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Radio wave propagation in heterogeneous media: implications on the electronics of Cosmic Neutrino Detectors

Periodic Reporting for period 2 - CosNeD (Radio wave propagation in heterogeneous media: implications on the electronics of Cosmic Neutrino Detectors)

Reporting period: 2018-05-01 to 2018-10-31

The enduring impact of this project will be to solve some of the outstanding conceptual problems in the origin of the high energy cosmic particles, their production, acceleration and propagation mechanisms. Thus detection of neutrinos can answer very important questions related to some extremely energetic yet unexplained astrophysical sources such as: compact binary stars, accreting black holes, supernovae etc., key elements in understanding the evolution and fate of the Universe. Moreover, these particles carry the highest energies per particle known to man, impossible to achieve in any present or foreseen man made accelerator devices thus their detection can test and probe extreme high energy physics.
Neutrino astronomy (NA) is a new multidisciplinary field of research studying the particles coming in the Universe, where Nuclear and Particle Physics, Astronomy, Astrophysics, Cosmology and engineering converge. As the cosmic messengers (gamma rays, charged particles, neutrinos) are rare and difficult to detect, the technique employed requires deployment of large area detectors and use of large volume natural detector media (atmosphere, see water, ice, salt ore). The infrastructures, technology and methods also have potential applications for environmental and climate studies.
The contribution of NA to other research fields represents more than the transfer of technology from one discipline to another. The technical requirements imposed by the construction of complex detectors enhanced cutting edge technology, especially in the radio domain, where many of the discoveries already have commercial applications.

To summarize, one goal of the project is to determine experimentally the radio attenuation length in salt mines and estimate the implications on a cosmic neutrino detector. The same type of measurements can be used: to validate and improve previous work on theoretical models of propagation in heterogeneous media (which represents the second goal of the project), and to study the behaviour of classical antennas in non-conventional media (third goal of the project).
The results to be obtained would be immediately relevant in determination of the key parameters that describe a cosmic neutrino detector, its performances and limitations. The events detected by such a telescope will allow identification of individual sources indicating a step forward in “neutrino astronomy”. The extensive propagation and antenna behaviour studies in heterogeneous media will be in the direct interest for the scientific community and have a prompt impact in telecommunications theory and industry.
"Our project is focused on both development of a radio indirect techniques for detecting cosmic neutrinos (with a km3 neutrino detector in a salt mine) to searching the High Energy Universe, and theoretical and experimental work to characterize radio wave propagation and antennas behaviour in a multi-layered medium, where each layer has a width of a few centimeters and different constituent impurities. As stated in the Description of the action (DoA) we had specific objectives in two directions: A. Propagation in unconventional media, and B. Cosmic neutrinos detection in salt domes. Table 3 in DoA specified as publications the following deliverables: (a) 2 articles submitted to conferences (month 14, 20), (b) 3 articles submitted to journals (months 17, 20 and 24). All this has been accomplished (details are given in the following).

Regarding direction A, as waves propagate in a non-ideal medium before being measured by radio antennas, it is impetuous to have first a good geophysical material description for radio wave propagation. This regime is not well understood thus both theoretical and experimental study was needed (objectives O2, O5). Moreover, the behaviour of antennas when buried in little known is little known (O6). The novel and/or unconventional methodologies used to characterize the two subjects are detailed in section 1.2 (i) and (ii), and lead to articles: “A.M. Badescu, 2018, The transfer function of a boreholed dipole antenna, IEEE Transactions on Antennas and propagation, vol. 66, no 11, pp 5757-57631”, and “A.M. Badescu, A large scale characterization of the dielectric properties of heterogeneous layered rock salt, submitted for publication at Measurement journal”. Validation of the antenna transfer function model was presented in a conference - A.M. Badescu, I. Mocanu, 2018, The scattering parameters of boreholed antennas in the UHF band, International Conference on Electromagnetics in Advanced Applications (ICEAA), 10-14 Sept. 2018, Cartagena, pp. 99 – 102, https://ieeexplore.ieee.org/document/8520422.
It should be stated that all results rely on performed measurements of the attenuation length in salt (O1) and require the knowledge of the radio noise margin, that has to be extracted from measurements (O3). Preliminary results on the attenuation length (O1) as recorded in “Unirea” salt mine (Slanic Prahova) were presented in a conference -A. Badescu, A. Saftoiu, I. Brancus, D. Stanca, B. Mitrica, 2017, Results on radio attenuation length recorded in a Romanian salt mine, Volume 301 - 35th International Cosmic Ray Conference (ICRC2017) -Session Neutrino. NU-instrumentation, (https://pos.sissa.it/301/1039/).

Regarding direction B, the optimization of a neutrino detector requires first that the results obtained in “direction A” (propagation and antenna behavior in salt) to be correlated with the radio signal produced by neutrinos’ interaction in salt (O4). The novel and/or unconventional methodologies used to characterize radio emission in neutrinos’ interaction are detailed in section 1.2 (iii), and represented the subject of the article A. Saftoiu, 2018, Estimation of radio emission from neutrino induced showers in rock salt above 10^18 eV, submitted for publication to Astroparticle Physics journal. A preliminary analysis with the overall results for “Unirea” site was carried out in A. Badescu A. Saftoiu, L. Dogariu, 2018, Radio detection of cosmic neutrinos"", on “V International Congreso Latinoamericano de Fisica”, 8-12 October 2018, Puebla (O4).
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The development of instruments and techniques for the study of cosmic particles using radio antennas placed in different dielectric media constitutes one of the top priorities in the international astroparticle physics development. Such activity, regarding the possibility to detect high energy neutrinos using radio detection in salt, is unique in the astroparticle research in Europe and the results will be of high interest for the whole scientific community.
This project represents a step forward in NA. The highest energy cosmic particles will be detected and explained. Not only information about these mysterious particles will be retrieved, but mechanisms of their production and acceleration will be explained.

This project represents a first, essential step for the construction of an international radio detector in a salt mine. The field itself has never been isolated from other domains like: nuclear physics, particle physics, astrophysics, cosmology, radio propagation, antenna design. This augments the impact of such results not only in the limited frame of neutrino astronomy but also in the related fields.
Results will have direct implications in understanding the nature of the cosmic neutrinos with immediate repercussions in astrophysics. The phenomena that influence radio wave propagation in heterogeneous media will be better understood. Another important subject that will be improved deals with description of antennas’ behaviour in non-conventional media.
Dissemination of the project in the EUResearch Magazine