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Design and Performance of the Upgraded Prototype Schwarzschild-Couder Telescope Camera Module

Giovanni Ambrosi, Carla Aramo, Mattia Barbanera, Chiara Bartolini, Wystan Benbow, Bruna Bertucci, Elisabetta Bissaldi, Massimiliano Bitossi, Massimo Capasso, Mirco Caprai, Davide Cerasole, Zachary Curtis-Ginsberg, Gaia De Palma, Leonardo Di Venere, Miguel Escobar Godoy, Qi Feng, Emanuele Fiandrini, Lucy Fortson, Stefan Funk, Amy Furniss, Alasdair Gent, Stefano Germani, Nicola Giglietto, Francesco Giordano, William Hanlon, Sam Heiman, Olivier Hervet, Maria Ionica, Weidong Jin, David Kieda, Francesco Licciulli, Pierpaolo Loizzo, Serena Loporchio, Giovanni Marsella, Reshmi Mukherjee, Nepomuk Otte, Francesca Romana Pantaleo, Riccardo Paoletti, Deivid Ribeiro, Luca Riitano, Emmet Roache, Duncan Ross, Lab Saha, Heiko Salzmann, Benjamin Schwab, Ruo-Yu Shang, Gianluigi Silvestre, Leonardo Stiaccini, Hiroyasu Tajima, Svanik Tandon, Giovanni Tripodo, Justin Vandenbroucke, Vladimir V. Vassiliev, Richard White, David A. Williams, Adrian Zink

TL;DR

This paper presents the design, calibration, and performance evaluation of the upgraded prototype Schwarzschild–Couder Telescope (pSCT) camera module for CTAO. It details a modular focal-plane architecture with 11,328 SiPM pixels organized into 177 modules, each featuring SMART ASICs and advanced readout via CTC/CT5TEA with TARGET-based sampling, aimed at reducing noise and crosstalk while enabling high-throughput operation. The authors describe calibration procedures (Vped, Wilkinson ramp, VTrimT, and TARGET DC transfer functions) and perform extensive performance tests, including trigger performance, baseline stability, electrical and optical pulse responses, generalized Poisson analysis, gain equalization, and crosstalk assessment; results show low noise, minimal electronics crosstalk, linear responses, and charge resolutions near Poisson limits at low light. The work demonstrates that the upgraded modules meet design goals and provides a clear path toward mass calibration and commissioning of all 177 modules, enabling robust performance validation at known VHE gamma-ray sources. These findings have direct implications for improving angular resolution, sensitivity, and linear dynamic range in the SCT-based CTAO arrays.

Abstract

The Cherenkov Telescope Array Observatory (CTAO) is a ground-based observatory that will improve upon the sensitivities of the current generation of very-high-energy gamma-ray instruments. The Schwarzschild-Couder Telescope (SCT) is a dual-mirror candidate design for a CTAO Medium-Sized Telescope (MST). The prototype Schwarzschild-Couder Telescope (pSCT) was inaugurated in 2019 at Fred Lawrence Whipple Observatory (FLWO) in Arizona and observed significant gamma-ray emission from the Crab Nebula with a partially populated camera. The pSCT camera is currently being upgraded to fully instrument the focal plane with 11,328 silicon photomultiplier (SiPM) pixels split between 177 camera modules. Additionally, the modules will feature upgraded electronics designed to reduce electronics crosstalk and noise. A module calibration procedure has been developed using a preproduction test module. Following this calibration procedure, performance testing shows that the upgrade module has low noise, minimal electronics crosstalk, and excellent charge resolution. After calibration and optimization, the 177 production modules will be installed in the pSCT camera for commissioning. This will be followed by observations of known VHE gamma-ray sources for camera performance validation.

