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:
enter image description here

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?

  • \$\begingroup\$ Contemplating whether or not this question belongs on the Chemistry SE... (maybe Physics SE....) While the question is about electricity, it could more of a material science type of question... \$\endgroup\$
    – user103380
    May 23, 2019 at 19:25
  • \$\begingroup\$ If I had a guess it would be that it’s more easily tunable to tune the triggering in all three dimensions. A disk is more appropriate for this due to it not having a biased side that would make uniform tuning harder. However, I only have my intuition for this, curious if someone has more information. \$\endgroup\$ May 23, 2019 at 20:25
  • \$\begingroup\$ I suspect that the ring makes it less likely that the spark will jump to the trigger electrode. But -- moderator, please migrate this to physics.stackexchange! \$\endgroup\$
    – TimWescott
    May 23, 2019 at 21:53

1 Answer 1


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

enter image description here

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

enter image description here
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).

  • 1
    \$\begingroup\$ That second image looks more like the magnetic field around a loop current than the electric field around a ring charge, but it's not quite either of those. I'm not sure what it is. \$\endgroup\$
    – Hearth
    May 23, 2019 at 22:25
  • \$\begingroup\$ They will be very similar, but not the same. I couldn't find a pic of a disk\ring \$\endgroup\$
    – Voltage Spike
    May 23, 2019 at 22:38

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