Calculating radio emissions of positive streamer phenomena using 3D simulations
arxiv(2024)
摘要
We study radio emissions from positive streamers in air using 3D simulations,
from which the radiated electric field is computed by solving Jefimenko's
equations. The simulations are performed at 0.5 bar using two photoionization
methods: the Helmholtz approximation for a photon density and a Monte Carlo
method using discrete photons, with the latter being the most realistic. We
consider cases with single streamers, streamer branching, streamers interacting
with preionization and streamer-streamer encounters. We do not observe a strong
VHF radio signal during or after branching, which is confirmed by lab
experiments. This indicates that the current inside a streamer discharges
evolves approximately continuously during branching. On the other hand,
stochastic fluctuations in streamer propagation due to Monte Carlo
photoionization lead to more radio emission being emitted at frequencies of 100
MHz and above. Another process that leads to such high-frequency emission is
the interaction of a streamer with a weakly preionized region, for example
present due to a previous discharge. In agreement with previous work, we
observe the strongest and highest-frequency emission from streamer encounters.
The amount of total energy that is radiated seems to depend primarily on the
background electric field, and less on the particular streamer evolution.
Finally, we present approximations for the maximal current along a streamer
channel and a fit formula for a streamer's current moment.
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