Toroid size selection

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Luke" <Bluu-at-cox-dot-net> 

I just joined the group and this is my first post.
I have played with TC's bout 12 years ago and my last one took up too much 
room for me at the time so I dismantled it.
I have regretted it since.  So now its time to make another.

My question is what is the best method / formula for selecting a toroid 
size?  And why?
Various opinions and methods would be appreciated so I can get an over all 
view of what everyone thinks.

I will be using 2 NST's in parallel each rated at 15KV 60mA.  For a total 
of 1800 watts.
The capacitance I have chosen is 0.0214 micro farads.
I will be winding a coil with a diameter of 8 inches and a 36 inch coil length.
How do I go about figuring out the best size toroid with the above information?

Thanx.

Luke Galyan
Bluu-at-cox-dot-net