Christos Zamantzas

Beam loss monitoring system for the LHC

One of the most critical elements for the protection of CERNs Large Hadron Collider (LHC) is its beam loss monitoring (BLM) system. It must prevent the superconducting magnets from quenching and protect the machine components from damages, as a result of critical beam losses. By measuring the loss pattern, the BLM system helps to identify the loss mechanism. Special monitors will be used for the setup and control of the collimators. The specification for the BLM system includes a very high reliability (tolerable failure rate of 10/sup -7/ per hour) and a high dynamic range of 10/sup 8/ (10/sup 13/ at certain locations) of the particle fluencies to be measured. In addition, a wide range of integration times (40 /spl mu/s to 84 s) and a fast (one turn) trigger generation for the dump signal are required. This paper describes the complete design of the BLM system, including the monitor types (ionization chambers and secondary emission monitors), the design of the analogue and digital readout electronics as well as the data links and the trigger decision logic.

The LHC beam loss measurement system

An unprecedented amount of energy will be stored in the circulating beams of LHC. The loss of even a very small fraction of a beam may induce a quench in the su- perconducting magnets or cause physical damage to machine components. A fast (one turn) loss of 3 . 10 -9 and a constant loss of 3 . 10 -12 times the nominal beam intensity can quench a dipole magnet. A fast loss of 3 . 10 -6 times nominal beam intensity can damage a magnet. The stored energy in the LHC beam is a factor of 200 (or more) higher than in existing hadron machines with superconducting magnets (HERA, TEVATRON, RHIC), while the quench levels of the LHC magnets are a factor of about 5 to 20 lower than the quench levels of these machines. To comply with these requirements the detectors, ionisation chambers and secondary emission monitors are designed very reliable with a large operational range. Several stages of the acquisition chain are doubled and frequent functionality tests are automatically executed. The failure probabilities of single components were identified and optimised. First measurements show the large dynamic range of the system.

The LHC Beam Loss Monitoring System's Surface Building Installation

The strategy for machine protection and quench prevention of the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN) is mainly based on the Beam Loss Monitoring (BLM) system. At each turn, there will be several thousands of data to record and process in order to decide if the beams should be permitted to continue circulating or their safe extraction is necessary. The BLM system can be sub-divided geographically to the tunnel and the surface building installations. In this paper the surface installation is explored, focusing not only to the parts used for the processing of the BLM data and the generation of the beam abort triggers, but also to the interconnections made with various other systems in order to provide the needed functionality.

An FPGA Based Implementation for Real-Time Processing of the LHC Beam Loss Monitoring System's Data

The strategy for machine protection and quench prevention of the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN) is mainly based on the beam loss monitoring (BLM) system. At each turn, there will be several thousands of data to record and process in order to decide if the beams should be permitted to continue circulating or their safe extraction is necessary to be triggered. The processing involves a proper analysis of the loss pattern in time and for the decision the energy of the beam needs to be accounted. This complexity needs to be minimized by all means to maximize the reliability of the BLM system and allow a feasible implementation. In this paper, a field programmable gate array (FPGA) based implementation is explored for the real-time processing of the LHC BLM data. It gives emphasis on the highly efficient successive running sums (SRS) technique used that allows many and long integration periods to be maintained for each detectors data with relatively small length shift registers that can be built around the embedded memory blocks.

UFOs in the LHC after LS1

UFOs (“Unidentified Falling Objects”) are potentially a major luminosity limitation for nominal LHC operation. With large-scale increases of the BLM thresholds, their impact on LHC availability was mitigated in the second half of 2011. For higher beam energy and lower magnet quench limits, the problem is expected to be considerably worse, though. Therefore, in 2011, the diagnostics for UFO events were significantly improved, dedicated experiments and measurements in the LHC and in the laboratory were made and complemented by FLUKA simulations and theoretical studies. In this paper, the state of knowledge is summarized and extrapolations for LHC operation after LS1 are presented. Mitigation strategies are proposed and related tests and measures for 2012 are specified.

