Re: very long sparks

To: tesla-at-pupman-dot-com
Subject: Re: very long sparks
From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sat, 08 Jan 2000 12:31:37 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme


> Couple of comments:
> 
> 1.  Having taken a look at the discharge, what amazes me is the path
taken.

Interestingly, the authors of the book make much the same comment.  In
fact, one of the theoretical issues that they spend quite a bit of time on
is why sparks take the path they do, because they certainly do not follow
the "lines" of the Efield.  Mind you, lightning is much the same, and the
source of much research for the same reason.

However, this picture isn't unique.  Sparks go where they want, and are
guided only in the vaguest of ways by the E field before the spark starts. 
Don't forget that there is a fair current in the spark, and it induces a
current (and therefore a voltage) in it's surroundings (i.e. the ground),
so the E field as the spark grows is always changing, and the path it
followed may well be the path of "highest field at the tip of the leader"
as it grew.

> 
> The discharge terminal at top of the building (you couldn't refer to 
> something this size as a "coil") is of comparatively small dimension and 
> the e-field should be such that the ground would have been a "better" 
> target long before the transmission tower ? 100m away.

Recall that this isn't a coil.. it is a big impulse generator, probably a
Marx generator.

> 
> Seems odd.  I bet if we built a coil to a scale of this and placed a 
> grounded tower equidistant as per the photo we would be waiting 'till
hell 
> freezes over before the tower was hit.

Hey it's Siberia, and it IS hell frozen over.... <grin>
> 
> 2.  I think it is hard to ascertain the true distance of this 
> discharge.  Granted it is large (and I'd be bloody pleased if it were my 
> coil !) but the perspective of the photo is "optimized" to make it look 
> larger.  Look at the fence leading to the towers, they are in fact well
in 
> the distance and we don't see the actual tower hit (which appears to be 
> back towards the viewer).

The text says the spark hit the "line" not the tower, but you're right, the
end of the spark is over to the camera's right and probably somewhat closer
to the camera than the generator.

> 
> 3.  The other thing which is strange is some of the shadowing in the 
> photo.  Seems to be lit from above ???   I would be interested to get an 
> expert photographic opinion !

Nighttime shot, Seems to be illuminated by a bunch of lights from behind
the camera. I'd guess that the camera was up on top of a tall building. 
This is a HV test facility, and it's likely that there is a whole
switchyard and so forth in the area, all lit up like daylight.

>