Mirror production for the Cherenkov telescopes of the ASTRI mini-array and the MST project for the Cherenkov Telescope Array

Abstract

The Cherenkov Telescope Array (CTA) is the next ground-based gamma-ray observatory in the TeV γ-ray spectral region operating with the Imaging Atmospheric Cherenkov Technique. It is based on almost 70 telescopes of different class diameters-Large-Sized Telescope, Medium-Sized Telescope (MST), and Small-Sized Telescope (SST) of 23, 12, and 4 m, respectively-to be installed in two sites in the two hemispheres (at La Palma, Canary Islands, and near Paranal, Chile). Several thousands of reflecting mirror tiles larger than 1 m 2 will be produced for realizing the segmented primary mirrors of a so large number of telescopes. Almost in parallel, the ASTRI mini-array (MA) is being implemented in Tenerife (Canary Islands), composed of nine 4-m diameter dual-mirror Cherenkov telescopes (very similar to the SSTs). We completed the mirror production for all nine telescopes of the ASTRI MA and two MSTs (400 segments in total) using the cold glass slumping replication technology. The results related to the quality achieved with a large-scale production are presented, also discussing the adopted testing methods and approaches. They will be very useful for the adoption and optimization of the quality assurance process for the huge production (almost 3000 m 2 of reflecting surface) of the MST and SST CTA telescopes. © The Authors.Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

The ASTRI Mini-Array: A New Pathfinder for Imaging Cherenkov Telescope Arrays

“…An example of how the project has dealt with such complex tasks can be found in Ref. [11] where the large-scale production of mirrors for the ASTRI Mini-Array (see also Section 2.1.1) as well as the adopted testing methods and approaches, first to qualify the production process and then to verify the mirrors' performance, are described. At the end of the production and after the verification process, each mirror is delivered with a unique identity card where its characteristics are reported and traced.…”

“…This technique, called cold slumping, is used on thin slabs that, once bent, need to be reinforced through a honeycomb structure that is finished with a second glass slab, thus giving the final product the shape of a sandwich (see Ref. [11] for details). The technique was developed by Media Lario Technologies Company under the scientific supervision of INAF, starting from the development for the ALMA panels, and subsequently applied to the MAGIC telescopes [18].…”

Status of the Medium-Sized Telescopes for the Cherenkov Telescope Array Observatory

“…The mirror reflectivity exceeds 85% within the range of 300 nm to 550 nm (see Figure 2b), meeting the CTAO requirements. The mirrors are produced in France, Italy and Poland [4,5].…”

Development of a blue-mirror multilayer coating on light concentrators for future SiPM cameras

“…Another approach for NSB rejection in IACTs is to apply a multilayer coating on the mirror surface or camera window. As regards the Small-Sized Telescopes (SSTs) of the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory [7,8], a fewlayer coating on the primary and secondary mirrors has been studied [9] to enhance the UV-blue reflectance and slightly decrease the reflectance at longer wavelengths. A multilayer coating on a Borofloat camera window installed in front of the photodetectors has also been studied to selectively reflect back photons with wavelengths longer than 550 nm [10].…”