Re: Marx spark gaps (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 31 May 2005 20:41:38 -0700
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Marx spark gaps (fwd)


----- Original Message -----
From: "High Voltage list" <hvlist@xxxxxxxxxx>
To: "hvlist" <hvlist@xxxxxxxxxxxxxxxxx>
Sent: Tuesday, May 31, 2005 8:19 PM
Subject: Marx spark gaps (fwd)


> Original poster: <sroys@xxxxxxxxxxxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Tue, 31 May 2005 17:57:40 +0200
> From: Herwig Roscher <herwig.roscher@xxxxxx>
> To: hvlist@xxxxxxxxxx
> Subject: Marx spark gaps
>
> Hello!
>
> Trying to understand the function of Marx generators, I searched the
> web and found several descriptions like this:
>
> "The charging voltage is applied to the system. The stage capacitors
> charge through the charging resistors (Rc). When fully charged,
> either the lowest gap is allowed to breakdown from overvoltage or it
> is triggered by an external source (if the gap spacing is set greater
> than the charging voltage breakdown spacing). This effectively puts
> the bottom two capacitors in series, overvoltaging the next gap up,
> which then puts the bottom three capacitors in series, which
> overvoltages the next gap, and so forth. This process is referred to
> as "erecting".
>
> For a charging voltage of e.g. 20 kV the first gap should break down
> at 20 kV, the second gap at 40 kV, the third gap at 60 kV and so on.
> Consequently the gap distance of the first gap should be about .27",
> that of the second gap about .54", that of the third gap about .81"
> and so on.

This is generally incorrect.  Ideally, you want all the gaps to fire at the
same instant.  In systems that use triggered gaps, they actually couple the
trigger pulse to all gaps.  In systems that use untriggered gaps, it's
important to have the UV from the first gap illuminate the others to get
them to all trigger together.


>
> To my surprise I found, that all of the described Marx generators
> were said to have EQUAL gap distances (with the exception of the
> first gap, which is set a little bit closer sometimes).
>
> Looking for the reason of this unexpected recommendation I found:
>
> "The Firing Probability of Coupling Spark Gaps of the Multiplying
> Circuit according to Marx" by A. Rodewald, Basel
>
> This technical documentation contains a lot of useful information and
> could be downloaded from
>
> http://www.haefely.com/literature/pdf/scientific/e1-04.pdf
>
> I am hoping that you will find it interesting as well.