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In general, St Elmos fire is probably not a corona discharge in the same
sense as we see on HV power supplies or tesla coils. A scientist friend
of mine has a different theory, and we've done some experiments, which
I've not yet had time to try on my TC, but others might..
OK here's the deal:
Corona typically has streamers, and emerges from sharp points, or as a
general diffuse glow. Anyone who has seen the big VDG at the Boston
Museum of Science has seen classic corona discharge on stuff around the
VDG when the voltage comes up.
The theory is that St Elmos fire is more of an electrospray phenomenon.
That is, you have an object that is covered with a conductive liquid
(sea water). The charge causes droplets to come off the surface
(electrospray). Once separated, the droplet is repelled from the
structure (same sign of the charge, and all). BUT, as the water
evaporates from the droplet, the radius decreases, while the charge
stays the same, so the field increases, causing a corona discharge from
the surface of the droplet.
This accounts for the description of St Elmo's fire looking like a
general glowing haze around masts, spars, etc. (which is VERY different
from high field corona, like at the MoS, which is clearly emanating from
"sharp" or "small radius" objects).
Our experiment was this:
An insulated pie pan with a bit of salt water in it had a wine cork
(also wet) standing up in it. Just over the top of the cork (but far
enough away) was another metal plate (using styrofoam cups as the
insulating supports. A 50kV power supply (variable) was hooked between
the piepan and the plate (so the field between the cork and the upper
plate was on the order of several kV/cm. As the voltage comes up, in a
dark room, you can see the droplets starting to come off the surface of
the cork, and sure enough, they glow.
A wet cloth works even better.
We were going to try this with a TC to find out if AC fields can do it.
We're not sure that it would work, because the time scale to form the
droplets and have them separate because of electrostatic forces is
longer than the RF period.
(same thing can be done with fine dust. A charge and a field causes the
dust to rise into the air and stick to the other plate. Sort of like the
demo where you put packing peanuts in a bucket on top of a VDG)