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Re: Laser Triggered Spark Gap

Hi Steve,
    Making the gap so far apart that it won't naturally break down and
triggering it has little advantage as the longer spark is very lossy.  The
advantage of a triggered spark gap is realized when the electrodes are put
into a pressurized vessel wherein they may be brought closer together and
then triggered.  The high pressure allows the spark gap electrodes to be
brought very close together.  The smaller inductance and resistance allows
the spark to form and quench faster.  This reduces the formation and
reformation losses which increase with frequency.  Triggered gaps at 50
psig can achieve risetimes below 10 ns.  As the pressure goes up the
spacing can be brought closer.  Triggering becomes easier.  I recently
designed a 5 coulomb, triggered spark gap switch that when pressurized will
hold off 50 kV and yet will trigger easily with only 15 kV on it at the
same pressure.  A pressurized switch is very dangerous.  If anyone on this
list decides to build one use 1/2 inch lexan!
 or 1 inch plywood to contain it for safety.  

Barry

-----Original Message-----
From: Tesla List +ADw-tesla+AEA-pupman-dot-com+AD4-
To: tesla+AEA-pupman-dot-com +ADw-tesla+AEA-pupman-dot-com+AD4-
Date: Tuesday, November 03, 1998 2:06 AM
Subject: Laser Triggered Spark Gap


Original Poster: +ACI-Steve Young+ACI- +ADw-youngs+AEA-konnections-dot-com+AD4- 

To fellow sparkers,

This list has a lot of discussion about spark gap performance, quenching,
etc., which certainly is valuable and needed.  For static gaps, discussions
seem to indicate quenching is improved for wider gaps.  But a point is
reached where the gap is too wide for spark initiation.  Thus the need for
a means to +ACI-help+ACI- a wider gap initiate a spark.

Occasionally the use of triggered spark gaps is mentioned, but the thread
soon dies.  I would think this is an area for experimentation which could
yield a LOT of benefits.  For one thing, the bps could be under our precise
control simply by varying the trigger frequency.  If one chose to lock the
trigger frequency to the AC line frequency and adjust the phase
relationship, one would in effect be able to duplicate the performance of a
RSG without having to mess with high RPM balanced rotors, etc.  Having the
gap fire when WE want it to instead of when it can no longer resist firing
itself would make for much better control and scope pictures for some of
the other testing Terry and others are doing. 

The various triggering mechanisms have been touched on in this list.  These
can range from pulse generator driven ignition coils to lasers.  My
experiments with SCR driven crummy ignition coils indicates they are good
for break rates up to at least 800 bps.  I don't know how the good GM
ignition coils perform at higher break rates - anyone have some experience?


Lasers would have the advantage of being able to simultaneously trigger a
bunch of aligned series gaps by aiming the beam through all the gaps.  I
suspect some Marx generators are fired that way.  But where can the
cash-strapped experimenter find a suitable laser which can sufficiently
ionize the air to initiate spark breakdown?  The only potential cheap
sources I am aware of would be to use a +ACQ-15 laser pointer in a pulse
mode. 
Would this work?  Specifically, can the laser diodes handle microsecond
pulses of a much higher energy without self destructing?  If so, could they
produce enough pulse energy to trigger spark gaps?  If so, what would the
pulse width and peak power need to be?  Does anyone know what the laser
diodes used for tattoo removal, etc. cost and where to get them?

In summary, isn't it time to move toward triggered spark gaps for
disruptive TCs?

Thanks in advance for your comments.

--Steve