The prototype of Gamma-ray Cherenkov Telescope (pGCT) is an Imaging Atmospheric Cherenkov Telescope (IACT) developed to detect Very High Energy (VHE) from various cosmic sources emitting gamma rays. It is based on a Schwarzschild-Couder (SC) dual-mirror configuration resulting in a compact telescope and an optimised PSF over a wide field of view. Moreover, some innovative features were implemented with the aim to ease and to fasten the assembly, integration, test (AIT) and maintenance activities. Both mirrors, the 4-meter tessellated primary mirror and the secondary mirror, are aspherical lightweight mirrors made by a subtractive manufacturing method. This process was improved several times leading to enhanced optical performance of the telescope in terms of Point Spread Function and improved signal to noise ratio. This paper deals with the optomechanical design of the pGCT and its latest measured performance. After a brief overview of the mechanical design of the telescope, the updated manufacturing process of the new generation mirrors and the optical performance of pGCT are given. Finally, recent operational performance of the telescope is given.
In 2015, the pGCT, a telescope prototype planned for the Cherenkov Telescope Array (CTA) gets its first Cherenkov light in the Meudon site of the Observatoire de Paris. As a part of the small-sized telescopes of the CTA, this telescope was designed to detect showers of secondary particles produced when very high energy gamma rays and cosmic rays enter in the upper atmosphere and interact with the atmospheric gas. It is now dedicated to a test bench for Cherenkov observation and to educational purposes. Within this last framework and in order to propose to the general public an easy way to observe high energy particles, we started in 2021 the development of a Langsdorf cloud chamber based on a previous model using Peltier cells and developed for students in Tours. Cloud chambers provide a convenient way to observe signatures of charged particles related to cosmic rays since they allow a direct detection also during daytime and are easier to use for the visits by the general public to concretely illustrate the existence of these high energy particles. This paper describes mechanical and electronic designs of this cloud chamber. Some results for educational purposes are also given.
The Small Sized Telescope (SST) is one of the three types of telescopes that will constitute the Cherenkov Telescope Array (CTA). For the CTA Southern site, 37 SST will be realized for the first alpha CTA configuration. Their design is based on the ASTRI-Horn dual-mirror telescope. Some modifications of the design are currently under study searching for possible improvements of the behaviour of the telescope. Amongst them, there are studies on the primary mirror dish (M1 Dish) led by a team of the Observatoire de Paris. The main purpose of these studies is to optimize the mass stiffness ratio of this structure. It means reducing its total mass while keeping its performance, mainly its stiffness, and taking into account existing constraints related to dependent fixed subsystems (counterweight, secondary mirror...) or environment (gravity, wind). This problem can be described as a classical optimization problem in the way it aims at finding an optimal mass distribution by minimizing the compliance with a constraint of mass reduction and under given boundary conditions. This methodology, previously used by the Observatoire de Paris for the design of lightweight mirrors and of components of another Cherenkov telescope, is applied to propose an alternative option to the ASTRI-Horn baseline design of the M1 Dish. Its lays on the use of structural optimization tools, which can help to get more quickly an accurate mass distribution and to improve the design process by reducing the number of iterations between phases of design definition under computer-aided design (CAD) and phases of design validation under finite-element analysis. This methodology and the corresponding results are presented in this paper.
The Cherenkov Telescope Array Observatory (CTAO) consists of three types of telescopes: large-sized (LST), mediumsized (MST), and small-sized (SST), distributed in two observing sites (North and South). For the CTA South “Alpha Configuration” the construction and installation of 37 (+5) SST telescopes (a number that could increase up to 70 in future upgrades) are planned. The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The SSTs rely on a Schwarzschild-Couder-like dual-mirror polynomial optical design, with a primary mirror of 4 m diameter, and are equipped with a focal plane camera based on SiPM detectors covering a field of view of ~9°. The current SST concept was validated by developing the prototype dual-mirror ASTRI-Horn Cherenkov telescope and the CHEC-S SiPM focal plane camera. In this contribution, we will present an overview of the SST key technologies, the current status of the SST project, and the planned schedule.
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