Re: breakout voltage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 24, 2004 1:29 PM
Subject: Re: breakout voltage


 > Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
 >
 > Tesla list wrote:
 >  >
 >  > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >  >
 >  > If this one is for DC voltages
 >  > May I ask what formula you use for the break out voltage of a toroid on
 >  > a TC.
 >
 > Breakout is a phenomenon that happens in the nanosecond scale, so
 > anything up to a few hundreds of MHz is "DC" in this case.
 > This story about breakdown voltage changing with frequency is a myth.
 > What happens is that in an AC system, -after- the first breakout,
 > the next ones usually require smaller voltages, because there is
 > remaining hot, or maybe ionized, air remaining from the last breakout,
 > and this effectively adds "points" to the original surface, where
 > breakout starts sooner.


There IS a bit of a difference for AC/RF, even for carefully designed gaps,
etc. for spark breakdown. Indeed, the first air breakdown next to the
electrode surface is identical and occurs on a nanosecond time scale,
however, what happens next is highly influenced by the dv/dt.  There's a
difference in spark gap voltage depending on the rise time (and polarity) of
the pulse, for instance.  In the RF situation, as the ions start to move
away from the electrode surface, the field can reverse and actually pull the
ions back.  In the extreme case of running in a vacuum, and at just the
right frequency (depending on the spacing in the gap) you can get
multipaction (where the electron hits the electrode and knocks off more than
one electron, which then gets accelerated aways as the field changes sign).

But, for the TC world, where the frequencies are fairly low, the dominant
effect is going to be the repeated "bangs" each propagating out in the hot
(even if not entirely ionized) spark column.