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Functional and Linearity test system for the LHC Beam Loss Monitoring data acquisition card
Abstract
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).
... The signals were integrated over 40µs via a Current to Frequency Converter (CFC) [4] and sent to the surface electronics using optical fibers for further processing. The surface electronics consists of a laptop and a test system for the BLM acquisition cards [5]. The device kept a history of the signals received and computed twelve running sums which correspond to the integrated signal in twelve different integration windows spanning 40 µs to 83.4 s.Figure 5: View of the detectors on the metallic cross in TSG45. ...
The Beam Loss Monitoring System (BLM) of the Large Hadron Collider (LHC) is based on parallel plate Ionization Chambers (IC) with active volume 1.5l and a nitrogen filling gas at 0.1 bar overpressure. At the largest loss locations, the ICs generate signals large enough to saturate the read-out electronics. A reduction of the active volume and filling pressure in the ICs would decrease the amount of charge collected in the electrodes, and so provide a higher saturation limit using the same electronics. This makes Little Ionization Chambers (LIC) with both reduced pressure and small active volume a good candidate for these high radiation areas. In this contribution we present measurements performed with several LIC monitors with reduced active volume and various filling pressures. These detectors were tested under various conditions with different beam setups, with standard LHC ICs used for calibration purposes
... Before the installation, a calibration and an initial test are performed using a BLECFT [7] USB card, which performs an automatically generated functional test pattern. This system will also be used for additional tests after tunnel installation. ...
The beam loss monitoring system is one of the most critical elements for the protection of the LHC. It must prevent the super conducting magnets from quenches and the machine components from damages, caused by beam losses. Ionization chambers and secondary emission based detectors are used at several locations around the ring. The sensors are producing a signal current, which is related to the losses. This current will be measured by a tunnel card, which acquires, digitizes and transmits the data via an optical link to the surface electronic. The usage of the system, for protection and tuning of the LHC and the scale of the LHC, imposed exceptional specifications of the dynamic range and radiation tolerance. The input dynamic allows measurements between 10pA and 1mA and its protected to high pulse of 1.5kV and its corresponding current. To cover this range, a current to frequency converter in combination with an ADC is used. The integrator output voltage is measured with an ADC to improve the resolution. The radiation tolerance required the adaption of conceptional design and a stringent selection of the components.
... Before the installation, a calibration and an initial test are performed using a BLECFT [7] USB card, which performs an automatically generated functional test pattern. This system will also be used for additional tests after tunnel installation. ...
The beam loss monitoring (BLM) system [1] of the LHC is one of the most critical elements for the protection of the LHC. It must prevent the super conducting magnets from quenches and the machine components from damages, caused by beam losses. Ionization chambers and secondary emission based beam loss detectors are used on several locations around the ring. The sensors are producing a signal current, which is related to the losses. This current will be measured by a tunnel electronic, which acquires, digitizes and transmits the data via an optical link to the surface electronic. The so called threshold comparator (TC) [2] collects, analyzes and compares the data with threshold table. It also gives a dump signal through the combiner card to the beam inter lock system (BIC). The usage of the system, for protection and tuning of the LHC and the scale of the LHC, imposed exceptional specification of the dynamic range and radiation tolerance. The input current dynamic range should allow measurements between 10pA and 1mA and it should also be protected to very high pulse of 1.5kV and its corresponding current. To cover this range, a current to frequency converter (CFC) is used in the tunnel card, which produces an output frequency of 0.05Hz at 10pA, and 5MHz at 1mA. In addition to the output frequency, the integrator output voltage is measured with a 12bit ADC to improve the resolution. The location of the CFC card next to the detector imposes the placement of the card in the LHC tunnel, exposing the card to radiation. The radiation tolerance was defined by assuming a 20 year operation period corresponding to 400Gy. A mixture of radiation tolerant Asics from the microelectronic group at CERN, and standard component was chosen to cope with these requirements.
The superconducting Large Hadron Collider (LHC) under construction at the European Organisation for Nuclear Research (CERN) is an accelerator unprecedented in terms of beam energy, particle production rate and also in the potential of self-destruction. Its operation requires a large variety of instrumentation, not only for the control of the beams, but also for the protection of the complex hardware systems. The Beam Loss Monitoring (BLM) system has to prevent the superconducting magnets from becoming normal conducting and protect the machine components against damages making it one of the most critical elements for the protection of the LHC. For its operation, the system requires 3600 detectors to be placed at various locations around the 27 km ring. The measurement system is sub-divided to the tunnel electronics, which are responsible for acquiring, digitising and transmitting the data, and the surface electronics, which receive the data via 2 km optical data links, process, analyze, store and issue warning and abort triggers. At the surface installation, the processing units (BLMTCs) include Field Programmable Gate Array (FPGA) devices. Each FPGA is treating the beam loss signals collected with a rate of 25 kHz from 16 detectors. It calculates and maintains 192 moving sum windows, giving loss duration integrations of up to the last 84 seconds. For the generation of the abort triggers, demanding the extraction of the circulating beams, it compares the moving sums calculated with threshold values chosen for the given beam energy. Those thresholds can be uniquely programmable for each detector allowing calibration and offset factors to be included. In this thesis, the BLMTC's design is explored giving emphasis to the methods followed in providing very reliable physical and data link communication layers, in merging the data from a Current-to-Frequency converter and an ADC into one value, and in keeping the moving sums updated in a way that gives the best compromise between memory needs, computation, and approximation error.
The Beam Loss Monitoring-system of the LHC is a complex measurement- and acquisition-system. The task of this system is to monitor the particle-beam and to request a dump in case of too big losses. Ionisation-chambers outside the magnets measure the losses of the beam and change this signal to a current signal. This signal will be converted to a frequency signal and prepared for the transmission to the surface inside a FPGA. On the surface the transmission is checked for errors. To analyse and observe the status of the particle-beam, this data must be transferred to a computer. This thesis covers the transmission, storage and visualisation of the data on the computer. The data are transmitted by an USB 2.0 module. The storage and visualisation is made in LabVIEW.