Driven by a 15 kV, 30 mA Neon Sign Transformer. Static 3 pole gap across the transformer. Primary C is made of three 2700 pF 40kV doorknob caps in parallel. Primary is an inverted cone of solid 14 ga wire with the insulation stripped off and supported on some foam core supports. Secondary is wound on PVC pipe. Toroid is flexible duct hose and aluminum tape.
The photos below show the different sparks with the ground rod spaced at two different distances. Click on the photos for a bigger version.
Jim's HV page
Jim's home page