L2 may consist of 500-2000+ turns of any magnet wire tightly wrapped on PVC , between half an inch and 3 inches in diameter. The longer the final the length of the wire, the more internal resistance it will have. TeslaTronix Tesla Coils use Inch and a quarter PVC. Within reason, the wider the ratio of windings between the primary and secondary, the grater the final output voltage of the tower. There is no connection from L2 to ground; only to the resistor, base, diode node. It is recommended to immediately spray with lacquer your L2 or wrap it in electrical tape double helix as changes in temperature will change the length of your coil, and cause imperfections.