Re: Torroids

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Original poster: "Christoph Bohr" <cb@xxxxxxxxxxxxxxx>

Hello Leo.


> Why does the top torroid have to be smooth?
hm, has to is realtive. It is usually preferred to be and
this is for some good reasons. If you think of an capacitance
to ground, the smoothness of the topload seems not very important.
But as a HV loading terminal you want to minimize corona leakage in
the first place which would be introduced by any sharp edges.
When streamers form, they tend to attach in these places, hindering
the streamer from wandering around the toroid. Further, the total
breakdown voltage will be lower than calculated  for the same size,
which might mess your design up, because the wrinkles of the foil
are hard to predict. The good new is, "smooth" usually means
smooth compared to the toriod size. A 1" bump in a 6" toroid
will cause a single breakout point. A 1" bump on a 10 feet
toroid will hardly be noticable.
You usually want the voltage to rise as high as possible with a
toroid / coil combination that can just break out, or even can not
break out on its own and uses a breakout point for longest
streamer performace.
Of course there are asthetic reasons to.

> Why can't you take a two foot in diameter beach ball and cover it with
> tin foil, aluminum tape, or copper flashing to make a large torroid?
Hm, to point out the obvious: because a ball is not a toroid..
Ok, I can be really annoying ... If you meant topload, this can
and has be done, tough a toroid proves advantagous in most designs
for its field shaping propperties. Aluminium tape can be applied
very smooth like with Gary Lau's great foam toroid:
http://www.laushaus.com/tesla/foamtoroid.htm

However, a ball or even nothing at all will work,
just nor very well.

best regards

Christoph Bohr