(Don Klipstein) wrote in message ...

I believe it takes around 200, maybe 300 volts to break through
air no matter how little, and where the voltage and/or electrode
geometry do not favor corona and where the electric field within
the spark gap is evenly distributed, it takes about 75 volts beyond
that 200-300 volt figure per .001 inch (3 volts per micrometer),
give or take a little depending on temperature and air pressure.

I wonder where this 300V (or 1350V from Jim Lux' page) actually
comes from?

Since the rest of the Paschen equation is simply the e-field needed
for air breakdown, the mysterious threshold voltage sounds like some
sort of microscopic "screening field" at the surface of the metal,
with half the threshold mystery-voltage appearing at each surface
(so 1350V would actually be 675V at each metal surface.) Since
any polarized air molecules near the metal surface will be attracted
to the metal by image effect, maybe the image effect somehow acts as
a proportionally-growing voltage barrier, and the air out between
the electrodes never even SEES any e-field until the 1350V threshold
is exceeded? Imagine something like a Helmholtz Double Layer
appearing against the electrodes, but in air rather than in
electrolyte?

If my above speculation isn't right, then there must be some sort
of mechanism which prevents the air in the gap from simply breaking
down when the usual value for e-field is reached. Why won't
the spark appear at a field strength of 30KV/cm? Or in other words,
what strange thing happens in the region within 1350/3000/2 = .23mm
from each metal surface which both prevents any air breakdown there,
and also prevents the air farther away from that region from breaking
down when 30KV/cm is reached?


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