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On 9/5/20 9:03 PM, David Varas via Tesla wrote:
We are debating in a social network, if the length of a serpentine requires a much lower voltage than theorized due to the channel of ionized gas that it is generating and that reduces the energy expenditure of said discharge.I argue that that theory has overlooked some issues.Is true, beyond a few tens of centimeters, the development of an electric arc cannot be simplified to a directly proportional relationship (an ascending straight line on an x-y diagram) because it becomes very complex and many variables are involved.
This is true - and is discussed at some length in books like Spark
Discharge by Bazelyan and Raizer - it's also true for lightning.
It is also true that each discharge pulse leaves an open channel of
ionized gas that makes the next discharge not need as much energy to
reach the point where the previous discharge was extinguished, and that
reserve of "unspent" energy allows it to reach a little further than the
previous one, and so on. So you might think that in the end, a streamer
can reach a distance x (for example 3.3m) driven by a voltage much
smaller than the theoretical one based o
n that directly proportional relationship.
Not so much even between "bangs" (illustrated in the "banjo effect
photos") but also on each half cycle of the RF, as the top load charges
up, discharges into the streamer, then waits for the next half cycle to
charge it.
So the streamer goes in "jumps"
But streamers are not a one-line channel of constant thickness and
directionality (like a tube or cable). Streamers behave like lightning
in a storm. In a storm, the discharge, with an average length of 10 km,
falls with a stepped structure, approx. every 45 meters, it branches and
/ or changes direction, dissipating a large amount of energy. Similarly,
the discharge that originates in the toroid, branches and / or changes
direction. and it is in those events where it loses the energy that
"supposedly was going to be saved" and even more, what in the end would
give rise to a discharge of length x (example 3.3 m) that actually
needed to be driven by a voltage even greater than that theorized by
calculations, due to all the energy that was dissipated in the route,
and that was not used to generate and maintain that channel of ionized gas.
Yes, the stepped behavior is apparent in both lightning and TC discharges.
That's why spark length in tesla coils is driven more by power (energy
available) than voltage - the voltage has to be above some minimum to
start the streamer, the topload C has to be big enough to have enough
charge to heat the streamer hot enough to keep it hot for the next RF
half cycle.
For lightning, the processes are a bit more complex - there's not a big
metal electrode holding the charge that is supplied for the next
streamer jump.
The basic process is similar - at the tip of a streamer, the voltage is
increasing as current flows through the ionized channel (keeping it
hot), then, the field gets above the breakdown voltage of air, and jumps
in some "quasi random" direction (probably determined by a combination
of local electric field shape and which atom got ionized first). Charge
flows from the streamer body into the new little length of streamer,
until it's at quasi-equilibrium, and the process starts over.
For TCs (as opposed to lightning) the process is fed by a pulsing
voltage (the RF), so that sets a "cycle time" for the streamer growth.