arXiv subjects

Carlos Delgado

Publications and source records attributed to Carlos Delgado.

8 recordsLinked to original sources

arXiv2023

Detecting gamma rays with high resolution and moderate field of view: the air Cherenkov technique

The Imaging Atmospheric Cherenkov technique allows to detect very high energy gamma rays from few tens of GeV to hundreds of TeV using ground-based instrumentation. At these energies a gamma ray generates a shower of secondary particles when it enters the Earth's atmosphere. These particles emit Cherenkov light in the visible and near UV ranges. The Cherenkov light produced by the shower reaches the ground as a short pulse of a few nanosecond duration over a large circle of around 100 m radius (a light pool). This pulse of light can be imaged with telescopes provided with fast photodetectors and electronics. Combining the images of several telescopes distributed over this light pool allows to estimate the gamma-ray energy and incident direction, and to reject gamma rays from the strong background of charged cosmic rays. The collection area of an array of a few telescopes is of the order of the area of the light pool, i.e. $>$10$^5$m$^2$. Such an array reaches a sensitivity of a few millicrabs at 100 GeV energies in 50 hours of observations, an angular resolution of $\sim$5 arcmin and a spectral resolution of $\sim$10%. This chapter describes the technical implementation of Imaging Atmospheric Cherenkov telescopes and describes how the data are analyzed to reconstruct the physical parameters of the primary gamma rays.

astro-ph.IM↗

arXiv2022

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

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.

astro-ph.IM↗

arXiv2021

Mapping Access to Water and Sanitation in Colombia using Publicly Accessible Satellite Imagery, Crowd-sourced Geospatial Information and RandomForests

Up-to-date, granular, and reliable quality of life data is crucial for humanitarian organizations to develop targeted interventions for vulnerable communities, especially in times of crisis. One such quality of life data is access to water, sanitation and hygeine (WASH). Traditionally, data collection is done through door-to-door surveys sampled over large areas. Unfortunately, the huge costs associated with collecting these data deter more frequent and large-coverage surveys. To address this challenge, we present a scalable and inexpensive end-to-end WASH estimation workflow using a combination of machine learning and census data, publicly available satellite images, and crowd-sourced geospatial information. We generate a map of WASH estimates at a granularity of 250m x 250m across the entire country of Colombia. The model was able to explain up to 65% of the variation in predicting access to water supply, sewage, and toilets. The code is made available with MIT License at https://github.com/thinkingmachines/geoai-immap-wash.

cs.CY↗

arXiv2017

Antiproton identification below threshold with AMS-02 RICH detector

The Alpha Magnetic Spectrometer (AMS-02) was installed on the International Space Station (ISS) and it has been collecting data successfully since May 2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays. In order to identify particle properties, AMS-02 includes several specialized sub-detectors. Among them, the AMS-02 Ring Imaging Cherenkov detector (RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles. We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV. Ray tracing integration method is used to maximize the statistics of $\bar{p}$ with the lowest possible $e^{-}$ background, providing 4 times rejection power gain for $e^{-}$ background with respect to only 3\% of $\bar{p}$ signal efficiency loss. By using the collected cosmic-rays data, $e^{-}$ contamination can be well suppressed within 3\% with $β\approx 1$, while keeping 76\% efficiency for $\bar{p}$ below the threshold.

physics.ins-det↗

arXiv2016

Reconfigurable ASIC for a Low Level Trigger System in Cherenkov Telescope Cameras

A versatile and reconfigurable ASIC is presented, which implements two different concepts of low level trigger (L0) for Cherenkov telescopes: the Majority trigger (sum of discriminated inputs) and the Sum trigger concept (analogue clipped sum of inputs). Up to 7 input signals can be processed following one or both of the previous trigger concepts. Each differential pair output of the discriminator is also available as a LVDS output. Differential circuitry using local feedback allows the ASIC to achieve high speed (500 MHz) while maintaining good linearity in a 1 Vpp range. Experimental results are presented. A number of prototype camera designs of the Cherenkov Telescope Array (CTA) project will use this ASIC.

astro-ph.IM↗

arXiv2015

Development of the photomultiplier tube readout system for the first Large-Sized Telescope of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next generation ground-based very high energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA targets 20 GeV -- 1 TeV gamma rays and has 1855 photomultiplier tubes (PMTs) installed in the focal plane camera. With the 23 m mirror dish, the night sky background (NSB) rate amounts to several hundreds MHz per pixel. In order to record clean images of gamma-ray showers with minimal NSB contamination, a fast sampling of the signal waveform is required so that the signal integration time can be as short as the Cherenkov light flash duration (a few ns). We have developed a readout board which samples waveforms of seven PMTs per board at a GHz rate. Since a GHz FADC has a high power consumption, leading to large heat dissipation, we adopted the analog memory ASIC "DRS4". The sampler has 1024 capacitors per channel and can sample the waveform at a GHz rate. Four channels of a chip are cascaded to obtain deeper sampling depth with 4096 capacitors. After a trigger is generated in a mezzanine on the board, the waveform stored in the capacitor array is subsequently digitized with a low speed (33 MHz) ADC and transferred via the FPGA-based Gigabit Ethernet to a data acquisition system. Both a low power consumption (2.64 W per channel) and high speed sampling with a bandwidth of $>$300 MHz have been achieved. In addition, in order to increase the dynamic range of the readout we adopted a two gain system achieving from 0.2 up to 2000 photoelectrons in total. We finalized the board design for the first LST and proceeded to mass production. Performance of produced boards are being checked with a series of quality control (QC) tests. We report the readout board specifications and QC results.

astro-ph.IM↗

arXiv2014

Analogue Sum ASIC for L1 Trigger Decision in Cherenkov Telescope Cameras

The Cherenkov Telescope Array (CTA) project aims to build the largest ground-based gamma-ray observatory based on an array of Imaging Atmospheric Cherenkov Telescopes (IACTs). The CTA will implement a multi-level trigger system to distinguish between gamma ray-like induced showers and background images induced by night sky background (NSB) light. The trigger system is based on coincident detections among pixels (level 0 trigger), clusters of pixels (level 1) or telescopes. In this article, the first version of the application specific integrated circuit (ASIC) for Level 1 trigger system is presented, capable of working with different Level 0 strategies and different trigger region sizes. In addition, it complies with all the requirements specified by the CTA project, specially the most critical ones as regards noise, bandwidth, dynamic range and power consumption. All these features make the presented system very suitable for use in the CTA cameras and improve the features of discrete components prototypes of the L1 trigger circuit in terms of compactness, noise, performance and power consumption.

physics.ins-det↗

arXiv2013

Mechanics and cooling system for the camera of the Large Size Telescopes of the Cherenkov Telescope Array (CTA)

Mechanics of the camera for the large size telescopes of CTA must protect and provide a stable environment for its instrumentation. This is achieved by a stiff support structure enclosed in an air and water tight volume. The structure is specially devised to facilitate extracting the power dissipated by the focal plane electronics while keeping its weight small enough to guarantee an optimum load on the telescope structure. A heat extraction system is designed to keep the electronics temperature within its optimal operation range, stable in time and homogeneous along the camera volume, whereas it is decoupled from the temperature in the telescope environment. In this contribution, we present the details of this system as well as its verification based in finite element analysis computations and tested prototypes. Finally, issues related to the integration of the camera mechanics and electronics will be dealt with.

astro-ph.IM↗