Re: Triggered spark gaps for coils

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-uswest-dot-net>" <mystuffs-at-orwell-dot-net>

bert, Gary, all
i to have been giving this some thought. i was actually looking at the
triggered xenon flash lamp as the source of the gap.
if you've ever noticed them, they have the trigger electrode dead center
between two tungsten points and are filled with the gas. it is built of
heavy pyrex or something like quartz so cooling could be overcome.
the one i had here met a sorrowful death under my cordless drill, but i
see them come up on ebay once in a while. i don't think one would quench
because the gap is only about an inch, but maybe three or four in series
with only the first one as the triggered unit?
or am i not understanding the xenon properties correctly? kind of a real
poor mans triggered gas spark gap?
marc

Tesla list wrote:
> 
> Original poster: "Bert Hickman by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>
> 
> Gary and all,
> 
> Hmmm... I was wondering why you just outbid me on that pulse transformer...
> :^)
> 
> I think it makes great sense! There should be no reason that you couldn't
> use a three terminal gap (such as a home built or commercial field
> distortion gap) to perform this task as long as you provided a flow of gas
> through the gap to help cool it and remove ions. In fact, field distortion
> gaps were often used to provide rapid pulsed switching for flashlamps to
> drive older pulsed excimer lasers prior to their replacement by hollow
> anode thyratrons (which will safely handle a degree of oscillatory
> bi-directional current flow). For example, older Lumonics pulsed lasers
> used field distortion gaps that looked a lot like little Claymore mines
> (about 5.5" in diameter, and 3" thick) - every now and then these come up
> for sale on Ebay.
> 
> You need to make sure that the middle electrode is centered between the two
> main electrodes and that is biased so that its potential is halfway between
> the voltage that's applied between the main electrodes (except for when you
> want to "fire" it). One way to do this is to use a pair of HV resistors to
> create a voltage divider. Triggering is done by coupling a HV pulse (from
> an ignition coil or a HV pulse transformer) through a blocking capacitor.
> The main gap spacing is adjusted such that the gap will self trigger at a
> voltage that's at least 20% higher than the maximum expected voltage from
> the HV supply. The triggering voltage needs to be at least half of the
> maximum applied gap voltage in order to reliably force breakdown. A LV
> pulse capacitor, SCR, and phase shifting circuit operating off fullwave
> rectified line voltage can then be used on the LV side of the trigger
> transformer to control the trigger point in a manner similar to adjusting a
> SRSG via a variac/capacitor phase shifter. Use a fixed font in order to see
> the diagram below:
> 
>                                         To HV1
>                                           |
>                                           |                ||
>                    |----------------------o----------------||-------------
>                    |                      |                ||  Ctank      |
>                    |                      |                               |
>                    |                      |                               |
>        _           |                      |                               |
>       | |          |              ------------------                      |
>     __| |_     R   --/\/\/\/---   |    Main 1      |                      O
>        HV                     |    ----------------                       O
>      Trigger        C1 ||     |                                           O
> Ltank
>          --------------||-----o--------------------- Trigger Electrode    O
>                        ||     |                                           O
>                               |    ----------------                       O
>                R   --/\/\/\/---   |    Main 2      |                      O
>                    |              ------------------                      |
>                    |                      |                               |
>                C1  |                      |                               |
>                    |                      |                               |
>                    |                      |                               |
>                    |----------------------o--------------------------------
>                                           |
>                                           |
>                                       To HV2
> 
> -- Bert --
> --
> Bert Hickman
> Stoneridge Engineering
> Email:    bert.hickman-at-aquila-dot-net
> Web Site: http://www.teslamania-dot-com
> 
> Tesla list wrote:
> >
> > Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <Gary.Lau-at-compaq-dot-com>
> >
> > >From my recent web searches and technical paper readings, there appears to
> > be a large variety of commercially available 3-terminal triggered spark
> > gaps.  And it seems that these can easily be home-made as well.  These
would
> > seem to be ideally suited for use as replacements for rotary spark
gaps, but
> > I've not been able to find any reference to this obvious application.  The
> > only reference I've seen towards "amateur" applications is in can and
> > quarter shrinkers.  While RSG's do have relative simplicity on their side,
> > it seems as though there ought to be some worthwhile benefits to using a
> > triggered static gap.  Has anyone attempted this?  Or am I attempting to
> > invent a square wheel?
> >
> > Gary Lau
> > Waltham, MA USA