1. ASTRI camera status Giovanni LA ROSA
INAF / IASF-Palermo
24-25/02/ CTA SCT SLAC

2. overview of the status of the ASTRI camera project
Mechanics and detectors
Electronics: FEE and Backplane
SiPM OACT Catania

3. Status of the design (1): mechanics and detectors
The ASTRI camera is designed as focal plane instrument of a SCT  CTA-SST.
The basic optics parameters are:
Equiv Focal Length = 2.15 m F# = FOV = 9.6°
pixel = 0.17°  6.2x6.2 mm camera Ø = 35cm RoC = 1m
A big effort was dedicated to the design of the mechanics of the focal plane.
Modularity implies to take care of to the curvature of the focal plane
We had to match a curved surface with a certain number of flat modules
without loosing the required focusing capability of the optic system.
A square module of ~6 cm fits the optics requirement and
optimize the numbers of detectors in a single module (16x16 detector units).
BUT: we cannot use staircase configuration!
Modules must follow the curvature!
After this, it was possible to begin the design of the Photon Detector Module (PDM)
How to assemble the detectors on top of the PDM

4. the Detector Unit.. HAMAMATSU S11828-3344M
The photon detection system is based on SiPM
There are many advantages in using SiPM: excellent single photon resolution, high QE, no HV, no damage when exposed to ambient light.
The drawbacks are: the high dark counts (1MHz/mm2), afterpulses, optical crosstalk and Gain strongly dependent on temperature
The photon detector is a monolithic multipixel SiPM
That can be composed in a bigger module
HAMAMATSU S M
A little border allows the anode signals to be routed on the back side of the detector
>dead area
Hamamatsu is going to realize a silicon feedthrough
4x4 pixels
pixel = 3x3 mm
3600 cells (50x50μ)
The cost of the detectors is 200 euro for an order of 500 pieces (496 in ASTRI camera)
Hamamatsu said that it could be still lower

5. from the Detector Unit to the PDM (Photon Detection Module)..
pixel dim. = 3x3mm
grouping 2x2 physical pixels to obtain 6.2x6.2mm optical pixel = 0.17°
PDM = Photon Detection Module
4x4 MPPC = 16x16 pixels (8x8 channels)
Dimensions = 56 x 56 mm

6. this is the way to couple the DUs to the top PCB of the FEE..

7. coupling the DU PCBs to the top PCB of the PDM

8. Light guides to recovery the dead area of the borders of the DUs
Light collector
SiPM detector UNIT (or 4 UNITS)
2.5mm
The dead area of the borders of the detector unit can be recovered with a light collector glued on it
This is made by glass of high refraction index with a pyramidal shape and tickness of 2.5mm
The upper part of the light collector can be coated
Simulation of the system (coating + light collector + UV glue) shows a transmission efficiency vs. incidence angle of ~90%
(up to 70° incidence angle).

9. this is the PDM building..
57 mm
LIGHT GUIDES
Detector unit (4x4 MPPCs)
PCB to I/F MPPC to FEE
FEE PCBs
35 mm
I/F to the main frame

10. and this is the way many PDMs compose the focal surface..

11. the focal surface view: front and lateral
Focal Surface is composed by:
37 PDMs (12 half module)  496 SiPMs  1984 optical pixels (0.17°)

12. and this is the first prototype frame with some PDM mock-up..

13. model view of the ASTRI camera
Estimated weight = 18 Kg
(only mechanical structure)

14. Status of the design (2): electronics Activity on the electronics:
The design of a little PCB to host the detector and place it in the upper PDM I/F board
The design of the PCB to I/F the detectors to the FEE PCBs
The design of the FEE: considering different “sampling memories” and “trigger”
(TARGET is our main choice, but.. we are evaluating other sampler ASICs)
The study of the design of the back-end electronics is started even if the design of the
FEE isn’t still frozen on a definite configuration
It was developed a SW for the simulation of the behavior of detector + FEE
taking into account even the statistical appearance of afterpulses and optical crosstalk
About the interfacing to the external archive and to the control computer, we are defining the data format and the tables of all the parameters that must be monitored
(people from Bologna joined the ASTRI project to bring their experience in DAS SW in satellites instruments)

15. PDM Front End Electronics 64 digitized analog channels
Volt
STEP-UP
16 ch
FPGA
PDM SENSORS
Control/setting
TARGET-2 ?
16 ch
Control/setting
Control/setting
16 ch
64 digitized analog channels
16 ch
Serial link
16 ch
TRIGGER LOGIC
TRIGGER
Control/setting
Control/setting

16. PDM Fornt End Electronics one big critical point: the ASIC
TARGET-2 was our first choice.. but what to do now ?
- is there any new TARGET chip ready in the very near future?
- do we go on with other “sampler” ASICs? (DRS4, ..)
- try to explore other ways? “shapers” ASICs (VATA, SPIROC, ..)
using TARGET-new depends on how long we have to wait
DRS4 is power consuming, 8 ASICs/PDM
“shapers” could be interesting:
Low power, 2 ASICs/PDM but.. the timing seems to be poor
OACT Catania is in charge to explore this choice

17. PDM Fornt End Electronics
Shaper 

18. Preliminary design ideas for the Back End Electronics
BACK END TASKS
- Trigger signals routing
Clock (GPS)
Event Time Tag
Store events in a Local Memory
Data Packing and Transmission
Voltages generation
HV / LV distribution
I/F to FEE
I/F to the external Camera Controller and Data Collection System
Operating Modes

19. ASTRI Back End Electronics
Local
Memory
GPS
antenna
GPS
board
CLOCK
DATA
Ethernet
I/F
ScienceConsole
I/F to DAS
FPGA
TRIGGER
PDMs
I/F to Controller
Ethernet
I/F
Camera Controller
SET-PROG
HKs
LVs
Power
DC line
DC/DC
converter HV

20. Status of the design (3): SiPM test @ OACT (Catania)
Gain measurements
Gain (lab): ± 0.14 x 31°C V
Gain (from cal) : 7.50 x @ 25°C – 71.13V

21. Status of the design (3): SiPM test @ OACT (Catania)
Photon Detection Efficiency measurements

22. some more news in Amsterdam !
Conclusions
Mechanical frame fits the required Radius of Curvature
PDMs dimensions maintain focusing requirements
FEE philosophy under study (depending on the ASIC to be used..)
different ASICs are under evaluation
Back-End design will start soon
simulator helps in the evaluation of different HW configurations
OACT Catania lab will continue to run other characterization tests on the Hamamatsu detectors
some more news in Amsterdam !
10 people are working on the camera: 5 in Palermo + 5 in Catania
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