Re: Brightness of streamers vs. ground strikes

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Steve,

On 18 Jun 2005, at 10:12, Tesla list wrote:

> Original poster: Steve Conner <steve@xxxxxxxxxxxx>
>
> Hi all
>
> I was puzzling over something recently. When messing around with my
> DRSSTC-
>
> http://www.scopeboy.com/tesla/drsstc/woot.jpg
> http://www.scopeboy.com/tesla/drsstc/zoot.jpg
>
> The ground strikes do not seem any brighter than air streamers. Now on
> pictures of larger coils, ground strikes always seem brighter and a
> different colour. I remember one picture by Peter Terren where the air
> streamers are dim purple and the ground arcs are a lightning-like
> blue-white.
>
> I wonder if this has to do with the frequency of the coil? As the
> frequency goes up, the current drawn by air streamers will increase
> and they will get brighter. Ground arcs won't change since they are
> purely resistive.
>
> If we thought about this- and it seems to happen about 200-250kHz for
> 3ft streamers since my 260kHz spark gap coil behaves about the same-
> maybe it would tell us something about the nature of streamer loading?
>
> To me it says that a 3ft streamer has a resistance about equal to or
> greater than its capacitive reactance at 200kHz. Also that the
> resistance of a 3 foot ground arc is much the same as that of an air
> streamer the same length. But I don't know if I'm reading too much
> into it.
>
> Also it should be qualified by length- I imagine if I let the coil arc
> to ground over a shorter distance it would be brighter.
>
> Steve Conner

I think the ground arcs really are brighter. Scope waveforms of the
secondary show that the oscillations last much longer for air
streamers than ground streamers which in turn reflects the much lower
loading (read higher loaded Q) of a secondary emitting air streamers.

Malcolm