The telescopes from the The telescopes from the technological point of view: technological point of view: structures and mirrors for tructures and mirrors for IACTs IACTs Rodolfo Canestrari Rodolfo Canestrari INAF INAF-Astronomical Observatory of Astronomical Observatory of Brera Brera
Outline - Introduction - The structures - Basics - Stow position - Nomenclature - Current experiments - The mirrors - The cold glass slumping technology
Introduction Meanwhile two guys are wasting time talking about the Two Chief World Systems Albert: “ Dio non gioca a dadi con l'universo. ” Niels: “Non dire a Dio come deve giocare. ”
Introduction Luckily, someone else does the dirty job! Mariastella: [ … ] “ alla costruzione del tunnel tra il Cern e i laboratori del Gran Sasso ” [ … ]
Introduction Luckily, someone else does the dirty job! Mariastella: [ … ] “ alla costruzione del tunnel tra il Cern e i laboratori del Gran Sasso ” [ … ]
Introduction We do both climb or marbles game with MAGIC
The structures Mostly of the Cherenkov telescopes look like these
The structures Mostly of the Cherenkov telescopes look like these
The structures Mostly of the Cherenkov telescopes look like these They are very large light collectors
The structures Mostly of the Cherenkov telescopes look like these They are very large light collectors camera mirrors structure
The Davies-Cotton layout • Originally (1957) proposed for solar concentrators. • Single reflection. • Discontinuous optical surface. • Many identical spherical mirrors accommodated on a spherical structure with the curvature being half of the mirrors one. • Better performances for off-axis rays when compared to a spherical or parabolic layout.
The structures Alt-Az mount alt: − 20 ° ÷ 100 ° az: ± 270 °
The structures Stow/safety position (below) Horizon pointing, toward North Pros : - easy access to camera body; - no Sunlight concentration; - no accumulation of snow Cons : - wind effect S N S N
The structures Foundation
The structures Aluminum tubes Elevation Fork Stainless still tubes
The structures Azimuth drive system Azimuth motor
The structures Elevation drive system Counterweights Foundation Pillar Azimuth drive system
The structures Elevation drive system
The structures Extract from “CTA Design Study” arXiv/1008.3703
The structures Lattice structure: carbon fiber Dish structure Lattice structure: stainless steel
The structures Arch Camera mast Quadrupod
Current experiments Layout : array with 4 telescopes 4 × 108 m 2 Mirror area : Site : The Khomas Highland of Namibia 23 ° 16 ’ 18 ” S, 16 ° 30 ’ 00 ” E at 1800 m asl Location : Operating since : 2002 (array in 2004) Website : http://www.mpi-hd.mpg.de/hfm/HESS/
Current experiments Extract from http://www.mpi-hd.mpg.de/hfm/HESS/
Current experiments Extract from http://www.mpi-hd.mpg.de/hfm/HESS/
Current experiments Layout : array with 4 telescopes 4 × 110 m 2 Mirror area : Site : Coronado National Forest, Arizona +31 ° 40 ’ 30 ” N, -110 ° 57 ’ 8 ” E at 1268 m asl Location : Operating since : 2003 (array in 2007) Website : http://veritas.sao.arizona.edu/index.php
Current experiments Extract from http://veritas.sao.arizona.edu/index.php
Current experiments Extract from http://veritas.sao.arizona.edu/index.php
Current experiments Layout : array with 2 telescopes 2 × 236 m 2 Mirror area : Site : Roque de los Muchachos, La Palma, Canary Islands +28 ° 45 ’ 42 ” N, -17 ° 53 ’ 25 ” E at 2200 m asl Location : Operating since : 2004 (array in 2009) Website : http://magic.mppmu.mpg.de/
Current experiments (a) Azimuth motor (b) Zenith motor fi fi fig Extract from PhD Thesis, Michele Doro (c) CFRP tubes (d) SBIG camera fi fi ◦ ∅ fig – ◦ ∅ fl fi – fi ∼ fig fl fi ∼ ◦ ∅ – fi – – – – fl ∼ fi – –
fl fl fi fi – – fi fi fi fi ∅ ∅ ◦ ◦ ◦ ◦ ◦ ◦ − − fl fl ∼ ∼ ◦ ◦ fl fl Current experiments fi fi ∼ ∼ fi fi – – 2.2.2 T 2.2.2 T he Re fl ector and Details on its Construction he Re fl ector and Details on its Construction – – The 17 m diameter re fl ector (17 m focal distance) follows a parabolic pr ofi le which was chosen The 17 m diameter re fl ector (17 m focal distance) follows a parabolic pr ofi le which was chosen to maintain the temporal structure of the shower light fl ashes. The re fl ector of MAGIC I is to maintain the temporal structure of the shower light fl ashes. The re fl ector of MAGIC I is tessellated and comprises 956 mirrors with a total area of 234 m 2 . Each mirror is a square of tessellated and comprises 956 mirrors with a total area of 234 m 2 . Each