I am designing a TC with a 62 kHz oscillating frequency. As I would like to
quench at the first notch with a rotary gap, I supposed I can set my
coupling coeff. so that the first notch will come after about 5
oscillations at 62 kHz. That makes about 80 us to reach the first notch.

So the quest is how to achieve such a short quenching time.

>From available literature I found that a spark can possibly form when the
electric field exeeds 40 kV/cm and surely forms when it exeeds 70 kV/cm.
So, if you write down how the stationary and rotating electrode distance
evolves with time, and calculate the time the electric field is greater
than 40 kV/cm, you should get a rough figure of your quench time.

I did that and for a peak voltage of 60 kV, rotating speed of 6000 rpm,
rotor diameter of 12" I got a quench time of over 500 us (!). Because I
cannot reasonably increase either speed or rotor diameter, I took the
book's solution and designed to insert a static spark gap in series with
the rotary one.

By doing that I plan to decrease the voltage at the RSG down to 15 kV: that
way the theoretical quench time drops down to 100 us, that gives at least
some hope to achieve the required 80 us.

I was thinking to use a high resistance voltage divider to have 15 kV on
the RSG and 45 kV on the static gap. The static gap would be a series of
sections, to easily set its trigger voltage. The voltage divider should
also remove a part of the randomness involved in air gap trigger voltage.

Any suggestions or comments about the above story?

Thanks to everybody.