Abstract

The High Energy Stereoscopic System (H.E.S.S.) is one of the three arrays of imaging atmospheric Cherenkov telescopes (IACTs) currently in operation. It is composed of four 12-meter telescopes and a 28-meter one, and is sensitive to gamma rays in the energy range ~ 30 GeV – 100 TeV. The cameras of the 12-m telescopes recently underwent a substantial upgrade, with the goal of improving their performance and robustness. The upgrade involved replacing all camera components except for the photomultiplier tubes (PMTs). This meant developing new hardware for the trigger, readout, power, cooling and mechanical systems, and new software for camera control and data acquisition. Several novel technologies were employed in the cameras: the readout is built around the new NECTAr digitizer chip, developed for the next generation of IACTs; the camera electronics is fully controlled and read out via Ethernet using a combination of FPGA and embedded ARM computers; the software uses modern libraries such as Apache Thrift, ØMQ and Protocol buffers. This work describes in detail the design and the performance of the upgraded cameras.

Highlights

  • The first Cherenkov telescopes of the H.E.S.S. array were the four 12-meter diameter CT1–4, built and commissioned between 2002 and 2004 at the H.E.S.S. site in the Khomas highlands in

  • The performance of the new camera readout and data acquisition systems, allows full waveform sampling with an region of interest (ROI) length of up to 48 samples, which is expected to increase the sensitivity of the array to high energy showers

  • We report some of the most significant performance metrics for the new Cherenkov cameras

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Summary

Introduction

The first Cherenkov telescopes of the H.E.S.S. array were the four 12-meter diameter CT1–4, built and commissioned between 2002 and 2004 at the H.E.S.S. site in the Khomas highlands in. An important reason to upgrade the 14-year-old CT1–4 cameras [4] was to enable the CT1–4 array to trigger at a lower threshold, resulting in more events being recorded stereoscopically with CT5. This could not be achieved with the original cameras because of their rather large readout dead-time of ~ 450 ÎŒs per event: lowering their trigger threshold by e.g. 30% would have increased the fraction of events lost due to dead-time to ~ 15%. This work is structured as follows: general description of design and architecture (Section 2); tests performed on individual components and on the integrated system (Section 3); calibration procedures employed for commissioning and deployment (Section 4); performance achieved in the field (Section 5); conclusions (Section 6)

Architecture of the new cameras
Front-end electronics
Back-end electronics
Auxiliary and calibration devices
Camera network and software
Test facilities and procedures
Table-top laboratory test bench
Single drawer black box test bench
Mini-camera
Full camera copy
Readout
PMT gain flat-fielding
Camera flat-fielding
Trigger
Performance
Analogue front-end
Readout and slow control
Commissioning and long-term stability
Findings
Conclusion

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