Re: Corona and Sphere - Puzzle -addition
The spark continues to extend not so much because it is a lower impedance,
but the extending leader/streamer causes a local concentration of the E
field at the end of the leader. It is likely that this end is "closer" to
the other electrode (which might be an extended "ground"), so the spark
will continue from there. It is much like the already existing leader is a
"wire" which extends from the electrode.
There are some important dynamic effects as well.. It takes a finite time
for charge to move from the electrode into the leader, as well as a finite
time for the leader itself to develop. For instance, the charge moving
along the leader has to heat the air enough to ionize it and make it a
conductor in the first place. Large top electrodes have large capacitance
and voltage (which means lots of stored charge), and, as well, low surface
inductance, so the charge can quickly move into the leader from the surface
of the toroid.
For a good theoretical development, with much of the latest research, I
suggest that you find a copy of Bazelyan and Raizer, "Spark Discharge"
published by CRC press.
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