Design and Performance of the Upgraded Prototype Schwarzschild-Couder Telescope Camera Module

TL;DR

This paper presents the design, calibration, and performance evaluation of the upgraded prototype Schwarzschild–Couder Telescope (pSCT) camera module for CTAO. It details a modular focal-plane architecture with 11,328 SiPM pixels organized into 177 modules, each featuring SMART ASICs and advanced readout via CTC/CT5TEA with TARGET-based sampling, aimed at reducing noise and crosstalk while enabling high-throughput operation. The authors describe calibration procedures (Vped, Wilkinson ramp, VTrimT, and TARGET DC transfer functions) and perform extensive performance tests, including trigger performance, baseline stability, electrical and optical pulse responses, generalized Poisson analysis, gain equalization, and crosstalk assessment; results show low noise, minimal electronics crosstalk, linear responses, and charge resolutions near Poisson limits at low light. The work demonstrates that the upgraded modules meet design goals and provides a clear path toward mass calibration and commissioning of all 177 modules, enabling robust performance validation at known VHE gamma-ray sources. These findings have direct implications for improving angular resolution, sensitivity, and linear dynamic range in the SCT-based CTAO arrays.

Abstract

The Cherenkov Telescope Array Observatory (CTAO) is a ground-based observatory that will improve upon the sensitivities of the current generation of very-high-energy gamma-ray instruments. The Schwarzschild-Couder Telescope (SCT) is a dual-mirror candidate design for a CTAO Medium-Sized Telescope (MST). The prototype Schwarzschild-Couder Telescope (pSCT) was inaugurated in 2019 at Fred Lawrence Whipple Observatory (FLWO) in Arizona and observed significant gamma-ray emission from the Crab Nebula with a partially populated camera. The pSCT camera is currently being upgraded to fully instrument the focal plane with 11,328 silicon photomultiplier (SiPM) pixels split between 177 camera modules. Additionally, the modules will feature upgraded electronics designed to reduce electronics crosstalk and noise. A module calibration procedure has been developed using a preproduction test module. Following this calibration procedure, performance testing shows that the upgrade module has low noise, minimal electronics crosstalk, and excellent charge resolution. After calibration and optimization, the 177 production modules will be installed in the pSCT camera for commissioning. This will be followed by observations of known VHE gamma-ray sources for camera performance validation.

Paper Structure

This paper contains 25 sections, 9 equations, 38 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Design Overview
  3. Focal Plane Module
  4. Front-End Electronics
  5. SiPM bias control system
  6. SiPM Temperature Monitoring and Control
  7. Calibration
  8. Vped DAC
  9. Wilkinson Ramp
  10. VTrimT
  11. TARGET DC Transfer Function
  12. Performance
  13. Testing Setup
  14. Trigger Performance
  15. SMART Slow monitoring calibration
  16. ...and 10 more sections

Figures (38)

  • Figure 1: Design of the SCT camera. The full camera is composed of nine sectors, each of which can hold up to 25 photo-detection modules. The entire camera has 177 modules (corner sectors are equipped with fewer modules to replicate a circular shape). Each module has 64 pixels, for a total of 11,328 pixels in the fully-equipped camera camera_paper_jatis.
  • Figure 2: Block diagram of the module signal path. The thicker lines indicate bundles of four channels that are not drawn out separately. The signal is first detected by the SiPMs before traveling to the SMART ASIC and then the FEE. The Vped DAC in the CT5TEA provides a DC bias that is AC coupled to the input signal. The signal from each channel then splits to travel to its respective trigger group (formed by four signal channels) for triggering and to the CTC ASIC for digitization. This diagram represents only one quadrant which contains 1/4 of the channels in the module.
  • Figure 3: Drawing of the pSCT camera upgraded module. The module consists of two main parts: the FPM (front) and the FEE (rear) parts. The FEE module is composed of an Auxiliary and a Primary board. Between the FPM and the FEE, a 3D-printed cage houses a Peltier cooling system to temperature stabilize the SiPMs 10.1117/12.2530431.
  • Figure 4: Photograph of the upgraded pSCT camera module.
  • Figure 5: Drawing of the FPM as seen from the front (left) and from the back (right). On the left side, the 4 SiPMs tiles are visible, connected to the SMART ASIC boards. The blue ribbon cable connects the SMART ASICs to the FEE. The system is supported by a base-plate (left drawing, on the right end) to avoid movements 10.1117/12.2530431.
  • ...and 33 more figures