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Re: Laser Triggered Spark Gap
At 08:20 PM 11/3/98 -0700, you wrote:
>Original Poster: "Steve Young" <youngs-at-konnections-dot-com>
>
>To fellow sparkers,
>
>This list has a lot of discussion about spark gap performance, quenching,
>etc., which certainly is valuable and needed.
IMHO, this is 'the' issue to attack. For an optimized 2ndary geometry and
toroid for power level, this is the determining element of performance.
>But a point is reached where the gap is too wide for spark initiation.
Thus the need for a means to "help" a wider gap initiate a spark.
Will a longer spark be benificial? The longer the spark, the more air will
dissipate power, but the better the quench.
>Occasionally the use of triggered spark gaps is mentioned, but the thread
>soon dies.
Is this because they are jealously guarded secrets to high performance?
>For one thing, the bps could be under our precise
>control simply by varying the trigger frequency.
Indeed! The pulse rate could be stabilized and optimized for resonant
charging modes too. The rate could be 'walked' into operating modes yet
unexplored.
>one would in effect be able to duplicate the performance of a
>RSG without having to mess with high RPM balanced rotors, etc.
Motors tear the arc apart and setup cooling airflows though.
>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.
Very true, without a digital storage scope the jitter is awfull. I would be
scared to take an expensive digital scope near a TC. Old, cheap, junked tube
scopes would probably work better after a few direct hits :)
>I don't know how the good GM
>ignition coils perform at higher break rates - anyone have some experience?
Yes, I'll post my recent thoughts & tests on ignition coils soon. But IMHO
they're not good over a few KHz because of the thin secondary wire, the Q
goes too low, even with the core removed. Maybe with the right ferrite this
could improve. TV flybacks would make a better triggering source, operating
10 - 100 KHz pulse widths.
>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.
Yes! I've seen rail gaps a meter long fired this way.
>But where can the
>cash-strapped experimenter find a suitable laser which can sufficiently
>ionize the air to initiate spark breakdown?
Search the web for nitrogen laser. An article in Scientific American's
Amature scientist describes how to build one. They need no mirrors.
Relatively, very simple, compared to a TC. And smaller capacitor. I can dig
up references & articles of the web if I must.
> The only potential cheap
>sources I am aware of would be to use a $15 laser pointer in a pulse mode.
>Would this work?
Doubt it. I would bet it would hardly decrease the jitter. Although I have
noticed room lighting will affect the rate common cheap strobe lights can
fire, and high-pressure sodium bulbs to ignite. But its statistical
variation, not reliable triggering.
> Specifically, can the laser diodes handle microsecond
>pulses of a much higher energy without self destructing?
Not the ones from laser pointers. I have an IR laser diode that can handle
15 W pulses if you want to find out. Over 10 years old. Some industrial
lasers probably can, having been fab'd into kilowatt arrays for kilo $$$.
> If so, could they produce enough pulse energy to trigger spark gaps?
A 10 micron CO2 laser can ionize air with 100KW of power. You want to create
ions to avalanche in the gaps electric field. What energy levels do O2 and
N2 atoms ionize at? LED IR levels? or UV Nitrogen laser levels? Atoms are
like TC's - they are tuned and respond best at their photon energy level, or
color.
>In summary, isn't it time to move toward triggered spark gaps for
>disruptive TCs?
It would be nice if a few of us could decide to research and investigate
different methods.
1. Trigatron-like spark gaps
2. Vacuum (as in low pressure) hollow cathode (pseudo-spark or
thyratron-like) switching
3. Surface discharge or dielectric flashover switching
4. Laser triggering
5. Corona/UV primed large area diffuse discharges (like electron-beam
triggered switch)
The last (5) is probably a looser for impulse switching, but might work for
kilowatt level continouse oscillations like a Poulsen arc. But rather than
transit time and negative resistance being the conductivity modulator, the
ionization caused by a corona would do. It would be configured like a
transistor in an oscillator. A plasma transistor oscillator would be a good
analogy.
Also, EGG's website explains thyratrons & why they need hollow cathodes for
things like Tesla Coils. Like virtualy everything else discussed here, its
back in the Tesla Archive somewhere.