Electrode shape in a triggered spark gap?

Question

I was reading about spark gaps which are triggered with a third electrode, and I think that the concept is pretty straightforward, but the resource described the usage of a third electrode which would be shaped like a ring or washer:

The article didn't really describe why the trigger electrode would be shaped like a disk instead of, say, a wire or some other pointed shape. Is a ring shaped electrode a more useful shape for causing a discharge, or are trigger electrodes just generally made this way?

Answer 1

The electric field of a cone or point looks like this:

The electric field of a ring or disk simmilar to the one shown above looks like this:

Source: https://demonstrations.wolfram.com/ElectricFieldAroundAChargedRing/

The field through the ring is symmetric, when activated would most likely draw down the field uniformly through the axis of the spark gap and lead to a break down of voltage in the middle. And odds are that it would be best for the spark to not touch the ring.

A point or cone off to one side would lower the electric field outside of the axis of the spark gap, and is not symmetric (if there is only one off to the side).