Calibration and performance of the readout system based on switched capacitor arrays for the Large-Sized Telescope of the Cherenkov Telescope Array

TL;DR

This paper details the calibration and performance evaluation of a high-speed readout system based on switched capacitor arrays for the Large-Sized Telescope of the Cherenkov Telescope Array, enhancing gamma-ray detection accuracy.

Contribution

It introduces a calibration method for the DRS4-based readout system and demonstrates its effective performance in a real telescope camera.

Findings

Calibrated the DRS4 output voltage and sampling intervals.

Achieved precise charge and time resolution measurements.

Validated system performance under various observational conditions.

Abstract

The Cherenkov Telescope Array (CTA) is the next-generation ground-based very-high-energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA is designed to detect gamma rays between 20 GeV and a few TeV with a 23-meter diameter mirror. We have developed the focal plane camera of the first LST, which has 1855 photomultiplier tubes (PMTs) and the readout system which samples a PMT waveform at GHz with switched capacitor arrays, Domino Ring Sampler ver4 (DRS4). To measure the precise pulse charge and arrival time of Cherenkov signals, we developed a method to calibrate the output voltage of DRS4 and the sampling time interval, as well as an analysis method to correct the spike noise of DRS4. Since the first LST was inaugurated in 2018, we have performed the commissioning tests and calibrated the camera. We characterised the camera in terms of the charge pedestal under various conditions of the night sky background, the charge resolution of each pixel, the charge uniformity of the whole camera, and the time resolutions with a test pulse and calibration laser.