Characterisation and testing of CHEC-M—A camera prototype for the small-sized telescopes of the Cherenkov telescope array

Abstract

The Compact High Energy Camera (CHEC) is a camera design for the Small-Sized Telescopes (SSTs; 4 m diameter mirror) of the Cherenkov Telescope Array (CTA). The SSTs are focused on very-high-energy γ-ray detection via atmospheric Cherenkov light detection over a very large area. This implies many individual units and hence cost-effective implementation, as well as shower detection at large impact distance, and hence large field of view (FoV), and efficient image capture in the presence of large time gradients in the shower image detected by the camera. CHEC relies on dual-mirror optics to reduce the plate-scale and make use of 6 × 6 mm 2 pixels, leading to a low-cost (∼150 ke), compact (0.5 m × 0.5 m), and light (∼45 kg) camera with 2048 pixels providing a camera FoV of ∼9 degrees. The CHEC electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application-specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs) sampling incoming signals at a gigasample per second, with flexible camera-level triggering within a single backplane FPGA. CHEC is designed to observe in the γ-ray energy range of 1-300 TeV, and at impact distances up to ∼500 m. To accommodate this and provide full flexibility for later data analysis, full waveforms with 96 samples for all 2048 pixels can be read out at rates up to ∼900 Hz. The first prototype, CHEC-M, based on multi-anode photomultipliers (MAPMs) as photosensors, was commissioned and characterised in the laboratory and during two measurement campaigns on a telescope structure at the Paris Observatory in Meudon. In this paper, the results and conclusions from the laboratory and on-site testing of CHEC-M are presented. They have provided essential input on the system design and on operational and data analysis procedures for a camera of this type. A second full-camera prototype based on Silicon photomultipliers (SiPMs), addressing the drawbacks of CHEC-M identified during the first prototype phase, has already been built and is currently being commissioned and tested in the laboratory.

Prospects for the Use of Photosensor Timing Information with Machine Learning Techniques in Background Rejection.

“…Parameters describing the Corsika simulations are shown in Table 1. The simulated array was of 4 Gamma Cherenkov Telescopes (GCTs) [17] equipped with the current version of the Compact High Energy Cameras (CHEC) [5], although the conclusions of this work are applicable to other telescopes with similar capabilities. The telescopes are arranged in a cross-configuration (+) on the Paranal site separated from the centre of the array by +-80 meters.…”

Assessment of the GCT Prototype’s Optical System Implementation and Other Key Performances for the Cherenkov Telescope Array

“…The optical system has been chosen to optimize the point spread function (PSF) and the plate scale while keeping a maximum incident angle of 60° on the detector surface. The telescope can be equipped with both CHEC-like [5] and ASTRI-like [12] cameras. Optimisation across a range of field angles resulted in a GCT design with a 2 m diameter secondary mirror (M2), placed 3.56 m in front of a 4 m diameter primary mirror (M1).…”

“…They allowed the involved teams to verify interfaces, to improve procedures, and to better understand the system variability and reliability. Data gathered during these campaigns have been proven useful in the development of the data-analysis chain and in understanding the levels of calibration that will be required for CTA [5].…”

Design and performance of the prototype Schwarzschild-Couder telescope camera

“…For vertical showers these opening angles produce a Cherenkov light pool with a radius of about 120 m at 1500 m above sea level. 2 IACTs record the Cherenkov light produced by these showers. At energies greater than 100 GeV, cosmic rays are much more abundant than gamma-ray events and hence are the primary backgrounds at these energies.…”