Natural sources of intense ultra-high-frequency radiation in high-voltage atmospheric discharges

We study the sources of intense ultra-high-frequency (UHF) radiation (in the frequency range 1–6 GHz) arising during the development of high-voltage atmospheric discharges. The discharges were initiated in a long discharge gap by applying an approximately 1-MV pulse with positive or negative polarity. By employing a radio registration system based on ultrawideband antennas, we managed to localize the UHF radiation sources in the discharge with centimeter accuracy and investigate their temporal and spatial correlation with the discharge structures. The vast majority of the localized sources turned out to be concentrated in the near-electrode regions. It is found that the generation mechanism of intense UHF radiation in a laboratory discharge cannot be unambiguously associated with such basic processes as the head-on collision of opposite-polarity streamers or the interaction of single streamers with the near-electrode plasma at the surface of metal electrodes. We discovered that the observed UHF emission appears basically as a precursor of the intense plasma development in a certain discharge region, whereinto a bright counterstreamer comes a bit later. The findings were confirmed by the statistical observations and results of imaging the dynamics of the discharge structures with a nanosecond temporal resolution.

Figure 1

Experimental setup: (a) pulse high-voltage installation, (b) investigated discharge gap, (c) integral photo of the resultant gap breakdown, (d) scheme of the device positions, (e) antenna design, and (f) antenna frequency characteristics.

Figure 2

Flowchart demonstrates the device triggering.

Figure 3

Determination of the first peaks of the UHF radiation signals from four antennas for the (a) very first burst and (b) burst within useful signals. The first peaks are employed to obtain relative delays between the recorded signals and then solve the localization problem.

Figure 4

Schematic representation of the source localization.

Figure 5

Schematic representation of the microwave generator: (a) top view and (b) side view. (c) The typical UHF radiation signal and (d) its spectrogram obtained for a particular time period. The inset demonstrates a characteristic burst profile ${\overline{P}}_f^{*}$ as a function of frequency $f$. The UHF radiation sources localized in five series of 50 events in the $XZ$ and $XY$ planes [(e), (f)] before and [(g), (h)] after the calibration of the radio registration system.

Figure 6

Accuracy of determining the position of the UHF radiation source in the (a) $XY$ and (b) $XZ$ planes.

Figure 7

Superimposed voltage waveforms and UHF radiation signals obtained in a number of shots for the (a) positive and (b) negative polarity of the HV pulse applied to the investigated discharge gap. Digits 1–8 in the voltage waveform indicate the time periods of the discharge imaging.

Figure 8

Images (frames 1–5) demonstrating the discharge evolution for the positive polarity of the applied HV pulse in shots 1–5 in Fig. 7.

Figure 9

Images (frames 1–8) demonstrating the discharge evolution for the negative polarity of the applied HV pulse in shots 1–8 in Fig. 7.

Figure 10

Discharge voltage and typical UHF radiation signals registered for (a) positive and (b) negative polarity of the applied HV pulse. Spectrograms (c) and (d) show the spectrum evolution for the considered UHF radiation signals. Insets 1 and 2 illustrate a characteristic burst profile evaluated as a function of frequency in numerous events.

Figure 11

The UHF emission regions localized in the discharge gap for the positive and negative polarity of the applied HV pulse. The source positions are presented in the $XZ$ (top view) and $XY$ (side view) planes. The bar charts show statistics of the source observations along the discharge axis. For the negative and positive polarity, counts are on the left and on the right.

Figure 12

Images demonstrate the discharge structures and localized UHF emission regions in single events for the positive polarity of the applied HV pulse.

Figure 13

Images demonstrate the discharge structures and localized UHF emission regions in single events for the positive polarity of the applied HV pulse.

Figure 14

Images demonstrate the discharge structures and localized UHF emission regions in single events for the positive polarity of the applied HV pulse.