A. Grillo

Characterization and performance of the ASIC (CITIROC) front-end of the ASTRI camera

Abstract The Cherenkov Imaging Telescope Integrated Read Out Chip, CITIROC, is a chip adopted as the front-end of the camera at the focal plane of the imaging Cherenkov ASTRI dual-mirror small size telescope (ASTRI SST-2M) prototype. This paper presents the results of the measurements performed to characterize CITIROC tailored for the ASTRI SST-2M focal plane requirements. In particular, we investigated the trigger linearity and efficiency, as a function of the pulse amplitude. Moreover, we tested its response by performing a set of measurements using a silicon photomultiplier (SiPM) in dark conditions and under light pulse illumination. The CITIROC output signal is found to vary linearly as a function of the input pulse amplitude. Our results show that it is suitable for the ASTRI SST-2M camera.

Silicon Photomultipliers Electrical Model Extensive Analytical Analysis

The present work aims to address a comprehensive analytical analysis of a new accurate equivalent electrical model of silicon photomultiplier (SiPM) detectors. The proposed circuit model allows to truthfully reproduce the output signal waveform generated by the light sensors apart from the specific technology adopted for the fabrication process, and can also be profitably exploited to perform reliable circuit-level simulations. A detailed and in-depth investigation of the functional parameters involved in the output pulse signals is here developed, and the most significant physical relationships are analytically derived as well. Experimental measurements are finally carried out on real devices, in order to validate the accuracy of the attained expressions, and good fittings are achieved between the analytical curve plots and the associated measurements results. The adopted analysis turns out to be particularly helpful when designing an optimum front-end architecture for SiPM detectors, since the performance of the entire detection system, especially in terms of dynamic range and timing resolution, can be accurately predicted as a function of the SiPM model parameters and the foremost features of the coupled front-end electronics.

UVSiPM: A light detector instrument based on a SiPM sensor working in single photon counting

Abstract UVSiPM is a light detector designed to measure the intensity of electromagnetic radiation in the 320–900 nm wavelength range. It has been developed in the framework of the ASTRI project whose main goal is the design and construction of an end-to-end Small Size class Telescope prototype for the Cherenkov Telescope Array. The UVSiPM instrument is composed by a multipixel Silicon Photo-Multiplier detector unit coupled to an electronic chain working in single photon counting mode with 10 nanosecond double pulse resolution, and by a disk emulator interface card for computer connection. The detector unit of UVSiPM is of the same kind as the ones forming the camera at the focal plane of the ASTRI prototype. Eventually, the UVSiPM instrument can be equipped with a collimator to regulate its angular aperture. UVSiPM, with its peculiar characteristics, will permit to perform several measurements both in lab and on field, allowing the absolute calibration of the ASTRI prototype.

Accurate Analytical Single-Photoelectron Response of Silicon Photomultipliers

This paper addresses a comprehensive analytical analysis of a new accurate electrical model of silicon photomultiplier (SiPM) detectors. The adopted circuit model allows to truly reproduce the SiPM output signal waveform apart from the specific technology employed for the fabrication process, and can also be profitably exploited to perform reliable circuit-level simulations. A novel analytical expression of the transient single-photoelectron response due to photon absorption is systematically developed. The attained function accurately reproduces the fast detector ignition, ensuing avalanche self-quenching, and final slow recharging operation. Predictive capabilities of the adopted analytical model are demonstrated by means of experimental measurements on a real detector.

Characterization of EASIROC as Front-End for the readout of the SiPM at the focal plane of the Cherenkov telescope ASTRI

The Extended Analogue Silicon Photo-multiplier Integrated Read Out Chip, EASIROC, is a chip proposed as front-end of the camera at the focal plane of the imaging Cherenkov ASTRI SST-2M telescope prototype. This paper presents the results of the measurements performed to characterize EASIROC in order to evaluate its compliance with the ASTRI SST-2M focal plane requirements. In particular, we investigated the trigger time walk and the jitter effects as a function of the pulse amplitude. The EASIROC output signal is found to vary linearly as a function of the input pulse amplitude with very low level of electronic noise and cross-talk (<1%). Our results show that it is suitable as front-end chip for the camera prototype, although, specific modifications are necessary to adopt the device in the final version of the telescope.

