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strange spark phenomena (fwd)
Date: Wed, 4 Feb 1998 10:02:28 -0700
From: dwight duncan <duncand-at-ccsalpha2.nrl.navy.mil>
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.