist of permanent magnets which are very sensitive to radiation damage. The operational goal is to keep demagnetization below 0.01% over the life of the LCLS. The BLM system is designed to help achieve this goal by detecting any loss radiation and indicating a fault condition if the radiation level exceeds a certain threshold. Upon reception of this fault signal, the LCLS Machine Protection System takes appropriate action by either halting or rate limiting the beam. The BLM detector consists of a PMT coupled to a Cherenkov radiator located near the upstream end of each undulator segment. There are 33 BLMs in the system, one per segment. The detectors are read out by a dedicated system that is integrated directly into the LCLS MPS. The BLM readout system provides monitoring of radiation levels, computation of integrated doses, detection of radiation excursions beyond set thresholds, fault reporting and control of BLM system functions. This paper describes the design, construction and operational performance of the BLM readout system.
CERN, Geneva
The LHC Beam Loss Monitoring (BLM) system is one of the most complex instrumentation systems deployed in the LHC. In addition to protecting the collider, the system also needs to provide a means of diagnosing machine faults and deliver feedback of losses to the control room as well as to several systems for their setup and analysis. It has to transmit and process signals from over 4,000 monitors, and has nearly 3 million configurable parameters. In a system of such complexity, firmware reliability is a critical issue. The integrity of the signal chain of the LHC BLM system and its ability to correctly detect unwanted scenarios and thus provide the required protection level must be ensured. In order to analyze the reliability and functionality, a test bench has been developed that emulates different types of loss signals and monitors the performance and response of the FPGA-based data analysis firmware. This paper will report on the numerous tests that have been performed and on how the results are used to quantify the reliability of the system.
ORNL, Oak Ridge, Tennessee
Recent improvements to the next generation beam loss monitor analog front end used on the SNS accelerator have proved successful. Particularly in the removal of incident EMI noise sources and the reduction of RF cavity X-Rays and non beam related "loss" signals. The prototype system under development allows the users to view true beam loss integrated as part of the machine protect system. Sucessful measurements of activation during non-beam times have also been made. This paper is an overview of the improved electronics and the results of the ongoing checkout and verification of this system.
DESY, Hamburg
The European XFEL is a 4th generation synchrotron radiation source, currently under construction in Hamburg. Based on different Free-Electron-Laser and spontaneous sources, driven by a 17.5 GeV superconducting accelerator, it will be able to provide several user stations with photons simultaneously. Due to the superconducting technology high average as well as peak brilliance can be produced. Flexible bunch pattern will allow for optimum tuning to the experiments demands. This paper will present the current planning of the electron beam diagnostics. An overview of the entire system will be given, as well as detailed insight into the main diagnostic systems, like BPM, charge and transmission diagnostics, beam size and beam loss monitor systems.
ORNL, Oak Ridge, Tennessee
Beam Loss Monitors are common devices used in hadron and lepton accelerators. Depending on accelerator specifics, BLMs could be just diagnostics or could play an essential role in the Machine Protection System (MPS). This tutorial discusses different types of BLMs and their applicability to different accelerators. It covers traditional BLMs like ionization chambers and scintillator-based devices, and also less common techniques like those based on fiber optics and avalanche diodes. The tutorial gives an overview of the underlying physics involved in beam loss detection, and recent advances in computer simulation of particle interaction with matter helpful for BLM modeling. Options for signal processing electronics are described, as well as interfaces to both the control system and the MPS.