Hi--
I AM THE TRIGGERED SPARK GAP WHISPERER. Well, at least I have
significant experience. A field distortion gap is the best---easiest to
trigger and easier to build. Visualize two brass cap (acorn) nuts, maybe
3/8, spaced just beyond breakdown. A tungsten needle comes in from the side
with the point centered. The trigger pulse is fed onto the needle through
an isolation cap (a little doorknob of 100 pF or so) and the needle is
biased midway between the electrodes with two big equal resistors (>10M). A
tiny thoriated tungsten welding rod works well for this. You can grind a
point on the end. It would probably work well extending through the gap
with no needle point, if you see what I mean. Keep everything symmetrical.
A trigatron gap has the needle coming just flush through a hole in one of
the electrodes, but is much more finicky. Few if any big pulsers or Marxes
use them.
You probably know all this stuff, but here it is. Let me know if I can
dispense any further wisdom.
--- Carl
PS--Sounds like a fun project. Let us know how it works.