Re: interrupter

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

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>

Mike,

What you are proposing could be very dangerous.  Your spark discharge (I
assume in air) is very low impedence, so all the remaining capacitor energy
will get dumped into your Wehnelt cell.  A spark discharge in a liquid
produces huge pressure waves which will rupture the container and blow the
contents out.  If it is acid, all the worse.  Spark discharges in liquid are
used in industry for forming metals - the high pressure wave pushes the
metal into a mold, for example.

I'll bet the Wehnelt cell was used with voltages measured in tens or
hundreds, so the Joules would be very low.  15 KV from a pulse cap is
entirely a different matter, and your Wehnelt cell could very well become a
bomb.
--Steve
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, January 18, 2002 9:54 PM
Subject: interrupter


> Original poster: "Mike Nolley by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<nolleym-at-willamette.edu>
>
>     This is a question for anyone who might know specifics about the
> Wehnelt interrupter.  The Wehnelt cell was used
> as an interrupter in early spark discharge circuits.  A small platinum
> electrode interrupts the circuit when gas
> formed through electrolysis forms around it.
>     I am in the process of designing a crowbar circuit for a pulse
> discharge application, and I was wondering if the
> Wehnelt cell might be useable in place of the ignitron.  I am concerned
> about finding a reasonable price for the
> ignitron, and the potential for mercury contamination if it explodes.
> Solid state crowbars at this voltage would also
> be too expensive.  My idea was to put a Wehnelt cells in series with the
> discharge path so that it would interrupt the
> pulse after a few 10's of  microseconds.  I need a short pulse that will
> eliminate ringing between the pulse discharge
> capacitors and an inductor.  I am hoping that since the pulse will be
large
> the cell won't re-connect before the pulse
> is over.  Also, since the cell acts as sort of a point-contact rectifier,
> no ringing will occur.  My questions are:
> is the Wehnelt cell capable of interrupting a large DC pulse like this,
> (without destroying the electrodes, container,
> and splashing sulfuric acid around) and/or: if it won't work, is there a
> type of crowbar circuit which might work
> instead?
>             --Mike
>
>
>
>