joules confusion sort of

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

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

When talking about a 900 watt NST (15KV 60mA) operating into a 120BPS 
static gap the joules has been said to be 7.5 per bang.
900 / 120 = 7.5
this makes sense to me since the 900 joules in one second will be displaced 
over 120 pulses.

but the cap size seems to dictate other wise.
A cap with a value of 0.016 mfd and a peak charge voltage of 21.2KV would 
only have 3.6 joules
0.000000016 * 0.5 * 21200^2 = 3.59552

I am assuming the static gap would be running at 120bps for this.

Even if a rotary gap were used and a cap size of 0.028 mfd were used the 
joules would be 6.29
That isn't even up to the 7.5 joules used by some for calculation.  Lets 
not go there on the rotary for the answers yet.  J don't want to confuse 
myself.  Only pointing out that that doesn't equate either.

Is there something I am missing?
Why do some use the 7.5 joules when the cap size would not let it store 
that much energy any way?

Any insights on this?

Luke Galyan
Bluu-at-cox-dot-net