Re: Water sparks (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 6 Aug 2003 13:51:25 -0600
From: Gomez <gomez@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Water sparks (fwd)

On Wednesday, August 6, 2003, at 08:19  AM, High Voltage list wrote:

> ---------- Forwarded message ----------
> Date: Tue, 5 Aug 2003 09:35:41 -0700
> From: Sean Taylor <sean.s.taylor@xxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Water sparks
>
> Hi all:
>
> A while back, there were several posts on the Tesla list about
> creeping arc
> discharges along water surface.  It was all started by a picture of
> the Z
> machine at Sandia. Anyhow - I have been trying to do this, and first I
> used
> a 10 kV DC PS I had, and just depended on the filter cap for the
> discharge
> (bad idea, I know, but it was just a test) and it worked pretty well.
> I had
> about 1 inchor so of arcs going out from the electrode (brass drawer
> pull).

Yow, must have been reasonably short pulse times.

> I recently just tried it again with a couple maxwell pusle caps, with
> higher
> voltage and more energy storage( 0.188 uF, ~15 kV) than the DC power
> supply.
> Results were quite disappointing though - only about 1/2" max creeping
> discharge, but plenty of noise.  There were more arcs across the
> surface,
> but not nearly the same length.  So, here's the question/my theory:
> Are the
> Maxwell pulse caps too good, and the current dies out too quickly so
> the
> arcs don't have time to form? Or is something else going on?

  I suspect that your pulse times with the larger energy store are not
fast enough.
Keep in mind that the water will begin to conduct after a very short
time (I don't
remember the time constant, but it's brief - in the mS regime IIRC), so
make sure
you're using distilled water and that you minimize your stray
inductance, use a
fast switch (perhaps with a "speed-up" cap directly across it, with
very small
inductance paths).  Also, which Maxwell caps are you using?  For this
kind of work,
careful design is required to make the pulse rise time very fast.