mirror is a square of 0.495 m side length and has a spherical pr ofi le whose radius of curvature is optimized for the 0.495 m side length and has a spherical pr ofi le whose radius of curvature is optimized for the position in the telescope to best approximate the paraboloid. MAGIC I mirrors are grouped position in the telescope to best approximate the paraboloid. MAGIC I mirrors are grouped onto panels of 4 or 3 elements and each panel can be moved by the Active Mirror Control onto panels of 4 or 3 elements and each panel can be moved by the Active Mirror Control system (AMC) [6]. system (AMC) [6]. The AMC was designed to correct small deformations of the mirror The AMC was designed to correct small deformations of the mirror support dish during telescope positioning and tracking. The mirrors are an all-aluminum, support dish during telescope positioning and tracking. The mirrors are an all-aluminum, light weight sandwich construction composed of an Al-skin and an Al-box and fil led with a light weight sandwich construction composed of an Al-skin and an Al-box and fil led with a Hexcell honeycomb structure [9]. A heating wire mesh, embedded in the sandwich, can be Hexcell honeycomb structure [9]. A heating wire mesh, embedded in the sandwich, can be switched on in cases of dew or ice deposits on the mirrors. The total power consumption for switched on in cases of dew or ice deposits on the mirrors. The total power consumption for heating theentirere fle ctor is40 KW. There fle cting aluminum surfaceof themirror elements is heating theentirere fle ctor is40 KW. There fle cting aluminum surfaceof themirror elements is diamond turned using the so-called fly -cutter technique, which provides an average roughness diamond turned using the so-called fly -cutter technique, which provides an average roughness of 4 nm and a mean re fl ectivity of 85%. The surface of the mirrors was coated with a thin of 4 nm and a mean re fl ectivity of 85%. The surface of the mirrors was coated with a thin layer of quartz (with someadmixtureof carbon) for protection against corrosion and acid rain. layer of quartz (with someadmixtureof carbon) for protection against corrosion and acid rain. Very little degradation (< 3%/ year) of the re fl ectivity was observed after 4 years exposure Very little degradation (< 3%/ year) of the re fl ectivity was observed after 4 years exposure to the atmosphere at La Palma. The overall adjusted re fl ector has, for an i nfini te point-like to the atmosphere at La Palma. The overall adjusted re fl ector has, for an i nfini te point-like source, a point spread function (PSF) of the re fl ected spot of ∼ 10 mm φ at the camera of source, a point spread function (PSF) of the re fl ected spot of ∼ 10 mm φ at the camera of –n –n the telescope. the telescope. A more complete description of the telescope optics and mirrors, which is a relevant part A more complete description of the telescope optics and mirrors, which is a relevant part – – fl fl of my PhD activities, is left to a dedicated section (Chapters 3 and 4). of my PhD activities, is left to a dedicated section (Chapters 3 and 4). M irrors The MAGIC II re fl ector is composed of two types of mirrors: 143 full – aluminum M irrors The MAGIC II re fl ector is composed of two types of mirrors: 143 full – aluminum mirrors similar to MAGIC I mirrors but with a larger area of 1 m 2 and improved design mirrors similar to MAGIC I mirrors but with a larger area of 1 m 2 and improved design ◦ fie ◦ fie ∅ ∅ and 104 cold –s lumped glass –al uminum sandwich developed at INAF – Milano. The work and 104 cold –s lumped glass –al uminum sandwich developed at INAF – Milano. The work on MAGIC II re fl ector and mirrors is the most relevant activity I performed during the on MAGIC II re fl ector and mirrors is the most relevant activity I performed during the PhD. This is therefore, dealt with in greater detail in the following two chapters 3 and PhD. This is therefore, dealt with in greater detail in the following two chapters 3 and 4. 4. Extract from PhD Thesis, Michele Doro
The solutions adopted for CTA SSTs LST MST
The mirrors Parameter Min Value Max Value Temperature range -25°C +60°C Winds speed 0 km/h 200 km/h Humidity 0% 100% Snow, ice Hail Sandblasting UV radiation
The mirrors
The mirrors Parameter Cherenkov Optical Optical quality few arcmin sub-arcsec Areal density 20 kg/m 2 70 kg/m 2 Cost 2 k € /m 2 100-300 k € /m 2
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