The camera of the ASTRI SST-2M prototype for the Cherenkov Telescope Array

In the context of the Cherenkov Telescope Array observatory project, the ASTRI SST-2M end-to-end prototype telescope, entirely supported by the Italian National Institute of Astrophysics, is designed to detect cosmic primary gamma ray energies from few TeV up to hundreds of TeV. The ASTRI SST-2M prototype camera is part of the challenging synergy of novel optical design, camera sensors, front-end electronics and telescope structure design. The camera is devoted to imaging and recording the Cherenkov images of air showers induced by primary particles into the Earth’s atmosphere. In order to match the energy range mentioned above, the camera must be able to trigger events within a few tens of nanoseconds with high detection efficiency. This is obtained by combining silicon photo-multiplier sensors and suitable front-end electronics. Due to the characteristic imprint of the Cherenkov image that is a function of the shower core distance, the signal dynamic range of the pixels and consequently of the front-end electronics must span three orders of magnitude (1:1000 photo-electrons). These and many other features of the ASTRI SST-2M prototype camera will be reported in this contribution together with a complete overview of the mechanical and thermodynamic camera system.

Characterization of the front-end EASIROC for read-out of SiPM in the ASTRI camera

Abstract The design and realization of a prototype for the Small-Size class Telescopes of the Cherenkov Telescope Array is one of the cornerstones of the ASTRI project. The prototype will adopt a focal plane camera based on Silicon Photo-Multiplier sensors that coupled with a dual mirror optics configuration represents an innovative solution for the detection of Atmospheric Cherenkov light. These detectors can be read by the Extended Analogue Silicon Photo-Multiplier Integrated Read Out Chip (EASIROC) equipped with 32-channels. In this paper, we report some preliminary results on measurements aimed to evaluate EASIROC capability of autotriggering and measurements of the trigger time walk, jitter, DAC linearity and trigger efficiency vs the injected charge. Moreover, the dynamic range of the ASIC is also reported.

The ASTRI camera for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) foresees, in its southern site (Chile), the implementation of up to 70 small-sized telescopes (SSTs), which will extend the energy coverage up to hundreds of TeV. It has been proposed that one of the first set of CTA SSTs will be represented by the ASTRI mini-array, which includes (at least) nine ASTRI telescopes. The endto-end prototype of such telescopes, named the ASTRI SST-2M, is installed in Italy and it is now completing the overall commissioning and entering the science verification phase. ASTRI telescopes are characterized by an optical system based on a dual-mirror Schwarzschild-Couder design and a camera at the focal plane composed of silicon photomultiplier sensors managed by a fast read-out electronics specifically designed. Based on a custom peak-detector mode, the ASTRI camera electronics is designed to perform Cherenkov signal detection, trigger generation, digital conversion of the signals and data transmission to the camera server. In this contribution we will describe the main features of the ASTRI camera, its performance and results obtained during the commissioning phase of the ASTRI SST-2M prototype in view of the ASTRI mini-array implementation.

A New Simple and Effective Procedure for SiPM Electrical Parameter Extraction

Silicon photomultipliers (SiPMs) are emerging semiconductor-based photosensors, addressing the challenge of low-light detection down to the single-photon counting level. A design of high-performance front-end electronics for SiPM readout requires the development of accurate electrical models. Numerous SiPM reliable models have matured in recent years; however, circuit parameter extraction is rather cumbersome and involves extensive measurement steps to be performed. Starting from a recently developed model of the SiPM device coupled to the conditioning electronics, a new effective analytical procedure is, here, devised for extracting the SiPM model parameters from experimental measurements. The proposed extraction technique is applied to a 3 × 3-mm2 SiPM sensor, and is validated by comparing SPICE simulations and measurement results. Independent cross-check validation based on experimental tests corroborates the effectiveness of the adopted extraction procedure.

The ASTRI/CTA mini-array software system

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is a Flagship Project financed by the Italian Ministry of Education, University and Research, and led by INAF, the Italian National Institute of Astrophysics. The main goals of the ASTRI project are the realization of an end-to-end prototype of a Small Size Telescope (SST) for the Cherenkov Telescope Array (CTA) in a dual- mirror configuration (SST-2M) and, subsequently, of a mini-array comprising seven SST-2M telescopes. The mini-array will be placed at the final CTA Southern Site, which will be part of the CTA seed array, around which the whole CTA observatory will be developed. The Mini-Array Software System (MASS) will provide a comprehensive set of tools to prepare an observing proposal, to perform the observations specified therein (monitoring and controlling all the hardware components of each telescope), to analyze the acquired data online and to store/retrieve all the data products to/from the archive. Here we present the main features of the MASS and its first version, to be tested on the ASTRI SST-2M prototype that will be installed at the INAF observing station located at Serra La Nave on Mount Etna in Sicily.