The Cherenkov Telescope Array SST-1M camera prototype commissioning - - PowerPoint PPT Presentation

Nicolaus Copernicus Astronomical Center

Taras Shevchenko National University of Kyiv

T .R.S. Njoh Ekoume*, C. Alispach for the CTA SST-1M Project

The Cherenkov Telescope Array SST-1M camera prototype commissioning

Joint Annual Meeting of SPS and ÖPG 2017, Geneva, Switzerland

Centrum Badań Kosmicznych Space Research Centre University College Dublin Ireland’s Global University

August 25, 2017

Outline

1.The CTA context 2.The SST-1M telescope 3.The SST-1M camera performance

August 25, 2017

The CTA context for SST-1M

• CTA is the new generation ground-based very high energy gamma-ray instrument
• Three telescope sizes to cover 4 orders of magnitude in energy (2 sites)

SSTs

(S:70, N:0)

MST

(S:25, N:15)

LST

(S:4, N:4)

~ 4 m 12 m 23 m

August 25, 2017

The CTA context for SST-1M

• CTA is the new generation ground-based very high energy gamma-ray instrument
• Three telescope sizes to cover 4 orders of magnitude in energy (2 sites)

 SSTs : CTA flux sensitivity above 3 TeV

SST s

SSTs

(S:70, N:0)

MST

(S:25, N:15)

LST

(S:4, N:4)

~ 4 m 12 m 23 m

August 25, 2017

• The SST-1M telescope combines proved technology for the telescope structure

and innovative photosensors for the camera.

Overview of the SST-1M telescope

SST-1M prototype in Krakow 15

• 15

15

• 15

y [ m m ] x [mm]

D80% = 11.3 mm

Number of mirrors 18 Number of pixels 1296 FoV 9° Focal length 5.6 m Pixel angular opening 0.24° D80% 11.3 mm D80% Requirement 23 mm

• T
• protect camera against

environmental efgects

• Used for camera calibration

in dark conditions

• Opening angle at 96° to

reduce shadowing

• Screen for mirror alignment
• Doors can sustain 100 km/h

wind (50 km/h required).

• Closing in 1 min.

Camera shutter On axis PSF

August 25, 2017

The PhotoDetection Plane (PDP)

• 1296 pixels (SiPM+Light Guides) developed @ UniGE
• Borofloat entrance window coated with AR filter + Cut-off Filter (540 nm)
• Aluminum Back Plate with water cooling
• Automatic bias voltage compensation for T variation through Slow Control board

August 25, 2017

• Digital sampling at 250 MHz
• PDP DC coupled to DigiCam

baseline shift to measure NSB

• Pixel digital sum for the trigger

➡ Highly fmexible trigger implementation in FPGA

Triggering and readout (DigiCam)

1 patch (3 pixels) Signal sum clipped at 8-bit 1 Cluster (1, 7 or 19 patches) Digital cluster signal > Threshold

August 25, 2017

Calibration: Camera Test Setup (CTS)

• Usage : Cable mapping, dead pixels, shower injection,

pixel characterization (charge resolution , flat fielding)

• Extract SiPM parameters : Dark count rate, Optical

cross-talk, Electronic noise, Gain, etc.

• Systematic uncertainties assessed with a toy MC

CTS = LED board AC-mode LED to emulate signal DC-mode LED to emulate background

August 25, 2017

Performance: Charge/Time resolution

• Charge resolution

⟺ Energy resolution

• Work in progress for each single pixel

 Well below CTA requirements

• Relative time resolution ~ 208 ps

 Further absolute time measurements with ps laser + diffuser  To be done as a function of NSB and Signal Pixel-to-pixel (relative) time resolution

August 25, 2017

Performance : Trigger and readout

central patch (1-bit info)

• Trigger rate derived with trigger counters in DigiCam
• Readout window length:

 No dead-time: trigger rate saturation as expected

August 25, 2017

Performance : Trigger and readout

triggered cluster: sum

• ver threshold

central patch (1-bit info)

• 500 [Hz] Safe threshold

 Full efficiency above 1.1 PE/pixel (23 PE/cluster) in dark night conditions

August 25, 2017

Performance : Trigger and readout

central patch (1-bit info)

• “Tail” at high thresholds
• Identified as cosmics going through PDP

Camera in horizontal position Camera in vertical position

track direction

August 25, 2017

Monte Carlo validation

• Simulation of camera response at difgerent NSB

conditions

• 2 independent simulations (CARE + T
• y MC)
• Low level distribution in good agreement (PDP

validated)

• High level distribution to validate (trigger

validation)

125 MHz 660 MHz

MC/DATA

[a.u]

MC/DATA

[a.u]

Preliminary

August 25, 2017

Measured p.e. MC (True p.e.) CTS injected p.e. Pixels Patches

Tests of the trigger

Sum of 3 pixels clipped [0, 255]

• Injection of simulated gamma showers out of CARE and loading into CTS
• T

rigger effjciency with CTS

• Parameters: Shower distance, Energy, NSB, T

rigger confjguration

Preliminary

Simulation: Effjciency out of 7 patches trigger confjguration Data: Injected simulated shower at 200 T eV ( r<250m)

August 25, 2017

Expected performances

Sum of 3 pixels clipped [0, 255]

• Simulation with CORSIKA+GrOptics+CARE with a trigger rate of 500 Hz

➡ Energy threshold at 0.3 TeV in dark night conditions ➡ Possible improvements by developing new trigger logic

August 25, 2017

Conclusion and outlook

Sum of 3 pixels clipped [0, 255]

✤ First data with the SST-1M camera confjrmed its excellent capabilities for

gamma-ray astronomy:

• Automated calibration with CTS
• Full effjciency observations at high moon (320 MHz/pixel) above

an average of 50 PE/cluster

• Performance reach CTA goals easily and also give margin for further

development (dedicated trigger algorithm, higher rates, etc)

✤ Camera is being installed on the prototype in these days.

First gamma-sky images by SST-1M in September!