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Camera demonstrators for Very High Energy astronomy – NectarCAM

NectarCAM, an innovative camera for Very igh Energy astronomy.

Construction of a mini-Camera aimed at testing the performances of a camera for the Medium Sized Telescopes of the future high energy gamma ray observatory CTA.

Very High Energy gamma ray astronomy : a window to the violent universe.

Very High Energy gamma ray astronomy is a very recent (thirty year old) subfield of astronomy. It aims at mapping and studying the cosmic sources of very high energy photons, thousand billions times more energetic than the visible light. Identifying the sources of high energy photons will give insight on the acceleration mechanisms of charged cosmic rays, detected a century ago for the first time by Victor Hess. The Crab nebula was the first source to be detected in 1988 and was followed by tens of others, thanks notably to the success of the H.E.S.S. array of Cherenkov telescopes, in years 2000. The CTA observatory is the first astronomical observatory dedicated to high energies. It will include tens of telescopes with mirrors sizes between 4 and 23 meters.<br />The NectarCAM consortium aims at building a new innovative camera to equip the medium-sized telescopes of the CTA observatory. Theses telescopes have 12 meter diameter mirrors and are the backbone of the CTA telescope arrays. The NectarCAM consortium involves fifteen labs from France, Spain and Germany. The design of NectarCAM was made difficult by the number and geographical dispersion of the teams involved. In particular, most french teams are spread between Paris, Toulouse, Annecy and Marseille.

NectarCAM is composed of 265 identical and mostly independent modules. Each of these modules includes 7 photodetectors, the associated high voltage board, a data readout system and a part of the trigger system. The photon arrivals are recorded continously. The expected signal from air showers is only a few nanoseconds long. The camera readout is triggered when a large burst of photons is detected in several phototubes located in adjacent modules. Once trigged, the data are sent to a camera server over the Ethernet and stored in a disk.
To achieve the design of NectarCAM, the consortium has created a roadmap based on prototypes with increasing complexity. The first prototypes were dealing with components of the camera. The most important of these components are the « detection unit » which include a light guide, a photodetector and a high voltage and preamplification board and the module. A mini-camera with enough modules to test the trigger system is necessary to achieve the proof of the NectarCAM concept. A 19-module mini-camera, with a camera controller, a full sized acquisition system including a network switch, a camera and a time server were installed at IRFU (CEA-Saclay).

The mini-camera setup allowed testing the full acquisition, measuring the dead time of the instrument, and finally evaluating the various trigger options. Setting-up the mini-camera and bringing together the teams to operate it on the IRFU integration site was made possible by the ANR grant. The NectarCAM consortium is now ready to build a full-sized camera for CTA. To achieve this goal, an enlarged consortium with new german, brasilian, italian and polished teams is under discussion. The credibility obtained with the mini-camera concept was a decisive breakthrough in the creation of this new consortium.

The « NectarCAM, camera demonstrators for Very High Energy Astronomy » project
is a fundamental research project coordinated by IRFU (CEA-Saclay). Around fifteen other labs are involved, from France (CNRS/IN2P3 and CNRS/INSU), Spain and Germany. It started in November 2014 and lasted 27 months. 65000 € were granted by ANR. The global cost of the first NectarCAM camera is of the order of 2.5 M€.

The results of the mini-caméra tests were shown at international conferences ICRC 2015 (The Hague) and Gamma 2016 (Heidelberg). They were also communicated inside the CTA consortium, notably at Consortia general meetings in Liverpool, Turku, Bologna and Kashiwa.

The NectarCAM consortium aims at building a new, innovative camera for Cherenkov telescopes, NectarCAM. The consortium, headed by CEA/IRFU (Saclay), IN2P3/LAPP (Annecy), IN2P3/LLR (Palaiseau) includes fourteen labs from France, Spain and Germany. NectarCAM will be finely pixelated and will image atmospheric showers by measuring the charge deposited in a few nanosecond time window, with the additional capacity of recording the full waveform with a 1 GHz sampling for every pixel and of measuring times with nanosecond accuracy. The hadronic background rejection and the kinematical reconstruction capabilities are improved compared to the existing H.E.S.S. cameras. The proof of concept of NectarCAM will be achieved by building camera demonstrators to test all the functionnalities including trigger, timing properties and data acquisition. The present proposal asks for financial support from the ANR for travel expenses for a period of two years, needed for installation, management purposes and organization of workshops.

Project coordination

Jean-François Glicenstein (Commissariat à l'énergie atomiques et aux énergies alternatives)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


CEA/IRFU Commissariat à l'énergie atomiques et aux énergies alternatives

Help of the ANR 65,000 euros
Beginning and duration of the scientific project: October 2014 - 24 Months

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