I'm studying discharge mechanism of the gas when high voltage applies. Longitudinally two ring-type electrodes are present while gas is transversely surrounded by a dielectric material.
I've heard that in such a configuration the region near the dielectric surface is normally discharged first.
Is it true? If so, what causes such a surface discharge? I suspected the electric field near the surface is higher than the other but COMSOL simulation shows the electric field distribution is about transversely uniform.
If the discharge is very strong, it is created a high magnetic field that compress the arc to the center line instead pushing it to the surface.
At the beginning perhaps at the surface of the dielectrics is not perfect polished so there are little edges that increases a little the electric field.
When the gas gets ionized, its electrons moves creating magnetic fields that reflects the current outside.
This effect is increased if the voltage is AC instead DC at high frequency.
A current through a conductor creates a magnetic field around it B= mu*I/(2*pi*r) where r is the distance to the conductor center line, in your case the discharged current.
The magnetic pressure is P=B^2/(2*mu)
The pressure avoid that the plasma at the center line abandon it due heating pressure, so that some fuses does not breaks.
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/magcur.gif
http://en.wikipedia.org/wiki/Pinch_%28plasma_physics%29
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