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[en] Many labs try to boost existing data acquisition systems by inserting high performance intelligent devices in the important nodes of the system's structure. This strategy finds its limits in the system's architecture. The CHADAC project proposes a simple and efficient solution to this problem, using a multiprocessor modular architecture. CHADAC main features are: a) Parallel acquisition of data: CHADAC is fast; it dedicates one processor per branch; each processor can read and store one 16 bit word in 800 ns. b) Original structure: each processor can work in its own private memory, in its own shared memory (double access) and in the shared memory of any other processor (this feature being particulary useful to avoid wasteful data transfers). Simple and fast communications between processors are also provided by local DMA'S. c) Flexibility: each processor is autonomous and may be used as an independent acquisition system for a branch, by connecting local peripherals to it. Adjunction of fast trigger logic is possible. By its architecture and performances, CHADAC is designed to provide a good support for local intelligent devices and transfer operators developped elsewhere, providing a way to implement systems well fitted to various types of data acquisition. (orig.)
[en] The High Energy Stereoscopic System (H.E.S.S.) is a new system of large atmospheric Cherenkov telescopes for GeV/TeV γ-ray astronomy. This paper describes the array level trigger system of H.E.S.S. The system trigger requires the simultaneous detection of air-showers by several telescopes at the hardware level. This requirement allows a suppression of background events which in turn leads to a lower system energy threshold for the detection of gamma-rays
[en] The current Imaging Arrays of Cherenkov Telescopes (IACT) show that this technique is mature. Front-end electronics based on analogue pipelines become a popular readout solution. Slow noise and low power consumption ASICs were developed with improved dynamical range and linearity. A large bandwidth preserves the characteristics of the signal and fast readout reduces dead time. Next generation of IACT should reach an order of magnitude in sensitivity in a wide energy band, ranging from 10 GeV to more than 100 TeV. This goal can be reached with an array of 50-100 telescopes of various sizes at various spacings. With about 2 000 channels per camera a significant effort must be done to lower the overall cost and improve the performances of the electronics. Mass production will be determinant for lowering the overall cost. A gain in cost and performances can be obtained by maximising the integration of the front-end electronics in an ASIC. The amplifiers, analogue memories, digitization and first level buffering can be embedded in the same component. The first stage of the first level trigger should be also considered in this integration. Integrated electronics leads to a more compact camera and an easier maintenance on site.
[en] The ARS0 (''Analogue Ring Sampler'') GigaHertz Analogue Memory was developed for the ANTARES experiment by DAPNIA-SEI. Its application for an imaging Cherenkov camera is considered. This chip contains five analogue ring buffers with 128 cells each, with sampling on the nanosecond time-scale. After the arrival of a trigger signal, the analogue data may be read out at a slower rate, up to several hundred microseconds later. These characteristics allow a fully-integrated, compact imaging camera to be built based on this circuit. Results of tests on prototype circuit boards, for a possible application to the HESS project, are presented
[en] A fully differential wideband amplifier for the camera of the Cherenkov Telescope Array (CTA) is presented. This amplifier would be part of a new ASIC, developed by the NECTAr collaboration, performing the digitization at 1 GS/s with a dynamic range of 16 bits. Input amplifiers must have a voltage gain up to 20 V/V and a bandwidth of 400 MHz. Being impossible to design a fully differential operational amplifier with an 8 GHz GBW product in a 0.35μm CMOS technology, an alternative implementation based on HF linearised transconductors is explored. Test results show that the required GBW product is achieved, with a linearity error smaller than 1% for a differential output voltage range up to 1 Vpp, and smaller than 3% for 2 Vpp.
