Plasma is a weird animal.  It is formed into superatoms where the electrons can be found well beyond the spdf energy shells/orbitals chemists are so familiar with.  And atomic neuclei organized without the insulating layer of electrons found in gases.  Some plasma's display negative specific heat.  The higher the heat content the lower the temperature.  I believe this is because as the electrons are unbound from the neuclides they are free to form a current which intensifies as the electrons are accelerated by the energy input.  The faster this current about the ionized core the more insulationn it forms around the ionized atoms.  This is similar to a tornadoe where the circulating currents about the eye of the storm insulate the eye from barometric pressure.  The relative pressure between the insulated eye of the storm and the ambient field increases.  The viscous nature of air continues to draw molecules from the eye region into the circulation about it.  Sticky electron theory applies in a plasma.  So a region of space that appears empty is just the eye region of a huge coherent plasma.  Here and there in the cosmos the plasma cools down enough to form gases and other forms of matter.  I beleive that a highly polarized  efield can be used to cool the primordial background plasma enough to capture some 13 billion year old energy.  A spark gap before any hot current flows issues a cooling field. Kinetic energy of accelerated mass or waves (particle wave duality) converts into potential energy in the gap.  The gap becomes charged and when it shorts a higher than would be anticipated current flows.  eg electron cascading in vacuum tubes.  This radiant flow of energy from the ambient INTO the gap is not anymore complicated than touching an ice cube.  The energy flows from your fingers into the ice cube faster than it would if you were touching a warm glass of water.  I guarantee if you pull a field up to around 36kv it will start to get cold around it.  The ambient thermal energy then flows at an accelerated rate into the field where thermal energy is converted to electrical potential. There is a goodly amount of reflection as the energy surges towards the gap that radiates in the form of transverse emwaves but the real deal is the stuff that gets caught in the gap and the circuit designed to convert it and distribute the gap gain.

These are my answers based on what i believe to be true, i could be wrong.

Is that the first moment?

As far as I understand it ,yes.

On which side we see the forming spark? What's happening in the meantime at the other side?

Assuming that Negative is always more powerful, and from my experience it is, I would say that the event would move negative to positive. I would assume that the other side was building a positive capacitance for a nanosecond.

Let's say we switch of the source before the spark could ionize the whole gap, but already formed out from a wire, what would we see in each end? Would be there two spark going in opposite direction, or one only?

The negative terminal would radiate breaking radiation and if the bias charge negative was maintained without oscillation a shock-wave exiting the event site at 90 deg. The Positive terminal would collect the incoming electrons and depending on the material and resistance would either conduct them or order them.

Let's say we insert an aluminum foil in the gap, copper wires at critical wide, spark would form,burn hole in the foil. How and why the hole was created?

Electrons would knock aluminum atoms out of state and move them to the opposing terminal or the plasma would modify the aluminum into aluminum oxide etc...

photon emission is correct, even if diplomatic, else you could not see it

How the photons manifest in the spark gap as a visible spark is my question to you.

My answer that the spark manifests from each side is "subjective" as this depends on several things.  Joseph Henry performed an experiement with three gaps and watched the arc with a rotating mirror - the middle gap always arced after the two outer gaps.  When I was working with triggered sparc gaps, I found you can place the trigger between the gap electrodes in a position where the arc will visibly jump from both electrodes.  This is not always the case as the arc can very visibly jump from on side or the other depending on parameters.  Also, just because you do not see a visible arc, does not imply that nothing occured.  Do not let our eyes fool us.

An arc to isolated conductor from a conductor in a continuously interupted induction coil circuit or similar does not make a visible mark on aluminum, but you can definitely see the arc.

I think that impact marks require "Electrons", supposedly they are dragged by the initial traveling displacement current wave, at the  speed of light.  This would make for a a traveling electric field, which will have a traveling magnetic field - all moving at the speed of light. 

Yes, that initial wave with dragged electrons is very powerful for an instant and then you have to create another traveling wave.  Which is exactly what you have to do, but you have to have all the parameters in the correct range for it to work.   Braking radiation has certain requirements and so does everything else.

Like I said before, you have to create the shockwave event and then you have to figure out how to utilize it.

Chef, how does one utilize the shockwave?

Photon isn't just a basic unit of light, it basic unit of the whole electromagnetic spectrum, and of course we couldn't observe the full spectrum, so we see only visible spark, when the emitting atom's radiate in visible spectrum. In this case, those atom's are from the airgap.

I know that a photon is the force carrier of electromagnetic fields.  Why are they present, in the visible spectrum, in the spark gap?  Is it actually a "full specrum"?   If it is, then it is all the more interesting.

One side of the spark has a pressure density, I don't think so they are electrons, but that's not important in our case. If one side have directed pressure, which can disintegrate the foil, what could have/do the other side? Especially, when the spark induced in a wire/coil by magnetic coupling, where there is no source connected to the secondary.

Compression on one side, rarefaction on the other, but depending on the circuit and the location of the gap, you may actually have high pressure on the first side, medium pressure on the other side of the gap, and low pressure at the other end of the circuit.  If your gap is not in the middle of the coil, then what I just stated is probably what you will have.  So applying 10kv at the gap, you may have 8kv on the other side.

I don't clearly know which shock wave you are referring. On which plane correlate to the travel of the current?

The shock wave that moves perpendicular to the conductor after the switch is opened.

Whatever it is composed of, it appears to me to be some sort of traveling wave in space.  I believe it is dipolar rather than monopolar like electrons.  I do not believe it is particulate, but i may only appear to travel through metal plates.  I can not verify that what hit the plate was the exact same as what comes out the other side.  I say "dipolar" because it is not deflected by electric fields yet has a magnetic moment.  I suspect it may follow magnetic lines, but I am not sure.  I does appear to couple to magnetic fields.  Can the current induced be increased this way? 

A moving "charge", dipole or monopole or multipole, has an associated magnetic field even if the charge is virtual , and as we all the know, the shock wave is inductive.

This will give you a better idea on how your spark happens. Same thing anyways.......
http://www.sun-sentinel.com/news/local/southflorida/sfl-lightning-flash,0,4105155.flash

@dankie

Well, I just saw your post on that other thread. Big man. Just take your GEET+HHO tube and stick it up where the sun don't shine, then set the dial to full production, wait a few minutes, open your mouth and light a match. That's about all the use you have here. You are totally sick in the head man. Get your brain checked, but you might need a specialist in micro particles to do that.

Wattsup and all the TPU groupies, you are clearly a bunch of amateurs with nothing but TPU propaganda in the head , you know more about intermodulation than you know about ohm's law .

Its time somebody starts bashing the hell out of you people .

The site is litterally filled with your filth .

Collector Detector.
This a little development device that may help. You can not be in all places with your probe at once, so you may be missing some energy at strange angles. This is built from 660/46 litz with a pair of ultra fast 1k diodes at each end of each loop. Do your tests in this tank and you will see it when it happens. 10 x 5 x 660 = 33000 loops of a good skin depth. Very reactive!

Can you post what you saw with that chamber?