Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada,...

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 1

Active Optics system for the ASTRI-2M prototype for the Cherenkov Telescope Array

Daniele GardiolINAF – Osservatorio Astrofisico di Torino

on behalf of the ASTRI Collaboration and the CTA consortium

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Active Optics team:

Gerardo Capobianco, Daniele Gardiol, Davide Loreggia, Federico Russo, Antonio Volpicelli

INAF – Osservatorio Astrofisico di Torino

Daniela Fantinel, Enrico Giro, Luigi Lessio, Gabriele Rodeghiero

INAF – Osservatorio Astronomico di Padova

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

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Overview of the talk

• Introduction: CTA (Cherenkov Telescope Array) and ASTRI (italian acronym…)

• Active Optics system of the ASTRI SST-2M prototype • Kinematic model and performance prediction • Active Optics system calibration • Conclusions


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IntroductionCherenkov Telescope Array in brief

Cherenkov Telescope Array is an initiative to build the next generation ground-based very high energy gamma-ray instrument


• LST (low energy): few 24 metre-class FoV ~ 4-5 degrees

• MST (medium energy range), from around 100 GeV to 1 TeV

10-12 metre-class FoV ~ 6-8 degrees.

• SST (high energy): a lot of 4-6 metre class FoV ~ 10 degrees.

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IntroductionItaly within CTA: ASTRI

ASTRI main goal is the production, within the CTA framework, of: an end-to-end prototype of the CTA SST to be placed and tested in Serra La

Nave (mount Etna, Sicily), end 2014 a SST mini-array to be placed at the chosen CTA site, 2016


Talk on ASTRI mini-array by G.Pareschi today at 11:40 (room 517D)

12 INAF InstitutionsIASF Milano, IASF Bologna, IASF Palermo, INAF HQ Roma, OA Brera, OA Torino, OA Padova, OA Bologna, OA Arcetri (Firenze), OA Roma, OA Capodimonte (Napoli), OA Catania2 University partners Padova, Perugia

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ASTRI SST-2MThe Prototype

Telescope

dual-mirror Schwarzschild-Couder

FoV = 9.6° EFL = 2150 mm


Secondary mirror

monolithic 1.8 m

Primary mirror

segmented 4.3 m 18 hex elements 850 mm side-to-side

Focal plane camera

compact (50x50x50 cm3) based on Si-PMs sensors.

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ASTRI SST-2MThe Prototype

Telescope

dual-mirror Schwarzschild-Couder

FoV = 9.6° EFL = 2150 mm


Secondary mirror

monolithic 1.8 m

Primary mirror

segmented 4.3 m 18 hex elements 850 mm side-to-side

Focal plane camera

compact (50x50x50 cm3) based on Si-PMs sensors.

Poster on SiPM detectors by G.Bonanno et al. this afternoon at 17:30 (room 516)

Talk on structure and mirrors manufacturing by R.Canestrari today at 11:20 (room 517D)

Poster on optics characterization and alignment by E.Giro et al. Wednesday from 18:00 to 20:00 (room 520D)

Talk on ASTRI camera by O.Catalano was yesterday…

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Active Optics systemPrimary Mirror active supports


M1 segment support

One fixed point Two axial actuators Total stroke > 10 mm Positioning accuracy < 3µm Prototype for lab test

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Active Optics systemSecondary Mirror active support


M2 active support

Three axial actuators Tilt + Focus Whiffletrees to share load Total stroke ~ 15 mm

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Active Optics systemAlignment tracking system


Each M1 segment is equipped with a laser which beam follows the optical path of the telescope

Spot position is tracked via two CCDs located at the camera edges and provides feedback on mirror tilt

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Active Optics systemActive Mirror Control Unit


Poster on Telescope Control Unit by E.Antolini et al. (room 516)

Telescope Control System

OPC-UA Client Telescope Control Unit

Active Mirror Control Unit (dedicated PC)

Twincat 3 (Beckhoff)

ATSKM M1 M2

Main OPC-UA ServerDB

Engineering interface

ADS

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Kinematic modelForward Analysis


Geometricalmodel

Opticalmodel

Segmentmodel

Behaviourprediction

5

0n

nknk pct

),(2/)(

),(2/)(

2121

2121

ttottv

ttottu

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Kinematic modelSegment model


5

0n

nknk pct

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Kinematic modelGeometrical model


,,,,, zyx

Provides the mirror position and tilt angles

as a function of the actuator axial position

for M1

for M2 ),( 21 tt ),,( 321 ttt

1 2

F

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Kinematic modelOptical model - u-type movement


Inner circle Median circle Outer circle

Δx

Δy

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Kinematic modelOptical model - v-type movement


Inner circle Median circle Outer circle

Δy

Δx

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Kinematic modelPerformance prediction vs. calibration


M1

M2

Δx Δy

Comp. inv. function

Residual estimate

KynematicModel

p1 p2

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Kinematic modelSystem calibration

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 18

Example:

Seventh order polynomial Image shifts up to

mm residuals for whole M1 (18 segments) > 99% of residuals are below the

hardware positioning accuracy of actuators

Residuals

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Conclusions


active positioning is performed by means of axial actuators driven by stepper motors

an alignment tracking system provides feedback on the mirrors alignment. It will be used also during calibrations

can operate in stand alone mode or within the Telescope Control System A complete kinematic model predicts system performance, quantifying non-

linearities (dominated by the M1 axial actuator behaviour) A simulation of the calibration procedure shows that it is possible to

describe and correct the image shift induced by mirrors tilt over the whole range allowed by the hardware with a seventh order polynomial, being the residuals well below the mechanical accuracy positioning of the actuators

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Kinematic modelPerformance prediction


M1

M2

Δx Δy

Δy (// El)

Δx

Focal Plane

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Kinematic modelBackward Analysis


Comp. inv. function

Residual estimate

KynematicModel (FA)

nm

nmnm

nm

nmnm

yxbyxp

yxayxp

,,2

,,1

),(

),(

]12000,0[,),(

]12000,0[,),(

,2,1,2,1,

,2,1,2,1,

hkhkhk

hkhkhk

ppppyy

ppppxx

Polynomial interpolation up to a suitable order

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada,...

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