Design and Characterisation of Calibration Systems for Small-Sized Telescope Cameras in the Cherenkov Telescope Array.

Abstract

The Cherenkov Telescope Array Observatory (CTAO) represents the next generation in very-high-energy gamma-ray astronomy, promising an order-of-magnitude improvement in sensitivity over existing instruments. With a diverse array of telescopes, including the Small-Sized Telescopes
(SSTs) optimized for the highest energies, CTAO will open new windows on the gamma-ray sky in the 20 GeV–300 TeV regime and beyond. A critical component enabling this scientific performance is the stability and reliability of the telescope cameras, which rely on fast photo sensors. For example - Silicon Photomultiplier (SiPM) in SST Camera. Since SiPM characteristics can drift due to temperature variations, aging, or operational conditions, a robust calibration system is essential to ensure data quality and long-term stability.
This thesis presents the design, testing, and integration of the calibration system developed for the SST camera (SSTCAM). Beginning with a review of calibration strategies employed in current-generation gamma ray telescopes, the work identifies the performance requirements imposed by CTAO and adapts them for the SSTCAM. The development process
is described across successive design iterations, including hardware prototypes and firmware implementations. Extensive performance studies of the calibration device are reported, covering dynamic range, operating condition dependencies, and beam profile characterization. Results demonstrate compliance with CTAO specifications while also revealing
areas for improvement.
Building on these findings, the thesis explores the transition from a single-channel device to a multi-channel calibration unit capable of supporting diverse activities such as flat-fielding, pixel linearity monitoring, and single photo-electron calibration. The final design integrates lessons learned from earlier versions and outlines a pathway toward full incorporation within the SSTCAM. In parallel, simulation studies are conducted
to assess the feasibility of applying the calibration procedures in practice, offering guidance for future system integration.
By providing a dedicated, flexible, and high-performance calibration solution, this work contributes a key technological element to the success
of the CTAO’s SST program.