The static spark gap is the simplest type of spark gap for Tesla Coil use. When the voltage across the spark gap electrodes becomes suitably high, the air in the gap ionizes, and an avalanche result takes place. The air within the gap is heated to an extremely elevated temperature and becomes a superior conductor of electricity. A great deal of current flows through the ionized air, heating the air, and maintains the conductive path. The process by which the spark gap starts to conduct is known as Firing and the voltage required to start this process is called the breakdown voltage. During conduction the arc between the electrodes is a meager conductor and posses a little resistance to the flow of current through it. Power dissipated due to the arc resistance is known as conduction loss and it is the power lost here as heat. The current necessary to keep the arc conductive is called the holding current. Quenching happens when the arc stops conducting. The five copper pipe electrodes offer a large surface area to assist in quenching. The electrodes are cooled by an air stream, which also removes hot ions from the gap during operation. A vacuum pulling air between each gap provides the air stream. Tab on pictures to the left to enlarge.