KM3NeT Collaboration(Adrian-Martinez, S. et al), Calvo Diaz-Aldagalan, D., Hernandez-Rey, J. J., Martinez-Mora, J. A., Real, D., Zornoza, J. D., et al. (2014). Deep sea tests of a prototype of the KM3NeT digital optical module. Eur. Phys. J. C, 74(9), 3056–8pp.
Abstract: The first prototype of a photo-detection unit of the future KM3NeT neutrino telescope has been deployed in the deepwaters of the Mediterranean Sea. This digital optical module has a novel design with a very large photocathode area segmented by the use of 31 three inch photomultiplier tubes. It has been integrated in the ANTARES detector for in-situ testing and validation. This paper reports on the first months of data taking and rate measurements. The analysis results highlight the capabilities of the new module design in terms of background suppression and signal recognition. The directionality of the optical module enables the recognition of multiple Cherenkov photons from the same (40)Kdecay and the localisation of bioluminescent activity in the neighbourhood. The single unit can cleanly identify atmospheric muons and provide sensitivity to the muon arrival directions.
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Real, D., Calvo, D., Manzaneda, M., Diaz, A., Gozzini, S. R., Zornoza, J. D., et al. (2025). Novel Hybrid Low-Resource Field-Programmable-Gate-Array Time-to-Digital-Converter Architecture. IEEE Trans. Instrum. Meas., 74, 2000812–12pp.
Abstract: Time measurements are challenging in electronics given their various applications. The main focus lies not in achieving greater precision, as conventional architectures have already reached picosecond levels. Instead, the challenge stems from the use of low resources and the substantial expansion in the number of channels. This study presents a novel architecture for the implementation of time-to-digital converters (TDCs) in applications where resources are constrained. The introduced field-programmable-gate-array (FPGA)-based TDC offers a resolution of 415.84 ps, a single-shot precision of 0.45 least significant bits (LSBs) (186 ps r.m.s.) while maintaining a minimal resource occupancy. Built upon a multishift phase counter, the TDC is extended with a tap delay using the input delay available in the FPGA hardware input, doubling the resolution of the TDC. The resource utilization is minimized when compared to low-resource state-of-the-art TDCs. The number of look-up tables (LUTs) has been reduced to 102, and the number of registers to 213. Furthermore, the presented TDC exhibits favorable differential nonlinearity (DNL) (0.2 LSBs) and integral nonlinearity (0.15 LSBs). The TDC has been successfully implemented on an Artix7-2 from Xilinx. This design provides a resource-effective solution for applications requiring high precision and low resource consumption.
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Real, D., Calvo, D., Diaz, A., Alves Garre, S., Carretero, V., Sanchez Losa, A., et al. (2023). An Ultra-Narrow Time Optical Pulse Emitter Based on a Laser: UNTOPEL. IEEE Trans. Nucl. Sci., 70(10), 2364–2372.
Abstract: Light sources that emit repetitive subnanosecond pulses are used in neutrino telescopes for time calibration. Optical pulses with an ultra-narrow (subnanosecond) width can replicate the light produced by neutrino interactions, and are an important calibration and test element. By measuring the time-of-flight of the light, it is possible to provide a relative time calibration for all the detector photomultipliers. This work presents the ultra-narrow time optical pulse emitter based on a laser (UNTOPEL), an instrument emitting ultra-short laser optical pulses with a duration of 500 ps, energies per pulse of four microjoules at a wavelength of 532 nm, and a timing precision of 400 ps. The UNTOPEL pulse intensity can be fine-tuned, which is a novelty and a significant advantage in those applications that need to illuminate light detectors located at different distances with the same light intensity. The UNTOPEL pulse intensity can be controlled remotely, allowing for its use in operating conditions where physical access is impossible or difficult. Moreover, it is easy to operate and can be easily controlled through an inter-integrated circuit bus. The UNTOPEL is a sound instrument used when subnanosecond pulses and variable energy emissions are needed.
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ANTARES Collaboration(Albert, A. et al), Alves, S., Calvo, D., Carretero, V., Gozzini, R., Hernandez-Rey, J. J., et al. (2025). Acoustic positioning for deep sea neutrino telescopes with a system of piezo sensors integrated into glass spheres. Exp. Astron., 59(1), 6–61pp.
Abstract: Position calibration in the deep sea is typically done by means of acoustic multilateration using three or more acoustic emitters installed at known positions. Rather than using hydrophones as receivers that are exposed to the ambient pressure, the sound signals can be coupled to piezo ceramics glued to the inside of existing containers for electronics or measuring instruments of a deep sea infrastructure. The ANTARES neutrino telescope operated from 2006 until 2022 in the Mediterranean Sea at a depth exceeding 2000 m. It comprised nearly 900 glass spheres with 432 mm diameter and 15 mm thickness, equipped with photomultiplier tubes to detect Cherenkov light from tracks of charged elementary particles. In an experimental setup within ANTARES, piezo sensors have been glued to the inside of such – otherwise empty – glass spheres. These sensors recorded signals from acoustic emitters with frequencies from 46545 to 60235 Hz. Two waves propagating through the glass sphere are found as a result of the excitation by the waves in the water. These can be qualitatively associated with symmetric and asymmetric Lamb-like waves of zeroth order: a fast (early) one with v(e) approximate to 5 mm/mu s and a slow (late) one with v(l) approximate to 2 mm/mu s. Taking these findings into account improves the accuracy of the position calibration. The results can be transferred to the KM3NeT neutrino telescope, currently under construction at multiple sites in the Mediterranean Sea, for which the concept of piezo sensors glued to the inside of glass spheres has been adapted for monitoring the positions of the photomultiplier tubes.
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Babiano-Suarez, V. et al, Lerendegui-Marco, J., Balibrea-Correa, J., Caballero, L., Calvo, D., Ladarescu, I., et al. (2021). Imaging neutron capture cross sections: i-TED proof-of-concept and future prospects based on Machine-Learning techniques. Eur. Phys. J. A, 57(6), 197–17pp.
Abstract: i-TED is an innovative detection system which exploits Compton imaging techniques to achieve a superior signal-to-background ratio in (n, gamma) cross-section measurements using time-of-flight technique. This work presents the first experimental validation of the i-TED apparatus for high-resolution time-of-flight experiments and demonstrates for the first time the concept proposed for background rejection. To this aim, the Au-197(n, gamma) and Fe-56(n, gamma) reactions were studied at CERN n_TOF using an i-TED demonstrator based on three position-sensitive detectors. Two C6D6 detectors were also used to benchmark the performance of i-TED. The i-TED prototype built for this study shows a factor of similar to 3 higher detection sensitivity than state-of-the-art C6D6 detectors in the 10 keV neutron-energy region of astrophysical interest. This paper explores also the perspectives of further enhancement in performance attainable with the final i-TED array consisting of twenty position-sensitive detectors and newanalysis methodologies based on Machine-Learning techniques.
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