Re: "Standing streamer"
Sulaiman, Tue Oct 27 2015, 11:08PM

speculation;

a question that has bugged me for a while is
why do arcs jump about all over the place rather than remain in the shortest path to the nearest grounded object ?
. hot air carries the ionised air upwards, but will break and the arc should (?) reform on the shortest path.
. the path of the current carrying arcs will be 'bent' by the magnetic field of the primary current which rotates in phase due to resonant frequency 'splitting' with useful coupling ... probably not !
so my query is exactly yours but backwards.

I have never made a 1/2-wavelength magnifier but ...
it would act as a very low turns ratio transformer once an arc is struck, allowing high arc currents,
maybe enough to create plasma ? (briefly)

Re: "Standing streamer"
Uspring, Wed Oct 28 2015, 11:35AM

Possibly this has to do with the speed secondary voltage increases. Very slow rampup, such as in QCWs, leads to straight, non branching arcs. Fast rampup to heavily branching types. I'd suggest getting a scope shot from the secondary voltage by placing a probe safely away from the secondary. It would be interesting to find out, whether placing the line shaped object affects secondary voltage rise up speed.

When the arc grows its direction will be influenced by the direction of the electric field and the presence of hot air from the previous bursts. The field at the tip of an arc will have a preferred direction mostly away from the tip but there are also sideways components. For rapidly rising voltages, the direction will be more random, possibly dependent also from the presence of ions in the air.

Re: "Standing streamer"
omegalabs, Wed Oct 28 2015, 08:16PM


This happens only when there is no connection from the plasma to the ground or any object, so only capacitive current can flow.

Re: "Standing streamer"
omegalabs, Wed Oct 28 2015, 08:24PM


Well the base is a classical ARSG tesla system, with a resonant frequency about 300kHz, so the rampup should not be slow. BPS was around 500 I think (it's sensitive to the BPS actually).
I don't have any reliable scope right now.
I know how a spark, or arc is formed, but never seen anything like this on any other coils I built (from small to big ones, like 20), or have seen everywhere else, especially not from a spark gap based design.
The most interesting thing for me is the change the thickness of the plasma, sadly the camera is not really good picking up intense UV light, especially with VGA resolution.

Re: "Standing streamer"
Sulaiman, Wed Oct 28 2015, 10:41PM


if there is sound, light or heat then there must be a 'real' current, because there is real power,
but my speculations above are NOT the answer to my question,
I still do not understand why arcs or sparks frequently do not follow a consistent path to ground,
even if only part of the way as in sparks
but brush corona behaves 'logically'

Re: "Standing streamer"
Sigurthr, Thu Oct 29 2015, 06:25AM

Ionized air channels have persistence that exceeds the burst length of most coil setups. Because of this streamers can appear to persist along a particular ionization path simply because it IS the path of least resistance, even if there is a shorter distance to ground. Likewise, there is a time of persistence where an ionized air channel appears to glow longer than there is actually current passing through it, this is particularly prevalent at high discharge currents due to I2R heating of the air resulting in incandescence. The hotter the air channel the more ionization, the longer it persists, but also the more convection has an effect on its placement, so there is a sweet spot of current density that results in a nearly stationary streamer.

Re: "Standing streamer"
Uspring, Thu Oct 29 2015, 10:50AM

omegalabs wrote:

Well the base is a classical ARSG tesla system, with a resonant frequency about 300kHz, so the rampup should not be slow.

There is an energy transfer from the primary to the first secondary and from the first secondary to the second secondary. Both of these take time. For the first secondary it depends mostly on the coupling, for the second secondary on the voltage, the first secondary produces. In general I'd guess, that this is slower than for a non magnifier coil.

Sulaiman wrote:

I still do not understand why arcs or sparks frequently do not follow a consistent path to ground,
even if only part of the way as in sparks
but brush corona behaves 'logically'

Think of a partially grown arc and mentally replace it by a piece of wire connected to a high voltage source. There will be corona at the tip and it will look like a brush. The arc will follow any direction of the brush, not necessarily only the path of highest field. For a second or later burst it will tend to follow into the region of hot air. This is dictated by Paschens law: Hot air is thinner than cold air and thus reduces the breakdown voltage.
I think the main difference between TC arcs and e.g. VDG (straighter) arcs is, that the latter are much faster and there is not so much time to transfer charge to the tip of the arc. Therefore the field is much less influenced by the local charge at the tip so it will follow mostly the field, that was there before the arc ignited, i.e. the straightest path.