Design and production of segment mirrors for the Large-Sized Telescopes of the Cherenkov Telescope Array

Tomohiro Inada; Satoshi Fukami; Koji Noda; Michiyuki Chikawa; Mika Kagaya; Hideaki Katagiri; Daniel Mazin; Koutaro Obara; Akira Okumura; Takayuki Saito; Masahiro Teshima; Tokonatsu Yamamoto; Tatsuo Yoshida; Ievgen Vovk

doi:10.1117/12.2562111

13 December 2020 Design and production of segment mirrors for the Large-Sized Telescopes of the Cherenkov Telescope Array

Tomohiro Inada, Satoshi Fukami, Koji Noda, Michiyuki Chikawa, Mika Kagaya, Hideaki Katagiri, Daniel Mazin, Koutaro Obara, Akira Okumura, Takayuki Saito, Masahiro Teshima, Tokonatsu Yamamoto, Tatsuo Yoshida, Ievgen Vovk

Author Affiliations +

Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV; 114510G (2020) https://doi.org/10.1117/12.2562111
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Abstract

CTA (Cherenkov Telescope Array) is a project for the next generation of the ground-based gamma-ray observatory. CTA will cover a wide energy range, 20 GeV and 300 TeV, by 3 types of the telescopes whose diameters are different. The Large-Sized Telescopes (LSTs) of the CTA are designed to cover the lowest energy range. We are working on mirrors for 4 LSTs which will be built at La Palma, Spain. The parabolic primary mirror of CTA-LST is 23 m diameter and its focal length is 28 m. The primary mirror consists of 198 segmented mirrors. Total effective reflective area is about 370 m2. Each mirror has a hexagonal shape of 1.51 m side-by-side size. It has a sandwich structure which consists of aluminum honeycomb (60 mm thickness) and two glass surfaces (2.7 mm) and the total weight is about 47 kg. We used a sputtering deposition technique to coat in the surface with 5 layer. The coated layers protect the surface for long operation such as 10 years at outside with a reflectance degradation of less than 1 % a year. The reflectance of the mirror reaches about 92 % at 400 nm and its resolution is 0.5 mrad in diameter that contains the 80 % light reflected by the mirror. The production technique based on cold slumping gave us the stable its production. We report on the design of the segment mirror and the production of about 950 hexagonal 2 m2 mirrors to achieve the parabolic shape of the optical system for 4 LSTs.

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Tomohiro Inada, Satoshi Fukami, Koji Noda, Michiyuki Chikawa, Mika Kagaya, Hideaki Katagiri, Daniel Mazin, Koutaro Obara, Akira Okumura, Takayuki Saito, Masahiro Teshima, Tokonatsu Yamamoto, Tatsuo Yoshida, and Ievgen Vovk "Design and production of segment mirrors for the Large-Sized Telescopes of the Cherenkov Telescope Array", Proc. SPIE 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV, 114510G (13 December 2020); https://doi.org/10.1117/12.2562111

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