1. Active Optics system for the ASTRI-2M prototype for the Cherenkov Telescope Array
Daniele Gardiol
INAF – Osservatorio Astrofisico di Torino
on behalf of the ASTRI Collaboration and the CTA consortium
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

2. Gerardo Capobianco, Daniele Gardiol,
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

3. 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
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 3 3

4. Cherenkov Telescope Array in brief
Introduction
Cherenkov 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.
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 4 4

5. Italy within CTA: ASTRI
Introduction
Italy 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
12 INAF Institutions
IASF 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 Catania
2 University partners
Padova, Perugia
Talk on ASTRI mini-array by G.Pareschi today at 11:40 (room 517D)
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 5 5

6. ASTRI SST-2M The Prototype monolithic 1.8 m
Secondary mirror
monolithic 1.8 m
Telescope
dual-mirror Schwarzschild- Couder
FoV = 9.6°
EFL = 2150 mm
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.
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

7. ASTRI SST-2M The Prototype monolithic 1.8 m
Secondary mirror
monolithic 1.8 m
Telescope
dual-mirror Schwarzschild- Couder
FoV = 9.6°
EFL = 2150 mm
Primary mirror
segmented 4.3 m
18 hex elements
850 mm side-to-side
Talk on structure and mirrors manufacturing by R.Canestrari today at 11:20 (room 517D)
Focal plane camera
compact (50x50x50 cm3)
based on Si-PMs sensors.
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…
Poster on SiPM detectors by G.Bonanno et al. this afternoon at 17:30 (room 516)
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

8. Primary Mirror active supports
Active Optics system
Primary Mirror active supports
M1 segment support
One fixed point
Two axial actuators
Total stroke > 10 mm
Positioning accuracy < 3µm
Prototype for lab test
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 8 8

9. Secondary Mirror active support
Active Optics system
Secondary Mirror active support
M2 active support
Three axial actuators
Tilt + Focus
Whiffletrees to share load
Total stroke ~ 15 mm
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 9 9

10. Alignment tracking system
Active Optics system
Alignment 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
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 10 10

11. Active Mirror Control Unit
Active Optics system
Active Mirror Control Unit
Active Mirror Control Unit (dedicated PC)
Telescope Control System
OPC-UA Client
Telescope Control Unit
Twincat 3 (Beckhoff)
Main
OPC-UA Server DB KM
ATS M1 M2
ADS
Engineering interface
Poster on Telescope Control Unit by E.Antolini et al. (room 516)
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 11 11

12. Kinematic model Forward Analysis Segment model Geometrical model
Optical
model
Behaviour
prediction
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 12 12

13. Kinematic model Segment model 13 13
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 13 13

14. Kinematic model Geometrical model F 2 1
Provides the mirror position and tilt angles
as a function of the actuator axial position
for M1
for M2
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 14 14

15. Optical model - u-type movement
Kinematic model
Optical model - u-type movement Δx Δy
Inner circle
Median circle
Outer circle
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 15 15

16. Optical model - v-type movement
Kinematic model
Optical model - v-type movement Δx Δy
Inner circle
Median circle
Outer circle
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 16 16

17. Performance prediction vs. calibration
Kinematic model
Performance prediction vs. calibration
Kynematic
Model M1
Comp. inv. function M2
Residual estimate Δx Δy
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 17 17

18. Kinematic model System calibration p1 p2 Seventh order polynomial
Residuals
Example:
Seventh order polynomial
Image shifts up to
d= ∆𝑥 + ∆𝑦 <80 mm
residuals for whole M1 (18 segments)
> 99% of residuals are below the hardware positioning accuracy of actuators
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 18 18 18

19. 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
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 19 19

20. Performance prediction
Kinematic model
Performance prediction
Δy (// El) Δx M1
Focal Plane M2 Δx Δy
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 20 20

21. Polynomial interpolation up to a suitable order
Kinematic model
Backward Analysis
Kynematic
Model (FA)
Comp. inv. function
Polynomial interpolation up to a suitable order
Residual estimate
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 21 21