SPARK GAP
I'm just getting going on this, but here's what I have so far... 
It's made with PVC and brass plumbing reducers.  It will soon be hooked up to a high airflow blower. 
The above gap is my attempt to copy Gary Lau's Design... 
see his gap and other coil info here: 
http://people.ne.mediaone.net/lau/tesla/vortexgap.htm
Here it is in the coil.  I used a vacuum motor to presurize two tupperware dishes.  The red tubes direct the air to the brass fittings of the spark gap.   the milk crate is perfect for providing the superstructure of the gap.