Roy Lewallen wrote:
Jim Lux wrote:
breakdown? Is there some distinction to "full?")

One often makes a distinction between a corona discharge which exists
as a steady state sort of thing and the streamers which precede a
"spark". Both are air breakdown phenomena, but qualitatively
different, and both are different from a low pressure discharge like
that found in a fluorescent lamp or neon bulb, or from phenomena like
St Elmo's Fire.
. . .

Most interesting. I've always thought that St. Elmo's fire was a corona
discharge, and a quick web search indicates that it's apparently a very
widely held misconception. What's the difference?

Roy Lewallen, W7EL
Indeed.. but St. Elmos fire has many characteristics not shared with
corona.. (the extent of the glow, for one.. corona tends to be a very
small sheath or longer leaders/fingers)

Most likely, it's glow discharge off small water droplets shed from the
surface from which is charged. Basically the process is like an
electrostatic sprayer.. small bumps in the liquid surface form from
whatever cause, and the surface charge tends to make the droplets come
off. They're charged to the maximum charge for the diameter, and as the
droplet evaporates, it gets smaller, causing the glow discharge to shed
charge. Or, a big droplet splits into smaller droplets because of
electrostatic forces.


You can set up a nice demo in a dark lab with something like a cork wet
with sal****er, a HV power supply, and some cookie sheets for electrodes.