Re: Sparks - Bright in the middle, how to verify it.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>




> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>

> > Depending on the exact way i (mis?)understand 'bright segment
> > at the center', one possibility is that several segments
> > at the end(s?) are running current thru one common 'arc channel',
> > that is, that that segment is brighter because it is carrying
> > more current.

> > The recombintion time for gasses (time to stop conducting) is
> > quite long.  A spark cahnnel, once formed, cam survive for
> > 're-use' if another suitable energy pulse floats along.
> > Similarly, the light output is maintained, so a short pulse
> > of current can leave a glowing trail alight for longer than
> > the impulse lasts...
 
> Possibly, but in the Van deGraaff example, the sparks are in different
> places, so I don't think the channel's being reused (although, it is hard to
> tell.. perhaps with a schlieren apparatus that could look at density
> variations??)

	Or a look at the radiated emi, with a scope...
 
> The recombination time may be long (but not all that long.. I think
> microseconds, not milliseconds, but I don't recall),

	Here we differ, but i lack a reference.  My recollection, from
	someplace i regarded as trustworthy was that, depending on
	gas, pressure, temperature, recombinstion times could be
	milliseconds plus, sometimes much longer.

	eg in Lightning, multiple stokes flow, in quick succession
	thru one plasma tube, at least on occiasion.  Stokes grow
	stepwise, each further step extending from the ionized tube
	of a preceding impulse.  The human eye is a very limited
	instument, for some things...
 
> but the channel cooling is much faster, and that probably has a larger
> effect than straight ionic recombination.  If the channel were still
> hot enough to be significantly conducting, then it would perturb the
> field and "attract" the sparks.

	I'd wonder even more so at rapid cooling.  (if, of course, there is
	data, then I'm wrong....) Cooling by pure radiation is not real
	fast....

	best
	dwp
> This is an area of much uncertainty in the literature.  Nobody is really
> quite sure why sparks go where they do when they do: Why is lightning jagged
> and forked?  The shape of the field will determine the general direction,
> but not the fine structure.