spark_gap_design

The spark gap is a very important part of the tesla coil circuit.
its job is to switch. but the high power levels in a tesla coil circuit prevent us from using now common methods of switching.
The spark gap works by the high vlotage breaking down the air until it ionises then the spark is formed. This closes the switch until the powr level drops then the gap extinguishes(or quenches) then the process starts again

Quenching of the gap is extremely important as if the gap doesnt extinguish at the correct time during the whole process then the gap can fire again before the tank cap is fully charged then this firing is obviously at lower power levels.

This is why the method of air movement is used as moving air prevents the ionised air lingering which prevents early reignition, so each bang in the cycle is of full power.

There are many other methods of spark gap used such as inert gases and the such.
but i believe the use of air movement is much better than gases or changes of pressure as vacumn causes a lower breakdown voltage