LHC beam loss detector design: Simulation and measurements

The beam loss monitoring (BLM) system is integrated in the active equipment protection system of the LHC. It determines the number of particles lost from the primary hadron beam by measuring the radiation field of the shower particles outside of the vacuum chamber. The LHC BLM system will use ionization chambers as its standard detectors but in the areas where very high dose rates are expected, the secondary emission monitor (SEM) chambers will be additionally employed because of their high linearity, low sensitivity and fast response. The sensitivity of the SEM was modeled in Geant4 via the Photo-Absorption Ionization module together with custom parameterization of the very low energy secondary electron production. The prototypes were calibrated by proton beams. For the calibration of the BLM system the signal response of the ionization chamber is simulated in Geant4 for all relevant particle types and energies (keV to TeV range). The results are validated by comparing the simulations to measurements using protons, neutrons, photons and mixed radiation fields at various energies and intensities.

10 orders of magnitude current measurement digitisers for the CERN beam loss systems

A wide range current digitizer card is needed for the acquisition module of the beam loss monitoring systems in the CERN Injector Complex. The fully differential frequency converter allows measuring positive and negative input currents with a resolution of 31 nA in an integration window of 2 μs. Increasing the integration window, the dynamic range covers 21010 were the upper part of the range is converted by measuring directly the voltage drop on a resistor. The key elements of this design are the fully differential integrator and the switches operated by an FPGA. The circuit is designed to avoid any dead time in the acquisition and reliability and failsafe operational considerations are main design goals. The circuit will be discussed in detail and lab and field measurements will be shown.

The LHC beam loss monitoring system’s data contribution to other systems

The strategy for machine protection and quench prevention of the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN) is presently based on the Beam Loss Monitoring (BLM) system. At each turn the BLM system is able to acquire and process in real-time data from approximately 4000 detectors in order to decide if the beams should be permitted to continue circulating or their safe extraction is necessary. At the same time in the system, by making full use of its VME based processing cards, data is continuously recorded from both the acquisition, the processing results as well as the status of the electronics which later will be provided to various systems in the LHC. Part of the recorded data will be used to drive an on-line event display and write an extensive logging database at a refresh rate of 1 Hz. Other parts of the same processing units, initiated by external triggers, will provide fast updates of the loss pattern seen in the last 84 ms by 2.54 ms integrals, necessary for the automated collimator adjustments, 100 ms worth of data for every beam injection and scheduled dump to verify the correctness of those procedures, and the last 1.7 s by 40 us integrals to be used for post-mortem analysis in the event of an unforeseen dump as well as FFT analysis studies. The paper discusses the realization of each of those recording functions and their verification with beam measurements.

Formal verification of real-time data processing of the LHC beam loss monitoring system: a case study

We describe a collaborative effort in which the HOL4 theorem prover is being used to formally verify properties of a structure within the Large Hadron Collider (LHC) machine protection system at the European Organization for Nuclear Research (CERN). This structure, known as Successive Running Sums (SRS), generates the primary input to the decision logic that must initiate a critical action by the LHC machine protection system in response to the detection of a dangerous level of beam particle loss. The use of mechanized logical deduction complements an intensive study of the SRS structure using simulation. We are especially interested in using logical deduction to obtain a generic result that will be applicable to variants of the SRS structure. This collaborative effort has individuals with diverse backgrounds ranging from theoretical physics to system safety. The use of a formal method has compelled the stakeholders to clarify intricate details of the SRS structure and behaviour.

Functional and Linearity Test System for the LHC Beam Loss Monitoring Data Acquisition Card

In the frame of the design and development of the Beam Loss Monitoring (BLM) system for the Large Hadron Collider (LHC) a flexible test system has been developed to qualify and verify during design and production the BLM LHC data acquisition card. It permits to test completely the functionalities of the board as well as realizing analog input signal generation to the acquisition card. The system utilize two optical receivers, a Field Programmable Gate Array (FPGA), eights flexible current sources and a Universal Serial Bus (USB) to link it to a PC where a software written in LabWindows/CVI© (National Instruments) runs. It includes an important part of the measurement processing developed for the BLM in the future LHC accelerator. It is called Beam Loss Electronic Current to Frequency Tester (BLECFT).