Re: Spark gap electrode wear paper

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

It could be thermal conductivity related.  If the thermal conductivity were
low, and the rep rate is high, you would always tend to strike the arc from
the same hot "cathode spot", which would increase the erosion.  At low rep
rates, the temperature of the cathode spot has time to drop, so the sparks
wouldn't all fire from the same point.  

Brass does have pretty good thermal conductivity.  Stainless is very low
conductivity.  I don't know about elconite.

You'd probably want something with high thermal conductivity, low mass, and
a high melting point.


Tesla list wrote:
> 
> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
> 
> The recent thread on the collapsable secondaries reminded me to take a look
> at the papers that I downloaded from the iop-dot-org web site before it
> restricted access.  Pertinant to the more recent thread on SS electrode wear
> was a very readable paper comparing spark gap electrode between brass,
> aluminum, stainless steel, and elconite (a copper/tungsten alloy)
> electrodes.  A surprising finding was that the discharge repetion rate
> affected which material was superior.  The experimental study only compared
> rep rates of 10HZ and 1KHz, well below and above what we typically see in
> our applications, so it's difficult to know which rate is more applicable.
> The gap discharged a 3 nF capacitor charged to 22.5kV.
> 
> Most remarkably, the authors concluded that of the 4 materials tested, BRASS
> was judged to have "the best overall performance", and stainless steel the
> worst!  Too bad that pure tungsten wasn't tested.  One of the factors cited
> as affecting errosion is the resistivity of the materials, so this makes me
> wonder if tungsten might be inferior to the presumably more conductive
> elconite alloy.
> 
> I have posted the paper on my web site at:
> http://people.ne.mediaone-dot-net/lau/tesla/electrodeerrosion.pdf
> 
> I have also included the closing summary of the paper below.
> 
> Regards, Gary Lau
> Waltham, MA USA
> 
> Electrode erosion and lifetime
> performance of a high repetition rate,
> triggered, corona-stabilized switch in
> air - J M Koutsoubis and S J MacGregor
> J. Phys. D: Appl. Phys. 33 (2000) 1093-1103. Printed in the UK
>