Intense electronic excitations and ionizations in electrical discharges in fluids
Project ID:LTC20061
Provider:Ministry of Education, Youth and Sports of the Czech Republic
Period:May 15, 2020 - Sep 11, 2022
Principal Investigator:Ing. Alexandr Frolov, Ph.D.
Co-investigatorsK. Koláček, P. Lukeš, J. Schmidt, V. Stelmashuk, P. Hoffer, J. Štraus, A. Tuholukov

Aims of the project: The common denominator of the proposed project is discharges in “exotic environments”. Liquids are the first such environment: electrical discharges in fluids are important for technological, biological and mechanical applications. An application of high voltage pulse with a fast rise time on electrodes submerged in water leads to generation and rapid expansion of a plasma channel. As a result of this expansion a shock wave is generated and a cavitation bubble is formed. Several theoretical models have been proposed for the simulation of acoustical properties of underwater electrical discharge, which can be divided according to their approach into two groups: with incompressible and compressible liquid. However, there is a burning question of what is the domain of an applicability of each approach. We believe that a simultaneous comparison of more calculated acoustical characteristics such as the spark expansion (based on electronic processes in the system with variable number of particles), the bubble cavitation dynamic and the shock wave waveform with the experimental data is necessary for reliable verification. Our colleagues from Technion, Israel will mainly participate in the simulation part of this project. The second “exotic environment” is long gap in gases at atmospheric pressure. Despite in the nature a lightning is a relatively frequent and common phenomenon, in its physics there are still “white places”. At present it seems to be established that the high-energy effects are caused by runaway electrons. For air at standard conditions, relativistic electrons with energies below several tens of MeV lose energy predominantly via ionization and excitation processes; for higher energies, the energy losses from bremsstrahlung become important as well. The study of long-gap laboratory high-voltage discharges in air at atmospheric pressure helps to elucidate some processes appearing in lightning and in this way to contribute to safety of air traffic, sensitive electronics, and to protection of human health. The basic features of lightning are already known: the runaway electrons are generated and due to that even X-rays are emitted. It turns out that moment of their birth is reasonably well known, however, the spatial localization as well as the instantaneous local environment are a little bit vague and should be improved. Sufficiently energetic X-rays initiate photonuclear reactions: from atmospheric nuclei fast neutrons are released, unstable isotopes are created that transform further to stable ones at simultaneous birth and later annihilation of positrons. The experimental part with a long high-voltage discharge will be solved in our laboratory, but the simulations of the processes taking place at the origin of this type of discharge will be carried out by colleagues from the Institute of Nuclear Fusion, Technical University of Madrid, Spain.

Results:

Frolov O., Stelmashuk V., Koláček K., Prukner V., Tuholukov A., Hoffer P., Štraus J., Schmidt J., Jirásek V., Oliva E.: Pressure in underwater spark discharge initiated with the help of bubble injection and its evaluation based on H-alpha line broadening. Journal of Physics D-Applied Physics 56 [28] (2023) č. článku 285201. [ Abstract ] [ Link ]

Stelmashuk V., Tuholukov A., Krasik Y. E., Hoffer P., Schmidt J., Štraus J., Frolov O.: Study of underwater discharge initiated by a high-voltage preliminary pulse produced by a Marx generator. Journal of Applied Physics 133 [3] (2023) č. článku 033301. [ Abstract ] [ Link ]

Stelmashuk V., Schmidt J.: An empirical resistance equation for the modelling of corona discharge in saline water. Plasma Sources Science & Technology 31 [1] (2022) č. článku 015011. [ Abstract ] [ Link ]

Cui H., Frolov O., Schmidt J., Štraus J., Burian T., Hájková V., Chalupský J., Zhao Y., Koláček K., Juha L.: Characterizing the Grating-like Nanostructures Formed on BaFinf2/inf Surfaces Exposed to Extreme Ultraviolet Laser Radiation. Applied Sciences-Basel 12 [3] (2022) č. článku 1251. E. [ Abstract ] [ Link ]

Schmidt J., Koláček K., Frolov O., Štraus J., Hoffer P., Stelmashuk V., Tuholukov A., Jiříček P., Houdková J.: Long-term changes in Al thin-film extreme ultraviolet filters. Applied Optics 60 [28] (2021) 8766-8773. [ Abstract ] [ Link ]

Koláček K., Stelmashuk V., Tuholukov A., Hoffer P., Schmidt J., Štraus J., Frolov O., Oliva E.: Modelling of time development of cylindrical underwater spark channel in compressible viscous liquid. Journal of Physics D-Applied Physics 53 [50] (2020) č. článku 505201. [ Abstract ] [ Link ]