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

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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??)

The recombination time may be long (but not all that long.. I think
microseconds, not milliseconds, but I don't recall), 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.

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.