We investigated features of corona point discharges when a grounded conductive rod is subject to a high background electric field. In the laboratory, high voltage is applied to an upper plate in a plane-to-point experiment, and the discharges are observed from a grounded rod using an ultraviolet camera and a photosensor. The current is measured using a shunt resistor, a current transformer, and a high impedance ammeter. We have found that corona current pulses have fast rise time (tens of nanoseconds) and slow decay (hundreds of nanoseconds). For the initial stage of the discharges, above a certain threshold, the frequency of pulses increases with the voltage applied. In the field, one current sensor coupled to a grounded rod, 1.5 m above a roof, was installed in a site located at an altitude of 2525 m above sea level. The same pulses observed in the laboratory are recorded during periods of electric field enhancement caused by the movement of charged clouds or lightning activity near the sensor. For that specific installation, the frequency of pulses is correlated with the ambient electric field measured 250 meters away. To the best knowledge of the authors, this is the first time in which such correlation is made for outdoor measurements, seeing that other works correlate the electric field with the average current flow. Pulses of positive corona were no longer observed when the electric field magnitude was lower than 1.8 kV/m and pulses of negative corona were more atypical and presented a higher threshold, of about 3.8 kV/m. This study is relevant for understanding the production of corona and space charges in high structures, such as wind turbine blades, towers, and buildings in general.
A: We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application.
A short description of the muon tomography demonstrator at the INFN Laboratori Nazionali di Legnaro near Padua, Italy, is given and the principal achievements owing to the data collected at that experimental facility are presented. In particular, the feasibility studies for several applications based on the muon-tomographic technology, within national and European projects, are discussed. The experimental problems and the procedures used to improve the performance are underlined. In addition, new activities and the related detector optimization are illustrated.
This article is part of the Theo Murphy meeting issue ‘Cosmic-ray muography’.
This work presents the first simultaneous X‐ray measurements from natural lightning in coincidence with a very high frequency (VHF) broadband interferometer. During an observational campaign in north‐central Colombia, five intense X‐ray bursts were detected from negative stepped leaders and two X‐ray emissions from a dart leader. Thanks to the high angular and time resolution of the interferometer, it was possible to locate the origin of high‐energy radiation during the lightning leader propagation. We study the correlation with VHF pulses and the two‐dimensional speed of the leader channels. A strong temporal correspondence has been observed between the high‐energy emissions and the most intense VHF pulses, which suggests the runaway electrons as a shared mechanism. The observations show that an X‐ray burst can have multiple high‐energy sources belonging to different leader branches, that can be several hundreds of meters apart. Therefore, from a spatial point of view, not a unique origin has to be searched, but an extensive origin of the X‐ray burst should be considered. We hypothesize similar conclusions in particular for downward TGFs and maybe for TGFs in general.
The advent of new technologies and the improvement of sensors embedded in satellites have allowed optical observations of diverse phenomena associated with lightning. Measurements of radiances from the cloud top consider all types of lightning during day and night, mainly based on the emissions of the oxygen triplet band at 777.4 nm (e.g.,
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