Roger Smith's high power Tesla Coil. His system uses DC resonant charging, and a rotary spark gap for switching. Roger's system is powered from a 19.8 kV distribution transformer. Streamers are intense, very hot, and look to be somewhere between 12 - 15 feet long... maybe more. This demonstration was captured at Roger's 2021 Tesla Fest, Chillicothe, OH, 8/14/21.
Some parameters for Roger's coil include:
LV-side ballast: None needed. HV DC supply, resonant charging circuit, tank cap, and spark gap break rate control output power.
Spark Gap: 17.5" diameter, 8 electrodes, 4 gaps per firing, ~400 breaks per second (BPS)
Tank capacitors: Two GE Surge Protection Capacitors in series. Each is a model 9L18BCL101 (new GE part number is now 18L0009WH). These are high Basic Impulse Level (BIL = 95 kV) capacitors made to connect directly to an incoming 13.8 kV distribution line. They are very ruggedly-built capacitors - one of the few types that can survive in this demanding environment.
Tank capacitance: The equivalent tank capacitance is 0.125 uF at 27.6 kV AC (RMS)
Secondary winding length: 12.5" x 50", #19 AWG close-wound
DC supply-side filter capacitance: 2 uF
Charging choke inductance: approximately 5 Henries
The actual tank capacitor charging voltage has not been measured. Also, it is not known whether this system operates with the charging choke in current-limiting mode, in resonant charging (DC voltage doubling) mode, or in some combination of the two. Further measurements would be required. It IS known that this is one high-performing coil!