Spark Gaps

From:  richard hull [SMTP:rhull-at-richmond.infi-dot-net]
Sent:  Sunday, April 12, 1998 5:05 AM
To:  Tesla List
Subject:  Re: Spark Gaps

At 08:33 PM 4/11/98 -0500, you wrote:
>From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
>Sent:  Friday, April 10, 1998 10:25 PM
>To:  Tesla List
>Subject:  Re: Spark Gaps

>Thratron or transistor switches were used by Richard Hull and Malcolm
>Watts respectively to switch off primary current at earlier current
>"zeros" (of the coil's fundamental operating frequency) during a number
>of very interesting quenching experiments last year. Malcolm's attempts
>to turn off a low-power transistor-switched primary circuit at points
>other than primary current zeros did result in the expected high voltage
>spikes stemming from rapid di/dt, but it's not clear that the an arc's
>characteristics will permit this to actually occur under any reasonable
>circumstance in higher power air-gap systems.
>The GOOD news is that nature has apparently conspired to turn the gap
>off when most of the energy is where we want it - in the secondary,
>thereby achieving a natural synchonism of sorts.  :^)
>The BAD news is that this usually doesn't happen at the first primary
>current notch (where the first primary-to-secondary energy transfer has
>completed). Instead, the arc reignites, letting the secondary's energy
>cycle back into the primary and back again to the secondary. In fact,
>most operating coils seem to actually quench at the 3rd-5th current
>notch (or worse!).  :^(
>However, EVEN BETTER news is that, as heavier streamer losses begin to
>remove increasingly more energy from the secondary, we begin to achieve
>1st or 2nd notch quenching just as the sparks really begin a flyin'. 
>Hmmm... Mother Nature must really love coilers after all!  :^)

>-- Bert --
Good Post Bert!

This is one of the best overall device and gap quench summaries I have yet
seen on this list.

Unfortunately,  There is just no switch available to the high power folks
better than the air arc of some sort.  The series rotary has the advantage
of separation velocities equal to < #gaps X peripheral velocity >.  It
offers the best in air type controlled quench, though it is just not needed
for regular coupled two coil systems.

The Hydrogen thyratron with hydrogen diode reversed across it can control to
only the "whole cycle" at negative crossing.  Back to back H2 Thyratrons can
control to the "half cycle".  This latter arrangement is somewhat
electronically complex, but I hope it to be worth the effort.  All of these
are outrageously expensive in the sizes which can handle more than a table
top system of 2KW averaged enrgy input or so.  The biggest H2 thyratron that
A coiler might realistically hope to encounter at a hamfest is the 5C22.  A
reasonable price might go as high as $25.00 in that chance environment. (I
have picked them up for $5.00 each)  Newark Electronics has them new for
$973.00.  This tube might make a 1KW average power system.

I currently am working with magnifier #13 and it is coupled to K=.77 at the
driver as the primary is wound dirctly on top of the secondary wire.  More
on this as time permits experiment here.

FETs are really a great way to get data, but are in the tit-mouse class at
their best. There are a lot of solid state items coming along now that can
give the H2 thyratron a run for its money when comparing raw specs but the
heavy kick back found in tight coupled Tesla systems will leave the solid
state devices a smoldering mass while the H2 thyratron keeps on ticking.  In
addition some these new solid state devices are in the kilobuck price range.
Great stuff to dream about though.

No, it looks like we are stuck for the foreseeable future with air gaps and
their limited control.

Richard Hull, TCBOR