Re: Why a toroid?
---------- Forwarded message ----------
Date: Fri, 10 Oct 1997 06:37:07 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Why a toroid?
Tesla List wrote:
> ---------- Forwarded message ----------
> Date: Wed, 08 Oct 1997 20:32:50 +0000
> From: Greg Leyh <lod-at-pacbell-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Why a toroid?
> Edward V. Phillips wrote:
> > You need a LARGE radius of curvature in order to keep the
> > "breakout voltage" high. A disk with a sharp edge would have a
> > much lower breakout voltage than the toroid, for dimensions which
> > gave the same capacitance.
> That's certainly true when the power is first applied, but how far
> is the breakout voltage compromised once a big sharp pointy streamer
> is hanging off of the toroid? Should it make such a difference then?
Greg and all,
It still should make a significant difference. At the beginning of the
next bang, there isn't much left of the highly conductive streamer
channel that hung off the toroid during the previous bang.
Recombination, diffusion, and thermal conduction remove a very large
proportion of the electrons and thermal ions left that formed the
conductive path from the previous channel. Even though vestiges of the
previous channel may remain at the beginning of the next bang, the
breakdown reignition voltage has recovered to a large extent. Breakout
at the next bang is still "sudden", even if it's at a somewhat lower
voltage than that seen with full recovery. However, with a disk,
breakdown will consistently occur at much lower voltages because of the
great E-field concentration at the edge of the disk, and the formation
of corona once we exceed E-field stresses over 30 KV/cm.
In smaller disruptive systems, the amount of time between bangs is
typically much longer than the ring-down time of the secondary when its
heavily loaded by streamer discharges. [BTW, this may not be the case in
your mega-coil for losses from air-only streamers, Greg]. If we slow
down the breakrate enough, a point is reached where there's virtually
complete recovery between successive bangs, and no reignition along the
previous channel. Under these conditions, individual, shorter, streamers
appear at random points around the toroid.
A disk, on the other hand, consistently breaks out at a much lower
voltage than a toroid's breakout voltage, typically at multiple points
due to the early edge corona and resulting heavy ionization all around
the edge. It still would be interesting to see what would look like at
the 130 KW level!
This explanation's probably clear as mud, huh! :^)
-- Bert H --