Lightning Under a Microscope: What High-Voltage Discharge Modeling Showed

Scientists from the P. N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI RAS) and the Moscow Institute of Physics and Technology (MIPT) conducted a series of experiments revealing the mechanisms of X-ray generation in artificial lightning. The study,published in Journal of Applied Physics, allowed for the first time to record the temporal and angular characteristics of this phenomenon with high accuracy, opening up new opportunities for studying natural lightning and developing technologies to protect against it.

Image source сгенерировано нейросетью Sora

In the experiments, scientists used a high-voltage setup that creates pulses with a voltage of up to 1 megavolt in an air gap of 55 cm. A system of 10 scintillation detectors, arranged in an arc with a step of 10 degrees, was used to register X-ray radiation. This made it possible not only to record flashes but also to determine their directionality.

Polar maps illustrating the spatio-temporal features of high-energy photon emissions during discharge. The radius of the map is the time axis, the angular axis is represented by ten positions of X-ray detectors with a step of 10 degrees, individual rays correspond to the angular position of the X-ray detector. Data from the detectors - temporal signals of radiation bursts - are correlated with temporal rays directed to the angular positions of the detectors. In the angular sectors, the data is interpolated linearly. The intensity of the polar map describes the dynamics of the signal amplitude. The figure shows data for series of measurements with an aluminum filter 3 mm thick (cutoff energy Ev≈17 keV), a lead filter 3 mm thick (Ev≈170 keV), and a lead filter 10 mm thick (Ev≈300keV).
Image source Naked Science

The main discovery was that X-ray radiation appears even before the lightning flash itself, at the moment when the voltage reaches its maximum value. At the same time, scientists discovered two different types of radiation. The first type propagates in all directions, but at high energies, the radiation is directed towards the negative electrode (anode). The second type turned out to be more mysterious - these are high-energy rays that appear on the periphery of the main discharge, which has not yet found a complete explanation.

Statistical maps illustrating all registered X-ray bursts from the point of view of their number of observations (obtained by averaging over time intervals of 1 ns) and total power (sum of the squares of the amplitudes of all useful signals above the noise level). The figure shows data for series of measurements with an aluminum filter 3 mm thick (cutoff energy Ev≈17 keV), a lead filter 3 mm thick (Ev≈170 keV), and a lead filter 10 mm thick (Ev ≈ 300 keV).
Image source Naked Science

(a) The region of the discharge gap selected for modeling the electric field strength. (b) Visualization of the electric field strength (kV/cm) at a voltage of 1 MV with a scale grid in millimeters. The field distributions for three control sections highlighted on the maps are shown.
Image source Journal of Applied Physics

Physicists have established that the reason for the appearance of X-ray radiation lies in the behavior of electrons. Under the influence of enormous voltage, electrons accelerate to extremely high speeds and collide with air molecules, which leads to the appearance of X-ray radiation.

Our results show that hard X-ray radiation in atmospheric discharges is associated with ultrafast ionization processes. This opens the way to a more accurate modeling of natural electrical discharges, such as lightning.

Yaroslav Bolotov, Assistant of the Phystech Cluster of Academic and Scientific Career of MIPT

This discovery will help to more accurately model lightning and develop methods to protect against it.

The studies conducted for the first time with high temporal and spatial accuracy established the time frame and angular characteristics of X-ray radiation in discharges. This allows us to revise the mechanisms of its generation and take into account the influence of complex plasma structures. These discoveries are important for understanding the physical processes occurring in thunderclouds and can also be used in technological developments.

Alexander Oginov, Acting Head of the Department of High Energy Density Physics of the P. N. Lebedev Physical Institute

Scientists plan to study the influence of other electrode configurations and environmental parameters, as well as increase the temporal resolution of measurements. These studies can be used not only in atmospheric physics but also in plasma technologies.

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