Gianluca Giavitto, Terry Ashton, Arnim Balzer, David Berge, Francois Brun, Thomas Chaminade, Eric Delagnes, Gérard Fontaine, Matthias Füßling, Berrie Giebels, Jean-François Glicenstein, Tobias Gräber, James Hinton, Albert Jahnke, Stefan Klepser, Marko Kossatz, Axel Kretzschmann, Valentin Lefranc, Holger Leich, Hartmut Lüdecke, Iryna Lypova, Pascal Manigot, Vincent Marandon, Emmanuel Moulin, Mathieu de Naurois, Patrick Nayman, Marek Penno, Duncan Ross, David Salek, Markus Schade, Thomas Schwab, Rachel Simoni, Christian Stegmann, Constantin Steppa, Julian Thornhill, François Toussnel
KEYWORDS: Cameras, Imaging systems, Atmospheric Cherenkov telescopes, Electronics, Control systems, Data acquisition, Imaging systems, Control systems, Analog electronics, Telescopes, Field programmable gate arrays, Calibration
The High Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes, sensitive to cosmic gamma rays of energies between ~30 GeV and several tens of TeV. Four of them started operations in 2003 and their photomultiplier tube (PMT) cameras are currently undergoing a major upgrade, with the goals of improving the overall performance of the array and reducing the failure rate of the ageing systems. With the exception of the 960 PMTs, all components inside the camera have been replaced: these include the readout and trigger electronics, the power, ventilation and pneumatic systems and the control and data acquisition software. New designs and technical solutions have been introduced: the readout makes use of the NECTAr analog memory chip, which samples and stores the PMT signals and was developed for the Cherenkov Telescope Array (CTA). The control of all hardware subsystems is carried out by an FPGA coupled to an embedded ARM computer, a modular design which has proven to be very fast and reliable. The new camera software is based on modern C++ libraries such as Apache Thrift, ØMQ and Protocol buffers, offering very good performance, robustness, flexibility and ease of development. The first camera was upgraded in 2015, the other three cameras are foreseen to follow in fall 2016. We describe the design, the performance, the results of the tests and the lessons learned from the first upgraded H.E.S.S. camera.
J.-F. Glicenstein, M. Barcelo, J.-A. Barrio, O. Blanch, J. Boix, J. Bolmont, C. Boutonnet, P. Brun, E. Chabanne, C. Champion, S. Colonges, P. Corona, B. Courty, E. Delagnes, C. Delgado, C. Diaz, J.-P. Ernenwein, S. Fegan, O. Ferreira, M. Fesquet, G. Fontaine, N. Fouque, F. Henault, D. Gascón, B. Giebels, D. Herranz, R. Hermel, D. Hoffmann, D. Horan, J. Houles, P. Jean, S. Karkar, J. Knödlseder, G. Martinez, G. Lamanna, T. LeFlour, A. Lévêque, R. Lopez-Coto, F. Louis, Y. Moudden, E. Moulin, P. Nayman, F. Nunio, J.-F. Olive, J.-L. Panazol, S. Pavy, P.-O. Petrucci, M. Punch, Julie Prast, P. Ramon, S. Rateau, M. Ribó, S. Rosier-Lees, A. Sanuy, P. Sizun, J. Sieiro, K.-H. Sulanke, J.-P. Tavernet, L. A. Tejedor, F. Toussenel, G. Vasileiadis, V. Voisin, V. Waegebert, C. Zurbach
NectarCAM is a camera designed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range 100 GeV to 30 TeV. It has a modular design based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 7 to 8 degrees. Each module includes the photomultiplier bases, High Voltage supply, pre-amplifier, trigger, readout and Thernet transceiver. Events recorded last between a few nanoseconds and tens of nanoseconds. A flexible trigger scheme allows to read out very long events. NectarCAM can sustain a data rate of 10 kHz. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, the cooling of electronics, read-out, clock distribution, slow control, data-acquisition, trigger, monitoring and services. A 133-pixel prototype with full scale mechanics, cooling, data acquisition and slow control will be built at the end of 2014.
The use of integrated Lamb wave sources (piezoelectric transducers) is known as a possible way of performing integrated, on-line health monitoring. Either omnidirectional (circular) or quasi-unidirectional (bar-shaped) transducers can be used. However, both of them have their own drawbacks, which makes them not optimal. A much more satisfying solution could be the use of phase-delayed multi-element arrays to perform angular steering of the emitted Lamb wave beam. In this paper both the proper conditions and the limitations for the applicability and performance of Lamb wave beam steering using integrated piezoelectric arrays are established. Then experimental damage detection capabilities using this principle are demonstrated.
Since a few years, Lamb waves have been seriously considered as a potential technique for integrated damage assessment systems. Since they are easily propagated over long distances in plate-shaped structures and are able to interact with inner material defects, Lamb waves are seen indeed as a most promising technique. Real-time, continuous health monitoring applications require the development of thin piezoelectric Lamb wave transducers intimately coupled to the structure to be monitored.
The DAMASCOS (DAMage Assessment in Smart COmposite Structures) project is a European Union funded program of work bringing together a number of academic and industrial partners throughout Europe. The aim of Damascos is to apply new ultrasonic detection and generation techniques integrated within the structure, together with advanced signal processing to realize damage assessment and ageing characterization in composite structures. This paper describes the background, experimental findings and future applications of the technology as the project moves into its final phase.
In this paper an experimental analysis of Lamb waves interaction with riveted aluminum plates representative of aircraft splice joints submitted to fatigue tests is given. In this joint evaluation technique Lamb waves are excited and received outside the joint area using piezoelectric transducers bonded onto the plates. Detected damages are cracks in joint resulting from fatigue loading. These cracks lead to waveform transformations. This phenomenon is studied in this paper by considering the first derivative of the envelope of the time domain signal. The position of the first derivative curve maximum during cyclical loading gives information about crack development. It suggests, that monitoring the change in the delay of this maximum may provide a means of sizing the defects. By using X-rays, it was possible to measure the size of the cracks and compare it with delay evolution. Results are obtained for two types of fatigue sequences. It is experimentally shown that the relative delay measured is very sensitive to crack development. With the continued progress in the field of damage assessment techniques such as methods relying on Lamb waves, the safety of such structures can be ensured.
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