Tesla Coil 4 by swimming pool. The aluminum toroid on top shapes the electric field around the coil and it's capacitance lowers the coils resonant frequency. The toroid's overall diameter is 49 inches. The large vertical column is the secondary coil. It is 525 turns of wire wound on a fiberglass tube 60 inches long and 20 inches in diamter. The flat spiral with 9 turns is the primary coil. The single turn just above the primary is a strike rail and is connected to ground. The box at the bottom contains the rotary spark gap and primary capacitor. The two wires leading to the foreground, go to the pole transformer.