A versatile digital camera trigger for telescopes in the Cherenkov Telescope Array

Abstract

a b s t r a c tThis paper describes the concept of an FPGA-based digital camera trigger for imaging atmospheric Cherenkov telescopes, developed for the future Cherenkov Telescope Array (CTA). The proposed camera trigger is designed to select images initiated by the Cherenkov emission of extended air showers from very-high energy (VHE, E 420 GeV) photons and charged particles while suppressing signatures from background light. The trigger comprises three stages. A first stage employs programmable discriminators to digitize the signals arriving from the camera channels (pixels). At the second stage, a grid of low-cost FPGAs is used to process the digitized signals for camera regions with 37 pixels. At the third stage, trigger conditions found independently in any of the overlapping 37-pixel regions are combined into a global camera trigger by few central FPGAs. Trigger prototype boards based on Xilinx FPGAs have been designed, built and tested and were shown to function properly. Using these components a full camera trigger with a power consumption and price per channel of about 0.5 W and 19 €, respectively, can be built. With the described design the camera trigger algorithm can take advantage of pixel information in both the space and the time domain allowing, for example, the creation of triggers sensitive to the timegradient of a shower image; the time information could also be exploited to online adjust the time window of the acquisition system for pixel data. Combining the results of the parallel execution of different trigger algorithms (optimized, for example, for the lowest and highest energies, respectively) on each FPGA can result in a better response over all photons energies (as demonstrated by Monte Carlo simulation in this work).

Pavement Damage Crack Recognition Method Based on High-Resolution Linear Array Cameras and Adaptive Lifting Algorithm

“…In this paper, high-resolution linear array cameras, image capture cards, combined with integrated LED lights, industrial personal computer(IPC), optical encoder, GPS and other auxiliary devices are used to acquire and store real-time road images, and are integrated as a whole system in a commercial vehicle [19][20][21][22]. By contrast, we use line frequency of 140kHz, a resolution of 4k, the model for the Basler sprint-spL4096-140km CMOS linear array cameras to capture road images [23][24][25][26].…”

NectarCAM, a camera for the medium sized telescopes of the Cherenkov telescope array

“…This trigger scheme is known to be very efficient at low energies and will be installed on the LSTCAM. The other possibility (see Reference [7]) is the Digital trigger which uses combinations of digitized input at L0. This fully digital trigger scheme is not as efficient for triggering at low energies but has more flexible for changing trigger algorithms.…”

NectarCAM : a camera for the medium size telescopes of the Cherenkov Telescope Array

“…This trigger scheme is known to be very efficient at low energies and will be installed on the LST camera. The other possibility, (see Reference [4]) is the 'Digital trigger' which uses combinations of digitized input at L0. This fully digital trigger scheme is not as efficient for triggering at low energies but is more flexible.…”