Появились новые сведения о генерации рентгеновских лучей с помощью атмосферных разрядов в лабораторных условиях.

The work has been published in Physical Review E. The X-ray radiation produced during high-voltage discharges in the air has been a subject of study for many years. This phenomenon is observed in both short and long discharges, as well as during lightning events in Earth's atmosphere. Despite a considerable amount of research, the mechanisms responsible for the generation of X-ray radiation in atmospheric discharges remain unclear. Previous studies have established that X-ray bursts are detected during the interaction of various plasma structures in the discharge – such as counter-streamers or streamer coronas of opposite polarity. However, the specific mechanisms behind the generation of X-ray radiation still require further investigation.

The recent research conducted by Russian physicists aimed to obtain comprehensive data on the spatial, temporal, and spectral characteristics of X-ray emissions in the peripheral area of a discharge initiated at voltages up to 1 MV in open air gaps measuring 55 centimeters in length. The scientists sought to identify the primary patterns in the occurrence of X-ray bursts recorded during the discharge development and to localize the spatial regions of the discharge responsible for their generation.

Experiments were carried out using high-voltage pulses with a rise time of about 200 nanoseconds and a total duration of approximately one microsecond. The discharge gap was designed with a "needle-in-cone" cathode and a hemispherical anode made of wire mesh. The parameters of the setup ensured stable conditions for observing X-ray emissions.

For precise measurements of voltage and current in the discharge, highly sensitive electrophysical devices with a temporal resolution of several nanoseconds were employed. An essential tool for the research was also six scintillation X-ray detectors (SD1-SD6), which allowed for the recording of X-ray bursts during the discharge. Each detector was equipped with a plastic scintillator (p-terphenyl+POPOP), connected to a highly sensitive photomultiplier with a temporal resolution of 3 ns, reliably shielded from electromagnetic interference and additionally placed inside a one-centimeter thick lead tube to enhance the accuracy of X-ray emission registration.

To analyze X-ray bursts from specific areas of the discharge, round lead diaphragms with a thickness of one centimeter were installed at the ends of the lead tubes. This allowed each detector to cover independent circular regions of the discharge, facilitating a more detailed study of the spatial characteristics of X-ray radiation. In some experiments, detectors without diaphragms were used, which expanded the field of view and enabled the capture of a broader energy spectrum of the radiation.

During the experiments, metallic absorption filters were used, providing a 100-fold attenuation of the photon flux with various energies. This enabled the researchers to analyze the energy spectrum of X-ray radiation and its spatiotemporal characteristics more accurately. In addition to the SD1-SD6 detector assembly, researchers utilized an assembly of wide-aperture detectors (SD1*, SD2*, SD3*), positioned closely together. Each detector was covered with an individual metal filter. Specifically, filters made of three-millimeter thick aluminum and seven and ten-millimeter thick lead were used. The SD1*-SD3* detector assembly allowed for the determination of the temporal nature of photon generation with high and low energies during a single X-ray burst.

In addition to the main X-ray detector assemblies, another highly sensitive X-ray detector (SD) with a wide aperture was used. In this detector, the photomultiplier was connected to a rectangular scintillator. The entire surface of the scintillator was covered with a 10 µm thick aluminum foil, protected by light-proof paper. The detector was not placed in a lead tube, while its large working surface allowed for the capture of more X-ray photons with various energies compared to the previously mentioned detector assemblies. The highly sensitive SD detector was primarily used to register the earliest moments associated with the appearance of the very first X-ray bursts in the discharge, complementing the key detector assemblies.

The experiments demonstrated that throughout the entire length of the discharge gap, the emission of photons with energies ranging from five to 17 keV predominates. Meanwhile, the generation of photons with energies in the hundreds of keV (but not exceeding 300 keV) is characteristic of the cathode, pre-cathode, anode, and near-anode regions of the discharge, whereas predominantly low-energy photons are observed approximately in the middle of the discharge gap (far from both electrodes).

“Our research provides new experimental data that can assist in understanding the mechanisms of X-ray generation during natural lightning discharges in Earth’s atmosphere,” noted Yaroslav Bolotov, assistant at the Physics Cluster of the Academic and Scientific Career at MIPT. “In particular, we were able to establish the existence of time delays between the onset of low-energy and high-energy photon emissions in single X-ray bursts, which may indicate a complex collective mechanism for their generation in a developed plasma system.”

“By utilizing nanosecond visualization of the dynamics of plasma structure development in the discharge, we demonstrated that the generation of X-ray radiation can begin almost synchronously along the entire discharge gap, occurring within tens of nanoseconds after the first interactions of counter-streamers growing from the anode with the cathode.

The very first X-ray bursts are observed during the discharge development stage, when a complex network of numerous plasma channels has already formed in the gap, and the pre-breakdown current and discharge voltage are around 500 A and 1 MV, respectively. The techniques and approaches presented in this work may be useful in developing new lightning protection methods and predicting electrical phenomena in Earth’s atmosphere,” explained Alexander Oginov, candidate of physical and mathematical sciences, acting head of the Department of High-Density Physics at IAP.

“The analysis of the spatiotemporal characteristics of the recorded X-ray bursts indicates that we are dealing with certain localized sources of this type of radiation that evolve rapidly over time and in space. Moreover, there may not be just one source; multiple sources could arise almost synchronously within the discharge volume. Most often, the first source appears far from the electrodes, approximately in the middle of the discharge gap, and can propagate from its origin both towards the anode and towards the cathode, at a colossal speed of about 10^10 cm/s. The results of the research qualitatively change current understandings of potential sources of X-ray radiation in laboratory atmospheric discharges,” stated Yegor Parkevich, candidate of physical and mathematical sciences and senior researcher at the Department of High Energy Density Physics at IAP.

The novelty of the conducted research lies in obtaining fundamentally new high-precision data on the spatiotemporal characteristics of X-ray emissions and insights into the patterns of their generation in laboratory atmospheric discharges. The work of Russian scientists opens up prospects for further research aimed at studying the mechanisms of X-ray generation under various conditions, particularly during lightning discharges in Earth’s atmosphere, as well as developing new methods for diagnosing emissions from complex plasma systems in real time. The researchers plan to continue their experiments to gain a deeper understanding of the physics of atmospheric discharges and their effects on the environment.

The research was supported by the Russian Science Foundation.