Re: Triggered spark gaps for coils

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

Typically, you trigger them with a voltage comparable to, or greater than,
the voltage the gap is holding off (depending on the gap design, and the
trigger polarity).  If it is a field distortion or irradiation gap, almost
any reasonably high trigger voltage works, because it works by creating a
bump in the formerly pretty uniform field which then breaks down, or by
irradiating the gap with a flood of UV from a small spark to one of the
electrodes.

If it is a swinging cascade design (like a three ball gap), then you need
enough voltage on the trigger to breakdown one of the two gaps. Either 50%
or 33% of the total gap voltage is usually enough.

Typically, the trigger pulse has a very fast rise time for two reaons: 1) A
smaller (cheaper) capacitor can be used to couple the trigger pulse to the
gap; 2) fast rise time reduces the gap firing time jitter.

Whether the gap stays "on" long enough is more determined by your external
circuitry. If there is charge to move, and the gap current stays above a
few amps, it will stay "lit".

There is an amazing variety of triggered gaps available, triggered by all
sorts of means (lasers, electrical pulses, electron beams, x-rays, etc.).
There are gaps that are designed to handle 10s of Coulombs charge transfer
at megaamp currents, all the way down to millicoulombs at less than an amp.


What you are probably most concerned about is electrode heating (hot spots
will cause premature triggering and rapid erosion)

A lot of the more exotic designs are done to insure very low jitter in the
triggering (i.e. < 1 ns) or very repeatable characteristics.  For the TC
application, I suspect that a pretty ratty trigger would work just fine.  A
1 microsecond jitter would be totally unacceptable for most triggered gap
applications, but just fine for TC use.


Tesla list wrote:
> 
> Original poster: "David Thomson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <dave-at-volantis-dot-org>
> 
> >From my recent web searches and technical paper readings, there appears to
> be a large variety of commercially available 3-terminal triggered spark
> gaps.
> 
> I'm interested in these, too.  I've found several sources for these
> interrupters but no information on trigger input voltage or whether the gap
> remains open long enough to allow sufficient ringing.  The triggers can be
> purchased with operating voltages between .3 and 100KV and can handle up to
> .5 Coulombs.  Here is one such site...
> 
> http://www.rellpower-dot-com/ipget_vacuumgaps.asp
> 
> I'd like to hear other's experience with these.
> 
> Dave