strange spark phenomena

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: strange spark phenomena
From: Tesla List <tesla-at-stic-dot-net>
Date: Sat, 7 Feb 1998 01:52:20 -0600
Approved: tesla-at-stic-dot-net


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From:  dwight duncan [SMTP:duncand-at-ccsalpha2.nrl.navy.mil]
Sent:  Friday, February 06, 1998 5:59 AM
To:  tesla-at-pupman-dot-com
Subject:  strange spark phenomena

Hi all,

    I can offer a possible explanation from a plasma physics point of view.
 What you might be seeing is a phenomena known as Faraday dark spots.  It
happens when you have an electron density depletion an a sheath is formed.
The mechanism for this could be a strong ion-acoustic wave traveling
longitudinally along the arc.  The plasma wave would create bright spots
and faint spots as you see the nodes and anit-nodes.  The wave length would
be on the order of 10 cm for a guess of electron temperature of 50 eV.
   The wave is destabilized when there is a potential gradient along the
plasma(arc) and when it can form a standing wave which is possible since
the growth rate of this wave is less than one wave period and the wave
velocity is on the order of 1 km/sec.
   Anyway, it is likely for this wave to form in a Tesla Coil discharge and
could be strong enough to cause these vacations in arc intensity of a few
inches in length.  Having that short of variation in length using
electromagnetic explanations require hundreds of megahertz in frequency.
  Hope I didn't go over board here.

Dwight.