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Re: Triggered Spark Gaps - Why?



An obvious solution to the problems you mention with N2 lasers: use a
nonconventional triggering system, such as the 60kV spark coil I plan to
use. About the problem with firing rate--that is a difficulty resulting from
low quench rate and/or inadequate power supply. If it should prove
impractical to quench at a high enough rate, there is a simple solution: use
more than one laser.


           --Mr. Postman (Doug Brunner)
                <dabrunner-at-earthlink-dot-net>

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Saturday, November 07, 1998 12:16 PM
Subject: Triggered Spark Gaps - Why?


>Original Poster: Gavin Hubbard <ghub005-at-xtra.co.nz>
>
>Hello list members.
>
>I don't want to sound unnecassarily negative, but I believe that some of
>the exotic triggering systems that are being suggested e.g. trigatrons,
>laser triggers, and pseudo-spark systems, are missing the point. IMHO the
>real beauty (and design strength) of a conventional Tesla coil is in its
>simplicity.
>
>For those not familiar with controlled HV triggering, a conventional
>trigatron is essentially an insulated rod that penetrates an earthed
>sphere. The tip of the rod is positioned flush inside a hole in the
>sphere's surface with approx 1mm annular clearance. A 10kV tripping pulse
>is applied to the needle which produces a spark between the tip of the rod
>and the earthed sphere. The space charges of the auxiliary spark distort
>the electrostatic field in the main gap and cause it to break down at a
>voltage much lower than that required in the absence of the trigger pulse.
>The sphere containing the trigger rod must be kept at earth potential or
>else insulation difficulties occur in providing the high voltage pulse to
>the rod. This means the trigatron IS polarity sensitive. This makes it
>UNSUITABLE for a conventional tesla coil tank circuit unless a polarity
>change over switch is placed in the trigger circuit.
>
>Similarly, laser triggering is also an unneccasary burden. Disregarding the
>obvious problems of optical containment and termination, the major problem
>is in producing a dicharge at a given time. For example, a nitrogen laser
>(as discussed in previous threads) is essentially a pulsed discharge across
>a nitrogen filled cavity. The pulse is usually produced by charging a bank
>of capacitors until the breakdown voltage is reached. I hope that the irony
>of using a non-controlled discharge to initiate a regular discharge in the
>TC is not lost. More importantly, most nitrogen lasers can NOT operate
>above 30-40HZ, this makes them UNSUITABLE for a tesla coil tank circuit.
>
>The near impossibility of obtaining psuedo-spark gaps, in itself makes them
>UNSUITABLE for a tesla coil tank circuit.
>
>
>I hope that I am not interpreted as being anti-innovation or unimaginative.
>I too have many blue-sky ideas. However, at the end of the day I believe
>that a well designed and constructed tesla coil is worth two unrealisable
>projects in the spares box.
>
>Cheers,
>
>Gavin Hubbard
>
>
>P.S. If any people out there are interested in simple triggered spark gaps.
>I have used the following circuit with great success in a seven stage 1.4MV
>Ferranti impulse generator. Because it is not designed to quench, I do NOT
>recommend this design for Tesla coil use.
>
>Two copper spheres are arranged close together. A pair of contacts is
>placed flush in a small hole in the sparking surface of one sphere. The
>contacts are connected to a low voltage battery (9V) through an inductance
>(230mH) in series. When the contacts are made to open, the energy stored in
>the inductance appears in the form of a spark across the contacts and the
>breakdown of the main gap follows. For safety, the contacts are operated
>using a photosensitive cell and a relay.
>
>The advantage of this circuit is that unlike a trigatron, the circuit can
>be situated at any point in the high voltage circuit, whether insulated
>from the earth or not. The operating range of voltage is about the same as
>that for a trigatron, for the smae polarity and gap length, and is hardly
>affected by the value of either the voltage or the inductance.
>
>
>P.P.S. To all of those who requested information on transformer design, I
>will use this weekend to start translating my notes into HTML.
>
>
>
>
>