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From: yerazuws@rpics.RPI.EDU (Crah)
Newsgroups: sci.electronics
Subject: Re: Tesla Coil - broadcast power
Message-ID: <556@rpics.RPI.EDU>
Date: Mon, 22-Dec-86 11:24:49 EST
Article-I.D.: rpics.556
Posted: Mon Dec 22 11:24:49 1986
Date-Received: Mon, 22-Dec-86 22:49:08 EST
References: <4815@reed.UUCP> <823@A60.UUCP> <824@A60.UUCP> 
	 The multisegment gap doesn't give you any more harmonics - but
Organization: RPI CS Dept., Troy NY, USA
Lines: 38
Summary: Why some coils use multisegment spark gaps

it does have a couple of other advantages:
	
	1) When a disk pits from spark erosion, it can be rotated without
having to remove and re-polish it.  When the entire periphery is eroded,
then you remove it and put it on a lathe for repolishing.
 
	2) Greater thermal mass - helpful in two ways.   First reason
is that the spark is quenched by cooling- which happens in two ways.
First way is by radiative transfer - the bluish light.  Second way is
by conduction to the electrodes (remember that plasma has a lot of properties
we normally associate with metals - and heat conduction is one of them)
 
	So, if we have a 1/4 inch spark gap as a single gap, the 
longest distance from an ion to a cool electrode is 1/8". 
If we break the 1/4 inch into four gaps, each 1/16" gap will have 
the same radiative cooling, but now no plasma ion will be more than 1/32" 
from a nice cool copper disk.  Net result is that the spark quenches
faster and more dependably.
 
	The second advantage of greater thermal mass is that as the 
electrodes heat up, they lose some of their quenching ability.  
Spreading the heat load over a number of electrodes helps this (in the
short term, at least)

	
	
	Note to people in the Pittsburgh area:  Buhl Planetarium had a
wonderful twenty-foot or so Tesla coil in operation last time I was
there (about 6 years ago).  It apparenty was built as an exhibit by
some engineers at Westinghouse, materials paid for by Westinghouse.
Maybe some CMUer can post a followup article on the coil (is it still
there?  Still in operation?  What are it's vital statistics?).  I saw 
this coil fired up once - the sparks were at least fifteen feet long.
Very impressive.


			-Bill Yerazunis