re using back emf into a resonant coil

I'm working with bifilar coils and have found some interesting effects,
Like pulsing a bifilar coil with back emf, at the resonant frequency of the coil,
creates a resonance that shows up like a usual Voltage sine wave.

But, where the sine wave is zero volts, there is normally a magnetic field.
This time, there is no magnetic field measurable. very interesting indeed.
Since the energy cant disappear, I suspect the field is a variation, of the magnetic field, that has different properties.

I'm now in the process, of getting a bafilar coil into resonance, via a parallel bifilar coil (both pancakes).
By pulsing one coil with a 50% square wave pulse, the other coil becomes resonant. (with magnetic field).

The pulsed coil, also produces back emf,
I capture this back emf, into a capacitor, and store it there shortly.

Then I quickly and shortly discharge the capacitor into the (already resonant) second coil.
This step proves to be very hard.
Goal, is to discharge the capacitor very shortly, into the resonant coil. So I intend to use a back emf pulse from another coil, to quickly turn a transistor on and off. basicly simulating a back emf spike.
This part is pretty hard for me to design.
The capacitor is charged with negative voltage from the back emf,
and the resonant coil, is swinging positive and negative.
So the mosfet is inbetween....
I want to trigger the mosfet , when the resonant coil hits 0 volt.

but since the capacitor is negative charged, and it wont completely discharge, the source is very negative relative to the gate. most mosfets dont like this...

I have also thought, about using positive back emf. but it seems harder to capture. altough the discharge in to the resonant coil should be easier.

I also wonder if i could use a mosfet since it has a reverse diode (body diode) . Maybe it would be better to use a transistor.