Re: RE>Best sparks (fwd)

---------- Forwarded message ----------
Date: Wed, 8 Jul 1998 12:12:24 -0600
From: terryf-at-verinet-dot-com
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: RE>Best sparks (fwd)

Hi Dale,

	Thanks for this info.  Since Resistance = Length / ( Conductivity * Area )
the higher ( Conductivity * Area ) is, the lower the resistance.  I added
the conductivities and multiplied them out:

Material	Skin Depth	Conductivity    SD*C

Silver          .064      	6.1		0.3904
Copper          .066      	5.7		0.3762
Gold            .075      	4.1		0.3075
Aluminum        .085      	3.5		0.2975
Chromium        .081      	?
Nickel          .014      	?
Brass           .126      	1.1		0.1386
Magnetic Iron   .011      	.2		0.0022
Mumetal         .00029    	?

SD is in mm at 1 MHz
Conductivity is x 10^7

Silver and copper are the winners here.  Mumetal will loose badly.

As mentioned in a past post, Aluminum has very thick oxide layers (Aluminum
oxide is a very good insulator) that really screws up it's conductivity in
practice.  We use silver plated copper conductors for high current (100 amps
13 MHZ) RF conductors.  Silver oxide is fairly conductive.  Thin gold over
copper is probably the best.  A copper sphere plated with gold would be
really neat!.  However, not very cheap.  Silver plated copper is best on
paper but in practice the oxide would look bad.  The gold over copper would
give the best performance while not having the oxidation problem and would
look good.

	Terry Fritz

At 10:35 PM 7/7/98 -0600, you wrote:
>---------- 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
>....... 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