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>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, March 17, 2001 11:29 AM
Subject: RE: Triggered spark gaps for coils


> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
>
> Hi Jim:
>
> That's exactly what I was thinking, though not necessarilly at supersonic
> speed.  I was going to modify my vortex gap (see
> http://people.mediaone-dot-net/lau/tesla/vortexgap.htm)
> by adding a small trigger electrode coaxially at the tip of one of the
brass
> reducer electrodes.  It seems that most commercial triggered gaps are
sealed
> and not rated for over 100 PPS.  I'm guessing that having moving airflow
> will improve cooling (and quenching) allowing for greater PPS rates.

I've been reading over Fruengel.. He has a typical spec for a Marx type Air
Blast gap switching 35 kW (!) at 10 kHz.  It uses only 6 cubic meters/minute
(211 CFM of air at a pressure of .5 Atm (7-8 psig), and I doubt it's
supersonic.  He comments that lower pressures at great volume work better
than high pressures.

I'll try and summarize the stuff in the pages in the next day or so. He's
talking about all sorts of high power gaps in induction heating and radio
transmitter service (i.e. damped sinusoids, etc.) at break rates up to 1
MHz, and powers up into the hundreds of kW.

I get the sort of impression from Fruengel's writing that he's not all that
enamored of rotary gaps, and prefers triggered gaps of some sort for most
the RSG kinds of applications.


>
> I'm also thinking that with the electrode configuration suggested by Bert
> with the trigger electrode located and biased midway between the two main
> electrodes, that the polarity of the trigger pulse needs to take into
> account the polarity of the main electrodes, which in our case, alternates
> between mains half-cycles.  This would make the trigger circuit more
> complex.  Am I correct in thinking that with the configuration you
describe,
> the trigger polarity is unimportant, since it's the UV irradiation and
> plasma that triggers the main gap into conduction?

This is true..

Fruengel recommends a scheme where you have two central pins as the main
electrodes, and an annular conical skirt around one of them as the trigger.
You form the spark between the skirt and the main electrode, and then, the
air flow sweeps the ions and spark into the gap between the main electrodes.
This way, you don't have to fool with biasing the trigger electrode, etc.
(and, it probably makes no difference what the polarity is..)
>
> Gary Lau
> Waltham, MA USA
>
>
> >Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> >>>><jimlux-at-earthlink-dot-net>
> >
> >A gentleman by the name of Marx (hmm.. high voltage? Marx? how odd?)...
> >actually developed a series of air blast triggered gaps about a century
> ago.
> >An interesting design.. the electrodes are basically conical, and have
> holes
> >in the center through which the air flows (at supersonic rates,
typically).
> >Either you can pressurise the centers and blow radially out through the
> gap,
> >or you can pressurize the outside and blow radially in.  A center pin in
> one
> >of the electrodes (coaxial with the main electrode) provided the
> triggering.
> >Of course, back in the 19th century, they didn't have nifty HV pulse
> >generators to generate the repetitive trigger pulses, so Marx used, of
all
> >things, a rotary spark gap to fire the trigger pulse.  The idea was that
> the
> >wear on the RSG would be much less because it switched a lot less power
> than
> >the main gap.
> >
> >By the way, getting supersonic flow in air is pretty easy.  100 psi
through
> >a 1/8" hole will easily get supersonic.  A regular old (pre-OSHA) blow
gun
> >will go supersonic as well.  If the weather is right, you can see nice
Mach
> >diamonds.
> >
> >> http://fp2.hughes-dot-net/brianb/pulse_discharge.htm
> >>
> >> Regards,
> >> Brian B.
> >>
>
>
>