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Abstract Evidence of positive polarity dominated streamers preceding fast negative breakdown (FNB) and of simultaneous positive and negative polarity streamer development in lightning initiation is reported. Observations of lightning initiation as FNB have remained a puzzle because simulations of lightning initiation have shown that negative streamers are not produced in virgin air without simultaneous positive streamers. Here, the authors observe positive streamer development forms first or at least simultaneously with negative streamers. Further evidence comes from observations of mixed fast breakdown (FB). The overall trajectory of the positive breakdown during such mixed events indicates that the positive streamers continuously propagate during the burst of strong negative breakdown. These observations indicate that even when negative streamers dominate the overall very high frequency (VHF) emissions, both positive and negative streamers are propagating simultaneously from the initiation point. These findings on the structure and dynamics of FB provide key new insight to our understanding of lightning initiation.
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Positive- and Negative-Polarity Nanosecond-Pulsed Cryogenic Plasma in Liquid Argon
This work reports on observations of positive and negative nanosecond-pulsed discharge in liquid argon. The structures of both positive and negative discharges, their sizes, and the propagation velocities exhibit remarkable similarity. Similar to the streamers in liquid nitrogen and gases, negative streamers require higher applied voltages (electric fields) and propagate to shorter distances. For both polarities, the spectra are almost identical and appear to be a superposition of strongly broadened atomic lines, with preliminary analysis of broadening indicating densities of about 40% that of liquid.
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- Award ID(s):
- 2108117
- PAR ID:
- 10536806
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Plasma
- Volume:
- 7
- Issue:
- 3
- ISSN:
- 2571-6182
- Page Range / eLocation ID:
- 510 to 516
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In this work we report the results of imaging and spectroscopic measurements of the optical emission spectrum of a negative nanosecond-pulsed cryogenic discharge in liquid nitrogen. With the application of a lower electric field, the discharge first ignites as a ‘faint glow’ around the high-voltage needle electrode, but when the applied electric field reaches the transition value of around 5 MV cm−1the discharge mode switches to a negative in-liquid streamer. The optical emission spectrum of the discharge is populated by the molecular nitrogen emission bands, and their analysis shows that the pressures and temperatures of the negative streamers in liquid nitrogen are at least of few tens of atmospheres and around 140–150 K. The results of this study demonstrate similarity of positive and neganive streamers in cryogenic in-liquid plasma conditions.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/plasma7030027
