Triggering a camera flash with a microcontroller
I suggest driving the TIC206 triac as suggested in data sheet from say 3V with current limiting R to gate. The transformer boosts the voltage to >1kV to a plate across tube  but the storage cap is only 250Vdc or so conducts the energy across to the tube.

The Triac shuts off below a low holding current which is decayed by cap discharge to ionized tube. 

So the secondary trigger voltage is not applied to Triac during trigger, only the stored Cap voltage which is across the tube electrodes thru the Triac switch. The Triac latches on the leading edge of the pulse with about 2 diode drops of Vbe’s.

You must control the semi-random intervals.