Actually, I just planned to begin triggering without regard to the charging state. My thought is that at such a low rep rate the caps will reach their maximum charge (determined by the variac) long before, as in many cycles, a pulse is sent to the lamps.I was thinking about your circuit earlier while eating lunch. Using the variac to adjust the voltage during steady state operation sounds fine. My concern would be the initial cap voltage before your first trigger pulse. Its possible the caps could be charged several percent more than during steady state operation. This could give a huge first pulse.
Edit: I guess you are probably starting the trigger pulses then slowly turning up the variac voltage. This would solve the possible big first pulse issue.
Isn't the field collapsing because it is being drained by the secondary? With the primary isolated from input current or from reverse current through the open relay, why would this cause spikes? Now, I am the first to admit that I do not understand this process well enough (that's why this thread), but if the relay is opened then the primary is isolated from the line and so it seems that the only effect at the secondary would be a collapsing field that would have a delta V/T no greater than when the field is driven by the line voltage.The collapsing field should cause a spike in the secondary as well. I am not sure how to calculate that.
Based on the papers I have looked at and more so on my single pulse experiments the caps will probably be around 1,000 V immediately after a discharge and will require something like 10 full cycles to reach the pre-discharge stateIts hard to say how low the cap voltage will be after each discharge