[en] The HESS experiment is now fully operational with the four telescopes installed by the end of December, 2003. Many galactic and extragalactic objects have been observed since operation began and the detection of various sources has proven the performance of the detector and validated the technical options chosen. The collaboration is currently studying the next phase of the HESS project. The detector system currently in operation has a threshold around 100 GeV. Many sources such as pulsars, micro-quasars, or neutralino annihilation are expected to emit gamma radiation at lower energy. The second phase of the HESS experiment consists of an additional larger telescope positioned in the centre of the existing four-telescope array. The new system may reach a threshold as low as 10-20 GeV in single telescope mode and about 50 GeV in coincidence with the four other telescopes. It will also improve the sensitivity of the existing system above 100 GeV. The construction should start next year and the installation is expected to take place in 2008, less than one year after the launch of the GLAST satellite. After a brief overview of the HESS phase I experiment, we will describe the upgraded parameters of the HESS camera. Then the set-up and expected performance are presented
[en] The H.E.S.S.-II front-end electronics, with its 20 GeV energy threshold, will require a much higher acquisition rate capability and a larger dynamic range than was relevant for H.E.S.S.-I. These constraints led to the development of a new ASIC, called SAM for Swift Analogue Memory, to replace the ARS used for H.E.S.S.-I. The SAM chip features 2 channels for the low and high gain outputs of a PMT, each channel having a depth of 256 analogue memory cells. The sampling frequency is adjustable from 0.7 up to 2 GS/s and the read-out time for one event is decreased from 275 down to 2.3 μs. The SAM input bandwidth and dynamic range are increased up to 300 MHz and more than 11 bits, respectively
[en] The European astroparticle physics community aims to design and build the next generation array of Imaging Atmospheric Cherenkov Telescopes (IACTs), that will benefit from the experience of the existing H.E.S.S. and MAGIC detectors, and further expand the very-high energy astronomy domain. In order to gain an order of magnitude in sensitivity in the 10 GeV to >100TeV range, the Cherenkov Telescope Array (CTA) will employ 50-100 mirrors of various sizes equipped with 1000-4000 channels per camera, to be compared with the 6000 channels of the final H.E.S.S. array. A 3-year program, started in 2009, aims to build and test a demonstrator module of a generic CTA camera. We present here the NECTAr design of front-end electronics for the CTA, adapted to the trigger and data acquisition of a large IACTs array, with simple production and maintenance. Cost and camera performances are optimized by maximizing integration of the front-end electronics (amplifiers, fast analog samplers, ADCs) in an ASIC, achieving several GS/s and a few μs readout dead-time. We present preliminary results and extrapolated performances from Monte Carlo simulations.
[en] H.E.S.S. and MAGIC experiments have demonstrated the high level of maturity of Imaging Atmospheric Cherenkov Telescopes (IACTs) dedicated to very-high-energy gamma ray astronomy domain. The astro-particle physics community is preparing the next generation of instruments, with sensitivity improved by an order of magnitude in the 10 GeV to 100 TeV range. To reach this goal, the Cherenkov Telescope Array (CTA) will consist in an array of 50-100 dishes of various sizes and various spacing, each equipped with a camera, made of few thousands fast photo-detectors and its associated front-end electronics. The total number of electronics channels will be larger than 100,000 to be compared to the total of 6,000 channels of the 5-telescopes H.E.S.S.-I H.E.S.S.-II array. To decrease the overall CTA cost, a consequent effort should be done to lower the cost of the electronics while keeping performance at least as good as the one demonstrated on the current experiments and simplifying its maintenance. This will be allowed by mass production, use of standardized modules and integration of front-end functions in ASICs. The 3-year NECTAr program started in 2009 addresses these two topics. Its final aim is to develop and test a demonstrator module of a generic CTA camera. The paper is mainly focused on one of the main components of this module, the NECTAr ASIC which samples the photo-detector signal in a circular analog memory at several GSPS and digitizes it over 12 bits after having received an external trigger. (authors)
[en] We describe the optimization of the read-out specifications of the NECTAr front-end electronics for the Cherenkov Telescope Array (CTA). The NECTAr project aims at building and testing a demonstrator module of a new front-end electronics design, which takes an advantage of the know-how acquired while building the cameras of the CAT, H.E.S.S.-I and H.E.S.S.-II experiments. The goal of the optimization work is to define the specifications of the digitizing electronics of a CTA camera, in particular integration time window, sampling rate, analog bandwidth using physics simulations. We employed for this work real photomultiplier pulses, sampled at 100 ps with a 600 MHz bandwidth oscilloscope. The individual pulses are drawn randomly at the times at which the photo-electrons, originating from atmospheric showers, arrive at the focal planes of imaging atmospheric Cherenkov telescopes. The timing information is extracted from the existing CTA simulations on the GRID and organized in a local database, together with all the relevant physical parameters (energy, primary particle type, zenith angle, distance from the shower axis, pixel offset from the optical axis, night-sky background level, etc.), and detector configurations (telescope types, camera/mirror configurations, etc.). While investigating the parameter space, an optimal pixel charge integration time window, which minimizes relative error in the measured charge, has been determined. This will allow to gain in sensitivity and to lower the energy threshold of CTA telescopes. We present results of our optimizations and first measurements obtained using the NECTAr demonstrator module.