RE>Best sparks (fwd)

---------- Forwarded message ----------
Date: 07 Jul 1998 13:26:04 -0700
From: Dale Hall <Dale.Hall-at-trw-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: RE>Best sparks

RE>Best sparks

Terry and List,

Re: Skin affect.  EM Fields & Waves text lists mm depth -at-1MHz in order:
                                           pg 339
Mumetal         .00029    9 (poorest conductivity)  (75 Ni  2Cr  5 Cu  18 Fe)
Magnetic Iron  .011       8
Nickel            .014        6
Silver             .064        1 (best conductivity)
Copper           .066       2
Gold              .075        3
Chromium      .081        5
Aluminum     .085        4
Brass            .126        7

Skin depth decreases if either the conductivity. permeability or frequency 

Does this suggest Mumetal would make the best material for Top Terminals?
followed by Iron, Nickel, etc. (plating?) ?

Note re: Spark Self Oscillation of recent general interest:

This same text explains Plasma Angular Frequency in a gas - resonance in
ionized gases (such as our spark gap & discharges) where f ranges from
 ~3Mhz (ionosphere) to 1 GHz (plasma). excerpt >electron current lags
electric field intensity by PI/2 radians, therefore electron current is inductive. 
....... by inducing a sudden voltage in this inductor it will oscillate at a
resonant frequency determined by the motion of electrons under the action
of the electric field created by their own nonuniform displacement oscillating
about their initial position with an angular velocity. pgs 344-8 LCCCN 62-14193

Comments and discussion welcome,

Dale,  Redondo Beach, Calif
Date: 7/1/98 10:14 PM
To: Dale Hall
From: Tesla List

From: terryf-at-verinet-dot-com <terryf-at-verinet-dot-com>
Date: Wednesday, July 01, 1998 12:58 PM
Subject: Re: Best sparks

Hi Kevin,

        This is very interesting and pretty much what I was expecting.  The
rough edges and such on the foil sphere probably cause small points that
tend to produce many small areas of discharge.  However, the foil should
give somewhat poor high-frequency performance which may be why it won't
produce the long arc of the smooth sphere.  The longer arcs may be drawing
too much high frequency power for a rough terminal to supply.  The long
roaming arc is obviously getting the power and current it needs.
        Theoretically, a copper sphere with a light gold plating (to prevent
oxidation) would be able to perform at high frequencies with minimal
problems.  This would probably be best for the long arcs.  Of course, the
many small arcs may be more pleasing to some in which case the rougher foil
type electrodes would be preferable.

Thanks for you great input.        Terry Fritz

>From:  Kevin Wahila [SMTP:kevinw-at-stny.lrun-dot-com]
>i have a tin foil covered ball as one top terminal and also and aluminum
>sphere from a Van De Graaf,  with the foil, i get bunches of sparks, with
>the sphere i get one long spark that roams around and occasionally
>straightens right out and gets really long, it has no side branches and
>seems to flow....actually it looks pretty damn cool....
>>Hi All,
>>        I have been playing with secondary arcs and such.  The data, both by
>>measurement and modeling, suggests that secondary arcs benefit greatly by
>>having very fast discharges.  In other words, the top terminal should be
>>large, smooth, and have low RF resistance.  The ground path should also
>>present low resistance.  The arcs need low resistance to RF currents in
the range of 5 to 20 MHz.
>>        I was wondering if anyone has noticed that smooth top terminals,
>>perhaps made of other materials besides aluminum, seem to give better
arcs, or that rough terminals give worse arcs.  I realize that this is very
>>subjective at best but I thought I would ask.
>>        Terry Fritz>>        terryf-at-verinet-dot-com