Graphite spark gaps (fwd)

---------- Forwarded message ----------
Date: Wed, 29 Apr 1998 09:22:02 -0400
From: Aric C Rothman <Aric_C_Rothman-at-email.whirlpool-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Graphite spark gaps

     Has anyone had success using graphite electrodes in a static spark 
     I've built one using hexagonal pieces of artist's graphite (approx. 
     1/2 inch across, 6B grade (alot of C, little binder)).  I tried it out 
     by connecting it across the series-connected secondaries of two 
     microwave transformers.  It produced a fierce, bright spark.  The 
     spark was so hot it ignited the wood base of the spark gap assembly.  
     I've read that graphite has a negative temperature coefficient (as it 
     gets hotter, its resistance goes down).  This property would appear to 
     make it a great choice for static spark gap material.  Other than the 
     mechanical problems associated with using graphite (fragile, can't be 
     soldered or welded), are there any reasons why graphite would be a bad 
     choice for Tesla coil use?
     BTW.  When I placed a very strong magnet under the gap, the steady, 
     sizzling spark mentioned above became a very loud staccato(sp?) spark. 
     I assume this is caused by destruction of the spark by its deflection 
     once current starts flowing through it.  Once the spark is broken and 
     current stops flowing, the magnetic field has no effect, leading to 
     spark formation, and...the cycle continues.
     BTW BTW.  I connected the same gap/magnet assembly to a NST with a 
     series resistor to limit current, and observed a swirling haze of 
     purple (plasma?) in a disk pattern.  The plane of the disk was normal 
     to the lines of force of the magnet.  Shifting the magnet around 
     (horseshoe type), caused the disk to tilt.  Neat.  Dr. Dan, my physics 
     prof., was right after all!