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SST-GATE: An innovative Telescope for the Very High Energy Astronomy

SST-GATE: a prototype for CTA consortium

Prototype of CTA-SST built at the Observatory of Paris in Meudon

Project lead from mechanical and electronics design to building and test phases

SST-GATE telescope as a Schwarzschild-Couder (SC) optical design:

- dual mirror optical formula never built before

- increase the FoV and minimise aberrations (no coma, no spherical aberration)

- telescope size, weight and camera cost decrease

Objective of the SST-GATE in CTA preparatory phase: 2010 – 2014

- prove the feasibility of such design at low cost (<250 k€)

- prove the optical performance

Challenge of building a SC Telescope for CTA

Constraints of building a telescope in an array:

- each telescope is ordered independently: SST-GATE has its own control system

- the telescope must be compliant with others LST, MST telescopes

- the telescope must comply with the power supply provided (10 kW max)

- maintainability made with less than 6pers.h/week and no more 3 nights/year loss

- the telescope life: 30 years without any protection

- reliability of operation: 97 % of observational hours

- each part of the telescope must be subcontracted

Status of the projectProject is well going as CTA schedule: - mechanical design is almost frozen, mechanical studies are made by FEM- last simulation and optimization are on-going as well as electronics and software

- risk analysis, alignment process, error budget and MAIT process are studied in parallel

Current status: - foundations already made- power supply and Ethernet will be provided by the end of 2012- AAS will be built in spring 2013, mirror provided in summer 2013- mechanical and optical tests will be started by the end of 2013

Conclusions and Perspectives of the SST-GATE project

CTA is a challenging project in both technical and scientific aspects

SST-GATE will prove the mechanical feasibility and the optical performances of a Schwarzschild-Couder design, never built before.

Camera

- for prototyping: CCD camera

- for science: CHEC camera from Leicester

Alt-Azimuthal Structure (AAS)

� Supporting the optical system

� Ability to point any direction in the sky and to track any source

> 90° / minSlew speed

< 5 arcsecSource localisation

< 5 arcminTracking precision

< 7 arcsecPointing precision

Environmental constraints for the telescope

0 to 1005 to 955 to 955 to 95Humidity range (%)

> 10065 to 10050 to 650 to 50 Wind speed range (km/h)

< - 20 or > + 50- 20 to + 50- 15 to + 45- 10 to + 40Temperature range (°C)

SurvivalEmergencyCriticalObservingConditions

- Critical conditions: observation with degraded performance

velocities and accelerations reduced down to 70% of max

- Emergency conditions: return to parking position

velocities and accelerations reduced down to 10% of max

- Survival conditions: telescope parked and no move allowed

A Schwarzschild-Couder optical system

� 2 mirrors M1 and M2 with the focal plane in between

� mirrors linked by the MTS (Mast and Truss Structure) which is 3 tubes of Φ 100 mm. Kneecaps between MTS and the M2 dish and pivot for the M1 dish

� Optical specifications:

- low level layer: Ethernet - software layer: Ethernet-based communications with OPC UA and Object-Oriented Programming (LabVIEW, Java or C++)

Shelter will be provided for Meudon considering:

- the climatic conditions in Paris

- our wish to decrease maintainability cost

- working under protection for the building phase

Trade-off realized for:

- Building material: steel chosen instead of aluminium for its low price, rigidity, easiness of manufacturing and mounting

- Safety system for the azimuthal axis in addition to the passive mechanism to decrease the telescope and human hazard if an undesired movement occurs

- Use of 1 or 2 motor in AAS: 1 motor chosen in order to simplify the elevation and azimuthal control systems

- Size of the fork: short fork preferred as it induces lower axial stresses as studied by FEM analysis

Choice of a high cylindrical tower with a small closed fork mount for low cost, simplification of welding operations and low stresses

Mirrors manufacturing - Mirror M1: Φ 4 m – Aspherical radius of curvature: 9.7 m

tessellated mirror: 2 rings of 12 panels each- Mirror M2: Φ 2 m – Aspherical radius of curvature: 2.1 m

monolithic mirror composed of 9 assembled panels Under procurement from CEA IRFU:

2.283 mFocal length

0.578f/#

9°FoV

75 % on axisThroughput

0.1° @80%PSF

0.025°/mmPlate scale

6x6 mm²Pixel size

1 mRadius of curvature

discΦ 362 mmDetecting surface

1.2 m0.9 m

After CTA phase A, SST-GATE will be used as:

- a test bed for CTA cameras

- for scientific experiences in Meudon, university practical works and public visits

Cherenkov Telescope Array CTA consortium

New generation of ground-based Imaging Air Cherenkov Telescope

2 arrays in Northern and Southern hemisphere with 3 kinds of telescopes:

- Large Size Telescope LST: primary mirror Φ 24 m – detection of lowest energy

- Middle Size Telescope MST: primary mirror Φ 12 m – detection of TeV energy range

- Small Size Telescope SST: primary mirror Φ 4 to 6 m – detection of up to 100 TeV

Scientific objectives: explore the very high energy events by the discovery of thousands sources as supernovae remnants, pulsar wind nebulae, binary systems…

Scientific questions to answer:

- the origin of cosmic rays and their role in the universe

- the nature of particle acceleration in systems containing black holes

- the ultimate nature of matter and physics beyond the Standard Model

- camera fastening to MTS result from trade-off already made

- innovative solution to remove the camera by rotation avoiding human, mirrors and camera hazards and allowing a low height to work on the camera

Philippe Laporte, Jean-Laurent Dournaux, Hélène Sol, Catherine Boisson, Delphine Dumas, Gilles Fasola, Fatima de-Frondat, Olivier Hervet, David Horville, Jean-Michel Huet, Isabelle Jégouzo, Andreas Zech – Observatoire de Paris à Meudon France Simon Blake, Paula Chadwik, Jürgen Schmoll – Durham University United Kingdom ∙ Tim Greenshaw University of Liverpool United Kingdom ∙ Jim Hinton, Richard White – University of Leicester United Kingdom

Telescope Control and Alignment (TCA)

� controlling the telescope adequately to perform scientific operations� use of a main PLC, a safety PLC, a local control panel and remote workstations for human interface

Mirror M2

Mirror M1

Focal surface

3.56 m

0.51 m