helical sparks

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gary Johnson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gjohnson-at-ksu.edu>

I was trying out a new digital camera yesterday, taking photos of sparks
from my solid state coil. Several of the photos are at my web site:
www.eece.ksu.edu/~gjohnson as the jpeg files.  The sparks are about 30
inches long, leaving a small bump on a 30 inch diameter sphere. The peak
power is about 25 kW when the spark begins.  Power is applied for 10 ms per
spark.

The main spark channel has a central shaft perhaps 5 to 10 mm in diameter.
In addition, there is a helix extending out another 10 to 20 mm.  It looks a
little like a drill bit or perhaps more like a grain auger. It does not form
until the spark is several inches away from the spark emitting point, and
will be smeared when the spark hits a dog leg. 

Is this a well known phenomenon of sparks, described in some classic paper
of many years ago?  I don't recall stumbling across it.  It could be an
instability that occurs in hot fusion. I suspect a quantitative explanation
would be challenging. In the meantime, I find the sparks to be pretty.

Gary Johnson