Magnifier questions

Dear All,

This weekend I built a prototype magnifier setup, a small one.   Performed
the tests in the living room on the coffee table.   I wound
the primary out of 1/4" pyro (copper covered mineral insulated electric
cable) 16 turns around a 6" daimeter former.  Held together with string and
bamboo plant sticks.   The secondary is 150 turns of 0.56mm magnet wire on 
a 4" former.   The 1/4 wave resonator is from my TC and is 700 turns of
0.56mm magnet wire on a 7" former. 

The 1/4 wave resonator from the TC has resonant frequency of 220KHz 
when in a two coil system with 12" toroid.

To tune in I had to put the tap on the primary on turn 16,
which supprised me as turn 8 is used for a TC.  Had to remove the toroid
to increase the resonant frequency to get better tune.

I could only run the system up to 20% input power before the primary/
secondary gap broke down.  

Power supply is 10KV -at-100mA

Got 8" crona/sparks as output.

My questions:
1)	Why do I need such a large primary?  Has the overall resonant 
	frequency fallen?

2)	How do you build a driver that does not break down?  Will dropping
	the whole lot in oil help?

Thanks for your help
Julian Green